On 11/12/2012 02:34, The Natural Philosopher wrote:
On 10/12/12 21:18, Andy Champ wrote:
On 10/12/2012 17:30, Corporal Jones wrote:
CCGT (I presume this is gas)

Yes. And as no-one has seen to enlighten you:

Combined Cycle Gas Turbine is basically a jet aircraft engine connected
to a generator. Then because the exhaust is hot you can run a steam
engine off it.

Open Cycle Gas Turbine doesn't have the steam engine, so it's less
efficient.

You can run a CCGT in open mode, and that part of it will fire up in
minutes. The steam part takes ages,

20 mins or so with modern kit.

which means it doesn't respond well
to a sudden increase in requirements when the wind drops.


no. It means it doesnt repsond well to cold starts. Its actually a fully
dispatchable power plant and whilst wear at say half power is obviously
not much less than full power, gas consumption tracks very well with
output.

So there is a tendency to use rather more than you need running below
full chat.

Giving you emergency headroom. And at the moment we have 2GW or so
pumped storage to take care of short term peak requirements.


How the heck do they get the steam side of it up and running in 20
minutes? I'd assumed it really was a shaft turbine (and you can fire
them up full power from cold, although it's cruel) feeding some kind of
boiler with the exhaust.

So - 20 minutes to get the oil warmed up, let the blades heat evenly,
and the GT part is running. I can easily believe that.

But surely the steam must take longer? And surely until the steam is up
to heat you're using just as much gas for the turbine side as you would
after the steam is running?

I'm obviously missing something. Comes of having fans an inch across in
my kit...

Though short term (~= ad. breaks) isn't what bothers me. It's the 3
days flat calm nationwide we get occasionally.

Andy