CW SYSTEM

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“The Beginning of knowledge is the discovery of something we do not understand”

-Frank Herbert

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PRESENTED BY DINESH GUPTA PRIYABRATA SATAPATHY

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Cooling TowersCooling Towers

Introduction

Types of cooling towers

Assessment of cooling towers

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IntroductionIntroduction

Main Features of Cooling Towers

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• Frame and casing: support exterior enclosures

• Fill: facilitate heat transfer by maximizing water / air contact

• Splash fill

• Film fill

• Cold water basin: receives water at bottom of tower

Components of a cooling tower


• Drift eliminators: capture droplets in air stream

• Air inlet: entry point of air

• Louvers: equalize air flow into the fill and retain water within tower

• Nozzles: spray water to wet the fill

• Fans: suck air flow in the tower

Components of a cooling tower

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Introduction



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Types of Cooling TowersTypes of Cooling Towers

• Hot air moves through tower

• Fresh cool air is drawn into the tower from bottom

• No fan required

• Concrete tower <200 m

• Used for large heat duties

Natural Draft Cooling Towers

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Natural Draft Cooling Towers

Cross flow

• Air drawn across falling water

• Fill located outside tower

Counter flow

• Air drawn up through falling water

• Fill located inside tower

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• Large fans to force air through circulated water

• Water falls over fill surfaces: maximum heat transfer

• Cooling rates depend on many parameters

• Large range of capacities

• Can be grouped, e.g. 8-cell tower

Mechanical Draft Cooling Towers

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Three types

• Forced draft

• Induced draft cross flow

• Induced draft counter flow

Mechanical Draft Cooling Towers

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• Air blown through tower by centrifugal fan at air inlet

• Advantages: suited for high air resistance

• Disadvantages: recirculation due to high air-entry and low air-exit velocities

Forced Draft Cooling Towers

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• Two types

• Cross flow

• Counter flow

• Advantage: less recirculation than forced draft towers

• Disadvantage: fans and motor drive mechanism require weather-proofing

Induced Draft Cooling Towers

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• Hot water enters at the top

• Air enters at bottom and exits at top

• Uses forced and induced draft fans

Induced Draft Counter Flow CT

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• Water enters top and passes over fill

• Air enters on one side or opposite sides

• Induced draft fan draws air across fill

Induced Draft Cross Flow CT

COOLING TOWER OF apmlManufacturer PAHARPURModel no 85454-6.0-22BHeight of CT 12.04mHeight of inlet pipe 8.23mAir flow rate (outside) 1100000cfm 20 nos CT fan are running & 2 nos are

standby for normal operation.

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SPECIFICATION (COOLING TOWER fan) Manufacturer PCTIL Model HP-6-8 Type Axial flow No of fans per cell 1 Total cells per unit 22 No of blade per fan 8 Dia of fan assembly 10m Hub dia 1.52 m Blade tip clearance 50mm(+1 - 0 .25”)

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Continued……. Fan blade of adjustable pitch YES Degree of adjustment 5 – 20 deg Blade angle design 14.750 at 58.6kw Fan blade and shank GRP Hub cover GRP Colour of fan blade Gray Blade type Aerofoil Wet bulb temp 27.10C Fan speed 98rpm M.I of fan 2542 kgm2

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SPECIFICATION (GEAR BOX) Model no 10-4001-2 Serial no J-1-775 Gear reducer ratio 14.54/1 Oil Turbine type mineral oil Oil is changed every 6 month or after 3000 hours of

operation.

