2nd Integrated Seminar 9.3.2005

9-3-2005 COOLING SYSTEM 2

INTRODUCTION

TYPES OF COOLING SYSTEMS

ONCE THROUGH COOLING SPRAY PONDS SPRAY TOWERS MECHANICAL DRAUGHT TOWERS

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BASICS

HOW IS WATER COOLED IN A COOLING TOWER

WATER DROPLET IN CONTACT WITH AIR WATER ON THE SURFACE OF THE DROPLET EVAPORATES EXTRACTS LATENT HEAT FROM THE REST OF THE DROPLET REST OF THE WATER COOLED WATER MAY BE COOLER OR HOTTER THAN AIR LIMIT IS THE WET BULB TEMPERATURE

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BASICS

WHY IS FILL USED

SURFACE OF DROPLET COOLS QUICKLY AIR FILM AROUND DROPLET SATURATED WITH WATER

VAPOUR CRITICAL PATH BECOMES HEAT TRANSFER WITHIN DROPLET WHEN DROPLET FALLS ON FILL, IT IS MIXED FRESH SURFACE EXPOSED TO AIR FALL OF WATER SLOWED RESIDENCE TIME INCREASED

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BASICS

HOW MUCH AIR DO YOU NEED

RATIO OF WATER TO AIR (L/G RATIO) HIGH L/G RATIO

MORE WATER TO LESS AIR AIR IS MORE SATURATED – DRIVING FORCE REDUCED MORE RESIDENCE TIME OF WATER NEEDED LESS COOLING IN GIVEN TIME LOW FAN POWER

LOW L/G RATIO LESS WATER TO MORE AIR LESS SATURATED AIR MORE COOLING IN LESS TIME HIGHER FAN POWER

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BASICS

IMPLICATIONS

EVAPORATION LOSS BULK OF COOLING TAKES PLACE BY EVAPORATION EVAPORATION LOSS INDEPENDENT OF TOWER DESIGN EVAPORATION VARIES WITH SEASON

SPRAY PONDS/ MIST COOLING DEPEND PURELY ON DROPLET COOLING NO MIXING OF DROPLETS NO INCREASE OF RESIDENCE TIME EFFECTIVENESS WILL BE LIMITED

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COOLING TOWER DESIGN

COOLING TOWER DESIGN IS A COMPROMISE

SPECIFICATION WATER FLOW RATE HOT WATER TEMPERATURE COLD WATER TEMPERATURE LOCATION MATERIAL OF CONSTRUCTION WATER QUALITY

TARGET LOW CAPITAL COST LOW OPERATING COST MEETING SPECIFICATIONS

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PITFALLS - SPECIFICATION WATER FLOW RATE

INCREASED FLOW PROVIDES DESIGN MARGIN TOO MUCH MARGIN CAUSES LOSS OF EFFICIENCY TOWER SHOULD BE TESTABLE AT REAL FLOW

WET BULB TEMPERATURE UNREALISTIC VALUE MAKES TESTING DIFFICULT POSSIBILITY OF UNFAIR DESIGN

RANGE INCREASED RANGE MAKES TESTING DIFFICULT TOWER SIZE INCREASE NOT LINEAR WITH RANGE

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PITFALLS - SPECIFICATION

COLD WATER TEMPERATURE LOW SPECIFICATION INCREASES TOWER COST INCREASES FAN POWER PROVIDES DESIGN MARGIN COST INCREASE NOT LINEAR

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PROCESS DESIGN PROCESS SELECT FILL TYPE

WATER QUALITY APPLICATION

SELECT TOWER TYPE FILL TYPE SPECIFICATION APPLICATION

SELECT MATERIALS OF CONSTRUCTION TOWER SIZE SPECIFICATION ECONOMICS

SELECT AND DESIGN MODEL

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DESIGN OPTIONS LOW FAN POWER

INCREASE TOWER SIZE REDUCE AIR VELOCITY REDUCE AIR PRESSURE DROP AND FAN POWER

INCREASE FILL VOLUME INCREASE WATER RESIDENCE TIME REDUCE AIR REQUIRED REDUCE FAN POWER

INCREASE FAN DIAMETER REDUCE EXIT VELOCITY REDUCE FAN POWER

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COOLING TOWER TYPES FLOW PATTERN

– CROSSFLOW COOLING TOWERS

– COUNTERFLOW COOLING TOWERS

STRUCTURE– STEEL/FRP STRUCTURE– TIMBER STRUCTURE– RCC STRUCTURE

FILL TYPE– SPLASH FILL– FILM FLOW FILL Fig – Cooling Towers

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TOWER TYPESCROSSFLOW

WATER AND AIR IN CROSSFLOW

COMMONLY USED WITH SPLASH FILL

LOW FAN POWER HIGHER PUMP HEAD HIGHER CAPITAL COST THAN

COUNTERFLOW

A = Mechanical Equipment E = Cold Water BasinB = Water Distribution F = Air Inlet LouversC = Fill Packing G = Redistribution AreaD = Drift Eliminators

