Boiler Water Training

Infrastructure Water & Process Technologies

More More Proof. Proof. More More Power. Power.

Boiler Technical Training At Reliance Industries Limited Hazira Manufacturing Division K S Rajan

RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material

February 26, 2008


More Proof. More Power.

BOILER WATER TREATMENT

• • • • •

BASIC WATER CHEMISTRY BOILER DESCRIPTION OXYGEN PITTING & CONTROL CONDENSATE TREATMENT INTERNAL TREATMENT, COORDINATED pH/PO4 • STEAM PURITY • BOILER STORAGE • DISCUSSION, Q&A RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material



Basics & Interpretation of Water Analysis



“The Basics”

• • • • • • • •



Hydrologic Cycle Properties of Water pH and Alkalinity Langelier Saturation Index Analytical Expressions Water Analysis/Deposit Analysis Corrosion and Deposition & Monitoring Chemical Feed

Properties of Water



•Density - 1 kg/l @ 4 oC ; 0.998 kg/l @ ambient temperature and varies inversely with temperature •Boiling point = 100 oC and freezing point @ 0 oC •Viscosity ~ 1 cps at ambient temperature and varies inversely with temperature •Specific heat - 1 BTU/lb-deg F or 1 kcal/kg-deg C or 4.2 kJ/kgdeg C •Universal solvent - dissolves most substances to some extent




Impurities found in Water

• 3 Categories •

SUSPENDED SOLIDS (Silt)

• DISSOLVED SOLIDS (Minerals) • DISSOLVED GASES

• Where do these things come from? RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material




Infrastructure Hydrologic Cycle Water & Process Technologies












•

Dissolved solids present as ions

•

Cations - Ions that carry net positive charges e.g. Calcium (Ca2+), Magnesium (Mg2+), Sodium (Na+), Iron (Fe2+), Aluminium (Al3+)

•

Anions - Ions that carry net negative charges e.g. Bicarbonates (HCO3-), Carbonates (CO32-), Sulfate (SO42-), Chlorides (Cl-), Oxides (O2-), Hydroxides (OH-)


Water Impurities



Impurity

Concern

Removal

Suspended Solids Silt, Iron, Microbiogical

Fouling Erosion Underdeposit corrosion

Clarification Filtration

Dissolved Solids Minerals, Organics

Scaling Corrosion

Ion Exchange Reverse Osmosis Evaporation

Dissolved Gases O2, CO2, NH3


Pitting General Corrosion Corrosion products

Deaeration Steam Stripping

Dissolved Solids

Cations Temporary Hardness

Ca++

Anions

Mg++

Permanent Hardness

HCO3possibly OH- & CO3-Cl-

Na+ K+ NH4+

F-

NO3- PO4 --SO4--

SiO2, possibly free CO2 Organic acids

Total Alkalinity

Mineral Acidity



Dissolved Solids Commonly Found in Water

Cation

Anion

Calcium

Bicarbonate Sulfate

Ca(HCO3)2 CaSO4

Magnesium

Bicarbonate Sulfate

Mg(HCO3)2 MgSO4

Sodium

Bicarbonate Sulfate Chloride

NaHCO3 Na2SO4 NaCl

Silica

Oxide

SiO2

Iron

Bicarbonate Hydroxide Sulfate

Fe(HCO3)2 Fe(OH)3 FeSO4


Chemical Name

Factors Affecting Solubility



•Temperature - Most salts increases except for Ca and Mg Salts with increasing temperature •Alkalinity - Most salt solubility increases with decreasing alkalinity with the exception of Silica •pH - most salts solubility increases as the pH drops •Oxidation state - Fe and Mn salt solubility increases with decreasing oxidation state






• Turbidity - suspended solids – silt, organic matters, precipitated salts • Color - suspended solids and dissolved solids • Dissolved gases e.g. CO2, O2, NH3, H2S • Organics - humus, vegetation, microorganisms

Typical Water Analysis


Parameter

Value

pH

7.3 150 0 20 15 10 20 15 5 0.05 1.5 12 <0.05 4 50 20 3 1

Conductivity μS/cm Alkalinity “P” as CaCO3, ppm Alkalinity “M” as CaCO3, ppm Sulfate as SO4, ppm Chloride as Cl, ppm Hardness, Total, as CaCO3, ppm Calcium Hardness, as CaCO3, ppm Magnesium Hardness, as CaCO3 ppm Copper, Total as Cu, ppm Iron, Total as Fe, ppm Sodium, as Na, ppm Phosphate, Total, as PO4, ppm Silica (reactive), as SiO2, ppm Turbidity, NTU TSS, ppm Color, Hazen RIL-Hazira/BWT-Technical Training TOC, as C, ppm GEWPT- Confidential Material



