April 22, 2023 1

WATER CHEMISTRY IN POWER PLANT

BY P. SRIVASTAVA SR. MANAGER(CHEM.)

April 22, 2023 2

WATER CHEMISTRY IN POWER PLANT

WATER CHEMISTRY IS A VERY IMPORTANT

DISCIPLINE IN POWER SECTOR. TO ACHIEVE HIGHER OPERATION

EFFICIENCY AND TO REDUCE PLANT DOWNTIME, HIGH WATER QUALITY STANDARDS ARE TO BE MAINTAINED

April 22, 2023 3

WATER CHEMISTRY IN POWER PLANT

PRODUCTION OF : - --- D.M. WATER FOR BOILER MAKE-UP. --- FILTER WATER FOR SOFTENING PLANT, D.M. PLANT, DRINKING WATER AND A.C. COOLING SYSTEM. MONITORING OF STEAM/ WATER PARAMETERS H.P./L.P. DOSING. TESTING OF COAL. TESTING OF LUB OIL.

April 22, 2023 4

WATER CHEMISTRY IN POWER PLANT

CIRCULATING WATER TREATMENT POLLUTION MONITORING

– STACK MONITORING– AMBIENT AIR– WATER EFFLUENT

EFFLUENT TREATMENT PLANT COMMISSIONING ACTIVITES

April 22, 2023 5

WATER FLOW DIAGRAM

CLARIFLOCCULATOR

GRAVITY FILTER

D.M. PLANT

SOFTENING PLANT

COOLING WATER

U/G STORAGE TANK

RAW WATER

DRINKING WATER

BOILER MAKEUP

C.W. MAKEUP

April 22, 2023 6

D.M. PLANT

WEAKACIDCATION

STRONG ACID CATION

ACF

WEAKBASE ANION

STRONGBASE ANION

MIXED BED

DEGASSER

D.M. WATERSTORAGETANK

April 22, 2023 7

D.M. WATER QUALITY

pH - 7.0 ± 0.2 CONDUCTIVITY < 0.2 mho TDS - NIL SiO2 < 20 ppb

April 22, 2023 8

WATER STEAM CYCLE (GAS PROJECT)

D.M. WATER RFT CONDENSER D/A

LP TURBINE LP STEAM LP BOILER

HP TURBINE HP STEAM HP BOILER

L.P. DOSING

H.P. DOSING

HP BFP

LP BFP

April 22, 2023 9

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

April 22, 2023 10

WATER/STEAM CHEMISTRY

PARAMETERS MONITORED– pH– Silica– Conductivity– After Cation Conductivity– Dissolved Oxygen– Sodium– Copper– Iron

April 22, 2023 11

WATER QUALITY

FEED WATER– ACC <0.2 uS/cm– pH 8.8-9.2– Total Iron+Copper <0.02 ppm– Silica <0.02 ppm– Dissolved Oxygen <7 ppb

April 22, 2023 12

WATER QUALITY

CONDENSATE WATER– ACC <0.2 uS/cm

– pH 8.8-9.2

– Silica <0.02 ppm

– Dissolved Oxygen <40 ppb

April 22, 2023 13

WATER QUALITY

BOILER WATER– Conductivity <30 uS/cm

– pH 9.2-9.6

– Silica <0.300 ppm

– Phosphate 2-4 ppm

April 22, 2023 14

WATER QUALITY

STEAM– ACC <0.2 uS/cm– pH 8.8-9.2– Total Iron+Copper <0.02 ppm– Silica <0.02 ppm– Sodium <10 ppb

April 22, 2023 15

DISTRIBUTION RATIO BETWEEN STEAM & BOILER WATER AT pH 9.5

Drum Pressure Silica in Boiler Water 194 Kg/Cm2 130 ppb176 Kg/Cm2 220 ppb159 Kg/Cm2 290 ppb 134 Kg/Cm2 500 ppb117 Kg/Cm2 1000 ppb100 Kg/Cm2 2220 ppb 65 Kg/Cm2 4000 ppb -- Boiller Drum Pressure is to be maintined as such,Silica value in Main Steam maintain bellow 20 ppb.

April 22, 2023 16

100

10-1

10-2

10-3

10-4

10-5

10-6

10-7

226 220 200 180 160 140 120 100 50 40 30

PRESSURE ( BAR)

PAR

TIT I

ON

CO

EFFI

CIE

NT

Kp

SiO2

NaOH

NaCl

PARTITION COEFFICIENT AT DIFFERENT PRESSURES

April 22, 2023 17

SOURCES OF IMPURITIES IN STEAM

By evaporation from the boiler drum By entrainment of boiler water droplets in

saturated steam. As impurity present in feed water used in

desuper heater spray.

April 22, 2023 18

EFFECTS OF SILICA

Silica has high partition coefficient, so it has tendency to deposit from steam onto turbine.

Silica can deposit on turbine blades specially on LP turbine, which can lead to significant loss of output.

April 22, 2023 19

H.P. DOSING

COORDINATED PHOSPHATE CONTROL

Na3PO4+H2O Na2HPO4 + NaOH

Na2HPO4+H2O NaH2PO4 + NaOH

NaOH + HCl (As Impurity) NaCl + H2O

April 22, 2023 20

L.P.DOSING

AMMONIA & HYDRAZINE HYDRATE DOSING

AMMONIA IS USED TO INCREASE THE pH OF THE SYSTEM AND HYDRAZINE IS USED TO REMOVE THE OXYGENN2H4 + O2 N2 + H2O3N2H4 4NH3 + N2

April 22, 2023 21

CHEMICAL CONTROL OF GENERATOR STATOR WATER COOLING CIRCUITS

GENERATOR STATOR COOLANT --- D.M. WATERSTATOR WATER PARAMETER TO BE MAINTAINED - pH 6.8 + .2 - K < 1.0 µs/cm - Copper < 50 PPb - D.O. < 10 PPb in low D.O. regime

2.0 to 5.0 PPM in high D.O. regime

April 22, 2023 22

CORROSION OF COPPER

There are two methods where the copper is

best passivated and minimum corrosion is found.

1. Low dissolved oxygen regime. 2. High dissolved oxygen regime.

April 22, 2023 23

LOW D.O. REGIME

- Limits below 10 PPb With low D.O. concentration, copper

corrosion is inhibited by a passive film of Cuprous Oxide(Cu2O).

April 22, 2023 24

HIGH D.O. REGIME

- Limits 2 to 5 PPM With high D.O. concentration, copper

corrosion is inhibited by a passive film of Cupric Oxide(CuO).

April 22, 2023 25