Water Treatment Handbook by ADIL

Water Treatment Hand Book

PREFACE Aqua Designs was started with the mission of providing eco friendly solutions which will be useful for individuals, industries and also to nature. Since its inception, Aqua Designs has offered successful solutions on environmental perspective which has created a unique place in the industrial sector. The vision of MD Mr. Suthakar is to spread the message of harvesting water, reducing its usage, recycling and reuse. This vision transformed into collection of data on water and its uses and sharing this knowledge with one and all in order to make this world a lively place to live. .......... and hence this book. With best compliments from S. Suthakar Managing Director – Aqua Designs

ABOUT US Aqua Designs – Offers A to Z solutions for water and waste water treatment. A one Stop Shop for all types of consultancies in water and waste water management. Aqua Designs commitment to the environment, keeps it in the forefront of product innovations, purification and recycling technologies. Aqua Designs provides water solutions for Institutions, Industry, Municipal Authorities, and Commercial and Public properties. The Company boasts of the widest range of specialty water-related products and services that are ISO 9001:2000 certified by RINA of Italy. Aqua Designs was the proud recipient of the prestigious Award for The “Best Upcoming Water Company 2006 – 2007”given by the magazine Water Digest in association with UNESCO, NDTV Profit & WES-Net India in order to acknowledge those persons and Organizations, who have contributed toward water and its industry. Aqua Designs was also the proud winner of the Awards for “Best Water Treatment Project – Industrial 2007-2008” & “Best Water R&D and Technological Breakthrough 2007-2008” instituted by Water Digest. For the year 2008-2009, Aqua Designs added one more feather in its cap. It bagged two more Awards instituted by the Water Digest for the categories Best Consultancy & Best Water Conservation IT Park showing its strength in IT Sector using MBR Technology. A proven track record of offering A – Z solutions was appreciated and the Best Consultancy Award is the proof for that. The Company has excellent marketing and sales team with a cumulative experience beyond 100 years. It is one of the major reason for Aqua Designs entering big corporate and Multi National Companies. Due to its expertise the Company is able to offer competitive Designs and proposals, which keeps the competitors at bay .This proven technology has made the company one of the front runners in this field.

Aqua Designs success depends on its human resources. From Designs, Proposals, Projects, Erection and commissioning to operation and maintenance, it has proved its capability in the market which gives them a clear edge over others in the market. Aqua Designs is supported by its own State-of-the-Art Laboratory for testing water, waste water, air & stack samples both for physiochemical and microbiological parameters as per PCB norms and IS standards. We have the facility to monitor stack emissions and ambient air quality...The facility is certified under ISO 9001:2000. The Laboratory handles and supports all in house requirements; specific client needs and also offers Pilot Plant studies. Aqua Designs provides services starting from EIA to Designs to implementation of Projects to Operation & Maintenance to Supply of Specialty Chemicals to run the operations and finally to analyze the various products of the treatment using its Laboratory facility. Aqua Designs also has its own chemical manufacturing and fabrication facilities to support its growing needs in business. Aqua Designs was formed with the sole intention of suggesting eco friendly solutions for Industries and Municipalities. The vision was to provide solutions to varied sectors in par with the developed nations. Aqua Designs not only offers the concepts and design to their customers, but also stay with the customer and successfully operate the scheme for years. The customer satisfaction has lead Aqua Designs to be successful in various types of Industries ranging from Petrochemicals, Automobile, Food and Beverages, Breweries and Distilleries, Chemicals, Electronics, Power Industries etc. Aqua Designs believes only in continual improvement. It keeps offering innovative solutions to its customers. One such is the concept of Membrane Bio Reactors technology for treating the Sewage. Aqua Designs has now set a trend such that big IT Parks have started using MBR Technology. Aqua Designs is leaping forward like a giant and nothing can stop it. In the near future it aspires to be a Global leader. Aqua designs “believes in Better the Best” and this has made everything possible.

CHAPTER 1 Impurities in Water................................ ................................................................ ......................

1

CHAPTER 2 Filters ................................................................ ................................ ...........................................

8

CHAPTER 3 Iron Removal Filters ................................ ................................................................ .....................

13

CHAPTER 4 Ion Exchange ................................ ................................................................ ................................

17

CHAPTER 5 Softener ................................................................ ................................ .......................................

36

CHAPTER 6 Membrane System................................ ................................................................ .......................

40

CHAPTER 7 Steam Boiler ................................ ................................................................ ................................

49

CHAPTER 8 Cooling Water Treatment................................ ................................ ................................ .............

62

CHAPTER 9 Pumps ................................................................ ................................ ..........................................

79

CHAPTER 10 Raw Water Treatment ................................ ................................................................ .................

84

CHAPTER 11 Industrial Waste Water Treatment ................................................................ ..............................

92

CHAPTER 12 Chemical Cleaning................................ ................................................................ ........................

97

WATER SAMPLE TEST PROCEDURES ................................................................ ........................ 107 Phenolphthalein (P) Alkalinity Test Procedure ................................ ................................ ........ 109 Total (M) Alkalinity Test Procedures ................................................................ ....................... 110 Conductivity Test Procedure ................................ ................................ ................................... 112 pH-Electrometric Method Test Procedures ................................................................ ............. 113 Total hardness Test Procedures ................................................................ .............................. 114 Sulphite testing procedure ................................ ................................ ...................................... 115 Chloride Test Procedure ................................ ................................ ................................ .......... 116 Checking Acid Solution Strength for Cleaning ................................ ................................ .......... 117

UNITS AND MEASUREMENT CONVERSION ...................................................... 118 BASICS................................................................ ................................ ..................................... 119

CHAPTER 1

01

Impurities in Water Water impurities Impurity in water technology is a relative term. For example Hardness is not considered as an impurity in drinking water but in industrial water treatment it leads to scaling of equipment and hence considered as an impurity. Common impurities in water, their effect and method of removal are as follows: Impurities

Can clog pipelines and equipment can choke Ion exchange resin and RO membranes

Coagulation, and filtration

Color

Indication of organic, iron etc. and can be harmful to the unit operation ahead.

Coagulation, settling filtration, followed by activated carbon filter.

Organic matter

Can foul Ion exchange resins membranes and may be detrimental to process.

Coagulation, setting, filtration, followed by activated carbon filtration.

Bacteria

Will depend upon the type of bacteria, can induce corrosion and also harmful to RO membrane.

Coagulation, filtration, setting and super chlorination, UV, ozonation

Iron

Red water, corrosion, deposit, interferes with dyeing, bleaching etc.

Aeration, coagulation, filtration, filtration through Manganese Zeolite

pH

High pH or low pH can both induce corrosion.

Ion exchange, addition of acid or alkali.

Calcium, Magnesium (Hardness)

Scaling, cruds with soap interfere with dyeing and also harmful to other process.

Ion exchange Lime Soda

Turbidity Suspended silica

02

Method of removal

Effect

setting

WATER TREATMENT HAND BOOK

Impurities

Effect

Method of removal

Sodium

Unharmful when low in concentration, increase TDS, high concentration can induce corrosion.

Ion Exchange through cation H+ resin. Reverse Osmosis

Bicarbonates, Carbonates, Alkalinity, Hydroxide (Alkalinity)

Corrosion, foaming and carry over

Acid addition Ion Exchange by WAC Resin Split stream by hydrogen cation resin Degassification after step 2 and 3

Sulphate

Scaling if associated with Calcium, harmful in construction water.

Ion Exchange Reverse Osmosis Evaporation Electrolysis.

Chloride

Corrosion

Ion Exchange Reverse Osmosis Evaporation Electrodylasis.

Nitrate

Normally not found in raw water. Harmful in food processes (especially baby food).

Ion Exchange Reverse Osmosis

Silica

Scaling and deposition on equipment.

Ion Exchange

Carbon Dioxide

Corrosion

Open aeration, Degasification, and Vacuum deaeration.

Hydrogen Sulphide

Corrosion

Aeration, filtration through Manganese Zeolite, aeration plus chlorination.

Oxygen

Corrosion

Deaeration Addition of chemicals likes sodium sulphite or hydrazine.

03

Impurities

Effect

Method of removal

Ammonia

Corrosion especially of Copper and Zinc

Aeration Hydrogenations exchange if ammonia is present in Ionic form.

Free chlorine

Corrosion

By adding chemicals Activated carbon

Definition of Terms Total Cations= TC= Ca++ + Na+ all as CaCO3 Total Anions=TA=T Alkalinity + Cl + SO4-- + NO3 all as CaCO3 Total Hardness=TH= Ca++ + Mg++ as CaCO3 Total Alkalinity=T.Alk= HCO3 - + CO3-- + OH- all as CACO3 EMA= Cl- + SO4-- + NO3- all as CaCO3 Total Acid Ions=EMA + CO2 + SiO2 all as CaCO3 Total electrolyte=TE=TC=TA Total dissolved solids=TDS=TE + SiO2 Total electrolyte: Electrolytes are strongly ionized compounds. TE is numerically equal to either TC or TA (not some of both). SiO2 and CO2 being weekly ionized are not included in total electrolyte. Leakage: Electrolyte or silica passing through the demineralizing unit due to incomplete ion exchange. Conductivity: The ability of a solution to carry current. Conductivity measurement is used to indicate the purity of water. It is measured as micro mhos or micro siemens/cm. Resistivity: Resistivity is a measurement used for ultra pure water. Its unit is megohm. Resistivity is reciprocal of conductivity

Water Analysis Format The following format which has been shown is for ease of designing calculation where total cation or anion can be easily seen, matched for correction of analysis and also for designing the Ion Exchange units. Water testing laboratories normally do not give analysis for many ions in CaCO3 units; example Chloride ion, given as Chloride (mg/liter) which should be converted to CaCO3ppm units, by multiplying by 1.41. Similar other ions, which are not mentioned in CaCO3 units, should be converted to CaCO3 units.

04


Substance

Symbol

Example

Calcium

Ca++

125

Magnesium

Mg++

Sodium

Substance

Symbol

Example

Bicarbonates

HCO3-

150

105

Carbonates, Hydroxides

CO3-OH-

0 0

Na+

100

Chlorides

Cl-

100

Potassium

K+

0

Sulphate Nitrate

SO4-No3-

80 0

Total Cation

TC

330

Total Anions

TA

330

Total Hardness

Ca + Mg

230

Alkalinity

HCO3- + CO3-- + OH-

150

Equivalent Mineral Acidity

ClSo4– No3-

180

SiO2 Co2

20 15

All the above are expressed as ppm CaCO3 Iron

Fe express ed in mg/liter as Fe

0.5

Silica Carbon Dioxide

Substance Turbidity Colour Total Dissolved Solids Suspend Solids Acidity/Alkalinity

Unit NTU Hazen Ppm Ppm pH

Example 5 NTU 5 Hazen Unit 350 ppm 20 ppm 7.3

05

Conversion Factors for conversion to Calcium Carbonate (CaCO3)

Ions

Symbol

Ionic weight

Equivalent weight

To convert to CaCO3 multiply by

CATIONS

06

Aluminum

Al+++

27.0

9.0

5.56

Ammonium

Nh4 +

18.0

18.0

2.78

Barium

Ba ++

137.4

68.7

.728

Calcium

Ca+

40.1

20.0

2.49

Copper

Cu++

63.6

31.8

1.57

Hydrogen

H+

1.0

1.0

50.0

Iron (Ferrous)

Fe++

55.85

27.8

1.80

Iron (Ferric)

Fe+++

55.85

18.6

2.69

Magnesium

Mg++

24.3

12.2

4.10

Manganese

Mn++

54.9

27.5

1.82

Potassium

K+

39.1

39.1

1.28

Sodium

Na+

23.0

23.0

2.17


Ions

Symbol

Ionic weight

Equivalent weight

To convert to CaCO3 multiply by

ANIONS Bicarbonate

Hc03-

61.0

61.0

0.82

Bisulphate

HSO4-

97.1

97.1

0.515

Bisulphite

HSO3 -

81.1

81.1

0.617

Carbonate

Co3–

60.0

30.0

1.67

Chloride

Cl-

35.5

35.5

1.41

Fluoride

F-

19.0

19.0

2.63

Hydroxide

OH-

17.0

17.0

2.94

Nitrate

No3-

62.0

62.0

0.807

Phosphate (monovalent)

H2PO4-

97.0

97.0

0.516

Phosphate (divalent)

HOP4–

96.0

48.0

1.04

Phosphate (trivalent)

Po4—

95.0

31.7

1.58

Sulphate

So4–

96.1

48.0

1.04

Sulphide

S–

32.1

16.0

3.12

Sulphite

So3–

80.1

40.0

1.25

07

CHAPTER 2

08


Filters Basic Operation of Filter The basic operation of Pressure Filter, Dual Media Filter and Activated Carbon and iron removal filters is same. All Units operate in down flow mode, where the water enters from the top, percolates through the media and treated water is collected from the bottom.

Sequence of Operation u Service: The water to be filtered enters from the top of the shell, percolates downward through the media and is drawn off from the bottom. u Backwash: The water enters from the bottom of the vessel, passes through the media and is drained from the top. This is called BACKWASH and it is done to carry the dirt accumulated on the top. Generally back washing is done once in every 24 hrs or when the pressure drop exceeds 8 psi. (0.5 kg/cm2). Rinse : The water enters from the top passed through the media and is drained off from the bottom.

Dirty Water Raw Water

Filter Media

Filter Media Collecting System Collecting System

Treated Water

Raw Water Backwash

Note When activated carbon is installed in a vessel, it should be soaked for 12 to 24 hours to remove trapped air and back washed to remove fines and stratify the bed. A necessary maintenance item, periodic back washing removes solids trapped in the carbon bed, as well as fine carbon particles. Since the dechlorination reaction oxidizes the carbon surface, which slowly breaks down the carbon structure, back washing is especially important in de-chlorination applications. Frequency is determined by the solids content of the feed water. Tests on activated carbon dechlorination systems indicate that regular back washing of carbon beds helps preserve the dechlorination and filtering efficiency. By back washing regularly and expanding the carbon by at least 30 percent, fouling or binding of the carbon bed does not occur.

09

CAUTION Wet activated carbon removes oxygen from air. In closed or partially closed containers and vessels, oxygen depletion may reach hazardous levels. If workers must enter a vessel containing activated carbon, appropriate sampling and work procedures for potentially low-oxygen spaces should be followed as required by salutatory requirements.

Thumb rules for designing a filter Calculate area of vessel by required volumetric flow rate and the velocity as mentioned in the following table. Area (m2) = Volumetric Flow Rate (m3/hr)/ Velocity (m/hr) (1) Based on above calculated area calculate diameter of the vessel by the following formulae: Diameter (m) = [Area (m2)/ 0.785] ½ (2) Parameters

Dual Media Filters

Sand Filters

Activated Carbon

Velocity (m3/m2/hr)

7.5 – 12

12-20

15-20

Effective size of Media (mm)

0.45 - 0.6 (fine sand)

0.65 - 0.76 (Anthracite)

0.35 - 0.5

Uniform coefficient

1.6 max

1.85

<2(115 typical)

Density (kg/m3)

2650

1600

Other requirements Parameters

10

Loss of head

0.03 M for clean bed to .2 to 3 M final

Length of run between cleaning

12 to 24 hours or when the pressure drop across the bed reaches 0.5 Kg/cm2

Method of cleaning

Back washing at rate of 36 M/Hr or 24 m/hr with air scouring at 36 M/hr at 0.35 to 0.5 kg/Cm2 pressure

Amount of wash water

1 to 4 %

Time for back washing

10 to 20 minutes

Time for air scouring

2 to 5 minutes


Important points on Filter: u Normally, pressure sand filter is used to filter suspended solids upto 30 ppm and dual filter for 50-55 ppm and water with higher suspended solids would require coagulation. Output quality of water from Pressure Sand Filter is 25 to 50 microns. u Normally, velocity for Sand velocity is taken for water treatment / residential filter are taken from 7.5 to 18 M3/M2/hr; for institutional filters 20 to 30 u M3/M2/hr. For recirculation of water like swimming pool velocities can be taken greater than 35 M3/M2/hr for low turbidity application u Higher velocity will induce higher head loss through the bed and frequency of backwash will increase.Back washing of filter should always be carried out using clean water. u Whenever air scouring is provided, it should be done before back washing step. u Where strainers are provided at bottom, pebbles and gravels need not be put.

Quantity of Media Quantity of media is Calculated in Cubic Meters (M3) and then converted to Kgs The depth for various media is Sand/ Anthracite 540 mm Crushed Gravels 100 mm Pebbles (1/2 to1/4) 100 mm Media Height Pebbles (1 to1/2) 100 mm Pebbles (11/2 to 1/4) 160 mm Volume = Area* (depth/1000)

Trouble Shooting of Filters PROBLEM

CAUSE

REMEDY

Turbidity Breakthrough

Change in Raw water

Analyze water Backwash

Loss of media

Broken Laterals High backwash flow

Change the laterals or rectify. Control Backwash

High Pressure Drop across Bed

Media Dirty

Give Backwash If backwash does not solve problem give extended backwash Change Filter media if Step 1 & 2 does not work

Mud Ball Formation

Change in Raw Water Quality

Air Scour & Give extended backwash Check pretreatment if any Decrease Velocity Change Media if nothing of above works.

11

Filter Details u Blower velocity is at 36 M / Hr at pressure is 0.5 Kg / cm2 u minimum service Velocity is 7.5 M/ Hr u Normal service Velocity is 9.0 M/Hr u Maximum service Velocity is 7.5 M/ Hr u Backwash velocity For Air scour type 24 M/Hr u Backwash velocity For Non Air scour type 24 M/Hr u Density of Media is 2600gm/cc Model Diameter in mm

500

600

800

1000 1200 1400 1600

Bed Area in M2

0.20

0.28

0.51

0.79 1.13

Height on straight (HOS)in M HVT

1500 1500 1500 1500 1500 1500 1500 15 00 1500 1500

Height on straight (HOS) in M for Air scour type

1400 1400 1400 1400 1400 1400 1400

Bed Depth in Meters

12

1

2.54

3.14 3.80

1400 1400 1400

1

1

1.5

2.1

3.83

5.93 8.48

Service Flow Normal) M3/Hr

1.8

2.52

4.59

7.11

10. 17

13. 86

18. 09

22. 86

Service Flow (Maxi) M3/Hr

2.0

2.8

5.1

7.9

11.3

15.4

20.1

31.4

4.8

6.72

12. 24

18. 96

27. 12

36. 96

48. 24

60. 96

BW Flow M3/Hr For Air Scouring type

1

2.01

1

Service Flow (mini) M3/Hr

1

1.54

1800 2000 2200

1

1

1

11.5 15.08 19.05 23.55 28.50

28. 26

34. 20

25.4 38.0

75. 36

91. 2


CHAPTER 3

13

Iron Removal Filters Many water supplies contain quantities of iron & manganese that may be detrimental to number of domestic and industrial use if not removed. Iron & manganese removal is very important pretreatment step in Ion Exchange & R.O. treatment. u Iron & manganese exists in water in the following forms u Insoluble iron & manganese u Soluble iron & manganese u Organic iron & manganese u Combination of all three Depending on the type of iron present in water different treatment methods are adopted. S.No

Type of impurity

1

Insoluble iron & manganese

No oxidation required. Simple Coagulation in solid contact Unit followed by filtration

2

Soluble iron & manganese

Oxidation by air, chlorine & filtration Lime / Lime soda softening Ion Exchange

3

Organic bound iron

Coagulation by alum, settling

4

Combination of three above

Manganese zeolite

Manganese Zeolite (manganese Greensand) Manganese zeolite is a natural green sand coated with manganese oxide that removes Iron & manganese from solution. The greensand is processed by treating with manganous sulfate and then with potassium permanganate. This results in the higher Oxides of manganese in and on the green sand granules. The resultant greensand is a manganese zeolite with following characteristics.

14

Removal method

Parameter Colour Density

Black 1360Kg/M3

Effective size Uniformity coefficient Mesh size Attrition loss per annum %

0.30- 0.35 mm

Bed Depth (minimum)

700 mm of greensand and 300mm of anthracite 50% of bed depth 5 –12 M3/hr/M2 20—25 M3/hr/M2

Freeboard Service flow rate Backwash flow rate

1.6 16—60 2—4 %


Removal process Manganese zeolite process is used in conjunction with above process when the concentration is more or as a standalone process if the concentrations of Fe & Mn are low. There are two methods, which is normally employed for removal of Fe & Mn by Manganese zeolite. u Batch process (intermediate Regeneration) u Continuous KMnO4 feed system

Batch process (intermediate Regeneration) The regenerative batch process uses Manganese zeolite both as oxidizing source and also as filter media. After the zeolite is saturated with metal ions, it is regenerated with KMnO4 (potassium per manganate). This process has its limitation. Batch process is employed when the concentration of iron & manganese is small (i.e. < 2 PPM) and also if the flowrate required is not very high. (Flow rate limited to about 5-6M/Hr) The capacity of manganese zeolite is (0.09lbs iron or manganese / Cu Ft) And the regeneration is done by 0.5 % KMnO4. The amount of KMnO4 required is about (0.18lbs of KMnO4 / Cu Ft of media). Backwashing at 20-25 M3/Hr /M2 is done once in 24 hours or when the pressure drop across the bed reaches to 7-8 psi, whichever is earlier.

