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8/11/2019 1basic Water Chemistry in Power Plants Opr - Copy - Copy
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WATER CHEMISTRY
IN
THERMAL POWER PLANTS(An Overview)
O.P.RANGWANI
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WATER
The purest available form is from water vapour inatmosphere, as rain, snow or produced by melting of ice.
This water on reaching the ground absorbs differenttypes of gases from atmosphere like nitrogen, oxygen andto a lesser extent carbon dioxide.
Other gasses like ammonia, oxides of nitrogen andsulphur etc. ,also dissolves during rain depending upon the
pollution level of the atmosphere.
Apart from this, the surface water travels to variousplaces and catches organic matter, suspended solids etc.
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SOURCES OF WATER
1. Rivers, lakes and reservoirs (surface drainage water)
2. Underground water (shallow well, deep well, springs)
3. Rain water
4. Sea water
5. Snow melting
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MAIN IMPURITIES IN WATER
1. Suspended (Macro size) - Sand, dirt, silt. This contributesturbidity to raw water.
2. Colloidal - Micro size particles(1-100nm)
3. Dissolved form - Alkaline salts and neutral salts, organicmatter,
Alkaline salts are mainly bicarbonates rarely carbonatesand hydrates of calcium, magnesium and sodium.
Neutral salts are sulphates, chlorides, nitrates of
calcium, magnesium and sodium.
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WATER SUPPLY
SEA 95-96%
FROZEN WATER 2% FRESH WATER 2-3%
Fresh water available is scarce.
We, the human beings, are bent upon polluting this preciousresource.
Imperative to take proper care to conserve and reuse water.
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TYPES OF WATER IN THERMALPOWER PLANT
Cooling water
Boiler water
Process water
Consumptive water
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Pretreatment of raw water
Filter water for softening & DM plant
Ultra pure /demineralised water for boiler makeup/steam generation
Cooling water system.
Monitoring of steam/ water parameters & H.P./L.P. Dosingsystems
WATER TREATMENT IN POWER PLANT
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WATER FLOW DIAGRAM
CLARIFLOCCULATOR
GRAVITYFILTER
D.M.PLANT
SOFTENINGPLANT
COOLINGWATER
U/GSTORAGE
TANK
RAWWATER
DRINKINGWATER
BOILERMAKEUP
C.W.MAKEUP
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PRE-TREATMENT
Pre-treatment takes care of organics, suspended matter andcolloidal silica to some extent.
CLARIFLOCC
ULATORGRAVITY
FILTER
D.M.
PLANT
SOFTENING
PLANT
U/G STORAGE
TANK
RAW
WATER
ALUM & Cl2
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CLARIFLOCCULATOR
Raw
water
ChlorineAlum
Lime Flash
Mixer
Clarification
Sludge
settling
pond
Clarified
water tofilters
Flocculation
Water quality at Clarifier outlet
Turbidity -
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DISINFECTION
Disinfection is destruction of Pathogenic bacteria, virus,germs and other organisms present in water.
It can be achieved by
Gaseous chlorine
Chlorine compounds such as hypo-chlorites, bleachingagent and chlorine dioxide
Ozone
Ultra-Violet radiation
Hydrogen peroxide
Heating
Combination of the above
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FILTRATION
Removal of solid particles from water by passing it througha filtering medium.
Filtration is usually a mechanical process & does notremove dissolved solids.
Filters are mainly of two types.1. Pressure Filters - steel, wood or concrete containers
that are open at the top and function at atmosphericpressure.
2. Gravity filters - closed, round steel shells and functionwith the pressure of the incoming water.
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GRAVITY SAND FILTER
Clarifiedwaterfrom
clarifier
IN
OUT
5th layer
4th layer
3rd layer
2nd layer
1st layer
Gravity Sand Filter
For back washing ofthe GSF water ispassed throughfilter in reverse
direction
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D.M. PLANT
WEAK
ACID
CATION
STRONG
ACIDCATION
ACF
WEAK
BASE
ANION
STRONG
BASE
ANION
MIXED
BED
DEGASSER
D.M.
WATER
STORAGETANK
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COOLING WATER
Type of cooling water
Cooling water chemistry
Cooling water treatment
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COOLING WATER CHEMISTRY
To avoid scale formation
To control corrosion
To control micro biological growth
To control vaccume in condenser
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SCALE FORMATION
scale formation can take place in condenser of thermalpower plants. This may lead to higher back pressure incondenser which in turn lead to loss in condenser vacuumthat causes loss of turbine efficiency resulting in higherheat rate than designed resulting in direct energy loss.
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INTRODUCTION
Circulating Water chemistry is maintained primarily tocontrol
-- Corrosion
-- Inhibit scale formation
-- To minimize micro-organism growth in condenser tube orin cooling water system.
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TYPES OF COOLING WATER SYSTEM
Once through cooling system
Open recirculation cooling system
Closed cycle cooling water system
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COOLING WATER TREATMENT
Softening plant for make up as soft water with
chlorination Chemical treatment for scale inhibition and corrosion
control
Acid dosing with chlorination
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MICROORGANISM FOULING
Micro organism growth in cooling water system leadsto choking of C.W. pumps strainers and coolingtower fills which reduce effective surface area forcooling and desired cooling efficiency is notachieved which leads to higher c.w.inlet cooling
water temperature and loss of condenser vacuum.
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Bio Fouling
Residual Chlorine about 0.5 ppm is being maintained Shock dosing is being done once in a day Bio fouling monitor is being installed Deposit monitor is being installed
Corrosion rack installed
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WATER REQUIREMENT AT DIFFERENT
COC
COC EVOPORATION
LOSS
M3/HR
DRIFT
LOSS
M3/HR
BLOW
DOWN
REQD
M3/HR
TOTAL
MAKE UP
REQD
M3/HR
2 1800 50 1850 3700
3 1800 50 925 2775
4 1800 50 617 2467
5 1800 50 463 2313
6 1800 50 370 2220
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