Balance of Plant Operation (Power Plant)

8/13/2019 Balance of Plant Operation (Power Plant)

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Jawad Aslam | December 31, 2013

TRAINING REPORT BALANCE OF PLANT (BOP)

Submitted to

Mr. Farhan Javed (Team Leader BOP)


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I

ACKNOWLEDGEMENT

I thank Almighty Allah for giving me the strength to complete this Report and for showering His blessings upon me throughout my training period at the BOP Area.

I would like to thank my Parents for their eternal love and support and for having faith in methroughout my life. I would like to express my deepest appreciation to my seniors and My TeamLeader Mr. Farhan Javed who continually and convincingly guided me throughout the process.Without their guidance and help this report would not have been possible.


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Table of Contents

ACKNOWLEDGEMENT ................................................................................................................ i

Introduction ..................................................................................................................................... 1

Pre-treatment of Intake Water ......................................................................................................... 2

Raw Water Intake ........................................................................................................................ 2

Settling Basins ............................................................................................................................. 3

Clarifier ........................................................................................................................................ 3

Choice of Coagulant ................................................................................................................ 5

Polymers ................................................................................................................................... 6

Dual Media Filters ....................................................................................................................... 8

DMF Cleaning / Backwash ...................................................................................................... 8 Demineralization System............................................................................................................... 10

Multimedia Filters...................................................................................................................... 10

Backwashing of Filters ........................................................................................................... 11

Reverse Osmosis System ........................................................................................................... 12

Reverse Osmosis..................................................................................................................... 12

Chemical Dosing in R.O. System ........................................................................................... 15

Demineralizer Train ................................................................................................................... 15

Regeneration of Demineralizer Train .................................................................................... 17

Cooling Towers ............................................................................................................................. 18

Components of Cooling Tower .................................................................................................. 19

Cooling Tower Specifications ................................................................................................... 21

Cooling Tower Performance ...................................................................................................... 21

Chemical Treatment of Cooling Tower ..................................................................................... 23

Hydrogen Generation System ........................................................................................................ 25

Electrolytic Cell ......................................................................................................................... 26

Cell Temperature ................................................................................................................... 26

Electrolyte .................................................................................................................................. 27

Electrolyte Strength ................................................................................................................ 28

Hydrogen Mist Eliminator ......................................................................................................... 28

Hydrogen Gas Holder ................................................................................................................ 28


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Hydrogen Purification System ................................................................................................... 28

Catalytic Purifier ........................................................................................................................ 29

After Cooler ............................................................................................................................... 29

Table of Figures ............................................................................................................................. 30


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Introduction

BOP (Balance of Plant) section at Lalpir Thermal Power Plant is responsible for providing wateraccording to desired specifications of different areas and equipment at plant, safe disposal of wastewater and hydrogen generation.

There are mainly two sources of raw water at Lalpir,

1. canal water, which is a seasonal source taken into service from April till October2. well water, which is taken into service when canal water is not available

Raw water from here on is treated to suit the requirement of systems that need water, such as

Firefighting system Service water system Portable water system Condenser Boiler

Boiler, amongst the other water consumers at Lalpir, is the most sensitive user that requiresdemineralized water of conductivity less than 0.1 s/cm and silica content less than 0.01 ppm.

Figure 1 Over-view of BOP Area


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CHAPTER 1

Pre-treatment of Intake Water

Raw Water Intake

Once raw water from the canal is taken, it is passed through a travelling band screen that removesany debris that may cause damage to the canal water pumps. There are 22 baskets that are in acontinuous revolution such that the water passes through their center. These baskets are made ofstrong mesh having a size of 1mm. The baskets scoop the raw water out one by one. Any debristhat may have made its way through the intake is taken up by these baskets and later sprayed intoa waste collecting pit which dumps this debris back into the canal. The debris free water is then

pumped to the plant by canal water pumps. These pumps supply water at a rate of 1200 m 3/hr, each.

There is a recirculation valve provided with each pump which when operational, will allow waterto circulate back to the bar screen. The total number of canal water pumps is four, two for each unit.When functional, one pump is in service and the other is on standby. All four pumps lubricatingoil and rubber bearings at shaft are cooled by cooling water. Two separate storage tanks are usedfor this purpose.

Figure 2 Raw Water Intake system

When canal goes dry, continuous demand of water is met by 18 well water pumps, 9 for each unit,located on the north bank on canal. Each pump has discharge rate of 240 m 3/hr and 6 pumps remainin service at a time.

The raw water intake from canal constitutes of the following subsystems:

Travelling band screens Canal water pumps Settling basins


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Clarifier supply pumps Distribution box Clarifiers Clear well

Dual media filters (DMF)

Settling Basins

There are three types of objects which can be found in water. In order from smallest to largest,these objects are chemicals in solution, colloidal solids, and suspended solids. The settling basinsare designed to provide ample retention time for settling of heavy suspended particles, debris anduncharged particles.

All sedimentation basins have four zones - the inlet zone, the settling zone, the sludge zone, andthe outlet zone. Each zone should provide a smooth transition between the zone before and the zoneafter. In addition, each zone has its own unique purpose.

Figure 3 Settling Basin

Water from canal pumps through their respective line (PakGen or Lalpir) comes to 3 settling basins(each of 1000 m 3 vol.) having common header with the provision of filling any settling basin, and

by pass line to cooling tower. Settling basins provide primary settling zone for large suspended particles, sand and silt in canal water. These basins reduce the coagulation cost in clarifier, load onfilters and provide proper suction for clarifier supply pumps.

Canal water from settling basins is fed to distribution box located on clarifiers for further treatment by clarifier supply pumps of 1050 m 3/hr discharge rate.

Clarifier

In clarifiers, water is pumped to the mixing zone, the rake and turbine area in the center, rather than being pumped at one end and being retrieved from the other. Clarifiers are used to reduce thenumber of total dissolved solids present in raw water by coagulation and flocculation.


