Power plant chemistry by ramesh

KOMMA RAMESH SENIOR CHEMIST/TSGENCO/KTPP CHELPUR
PRE TREATMENT OF RAW WATER
In the treatment of raw water involves
 De aeration
 Clarification
 Filtration
 Demineralization
DEAERATION
 Aeration is the process of bring water and air into close contact
 Removes dissolved gases such as carbon dioxide by decarboxylation H2S and NH3 by stripping
 Oxidize dissolved metals such as iron and manganese.
 It can also use to remove volatile organic chemicals
 Aeration is the effective method of bacterial control and Gases ( carbon dioxide, hydrogen
sulfide) Methane Ammonia
 Generally gases in water are in ionic form
 The common ion effect may be used to obtain almost complete removal of these gases by
aeration.
 In the case of carbon dioxide and hydrogen sulfide, hydrogen ion concentration may be
increased by the addition of an acid.
 HS-
forms H2S and Bicarbonate and carbonate ions in the water will form carbon dioxide, which
can be removed by aeration
H2S H+
+ HS-
H2O + CO2 H+
+ HCO3
Increase in hydroxyl ion concentration through the addition of caustic soda aids in the removal of
ammonia.
H2O + NH3 NH4+
+ OH-
2. Oxidizes – Iron and Manganese and are removed in later process
4Fe (HCO3) + O2 + H2O --------------- 4Fe(OH) +8CO2
2Mn (HCO3)2 + O2 ---------------- 2MnO2 +CO2 +H2O
3. Volatile organic chemicals such as benzene Di, Tri, and Perchloroethylene etc.

TYPE OF AERATORS
1. Cascade Aerators
Cascade aerators consist of a series of steps which the water flows over
2. Cone Aerators
3. Draft aerator
Draft aerator consist external blowers mounted at the bottom of the tower to induce air from the
bottom of the tower. Water is pumped to the top and allowed to cascade down through the rising air

OPERATIONAL TESTING
Three basic control tests are involved in the operation of the aeration process:
1. Dissolved oxygen 2. pH 3. Temperature
DO TEST : DO Test is used to estimate whether the process is over or under aerated.
PH TEST
The pH test will give an indication of the amount of carbon dioxide removal.
pH increases as the carbon dioxide is removed.
pH can also be used to monitor the effective range for hydrogen sulfide, iron, and manganese removal.
TEMPERATURE
The temperature is important as the saturation point of oxygen increases as the temperature decreases.
CLARIFICATION
Clarification process consist
1. Coagulation 2. Flocculation 3.Sedimentation
COAGULATION
Gravity settling
Colloids are so small: gravity settling not possible
Colloids have a net negative surface charge Electrostatic force prevents them from agglomeration
Brownian motion keeps the colloids in suspension. Impossible to remove colloids by gravity settling
Coagulation is the destabilization of colloids by addition of chemicals that neutralize the negative
charges the chemicals are known as coagulants, usually higher valence cationic salts (Al3+
, Fe3+
etc.)
Aluminum sulfate: Al2 (SO4)3.14 H2O Ferrous sulfate
Ferric sulfate: Fe2 (SO4)3 Ferric chloride: Fe2Cl3
Particle diameter (mm) Type Settling velocity
10 Pebble 0.73 m/s
1 Course san 0.23 m/s
0.1 Fine sand 0.6 m/min
0.01 Silt 8.6 m/d
0.0001(10 micron) Large colloids 0.3 m/y
0.000001 (1 nano) Small colloids 3 m/million y

FLOCCULATION
Flocculation is the agglomeration of destabilized particles into large size particles known as flocs which
can be effectively removed by sedimentation or flotation.
SEDIMENTATION
The large flocs formed by flocculation settles by gravity is called Sedimentation
JAR – TEST
 The jar test – a laboratory procedure to determine the optimum pH and the optimum coagulant
dose
CLARIFIER DIAGRAM

DIFFERENT COAGULANTS
1. ALUM
Extensively used coagulant, is aluminum sulfate (Al/S04)3 ·14 HP), also known as alum.
Alum is acidic in nature grey in color
Available in blocks, lumps and powder with a density of 1000 -1100 kg/ m3 and specific gravity of 1.25
to 1.36.
It is readily soluble in water and gives positively charged ions Al+3.
Al2(SO4)3 +3Ca(HCO3)2 ------------------ 2Al(OH)3 + 3CaSO4 +6CO2
ADVANTAGE S OF ALUM
 It readily dissolves with water,
 It does not cause the unsightly reddish brown staining of floors, walls and equipment like ferric
sulphate,
DISADVANTAGE S OF ALUM
 It is effective only at certain pH range,
 Good flocculation may not be possible with alum in some waters.
2. FERROUS SULPHATE
 Ferrous sulphate, ordinarily known as copperas,
 It is granular acid compound and green to brownish yellow color
 Available in granules, crystals and lumps.
 This is fed usually in solution form with strength of 4 to 8 %.
 The alkalinity and pH value of natural water are too low to react with copperas to form the
desired ferric hydroxide floc,
 But oxidation ferrous sluphate to ferric hydroxide occur at pH > 8.5.
 Along with the ferrous sulphate lime is added to water to increase pH
 The dose of lime required is approximately 0.27 mg/L to react with 1.0 mg/L of copperas.
 Generally the floc formed by the reaction of copperas and lime is feathery and fragile, but has a
high specific gravity.
Advantages of Ferrous sulphate
 Ferric hydroxide is formed at low pH values,
 Coagulation is possible with ferric sulphate at pH values as low as 4.0.
 The floc formed with ferric coagulants is heavier than alum floc.
 The ferric hydroxide floc does not redissolve at high pH values.
 Ferric coagulants may be used in color removal at the high pH values

FERRIC SULPHATE
 Ferric sulphate is available as a commercial water treatment coagulant in the form of an
anhydrous material
 It may be transported and stored in wooden barrels.
 The ferric sulphate will dissolve readily in a limited quantity of warm water so a special solution
pot must be used with chemical feeders,
 In which 1 part ferric sulphate by volume is dissolved in 2 parts water to produce a solution of
about 40% strength.
COAGULANT AIDS
 Coagulant aid is an inorganic material,
 Used along with main coagulant, improves or accelerates the process of coagulation and
flocculation.
 Coagulant aids increase the density of slow-settling flocs so settles rapidly
 Gives toughness to the flocs so that they will not break up during the mixing and settling
processes.
 Coagulant aids, are generally used to reduce flocculation time and when the raw water turbidity
is very low.
Coagulant aids are 1. Bentonite 2. Calcium carbonate
POLYELECTROLYTES
 Addition of organic polymers or poly electrolytes enhance the flocculation
 These polymers consist of long carbon chain with active groups such as amine nitrogen sulfates
along the chain

KOMMARAMESH SENIOR CHEMIST TSGENCO KTPP
QW
DM
CLARIFIER
NON DM
CLARIFIER
CASCADE
AERATOR
STILLING
CHAMBER
PARSHALL FLUEM
1800M3
/Hr
FLASH
MIXER
RAW WATER
PUMPS
2 X 1000M
3
/Hr
RESERVOIER
FLASH
MIXER
PARSHALL FLUEM
250M3/Hr
1
2
3
4
5
6
RAPID GRAVITY FILTERS
1&2 DM - 250M
3
/Hr
3 to 6 NON DM - 500M3
/Hr
DM
SUMP
5M
NON DM
SUMP
6M
FIRE
WATER
Gravel 2-5mm 500mm
Sand 0.5mm 50mm
Anthracite 1.0mm 500mm
Water 2500mm
Total depth of RGF 3750mm
2200M
3
/Hr
PRE TREATMENT PLANT KTPP
STAGE-I
Alum
&
Poly electrolytes
Chlorine
PRE TREATMENT PLANT

AERATION AND CHLORINATION
Aeration is the process of bring water and air into close contact and Removes
1. Dissolved gases such as carbon dioxide by decarboxylation
H2O + CO2 H
+
+ HCO3
2. H2S and NH3 by stripping
H2S H
+
+ HS
-
H2O + NH3 NH4
+
+ OH
-
3. Oxidize dissolved metals such as iron and manganese.
4Fe (HCO3) + O2 + H2O 4Fe (OH) +8CO2
2Mn (HCO3)2 + O2 2MnO2 +CO2 +H2O
4. Volatile organic chemicals such as benzene Di, Tri, and Perchloroethylene etc.
Chlorine is dosed at stilling chamber to control microorganism and algae
H2O + Cl2 H
+
+ Cl
-
+ HOCl
HOCl H
+
+ O Cl
-
At 7.5 pH 50% HOCl and 50% OCl
-
are exist and at lower than 7.5pH HOCl
predominates and controls microorganisms effectively

