Cooling tower

Introduction
Need
Types of cooling systems & towers
selection
Our cooling tower
Water management
Monitoring &Performance

RANKINE CYCLE

HEAT UTILISATION

TOTAL THERMAL RESISTANCE OF CONDENSER TUBE

WHAT HAPPENS IN A COOLING TOWER

»EVAPORATION OF SMALL PART OF COOLING WATER COOLS THE REST OF WATER.

»SOME AMOUNT OF SENSIBLE HEAT EXCHANGE OCCURS.

»COOLING WATER GETS SATURATED WITH OXYGEN & OTHER GASES PRESENT IN ATMOSPHERE.

»THE CURRENT OF DRY AIR ENTERING THE COOLING TOWER BRINGS WITH IT DUST(fly ash, iron ore dust,etc) , DIRT, MICRO BIOLOGICAL SPORES , ATMOSPHERIC CONTAMINENTS, PROCESS LEAKS VENTED TO ATMOSPHERE: THE COOLING WATER GETS CONTAMINATED.

»CONCENTRATION OF SALTS IN COOLING WATERR INCREASES. THE SALTS PRESENT IN MAKE UP WATER GET ADDED TO THE SALTS LEFT BEHIND BY THE EVAPORATED WATER.

»PROCESS LEAKS CONTAMINATE COOLING WATER.

»THESE CHANGES IN COOLING WATER & SOME OF THE INHERENT PROPERTIES OF WATER LEAD TO PROBLEMS OF CORROSION, SCALING, MICROBIAL GROWTH & FOULING OF THE SYSTEM.

The rate of evaporation of water in cooling tower & subsequent reduction in water temperature depends upon the following factors

Amount of water surface area exposed
Time of exposure
Relative velocity of air over the water droplets formed in cooling tower
RH of air & difference between the inlet air WBT and water inlet temperature
Direction of air flow relative to water

COMPONENTS OF COOLING TOWER

•CONSTRUCTION MATERIAL:(TIMBER,CONCRETE,FIBRE GLASS)

• FILLS : (HEART OF COOLING TOWER)

•DRIFT ELIMINATORS:

•WATER DISTRIBUTORS/SPRAY NOZZLES:

•HOT WATER CHANNEL:

•MAKE UP VALVE

•COOLING WATER PIPING

•FANS & MOTORS

•DRIVES

•PUMPS

TYPES OF COOLING SYSTEM

TYPES OF COOLING SYSTEMS

OPEN COOLING SYSTEM

HEAT FROM THE PROCESS IS REMOVED / COOLED BY WATER DRAWN FROM OPEN SOURCE LIKE SEA / RIVER / LAKE AND DISCHARGED BACK INTO THE SOURCE.

CLOSED RECIRCULATING COOLING.

HEAT FROM THE PROCESS REMOVED BY THE WATER DRAWN FROM A SOURCE LIKE SEA / RIVER ETC IS RECIRCULATED BACK AFTER COOLING THE SAME IN A COOLING TOWER.

DRY COOLING.

HEAT FROM THE PROCESS S REMOVED BY ATMOSPHERIC AIR EITHER DIRECTLY OR INDIRECTLY

ONCE THROUGH COOLING SYSTEM

CLOSED COOLING SYSTEM

Counterblow induced draft. cooling tower.

The fans at the top discharge the hot, moisture laden air upward and away from the air entering at the bottom of the tower, thus preventing any recirculation of warm air. Warm water from the building enters the distribution system located just under the drift eliminators. The fans and their drive mounted on the top deck.

OUR COOLING TOWER DATA
(COUNTER FLOW – INDUCED TYPE)

SIZING COOLING TOWER

Many choices and decisions required to properly size a tower. At minimum, be sure your specification to cooling tower manufacturers stipulates the following:

·Flow rate (m³/hr).

·Total heat rejection (kJ/hr).

·Cold water temperature (°C).

·Hot water temperature (°C).

·Design wet bulb temperature (°C).

·Elevation above sea level (Mt.).

·Tower type (cross flow or counter- flow).

·Materials of construction.

·Fill media choice (film, splash or anti fouling).

·Water quality.

·Noise limitations.