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Clarifiers normally consist of the following zones:

Reaction and mixing zone Settling zone

Figure 4 Over-view of a typical Clarifier

At Lalpir we have three clarifiers (A, B & C). Clarifier A & C are for Lalpir and PakGen unitrespectively, while clarifier B is kept at standby.

The suspended particles in water vary considerably in source, composition charge, particle size,shape and density. The small particles are stabilized (kept in suspension) by the action of physicalforces on the particles themselves. One of the forces playing a dominant role in stabilization resultsfrom the surface charge present on the particles. Most solids suspended in water possess a negative

charge and, since they have the same type of surface charge, they repel each other. Therefore, theywill remain in suspension rather than clumping together and settle out of the water.

As water is pumped into the clarifier, it is dosed with a coagulant, Ferric Sulfate. This is becauseraw water contains small suspended negatively charged particles that are not removed by travelling

band screens or settling basins. These particles need to be removed in order to reduce the totalsuspended solids in the water, thus reduction in water turbidity. Coagulation neutralizes thesecharged particles and flocculation ensures the removal of these suspended particles. The negativelycharged particles in water settle in with the positively charged particles of the coagulant, thusneutralizing and increasing in size and weight as well.

Coagulant, more formally, is defined as an electrochemical process of neutralization of surfacecharges to allow small colloidal particles to collide and form larger masses capable of settling orwithstanding pressure. Flocculation, on the other hand, is defined as the physical process of theformation of larger masses, often enhanced by the addition of long-chain polymeric compounds.Ferric Sulfate is dosed as the coagulant, whereas a polymer solution is injected into the clarifierreaction and mixing zone to initiate flocculation.


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Figure 5 Illustration of Coagulation Process

The suspended particles settle down on the base of the clarifier after coagulation and flocculation,thus forming a layer of sludge at the bottom. This level of sludge needs to be maintained at certainconditions in order to facilitate the filtration process. A rake keeps operating in the sludge area,thus ensuring that the sludge bed does not get solidified. In order to maintain the level of the sludge

bed, de-sludging is carried out by two de-sludge pumps at different intervals. At the clarifier outletthe turbidity is thus reduced to a minimum level as the majority of suspended solids have areremoved.

Figure 6 Water Quality at different turbidities

Choice of Coagulant

The choice of coagulant chemical depends upon the nature of the suspended solid to be removed,raw water conditions, facility design, and the cost of the amount of chemical necessary to producethe desired result. Final selection of the coagulant should be made following thorough jar testingand plant scale evaluation. Considerations must be given to required effluent quality, effect upondownstream treatment process performance, cost, method and cost of sludge handling and disposal,and net overall cost at the dose required for effective treatment.


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Inorganic Coagulants

Inorganic coagulants such as aluminum and iron salts are the most commonly used. When addedto the water, they furnish highly charged ions to neutralize the suspended particles. The inorganichydroxides formed produce short polymer chains which enhance microfloc formation. Inorganiccoagulants usually offer the lowest price per pound, are widely available, and, when properlyapplied, are quite effective in removing most suspended solids. They are also capable of removinga portion of the organic precursors which may combine with chlorine to form disinfection by-

products. They produce large volume of flocs which can entrap bacteria as they settle. However,they may alter the pH of the water since they consume alkalinity. When applied in a lime soda ashsoftening process, alum and iron salts generate demand for lime and soda ash.

They require corrosion-resistant storage and feed equipment. The large volumes of settled flocsmust be disposed of in an environmentally acceptable manner.

Inorganic Coagulant Chemical Equations

Common coagulant chemicals used are alum, ferric sulfate, ferric chloride, ferrous sulfate, andsodium aluminate. The first four will lower the alkalinity and pH of the solution while the sodiumaluminate will add alkalinity and raise the pH.

At Lalpir we use ferric sulfate as a coagulant and its equation is as follows:

Fe2(SO 4)3 + 3 Ca(HCO 3)2 2 Fe(OH) 3 + 3 CaSO 4 + 6 CO 2

Polymers

Polymers are becoming more widely used, especially as coagulant aids together with the regularinorganic coagulants. Anionic (negatively charged) polymers are often used with metal coagulants.

Low-to-medium weight positively charged (cationic) polymers may be used alone or incombination with the aluminum and iron type coagulants to attract the suspended solids andneutralize their surface charge. The manufacturer can produce a wide range of products that meeta variety of source-water conditions by controlling the amount and type of charge and relativemolecular weight of the polymer. Polymers are effective over a wider pH range than inorganiccoagulants. They can be applied at lower doses, and they do not consume alkalinity. They producesmaller volumes of more concentrated, rapidly settling floc. The floc formed from use of a properlyselected polymer will be more resistant to shear, resulting in less carryover and a cleaner effluent.

Polymers are generally several times more expensive in their price per pound than inorganiccoagulants. Selection of the proper polymer for the application requires considerable jar testing

under simulated plant conditions, followed by pilot or plant-scale trials. Factors Affecting Coagulation

In a well-run water treatment plant, adjustments are often necessary in order to maximize thecoagulation/flocculation process. These adjustments are a reaction to changes in the raw waterentering the plant. Coagulation will be affected by changes in the water's pH, alkalinity, temperature,time, velocity and zeta potential.


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The effectiveness of a coagulant is generally pH dependent. Water with a color willcoagulate better at low pH (4.4-6) with alum.

Alkalinity is needed to provide anions, such as (OH) for forming insoluble compounds to precipitate them out. It could be naturally present in the water or needed to be added as

hydroxides, carbonates, or bicarbonates. Generally 1 part alum uses 0.5 parts alkalinity for proper coagulation.

The higher the temperature , the faster the reaction, and the more effective is thecoagulation. Winter temperature will slow down the reaction rate, which can be helped byan extended detention time. Mostly, it is naturally provided due to lower water demand inwinter.

