s-k-sharma-water-chemistry-in-thermal-power-plants.pdf

8/20/2019 s-k-sharma-water-chemistry-in-thermal-power-plants.pdf

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WATER CHEMISTRY

IN

THERMAL POWER PLANTS

(An Overview)

Presentation by

S.K.SHARMA D.G.M(CHEMISTRY)

NCPS DADRI

NTPC LTD


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WATER

• The purest available form is from water vapour inatmosphere, as rain, snow or produced by melting of ice.

• This water on reaching the ground absorbs differenttypes of gases from atmosphere like nitrogen, oxygen and

to a lesser extent carbon dioxide.

• Other gasses like ammonia, oxides of nitrogen andsulphur etc. ,also dissolves during rain depending upon thepollution level of the atmosphere.

• Apart from this, the surface water travels to variousplaces and catches organic matter, suspended solids etc.


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SOURCES OF WATER

1. Rivers, lakes and reservoirs (surface drainage water)

2. Underground water (shallow well, deep well, springs)

3. Rain water

4. Sea water

5. Snow melting


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WATER SUPPLY

SEA 95-96%

FROZEN WATER 2% FRESH WATER 2-3%

•Fresh water available is scarce.

• We, the human beings, are bent upon polluting this preciousresource.

• Imperative to take proper care to conserve and reuse water.


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MAIN IMPURITIES IN WATER

1. Suspended (Macro size) - Sand, dirt, silt. This contributesturbidity to raw water.

2. Colloidal - Micro size particles(1-100nm)

3. Dissolved form - Alkaline salts and neutral salts, organic

matter,• Alkaline salts are mainly bicarbonates rarely carbonates

and hydrates of calcium, magnesium and sodium.

• Neutral salts are sulphates, chlorides, nitrates of

calcium, magnesium and sodium.


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TYPES OF WATER IN THERMALPOWER PLANT

• Cooling water

• Boiler water

• Process water

• Consumptive water


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• Pretreatment of raw water

• Filter water for softening & DM plant

• Ultra pure /demineralised water for boiler makeup/steam generation

• Cooling water system.

• Monitoring of steam/ water parameters & H.P./L.P. Dosingsystems

WATER TREATMENT IN POWER PLANT


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WATER FLOW DIAGRAM

CLARIFLOCCULATOR

GRAVITYFILTER

D.M.PLANT

SOFTENING

PLANT

COOLINGWATER

U/GSTORAGE

TANK

RAWWATER

DRINKINGWATER

BOILERMAKEUP

C.W.MAKEUP


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PRE-TREATMENT

Pre-treatment takes care of organics, suspended matter andcolloidal silica to some extent.

CLARIFLOCC

ULATORGRAVITY

FILTER

D.M.PLANT

SOFTENING

PLANT

U/G

STORAGE

TANK

RAW

WATER

ALUM & Cl2


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CLARIFLOCCULATOR

Raw

water

Chlorine Alum

Lime Flash

Mixer

Clarification

Sludge

settling

pond

Clarified

water to

filters

Flocculation

Water quality at Clarifier outlet

Turbidity -


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DISINFECTION

Disinfection is destruction of Pathogenic bacteria, virus,germs and other organisms present in water.

It can be achieved by

• Gaseous chlorine

• Chlorine compounds such as hypo-chlorites, bleachingagent and chlorine dioxide

• Ozone• Ultra-Violet radiation

• Hydrogen peroxide

• Heating

• Combination of the above


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FILTRATION

Removal of solid particles from water by passing it througha filtering medium.

Filtration is usually a mechanical process & does notremove dissolved solids.

Filters are mainly of two types.

1. Pressure Filters - steel, wood or concrete containersthat are open at the top and function at atmosphericpressure.

2. Gravity filters - closed, round steel shells and function

with the pressure of the incoming water.


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GRAVITY SAND FILTER

Clarifiedwaterfromclarifier

IN

OUT

5th layer

4th layer

3rd layer

2nd layer

1st layer

Gravity Sand Filter

For back washing ofthe GSF water ispassed throughfilter in reversedirection


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D.M. PLANT

WEAK

ACID

CATION

STRONG

ACID

CATION

ACF

WEAK

BASE

ANION

STRONG

BASE

ANION

MIXED

BED

DEGASSER

D.M.