Continuous KMnO4 feed system: Batch process is still used but is being replaced quite rapidly by continuous feed system. In this process KMnO4 solution is added before the pressure filter that contains dual media and manganese zeolite. The Anthracite on the top of Manganese zeolite acts as a filter and removes the iron & manganese oxidized by permanganate. MnO2 oxidizes the residual ions that are not oxidized by permanganate. MnO2 also removes excess KMnO4. When the bed gets saturated with metal oxides, it is backwashed to remove all particulate matters.

Reaction times Permanganate is fed as 1-2 % solution directly to the inlet line. Contact time for oxidation is about 20—60 seconds; hence it is fed 20 '(50-60 mm) upstream from the zeolite bed Alkali is added to low pH water for optimum removal but utmost care should be taken during alkali addition due to precipitation problem KMnO4 is used either in conjunction with chlorine or alone. KMnO4 dosage differs depending on whether it is used alone or with chlorine.

15

Dosage of KMnO4 With chlorine 1 mg/liter ofCl2 / 1ppm of Fe KMnO4 mg/liter = (0.2mg/literKMnO4 for 1ppm of Fe) + (2 mg/liter of KMnO4 for 1ppm Of Mn) + (5mg/liter of KMnO4 for1ppm of H2S)

Without Chlorine KMnO4 mg/liter = (1.mg/literKMnO4 for 1ppm of Fe) + (2 mg/liter of KMnO4 for 1ppm Of Mn) + (5mg/liter of KMnO4 for 1ppm ofH2S)

Birm Birm is another type of manganese dioxide. It is a silicon dioxide core that has been coated with manganese dioxide. This makes Birm much lighter than its ore counterpart, less than 400gms/liter. The benefit of this type of product is that it can be backwashed at a flowrate of 0.8Kg. / Liter. Birm does require dissolved oxygen in the water for the precipitation of iron, where the manganese dioxide ore does not. Birm relies on its ability to act as a catalyst between iron and oxygen. It has a limited amount of MnO2 available, so it does not have the ability to supply oxygen through a redox reaction. The oxygen content should be, at least, equivalent to 15% of the total iron content. If the oxygen content is less than 15%, aeration is required. Birm is recommended on levels of iron less than 10 ppm. It can be utilized on higher concentrations, but the frequency of regeneration (backwashing) becomes excessive. Birm has a capacity of approximately 900 -1100 grams/Cu meter. It can treat up to 3 cubic meters of water containing 10 ppm Fe as CaCO3. Birm should not be used on waters that have oil or hydrogen sulfide, and the organic matter should not exceed 5 ppm. As with any product, consult the manufacturer for operational guidelines. (Sybron Chemicals).

16


CHAPTER 4

17

Ion Exchange Ion Exchange Load Calculation Let us take the following examples Feed water analysis as ppm CaCO3 Cations

Unit as ppm CaCO3

Calcium Magnesium Sodium

Anions

210

Bicarbonate

200

40

Chloride

120

Sulphate

85

Nitrate

20

Potassium

5

Iron

0

Total

375

70

375

Total

Free CO2 - 15, Silica – 5 Ion Exchange load w.r.t different unit operation

Unit Operation

18

Ion Exchange Load

Concentration (as ppm CaCO3)

Softening

Total Hardness (Ca +Mg)

250

Dealkaization

HCO3

200

Strongly acid Cation(TC)

Total Cations (Ca+Mg+Na+K)

375

Weakly Basic Anion

EMA (SO4+Cl+NO3)

175

Strongly acid Cation after dealkalization

Total Cations – Carbonate Hardness

175

Strongly Basic Anion after WBA

Total Anions – EMA

225

Strongly Basic Anion

Total Anions

375

Strongly Basic Anion after Degassing

(Cl+SO4+NO3+SiO2) (Alkalinity + CO2)

185 (assuming 5 ppm leakage of CO2)

Strongly basic Anion after degassing and WBA

Total Anion – (T.Alk + EMA ) +SiO2

10 ppm (assuming 5 ppm leakage )


Ion Exchange load w.r.t different unit operation u Match total cations to total cations to total Anions. They should be equal. (Error of +_ 5% can be considered) u Refer to the table for calculating the Resin Quantity. The Ion Exchange load can be taken as mentioned in the table.

Ion Exchange Resin Quantity (liters) = [Flow (m3/hr)* Ion Exchange load(ppm)* Time] / Ex.capacity of Resin (gms/liter)

Sizing consideration for Ion Exchange System Parameters

Cation

Anion

Mixed bed

Degassifier

30-44 M/hr

Velocity*

15-20 M/hr

Bed Depth

900-2000 mm 900-2000mm

15-20 M/hr

50-70 M/hr 2400-3600 1000-2000 mm mm 60-100%

Free Board * 60-100% 60-100% Type of Hub/radial Hub/radial Hub/radial Rasching rings Internal Strain on plate Strain on plate Strain on plate Pall rings

Approximate regenerate Level and operating Capacity Parameters

WAC

SAC

Regeneration level gm/L Cation

110

80

Regeneration level gm/L ANION EC for CATION gm CaCO3/L

WBA SBA Type 1 SBA Type 2

80 55

110

80

80

80

54

EC for ANION gm CaCO3/L

MB

40 50

35

25

20

Design parameters Unit

WAC

SAC

Regenerant flowrate

M3/Hr/M3

4

4.8

2.1

4

4

Total rinse

BV

5

5

5

5

5

1.5

1.5

1.5

1.5

1.5

6

9

6

6

6

16

16

8

8

8

Parameters

Displacement BV Rinse Backwash M3/Hr/M2 velocity Fast Rinse

M3/Hr/M3

WBA SBA Type 1 SBA Type 2

19

4 % NaOH contains 41.75 gms NaOH per liter 50 % NaOH contains 763 gms NaOH per liter 99% NaOH contains 803 gms NaOH per liter 4 % HCl contains 40.72 gms HCl per liter 32 % HCl contains 479.2 gms HCl per liter

Ion exchange systems Following different schemes of DM / Ion exchange systems are possible depending upon the application and the outlet water quality required Note: u Detailed parameters on the quality of water required in various industries is given in Chapter 9. u SA – Strong Acid Resin (H+) u SA*- Strong Acid Resin (Na+) u WB – Weak Base Anion Resin u D – Degasser u SB – Strong Base Anion Resin u WC – Weak Acid Cation Resin u MB – Mixed bed (mixture of Strong Acid Cation Resin (H+) and u strong base anion resin (OH-) #

Type Of DM/ Ion Exchange Systems

1 WB

SA

2 SB

SA

3 SB

D

SA

4 SA

20

D

WB

SB

Application

Outlet Water Quality

Removal of silica, removal of CO2 is not required

Conductivity < 50 micro mhos

Where CO2 and silica removal is required, low alkalinity water

Conductivity < 30 micro mhos, silica < 0.5 ppm

Where CO2 content is high, i.e. high alkalinity water


EMA and alkalinity Conductivity < high in raw water 30 micro mhos, silica < 0.5 ppm


5 WC

SA

D

WB

6 SA*

7 WC

D

8 SA*

SA

9 MB1

10 MB1

MB2

D

SB

High EMA and high alkalinity in raw water Hardness > =1 Alkalinity


Softening, where only hardness to be removed

Hardness less than 5 ppm as CaCO3

Dealkalization when only temporary hardness is present

10 % of the influent alkalinity TDS reduction upto alkalinity removal 10 % of the influent alkalinity TDS reduction alkalinity removal Conductivity < 1 micro mhos, silica < 0.002 ppm

Dealkalization alkalinity with permanent hardness

Low conductivity water required MB is installed after SBA When ultrapure water is required for pharmaceutical or electronic industries

Conductivity < 0.02 micro mhos, resistivity 14-18 mega ohms silica < 0.002 ppm

Service Raw Water is passed through ion exchange unit till the required quality of water is being produced. This is known as service cycle. When the resin stops producing desired quality water, the Resin is said to be exhausted and will have to be regenerated. Service flow can be down flow (top to bottom) or upflow (bottom to top).

Regeneration The restoration of resin back to its original form is called Regeneration. Depending upon the resin, regeneration is usually done by using acid, alkali or common salt. These chemicals are known as regenerant. Sequence of Regeneration for down flow unit is :1. Backwash 2. Chemical injection 3. Displacement (slow rinse) 4. Fast rinse or Final rinse In the up flow unit upward wash is only done for a minute or so.

21

Operation of Ion Exchange unit

Downflow Coflow Regeneration 2 Backwash

Chemical Injection

1 2 3 4 5

3

4

Raw water Backwash outlet Chemical Injection inlet Power water for ejector Drain for chemical and final rinse

Regeneration Tank 1

5

Fast Rinse

Slow Rinse 3

1 4

5

22

5


Upflow Countercurrent Regeneration

Chemical Injection

Slow Rinse

Regenerant Flow 4

3

3 5

Power Water

Drain

Power Water

5 Drain 2

Final Rinse

2 6 6 Final Rinse Raw water or feed water

Raw water or feed water

Final Rinse

1

1

23

Typical Regeneration Efficiencies for different type of resins Resin Type / Configuration

Strong Acid Cation

Regeneration System

Typical Regeneration Efficiencies (%)

Co-current HCl Counter-current HCl Co-current H2SO4 Counter-current H2SO4

200-250 120-150 250-300 150-200

Weak Acid Cation

105-115

Weak Acid Cation + Strong Acid Cation

105-115

Strong Base Anion Type 1

Co-current Counter current

250-300 140-220

Strong Base Anion Type 2

Co-current Counter-current

150-200 125-140 120-150

Weak Base Anion

Typical Regeneration level ranges for single resin column Regenerant Level g/liter Co-current Regeneration

Regenerant System

Typical operating capacity mg/liter

Hcl

60 - 80

40 – 60

H2SO4

60 - 80

45 – 65

NaOH

60 - 80

30 – 40

Counter current Regeneration

24

Hcl

60 - 80

50 – 70

H2SO4

60 - 80

55 – 75

NaOH

60 - 80

55 – 75


Design Guide lines for Operating and Designing Resin System Parameter Swelling Strong Acid Cation Na → H Weak Acid Cation H → Ca Strong Base Anion Cl → OH Weak Base Anion Free base → Cl

Guideline 5-8 % 15-20 % 15-25 % 15-25 %

Bed Depth Minimum Cocurrent single Resin Counter current Single Resin

750 mm 1000 mm

Backwash Flow Rate SAC Resin WAC Resin SBA Resin WBA Resin

10-25 M/hr 10-20 m/hr 5-15 M/hr 3-10M/Hr

Flow Rates Service/Fast Rinse Co-current Regeneration Counter- current Regeneration

5-60M/hr 1-10 M/hr 5-20M/hr

Total Rinse Requirements SAC Resin WAC Resin SBA Resin

2-6 3-6 3-6 2-4

Bed Bed Bed Bed

Volumes Volume Volume Volume

Note:- These are only for help. Actual data should be obtained from the resin manufacturer. Most resins have similar data.

Degasser The forced-draft degasifier blows an air stream countercurrent to the water flow. The undesirable gas escapes through the vent on the top of the aerator. A disadvantage to this process is that the water is saturated with oxygen after aeration.

25

Packing Data Number of rings in 1 M3 of random packing

Free Volume M3/M3

Packing Surface Area M2/M3

Hydraulic radius of passage

Equivalent Diameter of Packing D=4r

Mass of 1 M3 of rings Kg

25 X 25 X 3

53200

0.74

204

0.00363

0.01452

532

35 X 35 X4

20200

0.74

140

0.00555

0.02220

505

50 X 50 X4

6000

0.785

87.5

0.00900

0.0360

530

Ring Size mm

Ceramic Raschig ring – There are 145 pieces of raschig ring per liter. The ring size is 38 mm X 38 mm and weighs about 6 kg.

26


Degassifier Height and Raschig rings Heights Inlet CO2 ppm 500

200

150

100

50

35

Outlet CO2 ppm 8 5 2 8 5 2 8 5 2 8 5 2 8 5 2 8 5 2

Degassifier Heights Meters 4.26 4.90 5.49 3.65 4.26 4.90 3.65 3.65 4.26 3.04 3.65 4.26 2.43 3.04 3.65 2.43 3.04 3.65

Raschig rings Heights Meters 2.90 3.20 3.96 2.29 2.59 3.35 2.00 2.43 3.04 1.67 2.13 2.89 1.21 1.67 2.43 1.21 1.37 2.13

Degassifier Flow & Area (velocity taken is 60 m3/h/m2) Degassifier Cross Sectional Internal Diameter Required air flow 3 Flow M3/Hour Area in M2 Of degasser in mm rate in M /Hour 0.083 75 5 325 7.5 0.125 112.5 400 10

0.167

460

150

12.5

0.208

512

187.5

15

0.250

560

225

17.5

0.291

600

262.5

20

0.333

650

300

22.5

0.375

691

337.5

25

0.416

728

375

27.5

0.458

764

412.5

30

0.500

800

450

35

0.583

862

525

40

0.667

925

600

45

0.750

977

675

50

0.833

1030

750

27

Failure to produce specified quality of water The failure to produce specified quality treated water will depend upon the specific Ion Exchange unit. The causes for deteriorating water quality from each Ion Exchanged bed are given in the tabulated form. Quality of water can also deteriorate due to resin fouling. Various types of foulants which can contaminate the Ion Exchange resin. Defects 1.Change in Raw water Composition

Service cycle Exceeding Specification

Faulty regeneration

Loss of ion exchange Resin

28

Causes

Remedies

Increase in TDS

Obtain new water analysis and Set water meter to new capacity.

% change in Na/TC or Alk/TA

Calculate new capacity to the increased load.

Flow meter not working or out of calibration

Check, rectify or replace

Conductivity meter not working or working inaccurately

Check power to conductivity meter Calibrate meter Cell dirty, Replanitinize.

Insufficient chemical Weak regenerant (less Chemical or too much dilution water) Poor distribution of regenerant Ejector not functioning or Chemical going very slowly

High Backwash in Downflow system Chemical attack by Oxidizing agent like chlorine Excessive high pressure flow rate Broken Strainers in Upflow system/ Upset supporting bed or damaged underdrain. Air sucking through ejector in Pack bed system

Check and follow proper regeneration Check and rectify. Faulty internal distributor or broken strainer on top in pack bed system.Insufficient power water flow at required pressure to ejector Check rubber lining above ejector, check for chokage in ejector, air lock in vessel or if every thing is ok change faulty ejector. Reduce Backwash flow rate. Dechlorinate. Check performance of ACF Unit. If no ACF unit is there, use reducing agent (like sodium sulphite). Check & Rectify. Do not exceed specification Check for resin in effluent or resin or in resin trap.. Change strainer Rectify bottom distributor. This happens sometime during injection. Take care


Fouling of Ion Exchange material

Channeling or short Circuiting

Oxidized iron or manganese in raw water(Normally effects cation)Excessive turbidity in raw

Excessive turbidity in raw water Excessive Resin fines Resin degraded Excessive high flow rates or operating pressure Cross Contamination of Resin in Mix bed

1 Air, chlorine or other oxidizing agent can oxidize iron and manganese Pretreatment with any of the above Cleaning by Hcl for cation or by Brine for Anion

See fouling of resins Short circuiting for possible cause Resin Dirty

See fouling of resins Short circuiting for possible cause Resin Dirty

See in Fouling of Resin Use Clean regenerant chemical, Use DM water for dilution

Obstructions in pipelines p u m p Ve s s e l s e t c ., Damaged Rubber lining Valves not properly opened Strainer clogged due to dirt and resin fines

Inspect pipeline clean and remove obstruction. Replace pipe with good rubber lining or rectify Open valve fully (except control valve) Clean strainers (For removal of resin)

Pump not delivering

1. See pump trouble shooting chart for cause

1. See Pump Trouble Shooting for solution

Excessive Rinsing

Organic Fouling of Anion Ion Exchange Resin

Brine Treatment. For extreme Condition Sodium hypochlorite dosing, Should be done under supervision

High Pressure drop across resin bed

Restricted flow

29

Improper Regeneration

Increased Concen-tration of sulphuric acid in cation regeneration Regen-erant dosage too low or too weak Inadequate backwash Damage underdrain or internal distributor

See method of Regeneration Use correct method of regeneration Give extended backwash (30 minutes or more) to clean the resin bed. Replace or Rectify

Low service flow rate

Very slow service rate increases leakage from unit (will reflect on anion unit )

Have storage system and operate at higher flow or use recycle system.Minimum linear velocity should not fall below 2 M3/Hr /M2

Valve leakage

Defective Valve

Replace Note :- Valve Leakage can give wrong reading in instruments & water analysis

Nominal aging of Resin

Cation Life – 5 to 10 years Anion Resin – 3 to 5 years

1 Replace old resin

Attrition Loss

3 to 5 % per annum

1 Top up resin lost

Inadequate mixing of Resin. Applies to Mixed Bed only

Problem of middle collector in mixed bed

30

Improper Drain down Air Mixing time too short Not Enough air

Can be caused by leakage of cation Resin Improper dilution of regenerant Broken collector

Water should not be totally drained after rinsing. The level of water should always be above resin bed Air mixing should be done for minimum of ten minutes Check air requirement & blower capacity

Add Cation Resin to make up Loss or add inert resin Check Change


Indian standard grade for the commonly used regeneration chemicals Hydrochloric Acid -Sulphuric Acid -Sodium Hydroxide -IS 1021 (Pure Grade - Flakes) Sodium Carbonate -Sodium Sulphite -Sodium chloride -Alum --

IS 265 IS 266 IS 252 (Tech/Rayon Grade 46% lye) IS IS IS IS

251 247 297 260

(Tech (Tech (Tech (Tech

Grade) Grade) Grade) Grade)

Recommended impurity level for Hydrochloric Acid Impurity Fe

Maximum level 0.01% 10 ppm

Other metals(total) Organic Matter H2SO4 as SO3 Oxidants(HNO3,Cl2)

0.01 % 0.4 % 5 ppm

Suspended matter as turbidity

0

Inhibitors

none

Concentration and density of HCl solution Percent 1 2 4 6 8 10 12 14

Sp.Gravity 1.0032 1.0082 1.0181 1.0279 1.0376 1.0474 1.0574 1.0675

Grams/Liter 10.03 20.16 40.72 61.67 83.01 104.7 126.9 149.5

16 18

1.0776 1.0878

172.4 195.8

20

1.0980

219.6

22 24

1.1083 1.1187

243.8 268.5

26 28 30 32 34 36

1.1290 1.1392 1.1493 1.1593 1.1691 1.1789

293.5 319.5 344.8 371.0 397.5 424.4

31

Recommended impurity level for Sodium Hydroxide Impurity Maximum level 0.6% NaCl 30 ppm NaClO3 0.75% Na2CO3 Fe 10 ppm 5 ppm Heavy metals(Total) 50 ppm SiO2 Na2SO4 0.2 %

Concentration and density of NaOH solution Percent 1 2 3 4 5 6 7 8 9 10 16 20 26 30 36 40 46 50

Sp.Gravity 1.0095 1.0207 1.0318 1.0428 1.0538 1.0648 1.0758 1.0869 1.0979 1.1089 1.1751 1.2191 1.2848 1.3279 1.3900 1.4300 1.4873 1.5253

Grams/Liter 10.10 20.41 30.95 41.71 52.69 63.89 75.31 86.95 98.81 110.9 188.0 243.8 334.0 398.4 500.4 572.0 684.2 762.7

Recommended impurity level for Sodium Chloride Impurity Sulphate Magnesium and Calcium

Maximum level 0.6% 30 ppm

Concentration and density of NaCl solution Specific Gravity 1.005 1.012 1.027 1.041 1.056 1.071 1.086 1.101 1.116 1.132 1.148 1.164 1.180 1.197

32

Percent 1 2 4 6 8 10 12 14 16 18 20 22 24 26

Grams/Liter 10.05 20.25 41.07 62.47 84.47 107.1 130.2 154.1 178.5 203.7 229.5 256.0 283.2 311.2


Concentration and density of H2SO4 solution Percent 1

Sp.Gravity

1.5 2 3

1.008 1.012 1.018 1.025 1.032

Grams/Liter 10.05 15.12

1.005

4 5 10 15 20 30 40 50 98

20.24 30.54 41.00 51.60

1.066

106

1.109 1.140 1.219 1.303 1.395

166.1 228 365.7 521.2 697.5 1799 1831

1.906 1.944

100

Common conversion factors for ion exchange calculation To convert from Kgr/ft3 as CaCO3 Kgr/ft3 as CaCO3 Kgr/ft3 as CaCO3 g CaCO3/litre g CaO/litre

Multiply by 1.28 2.29 0.0458 0.436 0.780

To g CaO/Litre g CaCO3/Litre eq/litre Kgr/ft3 (as CaCO3) Kgr/ft3 (as CaCO3)

Flow Rate To convert from U.S. gpm/ft3 U.S. gpm/ft2 U.S. gpm BV/min

Multiply by

To BV/hr

8.02

M/hr M3/hr U.S. gpm/ft3

2.45 0.227 7.446

Other Parameters Parameter

To convert from

To

Multiply by

Pressure drop

PSI/ft PSI/ft

MH2O/M of Resin G/cm2/M

2.30 230

Ibs/ft3

g/litre

16.0

Ibs/ft3 U.S. gal/ft3

g/litre BV

16.0 0.134

Regenerant concentration Density Rinse requirement

33

1 gallon of water weighs 8.33 pounds 1 Cubic foot of water weighs 62.4 pounds 1 cubic centimeter of water weighs 1 gram 1 liter of water weighs 1 kilogram 1 cubic meter of water weighs 1 metric ton 1 metric ton = 2240 lb.