CLARIFICATION OF WATER
Large particles in water is settled by gravity but colloid particles (0.0001micron and 0.00001micron) are so small gravity settling not possible
Colloids have a net negative surface charge Electrostatic force prevents them from agglomeration. Brownian motion keeps the colloids in
suspension. Impossible to remove colloids by gravity settling. Colloid particles are removed by coagulation, flocculation and sedimentation in
clarifier.
Coagulation is the destabilization of colloids by addition of chemicals that neutralize the negative charges. The chemicals are known as coagulants,
usually higher valence cationic salts (Al
3+
, Fe
3+
etc.)1.Aluminum sulfate: Al2 (SO4)3.14 H2O 2. Ferrous sulfate 3.Ferric sulfate: Fe2 (SO4)3
Ferric chloride: Fe2Cl3
Flocculation is the agglomeration of destabilized particles into large size particles known as flocs which can be effectively removed by
sedimentation
Sedimentation The large flocs formed by flocculation settles by gravity is called Sedimentation
Poly electrolytes are dosed to enhance the flocculation and the Lime is dosed to improve the pH of water
The coagulation most effective at pH 6.3 to 7.8
CLARIFIER OUT LET WATER
TURBIDITY = <10NTU
FREE RESIDUAL CHLORINE = 0.5 PPM
FILTER OUT LET WATER
Rapid Gravity Filters removes odour and turbidity
TURBIDITY = <2NTU
RESIDUAL CHLORINE = 0.2 PPM
ODOUR =

I
BY
RAMESH KOMMA
Senior Chemist /TSGENCO
KTPP-CHELPUR
DEMINERALIZATION OF
WATER

DEMINERALIZATION PLANT
Demineralization plant equipped with filters and series of ion exchange shells
FILTRATION
Filtration is used in addition to regular coagulation and sedimentation for removal of solids from
clarification water
Filtration is a simple mechanical process, actually involves the mechanisms of adsorption (physical and
chemical), straining, sedimentation, interception, diffusion, and inertial compaction.
Filters, designed vertically or horizon-tally, have cylindrical steel shells and dished heads filled with filter
media
DIFFERENT FILTER MEDIA
SAND GRAVELS SILICA SAND
ANTHRACITE GRANET QUARTZ SAND

TYPE OF FILTERS
GRAVITY FILTERS
Gravity filters use relatively coarse sand and other granular media E.g. Paterson's filter,
PRESSURE FILTERS
Pressure filters are similar to gravity filters
Pressure filters are usually operated at a service flow rate of 3 gpm/ft². E.g. Candy's filter
ACTIVE CARBON FILTRATION
Activated carbon filter is generally used for removing free chlorine and / or organic compounds. Such as
humic or fulvic trihalomethanes (a class of known carcinogens)
Three forms of activated carbon used in water filtration systems are granulated activated carbon (GAC),
activated-carbon block and catalytic carbon.
Activated carbon can be made from coal, wood or coconut shells. Carbon is "activated” by adding a
positive charge,
This enhances the adsorption of contaminants that have a negative charge.
DUAL MEDIA FILTRATION
Dual media filter contain anthracite (125-2.5mm) in combination with sand (1-1.5mm) supported by
pebble and gravels.
MIXED - MEDIA FILTRATION
Mixed-media filters have two or more types of filter material to remove specific compounds from the
water. Contain fine sand to remove larger particles in the water, activated carbon to remove odors and
other compounds followed by a micro-screen filter that may contain bacteriostatic control agents.
Water Quality Before and after filters
Suspended solids at filter inlet = 20 NTU
Suspended solids at out let = 2 NTU
Filter out let metal ions (Al & Fe) = <0.2 mg/kg
Filter out let Color Hazen = <5

ION EXCHANGE
Ion exchange is an exchange of ions between two electrolytes or between electrolyte solutions. Ion
exchangers used for demineralization are resins, zeolites, montmorillonite, clay, and soil humus.
In power industry Reins are used for demineralization of water
HISTORY OF RESINS
In 1905, Gans, Invented synthetic aluminosilicate materials known as zeolites
Zeolite is the first ion exchange water softeners.
1940's, ion exchange resins were developed based on the copolymerization of styrene cross and
divinylbenzene
More recently acrylic polymers have been developed Polystyrene-divinylbenzene resins are still used in
the majority of ion exchange applications
CHARACTERISTICS OF RESIN
 Insoluble but permeated by water
 An ability to exchange ions with in solution
 Allows a flow of water through a bed of resin
CLASIFICATION OF RESINS
Industrial water treatment resins are classified into four basic categories:
1. CATION RESIN 2. ANION RESIN
Strong Base Anion (SBA) Weak Acid Cation (WAC)
Weak Base Anion (WBA) Strong Acid Cation (SAC)
STRONG ACID CATION (SAC)
Functional
groups
Sulphonic acid —SO3– H+
What they do
In sodium form, they remove hardness (essentially calcium
and magnesium) from water and other solutions
In hydrogen form, they remove all cations
They are also used as acidic catalysts
Examples
AmberjetTM 1000 Na
DowexTM Marathon C
LewatitTM Monoplus S100
Typical total capacity 1.9 to 2.2 eq/L [Na+]

WEAK ACID CATION (WAC)
Functional groups Carboxylic acid —COOH
What they do
In hydrogen form, they remove preferentially divalent ions
(e.g. calcium and magnesium) from solutions containing
alkalinity
Examples
AmberliteTM IRC86
DowexTM MAC3
LewatitTM CNP80
Typical total capacity 3.7 to 4.5 eq/L [H+]
STRONG BASE ANION (SBA)
Functional groups
Quaternary ammonium
—N(CH3)3+ OH–
What they do
In hydroxyl form, they remove all anions
In chloride form, they remove nitrate, sulphate and several
other ions
Examples
AmberjetTM 4200 Cl
DowexTM Marathon A
LewatitTM Monoplus M500
Typical total capacity 1.0 to 1.5 eq/L [Cl–]
WEAK BASE ANION (WBA)
Functional groups Amines —N(CH3)2
What they do
After cation exchange, they remove chloride, sulphate, nitrate,
and other anions of strong acids, but they do not remove weak
acids (SiO2 and CO2)
Examples
AmberliteTM IRA96
DowexTM Marathon MWA
LewatitTM Monoplus MP64
Typical total capacity 1.1 to 1.7 eq/L [free base]

DEMINERALIZATION
 In demineralization process water from filter passes through SAC, DEGASSER ,BA and MB
 In special cases we have WAC before SAC and WAB after SAC
 The ion exchange reactions of these units described below
SAC ION EXCHANGE
 SAC resins can neutralize salts into their corresponding acids
 SAC resins has functionality sulfonic acid groups HSO3¯)
 SAC resins remove nearly all raw water cations, replacing them with hydrogen ions, as shown below:
WAC ION EXCHANGE
 WAC resins have functional group carboxylic group (-COOH)
 WAC resins remove cations that are associated with alkalinity, producing carbonic acid
 Weak acid cation resins are used primarily for softening and de alkalization of high-hardness
CATION OUTLET WATER CHARECTARISTICS
SODIUM = < 2 ppm
HARDNESS = NIL
PH = 7.0 – 9.2
FMA = 71

SBA ION EXCHANGE
 SBA resins can neutralize strong acids and convert neutral salts into their corresponding bases.
 SBA resins derive their functionality from quaternary ammonium functional groups
WBA ION EXCHANGE
 WBA functional groups primary (R-NH2), secondary (R-NHR'), or tertiary (R-NR'2) amine groups.
 WBA resins readily re-move sulfuric, nitric, and hydrochloric acids,
ANION WATER CHARECTARISTICS
REACTIVE SILICA = <0. 2 ppm
FREE CO2 = NIL
PH = 7.0 – 9.2
CONDUCTIVITY = <5µs/cm @ 250
C
DISSOLVED OXYGEN = NIL