Time is an important factor as well. Proper mixing and detention times are very importantto coagulation.

The higher velocity causes the shearing or breaking of floc particles and lower velocitywill let them settle in the flocculation basins. Velocity around 1 ft/sec in the flocculation

basins should be maintained.

Zeta potential is the charge at the boundary of the colloidal turbidity particle and thesurrounding water. The higher the charge the more is the repulsion between the turbidity

particles, less the coagulation, and vice versa. Higher zeta potential requires the highercoagulant dose. An effective coagulation is aimed at reducing zeta potential charge toalmost 0.

TECHNICAL DATA

Canal Water Pump Capacity 1200 m 3/hr

Well Water Pump Capacity 240 m3

/hr Travelling screen baskets 22

Travelling screen wash pump 10 m 3/hr

Canal water pumps flow 1200 m 3/hr

Clarifier supply pump 1100 m 3/hr

Inlet distribution box flow 1023 m 3/hr

Clarifier Capacity 2400 m 3

Clear well Capacity 165 m 3

Coagulant Tank Capacity 15 m3

Polymer Tank Capacity 12 m 3


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Dual Media Filters

The filter media is the part of the filter which actually removes the particles from the water beingtreated. Filter media is most commonly sand, though other types of media can be used, usually incombination with sand. The gravel at the bottom of the filter is not part of the filter media, merely

providing a support between the under drains and the media and allowing an even flow of waterduring filtering and backwashing.

The sand used in rapid sand filters is coarser (larger) than the sand used in slow sand filters. Thislarger sand has larger pores which do not fill as quickly with particles out of the water. Coarse sandalso costs less and is more readily available than the finer sand used in slow sand filtration.

In many cases, multiple types of media are layered within the filter. Typically, the layers (startingat the bottom of the filter and advancing upward) are sand and anthracite coal, or garnet, sand, andanthracite coal. The picture below shows a cross-section through a dual media filter.

Figure 7 Media Layers in DMF

The media in a dual or multi-media filter are arranged so that the water moves through media with progressively smaller pores. The largest particles are strained out by the anthracite. Then the sandand garnet trap the rest of the particulate matter though a combination of adhesion and straining.Since the particles in the water are filtered out at various depths in a dual or multimedia filter, thefilter does not clog as quickly as if all of the particles were all caught by the top layer.

DMF Cleaning / BackwashAfter 2 hours of running DMF Filters are cleaned/backwashed to remove the carryover suspended

particles. Clear well Level should be above 70%.

Drain D own (5 Min)

Here the air outlet valve and drain down valves are opened so that any previous reserve isdrained because standing water in DMF is rich in silica. Flow rate is 90 m 3 /hr


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Air M ix (5 min)

In this step air mix inlet valve (air from the DMF air blowers) and air outlet valve are openedthis steps evens the DMF surface same as air scouring. Flow rate is 1380 m 3 /hr

Fi ll (5 min)

In this step service inlet of water and air outlet valve opens in this step DMF fills itself withwater. Flow rate is 225 m 3 /hr

Backwash (5 mi n)

Here back wash inlet and outlet valves opens and the water goes to Settling Basin. Flow rate is680 m 3 /hr

Rinse (5 min)

Service inlet and rinse outlet valves open and the waste water goes to distribution chamber.Flow rate is 170 m 3 /hr.

After these steps DMF is ready for service. DMF Backwash and clear well overflow goes to settling basin A&B.

By-Passing the Pre-treatment System

All pre-treatment steps (i.e. settling basin, clarifier, DMF) are bypassed when well water is takeninto service. Following steps are used for by-pass

Close the inlet FCV of clarifier manually from PLC.

Open the clarifier bypass valve. If PG Unit is operating then clarifier pump C discharge bypass valve to cooling tower

would be opened. DMF pumps should be OFF and DMF bypass valve must be open.


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CHAPTER 2

Demineralization SystemThe demineralization system is designed to produce demineralized treated water with aconductivity of less than 0.1 /cm and silica content of less than 0.01 ppm.

Multimedia Filters

Multimedia filtration refers to a pressure filter vessel which utilizes three or more different mediaas opposed to a "sand filter" that typically uses one grade of sand alone as the filtration media. In asingle media filter, during the "settling" cycle, the finest or smallest media particles remain on topof the media bed while the larger, and heavier particles, stratify proportional to their mass lower inthe filter. This results in very limited use of the media depth since virtually all filterable particlesare trapped at the very top of the filter bed or within 1-2 inches of the top where the filter media

particles have the least space between them. The filter run times are thus very short before the filterblinds or develop much differential pressure that it must be backwashed to avoid seriouslyimpeding or stopping the flow.

Multi-media filters typically have three layers, consisting of anthracite, sand and garnet. These areoften the media of choice because of the differences in mass between the materials. Garnet is byfar the heaviest per unit volume, sand is intermediate while anthracite is the lightest. The idea

behind using these three media of differing densities is that anthracite media, with the largest particle size, will stratify on top following backwash while the intermediate size media (sand) willsettle in the middle and garnet, the heaviest but having the smallest particle diameter, will settle to

the bottom.

Figure 8 Media Layers in MMF


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This filter media arrangement allows the largest dirt particles to be removed near the top of themedia bed with the smaller and smaller dirt particles being retained deeper and deeper in the media.This allows much longer filter run times between backwash and much more efficient dirt orturbidity removal. Sand filters typically remove particles down to 25-50 microns while a well-

operated multi-media filter may remove particles from 10-25 microns.Pre-treated water fromthe filtered water basinis directed to twoMulti-Media Filterswhich remove residualturbidity andsuspended solids fromthe water. Followingmulti-media filtration,the water is injectedwith sodium bi-sulfateto remove tracequantities of freechlorine. Multi- Mediafilter backwash andrinse water is directedto the inlet distribution

box. A portion of themulti-media filteredwater is directed to the

potable water tank and chlorinator. If the raw water source is canal water, the multi-media filteredwater effluent is directed to the permeate tank .If the raw water source is well water, the multi-media filtered water is directed to the reverse osmosis system. Each multi-media filter is designedto treat 97 m 3 / hr of pre-treated water.

