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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