MB ION EXCHANGE
MB vessel contains both cation resin and anion resin removes both ions as above
MB WATER CHARECTARISTICS
REACTIVE SILICA = <0.02 ppm
FREE CO2 = NIL
IRON CONTENT = NIL
TOTAL HARDNESS = NIL
PH = 6.5 – 7.5
CONDUCTIVITY = <0.5µs/cm @ 250
C
DISSOLVED OXYGEN = same as in the effluent
SELECTIVITY COEFFICIENTS
Preference for ions of particular resins is often expressed through an equilibrium relationship using the selectivity
coefficient. The coefficient is described below.
Resin X + Y Resin Y + X
X = Cation or Anion attached to Resin
Y = Cation or Anion in solution
Equilibrium represented by
K = equilibrium constant or selectivity constant for particular resin used
CATION RESIN SELECTIVITY OF IONS
Ba > Pb > Sr > Ca > Ni > Cu > Mg > Ag >> Cs > K > NH4 > Na > H > Li
TRIVALENT > DIVALENT > MONOVALENT
ANION RESING SELECTIVITY OF IONS
SO4 > CrO4 > NO3 > CH3COO > I > Br > Cl > F > OH

RESINS EXHAUSTION AND REGENERATION
A resin is considered to be exhausted when the ions in the resin have mostly been replaced by the
ions that are being removed from the solution.
CATION EXHAUSTION
Exhaustion of cation determined by sodium leakage, decrease in conductivity of cation leaving water
and increase in conductivity of anion leaving water
During exhaustion of cation bed consist layers of resin in different ionic form
CATION REGENERATION TECHNIQUE
For cation regeneration 4% HCl OR H2SO4 is used
H2SO4 is usually employed to regenerate cation resin because it cheaper than the HCl
H2SO4 has a disadvantage that is it can form calcium sulfate precipitate if use excess
Cation regeneration carried out in two ways i.e
1.CO-FLOW REGENERATION 2. COUNTER-FLOW REGENERATION
CO-FLOW REGENERATION
In co flow regeneration regenerate solution and water flows in same direction
After Co – flow regeneration upper layer of resin in H+ form bottom layer in Na+ form
During subsequent exhaustion H+ ions of water replaces Na+ ions at outlet of the bed and appears in
treated water this is called sodium slippage
Ca++
Mg++
Na+
H+
Ca++
Mg++
Na+
H+

COUNTER-FLOW REGENERATION
In counter – flow regeneration the water and regenerate solution flows in opposite direction
Water leaving the bed would be in equilibrium with the most highly regenerated resin
So extremely low levels of sodium leakage will be observed because Na+
ions layer present on top of the
bed after regeneration. so sodium slippage in counter flow regeneration beds is low when compared to
Co -flow regeneration
In the counter flow regeneration the chemicals are passed through the bed in opposite direction to the
service water flow
In this service flows upwards and regenerate flows downwards and vice versa
Several designs of unit have been adopted to prevent rise and mix they are discussed below
AIR HOLD - DOWN
An inert granular material pushes the bed down during regeneration, under air compression.
The inert material is usually polypropylene, which floats when the upper part of the vessel is filled with
water, and comes down when it is full of air
The inert resin prevents contact between the air and the active resin.
The acid passes through bed from bottom and leaves by regenerant collector
Ca++
Mg++
Na+
H+
Ca++
Mg++
Na+
H+
AIR
INLET
ACID
INLET
SERVICE
INLET
SERVICE OUTLET
OUTLETOUTET
WASTE
ACID
REGENERANT
COLLECTOR
COLLECTOR

WATER HOLD-DOWN
 These are the same as the air hold-down units,
 The counter pressure needed during regeneration is exerted with a flow of water from the top
 The part of the resin that is located above the collector never gets regenerated, and is thus called
"inactive".
 The disadvantage of this system is that it consumes more water in the regeneration process
SPLIT
 In split-flow vessels, regeneration is carried out simultaneously from the top and from the bottom
of the bed.
 The regenerant collector is located in the upper third of the resin bed. An additional regenerant
distributor is required above the resin bed.
 The idea is to allow the upper part of the bed to be backwashed to remove accumulated debris
without disturbing the lower layers of the bed that are responsible for the good treated water
quality.
 There is no inert or inactive resin,
 the system does not consume extra water,
 but the regeneration flows are sometimes difficult to adjust.
WATER PRESSURE
ACID INLET
SERVICE INLET
SERVICE OUTLET
WASTE WATER

ANION EXHAUSTION AND REGENERATION
ANION EXHAUSTION
Anion exhaustion determined by silica leakage as it releases first and decrease in conductivity of anion
leaving water
ANION REGENERATION
For Anion regeneration 4% NaOH caustic soda is used
Lye (liquid NaOH) or pellets (solid NaOH) are used
1. CO-FLOW REGENERATION
DURING EXUASTION AFTER REGENERATION
2. COUNTER FLOW REGENERATION
DRING EXUASTION AFTER REGENERATION
SiO2
-
Cl-
SO4--
OH-SO4
Cl
SiO2
SiO2
-
Cl-
SO4--
OH-
SO4
Cl
SiO2

KAKATIYA THERMAL POWER PROJECT 500MW
Item Description Qty Capacity / Size
DM Supply Pumps 2 100m3/hr x 55m WC
Activated Carbon Filter (MSEP) 2 2800mm Dia x 2100mm HOS
Strong Acid Cation Exchanger 2 3000mm Dia x 3200mm HOS
(MSRL)
Degasser Tower (MSRL) 1 2000mm Dia x 3000mm HOS
Degassed water storage Tank (RCC 1 200m3, 8.0m x 8.0m x 3.2m + 0.3m
Epoxy)
FB
Degasser Blower 2 4000m3/hr x 150mm WC
Degassed Water Transfer Pumps 2 90m3/hr x 50m WC
Weak Base Anion Exchanger 2 2000mm Dia x 3200mm HOS
(MSRL)
Strong Base Anion Exchanger 2 1800mm Dia x 2200mm HOS
(MSRL)
Mixed Bed Exchanger (MSRL) 2 1600mm Dia x 2000mm HOS
Mixed Bed Blower 2 200m3/hr x 0.45 kg/cm2
Intermediate Tank (MSEP) 1 150m3, 6.0m Dia x 6.5m HT
DM Regeneration Water Pumps 2 30m3/hr x 30m WC
Bulk Acid Storage Tanks (MSRL) 2 50m3, 3000mm Dia x 6200mm LOS
Bulk Alkali Storage Tanks (MSRL) 2 30m3, 2500mm Dia x 5600mm LOS
Acid Measuring Tanks for Cation 1 1800mm Dia x 1200mm Ht
(MSRL)
Acid Measuring Tanks for MB 1 700mm Dia x 1000mm Ht
(MSRL)
Acid Measuring Tanks for NP 1 700mm Dia x 1000mm Ht
(MSRL)
Alkali Measuring Tanks for Anion 1 1000mm Dia x 1000mm Ht
with Agitator (MSRL)

Alkali Measuring Tanks for MB 1 700mm Dia x 1000mm Ht
Alkali Measuring Tanks for NP 1 700mm Dia x 1000mm Ht
Acid Unloading / Transfer Pumps 2 10m3/hr, 15mWc
Alkali Unloading / Transfer Pumps 2 10m3/hr, 15mWc
Neutralised Effluent Disposal 2 100m3/hr, 30mWC
Pumps
Neutralisation Pit (Twin 1 600m3, 20m x 10m x 3.0m
Compartment)
300m3, 10m x 10m x 3.0m each
compart.
UF feed / forward flush Pumps 2 85m3/hr x 30m WC
UF back wash Pumps 2 170m3/hr x 30m WC
UF membrane for two units 16 400mm Dia x 1530mm HT
modified polyether sulphone
capillary multibore
Strainer (SS 316) 2 100 micron for both feed /
backwash pumps
Chemical cleaning / disinfection 2 500LPH, 40mWC
dosing pump
Chemical clean in process tank 1 5000 Liters
(HDPE)
Disinfection tank (HDPE) 1 500 Liters
DM water storage tanks (MSEP) 2 1000m3, 12m Dia x 10m HT
Design capacity of plant
A) DM Plant Normal feed 80 m3/Hr (Net) per stream
B) No. of Streams Two (one working + one Standby)
C) Service Hours 20 hrs.
D) Service cycle (MB) 140 hrs
E) Regeneration cycle (DMF, ACF, SAC, SBA) 4 hrs
F) Regeneration cycle (MB) 4.00 hrs.
For UF Plant
A) No. Units Two (1W+1S)
B) Normal design flow rate per unit, Net 80m3/hr
C) Cycle time 22 hrs
D) Regeneration time 2 hrs

