Here I explained about power plant chemistry. Explained in details how to produce DM water, cooling water, drinking water etc from raw water. Also discussed about main plant steam cycle chemistry.

1. Presented by
Raghab Gorain
A Maharatna Company
Date- 28/05/2020NTPC TSTPS

2. Coal Storage
Conveyer Belt
Coal
Pulverizer
Furnace
Boiler
Turbine
Condenser
Generator
Transformer
Fly Ash
Chimney
ESP
DM
Plant
PT Plant
Cooling
Tower
Bus Bar
Overview OF Thermal Power Plant
Eco
Bottom
Ash
Raw Water

3. WATER TREATMENT
PLANT MAIN PLANT
CHEMISTRY
COAL & OIL ENVIRONMT
& SPECIAL LAB
CW& ETP
TREATMENT
Role Of Chemistry In Power Plant
Chemistry Activities

4. DM Plant (Stg-1)Alum PAC Lime
DM Tank-1
(2000m3)
DM Tank-2
(2000m3)
WAC
Sludge
Backwash Filter
(3+2)175m3/hr
Sand Filter
Sump Filter
water
p/p(4)
3*130m3/hr
3*130m3/hr
Degasser Tower
Clarifier
Aerator
River
MB
A
B
C
Cl2
ACF
A AB S B S
A B S
A B S
SBA
Degasser Tank
WBA
SAC
SBA
Air Blower
Main Plant
DMP
Boiler Fill p/p
Make up p/p
DM Reg. p/p
A B S
4*2300m3/hr
4*2300m3/hr
3*130m3/hr
3*50m3
Degasser p/p 140m3/hr
(3w+1S)
2*100m3/hr
3*100m3/hr
2*50m3/hr

5. Sources of water
Sources Of Water

6. Water Requirement
Requirement of Water in Power Plant

7. Dissolved
form
Suspended
Form
Colloidal
form
ORGANICS
Impurities
in Water
Impurities Present in water

8. Pretreatment of water
Impurities present in Raw water
 Suspended
impurities
 Ionic solids
 Micro-organisms
 Dissolved Gasses
Treatment of water in PT plant
Mainly four steps are used to remove the impurities in raw water
 Oxygenation- Aeration of the water to precipitate out the ferric salt. Here ferrous salts are converted to
ferric salt and also it removes the dissolved CO2
 Coagulation-In this process a flux mixture is produced by the addition of FeCl3 and polyelectrolyte.
 Flocculation & Settlement-It is the process to precipitate out the solids from the clarifier.
 Filtration- To remove the impurities
Aeration of water
4

9. Raw water
Aeration
Exposing Water to Atmospheric air thereby
oxidizing some of the dissolved salts.
During aeration, two impurities viz. Ferrous
Bicarbonate and Manganous Bicarbonate
are oxidized as follows;
4Fe(HCO3)2 + O2 + 2H2O =4Fe(OH)3 + 8CO2
2Mn(HCO3)2 + O2 = 2MnO2 + 4CO2 + 2H2O
Raw Water To Clarified Water Treatment Process

10. Raw water
(disinfection, to
control bacteria, virus
& org. mat)
(coagulant)
(pH adjustment,
softening)
Raw Water Clarified Water Treatment Process

11. Clariflocculator
Coagulation & Sedimentation
Raw Water Clarified Water Treatment Process
Dividing Chamber

12. Clarified water
from clarifier
IN
FILTERED WATER OUT
5th layer
4th layer
3rd layer
2nd layer
1st layer
For back washing of the GSF
water is passed through filter in
reverse direction
BACK WASH WATER OUT
BACK WASH WATER INLET
FROM FILTER WTR. O/H TANK
Gravity Sand Filter 1st layer - 50 mm X 37 mm gravel
2nd layer - 37 mm X 12 mm gravel
3rd layer – 12 mm X 6 mm gravel
4th layer – 6 mm X 2.5 mm grit
5th layer – 0.35 mm X 0.5 mm sand