Like DMF gravel layer is also used here for supporting the media. The arrangement of media fromtop to bottom is as follows:

Material Quantity (m 3) Average size (mm)Garnet 1.06 0.35Anthracite 1.50 0.90 - 1.00Filter Sand 1.45 0.45 - 0.55

Fine Gravel 0.50 3.35 - 1.70Medium Gravel 0.50 6.30 - 12.70Coarse Gravel 1.90 12.70 - 19

Backwashing of Filters

Backwash and rinse waste water is returned to the distribution box. With one (I) filter in serviceand the other in backwash, a second filter feed pump will be activated. Treated water is fed to thereverse osmosis system when a high total dissolved solids raw water is utilized. Under normal

Figure 9 Multi Media Filter


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circumstances, the R.O. system is bypassed and the multimedia filter effluent is directed to the R.O. permeate tank. Sodium bi-sulfate is injected into the multimedia filter effluent at a constant,manually set rate. A flow switch will control the start/stop operation of the bi-sulfate pumps.

Reverse Osmosis SystemOsmosis is a natural process involving the fluid flow of across a semi-permeable membrane barrier.Consider a tank of pure water with a semi-permeable membrane dividing it into two sides. Purewater in contact with both sides of an ideal semi-permeable membrane at equal pressure andtemperature has no net flow across the membrane because the chemical potential is equal on bothsides. If a soluble salt is added on one side, the chemical potential of this salt solution is reduced.

Osmotic flow from the pure water side across the membrane to the salt solution side will occuruntil the equilibrium of chemical potential is restored. In scientific terms, the two sides of the tankhave a difference in their chemical potentials and the solution equalizes , by osmosis, its chemical

potential throughout the system. Equilibrium occurs when the hydrostatic pressure differential

resulting from the volume changes on both sides is equal to the osmotic pressure. The osmotic pressure is a solution property proportional to the salt concentration and independent of themembrane.

Reverse Osmosis

Application of an external pressure to the salt solution side equal to the osmotic pressure will alsocause equilibrium. Additional pressure will raise the chemical potential of the water in the saltsolution and cause a solvent flow to the pure water side, because it now has a lower chemical

potential. This phenomenon is called reverse osmosis.

Figure 10 Osmosis vs. Reverse Osmosis


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Technical Data for RO system

5 micron Fi lters

Quantity/unit 2Diameter 406 mmHeight 2108 mmMaterial 316 stainless steelDesign pressure 10.5 kg/ cm 2

Cartri dges for 5 micron f il ters

Manufacturer FilteriteQuantity 22 per filter

Size 5 micronMaterial PolypropyleneDesign flow rate / filter 88 m 3/ hrMaximum DP 0.7 kg/ cm 2

R.O Booster pumps

Quantity 3Manufacturer TonkafloMaterial 316 stainless steel

Design flow rate/pump 44 m3

/ hrOperating pressure 24.5 kg/cm 2

Min. operating pressure 15.5 kg/cm 2 Pump speed 2900 rpmMotor power rating 56 KWElectrical Ratings 380V/ 3ph / 50 Hz

R.O membrane element

Manufacturer Hydranautics

Number of elements 72 (36 per R.O bank)Model no 8040-LSY-CPA2Membrane type Spiral wound thin film compositeDiameter 201.9 mmLength 1016 mmSurface area / element 30.2 m 2 Max. Operating temp 45 C

Feed water pH range 3-10


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Nominal permeate flow 1.42 m 3/ hr Nominal salt rejection 99%

M embran e Pressure Vessels

Manufacturer Advance structureMaterial of construction FRPDesign pressure 28 kg/cm 2 Size 289 mm dia 6594 mm long

No. of housings 12(6 per R.O. bank) No. of elements/housing 6

R.O System design data

No of R.O banks 2 No of housing/bank 6 (series staged 4:2) No. Of elements/bank 36Inlet feed temperature (design) 22 C

Minimum temp. 20 C

Maximum temp. 38 C

Feed pressure (design) 24.5 kg/ cm 2

Minimum pressure 15.5 kg/ cm 2

Maximum pressure 31.6 kg/ cm 2

Product back pressure (design) 0.7 kg/ cm 2

Maximum 3.5 kg/cm 2

Design feed flow rate per bank 44 m 3/ hrDesign permeate flow rate/bank 32.5 m 3/ hrDesign reject flow rate/bank 11.5 m 3/ hrPermeate recovery 74%


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Figure 11 Reverse Osmosis (R.O.) banks

Chemical Dosing in R.O. System

Sulfuric Acid (4%)

It is injected into the reverse osmosis feed water to lower the pH. Control of the feed water pH isaffected by pH measurement and modulation of the sulfuric acid pumps stroke positioned. The acidtank refill is automatically initiated based on the level in the acid tank. Refill is accomplished withthe activation of a dilution water pump, an acid pump and the opening of the mixed bed dilutionwater valve and the R.O. acid tank inlet valve. Manual initiation for R.O. acid tank refill is also

available. The R.O. acid tank refill sequence is interlocked with the cation and mixed bedregeneration sequences to prevent refilling the tank during regeneration of either primary or mixed

bed trains.

Anti - Scalant

The solution is also injected into the reverse osmosis feed water at a constant rate. In the automaticmode, the acid and anti-sealant feed pumps are started and stopped automatically with the reverseosmosis booster pumps. Refill of the anti-scalant tank is a manually controlled sequence.

