Typically, steam cycle (Rankine cycle) powerplants are used when you have a heat source that is hot enough to run a steam turbine. For example if you are burning coal or natural gas.
ORC's are typically used when the temperature source is too low to run a conventional steam cycle. They can also be used as a "bottoming" cycle where the discharge from a conventional steam turbine then cross exchanges with the inlet of the ORC. This is called a combined cycle power plant.
More commonly, you may hear of a combined cycle power plant when referring to a natural gas turbine that is "stacked" on a steam turbine (the discharge from the natural gas turbine heats water to create steam and run a steam turbine).
So they are meant for different applications. The use of ORC's is growing fairly rapidly since the most common geothermal resources in the world are relatively low temperature (not hot enough to run a steam cycle).
Fairly interesting stuff, although I would say that it really isn't a DIY project.
i would not recommend that!
Originally Posted by eng1
true knowledge exists in knowing that you know nothing.
Screw expanders are not a new concept. Neither is an induction generator (or induction motor, they are the same thing).
Screw compressors built for refrigeration servicve have been used as expanders (so have re-wheeled centrifugals). See attached.
Kind of a neat one using a Carrier 19xr
I would be curious as to what fuel is to be burned to operate this creature. You mentioned a 20 HP compressor; Onan's standard of 1 HP for every 500 watts of electricity means you're trying to come up with about 10 KW. If you're using propane, natural gas, gasoline, or diesel fuel as your source, just get a generator unit that runs on that type fuel and be done with it!
By the way, no form of "make-it-yourself" electricity can be done as economically as purchasing it from your local utility (one guy tried to run a major hotel on three natural-gas generators - worked well until the generators wore out LONG befure he broke even!). Solar is as close as it gets, except for the cost of the panels. Geothermal would be great if you were to own a geyser.
If you're doing this as an experiment/hobby/"see-if-I-can-do-it", good luck!