Design of a Wastewater Treatment Plant For a Petroleum Refinery
Waste Water Treatment [1]:-
Technically, wastewater can be defined as any liquid that contains infirmities or pollutants in the form of solids, liquids or the gases or their combination in such a concentration that in harmful if disposed to the environment. The treatment of wastewater means the partial reduction or complete remo remova vall of exer exerci cise se impu impuri riti ties es pres presen entt in wast wastew ewat ater er.. The The incu incursi rsive ve impurities imply to the constituent (s) that is more them their acceptable levels (s) the partial reduction or complete removal of impurities depends on the intended level of treatment. The task at hand therefore is to transform harmful substances into ---harm harmfu full & prob probab ably ly iner inertt subst substanc ances es.. The The slud sludge ge & othe otherr by prod produc ucts ts produced can be used in many possible ways. The activated sludge produced can can be, be, afte afterr mecha echani nica call & chem chemic ical al dewa dewate teri ring ng,, be used used as a weed weed suppreuor if placed on the ground absorbing sunlight. It may also be used as a soil amendment since it contains nitrogen or hosts species that assimilate nitrogen from air. TREATMENT MECHANISMS:-
Usually physical, chemical or biological means are applied for wastewater trea treatm tmen entt 2 the the trea treatm tmen entt with with are desi design gned ed to carr carry y out out the the spec specif ific ic formations on the principles of either one or a combination of the means employed. Based on the means used, the treatment methods are classified as Unit operations and Unit Processes. 1
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Unit operations:
The means of treatment in which the application of physical forces predominates are known as unit operations. Major treatment methods falling in this category are: Screening Mining Flocculation Sedimentation Floatation Elutriation Vacuum filtration/ Pressure filtration Heat transfer & drying Unit Processes:-
The types of treatment in which removal of contaminants is brought about by the the addi additi tion on of chem chemic ical als s or the the use use of biol biologi ogica call mass mass or micr microb obia iall activities are k/a unit processes. Based on the type of agent used, they are further classified as:-
1. Chemical Chemical unit Process: Process: 2
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Unit operations:
The means of treatment in which the application of physical forces predominates are known as unit operations. Major treatment methods falling in this category are: Screening Mining Flocculation Sedimentation Floatation Elutriation Vacuum filtration/ Pressure filtration Heat transfer & drying Unit Processes:-
The types of treatment in which removal of contaminants is brought about by the the addi additi tion on of chem chemic ical als s or the the use use of biol biologi ogica call mass mass or micr microb obia iall activities are k/a unit processes. Based on the type of agent used, they are further classified as:-
1. Chemical Chemical unit Process: Process: 2
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Reduction Reduction or removal removal is brought brought about by the addition addition of chemical chemicals s& thei theirr
subs subseq eque uent nt reac reacti tion ons. s.
It incl includ udes es chem chemic ical al neut neutra rali liza zati tion on,,
chemical coagulation chemical precipitation, chemical oxidation, and chemical disinfection. However, these processes are often expensive due to the chemicals employed & the expenditure in handling large volumes of these chemicals. 2. Biologic Biological al Unit Unit Process Process::
Redu Reduct ctio ion n or remo remova vall in brou brough ghtt abou aboutt by micr microo oorg rgan anis ism. m. Majo Majorr treatment methods falling under this category are classified as follows: Susp Suspen ende ded d grow growth th proc proces ess: s: Ac Acti tiva vate ted d slud sludge ge Proc Proces ess, s, Aerat Aerated ed lago lagoon on,, Oxidation Pond, Aerobic & anaerobic digestion etc. Attached growth Processes: trickling filter, Rotating Contactors, Bio towers, Up-f Up -flo low w filt filter ers. s. Such Such plan plants ts are norm normal ally ly desi design gned ed to remo remove ve floa floati ting ng materials & inorganic & organic solids. Treatment Systems: Preliminary Treatment Systems:
The preliminary treatment system in mainly selected to remove floating materials & large inorganic particulate content of wastewater that usually causes maintenance operational problems in primary Secondary treatment systems.
3
Design of a Wastewater Treatment Plant For a Petroleum Refinery
This system includes: 1) Sump & Pump unit 2) Approach channel 3) Grit chamber Primary Treatment Systems: The major equipments include primary setting tank or primary clarifier. It in compares the removal of most of the large floating naturals & reduces fire solids by about 60-70% which includes 30-32% of organic suspended solids, colloidal & soluble (dissolved) organic matter is not removed.
Sump & pump
Primary Setting Yank
Primary Treatment
Primary treatment
Secondary treatment system:
After primary treatment, if wastewater in further treated for removal of colloidal & soluble organic matter present in wastewater, then it is k/a secondary treatment of wastewater. The treatment system consists of Activated sludge Process (ASP) or Trickling filter/Bio tower (a basin with fined-filter media filter) & secondary settling tanks. Primary settling Tank
Trickling filter
Aeration Tank
4
Secondary Settling Tank
Design of a Wastewater Treatment Plant For a Petroleum Refinery Secondary Treatment
Tertiary or Advanced treatment system:
If the effluent from the secondary treatment system in further treated to reduce or remove the concentration of residual impurities, then it is k/a tertiary treatment of wastewater. It is employed for rearing of industrial wastewater & is usually very expensive. For a refinery the advanced treatment units employed are Pressure sand filter Activated carbon filter ‘ Dual Media filter. Biology of the Biological processes:-
A wastewater treatment plant hosts species from several tropics revels & it is not possible model all of them. Bacteria are the most common group of microorganisms in wastewater treatment plant they are divided into autorophs & heterotrophs based are their required source of carbon. Heterotrophs assimilate organic carbon that is also used for beneficial energy conversion. Autotrophs absorb carbon dioxide &
oxidize ammonium
for energy purposes. Heterotrophic strands grow with in the absence & present of oxygen & without oxygen nitrate in used as an e - accepter & reduced to nitrogen gas. This anaerobic respiration in an efficient than
5
Design of a Wastewater Treatment Plant For a Petroleum Refinery
aerobic & produces less biomass & more Co 2 from the substrate. Autotrophs have lower growth rates due to their choice of food. A separation based on appearance gives flock forming bacteria & filamentous bacteria. Hocks have desirable settling properties & are the preferred type. However, a small amount of filamentous bacteria will improve the settle ability as they form the backbone for flocks to adhere to. At how sludge age flock forming proteins are not formed & settling in poor. Protozoan, feed primarily on bacteria, improve the effluent quality by reducing the amount of particles. Also, when a bio film in used & the sludge age is high, the concentration of higher organisms maybe too high that bacterial growth is impaired.
6
Design of a Wastewater Treatment Plant For a Petroleum Refinery
REFINERY WASTE WATER [2]
Petroleum refineries constitute systems of multiple operations that depend on the type of --- refined & the desired products there reasons, no two refineries are alike. With a refinery, the water usage is as unique as the processes inside it. Overall refinery water balance:
Many processes in a petroleum refinery use water, however not each process needs raw or treated water & water can be cascaded & reused in many places. A large portion of the water in a petroleum refinery can be recycled & reused. There are louses to the atmosphere including steam bosses & cooling tomes evaporation & drift. Understanding water balance is a key step towards optimizing the wastewater treatment & recycle.
Rain/ Storm
Steam
Evaporator and cooling
Surface
REFINERY PROCESS UNITS
Purchased Water in
Ground Recycled
7 the water balance in an A schematic diagram for
Water in Waste
Design of a Wastewater Treatment Plant For a Petroleum Refinery
SOURCES OF WATER:
i)
Surface water: water to the refineries can be supplied from
various surface water sources such as rivers & lakes in some cases it might also be from the seas. Addition sources are ground water located in a aquifers. Typical characteristics of surface water includes, total suspended solids (TSS), total dissolved solids (TDS) & turbidity. The water may require pretreatment based on the level of solids & salts that are compatible in the process. ii)
Purchased water: water can also be sufficed from municipalities
which generally supply portable water. The water can be used for other better purposes than for use in refinery. iii)
Water in crude: When crude arrives at a refinery, it often carrier
untrained water that remains from the oil well extraction process and for picking up during shipment. The water is typically removed as storage tank bottom sediment or in the De Salter & dehydrator setup in refinery & might be sent to wastewater treatment. iv)
Rain: Another source of water is the rain. Rain that falls within the
refinery battery limits is typically started before discharge. Storm water harvesting can be a technique that is used to capture all
8
Design of a Wastewater Treatment Plant For a Petroleum Refinery
contaminated storm water. With proper storage, the storm water can be used for processes like equipment washing. WATER LEAVING THE REFINERY:
i)
Wastewater: refineries can generate a significant amount of
wastewater that has been in contact with the hydrocarbons. Wastewater can refer to the cooling water blow down steam or even once through cooling water doesn’t receive any treatment before discharge. Cooling tower blow down water & wastewater from raw water tanking may or may not receive treatment at the WWTP before discharge. Contaminated water in either sent to a WWTP that is located is the facility or that owned by a third-party. Water that has not been in direct contact with the hydrocarbons or which has only minimal contamination can be sure for sense. ii)
Steam losses:- Low pressure steam that in produced in the
refinery is vented to the atmosphere when in excess. Proper provisioning of the steam system in the refinery will help minimize the production of excess steam & the need for venting it. iii)
Cooling water losses:- as water is cooled in the tomes by
evaporation, this results in a low of water in the refinery. Some of the water in the cooling tomes is untrained by the air moving through the tower & are lost to the atmosphere. These losses are k/a cooling tower drift. 9
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Oil refineries Wastewater:
Post independence, refineries in India are located away from the sea share & therefore discharge all their waste water into land water bodies. The major sources of wastewater for Indian refineries are as follows: -
A large quality of it comes out after getting polluted by oil & other toxic substances.
-
Major requirement in from cooling purpose. The extent of recycle & reuse of this water will determine the amount of wastewater generated by refinery.
-
Another major use of water in for boiler feed. The steam obtained in utilized for different operations like desalting of crude oil, steam stripping in hopping etc. steam is also used in stripping of the spent catalyst before the latter is sent for regeneration.
-
Water is also used to wash products like gas alive to strip off the reagents used in its processing earlier.
MAJOR CONTAMINANTS OF INDUSTRIAL WASTEWATER:
Thus, the wastewater contains, in small or large amounts, varying proportions of: 10
Design of a Wastewater Treatment Plant For a Petroleum Refinery
-
Free & emulsified oil
-
Spend caustic
-
Impurities of oil like NH3, phenols, H2s & CN-
-
BOD as a result of the organic content.
-
Dissolved & suspended solids.
MAJOR CONTAMINANTS OF OIL REFINERY WASTEWATER:-
Contaminant Turbidity
Problems it can cause Removal Methods Washes water cloudy & Coagulation, settling & deposits in water lines & filtering
Sulphates
process equipments Adds to the solids Demineralization content
of
water
&
& desalting
combines with calcium to from calcium sulfate Oil
scale Source of scale, sludge, Oil/water foaming
Oxygen
in
separators
boilers, strainers, regulation &
impedes water change. filtrations Corrosion of water lines, De aeration, corrosion heat
exchange inhibitions, etc.
Hydrogen sulphide
equipment, boilers etc. Cause of ‘rather’ egg Highly
Dissolved solids
odor, corrosions toxicity. exchange Dissolved solids are the Various 11
basic
anion softening
Design of a Wastewater Treatment Plant For a Petroleum Refinery
total measure amount
of
of
the processes --- as time
discoursed softening
&
cation
material. It integers with exchange processes. process Suspended solids
&
causes
sealing. These plug flow lines, Sedimentation, cause deposits on that filtrations,
usually
exchange equipment & preceded by coagulation erosion of equipment.
