Evaluacion Torre de Agua de Enfriamiento

7/29/2019 Evaluacion Torre de Agua de Enfriamiento

1/4

PERFORMANCE EVALUATION OF INDUCED-DRAFT CROSS-FLOW

COOLING TOWER.

Pipat Juangjandee

Thawan Sucharitakul

Department of MechanicalEngineeringFaculty of EngineeringChiang Mai UniversityChiang Mai 50200, ThailandTel.: 0-9553-0632Tel.: 0-5394-4147

E-mail: [email protected]: [email protected]

AbstractThis research work is to study the performance of the cooling tower of

300 MW Mae Moh coal-fire power plant. Normally, this cooling towersmain function is to cool heated circulating water from a condenser byexposing it to air. The cooled water is then circulated through the systemby circulating water pumps.

From this study, it was found that the cooling tower thermal efficiencyis 51.63%, lower than designed and guarantee values, 70.97% and 70.97%

respectively.The condition and age of cooling tower would tend to poor condition

such as less hot water flow due to plugged spray nozzles, high turbidity,and poor hot water flow distribution. It is recommended to clean, clear, anderadicate the thallophytic plant in hot water basin, repair spray nozzles andanalysis of the causes.

1. IntroductionIn power plant system, there are so many equipments

are used. One major equipment is a cooling tower, whichfound in most power plants. The cooling towers mainfunction is to cool heated circulating water from a

condenser by exposing it to air. Water that has beencooled by the air flowing through it is stored in a basin

located below the cooling tower. The cooled water isthen circulated through the system by circulating waterpumps. In a cooling tower, heat is removed from waterin two ways such as by convection and by evaporation.As cool air flows over the water, the movement of aircauses heat to transfer from the water directly into thecooler air, this is called convection. In addition, when theheated water is exposed to air, some of the waterevaporates, and this also helps cool the water.

In Mae Moh power plant, there are many cooling

towers have been used for along time ago. The coolingtower performance should be determined so the plantefficient can be improved by this result diagnosis.

Therefore, the objective of this research work is toinvestigate the performance of the inducted-draft cross-flow cooling tower.

2. TheoryA performance of cooling tower is measured in term

of its approach , how close temperature of cooled watercomes comes to wet-bulb temperature of the ambient air,when water is cooled through the desired range. Forgiven heat load, approach depends mainly on designwet-bulb, cooling range and type of tower selected.

In this work, the cooling range and approach are

defined as

Cooling range = wowi TT (1)

Approach = WBwo TT (2)

Cooling tower thermal efficiency can be calculated as

WBwi

wowiCT

TT

TT

= (3)

The convective heat transfer rate (Q ) of hot water

can be calculated as

)(, wowiwpw TTcmQ = && (4)

The humidity, Y of an air-water mixture is definedas mass of water vapor per mass of dry air.

TRMpp

TRMpY

aw

ww

0

0

)(

= (5)

The humidity is thus given by

aw

ww

Mpp

MpY

)( = (6)

Humid heat (s) is defined as

Yccs pwap += , (7)

The motor power of cooling tower fan can becalculated as

cos3IEPmtr = (8)


2/4

3. Performance DataIn this work, the cooling tower of 300 MW Mae Moh

power plant, unit 10, induced-draft cross-flow type wasselected for investigating. The configuration of this type

is shown on figure 1.

Figure 1 Inducted-draft cross-flow cooling tower.

The designed technical specification of this coolingtower is shown in table 1.

Table 1 Power plant specification at rated condition.

Categories Values

Heat load of cooling tower (kW) 417000

Water rate (m3/s) 9.1

Hot water temperature ( C ) 39.0

Cold water temperature ( C ) 28.0

Cooling range 11.0

Approach 4.5

Temperature of inlet air, wet bulb ( C ) 23.5

Temperature of inlet air, dry bulb ( C ) 27.5

No. of cooling tower cell per unit 9

Cooling tower age (year) 16

The cooling tower performance test data wererecorded on Nov.16 2004 which shown in the form ofaverage values, the designed data and guarantee data as

illustrated in Table 2.

Table 2 Collected data of the tested cooling tower on

Nov.16 2004, designed data, and guarantee data.Categories

Design Guarantee Test

wm& 9.1 9.1 8.56Twi 39.0 39.0 42.05

Two 28.0 28.0 32.49

TWB 23.5 23.5 23.53

Cooling range 11.0 11.0 9.57

Approach 4.5 4.5 8.96

Pmtr 1245 1245 1018.38

Qw (x10-3) 417.0 417.0 341.03

ax

V 2.36

CT 70.97 70.97 51.63

4. Results and DiscussionFigure 2 shows cooling tower performance data

which recorded on Nov.16 2004. It was found that thecooling tower efficiency, 51.63% is lower than the

designed and guarantee values, 70.97% and 70.97%respectively.

Series

70.9770.97

51.63

0

10

20

30

40

50

60

70

80

CTefficiency(%)

Design

Guarantee

Test

Figure 2 Cooling tower thermal efficiency.

-

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

11:00

11:30

12:00

12:30

13:00

13:30

14:00

Time

Temp.

(Deg.C

)&f

low(

m3/s)

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

Efficiency(%

)

Ambient air temp.

Wet bulb temp.

Hot water temp.

Recooled water temp.