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Design parameters of apmlDrift loss (max) 0.05%Space of each drift blade 49mmFill material PVC film fill pack-

MC-67length of fill pack 1.829mDrift blade height 146mmFill pack coating TiO2 Coupling type Flexible bush

type

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SPECIFICATION (MOTOR)Manufacturer MARATHONType 3 phase squirrel cage

induction motorVoltage 415 voltFrequency 50 HzRated Power 75 kw,100hpCurrent 128 ampSpeed 1480 rpmEfficiency 93.6%Power factor 0.87Winding connection ∆(delta)

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SPECIFICATION (RISER VALVE)Manufacturer AUDCO INDIA

LTDModel G400 MSGear ratio 70:1Rated torque 4000Nm Size 800 mmMax pressure 0.6kg/cm2 Max. temp 950C

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PRESTART CHECK LIST

No permit to work pendingRiser valve should be opened 100%Ensured equal distribution of water.Lube oil level should be normal and ensured no

oil leakage.CT blower should be electrically normal.

STARTING PROCEDUREStart CT blower ,check vibration, current, rotation and

abnormal sound of motor.

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shutdownCT fan stoppedElectrically isolate the systemRiser valve is closed

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Introduction



Assessment of Cooling TowersAssessment of Cooling Towers

Measured Parameters

• Wet bulb temperature of air

• Dry bulb temperature of air

• Cooling tower inlet water temperature

• Cooling tower outlet water temperature

• Exhaust air temperature

• Electrical readings of pump and fan motors

• Water flow rate

• Air flow rate

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Performance Parameters

1. Range

2. Approach

3. Effectiveness

4. Cooling capacity

5. Evaporation loss

6. Cycles of concentration

7. Blow down losses

8. Liquid / Gas ratio


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1. Range

Difference between cooling water inlet and outlet temperature:

Range (°C) = CW inlet temp – CW outlet temp

High range = good performance

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Hot Water Temperature (In)

Cold Water Temperature (Out)

Wet Bulb Temperature (Ambient)

(In) to the Tower(Out) from the Tower


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2. Approach

Difference between cooling tower outlet cold water temperature and ambient wet bulb temperature:

Approach (°C) = CW outlet temp – Wet bulb temp

Low approach = good performance

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3. Effectiveness

Effectiveness in %

= Range / (Range + Approach)

= 100 x (CW temp – CW out temp) / (CW in temp – Wet bulb temp)

High effectiveness = good performance

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4. Cooling Capacity

Heat rejected in kCal/hr or tons of refrigeration (TR)

= mass flow rate of water X specific heat X temperature difference

High cooling capacity = good performance

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5. Evaporation Loss

Water quantity (m3/hr) evaporated for cooling duty

= theoretically, 1.8 m3 for every 10,000,000 kCal heat rejected

= 0.00085 x 1.8 x circulation rate (m3/hr) x (T1-T2)

T1-T2 = Temp. difference between inlet and outlet water

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6. Cycles of concentration (C.O.C.)

Ratio of dissolved solids in circulating water to the dissolved solids in make up water

Depend on cycles of concentration and the evaporation losses

Blow Down = Evaporation Loss / (C.O.C. – 1)


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7. Liquid Gas (L/G) Ratio

Ratio between water and air mass flow rates

Heat removed from the water must be equal to the heat absorbed by the surrounding air

L(T1 – T2) = G(h2 – h1)

L/G = (h2 – h1) / (T1 – T2)

T1 = hot water temp (oC)

T2 = cold water temp (oC)

Enthalpy of air water vapor mixture at inlet wet bulb temp (h1) and outlet wet bulb temp (h2)


Parameters calculations of apmlWater I/L temp = 41ocWater O/L temp =32.1oc Range = 41-32.1 = 8.9ocWet bulb temp = 27.1ocApproach = 32.1-27.1 = 5ocEffectiveness = 8.9/(8.9+5) = 64%Cooling capacity = 79650*8.9*1 = 708.885kcal/hrEvaporation loss = 0.00085*1.8*79650*8.9

=1084.594m3/hCycles of concentration = 6Blow down = 1084.594/(6-1) = 216.9188m3/hr Net heat transferred = 790497kj/s Drift loss = 0.0005*79650 = 39.825m3/hr

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Cooling water treatment system

Provided to make the circulating water conductive for effective heat exchange in condenser and ACW system.