12
& settling
Design of a Wastewater Treatment Plant For a Petroleum Refinery
CHARACTERISTICS OF WASTEWATER FROM AN OIL REFINERY: BOD: Biological oxygen demand stands for the organic matter present in the
wastewater in the form of carbonaceous & nitrogen matter. It is most commonly measured in the form of BOD5 i.e. for a period at 20°. COD: stands for the chemical oxidation demand & in the oxygen equivalent
of those constituents in a sample which are susceptible to permanganate or dichromate oxidation in an acid solution. COD in always greater than BOD 5 TOC: Total organic carbon in the total amount of organic carbon present
wastewater. Total solids: Analytically, the total solid content of wastewater is defined as
all the matter that remains as residue upon evaporation at 103 °C. settable solids are those solids which settle at the bottom of cone shaped container called an Imhoff cone in a 60 minute period. Settle able solids are an approximate measure of the sludge that will be produced during primary sedimentation. Total solids are further classified into suspended solids of filterable by passing a known volume of liquid through the filter. Each of the categories of solids may be further classified on the basis their volatility at 550 ±50°C. the organic fraction will oxidize & will driver off as gas at this temperature & the inorganic fraction will remain behind as ash. Thus
13
Design of a Wastewater Treatment Plant For a Petroleum Refinery
the terms, volatile suspended solids & fined suspends solids are given to the organic & inorganic fractions respectively.
Imhoff cone
Settle able solids
SAMP
Evaporatio
Total Solids
Filter (Glass Fiber) Evaporati
Evaporatio
Fixed Solids
Suspended
Muffle Oven
Muffle Oven
Volatile Suspended solids
Fixed Suspended solids
Volatile Filterable solids
Fixed Filterable
Total Fixed solids Total Volatile
Total solids
Oil & grease: oils have a deleterious effect on the treatment system &
receiving water bodies. Oil may be free, simplified or soluble.
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
Phenolic compounds: Persistent in refineries & is toxic to aquatic life &
causes an oxygen demand. Acidity: Acidity in of note as the pH of water in the bio-treatment must be or
near to neutral for proper growth of micro organisms. Mostly inorganic contribute to acidity. Alkalinity: Spent caustic containing Na, Ca & K salts. N 2 in ammonia can
generate alkalinity. − Inorganic ions: Cl-, so42-, No3 etc. This parameter in important in quality
control for cooling tower & voiles blow down waters. Ammonia, nitrogen & sulphides: there enter the water during steam
washing of various H/Ls where they are removed as volatiles. Taste & dour: The foul taste & odor of a rotten egg from wastewater is due
to the presence of H2S in the water. Temperature: an increase in temperature results in the die in solubility of
oxygen in the available water bodies. Heavy Metals: heavy metallic ions are generally common to industrial
wastewater resulting from corrosion inhibition additives, catalyst usage & product additives. Color & Turbidity : wastewater contains suspended particles that tend to
scatter light & the water is then said to be turbid.
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
Schematic Representation of the sources of wastewater:
NORMAL PROCESS OPERATIONS Primary pollutant, dissolved organics, oil & grease. UTILITY OPERATIONS Primary pollutants,
dissolved
salts,
temperature, cooling tower additives. SANITARY SEWAGE Primary pollutants,
organics,
pathogens
nutrients
CONTAMINATED STORM RUN-OFF Primary pollutant, dissolved oxygen oil & grease
Primary pollutants, dissolved oxygen oil & grease MISCELLANEOUS DISCHARGES Primary pollutants dissolved oxygen oil & grease.
16
COMBINED EFFLUENT
Design of a Wastewater Treatment Plant For a Petroleum Refinery
POLLUTANTS PRESENT AND THEIR EFFECTS
[3]
Major pollutants present in refinery efficient water & their effects are as follows: OIL
In refinery crude oil in procured & this oil, through different sources find its way into the water used for various purpose e.g.: cooling, product washing, tank draining it has the following effects:i)
It imparts unpleasant taste & odor to waste.
ii)
Destroys algae & other mater plants thus destroying the food supply of fish.
iii)
Blocks the atmospheric oxygen by water bodies (line fish) & coated on fish & other animals & water birds affecting their survival.
iv)
Creates fire hazard when oil gets accumulated in stagnant portion of water.
v)
Organic content present in oil may deplete the dissolved oxygen sufficiently to kill the fish.
vi)
The presence of timidity of films affects the aesthetic of beaches or seas used for recreation.
17
Design of a Wastewater Treatment Plant For a Petroleum Refinery
PHENOL
Phenol is a chemical compound formed during cracking operation of petroleum fractions, for e.g. i)
Phenol imports unpleasant taste & odor to water.
ii)
In high cone, phenols are tonic to many living organisms.
SULPHIDES
Wastewater from cracking, desulphurization unit, distillation unit & spent caustic from caustic treatment system contains sulphides. Their cone depends on type of crude used. i)
Sulphides import objectionable taste & odor to waste.
ii)
They rapidly consume oxygen present in water & thereby depriving fish & other water organisms of oxygen & read to their death.
iii)
Sulphides are also corrosive & toxic.
SUSPENDED SOLIDS
Suspended solids can be sand particles, iron compounds, algae/fungi, flocs etc. i)
They cause diminished sunlight penetration & thereby retained photo synthesis of replenishment oxygen.
ii)
They injure fish gills & damage aquatic life. 18
Design of a Wastewater Treatment Plant For a Petroleum Refinery
iii)
They deposit in the bottom of the water ways & affect the ‘Bottom Life’.
iv)
They tend to clog sewers & thereby restrict water flow.
BIOLOGICAL OXYGEN DEMAND
BOD is a characteristic & not a specific substance. It indicates the content of demand of oxygen in eater. Microorganisms like bacteria etc. present in water assimilate organic pollution & multiply. For this process & also for respiration, microorganisms utilize oxygen dissolved in water. This less of oxygen is splashed by reservation from atmosphere. But if the demand of oxygen is more, resulting less cannot be made up fast. That is waste water containing pollutant like sulphides, phenol & hydrocarbons etc. will have high BOD resulting in reduction of oxygen level in water bodies & thereby affecting the survival of water bodies. The effect of high BOD value is: i)
The water bodies become anaerobic & give rise to foul smell.
ii)
The water bodies become unfit for beneficial use. BOD is measured in terms of oxygen impressed in mg/L required to oxidize component of wastewater. 19
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Chemical Oxygen Demand
Like BOD, chemical oxygen demand denotes the oxygen demand level of water. The difference b/w BOD & COD is only the testing method in the laboratory. In BOD testing, the oxygen requirements are determined by the use of microorganisms like bacteria for oxidizing the imperatives & takes 5 days to complete the test. COD is defined as the amount of oxygen expressed as nrg/L, required to oxidize components of wastewater by chemical reaction. pH value
The pH value indicates the hydrogen ion concentration, which is vital in discharged water. It affects the test, corrosiveness & efficiency of chlorination & other treatment, process. Cyanides
Significant concentrations of cyanides occur in wastewater from cracker units. These compounds vary in toxicity to aquatic life. Free cyanides are very tonic. Lead
The use of tetraethyl lead for boosting octane of motor spirit is the chief source of read in refinery waste. In human body lead is acting as a
20
Design of a Wastewater Treatment Plant For a Petroleum Refinery
cumulative poison & may cause chronic poisoning if lead contaminated water in used continuously. TDS
Total dissolved solids in irrigation water have direct physical effect in permeation of water uptake by plants by the osmotic effect. It also changes soil structure, permeability & aeration. Sulphates & Chlorides:
Moderate concentration of chloride in the root zone usually causes chloride to a cumulate in the leaves to about 1-2% dry weight. At such concentration, marginal leaf burn develops, leading ultimately to leaf chop. Sodium a cumulate of 0.2-0.3% in leaves causes burns & injuries. Chloride salts are highly soluble. Sulphates are less toxic. The potential salinity of water in defined as chloride concentration press half of the sulphates concentration in mg/L Sodium
Soil dispersion & as a result drainage & soil aeration becomes poor due to high radium content of the irrigation water. Soil irrigated with water having high sodium content will have comes calcium content & effects plants requiring high calcium. TREATMENT PHILISOPHY [4]
21
Design of a Wastewater Treatment Plant For a Petroleum Refinery
The principal contaminants present in these streams are mainly oil (free and emulsified), suspended solids, phenols, sulphides and organic matter contributing to BOD/COD. The treatment procedure for different contaminants is as follows: TREATMENT FOR FREE AND EMULSIFIED OIL
Free oil (Dai > 60 microns) present in the process stream is removed with the help of gravity, by the density difference between the dispensed phase (oil) and the dispersion medium (water). The efficiency of oil-water separation is directly proportional to the unit surface area. For this purpose, a highly efficient compact Tilted Plate Interceptor (TPI) unit is used. Effluent is fed into the TPI, under laminar conditions and through a number of closely spaced corrugated plates; oil globules rise and coalesce with other globules. Heavier settling particles also slide down through these plates. The floating oil is skimmed from the top while the solids are removed from the bottom. Emulsified oil (oil particle Dai. < 60 u) present in the effluent is removed by chemical flocculation followed by floatation in a Dissolved Air Floatation Unit (DAF). It essentially consists of a flash mixer, a flocculator and a floatation unit. The DAF process relies on the release of dissolved air as a cloud of micro bobbles into the incoming effluent stream. These bubbles attach themselves to the emulsified oil globules (<60u) and lift them on to the surface to form a floating blanket. De-emulsifying agents are also employed in the floatation units to break the oil-in-water emulsion by neutralizing the charge carried by the oil droplets. The oil layer is formed at the surface and is skimmed away by a skimmer mechanism. TREATMENT FOR SULPHIDE
Sulphides present in the effluent stream emanating from process unit are removed by chemical precipitation using chlorinated copperas. Chlorinated copperas, formed by the reaction of chlorine with Ferrous Sulphate, is very effective for sulphide precipitation. The following reactions occur during sulphide precipitation, in an alkaline pH range. 2Na OH + H2S
=
3FeSO4 . 7H2O + 1.5 CL2 H2O
Na2S + 2 H2O =
22
Fe2 (SO4)3 +
FeCl 3 . 21
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Fe2 (SO4)3 + 3 Na 2 S
=
Fe2 S3 + 3 Na2 SO4
Fe 2 S3 (Hydrolysis)
=
2 FeS + S
FeCl3 + 3 NaOH
=
Fe (OH)3 + 3 Na Cl
Chlorinated copperas solution is dosed in the flash mixer of the DAF system and the precipitate is separated in the floatation unit of the same. Presently sulphide removal is done by Hydrogen Peroxide& chlorinated copperas dosing facility is kept for emergency. HYDROGEN PEROXIDE DOSING
To remove organic sulphide , we were using chlorinated copperas, which results in sludge generation. It is difficult to dispose the sludge. To avoid such problems we have started to dose H2O2 and to maintain Eco-friendly environment system. Hydrogen Peroxide is a most versatile chemical used in effluent treatment. Hydrogen Peroxide is an oxidizing agent. It gives active oxygen, which is obtained by controlled decomposition of H2O2 with water as a byproduct. Hence it provides a very clean process without producing harmful or environmentally unsafe product. Chemical Properties
The most important chemical property of Hydrogen Peroxide is its ability to provide “ active Oxygen” to process concerned. It reacts as: A) B) C) D)
as an oxidant As a reductant To perform other inorganic & organic peroxy compounds. To form addition compounds. O O H2O2
|||
A) R-S-R
| ||
R-S-R
B) 2Ce 4+ + H2O2
R-S-R
2Ce 3+ + 2H+ + O2
C) Peroxy compounds CH3COOH + H2O2
CH3COOH + H2O
E) Addition compounds 23
Design of a Wastewater Treatment Plant For a Petroleum Refinery
2Na2Co3 +3 H2O2
2Na2Co3.3 H2O2
decomposition takes place as follows 2 H2O2
2H2O + O2
HYDROGEN SULPHIDE CONTROL
Hydrogen peroxide also treats the toxic pollutants such as cyanides, phenols, nitrites & sulphides. It is carried out by oxidation process. H 2O2 also serves the purpose of oxygenation. As a potential source of oxygen, it is used in biological treatment particularly at times of overload, for treatment of bulking sludge, and for the prevention of denitrification in settling tanks. TREATMENT CHEMISTRY
H2O2 as stated before is a strong oxidizing agent and reacts with sulphides over a wide range of pH. Reactions are shown below for acidic / neutral as well as alkaline conditions. Acidic/ neutral conditions.
