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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
9-3-2005 COOLING SYSTEM 3
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
9-3-2005 COOLING SYSTEM 4
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
9-3-2005 COOLING SYSTEM 5
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
9-3-2005 COOLING SYSTEM 6
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
9-3-2005 COOLING SYSTEM 7
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
9-3-2005 COOLING SYSTEM 8
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
9-3-2005 COOLING SYSTEM 9
PITFALLS - SPECIFICATION
COLD WATER TEMPERATURE LOW SPECIFICATION INCREASES TOWER COST INCREASES FAN POWER PROVIDES DESIGN MARGIN COST INCREASE NOT LINEAR
9-3-2005 COOLING SYSTEM 10
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
9-3-2005 COOLING SYSTEM 11
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
9-3-2005 COOLING SYSTEM 12
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
9-3-2005 COOLING SYSTEM 13
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
9-3-2005 COOLING SYSTEM 14
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
9-3-2005 COOLING SYSTEM 15
CROSS FLOW FILLS
SPLASH FILLS RECTANGULAR TIMBER TRIANGULAR TIMBER PVC VEEBAR TRIANGULAR PVC PRE STRESSED RCC
Fig – Examples for Crossflow Fills
9-3-2005 COOLING SYSTEM 16
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
9-3-2005 COOLING SYSTEM 17
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
9-3-2005 COOLING SYSTEM 18
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
9-3-2005 COOLING SYSTEM 19
COMPONENTSDRIFT ELIMINATORS
TIMBER AND PVC HERRINGBONE CELLULAR PVC PVC EXTRUDED PROFILE LOW DRIFT LOSSES LOW PRESSURE DROP
Fig – Sample Drift Eliminators
9-3-2005 COOLING SYSTEM 20
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
9-3-2005 COOLING SYSTEM 21
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
9-3-2005 COOLING SYSTEM 22
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
9-3-2005 COOLING SYSTEM 23
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/-
9-3-2005 COOLING SYSTEM 24
OPERATING COSTS ONE YEAR
Fig - Typical Illustration of Operation Costs for One Year
9-3-2005 COOLING SYSTEM 25
OPERATING COSTS FIVE YEARS
Fig - Typical Illustration of Operation Costs for Five Year
9-3-2005 COOLING SYSTEM 26
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
9-3-2005 COOLING SYSTEM 27
REFERENCE
AUTHOR ---- T.SHIVARAMAN
CHIEF TECHNICAL
SHRIRAM TOWERTECH LIMITED
http://www.shriramtowertech.com
9-3-2005 COOLING SYSTEM 28
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