13. Pretreatment of Water
Exposing the raw water to atmospheric air. So
some of the dissolved salts oxidized, specially
ferrous and manganous bicarbonate as follows
4Fe(HCO3)2 + O2 + 2H2O =4Fe(OH)3 + 8CO2
2Mn(HCO3)2 + O2 = 2MnO2 + 4CO2 + 2H2O
Aeration
Clarification
Cl2: As disinfectant
Alum: Used as flocculating agent
Lime : To maintain pH
Schulze-Hardy rule
Greater the valency of the flocculating ion,
greater will be its coagulation power.
Fe3+ ion is 1000 times more effective than that of
monovalent ion. So FeCl3 is used in clarifier.
Fe3+ + PO4
3- = FePO4
Cl2 +H2O = HOCl + HCl
Gravity Sand Filter(GSF)
It is used to remove the suspended particles
and the microbial organisms from the clarified
water.
Filtered water turbidity: <5 NTU
Residual Cl2: 0.2-0.5 ppm
GSF
5

14. DM Plant
Raw water contains various dissolved salts & suspended solids. For use as feed
in boiler these are to be removed as they may get deposited in heat transfer
zones thereby restricting heat transfer & may lead to corrosion also.
Why Demineralization Require?
What is DM water?
DM water defined as that water which does not contain any mineral or
ions. It is also called De – ionized water.

15. Degasser
FILTER water
ACF WAC SAC
WBA SBA MB
CST
DM Plant

16. Degasser
FW water
ACF WAC SAC
WBA SBA MB
CST
ACF
Acts on principle of adsorption which is a surface active phenomenon
 It removes residual turbidity (<2 NTU) of water to its 1/10 level.
 It removes organic molecules to control colour and odour.
 It removes free residual chlorine present in filtered water(0.5 ppm Nil)
Activated Carbon Filter(ACF)

17. Cation Exchange Resin
2R-H + Na2CO3 2R-Na+H2CO3
Reaction mechanism of Cation exchange Resin
During service condition
During Regeneration condition R-Na + HCl  R-H + NaCl
R=
20

18. Degasser
FW water
ACF WAC SAC
WBA SBA MB
CST
WAC resin is capable to exchange cations of alkalinity producing salts only ie,
for carbonate hardness removal purpose.
2 R-COOH + Ca(HCO3)2  (RCOO)2Ca2+ + H2CO3
 WAC resin can exchange ions only in neutral to alkaline pH range.
 WAC results efficient TDS reduction in high carbonate hardness water.
 Efficient regeneration takes place even with very dilute acid solution.
Weak Acid Cation Exchange Resin

19. Degasser
FW water
ACF WAC SAC
WBA SBA MB
CST
Strong Acid Cation Exchange Resin

20. Degasser
FW water
ACF WAC SAC
WBA SBA MB
CST
 Water from the ex-cation contains carbonic acid which is very weak acid and
difficult to be removed by strongly basic anion resin and causing hindrance to
remove silicate ions from the bed.
 The ex-cation water is trickled in fine streams from top of a tall tower packed
with rasching rings, and compressed air is passed from the bottom
 Carbonic acid break into CO2 and water. carbon dioxide escapes into the
atmosphere. Water is pumped back to anion exchanger bed
DM Plant (Degasser Tower)

21. Anion Exchange Resin
Reaction mechanism of Anion exchange Resin
2R’-OH + H2SO4 R’2SO4+2H2ODuring service condition
During Regeneration condition R’2SO4 + NaOH2R’-OH + Na2SO4
Anion Exchange Resin
Chemicals NaOH
Level(g/L) 30-150
Flow Rate(BV/hr) 3-5
Concentration(%) 5-8
Min. contact time 30 min
R’=
21

22. Degasser
FW water
ACF WAC SAC
WBA SBA MB
CST
 Weak anion resins derive their functionality from primary
(RNH2),secondary(R-NHR’)& tertiary amine (R3N)groups.
 The weak weak-base anion resins remove free minerals
acidity(FMA) such as HCl & H2SO4 but doesn’t remove weakly
ionized acids such silicic acid and bicarbonates
Weak Acid Anion Exchange Resin

23. Degasser
FW water
ACF WAC SAC
WBA SBA MB
CST
The Strong base anion resins derived their
functionality from quaternary ammonium exchange
sites. These are capable of exchanging anions like Cl-
,HCO3
-,Silica.
Strong Base Anion Exchange Resin(SBA)

24. Degasser
FW water
ACF WAC SAC
WBA SBA MB
CST
 Ex-anion water is fed to the mixed bed exchanger containing both cationic resin and
anionic resin.
 This bed not only takes care of sodium slip from cation but also silica slip from anion
exchanger very effectively
 The final output from the mixed bed is an extra-ordinarily pure water having less than
0.2/Mho conductivity, pH 7.0 and silica content less than 20 ppb.
Mixed Bed

