Doc - 07 Water Systems

7/27/2019 Doc - 07 Water Systems

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LARSEN & TOUBRO LIMITED EPC POWER

TRAINING MANUAL

PROJECT 388.5 MW Combined Cycle Power Plant DOC No. IBDC/ L&T/ VCCPP/ 07

DOC. TITLE Water Systems Page No. Page 1 of 43

Water systems

Introduction:

Today, large power plants are usually designed as forced-circulation steamgenerators. In this type of steam generators, the water is evaporated andsuperheated in direct circulation.

Two measures are taken today to minimize the quantity of corrosion products andprecipitation of salts when the steam-solubility is exceeded: Demineralization systems are used for treatment of make-up water to

compensate for losses in the water/steam cycle. Condensate polishing plants are used to continuously remove salts and corrosion

products from the water/steam cycle.

Apart from water for internal heat transfer within the power plant, also cooling wateris required for temperature reduction to condense the steam in the turbine

condenser. Depending on the power plant site, open-circuit cooling or closed-circuit

cooling systems with or without evaporation are possible. Which cooling watertreatment methods are applied depends on the chosen type of cooling system.Another important aspect is preventive maintenance work to be carried out on the

water side in order to ensure economically efficient operation and to eliminatechemical influences on components, operation and availability of a power plant as faras possible.

The schematic diagram in the Figure below illustrates the integration of the watertreatment systems into a large power plant process.

Arrangement of water treatment systems in the power plant


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Natural water:

In the course of its natural circulation process, water absorbs various substances.Without undergoing special treatment it can thus be used in power plants only for

once-through cooling. If used for other purposes, the substances contained in thewater may cause damage to components and systems. Thus it is absolutely

necessary that the water is subjected to suitable treatment.

Classification of the natural types of waterThe water occurring in nature is classified according to its origin. For use in power

plants, however, only water is significant that is available at the respective powerplant site in large quantities:1. Water from precipitation of any type, e.g. rain, snow.

2. Groundwater, natural spring water, well water.3. Surface water

Surface water includes all surface water bodies, in distinction to subterraneous water

bodies.

This includes: flowing water: rivers, creeks, canals,

stagnant water: lakes, ponds; cooling, treatment and storage facilities,

seawater.

Water Systems at Power PlantWater is used at many places in the power plant for different purposes. Use of waterin the power plant includes: supply of the water/steam cycle with feed water via the demineralization plant, supply of the turbine condenser with cooling water (open-circuit cooling) or of the

closed cooling water circuit with make-up water, supply of the service cooling water system with make-up water, fire-fighting water,

service water for general technical use, and potable water for consumption by the staff, for staff facilities etc.

Procurement and cleaning of waterFigure below shows schematically the arrangement of the water procurement,treatment and distribution system.


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water filtering plant

storage

basins

Water treatment and supply system (diagrammatic illustration)

Cleaning of the raw water between the water source and the storage basin is carriedout by mechanical filtering.

Figure below shows the system of a mechanical filtering plant. It consists mainly ofthe coarse and fine screens and sieve belts or sieve drums, the cooling water pumpsand the concrete structure.

bulkhead

coarsescreen

road

bulkhead

finescreen

beltsieve

bulkhead

pumps

electricalsystems

Mechanical filtering plant

A cleaning device is used to clean the bar screens of impurities. Downstream of the

bar screens, the automatically operated sieve belts or sieve drums with a mesh sizeof < 1mm are arranged. Velocity of the water flow in the intake construction is 0.5 to1.5 m/sec. Cooling water pumps are employed to transport the water to thecondenser.

During the necessary inspections and repair measures, the individual plant parts canbe shut off by bulkheads.


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River Water System at Vemagiri

The source of raw water for the Vemagiri Plant is the river Godavari at about 8 km.from the plant site. The function of river water intake system is to draw water fromthe river and supply river water to plant raw water reservoir by intake pumps.The river water intake system consists of two x 100% vertical river water intakepumps (one working + one standby), about 8km long transfer piping and one rawwater storage reservoir in two compartments. The raw water storage reservoir is of 2

Lakh m3 capacity (equivalent to 15 days storage), located inside the plant boundary.The river water intake pumps are housed in the river water pump house, which islocated at the river water intake point. The river water pumps are installed in

separate chambers, with coarse screens/trash racks and stop-logs which is locatedoutside the pump house.Provision is made for isolation of individual river water pumps for maintenance. Riverwater pumps are of the vertical turbine type provided with expansion joints,

motorized butterfly valves, and necessary fittings on individual pump discharge lines.Capacity of the River water intake is equal to 110% of plant water requirement. Theriver water pump set is capable of permitting back flow of water from the otherrunning pump in the event of tripping of the pump for a short duration of time

(about 5 minutes).

System Control:

(i) Each pump will be provided with start / stop facility and start/stop and trip

indication on the PLC based control panel at River Water Intake Pump House.(ii) Auto changeover of river water intake pumps when running pump trips anddischarge header pressure is low.(iii) Each pump drive will be provided with one stop push button (PB) at field (near todrive), which will be lockable in stop position. This PB will be treated as EmergencyStop and will trip the drive whenever this PB is activated. In addition to above, the

following interlocks & protections have been provided:

Low level signal in the well will be provided in the PLC for alarm & startpermissive of pumps.

Low Low level signal will be provided in the PLC for tripping of pumps.


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Low Pressure switch at the common discharge header of pumps for alarm

indication at PLC.Further, following instruments have been provided for indication purpose:

One discharge pressure indicator for each pump Level transmitter for river water intake well for indication of level at the PLC

Flow orifice with flow transmitter, flow totalizer on the river water intake pumpdischarge header for flow measurement and indication in PLC.

Motor winding temperature detector and dial type bearing temperatureindicators with alarm contacts, where the drive motors of the pumps are HT

motors.River water intake system will be interfaced with the plant DCS through serial link.

Substances contained in waterDepending on its origin, water contains various substances, which - depending on

the intended use - must be removed by a suitable water treatment plant. During itsnatural circulation process - evaporation, clouds, precipitation, groundwater, rivers,

sea and again evaporation - water is impured by a variety of foreign matter, bothdissolved and undissolved substances. From the air, rain water absorbs the gases

nitrogen, oxygen, carbon dioxide and other gaseous, liquid and solid impurities (e.g.dust). When getting into contact with the ground surface, rainwater absorbs solidand dissolved substances. Particularly salts are dissolved by water as it penetratesthe soil and rock layers.

Undissolved visible substancesThese are coarse or fine disperse substances (disperse - solid matter that is

dispersed in water). The undissolved solid substances can either be organic orinorganic. Inorganic impurities are e.g. dust or sand, organic impurities e.g. leaves,branches etc. Undissolved solid particles have a size of more than 10-5 cm indiameter.

Undissolved solids are categorized into three groups:1. floating matter: density lower than the density of water,2. suspended matter: density approximately equal to the density of water,

3. settling matter: density higher than the density of water.

Undissolved invisible substancesThese are colloid-dispersed substances. Substances with particle sizes ranging from

10-5 to 10-7 cm are referred to as colloidal particles. In natural water, humic acidsand silicic acid occur as colloid-dispersed matter.

Silicic acid, for instance, is constituted of finest particles of quartz sand that arecolloidally dispersed in water.

Examples of undissolved, invisible substances are

microorganisms, phosphates, humic acids (frequently in marsh areas).

Dissolved invisible substances

Genuinely dissolved particles occur in particle sizes below 10-7 cm.The raw water at the power plant water intake structure contains a number ofchemical compounds in dissolved state, which can be categorized into certain

groups:a) hardening constituents e.g. Ca(HCO3)2, CaSO4),

b) neutral salts (Na2SO4, NaCl)


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c) silicic acid (SiO2)

The water that occurs naturally is referred to as untreated water; after having

undergone conditioning for human consumption it is called potable water. Watertreatment technology deals mainly with the following dissolved constituents.