WATER

STORAGE

TANK


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COOLING WATER CHEMISTRY

• To avoid scale formation

• To control corrosion

• To control micro biological growth

• To control vaccume in condenser


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INTRODUCTION

Circulating Water chemistry is maintained primarily tocontrol

-- Corrosion

-- Inhibit scale formation

-- To minimize micro-organism growth in condenser tube orin cooling water system.


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SCALE FORMATION

• scale formation can take place in condenser of thermalpower plants. This may lead to higher back pressure incondenser which in turn lead to loss in condenser vacuumthat causes loss of turbine efficiency resulting in higherheat rate than designed resulting in direct energy loss.


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TYPES OF COOLING WATERSYSTEM

• Once through cooling system

• Open recirculation cooling system

• Closed cycle cooling water system


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COOLING WATER TREATMENT

• Softening plant for make up as soft water withchlorination

• Chemical treatment for scale inhibition and corrosioncontrol

• Acid dosing with chlorination


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MICROORGANISM FOULING

Micro organism growth in cooling water systemleads to choking of C.W. pumps strainers andcooling tower fills which reduce effective surfacearea for cooling and desired cooling efficiency is notachieved which leads to higher c.w.inlet coolingwater temperature and loss of condenser vacuum.


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• CHLORINATION: This is the most practiced technique forcooling water treatment in power plants. Chlorine is apowerful oxidizing agent and reacts with the nitrogenous

part of microbial substances to form chloramines.

• Cl2 + H2O HOCl + H+ + Cl-

• HOCl H+ + OCl-

• NH3

+ HOCl NH2

Cl + H2

O (Monochloramine)

• NH2 Cl + HOCl NH Cl2+ H2O (Dichloramine)


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For all ferrous feed water system, generation &transport of corrosion products –

magnetite,haematite and ferric oxide hydrate occursdue to :

•Corrosion

•and,flow accelerated corrosion

of low & high pressure heaters,de-aerator,eco inlettubing & piping, feed water piping &drain lines

CYCLE CHEMISTRY

• Corrosion products generated flow around the cycle, depositin various areas and act as initiating centers for major failuremechanisms.

• And are often removed by chemical cleaning.


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FEED WATER TREATMENT

• AVT (R):

• Ammonia + a reducing agent

• ORP should be in the range: -300 to -350 mV,necessary toprotect mixed metallurgy systems.

• AVT (O):

• Reducing agent has been eliminated. ORP will be positive.

•The basis of either AVT treatment is elevated pH.

•Common alkalizing agent is Ammonia.


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• AVT(R): oxygen level at CEP discharge is low enough (


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FEED WATER LIMIT FOR ALL FERROUS SYSTEM.

Parameter AVT(O) AVT(R)

pH 9.2-9.6 9.2-9.6

ACC


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CONVERSION OF ALL FERROUS FEEDWATER CHEMISTRY TO AVT (O).

• Perform baseline monitoring: feed water parameters-ACC,pH, chloride, DO, Steam parameters-ACC, Na, Chloride and

silica•Minimize air in-leakage so that DO is


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WATER STEAM CYCLE (THERMALPROJECT)

D.M. WATER CST CONDENSER D/A

TURBINE STEAM BOILER

T.S.P. DOSING

HYDRAZINE

DOSING

BFP

AMMONIA

DOSING

CEP


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WATER STEAM CYCLE (GAS PROJECT)

L.P. DOSING

D.M. WATER RFT CONDENSER D/A

LP TURBINE LP STEAM LP BOILER

HP TURBINE HP STEAM HP BOILER

H.P. DOSING

HP BFP

LP BFP


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WATER/STEAM CHEMISTRY

PARAMETERS TO BE MONITORED

– pH

– Silica

– Conductivity

– After Cation Conductivity

– Dissolved Oxygen – Sodium

– Copper

– Iron

– Carbon dioxide – Chloride

– Hardness


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SUPER CRITICAL BOILER:CRITICAL PARAMETERS

• SUPERCRITICAL BOILER OERATE AT PRESSURE >203 Kg/cm2

AND TEMPERATURE IS >600 deg.CTHEREFORE THE CONSTRUCTION OF HAVE HIGH

MECHANICAL STRENGTH AND LOW CREEP.