Water analysis conversion factor Substance

Atomic /molecular weight

Equivalent Weight

To CaCO3

Calcium

40.0

20

43.8

Magnesium

24.3

12.25

4.12

Sodium

23.0

23.0

2.17

Potassium

39.1

39.1

1.28

Iron (ferrous)

55.8

27.9

1.79

Iron (ferric)

55.8

18.6

2.69

Aluminium

27.0

9.0

5.56

Barium

137.4

68.7

0.73

Strontium

87.6

43.8

1.14

Anions Substance

34

Atomic / molecular weight

Equivalent Weight

To CaCO3

Bicarbonate

61.0

61.0

0.82

Carbonate

60.0

60.0

0.83

Chloride

35.5

35.5

1.41

Sulphate

95.1

48.0

1.04

Nitrate

62.0

62.0

0.81

Phosphate

95.0

31.7

1.58

Sulphide

32.1

16.0

3.13

Co2

44.0

44

1.14

Silica

60.1

60.1

0.83


Set-Points for Brine regeneration to remove organic fouling

Parameter

Units

Subsequent First Salt Caustic Caustic Regeneration Regeneration Regeneration

Quantity of Regenerant

Gm/liter

32

112

32

Regenerant Strength

%

3.5

15

5

912

745.6

640

Quantity of dilute Regenerant

Grams /liter

Volume of Regenerant

Liter/liter of resin

0.9246

0.6968

0.6432

Flow Rate of Regenerant

M3/Hr/M3 of resin

2.8

1.6

1.92

Time for Regeneration

Minutes

20

25

20

Flow Rate of Rinse Water

M3/Hr/M3 of resin

1.6

4

1.6

Time for Rinsing

Minutes

10

15

10

35

CHAPTER 5

36


Softener (Basic ion exchange process) Thumb rules of designing a Softener STEP 1 – To select resin quantity (liters) for a particular hardness (ppm) for a particular output (m3) per regeneration per hour based on regeneration level 160 gm/liter, ion exchange capacity = 55, TDS limit = 1500 ppm, refer TABLE 1 Resin Quantity = Load (ppm as CaCO3) * Flow * time Ex. Capacity For example Load = Hardness = 100 ppm as CaCO3 Flow = 5M3 /hr Time = (Service cycle) = 12 hrs. Ex. Capacity = 60 gm as CaCO3 = 100 liters Resin Quantity = 100 * 5 * 12 60 Note: Na / TC and TDS and correction factor should be applied. Actual Resin Quantity = 60 * correction due Na/TC factor * Correction due to TH factor = 60 * 0.96 * 0.97 = 56 (approximately) Hence Ion Exchange load for designing a softener is 56. These calculations are based on Ion Exchange resin and will vary from manufacturer to manufacturer resin. STEP 2 – To select vessel model for a selected resin quantity, approx. flow rates based on linear velocity- min (8 M3/M2/hr) and max (25 M3/M2/hr), and free board 5-100 %, refer TABLE 2

Important points on Softener Regeneration level, hardness leakage desired and correction factors can be found from resin supplier's graph.

Suggested vessel selection chart for softeners TABLE 1: STEP 1 – To select resin quantity ( liters) for a particular hardness (ppm) for a particular output(m3) per regeneration per hour based on regeneration level 160 gm/liter, ion exchange capacity = 55, TDS limit=1500 ppm) Output b/w Regen-eration (OBR M3)

Resin Qty in liters for various hardness Hardness Hardness = 150 = 250 ppm ppm

Hardness = 350 ppm

Hardness = 500 ppm

Hardness Hardness Hardness = 650 = 800 = 1000 ppm ppm ppm

5

13.5

22.5

31.5

45.0

58.5

72.0

90.0

10

27.0

45.0

63.0

90.0

117.0

144.0

180.0

37

15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

39.0 52.5 66.0 79.5 91.5 105.0 118.5 132.0 144.0 157.2 171.0 184.5 198.0 210.0 223.0 237.0 250.5 262.5

65.0 87.5 110.0 132.5 152.5 175.0 197.5 220.0 240.0 262.0 285.0 307.5 330.0 350.0 372.0 395.0 417.5 437.5

91.0 122.5 154.0 111.3 213.5 245.0 276.5 308.0 336.0 366.8 399.0 430.5 462.0 490.0 521.0 553.0 584.5 612.5

135 180 225 270 315 360 405 450 495 540 585 630 675 720 765 810 855 900

175.5 234.0 292.5 351.0 409.5 468.0 526.5 585.0 643.5 702.0 760.5 819.0 877.5 936.0 994.5 1053.0 1111.5 1170.5

216.0 288.0 360.0 432.0 504.0 576.0 648.0 720.0 792.0 864.0 936.0 1008.0 1080.0 1152.0 1224.0 1296.0 1368.0 1440.0

270.0 360.0 450.0 540.0 630.0 720.0 810.0 900.0 990.0 1080.0 1170.0 1260.0 13500 1440.0 1530.0 1620.0 1710.0 1800.0

TABLE 2: STEP 2 – To select vessel model for a selected resin quantity, approx. flow rates based on linear velocity min=8 m3/m2/hr and max=25 m3/m2/hr, and free board 5-30 % Vessel Resin Approx. Free Resin Model Flow Rate Qty Board Qty Capacity Min-max (liters) (%) (liters) (liters) LPH 6 x 32 160-500 8% (14.6 liters) 13.5

160-500

160-500

212-663

20 % 6 x 35 (16. l liters)

22.5

27.0

7 x 40 (24.5 ltrs)

415-1,295 6 %

10x54 (63.8 ltrs)

584-1,825 30 %

12x48 (78.5 ltrs)

584-1,825 12 %

12x48 (78.5 ltrs)

704-2,200 50 %

13x54 (106 ltrs)

70

212-663

20 %

7 x 44 (27.1 ltrs)

80

704-2,200 33 %

13x54 (106 ltrs)

276-865

8x40 16 % (31.4 ltrs)

90

704-2,200 18 %

13x54 (106 ltrs)

276-865

8x44 29 % (34.9 ltrs)

100

704-2,200 6 %

13x54 (106 ltrs)

822-2,570 50 %

14x65 (150 ltrs)

9x35 350-1,093 26 % (33.9 ltrs)

38

Vessel Free Board Model Capacity (%) (liters)

60

6 x 35 33 % (18.0) 9%

Approx. Flow Rate Min-max LPH


31.5 350-1,093

415-1,295

415-1,295

39

415-1,295

415-1,295

415-1,295

45

415-1,295

415-1,295

415-1,295 415-1,295

8%

9x35 (33.9 ltrs)

27 %

10x35 (40.1 ltrs)

48 %

3%

19 %

33 %

3%

15 %

10x40 (46.5 ltrs) 10x35 (40.1 ltrs) 10x40 (46.5 ltrs) 10x44 (51.7 ltrs) 10x40 (46.5 ltrs) 10x44 (51.7 ltrs)

22 %

10x47 (55.0 ltrs)

42 %

10x54 (63.8 ltrs)

>100 <140

8222,570

~

14x65 (150 ltrs)

>140 <180

1,0003,140

~

16x65 (182 ltrs)

>180 <240

1,4004,370

~

18x65 (250 ltrs)

>240 <300

1,9006,000

~

21x62 (310 ltrs)

>300 <430

2,3007,300

~

24x62 (450 ltrs)

>430 <650

3,70011,600

~

30x72 (710 ltr)

>650 <950

5,40016,800

~

36x72 (1020 ltr)

>950 <1250

9,40029,448

~

48x72 (1840 ltr)

~

63x64 (2500 ltr)

> 1250 16,000<1700 50,240

39

CHAPTER 6

40


Membrane System Conventional and membrane process solutions to common water problems Conventional process

Constituent of concern

Membrane process

Coagulation/flocculation Turbidity Suspended solids Media filtration Microfiltration Biological contamination Disinfection Color Activated carbon Ultrafiltration Odor Cl, + media filtration Volatile organics aeration Hardness Sulfates Manganese Iron Heavy metals

Lime softening ion exchange Nanofiltration Oxidation, filtration Ion exchange Coagulation/flocculation

Total dissolved solids Nitrate

Distillation Ion exchange

Reverse osmosis Electrodialysis

Pretreatment water quality for membrane processes Spiral CA

Spiral PA

EDR

Suspended matter Turbidity NTU

<1.0

<1.0

<5

SDI Ionic content Iron, mg/L (ferrous) Manganese mg/L Silica mg/L(w/o) in concentrate Chemical Feed Residual Chlorine ppm Scale inhibitor mg/l in concentrate

<4.0

<4.0

<15

<2.0

<2.0

<0.1

<0.5

<0.5

<0.1

<160

<160

<1.0

ND

ND

12-18

12-18

As required

5.5-6.0

4-10

As required

40

45

43

Note

+2.45-+2.8

2.1

Acidification pH Maximum feed temperature oC Maximum LSI with Scale inhibitor

41

Note:- Type of Membrane PA = polyamide, CA = Cellulose Acetate and EDR = Electrodialysis Reversal CA membranes work in Narrow pH range 5.5-6.0 and require acidification to prevent hydrolysis. Therefore, the Langelier Saturation Index of the existing concentrate tends to be low enough and scale inhibitor for calcium carbonate scale is not required.

Troubleshooting Guide CHECK

EFFECT

Pressure drop between feed and reject.

Has not increased by more than 15%.

More than 15% indicates fouling of feed path and membrane surface. Requires cleaning

Pressure drop between feed and permeate


More indicates fouling of membrane surface. Requires cleaning.

Permeate conductivity


More indicates fouling of membrane surface. Requires cleaning.

Acid dosing

Is within recommended value.

More can cause membrane damage or sulfate scaling. Less can cause carbonate scaling or metal oxide fouling.

Instruments Reading

Verify by calibration and carry out of lab check of the parameters the instrument is monitoring.

pH meter calibration & control

42

VERIFY

Wrong operation False sense of security that everything is OK.

The pH controller generally controls acid dosing pumps. The pH controller should be calibrated periodically and tripping of dosing pump to the set point should be checked.

More or less acid dosing than required.Effect of this has already been mentioned earlier.


O ring

Brine valve

Probing with ¼ 'plastic tube and by measuring how far it has been inserted.

Should not be closed fully.

Failure can lead to increase salt passage, increase permeate flow. Decrease pressure drop. If fully closed, 100% recovery will result and cause membrane damage due to precipitation of inorganic salt.

Foulants & Their Impact Foulants

Possible Location

Pressure drop

Permeate Flow

Metal Oxide

1St Stage

Normal to increased

Decreased

Normal to increased

Colloidal Fouling

1St Stage

Normal to increased

Decreased

Normal to increased

Scaling

Last Stage

Increased

Decreased

Increased

Biological Fouling

Any Stage

Normal to increased

Decreased

Normal to increased

Organic Fouling

All Stages

Normal

Decreased

Decreased to increase

Oxidant(Cl2)

1St Stage (Most Severe)

Normal to increased

Increased

Increased

Abrasion (carbon,Silt)

1st Stage

Decreased

Increased

O-ring or glue leaks

Random

Normal to decreased

Normal to increased

Increased

All stages

Decreased

Normal to Decreased

Increased

Recovery too high

Salt Passage

Increased

43

Cleaning of RO Membrane RO membranes get fouled with suspended solids contained in the feedwater or with sparingly soluble salts, as minerals are concentrated. Pretreatment is done to reduce the fouling potential of feedwater but inspite of that fouling occurs over a period of time. Symptom of fouling 1. Decrease in Product flow. 2. Increase in salt passage. 3. Increase in differential pressure 4. Deterioration in permeate quality 5. Increase in the differential pressure across the RO stage. Indications that the system requires cleaning 1. A 10 to 15 % decline in normalized Product flow. 2. A 10 % increase in salt passage. 3. 15 % increase in differential pressure. Types of Foulants 1. Inorganic fouling – Like Calcium Scales or Metal Oxides 2. Organic Fouling – Example Humic Acid 3. Particulate Deposition or colloidal fouling –Particulate matter 4. Biofouling Types of Membrane Cleaning Solutions The number of formulation for cleaning solutions is varied but we are mentioning only the common type of cleaners used for most common fouling problems. Foulant Inorganic Salts Metal Oxides (Iron) Inorganic Colloids (silt) Biofilms

Organics

44

Cleaning Chemicals

Remarks

0.2 % HCl 0.5 % Phosphoric Acid 2.0 % Citric Acid 0.5 % Phosphoric Acid 1.0 % Sodium Hydrosulphite 0.1%Sodium Hydroxide,30 oC 0.025 % Sodium Dodecylsulphate 0.1 % NaOH, 30 oC 0.1 % NaOH, 30 oC 1 % Sodium salt of ETDA and 0.1 % NaOH 0.025 % Sodium Dodecylsulphate 0.1 % NaOH 30 oC 0.1% sodium triphosphate 1.0 % Sodium salt of ETDA


Flux The throughput of a pressure-driven membrane filtration system expressed as flow per unit of membrane area (e.g., gallons per square foot per day (gfd) or liters per hour per square meter (Lmh). Type of Water

System Operating Water Flux (gpd/ft2) & (M3/M2.d)

Municipal wastewater (sewerage)

8-12 - or

0.33-0.49

Treated River or Canal water

8-14 – or

0.33-0.57

Surface Water (lakes/Reservoir)

8-14 – or

0.33-0.57

Deep Wells (low turbidity)

14-18- or

0.33-0.73

RO Permeate Water

20-30 –or

0.81-1.22

Surface seawater

7-10 - or

0.29 –0.40

Beach well seawater

7-10 - or

0.29 –0.40

If the water quality is better, higher flux that can be used without causing excessive fouling. Number of Elements: When the flux has been set and the element area (a function of the specific membrane selected) is known, the required number of elements can be calculated: Number of elements =Permeate Flow (LPD)/(LMH)*Active Membrane area (M2) Recovery Rate = (Permeate Flow rate / Feed flow rate)*100 Osmotic pressure Osmotic pressure can be defined as the pressure and potential energy difference that exists between two solutions on either side of a semipermeable membrane. A rule of thumb for osmosis is that 1 psi of osmotic pressure is caused by every 100 ppm (mg/l) difference in total dissolved solids concentration (TDS). Selection of Feed pumps Feed pumps should be selected on the basis of high efficiency. Variable frequency drives now are commonplace in brackish water RO Plants. These frequency drives should also be selected on similar basis. Typical feed pump energy requirements for brackish water RO plants range from 0.5 to 2 kWh/M3 and for seawater it is less than 3 kWh/M3 with the use of energy recovery device. Scaling of Membrane Process Scaling is predicted by Langelier Saturation Index (LSI) or at a higher ionic strength the Stiff & Davis Index predicts the scaling tendency more accurately.

45

u If pH >pHs (or pHsd) then water is saturated with calcium carbonate. u If pH
To predict the product and concentrate composition and volume: u There are four important pieces of information needed to predict the product and concentrate composition and volume: u Recovery rate, (Ret): -The recovery rate is limited by the concentration of sparingly soluble salts in the feed water. Lowering the pH and adding anti-scalants can increase the potential recovery rate. The other determining factor is the configuration of the membrane system. Each element can recover approximately 10 percent of the feed flow as product. Generally, 50 percent recovery is assumed for a 6-element vessel. u Rejection rate: -Manufacturers lists a rejection rate for chloride and one for sulfate or other divalent ions for NF membranes. For greater accuracy, use a weighted average based on the feed water composition. For instance, if the feed water has a ratio of 3: 1 monovalent to multi-valent ions and the rejection rates are 90 percent for chloride and 99.5 percent for sulfate, the weighted average rejection rate would be Rejection = (0.75*0.9)+(0.25*0.995) / (0.75+0.25) =0.924 If the goal is to minimize concentrate volume, choose a membrane with a very high rejection. However, if the goal is to minimize concentrate TDS, choose a membrane that will produce the target water quality. NF membranes are sufficient in many cases.

46


u Feed water-dissolved solids concentration, C, in mg/L. u Target delivery water concentration after blending, C, in mg/L. u Accurate

product

and

concentrate

concentration

prediction

calculations that take concentration polarization into consideration can get quite complex, but do no provide that much more accuracy in a first pass cost estimate. Product concentration, Cp in mg/L: Cp= Cf (1-Rejection) / Recovery Concentrate concentration Cc in mg/L Cc =Cf* Rejection / (1-Recovery) The maximum amount of blend water that can be mixed with the membrane product and still achieve the target water quality is calculated as follows, assuming filtered feed water is used for the blend water: Qb = Qt (Ct- Cp) / (Cf-Cp) Where Qb is the maximum blend volume in m3/day, Q, is the target volume in m3/day, and Ct is the target dissolved solids concentration in mg/L. If there is a component of the blend water that is more limiting than the total dissolved solids, there are two options. Either plan to remove that component from the blend water or use the concentration of that component in the blend water for Cf and the estimated remaining concentration of it in the membrane product water for Cp. As an example, consider the following situation: Cf = 900 mg/L with 0.5 mg/L manganese Rejection = 0.95 Recovery = 0.85 Ct = 300 mg/L with less than 0.05 mg/L manganese Cp = 900*(l-0.95)/0.85 = 56 mg/L Cb = (300-56)/ (900-56) = 0.29 or 29 percent blending with feed water. When the manganese concentration is considered as the limiting component: Cf = 0.5 mg/L manganese Rejection = 0.95

Recovery = 0.85

Ct = Less than 0.05 mg/L manganese Cp = 0.05*(l-0.95) / 0.85 = 0.03 mg/L Cb = (0.05-0.03) / (0.5-0.03) = 0.04 or 4 percent blending with feed water.

47

If the blend water is filtered with greensand or the manganese is removed in some other way, the higher level of blending is possible, otherwise not. However it is decided, once the blend volume has been established, the membrane process feed, product, and concentrate flows are set (all in m3/day): Qp = Qt- Qb Qf = Qp / Recovery Qc = Qp (1-Recovery) / (Recovery)

Pump Horsepower for RO Using the following assumptions: Feed water is being pumped from a tank of approximately the same height as the membrane skid, 10 meters of pipe Pipe is a 10 cm (4 in.) in diameter for 20cm (8-in.) modules and 5 cm (2 in.) for 10 cm (4 in.) module. Horsepower (Hp) without energy recovery Hp = hg+0.5v2+p*Qf*1000/(746*Ef) Horsepower (Hp) with energy recovery Hp = (hg+0.5v2+p)(1-Er)*Qf*1000/746 Where h is height difference between top of tank and membrane inlet in m, g is gravitational constant, 9.81 m/s2 v is velocity = Q / pipe area, m/s, Qf = membrane feed flow, m3/sec, 1000 = mass of one m3 of water in kg, 746 = conversion factor from J/s to hp, Ef= combined Efficiency of Pump and Motor E recovery = energy recovery in decimal, 0.20 - 0.30 depending on concentrate pressure.

48


CHAPTER 7

49

Steam Boiler Steam Boiler System The principal components of a steam boiler system include a steam boiler, condensate return tank, condensate pump, deaerator, feedwater pump, steam traps, low water flame cut-off controller, chemical feeder, and make-up water treatment equipment. However, depending on the size of the system and the end use of the steam, other components may include a converter or heating coils, unit heater, steam sparger, jacketed steam cooker, and/or steam sterilizer

List of Problems Caused by Impurities in Water Impurity(Chemical Formula)

50

Problems

Common Chemical Treatment Methods

Alkalinity (HCO3-, CO3 2- and CaCO3)

Carryover of feedwater into steam,produce CO2 in steam leading to formation of carbonic acid (acid attack)

Neutralizing amines, filming amines, combination of both, and lime-soda.

Hardness (calcium and magnesium salts, CaCO3)

Primary source of scale in heat exchange equipment

Lime softening, phosphate, chelates and polymers

Iron (Fe3+and Fe2+)

Causes boiler and water line deposits

Phosphate, chelates and polymers

Oxygen (O2)

Corrosion of water lines, boiler, return lines, heat exchanger equipment,etc. (oxygen attack)

Oxygen scavengers, filming amines and deaeration

pH

Corrosion occurs when pH drops below 8.5

pH can be lowered by addition of acids and increased by addition of alkalis

Hydrogen Sulfide (H2S)

Corrosion

Chlorination

Chlorination

Scale in boilers and cooling water systems

Scale in boilers and cooling water systems


Troubleshooting Water system for Boiler Condition

Hardness in Boiler feed Water

Dissolved oxygen in Feedwater exceeds the recommended range.