In acidic range and neutral conditions sulphide in the effluent mostly present in the form of H2S. The H2O2 reacts with H 2S to give products of oxidation as water and elemental sulphur as below. H2O2+ H2S -- 2H2O +S ALKALINE RANGE
In alkaline range sulphide present in the effluent is generally in the form of Na2S. The H2O2 reacts with Na2S to give end products as water & Na 2So4 as shown below. 2RSH+ H2O2- RSSR+H2O( for mercaptans) SO3 3+ H2O2 SO2 4 + H2O (for sulphites) Fe++ C6H6O+14 H2O2
----- 6CO2+17H 2O(for phenols)
CN+ H2O2----- CNO+ H2O (acidic ph) CNO+2H2O-- Co2+NH3 +OH ( for cynides) 50% H2O2 ( as commercially available) is used in feeding for removal of sulphides. TREATMENT FOR BOD/COD/RESIDUAL SULPHIDES/PHENOLS 24
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Organic matter, phenols, residual sulphides, non-recoverable oil and hydrocarbons contribute to the effluent’s Biological Oxygen Demand (BOD), and Chemical Oxygen Demand (COD). BOD is indicative of the quantity of oxygen required to biologically stabilize the organic matter present in the waste water, while COD indicates the oxygen requirement for oxidizing the organic matter by a strong chemical in an acidic medium, an elevated temperature. In order to stabilize the organic matter, biological treatment of waste water is to be accomplished by aerobic digestion of the organic matter. Waste water treatment plant (WWTP) in Panipat Refinery employs a Biotower (Plastic media trickling filters), in conjunction with an activated sludge process (Aeration tank). BIOTOWER
The biotower consists of a bed of highly permeable media made of plastic (Poly propylene) to which microorganisms are attached and through which waste water is percolated. The organic material present in the waste water is degraded by a population of microorganisms attached to the filter media. ACTIVATED SLUDGE PROCESS AERATION TANK
In the activated sludge system, the bacteria is continuously mixed with waste water and aerated by motor operated aerators. Here also bacteria eat away the impurities. The bacteria water mixture (mixed liquor) is then sent to clarifier from Aeration tank where bacteria mass is separated from water. The bacteria mass recycled back to aeration tank to maintain required level of bacteria mass in Aeration tank. The balance material is pumped out to sludge management system. The part of treated water from clarifier is recycled back and the rest is discharged to Guard Ponds. The activated sludge process is an aerobic biological process, which uses the metabolic reactions of variety of microorganisms to attain an acceptable effluent quality by removing substance exerting an oxygen demand. In simple form the reaction may be written as: Food
+ Microbes + Nutrient 25
+
O2
Design of a Wastewater Treatment Plant For a Petroleum Refinery
(Organic waste) (Sludge) =
(N+P)
New cells + CO2 + H2O
+ NOX
(Air) +
energy
The process basically involves two unit operations viz. contacting and liquid solid separation. The contacting operation involves mixing of wastewater and microorganisms and the microbial floc particles are brought into contact with the organic components of the waste water. The organic matter serves as a carbon and energy sources for microbial growth and is converted into microbial cell tissues. After the treatment, the mixed liquor is separated in a clarifier. The concentrated (settled) microbial solids are recycled back to the system for maintaining bacteria population. As the microorganisms are continuously produced, the mass of microorganisms would keep increasing until the system could no longer contain them. A purge stream is, therefore, withdrawn from microorganism recycle stream for purging out of the system. The concentration, at which the biological mass should be kept, depends on the desired treatment efficiency and other consideration related to growth. Since counting million of bacteria are impossible, weight of bacterial mass present in one litre of water is used. This is expressed as Mixed Liquor Suspended Solids (MLSS). This term is used to control bacteria population in bioreactor operation at a particular level. To know MLSS, one litre of water from aeration tank outlet is taken and filtered. Filtered solids are dried and weighed and expressed in milligrams per litre. However, solids thus filtered may contain inorganic material like sand and iron sulphides. Our interest is in organic portion, which is bacterial mass. To obtain sulphides this, MLSS is heated to 600° C; organic matter is converted into carbon monoxide and water. The residue is the inorganic matter. The difference of MLSS and inorganic matter is reported as Mixed Liquor Volatile Suspended Solid (MLVSS). Generally the concentration of MLVSS is 1800 mg/lt. in this system. In the field, an operator can take aeration tank outlet sample in a bottle and note the volume of MLSS after settling the sample for 30 mts. This gives fair idea of MLSS, which can be correlated, to laboratory results. Another characteristic that can be monitored is Sludge Volume Index (SVI). It is the volume occupied by one gram of MLSS after a litre sample has been allowed to settle for 30 mts. It indicates how bacteria can settle and separate out 26
Design of a Wastewater Treatment Plant For a Petroleum Refinery
from water. Sludge of higher SVI settles poorly in clarifier and is likely to be carried away in clarifier over flow water. Then nutrients need to be increased at the inlet of biological system. TREATMENT HYDROCARBON
FOR
SUSPENDED
SOLIDS
AND
UNTREATED
In order to achieve supplemental removal of suspended solids (including BOD contributed by particulate matter) from waste water, single/multimedia filtration is one of the principal unit operations employed. The removal of S.S. and residual BOD/COD are accomplished by a complex process involving straining interception, impaction. Sedimentation and absorption within the filters. The two most popular filters used in refinery WWTP’s are sand filters and Dual-media filter. In order to remove the dissolved, untreated hydrocarbon, activated Carbon filters are employed, which uses granular activated carbon to absorb the hydrocarbon on its surface by chemical and physical bonding.
27
Design of a Wastewater Treatment Plant For a Petroleum Refinery
MATERIAL BALANCE CALCULATIONS
Basis: 1 day operation F1 = 9600 m3/D
[4]
F3 = 480m3/D
: surface run off/contaminated rain mater stream.
: oily water stream
[4]
F1=F2=9600 [3]/D When the two streams of oily water & contaminated rain water are mixed, the new waste water characteristics are: Characteristic Free oil Emulsified oil BODs COD TSS Sulphides Phenols N1+3 CN-
F2 (OWS) mg/L 600 400 500 1000 150 60 30 30 5
F3 (CRWS) mg/L 190 35 65 125 350
F2+F3 (mg/L) 580.476 382.619 479.286 958.334 159.523 57.143 28.571 28.571 4.762
1) GRIT CHAMBER: capable of removing grit particles of density 2650 kg/m3 [5]
Grit removed =
.03m 3
υ 3
1000 m of wastewater
×10080 = 0.3024m 3
Weight of grit removed = 0.3024 ×2650 kg/m3 = 801.36 kg/d of grit removed. Applying flow balance on grit chamber, 28
Design of a Wastewater Treatment Plant For a Petroleum Refinery
F5=F3+F2-F4=10079.697m3/D 2) TILTED PLAT INTERCEPTOR :
As per the data available on the EPA handbook, we assume, 80% free oil removal, 20% suspended solids removal, 5% BOD removal & 5% COD removal.[6] F5=10079.697 m 3/D
Influent free oil =
10079.697 ×580.476 1000
= 5851.022 kg / D
Fee oil removed = 4680.818 kg/D= 0.8 ×5851.022 kg/D Effluent free oil = 1170.204kg /D
Flow rate of oil removal =
4680.818 960
= 4.876m 3 / D
density of oil = 960m / D 3
Influent suspended solids road =
10079 .697 ×159.23 1000
= 1607.943 kg/D Suspended solids removed = 0.2×1607.943 kg/D = 321.589 kg/D Assuming 6% solids concentration & density of [8]
29
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Primary sludge = 120 kg/m3 as for Metcalf & eddy, wastewater engineering,
Suspended solids removed =
321.589 0.06 ×1020
= 5.25m 3 / D
Effluent & suspended solids = 1286.354 kg/D Effluent flow rate = F8=F5-F6-F7 = 10079.697-4.876-5.25 = 10069.571 m 3/D
Influent BOD5 load =
10079.69 × 479.286 1000
= 4831.058kg . / D
BOD5 removed = 241.553 kg/D=4831.058 ×0.05 kg/D Effluent BOD5= 4589.505 kg/D
Influent COD=
985.334 ×10079.69 1000
= 9659.716 kg / D
COD removed = 482.986 kg/D Effluent COD= 9176.73 kg/D. Effluent flow = 10069.571 m 3/D=F8 S.S = 127.75 mg/L Free oil = 126.212 mg/L
30
Design of a Wastewater Treatment Plant For a Petroleum Refinery
BOD5 = 455.78 mg/L COD = 911.333 mg/L 3) PRIMARY SETTLING TANK: As per the EPA handbook, we can safely assume a reduction of 30% in BOD, 20% in COD, 50% in TSS & 60% in free oil.[6] F8 = 10069.571 m 3/D Influent SS = 127.75 mg/L Influent BOD5 = 455.70 mg/L Influent COD = 911.333 mg/L Influent free oil = 126.212 mg/L
Influent TSS =
127.75 ×10069.571 1000
=1286.388 kg / D
S.S removed = 643.194 kg/D = 1286.388 ×0.5 kg/D Assuming 6% solids concentration & density of primary sludge
Flow rate =
643.194 0.06 ×1020
= 10.51 m3/D Effluent T.S.S = 643.194 kg/D.
31
[8]
=
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Influent free oil =
116.212 ×10069.571 1000
= 1170.205 kg / D
Free oil removed = 1170.205 ×0.6 = 702.123 kg/D Assuming, density of oil = 960 kg/m3
[7]
Flow rate of free oil removed = 0.731 m 3/D
Influent BOD5 =
10069.871× 455.78 1000
= 4589.509kg / D
BOD5 removed = 4589.509 ×0.3=1376.856 kg/D BOD5 removed = 3212.656 kg/D
Effluent COD =
911.333 ×10069.871 1000
= 9176.732 kg / D
COD removed = 9176.732 ×0.2 = 1835.346 kg/D Effluent COD = 7341.386 kg/D Applying flow balance, F10=F8-F9- oil removed = (10069.571-10.51-0.731)m 3/D = 10058.33 m3/D
Effluent free oil =
486.012 ×1000 10058.33
= 46.537mg / L
32
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Effluent S.S. = 63.946 mg/L Effluent BOD5 = 319.403 mg/L Effluent COD = 729.881 mg/L 4) DISSOLVED AIR FLOATATION UNIT: as per the EPA handbook, the following assumptions are made: 50% removal of suspended solids. Free oil 75% emulsified oil removal 75%, BOD 5 removal 20% COD removal 10%
[6]
Applying threw balance over the unit, F10+R×F12 = F12+F11
(i)
F10 = influent flow = 10058.33m 3/D R = recycle from total effluent F12, m 3/D F12 = Total effluent, 3/D F11 = solid sludge removal, m3/D. As per, Metcalf & Eddy, wastewater engineering recycle ratio in large treatment plant is assumed to be around 20%
[9]
∴ F10+0.2F12=F12+F11+Oil removed.
F10=0.8F12+F11+oil removed.
