PLF of Thermal Power Plant

One or more of these, sooner or later:

• Supply shortage constraint
• Waste disposal constraint
• Equipment (wo)manpower constraint
• Process fluid throughput constraint
• Process fluid condition/quality constraint
• Something will run too hot and fail
• Something will wear out and fail
• An overcurrent device will operate, disconnecting the load
• Supply quality constraint
• Maintenance backlog constraint
• Catastrophic self-disassembly
• etc., etc.

In effect you will be shortchanging the factor of safety built into the system when designed.

In thermal power plant output is electricity & inputs are water, coal & air. These three inputs & their product works on your system (boiler, turbine, generator, their aux, etc) and electricity generated. If any one system run continuously over rated that system may fail & your production may stop. For example your system is designed for 135 MW normal running & you continuously run with 145 MW i.c. approx 7% higher. More coal to be burn in boiler & for more coal more air is required means more tube lkg in boiler , quality of steam may not maintained by your chemistry tends to turbine blade damage & same analogy for your generator also . Your PLF (yearly basis) ultimately reduce by running continuously more than 5%.

Normally we get questions about overloading small kW-sized generators or motors, but the same goes when you scale up to MW size.

Try reading the manuals or manufacturer's literature regarding operation in this way for more information as the detailed answer is rather complex and application, equipment and environment specific.

I am also into Operations of 135 MW set. well ur running ur unit at 142 MW and if its constant ur Days PLF wud be higher no doubt. but then consider the amount of Main steam pressure ur operating on which if its lower fine but in case its arnd n above the rated design pressure (14MPa) guess....then surely ur water wall tubes and drum r getting more pressurised than required. If the coal quality is gud then its fine but else it wud very soon cause boiler tube failure for sure.

Dear Mr. pradeepdhoni,

You should not run continuously. Continuos over-loading means, the design parameters will undergo changes, which may lead to problems by way of break-down etc.

For best performance - the loading should be between 85 to 90%. Occassionally we can load 100% for a short, very short duration since machinery, supplier keeps some margin 5% to 10% in design/Capacity.

DHAYANANDHAN.S

Thanks for all answers, But I heard from my plant operator that they can run upto a maximum of 10% of the rated. I also do not see any problems since they are running at the rated main steam pressure of (13.6-13.8)MPA. And the boiler tubes can withstand the maximum temperature of 540C.

The Specific steam consumption is very good and it is meeting the rated.

Then either the design is wrong or #1↑ applies. What do the commissioning records say about plant performance?

Power supply in your case is from Boiler -> turbine -> generator. Each have its limitation and efficiency ratings. Abuse any one in the chain and as rightly pointed out above will start to shorten their respective life cycles.

Your operator may have told you that they are running within rated design of the boiler pressure ( 13.6 -13.8 Mpa) against 14 Mpa. Congratulations, but have you checked the steam flow rate coming out of the boiler ? Is it within the Boiler MCR ( max continuous rating) ? Have you checked the flue gas quality emitting from the stack ? Has the colour changed from a healthy grey to a darker shade ? have a look at the stack during night - do you see sparks streaking out from the stack top?

How about your turbine - check to see the effect of the poorer steam quality on your rotor blades ? And also wear at the nozzle block.

It will be interesting to do a IR test on your generator stator. See how far the overheating has affected them.

It is better that the system is run to design spec to safeguard your company against a huge re-engineering job later, my friend.