Consistently low Chemical residual in system(General).

Low phosphate residual.

Possible Cause

Action

Infiltration of raw water at converters.

Regenerate/repair water softener. Take condensate samples at all steam converters to pinpoint place of infiltration. Make necessary repair.

Deaerator malfunction. Feedwater pump sucking air at the seal. Insufficient sodium sulfite residual.

Check deaerator press /temp.Check deaerator valve to ensure the most effective opening. Repair feedwater pump seal.

Testing reagent shelf life expired. Chemical feed pump inoperative or out of adjustment. Restriction in the chemical feedline. Mistake in chemical identification. Inadequate amount of treatment chemical. Makeup water increase due to lead in the system (boiler section or condensate).

Replenish test reagents. Repair or adjust chemical feed pump. Clean or replace chemical feedline. Make sure the chemical you are using is what you want. Increase chemical dosage. Inspect boiler and condensate piping system for any indication of leaks. Make sure drain valves on condensate receiving tanks are closed. Check boiler blowdown valves to ensure 100% shut-off. Check continuous blowdown valves setting.

Improper functioning of Water softener

Increased hardness in feedwater. Wrong type/choice of phosphate.

Check water softener. See action for “Hardness in boiler feed water.” Select phosphate based on the needed Po4 percent to ensure the highest quality for the hardness content.

51

Low sulfite residual.

Total dissolved solids exceed the recommended range.

High total dissolved solids in condensate.

Chemicals feed pump inoperative. An increase of oxygen content in feedwater. Improper sampling or testing technique.

Check sulfite feed system and make necessary adjustment/repair. Check deaerator operation and make necessary adjustment/repair. Increase sodium sulfite feed rate. “Collecting Water Samples. Test for sulfite first. Stir sample smoothly. Increase blowdown rate. Adjust the surface blow down valve. Analyze boiler water to determine treatment chemical residual and make adjustments.

Insufficient boiler blowdown. Excessive chemical addition.

Boiler water carryover with the steam. Too much amine injected. Infiltration of raw water at converters. Active corrosion occurring in the system.

Reduce the total dissolved solids in the boiler by blowdown. Make sure water level is not too high. Reduce amine injection, but maintain the recommended pH. Take condensate samples at all steam converters and test for hardness and TDS to find the point of infiltration. Make necessary repair. Analyze the condensate for iron/copper content. Ensure amine treatment is reaching all points in the condensate system.

Boilers Boilers use varying amounts of water to produce steam or hot water, depending on their size. They require make up water to compensate for uncollected condensate or to replace blow down water. These units have a tendency to develop leaks as they age.

52


Water Efficiency Opportunities: 1.

Install a condensate return system – A condensate returns system reuses condensate water as make-up water. This can save up to 50-70 percent of the water used and can save energy as well.

2.

Locate and repair leaks – Boilers can develop leaks in steam traps and the distribution system. Escaping steam wastes both water and energy. Limit blow down – Adjust blow down limits to near the minimum required to properly flush the system and maintain desired water quality. Establish an effective corrosion and scale program –Regularly inspect boiler water and fire tubes. Reducing scale by chemical treatment or mechanical removal will increase heat transfer and energy efficiency and will reduce the amount of blow down necessary to maintain water quality.

3. 4.

5. Install automatic controls to treat boiler make up water. Eliminate systems that mix condensate with cool fresh water for blow down to the sewer.

Water Treatment Recommendation

A

1.The make-up water treatment to these systems depends on the boiler pressure and the end use of the steam. 2.The make-up should preferably be softened for low pressure steam boiler. 3.The make-up must be softened & dealkalized for steam boiler systems when the total alkalinity concentration in the make-up is high (i.e., systems where the boiler is blown down to control alkalinity rather than TDS). 4. In boiler system where silica controls the blowdown, the make up water should be demineralized.

B

1.Sodium sulphite must be added at a point after mechanical deaeration such that a residual sulphite concentration of 30-60 ppm (50 – 100 ppm Na2SO3) is maintained in the boiler water. 2.It does not matter if the sulphite concentration is more but it should not be less than 30 ppm SO3 or 50 ppm Na2SO3. 3.The sulphite-oxygen reaction may be catalyzed by adding 5 ml of cobaltous chloride solution per 100 g of sodium sulphite.

C

1. If the pH of the boiler water is less than 10.5, caustic must be added to the boiler. 2. If the pH of the boiler water is greater than 11.5, the blowdown rate must be increased and the caustic addition must be decreased—the boiler water pH level must be 10.5-11.5 pH.

53

D

E

F

G

H

1. If the boiler water total alkalinity concentration is greater than 700 ppmCaCO3, then the blowdown rate must be increased and the caustic or trisodium phosphate addition must be decreased. 2. The boiler water total alkalinity concentration must be less than 700 ppm CaCO3; 1. If the boiler water hydroxide alkalinity concentration is less than 150 ppm CaCO3, caustic or tri-sodium phosphate must be added to the boiler water. 2. Alternately, if the boiler water hydroxide alkalinity concentration is greater than 300 ppm CaCO3, the blowdown rate must be increased and the caustic or tri-sodium phosphate addition must be decreased—the boiler water hydroxide alkalinity must be 150-300 ppm CaCO3 1. If the phosphate is added upstream of the boiler feed pumps, hexameta phosphate must be used since tri-sodium phosphate would precipitate hardness salts, thus increasing the wear on pump seals. Hexameta phosphate on the other hand keeps hardness in solution until it reaches the boiler, at which point the alkalinity and increased temperature there converts it to trisodium phosphate; 2. If the phosphate is added directly to the boiler water, either hexameta or tri-sodium phosphate may be used; 3. If the phosphate is being consumed more rapidly than trisodium phosphate is being added (i.e.,hardness in leakage into the system), hexameta phosphate should be used at least temporarily because it has a higher phosphate concentration and thus a higher capacity for hardness than tri-sodium phosphate; 4. When hexameta phosphate is used, its conversion to trisodium phosphate in the boiler effectively reduces the OH alkalinity concentration and the pH level of the boiler water; 1. If the pH level of the condensate return is less than 8.5, a neutralizing amine such as morpholine must be added to the feedwater after the make-up location. 2. If the pH level of the condensate return is greater than 9.5, the amine addition must be decreased the condensate return pH level must be 8.5-9.5. 3. If problems persist in achieving proper pH levels in the condensate return system, seek the advice of the water treatment consultant. If there is no condensate return, amine must not be added In conjunction with the above controls and regulation of boiler blowdown, the boiler water neutralized total dissolved solids must be controlled within the limits of 1500-3000 ppm (or 2000-4000 micromhos/cm).

Note:- For Details See Boiler Water Treatment Manual.

54


Note Hydrazine Sulphate oxygen scavenging should only be used with drum type boilers. Drum boilers have blowdown facilities. TDS levels should be monitored more rigorously when using hydrazine sulphate as an oxygen scavenger, since TDS levels may increase with the formation of ferrous sulphate. The venting is not sufficient. Increase venting by opening the manually operating vent valve. Excessive oxygen content in deaerator effluent

The steam pressure reducing valve not working properly. Check valve for free operation. Check water and, if possible, steam flow rates vs. design. Trays or scrubber and inlet valves are designed for specific flow ranges.

Temperature in storage tank does not correspond within 5 º F of saturation temperature of the steam

Spray nozzle not working. There could be deposit or sediment on the nozzle on the spring broken or seat. Leaking stuffing boxes of pump upstream of deaerator can be the cause Repair stuffing box or seal with deaerated water.

Excessive consumption of oxygen scavenger

Trays collapsed-possibly from interrupted steam supply or sudden supply of cold water causing a vacuum. Condensate may be too hot. Water entering the deaerating heater must usually be cooled if the temperature.

55

Chemical dosage Oxygen scavenger Sodium sulphite 7.88 ppm of sodium sulphite is required to remove 1ppm of dissolved oxygen. This requirement is for pure sodium sulphite. 93 % pure sodium sulphite will require 10 ppm of sodium sulphite per ppm of oxygen. The amount of catalyst required is 0.25 %

Hydrazine Theoretically 1 ppm of Hydrazine reacts with 1 ppm of dissolved oxygen. In practice of 1.5 to 2 ppm is used for 1 ppm of dissolved oxygen Amine Requirement Amount of amine required for maintaining pH of 8.0 in water containing 10 ppm CO2 Morpholine –37 ppm: - It has a specific gravity of 1.002 and has a pH of 9.7 for 100-ppm solution Cyclohexylamine –15 ppm: - It has a specific gravity of 0.86 and has a pH of 10.7 for 100-ppm solution Suggested dosage of Sodium sulphite & Hydrazine

Dosage of Sodium sulphite Boiler pressure (Kg/Cm2) 14.00 21.00 31.00 42.00 52.00 64.00 70.00 105.00

Ppm Na2SO3. 80-90 60-70 45-60 30-45 25-30 15-20 Not recommended Not recommended

Recommended Hydrazine Residual Drum pressure (Kg/Cm2) 63.00 70.00 105.00 175.00 210.00

56

Residual Hydrazine in ppm. 0.1-0.15 0.1-0.15 0.05-0.10 0.02-0.03 0.01-0.02


Conditions

Type of Amine Ammonia

Co2 Absent

Cyclohexylamine

Co2 Absent CO2 Present

Amount needed 0.2 ppm to give pH 9.0 1 ppm to give pH 9.0 2.3 parts per part of CO2 to give pH 8.1 (corresponds to bicarbonate) 2.0 parts per part of CO2 to give pH 7.4 1.4 ppm per ppm of Co2 to give pH of 7.0

Notes Cyclohexylamine is not for use in systems having a feedwater alkalinity more than 75 ppm These system lengths are for classification only and are not absolute. For example a medium length system may have more of the characteristics of a long system if lines are poorly insulated or because of bad design.

Amine Limits Amine

Limitation

Cyclohexylamine

Not to exceed 10 ppm in steam.

DEAE Hydrazine

Not to exceed 10 ppm in steam. Zero in steam

Morpholine


Octadecylamine


Note:- These should not come in contact with food products and hence any steam in contact with milk and other such products should not have amine.

57

Limits on Boiler water conditions for an effective treatment program Boiler MaxiPressure -mum psig(kg/ TDS (ppm) cm2) 1-15 6000 (1.05) 16-149 (1.12-10.5) 4000 150-299 4000 (10.5-20) 300-449 3500 (20-30) 450-599 3000 (31-40) 600-749 2500 (41-52) 750 2000 (>52)

Maxim um Con ductivity ( mho)

Maxi-mum Silica (ppm)

Range Sulfite (ppm SO3)

Range Phosph ate(pp mPO4)

Range Alkalini ty(ppm CaCO3)

*Lign osulphon ate (ppm)

9000

200

30-60

30-60

300-500

70-100

6000

200

30-60

30-60

220-500

70-100

6000

150

30-60

30-60

220-500

70-100

5250

90

20-40

30-60

180-450

70-100

4500

40

20-40

30-60

170-425

60-90

3750

30

15-30

30-60

170-425

50-80

3000

20

15-30

30-60

170-425

40-90

NOTE Ortho-Phosphate Hydroxyl Alkalinity (Causticity) Sodium Lignosulfonate (as tannic acid) Range BIS Standard for Feed water and Boiler Water 1st Standard (10392-1982)

Chemical requirements for feed water and boiler for low and medium pressure boilers: Feed Water: Parameters

21 Kg/cm2 - 39Kg/cm2

40Kg/cm2 - 59Kg/cm2

Unit

Total Hardness

<10

<1.0

<0.5

pH Value

8.5-9.5

8.5-9.5

8.5-9.5

Dissolved Oxygen

0.1

0.02

0.01

As ppm

5

0.5

As ppm SiO2

Silica

58

Upto20Kg /cm2

ppm as CaCO3


Boiler water

Parameters

Upto20 Kg/cm2

21 Kg/cm2to 39 Kg/cm2

40Kg/cm2 59Kg/cm2

Unit

Total Hardness

Not Detectable

Not Detectable

Not Detectable

Total Alkalinity

700

500

300

As ppm CaCO3

Caustic alkalinity

350

200

60

As ppm CaCO3

pH Value

11.0 to 12.0

11.0 to 12.0

10.5 to 11.0

Residual Sodium Sulphite

30 to 50

20 to 30

--

ppm as Na2SO3

Residual Hydrazine

0.1 to 1.0

0.1 to 0.5

0.05 to 0.3

ppm as N2H4

Ratio Na2SO4 /Caustic Al kalinity (NaOH)

Above 2.5

Above 2.5

Above 2.5

Ratio Na2SO4/ Totallkalinity (as NaOH)

Above 0.4

Above 0.4

Above 0.4

Phosphate

20 to 40

15 to 30

5 to 20

ppm as PO4

Total Dissolved Solids

3500

2500

1500

ppm

Silica

<0.4 of Caustic Alkalinity

<0.4 of Caustic Alkalinity

15

As ppm SiO2

59

ASME Guidelines for Water Quality in Modern Industrial Water Tube Boilers for Reliable Continuous Operation Boiler Feed Water

Boiler Water Specific Total Conductance Alkalin (micro mh ity**(ppm os/cm)(unn CaCO3) eutralized)

Drum Pressure (psi) (kg/cm2)

Iron (ppm Fe)

Copper (ppm Cu)

Total Hardness (ppm CaCO3)

0-300 (0-20)

0.100

0.050

0.300

150

700*

7000

301-450 (21-30)

0.050

0.025

0.300

90

600*

6000

451-600 (31-42)

0.030

0.020

0.200

40

500*

5000

601-750 (43 –52)

0.025

0.020

0.200

30

400*

4000

751-900 (53-63)

0.020

0.015

0.100

20

300*

3000

901-1000 (64-70)

0.020

0.015

0.050

8

200*

2000

1001-1500 0.010 (71-105)

0.010

0.0

2

0***

150

1001-1500 0.010 (71-105)

0.010

0.0

1

0***

100

Silica (ppm SiO2)

ABMA Standard Boiler Water Concentrations for Minimizing Carryover Drum Pressure (psig) 0-300 301-450 451-600 601-750 751-900 901-1000 1001-1500 1501-2000

Total Silica*(ppm SiO2) 150 90 40 30 20 8 2 1

Boiler Water Conductance Specific** (micromhos Alkalinity (ppm CaCO3) /cm) 700 7000 600 6000 500 5000 400 5000 300 3000 200 2000 0 150 0 100

This value will limit the silica content of the steam to 0.25 ppm as a function of selective.

60


Boiler Water Limits

Boiler Pressure psig

TDS

Alkalinity

Suspended Solids

Silica*

0 to 300

3500

700

300

125

301 to 450

3000

600

250

90

451 to 600

2500

500

150

50

601 to 750

2000

400

100

35

751 to 900

1500

300

60

20

901 to 1000

1250

250

40

8.0

1001 to 1500

1000

200

20

2.5

1501 to 2000

750

150

10

1.0

Over 2000

500

100

5

0.5

Silica Levels Allowed in Boiler Water

Boiler Pressure (psi)

Allowable Silica (as ppm SiO2)

0-15

150

16-149

150

150-299

150

300-449

90

450-599

30

40

750

600-749

20

61

CHAPTER 8

62


Cooling Water Treatment Description of Process Cooling towers are heat exchangers that are used to dissipate large heat loads to the atmosphere. They are used in a variety of settings, including process cooling, power generation cycles, and air conditioning cycles. All cooling towers that are used to remove heat from an industrial process or chemical reaction are referred to as industrial process cooling towers (IPCT). Cooling towers used for heating, ventilation, and air conditioning (HVAC), are referred to as comfort cooling towers (CCT). Cooling towers are classified as either wet towers or dry towers. Dry towers use a radiator like cooling unit instead of water evaporation.

Objective for Cooling Water Treatment The following four basic objectives for Cooling Water Treatment are 1.

Minimize problems from corrosion, scale, deposition, and growth to obtain maximum efficiency.

2.

Implementation and control must be "do-able" with a minimum input of labor and money.

3.

Cost effective as possible considering the total water system capital and operating costs.

4.

Must be environmentally acceptable.

Factors important for cooling System Following steps are necessary to optimize the cycle of concentration (COC) for a cooling tower and evaluate cooling water requirement or replacement 1.

Evaluate the cooling system

2.

Determine the water quality constituents sand concentration limits for cooling system protection

3.

Evaluate water treatment requirements

4. Choosing monitoring and maintenance requirement Create a plan to change chemistry or flow rates, if problem occurs.

63

Equipment Cooling tower

Wood, Plastic, Metal and fiber glass

Piping for cold water

Mild steel (MS), PVC, Stainless steel (SS) and fiber glass

Heat exchangers(Chillers, Jacketed vessel, etc)

Copper, copper alloy, SS, & galvanized steel tubes

Covers of Heat exchangers & Support plates

Mild steel Water lines may be of copper

Type of Material

64

Material of construction

Effect of impurity

GI Pipes

Corrosion (white rust) at High TDS and pH above 8.5 or less than 6.5

Stainless steel

Corrosion due to chloride, Chloride above 200 ppm can create problem in Ss304 when deposit forming conditions exist but if no deposit forming surface can withstand around 1000 ppm Cl. 316 SS can withstand about 5000 ppm Cl even with deposit forming surface

Mild steel

Highly corrosive due to solids and also due to acidic or basic conditions Oxygen also corrosive to mild steel

Copper & Copper alloys

Corrosion to ammonia

Wood

Natural decay. Can get chemically attacked.

Plastic

Corrosion resistant. Biomass can get built up on plastic film


Cooling Tower Maintenance Schedule

Daily/Weekly 1.Test water sample for proper concentration of dissolved solids. Adjust bleed water flow as needed. 2.Measure the water treat-ment chemical residual in the circulating water. Maintain the residual recommended by your water treatment specialist. 3.Check the strainer on the bottom of the collection basin and clean it if necessary. 4.Operate the make-up water float switch manually to ensure proper operation. 5.Inspect all moving parts such as drive shafts,pulleys, and belts. 6.Check for excessive vibration in motors, fans, and pumps. 7.Manually test the vibration limit switch by jarring it. 8.Look for oil leaks in gearboxes. 9.Check for structural deterioration, loose connectors, water leaks, and openings in the casing. 10.During periods of cold weather, check winterization equipment. Make sure any ice accumulation is within acceptable limits.

Periodic 1.Check the distribution spray nozzles to ensure even distribution over the fill. 2.Check the distribution basin for corrosion,leaks, and sediment. 3.Operate flow control valves through their range of travel and re-set for even water flow through the fill. 4.Remove any sludge from the collection basin and check for corrosion that could develop into leaks. 5.Check the drift elimina tors, air intake louvers, and fill for scale build-up. Clean as needed. 6.Look for damaged or out- of-place fill elements. 7.Inspect motor supports, fan lades, and other mechanical parts for excessive wear or cracks. 8.Lubricate bearings and bushings. Check the level of oil in the gearbox. Add oil as needed. 9.Adjust belts and pulleys. 10.Make sure there is proper clearance between the fan blades and the shroud. 11.Check for excessive vertical or rotational replay in the gearbox output shaft to the fan.

Annual 1.Check the casing basin,and piping for corrosion and decay.Without proper mainte -nance,cooling towers may suffer from corrosion and wood decay. Welded repairs are especially susceptible to corrosion. The protective zinc coating on galva -nized steel towers is burned off during the welding process. Prime and paint any welded repairs with a corrosion resistant coating. 2.Leaks in the cooling tower casing may allow air to bypass the fill. All cracks, holes, gaps, and door access panels should be properly sealed.Remove dust, scale, and algae from the fill, basin, and distribution spray nozzles to maintain proper water flow.

65

Cooling Tower Inspection Process Generally, the cooling tower structure and system should be inspected every six months in temperate climates. In more tropical and desert climates the interval should be more frequent, in accordance with equipment manufacturer and engineering recommendations. A list of items that need to be inspected is shown below: u Wooden structural members: - Look for rotten and broken boards, loose hardware and excessive fungal growth. The plenum area after the drift eliminators is the most likely to suffer wood rot, since biocides added to the water do not reach this area. Pay particular attention to structural members in this area. u Other structural members: - Check concrete supports and members for excessive weathering and cracking. Look for metal corrosion. On fiberglass ductwork and piping, check for cracking and splitting. u Water distribution throughout the tower should be uniform. Check piping for leaks. u Fans should be free of excessive vibration. Check mounts for deterioration and looseness. Examine blade leading edges for fouling, corrosion and dirt buildup. Check the fan stack for integrity, shape and stack-to-blade clearance. u Inspect for broken fill, debris in the fill, scale on fill water outlet. u Look for debris and plant growth in the drift eliminator. Make sure the eliminator is not broken or missing altogether. u Check for alga growth, scale and plugged nozzles in the hot water bay (cross flow towers). Nozzles should be checked monthly during the cooling season. u Record all observations on the Operator Checklist. This should include gearbox oil levels, oil additions (frequent refills could be a sign of bearing wear or leaks), water data, chemical inventories and hot water bay observations.