(ii)
To obtain sludge flow rate,
33
Design of a Wastewater Treatment Plant For a Petroleum Refinery
F11 =
TSS removed solids conc ×density of solids sludge
(iii)
S.s. influent = in coming S.S. +S.S. in recycle stream
63.946 ×10058.53 + 0.2 × F 12 × 63.946 × 0.5 = 1000 1000 = 643.19 + (6.395 ×10-3) F12 S.S. removed = (643.19 + (6.395 ×10-3) F12) 0.5 [8]
(iv)
Oil removal
46.537 ×10058.33 + 0.2 × F 12 × 46.537 × 0.25 Influent free oil = 1000 1000 = 468.085 + (2.33 ×10-3) F12) 0.75 -(v)
382.619 +10058.33 + 0.2 × F 12 ×382.619 × 0.25 Influent emulsified oil = 1000 1000 = 3848.508+ (19.13 ×10-3) F12
-(vi)
Total flow rate of oil removed (468.085 +3848.5058+(21.46 ×10-3)F12)0.75 Using
(vii) & (iv) in (ii) 10052.33 = 0.8F12+3.494+5.25+6.9 ×10-5 F12 10049.586 = (0.8-6.9 ×10-5) F12 34
-(vii)
Design of a Wastewater Treatment Plant For a Petroleum Refinery
F12 =
10049.586 0.8
= 12561.9825 m 3 / D
Recycle rate = 0.2 ×F112= 2512.397 m 3/D Effluent flow rate = 10049.59 m3/D Now, Influent suspended solids = 643.19 + (6.395×10-3) 2512.397 = 659.257 kg/D Suspended solids removal = 329.628 kg/D Effluent suspended solids = 329.628 kg/D Influent free oil = 468.085 + (2.33×10-12) 2512.397 = 473.94 kg/D Free oil removed = 355.454 kg/D Effluent free oil = 118.486 kg/D Influent emulsified oil = 3848.508 + (19.13 ×10-3×2512.397) = 3896.563 kg/D Emulsified oil removed = 3896.563 ×0.75=2922.422 kg/D Effluent emulsified oil = 974.141 kg/D
35
Design of a Wastewater Treatment Plant For a Petroleum Refinery
319.403 ×10058.33 + 2512.397 ×319.403 × 0.8 Influent BOD5 = 1000 1000 = 3854.533 kg/D BOD5 removed = 770.907 kg/D Effluent BOD5 = 3083.626 kg/D
729.88 ×10058.33 + 2512 × 729.88 × 0.9 Influent COD = 1000 1000 = 7341.384+1650.373 = 8991.757 kg/D COD removed = 8991.757×0.1=899.176 kg/D Effluent Cod = 8092.581 kg/D Now, Effluent S.S. = 329.628 kg/D 20% of this passes in the recycle
Remaining S.S. = 263.702 kg/D =
263.702 ×1000 10049.59
= 26.24 mg/L Effluent free oil = 118.486 kg/D In recycle = 23.697 kg/D = 9.43 mg/L 36
Design of a Wastewater Treatment Plant For a Petroleum Refinery
In effluent = 94.789 kg/D = 9.43 mg/L Effluent emulsified oil = 974.141 kg/D
In recycle = 194.828 kg/D =
In effluent = 779.313 kg/D =
194.828 ×1000 2512.397 773.313 ×1000 10049.59
= 77.547 mg / L
= 77.547 mg / L
Total effluent oil = 86.98 mg/L Effluent BOD5 = 3083.626 kg/D In recycle = 616.725kg/D = 245.473 mg/L In effluent = 2466.901 kg/D = 245.473 mg/L Effluent COD = 3092.581 kg/D COD in recycle 1618.8.516 kg/D = 644.212 mg/L COD in effluent = 6474.065 kg/d = 644.212 mg/L
10058.33 × 28.571 + 2512.397 × 28571 × 9 1000 1000
Influent phenol =
= 351.98 kg/D Phenol removed = 351.98×0.1 = 35.198 kg/D Effluent phenol = 316.782 kg/d Phenol in recycle = 316.782×0.2= 63.356 kg/D 37
Design of a Wastewater Treatment Plant For a Petroleum Refinery
= 25.218 mg/L Phenol in effluent = 253.426 kg/D = 25.218 mg/L Effluent flow = 10049.59 m 3/D COD = 644.212 mg/L BOD5 = 245.473 mg/L Total oil = 86.98 mg/L S.S. = 26.24 mg/L Phenol = 25.218 mg/L 5) BIO TOWER
The bio tower is a trickling filter of greater media depth at a petroleum refinery is made up of plastic media (polypropylene) with 90% void age. Assuming, BOD reduction = 60%, COD reduction= 30%, Suspended solids reduction = 60%, oil reduction = 50% Phenols reduction = 70%, NH3=20%, sulphides =70%, CN-=80% Applying flow balance, F14+0.5+F15=F15
38
[6]
Design of a Wastewater Treatment Plant For a Petroleum Refinery
F14= influent flow 0.5 = recycle ratio from total effluent as per IOCL
[10]
Panipat, ETP-1 operating manual F15 = Total effluent
F15 =
F 14 0.5
=
10049.59 0.5
= 20099.18m 3 / D
F 16 (effluent) = 10049.59m 3/D
Influent BOD5 =
10049.59 × 245.473 1000
+
10049.59 × 245.473 ×0.4 1000
= 3453.664 kg/D BOD5 removed = 3453.664 ×0.6 = 2072.198 kg/D Effluent BOD5 = 1381.466 kg/D
BOD5 in recycle = 690.733 kg/D =
690.733 ×1000 10049.59
= 68.732 mg / L
BOD5 in effluent (F16) = 690.733 = 62.732 mg/L
Influent COD =
10049.59 ×644.212 1000
+
10049.59 ×644.212 ×0.7 1000
= 11005.913 kg/D COD removed = 11005.93×0.3=3301.774 kd/D Effluent COD = 7704.139 kd/D 39
Design of a Wastewater Treatment Plant For a Petroleum Refinery
COD recycle = 3852.069 kg/D =
3852.069 ×1000 10049.59
= 383.306 mg / L
COD in effluent (F16) = 3052.069 kg/D= 383.306 mg/L
Influent suspended solids =
10049.59 × 26.24 1000
+
10049.59 × 26.24 ×0.4 1000
kg/D S.S. removed = 369.182 kg/D = 221.509 kg/D S.S. in effluent = 147.673 kg/D S.S. in recycle = 73.837 kg/D = 7.34 mg/L S.S. in effluent (F16) = 73.837 kg/D = 7.34 mg/L
Influent oil =
10049.59 ×86.98 1000
+
10049.59 ×86.98 ×0.5 1000
= 1311.17 kg/D Oil removed = 1311.17 ×0.5 = 655.585 kg/D Effluent oil = 655.585 kg/D Oil in recycle = 327.793 kg/D = 32.618 mg/L Oil in effluent (F16) = 327.793 kg/D = 32.618 mg/L
Influent sulphides =
10049.59 ×57.146 1000
+
10049.59 ×143 ×0.3
= 746.543 kg/D 40
1000
=369.102
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Sulphides removed = 522.58 kg/D Effluent sulphides = 223.963 kg/D Sulphides 111.982 ×1000 10049.54
in
recycle
=
111.982
kg/D
=11.143 mg / L
Sulphides in effluent (F16) = 111.982 kg/D = 11.143 mg/L
Influent Phenols =
10049.59 × 25.218 1000
+
10049.59 × 25.218 ×0.3 1000
= 329.46 kg/D Phenols removed = 230.622 kg/D Effluent phenols = 98.838 kg/D
Phenols in recycle = 49.419 kg/D =
49.419 10049.59
×1000 = 4.918 mg / L
Phenols in effluent (F16) = 49.419 kg/D = 4.918 mg/L
Influent CN- =
10049.59 × 4.762 1000
+
10049.59 × 4.762 × 0.2 1000
= 57.427 kg/D CN- removed = 45.942 kg/D Effluent CN- = 11.485 kg/D
41
=
Design of a Wastewater Treatment Plant For a Petroleum Refinery
CN- is recycle = 5.743 kg/D =
5.743 ×1000 10049.59
= 0.571mg / L
CN- is effluent (F16) = 5.743 kg/D = 0.571 mg/L Influent TKN (Total Kjeldahl nitrogen, i.e. the total nitrogen present as NH 3, NH 4+ or N2
=
28.571×10049.59 1000
+
28.571×10049.59 ×0.8 1000
= 516.828 kg/D NH3 nitrified = 516.828 × 0.2= 103.366 kg/D Effluent TKN = 413.462 kg/D TKN in recycle = 206.731 kg/d = (206.731/10049.59) ×1000=20.57 mg/L TKN is effluent (F16) = 206.731 kg/D = 20.57 mg/L De-nitrification Step = As per Metcalf & Eddy, wastewater engineering, de-nitrification rate in given b y the formula, UDN = UDN ×(1.09) T-20 (1-DO) Assuming operating temperature to be 30 °C, D.O. = 0.07 mg/L 1
U DN ( 20°C )
= 0.1day −1 42
Design of a Wastewater Treatment Plant For a Petroleum Refinery
UDN = 0.1×(1.09)10 (1.0.07) = 0.22
Now the minimum
BOD applied MLVSS in vactor
∴ De-nitrification rate = 0.22
Kg No 3
− N 2
kg MLVSS . D
is
I
kg NO 3
− N
kg BOD applied . D
×3453.664
= 759.806 kg NO -3-N/D Since this value is greater than the available NO3− , then, the whole NO −3 is concerted to N2 gas which leaves as bubbles. Final effluent flow = 10049.59 m 3/D BOD5= 68.732 mg/L COD = 383.306 mg/L S.S. = 7.34 mg/L Oil = 32.618 mg/L Sulphides = 11.143 mg/L Phenols = 4.918 mg/L CN- = 0.571 mg/L NH3 = 20.57 mg/L
43
Design of a Wastewater Treatment Plant For a Petroleum Refinery
ACTIVATED SLUDGE PROCESS:
Consider a connectional plug flow type process. The critical parameter of Food to microorganism (F/M) is taken as 0.3 we also assure øC= mean we credence time, of 10 days we also assure that the solids entering the classifier are same as the solids leaving the aeration tank & that there is no digestion in the clarifier. As per the EPA standards, BOD5 removal = 90%, COD removed = 50%, 55 removal = 60%, oil removal = 80%, Phenol removed = 95% NH 3 removed = 50%, sulphide removal = 97% CN - removal 95% [6] Applying flow balance, F17+F21 = F19+F18 F19=F20+F21 X (bio mass present in the reactor, mg/L) = 2000mg/L[11] Influent flow = 10049.59 m 3/D By material balance on the aeration tank, me have (Q + Q r) X = Qr Xr [12] Xr = MLSS present in recycle stream, mg/L Xr = 106/SVI
[11]
SVI = Sludge volume index F/M =0.3 produces a sludge of SVI =100 44
[11]
Design of a Wastewater Treatment Plant For a Petroleum Refinery
∴
Qr
=
Q
X X 2
−
X
2000
=
1000 − 2000
=
0.25
Qr= 2512.398 m 3/D
0.3
=
BOD applied to the reactor , kg / D MLVSS in the reactor , kg / D
10049.59 × 68.732
MLVSS =
0.3
= 2302.428 kg / D
Amount of sludge removed: = 0.06 day -1 [11]
(kd)
00
(kd )
30
(Y)
30
= 0.06 × (1.047) 10 = 0.095 day-1
= 0.6×(1.047) 10 = 0.95[11]
(Yobs) =
P
-
(ss)
=
1 0.8
0.95 1 + 0.0965 ×10
= 0.487
[10049 .59 ×68.732 × 0.8 × 0.487][11]
[0.095 ×2302.428] = 62.971 kg/D = 7.793 m3/D ∴ Effluent flow = 10049.59-7.773 m 3/D
= 10041.797 m 3/D 45
[11]
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Influent BOD5 =
10049.559 × 68.732 1000
= 690.728 kg / D
BOD5 removed= 690.728 ×0.8 = 552.583 kg/D Effluent BOD5 = 138.145 kg/D = 13.76 mg/L
Influent COD =
10049.59 × 383.06 1000
= 3852.068 kg / D
COD removed = 1926.034 kg/D Effluent COD = 1926.034 kg/D = 191.8 mg/L
Influent oil =
10049.59 ×32.618 1000
= 327.798 kg / D
Oil removed = 262.238 kg/D Effluent oil = 65.56 kg/D = 6.529 mg/L
Influent suspended solids =
10049.59 × 7.34 1000
= 73.704 kg / D
