power plant chemistry( water treatment for boilers)

TREATMENT OF WATER FOR HIGH PRESSURE BOILERS& STEAM-WATER QUALITY PARAMETERS

BYDILIP KUMARsimdilip@yahoo.com

POWER PLANT CHEMISTRY

PRETREATMENT PLANT

AERETOR

BY GANGA MAKEUP PUMPS

RIVER GANGA

•Suspended particles

•Dissolved inorganic salts

•Dissolved organic compounds

•Micro organisms &

•Dissolved gasses

IMPURITIES IN 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;

Fe(HCO3) + O2 -- FeO(OH) + CO2 + H2O

Mn(HCO3) + O2 --MnO2(OH) + CO2 + H2O

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;

Fe(HCO3) + O2 -- FeO(OH) + CO2 + H2O

Mn(HCO3) + O2 --MnO2(OH) + CO2 + H2O

•Alum Al2 (SO4)3, 18H2O : For coagulation.

•Lime Ca (OH)2 : To maintain the pH.

•Chlorine Cl2 : As a disinfectant.

DOSING OF CHEMICALS

Al2(SO4)3.18 H2O + 3 Ca(HCO3)2 =2AI(OH)3 + 3CaSO4 + 18H2O + 6CO2

Al2(SO4)3.18 H2O + 3 Ca(OH)2 = 2AI(OH)3 + 3CaSO4 + 18H2O

Cl2 + H2O HOCL + HCl

CLARIFIER

CASCADE AERATOR

Clarifier outlet turbidity < 20NTUClarifier outlet residual Cl2: 0.2-0.5 ppm

RAW WATER INLET

CLARIFIED WATER OUTLET

SLUDGE OUTLET

Clarified water turbidity < 20NTUClarified water residual Cl2: 0.2-0.5 ppm

CLARIFIER

Turbidity reduced

Micro-organisms are killed

GRAVITY SAND FILTER (GSF)

Sand

Gravel

Rapid rate gravity filtration is the most widely used technology for removing turbidity and microbial contaminants from pretreated surface water and groundwater.

FILTERATION

Filtered water turbidity < 5 NTUClarified water residual Cl2: 0.2-0.5 ppm

FOR DRINKING

FOR DEMINERALIZATIONTO DM PLANT

FILTERED WATER SUMP

Filtered water turbidity < 5 NTUClarified water residual Cl2: 0.2-0.5 ppm

REMAINING IMPURITIESDissolved inorganic salts

Dissolved gasses

Dissolved organic compounds

Degasser

FW water

ACF WAC SAC

WBASBA MB

CST

Processes …..

DEMINERALISATION STREAM

Degasser

FW water

ACF WAC SAC

WBA SBA MB

CST

ACFActs on principle of adsorption which is a surface active phenomenonIt 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)

Processes …..

Degasser

FW water

ACF WAC SAC

WBA SBAMB

CST

WAC resin is capable to exchange cations of alkalinity producing salts only

i.e., for carbonate hardness removal purpose.

2 R-COOH + Ca(HCO3)2 (RCOO)2Ca2+ 2 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.

Processes …..

Degasser

FW water

ACF WAC SAC

WBA SBA MB

CST

SAC resin works over wide pH range & is capable to

exchange any type of cations present in salts as sulphonic

acid group is strongly acidic.

2 R-SO3-H+ + CaCl2 (RSO3)2Ca2+ 2 (H+ + Cl- )

Processes …..

Degasser

FW water

ACF WAC SAC

WBA SBAMB

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 CO^ and water. carbon dioxide escapes into the

atmosphere. Water is pumped back to anion exchanger bed

Processes …..

Degasser

FW water

ACF WAC SAC

WBA SBAMB

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

Processes …..

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.

Processes …..

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, H 7.0 and silica content less than 0.02 ppm.

Processes …..