Untreated watercations: calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), etc.

anions: chloride ( Cl-), sulfate (SO42-), nitrate (NO3

-), hydrocarbonate (HCO3-),

silicic acid SiO2-)

gases: oxygen (O2), carbon dioxide (CO2)

Hardness of water

A special group of dissolved minerals are the salts of the alkaline earths calcium,magnesium, barium and strontium, which are referred to as hardeningconstituents. In most types of natural water, however, only the salts of calcium andmagnesium do occur. According to the International System of Units (SI), the

hardening constituent content of water is no longer expressed in dH but in mmol/l,as sum of the calcium and magnesium ions1dH corresponds to 10 mg CaO/l

1 mmol/l corresponds to 40 mg Ca++/l or 23.3 mg Mg++/lIf a certain water contains a lot of hardening constituents, it is called hard water; ifthe opposite is true, viz the calcium and magnesium content is low, it is called softwater.

A distinction is made between carbonate hardness which is also referred to astemporary hardness and the non-carbonate hardness which is also referred to aspermanent hardness.

Carbonate hardness

Carbonate hardness is caused by carbonates and hydrocarbonates of Ca++ and Mg++.Carbonate hardness is caused by naturally occurring limestone, marble and chalk, allof which consist of calcium carbonate, and are dissolved in carbonic-acid containingwater. Carbonic-acid containing water results from the balance that is achieved in

the reaction of dissolution of carbon dioxide contained in the air in water:H O CO H CO2 2 2 3+

In this reaction the calcium carbonate which is almost insoluble in pure water is

dissolved, thus producing calcium hydrocarbonate:CaCO H CO Ca HCO3 2 3 3 2+ ( )

However, in order to keep the carbonate hardness in dissolution, a certain surplus ofcarbonic acid is necessary. When the carbonic acid is removed, e.g. by heating,carbonate hardness can no longer be maintained in a dissolved state and calcium

carbonate precipitates:

Ca HCO CaCO H O COC

( )3 250

3 2 2 + +>

When this process occurs in a boiler or at hot heat exchanger surfaces, deposits ofboiler scale occur, viz deposits with poor thermal conductivity. By this, a part of the

hardness is removed from the water. On this process also the designation"temporary hardness" is based. In power plant operation it is thus necessary toremove carbonate hardness to a large extent or even completely from the water byimplementing suitable decarbonization methods.

Figure below illustrates the concept: total hardness = carbonate hardness + non-carbonate hardness.


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Types of hardness of untreated water

Non-carbonate hardness

Non-carbonate hardness includes all salts of Ca++ and Mg++ except for carbonatesand hydrocarbonates, like, chlorides [CaCl2, MgCl2]

sulfates [CaSO4, MgSO4]

nitrates [Ca(NO3)2, Mg(NO3)2]

This permanent hardness cannot be removed by boiling the water.

Salts, acids and conductivityHigh-purity water practically does not conduct electricity. Only when it containsdissolved salts is water capable of conducting electricity which can be proven by

conductivity measurement.Substances which provide water with the capacity to conduct electricity are referred

to as "electrolytes". Acids, bases and salts are electrolytes.

Electrolytical dissociation and formation of ionsIn aqueous solution, acids, bases and salts tend to dissociate into electrically chargedparticles, one of which shows an excess of electrons (negative charge) and the other

a shortage of electrons. Inversely charged particles emerge which are referred to asions. The solution as a whole continues to be electrically neutral towards the outside.When direct current is put on the solution, the ions carrying a negative charge moveto the positive anode, that is why they are called anions. The positively charged

ions, the so-called cations, move to the negative cathode. The charge of the ion -positive or negative - and the number of charges are stated by plus or minus signs.


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Examples:

1. Acid: hydrochloric acid HCL H CL ++

2. Base: calcium hydroxide Ca OH Ca OH 2

2

22

+ + +( )

3. Salt: sodium chloride NaCl Na Cl ++

Acids

The oxides of nonmetals disolved in water form acids. A part of the nonmetals isgaseous. Nonmetals are, for instance, the elements carbon, sulfur, nitrogen,chlorine, phosphorous. When a nonmetal bonds with oxygen, a nonmetal oxide iscreated.

C + O2 CO2 (carbon dioxide)

2 S + 3 O2 2 SO3 (sulfur trioxide)

2 N2 + 5 O2 2 N2O5 (nitrogen pentoxide)

Nonmetal oxides react with water and form acids. For this reason, nonmetal oxidesare referred to as acid anhydrites. "Anhydrite" means "without water".

CO2 + H2O H2CO3 (carbonic acid)

SO3 + H2O H2SO4 (sulfuric acid)

N2O5 + H2O 2 HNO3 (nitric acid)

The acid solutions conduct electricity because the acid has dissociated into ions. Inaqeuous solution it dissociates into positive hydrogen ions and the negative acid partassociated with the acid.

Acid Positive hydrogen Negativeion (cation) acid part (anion)

H2CO3 2 H+ + CO3

- -

H2SO4 2 H+ + SO4- -HNO3 H

+ + NO3-

Apart from the already mentioned "oxygen acids", viz such acids that contain oxygen

in the anion, there is another type of acids. It occurs by direct bonding betweencertain elements and hydrogen and releases also hydrogen ions in aqueous solution

H2 + Cl2 2 HCl ( hydrochloric acid)

H2 + S H2S (hydrogen sulfide)

Dissociation of the acid:

Acid Positive hydrogen Negative

ion (cation) acid part (anion)HCL H+ + Cl-

H2S 2 H+ + S- -

According to the characteristic feature of releasing hydrogen ions, an acid is definedas those compounds that give rise to hydrogen ions in aqueous solution.


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Alkaline solutions (alkalis, bases)

The oxides of metals, dissolved in water, form bases. Metals are, for instance, theelements sodium, potassium, calcium, magnesium. When a metal unites with

oxygen, a metal oxide is created.4 Na + O2 2 Na2O sodium oxide

4 K + O2 2 K2O potassium oxide

2 Ca + O2 2 CaO calcium oxide

Because of their ability to react with water and form bases, metal oxides are referred

to as base anhydrites.Reaction of metal oxides with water:

Na2O + H2O 2 NaOH sodium hydroxide caustic soda lye)

K2O + H2O 2 KOH potassium hydroxide (caustic potash sol.)

CaO + H2O Ca(OH)2 calcium hydroxide (lime hydrate)

Aqueous solutions of bases conduct electricity because the base has dissociated intoions. In aqueous solution it has dissociated into the positive metal ion and the

negative hydroxide ion OH-.

NaOH Na+ + OH-

KOH K+ + OH-

Ca(OH)2 Ca++ + 2 OH-

In analogy to the acids, there is another type of alkaline solutions. It is formed bydissolution of various chemical compounds, e.g. ammonia (NH3) or hydrazine (N2H4)in water, and releases also hydroxide ions.

NH3 + H2O NH4OH ammonium hydroxide

N2H4 + H2O N2H5OH hydrazine hydroxide

Dissociation of the base:

NH4OH NH4+ + OH-

N2H5OH N2H5+ + OH-

According to the characteristic feature of hydroxide ion release, a base is defined as

those compounds that give rise to hydroxide ions in aqueous solutions:

NeutralizationWhen an acid reacts with a base in aqueous solution, the hydrogen ions of the acid

react with the hydroxide ions of the base to produce water which is dissociated onlyto an extraordinarily small extent. The reaction between the anion of the acid andthe cation of the base gives rise to a salt. Since the acid constituents of the acid

(hydrogen ions) and the alkaline constituents of the base (hydroxide ions) neutralizetheir effect mutually, the solution is neutral when equivalent (chemically equivalent)quantities of acid and base are available in the solution.

H+ + OH- H2O

H+Cl- + Na+OH- H2O + Na+Cl-

H2+SO4

- + Ca++(OH)2 2 H2O + Ca++SO4

--

Salts

Salts are the third group of electrolytes. Salts consist of a cation and an acid part asanion. In principle, it is thus necessary in any case that an acid is involved in theformation of salts. The cation may either be contributed by a base or directly by a

metal.


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When a metal is being dissolved directly in acid, hydrogen is released during the

process of formation of salts. The designation of the salts is based on the name ofthe acid part.

Acid Designation of the salts

HCl chloridesH2SO4 sulfatesHNO3 nitratesH2CO3 carbonates

Some examples for the formation of salts are:

Acid Base or metal Salt Designation

HCl + NaOH NaCl + H2O sodium chloride

2 HCl + Ca(OH)2 CaCl2 + 2 H2O calcium chloride

2 HCl + Fe FeCl2 + H2 ferrous chlorideH2SO4 + 2 NaOH Na2SO4 + 2 H2O sodium sulfate

H2SO4 + Mg MgSO4 + H2 magnesium sulfate

HNO3 + KOH KNO3 + H2O potassium nitrate

H2CO3 + Ca(OH)2 CaCO3 + 2 H2O calcium carbonate

When salts are dissolved in water, the water conducts electricity because the saltsare dissociated in positive ions (cations) and negative acid parts (anions).