KOMMA RAMESH/SENIOR CHEMIST/KTPP/TSGENCO
;’n
ACF WAC SAC
WBA SBA
MB
It removes organic molecules
to control colour and odour.
It removes free residual
chlorine present in filtered
water (0.5 ppm Nil)
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.
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- )
Weak anion resins derive their functionality from
primary (RNH2),secondary(R-NHR’)& ter[3tiary
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
The Strong base anion resins derived their
functionality from quaternary ammonium
exchange sites.These are capable of
exchanging anions like Cl-,HCO3-,Silica.
];g
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.
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
ranching rings, and
compressed air is passed from
the bottom
Carbonic acid breaks into CO2
and water. Carbon dioxide
escapes into the atmosphere.
DG
RFT
DM PLANT

KOMMA RAMESH / SENIOR CHEMIST /KTPP STAGE-I TSGENCO
`
ESP
COOLING TOWER
BFP
LPH 1,2,3
DEAERATOR
HPH 5A 5B
6A 6B
IDF
ECONOMISER
CONDENSER
HOT WELL
MILL
CEP
TURBINE
GENERATOR
500MW
21000V
COOLING WATER PUMPS
FDF
S
Coalpowder
&Air
DRUM
PAF
A B
CPU
SUPER
HEATER
RE
HEATER HPHPHP IP
LP
FOREBAY

A B
A B A B
TSP DOSING
PUMPS
SULPHURIC ACID (H2SO4) to decrease ph
ANTI SCALENT to inhibit corrosion
BIOCIDES to kill micro organism
BIO-DISPERSANT
CHLORIN
CHEMICALS DOSING TO
COOLING WATER
NH3 DOSING
PUMPS
N2H4 DOSING
PUMPS
CHEMICAL DOSING POINTS IN THERMAL POWER PLANT
TSP INCREASES PH OF BOILER WATER
Na3PO4+H2O = Na2HPO4 + NaOH
Na2HPO4+H2O = NaH2PO4 + NaOH
NaOH + HCl = NaCl + H2O
TSP Converts Ca/Mg /SiO2 Salts into
insoluble phosphate and passes out
through CBD
AMMONIA IS USED TO INCREASE THE pH OF THE SYSTEM
HYDRAZINE WORKS AS OXYGEN SCAVENGER
3N2H4 = 4NH3 + N2
NH3+ CO2 = (NH4)2CO3
N2H4 + O2 =N2 + H2O
3N2H4 =4NH3 + N2 (this reaction takes place in the boiler drum

DRUM SAMPLE
SUPER SATURATED SAMPLE SUPER HEATED SAMPLE
COOLING
WATER SAMPLE
CONDENSATE SAMPLEFEED SAMPLE CPU OUT LET SAMPLE
CPU IN LET
SAMPLE
WATER SAMPLES COLLECTING POINTS IN
THERMAL POWER PLANT
Ph=

KOMMA RAMESH SENIOR CHEMIST TSGENCO KTPP-CHELPUR Page 1
‘
I
BY
RAMESH KOMMA
Senior Chemist /TSGENCO KTPP Stage-I
CHELPUR
BOILER WATER CHEMISTRY
TSGENCO

NTRODUCTION OF WATER
Water is most important raw material used in many industries.
It has good heat carrying capacity.
It is a universal solvent.
Chemical formula of water is H2O
Pure water is virtually a non-conductor of electricity.
Pure water at room temperature acts on alkaline metals and on alkaline earth metals rapidly
with evolution of hydrogen.
Magnesium, iron, zinc and carbon react with water at high temperature.
Iron and lead are also attacked by water in the presence of air.
Based on hardness water is classified into two types
SOFTWATER
Water that easily forms, lather with a soap solution is known as soft water.
HARDWATER
Water that reacts with soap solution to form a white scum only without producing lather easily, is said
to be hard water. Hardness Of water is two types
1. Temporary hardness 2. Permanent hardness
TEMPERORAY HARDNESS
The hardness of water is due to Calcium bicarbonate [Ca(HCO3)2]
Magnesium bicarbonate [Mg (HCO3)2 is called temporary hardness because on heating, all are
substantially removed as insoluble carbonates
PERMANENT HARDNESS
The hardness of water is due to CaCl2, CaSO4 and MgCl, MgSO4 known as permanent hardness. Since
the solutions are stable to heat at normal pressure.
ALKALINITY IN WATER
Alkalinity is the total of all bases that occupying in the water
Alkalinity is due to 1) Caustic alkalinity 2) Temporary hardness
NaOH or KOH [Ca (HCO3)2]
Na2C03 or K2CO3 [Mg (HCO3)2]
NaHCO3 or KHCO3

SOURCE OF WATER
Surface water - contains high suspended matter and dissolved solids.
Ground water - free from suspended matter but high TDS
Sea water - contain high dissolved mineral salts
For thermal power stations surface water is preferred, due to low TDS and high abundance
USE OF WATER IN POWER PLANT
1. As Cooling water for condenser (Raw water)
2. As Cooling water for unit auxiliaries (Clarified water)
3. DM Water as make up water
4. Drinking Water (Clarified and filter Water)
5. For Ash disposal
MAJOR IMPURITIES OF WATER AND THERE EFFECTS
EFFECT OF IMPURE WATER
1. Scaling
2. Deposition
3. Corrosion of plant items
4. Effects water treatment process
Soluble
gases
H2S, O2,CO2 Corrosion of boiler tubes
Suspended
solids
Sediment and
turbidity
Organicmatter
Oils and greases
Sludge and scale carryover
Carryover foaming and corrosion
Foaming and deposition
Dissolved
solids Salts of Ca,Mg, Na,Si Scale and corrosion

DEPOSITS AND SCALE
The amount of solute dissolve in a solvent is called its solubility. Solubility is different for different
solutes. Solubility of compounds depends on temperature. If solubility of compound decreases with
increase temperature ,then the solubility limit may exceeded as the temperature raises excess solute
initially in the solution as will now separate from the solution as solid. It precipitate and form a hard
deposit (scale) on heat transfer surface. This could leads to serious loss of heat transfer area
When two different type of electrolytes are dissolved, interaction of ions from dissolved compounds can
lead to precipitation of third compound which may form scale on heat transfer area of plant
CORROSION
When environment favors metals converts into metal oxide by reaction with oxygen or oxygen source
such as water is called corrosion
The most common causes of corrosion are
1. Dissolved gases (primarily oxygen and carbon dioxide)
2. Low Ph
3. Attack of areas weakened by mechanical stress, leading to stress and fatigue cracking.
Many corrosion problems occur in the hottest areas of the boiler like
1. Water wall, 2. Super heater tubes 3. Deaerators, 4 Feed water heaters, 5. Economizers.
CORROSION MECHANISM
In this corrosion cell Iron anode and Cu cathode immersed in sodium chloride salt solution
At anode at cathode
Fe Fe+
O2 + 2H2O + 4e 4(OH-
)
The product of anode and cathode diffuse to wards one another and form precipitate of Ferrous
Hydroxide
Fe+2
2OH-
Fe (OH) 2
OR
4Fe(OH)2 + O2 + 2H2O 2Fe2O3

FORMATION OF PROTUCTIVE OXIDE FILM
When mild steel immersed in de aerated water treated with alkali forms magnetite Fe3O4. Magnetite
is dense oxide layer firmly adhere to metal surface, this oxide film becomes a physical barrier between
the metal and the water this is called as “passivity”
Fe + 2H2O Fe+2
+ 2OH-
+ H2
Fe+2
+ 4H2O Fe3O4 (magnetite) + 4H2
Fe+2
+ 3H2O Fe2O3 (hematite) + 3H2
THE CORROSION O F SINGLE METAL (GALVANIC CORROSION)
Metal poses oxide film on its surface, when it is exposed to air or water the film may crack at some
points due to differential stresses, temperature, conductive deposits
The cracked area becomes anode and remaining area become cathode, at this point it will be easier for
metal ion to leave the metal lattice (i.e. corrosion)
DIFFERENTIAL AERATION
Areas of metal where the oxygen concentrations are high will become cathode. Areas of metal where
the oxygen concentration is low will become anode this effect is known as differential aeration
E.g. two pieces of steel are to be welded together
This type of corrosion occur in boiler tube, water tanks, condenser tube and in the situation where
deposits impede access of oxygen
AERATED AREAPOOR OXYGEN AREA