Mainly following treatment methods are used.

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Scale cum Corrosion Inhibitor Dosing System done at the CW Common Forebay. to prevent scaling caused by circulating

water in the Condenser and the CW piping. Two (2) Nos. MSRL tanks with motorized

Agitator & all accessories.Tank capacity 1.2 m3 *2. Two (2) x 100% dosing pumps.

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Bio dispersant Dosing System Done at CW Common Forebay. Done for prevention control of organic

fouling. Two (2) Nos. MSRL tank with motorized

Agitator & all accessories.Tank capacity 1.2m3 *2. Two (2) x 100% dosing pumps

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Sulphuric Acid Dosing System Dosed in the CW pump common Forebay . To convert scale forming calcium and

magnesium bi-carbonates into corresponding sulphate compounds having higher solubility.

Two (2) Nos. Sulphuric acid storage tanks with accessories.

Tank capacity 30m3 *2. Two (2) x 100% Sulphuric Acid Unloading

pumps Two (2) x 100% Sulphuric Acid Dosing pumps

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Biocide DosingBiocide shall be fed into the circulating water

forebay for protection against microbiological growth in the circulating water system. Biocide shall be dumped into the CW

forebay as per stipulated interval of time. One (1) No MSRL tank with motorized

Agitator & all accessories.Tank capacity 3.2m3.

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Side Stream Filtration System Provided near the CW forebay, Sized for 1% of total CW flow of all Cooling

Towers and designed for CW Pumps’ shutoff pressure.

From the CW return header, cooling water is fed to the filters. The filtered water is fed back to CW forebay.

The Backwash for the side stream filters shall be from CW pump discharge header in a counter flow manner .

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Continued…………… Nine (9) nos Pressure sand Filter units with

interconnecting piping, necessary instrumentation for complete automation.

Two (2) x 100% backwash waste transfer Pumps of required capacity and Head.

One (1) x 100% backwash collection sump.

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Cw pump house

The function of CW Pump is to circulate

cooling water in condenser and condense turbine exhaust Steam.

Pump discharge valve is hydraulic operated.Pump discharge water is used to cool motor

windings.For initial start-up, service water will be

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PUMP SPECIFICATION & OTHER DETAILS

Manufacture KIRLOSKAR BROTHERS LIMITED Pump type : BHM135, Single stage, Self water lubricating pump Motor Rating :3600 KW Speed : 330 RPM (NOM) Make : WEG Motor Weight : 35300 KG Pump Discharge : 39825 M^3/HR Total Head : 26 M Pump Efficiency : 92 % Pump Input : 3049.73 KW

SPECIFICATION(MOTOR)Type Three phase induction motorPower 3600 kwSpeed 330 rpmFrequency 50HzDuty S1Voltage 11kvCurrent 245.5 ampInsulation class FEfficiency 96(-2%)

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Pre CHECK LISTNo PTW pending of CT, MCWP, CWS &

condenser.Min. 10 nos. riser v/v in open condition for

one pump.All air relief v/v in service.MCWP discharge header in fill up condition.Sump level normal.

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START PERMISSIVE Discharge BFV 100% close. Discharge BFV hydraulic system is available

and ready for remote operation. Motor Winding temperature not High. Motor DE & NDE Bearing temperature not

High. Pump Thrust Bearing Metal Temperature not

High.

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Continued…..Pump Thrust Bearing Oil Temperature not

High.Sump water level of MCW pumps should not

be lower than normal water level.MCW Pump & Booster Pump in cooling water

system switchgear is available and ready for remote operation.

Cooling water skid (CWS) are available and ready for operation.

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Continued…Physically check and confirm that all the

Manual Valves on the CWS are in open condition.

Condenser Inlet / outlet path is open.Manual confirmation that inlet/outlet valve

of duty booster CWS pump & duty strainer is open.