Salt Cation AnionNaCl Na+ + Cl-

CaCl2 Ca++ + 2 Cl-

Na2SO4 2 Na++ + SO4

-

MgSO4 Mg++ + SO4

-

KNO3 K+ + NO3

-

CaCO3 Ca++ + CO3

--

pH-value

The degree of alkalinity or acidity of a solution depends on the concentration ofhydrogen ions (CH

+) or hydroxide ions (COH-). Ion concentrations are expressed in

mol/l. This interrelation is also referred to as ion product of water. A solution isneutral if equal quantities of hydrogen ions and hydroxide ions occur in a solution.

Considering the interdependence of hydrogen ion and hydroxide ion concentrations,the product of which is constant, the hydroxide ion concentration is also given bystating the hydrogen ion concentration. The strength of an acid or base can beexpressed by the H+ or OH- concentration. For practical reasons, the hydrogen ion

concentration is stated not in negative decimal power mode or decimal figures but ashydrogen ion exponent. This value is referred to as "pH".

Measurement of pH is almost exclusively made by means of physical/chemicalmethods with electrical pH measuring instruments.The following examples are to give a general idea of the significance of pHmeasurement in the power plant: determination of the pH in neutralization of waste water from demineralization,

condensate polishing and FGD waste water; control of lime/limestone proportioning in the flue gas desulfurization plant via

the pH; monitoring of cooling water for pH; monitoring of waste water for pH.


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pH indicators

pH indicators are organic compounds which show a different color, depending on thepH, i.e. the hydrogen ion concentration. The change of color occurs in a narrow pH

range. Color may change from colorless to color (or vice versa) or from one color toanother color.

The most common indicators used in the power plant include phenolphtalein andthe composite indicator Cooper. Another indicator is litmus. By means of litmus it isquite easy to determine whether we are dealing with an acid or with a base. Litmusis colored red by acids and blue by bases.

Indicator pH of change color inacid solution alkaline solution

Phenolphthalein 8.2 colorless redCooper indicator 4.3 red blue-green

For precise pH measurement, however, electrical instruments of suitable design are

required.

Measurement of conductivityFor determination of the salt content of liquids, the method of conductivitymeasurement is used. It is a reliable method that is easy to handle to get an

overview of the salt concentration.The applicability of industrial conductivity measurement is mainly limited to low-concentration solutions of salts, acids or bases. In such solutions there is a linearinterrelation between conductivity and concentration. Unambiguous results are

obtained in the power plant where determination of salt content in boiler feedwater,condensate and steam is important.For operation of a steam power plant with condensation it is important to know

whether undesired ingress of salts, acids or bases occurs which may cause damageto the steam boiler or form deposits on the turbine blades.

Here, the total of ions is of interest which may result in an increase of conductivity inthe steam/condensate cycle, no matter which type of ions are present.

A List of impurities found in water, their effect and method of removal is tabulatedbelow.

Sr.No.

Impurities Effect Method of removal

1 Turbidity or S.S. clog pipelines & equipment,can choke ion exchangeresin

Coagulation, Settling &filtrations.

2 Color Indication of organic Coagulation, Settling & by

activated carbon filter.

3 Organic matter Can foul the ion exchange

resin

Coagulation, Settling, filtrations

& super chlorination.4 Iron Corrosion deposits Coagulation, Settling &

filtrations.

5 pH High & low both pH caninduce corrosion

Ion exchange, addition of acidor alkali.

6 Hardness Scaling Ion exchange, lime soda.

7 Sodium High concentrationincreases corrosion rate

Ion exchange through cation

8 Bicarbonates ,carbonate , &Hydroxide

Corrosion, foaming,carryover.

Ion exchange, degasification.


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alkalinity

9 Sulphate Scaling if associates withcalcium

Ion exchange, Reverse osmosis.

9 Chloride Corrosion Ion exchange, Reverse osmosis.10 Nitrate Normally not found in raw

waterIon exchange, Reverse osmosis.

11 Silica Scaling & deposition Ion exchange.

12 Carbon dioxide Corrosion Degasification, deaeration.

13 Oxygen Corrosion deaeration , addition of

chemicals


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Water Purification:

Mechanical methods of purification

Removal of coarse-disperse substances (undissolved, visible particles)Treatment of raw water for cooling water purposes aims at removing coarse-disperse

impurities and can be effected by mechanical purification methods.Removal of coarse impurities, which include floating, suspended and settling matter,is carried out in screen, strainer, settling and filter systems.For removal of very coarse floating or suspended matter (driftwood, branches,

plants), which is exclusively contained in surface waters, coarse or fine screens orstrainer systems (cage, belt, drum-type strainer systems) are used. For finerimpurities, in general filter plants are used.The suspended particles are retained by the filter. Usually quartz rubble is used asfilter material in water treatment technology.

In the course of time every kind of filter clogs, and this the more rapidly, the heavierthe filter bed is polluted with retained matter.

When clogging, which is manifested by an increase of head loss, reaches an upperlimit, the filter must be backwashed. As a criteria for backwashing, often a head loss

of 0.5 bar is established.

Backwashing is carried out in two stages:a) combined air-water flushing, with air and water at the same time,

b) rinsing with clear water, until the backwashing water is clear.

Backwashing is carried out from the bottom to the top. Sampling establishes whether

part of the rubble is as well removed or not.

Removal of colloid-disperse substances (undissolved, invisible particles)Not all constituents can be removed by filtering in rubble filters, e.g. the salts

genuinely dissolved in water. Between the substances that can be filtered and thedissolved salts, there is another group of chemical compounds called colloids.Decisive for the designation of the constituents is their respective degree of

dissolution in water, viz the diameter of the particles.By means of flocculation it is possible to transform the colloidal matter that canonly be filtered with difficulty, into filterable matter. The essence of the flocculationprocess is that flocculating chemicals are added to the water, which cause thecolloidal matter to agglomerate and thus to become filterable. The overall process offlocculation can be broken down into three partial processes which occur

consecutively:1. Neutralization of similar electrical charges of the particles. The similarity of

charges causes repulsion forces between the particles which prevent

agglomeration of the particles. By neutralizing the similarity, the repulsion forces

are reduced.2. Formation of microflakes.3. Formation of macroflakes by agglomeration of the microflakes.

The flocculation method is used for removal of colloidal particles, phosphate andbiological impurities from the water. Ferric chloride and aluminum sulfate are used asflocculating agents, e.g.FeCl H O Fe OH HCl3 2 33 3+ +( )

The hydrochloric acid arising from this process is neutralized by the carbonatehardness. In the most simple form of the process, ferric chloride is added in thewater-bearing pipe. The flow of water ensures a good mixture with the water. After a


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reaction section, the arising flakes are separated from the water by means of rubble

filters.

Removal of disperse undissolved substancesMechanical filter methods are also used in the field of condensate treatment. Since

the particles to be removed are much smaller than in case of raw water treatment,apart from pressure filters with activated carbon or hydroanthracite as filter bed, alsocartridge filter with or without precoating are used. As is the case with rubble filters,also cartridge filters can be backwashed; however, in case of the cartridge filters

backwashing is carried out only by means of water washing. Figure below gives aschematic diagram of an alluvial filter system.

Schematic diagram of an alluvial filter system

Upon backwashing, the actual filter layer, i.e. the precoating, is applied on the filter

elements. The precoating, prepared in an open tank as a 3% suspension of the filteraid, must be applied in an equal thickness all over the filter elements. By means of arecirculation pump, the flow rate of which is adjusted to the filter capacity, this

suspension is recirculated through the filter until the water is clear. Then the filteroperation is started without interrupting the flow. The medium to be treated entersthe tank in the center, flows through the filter element and leaves the filter through

a collecting line.Magnetic filters are a special type of filters, which remove magnetite (Fe3O4) from

the condensate by means of an electromagnet. The medium to be purified flows

through the filter from the bottom to the top. The magnetic field of the outer coilsmagnetizes the spherical elements accommodated by the inner filter vessel whichthus are able to retain the iron particles dissolved in the medium flowing through the

filter vessel. With the electromagnet switched off, the magnetite can be removedfrom the filter by means of backwashing.


