April 18, 20231
WATER CHEMISTRY IN POWER PLANT
BY
P. SRIVASTAVA
SR. MANAGER(CHEM.)
April 18, 20232
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 18, 20233
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 18, 20234
WATER CHEMISTRY IN POWER PLANT
CIRCULATING WATER TREATMENT POLLUTION MONITORING
– STACK MONITORING– AMBIENT AIR– WATER EFFLUENT
EFFLUENT TREATMENT PLANT COMMISSIONING ACTIVITES
April 18, 20235
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 18, 20236
D.M. PLANT
WEAKACIDCATION
STRONG ACID CATION
ACF
WEAKBASE ANION
STRONGBASE ANION
MIXED BED
DEGASSER
D.M. WATERSTORAGETANK
April 18, 20237
D.M. WATER QUALITY
pH - 7.0 ± 0.2 CONDUCTIVITY < 0.1 mho TDS - NIL SiO2 < 20 ppb
April 18, 20238
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 18, 20239
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 18, 202310
WATER/STEAM CHEMISTRY
PARAMETERS MONITORED– pH– Silica– Conductivity– After Cation Conductivity– Dissolved Oxygen– Sodium– Copper– Iron
April 18, 202311
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 18, 202312
WATER QUALITY
CONDENSATE WATER– ACC <0.2 uS/cm
– pH 8.8-9.2
– Silica <0.02 ppm
– Dissolved Oxygen <40 ppb
April 18, 202313
WATER QUALITY
BOILER WATER– Conductivity <30 uS/cm
– pH 9.2-9.6
– Silica <0.300 ppm
– Phosphate 2-4 ppm
April 18, 202314
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 18, 202315
DISTRIBUTION RATIO BETWEEN STEAM & BOILER WATER AT pH 9.5
Drum Pressure Silica in Boiler Water 194 Kg/Cm2 130 ppb
176 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 18, 202316
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)
PA
RT
ITIO
N C
OE
FF
ICIE
NT
K
p
SiO2
NaOH
NaCl
PARTITION COEFFICIENT AT DIFFERENT PRESSURES
April 18, 202317
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 de-
super heater spray.
April 18, 202318
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 18, 202319
H.P. DOSING
COORDINATED PHOSPHATE CONTROL
Na3PO4+H2O Na2HPO4 + NaOH
Na2HPO4+H2O NaH2PO4 + NaOH
NaOH + HCl (As Impurity) NaCl + H2O
April 18, 202320
L.P.DOSING
AMMONIA & HYDRAZINE HYDRATE DOSING
AMMONIA IS USED TO INCREASE THE pH OF THE SYSTEM AND HYDRAZINE IS USED TO REMOVE THE OXYGEN
N2H4 + O2 N2 + H2O
3N2H4 4NH3 + N2
April 18, 202321
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 18, 202322
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 18, 202323
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 18, 202324
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 18, 202325