Cooling Water Monitoring u Be sure to keep the water log sheet records up to date. Maintain a record of necessary components, control ranges, control capabilities (especially for calcium, pH, alkalinity, biocide, chemical feeds, conductivity, possible phosphate content.) Follow water treatment procedures closely. u Periodically check the water appearance for turbidity and foam. u Inspect wet surfaces for evidence of slime, algae or scale. Do the same for submerged surfaces. Use a corrosion coupon to monitor system corrosion rates where potential corrosion problems are indicated. u Monitor chemical additions for visible and uniform flow and proper rate.

66


u Heat exchangers can also be monitored for heat transfer performance to give an early warning of water treatment deficiencies. Small side stream test heat exchangers are available commercially for monitoring cooling water site fouling. Biological growth can rapidly cause systems to get fouled. Slime appearing on a submerged coupon is a good indicator that there is a problem. Submerged coupons, which are found in the cooling tower reservoir, indicate growth in less accessible areas of the cooling tower. Treatment Chlorination Filtration Sulphuric acid Inhibitors Antiscalant Antifoulant Fouling in cooling system Reasons of Fouling If fouling is not controlled, it will result in heavy deposits inside Silt introduced by the makeup water cooling water tubes, resulting in Dirt from air reduced tube diameter. Reaction of residues from chemical treatment Fouling is controlled by filtration and by chemicals and oxidation by Microbiological debris chlorine and or ozone Products produced by corrosion such as hydroxides and insoluble salts Selection of capacity of side stream filter % reduction of undissolved solids Select 80 % Time desired for reduction in hours = t= 48 hours maximum select maximum in 48 hours Blowdown = b in M3/hrs b=100 M3/Hrs V= total volume of cooling system M3 6000 Filtration rate F= v/t Loge[(100)/(100-%reduction)]-b Microorganism Bacteria, algae and fungi present in cooling water decreases the efficiency of heat transfer in cooling tower and condensers. Chlorine is the most widely used chemical in industry as oxidizing agent for destruction and dissolution of microorganism Chlorine is only effective when pH is between 6 to 7 Cooling water pH %of HOCl for effective oxidation 6 97 7 76 8 24 9 3 At pH 7 in CW system every 1 ppm Cl2 dosed only 0.76 ppm is used as oxidizing agent for control of microorganism General guidelines for chlorine dosing of reasonably good water Cooling Water System Estimated Chlorine dosage

67

Cooling Water System Once Through inland Lake /river/seawater

Estimated Chlorine dosage Continuous dosing of 1-2 ppm + shock dosing of 3-5 ppm for 15 minutes after every 8 hour cycle

Recirculation cooling water system

Continuous 1-2 ppm. Shock dose of 3-5 ppm

Makeup water for CW circulation water

Continuous 1-2 ppm.

Calculation of H2SO4 Dosing System CW circulation rate

CWR=34000

Makeup water percentage

P=2

M Alkalinity to be maintained ppm

M=150

M.Alkalinity in Makeup water ppm

A=140

Cycle of concentration

C=2

Quantum of M.Alkalinity ppm

68

(CWR*P/100 *Q) /1000 Acid dosing =34000* Required AH 0.02*130/ 1000=88.4 kgs at 98 %

Dosage Quantity at 30oC

Q=[(A*C)-M]=[(140*2) -150]=130

H2SO4 %

Sp.Gr

98

1.826

Dosing D=AH/ Sp.Gr =88.4/ 1.826 =48.4 lph


Impact of Water quality Parameters on Cooling Systems Water Quality Parameters

Hardness (Ca +Mg )

Alkalinity mainly due bicarbonate Silica TSS

Impact on System Scaling Calcium scaling more troublesome because of inverse solubility of some calcium salts) Magnesium salt problematic whenn silica levels high. Can be corrosive. Useful in predicting Calcium carbonate scale potential

Treatment

Softening by external treatment Antiscalant Descaling if scaling has taken place Dealkalization

Difficult to remove silica deposit Apart from makeup water, SS can also be present as corrosion and deposit by products. Can be cause of Under deposit corrosion by adhering to bio film. Ideal nutrient for Micro organism, Highly corrosive to copper, Reduces chlorine effectiveness as Disinfectant Problem when in high concentration (Ca>1000 ppm) & (PO4 >20 ppm) Calcium Phosphate deposit Corrosive at higher concentration For SS 300 ppm considered corrosive but for other metals >1000 ppm considered corrosive Forms undesirable foulants with Phosphate.Deactivates specialized polymers used to inhibit calcium phosphate scaling.

Pretreatment like coagulation and clarification Side stream filtration

BOD

Indication of Bio growth

Oxidizing Biocide

Zinc

Good at low levels but can contribute to deposit at higher level

Organism

Manure for microorganism

Heavy Metal

Galvanized Corrosion

Ammonia

Phosphate

Chloride

Iron

Bromine better disinfectant in presence of Ammonia Air stripping Close monitoring of Blowdown. Proper use of dispersant

69

Non Oxidizing Biocides Material

% Formula Form active

Min Dose ppm

Max Dose ppm

Feed Time

Min pH

Max pH

1 Methylenebisthiocya-nate

SCNCH2SCN

SS

10

25

50

1/wk

6

8

Tetrahydro 3,5Dimethyl2H-1-3,52 Thiadiazone-2Thione

C5H10 N2S2

Sol

24

30

60

1/wk

6.5

14

Na Dimethyl– Dithio3 carbamate

C3H6NS2 Na

Sol

30

20

40

1/wk

7

14

DibromoNitrilo4 Propion-amide

C3H2N2 OBr

Sol

20

6

15

1/wk

6

8

(Chloro) 5 Methylisothiazolin one

C4H4NOS Cl & C4H5NOS

Sol

1.15

25

50

1/wk

6

9.5

Glutaral 6 dehyde

O=CH (CH2)3 CH=O

Sol

45

25

100

1/wk

6

14

AlkylBenzylRC6H5 7 Dimethyl Ammonium (CH3)3 NCl Chloride

Sol

9.4

30

120

1/wk

6

14

Dioctyl(C6H17)2 Dimethyl (CH 3)2 8 Ammonium NCl Chlorite

Sol

50

30

120

1/wk

6

14

SS-suspension & Sol=Solution (Source –Technical Data sheet of Vulcan Chemicals).

70


Oxidizing Biocides: Material

Formula

Form

% FAC

Residual Requirements Min Dose ppm

Max Dose ppm

Feed Type

Min pH

Max pH

Chlorine Dioxide

ClO2

sol

–

0.2

0.5

C

5

9

Chlorine

Cl2

gas

100

0.5

1.0

C

6

7.5

Calcium Hypochlorite

Ca (OCl)2

solid

65

0.5

1.0

C

6

7.5

Sodium Hypochlorite (I)

NaOCl

solution

12

0.5

1.0

C

6

7.5

Sodium Hypochlorite(D)

NaOCl

solution

5

0.5

1.0

C

6

7.5

Lithium Hypochl orite

LiOCl

solid

35

0.5

1.0

C

6

7.5

(CON Cl)3

solid

89

0.5

1.0

C

6

7.5

(CON)3 Cl2 Na

solid

56

0.5

1.0

C

6

7.5

solid

––

0.2

0.5

C

7

10

varies

38% as NaBr

2.0

4.0

C

7

10

Trichloro Isocyanuric acid Sodium Dichloro Isocyanuric acid Bromo, Chloro, Dimethyl Hydantion Sodium Bromide“Chlorine”

C5H6N2 O2ClBr

NaBr

71

Diagnostic Indicators for Cooling Systems Indicator

72

Possible Problem

Possible Solution

Metals: Copper>0.25 mg/l Iron>1.0 mg/l Zinc>0.5 mg/l OR Measured corrosion rates Copper>0.2MPY Mild steel piping>3 MPY Mild steel Hex tubing> 0.5 MPY Galvanized steel>4 MPY

High corrosion rate Inadequate chemical dosage control Use of conditioning chemicals containing copper or zinc

Improve corrosion protection through use of an additive or by other means Improve additive dosage control and/or monitoring Eliminate use of additives containing copper or zinc Consider replacing copper components or piping

Additives: Chlorine > 0.5 mg/l Ozone >0.2 mg/l

Overuse of these oxidizing chemicals leads to high corrosion rates

Reduce or stabilize additive dosage Improve monitoring Install an automatic conductivity probe controlled oxidizing agent feed system.

Carbon dioxide> 5 mg/l

Copper oxide protection is inhibited

pH < 7.0

Inadequate pH control

Implement pH control Check dosage of low-pH additives

Water velocity: > 3 feet/sec @ >150ºF > 5 feet/sec @ 120ºF > 8 feet/sec @ <90ºF

Leaks or system failure High rate of corrosion of copper piping;could cause leaks or system failure

Reduce recirculation rate Increase line size Replace copper elements with non metallic parts or other non copper parts

Conductivity outside the manufacturer's recommended range

System operation not optimized Possible misuse of additives Improper blowdown rate

Investigate: System settings Chemical dosing rates Blow down system operation

The water consumption rate has increased greatly.

The heat load to the system has greatly increased. Possible massive system leak.

Check if additional heat load has been added on the system today. Check the system for leaks. Inspect sanitary sewer and storm sewer manholes on site for unusually high flows.

Raise pH


Cooling water distribution headers in all plants are generally of carbon steel without any protective lining. In some places Hume pipe are also used to severe corrosion.

Coolers and condensers (tube Bundles) Fertilizers – Stainless steel and carbon steel Oil refineries – general admiralty brass but in some cases combination of admiralty brass and carbon steel Petrochemicals- Combination of 90-10 Copper Nickel, admiralty brass, SS and carbon steel LPG Plants- mainly carbon steel Acrylic Fiber Plants – Stainless steel, Copper –Nickel and carbon steel Chilling and refrigeration - 90-10 copper Nickel, Copper / SS Air compressor & Nitrogen Plants – Admiralty Brass Power plants – Copper-Nickel /Copper /SS Control limits for various cooling water treatments

Table1 SHMP + Zn

SHMP+CrO4+Zn

Characteristics

Unit

1

pH

Mg/L

2

MO Alkalinity

Mg/L

3

Ca Hardness

Mg/L

200-300

300

200-300

300

4

Total hardness

Mg/L

300-500

500

300-500

500

5

Chloride as Cl

Mg/L

200-300

300

200-300

300*2

6

Sulphate as SO4

Mg/L

800-1000

1000

800-1000

1000

7

Silica as SiO2

Mg/L

100

75-100

100

8

TSS

Mg/L

75-100 20-30 (30-50)

*3

30 (50)

20-30

30

15-20

25*4

10-15

15*4

––

20-25

30*4

Organo Phosphate Mg/L (HEDP) as PO4 10 Total Inorganic Phosphate as PO4 Mg/L

Normal Maximum Normal Maximum 6.3

6.5-7.0

6.8 *1

7.0 *1

*2

9

––

11 Chromate as CrO4

Mg/L

Zinc Sulphate as Zn Polymeric 13 dispersant

Mg/L

3-5

5*4

Mg/L

5-10

10

12

14

TDS

Mg/L

1200-1500 1500

2-3 ––

3*4 ––

1500-2000 2000

*1-MO Alkalinity will find its own level based on pH to be maintained. *2- In case of stainless steel exchangers, chloride levels will be low depending on design. *3- With polymeric dispersant *4 Actual inhibitors levels depend on operating conditions

73

Table2 Zn+O-PO4+ Polymer Characte ristics

Unit

Normal

Maxi mum

7.5–8.0

8.0

1

pH

Mg/L

2

MO Alkalinity

Mg/L

Zn +HEDP Normal

*1

Maxi mum

Zn +HEDP + SHMP (max) Nor Maxi mal mum

*1

*1

3

Ca Hardness

Mg/L

300400

4

Total hardness

Mg/L

600800

800

600-800

800

600-800

800

5

Chloride as Cl

Mg/L

200-300

300*1

200-300

300*2

200-300

300*2

6

Sulphate as SO4

Mg/L

8001000

1200

800-100

1200

8001000

1200

7

Silica as SiO2

Mg/L

75-100

125

75-100

125

75-100

125

TSS

Mg/L

30-50

50

20-30 (30-50)*3

30 (50)*3

20-30 30 (30-50)*3 (50)*3

Organo Phos phate(HEDP) as PO4

Mg/L

–

–

8-10*4

10*4

4-6*4

4-6*4

Mg/L

–

–

–

–

6-8*4

8*4

Orthophos 11 phate as PO4

Mg/L

8-10*4

15*4

–

–

–

–

12 Zinc Sulphate as Zn

Mg/L

1-1.5

1.5

2-3

3

1.5-2

2

Polymeric 13 dispersant

Mg/L

20-30

50

5-10

10

15-20

20

14 TDS

Mg/L

15002000

2000

15002000

2000

15002000

8

9

Total Inorga 10 nic Phosp-hate as PO4

400

300-400

400

300-400

400

*1-MO Alkalinity will find its own level based on pH to be maintained. *2- In case of stainless steel exchangers, chloride levels will be low depending on design. *3- With polymeric dispersant *4 Actual inhibitors levels depend on operating conditions

74


Puckorius Scaling Index The Langelier Saturation Index and Ryznar Stability Index were originally developed to identify scaling (calcium carbonate) and corrosion tendencies of water in supply piping. These indexes, which are still in wide use today, are considered very conservative. Most scaling and corrosion conditions identified by these indexes can typically be controlled by specialty chemicals. Their usefulness is therefore limited, but because of their common use, the following calculation procedure is provided The Puckorius Scaling Index modifies the Ryznar Stability Index by calculating the pH of the bulk water, and thus, more accurately predicts scaling conditions. LSI = (measured pH) - (pHs). A positive value indicates scale; a negative value, no scale. RSI = (2 pHs) - (measured pH). A value below 6 means scale; above 6, no scale. Calculating pH of saturation (pHs). The pH of saturation (pHs) can be determined from the relationship between various characteristics of water. The following factors and formula are used in determining the pHs: (1) Factors Needed to Calculate pHs: A = Total Dissolved Solids (ppm), table B-1 B = Temperature (oF), table B-2 C = Calcium Hardness (ppm as CaCO3), table B-3 D = Total Alkalinity (ppm as CaCO3), table B-4 (2) pHs = 9.30 + A + B - (C + D) Calculation of Calcium Carbonate Saturation Index Factor "B" FOR Temperature

Factor "A" FOR Total dissolved Solids Total Solid Mg /liter

Value of “A”

50

0.07

100

0.1

600

0.18

1000

0.2

2000

0.22

3000

0.24

4000

0.25

5000

0.26

o

o

C 0-1 2-6 7-9

F 32-34 36-42 44-48

10-13 14-17 18-21 2.1 28-31 32-37 38-43 44-50 51-55 56-64 65-71 72-81

50-56 58-62 64-70 72-80 82-88 90-98 100-110 112-122 124-132 134-146 148-160 162-178

Value of “B” 2.6 2.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2

75

Factors "C" for Calcium Hardness (as ppm CaCO3)* Zero to 1000 ppm Calcium Hardness Value of “C” As CaCO3

76

Calcium Hardness Value of “C” As CaCO3

10-11

0.6

10-11

1.0

12-13

0.7

12-13

1.1

14-17

0.8

14-17

1.2

18-22

0.9

18-22

1.3

23-27

1.0

23-27

1.4

28-34

1.1

28-34

1.5

35-43

1.2

35-43

1.6

44-55

1.3

44-55

1.7

56-69

1.4

56-69

1.8

70-87

1.5

70-87

1.9

88-110

1.6

88-110

2.0

111-138

1.7

111-138

2.1

139-174

1.8

139-174

2.2

175-220

1.9

175-220

2.3

221-270

2.0

221-270

2.4

271-340

2.1

271-340

2.5

341-430

2.2

341-430

2.6

440-550

2.3

440-550

2.7

551-690

2.4

551-690

2.8

691-870

2.5

691-870

2.+

871-1000

2.6

871-1000

3.0


Equilibrium pH Value (pHeq) determined from Total Alkalinity Alkalinity ppm hundreds

Alkalinity, ppm CaCO3, tens 0 ––

10

20

30

40

50

60

70

80

90

6.00 6.45 6.70 6.89 7.03

7.14 7.24

7.33

7.44

100

7.47 7.53 7.59 7.64 7.68 7.73

7.77 7.81

7.84

7.88

200

7.91 7.94 7.97 8.00 8.03 8.05

8.08 8.10

8.15

8.15

300

8.17 8.19 8.21 8.23 8.25 8.27

8.29 8.30

8.32

8.34

400

8.35 8.37 8.38 8.40 8.41 8.43

8.44 8.46

8.47

8.48

500

8.49 8.51 8.52 8.53 8.54 8.56

8.57 8.58

8.59

8.60

600

8.61 8.62 8.63 8.64 8.65 8.66

8.67 8.67

8.68

8.70

700

8.71 8.72 8.73 8.74 8.74 8.75

8.76 8.77

8.78

8.79

800

8.79 8.80 8.81 8.82 8.82 8.83

8.84 8.85

8.85

8.86

900

8.87 8.88 8.89 8.89 8.90 8.90

8.91 8.92

8.92

8.93

0

Example 1 Water from a cooling tower has a TDS of 1,000 ppm, calcium hardness of 500 ppm (as CaCO3), total alkalinity of 100 ppm (as CaCO3) and measured pH of 8.2. The hottest temperature on the waterside of the heat exchanger is 120oF. pHs = 9.30 + A + B - (C + D) pHs = 9.30 + 0.20 + 1.57 - (2.30+2.00) = 6.77

Example 2 Water from a cooling tower has a total alkalinity of 100 ppm (as CaCO3) and a measured pH of 8.2 (same as example 1). From table 5, the pHeq is 7.47. PSI = (2pHs) - (pHeq) = 2 (6.77) - 7.47 = 13.54 - 7.47 = 6.07 RSI = (2pHs) - (measured pH) = 13.54 8.2 = 5.34 LSI = (measured pH) - (pHs) = 8.2 6.77 = +1.43 The pHeq may also be calculated as follows: pH eq = 1.485 log TA + 4.54 where TA denotes total alkalinity.

77

Scaling Indices versus conditions LSI

PSI/RSI

Condition

3.0

3.0

Extremely severe scaling

2.0

4.0

Very severe scaling

1.0

5.0

Severe scaling

0.5

5.5

Moderate scaling

0.2

5.8

Slight scaling

0.0

6.0

Stable water, no scaling, no tendency to dissolve scale

-0.2

6.5

No scaling, very slight tendency to dissolve scale

-0.5

7.0

No scaling, slight tendency to dissolve scale

-1.0

8.0

No scaling, moderate tendency to dissolve scale

-2.0

9.0

No scaling, strong tendency to dissolve scale

-3.0

10.0

No scaling, very strong tendency to dissolve scale

Selection of capacity for side stream Filter for cooling tower F=V/t loge [(100) / (100-% reduction)]-b % of reduction of undissolved solids (select 80 %) t= time desired for reduction in hours (select maximum of 48 hours) b= blowdown rate in m3/hr V= total volume of cooling system in M3 Example for V=6000 M3, t=48 hours and b=100 M3/Hr F=100 M3/H

78


CHAPTER 9

79

Pumps Introduction Pumps play a vital role in any water treatment system. Pump moves liquid from one place to another. Hence selection of pump is very critical in all water treatment system. Here we are giving general guideline, which will help, in discussing with the pump manufacturer or supplier.

Types of Pump The three types of pump most commonly employed are Centrifugal, Rotary and Reciprocating. Each class of pump is further divided into. Pump Class

Centrifugal

Rotary

Reciprocating

Type Volute Diffuser Regenerative turbine Vertical Turbine Mixed Axial Flow Axial flow (Propeller)

Single stage and Multistage. See manual on pumps

Gear Vane Cam & Piston Screw Lobe Shuttle Block Direct acting Power(including Crank & Flywheel) Diaphragm Piston

Simplex Duplex Triplex

Characteristics of different types of pumps

80

Characteristics

Centrifugal

Rotary

Reciprocating

Discharge Flow

Steady

steady

steady

Usual Maximum suction lift (Meters)

4.6

6.7

6.7

Liquid handled

Clean, clear dirty abrasive and liquids with high solid content.