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Chemical methods (removal of genuinely dissolved matter


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slurry of solid Ca(OH)2 - with the water to be decarbonized, a whirl chamber is

arranged at the inlet of the reactors, which is entered by the water in tangentialdirection.

Upon completion of the chemical reaction, the water leaves the reactor more or less

clear and is led through rubble filters for a possibly required secondary purification .

Slow decarbonizationIn case of the slow decarbonization, the CaCO3 arises as sludge. This method is

frequently used in combination with flocculation as indicated by the figure below.

This process is thus also referred to as flocculation-precipitation method. Thechemical reaction and the clarification of the water are carried out in suspendedmatter contact system, the design of which may vary widely. Reaction and retentiontime of the water to be treated are of high importance for the efficiency of such a

system.

Schematic representation of a flocculation decarbonization system

The advantages of the fast decarbonization method, such as small reactor, reactionproducts arising in solid form, low water loss during removal of the reactor mass

cannot be counted on in case of all waters, since waters with a high suspendedmatter content, exceedingly high magnesium hardness or high phosphate contentexert a negative influence on the separation process in the reactor.


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Raw Water System at Vemagiri

The source of the raw water for the plant is river Godavari. The Raw water analysis is

as below.Sr.No.

Parameter Unit as CaCO3 Analysis result

1 Calcium mg/lit as CaCO3 78

2 Magnesium mg/lit as CaCO3 72

3 Sodium mg/lit as CaCO3 80

4 Potassium mg/lit as CaCO3 0

5 Total Cat ion mg/lit as CaCO3 230

6 Bicarbonate mg/lit as CaCO3 132

7 Carbonate mg/lit as CaCO3 24

8 Chloride mg/lit as CaCO3 60

9 Sulphate mg/lit as CaCO3 14

10 Nitrate mg/lit as CaCO3 0

11 Total anion mg/lit as CaCO3 21212 Silica mg/lit as SiO2 25

13 Iron mg/lit as Fe 0.8

14 pH 8.5 to 9.0

15 T.D.S. Mg/lit as CaCO3 250

16 Turbidity NTU 1 to 200

17 Conductivity uS/cm

Raw Water Pre-treatment:

Raw Water Clarification system at Vemagiri

The function of the raw water pre-treatment system is to treat raw water availablefrom river water intake system and supply the clarified water for various plant

consumptive uses like makeup to the cooling water system, fire protection system,service water system (air-conditioning & ventilation system and miscellaneous


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services) and to supply the clarified water to the water treatment (DM) plant which

in turn will meet the filtered water and DM water requirements of the plant.The pre-treatment plant consist of two clariflocculators one for producing clarified

water to be used for CW make-up, fire protection, service water system (airconditioning & ventilation system and miscellaneous services) requirement and the

other for producing clarified water to be fed to Water treatment Plant for producingDM water as power cycle make up. The other components of the system areseparate clarified water storage tanks, chemical dosing system for individualclariflocculators, common sludge handling system with sludge thickener, centrifuge

etc.

Raw water from raw water reservoir is pumped to the individual stilling chambers ofthe raw water clariflocculator and DM Plant clariflocculator by common 3 x 50%(2W+1S) raw water supply pumps for breaking the turbulence of the water.

The raw water then flows by gravity into the flash mixers of the individualclariflocculators through Parshall flume of the respective system, for measurement of

flow. Alum and lime are dosed in the flash mixers and/ or flocculation zone fromwhere the water flows by gravity into the respective clariflocculators for removal ofsuspended impurities.Both the clariflocculators are of reactivated solid contact type and polyelectrolyte isdosed in the flocculating zone of the clariflocculator to augment the flocculationprocess.

Clarified water from the raw water clariflocculator is stored in an above ground,clarified water storage tank the capacity of which is adequate to store six hoursrequirement of the system and also fire protection system water requirement as per

Tariff Advisory Committee. The tank is divided into two compartments to facilitatecleaning and maintenance.Clarified water from the DM plant clariflocculator is stored in a separate, aboveground, DM plant clarified water storage tank, adjoining the above clarified water

storage tank. The capacity of this tank is adequate to store six hours requirement ofsystem.Separate alum, lime and polyelectrolyte dosing systems are provided for respectiveclarification systems. Chlorine solution is dosed in the common discharge header of

the raw water supply pumps for destroying microbiological contaminants if any.Dosing rate of coagulant, polyelectrolyte and chlorine is to be set manually as perthe requirement.

Make-up water for the circulating water system is supplied from the clarified waterstorage tank to the cooling tower basin by gravity through pipes. Motor operated


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make-up control valves are provided in the make up water line, which are controlled

by the level controllers in the cooling tower basin. There are 2x100% service waterpumps for supplying clarified water to service water overhead tank, HVAC make-up,

and misc. services.Influent water to water treatment (DM) plant is supplied from the DM plant clarified

water storage tank by two (1W + 1S) water treatment plant supply pumps.The service water pumps, water treatment plant supply pumps, and fire protectionsystem pumps are located in a common clarified water pump house adjoining theclarified water storage tanks.

The sludge from the raw water and DM water clariflocculators are collected in acommon sludge pit and pumped by two (1W + 1S) sludge transfer pumps to thesludge treatment plant which includes one thickener and two (1W + 1S) centrifuges.

Poly dosing arrangement is provided at the inlet of centrifuge for proper sludgedehydration. Suitable arrangement for disposal of sludge into a truck has to bemade.The pre-treatment plant consists of following principal components:

Three (3x50%) Raw water supply pumps

Two stilling chambers (one each for raw water clariflocculator and DM Plantclariflocculator).

Two flash Mixers with motor driven agitator (one each for Raw waterclariflocculator and DM Plant clariflocculator)

One reactivator solid contact type clariflocculator for Raw water clarification

One reactivator solid contact type clariflocculator for DM Plant clarification

One above ground clarified water storage tank in two compartments

One above ground DM Plant clarified water storage tank

Chlorine dosing system consisting two (2x50%) vacuum solution feed tonnermounted type chlorinators and two (2x100%) capacity booster pumps for dosingat the discharge header of the raw water supply pumps. Provision for dosing the

liquid chlorine solution at the reservoir inlet has also been made.

Alum dosing system consisting of two alum solution preparation cum dosing

tanks and two (2x100%) dosing pumps each both for Raw water and DM waterclariflocculator.

Lime dosing system consisting of two solution preparation cum dosing tanks andtwo (2x100%) dosing pumps each both for Raw water and DM waterclariflocculator.

Polyelectrolyte solution dosing system consisting of one Polyelectrolyte solution

dosing tanks and two (2x100%) dosing pumps each both for raw water and DMwater clariflocculator.

One common sludge pit

Two (1W + 1S) sludge transfer pumps

One thickener

Two (1W + 1S) centrifuges

Poly dosing system consisting of one dosing tanks and two (2x100%) dosingpumps for dosing at the inlet of centrifuge for proper sludge dehydration.

Piping and valves, control and instrumentation and electrical items and

accessories

Pre-treatment system

The Pre-treatment system has been designed based on raw water quality at Vemagiriplant and turbidity of treated water at the outlet of clariflocculator not exceeding 20NTU.

Stilling chamber is sized for two minutes retention time while flash mixers for one-minute retention of inlet raw water flow.For design purpose following indicative dosage rates has been used:


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Chemicals Dosage Rates

Alum 50 ppmLime 15 ppm

Polyelectrolyte 0.5 ppmChlorine Solution 5 ppm

Hydraulic circuit is designed in such a way that the water from stilling chamber willflow to clariflocculator by gravity and clarified water will also flow by gravity toclarified water storage tank.

DemineralizationIn steam power plant operation, the significance of feedwater treatment increasesthe higher the superheated steam temperature and the pressure of the steam

generator are. In the high-pressure range, i.e. at pressures above 64 bar, steamgenerators must be operated with demineralized water. In case of once-throughsteam generators, all the water fed into the steam generator is transformed intosteam. Salts still occurring in the water would form deposits at the tube walls and

would thus cause a heat build-up.

Types of ion exchangers

Ion exchangers are insoluble resins which are used in the form of spherical particles.These are capable of taking up ions from solutions and giving off other ions to thesolution in turn. The exchange can only be carried out between ions with charges ofthe same kind. Cation exchangers thus exchange only cations, anion exchangers

only anions. This process takes place in a very short time during the contact of asolution with the ion exchanger material. A given volume of exchanger has a definedcapacity. If this capacity is exhausted, a regeneration is carried out in order to returnthe exchanger into the desired state of being capable of performing the ion

exchange.