ACID CHLORIDE CORROSION
Both acid and alkali cause serious boiler tube corrosion. Contaminants of boiler water (from feed and
condenser leakage) like magnesium chloride MgCl2 and NaCl can form acid
MgCl2 + H2O HCl + MgO
NaCl + H2O HCl + NaOH
This acid attacks oxide film and underlying metal
Fe3O4 + HCl FeCl2 + FeCl3 + H2O
Fe + 2HCl FeCl2 + H2
Under operation condition FeCl2 FeCl3 are not stable, diffuses away from reaction and forms Fe3O4 and
HCl again. This acid is then available to attack more iron The reaction sequence produces a rapid
thickening of iron oxide layer on metal surface This process once established cannot stopped even if we
increase the alkali content.
To arrest the acid corrosion, boiler tubes are soaked with hot NaOH, Plant operated at low load with a
boiler water containing substantially excess of NaOH. NaOH slowly penetrates into corrosion area and
neutralizes acid chloride
Low makeup or feedwater pH can cause serious acid attack on metal surfaces in the preboiler and
boiler system. , feedwater can become acid by improper operation or control of demineralizer cation
units and cooling water contamination from condensers
Acid corrosion can also be caused by chemical cleaning operations, Excessive exposure of metal to
cleaning agent, and high cleaning agent concentration. Failure to neutralize acid solvents completely
before start-up has also caused problems.
In a boiler and feedwater system, acidic attack can be localized at areas of high stress such as drum
baffles, "U" bolts, acorn nuts, and tube ends.
Another effect frequently observed is Hydrogen embrittlement or decarburization of the tube metal i.e.
H2 formed in corrosion reaction reacts with carbon in alloys and form CH4. Carburization of metal
reduces the thickness of tube. The extent of carburization depends on rate of corrosion. Once the cyclic
process of corrosion and carburization established can continue even alkali concentration of boiler
water increased or boiler is taken off load. To arrest this kind of corrosion Replacement of tubes is
preferred

CAUSCAUSCAUSTIC CORROSION
Concentration of caustic (NaOH) can occur either as a result of steam blanketing or by localized boiling
beneath porous deposits on tube surfaces.
As we know NaOH can deposit on surface metal by hide out mechanism. Protective Iron oxide layer of
metal easily soluble in deposited NaOH leads to caustic corrosion. Caustic corrosion forms clean pits
and loosely packed oxide layer patterned in the surface of metal is called gouging.
STRESS CORROSION
Localized concentration of dissolved salts in the evaporation section of plant causes stress corrosion
cracking. Stress conditions is may be due to operating condition, structural constraints and residual
stress in the tubing,
Stress corrosion is less common than acid chloride and caustic attack
Stress corrosion observed in mild steel and austenitic steel
FACTORS EFFECTIN CORROSION RATE
1. The rate of corrosion of iron depends on different factors like temperature, fluid velocity, pH and
content of oxygen.
2. Low pH, acid solution, aerated solution is more corrosive than neutral solution.
3. High ph value and low oxygen level giving the lowest corrosion.
4. The minimum corrosion rates occur at pH value 9 – 12
5. , However serious corrosion occur in high alkaline as well as acid condition
6. Corrosion reaction also depends on rate of cathode and anode reactions
7. When large cathodic area coupled to small anodic area attack on the anode will be intense E.g.
steel bolts are used to faster copper or brass compound the bolts could sufferer very severe corrosion

SCALE FORMATION
Scale is a deposited layer of slightly soluble salt formed on a heat transfer surface. Scale consist of Ca
and Mg combined with sulphate, carbonate or phosphate and may also contains silica
A carbonate deposit is usually granular and sometimes of a very porous nature. the scale looks dense
and uniform Carbonate scale can easily identified by dropping scale in acid solution give carbon dioxide
effervescence
A sulphate deposit is much harder and more dense than a carbonate deposit because the crystals are
smaller and cement together tighter.
A Sulphate deposit is brittle, does not pulverize easily, and does not effervesce when dropped into acid.
A high silica deposit is very hard, resembling porcelain. The crystal of silica is extremely small, forming
a very dense and impervious scale. This scale is extremely brittle and very difficult to pulverize.
It is not soluble in hydrochloric acid and is usually very light colored.
Iron deposits, due either to corrosion or iron contamination in the water, are very dark colored Iron
deposits in boilers are most often magnetic. They are soluble in hot acid giving a dark brown colored
solution.
The formation of scale on boiler tubes would result in a loss of heat transfer and consequently a loss of
boiler output. If thickness of scale increases it could result in serious over heating and boiler tube
failure. Scale can be removed by chemical cleaning
Tri sodium phosphate is used to remove Ca and Mg sulphates. Tri sodium phosphate converts Ca and
Mg sulphates into insoluble Ca and Mg phosphates. These are removed by continuous blow down
BOILER WATER TREATMENT AND STEAM PURITY
The water treatment and steam purity maintain boiler and turbines at high level of availability and
efficiency by preventing
1. Corrosion in feed, boiler and steam systems
2. Scale and deposit formation on heat transfer surface
3. Deposition and corrosion in turbines

SOURCE OF ALKALINITY OF BOILER WATER
Generally minimum corrosion rates occur at ph value 9 – 12(i.e. alkaline medium) but the DM water ph
is 6.8-7.2 to increase ph alkaline agents are dosed to boiler water
In low pressure boiler NaOH and Na2CO3 are used as alkalinity source. In high pressure boiler NaOH and
Na2CO3 are not used because solubility of Na2CO3 is very less at high pressure and deposits on tube
surface this is called Hide Out
NaOH and Na2CO3 neutralizes acid in boiler water as below
HCl + NaOH NaCl + H2O
But NaOH converts into Na2CO3 it is insoluble at high pressure and deposits on tube surfaces
2NaOH + CO2 Na2CO3 + H2O
In high pressure boiler Tri Sodium Phosphate TSP (Na3PO4) and Na2HPO4 are used as alkalinity source
Na3PO4 + H2O Na2HPO4 + NaOH
Na2HPO4+ H2O NaH2PO4 + NaOH
They neutralizes Acid species in boiler water as below
HCl + NaOH NaCl + H2O
If concentration of NaOH increases reaction moves to left side this is called coordinated phosphate. This
TSP and DSP maintain PH of boiler water between 9-12 and protect boiler from corrosion
In poor circulation and zone of high heat flux areas of boiler (feed and condensate). Alkaline agents like
Ammonia, hydrazine, occasionally organic amines are also used this called all volatile treatment (AVT).
Ammonia used to boost up PH and Hydrazine used to remove oxygen
PHOSPHATE VS PH GRAPHS
Phosphate Vs. PH graphs shows concentration of phosphate and at which corrosion can be minimized

PROBLEMS IN DIFFERENT PARTS OF BOILER
FEED WATER HEATERS
Feed water heaters constructed of copper alloy and/or stainless steel, Feed water heaters are generally
classified into two types
1. Low-pressure heaters (ahead of the deaerator)
2. High-pressure heaters (after the deaerator)
PROBLEMS IN FEED HEATERS
1. The primary problems is corrosion, due to oxygen and improper Ph,
2. Due to the temperature increase across the heater, incoming metal oxides are deposited in the heater
3. Stress cracking of welded components can also be a problem
4. Erosion is common in the shell side, due to high-velocity steam impingement on tubes and baffles.
Causes of corrosion are 1. Lack of control of feed water chemistry 2. Design feature
In feed and condensate system corrosion problems arises during start – up. During start – up initial
condensate formed on the steam side of feed heater tubes contains low level of ammonia (and pH) and
high in oxygen and carbon dioxide, this combination can lead to a much enhanced attack of copper based
alloy tubes
4Cu + O2 2Cu2O
If alloy contains Ni
Cu2O + Ni 2NiO + 2Cu
In above process Cu metal forms a very thin film on the outside of the nickel oxide layer (exfoliation
corrosion) that readily become detached and are carried away with the heater drains into the feed water
Mild steel, alloy steel and titanium are used in feed and condensate system, greater than 9.2 PH and up
to 50µg/kg of oxygen develops stable protective oxide layer on metal surface, and corrosion can be
minimised
Oxygen levels in feed water is controlled by deoxygenating agents like Hydrazine N2H4 and PH is
increased by
ammonia NH3

