You seem to be looking for the net heat rate which will depend on the turbine auxilliaries as much as the turbine itself. This situation puts you firmly at the manufacturers' discretion unless you have in-house facilites to analyse the turbine geometry etc.

The easiest way is to compare the results from the different manufacturers websites where you will be able to find little interactive dialogue boxes which ask you for the superheat & flow data & then pump out a power figure; or vice versa. .

I've used them to evaluate waste steam utilisation & never bothered about their accuracy on the understanding 'like for like'. When I used them the dialogue didn't offer reheat stage selection etc. See if does nowadays. Good luck.

For guidance the net heat rate should be around 10,000Btu/kWh & nobody apologises for the mixed units because General Electric et al were forced into them because nobody on dry land used shaft horsepower. ■

There is an ambiguity behind the question. Either you are trying to estimate the power acheivable from your waste process steam or you are trying to reconcile the performance of a turbine in service. Whatever.

Both scenarios are reliant on the turbine manufacturer. Large scale test facilities are available to verify the turbine performance before shipment & test witnessing is an integral part of the professional engineering process for procurement of any serious rotating equipment. If you ignore test witness procedures or furnish an ill considered purchase order then you are, I'll say it again, relying on the manufacturer for your mythical efficiency value.

Persistent requests for magic formulae will not bear fruit. There are no such equations.

What has turbine rpm got to do with power from steam at given conditions?

This one really needs knocking on the head, right now: it's off topic & only promises a proliferation of attempted confusion. ■