In practice, the ion exchange process is carried out in such a way that an aqueoussolution is allowed to flow through the filter which is filled with the ion exchangermaterial, either from top to bottom or from bottom to top. In this process the ions of

the solution are exchanged against the ions of the exchanger carrying the sameelectrical charge. This process is referred to as "loading" of the exchanger.

In flow direction of the water, initially in any case the cation exchange is carried out:

Na Cl H R Na R H Cl+ + + + + +

Na+ ion to be exchangedH+ ion at the exchanger, being capable of performing the exchangeR resin

In the anion exchange stage, the acid arising from this process (HCl) is convertedinto water.

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

Cl- ion to be exchanged

OH- ion at the exchanger, capable of performing the exchangeR resin

The exchanger is loaded with the ions until the content of residual ions in theoutflowing filtrate exceeds the still admissible value.This is called "inrush" in which case we say that the ion exchanger is exhausted. Inorder to return it to an operative state, it is to be activated again. This process iscalled regeneration.


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As there are two types of ions, i.e. cations and anions, also a distinction is madebetween two types of exchangers: the cation exchanger and the anion exchanger.

Depending on the tasks that an exchanger is designed to perform, in case of thecation exchanger we differentiate between weak-acid cation exchangers and strong-acid cation exchangers,

and in case of the anion exchangers, between weak-base anion exchangers and strong-base anion exchangers.

The difference between weak-acid and strong-acid or weak-base and strong-baseexchangers is their respective active group which makes the exchange processpossible. This results in different fields of applications of the exchanger types:

weak-acid cation: only cations which are combined with HCO3

or CO

3

2;

strong-acid cation: all types of cations; weak-base anion: only anions of the mineral acids (HCl, H2SO4, HNO3);

strong-base anion: all anions, CO2, SiO2.

Weak-acid cation exchangerThe weak-acid cation exchanger is usually regenerated by means of hydrochloric acid

(HCl). The exchangeable ion is the H+ ion. The weak-acid cation exchanger is able toexchange the calcium, magnesium and sodium ions combined with hydrocarbonate

and carbonate against H+ ions. This process is a decarbonization by means of ion

exchanger. The outflowing water thus still contains all minerals except the cations ofthe hydrocarbonates.

Examples of weak-acid cation exchanger reactions:

Ca HCO R Ca R H O COHH

( )3 2 2 22 2+ = + +

Mg HCO R Mg R H O COHH( )3 2 2 22 2+ = + +

R = Resin

Since the mineral content of the treated water is reduced by the cations from thehydrocarbonates, this process step is also called partial demineralization. This

process releases carbon dioxide which must be removed in order to avoid corrosion.For its regeneration, the weak-acid cation exchanger requires a quantity of acid, theeffect of which is theoretically exactly equivalent to the amount of absorbed ions.

The actual regenerant demand is given in percent of the theoretically requiredquantity. In case of the weak-acid cation exchanger, 100% to 110% of the

theoretical quantity of HCl are required for regeneration.

Strong-acid cation exchangerThe strong-acid cation exchanger is regenerated by means of hydrochloric acid (HCl).

The exchangeable ion is the H+ ion. The strong-acid cation exchanger is able to

exchange all cations against H+ ions, thus forming the free acids of the respective

anion.Examples of strong-acid cation exchanger reactions:

KCl H R K R H O+ + 2


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MgCl R K R H OHH

2 2+ +

Na SO R R H SOHH

Na

Na

2 4 2 4+ +

Ca HCO R Ca R H O COHH

( )3 2 2 22 2+ = + + R=Resin

The regenerant demand for the regeneration process is 150% to 250% of the

theoretical quantity of HCl (in case of parallel flow regeneration), i.e. about 1.5 to2.5 times the theoretically required quantity. The lower consumption of regenerant ispossible only by means of a combined regeneration process, i.e. the excess quantityof the regenerant of the strong-acid cation exchanger is used for regeneration of the

weak-acid cation exchanger.

Weak-base anion exchanger

The weak-alkaline anion exchanger is regenerated by means of sodium hydroxide

(NaOH). The exchangeable ion is the OH- ion. The weak-alkaline anion exchanger is

only capable of exchanging free mineral acids, HCl, H2SO4, HNO3 , forming H2O. Inother words: This process is the neutralization of an acid (as a result of the cation

exchange stage!) by means of an alkaline solution (exchangeable OH- combined withthe resin). This process produces salt (anion remains absorbed by the exchanger)and water.Examples of weak-alkaline anion exchanger reactions:

HCl OH R Cl R H O+ + 2

HNO OH R NO R H O3 3 2+ +

H SO R SO R H OOHOH

2 4 4 22+ = +

R = Resin

The actual regenerant demand is 125% to 150% of the theoretically requiredquantity of NaOH.

Strong-base anion exchangerThe strong-alkaline anion exchanger is regenerated by means of sodium hydroxide

(NaOH). The exchangeable ion is the OH- ion. The strong-alkaline anion exchanger iscapable of exchanging free mineral acids, salts, carbon dioxide and silicic acid

against OH- ions.Examples of strong-alkaline anion exchanger reactions:

HCl OH R Cl R H O+ + 2

NaCl OH R Cl R NaOH+ +

CO OH R HCO R2 3+ SiO OH R HSiO R2 3+

R = Resin

The actual regenerant demand is 250% to 400% of the theoretically requiredquantity of NaOH (in case of parallel flow regeneration). Also in this case it ispossible to reduce the regenerant consumption by means of using a combined

regeneration.


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Mixed bed exchangers

A mixed bed exchanger contains a mixture of strong-acid cation and strong-alkalineanion exchanger material, which is present in a mixed state during the exchange

process. The adjacent cation and anion exchanger resin particles act like a very longchain of cation and anion exchangers connected in series. This is the basis of the

good demineralization effect of the mixed bed exchanger. The main field ofapplication of the mixed bed exchanger is its use as safety filter, which is arrangedas the final filter stage in a demineralization plant. It is to absorb the very smallamounts of cations, anions and silicic acid which still emerge from the strong-alkaline

exchanger. By using a mixed bed filter, the conductivity of the demineralized wateris reduced to values below 0.1 S/cm (0.01 mS/m). The residual content of silicicacid (SiO2) is below 0.01 mg/l.

Reverse osmosis (RO)

For untreated water with higher salt content a preliminary desalination may be madeby means of reverse osmosis. Residual demineralization to reach boiler feedwaterquality is made by means of ion exchangers. Osmosis is the separation of substancesby means of semipermeable diaphragms which allow the molecules of the solvent to

pass through, while retaining molecules or ions of the dissolved substances to a largeextent. The pressure at which equilibrium is reached is referred to as osmoticpressure. When a pressure is put on the higher concentration side, which exceeds

the osmotic pressure, the transition of the solvent occurs in reverse direction. Thisprocess is referred to as "reverse osmosis".Compared to conventional demineralization methods, viz ion exchange andelectrodialysis, reverse osmosis offers the advantage that more than 90 percent of

salts can be removed in a one-step process.Figure below shows a comparison of the waste water salt load of differentdemineralization systems, in relation to one cubic meter of clean water. A

disadvantage of the reverse osmosis method is the required preliminary treatment ofthe untreated water to ensure that the diaphragms are not being blocked by

interfering substances. This includes a good separation of solid matter, includingcolloidal impurities, prevention of fouling by chlorination and of scaling byproportioning of acid.Waste water salt load obtained by different demineralization systems

a Parallel-flow ion exchangerb Counter-flow ion exchangerc Reverse Osmosis and continuous ion exchanger


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Configuration of demineralization plants

Figure below shows some examples of possible configurations of DM plants.

Examples of the combination of exchanger stages

When a strong-acid cation exchanger is regenerated by means of sodium chloride(NaCl), it will, during the exchange process, work as a softening filter.