PROBLEMS IN DEAERATORS
Deaerators are used to heat feed water and reduce oxygen and other dissolved gases to acceptable
levels the problems in dearator are
Corrosion fatigue at or near welds is a major problem in Deaerators Most of corrosion fatigue cracking
is due to manufacturing procedures, poor welds, and lack of stress-relieved welds .Operational
problems such as water/steam hammer can also be a factor.
Other forms of corrosive attack in Deaerators are
1. Stress corrosion cracking of the stainless steel tray chamber
2. Inlet spray valve spring cracking, corrosion of vent condensers due to oxygen pitting,
3. Erosion of the impingement baffles near the steam inlet connection.
PROBLEMS IN ECONAMIZER
1. Economizers improve boiler efficiency by extracting heat from flue gases discharged from the fireside
of a boiler. Economizers are arranged for downward flow of gas and upward flow of water
.
2. in a steaming economizer, 5-20% of the incoming feed water becomes steam. Steaming economizers
are particularly sensitive to deposition from feed water contaminants and resultant under-deposit
corrosion.
3. Erosion at tube bends is also a problem in steaming economizers.
Oxygen pitting, caused by the presence of oxygen and temperature increase, is a major problem in
economizers
4. Corrosion can also occur on the gas side of the economizer due to contaminants in the flue gas,
forming low-pH compounds
PROBLEMS IN SUPERHEATER
Super heater corrosion problems are caused by a number of mechanical and chemical conditions
1. Major problem is the oxidation of super heater metal due to high gas temperatures
Deposits due to carryover from feed water (failures usually occur in the bottom loops-the hottest areas
of the super heater tubes)
2. Oxygen pitting, particularly in the pendant loop area, is another major corrosion problem in super
heaters. It is caused when water is exposed to oxygen during downtime.
Note: A nitrogen blanket and chemical oxygen scavenger can be used to maintain oxygen-free
conditions during downtime.
WATER WALL TUBE CORROSION
We use NaOH and Na2CO3 for alkaline source for boiler but the solubility of Na2CO3 is very less at high
pressure and deposits on tube surface this is called Hide Out. In boiler tubes alkali hide out is enhanced
by the pores oxide layer on metal surface or where the crevice are present. Within the pores of the oxide
layer or the crevice wick boiling can takes place. Initially pores and crevices are flooded with bulk boiler
water containing dissolved salts and alkali. When boiling occurs the steam is ejected from the pores
leaving behind a concentrated solution as the pores approach dryness the volume of steam being

produced fall away and the pores re flooded with boiler water and cycle is repeated. Finally less soluble
salts (Na3PO4, NaCl CaSO4) and more soluble alkali (NaOH) will deposit in pores and crevices the oxide
layer thickness increases as cycle’s repeats. For e.g. in large boiler operating at 160 bar the oxide layer
growth rate is approximately 15 µm per 10000 hrs.
Boiler tubes are chemically cleaned when the oxide thickness has increased to 50-100µm
Neutral salts like Na2SO4, CaSO4, and Si deposit in the pores and crevices without damaging the
protective oxide film on the metal surface. If how ever the salts present in the boiler water when
concentrated up can produce an acid solution or a strongly alkaline solution lead to the acid or alkaline
corrosion
Hide out effects can be minimized by design or by regular chemical cleaning
STEAM
Steam contains sodium salts (NaCl, Na2SO4), NaOH and silica as impurities, these impurities enters in to
steam via
1. Evaporation from boiler water,
2. Entrainment of boiler water droplets into the saturated steam
4. Spray or leakage of boiler water in to super heater steam
SODIUM SALTS IN STEAM
Low concentration of sodium salts observed in steam, form corrosion in super heater
As increasing temperature in super heater solubility of sodium salts and NaOH decrease, will deposit on
super heater tubes. Deposited sodium salts will form concentrated solution of NaOH in tube surface
and cause stress corrosion
SILICA IN STEAM
Allowed concentration of silica in steam is <20ppb. Excess concentration of silica in steam will deposit on
turbine blades leads to significant loss of unit output
When minor deposition of silica occur it will normally washed with condensate water When more
extensive deposits have been formed it may be wash with warm alkali, it re dissolves silica effectively
Silica in steam is controlled by solid alkali i.e. trisodium phosphate form silicates with silica. Then silicates
passed out by blow down
After over haul work or boiler tube repair silica concentration is high. During the over haul work or boiler
tube repair silica containing material like coal, ash and insulating material enters into boiler water. In
this case boiler can be operated with silica level of 50ppb and at reduced pressure and load un till the
concentration of silica in boiler water has been reduced
NON REACTIVE SILICA
Generally silica is two types’ soluble silica and non reactive silica. Soluble silica can easily removed from
by water treatment process, where as non reactive silica can not removed by water treatment process
and carried forward with the make up water
This non reactive silica converts into soluble silica at boiler temperature and pressure

DEPOSITION OF SODIUM SALTS IN TURBINE AND REHEATERS
As super heated steam passed through the HP turbine, pressure and temperature decreases solubility
of sodium salts and NaOH decreases and will deposit on surface of turbine leads to stress corrosion
If reaheaters are pendent shape the condensate formed will then drain down to bottom bends with
Sodium sulphate
When the unit is taken offload and allowed to cool down condensation of steam occur in reheater lead
to re solution of the deposited salts. On return to service this Sodium sulphate solution will re-
evaporate leaving dry salt in the bottom. This cycle of on-load deposition off-load resolution and
accumulation of salt in the bottom bends of reheater leads to high concentration of Sodium sulphate
When air is admitted the reheater pitting attack of the reheater tubes and stress corrosion can takes
place which is enhanced by the Sodium sulphate
To avoid this problem, limiting the concentration of sodium and sulphate in steam and avoiding
carryover,

‘
I
BY
RAMESH KOMMA
KTPP-CHELPUR
PRIMARY WATER FOR
GENERATOR COOLING
IN THERMAL POWER PLANT
TSGENCO

NTRODUCTION
Kinetic energy from Turbine converts in electrical energy by generator
When mechanical energy do the work against electromagnetic force electricity is produced, during this
process high current flow through stator of generator and heat is generated in stator coil
Demineralized water is used to remove the heat from stator coil is called primary water or Stator
water
There are three types of cooling systems
Air cooling Below 150MW
Hydrogen cooling 150-400MW
Hydrogen & water cooling Above 400MW
In KTPP 500 and 600MW Hydrogen & water cooling system used remove the heat from stator coil
For stator water cooling the stator bars are equipped with hallow strands
SCHEMATIC DIAGRAM OF HYDROGEN AND WATER COOLING OF GENERATOR

WATER COOLING SYSTEM
NOTE :- Filters are used to remove the debris in stator water circuits that may block stator coil because
stator coil hallow conductors are typically 1 to 3mm wide and 3500 to 12000mm long they are packed in to
the stator bar with numeric bends
Deionizer used to remove dissolved solids in stator water, in this deionizer strong acid cation and strong base
anion resin used in 1:1 ration. The deionizer resin is replaced when primary water conductivity is raised
Plate heat exchanger are used to cool the circulating stator water which gains heat in generator
PHE
PHE
MAKE UP
WATER
DEIONIZER
STORAGE
TANK
MAKEUPFILTER
MAINFILTER
NaOH
GENERATOR
2PUMPS

COOLING WATER CHEMISTRY
Generator provided with hallows strands/conductors connected to common header at inlet and outlet of the
winding. The conductors and headers are commonly made up of copper
As the water enters into the hallow conductor , Copper comes in contact with water and forms cuprous oxide
( Cu2O) red colour and cupric Oxide (CuO) black colour depends on the electrochemical potential which
varies with temperature and PH of water. The copper Oxide forms passive layer on the inner surface hallow
copper conductor, the stability of the passive layer increases with increase in pH.
The copper corrosion low at high oxygen level but has the maximum in the 100 to 500ppb range. Also an
increase in PH reduces copper corrosion considerably, it suggest that alkalization of stator water could
bebeneficial. the rate of corrosion depends on PH and DO
The makeup water enters into low DO type stator water system, copper release copper oxide excess of the
solubility limit at operating temperature (85o
C ). One part of copper oxide forms passive layer another part
moves in circuit and deposits at critical areas of the winding it is called plugging. The re deposition of copper
oxides causes blockage of strands. The solubility of the copper oxides depends up on PH and temperature of
water

In low oxygen system and neutral PH cuprous oxide Cu2O will be predominant, while in high oxygen and
alkaline system the oxide will be mainly cupric oxide CuO
Stator Water Treatment Options
1. Low dissolved oxygen (<10ppb) and neutral PH
2. High dissolved oxygen (>200ppb) and neutral pH
3. Low dissolved oxygen(<10ppb) and at alkaline pH(8-9)
4. High dissolved oxygen (>200ppb)and at alkaline pH(8-9) not suitable for cooling due to clip corrosion
Problems In Stator Water Coil
1. Leaks in stator winding at brazed connections
2. Water box leakage combined with strand to strand leakage
3. Small leakage will not damage winding in normal operation because H2 gas pressure maintained
above the stator cooling water but causes when generator is degassed
4. Leakage in stator hydraulic components and connections
5. Clip to strand leakage due to crevice corrosion
Primary Water Parameters
pH 8 to 9
DO <100
CONDUCTIVITY
at 25oC µS/cm
<2
Total Cu µg/l <20
Total Fe µg/l <20