Vibration High earlier alarm if any is to be reset.

Motor leak detector signal healthy.

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START SEQUENCE First selected MCW Pump is given start

command. MCW Pump ON feedback is monitored BFV open command is given. BFV opening initiated (Full close limit switch

feedback withdrawn) is monitored. Flow switch contacts in cooling circuit are

bypassed for set time of 60 seconds.

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Contd……..Rated Flow of CWS achieved is monitored

after above 60 seconds set time.Timer is initiated for monitoring full opening

of Main Discharge BFV and BFV to open fully within 60 seconds.

If all the above requirements are achieved as designed, Pump set successful start is established.

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Contd………If in the CWS the required pressure & flow of

cooling water in the discharge booster pump is not established within set time , alarm is generated.

Additionally the system should take care that minimum 60 seconds time gap is there after start command is given for the first MCW Pump.

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STOP SEQUENCEGive MCW Pump stop command.The BFV will be given close command.BFV closing initiated (Full open limit switch

feedback withdrawn) is monitored.BFV to close up to 80% on arrival of this

feedback, main MCW Pump switch gear to be given stop command.

MCW Pump off feedback is monitored.BFV full closing time is initiated.

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Contd……….BFV to close within above set time.BFV should close fully (100%) within 20

seconds of receiving MCW Pump OFF feedback.

If BFV fails to close fully (from 80% close to 100% close) within set time then give alarm “BFV closing trouble”.

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TRIP CONDITIONS:Motor Stator Winding Temperature is “High

High” (1400C).Motor DE & NDE Bearing Temperature

“High High” (1050C).Pump Thrust Bearing Temperature “High

High”.(850C)

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Contd……….Pump Thrust Bearing Vibrations “High High”.Motor DE & NDE Bearing Vibrations “High

High”(10mm\s)On arrival of this signal both/all the MCW

Pumps of a unit will trip, CWS discharge pressure sustained“Low Low”.

On arrival of this signal both/all the MCW Pumps of a unit will trip, CWS Differential Pressure sustained across strainer is High.

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Contd……..Cooling water sustained flow Low at any of the 4 flow inlets.

On arrival of this signal both/all the MCW Pumps of a unit will trip, Sump Water Level of MCW Pumps is at Low Low Level(7.55).

BFV do not open fully (100%) within approx. 60 seconds. No trip but sequence stops.

MCW pump discharge pressure High High for more then 300 seconds.

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Forebay level

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TRIP SEQUENCEThis sequence is executed when any one or

more of the Trip condition arrives.The MCW Pump Motor will immediately stop

and the BFV will be open more than 20% (Most of the times 100% open) and alarm is generated.

The BFV should be given emergency close command so that it closes from 100% open to 20% open within10 seconds and the balance 20% within 20 seconds.

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Daily Check listOil level of Gear box & pump thrust bearing.Vibration of CT fan. Motor, pumps.Temps of brg. & wdg.Any abnormal sound.Any cable & switch gear heating.DP of booster p/p filter.House keeping of concerned area.

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Surge Protection Valve for CW System COMBINATION AIR VALVE LOCATION

One each near the elbow downstream of pump discharge valve.

On top of inlet water box of LP Shell. On top of outlet water box of LP Shell. On top of outlet water box of HP Shell.

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Vacuum breaker valve LOCATIONNear the elbow downstream of vacuum pump

cooler 1A. Near the elbow downstream of vacuum pump

cooler 1B. Near the elbow upstream of vacuum pump

cooler 1B.

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DO S & DON’T S OF cwphDo:Ensure safety.Follow SOPsMaintain house keeping.Maintain proper lighting.

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Don’tDon’t open CT fan enclosure.Don’t start pump if sump level low.Don’t start CT fan if oil level low.Don’t waste electricity.Optimum utilization of water & chemicals.Don’t touch any rotating parts.Don’t panic during emergencies etc .

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CW SYSTEM