Many thermal power plants across the world are between 10-50 years old with an median average of about 30 years. Considering that no new plants are being built now a days, but still such plants are essential for continuous and reliable power supply, more attention should be paid to improve the efficiency and maintaining it. In this article, we highlight few basic approaches on how to investigate the efficiency loss. In a follow-up article, we will discuss methods to maintain the efficiency.
So lets take a coal or oil-fired thermal plant as an example. First thing, you should do is check ratio of steam flow/MW at a given load, and compare this with design condition. Ensure that all feedwater heaters are in service and spray is not used for reheater. If the ratio is higher than the design, you know that the performance issue is occuring in steam cycle part. if the ratio is within design range, but your fuel consumption is still high, then obviously performance loss is happening in boiler cycle. So lets analyze further on what could be potentially wrong in these cycles.
Steam Cycle
- If your vacuum is bad, then you should check why.? is it because of air ingress into system, or because of deposits on tubes, or poor performance of vacuum pumps or poor water chemistry control etc.
- Is emergency drain of any feedwater heater is periodically or continuously open?. Make sure level is controlled properly.
- Is there passing of valves.? There are lot of valves in steam cycle used for purpose of start-up or draining/ periodically removing condensate from pipes. If they are passing, they would normally be draining into a flash tank to the condenser. Any steam that goes to condenser is a loss.
- Have you checked the amount of steam going for auxiliary consumers from auxiliary steam header?. Like for steam atomization, for steam coil air preheater, for demin water production, for steam seal system, for steam driven turbine feedwater pumps, for fuel heating etc.
- Even after investigating these potential causes, you are still having performance issue, then culprit is most likely with in main turbines. Like internal blade losses, bigger seal clearance etc.
Any other loss like venting loss from deaerator, or vent line of safety valve passing etc would be visible and is not expected to be big factor. Similarly we have assumed that generator efficiency is same as per original design.
Boiler Cycle
- Can you reduce your stack temperature? Sometimes the fuel you may be burning does not require even to operate at high stack temperature.
- Is your excess air within the design values.?
- Is your air leakage in rotary air preheater with in design value?. It is extremely important to ensue that air leakage is checked periodically.
- Is insulation condition of ducts and boiler island ok?.
- Is there any valve passing on your boiler drain system?. This will also shows up in higher makeup water value.
Each of the above mentioned potential causes requires thorough investigation which obviously depends upon the tools/techniques used. We have been able to reduce 4-6% fuel consumption from old plants by following simple investigation.
Trust us, because of age there should be only minor efficiency loss (0-2%) that is due to irrecoverable losses in turbine, or insulation looseness, or slight degradation in pump efficiency. If its more and you really want to improve efficiency, its not hard. Remember, improving the efficiency is low hanging sweet fruit! If you pay attention, it could not only reduce emissions, auxiliary electrical losses but also increase your utilization/load factor.