Demineralization Plant at VemagiriThe function of the DM Plant is to provide the demineralised water for the plant DMwater requirement. The treatment will be done in two stages filtration anddemineralization. The filtered water serves as an influent to the DM Plant and alsoused as plant potable water.The demineralized water from DM Plant is stored in DM water storage tank and used

for HRSG feed cycle make-up in the condenser, make-up in gas turbine compressorwater wash skids, CCW make-up; initial filling of HRSG and boiler feed chemicalsolution preparation.It is also used in hydrotesting, chemical cleaning; displacement flushes after cleaning

and wet storage of HRSG during commissioning.The system boundary for Demineralization (DM) plant starts from DM Plant clarifiedwater storage tank and ends at the DM water storage tank (inlet) including all plantand equipment, acid /alkali storage tank and neutralization pit outside the building.


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Filtration System

The clarified water from the DM Plant clarified water storage tank is pumped by 2 x100% (1W+1S) capacity WTP supply pumps to 2 x 100% Pressure Sand Filters(PSF). Sodium hypochlorite solution is dosed in the DM Plant clarified water storagetank to destroy organic and microbiological contaminants if any. Alum solution is also

dosed at the WTP supply pump discharge for online coagulation and subsequentremoval of suspended particulate matter in the PSF.Sodium hypochlorite dosing system consists of a storage-cum-dosing tank, 2x100%

dosing pumps and 2 x 100% sodium hypochlorite unloading pumps with theassociated piping and accessories.

Alum dosing system consists of 2x100% dosing tank and 2x100% dosing pumps with

the associated piping and accessories.The filtered water from the PSF is used as an influent to the DM Plant.A part of the filtered water tapped from the outlet line of PSF is used for backwashing of PSF and stored in the overhead filter backwash water storage tank.Another part of the filtered water is used as potable water and stored in the

overhead potable water storage tank. Both the tanks are located on the top of watertreatment Plant building.

2 x 100% capacity air blowers are provided for air scouring of pressure sand filters.

DM SystemThe DM plant consists of 2x50% streams. Each stream will consists of ActivatedCarbon Filter, Strong Acid Cation exchanger, Degasser system common to both

streams (with one degassed water storage tank, 2x100% degasser blowers and3x50% (2W+1S) degasser pumps), Strong Base Anion exchanger, Mixed Bedexchanger.


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The filtered water passes through 2 x 50% Activated Carbon filters (ACF) for theremoval of organic impurities and traces of chlorine, if present.The water is then led through 2 x 50% Strong Acid Cation (SAC) for removal of

cations. The decationised water is then passed through 1 x 100% degasser towerprovided with 2 x 100% degasser air blowers for the removal of carbon di-oxide andthe degassed water is stored in 1 x 100% degassed water storage tank. Thedegasser tower, blowers and storage tank are common for both the streams.

The degassed water is then pumped by three 3 x 50% (2W+1S) degassed waterpumps (common to both the streams) through two 2 x 50% Strong Base Anioncolumn (SBA) for the removal of anions and subsequently SBA outlet water is passed

through 2 x 50% capacity Mixed Bed (MB) exchangers for final polishing of DM waterand the polished demineralised water is then led to 2 x 50% DM water storage tank.2 x 100% capacity air blowers are provided for air scouring of ACF. Similarly 2 x100% capacity air blowers are provided for resin remixing in MB Exchanger.

Two 2 x 100% regeneration water pumps supply DM water from DM water storagetank to acid/alkali ejectors for regeneration of SBA & MB exchanger units. Degassedwater from the degassed water pump outlet will be used for regeneration of cationbed. 30% HCL and 48% NaOH will be used as regenerants.The regeneration facilities consist of 2 Nos. bulk acid storage tanks, 2 Nos. bulk alkali

storage tank, acid and alkali measuring tanks, unloading hose arrangements and 2

x100% unloading pumps for acid & alkali, ejectors for acid & alkali injection etc.Regeneration effluent from all the units, waste water from DM Plant and filters are tobe led to a common neutralization pit. The plant is designed in such a way that the

regenerant effluent from cation, anion and mixed bed units neutralise each other.Facilities for addition of acid/alkali to neutralize the effluent are also provided. Theneutralizing pit has two compartments and the active volume of each pit is at least

120% of the total waste arising from the regeneration of one complete DM Plantstream and filter back wash water. The neutralized effluent then is to be pumped tothe guard pond by means of 2 x 100% neutralized effluent disposal pumps.Morpholine is dosed by 2x100% Morpholine dosing pumps at the discharge header of

DM water transfer pumps and HRSG fill pump to correct the pH of the DM water.


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The design of each stream of DM Plant is such that in the event of one of the

streams not working / out for maintenance, the other stream shall be capable ofcatering to twice the load with two regenerations per day.

The DM plant will consists of the following components: Two (2x100%) horizontal centrifugal type water treatment plant supply pumps

One Sodium hypochlorite storage tank

Two (2x100%) sodium hypochlorite dosing pumps

Two (2x100%) sodium hypochlorite unloading pumps

Two (2x100%) alum dosing tanks with agitator

Two (2x100%) alum dosing pumps

Two (2x100%) Pressure sand filters (PSF)

One O/H filter backwash water storage tank

One O/H potable water storage tank

Two (2x100%) Pressure sand filter air blowers

Two (2x50%) Activated Carbon filters (ACF)

Two (2x50%) Strong Acid Cation exchanger (SAC)

One Degasser tower

Two (2x 100%) Degasser air blowers One Degassed water tank

Three (3x 50%) Degassed water pumps (2W+1S)

Two (2x50%) Strong Base Anion exchanger (SBA)

Two (2x50%) Mixed Bed exchanger (MB)

Two (2x100%) Mixed Bed exchanger air blower

Two (2x100%) air blower for ACF

Two (2x50%) DM water storage tank

One Morpholine dosing skid comprising one tank and 2 x100% Morpholinedosing pumps

Two (2x100%) regeneration water pumps

Two (2x100%) acid unloading pumps

Two (2x100%) alkali unloading pumps

Two bulk acid storage tanks Two bulk alkali storage tanks

Two acid measuring tanks (one for cation and one for mixed bed)

Two alkali measuring tanks (one for anion and one for mixed bed)

One alkali measuring tank for neutralization

One acid measuring tank for neutralization

Two (2x100%) Neutralized effluent disposal pumps

One Neutralization pit (with two compartments)

Piping and valves, Control and instrumentation, Electrical items and accessories

The net capacity of DM Plant has been designed based on 3% of HRSG MCR as makeup, DM water required for evaporative cooling make up plus 5% margin and DMwater required for CCW system make up, dilution water for preparation of chemicaland chemical dosing and requirement of regeneration water for ion exchange bedsper manufacturer recommendation.

Treated water quality at Vemagiri:At the outlet of Mixed Bed, the treated water quality would be as under:

Conductivity Not greater than 0.1 Micro -mho / Cm at 25oC.

pH 7.0 +_0.2 at 25oC.

Sodium Shall not be greater than 0.05 ppm


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Total Organics Nil

Iron as Fe Not detectable as per ASTM methods

Free CO2 ppm as CO2 Not detectable as per ASTM methods

Total Hardness Not detectable as per ASTM method

Total solids at outlet Shall not be greater than 0.15 ppm in which silica

shall not exceed 0.02 ppm

Operation & Control PhilosophyThe control philosophy of DM plant is such that the operation of the plant can bemonitored and controlled through a microprocessor based programmable logiccontroller (PLC). The PLC is provided with a PC based programmer station for

performing software changes.Taking the equipment into service and initiation of back washing of filters andregeneration of all the exchangers will be done manually from the control panel andbalance operation will be carried out sequentially by the PLC.

However, manual override facility for all operations has been provided.Once a filter/exchanger has been backwashed/ regenerated, it will not be put backinto service automatically, but operator will have to do manually through a selector

switch.On exhaustion of unit, the particular filter/exchanger will be completely isolated fromthe system automatically and an alarm status is displayed on the CRT screen.Complete stream will be automatically isolated from the service in case any of the

following takes place and an alarm displayed on the CRT.

On reaching high differential conductivity of effluent or on exceeding thetotalized flow of de-cationised water through cation exchanger, whichever

occurs first. On reaching higher conductivity of effluent at outlet of anion exchanger or on

exceeding the totalised flow of de-anionised water through anion exchanger,whichever occurs first.

On reaching higher conductivity of effluent at outlet of mixed bed exchanger oron exceeding the totalised flow of deionised water through MB unit or onreaching high silica content of effluent at MB outlet, whichever occurs first.