Suspended solids = 44.258 kg/D Effluent suspended solids = 29.506 kg/D = 2.938 mg/L
Influent phenol =
10049.59 × 4.918 1000
= 42.189 kg / D
Phenol removal = 40.079 kg/D Effluent phenol = 2.11 kg/D = 0.210 mg/L
46
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Influent sulphides =
10049.59 ×11.143 1000
= 111.983 kg / D
Sulphides removed = 108.623 kg/D Effluent sulphides = 3.36 kg/D
Influent CN- =
10049.59 × 0.571 1000
= 5.738 kg / D
CN- removed = 5.451 kg/D
Influent TKN =
10049.59 × 20.57 1000
= 206.72 kg / D
TKN removed = 206.72×0.5=103.36 kg/D NO 3− in
effluent = 103.36 kg/D
NH3 = in effluent = 103.36 kg/D =
De nitrification step: U DN
− =U DN × (1.09) t −20 (1 − 00) [12]
− U DN
= 0.1 day −1
T= 30°C D.O. = 0.0+mg/L −
UDN = 0.22
Kg NO3
→ N 2
[12]
Kg MLVSS . / D
47
103.36 10041.797
×1000 =10.293 mg / L
Design of a Wastewater Treatment Plant For a Petroleum Refinery
MLVSS in reactor = 2302.428 kg/D −
NO3
→ N = 0.22 × 2302.428
= 506.534 kg/D Since this value is greater than the available No complete change of No 3- N2 occurs Effluent flow = 10041.797 m 3/D BOD5 = 13.76 mg/L COD = 191.8 mg/L Oil = 6.529 mg/L S.S. = 2.938 mg/L Phenol = 0.210 mg/L Sulphides = 0.335mg/L CN-= 0.028 mg/L NH3 = 10.293 mg/L
PRESSURE SAND FILTER:
48
Design of a Wastewater Treatment Plant For a Petroleum Refinery
As per EPA standards, assure S.S. removal = 75%, oil removal = 65%, phenols removal =5%
[6]
Influent flow = 10041.797 m 3/D
Influent suspended solids =
2.949 ×10041.797 1000
= 29.61 kg/D S.S. removed = 22.209 kg/D Effluent S.S. = 7.401 kg/D = 0.737 mg/L
Influent oil =
6.553 ×10041.797 1000
= 65.804 kg / D
Oil removed = 42.773 kg/D Effluent oil = 23.031 kg/D = 2.294 mg/L
Influent phenol:
10041.797 × 0.211 1000
= 2.119kg / D
Phenol removed = 0.05 N ×2.119 = 0.106 kg/D Effluent phenol = 2.013 kg/D = 0.2 mg/L
49
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Effluent flow rate = 10041.797 m 3/D Phenol = 0.2 mg/L S.S. = 0.737 mg/L Oil = 2.294 mg/L 8) ACTIVATED CARBON FILTERS:
As per the EPA standards, BOD removal = 91%, COD removal = 90%, S.S removal =60%, oil removal = 70% phenol removal =90%, NH3 removal=60% Influent flow = 10041.797 m 3/D[6]
Influent BOD5 =
13.76 ×10041.797 1000
= 138.175 kg / D
BOD5 removed = 125.739 kg/D Effluent BOD5 = 12.436 kg/D
=
Influent COD =
12.436 ×1000 10041.797
10041.747 ×191.8 1000
=1.239mg / L
= 1926.016 kg / D
COD removed = 1733.415 kg/D
Effluent COD = 192.601 kg/D =
Influent suspended solids =
192.601 ×1000 10041.797
0.737 ×10041.797 1000
50
=1918mg / L
= 7.401kg / D
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Suspended Solids removed = 4.441 kg/D Effluent suspended solids = 2.960 kg/D 2.960 ×1000
=
Influent oil =
= 0.295 mg / L
10011.797
2.294 ×10011.797
= 23.036 kg / D
1000
Oil removed = 16.125 kg/D
Effluent oil = 6.911 kg/D =
Influent phenol =
6.911 ×1000 10041.797
0.2 ×10041.797 1000
= 0.69 mg / L
= 2.008 kg / D
Phenol removed = 1.808 kg/D Effluent phenol = 0.2 kg/D
=
Influent NH3 =
0.2 ×1000 10041.797
10041.797 ×10.243 1000
= 0.02 mg / L
= 102.858 kg / D
NH3 removed = 61.715 kg/D Effluent NH3 = 41.143 kg/D
=
41.143 ×1000 10041.797
= 4.10 mg / L 51
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Effluent flow rate = 10041.797 m 3/D BOD5 = 1.239 mg/L COD = 19.18 mg/L Suspended solids= 0.295 mg/L Phenol = 0.02 mg/L Oil = 0.69 mg/L NH3 = 4.10 mg/L 9) DUAL MEDIA FILTERS
As per EPA standards, are assume a reduction of 75% in suspended solids, 65% 65% in oil, phenol almost negligible.
[6]
Influent flow rate = 10041.797 m 3/D
Influent suspended solids =
0.295 ×10041.797 1000
Suspended solids removed = 2.223 kg/D Effluent suspended solids = 0.739 kg/D
=
0.739 ×1000 10041.797
= 0.074 mg / L
52
= 2.962 kg / D
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Influent oil =
0.69 ×10041.797 1000
= 6.93 kg / D
Oil removed = 4.505 kg/D Effluent oil = 2.425 kg/D
=
2.425 ×1000 10041.797
= 0.241 mg / L
Final wastewater characteristics:
How rate = 10041.797 m 3/D BOD5 = 1.239 mg/L COD = 19.18 mg/L Suspended solids = 0.074 mg/L Oil = 0.241 mg/L Phenol = 0.02 mg/L CN- = 0.028 mg/L NH3 = 9.10 mg/L Sulphides = 0.335 mg/L OXYGEN REQUIREMENT OF ACTIVATED SLUDGE PROCESS
53
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Theoretically
the
amount
of
oxygen
required
for
the
removal
of
carbonaceous organic & nitrogenous organic content of waste water is determined by: For carbonaceous:-
(O2 ) reqd =
=
-
Qo [ So − S ] f
−1.42[ Pexcess] kg / D [13]
10049.59[68.732 −1376] 6.56 ×1000
1.42 ×[50.38] = 914.971 kg/D O2 required for nitrogenous waste:4.57×Q0 (No-N) kg/D [13] = 4.57×10049.59 ×(20.57-10.293) Mass fractions of O2 in air = 23.2% ∴ Total air required = 5978.267 kg/D
During of air at 30°C = --- PV/RT =
101.35 × 28.84 8.315 ×303
= 5153.679 m 3/D Assuming 8% efficiency of the aeration:
54
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Actual air requirement =
5153.679 0.08
= 64420.988m 3 / D
SLUDGE DIGESTION/ TREATMENT
The sludge produced during the treatment of wastewater from primary settling tank, tilted plate interceptor, DAF & waste activated sludge. I)
Sludge from PST & TPI = F6+F9
Not influent flow rate = (5.25+10.51)m3/d = 15.76m3/D
Influent solids cone =
=
solids in TPI +Solids in PST Not flow rate
( 641.8194 + 321.589) ×10 3 15.76
= 61090.212 g/m 3 ∴ Influent solids = (61090.212 ×15.76)/1000
= 962.782 kg/D 1) Gravity thickness: The combined flow from TPI & PST go into the gravity thicker assuming 8% solids concentration & 90% solids recovery[14] Applying solids balance, the solids in effluent will be 90% of those in the influent. 55
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Effluent solids =
90 100
× 962.782kg / D = 866.504
866.504=F22 ×0.08×1020 F22=10.619 m3/D
F23=5.141m 3/D i.e. water +dissolved solids
Effluent solids cone =
66.504 ×1000 10.619
= 73439.458 g/m 3 2) Centrifuge:
The sludge entering the centrifuge in mixed with DWPE (oily) (DE metering poly electrolyte) Influent solids = 866.504 kg/D
Amount of DWPE required for primary sludge =
2.3 g kg of solids
Amount of DWPE required = 1.99 kg/D Influent flow rate = 10.619 m3/D Assuming 95% solids recovery & a sludge thickening of 35% applying solids balance
56
[14]
Design of a Wastewater Treatment Plant For a Petroleum Refinery
866.504 ×0.95=823.179 kg/D 823.179=2.306 m 3/D F24 = 2.306 m3/D F25=8.313 m3/D
(water + dissolved solids)
F24= effluent waste sludge =
823.179 2.306
×1000
= 356972.68 kg/D
II)
Sludge from DAF: Primary sludge of flow rate, F11=5.255m 3/D
Influent solids cone =
321.595 5.255
×1000 = 61197.907 g / m 3
1) Gravity thickener:
Assuming 8% solids concentration& a total of 90% solids recovery Applying solids balance 321.595 ×0.9=F26×0.08×1020 F26=3.547 m3/D F2 = (water +dissolved solids) = 1.708 m3/D
Solids concentration In F26 =
0.9 × 321.595 ×1000
= 81600.085 g/m 3 57
3.547
[14]
Design of a Wastewater Treatment Plant For a Petroleum Refinery
2) Centrifuge :
Assuming solids concentration to be 35% & solids concentration to be 95%
[14]
Influent flow = 3.547 m3/D Influent dry solids = 289.436 kg/D DWPE (Chemical) = 2.5g/kg of dry solids = 723.589 g/D Applying solids balance, 0.95×289.436=F28 ×0.35×1020 F28 = 0.770m 3/D F29 (water + D.S.)= 2.778 m3/D 3) Waste activated Sludge:
Influent from rate = 7.793 m3/D Influent dry solids = 62.971 kg/D DWPE (WAS) = 3.0g/kg of dry solids = 188.913 g of DWPE /D a) Gravity thickener:
58
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Assuming 2.5% solids concentration& 80% solids scenery (reduced due to free formation)
[14]
Applying solids balance, 0.8×62.971= F30 ×.025×1010 F30 = 1.995 m 3/D F31 (water + D.S.) = 5.798 m3/D
Effluent solids concentration=
0.8 × 62.971 ×1000 1.995
= 25251.529 mg/L b)
Centrifuge: summing solids concentration to be 35% & solids
recovery to be 85%
[14]
Influent solids = 50.377 kg/D Influent flow, F30= 1.995 m 3/D Applying solids balance 0.85×50.377=F31 ×0.35×1010 F31= 0.121 m 3/D F32 (water + D.S.) =1.871 m3/D
Effluent solids concentration = 59
0.85 × 50.377 ×1000 0.121
Design of a Wastewater Treatment Plant For a Petroleum Refinery
= 353888.017 mg/L
ENERGY REQUIREMENT CALCULATIONS
Since, these are no heat trams for equipment involved in the plant design, nor changes in the temperature of wastewater during flow condition, the energy balance essentially involves the power requirements of the plant for its various equipments, which is listed as below. i)
POWER REQUIRES BY THE AERATION TANKS IN THE ASP:
60
Design of a Wastewater Treatment Plant For a Petroleum Refinery
The power required for oxygenation in given by,
β C s ( temp, alt ) − C l T 20 (1.024) − Cs( 20 )
NF = N oα
Where, Nƒ : Rate of oxygen transfer under field conditions, Kg o 2/HP-h No: Rate of oxygen transfer at standard condition of 20 °C & zero D.O. in water, kg O2/HP-h a = oxygen transfer correction factor for wastewater, usually 0.95 for industrial wastewater. β : Salinity correction factor, usually 1.0.