25. CATIONS
Ca2+,Mg2+
Na+,Fe3+,
K+
ANIONS
Cl-,SO4
2-,
NO3
-,CO3
2-
HCO3,SiO2
2
WATER
SAC
R-H+R-H+
R-H+
R-H+
R-H+
R-H+
R-H+
CATIONS
H+
ANIONS
Cl-,SO4
2-,
NO3,CO3
2-
HCO3,SiO2
2-
AIR
DG
CATIONS
H+
ANIONS
Cl-,SO4
2-,
NO3
-,SiO2
2-
WATER
WATER
R-OH-
R-OH- R-OH-
R-OH-
R-OH- R-OH-
CATIONS
H+
ANIONS
OH-
WBA+SBA
CO2
DM Plant during service

26. R2-Ca2+ R2Mg2+
R-Na+ R-K+
R3-Fe+3 R3-Al+3
HCl
R-H+ R-H+
R-H+ R-H+
R-H+ R-H+
TO DRAIN
(NaCl, CaCl2 etc
SAC WAC
R-Cl
R2-SO4
R-NO3
R-Cl
NaOH
TO DRAIN
R-Cl
R-SO4 R-NO3
R2Ca2+
R2Fe2+ R-K+
SBA MB
R2-SiO2
R2-SiO2
R2-SiO2
WBA
DM Plant during Regeneration
HCl
NaOH
TO DRAIN

27. Parameters pH Conductivity Turbidity Residual
Chlorine
Silica
ACF 6.5 – 7.5 -- <2.0 NTU Nil --
Anion 6.5 – 8.0 <20 Nil Nil <200 ppb
Mixed Bed 6.5-7.0 <0.2 Nil Nil < 20 ppb
DM Plant Parameters

28. MAIN Plant
Why DM water can’t be used directly in boiler?
- Principle says if water is acidic – Corrosive.
- Principle say if water is alkaline – Scale forming.
As DM water (also called as hungry water) is having no salt,
when it comes in contact with metal surface attacks the metal.
DM Water is called ‘Hungry Water’

29. 14
Boiler Water Treatment
9
GEN.
R Y B
C P U
TURBINE
DE-AERATOR
CONDENSER
H P HEATER
L P HEATER
CONDENSATE
EXTRACTION PUMP
By Pass v/v
LP Dosing
(Ammonia)
BOILER
FEED
PUMP
BOILER
BLOW
DOWN
H P Dosing
(Phosphate)
BOILER
SUPER HEATED STEAM 

30. HP Dosing
Na3PO4+H2O= Na2HPO4 + NaOH
Na2HPO4+H2O= NaH2PO4 + NaOH
NaOH + HCl (As Impurity)= NaCl + H2O

31. AMMONIA IS USED TO INCREASE THE
pH OF THE SYSTEM.
LP Dosing

32. Condensate Polishing Unit(CPU)
24
 Removes dissolved solids from feed water (sodium, silica, sulphate ,chloride etc.)
by ion-exchange method in an extremely low level
 Removes suspended solids from feed water(crud of ferric oxide and other
impurities) by filtration
Function of CPU
Stabilizes the steam- water parameters very rapidly during start up
Reduces boiler tube failure
Reduces turbine maintenance related to steam purity
Provides protection against condenser tube leakage
Reduces boiler blow down hours
Reduces DM water make up
Benefits of CPU

33. CPUBoiler
De aerator
IPT LPTHPT
HP Heaters LP Heaters
Condenser
CPU I/L
Parameter Sample Limit
Sodium, ppb C <2
ACC, µS C <0.10
Silica, ppb C or S <10
Parameters Sample Limit
pH C or S 9.2-9.6
ACC, µS C <0.2
DO, ppb C <5
Silica, PPB C or S <20
Parameters Sample Limit
Sodium, ppb C <2
ACC, µS C <0.2
Silica, ppb C or S <20
Parameters Sample Limits
pH C or S 9.2-9.6
Silica, ppb C or S 400/100
Chloride, ppb C or S <100
Parameter Sample Limit
Sodium, ppb C <2
ACC, µS C <0.20
DO, ppb C <20
Silica, ppb C or S <20
MAIN STEAM
CPU O/L
BOILER WATER
FEED WATER
Legend:
C = Continuous, Online
S = Grab, Once in shift
Cycle Chemistry Diagram For A Drum Unit- Core Parameters Only

34. 25