‘
I
BY
RAMESH KOMMA
Senior Chemist /TSGENCO KTPP Stage-I
CHELPUR
COAL
TSGENCO

COAL
Definition:
Coal is a combustible fossil fuel sedimentary rock composed mostly of carbon and hydrocarbons.
Advantage of Coal:
Easily combustible produces high energy upon combustion, distributed all over the world. It is easy to transport and
comparatively inexpensive due to large reserves and easy accessibility
Very large amounts of electricity can be generated in one place using coal, fairly cheaply.
The oil and gas transportation needs to setup high-pressure pipelines and back them with necessary security cover.
Most of the coal mining regions are well connected to the industrial belts by a rail network, which is again the one of the
cheapest mode of transportation available.
Disadvantages of Coal
it is Non-renewable and fast depleting. One of the biggest disadvantages of coal is air pollution. Numerous harmful gases,
including carbon dioxide, Sulphur dioxide and ash, are released. In fact, it tends to emit twice as much CO2 than the other
fossil fuels.
Coal storage cost is high especially if required to have enough stock for few years to assure power production availability.
Coal power puts the lives of the people who dig the coal in danger, and it gives them poor lung quality. Coal-fired power
plants emit mercury, selenium, and arsenic which are harmful to human health and the environment
A coal plant generates about 3,700,000 tons of carbon dioxide every year; this is one of the main causes of global warming.
A single coal plant creates 10,000 tons of sulphur dioxide, which causes acid rain that damages forests, lakes, and buildings.
Energy Content in Coal
The basic function of the power plant is to convert energy in coal to electricity. Therefore, the first thing we should know is
how much energy there is in coal. Energy content of coal is given in terms of Kilojoules (kJ) per Kilogram (kg) of coal as the
Gross calorific value (GCV) or the Higher Heating value (HHV) of coal. This value can vary from 10500 kJ/kg to 25000 kJ/kg
depending on the quality and type of the coal.
Calorific Value or Heating Value
This is the most important parameter that determines the economics of the power plant operation.It indicates the amount
of heat that is released when the coal is burned.
The Calorific Value varies on the geographical age, formation, ranking and location of the coal mines.
It is expressed as kJ/kg in the SI unit system. Coal has a Calorific Value in the range of 9500 kJ/kg to 27000 kJ/ kg.
The calorific value is expressed in two different ways on account the moisture in the coal
1. Gross Calorific Value or Higher Heating Value it is the total heat released when burning the coal.
2. Net Calorific Value or Lower Heating Value it is the heat energy available after reducing the loss due to moisture.

CV of Coal analyzed in three ways
1. As Received’ coal is the coal received in the power plant premises. The payment to the coal companies are normally made
based on the ‘As Received’ coal properties.
2. As Fired’ coal is the coal entering the boiler system. The performance of the boiler and power plant is based on the ‘As
Fired’ coal properties.
3. Air Dried’ coal is what is used in the laboratory for analysis. This coal is dried in atmosphere and has the lowest amount of
moisture. Laboratory results are reported as ‘Air Dried’ coal properties.
The difference between the above three conditions is the proportion of the Moisture.
The Calorific Value and other coal constituents analysed in the laboratory on ‘Air Dried’ basis is converted to ‘As received’ or
‘As Fired’ basis proportional to the moisture content.
Useful Heat Value (UHV) = 8900 - 138(A% + M %) Kcal/Kg
Gross Calorific Value (GCV) = (UHV + 3645 – 75.4 M %) 1.466 Kcal/Kg
(Air Dry Basis)
Gross Calorific Value (GCV) = [GCVAD] (100 – TM %)( 100 – M %) Kcal/Kg
(As fired Basis)
Net Calorific value = [GCV] – 10.02 M% Kcal/Kg
Coal Price
COAL
GRADE
GCV PRICE
COAL
GRADE
GCV PRICE
G1 above 7000 3896 G10 4301 - 4600 1400
G2 6701 - 700 3733 G11 4001 - 4300 1130
G3 6401 - 6700 3569 G12 3701 - 4000 910
G4 6101 - 6400 3336 G13 3401 - 3700 690
G5 5801 - 6100 3319 G14 3101 - 3400 610
G6 5501 - 5800 2360 G15 2801 - 3100 510
G7 5201 - 5500 1840 G16 2501 - 2800 574
G8 4901 - 5200 1700 G17 2201 - 2500 420
G9 4601 - 4900 1500
Heat Rate
Heat rate is the heat input required to produce one unit of electricity. (1 kw/ hr) One Kw is 3600 kJ/hr.
If the energy conversion is 100 % efficient then to produce one unit of electricity we require 3600 kJ.

Types of Coal
 Peat
 Lignite
 Sub bituminous coal
 Bituminous coal
 Anthracite
Peat
It is initial stage of Coal formation.
A soft brown mass of compressed, partially decomposed vegetation that forms in a water-saturated environment .Dried
peat can be burned as fuel
Lignite
Lignite, often referred to as brown coal, is brownish-black in color.
It has carbon contents around 25-35%, a high inherent moisture content sometimes as high as 66%, and an ash content
ranging from 6% to 19%.
It is considered an “immature” coal that is still soft.
The energy content of lignite ranges from 10 to 20 MJ/kg on a moist, mineral-matter-free basis.
Lignite has a high content of volatile matter which makes it easier to convert into gas and liquid petroleum products than
higher ranking coals.
It is used for generating electricity.
Its high moisture content and susceptibility to spontaneous combustion can cause problems in transportation and storage.

Sub bituminous coal
This is a dull black coal with a higher heating value than lignite, and is used principally for electricity and space heating.
It has 35-45 percent carbon contents.
The heat content of sub-bituminous coals range from 19,306 to 26,749 kJ/kg.
Bituminous coal
Bituminous Coal or Black Coal is of higher quality than lignite coal but of poorer quality than anthracite coal.
The carbon content of bituminous coal is around 60-80%; the rest is composed of water, air, hydrogen, and sulfur.
The heat content of bituminous coal ranges from (24 to 35 MJ/kg) on a moist, mineral-matter-free basis.
Bituminous coal is used primarily to generate electricity and make coke for the steel industry.
Anthracite
Also known as "hard coal" that was formed from bituminous coal.
It is very hard and shiny. This type of coal is the most compact and therefore, has the highest energy content of the five
levels of coal. It is used for space heating and generating electricity. Anthracite is coal has the highest carbon contents,
between 86 and 98 percent
The heat content of anthracite ranges from 26 to 33 MJ/kg on a moist, mineral-matter-free basis.

Proximate Analysis:
Indicates the contents in the fuels in percentage by weight.
 Moisture
 Volatile material
 Fixed carbon
 Ash
Moisture Content:
Water expelled from the fuel by specified methods without causing any chemical change to fuel.
1 g of fine powdered air dried coal is weighed in crucible. Crucible is placed inside oven & Temperature is maintained at 105
to 110◦ C for 1 hour. Then sample is taken out & weighed.
Loss in weight is the moisture content in the fuel.
Loss in weight
Percentage of moisture = ------------------------ x 100
Wt. of coal taken
Moisture in coal evaporates during burning taking Latent heat of evaporation; hence moisture lowers the calorific value
“Lesser the moisture content, better the quality of coal as a fuel”
Volatile Matter:
Dried sample from the crucible is covered with a lid & placed in an electric furnace.
Temperature is maintained at 925
◦
C + 25
◦
C for 7 minute. Then cooled first in air, then in a desiccator & weighed again.
Loss in weight is reported as volatile matter present in coal.
Loss in weight due to removal of volatile matter
Volatile material = ------------------------------------------------------------- x 100
Wt. of coal sample taken
High volatile matter content means that high proportion of fuel will distill over as gas or vapour, a large proportion of which
escapes as unburnt. It will burns with long flame, high smoke and has low calorific value.
“Lesser the volatile matter, better the rank of the coal”

Ash:
Residual coal in crucible is heated without a lid in a muffle furnace at 750 to 800
◦
C for one hour. Then cooled first in
air and next in desiccator. Then weighed and the ash content is reported.
Wt. of Ash left
Percentage of Ash = ---------------------- x 100
Wt. of coal taken
Ash is a useless, non-combustible matter and it reduces the calorific value of coal.
Ash also causes hindrance to flow of air and heat, thereby lowering the temperature.
“Lower the ash content, better the quality of coal”.
Fixed carbon
Percentage of Fixed carbon = 100 - % of (moisture + Volatile matter + Ash)
“Higher the percentage of fixed carbon, greater is it’s calorific and betters the quality of coal.”
Ultimate Analysis:
Gives the Elementary composition of
 Carbon
 Hydrogen
 Oxygen
 Nitrogen
 Sulphur in percentage by Weight
Determination of Carbon & Hydrogen:
1 g of coal is burnt in current of oxygen in a combustion apparatus.
C & H are converted into CO2 and H2O.
Gaseous products are absorbed in KOH & CaCl2 of known weights.
Increases in weights are determined.
Carbon:
Increase in weight of KOH tube * 12
% of C = ------------------------------------------------------- x 100
Weight of coal sample taken * 44
Hydrogen:
Increase in weight of CaCl2 tube * 2
% of H = ---------------------------------------------------- x 100
Weight of coal sample taken * 18
“Greater the percentage of Carbon and Hydrogen, better is the coal in quality and calorific value”.

