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NTPC Limited

Centre for Power Efficiency & Environmental Protection (CenPEEP)

Performance Capability Test Cooling Tower 1&2 – NTPC Unchahar

Date: 23.08.2013

1.0 Introduction

Cooling Tower performance capability test was carried out jointly by Station and CenPEEP (CC) on 16-17th July, 2013 of CT-1 & CT-2 of NTPC Unchahar Thermal Power Plant. The test was conducted at stable load conditions. Cooling tower flow measurement was carried out using Ultrasonic Flow meter. The inlet air wet bulb temperature measurement was carried out using a battery operated psychrometer. The cold water temp measurement was carried out in the CT outlet channel using a grid arrangement.

2.0 Tower Description Cooling tower at NTPC - Unchahar is of M/S Gammon make Induced draft counter flow type concrete splash bars. The tower is designed for rated Cold Water temperature of 33 deg C with 14 cells in operation at full load condition.

3.0 Water Distribution System Hot cooling water outlet from Condenser of Unit#1&2 is supplied to cooling tower using CT Pumps. Two CT Pumps each for tower 1&2 are being used. Discharge of CT Pumps 1&2 are fed individually to two sides of CT 1 and that of CT Pumps 3&4 are fed individually to two sides of CT 2. Hot water from these two common inlet header of cooling tower is distributed in all the 14 risers (7 risers in either side) of CT 1&2 which supply hot water to the cells in either sides of tower through the channel. Within each cell a distribution network supplies the hot water to the concrete splash bar through the nozzles. The cold water flows via gravity from the collection basin of the tower to an open channel which in turn flows to a common sump at the suction to the CW pumps.

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4.0 Measurement set up

Circulating water flow Measurement

CW flow was measured at the CW inlet header to each risers of cooling tower by the Ultrasonic Flow meter. The ID and thickness of riser was 700 mm and 6 mm respectively with 3 mm of internal lining and pipe material was MS.

CW flow measurement using ultrasonic flow meter

Hot Water Temperature Measurement

Hot water temperature is measured at the CW inlet distribution header to the cooling tower on the top of tower and average was taken for the calculation purpose.

Cold Water Temperature Measurement Grid measurement of Cold water temperature of the tower was done using Thermocouples, inserted at different heights and different locations across the width in the cold water channel. The thermocouple connections were brought out and connected to a temperature read out outside for cold water temperature measurement. Average temperatures of all such points are taken for the purpose of calculation of cold water temperature.

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Location of measurement of CW Temp

Inlet air Wet Bulb Temperature

A battery operated psychrometer is used for measuring Wet Bulb Temperature. The measurement was taken about 1 meter from the air intake and at two elevations above the ground. The measurement was taken at different locations on both sides of the tower and the average values of all the measurements are taken for calculation of Inlet air Wet Bulb Temperature.

Fan Power Measurement

Fan Power Measurement was done using the offline power analyzer at the individual switchgear. The average powers of the 14 fans which were in service are taken for the purpose of calculation of the Fan Power.

Wind Velocity Measurement Wind velocity measurement was carried out at a distance of about 30 m from cell inlet on both sides of the tower using an anemometer.

5.0 Test Results (Test Report enclosed) The average values of cold water, hot water and inlet air wet bulb temperature measurements and CW flow measurements were used along with the curves provided by the manufacturer (M/s Gammon) for deriving the tower capability. Cooling tower capability was determined using the performance curve method as specified in CTI ATC-105 part-II, Section 6, document on Mechanical Draft Cooling Tower Performance Curve Method. In the Performance Curve method, the cold water temperature is read at the test WBT on the three cooling ranges on each of the 90%, 100%, and 110% flows. This gives nine points and these nine points are used to generate the first cross plot of cold water temperature vs cooling range. Each of these plots represents the cold water temperature as a function of cooling range and water flow rate.

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A second cross plot of cold water temperature versus predicted water flow rate is then generated from the three points read from the first cross plot at the test cooling range. The predicted water flow is obtained from the second cross plot corresponding to the test cold water temperature. Finally, capability and effectiveness are calculated using the following formulae: Capability = [QT/Qpred] x [CellD / CellT] x [PD/PT] 1/3 x 100 Where, Cap = Tower capability, % QT = Measured water flow rate, M3/hr Qpred = Predicted water Flow rate, M3/hr Cell D = No. of cells as per design CellT = No. of cells in operation during test PD = Fan motor power design, KW PT = Fan motor power measured, KW

Effectiveness = Range / (Range + Approach)

5.1 A summary of the design and performance test values are provided in table

given below:

Sr.

No.

Description Unit Design

Value

Test Value

CT - 1 CT - 2

1 No. of Cells No 14

14 14

2 Circulating water

flow rate

m3/hr 33000 33269 32816

3 Hot water temp. deg.C 42 44.1 44.1

4 Cold water temp. deg.C 33

36 35.89

5 Inlet air wet bulb

temp.

deg.C 28.5 28.60 29

6 Fan Motor

Power/Cell

Watt 75

64 60.8

7 Range deg.C 9

8.10 8.21

8 Exp cold water

temp

deg.C --- 32.88 33.17

9 Shortfall in CW

temp

deg.C ---- 3.12 2.72

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5.2 The table containing the Fan Powers of individual cells and corresponding

fan blade angles are given below:

Cooling Tower 1&2 CT Fans Power

CT-1 Power CT-2 Power

CT Fan No Power (KW)

Fan Blade Angle (Deg)

CT Fan No Power (KW)

