Report on the Energy Audit Workshop

A Report on Energy Audit Workshop conducted by Engineering Staff College of India

An workshop on Energy Audit for Thermal Power Plants was held for 3 days         (8.10.2003 to 10.10.2003) at the Hyderabad Campus of Engineering Staff College of India wherein honorable Faculties/Experts of ESCI and different participants from different Power Utilities were present to exchange their views in achieving most efficient energy oriented design and management of Thermal Power Plants. The leading power plant experts and faculties from different sector of the Country have presented their papers, shared their knowledge and vast experiences in the said workshop. Not only that, Engineers of Senior Management level who are in-charge of either Operation or Maintenance or Efficiency department have contributed a lot during such interaction.

The crux of the said workshop is how we can minimize/optimize 

(i)           Specific coal consumption,

(ii)          Specific oil consumption and

(iii)        Auxiliary power consumption 

in the running power plants or future power projects which are in the pipe line for implementation. It is of the prime importance to consider all the aspects during preparation of technical specifications in ascertaining most energy efficient design and its implementation during finalization of detailed engineering. Thereafter construction, erection, testing & commissioning are to be completed and energy efficient performance is to be achieved through PG Test. Not only that necessary     corrective measures are to be undertaken in the running power plants by implementing all the recommendations of energy audit experts which has now become mandatory for each and every power station as per recent directive of Central Electricity Authority, Ministry of Power, GOI. 

In order to achieve most energy efficient design, the following aspects need to be considered and incorporated during preparation of the technical specifications:-

1. Bowl and Roller Mill – As has been improved in the latest modified design of BHEL, a rotary or dynamic classifier has been incorporated in place of fixed

classifier so that uniform particle size could be achieved and auxiliary power consumption could be reduced as a result of reduction of re-circulating particles in the grinding zone of the mill.

It has also to be pointed out that the location of the rejection door shall be at a height top 3’ from the ground level so as to facilitate ease of operation while it is in service.

2. Horizontal / Vertical Pump -  A suitable PVC coating of required DFT is to be applied along  the inner surface of the pump casing / suction bowl and outer surface of the impeller so that corrosion & pitting could be minimized and auxiliary power consumption could also be reduced as the frictional loss will be less with such coating.

3. Cooling Tower – In practice, it has been found that hollow blades are performing poor compared to solid blades. Accordingly, it is wise to go for solid blades having proper blade angle and sweep so that sufficient air suction could be produced in maintaining optimum L/G ratio. It is also advised to isolate a particular cell completely when the dedicated fan is not in service.

4. Variable Frequency Drive – Not only the experts & faculties but also the Senior Engineers of different power utilities across the country have unequivocally recommended for the installation of VFD where there is variation of out put of a particular equipment to accommodate the Unit load variation during a day span in equipment like ID fan, PA fan, Coal feeder, BF pump, Vacuum pump and even CW pump. The plants which are already having such facilities are enjoying the advantage of substantial reduction in auxiliary power as well as minimum need for VFD maintenance. In case of CW pump aided with VFD optimum cooling water flow is allowed to maintain the desired condenser vacuum.

5. Vacuum Pump – Vacuum pumps are more users’ friendly in the running power station of NTPC and other power utilities of different States since vacuum pumps are found to be more efficient compared to steam ejector system. Another positive aspect of this pump is that it will draw less power when aided by a BFD in maintaining the optimum value of the condenser vacuum. Accordingly, all the participants and faculties recommended strongly in favour of vacuum pump, however, undersigned was the sole advocator who tried to unfold strongly all the merits of steam erector system.

