Now we are running a gas turbine PG 6541B on natural gas. Now its winter here and load consumption at night is very low almost 5~6 MW. So if we want to use this plant as a peaking plant (running hour 16 hrs and off time 8 hrs) i.e. start GT at morning and stop that at night everyday, what problems might arise?

Please, Tell me about all the possible damage that can occur.

 

After foreign object damage, the biggest "enemy" of combustion turbines is thermal cycling. This includes the thermal cycles experienced during normal starting and loading, loading and shutdown, and tripping.

The more that can be done to start a turbine, load it to a steady load, and leave it at that load for the longest possible period of time, then shut it down normally (normal, fired shutdown; not emergency trip(s)), the better it is for the hot gas path parts in the turbine, and it's exhaust (particularly if there is a waste heat recovery unit (boiler)).

So, the more a turbine is started and loaded and unloaded and shutdown, the more the thermal stresses associated with heating and cooling are going to have a negative impact on the hot gas path parts (combustion liners; transition pieces; nozzles; buckets; exhaust diffusers; etc.).

If a turbine is "fast-started", that also impacts the hot gas path parts life negatively. Fast loading (and unloading) also negatively impacts hot gas path parts life.

GE publishes a document, a GER (sorry, I don't remember the number at this moment) which describes in great detail the effects of starts, stops, loading/unloading rates, shutdowns, and trips on the maintenance intervals. Each start, stop, and trip, and even loading rates has a "factor" which can be used to determine when the next maintenance inspection (shutdown) needs to be performed.

Maintenance intervals are chosen based on the expected life of the hot gas path parts, so if the life expectancy decreases, the interval between maintenance outages decreases. Which means that it's more likely that hot gas path parts will need to be replaced, which means more will have to be purchased. Which increases the cost of maintenance, and as well as lost generation income.

 

I agree with all that CSA has mentioned except the last sentence, well actually the context it was put in. It is true that with cyclic operation maintenance costs will increase appreciably, however keeping the GT running at low loads, will increase much more the fuel costs. One will discover that cost of the fuel lost in operating the GT at low loads and thus very low efficiencies will more than balance the increased maintenance costs resulting from cyclic operation.

Unfortunately this is a case where engineers and accountants end up at loggerheads (figuratively speaking). What is more important having a machine that works like a clock but wastes money, or one which in the way it is operated has increased maintenance costs but overall saves money?