Viscous, Nonabrasive

Clean and clear

Discharge Pressure range

Low to high

Medium

Low to high


Smallest to largest available

Usual capacity range

Small to medium

Relatively small

How increased head affects capacity

Decrease

None

Decrease and None for duplex and triplex

Power input

Depends on specific speed

Increase

Increase

How decreased head affects capacity

Increase

None

Increases marginally

Depends on specific speed

Decrease

Decrease

Power input

Liter/sec

5

2

3

100

200

34

44

50

58

66

72

75

78

81

83

5

0.15

1.23

0.30

0.43

0.75

1.47

1.96

3.15

6.05

11.8

7

0.20

0.31

0.41

0.59

1.04

1.91

2.75

4.4

8.48

16.6

10

0.29

0.45

0.59

0.85

1.49

2.73

3.92

6.3

12.1

23.6

20

0.58

0.89

1.18

1.69

2.97

5.45

7.84

12.6

24.2

47.3

30

0.87

1.34

1.77

2.54

4.46

8.18

11.8

18.9

36.3

71.0

50

1.44

2.23

2.94

4.23

7.43

13.6

19.6

31.5

60.5

118

70

2.02

3.12

4.12

5.92

10.4

19.1

27.5

44.0

84.8

166

100

2.88

4.46

5.88

8.45

14.9

27.3

39.2

63.0

121

236

200

5.77

8.92

11.8

16.9

29.7

54.5

78.4

126

242

473

300

8.65

13.4

17.7

25.4

44.6

81.8

118

189

363

710

500

14.4

22.3

29.4

42.3

74.3

136

196

315

605

1180

Average efficiency

1

10

20

30

50

Total head in meters

81

Basic guideline for selecting Pump 1. 2.

3. 4. 5. 6.

Sketch the proposed piping layout. Base the sketch on actual job condition. Single line diagram can be used Determine the required capacity of pump. The required capacity is the flow rate, which has to be handled at a particular pressure. Once the flow rate has been determined a suitable factor of safety is applied. In any case it should not be less than 10 % Compute the total head on pump Analyze the liquid conditions. Obtain complete data on liquid to be pumped. Select the class and type as given in the table Evaluate the pump chosen for installation. Check specific speed, impeller type and operating efficiency.

Formulas required for pump Calculation Specific speed of impeller Nq=3.65*n*Q ½ / H ¾, Where n= speed in rpm H= head in meters, Q= discharge in Cubic meter /sec This calculation allows comparison of all types of rotodyanmic pump on equal footing.

Pressure and Specific Gravity Pressure developed by pump is proportional to specific gravity of liquid. P=H, Where Y is the specific gravity H in meters = Pressure in absolute atmosphere/ Sp.Gravity H in Feet = Pressure psi/Sp.

Power Absorbed by pump Power = *Q*H /C1*n, Where Y is Sp.Gravity Q –Discharge rate (capacity) in Cubic meter /sec H= head in Meter C1 = 75 for power in Metric HP = 76.04 for power in British HP = 101.98 for power in Kw =1000 kgf/M3 at 4C Motor, brake, and water horsepower can be calculated as follows: Mhp = Brake horsepower / Motor efficiency Bhp = Water horsepower / pump efficiency Whp = head (ft) x flow (gpm) /3960 To better understand the performance and operating characteristics of pumps, operators should become familiar with the pump curve that is supplied by the manufacturer for each pump.

82


Pump curves usually show three curves on one sheet: u The head-capacity curve shows the discharge in gallons per minute (gpm) the pump will deliver against various heads when operated at the proper speed. This curve shows that as the head increases, the discharge decreases, until there is no further discharge. Conversely, as head decreases, flow increases. u The second curve, also plotted against flow, shows the efficiency at which the pump operates at various points on the head capacity curve. This curve shows that no pump is 100% efficient, due to internal friction losses. The highest efficiency that can be hoped for is around 85%. Efficiency can be expected to decrease with age and wear. u The third curve, the brake horsepower curve, shows power consumed plotted against flow. If we know the total head at which the pump is operating, we can use the curve to find the gallons pumped. The power required by the pump, as well as the pump efficiency, can also be read from the curve for any set of conditions. This curve shows that it usually takes more horsepower to pump more water: the lower the flow, the lower the horsepower required, and the higher the flow, the higher the horsepower required.

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CHAPTER 10

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Raw Water Treatment Objectives The objectives of a public water supply water system are to provide safe and aesthetically appealing water to the customers without interruption and at a reasonable cost- an adequate quantity of water at sufficient pressure for fire protection and industrial water for manufacturing.

Selection of Water Treatment Processes Selection of a suitable water treatment process for a given utility is always a complex and diverse task. Conditions are likely to be different for different water utility. Adoption of an appropriate water treatment process by a water utility is influenced by the necessity to meet the regulatory guidelines, the desire of the utility and its customers to meet other water quality standards and objectives and the need to provide water service at the lowest reasonable cost. A water treatment plant should be designed considering the fact that it should supply continuous and safe water to the customers regardless of the raw water characteristics and the environmental conditions. Hence, the selection of treatment process is important in the plant design. The ultimate plant design has a system that is proven to be simple, effective, reliable, durable and costeffective. The design of water treatment plant starts with the preliminary studies that include: 1. Design period; 2. Water supply areas – identifying the areas to be served; 3. Population – estimating the present and future population; 4. Estimating maximum daily water demand; 5. Evaluation and selection of the water source; 6. Size of the treatment plant; 7. Location of the treatment plant site; and 8. Financing. The selection of package treatment plants and special proprietary devices or processes should be based on proper consideration of: Raw water condition and demand variability; 1. Operation and maintenance; 2. Servicing, repairs or replacement; and Operational flexibility.

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Water Treatment Processes Aeration Aeration is the process of bringing water and air into close contact in order to remove dissolved gases, such as carbon dioxide, and to oxidize dissolved metals such as iron. It can also be used to remove volatile organic chemicals (VOC) in the water. Aeration is often the first major process at the treatment plant. During aeration, constituents are removed or modified before they can interfere with the treatment processes. Examples of aeration processes include diffused mechanical nozzle spraying, multiple tray cascading and packed power type.

Coagulation The first step destabilizes the particle's charges. Coagulants with charges opposite those of the suspended solids are added to the water to neutralize the negative charges on dispersed non-settlable solids such as clay and colorproducing organic substances. Once the charge is neutralized, the small-suspended particles are capable of sticking together. The slightly larger particles formed through this process and called microflocs, are not visible to the naked eye. The water surrounding the newly formed microflocs should be clear. If it is not, all the particles' charges have not been neutralized, and coagulation has not been carried to completion. More coagulant may need to be added.

Flocculation Following the first step of coagulation, a second process called flocculation occurs. Flocculation, a gentle mixing stage, increases the particle size from submicroscopic microfloc to visible suspended particles. The microflocs are brought into contact with each other through the process of slow mixing. Collisions of the microfloc particles cause them to bond to produce larger, visible flocs called pinflocs. The floc size continues to build through additional collisions and interaction with inorganic polymers formed by the coagulant or with organic polymers added. Macroflocs are formed. High molecular weight polymers, called coagulant aids, may be added during this step to help bridge, bind, and strengthen the floc, add weight, and increase settling rate. Once the floc has reached it optimum size and strength, the water is ready for the sedimentation process.

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Sedimentation Sedimentation basins are used to settle out the floc before going to the filters. Some type of sludge collection device should be used to remove sludge from the bottom of the basin.

Filtration Removal of suspended solids by filtration plays an important role in the natural treatment of groundwater as it percolates through the soil. It is also a major part of most water treatment. Groundwater that has been softened or treated through iron and manganese removal will require filtration to remove floc created by coagulation or oxidation processes. Since surface water sources are subject to run-off and do not undergo natural particles and impurities. Iron and manganese in water also promote the growth of iron bacteria, a group of organisms that obtains its energy for growth from the chemical reaction that occurs when iron and manganese mix with dissolved oxygen. These bacteria form thick slime growths on the walls of the piping system and on well screens. Such shines are rust-colored from the iron and black-colored from the manganese. Variations in flow can cause these slime growths to come loose, resulting in dirty water in the system.

Disinfection The object of disinfection is to kill disease-causing organisms present in the water. With regard to water treatment, disinfection refers to the destruction of most intestinal or fecal bacteria. Sometimes disinfection is not complete. Some viruses and especially some protozoa, such as Giardia or cryptosporidium, could survive the disinfection process. The only method of complete protection is to sterilize the water by boiling it for a period of 15 to 20 minutes The methods of disinfection practical in public water supplies are chlorination, ozonation, use of ultra-violet light, and over-liming. Potassium permanganate, iodine, bromine, and silver are also used, but less frequently. Chlorination is so widely used that the term disinfection and chlorination are almost the same in waterworks practice. Coarse Screen Coarse screens, often termed bar screens or racks, and must be provided to intercept large, suspended or floating material. Such screens or racks are made of l/2-inch to 3/4-inch metal bars spaced to provide 1- to 3-inch openings. Fine Screen Surface waters require screens or strainers for removal of material too small to be intercepted by the coarse rack, These may be basket-type, in-line strainers, manually or hydraulically cleaned by back washing or of the traveling type, which are cleaned by water jets. Fine screen, clear openings should be approximately 3/8 inch.

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Design Parameters for Water Treatment Processes Aeration Forced or induced draft aeration devices should be designed to ensure even water distribution, adequate counter currents of air and proper external exhausting. As a guide, the loading should be within the range of 0.7 to 3.4 L/s per m² of total tray area (0.8 to 4 gpm/ft.) and 5 or more trays used with separations not less than 150 mm (6 inches). Where pressure aeration is proposed for oxidation purposes, consideration should be given to compressed air quality and mixing, the scaling potential of the water and subsequent air release. Aerators should have a bypass and provisions should be made for inspection and cleaning of the devices. Exhaust gases should be vented outside the building. Coagulation To achieve proper coagulation, high intensity rapid mixing is considered necessary. It is recommended that rapid mixing be accomplished by either an in- line-mixing device or mixing in a separate process tank. Typical energy gradients (G values) would be in the range of 1000 sec-1. It is recommended that some flexibility be provided in rapid mix design if possible. Flocculation The design of flocculation systems should allow for low velocities and avoidance of rapid acceleration to ensure maintenance of a good floc. When designing a flocculation process, selection of the mode of mixing and determination of the physical relations and characteristics of the flocculation tanks and clarifiers (sedimentation tanks) are among the first decisions to be made; either hydraulic mixing or mechanical mixing may be chosen. Where sedimentation follows flocculation, the retention time for floc formation should be at least 30 minutes. Sedimentation This process is designed to remove a majority of the settleable solids by gravitational settling, thereby maximizing the downstream unit processes such as filtration. The factors that influence sedimentation efficiency include: Surface overflow rate (also known as surface loading rate); Inlet and outlet arrangements; type of sedimentation tank; Raw water characteristics and local climate conditions. There are three main configurations for sedimentation tanks: horizontal rectangular basins; upflow sedimentation tanks; and upflow clarifiers with sludge blanket.

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Design Data

Equipment

Design Parameter

Typical Design Values

Unit

Remarks Design should have provision for disposing Debris removed by screens

Coarse Screen

Coarse Screen

0.05–0.08

Meter /sec

Fine Screen

Velocity

0.4 –0.8

Meter /sec

Aeration

Tray type Water velocity Air requirement Tray spacing Area required Cascade Type Head Area Flow velocity Spray Type Head Nozzle diameter Nozzle spacing Nozzle discharge Basin are Spray pressure

0.8-1.5 7.5 30-75 50-160

m3/m2/min m3/m3 water cm m2/m3.s

1.0-3.0 85-105 0.3

meter m2/m3.s m/s

1.2-9 2.5-4.0 0.6-3.6 5-10 105-320 about 70

meter cm meter liter/sec m2/m3.s kPa

Coagulation

Rapid Mix Detention time Velocity gradient Gt

0.2-5 700-1000 3X104 –6X104

Min S-1

Flocculation

Slow Mix Detention time Velocity gradient Gt

0.2-5 15-60 1X104 –15X104

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Sedime-ntation

Rectangular Tanks Surface overflow rate: Detention time: Water depth: Width/Length Weir loading: Upflow Clarifiers Surface overflow rate: Detention(settling) time: Water depth: Weir loading: Upflow velocity Sludge Blanket Clarifiers Surface overflow rate: Detention (settling) time: Weir loading: Upflow velocity: Flocculation time

Rapid sand filter Filtration Rate Backwash rate Air scour Filtration system Minimum filtration cycle Filter media depths Dual Media Silica Anthracite Pressure Filters Filtration rate

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0.8 – 2.5 1.5 – 3 3–5 > 1/5 < 11 1.3 – 1.9 1–3 3–5 7 <3 1– 3 1–2 7 - 15 < 0.6 20

Meter/Hr Hour Meter M3/Hr.M Meter/Hr Hour Meter M3/Hr.M m/h Meter/Hr Hour M3/Hr.M m/h minutes

120-140 37-50 37-73 24

M3/M2.day M3/M2.Hr M3/M2.Hr Hour

>24(600)

Inches (mm)

>200 >450

mm mm M/hour

<15

Taste & Odour Control

Aeration as described before. KMnO 4 Dosage PAC dosage

0.5-2.5 0.5-5

Mg/liter Mg/liter

Disinfe-ction

Chlorine Dose Chlorine residual Ozone dose

1-5 0.5-1 1-5

Mg/liter Mg/liter Mg/liter

Fluoride

Fluoride Dose

0.7-1.2

Mg/liter

PAC is Powdered activated carbon. The dosage of PAC can at times go upto 50 mg/L


Membrane Processes

Microfiltration (MF) Pore size Pressure Ultrafiltration (UF) Pore size Pressure Nanofiltration (NF) Pore size Pressure Reverse osmosis (RO) Pore size Pressure

Distribution Velocity in mains Pressure

m kg/cm2 psig

0.1– 0.2 0.7 – 1.4 (10 – 20) 0.003 – 0.01 0.7 – 7.8 (10-40) 0.001 – 0.005 5.3 – 10.6 (150)

m mm kg/cm2 psig m mm kg/cm2 psig

<1 nm > > 14 (200) kg/cm2(psi)

1-2 138-1000

M/sec kPa

Detention Parameters for Sedimentation coagulants in Water treatment Type of Treatment

Overflow Rate M3/M2/day

Detention Time hours

for

various

Channel Loadings M3/M/Day

Alum coagulation

20-30

2-8

150-220

Iron coagulation

28-40

2-8

200-275

Lime-soda coagulation

28-45

4-8

200-275

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CHAPTER 11

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Industrial Waste Water Treatment Industrial Pretreatment Processes The treatment of industrial wastewater involves the same processes as those used in the treatment of civil water. However, because of specific compositions, the systems tend to vary. The chemical-physical type processes are especially important for the removal of inorganic matter. The basic processes used are

Wastewater Unit operation Unit Operation

Physical

Chemical

Biological

Screening Comminution Flow equalization Sedimentation Flotation Granular –medium Filtration Precipitation Adsorption Disinfection Dechlorination Other Chemical Processes Activated sludge Process Aerated Lagoon Trickling Filters RBC Pond Stabilization Anaerobic digestion Biological nutrient removal

Physical u Screening is removal of coarse solids by use of a straining device. u Sedimentation is gravity settling of pollutants out of the wastewater. u Flotation is the use of small gas bubbles injected into the wastewater,

which causes pollutant particles in the wastewater to rise to the surface for subsequent removal. Air stripping is removal of volatile and semi-volatile organic u compounds from wastewater by use of airflow.

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Chemical Neutralization is adjustment of alkalinity and acidity to the same u concentration (pH 7). Precipitation is addition of chemicals to wastewater to change the u chemical composition of pollutants so that the newly formed compounds settle out during sedimentation. Coagulation is use of chemicals to cause pollutants to agglomerate u and subsequently settle out during sedimentation. Adsorption is use of a chemical, which causes certain pollutants to u adhere to the surface of that chemical. Disinfection is use of a chemical (or other method such as ultraviolet u radiation) to selectively destroy disease-causing organisms. (Sterilization is the destruction of all organisms.) Breakpoint chlorination is the addition of chlorine to the level that u chloramines will be oxidized to nitrous oxide and nitrogen, and chlorine will be reduced to chloride ions.

Biological Air activated sludge is an aerobic process in which bacteria consume u organic matter, nitrogen and oxygen from the wastewater and grow new bacteria. The bacteria are suspended in the aeration tank by the mixing action of the air blown into the wastewater. This is shown schematically in Figure 1. There are many derivations of the activated sludge process, several of which are described in this section. High purity oxygen activated sludge is an aerobic process very similar u to air activated sludge except that pure oxygen rather than air is injected into the wastewater. Aerated pond/lagoon is an aerobic process very similar to air activated u sludge. Mechanical aerators are generally used to either inject air into the wastewater or to cause violent agitation of the wastewater and air in order to achieve oxygen transfer to the wastewater. As in air activated sludge, the bacteria grow while suspended in the wastewater. Trickling filter is a fixed film aerobic process. A tank containing media u with a high surface to volume ratio is constructed. Wastewater is discharged at the top of the tank and percolates (trickles) down the media. Bacteria grow on the media utilizing organic matter and nitrogen from the wastewater. Rotating biological contactor (RBC) is a fixed film aerobic process u similar to the trickling filter process except that the media is supported horizontally across a tank of wastewater. The media upon whom the bacteria grow is continuously rotated so that it is alternately in the wastewater and the air. Oxidation ditch is an aerobic process similar to the activated sludge u process. Physically, however, an oxidation ditch is ring-shaped and is equipped with mechanical aeration devices.

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Pollutant Bio-Chemical Oxygen Demand (BOD)

Pretreatment Processes Activated Sludge Trickling filter or RBC Aerated lagoon Oxidation ditch

Total Suspended Solids (TSS)

Sedimentation Screening Flotation Chemical precipitation

Nitrogen

Nitrification/denitrification Air stripping Breakpoint chlorination

Phosphorus

Chemical precipitation Biological treatment Air stripping

Heavy metals

Biological treatment Chemical precipitation Evaporation Membrane process

Fats, Oil and Grease (FOG)

Coagulation Flotation Biological treatment Membrane process

Volatile Organic Compounds

Air stripping Biological treatment Carbon adsorption

Pathogens

Chemical disinfection UV radiation ozonation

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Pretreatment Process

Items to Look for in the Field for Efficient Operation

Physical Screening

No blinding or clogging of screens, no excessive build-up of material on the screen

Sedimentation

Low flow rate, no short circuiting of flow, no floating sludge, scum removal if appropriate

Centrifugation Air stripping

No scaling of packing and piping, or freezing problems at low temperatures

Chemical Neutralization

pH monitoring, automated chemical feed, adequate mixing

Precipitation

Automated chemical feed system, adequate mixing & contact timer

Coagulation


Adsorption

Efficient means of regeneration is key to performance

Disinfection


Biological

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Activated sludge

Fine bubble aeration, even distribution of air and mixing, dissolved oxygen concentration monitoring, air flow turndown capability, no bulking/floating sludge

Trickling filter

Method for positive air circulation, even & periodic dousing of filter media

Rotating biological contactor (RBC)

Steady shaft rotation


CHAPTER 12

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Chemical Cleaning General Guidance Chemical cleaning of water systems can be divided into two classifications: preoperational and remedial. Pre-operational cleaning is performed to prepare the water-contacted metal surfaces to receive chemical treatment, which provides protection from scale, corrosion, and microbiological growth. Remedial cleaning is performed to restore water systems that have been fouled with scale, corrosion products, and microbiological growth due to inadequate or ineffective water treatment. Cleaning, particularly remedial cleaning is often performed by outside contractors familiar with cleaning procedures, techniques, and safety. It should be noted that if the water system is significantly scaled, the chemical treatment program was obviously inadequate and was not properly designed, set-up, controlled, or applied. After cleaning has been completed, the chemical treatment program and QC program must be improved so the same problem does not recur. Use of a well-designed QA program would have produced identification and notification of potential and developing problems before they became serious. Pre-operational cleaning is often performed by contractors responsible for the fabrication of the water system before turning it over to the military installation. Water system operations personnel must assess the effectiveness of any cleaning process that has been performed.

Pre-Operational Cleaning Pre-operational cleaning can be performed on all new systems or pieces of equipment installed in any existing system, including new boiler tubes or new chiller copper tube bundles. New piping and coils will usually be contaminated with materials such as mill scale, rust, oil, and grease resulting from the fabrication, storage, and installation of the equipment. Pre-operational cleaning is performed to remove these materials and prepare metal surfaces to receive corrosion protection from chemical treatment. Pre-operational cleaning agents that are used include detergents, wetting agents, rust removers, and dispersants. These cleaning agents have a pH in the range of 9 to 11. Water systems containing piping or components constructed of galvanized steel and aluminum should not be subjected to procedures that require high pH (greater than 8.5) because this would contribute to initiating corrosion of these surfaces. The requirement for performing a pre-operational cleaning process is usually written into the specification for new construction of a water system that must be performed by a mechanical contractor. The mechanical contractor is required to perform the work as directed in the specifications. However, if the specifications are not appropriate for the specific system, including consideration of all system metallurgy, the cleaning process may contribute to corrosion to mild steel, galvanized steel, copper, or aluminum, or it may result in incomplete cleaning of dirty and corroded metal surfaces. A qualified inspector should review the specifications or qualified independent consultant to ensure that cleaning agents and procedures have been specified appropriately.

