3boiler Steam Water Chemistry in Power Plants - Copy

8/11/2019 3boiler Steam Water Chemistry in Power Plants - Copy

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BOILER/STEAM WATER CHEMISTRY

IN

THERMAL POWER PLANTS(An Overview)

O.P.RANGWANI


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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

SOFTENINGPLANT

COOLINGWATER

U/GSTORAGE

TANK

RAWWATER

DRINKINGWATER

BOILERMAKEUP

C.W.MAKEUP


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COOLING WATER

Type of cooling water

Cooling water chemistry

Cooling water treatment


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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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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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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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For all ferrous feed water system, generation &transport of corrosion products magnetite,haematiteand ferric oxide hydrate occurs due to :

Corrosion

and,flow accelerated corrosionof 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 to

protect 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 FORALL 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 FEED

WATER CHEMISTRY TO AVT (O).

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

Minimize air in-leakage so that DO is


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WATER STEAM CYCLE (THERMAL

PROJECT)

D.M. WATER CST CONDENSER D/A

TURBINE STEAM BOILER

T.S.P. DOSING

HYDRAZINE

DOSING

BFP

AMMONIA

DOSING

CEP


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WATERSTEAM 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.C

THEREFORE THE CONSTRUCTION OF HAVE HIGHMECHANICAL STRENGTH AND LOW CREEP.

AT SUPER CRITICAL CONDITION THE MEDIUM IS JUST A

HOMOGENEOUS FLUID RATHER THAN WATER OR STEAM.THEREFORE USUALLY SUPERCRITICAL BOILER ARE OF ONCETHROUGH TYPE.


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ROLE OF CHEMISTRY IN POWER

PLANT

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 inview of upcoming super critical boilers


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

Make- up Consumptive Effluents

water water water

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

Improved Scheme 6075 4030 2045

Zero Discharge 4031 4030 ZEROpractically


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ATER REQMNT. AT DIFFERENT COC AT A

4x210 MW POWER STATION

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 using

side stream softeners thereby conserving water dueto reduced system blow down.

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


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3boiler Steam Water Chemistry in Power Plants - Copy

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