Presentation on Cooling Towers

A Presentation on Cooling Towers1Basic DefinitionHeat Rejection Device

Extracts waste heat to the atmosphere though the cooling of a water stream to a lower temperature.2Basic PrincipleEvaporative Cooling

A small portion of the water being cooled to evaporate into a moving air stream to provide significant cooling to the rest of that water stream.3Animation of Cooling Towers

4Importance of Cooling Towers

5Terms used in Cooling TowersDry Bulb TemperatureWet Bulb TemperatureRangeApproachHeat LoadMake UpDrift6

Basic Definitions of Cooling TowersBlow DownCycles of ConcentrationL/G Ratio

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Definitions of TermsDry Bulb Temperature:Temperature ofairmeasured by athermometer freely exposed to the air but shielded fromradiationandmoisture.Wet Bulb Temperature:Lowest temperature that can be reached under current ambient conditions by the evaporation of water only.Range:Temperature difference between the water inlet and exit states.Approach:Difference in temperature between the cooled-water temperature and the entering-airwet bulb.

8Definitions of TermsHeat Load:The amount of heat to be removed from the circulating water within the tower.Make Up:The amount of water required to replace normal losses caused by bleed off, drift, and evaporation. Drift:The water entrained in the air flow and discharged to the atmosphere. Drift loss does not include water lost by evaporation. Blow Down:The portion of the circulating water flow that is removed (usually discharged to a drain) in order to maintain the amount ofTDS & other impurities at an acceptably low level.L/G Ratio:A ratio of the total mass flows of water and dry air in a cooling tower.

9Cycles of Concentration1 CycleWhen water evaporates is leaves it solids behind. If you completely evaporate a sample of water and then refill the container with the same water the mineral content doubles. This is called Cycling Up.Cycles of Concentration11As cycles increase the amount of solids increase. This means:The Conductivity increases.The total hardness increasesThe pH will go up as the alkalinity increasesThe risk of scale formation increasesCycles of Concentration12Components of Cooling Towers

13Components of Cooling TowersFrame and casing: support exterior enclosuresFill: facilitate heat transfer by maximizing water / air contactSplash fillFilm fillCold water basin: receives water at bottom of tower

14Components of Cooling TowersDrift eliminators: capture droplets in air streamAir inlet: entry point of airLouvers: equalize air flow into the fill and retain water within towerNozzles: spray water to wet the fillFans: deliver air flow in the tower

1515Working of Cooling Towers

16Types of Cooling Towers2 main types of Cooling Towers

17Natural Draft Cooling TowersDensity Diff is the main reason for air flow.Hot air moves through towerFresh cool air is drawn into the tower from bottomNo fan requiredMaterial of Construction : Concrete

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Mechanical Draft Cooling Towers19Induced Draft Cooling Towers

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Forced Draft Cooling Towers

21Forced Draft Cooling Towers

22Advantages and Disadvantages of Cooling TowersTypes of Cooling TowersProcessAdvantagesDisadvantages Forced Draft Cooling TowersAir is blown through the tower by a fan located in the air inlet.Suited for high air resistance due to centrifugal blower.Re-circulation due to high air-entry and low air exit velocities which can be solved by locating towers in plant rooms combined with discharge ducts.Induced Draft Cooling Towers1. Water enters at the top and passes over fill.2. Air enters on one side or opposite sides.3. An induced draft fan draws air across fill towards exit at the top of tower.Less re-circulation than forced draft towers because the speed of exit air is 3-4 times greater than entering air.Fans and the motor drive mechanism require weather-proofing against moisture and corrosion because they are in the path of humid exit air.23COOLING TOWER SETUP AT EEAP24Components of CT on EEAPCooling Tower-1 (CT-501)Cooling Tower-2 (CT-502)Cooling Water Supply Pump (P-501 A/B/C)Inline Split-Stream Filter (FT-501)Cooling Towers are Induced Draft.