Cs
: saturation concentration of dissolved oxygen on elevation at a
(temp, alt)
given temperature & altitude, mg/L CL: concentration of dissolved oxygen in the reactor cooperating O 2), mg/L T- Operating temperature, °C Cs (20): Saturated concentration of DO in water at 20 °C Now, assuming, β = 1.0, χ = 0.95, 4=2.0 mg/L & assuming plant operating at temperature of 30°C & at an altitude of 200300m above sea level, ∴ F = 0.94
[15]
61
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Oxygen saturation concentration for water at field temperature is L SW= 8.24 g/m3 at 25°C β Cs (temp, alt) = 1×0.94×8.24
= 7.756 mg/L Now, assuming the oxygenation capacity of aerators is 1.5 kg of O 2/HP-hr at standard conditions, connecting this to field conditions:
β C s ( temp , alt ) −C L Nƒ = No Cs
T −20. χ (1.024)
1 ×7.756 − 2 (1.024)5 ×0.95 9.08
= 1.5 (kg/HP-h)
= 1.02 kg/HP-h i.e. the aeration can supply 1.50kg of oxygen/HP-hr at standard condition & 1.02 kg of oxygen /HP-hr at field conditions ∴ the total power requirement is,
Pƒ =
= 1005.127 HP 1.02 (kg o2 / HP − h) ≅ 1006 HP
1025.23 (kg o2 / h)
Assuming 80% efficiency of the aeration, Pƒ = 1256.409 HP ≅ 1260 HP 62
Design of a Wastewater Treatment Plant For a Petroleum Refinery
DESIGN CALCULATIONS 1) GRIT CHAMBERS
Assuming a rectangular flow type grit chamber as a min of 2 channels is required for the continuous operation of the chamber, n=2. Average flow rate = 10080 m 3/D
63
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Pleasing factor = 2.5 ∴ Peak flow rate = 10080 ×2.5 = 25200 m 3/D
∴ Peak flow rate for each channel =
25200 2
=12600 m 3 / D
= 0.146 m3/s Cross sectional area Q1= AxVx Q1 = mass flow rate in one channel. Vx = flow through velocity = 0.2m/s as per design criteria
Ax=
0.146 0.2
= 0.73 m 2
Length of the channel
Assuming residence time = 605 as per design criteria
[16]
L= Vx ×t = 0.2×60 = 12m Total length = length + 10% of length for I/L & O/L provisions = 12+1.2=13.2m ---- 14m Breadth of channel = 1.5 m (assumed)
64
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Depth, D= Ax/B =
0.73 1.5
= 0.487 ≅ 0.5m
Total depth = net depth + free board+ depth for grit collection
= 0.5+0.3+0.2 (assumed)
= 1.0 m
Volume/capacity of each channel:
1
V = 12×1×15
3
= 8.76 m
This value is too low & the design can be made more economic
x
∴ assume V = 0.1 m/S
Cross sectional area = Ax=
Q1 vh
=
0.146 0.1
= 1.46m2
65
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Length of the channel = 0.1×60= 6m Total length = 0.6+6=6.6 =7m
Depth of the liquid = Ax/B =
1.46 1 .5
≅1.0
Total depth = 1.0+0.3+0.2 1.5 m Volume of the tank = 7 ×1.5×1.5=15.75 m3 Check for volume of tank = v= Q ×t=0.146 ×60 = 8.76m3 This is more economic than the previous value Q max
Check for solids loading rate = SLR =
AS
12600
=
7 ×1.5
= 1200 m 3 / m2 − D
Check for settling velocity:
Assuming 0.2 mm particle size
VS =
=
4( Pp − Pw) d 3cd Pw
× g
4( 2650 − 995.7) × 0.2 ×10
−3
3 × C D ×995.7
66
×9.81
Design of a Wastewater Treatment Plant For a Petroleum Refinery
= 0.066/
C D
Re = d Vs Pw/µ Assume Vs = 0.02 m/s
Re =
0.2 ×10
−3
× 0.02 × 995.7 = 0.497 ≅ 5 0.8 ×10−3
∴ it lies in the transition region
CD = 24/Re+ 3 /
Re
+
0.35 = 6.48
∴Vs = 0.026
The assumed value is nearer to the range of 0.016-0.027 & hence our assumption in correct.
Vs = SLR=
1200 3600 × 24
= 0.014 m / s
The value is slightly less but acceptable ∴ The net dimensions are:
No. of channels =2 Length of channel = 7m Depth of channel = 1.5 m Width of channel = 1.5 m
67
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Width of chamber = 1.5+1.5+0.2+0.2+0.2 = 3.6 m Detention time = 60 seconds {0.2m –side wall & centre partition thickeners} Design of proportional flow control weir:
It is a simple plate with a cut through it to provide the required opening for flow control normally fixed at the ends of the grit chamber. No. of channels l=2 Passing factor = 2.5
Total depth of flow, d =
1.46 1.5
peak flow rate = 0.146 m3/S
= 1 + 0.2 = 1.2m
The values of coordinates of the points (x, y) on the parabolic section are determined from the design crest.
68
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Hmax = [1.2-(0.3+0.2)]
A & b are weir constants, a= 0.3m Q=0.45 m
= 0.7m Flow for each channel = 12600 m 3/D = 252m3/hr
In order to determine the points of crest for the proportional flow weir find values of n (their width at liquid surface) & y (liquid depth), using: Q= 15586 K x H
K= n y 15586= constant H= depth of liquid
[17]
An h = Hmax = 0.7m the depth of waste water is maximum through the weir in the grit chamber above the design crest. 525 = 15586 ×K ×0.7 K= 0.0481
N=
0 .0481 y
Tabulating these values, Y x
0.1
0.2
0.3
0.15 0.11 0.088
0.4
0.5
0.6
0.7
0.076
0.068
0.062
0.037
69
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Therefore, Width of design crest = 0.7+0.1=0.8m Width of weir at Hmax = 0.06m Man liquid depth = 0.7n Total width of weir plate = 1.5m Total depth of weir plate = 1.2m
2) TITLED PLATE INTERCEPTOR:
Parameter required for the design -
Man flow rate = 2.5×10079.697 m 3/D = 25199.242 m 3/D 70
Design of a Wastewater Treatment Plant For a Petroleum Refinery
-
Wastewater temperature = 30°C
-
Wastewater specific gravity- Sw=0.996
-
Wastewater viscosity= µ= 0.8×10-2 g/cms
-
Fraction of oil specific gravity = So=0.960
-
Globule size, usually, 0.0069 cm
[18]
Oil globule rise velocity:
As per the conditions, seminar flow prevails in a TPI & hence the stories low for rice velocity is used. 2
V t
= g
d ( Sw − S 0 ) 18u
Vt = rise velocity cm/S G = 981 cm/S 2, acceleration due to gravity Sw = specific gravity of wastewater So = specific gravity of oil µ = viscosity of wastewater, g/cm-S
D= globule size, cm
vt
=
0.00196(0.0996 − 0.960) 0.8 ×10
−2
71
Design of a Wastewater Treatment Plant For a Petroleum Refinery
= 0.0883 cm/sec As per the design criteria Vt ≤ 0.1 cm/sec & the hence the value is acceptable [18]
Vh = 15×0.0883 = 1.32 cm/sec Minimum vertical cross section area :
Ac =
Qm
×100 Vh
Qm = man flow rate, m3/S Vh =horizontal velocity = 1.32 cm/S 100= factor to convert m-cm.
25199.242 ×100 Ac= 24.3600 = 22.09 ≅ 23m 2 1.32
Channel & width & breadth:
As per the design criteria, B= 1.8-6 m & no. of channels = 2
Depth, d=
23 2 ×6
=1.91 ≅ 2m
Acceptable in the design range of 1-2.4m 72
Design of a Wastewater Treatment Plant For a Petroleum Refinery
d/B = 0.33 acceptable in the design range of 3-5 Separator length:-
V
h L= Ft V d t
[18]
Ft = factor for turbulences. un vt
= 14.95
Through the graph b/w Ft & (Vh/Vt) we compute the value of F t to be= 1.63 [18] ∴length, L = 1.63×(14.95) ×2
= 48.737 m Providing additional 10% for I/L & O/L provisions Total length = 54m Horizontal Surface area:
AH =
25199.242 ×100 24 ×3600
F t
vt
=
25199.2 ×100 24 ×3600
1.63
0.0883
73
Design of a Wastewater Treatment Plant For a Petroleum Refinery
= 545 m2
Check for surface loading rate =
=
Peak flow ( m 3 / D) horizontal area (m 2 )
25199.242 545
= 46.24m3/m2-D = 0.0535cm/sec It is well within the acceptable range of 0.02-0.4 cm/sec. Plates:
As per the design criteria Perpendicular distances b/w the plates =2 cm Angle between the plates = 45 ° [18] direction of waste flow = cross flow, down flow Vt=0.0883 cm/sec Residence time per plate = 22.65 ≅ 23 sec. Overall residence time = V/Q
=
24 ×50 ×23 25200
1.1h
74
Design of a Wastewater Treatment Plant For a Petroleum Refinery
=3960 sec
Therefore no. of plates =
3960 23
=172.17 ≅ 173 plates.
Bottom hopper design
Mass of sludge produced = 321.589 kg/D = 13.399 ≅14 kg/r
Volume of sludge produced =
14 0.06 ×1020
= 0.229 m3/hr Assuming that sludge in pumped out every 4 hours Capacity of hopper = 0.915 m3 = 1m3 Let the bottom be trapezoidal in shape & let’s assume L=28,
B=1m
Volume of hopper =
=
& D=0.5m 1 3
1 3
× D (l 2 + LB + B 2 )
×0.5(4 + 2 +1)
= 1.2m3 Since, 1.2 m3>1.0m3, the values are acceptable 75
Design of a Wastewater Treatment Plant For a Petroleum Refinery
The net dimensions are:
Length of channel = 54 m Breadth of channel = 6m Depth of channel = 2m No. of plates = 173 Perpendicular distance between the plates = 2cm Hopper length = 2.0 m Hopper breadth = 1.0m Hopper depth = 0.5m
3) PRIMARY SETTLING TANK:
Flow rate of water = 10069.571 m3/D Peaking factor = 2.5 Assuming a circular tank Assume surface loading rate = 35m3/m2-D
76
[19]
Design of a Wastewater Treatment Plant For a Petroleum Refinery
crolumetric flow rate Surface area =
SLR
2
10069.571 =
35
=
287.70m ≅
Diameter of tank =
4 × AS n
4 × 287
=
n
288m
2
=19.14m ≅ 20,
The total volume of tank, V= Qavg X t t= 2 hours of detention time as per design criteria
[19]
V= 839.13 ≅840 m3 ∴ We provide a tank of volume 840 m 3
Side water depth = D1 v/As =
Check for weir loading rate =
=
839 288
Acceptable in the range 3-5m
= 2m
flow( m 3 / D ) lenght of weir
10069.571 pi ×20
= 160.26 m 3/m2-D Acceptable in the range 25-600m3/m2 D Check for SLR at peak flow:
77
[19]
Design of a Wastewater Treatment Plant For a Petroleum Refinery
=
peak flow rate S . A.
=
2.5 ×10069.571 288
= 87.17m 3 / m 2 − D
Acceptable in the range of 80-120 m3/m2-D
[19]
Since both the checks are acceptable in the recommended range of design criteria, the compiled volume diameter of tank & depth of liquid an acceptable. Amount of sludge produced = 643.194 kg/D = 26.8 kg/hr.
Volume of sludge produced =
26.8 0.06 ×1020
= 0.438 m3/hr Assuming sludge is pumped every 4 hours, ∴ The capacity = 4×0.438 m3 = 1.8 m3
The bottom hopper is normally trapezoidal in shape & so the length, breadth & depth are assumed to be L= 3m, B=1m, D=0.5m 1
V= × D( L2 + LB + B 2 ) 3
V=
1 3
×0.5(9 +1 +3)
= 2.2 m3
78
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Since 2.2 m3 is greater than 1.8 m3, our design is acceptable Overall depth liquid = liquid depth = +fee board +depth for tank Bottom slope + hopper bottom depth. Depth for tank bottom shape = (d/2 –B/2)×0.1 = (10-0.5) ×0.1 = 0.95m Total depth = 3+0.3+0.95+0.5 = 4.95m ≅5m Diameter of central food pipe Assuming flow through velocity = 0.3m/min = 0.005m/sec
As=
flow velocity
=
10069.571 24 ×3600 ×0.005
Diameter of food pipe =
4 × As n
= 0.0233m 2
= 0.17224m
= 173 mm. Diameters of sludge removal pipe = 200 mm as per the design criteria
79
[19]
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Diameter of pipe =
4 × As n
= 0.17224m
= 173 mm Diameter of sludge removal pipe = 200 mm as per the design criteria.
80
Design of a Wastewater Treatment Plant For a Petroleum Refinery
4) DISSOLVED AIR FLOATATION UNIT
Flow rate, average = 10058.530 m 3/D Recycle rate = 5.12.397m 3/D The crucial parameter in the design of DAF is the Air –Solid ratio. A S
=
1.3 ×Sa ' ( f × P −1) ×Qr [ 20 ] Si ×Q
A = volume of air in ml S= mass of solids in mg 1.3 = weight of 1ml of air in mg Sa’ = solubility of air in mg/L (temperature dependent) F= fraction of air dissolved at pressure P in atm P = operating pressure in atm
=
P +101.35 101.35
, P − Gaugepressure in kPa
Si = influent suspended solids mg/L Qr = pressurized recycle flow m3/D Q = mixed liquor in m3/D
81
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Assuming A/S = 0.04 ml/mg
[20]
T= 30°C Q= 10058.330 m 3/D Qr = 2512.397 m 3/D F= 0.5 [20] Sa1 = 15.7/L[20] With the above equation are can calculate the pressure acquired to pressurize the recycle steam.