Demineralizer TrainTwo Demineralizer trains each comprised of a cation unit, anion unit and mixed bed unit,

produce treated water that is stored in the demineralized water storage tanks. A de-carbonatortower/clear well and de-carbonator water forwarding pumps are common to both trains. Alevel transmitter installed in the de-carbonator clear well controls the operation of the de-carbonator inlet modulating control valve. Level controls in the demineralized water storagetank controls the ope ration of the Demineralizer trains. On high level, the In Service primary and mixed bed units will be placed in standby. Return to service is operatorinitiated. Water flows through the ion exchangers water inlet and into the diffuser. Thediffuser spreads the water over the resin bed. As the water flows through the resin bed, ions


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are removed from the water and exchanged with the hydrogen ions (Cation unit) or hydroxylions (Anion unit) occupying the sites on the resin beads.The effluent of a cation exchanger is generally acidic, because the hydrogen ions present inthe water form acids. However, after the effluent from a cation exchanger flows throughanion exchanger and mixed bed, it is almost pure demineralized water.

The model reactions that are carried out in demineralizers are described as follows:

Strong Acid Cation Exchange

The following reactions take place in the Cation bed during service.

Ca+ (HCO 3)- 2 Ca+

+ R - H 2 R - + 2 H 2CO 3Mg +(HCO 3)-2 Mg +

Ca+SO 4- Ca +

+

R H2 R - + H 2SO 4 Mg +SO 4- Mg +

Ca+Cl - Ca + + R H2 R - + 2 HCl

Mg +Cl - Mg -

(Where R = resin)

De carbonator

De-carbonator is a device which is used to remove CO 2 from the water, produced during cationremoval as:

Ca+(HCO 3)2- + R H2 R Ca + + 2 H 2CO 3

De-carbonator is used to reduce load on anionic bed. Carbonic acid produced is a weak acid and isdissociated very easily giving carbon dioxide and water as

H2CO 3 H2O + CO 2

Strong Base Anion ResinFrom the above equations it is clear that during cation exchange process, acids are produced (H 2SO 4,HCl). Secondly, anions entered into the bed along with water are still present. So in the anionexchange step these ions are removed and the reactions taking place are

H2+SO4- + R - OH - R - SO 4- + H 2O

H+Cl - + R - OH - R - Cl - + H 2O


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After all the minerals have are removed, ultra-pure water is produced that is stored in demineralizedwater storage tank from where it is supplied to boiler.

Regeneration of Demineralizer Train

The resin beads used for ion exchanger have thousands of sites available for exchanging ions.However, once the hydrogen or hydroxyl ions have been depleted, the beads are no longer usefulfor ion exchange. In the exhausted state, the resin bed cannot remove ions from the incoming water.There are two parameters to monitor resin exhaustion, Silica & Conductivity monitori ng .Demineralized trains are exhausted after cleaning particular amount of water. They are regeneratedwith injecting fresh hydrogen & hydroxyl ions. Regeneration is pushbutton initiated. Initiation ofa primary train regeneration sequence will automatically regenerate a cation unit and itscorresponding anion unit concurrently. Following regeneration of a primary train and/or a mixed

bed unit, the units are placed in standby and return to service is pushbutton initiated. The standbyregenerated train may be placed in service during the regeneration procedure when in the semi-automode. Both trains may be placed in service together only in the semi-auto mode. During normal

operation, one train will be in service and one train in standby. During the regeneration of ademineralizer train, one train remains on standby mode.

Regeneration of the Demineralizer system is normally performed on a train basis by regeneratingthe cation and anion units of the same train concurrently or a mixed bed unit. Interlocks are providedto ensure that only one train or a mixed bed unit can be regenerated at any given time. To initiateregeneration, both trains must first be placed into Standby and then press the appropriateregeneration key(s).

The cation and anion units are regenerated in a split flow counter current manner and therefore willnot be given a full backwash every regeneration. When these units are backwashed (approximatelyevery 20 regenerations), a double chemical injection will be automatically provided to reconditionthe resin at the bottom of the bed.

Regeneration controls are programmed for each cation and anion unit to totalize the number ofregenerations without a full backwash. When the preset value is reached, the unit will be given a

backwash and double chemical injection during its next regeneration cycle and the appropriateregeneration tantalizers will be reset to zero after this upset regeneration. Provisions have beenmade to override the regeneration if necessary; however, under normal operating conditions theregeneration cycles should be allowed to time out and sequence through to completion. Dilutionwater for the acid and caustic regenerate solutions is demineralized water delivered by the diluentswater pumps. Interlocks are provided to ensure that the acid and caustic regenerate solutions aredelivered at the correct flow rates and chemical strength. A heat exchanger is provided to heat thedilution water during preheat caustic injection and displacement steps of the anion and mixed bedregeneration procedure. Interlocks are provided to ensure that the minimum anion dilution watertemperature is at 35 oC and the mixed bed dilution water is at 49 oC. Dilution water flow is controlled

by rate set valves provided for cation acid dilution, mixed bed acid dilution, anion caustic dilutionand mixed bed caustic dilution.


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CHAPTER 3

Cooling Towers A Cooling Tower is an equipment used to reduce the temperature of a water stream by

extracting heat from water and emitting it to the atmosphere.

Cooling towers are a very important part of many industrial plants. They represent a relativelyinexpensive and dependable means of removing low-grade heat from cooling water. The make-upwater source is used to replenish water lost to evaporation. Hot water from heat exchangers is sentto the cooling tower. The water exiting the cooling tower is sent back to the exchangers or to otherunits for further cooling.

Cooling towers fall into two main categories: Natural draft and Mechanical draft.

Cooling towers at Lalpir are I nduced Dr aft counter f low open r ecir culati ng type.

CoolingTowers

MechanicalDraft

InducedDraft

Cross FlowCounterFlow

ForcedDraft

Cross FlowCounterFlow

NaturalDraft


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Figure 12 Typical Induced Draft Counter flow Cooling Tower

In the counter flow induced draft design, hot water enters at the top, while the air is introduced atthe bottom and exits at the top.