Special Ions


• pH

Hydrogen, H+ • Hydroxide, OH-

•

• Alkalinity • Bicarbonate, HCO3• Carbonate, CO3-• Hydroxide, OH-



pH


• • • •


Hydrogen Ion Concentration Logarithmic Scale pH = -log [H+] Unit change in log scale



How Does pH Apply to Us?


• pH < 7: Acidic (corrosion) • pH > 7: Alkaline (deposition)



Alkalinity Relationships

•M-Alkalinity = Total – Titration to pH = 4.3 – Sum of: HCO3- + CO3- + OH•P-Alkalinity = OH- + 1/2 CO3– Titration to pH 8.3 •OH-Alkalinity = 2P - M or titration – Neutral barium chloride precipitates CO3-


Conductivity



• Inverse of Resistance [mho] • Measure of concentration of ions in solution


Types of Solubility



Normal: Increases with Temperature • Table Salt (NaCl) • Sugar

Retrograde: Decreases with Temperature • Calcium Carbonate • Calcium Phosphate




How Do We Quantify What Is in the Water?



Analytical Expressions


• •

“Concentration” units of solute per unit of solvent: • PPM (parts per million) –

•

mg/l (milligrams per liter) –

•


parts of solute per million parts of solvent 1 gram solute/1,000,000 grams solvent PPB (Parts Per Billion) parts of solute per Billion parts of solvent




•“Mg as CaCO3”

Magnesium expressed as its Equivalent weight in Calcium Carbonate 100 (MW CaCO3) = 4.1 24 (MW Mg)



• • • • • • •



Different Conventions We use “ppm as CaCO3” ppm as substance factors Ca 50 2.5 Mg 20 4.1


ppm as CaCO3

125 82



Boiler Boiler Descriptions Descriptions


FIRETUBE BOILERS ADVANTAGES High load swing capacity Ease of repair Low space requirement Self contained package Relatively low cost Ease of installation

DISADVANTAGES Low pressure Capacity limit Usually no superheater Usually no economizer Usually low efficiency One fuel at a time FOUR-PASS FIRETUBE BOILER

WATERTUBE BOILERS

Typical Parts of a Water Tube Boiler Includes:

– – – – –

Economizer Steam drum Mud Drum Headers Boiler Bank • Downcomers - Risers • Waterwalls • Screen tubes • Arches • Floor tubes • Roof tubes – Superheater – Air Heater

WATERTUBE BOILERS RISERS SUPERHEATER

DOWNCOMERS STEAM DRUM

SCREEN TUBES

ECONOMIZER WATER WALLS

AIR HEATER

MUD DRUM

Coal

140-150 C

To stack

BOILER DESIGN

Lower Water Walls Header

Comparison - Watertube vs. Firetube: Water Tube

Fire Tube

Steam Feedwater

Steam Drum

CBD

Risers

Flue Gases

Mud Drum

Downcomers IBD

Water

Flue Gases

WATERTUBE BOILERS ADVANTAGES

Low to super critical pressure z Virtually unlimited capacity z Typically high efficiency z Superheaters zEconomizers z Multiple fuels z Drum or once-through z Package or field-erected

DISADVANTAGES z High Cost

Require Large Space z Usually require higher quality feedwater z Sensitive to low load operation z

WATERTUBE BOILER: A-TYPE

Risers

Steam Exit Drum

W BF

Downcomers

Burner

Flue Gas Path

Sidewall Problem Area

Steam Drum

D-Frame Package Boiler

Downcomers

Furnace Wall Tubes Risers

Infrastructure Water & Process Technologies Babcock & Wilcox More Proof.

Coal FiredMore Boiler Power.