CATIONS

Ca2+,Mg2+

Na+,Fe3+,

K+

ANIONS

Cl-,SO42-,

NO3-,CO3

2-

HCO3,SiO22

WATER

SAC

R-H+R-H+

R-H+

R-H+R-H+

R-H+

R-H+

CATIONS

H+

ANIONS

Cl-,SO42-,

NO3,CO32-

HCO3,SiO22-

AIR

DG

CATIONS

H+

ANIONS

Cl-,SO42-,

NO3-,SiO2

2-

WATER

WATER

R-OH-

R-OH- R-OH-

R-OH-

R-OH- R-OH-

CATIONS

H+

ANIONS

OH-

WBA+SBA

CO2

ION EXCHANGE - PROCESS CHEMISTRY

WAC +

REGENERATION PROCESS

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+NaCl,CaCl2 etc.

TO DRAIN

SAC SAC

R-Cl

R2-SO4

R-NO3

R-ClNaOH

TO DRAIN

R-OH-

R-OH- R-OH-

R-OH-

R-OH- R-OH-

SBA SBA+ WBA

R2-SiO2

R2-SiO2

R2-SiO2

WBA

Parameters pH Conductivity Turbidity Residual Chlorine

Silica

ACF 6.5 – 7.5 -- <2.0 NTU Nil --

Anion 6.5 – 8.0 <10 Nil Nil <200 ppb

Mixed Bed 6.5-7.0 <0.2 Nil Nil < 20 ppb

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.

CONDENSER

CEP

LPH

DEAERATOR

HPH

ECONOMISER

WATER WALLS

BOILER DRUM

TURBOGENERATOR GT SWITCHYARD

BOTTOM RING HEADER

UPPER RING HEADER

DOWNCOMMERS

SH

TO STACK TO ESP BFP

CT

BFP

DOSING OF CHEMICALS TO PROTECT THE BOILER AND PREBOILER SYSTEM FROM CORROSION

BFP

AMMONIA IS USED TO INCREASE THE pH OF THE SYSTEM &NH3+ CO2 = (NH4)2CO3N2H4 + O2 =N2 + H2O3N2H4 =4NH3 + N2 ( this reaction takes place in the boiler

drum

AMMONIA DOSING

BFP

Tri-sodium phosphate hydrolyses & givesNa3PO4+H2O= Na2HPO4 + NaOHNa2HPO4+H2O= NaH2PO4 + NaOHNaOH + HCl (As Impurity)= NaCl + H2O

TRISODIUM PHOSPHATE DOSING IN BOILER DRUM

BFP

SAMPLING POINTS AND PARAMETERS

CONDENSATE SAMPLE COLLECTED FROM CEP DISCHARGEPH 9.0-9.2K 3.0-4.0 µs/cmSILICA 10 ppbDO <40 ppbNH3 1.0 ppmFe <10 ppbCu <3.0 ppb

BFP

SAMPLING POINTS AND PARAMETERS

FEED SAMPLE COLLECTED FROM ECONOMIZER INLETPH 9.0-9.2K 3.0-5.0 µs/cmACC 0.2 µs/cmSILICA 10 ppbDO <5 ppbFe <10 ppbCu <3.0 ppb

BFP

SAMPLING POINTS AND PARAMETERS

BOILER DRUM(BD) SAMPLE COLLECTED FROM BOILER DRUMPH 9.1-9.4K <20 µs/cmSILICA 0.1 ppmPHOSPHATE 1.0-2.0 ppmCHLORIDE 0.5 ppm TDS 10 ppb

BFP

SAMPLING POINTS AND PARAMETERS

SATURATED STEAM SAMPLE COLLECTED FROM BOILER DRUM OUTLETPH 9.0-9.2K 3.0-5.0 µs/cmACC 0.2 ppmSILICA 10 ppbNa <5.0 ppbNH3 <1.0 ppmFe <10 ppbCu <3.0 ppb

BFP

SAMPLING POINTS AND PARAMETERS

MAIN STEAM SAMPLE COLLECTED FROM SUPER HEATER OUTLETPH 9.0-9.2K 3.0-5.0 µs/cmSILICA 10 ppbNa <5.0 ppbNH3 1.0 ppmFe <10 ppbCu <3.0 ppb