0.04 =
1.3 ×15.7(0.5 × P −1) × 2512.397 10058.33 × 63.946
0.501 = 0.5 P-1 0.5 P = 1.502 P= 3.004
∴3.004=
P +101.35 101.35
P = 203.105 kPa Thus a gauge pressure of 203.105 kPa in required above the atmospheric pressure to keep the recycle stream pressurized
82
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Surface area of the unit = sludgeflowrate, m 3
SLR, m / m
2
3
− min
As per the design criteria, SLR = 0.1m3/m2-min
10058.33 + 2512.397 = 87.296m 2 ≅ 88m 2 0.1× 60 × 24
S.A. =
Now to compute the dimensions of the tank assume L= 10 m
LB=9m
∴ Area = 90m
Since 90m2>88m2, our design is acceptable. Volume of the unit = Qtot X t T= 30min
V=
10058.33 + 2512.397 24 ×60 ×30
= 290.98 ≅ 291 m3
Depth =
Volume S . A.
= 3.31m
Total depth = 3.31+0.3m
83
Design of a Wastewater Treatment Plant For a Petroleum Refinery
= 3.61 ≅ 3.7 m Check for solids loading rate
=
=
inf luent oil , kg / D area, m 2
473.94 + 3896.563 90
= 48.561 kg/m 2-D [20] This is acceptable in the range of 25-75 kg/m2-D & hence Our Design Is Acceptable
5) TRICKLING FILTERS/BIO-TOWER
Influent flow = 10049.59m 10049.59m 3/D Recycle ratio = 1 Recycle flow = 10049.59m 3/D Net influent flow = 2×10049.59 m 3/D = 20099.18m 3/D
Influent BOD =
10049.59 × 245.473 1000
+
10049.59 × 245.473 ×1.4 1000
= 3453.664 kg/D = 171.831 mg/L 84
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Effluent BOD = 1381.466 kg/D = 68.732 mg/L By Velz equation, C D C a
= 10 −KD
[ 20 ]
CD = BOD in mg/L at a depth D Ca = influent BOD in mg/L D= depth, m K= 0.15 = treatability constant in m-1[21]
4)
68.732 171.831
=10 −KD
Taking log10 on both sides,
68.732 = −0.15 × D 171.831
Log
-
0.3979= -0.15 ×D D= 2.65 ≅ 2.7m
Applying 0.5m of free board Total depth = 3.2 m = Surface Area. The surface area in calculated using the Eckenfelder Eckenfelder eq given as:85
Design of a Wastewater Treatment Plant For a Petroleum Refinery n
Q = A
K × D
[ 21]
RSe + Sa + Se ( 1 R )
log
Where, Q= net influent flow rate in m 3/D A= area in m2, K= treatability constant at 30°C for a depth of 8.9 ft. Se = effluent BOD in, mg/L Sa = influent BOD in mg/L R = recycle ratio D = depth in m Q = 2×10049.59 m 3/D
R=1
D = 2.7m
n=0.5 {for vertical trickling filter}
Sc = 68.732 mg/L Sa = 171.831 mg/L
R Se + Sa 68.732 + 171.831 = log = 0.56 2 × 68.732 Se(1 + R )
∴Log
K 20/D20 20/D20= treatability constant at 20 °C at a depth of 20ft. As per Metcalf & Eddy, wastewater Engineering,
86
Design of a Wastewater Treatment Plant For a Petroleum Refinery
K 20/D20 =
K T / D 20
0.07 ( gal / min) 0.5 ft
K 20 / D 20 × (1.035 ) T
−
=
K 30 / D 20
20
= 0.07 ×(1.035)10 [21]
= 0.1 0.5
K 30 / D 5
20 = K 30 / D 20 × 5
0.1 ×( 4) 0.5
=
( gal / m) 0.5 0.2 ft
0.5
1 0.103 0.2 × 0.3048
3
(m / D)
0.5
m
3
=1.54
∴substituting all the values,
(Q / A)
=
n
1.54 × 2.7 0.56
= 7.425
n = 0.5
As =
10049.59 × 2 (7.425)
2
= 364.573 ≅ 365m 2
For a circular tank,
87
(m / D) m
0.5
Design of a Wastewater Treatment Plant For a Petroleum Refinery
A s
d=
×4 n
= 21.55 ≅ 22m
5) Volume of the tank = 1168 m3
6) Check for by hydraulic loading =
Q V
=
2 ×10049.59 365
= 55.066 (m3/D)/(m2) It is acceptable in the recommended range of 11.79-70.4 m 3/m2-D [21] Check for organic loading : BOD Vol
=
, Kg / m3 − D
3453.664 365 × 3.2
= 2.9hg / m 3 − D
It is acceptable in the recommended range of 0.35-2.9 kg/m 3-D Since our checks are acceptable our design is acceptable
Retention time :- t= v / Q =
1168 × 24 2 ×10049.59
= 1.5hours
Rotational speed of diminutions:-
N=
1.6QT A × D. R.
[ 21]
A – no. of arms =2
88
Design of a Wastewater Treatment Plant For a Petroleum Refinery gPm
QT = total hydraulic rate =
ft 2
D.R. per in /pass of arm.
Total BOD applied =
3453.664 1168
= 2.957
kg m
3
− D
2.957 lbBOD
Thus required dosing rate = 0.12× 0.0160 10 3 ft 3 =2.2.178 in /pass of arm.
Qt = 55.066
m m
2
1.6 × 0.93671
∴ n = 2 × 22.178
3
− D
× 0.183
gal / min 3
m / D
2
×
0.3048 m 2
ft
0.0338 rev / min
=
=
1revoulutio n every 30 min
6) ACTIVATED SLUDGE PROCESS:
Influent flow rate = 10049.89m3/D Influent BOD = 68.732 mg/L F/M = 0.3 Qc = 10 days Kd = 0.095 day-1 Y = 0.95 Yobs = 0.487 89
2
= 0.9361
gpm 2
ft
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Qr/Q = 0.25, Qr = 2512.398 m3/D X = 2000mg/L Amount of sludge to be wasted = 7.793m 3/D Effluent flow = 10041.497 m 3/D Effluent BOD = 13.76 mg/L. Volume of reactor:
V 2 =
=
Qc × (Q + Q2 ) × Y × ( BOD removed ) [ 22] X × (1 + Kd Θc)
10 ×(10049.59 +1512.398) ×0.95 ×(68.732 −13.76) 2000 ×(1 + 0.095 ×10)
= 1682.127m 3 = 16.83m 3 Assuming depth = 6m for differed air aeration system, & 0.5m of free board, Total depth = 6.5m
Assume 6 tanks, ∴ volume of each tank =
Surface area of each tank =
281 6.5
1683 6
= 280.5 ≅ 281m 3
= 43.231m 2 ≅ 44m 2
Now, as per design criteria, L:B=5:1 7) L×B = 44m2
90
Design of a Wastewater Treatment Plant For a Petroleum Refinery
5B2=44m2 B=3m 8) L=15m
Residence time = Q =
F/M ratio =
S o Q × X
=
1683 × 24 10049.59 + 2512.398
68.732 × 24 2000 × 3.22
= 3.22h
= 0.256 ≅ 0.3
It is close to our assumed value & hence our design is correct. 68.732 ×10049.59
Volume loading:
1000 1683
= 410.441
kg m
3
− d
Since, this is acceptable in the recommended range of
300 − 600
kg m
3
− d
,
our design in correct
[22]
Design of secondary settling tank:
Influent flow rate = 10049.59 m3/D The SST is designed on the basis of only Q & not Qr, as it passes out through the SST back to the aeration tank. Assuming over flow loading rate = 20 m3/m2-d Flow 10049.59
surface area = As
=
OFR =
[23]
= 502.48m 2 ≅ 503m 2
20
91
Design of a Wastewater Treatment Plant For a Petroleum Refinery
9) Diameter of the tank =
4 × AS n
= 26m
Volume of tank = Assure side mater depth = 3.7m For a free board of 0.3m Total depth = 4m. Total volume = 503×4=2012 m3 Applying checks: i)
Check for weir loading rate at peak flow rate :
WLR =
peak flow surface
=
2.5 ×10049.59 n × 26
= 307.585m 3 / m − D
In a acceptable in the recommended range of 250-375m3/m-D [23] ii)
Check for surface loading rate at peak flow rate:
SLR =
peak flow S . A.
=
2.5 ×10049.59 503
= 49.95m 3 / m2 − D
It is acceptable in the range 40-64m3/m2-D[23] 10)
Solids loading rate at peak flow:
SL=
peak flow S . A.
=
2000 ×10
−3
× 2.5 ×10049.59 503
92
Design of a Wastewater Treatment Plant For a Petroleum Refinery
= 99.89kg/m2-D It is acceptable in the range <244 kg/D-m 2 11) volume flow Rate
[23]
Q = Retention time
=
2012 10049.59
=
4.8 hours.
It is acceptable in the recommended range. Since, all our checks qualify the recommended ranges our design is acceptable. Design Summary
Aeration tank: No. of tanks =6 Volume of each tanks = 28/m3 Breadth of each channel = 3m Depth of each channel =
6.5m
Length of each channel = 15m. Retention time = 3.22h. Secondary settling tank: No of tanks =1
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
Volume of tank = 2012 m3 Diameter of tank = 26m Side water depth =4m Retention time = 4.8 h.
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
PLANT UTILITIES
The utility system consists of Air, drinking water, electricity for various purposes: Air INSTRUMENT PNEUMATIC CONTROL SYSTEM
Instrument air is required in industry for pneumatic control of values & various other devices. In industries, then are PT & P controllers. The function of both the controller is to connect the signal from one form to the other. Os other operation sends the signal in the form of electricity which is concerted to pneumatic signal & the control is done pneumatically. SERVICE AIR SYSTEM
The aeration process requires supply of air. COMPRESSED AIR
Compressed air will be needed for DAF unit & for pneumatic controllers DRINKING WATER
In must be made available for the personals there at the plant site at various locations. FIRE FIGHTING WATER LINES
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
In case of fire at the oily sludge jump, firefighting equipment must be left handy. ELECTRICITY:
Electricity is majorly used to run the aerators & the pumps. About 80% of the electricity is used up here & the rest for other service purposes.
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
INSTRUMENTATION AND PROCESS CONTROL
Instruments are provided to maintain the process variables during plant operation. They may also be part of an automatic computer data logging system. INSTRUMENTATION AND CONTROL OBJECTIVE
The primary objective of the designer when specifying instrumentation and control are: 1) Safe plant operation a) To keep the process variables within known safe operating limits. b) To detect dangerous situations and to provide alarms. c) To provide inter lochs & alarms to prevent dangerous operating procedures. 2) Production Rates: To achieve the desired product/effluent product 3) To maintain effluent composition within accepted quality. 4) Lost. THE WASTEWATER PERSPECTIVE:
The ultimate goal of the operation of wastewater treatment plant is to satisfy the effluent criteria. They can be expressed in terms of organic material content, total nitrogen & suspended solids. However, given the many steps 97
Design of a Wastewater Treatment Plant For a Petroleum Refinery
of the operations from the influent to the effluent it is most often almost impossible to base any control action on measurements of the effluent quality. A no. of intermediate goals have to be formulated in order to synthesize same control action. Examples of such are:•
Growth of the right biomass population.
•
Maintain adequate mixing
•
Keep the level of dissolved oxygen at the light smel
•
Maintain are adequate air flow rate while minimizing the pressure.
•
Keep the sludge blanket level in the settler between given limits.