Infrastructure Power Utility Boiler Simplified Flow Diagram Water & Process Technologies

Hot Reheat


HP Turbine HP SH Steam Sat Steam Condenser IP Turbine

LP Turbine

B&W Boiler BD Cold Reheat LP Heaters Cond Polisher

HP Heaters Deaerator BFW


MB MU

CAUSE AND EFFECT DIAGRAM FOR BOILER PROBLEMS POOR pH CONTROL

OXYGEN PITTING POOR CHEMICAL FEED CONTROL

INADEQUATE BLOWDOWN CONTROL

OXYGEN IN-LEAKAGE

MECHANICAL DEAERATOR PERFORMANCE

DOWNTIME CORROSION

POOR BOILER FEEDWATER QUALITY

SCAVENGER UNDERFEED

CONDENSATE CONTAMINATION

DOWNTIME CORROSION

POOR EXTERNAL TREATMENT

BOILER CORROSION

POOR BOILER FEEDWATER QUALITY CONDENSATE CONTAMINATION POOR EXTERNAL TREATMENT INADEQUATE BLOWDOWN CONTROL

STRESSED AREA

CONCENTRATING MECHANISM

POOR CHEMICAL FEED CONTROL EMBRITTLING WATER CHARACTERISTICS

DEPOSITION

STRESS CORROSION CRACKING



Boiler Calculations

FeedWater = Steam + Blowdown % Blowdown =

1 X 100 Cycles

FeedWater (kg/hr) = Steam Generation (kg/hr) 1 – (%blowdown) 100 FW= STM ( C ) C-1



Determining Cycles of Concentration


•Feedwater vs. Boiler Water analysis •BFW Cycles = [Boiler Conc.] / [FW Conc.] •

Cycles =

Neutralized Boiler Water Cond. (umhos at 25C) ___________________________________________ Feedwater Cond. (umhos at 25C)

•

Check via Chlorides, Silica

•

Do not use compounds that routinely precipitate (phosphate, hardness) or that are part of treatment (sulfite/sulfate)

•Demineralized or RO make-up – Tracer methods • Molybdate



Steam, Feed Water & Blowdown Relationships


% Blowdown = 100 / FW Cycles • % BD at 20 FW cycles = 100/20 = 5%

Feedwater = Steam X [Cycles / (Cycles –1)] • FW = 100 MM ppy steam X [20 / (20 – 1)] = 105.3


Feedwater = Steam + Blowdown • BD = FW – ST = (105.3 – 100) MM ppy = 5.3 MM ppy

Feedwater = Make-up + Condensate



Oxygen Control

• Deaeration • Chemical treatment


Corrosion of Iron by Oxygen



O2 Fe(OH)3 Fe2+

OH-

O2

WATER ELECTRON FLOW

ANODE

CATHODE

ANODE REACTION Fe. = Fe++ 2e-

CATHODE REACTION 1/2 O2 + H2O + 2e- = 20H-

MECHANISM • •


Iron Is Oxidized on the Surface (Anode) - Metal Loss Oxygen Is Reduced (Cathode)



Oxygen Corrosion • Corrosion Rate Doubles With Every 10 C Increase in Water Temperature • Metal Loss is low • Localized attack • Pit Formation • Rapid Failure



Rapid Perforation ~ Equipment Failure



Oxygen Guidelines



Organization


Dissolved O2 Level, ppb ASME

<7

TAPPI

<7

ABMA

NO RECOMMENDATION

EPRI

<5

DEAERATOR GUARANTEE

7

TYPICAL DEAERATOR O2 LEVELS

15 - 40


Types of Oxygen Scavengers • Solid

– Sodium Bisulfite – Sodium Sulfite • Non-Solids – Hydrazine – Hydroquinone – Diethylhydroxlamine (DEHA) – CARBOHYDRAZIDE – ASCORBIC ACID





RECOMMENDED SULFITE CONTROL LIMITS

Residual (ppm SO3-) 30 - 60 10 - 20

Pressure < 40 bar 40 - 60 bar

ATTEMPERATION / DESUPERHEATING: NO




Hydrazine

Reaction: N2H4 + O2 N2 + 2H2O Decomposition Reaction: 2N2H4 + HEAT + 2H2O 4NH3 + O2 Feedrates: 3 x (ppm O2 + Residual) Control Limits: 0.1 ppm Residual N2H4 at Economizer Inlet Attemperation / Desuperheating: Yes


Infrastructure Hydrazine Water & Process Technologies

Hydrazine



• Advantages: – Doesn’t contribute to TDS – True residual test • Disadvantages: – Poor reactivity with low temperature – Expensive compared to Sulfite – Suspect carcinogen – Requires special handling / feed equipment – Decomposes to NH3, which can lead to copper corrosion


Organic O2 Scavengers

• Pressure > 900 psig (60 bar) • BFW used for superheat attemperation • Condensing turbine present • High-Purity Makeup (Demin./RO) • Coordinated PO4 / pH control