Pressure sand filter and Activated Carbon Filter will be back washed at the time of

regeneration of a stream or after every 24-hrs interval.The operator should initiate operation of regeneration/rinsing of each exchanger unitand after that the change from one step of the sequence to the next will beautomatic.

Auto-Manual operation is possible for degassed water pumps, degasser blowers, MBblowers and regeneration pumps. Auto/ Manual, selection can be done from the PLCWorkstation. Each pumps/blowers are provided with one stop push button (PB) atfield (near to drive), which is lockable in stop position. This PB will be treated as

Emergency Stop and will trip the drive whenever pressed. Local start for each pumpis directed through PLC.Although the basic operation of DM plant is semi-automatic in nature, some of the

operations like unloading & transfer of acid and alkali are manual while the transferof acid & alkali from the measuring tanks to the each exchanger units is automatic.The neutralization and transfer of regeneration effluent will be done manually.Following plant instrumentation have been provided:


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Inlet and outlet pressure indicators for vessels and discharge pressure

indicators for various pumps.

Inlet (rate of) flow indicators and outlet flow totalizers for exchanger units.

Flow switches at filter outlet. Conductivity comparator at cation outlet.

Individual outlet pH recorder-indicators, conductivity recorder-indicators foranion & MB units.

Outlet silica analyser cum recorder common for both streams and common forboth anion and MB units with multipoint recorder.

Density indicators for regenerant chemical solutions.

Level indicators and level switches with protection interlocks for filtered waterstorage tank, degassed water storage tank and DM water storage tank and

associated pumps.

Annunciation for abnormal conditions like conductivity, pH and silica levels, high flowthrough filters and ion exchange units, high and low levels in the chemical tanks,

filtered water tank, degassed water tank, DM water storage tanks and neutralization

pit are provided in the control panel.The critical parameters such as pH at MB outlet, conductivity at MB outlet, Silica atMB outlet, DM tank level can be monitored in the main plant DCS CRT through serialinterface with PLC.

Each DM water storage tank has one number on/off type inlet valve, this valve closeswhen the level in the DM storage tank reaches high high and opens when the levelreaches low. The DM water storage tank has also been provided with necessaryredundant very low level (low-low) interlocks for DM water pumps.

Water distributionThe water is distributed within the power plant site by the service water system. Theservice water system includes the necessary pumps, valves and piping to deliver thewater from the storage basin to the water demineralization plant, the fire-fighting

piping system, the cooling water systems and all other water consumers in the plant.

Potable water and Service water system at Vemagiri Plant

Potable Water System:The function of Potable water system is to supply drinking water (of filtered waterquality) to various facilities and buildings of the plant to cater to the need of theoperating personnel.

The Potable water system at Vemagiri consists of 2x100% horizontal potable watersupply pumps taking suction from a dedicated filtered water storage tank (locatedatop the water treatment plant building). The potable water supply pumps convey

the potable water to the potable water storage tanks located on suitable elevated

structures on the respective buildings. From these overhead tanks potable water iscirculated to individual Potable water distribution network within plant.

At each drinking water point, a treatment unit such as aqua guard (or equivalent)and a water cooler have been provided.


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The plant potable water pumps are located in the water treatment plant building andderive power from the WT Plant MCC. The potable water system is sized based onthe total number of personnel required for the plant and considering 45 litres ofwater per person per day.

Potable Water Pumps:The potable water pumps can be started or stopped from the DCS.Auto-Manual operation is possible for each pump. Auto/ Manual, selection can be

done from the DCS. Manual start/stop operation of each pump is possible from DCS.

Each drive is provided with one stop push button (PB) at field (near to drive), whichis lockable in stop position. This PB would be treated as Emergency Stop and will

trip the drive whenever this PB is activated. The pump is to be operated by theoperator for a pre defined period in a day.In addition to above, following interlocks & protections have been provided:

Filtered water storage tank level not low will be used as start permissive for thepotable water pumps.

Filtered water storage tank outlet isolation valve locked open condition

Low level signal from operating filtered water storage tank Auto start of pumps from low level switch in the potable water over head tank

or low potable water discharge header pressure.

Further, one discharge pressure indicator for each pump has been provided forindication purpose

Service Water System:

The function of the service water system is to supply the service water to thedifferent consumption points in the plant building, including makeup to the air-conditioning & ventilation system and other miscellaneous services.


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The Service water system at Vemagiri consisting of 2x100% horizontal service water

pumps taking suction from clarified water storage tank and the service water ispumped to the service water overhead tank, of eight (8) hours storage capacity. Thetank is located at a suitable elevation.The distribution of water to all the consumption points is by gravity, which alsocaters to the make up for air conditioning and ventilation requirements.The service water pumps are housed in the clarified water pump house.

Hose points are provided as required for cleaning floors of various buildings. Forcleaning purpose, quantity of water required at each hose point has been consideredas 10 gal/min (2.27 m3 /hr).

The service water pump capacity has been calculated considering 3 hoses inoperation simultaneously at a given point of time the and make up waterrequirement for the Air Conditioning and ventilation system.

Service Water PumpsThe service water pumps can be started or stopped from the DCS.Auto-Manual operation is possible for each pump. Auto/ Manual, selection can bedone from the DCS. Manual start/stop operation of each pump is possible from DCS.

Each drive is provided with one stop push button (PB) at field (near to drive), whichis lockable in stop position. This PB would be treated as Emergency Stop and willtrip the drive whenever this PB is activated.

In addition to above, following interlocks & protections have been provided: Level transmitter signal in clarified water storage tank will be used for

generation of alarm & start permissive of pumps in DCS. Low low level signal from clarified water storage tank for tripping of pumps. Auto start of standby pump on low level in the Service Water Overhead Tank.

Further, one discharge pressure indicator for each pump has been provided forindication purpose:

A main shut-off or isolation valve is provided within the building at the entry point of

all potable and service water supply piping.


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Cooling Water System(CW)There is a variety of power plant parts which need to be supplied with cooling water,e.g. bearings at different types of equipment and coolers for air and oil.

The most extensive cooling requirements arise from condensation of the steam in theturbine condenser. The waste heat arising from condensation is to be removed by acoolant.

There are different process types to achieve this goal. Atmospheric air is also used ascoolant for the condensation process because the required large volumes of coolingwater are not always available in unlimited quantities due to the size of thecondensing turbines and due to the growing number of power plants in limited areas.

Different types of cooling water systems are possible. We will discuss the two maintypes, direct cooling and indirect cooling.In case of the direct cooling water system, water is taken from the water source(normally a river), sent through the turbine condenser, and returned into the river asindicated in the figure below.

live steam

turbine generator

steam

generator

condensate

condenser cooling water

river Direct cooling system

In the indirect cooling water system, the water itself is cooled in a cooling towerbefore being returned into the river as shown in the figure below. A bypass of the

cooling tower is generally provided.

live steam

turbine generator

steam

generator

condensate

condensercooling water

river

air

coolingtower air

Indirect cooling system


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Auxiliary cooling water system (ACW)

The auxiliary cooling water system uses circulating water to transfer heat removedby various plant equipment heat exchangers into the main auxiliary cooling water

heat exchanger where the collected heat is transferred to the main cooling systemflow. Some examples of the various equipment giving off waste heat: electric drives, generators (ultra-pure water, hydrogen), hydraulic systems (oil coolers), sampling coolers, gland coolers, air-conditioning systems, and emergency diesel generators.

Cooling TowersFunction and types of cooling towersFor closed-circuit cooling, wet-type cooling towers use cooling water as cooling

agent. The cooling water is recirculated by means of cooling-water pumps in a circuit

between condenser and cooling tower. In case of the dry-type cooling tower, air isused as cooling agent, which - instead of the cooling water - flows through thecooling tower.

Wet-type cooling towerIn the cooling-water circuit, evaporation loss and water discharge loss are to becompensated by make-up water.The wet-type cooling tower with natural draught includes a suitably high chimney to

generate the draught. It is also referred to as natural draught cooling tower. Figurebelow shows a natural draught cooling tower.

air inlet

openings

drift

eliminator

water distributing

pipes

trickling trays

spray nozzles

water basin

Natural draught cooling tower

Distribution and spraying of the supplied water is effected by a system of gutters orpipe manifolds. They are arranged in the lower part of the cooling tower chimney in


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1 condensing turbine

2 dry cooling tower withpressing ventilator

3 condensate pump

Closed-circuit cooling with dry cooling tower (direct process)

The indirect process again works with water as intermediate agent, which, however,

does not evaporate. The water circulates within the cooling tower in a closed pipingand cooling system and can not flow freely and irrigate as in case of the wet-typecooling tower. In the indirect process with direct-contact condenser as shown in theFigure below, the exhaust steam of the condensing turbine (1) is condensed in the

direct-contact condenser (2).