BFP

SAMPLING POINTS AND PARAMETERS

DEAERATOR OUTLET SAMPLEDO <5 ppb

GENERAL LAYOUT OF MAIN PLANT

FUEL SYSTEM

COAL UNLOADING

CRUSHER HOUSE

CONVEYOR BELT

COAL BUNKERS

COAL FEEDERS

COAL MILLS

FUEL SYSTEM

COAL HANDLING PLANT

CRUSHER HOUSE

CONVEYOR BELT

COAL BUNKERS

COAL MILLS PULVERIZED THE COAL INTO 75 µ SIZE

VARIOUS SIZED COAL

20 mm SIZE

FUEL SYSTEM

COAL HANDLING PLANT

CRUSHER HOUSE

CONVEYOR BELT

COAL BUNKERS

COAL MILLS PULVERIZED THE COAL INTO 75 µ SIZE

COAL SAMPLES COLLECTED FROM COAL FEEDER S FOR DETAILED ANALYSIS (PROXIMATE ANALYSIS & GCV)

PA FAN

AIR

AIR PREHEATER

HEATED AIR

COAL MILL

FD FAN

AIR

PA FAN

AIR

AIR PREHEATER

HEATED AIR

COAL MILL

FD FAN

AIR

Coal sample sampling point for

MILL FINENESS

PA FAN

AIR

AIR PREHEATER

HEATED AIR

COAL MILL

FD FAN

AIR

MILL FINENESS+50 3.00%-100-200 70%

PA FAN

AIR

AIR PREHEATER

HEATED AIR

COAL MILL

FD FAN

AIR

Oxygen % in flue gas>4% for efficient combustion of fuel

Bottom Ash Hopper

COAL MILL

Bottom Ash HopperSamples for determination of combustibles in bottom ash

Bottom Ash Hopper

COAL MILL

Combustibles in bottom ash <3.00%Combustibles in Fly ash <1.00%

ESPs

SAMPLING POINT FOR FLY ASH ANALYSIS

16 April 2015 PMI Revision 00 39

GENERATOR CHEMISTRY

Basic Generator Theory

GENERATOR PARTS

STATOR OF GENERATOR

ROTOR WINDING & ROTOR

GENERATOR PARTS

GENERATOR INTERNALS COOLING

STATOR COOLED BY PRIMARY WATER

GENERATOR INTERNALS COOLING

ROTOR COOLED BY HYDROGEN GASHYDROGEN PURITY MAINTAINED >97%

GENERATOR INTERNALS COOLING

LOWER FLAMABILITY LIMIT OF H2 4% H2 IN AIRUPPER FLAMABILITY LIMIT OF H2 74% H2 IN AIR

PRIMARY WATER SYSTEM

P W PUMPS

P W COOLERS

FILTERS

ALKALIZERION

EX

CH

AN

GE

R

GENERATOR WINDING

EXPANSION TANK

PRIMARY WATER SYSTEM

P W PUMPS

P W COOLERS

FILTERS

In Case Of Low PH (6.0-8.0) & High DO (<100ppb)Protective Layer formed in Winding is CuO

EXPANSION TANK

PRIMARY WATER SYSTEM

P W PUMPS

P W COOLERS

FILTERS

In Case Of High DO (Without alkalizer)Control limits arepH 6.0-8.0K <1.5 µs/cmCu <20ppbFe <20 ppb

EXPANSION TANK

PRIMARY WATER SYSTEM

P W PUMPS

P W COOLERS

FILTERS

ALKALIZERION

EX

CH

AN

GE

R

In Case Of High PH (8.5-9.0) & Low DO (<10 ppb)Protective Layer formed in Winding is Cu2O

EXPANSION TANK

PRIMARY WATER SYSTEM

P W PUMPS

P W COOLERS

FILTERS

ALKALIZERION

EX

CH

AN

GE

R

In Case Of High DO (With alkalizer)Control limits arepH 8.5-9.0K <2.2 µs/cmCu <20ppbFe <20 ppb

EXPANSION TANK