• AT SUPER CRITICAL CONDITION THE MEDIUM IS JUST AHOMOGENEOUS FLUID RATHER THAN WATER OR STEAM.

THEREFORE USUALLY SUPERCRITICAL BOILER ARE OF ONCETHROUGH TYPE.


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ROLE OF CHEMISTRY IN POWERPLANT

Water chemistry is important to

• achieve higher operation efficiency,

• Minimize corrosion & scale formation problems and• to reduce plant downtime

High water quality standards are to be maintained, particularly in

view of upcoming super critical boilers


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•• WASTE WATER FROM A THERMALWASTE WATER FROM A THERMALPOWER PLANTPOWER PLANT


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WATER BALANCE (for 4 Units)

(all in M3/hr)

Evap. & Unaccounted loss 1665

Raw Water3040

ColonyDrinking

340 (18Hrs)

EDP1900

(3.2Hrs)

Fire Water

350

BHEL

2100

(3.5Hrs)

PlantSewage

30 (18Hrs)

GasPlant1036DADRIDADRI

THERMALTHERMAL


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TREATMENT OF WASTEWATER

CMBPump

Clarifier

Low Pressure Membrane

Technology

MF/UF System

RO 1 & 2

DM Plant

CT Makeup

To Boiler

Feed

CT Blow-down

DM Neutralizationwaste

Service waste water

Oily waste water-

post t reatment

CASE-II : RECYCLE THROUGH MEMBRANE TECHNOLOGY

Backwash

water Recycle


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ADVANTAGES OF REVERSE OSMOSISS.NO. REVERSE OSMOSIS DM PLANT

1 Continuous operation. No need forregeneration 1 or 2 regenerationreqd. Everyday

2 No need for bulk storage of acid/alkali Bulk storage required

3 No effluent treatment required Effluent treatmentrequired

4 Operating cost mainly power,cartridge filter replacement andmembrane replacement

(Low operating cost except cost ofmembrane)

Operating cost mainlypower, cost ofchemicals & cost of

resin

(Higher operating cost)

5 Excellent silica removal Good silica removal


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Expected Reduction of Effluents &makeup water for a 1200 MW station

Make- up Consumptive Effluentswater water water

(cum/Hr) (cum/Hr) (cum/Hr)Conventional 9925 4030 5895

Improved Scheme 6075 4030 2045

Zero Discharge 4031 4030 ZERO

practically


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EXISTING SYSTEM

Regeneration waste

Filter

House

B/W sump

EDPPUMP

HOUSEDM plant

CWSystem

Softening

plantSettlingpit

DMwater

Effluent pit

For Horticulture& Gardening., AHP, CHP

Make Up

RESERVOIR

A/C COMPRESSOR COOLING

ClarifiersClarifiers

Blow down


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RO

PROPOSED SYSTEM

EDPPUMP

HOUSE

CWSystem

SEWAGE

TREATMENT

ULTRAFILTRATION

BHELPUMPHOUSE

ClarifiersClarifiers


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WATER REQUIREMENT AT DIFFERENTCOC

COC EVOPORATION

LOSS

M3/HR

DRIFT

LOSS

M3/HR

BLOW

DOWN

REQD

M3/HR

TOTAL

MAKE UP

REQD

M3/HR

2 1800 50 1850 3700

3 1800 50 925 2775

4 1800 50 617 2467

5 1800 50 463 2313

6 1800 50 370 2220


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CONSERVATION OF WASTE

• Operate CW system at COC of 7.0 to 8.0 by usingside stream softeners thereby conserving water

due to reduced system blow down.

• Adopting new Technologies i.e RO (ReverseOsmosis) in combination with Mixed bed ion

exchanger.


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s-k-sharma-water-chemistry-in-thermal-power-plants.pdf