•
Avoid over load of the clarifier. The two major energy consumers in wastewater treatment are cost of pumping & aeration. Aeration can be controlled by the connect amount of oxygen in the tanks.
The major control instrument used in WWTP are enlisted bleow:
Pressure control & indicator → PIC
Dissolved oxygen indicator/sensor
Flow indicator & control → FIC 98
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Liquid level control → LLC
Sludge level control →LLC
Biomass securer/indicator.
PRESSURE CONTROL :
Pressure controls are required in DAF unit where pressuried air at required pressure as per the design calculations. Pressure controls are required in aerations to control the amount of oxygen entering the aeration tank of the activated sludge process & the biotower. DISSOLVED OXYGEN INDICATOR/SENSOR:
The D.O. content of wastewater is errential for removal of the biodegradable content of the water. A sensor to estimate the amount D.O. would control the amount of Air of O 2 entering Flow indicator: Flow indicator & control are used to estimate & control the
flow of wastewater to the respective tanks as the flow rate of water is an essential factor in the efficiency of the equipments especially the secondary waste water treatment processes where the shode loads can induce inefficiency in the viological activity. Liquid level control: These are essential in order to maintain proper level
of liquids in the I/L & O/L weirs. The height of wastewater in an equipment is critical to its processing efficiency. 99
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Sludge level controller: The is inertial in secondary setting tanks where an
optimum level of sludge blanket is essential for proper removal of MLSS from the effluent wastewater. Biomass terror: This is critical in the Activated sludge process where a
biomass terror is installed inside the aeration tanks & recycle line where active biomass cone. (MLCSS) is critically important.
PLANT LOCATION
One of the most important parameters in the final framing of the plant location are enlisted below. If care in not taken it cripes of out average of process of careful engineering, research & development works. The plant should be located in such a location that yields maximum profit. In selection of location of plant two major factors must be considered. -
Primary factors
-
Secondary factors
PRIMARY FACTORS
SECONDARY TALTORS
-RAW MATERIAL
- LABOR
- ENERGY AVAILABILITY
- TRANSPORTATION
-WATER
- SITE CHARACTERISTICS
-CLIMATE
- WASTE DISPOSAL
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
- FLOOD AND OTHER PROTECTION OTHER IMPORTANT CONSIDERATIONS:
Equipment availability: the availability of equipment plays an important role in process selection because of (1) Need to provide redundant systems when there are beng delivery times for spare parts & replacement units. (2) When equipment delivery is critical to the construction schedule. Most of the equipments in wastewater treatment plants are custom manufactured except for pump & motors 5) Personal Requirement: the selection of a treatment process should consider not only the amount of operating & maintenance personnel needed but also the skills required. The simpler & less complex the process, the few highly skilled people is required eq: Aerated lagoons is less complex than Activated sludge process. Proper instrumentation & controls can save labor & even allow some of the small plants to operate unattended. However, this may require highly shelled instrumentation technicians.
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
PLANT LAYOUT
Layout may have several objectives such as increased output, reduced rish to health of employs, improved earning hour, lever product delays, searing in floor space, reduced material washing, greater cultivation of main power services & machinery. Reduce inventory in process, shorter manufacturing time, easier adjustment to changing condition etc. the major objective is to arrange the physical facilities in such a way that we have overall integration of all these factors affecting the plant layout. -
Overall integration of all factors affecting plant layout
-
All space effectively utilized
-
Flexible arrangement
-
Material meaning a minimum distance
-
Safety of workers
-
Protection against fires, fumes.
The plant layout in affected by:-
Manufacturing process
- Storage of materials
-
Lightning & & ventilation
- Future expression
-
Butting & construction material
- Movement of auxiliary equipment
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
-
Plant machinery
- Piping network
-
Materials used
-
Location & site of plants
-
Material handling
PRINCIPLES OF PLANT LAYOUT
1) Storage layout:
Storage
facility
of
raw
materials
&
located
wastewater be located in isolated areas or in adjoining areas. Arranging storage of materials to as to facilitate simple handling is also a paint to be considered in the design. 2) Equipment layout: Ample space should
be assigned for
each
equipment. Accessibility is an important factor for maintenance. All equipment should be arranged in order with minimum pumping & pipelines. 3) Plant expansion: Plant expansion must be left in mind for future development of plant & to increases the capacity of the plant. 4) Floor space: The floor space major may not be a major factor in the design. Space to permit working on parts of equipment. That frequent servicing & safety consideration.
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
5) Building: It is fundamental in chemical engineering industries that the buildings should be built around the process instead of process being made to fill the buildings/commotional design. 6) Rail, Roads & Highways: The plan site should be near to rail, roads & highways for easy transportation.
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
ENVIRONMENTAL CONSIDERATIONS
The protocol for evaluation of environmental imparts is set for the in the National Environmental Policy Act (NEPA)of 1969. Environmental evaluations should focus on social, technical, organization, & ecological, economic, political, legal & institutional criteria. The NEPA regulations ensure that he probable environmental effects are identified, that a reasonable no. of alternative action & their environmental import ate considered, that the information in available for public understanding searching & that all government & Perivale agencies take part in the decision making process .The social responsibility of the concerned refineries to produce wastewater as per the pertaining regulations set for the by the local & national authorities & ensure that the mask leaning the plant is safe to all living species, whether aquatic or ground.
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
START-UP AND OPERATION
Some of the principal concerns in wastewater engineering are related to the startup, operation & maintenance of treatment plants. The challenges faced by the design engineer. & the plant operators include the following: -
Providing, operating & maintaining a treatment plant that consistently meets its performance requirements;
-
Managing
operation
&
maintenance
rest
within
the
required
performance levels. -
Maintaining equipment to ensure proper operation & service
-
Training operation personal.
One of the principal tools used for plant startup, operation & maintenance is the operations & maintenance manual (0&M). the purpose of the O&M manual is to provide treatment system personnel with proper understanding of recommended operating techniques & procedures & the references necessary to operate & maintain the facilities.
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
COST ESTIMATION
The plant design must obviously be capable of operating conditions, which will yield profit. Since net profit is total income minus all expresses, it is essential that chemical engineer be aware of many different types of costs involved. For a processing plant like wastewater treatment which is more of a social responsibility than a profit making process. However, if all the mater processed is recycled after processing each to the refinery it can be used as an impure cutter for the purchasing of new water from the local municipality or water bodies which is sold at 40/m3 in the northern region of India. Also, the costs of all the equipments are rough approximates as per the Environment Protection Agency, United States of America for Advanced wastewater treatment with nitrification. The plan includes construction costs & step III non construction costs which include fields like Administration legal, land development, indirect costs.
ESTIMATION OF CAPITAL INVESTMENT:
Total cost capital investment (TCI) = fixed capital investment (FCI)=washing Capital investment (WCI)
[24]
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
1) FIXED CAPITAL INVESTMENT Process equipment cost (PEC) S.No
[25]
Equipment
Estimated
1
Grit chamber
(Rs) 150000/-
2
(1.43×104×Q0.76 ) Titled plate interpretation
1435000/-
3
(2.11×104×Q0.45) Primary settling yank
1415000/-
4
(1.43×104×Q0.46) BIO-Tower
1636000/-
5
(1.66×104×Q0.46) Activated sludge Process with diffused 9226000/aeration system & SST
6
(1.19×105×Q0.45) Pressure Sand filter
883800/-
7
(1.14×105×Q0.46) Activated carbon filter
8925000/-
8
(1.15×105×Q0.46 Dual Media filter
8683000/-
9
(1.16×105×Q0.45) Thickener (Gravity)
180000/-
10
(1.91×104×Q0.7) Thickener (centrifuge)
1976000/-
108
cost
Design of a Wastewater Treatment Plant For a Petroleum Refinery
11
(1.31×104×Q0.63) Pumps
909100 ×8
12
(1.94×104×Q0.73) Dosing tanks
7266001908000 ×3
(1.17×104×Q0.48) Total
=2724000 4.7 Crores (PEC)
(Q is in MGD)
TOTAL DIRECT COSTS
[24]
S.No 1 2 3 4 5 6 7 8 9
Item Purchased equipment costs Purchased equipment installation Instrumentation & control Piping (installed) Electrical (installed) Yard improvement Utilities Storage facility Control room/lab building
%PEC
Costs in Crores
100 45 20 70 12 10 25 18 60
(2) 4.7 2.11 0.94 3.29 0.56 0.47 1.18 0.85 2.82
(including secrecies of sanitation & 10 11 12
rest rooms) Site work & excavation Pilings & special foundation HVAC Total construction costs
Step III non construction cots
S.No 1 2
8 2.4 2.2
0.38 0.11 0.10 217.51
% of TCC
Costs in Crores
1.17 4.72
(Rs.) 0.21 0.77
[15]
Item Admin /Legal Land, structure 109
Design of a Wastewater Treatment Plant For a Petroleum Refinery
3 4 5
Land development Indirect costs (engg. & supervision) Miscellaneous Total
Step II non construction cost
0.96 0.37 2.97
0.17 0.06 0.52 1.73
[25]
2.33%of TCC
Rs. 0.40 crore
Step I non construction costs [25]
5.55%of TCC Total
Rs. 0.96 crore Rs. 1.36 crore
Total direct & indirect cost (TDIC) – total direct costs Step III, Step II & Step I non construction costs = Rs. 20.6 crore Contingency = 25% of TDIC = Rs. 5.15 crore FCI = TDIC + contingency Fixed capital investment = 20.6+5015 = Rs. 25.75 crore Total capital investment= working capital investment +fined capital investment
= 25.75+5.15 crore = Rs. 30.9 crore
PROCESSING COST: RAW MATERIALS 110
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Chemical Additives
[15]
Cost = 1.35×104×Q0.75= Rs. 0.141 crore Q→ MGD
(Alum, H2So4, Urea, Poly electrolytes)
OPERATING LABOUR COSTS : Designation
Manager Engineer Operator Worker Watchman Office staff Peon Lab staff
Salary/mont h Rs.
22500 18000 9000 4500 3000 6000 2250 5250 Total
Salary/Year Rs.
No.
Rs. N crores
270000 216000 108000 54000 36000 72000 27000 63000
1 4 10 20 4 6 3 5
0.027 0.086 0.11 0.11 0.014 0.043 0.008 0.032 Rs. 0.43 crores
Power & utilities = 15% FCI = Rs. 3.86 crores Maintenance & Repair = 5% of FCI = Rs. 1.28 crores Operating supplies = 10% of maintenance cost = Rs. 0.043 crore Total direct processing cost = 0.141+0.43+3.86+1.28+0.13+0.043
= 5.884 crore
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
Fined charges
Deprication = 20% of FCI = Rs. 5.15 crore Local Taxes = 3% of FCI = Rs. 0.77 crore Insurance = 1% of FCI = Rs. 0.26 crore Total fined charges =
Rs. 6.18 crore
Plant overhead costs = 1.5× operating labor cost = 1.5×0.43 = Rs. 0.645 crore Total processing cost = direct processing cost +fined charges +plant overhead costs = Rs. 12.709 crore General expresses
1) Financing Interest = 10% of FIC = Rs. 0.26 crore 2) Administration cost = 10% of labor cost = Rs. 0.043 crores Total processing cost = of general expresses +processing cost = 12.709+0.26+0.043 = Rs. 13.012 crore 112
Design of a Wastewater Treatment Plant For a Petroleum Refinery
Cost of water saved:
Price of water of industries = Rs. 40/m3 Amount of water processed = 10080m3/D Price of water saved per year = 147160000/= 147200000/Gross profit per year = Rs. 147200000-13.012 ×107 crores = Rs. 17080000/-
Payback period =
Rate of Return =
FCI depriciation + net profit
Gross profit TIC
=
25.75 5.15 +1.71
= 3.75 years
7
×100 =
1.71×10
30.9 ×107
×100 = 5.51%
BREAK EVEN POINT
Considering 3 year for construction & commissioning of the plant, Payback period = 3 years +3years 9 moths = 6 years 9 months
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
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Indi India, a, 2006 2006,,
waste astewa wate terr
&
trea treatm tmen entt
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
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Design of a Wastewater Treatment Plant For a Petroleum Refinery
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Indi India, a,
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