Fig – Crossflow Tower

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WHY CROSSFLOW

THE DOMINANT TOWER TYPE FOR 30 YEARS VERY EFFICIENT UTILISATION OF SPLASH FILL LOW FAN POWER CONSUMPTION WITH SPLASH FILL RESISTANT TO POOR WATER QUALITY LOW PLAN AREA

PROBLEMS

HIGH PUMP HEAD (UPTO 12 M) NOT EFFICIENT WITH FILM FILLS HIGHER TOWER SIZE-HIGHER CIVIL COSTS HIGHER CAPITAL COST THAN COUNTERFLOW WITH FILM FILLS

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CROSS FLOW FILLS

SPLASH FILLS RECTANGULAR TIMBER TRIANGULAR TIMBER PVC VEEBAR TRIANGULAR PVC PRE STRESSED RCC

Fig – Examples for Crossflow Fills

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TOWER TYPES COUNTERFLOW

WATER AND AIR IN COUNTERFLOW

USUALLY WITH FILM FILL LOW PUMP HEAD LOW FAN POWER LOW CAPITAL COST ECONOMICAL CIVIL DESIGN DEFAULT OPTION FOR POWER

PLANTS

A = Mechanical Equipment D = Drift EliminatorsB = Water Distribution E = Cold Water BasinC = Fill Packing F = No Inlet Louvers

Fig – Counterflow Tower

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WHY COUNTERFLOW

THE ORIGINAL COOLING TOWER TYPE VERY EFFICIENT UTILISATION OF FILM FILL COMPETITIVE FAN POWER WITH FILM FILL LOW PUMP HEAD EASY CONSTRUCTION, LOW CIVIL COSTS LOWEST CAPITAL COST WITH FILM FILLS

PROBLEMS

HIGH FAN POWER WITH SPLASH FILL FILM FILL IS SENSITIVE TO WATER QUALITY

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COUNTERFLOW FILLS

FILM FLOW FILLS HIGH EFFICIENCY CROSS CORRUGATED FILLS RANGE OF FLUTE SIZES SPECIAL VERTICAL FLUTED FILLS FOR POOR WATER

QUALITY

Fig – Examples for Counterflow Fills

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COMPONENTSDRIFT ELIMINATORS

TIMBER AND PVC HERRINGBONE CELLULAR PVC PVC EXTRUDED PROFILE LOW DRIFT LOSSES LOW PRESSURE DROP

Fig – Sample Drift Eliminators

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OPERATING COSTS FAN POWER

CAN BE REDUCED BY DESIGN OPERATING COST REDUCED WITH SPEED CONTROL

PUMP POWER USUALLY OVERLOOKED IN ANALYSIS LOWER FOR FILM FILLED TOWERS OPERATING COST IS FIXED

WATER TREATMENT COST BIOLOGICAL CONTROL CORROSION CONTROL SCALING CONTROL

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OPERATING COSTS

STRATEGY FOR REDUCTION

FAN POWER DUAL SPEED MOTOR CAN SAVE 25-30% VARIABLE FREQUENCY DRIVE CAN SAVE 35-40 % CYCLING OF FANS CAN SAVE 20-40%

PUMP POWER ONCE INSTALLED, SAVING IS DIFFICULT FULL POWER CONSUMPTION EVEN AT LOW PLANT LOADS

CHEMICAL TREATMENT SIDE STREAM FILTRATION CHANGE IN TOWER DESIGN

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OTHER IDEAS

FRP FANS POWER SAVINGS OF MAX 10% OVER GOOD ALUMINIUM FANS INCREASES GEARBOX BEARING LIFE

PERFORMANCE UPGRADE OF TOWER CAN REDUCE POWER CONSUMPTION BY UPTO 40% PAYBACK IN MONTHS

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TYPICAL COSTSTOWER CAPACITY 2000 M3/HR

CAPITAL COST- Rs 18,00,000.

POWER COST (per annum)• FAN POWER Rs 12,00,000/-• PUMP POWER - Rs 15,00,000/-

TOTAL: Rs 27,00,000/-

CHEMICAL TREATMENT COST (per annum)• SCALE AND CORROSION CONTROL: Rs 4,50,000/• BIOLOGICAL CONTROL Rs 2,50,000/-

TOTAL: Rs 7,00,000/-

ANNUAL OPERATING COST Rs 34,00,000/-

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OPERATING COSTS ONE YEAR

Fig - Typical Illustration of Operation Costs for One Year

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OPERATING COSTS FIVE YEARS

Fig - Typical Illustration of Operation Costs for Five Year

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ALTERNATIVES TO COOLING TOWERS

AIR COOLED EXCHANGERS HIGHER CAPITAL COSTS MUCH HIGHER POWER COSTS HIGHER COOLED WATER TEMPERATURE NO WATER REQUIREMENTS LOWER MAINTENANCE

Fig – Air Cooled Exchangers

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REFERENCE

AUTHOR ---- T.SHIVARAMAN

CHIEF TECHNICAL

SHRIRAM TOWERTECH LIMITED

http://www.shriramtowertech.com

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