HYDROQUINONE

OH REACTION: C6H6O2 + 1/2O2

CONTROL LIMITS: DISSOLVED OXYGEN TEST IRON REDUCTION TEST


H2O + C6H4O2

OH

HYDROQUINONE



ADVANTAGES • • • • • •

DOES NOT CONTRIBUTE TO TDS FASTEST ORGANIC OXYGEN SCAVENGER REQUIRES NO SPECIAL HANDLING EXCELLENT FOR WET LAY-UP AVOIDS SULFUR CATALYST POISON NOT A LISTED CARCINOGENIC

O

OH

+ O2 = RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material

OH

O


Carbohydrazide


O REACTION:

-C

N4H6CO + O2

2 N2

+ 3H2O + CO2

H

DECOMPOSITION REACTION: N4H6CO + H2O + HEAT

2N2H4 + CO2

2N2H4 + HEAT + 2H2O

4NH3

+ O2

CORTROL-OS-5613 RESIDUAL(0.3-0.5 ppm product)


2 N 3

-N

3 H 2



Carbohydrazide Advantages • Low/no cation conductivity contribution – Does not form LMW organic acids – CO2 contribute to non degassed cationic conductivity • Well-accepted in Industry • Much safer than hydrazine RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material


Variables Influencing Scavenger Reaction


• • • •


Time Temperature pH Catalyst



pH and Temperature Recommendations OXYGEN SCAVENGER

MINIMUM TEMP*

MINIMUM pH*

SULFITES

80 OF (27 C)

>8.5

HYDRAZINE

190 OF (88 C)

>8.5

HYDROQUINONE (HQ)

80 OF (27 C)

>8.5

>200 OF (> 93 C)

>8.5

180 OF (82 C)

>8.5

>200 oF(> 93 C)

>8.5

HYDROXYLAMINES (HA) ASCORBIC ACID CARBOHYDRAZIDE

*FOR EFFICIENT OXYGEN SCAVENGING PERFORMANCE RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material


Monitoring


Ideal Point

1 ECONOMIZER 2

1) 2)


Primary sample point for oxygen testing Sample point necessary for deaerator studies and for troubleshooting oxygen intrusion through the pump

MONITORING

• • • • •

pH Conductivity Hardness, silica Oxygen Corrosion – metals analysis – corrosion coupons

Millipore Iron Testing



Feed Water and Condensate System Treatment • Ammonia • Amines • Condensate polishing




Condensate Treatment In The Condensate: • Carbon Dioxide CO2 + H2O H2CO3

H2CO3 H+ + HCO3-

pH DECREASES



Feedwater Alkalinity Is a Source of CO2 in Condensate


IN THE BOILER:

2HCO3CO3=

CO3= + H20 + CO2 CO2 + 2OHSTEAM CO2

FEEDWATER HCO3CO3=

OH-

BLOWDOWN RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material


Relative Corrosion Rate of Copper Alloys and Carbon Steel vs pH


CARBON STEEL CORROSION RATE COPPER

7

8

9 pH


10



Fundamental Amine Characteristics • Distribution Ratio • Neutralizing Capacity • Basicity • Thermal Stability


NEUTRALIZING AMINES



R - NH3+ + HCO3-

R - NH2 + H2CO3

R - NH3+ + OH-

R - NH2 + H2O

CONDENSATE, pH

10

9

8

7

6

5

0

2


4

6 8 10 AMINE FEED (ppm)

12

14

16



BASICITY

Neutralizing Basicity Constant Morpholine Ammonia Ethanolamine DEAE MOPA Cyclohexylamine


2 18 32 66 126 440

DISTRIBUTION RATIOS



DR = Concentration in steam Concentration in liquid

VAPOR LIQUID HIGH DISTRIBUTION RATIO RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material

LOW DISTRIBUTION RATIO

DISTRIBUTION RATIOS

AMINE AMMONIA CYCLOHEXYLAMINE DEAE MOPA MORPHOLINE ETHANOLAMINE DIAMINE CONTAMINANTS CO2




0 PSIG 10 4.0 1.7 1.0 0.4 0.07 0.45 5400

DR 200 PSIG 1000 PSIG 7.1 3.6 16.0 9.3 4.5 3.4 2.4 2.5 1.6 1.0 0.15 0.29 1.9 2.7 500

100



Boiler Internal Treatment & Steam Purity • Coordinated PO4 /pH • Steam purity


Deposit Formation

• • • • •

Deposition rate increases with heat flux (Btu/Ft2) Reduces Heat Transfer Increases tube wall temperature Induces corrosion Ultimately - Tube failure