25Specifications of Components of CTOperating Flow (in each): 1500 m/hrNumber of cells (in each): 4Cooling Water Return Temperature: 37CCooling Water Supply Temperature: 30CDesign Wet bulb Temperature: 27COperating Duty (Refrigeration Ton): 6,900Design Duty (Refrigeration Ton): 8,000Approach = 4-5C26Specifications of PumpPump SpecificationDesign Flow-rate: 1500 m/hrDifferential Pressure: 6 barg

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Specifications of FilterPressure Drop (Maximum): 0.2 barg

28Pictures of CT on EEAP

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Pictures

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Pictures

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Pictures

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Flow Diagram of CT33CT-501 and CT-502Water coming from exchangerWater from T-100 for Make upTo ETPDrainFilterPumpFilterTowards Turbine HallBasinAirParameters of Selection of CTEntering air Wet Bulb TemperatureApproachCondenser Water Flow rate34Choice b/w Diff. Types of FillsParametersSplash FillFilm FillPossible L/G1.1-1.51.5-2.0Effective A30-45 m150 mFill Height Required5-10 m1.2-1.5 mPumping Head Required9-12 m5-8 mQuantity of Air RequiredHigh Much Low35Problems on CTScaling CorrosionBiological Growth36What is Scale?Deposits of pre-dominantly inorganic material on heat transfer surfaces caused by the precipitation of mineral particles in water.

Decreases heat transfer rate.37Reasons for formation of ScaleAs alkalinity increases, calcium carbonate- the most common scale constituent in cooling systems - decreases in solubility and deposits.

High TDS water will have greater potential for scale formation.

38Salts that promote ScaleCalcium Carbonate ScaleCalcium Sulfate ScaleCalcium and Magnesium Silicate ScaleCalcium Phosphate ScaleCalcium and Magnesium Bi-carbonates39How to Control Scale FormationWater Softening Equipment (Ion Exchange Method)Adjusting pH to lower values (Addition of Acid)Controlling Cycles of ConcentrationChemical Dosage (e.g. PMA, Phosponate, Aluminates etc.)Physical Water Treatment Methods (Filtration)40What is Corrosion?Destruction or loss of metal through chemical or electrochemical reaction with its surrounding environment.M.O.C is mostly Mild Steel which is more susceptible to corrosion.Other metals in general, such as copper, stainless steel, aluminum alloys also do corrode but the process is slow. However in some waters and in presence of dissolved gases, such as H2S or NH3, the corrosion to these metals is more severe & destructive than to mild steel41Reasons for CorrosionDissolved OxygenAlkalinity and AcidityTDSMicrobial GrowthTemperature42How to Control CorrosionSelection of suitable M.O.CControl of Scale and Microbial GrowthAddition of protective film- forming chemical inhibitors that the water can distribute to all wetted parts of the system.Chromate, Zinc, Molybdate, Azoles, Nitrate, o-phosphate, polyphosphateApply protective coatings such as paints, metal plating, tar or plastics on external surface.43Biological Growth?Biological Growth is due to the presence of biological materials likeAlgaeBacteriaFungi44Problems that are caused by AlgaeProvide a nutrient source for bacterial growthDeposit on surface contributes to localized corrosion processLoosened deposits can block and foul pipe work and other heat exchange surfaces45Problems that are caused by FungiProliferate to high number and foul heat exchanger surfaces46Problems that are caused by BacteriaSome types of pathogenic bacteria such as Legionella may cause health hazards Sulfate reducing bacteria can reduce sulfate to corrosive hydrogen sulfide. Cathodic depolarization by removal of hydrogen from the cathodic portion of corrosion cell.

47Control of Microbiological GrowthThree types of Chemical BiocidesOxidizingNon-OxidizingBio-dispersent48Oxidizing BiocideChlorine (Most Effective)Chlorine DioxideBromineOzone

49Non-Oxidizing BiocideOrganic compounds ammonium salts, Isothiazolinones, organo-metallics organo-sulfur compounds. which kill micro-organisms by targeting specific element of the cell structure or its metabolic or reproductive process.Not consumed as fast as Oxidizing Biocides and have a good retention time.Effective in the non-effectiveness of chlorine.Broke down into the non-toxic and harmless materials after doing their necessary action.Very Costly.High pH sensitivity50Bio-dispersantsDo not kill micro-organism.Just loosen the microbial deposits which then can be flushed away.Effective in increasing action of Oxidizing biocide.Possible bio-dispersants include:AcrylatesLignosulphonatesMethacrylatesPolycarboxylic Acids51THANK YOU52