Water rate

Cooling range

CT thermal efficiency

Figure 3 Cooling tower performance.

Cooling tower performance as shown on figure 3 werefound in fair level such as cooling tower thermalefficiency were 49.7252.71 %, cooling range were8.749.88 C, and approach were 8.80-9.36 C. Actualapproach values were higher than designed values, so the

cooling tower performance is lower than designedvalues.

20.00

21.00

22.00

23.00

24.00

25.00

1 2 3 4 5 6 7

Wet-bulbtemp.(De

g.C

)

-

1.00

2.00

3.00

4.00

5.00

Windvelocity(m/s)

Wetbulb temp. Wind vel.

Figure 4 Wind velocity and inlet air temperature,

wet-bulb.

From figure 4, the wind velocity at hot basin were found

in low level, 0.9-3.6 m/s. The wet-bulb temperatureswere 22.78-24.52 C and varied.


3/4

Series

1,245.001,245.00

1,018.38

0

200

400

600

800

1000

1200

1400

Totalfanpower(kW)

Design

Guarantee

Test

Figure 5 Cooling tower fan power.

From figure 5, the cooling tower fan power values attesting condition were lower than designed values, sothat air capacity can be improved because they still havemargin.

Series

416.94416.94

341.03

-

50.00

100.00

150.00

200.00

250.00

300.00

350.00

400.00450.00

Heatload(MW)

Design

Guarantee

Test

Figure 6 Heat load of cooling tower.

From figure 6, heat load values of tested cooling towerwere lower than designed values, so that this coolingtower can be received more heat load.

Series

9.1 9.1

8.56

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

Waterrate

(m3/s)

Design

Guarantee

Test

Figure 7 Water rate of cooling tower.

Figure 7, the water flow rate of designed and guaranteevalues were 9.1 an 9.1 m

3/s respectively but in testing

conditions was 8.56 m3/s. The less water flow rate is oneof many factors in low cooling tower performance.

Figure 8 Hot water basin flood over overflow pipes.

In figure 8, so much water flood over the overflow pipeswere occurred on hot water basin, then operators reduced

water flow by closing some cooling water inlet valves.

Figure 9 A thallophytic plant growing on wood long

immersed in water in hot water basin.

Figure 9, A thallophytic plant growing on wood long

immersed in water were found in the hot water basin ofcooling tower, these plant effecting the water flow. Somewater spray nozzles at the hot water basin were clogged.

5. ConclusionThe condition and age of cooling tower would tend to

dictate that research, modification and repair.5.1 It was found that the cooling tower thermal

efficiency was 51.63%, lower than the designed andguaranteed values, 70.97% and 70.97% respectively.

5.2 High turbidity was occurred on hot water basin ofcooling tower, it is recommended to clean, clear, anderadicate the thallophytic plant in hot water basin.5.3 Some nozzles at hot water basin are damaged andplugged, its recommended to repair as soon as possible.5.4 Water flow should be analyzed and readjusted

because it less than the designed value quite big. The hotwater flow distribution is in poor condition. All

distribution valves have to be readjusted.

6. AcknowledgementThe authors gratefully acknowledge the support

provided by the Electricity Generating Authority of

Thailand.

7.Reference


4/4

[1] Hewitt, G.F., Shires, G.L. and Bott, T.R. (1994),Process Heat Transfer, Boca Raton, CRC Press,1042.

[2] Incropera, F.P. and Dewitt, D.P. (2002),Introduction to heat transfer, 4th edition, John Wiley& Sons Inc., USA.

[3] Elonka, S. (1967), Plant energy system, McGraw-Hill, USA.[4] Hensley, J. (1982), Cooling tower fundamentals,

The Marley cooling tower company, Kansas, USA.

8. Nomenclature

A area (m2)

CT cooling towercp specific heat at constant pressure (J/kg K)cp,a specific heat of air at constant pressure

(J/kg K)

cp,w specific heat of water at constant pressure(J/kg K)

cpw specific heat of water vapor at constantpressure (J/kg K)

D diameter (m)E voltage (V)H tower height (m)h heat transfer coefficient (W/m

2K)

ha enthalpy of dry air (J/kg)hi heat transfer coefficient at inlet (W/m

2 K)ho heat transfer coefficient at outlet (W/m

2 K)hw enthalpy of water vapor (J/kg)

I current (A)

k thermal conductivity (W/m K)L length (m)Ma molecular weight of air, 29Mw molecular weight of water, 18

m& mass flow rate (kg/s)

wm& mass flow rate of water (kg/s)

P power (kW)Pmtr motor power (kW)p total pressure (Pa)pa partial pressure of air (Pa)

pw partial pressure of water vapor in the mixture(Pa)

Q heat transfer rate (W)Qw heat load of cooling tower (kW)R0 universal gas constant, 8.314 (kJ/kmol K)

T temperature (C)

TWB wet bulb temperature (C)

Twi temperature of water inlet (C)

Two temperature of water outlet (C)U overall heat transfer coefficient (W/m2K)

V velocity (m/s)

axV air velocity, horizontal direction

(m/s)Y humidity

angle ( ) density (kg/m3)

a air stream density (kg/m3)

Dynamic viscosity (Pas)

Evaluacion Torre de Agua de Enfriamiento

Documents

Transcript of Evaluacion Torre de Agua de Enfriamiento