Effect of Deposition on Heat Transfer Tube Metal

Insulating Scale

800°F Fireside Combustion Gases

600°F Fireside 500°F Waterside

Scaled Tube Surface

500°F Waterside

Clean Tube Surface

Cause and Effect Diagram for Boiler Deposition Infrastructure Water & Process Technologies


Monitoring Tools 1. Monitor NaZ Performance: 2. Monitoring Boiler Feedwater/ Condensate Hardness 3. On-Line Hardness Analyzers 4. Equipment Inspections 5. Routine Blowdown Testing 6. Data Tracking

Monitoring Tools 1. Boiler Feedwater/ Condensate Iron Monitoring 2. Turbidity Monitoring 3. Equipment Inspections

Hardness Salts

Iron

Intermittent Contamination

Intermittent Contamination

Condensate Hardness Contamination

Condensate Corrosion

Poor NaZ Performance Chemical Underfeed Poor Blowdown Control

Chemical Underfeed Poor Blowdown Control Poor Storage Practices Deposition Fouling

Poor Chemical Feed Control Condensate Hydrocarbon Contamination

High Boiler Silica Poor Separation Equipment Performance Rapid Load Swings Hydrocarbon Contamination Poor Blowdown Control

Hydrocarbon Monitoring Tools 1. On-Line Total Analyzer 2. Boiler Feedwater Inspection 3. Equipment Inspections


Header Pressure Swings

Superheater/Turbine Fouling Monitoring Tools 1. Steam Purity Monitoring 2. Routine Boiler Testing 3. On-Line Sodium Analyzer 4. Equipment Inspections 5. Data Tracking


Coordinated Phosphate/pH Programs



z

Used Primarily in high pressure boilers to protect against caustic gouging

z

Applicable for lower pressure boiler systems on demin quality makeup

z

Sodium (caustic) is primary feedwater contaminant

z

Iron may also be a problem polymers used for iron control


Coordinated PO4/pH Boiler Treatment • To control boiler water pH...... • ......Create a buffer system between PO4 and NaOH



Under-Deposit Corrosion

High or Low Boiler Water pH Corrodes Boiler Steel



RELATIVE CORROSIVE ATTACK

8.5 pH

12.7 pH SAFE RANGE

1

2

3

4

5

6

7

8

pH RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material

9

10 11 12 13 14



Na: PO4 RATIO OUT OF CONTROL EXCESS “SODIUM LEAKAGE”

Na2 HPO4 + 2NaOH

Na3PO4 + NaOH + H2O

Low DSP Fed

“Free Caustic”

4Na + 1PO4 Na:PO4 = 4:1


PREVENTING CAUSTIC CONCENTRATION


NaOH + Na2HPO4 Caustic

Disodium Phosphate



Na3PO4 + H2O Trisodium Phosphate

Water


Coordinated Phosphate/pH Control

2Na2 HPO4 + 2NaOH “Exact” DSP Fed 6Na + 2PO4 Na:PO4 = 3:1



2Na3PO4 + 2H2O

Under-Deposit Neutralization



C O O R D IN A T E D p H /P H O S P H A T E C O N T R O L 1 0 .8 1 0 .6

M A X IM U M B O U N D A R Y 3 .0 :1 M O L A R R A T IO ``F re e '' C a u s tic

1 0 .4

R e g io n

1 0 .2

2 .8 :1 N a /P O 4

C o n tr o l A r e a

<900 psi

1 0 .0 2 .7 :1 N a /P O 4

9 .8

pH AT 25C

C o n tr o l A r e a

`` C a p tiv e ''

9 0 1 -1 5 0 0 p s i

A lk a lin ity R e g io n

9 .6 9 .4

2 .6 :1 N a /P O 4 C o n tr o l A r e a

1 5 0 1 -2 0 0 0 p s i

9 .0

C o n tr o l A r e a V e c to r 2 0 0 1 -2 5 0 0 p s i C O N T R O L B O U N D A R Y C o n tro l