Components of Cooling Tower

The basic components of an evaporative tower are: Frame and casing, fill, cold water basin, drifteliminators, air inlet, louvers, nozzles and fans.

Frame and Casing

Most towers have structural frames that support the exterior enclosures (casings), motors, fans, andother components. With some smaller designs, such as some glass fiber units, the casing mayessentially be the frame.

Fill

Most towers employ fills (made of plastic or wood) to facilitate heat transfer by maximizing waterand air contact. Fill can either be splash or film type.

With splash fill, water falls over successive layers of horizontal splash bars, continuously breakinginto smaller droplets, while also wetting the fill surface. Plastic splash fill promotes better heattransfer than the wood splash fill.

Film fill consists of thin, closely spaced plastic surfaces over which the water spreads, forming athin film in contact with the air. These surfaces may be flat, corrugated, honeycombed, or other


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patterns. The film type of fill is the more efficient and provides same heat transfer in a smallervolume than the splash fill.

Cold Water Basin

The cold water basin, located at or near the bottom of the tower, receives the cooled water thatflows down through the tower and fill. The basin usually has a sump or low point for the cold waterdischarge connection. In many tower designs, the cold water basin is beneath the entire fill.

Some forced draft counter flow design, however, the water at the bottom of the fill is channeled toa perimeter trough that functions as the cold water basin. Propeller fans are mounted beneath thefill to blow the air up through the tower. With this design, the tower is mounted on legs, providingeasy access to the fans and their motors.

Drift Eliminators

These capture water droplets entrapped in the air stream that otherwise would be lost to the

atmosphere.

Air In-let

This is the point of entry for the air entering a tower. The inlet may take up an entire side of a tower(cross flow design ) or be located low on the side or the bottom of (counter flow designs).

Louvers

Generally, cross-flow towers have inlet louvers. The purpose of louvers is to equalize air flow intothe fill and retain the water within the tower. Many counter flow tower designs do not requirelouvers.

Nozzles

These spray water to wet the fill. Uniform water distribution at the top of the fill is essential toachieve proper wetting of the entire fill surface. Nozzles can either be fixed and spray in a roundor square patterns, or they can be part of a rotating assembly as found in some circular cross-sectiontowers.

Fans

Both axial (propeller type) and centrifugal fans are used in towers. Generally, propeller fans areused in induced draft towers and both propeller and centrifugal fans are found in forced draft towers.Depending upon their size, the type of propeller fans used is either fixed or variable pitch. A fan

with non-automatic adjustable pitch blades can be used over a wide kW range because the fan can be adjusted to deliver the desired air flow at the lowest power consumption. Automatic variable pitch blades can vary air flow in response to changing load conditions.


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Cooling Tower Specifications

TECHNICAL DATA

Type Mechanical Induced Draft-Counter flowCirc. Water flow rate 35,000m 3 / hour for 2 pumps

Nominal Cell dimension 15.8 m x 19.2 m

Fan stack height 3.8 m

Overall tower height 14.8 m

Number of Cells 8 (per unit)

Total number of fans 8 (per unit)

Design Summer Winter

Hot water (inlet) temperature 41 49 41Cold water (outlet) temperature 30 36 27

L/G ratio 1.50 1.33 1.26

Drift losses 0.1 % 0.1 % 0.1 %

FANS

Type & Model Axial Flow Propeller Fan (Pitch adjustable)

Manufacturer Hudson Products Corporation

Diameter 9.76 m

Number of Blades 10 per fan

Fan speed 114 RPM

Tip speed 58.2 m/sec

Air delivery(fan) 754 m 3 /sec

Pitch angle 13 - 15 degree

Fan static efficiency 64 %

Cooling Tower Performance

Following are the factors that affect cooling tower performance and their calculated values underdifferent conditions that are observed at Lalpir cooling towers

1. Range is the difference between the cooling tower water inlet and outlet temperature. Inother words, high range would mean better cooling tower performance.


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Range (summer) = 49 36 = 13 oC

Range (winter) = 41 27 = 14 oC

2. Approach is the difference between the cooling tower outlet cold water temperature andambient wet bulb temperature. Lower approach means better cooling tower performance.

Approach (summer) = 36 28 = 8 oC

Approach (winter) = 27 8 = 19 oC

3. Effectiveness (in percentage) is the ratio of range, to the ideal range, i.e., difference between cooling water inlet temperature and ambient wet bulb temperature, or in otherwords it is = Range / (Range + Approach).

Effectiveness (summer) = [13 / (13+8)] x 100 = 62 %

Effectiveness (winter) = [14 / (14+19)] x 100 = 42 %

Figure 13 Temperature profiles

4. Cooling Capacity is the heat rejected in kCal/hr or TR, given as product of mass flowrate of water, specific heat and temperature difference.

5. Evaporation loss is the water quantity (m3/hr) evaporated for cooling duty. Ideally, for

every 10F cooling, one percent of the cooling water evaporates. Mathematically,

Evaporation Loss (m 3 /hr) = 0.00153 x Circulation Rate (m 3 /hr) x (T1-T2)

Evaporation loss (summer) = 0.00153 x 33600 x (49 36) = 668 m 3 / hr Evaporation loss (winter) = 0.00153 x 33600 x (41 27) = 720 m 3 / hr

6. Cycles of concentration (C.O.C) is the ratio of dissolved solids in circulating water tothe dissolved solids in make-up water. Mathematically,


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CoC = Cooling water concentration / Makeup water concentration

CoC (canal) = 560 ppm / 80 ppm = 7.00

CoC (well) = 560 ppm / 120 ppm = 4.66

7. Blow down loss is generally defined as the water lost from the system for all the reasonsexcept evaporation. Mathematically,

Blow down rate = Evaporation Volume (CoC 1)

Blow down (canal) = 668 / (7 1) = 111 m 3 / hr

Blow down (well) = 720 / (5 1) = 180 m 3 / hr

8. Liquid-to-gas ration (L/G) of a cooling tower is the ratio between the water and the airmass flow rates. Cooling towers have certain design values, but seasonal variations require

adjustment and tuning of water and air flow rates to get the best cooling tower effectiveness.Adjustments can be made by water box loading changes or blade angle adjustments.Thermodynamic rules also dictate that the heat removed from the water must be equal tothe heat absorbed by the surrounding air.

