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

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 Pune 18 th July 2014. 1.

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

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  1. 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 Pune 18th July 2014 1

  2. 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.

  3. 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

  4. Power input rating of the Generators

  5. CASE -1 21 MW STEAM TURBO-GENERATOR

  6. 21 MW STG Air Water Circuit -Existing .

  7. 21 MW Steam Turbo-GENERATOR Temperature record of Generator Winding and other related temperatures PF : High [0.97-0.98 ]

  8. CASE -2 16 MW STEAM TURBO-GENERATOR

  9. 16 MW STG Air Water Circuit -Existing

  10. Power input rating of the Generators

  11. 16 MW Steam Turbo-GENERATOR Temperature record of Generator Winding and other related temperatures IMPACT OF HIGH & LOW PF ON WINDING & AIR TEMPERATURES

  12. 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. 

  13. 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.

  14. 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

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

  16. 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).

  17. MEASURESADVOCATED • 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.

  18. 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.

  19. 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.

  20. GALVANIC CORROSION OF HX & MITIGATIONAL MEASURES

  21. 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.

  22. 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 <34°C & the flow should be maintained to have low temperature difference (say 3 to 4 °C). • Zinc bars attached to the tube sheet should be checked at any available opportunity to be healthy • The successful operating concept shall be extended to all Generator Air water Heat exchangers for increased Productivity

  23. Good Maintenance Practice Ensures Productivity . . 27

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