8 .8 8 .6

T R I-S O D IU M PHO SPHATE

C A U S T IC

9 .2

C o n tr o l A r e a >2600 psi

8 .4 8 .2 1 .0

2 .2 :1 N a /P O 4 M O L A R R A T IO

D I-S O D IU M PHO SPHATE

D ia g ra m

BLOW DOW N

M O N O -S O D IU M PHO SPHATE

CO NTRO L AR EA 2 5 0 1 -2 6 0 0 p s i 2

3

4

5 6

7

8

10

15

20

30

p p m O rth o p h o s p h a te , a s P O 4


40

50

60


Caustic-Phosphate Equilibrium

Caustic


Tri-sodium PO4

Di-sodium PO4 Blowdown Mono-sodium PO4 RIL-Hazira/BWT-Technical Training GEWPT- Confidential Material

Reality Check Your 90 bar boiler has a pH 9.5 and PO4 of 30 ppm. Boiler PO4 control range is 10 - 20 ppm How should we respond?

[A]

Reality Check Your readings for this 100 bar boiler are pH 10.2 and PO4 of 6. PO4 control range is 4 - 8 ppm. What actions will put you back into control?

[A]

Acid Phosphate Corrosion zAcid

PO4 corrosion potential exists when boiler water Na/PO4 ratio is less than 2.3

zSodium

PO4 (Di or Mono) can react with Magnetite or Iron to form Maricite (NaFePO4) under high temperature (>300 C)

Steam Purity


Importance of Steam Purity z

Protect Capital Investments, such as: – Superheaters – Turbines – Steam lines and valves

z

Maintain Production

z

Prevent Process Contamination





Definitions

• Steam Purity Solid, liquid or vaporous contamination in the steam • Steam Quality A measure of the moisture in the steam




Steam Purity Guidelines

• Turbine manufacturer (ppb levels) • Boiler manufacturer (ppm levels) • Industry professional organizations • Operations




Turbine Manufacturers’ Steam Purity Limits

PARAMETER

General Electric NORMAL

100 HR.

24 HR.

Westing house NORMAL

2 WEEK

24 HR.

Allis Chalmers NORMAL

Cation Cond. uS/cm Sodium, ppb

0.2

0.5

1

0.3

0.3-0.5

0.5-1.1

0.1

3

6

10

5

5-10

10-20

10

Chloride, ppb

A

A

A

5

5-10

10-20

10

Silica, ppb

A

A

A

10

10-20

20-50

10

Iron, ppb

A

A

A

20

5

Copper, ppb

A

A

A

2

1

Oxygen, ppb

A

A

A

10

A - Governed by requirements of the steam-generator manufactureer


10-30

30-100

5

Steam Turbine - Problems • Deposition

– Deposit thickness 0.1 mm reduces stage efficiency by 3% • Surface Roughness

– Affects flow passage width – Reduce stage efficiency • LP Blade corrosion

– Stress corrosion cracking (NaOH, Cl) – Pitting – Erosion

Industrial Steam Turbines Typical Sources of Impurities Chemical Cleaning

Makeup Water

Air In-Leakage

Demineralizers Water and Steam

Condenser Leaks

Corrosion Products

Water Treatment Chemicals

Process Chemicals

STEAM PURITY Steam Purity vs Steam Quality • Steam purity is the solid, liquid, or vaporous contamination in the steam • Steam quality is the measurement of moisture in steam

Steam Purity Guidelines • Turbine & Boiler Manufacturers • Industry Professional Organizations

– (ASME, ABMA, EPRI, VGB, BS ) • Boiler Manufacturers • Operations

Steam Purity Guidelines Normal Operation

Parameter

ABB

GE

Na,

ppb

< 10

<20

< 10

< 10

SiO2,

ppb

< 20

< 20

< 20

< 15

Total Fe, ppb

< 20

< 20

<5

Cu,

ppb

<3

<2

Cl,

ppb

Cationic Cond. us/cm

<0.2

< 0.2

Westinghouse Mitsubishi

< 15

<2

< 0.3

< 0.2

Steam Purity Guidelines Abnormal Operation (Westinghouse) * Time refers to continuous time in the range and also to total time in a 12-month period in the range