L/G (summer) = 1.33

L/G (winter) = 1.28

Chemical Treatment of Cooling Tower

Chemicals are injected in circulating water system to stop microbiological growth and corrosion

formation. Chemical treatments that are practiced at Lalpir cooling towers are;

Scale Inhibitor

Nalco 23212 is used as a scale inhibitor in the Cooling Tower. It is commonly known as phosphatetreatment. The pH of the circulating water is kept in range (8.5 10) so there are less chances ofscale formation in the system. The value of phosphate in circulating water is maintained at 1.5-2.2

ppm.

Acid Dosage

Sulfuric acid is added to reduce the pH of the circulating water & to reduce M-alkalinity. The pHof the cooling tower is maintained at about 8.2 so as to avoid any scale formation in the system.

Dispersant

The scale formed tends to stay suspended long enough to be removed by either the blow-down ora filtration system. Dispersant is added to keep microbial scale in system suspended so it can betreated with biocides and removed from the cooling tower basin.


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Two approaches can be taken to ensure adequate control

a. Increase blow-down rate to remove solids and prevent their concentrations from going toohigh. Unfortunately this approach also increases the quantities of water and treatment

products used and tends not to be cost effective. b. Utilize heavy dosage of treatment products to prevent deposition possibly with the

incorporation of an acid-feed system to keep the carbonate equilibrium system in the moresoluble bicarbonate form. This approach can be very costly and is counter to goodenvironmental practice.

Biocide

The tendency for biological activity and fouling can be effectively controlled by adding biocides.Chlorine is added as a shock dose, usually at night, to prevent microbial growth. It can be added asCl2 or as hypochlorite depending upon the size of the system. The hypochlorite should be sodiumas opposed to calcium (HTH) as the calcium would add to the system's scaling potential. Since

2009, chlorine is replaced by sodium hypo-chloride as a biocide for cooling towers at Lalpir.

Chemical Quantity Remarks

Sodium hypo-chloride 0.3 0.5 ppm Periodic dosing

Dispersant 5 ppm Periodic dosing; done 30mins beforesodium hypo-chloride dosage

Scale Inhibitor 35 ppm Batch dosing

Acid 1.5 2.5 TPD (well season)

0.6 0.9 TPD (canal season)

Batch dosing


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CHAPTER 4

Hydrogen Generation SystemHydrogen generation system is designed to produce 5 normal cubic meters of hydrogen (whenmeasured at o degree centigrade and 760 mm of Hg). It can compress and purify 5 normal cubicmeters of hydrogen to a pressure of 175 kg/cm 2.

Figure 14 Over-view of Hydrogen Generation system


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Hydrogen gas generating system consists of air cooled silicon rectifier, transformer and six Stuartelectrolytic cells connected in series.

Rectifier Specifications

Rated Power 30 KW

Rated AC Voltage 380 +/- 10 Volts

Rated AC Current 58 Amps

Rated Frequency 50 +/- 5% Hz

Number of Phases 3

Rated DC Voltage 15 Volts

Rated DC Current 0 2000 A

Percent Ripple 5 %

Percent Regulation 1 %

Ambient Temperature 50 oC

AC power at 380 volts, 3 phase, and 50 hertz is supplied from the power feeder panel throughcircuit breaker to rectifier and transformer. Circuit breaker is provided for short circuit protection.In rectifier, voltage is reduced by a rectifier transformer and converted to a DC at Voltage up to 14volts. DC power from rectifier is supplied to electrolytic cells through copper bus bar.

Electrolytic Cell

The Stuart electrolytic cells are of the uni-polar tank type. The cell is known as a 3-plate cell, havingone nickel-plated iron anode plates and two iron cathode plate. The anodes are surrounded by clothdiaphragms which prevent mixing of the hydrogen and oxygen gases formed in the cell. Theelectrolyte is a 25% solution of potassium hydroxide (also referred to as caustic potash or KOHin water)

Cell Temperature

Voltage tends to decrease as cell temperature increases. The recommended cell temperature is between 65 to 70 C above which the rate of corrosion of cell component increases significantly.


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Figure 15 Electrolytic Cell

Electrolyte

The optimum concentration of KOH is 25% by weight (Specific Gravity of 1.24 measured at15.5 C).

DC current from the positive terminal of the rectifier enters the first cell in the bank at the terminals

of the anodes. The current flows down the anodes into the cell, through the electrolyte to thecathodes, up the cathodes to the cathode terminals (two per cathode), and then on to the anodeterminals of the next cell in the bank. From the last cell in the bank the current flows back to thenegative terminal of the rectifier.

Passage of direct current through the cell causes the water in the cell to be converted intohydrogen and oxygen gases. Hydrogen forms on the cathode plates while oxygen forms on theanode plates. This process is known as electrolysis and the cell is called an electrolytic cell . Thediaphragms surrounding the anodes are very effective at keeping bubbles of oxygen separatedfrom bubbles of hydrogen. However, they are less efficient at keeping the actual gases separated.For this reason the cell is normally operated so that the diaphragms are submerged in theelectrolyte.

If for some reason the electrolyte level should drop to the point where the diaphragms were nolonger submerged, hydrogen could pass through the diaphragms into the oxygen, and vice-versa.Before this could happen however, the end of the vent pipe would be exposed, allowing the gasesto escape into the cell room.

This reduces the risk of compressing impure gases. The amount of hydrogen vented into the roomis not a hazard provided the room is adequately ventilated.