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Remedial Cleaning Remedial cleaning is performed to restore a water system that is fouled with scale, corrosion products, or microbiological biomass due to inadequate or ineffective waters treatment. The problem could have resulted from using improper chemical technology, failure to maintain treatment levels within control parameters or the failure of pretreatment equipment. The cleaning agents used for remedial cleaning usually include acids, chelants, neutralizing agents, and specialty cleaning chemicals.

Safety and Environmental Issues Remedial cleaning may pose safety issues for personnel handling acids, caustics, and various chemicals. There could also be environmental concerns associated with chemical disposal. Inexperienced personnel should not perform the chemical cleaning of an industrial water system.

Contracting Cleaning Services For some cleaning jobs, such as large boilers and cooling towers, it may be advisable to engage a service company specializing in chemical cleaning. If the cleaning service is contracted, it is vital that adequate lines of communication be established, and that safety procedures employed by the service company comply with military regulations. An orientation meeting should be scheduled between military installation personnel and the service company representatives. At that time, the scope of the work can be defined, proper procedures initiated, and the nature of the hazards described thoroughly. The use of proprietary cleaning chemicals or chemical formulations may be involved; disclosure of the use and nature of these chemicals should be made at the orientation meeting. Military policies and restrictions can also be explained.

Reasons for Cleaning Maintenance of an effective water treatment program is essential to minimize scale and corrosion problems in industrial water systems; however, scale and deposits that form will require remedial cleaning (descaling). If not removed, these scale and water-caused deposits may impact the safety of operations personnel, interfere with heat transfer, and cause excessive damage to, or destruction of, the water-using equipment. Cleaning is not appropriate for the removal of deposits when corrosion of the system has advanced to the point where a large number of leaks may result from the removal of the deposits.

Types of Deposits The deposits that occur in water systems can be inorganic mineral salts and corrosion products or organic (oily) or biological in nature. Deposits range in composition from very dense crystalline structures, to very porous and loosely bound materials, to gelatinous slimes. Most of the deposits formed from water constituents consist of corrosion products such as iron and copper oxides, mineral scales, or mixtures of these materials.

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Waterside Deposits Located in Heat Exchangers Water deposits located in heat exchangers are usually carbonate-based scales, while steamside deposits may be a mixture of metallic oxides and organic residuals from lubricating oil, particularly where reciprocating-type engines are used. In steam systems, the oxides are usually iron and copper, resulting from aggressive condensate. Microbiological deposits may form in cooling systems from bacterial or algae growths, or from decomposition products of various microorganisms.

Boiler Deposits Boiler deposits may take various forms. In low-pressure boilers using a relatively hard feedwater, deposits are essentially calcium and magnesium, silicates, sulfates, carbonates, phosphates and hydroxides, plus some organics. Deposits may also contain considerable amounts of silica, iron, and copper. These deposits can be spongy or porous or relatively hard and glasslike. Deposits of the latter characteristic occur where silica is present in appreciable quantities in the boiler water. Deposits in medium-pressure to high-pressure boiler systems usually are mixtures of iron and copper oxides and phosphates. Dense deposits may tend to form in high-heat transfer areas. Considerable quantities of sludge-type accumulations may be found in downcomers, mud drums, waterwall headers, crossover tubes, and areas of low water circulation in the boiler.

Remedial Cleaning Procedure Cleaning procedure information and procedures presented in this Chapter are general in nature and must be modified to fit specific applications. Because contractors perform most cleanings, these procedures are provided only for general information.

Cleaning Methods There are two methods generally adopted for cleaning 1. Mechanical 2. Chemical

Mechanical Methods Mechanical methods are the oldest techniques used for removing deposits. To perform an adequate mechanical-type cleaning, the equipment to be cleaned may need to be partially or entirely dismantled. Even when equipment is dismantled, some areas may be extremely difficult to reach and clean. Chemical cleaning has largely replaced mechanical process equipment cleaning as the most satisfactory method of removing deposits; however, mechanical methods such as wire brushing, tumbling, scraping, and abrasive blasting with sand and grit are still employed in special applications.

Chemical Methods In this method acid or alkali is generally used for cleaning. At times there are other chemicals which are also used for cleaning.

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Cleaning Agents Cleaning agents may be broadly classified as being acid, alkaline, organic, or solvent cleaners. There is no general or universal cleaner that removes all deposits. The selection of a solvent or cleaning agent is based on the material's ability to remove or dissolve the deposit, as well as on cost considerations, safety hazards, and the effect of the cleaning material on the metals involved. General Guidance and Procedures for Preparing Cleaning Solutions General guidance and procedures for preparing cleaning solutions of inhibited hydrochloric (muriatic) acid and inhibited sulfamic acids are provided in paragraphs below. Inhibited acid contains special chemical inhibitors that prevent the acid cleaner from attacking the base metal while allowing the acid to remove the unwanted corrosion product or scale deposit. Hydrochloric (Muriatic) Acid Inhibited hydrochloric (muriatic) acid in strengths of 5 to 20% is very effective for removing calcium scale and iron oxide; however, for most applications, a 10% solution is adequate. The following formulation is for a 10% hydrochloric acid solution. It can be used for removing scale consisting primarily of carbonates with lesser amounts of phosphates, sulfates, and silicates. This type of scale is typically found in a steam boiler system containing copper alloys that has been treated with a phosphate-based program. Depending on the specific descaling application, some of these ingredients can be omitted from the formulation. Example Procedure for 10% Solution The following is an example procedure that can be used to make 3785 liters (1000 gallons) of a 10% solution: 1. Add 1079 liters (285 gallons) concentrated (36% strength) hydrochloric acid, American Society for Testing and Materials (ASTM) E 1146, Specification for Muriatic Acid (Technical Grade Hydrochloric Acid), to approximately 2271 liters (600 gallons) of water. 2. Add the proper amount of a corrosion inhibitor, Military Specification MIL-I17433, Inhibitor, Hydrochloric Acid, Descaling and Pickling, recommended by the manufacturer to the diluted acid solution. The inhibitor must be compatible with hydrochloric acid and must not precipitate under any condition during the cleaning operation. 3. In a separate tank containing about 284 liters (75 gallons) of water: 4. Add 39 kilograms (85 pounds) of the chemical (1,3) diethylthiourea to complex any copper and keep it from depositing. Do not use the diethylthiourea as the corrosion inhibitor required in paragraph 92.2.1(step 2) above. 5. Add 55 kilograms (120 pounds) of ammonium bifluoride, technical grade, to help dissolve certain iron and silica scales. 6. Add 3.79 liters (1 gallon) of wetting agent, Add the dissolved diethylthiourea, ammonium bifluoride, and wetting agent to the diluted acid solution. Add sufficient water to obtain 3785 liters (1000 gallons).

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Carbonate Deposits. Carbonate deposits dissolve rapidly in hydrochloric acid, with evolution of free carbon dioxide. The escaping carbon dioxide tends to create some circulation or agitation of the acid, which ensures the continual contact of fresh acid with the scale. Once the carbonate has been dissolved from a mixed deposit, a loose, porous structure may be left behind. This residual material can be effectively removed from the equipment either mechanically or by washing with highpressure water.

Phosphate Deposits The removal of phosphate deposits can usually be accomplished by using hydrochloric acid; however, phosphate deposits have a tendency to dissolve rather slowly. To minimize the total cleaning time, a temperature of 49 to 60 °C (120 to 140 °F) is usually necessary to remove a predominantly phosphate scale.

Metallic Oxides Most metallic oxides found in deposits can be removed with hydrochloric acid. The rate of dissolution is a function of temperature and solution velocity. If copper oxides are present on steel surfaces, special precautions are needed to prevent copper metal plate-out on the steel.

Silica and Sulfate Scale Heavy silica and sulfate scale is almost impossible to remove with hydrochloric acid. Special chemicals and procedures are required to remove this scale.

Hydrochloric Acid Limitations Hydrochloric acid is not used to clean stainless steel because the chloride ion in the acid solution may cause pitting or stress corrosion cracking. Hydrochloric acid is not used for removing scale from galvanized steel surfaces since the galvanizing will corrode. Aluminum is not cleaned using hydrochloric acid.

Sulfamic Acid Sulfamic acid is an odorless, white, crystalline solid organic acid that is readily soluble in water. An inhibited sulfamic acid compound, in a dry powder form, is available. A 5 to 20% solution (2 to 9 kilograms to approximately 38 liters of water [5 to 20 pounds to approximately 10 gallons of water]) is used for removing scale from metal surfaces. The following information pertaining to sulfamic acid should be considered. u ?Carbonate deposits are dissolved in sulfamic acid in a similar manner as in hydrochloric acid. All the common sulfamate salts (including calcium) are very soluble in water. u The dry powder form of sulfamic acid is safer to handle than a liquid solution of hydrochloric acid; however, aqueous solutions of sulfamic acid are much slower in action and require heating to remove scale. The sulfamic acid solution is heated to a temperature in the range of 54 to 71 oC (130 to 160 oF) to obtain the same fast cleaning time that is achieved by using hydrochloric acid at room temperature. Sulfamic acid is more effective on sulfate scale than hydrochloric acid.

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u Inhibited sulfamic acid, used at temperatures up to 43 oC (110 oF), will not corrode galvanized steel. Its use is recommended for removing scale in cooling towers, evaporative condensers, and other equipment containing galvanized steel. In general, sulfamic acid can be applied to equipment while it is operating but should be drained from the system after a few hours, and the concentration of the normally used corrosion inhibitor should be increased several-fold to protect the metal surfaces. u ?Commercially prepared descaling compounds consisting of concentrated or diluted inhibited acid (containing 7 to 28% of the acid and inhibitor) may be purchased under various trade names at prices 4 to 30 times the cost of the ingredients themselves if purchased as generic chemicals. u ?Advertisements of some of these products may contain claims that the acid does not attack cotton clothing and skin. These claims are usually based on a very dilute solution of the acid that causes a minimal attack on clothes and skin; however, the cost of the cleaning process may be increased because a higher quantity of dilute product may be needed. Be aware that handling acid in any strength must be performed with considerable care, caution, and adherence to safety procedures. u The cost of diluted acid is expensive; therefore, concentrated acid of government specifications should be purchased and diluted to usable strengths. The necessary corrosion inhibitors can be added to the dilute acid solution. Users of small quantities of acid cleaners (possibly less than 38 liters [10 gallons] of diluted acid per year) may not be able to justify purchasing undiluted acid and spending the time, cost, and effort to prepare the cleaning solution. Cleaning Preparation u The unit to be cleaned must be isolated from other parts of the system. For systems that cannot be isolated by the closing of valves, isolation may be accomplished using rubber blankets, wooden bulkheads with seals, inflatable nylon or rubber bags, rubber sponge-covered plugs, or blind flanges and steel plates with rubber seals. u Decide whether to clean using a soaking process or by circulating the cleaning solution. In either case, temporary piping or hose lines will be required to connect the cleaning solution mixing tanks or trucks to the unit, with return lines to tanks or drains. Proper precautions and adequate provisions must be made to protect equipment, isolate control lines, replace liquid level sight glasses with expendable materials, and provide suitable points for checking temperatures. u The entire cleaning procedure/process must be developed in detail before starting chemical cleaning operations. Factors to be considered include: the methods for controlling temperatures; the means of mixing, heating, and circulating the chemical solution; proper venting of dangerous gases from equipment to a safe area.

103

Methods for Removing Scale Removing scale may be accomplished by circulating the inhibited acid solution through the equipment or by soaking the equipment in a tank of inhibited acid. Before starting any descaling process, check the acid to make sure it is properly inhibited. You may check the acid by placing a mild steel coupon into a beaker containing the prepared, diluted acid. You should notice no reaction around the coupon. If you observe a reaction generating hydrogen gas bubbles around the coupon, add more inhibitor.

Recirculating Cleaning Process for Boilers The following example is an appropriate procedure for cleaning small boilers or other systems using a hot recirculating inhibited acid solution: 1. Fill the boiler or system with preheated (71 to 77 oC [160 to 170 oF]) dilutes inhibited acid solution. 2. Allow the dilute inhibited acid solution to remain in place for 8 hours. Circulate the acid solution for approximately 15 minutes each hour at a rate of about 3.15 liters per second (50 gallons per minute) to ensure good mixing. 3. Keep the temperature of the acid solution preheated at 71 to 77 oC (160 to 170 oF). Measure and record the temperature at least once every 30 minutes. 4. Check and record the acid strength at least every hour 5. Drain the system by forcing the acid solution out using 276 to 345 kilopascals (40 to 50 pounds per square inch gauge) nitrogen; follow Specification A-A-59503, Nitrogen, Technical, Class 1. If leaks develop when the system is under nitrogen pressure, you must use an alternate method for removing the acid, such as pumping. 6. Fill the boiler with preheated (65 to 71 oC [150 to 160 oF]) water and soak at this temperature for 15 minutes. 7. Drain under nitrogen pressure of 276 to 345 kilopascals (40 to 50 pounds per square inch gauge). 8. Prepare this mild, acid-rinse solution: Add 7.57 liters (2 gallons) of hydrochloric acid (ASTM E 1146 or IS 226) for each 3785 liters (1000 gallons) of water. Also add corrosion inhibitor, in the amount recommended by the manufacturer. 9. Fill the boiler with the preheated (71 to 77 oC [160 to 170 oF]) mild acidrinse solution and soak for 30 minutes. 10. Drain the mild acid-rinse solution under nitrogen pressure at 276 to 345 kilopascals (40 to 50 pounds per square inch gauge). Maintain a positive pressure of nitrogen in the boiler to prevent outside air from leaking inside. 11. Fill the boiler with the passivating solution preheated to 65 to 71 oC (150 to 160 oF), circulate for 10 minutes, and hold in the boiler at 65 to 71 oC for an additional 30 minutes. Drain and rinse boiler until the pH of the rinse water is pH 8 to 10.

104


Circulating Method without Heat The steps below describe a typical process for descaling smaller equipment, such as enclosed vessels or hot water heater coils, without heating the inhibited acid solution: 1. Note that an acid cleaning assembly may consist of a small cart on which is mounted a pump and an 18.9- to 189-liter (5- to 50-gallon) steel or polyethylene tank with a bottom outlet to the pump. 2. Install sill cocks at the bottom of the water inlet of the heat exchanger and the top of the water outlet so that a return line can be connected directly from the acid pump and from the heat exchanger to the acid tank. 3. Prepare an inhibited acid cleaning solution 4. Pump the acid solution into the heat exchanger through the hose connection. Continue circulation until the reaction is complete, as indicated by foam subsidence or acid depletion. 5. If the scale is not completely removed, check the acid strength in the system If the acid strength is less than 3%, add fresh acid solution and continue circulation until the remaining scale is removed. Usually an hour of circulation is adequate. 6. Drain the heat exchanger. 7. Neutralize remaining acid by circulating a 1-% sodium carbonate (soda ash) solution {about 3.6 kilograms per 38 liters (8 pounds per 100 gallons)}for about 10 minutes. 8. Rinse thoroughly with water until the pH of the rinse water is pH 8 to 10.

Fill and Soak Method 1. 2.

Prepare an inhibited dilute acid solution in a container of suitable size. Depending on the item to be cleaned and the types of scale involved, you may want to place an agitator (mixer) in the tank or install a pump outside the tank to circulate the acid solution. A method to heat the acid may be required, such as a steam coil. All equipment must be explosion-proof and acid-resistant. 3. Immerse the item to be cleaned in the dilute acid solution. Continue soaking until the reaction is complete as indicated by foam subsidence or acid depletion. 4. If the scale is not completely removed, check the acid strength. If it is less than 3%, add additional acid and continue soaking the items until the remaining scale is dissolved. Usually 1 to 2 hours of soaking is adequate. 5. Remove item from tank. 6. To neutralize remaining acid, immerse the item in a 1% sodium carbonate (soda ash) solution (about 3.6 kilograms per 38 liters [8 pounds per 100 gallons]) for 2 to 3 minutes. Rinse the item thoroughly with water.

105

Checking Acid Solution Strength The initial strength of the dilute inhibited acid will vary from 5 to 20%, although 10% is typical. The strength of the acid decreases since acid is consumed in dissolving the scale. The strength of the acid solution should be measured periodically during a cleaning operation. When the acid strength falls below 3%, the solution may be discarded since most of its scale-dissolving capability will have been used. Use the following procedure to check the acid strength:

Apparatus: 1. 2. 3. 4. 5.

Burette, 25 milliliters (0.8 ounce) automatic (for sodium hydroxide solution) Bottle, with dropper, 50 milliliters (2 ounces) (for phenolphthalein indicator solution) Graduated cylinder, 10 milliliters (0.3 ounce) Casserole, porcelain, heavy duty, 210-milliliter (7.1-ounce) capacity Stirring rod

Reagents: 1. 2.

Sodium hydroxide solution, 1.0 normality (N) Phenolphthalein indicator solution, 0.5%

Method: 1. 2. 3. 4. 5.

Measure 10 milliliters of acid solution accurately in the graduated cylinder. Pour into the casserole. Add 2 to 4 drops of phenolphthalein indicator solution to the casserole and stir. Fill the automatic burette with the 1.0 N sodium hydroxide solution; allow the excess to drain back into the bottle. While stirring the acid solution constantly, add sodium hydroxide solution from the burette to the casserole until color changes to a permanent faint pink. This is the endpoint. Read the burette to the nearest 0.1-milliliter (0.003-ounce).

Results: For hydrochloric acid: Percent hydrochloric acid = milliliter of 1.0 N sodium hydroxide x 0.36. For sulfamic acid: Percent sulfamic acid = milliliter of 1.0 N sodium hydroxide x 0.97

106


WATER SAMPLE TEST PROCEDURES

107

WATER SAMPLE TEST PROCEDURES Purpose of Testing Testing of industrial water is done to determine the amount of treatment chemicals in the water so that dosage levels can be properly regulated. These tests are the only known means of having reliable operations, as far as the water is concerned.

Testing Techniques Accurate test results depend on following good basic laboratory procedures and techniques. 1.

2.

3.

4.

5.

Water analyses require certain chemical apparatus. These are scientific instruments and are to be treated as such. The apparatus should be HANDLED WITH CARE! It is necessary to keep everything in GOOD ORDER at all times. Have a place for everything and everything in its place! Be sure all bottles are properly labeled and avoid mixing bottles! All bottles should be tightly closed. Keep any reserve stock of solutions and reagents in cool, dark place. All equipment and apparatus should be kept CLEAN! Unless this is done, the tests will not be reliable and errors will be introduced. Thoroughly rinse and dry all glassware immediately after use. If color apparatus are employed, do not expose to heat or to direct sunlight. If any liquid is spilled on any of the equipment or apparatus, wipe off at once and dry. MEASURE CAREFULLY! The apparatus are precision instruments that are capable of very fine measurements. The results will be “off” if improper amounts of samples are taken, if incorrect volumes of solution are added, if the burette is not read correctly, of if the methods prescribed on the following pages are not performed exactly as written. The SUSPENDED MATTER OR SLUDGE will generally settle to the bottom if the sample is allowed to stand before testing. The clear water can then be used for the tests, making it unnecessary to filter (except for specific tests). Theoretically, all water analyses should be made at 77oF (25oC); however, no appreciable error will be introduced if the test is made between 68 and 86oF (20 to 30oC). In general, the shorter the time between the collection and the analysis of the sample, the more reliable will be the results.

When the water sample color interferes with the analysis, it may be necessary to filter the sample through activated charcoal, except for the sulfite and nitrite tests.

108


Phenolphthalein (P) Alkalinity Test Procedure APPARATUS: Graduated Cylinder, 50 ml, Plastic Bottle, w/Dropper (for Phenolphthalein Indicator) 2 oz Casserole, Porcelain, Heavy Duty, 200 ml Capacity Stirring Rod, Plastic REAGENTS: Standard Sulfuric Acid Solution, N/50 Phenolphthalein Indicator Solution, 1 percent METHOD: Measure the amount of water to be tested in the graduated cylinder. The amount should be based on the expected results of the test according to the following: u Pour into the casserole. u Add 6 drops of Phenolphthalein Indicator Solution to the casserole and stir. If the water does not change to a red color, there is no phenolphthalein alkalinity present and the “P” reading is reported as “zero.” If the water does change to red color, “P” alkalinity is present and the test should be continued. u Squeeze the rubber bulb to force the Standard Sulfuric Acid Solution from the bottle to fill the burette just above the zero mark; then allow the excess to drain back automatically into the bottle. u While stirring the water constantly, add Standard Sulfuric Acid slowly from the burette to the casserole until the red color disappears and the water resumes the original color of the sample before the Phenolphthalein Indicator Solution was added. This is the end point. Read the burette to the nearest 0.1-ml. u RESULTS: The P alkalinity (ppm as CaCO3) is calculated as follows: P alkalinity (ppm as CaCO3) = (ml acid) x (factor) P Alkalinity Expected, As CaCO3

Sample Size

Factor

Less than 100

50ml

20

More than 100

20ml

50

EXAMPLE: 4.3 ml of N/50 sulfuric acid were required to change the color of a 50 ml sample of water from red to colorless: P alkalinity = 4.3 x 20 = 86 ppm as CaC

109

Total (M) Alkalinity Test Procedures APPARATUS: Burette, 10 ml, Automatic (for N/50 Sulfuric Acid) (item 1001) Graduated Cylinder, 50 ml, Plastic (item 1004) Bottle, w/Dropper (for Mixed Indicator) 2 oz (item 1005) Casserole, Porcelain, Heavy Duty, 200 ml Capacity (item 1003) Stirring Rod, Plastic (item 1006) REAGENTS: Standard Sulfuric Acid Solution, N/50 (item 2001) Mixed Indicator Solution, (item 2036) METHOD: Measure the amount of water to be tested in the graduated cylinder. The amount should be based on the expected results of the tests according to the following: u Pour into the casserole. u Add 10 drops of Mixed Indicator Solution to the casserole and stir. If the water changes to a light pink color, free mineral acid is present. There is no mixed indicator alkalinity, and the “M” reading is reported as “zero.” If the water changes to a green or blue color, “M” alkalinity is present and the test should be continued. u Squeeze the rubber bulb to force the Standard Sulfuric Acid Solution to fill the burette to just above the zero mark; then allow the excess to drain back automatically into the bottle. u While stirring the water constantly, add Standard Sulfuric Acid Solution slowly from the burette to the casserole until the green or blue color changes to light pink. This is the end point. Read the burette to the nearest 0.1-ml.

