09. Best Maintenance Practices in 21 MW & 16 MW Steam

BEST OPERATING & MAINTENANCE PRACTICES RELATED TO 21 MW & 16 MW STEAM TURBO-GENERATORS

Dr T. G. Sundara Raman Seshasayee Paper & Boards Limited IPPTA Zonal Seminar

Best Maintenance Practices in Pulp & Paper Mill to Improve Profitability

18th

Pune July 2014 1

Steam turbo-generators Generator Winding Section • Power generation enhancement is directly related to increase in current produced [I**2] • In turn , it heats up the core winding [stator and rotor]. • It results in winding temperature increase. • Heat is dissipated to air in closed circulation on the exterior enclosed air duct. • Hot air in turn is cooled by cooling water flowing inside the finned tubes of the heat exchanger.

• The cycle continues with windings being kept below a set temperature with alarm set at 85 deg C and trip at 95 deg c.

Steam turbo-generators in SPB –Erode Unit • CPP- 21 MW Double Extraction Condensing Steam Turbo-generator of BHEL • Chemical Recovery Complex- 16 MW Extraction Back Pressure Steam TurboGenerator of BHEL

Power input rating of the Generators Rated Power

21 MW

16 MW

Power Factor

0.80

0.80

Power input [MVA]

26.25

20.0

CASE -1 21 MW STEAM TURBO-GENERATOR

21 MW STG Air Water Circuit -Existing

.

21 MW Steam Turbo-GENERATOR Temperature record of Generator Winding and other related temperatures PF : High [0.97-0.98 ]

Before Cleaning of HX

After Cleaning of HX

05/06/14: 14 h

19/06/14 : 20 h

0.97

0.98

MW

15.3

15.3

#1

C

85.3

77.2

8

#2

C

-

-

-

#3

C

88.1

80.1

8

#4

C

76.1

73.6

3

#5

C

72.9

65.2

8

#6

C

86.7

78.3

8

#7

C

87.5

79.4

8

#8

C

89.6

81.2

8

Cold air temperature

C

54/56

49

6

Hot air temperature

C

65/66

58/59

7

CW in temperature

C

37

35

2

CW out temperature

C

42

39

3

Date/Time P.F. Power Generation

Temperature reduction ,°C

Winding Temperature

100

21 MW ST GeneratorTem perature Schedule [Before & After Cleaning of Air & Water Sides]

Temperature Deg C

90 80 70 60 50 40 30 20 W1 W2 W3 W4 W5 W6 W7 W8 Bef Clean After Clean Cold Air Hot Air

CW in

CW out

CASE -2 • 16 MW STEAM TURBO-GENERATOR

16 MW STG Air Water Circuit -Existing

Power input rating of the Generators 21 MW

16 MW

Rated Power Power Factor

0.80

0.98

0.80

0.98

Power input [MVA]

26.25

20.6

20

16.3

16 MW Steam Turbo-GENERATOR Temperature record of Generator Winding and other related temperatures IMPACT OF HIGH & LOW PF ON WINDING & AIR TEMPERATURES Temperature increase ,°C

0.98

0.81

13/06/14

11/06/14

After

After

MW

11.13

10.7

#1

C

72.2

81.8

10

#2

C

74.0

82.7

9

#3

C

73.0

83.5

10.5

#4

C

75.0

83.7

9

#5

C

71.7

82.5

9

#6

C

73.6

83.5

10

Cold air temperature

C

42/41

44.6/44.4

3

Hot air temperature

C

59.6/55.6

62.2/58.8

3

CW in temperature

C

27

28

CW out temperature

C

34

35

Power Factor Date/Time Cleaning of HX Power Generation Winding Temperature

ΔT : 7°C

16 MW ST GeneratorTem perature Schedule

Temperature Deg C

90 [Impact of High & Low P.F.on Winding Temperatures] 80 70 60 50 40 30 20 W1 W2 W3 W4 W5 W6 W7 W8 PF :0.98 PF:0.81 Cold Air Hot Air

CW in

CW out

21 MW Generator Issue : High Winding Temperature •

High Cooling water inlet temperature of ~ 36 37°C due to poor cooling tower performance.

• Cooling water chemical treatment need to be improved & should be commensurate with the operating COC. • All the 8 coolers are on line.

16 MW Generator Issue : High Winding Temperature • CW temperature differential across generator had gone up from 4°C to 7°C.

• More than heat dissipation, probably cooling water flow through generator cooler would have dropped. CW flow restriction needs to be looked into & cleared.

Winding temperature increase Due to • Stator & Rotor Core heat losses directly proportional to square of increasing current • Copper & Iron Core heat loss with increase in Winding temperature associated with the above

• Frictional Heat & Field Losses • Reduced Power factor results in Reactive Power loss • Harmonic current heat losses

Heat loss reduction achieved through • Increase in Power Factor • Reduced Generation load • Harmonic loss reduction

Winding temperature reduction Achieved through • Lowered hot air temperature • Lowered cold air temperature • Lowered inlet cooling water temperature

• High cleanliness of air ducts & HX exterior • Minimal dirt/deposits over the winding coils • Ensuring Quality cooling water devoid of suspended impurities & foulant ( scales).

MEASURES ADVOCATED • Quality cooling water to be ensured • Periodic cleaning of heat exchanger tubes ( waterside) • Occasional cleaning of air side/duct off dust/dirt • Occasional cleaning of winding coil exterior ( during annual shut of the STG), if there is approach. • Cooling tower & chemical conditioning of CW to be in order.

CONCLUSIONS & RECOMMENDATIONS • Quality cooling water to be ensured • Periodic cleaning of heat exchanger tubes ( water-side)

• Occasional cleaning of air side/duct off dust/dirt • Occasional cleaning of winding coil exterior ( during annual shut of the STG), if there is approach.

CONCLUSIONS & RECOMMENDATIONS • Ensure desired rate of cooling water flow ( say to maintain 2.5 to 3.5 Deg C temperature differential) • Cooling tower & chemical conditioning of CW to be in order. • High Power factor leads to lowered heat losses from the Generator resulting in reduction in Winding temperatures. • All of the above if practiced on a sustained basis would ensure longevity of the Generator unit , thereby resulting in 100% availability of the same.

GALVANIC CORROSION OF HX & MITIGATIONAL MEASURES

Cathodic Protection • Tube sheet and finned tubes are of different materials. • Hence there will be Galvanic Corrosion due to high Electrochemical Potential difference between the materials resulting in corrosion of tube sheet. • Hence Zinc anode ( sacrificial anode) pieces are installed over the tube sheet cover to ensure longevity life of tube sheet/tubes.

WAY FORWARD • For ensuring Winding temperatures to be well within the recommended limits , be it at full load or low power factor operation of the Generator, both water and air sides are to be cleaned off deposit/silt/foulant on sustained basis. • As for cooling water, the quality should be good devoid of foulant; the cooling water temperature should be preferably