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Is there a rule of thumb for estimating (guestimating) the load of the ST & GT when the Generated load is known?

Example, on a single shaft where there is one generator, we can only see the generated load.

How would you split the Generated load between the GT and ST?

I understand that at varying loads the "split" will migrate due to fluctuation in back pressure, opening of blow downs, etc.
But I was hoping that somewhere at a quick glance there was a common train of thought that said the split would be 'x' %GT and 'x' %ST.

Anyone??

Andrew,

not sure if this answers your question but I will try. As you say it will depend on the efficiency and heat rate of your gas turbine, steam turbine and boiler. But my experience is that you can expect to get 40-60% of the gas turbine load from the steam turbine on most newer gas turbines with systems that have logic to maximize heat efficiency from the GTG. For instance with gas turbine load at 50MW expect 25-30MW from the STG.

The general rule of thumb is the gas turbine(s) will provide 2/3 of the load and the steam turbine will provide 1/3 of the load. These numbers are approximate, and will vary when the load is changing. This split is true for single shaft and multi shaft combined cycle applications, where all the steam produced goes to the steam turbine and there are no extractions (cogeneration applications).

Thank you very much. I thought I would share my findings after much data crunching, and I must say the rule of thumb of 40/60 split or 2/3 over 1/3 is as close as one can get. The grater the load is, the greater the split. Using linier data the best I can pin it down to is that the ST will be delivering approximately 50 & 54% of the GT (depending on load).

@ High load GT/ST Split of: 68 % & 32 %
Ex: Generated load 370 = GT @68%=252MW & ST @32%=118 MW =(46% of GT load)

@ Low load 63% & 37 %
Ex: Generated load 230 = GT @63%=145MW & ST @37%=85 = (58% of GT load)

Thanks for the feedback!

Andrew, thanks for the feedback!!