Parameter

2-week *

24-Hour *

Immediate Shut Down

Cation Cond. us/cm Na, ppb

0.3 - 0.5

0.5 - 1.0

> 1.0

10 - 20

20 - 35

> 35

SiO 2, ppb

20 - 40

40 - 80

> 80

Cl, ppb

15 -30

30 - 50

> 50

SO 4, ppb

15 -30

30 - 50

> 50

CARRYOVER: MECHANICAL CAUSES

• STEAM SEPARATION EQUIPMENT • STEAM DRUM LEVEL • STEAM LOAD • OVERFIRING

CARRYOVER: CHEMICAL CAUSES • FOAMING

– TDS – Alkalinity – Organics/ Polymer Overfeeding – Antifoam • SELECTIVE VAPOROUS CARRYOVER (GOVERNED BY DRUM pH, PRESSURE AND TEMPERATURE

– Silica – Others - Cl, SO4, Fe

ATTEMPERATION WATER

• FEEDWATER

–Quality of Feed water –Chemical Treatment • SWEET WATER CONDENSER

–Source of Coolant –Purity of Steam Source • CONDENSATE

MONITORING STEAM PURITY

SODIUM • On Line Analyzer • Isokinetic Sampling • Bottle Study (Na free bottles)

• Saturated Steam


Boiler Storage


• Most oxygen corrosion occurs or is initiated when boiler is off-line (wet storage) • Key to Success - Alkaline & oxygen-free during wet storage



Boiler Storage


• Dry Storage with a desiccant is recommended for long-term storage • What constitutes ‘long-term’? – Off-season storage – Rule-of-thumb: Normally recommend dry storage if lay-up will be >1 month and boiler will not be needed on short notice



Boiler Storage


• Wet storage is recommended when: – Boiler is required for emergency stand-by or on short notice – Capacity required to meet peak demand – Unit will be out-of-service for < 1 month




Wet Storage Methods 1. Volatile Chemicals 2. Sulfite & Caustic 3. Cascade lay-up / Hot standby 4. Dry lay-up with desiccant


General guidelines for wet storage with chemicals



• Add chemicals to fill water as it is pumped into boiler • Fire boiler moderately after chemical addition to circulate & distribute or utilize external circulation pump – Always follow boiler manufacturers recommendations for firing the boiler • Adjust pH/alkalinity with amine or caustic consistent with the lay-up chemical being used.



General guidelines for wet storage of high-pressure boilers with chemicals


• Weekly testing during wet storage – Measure pH/Alkalinity – Test dissolved oxygen and/or scavenger residual – Maintain dissolved oxygen level below 10 ppb – Supplement scavenger/amine as required • Preventing oxygen ingress during storage: – Connect surge tank (drum) filled with lay-up solution to upper vent – Alternative - 5 psig (0.34 bar) nitrogen ‘cap’




Volatile Chemicals • Required when: – Above 900 psig (60 bar) – Non-drainable superheaters – Turbines – High-purity make-up • Sulfite is NOT suitable



Volatile Chemicals


• Acceptable water for preparation of highpressure boiler lay-up solutions: – Good-quality demineralized H2O – Good quality condensate (no solids) – No softened-quality, RO or raw water with appreciable TDS • Add chemicals to fill water as it is pumped into boiler



Suitable volatile oxygen scavengers


• Hydroquinone – Fastest reaction with oxygen at ambient temp – Must use neutralizing amine with HQ – Important - Amine MUST be compatible with HQ (or will develop sludge): • Hydroxylamines – Most volatile & compatible with amines




Suitable volatile oxygen scavengers

• Hydrazine - 200 ppm as N2H4 – Excellent passivator at > 200 ppm as N2H4, BUT: – Not recommended - Safety hazard! – Amine is not typically required • Ascorbic acid - Not recommended: – Poor thermal stability – Acidic decomposition products – Non-volatile



Volatile Chemicals


• Special lay-up product - CorTrol OS7700 • HQ plus special low-volatility amine package • Avoids low pH excursions on re-start • Feedrate: 2000 ppm product – 4000 ppm in new systems (nonpassivated) – Maintain pH above 10.5 throughout



Dry Lay-up with Desiccant (Long-term storage)


• Drain boiler • Hot air/heat to remove all moisture • Use desiccant (with color indicator) – Silica gel – Quick lime – Activated alumina



PRESENT TREATMENT PROGRAM AT HAZIRA

• CORTROL-5613-OXYGEN SCAVENGER – FEED RATE 0.5-1.0 PPM – RESIDUAL MONITORING. • STEAMATE-NA8590 – CONDENSATE TREATMENT – LOW DR AMINE • TRI SODIUM PHOSPHATE – FOR pH/PO4 coordination • AMMONIA – FEED WATER & STEAM pH CONTROL





Thank You


Boiler Water Training

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