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The amounts of hydrogen and oxygen formed are directly proportional to the amount of DC currentflow through the cell. At 2000 amperes (maximum cell current each cell will produce 0.7 cubicmeters of hydrogen and 0.35 cubic meters of oxygen per hour. (When measured dry at 0 C, 760mm of mercury).

The oxygen gas formed on the anodes bubbles up through the electrolyte, inside the diaphragmswhich surrounds the anodes, and flows into the oxygen compartment above the electrolyte level.Similarly, the hydrogen formed on the cathodes bubbles up through the electrolyte, outside thediaphragms, and flows into the hydrogen compartment above the electrolyte level.

Electrolyte Strength

The recommended electrolyte concentration is 25% by weight, concentrations above or below thistend to increase cell voltage.

Concentration above 25% also tends to increase the rate of corrosion of cell components. As currentflow through electrolyte to produce hydrogen and oxygen some heat is also evolved.

The gases leaving the cell are cooled in water-cooled gas coolers. Cooling water enters from thewater header flows through the hydrogen and oxygen gas coolers for each cell in series and thenflows to waste.

Hydrogen Mist Eliminator

The hydrogen gas leaving the cells carries off some of the Potassium Hydroxide electrolyte in theform of an entrained mist. Most of this entrainment is removed in the cell gas cooler and is returnedto the cells. Some is removed at water seal. The remainder is removed in the mist eliminator.

The mist eliminator element consists of a hollow cylindrical fiber packed unit with a mountingflange at the top end. Mist laden gas flows through the walls of the hollow cylinder. Clean gasleaves at the center at the top. The entrained mist collects in the fibers of the element and flowsdownward to the closed bottom end of the element and rains throughput the dip pipe to the bottomof the tank. Entrained mist then flows out through the overflow pipe to waste.

Hydrogen Gas Holder

The hydrogen gasholder is a wet-seal type gasholder with a nominal volume of 30 m 3. Theoperating pressure is approximately 125mm water column.

Gasholder is fitted with four level switches for control of the hydrogen compressors.

Hydrogen Purification System

The hydrogen at the discharge of the oil lubricated compressors contain the following impurities

Oxygen gas, approximately 0.2% by volume Water vapor, 100 percent relative humidity at operating conditions Oil Vapor and oil droplets picked up in the oil lubricated compressors Moisture condensed out of the hydrogen gas as a result of the increase in pressure


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The moisture, oil droplets and oil vapor are removed in a series of filter. Two banks of these filtersare supplied so that one bank can be in service while the other bank is being standby

Catalytic purifier for removal of oxygen impurity in the hydrogen gas. The purifier is fitted withinlet and outlet temperature gauges, as well as coalescing filter and high temperature switches.Water cooled heat exchanger for cooling the hot hydrogen leaving the catalytic purifier. The heatexchanger is fitted with outlet temperature gauge. Condensed water is collected in filter.

The hydrogen then flows to the hydrogen dryer, where it is dried to a dew point of -50 C. Thehydrogen dryer is a molecular sieve dual column heatless pressure swing type.

The hydrogen then flows through the dust filter where any dirt particles carried over from the dryerare filtered out. From the dust filter the hydrogen flows through back pressure maintaining valve,this valve serves to impose a minimum back pressure on the hydrogen dryer of approximately175kg/cm 2 regardless of the pressure in the downstream cylinder storage, thereby ensuring that thedryer operates at its maximum efficiency.

Catalytic Purifier

The catalytic purifier is used to remove oxygen impurity from the hydrogen gas by causing theoxygen to catalytically combine with hydrogen to form water vapor. When operating properly the

purifier should remove oxygen to a residual impurity of less than ten parts per million.

A special wettable type catalyst is used, which does not require the use of preheaters, temperaturecontrollers, etc.

When oxygen is catalytically combined with hydrogen, heat is given off and the temperature of thegas increases. A temperature rise of 16 C can be expected for each tenth of one percent oxygen

reacted. If too much oxygen is present (more than 4 %) the gas mixture could explode. For thisreason extreme caution must be taken to exclude excessive oxygen from hydrogen in the catalytic

purifier.

After Cooler

The after cooler is supplied to cool the hot hydrogen leaving catalytic purifier, before it enters thedesiccant dryer. If the hydrogen is not sufficiently cooled the desiccant dryer could be overloadedwith harmful effects on the exit dew point.

The After cooler is a shell and tube type heat exchanger, with hydrogen flowing on the tube sideand cooling water flowing on the shell side. Temperature gauge at the after cooler outlet indicates

hydrogen temperature.

From after cooler the hydrogen gas goes to hydrogen storage bottles through coalescing filters.There are 6 horizontally placed storage bottles with the storage capacity of 1200 m 3 of hydrogengas at 175 kg/cm 2.


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Table of Figures

Figure 1 Over-view of BOP Area .................................................................................................... 1

Figure 2 Raw Water Intake system ................................................................................................. 2

Figure 3 Settling Basin .................................................................................................................... 3

Figure 4 Over-view of a typical Clarifier ........................................................................................ 4

Figure 5 Illustration of Coagulation Process ................................................................................... 5

Figure 6 Water Quality at different turbidities ................................................................................ 5

Figure 7 Media Layers in DMF ....................................................................................................... 8

Figure 8 Media Layers in MMF .................................................................................................... 10

Figure 9 Multi Media Filter ........................................................................................................... 11 Figure 10 Osmosis vs. Reverse Osmosis ....................................................................................... 12

Figure 11 Reverse Osmosis (R.O.) banks ..................................................................................... 15

Figure 12 Typical Induced Draft Counter flow Cooling Tower .................................................... 19

Figure 13 Temperature profiles ..................................................................................................... 22

Figure 14 Over-view of Hydrogen Generation system ................................................................. 25

Figure 15 Electrolytic Cell ............................................................................................................ 27
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Balance of Plant Operation (Power Plant)

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