6. Screw Compressors – There were detailed deliberations regarding choice and selection of compressors either reciprocating or screw type. Based on feed back from running plants it was agreed by all that reciprocating compressors are maintenance prone whereas screw compressors are of “fit and forget” type. However, it has also been specifically pointed out that until and unless judicious surveillance is enforced regarding full / partial / no load running conditions of the screw compressor, it will draw rated power irrespective of its different loading conditions whereas reciprocating compressor will draw lesser power at no load condition. It has also been checked through performance curve of the screw compressor, either single stage or double stage, it is quite capable to deliver, as continuous duty, required discharge (15 NM³/minute) at desired pressure (7/8 kg/cm²) as per our requirement. However, the cost of dry type (oil free) screw compressor is higher than that of reciprocating type compressor.

7. Turbine Driven BF Pump – Though it is not widely used in lower capacity Units (less than 500 MW) the faculties and experts have advocated to go for 1x30% electric driven and 2x100% steam driven BF pump to reduce the auxiliary power consumption to a substantial level. They recommended the same for Unit capacity of 250 MW or above.

8. Two Cylinder Turbine – It has also been discussed elaborately how to achieve best possible heat rate for a steam turbine. The faculties and experts explained in detailed the acceptance in favour of two cylinder machine wherein HP & IP shall be accommodated in the double casing of a single cylinder and the LP in the 2^nd cylinder. In such a combination, the turbine heat rate is found to be better compared to three cylinder machine of a same capacity. The reasons behind is that combined HP & IP in a single cylinder will attract less steam leakage.

9. Condenser – The undersigned has raised the issue of fixing of metallic inserts/shields as an end cap at the both ends of Condenser tubes in place of conventional PVC ferrule, widely used since long in our existing power stations. Based on feed back available with them, the Faculties/Experts recommended in favour of metallic inserts/shields which they believe will substantially reduce the down time of the Condenser which is, at present, facing frequent condenser tube leakage.

10. MS/RH Attemperation – It has been recommended by the Experts to draw the Attemperation spray line for SH from the up stream of HP Heater-6 and for RH it is to be drawn from the matching kicker stage of BF pump.

11. Thermal Insulation – Every one felt that less importance is given in regard to thermal insulation though it is a very important area from where substantial drainage heat energy is caused in the power plant. Utmost importance is to be given on this area in selecting suitable insulation material and specific form of such insulation material so that the outer skin temperature of the heat source could be as close as the highest ambient temperature. A good amount of heat energy could be saved by judicious management providing proper thermal insulation and accordingly specific coal consumption could be reduced to some level.

12. Out Door Motors – Out door motors, specifically which for Cooling Tower, ID fan, FD fan etc. should have been designed in a proper manner and its insulation class is to be chosen accordingly so that no space heater is needed through which drainage of electrical energy could be averted.

13. Ammonia Injection – The undersigned has raised the issue of ammonia injection at the up stream of ESP and advocated in its favour since the result achieved as on date to reduce SPM level is pretty encouraging. When asked regarding any adverse feed back in other stations in the country, it has been confirmed that as on date they did not have any discouraging information in this regard. They have also recommended that such provision may be incorporated in the technical specifications for the new projects which are in the pipe line for implementation.

14. Illumination – This is another area which, normally, is given less importance by the project authority during implementation of a project, as felt by the Faculties/Experts. It has been emphasized that there may be good amount of energy saving if scientific approach is given for selection of energy efficient lamps in achieving required lumen level in different areas of the thermal power plant. The initial installation cost may be little high but there will be continuous energy savings in the entire life of the plant for a period of 25-30 years which will add up the sent out energy to the consumers in earning higher revenues. Faculties/Experts recommended incorporating this sort of scientific approach in the technical specifications.

15. Blending of Coal – The undersigned raised the issue of blending of coal since the fuel cost is increasing day by day and almost eating away 85% of the cost of generation. The Senior Engineers of power utilities including Faculties and Experts unequivocally pleaded for such blending of coal at a reasonable ratio so that fuel cost could be reduced to a lower level in achieving the least possible cost of generation. Senior Engineers from Dhahanu TPS has informed that they are importing coal from Australia & Malaysia and such blending of coal is a normal practice in their power stations for a pretty long time.
    
    
    Prepared by Debabrata Dey

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