BEST OPERATING & MAINTENANCE PRACTICES RELATED BEST OPERATING & MAINTENANCE PRACTICES RELATED TO TO

21 MW & 16 MW STEAM TURBO-GENERATORS 21 MW & 16 MW STEAM TURBO-GENERATORS

Dr T. G. Sundara RamanDr T. G. Sundara Raman

Seshasayee Paper & Boards LimitedSeshasayee Paper & Boards Limited

IPPTA Zonal Seminar

Best Maintenance Practices in Pulp & Paper Mill to Improve Profitability

PunePune

1818thth July 2014 July 20141

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 Turbo-Generator 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 -1CASE -1

21 MW STEAM TURBO-GENERATOR21 MW STEAM TURBO-GENERATOR

. 21 MW STG Air Water Circuit -Existing

21 MW Steam Turbo-GENERATORTemperature record of Generator Winding and other related temperatures

PF : High [0.97-0.98 ]

Before Cleaning of HX

After Cleaning of HX

Temperature reduction ,°C

Date/Time 05/06/14: 14 h 19/06/14 : 20 h

P.F. 0.97 0.98

Power Generation MW 15.3 15.3

Winding Temperature

# 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

21 MW ST Generator- Temperature Schedule

[Before & After Cleaning of Air & Water Sides]

20

30

40

50

60

70

80

90

100

W1 W2 W3 W4 W5 W6 W7 W8

Tem

pera

ture

Deg

C

Bef Clean After Clean Cold Air Hot Air CW in CW out

CASE -2CASE -2

• 16 MW STEAM TURBO-GENERATOR16 MW STEAM TURBO-GENERATOR

16 MW STG Air Water Circuit -Existing

Power input rating of the Generators

Rated Power21 MW 16 MW

Power Factor 0.80 0.98 0.80 0.98

Power input [MVA]

26.25 20.6 20 16.3

16 MW Steam Turbo-GENERATORTemperature record of Generator Winding and other related temperatures

IMPACT OF HIGH & LOW PF ON WINDING & AIR TEMPERATURES

Power Factor0.98 0.81 Temperature

increase ,°C

Date/Time 13/06/14 11/06/14

Cleaning of HX After After

Power Generation MW 11.13 10.7

Winding Temperature

# 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 ΔT : 7°C

16 MW ST Generator- Temperature Schedule

[Impact of High & Low P.F.on Winding Temperatures]

20

30

40

50

60

70

80

90

W1 W2 W3 W4 W5 W6 W7 W8

Tem

pera

ture

Deg

C

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 reductionAchieved 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 ( 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.

• 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 HXGALVANIC CORROSION OF HX

&&

MITIGATIONAL MEASURESMITIGATIONAL MEASURES

Cathodic Protection

• Tube sheet and finned tubes are of different Tube sheet and finned tubes are of different materialsmaterials..

• Hence there will be Galvanic Corrosion due to Hence there will be Galvanic Corrosion due to high Electrochemical Potential difference high Electrochemical Potential difference between the materials resulting in corrosion of between the materials resulting in corrosion of tube sheet.tube sheet.

• Hence Zinc anode ( sacrificial anode) pieces Hence Zinc anode ( sacrificial anode) pieces are installed over the tube sheet cover to are installed over the tube sheet cover to ensure longevity life of tube sheet/tubes.ensure longevity life of tube sheet/tubes.

WAY FORWARD• For ensuring Winding temperatures to be well within the For ensuring Winding temperatures to be well within the

recommended limits , be it at full load or low power recommended limits , be it at full load or low power factor operation of the Generator, both water and air factor operation of the Generator, both water and air sides are to be cleaned off deposit/silt/foulant on sides are to be cleaned off deposit/silt/foulant on sustained basis.sustained basis.

• As for cooling water, the quality should be good devoid As for cooling water, the quality should be good devoid of foulant; the cooling water temperature should be of foulant; the cooling water temperature should be preferably <34preferably <34°°C & the flow should be maintained to C & the flow should be maintained to have low temperature difference (say 3 to 4 have low temperature difference (say 3 to 4 °°C).C).

• Zinc bars attached to the tube sheet should be checked Zinc bars attached to the tube sheet should be checked at any available opportunity to be healthy at any available opportunity to be healthy

• The successful operating concept shall be extended to The successful operating concept shall be extended to all Generator Air water Heat exchangers for increased all Generator Air water Heat exchangers for increased ProductivityProductivity

.

27

.

Good Maintenance

Practice

Ensures Productivity