CONSTRUCTION FEATURES

Less Number Of Columns And Beams Result In Better Thermal Performance Due To

Minimum Obstruction

Minimum Wall Water Effect

Less Power Consumption

Less Noise Levels

Better Thermal Performance

Precasting For Faster Construction

Fan Stacks

Fill,drift Eliminators&pipe Support Beams

Complete Fill Support Beams For Natural Draft Cooling Towers

Shell Supporting Raker Columns

Special Features

Smooth Fan Entry Shapes(round/elliptical)

Wind Baffle Walls To Avoid Water Splashing Outside

ESTIMATING WATER BALANCE

FEW TIPS FOR BETTER PERFORMANCE

FOR OPTIMUM & BETTER PERFORMANCE OF THE TOWER,ENSURE THE FOLLOWING:

TOWER SHOULD OPERATE WITH WATER FLOW BETWEEN 90 TO 110%

ALL BLADES OF THE FAN ARE PITCHED AT THE SAME ANGLE

CLOCKWISE ROTATION WHILE VIEWING FROM TOP

ALL THE DOORS ARE CLOSED PROPERLY DURING THE OPERATION OF COOLING TOWER

ENSURE THAT SPRAY NOZZLES ARE FITTED PROPERLY WITH THE HOT WATER DISTRIBUTION PIPES TO AVOID DAMAGE TO FILL AND FOR ACHIVING DESIGNED COOLING DUTY

CHECK/INSPECT ALL TOWER COMPONENTS PERIODICALLY AS PER MAINTAINANCE CHART.

PERFORMANCE TESTING

WATER FLOW -1% ACCURACY

•Sensitivity To Decide The Test

•For A Valid Test Flow Should Be Between 90-110% Of Design

WET BULB ,HOT AND COLD WATER TEMPERATURE

•0.05 Deg C Accuracy

•Sensitive to Decide Test

HEAT LOAD

For A Valid Test Heat Load Should Be Between 80-120 % Of Designed heat Load

Mixed Heat Sources Will Not Supply Heat Loads Within These Limits.Hence Conservative Estimates Of Flow/range May Result In An Invalid Test.

WIND VELOCITY

More Sensitive For Performance Of Natural Draft Cooling Towers,hence Wind Correction Curves Are To Be Considered Along With The Performance Curves

RELATIVE HUMIDITY

More Sensitive For Natural Draft Cooling Towers, hence Shall Be Measured Accurately

SCALING

•Scaling is defined as the precipitation and deposition of hard crystalline water insoluble salts on heat transfer surfaces and return lines.

•Commonly encountered scales in cooling water systems

•CACO3 (Calcium carbonate, marble ,lime scales).

•CASO4,2H2O (Calcium sulphate, gypsum).

•MgSiO3 (Magnesium Silicate).

•CA5 (PO4)3(OH): (Calcium phosphate, Hydroxyapatite)

•All naturally occurring waters will contain varying amounts of Ca, Mg ( Hardness Salts ) with HCO3-, CO3-, SO4-, SiO2 etc.

•as their concentration increases ,and the cooling water comes in contact with hot metal surfaces ,these ions combine and precipitate to give rise to scaling.

FACTORS INFLUENCING CORROSION RATE

FACTORS INFLUENCING MICROBIAL GROWTH

P^H

MOST CW SYSTEM OPERATE AT NEUTRAL OR SLIGHTLY ALKALINE PH WHICH IS IDEAL FOR MICROBIOAL GROWTH

TEMPERATURE

RANGE IS 35 TO 45 DEG.C-THIS IS ALSO IDEAL FOR MICROBIOAL GROWTH

STAGNANT CONDITION

THE CT BASIN,HEAT EXCHANGERS WITH LOW FLOW (SHELL SIDE COOLING),

SIDE STREAM FILTERS SHELTER LARGE MICROBIOAL POPULATION

ENSURING CLEAN WATER & KEEPING CONTAINMENTS TO A BARE MINIMUM CAN GREATLY HELP IN REDUCING BACTRERIAL PROBLEMS

FOULING

•Accumulation of deposits in heat transfer equipment is know as fouling .fouling originates.

• 1.Corrosion

• 2.Scale formation , precipitation, sludge

• 3.Microbial slimes

• 4.Deposition of suspended matter brought in by make up water and air.

Control Techniques

•Control techniques to over come all the problems of a cooling water system can be broadly divided into two parts

•Part A : controlling CW Quality by good operating techniques , using commonly available commodity chemicals and using mechanical means

•Part B : Modifying CW properties By using chemical Inhibitors

EFFECT OF HIGH EVALUATION FACTORS

•Variation in Tower Dimension become predominant between various bids leading to confusion during evaluation . Such variations are not so evident in designs produced in developed countries.

•Major Variation in Power Consumption between various bids may be noted.

•Result in over Optimised cooling tower design to reduce the Power consumption leading to design in violation of minimum air velocities & rain densities etc.

•Claiming high efficiencies for the drive system to reduce Power consumption

Sometimes leads to aberration like power loading value working out more than the cost of cooling tower

Recirculation allowance may get neglected to reduce the power Consumption

High evaluation factor & low penalty factor is disadvantages to the owner