M Alkalinity Expected, As CaCO3

Sample Size

Factor

Less than 100

50ml

20

More than 100

20ml

50

RESULTS: The M alkalinity (ppm as CaCO3) is calculated as follows: M alkalinity (ppm as CaCO3) = (ml acid) x (factor)

110


EXAMPLE: 5.9 ml of N/50 sulfuric acid were required to change the color of a 50 ml sample of water from green to light pink: M alkalinity = 5.9 x 20 = 118 ppm as CaCO3 NOTES: u If the end point color is difficult to see, repeat the entire test using 15 drops of Mixed Indicator Solution. u Just before the end point is reached, the green or blue color fades to a light blue color and then becomes light pink. The end point is the first appearance of a permanent pink color. Value of P & M

Bicarbonate

Carbonate

Hydroxide

Total

Alkalinity

Alkalinity

Alkalinity

Alkalinity

Alkalinity

P= Zero

M

Nil

Nil

M

P< 1/2M

M-2P

2P

Nil

M

P=1/2M

Nil

2P

Nil

M

P>1/2M

Nil

2(M-P)

2P – M

M

111

Conductivity Test Procedure Apparatus Conductivity Meter & cell In general, there are two types of conductivity meters. One has an electrode that is put into a cell containing the water to be tested. The other has a small cup mounted on the meter into which the water to be tested is poured. Either type of meter may be automatically temperature compensated, or the meter may require a temperature correction. The meter may indicate TDS or conductivity as micromhos, but either measurement represents the same characteristic of the water sample. Where the meter is designed to give either measurement, it is important to always use the same measurement to avoid an error. Thermometer Beaker Graduated cylinder

Procedure Determine the cell constant if necessary, either directly with a standard potassium chloride solution (say 0.002N) or by comparison with a cell the constant of which is known accurately. (In the later case, the concentration and nature of the electrolytes in the liquid which is used for the comparison should be the same and should be similar respectively to those of the liquids with which the cell is likely to be used in practice. Use some of the samples to washout the conductivity cell thoroughly. Fill the conductivity cell with the sample. Measure the conductivity in accordance with the instruction of the instrument manufacturer.

Results Depending upon the type of meter used, the results are read as either conductivity in micromhos or TDS in ppm. The relationship between these measurements when these procedures are used is as follows: TDS, ppm = 0.66 x Conductivity, micromhos Conductivity, micromhos = 1.5 x TDS, ppm.

112


pH-Electrometric Method Test Procedures Apparatus pH Meter, Complete Beaker, 150 ml, Heavy Duty Plastic (3 each) Wash Bottle, 500 ml, Heavy Duty Plastic Reagents Standard pH Buffer Solution, pH-4 Standard pH Buffer Solution, pH-7 Standard pH Buffer Solution, pH-10 METHOD: Carefully follow the procedures provided with the pH meter. They should be similar to the following: u Turn the meter from “standby” to “on” position. u Standardize instrument by immersing the electrode(s) into two different Standard pH buffer Solutions in the test beaker as follows: (a.) Place electrode(s) in pH-7 Buffer Solution and adjust the meter to read pH-7.(b). Place electrode(s) in the second pH Buffer Solution, either the pH-4 or pH-10, depending on the suspected range of the unknown sample to be tested, and adjust the meter to the same pH. u Remove electrode(s) and thoroughly wash with distilled or condensate water. u Immerse the electrode(s) in the water sample and turn the meter to “test” or “pH” position and read meter. u Rinse the electrodes with distilled or condensate water and turn the instrument to the “standby” position. Do not turn off. Notes: u When not in use, keep the glass electrodes soaking in a pH-4 Buffer Solution. u When not in use, keep the plastic cap on the reference electrode. Some reference electrodes must be kept full of electrolyte. Follow the instrument instructions on this.

113

Total hardness Test Procedures Introduction Hardness is defined as the sum of the calcium and magnesium ions in water expressed in milligrams per liter (or ppm) as calcium carbonate. Hardness tests should be done on softeners to make sure they are functioning and deaerator water to make sure no contamination is occurring. This test is based on the determination of the total calcium and magnesium content of simple by titration with a sequestering agent in the presence of organic dye sensitive to calcium and magnesium ions. The red to blue color change endpoint is observed when all calcium and magnesium ions are sequestered. Hardness tests should be conducted on water softeners and condensate but not on boiler water as elevated iron concentrations can lead to chemical interference and poor test results.

Reagent required Hardness Reagent 0.01 M Hardness Buffer Hardness Indicator Powder

Procedure u Rinse the graduated cylinder and beaker or a test tube with the sample to be tested. Fill the graduated cylinder to 50 mL and add this water to the beaker or a test tube u If hardness is expected to be greater than 100 take a 50 ml sample and if less than 100 then the sample can be of 20 ml u Add 5 drops of Hardness Buffer to the beaker using the plastic pipette. Swirl to mix. u Add 1 spoon of Hardness Indicator Powder. Swirl to dissolve completely. The sample will turn red if hardness is present. If the sample is blue, the hardness level is completed to be zero. u If the sample colour is purple or red, add standard hardness titrating solution slowly from the burette to the beaker until the purple or red colour changes to blue. This is the end point. Read to nearest 0.1 ml

Calculation u For a 50 mL sample, ppm Hardness as CaCO3 = mL of Hardness Reagent X 20. u For a 20 mL sample, ppm Hardness as CaCO3 = mL of Hardness Reagent X 50.

114


Sulphite testing procedure Introduction Sulfite is used in boiler feedwater conditioning to prevent oxygen pitting by the removal of dissolved oxygen. It is necessary to maintain an excess sulfite level to ensure rapid and complete oxygen removal. This test is based on the reaction of sulfite with iodine in acidic solution. The iodide-iodate titrant generates iodine in the acidic solution. This iodine is consumed in a reaction with excess sulfite. At the endpoint, excess iodine combines with the indicator to form a blue colour.

Reagents required Iodide-Iodate Reagent N/40 Acid Starch Indicator Powder Phenolphthalein Indicator

Procedure u Rinse the graduated cylinder and beaker or a test tube with the sample to be tested. Fill the graduated cylinder to 50 mL and add this water to the beaker or a test tube u If sulphite is expected to be greater than 100ppm take a 50-ml sample and if less than 100 ppm then the sample can be of 20 ml u Add 1 drops of Phenolphthalein Indicator to the beaker using the plastic pipette. Swirl to mix. u If the sample remains colourless proceed with step 5. If the sample turns pink add Acid Starch indicator Powder one, 1gram at a time until the sample becomes colorless. Swirl to mix between each addition of indicator. u Fill the Titration Burette to the zero mark with Iodide-Iodate Reagent N/40. Add the reagent slowly to the Erlenmeyer flask with constant stirring. Continue to titrate until a permanent blue color develops in the sample. Read the titrated volume from the burette.

Calculation For a 50 mL sample, Ppm sulphite as CaCO3 = mL of Iodide-Iodate Reagent X 20. For a 20 mL sample, Ppm sulphite as CaCO3 = mL of Iodide-Iodate Reagent X 50.

115

Chloride Test Procedure Apparatus: Burette, 10 ml Automatic (for Mercuric Nitrate Solution) Graduated Cylinder, 50 ml, Plastic Casserole, Porcelain, Heavy Duty, 200 ml Capacity Stirring Rod, Plastic Bottle, w/Dropper, 2 oz (for Chloride Indicator Solution)

Reagents Standard Mercuric Nitrate Solution, 0.0141 N Chloride Indicator Solution Standard Sulfuric Acid Solution, N/50

Procedure u Measure the amount of water to be tested in the graduated cylinder. The amount should be based on the expected results of the tests according to the following: u Pour into the casserole. u Add 1.0 ml of Chloride Indicator Solution to the water in the casserole and stir for 10 seconds. The color of the water should be a green-blue color at this point. u Add the standard Sulfuric Acid Solution a drop at a time until the water turns from greenblue to yellow. u Squeeze the rubber bulb to force the Standard Mercuric Nitrate Solution from the bottle to fill the burette just above the zero mark; then allow the excess to drain back automatically into the bottle. While stirring the sample constantly, add Standard Mercuric Nitrite Solution slowly from the burette to the casserole until a definite purple color appears. This is the end point.(The solution will turn from green-blue to blue a few drops from the end point.) Read the burette to the nearest 0.1-ml.

Results The Chloride, in ppm C1, is calculated as follows: Chloride, ppm C1 = (ml of Mercuric Nitrate – 0.2) x factor.

Example 11.2 ml of 0.0141 N Mercuric Nitrate Solution was required to change the color of a 50-ml sample of water from a green-blue to purple. Chloride = (11.2 – 0.2) x 20 = 220 ppm) Chloride Expected as Cl

116

Sample Size

Factor

Less than 20 ppm

50ml

10

More than 20 ppm

20ml

20


Checking Acid Solution Strength for Cleaning The initial strength of the dilute inhibited acid will vary from 5 to 20%, although 10% is typical. Since the acid is consumed by dissolving the scale, the strength of the acid decreases. The strength of the acid solution should be measured periodically during a cleaning operation. When the acid strength falls below 3%, the solution may be discarded since most of its scale-dissolving capability will have been used. Use the following procedure to check the acid strength:

Apparatus: Burette, 25 milliliters (0.8 ounce) automatic (for sodium hydroxide solution) Bottle, with dropper, 50 milliliters (2 ounces) (for phenolphthalein indicator solution) Graduated cylinder, 10 milliliters (0.3 ounce) Casserole, porcelain, heavy duty, 210-milliliter (7.1-ounce) capacity Stirring rod

Reagents: Sodium hydroxide solution, 1.0 normality (N) Phenolphthalein indicator solution, 0.5%

Method: u Measure 10 milliliters of acid solution accurately in the graduated cylinder. u Pour into the casserole. u Add 2 to 4 drops of phenolphthalein indicator solution to the casserole and stir. u Fill the automatic burette with the 1.0 N sodium hydroxide solution; allow the excess to drain back into the bottle. u While stirring the acid solution constantly, add sodium hydroxide solution from the burette to the casserole until color changes to a permanent faint pink. This is the endpoint. Read the burette to the nearest 0.1-milliliter (0.003-ounce).

Results: For hydrochloric acid: Percent hydrochloric acid = milliliter of 1.0 N sodium hydroxide x 0.36 For sulfamic acid: Percent sulfamic acid = milliliter of 1.0 N sodium hydroxide x 0.97

117

Units and Measurement conversion

118


BASICS Length 1 m = 39. 37 " | in = 3,281 ' | feet 1 in | " = 25.40 mm = 2,540·10-2 m 1 ft | ' = 304. 8 mm = 0.3048 m Area 1 m² = 10.76 ft² = 1550 in² 1 ft² = 9,290·10-2 m² 1 in² = 6,452·10-4 m² Volume 1 m³ = 6,102·104 in³ 1 m³ = 35.31 cf | ft³ = 264.2 US Gallon 1 cf | ft³ = 2,832·10-2 m³ = 28.32 Liter | dm³ 1 in³ = 1,639·105m³ = 1,639·10-2 Liter | dm³ 1 US Gallon = 3,785·10-3 m³ = 3,785 Liter | dm³ 1 UK Gallon = 4,546·10-3 m³ = 4,546 Liter | dm 1 mn3 Air=38.04 SCF Air=1.292 kg Air 1 SCF Air =2,629·10-2 mn 3 Air=3,397·10-2 kg Air Density 1 kg/m³ = 6.243·10-2 lb/ft³ 1 lb/ft³ = 16.02 kg/m³ Mass 1 kg = 2.205 lb | lbs 1 lb | lbs = 0.4536 kg Velocity 1 m/s = 3.281 ft/s 1 m/s = 196.9 ft/min | FPM 1 FPM = 5.080·10-3 m/s 1 ft/sec. = 0.3048 m/s Volume Flow 1 m³/h = 0.5885 CFM | ft³/min 1 CFM = 1.699 m³/h 1 SCFM = 1.577 mn 3/h Air (only) Mass Flow 1 kg/h = 2.205 lb/h 1 lb/h = 0.4536 kg/h

119

Pressure 1 bar = 14.50 psi 1 bar = 100.0 kPa 1 bar = 0.9869 Atm. 1 mbar = 0.7501 mm Hg | Torr 1 mbar = 10.20 mm WG 1 mbar = 100.0 Pa 1 psi | lbf/in² = 6,895·10-2 bar 1 psi | lbf/in² = 6,804·10-2 Atm. 1 psi | lbf/in² = 6,895 kPa Kinematic Viscosity 1 Pa·s = 1.000 cP 1 Pa·s = 0. 6720 lb/ (ft·s) 1 cP = 1,000·10-3 Pa·s | Ns/m² 1 cP = 1,000·10-3 kg/ (m·s) 1 lb/ (ft·s) = 1.488 Pa·s 1 lb/ (ft·s) = 1488 cP | mPa·s Temperature °C | Celsius = 5 · (°F – 32) / 9 °F | Fahrenheit = 32 + 9 · °C / 5 Heat Content & Energy 1 kJ | KN·m = 0.9478 Btu 1 kJ | KN·m = 0.2388 Kcal 1 Btu = 1.055 kJ 1 Btu = 0.2520 Kcal 1 kcal = 4,187 kJ 1 kcal = 3.968 Btu 1 kWh = 859.8 Kcal Heat Load | Power 1 kW = 3412 Btu/h 1 kW = 859.8 Kcal/h 1 Btu/h = 2,931·10-4 kW 1 Btu/h = 0.2520 Kcal/h 1 kcal/h = 1,163·10-3 kW 1 kcal/h = 3.968 Btu/h 1 Boiler HP = 9.81 kW Specific Heat 1 kJ/ (kg·K) = 0.2388 Btu/ (lb·°F) 1 kJ/ (kg·K) = 0.2388 kcal/ (kg·°C) 1 Btu/ (lb·°F) = 4,187 kJ/ (kg·K) 1 kcal/ (kg·°C) = 4,187 kJ/ (kg·K)

120


Common conversion factors for ion exchange calculation Capacity To Convert Kgr/ft3 (as CaCO3) Kgr/ft3 (as CaCO3) Kgr/ft3 (as CaCO3) g CaCO3/litre g CaO/litre

Multiply by

To g CaO/Litre g CaCO3/Litre eq/litre Kgr/ft3 (as CaCO3) Kgr/ft3 (as CaCO3)

1.28 2.29 0.0458 0.436 0.780

Flow Rate To Convert U.S.gpm/ft3 U.S.gpm/ft2 U.S gpm BV/min

To BV/hr M/hr M3/hr U.S. gpm/ft3

Multiply by 8.02 2.45 0.227 7.46

Pressure drop To Convert PSI/ft

To MH2O/M of Resin G/cm/M

Multiply by 2.30 230

Density To Convert

To

Multiply by

Lbs/ft3

gm/litre

16.0

Rinse requirement To Convert U.S. gal/ft3

To BV

Multiply by 0.134

121

Water Equivalents One U.S. gallon One U.S. gallon One U.S. gallon One U.S. gallon One U.S. gallon One U.S. gallon water One cubic foot One cubic foot of water One litre/second One cubic meter per hour One kgr / sq. cm One Pound/1000 gel One inch/minute rise rate One cubic meter One cubic meter One cubic meter

Water Analysis Conver-sion table

Kilogr ains per cubic foot Kgr/ cu.ft

.1

.0583

.07

.0004

.001

.1

.0583

.07

.0004

1

100

58.3

70

.435

.01

1

.583

.7

.00436

Grams per Liter gms/L

1

1

.001

1

1

1 gram per litre(1m /litre)

1000

1000

1 Parts per hundred thousand 1pt /100 0000)

10

10

Parts per hund-red thous and pts/ 100000

Grains per British Imp gallon grs/Im gal

Milli-grams per liter mg/L

1 milli gram per litre (1mg /litre)

0.1337 cubic foot 231 cubic inches 0.833 British Imp gallons 3.785 Liters 3785 cubic cm (Milliliters) 8.33 Pounds (Lb) 7.48 U.S. gallons 62.43 Pounds 15.9 (US) gal/Min 4.4 (US) gal/min 14.2 pounds/sq. inch 120 parts per million 0.625 gpm/sq.ft 1000 liter 264.2 U.S gallons 220 British Imp gallons Grains per U.S. gallons grs/U.S gal

Parts per million (ppm)

1 Part per million (1 ppm)

122

-


Water Analysis Conversion Table for Units Employed: Equivalents Water Analysis Conver-sion table

Parts per million (ppm)

Milli-grams per liter mg/L

Grams per Liter gms/L

17.1

17.1

.017

14.3

14.3

1 Kilograin per cubic foot (1 kgr /cu.ft)

2294

1 Parts per million (1 ppm)

Parts per hund-red thous and pts/ 100000

Grains per U.S. gallons grs/U.S gal

Grains per British Imp gallon grs/Im gal

Kilogr ains per cubic foot Kgr/ cu.ft

1.71

1

1.2

.0075

.014

1.43

.833

1

.0052

2294

2.294

229.4

134

161

1

1

0.1

.0583

.07

.1

.0560

.020

10

1

0.583

0.7

1

0.560

.20

1 Grain per US gallon (1 gpg)

17.1

1.71

1

1.2

1.71

0.958

.343

1 English or Clark degree

14.3

1.43

.833

1

1.43

0.800

.286

10

1

.583

.7

1

0.560

.20

17.9

1.79

1.04

1.24

1.79

1

.357

1 Grain per U.S gallon(1 gr/U.S gal) 1 Grain per British Imp gal-lon (1 gr /Imp gal)

1 Part per hundred thousand (1 pt /100000)

1 French Degrees (1.French) 1 German Degrees (1 German)

123

Indian standard grade for the commonly used regeneration chemicals

IS Number

Regeneration Chemicals

124

Hydrochloric Acid

IS 265

Sulphuric Acid

IS 266

Sodium Hydroxide

IS 252 (Tech/Rayon Grade 46% lyes) IS1021 (Pure Grade - Flakes)

Sodium Carbonate

Is251 (Tech Grade)

Sodium Sulphite

Is251 (Tech Grade)

Sodium chloride

IS 297 (Tech Grade)

Alum

Is260 (Tech Grade)


Brief List of Reference Betz Handbook Demineralization by Ion exchange – S. Applebaum – Academic press Reverse osmosis by Zahid Amjad – Van Nostrand Reinhold (NY) Membrane Manual –Dow Chemical Company Army Engineering Publications- Public bulletin No. 420-49-05 CIBO Energy efficiency handbook WARE Boiler book on-line “Chemical Treatment of Cooling Water in Industrial Plants”by Timothy Keister (Basic Principals and Technology) ProChemTech International, Inc. Brockway, Pennsylvania Glegg handbook Water and Wastewater by Hammer and Hammer Dorfner, K., Ion Exchangers, Properties and Applications, Ann Arbor Science, Ann Arbor, Michigan, 972 Kunin, R., Ion Exchange Resins, Robert E. Krieger Publ. Co., Huntington, N.Y., 1957 Nachod, F. C. and Schubert, J., editors, Ion Exchange technology, Academic Press, New York, N.Y., 1957 Water treatment technology program Report no 29 Pure water handbook by osmonics "Pretreatment of Industrial Wastes," Manual of Practice No. FD-3 Public Works Technical Bulletin 420-49-21 Boiler water treatment lessons learned Public Works Technical Bulletin 420-49-22 Cooling water treatment lessons learned (Published by the U.S. Army Installation Support Center) International site for Spirax Sarco Industrial Water Treatment Primer TYNDALL AFB, FL 32403-6001 Sedifilt.com Web site of N.E.M Business Solutions Website of Portland water bureau How to Manage Cooling Tower Water Quality by Ken Mortensen in RSES journal _5-03pd And many more

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