Effect of more starts 1

[athomas236]

We have a client that runs 100MWe of diesels on the same site as a combined cycle plant. At about 10.00pm each day the client shuts down the combined cycle plant because of the fall off in electrical demand.

I have been asked to study if the clients approach could be improved and would welcome any advice.

Some of the factors I have thought about are:

1. More starts on the GT's will increase the number of operating hours thus bringing forward GT maintenance which increases annual maintenance costs

2. More starts means higher fuel consumption without generation which increases costs

3. More starts means more water used/wasted because of boiler blowdown which again increases costs

Regards

athomas236

 

[rmw]

athomas236,

It is a power density issue. Look at the real estate that your few hundred MW of diesels occupy, and imagine what the site would look like if all the CCGT capacity had to be replaced with diesel engines.

Yours seems to be an older GTCC plant, built before the GT's were capable of 150-170 MW by themselves. I built a few of those older CC plants, and even though small, they had heat rates that would knock the socks off of even the most efficient of the big boys (large central station plants.) Often they were put in by small municipal utility systems that already had plenty of recips in their system, gas and diesel.

Now imagine the same comparison against one of the newer more modern 500-550 MW, 2 on 1 or 800 MW 3 on 1 GTCC plants. There would be diesels all the way to the horizon, figurative speaking, of course.

The diesels have a practical limit of max HP per engine, and each engine has to have its associated switch gear, etc. They can have a heat recovery bottoming cycle, but not as effective as the GTCC plants, where the exhaust from the GT's starts at 950-1000F.

I believe diesel as a fuel has viability, whether burned in recips or turbines. Google the words "fisher tropsch" or "f-t diesel" for an interesting read. I believe there will be a lot of it available, competing with LNG within my lifetime.

rmw

 

[athomas236]

taylorg and rmw
Thank you both for your valuable advice.

For your information the combined cycle plant rated at 135MW achieved commercial operation in 2003, burns gas oil at about $300 per tonne and has a sent out efficiency based on NCV of about 44%.

The diesels entered service between 1987 to 1996 are rated at 53MW and burn HFO at $200 per tonne and have an efficiecy of about 40%.

Considering the running costs of fuel, water, ammonia and spare parts used I reckon diesels produce power at 6cents per kWh and the combined cycle at 6.5 cents per kWh.

At the moment I have little information about spares and am basing on $13 per MWh for diesels and $4 for combined cycle.

It is true that there are CCGT plants available that are bigger than 135MW and that CCGT plant have a lower specific capital cost than diesels. The size of the CCGT plant being considered was limited by the max peak demand for the grid which is about 350MW

Regards,

athomas236