Fan Blade Angle (Deg)

1.1 72 17 3.1 60 18

1.2 63.8 17 3.2 63 17

1.3 61 18 3.3 64 18

1.4 60 8 3.4 62 17

1.5 68 17 3.5 58 17

1.6 67 17 3.6 61 17

1.7 59 19 3.7 62.8 17

2.1 56 17 4.1 57.5 17

2.2 57 17 4.2 72 17

2.3 72 17 4.3 63 17

2.4 73 17 4.4 57 17

2.5 59 17 4.5 58 17

2.6 67 17 4.6 58 17

2.7 62 17 4.7 55 17

5.3 Following are the test temperatures measurement of CT 1&2:

Temperatures Measurement of CT 1&2

CT-1 CT-2

WBT Near

Risers DBT CWT Grid HWT

WBT Near

Risers DBT CWT Grid HWT

28.8 35.5 35.3 44.1 28.6 34 35.6 44.1

29.5 36 35.4 28.6 34 35.5

29 34 36.9 29 34.5 36.1

29 34 36.6 28.7 34.5 36

28.8 34 35.4 28.8 34.5 35.8

28.2 34 35.3 29.4 34.5 36

28.3 34 35.2 29 34.5 35.9

28.8 35.5 35.3 29.4 33.5 36.3

28.5 35.5 37.1 28.8 33.5 35.6

10 Approach deg.C 4.5 7.40 6.89

11 Effectiveness % 66.67 52.26 54.37

12 Tower Capability % 100 69.44 71.47

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28.3 35.5 37.3 28.5 33.5 35.5

28.2 35 35.5 28.6 34 35.8

28.2 35 35.6 28.8 34.2 36.3

28.5 35.2 35.8 29.2 34.5 36.4

29 35.5

35.7

29.8 35

35.9

37.8 35.6

Average

28.65 34.91 36.01 44.10 28.94 34.19 35.89 44.10

6.0 Observations 1. The tower capability was found to be 69.44 % and 71.47% of CT-1&2

respectively as compared to design value of 100 %. The estimated Heat rate loss for tower 1 and 2 are approximately 19 Kcal/KWHr and 17 Kcal/KWHr respectively

2. The cold water temperature at tower outlet for CT – 1 & 2 was 36 deg C & 35.89 deg C as against the expected value of 32.88 deg C & 33.17 deg C and thereby having a shortfall of 3.12 deg C & 2.72 deg C respectively.

3. The CW flow to the tower measured with the Ultrasonic Flow meter for CT – 1 & 2 was 33269 m3/hr and 32816 m3/hr respectively as against the design value of 33000 m3/hr.

4. It is observed that overall water distribution is very poor in both the towers. It is observed that in CT – 1.1 & 1.2 no water flow in major portion of the cells. It is also observed that in CT – 1.3, direct water is falling in many locations.

5. Lots of damaged concrete splash bars have been observed in both the cooling towers. Lot of Algae formation is observed in CT structure and basin and on splash bars. Presently no chemical treatment is being carried out in CW system of Stage – I.

6. The average fan motor power for CT – 1 & 2 was 64.00 KW and 60.80 KW respectively against the design value of 75 KW. Low fan power indicates less air flow through the tower. It is observed that only four

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fans i.e. CT Fan – 1.1, 2.3, 2.4 & 4.2 were taking highest power of 72/73 KW which is close to design value.

7.0 Remarks/ Recommendations

1. Replacing of damaged Concrete splash bars and cleaning of

algae:

Station may carry out cleaning of algae and replacement of damaged concrete splash bars in a fixed time-frame schedule to improve the performance level of cooling tower. It is also suggested to carry out proper chemical treatments of CW system to prevent algae formation.

2. Checking of nozzles and replacing damaged/missing nozzles:

Inspection of nozzles is to be carried out in a phased manner and undertake replacement/replenishment as required in a fixed time-frame schedule to improve the water distribution across the tower.

3. Optimization of Air Flow: It is observed that only four fans i.e. CT Fan – 1.1, 2.3, 2.4 & 4.2 were taking highest power of 72/73 KW which is close to design value. But the average Fan Power for CT – 1 & 2 were 64 & 60.8 KW which is low as compared to maximum value achieved. It is therefore suggested that optimization of air flow in individual cells through cell cleaning and fan blade angle adjustment is required to be carried out to achieve maximum air flow through individual cells. This will improve the heat transfer through the tower thus improving the tower capability and reducing the Cold Water temperature shortfall. The blade tip clearances of all the fans to be checked and appropriate action may be taken to minimize the possible air recirculation across the fan.

4. Cold water Basin cleaning:

Practice of cleaning of cold water basin is to be introduced and to be carried out on opportunity.

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5. Trimming of vegetation in the vicinity of Cooling Towers:

For better performance of Cooling Towers the surrounding area of the tower should be properly maintained to enhance the air flow through the tower. It was observed during the test that dense jungles/unwanted plants has been grown to greater heights which are restricting the air flow and hence contributing for poor performance of tower. It is suggested that the jungle thus grown should be trimmed immediately and may be maintained on sustainable basis for better performance of Cooling Towers.

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Vegetations grown near the tower

6. Cleaning of vegetations on the bank of cold water channel to CW Pumps:

It was also observed that the banks of cooling water channel are full of unwanted

grown vegetations. There is chances of entering of foreign material in CT pump

suction side and may cause the damage to the system. It is suggested to maintain

the vicinity of channel bank.

Vegetations grown in the vicinity of banks of channels