Determination of Nitrogen:
1. 1g of powdered coal is heated with conc. H2SO4 with K2SO4 as catalyst in a Kjeldal flask.
2. After solution becomes clear, treated with excess KOH.
3. NH3 is liberated & absorbed in known volume of standard acid solution.
4. Unused acid is determined with NaOH.
5. From the volume of the acid used by NH3 liberated % of N in coal is determined.
Volume of acid used x Normality x 1.4
% of N = ------------------------------------------------------
Weight of coal taken
“Nitrogen has no influence in the calorific value. A good quality coal should have very little nitrogen.”
Determination of Sulphur content:
From washings of bomb in bomb calorimeter, Sulphur is converted into into sulphate.
S + 2H +2O2 2SO4
H2SO4 + BaCl2 4 + 2HCl
Weight of BaSO4 obtained *32
% of S = ------------------------------------------------------------------ x 100
233 * weight of coal sample taken in bomb calorimeter
Determination of Oxygen:
It is determined from the difference.
% of O = 100 – percentage of ( H + S + N + Ash ).
Oxygen content decreases the Calorific value of coal
Oxygen is in combined form with Hydrogen, thus hydrogen available for combustion is lesser than actual.
“Good quality coal should have low percentage of Oxygen”
Reporting:
Fuels are Heterogeneous in Nature so it is essential to report all the data analytically.
Basis of reporting
 Run-of-mine (ROM).
 As-received.
 Air dried.
 Dry.
 Dry and ash free ( d.a.f ).
 Dry and mineral matter free ( d.m.m.f ).
 Moist mineral matter free or simply mineral free.

KTPP STAGE – I and II RECCEIVES COAL FROM
COAL MINE GCV
Tadicherla G8
Kakatiya khani OCP – II bhupalapally G11
Kakatiya khani OCP – II bhupalapally G9
Kakatiya khani 1A SLK bhupalapally G11
Kakatiya khani 1A RND bhupalapally G10
Kakatiya khani CHP RND bhupalapally G11
Kakatiya khani CHP SLK bhupalapally G11
RECHINI G12
OCP – III G11
RAMAKRISHNAPUR G12

‘
I
BY
RAMESH KOMMA
KTPP-CHELPUR
MILLS OR PULVARISERS
IN THERMAL POWER PLANT
TSGENCO

NTRODUCTION
The most efficient way of utilizing coal for steam generation is to burn it in pulverized form
Pulverized coal burns like gas, can be easily lightened and controlled
the pulverizer receives raw coal from coal feeder and pulverizes it to fine powder
The four principles involved in pulverization
1) Drying
2) Grinding
3) Circulation
4) Classification
Drying
In pulverizer Inherent and surface moisture of the coal is reduced by the hot from the air heaters
Grinding
Grinding of coal involves
1. Impaction: - coal is impacted by an outside force
2. Crushing: - coal is forced between two fixed objects
3. Attrition: - where the coal is ground by rubbing or friction
IMPACT CRUSHING ATTRITION
Circulation
With the help of primary air circulate through the pulaverizer due to the circulation of coal heavy
particles are removed by centripetal force
Classification
The circulation air is also used to classify the pulverized coal while carrying it to the burners
Classifier located at the top of the mill. It returns the oversize particles back to the pulverizer and allows
the proper sized coal to pass out the mills to the burners
Classifiers provides desired fine coal to the burners

TYPE OF PULVERIZERS
BALL MILL BOWL MILL HAMER MILL

KTPP BOWL MILL SPECIFICATIONS
500MW 600MW
TYPE OF MILL XRP 1043 BOWL MILL
MILL BASE CAPACITY(T/Hr)* 73.6 (Design Coal
MOTOR SPEED(RPM) 985
TOTAL WEIGHT OF MILL(T)
(including motor) 30
TYPE OF LOAD Moderate Shock
ROTATING WEIGHT OF MILL(T) 22.88
SPRING RATE(Kg/cm) 2730
SPRING PRE LOAD(Kg) 9500
MILLOUTLETTEMPERATURE
RANGE
66ºC -100ºC
AIR FLOW (T/Hr) 111
FINENESS * 70%rough 200 Mesh
The capacity for bituminous/ sub-bituminous coal having hard grove index (HGI) as 52 and moisture
less than 9% and outlet fineness 70% thru’ 200 Mesh and 98% through 50 Mesh.

MILL PERFORMANCE CRITERIA
1. Fineness
2. Coal grindability
3. Rejects
4. Capacity
FINENESS:
Fineness is the indication of quality of the pulverizer action, fineness of coal is measured by passing
100gr of coal through set of sieves i.e. 50,100,200.
A 70% coal passing through 200 sieve, 90% through 100 sieve and above 98% through 50 sieve indicates
optimum mill performance
If more than 70% coal passes through 200 sieve, power consumption and mill wears are increased
If less than 70% coal passes through 200 sieve, higher the carbon loss and fuel consumption
less than 98% of coal passing through 50 sieve indicates improper internal settings, boiler slagging and
high unburned carbon
Reduced fineness is the indication of problems in classifier vane position, loss of roller tension Roller wear
Classifier vane wear and exceeding mill capacity
COAL GRINDABILITY
The measure of the coal resistance to crushing is called coal grind ability
Grind ability of coal is measured by hard grove index (HGI) test
Moisture and ash content effects the grind ability of coal
HGI is determined through a multi-step procedure:
1. A 50-gram sample of prepared coal that is uniform in size is placed inside a grinding unit
2. The unit undergoes a standard number of revolutions 60 under a specified pressure
3. Steel balls within the unit crush the coal sample
4. The coal fines are sorted and the quantity of coal less than a specified size is recorded and
converted into a Hardgrove Grind ability Index (HGI) value
HGI=13+6.93*W

COAL REJECTS
The foreign material, mixed with the coal, that cannot be grinded is rejected by the mills and
discharged in a “pyrites box”
Rejects are the mixer of different materials such as pyrites, stones, tramp iron, Iron disulphide etc.
The amount of pulverizer rejects is one indication of mill performance
MILL CAPACITY
The grinding capacity of a mill depends upon the grinding mechanism and the operational conditions

NaOH
Tank DMCW overhead tank
10M3
DM Water from CEP Discharge
&
Hot well make up pumps
3 PLATE HEAT EXCHANGERS3 DMCW PUMPS
TD
BFP
CEP TURBINE
OIL
HYDROGEN
COOLER
PRIMARY
WATER
COOLER
EXCITER
AIR
COOLER
SEAL OIL
COOLER
2 DMCW PUMPS
SWAS
ROOM
RACK
SWAS
ROOM
CHILLER
BOILER AUX
FD, ID.PA
FANS & APH
MILLS
COMPRESSOR
2 PLATE HEAT EXCHANGERS
MD BFP
&
BOILER
FILL
PUMP
TG COOLING SYSTEM
SG COOLING SYSTEM
DMCW SYSTEM IN THERMAL POWER
PLANT
DMCW SYSTEM IN THERMAL POWER PLANT
In thermal power plant demineralised water is also
used to cool the oil of different pumps and motors
The demineralised water used to cool the turbine
auxiliary pumps and motors is called TG water
The demineralised water used to cool the boiler
auxiliary pumps and motors is called SG water
The DMCW system pipe line and pumps are made up
of carbon steel and mild steel
The rate of corrosion of carbon is minimum in
alkaline medium
To protect the pipe line and pumps of DMCW system
from corrosion, DMC Water is conditioned with
NaoH solution to maintain the PH 8.0 to 9.0 at this
pH the corrosion is minimum

Power plant chemistry by ramesh

Power plant chemistry by ramesh

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Power plant chemistry by ramesh

Similar to Power plant chemistry by ramesh (20)

Recently uploaded

Recently uploaded (20)

Power plant chemistry by ramesh