1 condensing turbine

2 barometric condenser

3 condensate pump

4 cooling water pump

5 dry-type natural draught

cooling tower

Closed-circuit cooling with dry-type cooling tower and direct-contact

condenser (indirect process)

Mechanical-draught cooling towerThe quality of a cooling tower is judged by the attained cooling water temperature.

The lower air temperature and humidity are, the lower is the attained cooling watertemperature. Because of this a better cooling effect can be obtained with cold anddry air than with warm and damp air.In the mechanical-draught cooling tower, ventilation is carried out by means of

ventilators. Therefore, in comparison with natural draught cooling towers,mechanical-draught cooling towers with a sucking ventilator have only a short,constricted chimney which acts as diffuser, as shown in Figure below.


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1 ventilator

2 tower shell

3 shaft

4 drift eliminator5 water distribution

6 cooling tower fill

7 drive shaft, arranged

vertically

8 dry motor hall

9 driving system with

motor and variable-speed

gear

Mechanical-draught cooling tower with a sucking ventilator

There are also mechanical-draught cooling towers with pressing ventilators of acellular design. Depending on weather and load conditions, the ventilators of the

individual cells can be switched on or off. Thus it is possible to control the coolingwater temperature.

The advantage of mechanical draught coolers in comparison with natural draughtcooling towers is the lower space requirement. Moreover, it is possible to achievelower cooling water temperatures with the mechanical-draught cooling tower.

CW System at Vemagiri

The function of the circulating water (CW) system is to dissipate the thermal load ofsteam turbine by providing a continuous supply of cooling water to the maincondenser, vacuum pump coolers, motive water requirement for chlorination system

and for the ACW pumps to meet the requirement of ACW Heat exchanger opencircuit.A re-circulating type of circulating cooling water system with one number InducedDraft Cooling Tower (IDCT) and three 60% (2W + 1S) circulating water pumps have


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been provided. The circulating water make-up will be by gravity flow of water from

the clarified water storage tank.The CW system returns the hot circulating water to hot water return header, which

goes to the cooling tower, where the heat absorbed by the circulating water isreleased to the atmosphere. A tap-off from the CW discharge header is taken to the

side stream filters.2 x 100% Side stream filter of dual media / pressure sand filter /auto valve lessgravity filter type, are provided to control the circulating cooling water turbidity. Theside stream filter is sized based on 1% CW system flow. The side stream filters have

manual back washing facility with proper valves and back washing water supply anddisposal arrangement. The outlet filtered water is discharged in the CW fore bay.The CW pumps are located indoor inside the CW pump house. Principal components

of the CW system are:

Three x 60% vertical circulating water pumps (2W + 1S)

One mechanical Induced draft cooling tower

Two x 100% Side stream filters with back washing facility.

Two x 100% Blowdown Pumps

Cooling Tower make-up system Associated piping, valves and instruments & controls required to circulate the

water through the main condenser.

Cooling TowerThe cooling tower is of mechanical induced draft, counter-flow, multi-cell (11)construction type. The cooling tower is having reinforced concrete structure, highperformance PVC film type fill and PVC drift eliminators. The area covered by the

projected circle at 45o angle from the fan cylinder opening on the drift eliminatorplan area is not less than 80% of the drift eliminator plan area.The re-cooled cooling water temperature at the outlet of the cooling tower basin will

be 28.9C and a temperature rise across the condenser will be 8 C (approx.) atdesign reference conditions of the project.

The cooling tower basin has a storage capacity of about six (6) hours (excluding freeboard) of make-up water flow. The basin is partitioned into two compartments

complete with draining facilities, cold water outlet channel with screens and stoplogs. Axial flow induced draft type single speed motor driven fans (FRP blades). Theheat-duty of the cooling tower will be sum of condenser heat duty and the auxiliarycirculating water (ACW) system heat duty.

Circulating Water PumpsThe circulating water pumps are of indoor vertical turbine, non pull out, mixed flow,

wet pit type and motor driven with pump bowel and discharge elbow will be of CI toIS 210 FG 260, column pipes will be fabricated to IS 2062 with epoxy painting.Line shaft bearing are self lubricated type. Bearing above minimum water level shallbe either suitable for starting the pump without pre lubrication or pre lubrication tankhave been provided.


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CW ACW Pumps

1) The pump set is capable of reverse rotation due to back flow of water from the

other running pump in the event of tripping of the pump for a short duration of time(about 5 minutes).2) Each pump is been provided with Motor winding temperature detectors and dialtype bearing temperature indicators with alarm contacts.

3) The pump shall be capable of operation under shut-off conditions for duration of 5minutes4) Total capacity of two pumps shall be equal to 120 % of cooling water system

requirement.5) The pumps are capable of operating from shut-off point to a maximum flow of10% over the point of intersection between system resistance curve and pump HQcurve for single pump operation

6) Motor rating is suitable to support above operating condition at 50 Hz frequency

Auxiliary & Closed cooling water system

The auxiliary cooling water system uses circulating water to transfer heat removedby various plant equipment heat exchangers into the main auxiliary cooling waterheat exchanger where the collected heat is transferred to the main cooling system

flow.Some examples of the various equipment giving off waste heat: electric drives, generators (ultra-pure water, hydrogen), hydraulic systems (oil coolers), sampling coolers,

gland coolers, air-conditioning systems, and emergency diesel generators.


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Auxiliary Cooling Water (ACW) & Closed Cooling Water (CCW) System at

VemagiriThe auxiliary cooling water system takes cooling water from CW supply header to

ACW / CCW heat exchanger where it picks up the heat released by CCW system andreturns to CW hot return header which leads to the cooling tower return system.

The closed cooling cycle system provides cooling of various heat loads such as GTGcoolers STG coolers, lube oil coolers, sample coolers, HRSG and auxiliaries, HP/IPBFP coolers, air compressor coolers. The closed cooling water will be passivated DMwater which is circulated through the primary side of ACW / CCW heat exchanger.

DM water is used as a make up water to the system. The secondary side circulatesauxiliary cooling water.

Three CCW pumps of 50% (2W+1S) capacity circulate the DM water in a closed loopsystem through plate type heat exchangers (ACW / CCW heat exchanger). ThreeACW pumps of 50% (2W+1S) capacity are provided to circulate cooling water on thesecondary side of the plate type heat exchangers. In the secondary loop the ACWpumps draw suction from tap-off from main circulating water pump discharge header

and circulate the cooling water through the plate type heat exchangers back into thecirculating water line downstream of the condenser.The CCW pumps, the ACW pumps and the plate type heat exchangers are located inthe STG building. Make-up to the CCW system is through the CCW expansion tank

located on the roof of the STG building.

A minimum flow recirculation line for CCW pumps through an automatic recirculationcum non return valve or an automatic flow control valve controlled by a differential

pressure switch on a flow element are provided in the common discharge line.In the ACW system a control valve is provided to maintain a constant pressuredifferential between the main supply and return headers. This bypasses flow tomaintain a constant return header pressure to compensate for fluctuation in coolant

flow to the plate heat exchangers.Principal components of the ACW/ CCW system are:

Two 100% ACW / CCW plate type heat exchangers Three 50% CCW pumps (2W + 1S) Three 50% ACW pumps (2W + 1S)


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Chemical dosing system in the closed loop DM water circuit. 2x100% self cleaning type debris filter (1W + 1S) CCW expansion tank, Associated piping, valves and controls required to circulate cooling waterthrough various heat exchangers.

The CCW system is to be treated with suitable chemical dosing in the closed loop DMwater circuit to control pH and the iron level.

CCW System Recirculation Control

CCW system recirculation is controlled by modulating the control valve 1WC004V.Total flow at the CCW pumps discharge header is measured by the flow transmitter1FT-WC004V. Control Valve 1WC004V is modulated by the Controller 1FIC-WC004V.

The control loop trips to manual on high differential between the set point (SP) & themeasured signal (MV) and the control system fault.

Circulating Water Chemical Feed System & Chlorination System at Vemagiri

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