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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!
Dave E

Kind of a neat one using a Carrier 19xr
http://www.yourownpower.com/Power/

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.

i would not recommend that!

Originally Posted by eng1

What you are describing is an ORC (Organic Rankine Cycle). It uses the same basic thermodynamic cycle as a steam powerplant (steam meaning water for the working fluid) although it uses a organic (meaning carbon in the molecule) working fluid. Some even use typical commercial refrigerants such as R134a. There have been special refrigerants that are designed specifically for ORC applications (R245FA for example).

The cycle efficiency is dependent on the temperature gradient that you have (how cold the cold sink, or condensor, is versus how hot the heat source, or evaporator is). In very basic terms it is a refrigeration cycle in reverse. If you have a "hot source" of about 200F and a cold source of 70F (typical outside air temp) then the cycle efficiency will be somewhere around 5-6%.

You read that right Five to Six percent efficient.

That means that in order to generate 20 HP, you need about twenty times that from your heat source. This also means that you have to reject about nineteen times that to the cold source (this means a fairly large condensor is required).

You could build one on your own, but it would be fairly costly and you really need to read up on it (and thermodynamics). I would suggest using a screw compressor, they have been used in some small applications as expanders. A centrifugal compressor would most likely need to be re-wheeled to be an expander (the blade angles are basically completely different, plus you need some kind of guide vane to guide the gas into the wheel). A screw compressor run backwards is much simpler.
If you really feel the need after reading this to learn more, I would suggest RefProp, which is a thermodynamic software that can be used to design the cycle.

Also, for those HVAC guys interested, Carrier built some small ORC's (~200 kW) using chiller parts. They are now built by UTC under the brand Pratt and Whitney (the power division). The marketing geniuses came up with the name "purecycle".

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.

It's on the market, I bought one from jc witney,It works great! 375.00 + shipping.
I use it to power my dope grow lights and sell the remaining power back to the local utility and clear 1500 a day!

Google "ACME perpetual motion machine". I believe Wlie E. Coyote holds the patent


Go here for your best alternative process: http://www.toolbase.org/Technology-I...ned-heat-power

Gotta give the guy credit for thinking somewhat outside the box, it's a pretty cool idea.

The nice thing about steam vs refrigerant though, is it's easy to generate steam with fire, and it's tough to give fire a horsepower rating, but generally fire would be easier / cheaper to create steam with vs refrigeration methods and the means to move it.

While we can't help you (especially me, cuz I can barely wrap my brain around the refrigeration cycle when running the right way), I wish you luck if you're determined to keep pursuing this. Stay safe!

Yeah yeah yeah... Keep giving him links so he can go blow himself up.

What you are describing is an ORC (Organic Rankine Cycle). It uses the same basic thermodynamic cycle as a steam powerplant (steam meaning water for the working fluid) although it uses a organic (meaning carbon in the molecule) working fluid. Some even use typical commercial refrigerants such as R134a. There have been special refrigerants that are designed specifically for ORC applications (R245FA for example).

The cycle efficiency is dependent on the temperature gradient that you have (how cold the cold sink, or condensor, is versus how hot the heat source, or evaporator is). In very basic terms it is a refrigeration cycle in reverse. If you have a "hot source" of about 200F and a cold source of 70F (typical outside air temp) then the cycle efficiency will be somewhere around 5-6%.

You read that right Five to Six percent efficient.

That means that in order to generate 20 HP, you need about twenty times that from your heat source. This also means that you have to reject about nineteen times that to the cold source (this means a fairly large condensor is required).

You could build one on your own, but it would be fairly costly and you really need to read up on it (and thermodynamics). I would suggest using a screw compressor, they have been used in some small applications as expanders. A centrifugal compressor would most likely need to be re-wheeled to be an expander (the blade angles are basically completely different, plus you need some kind of guide vane to guide the gas into the wheel). A screw compressor run backwards is much simpler.

If you really feel the need after reading this to learn more, I would suggest RefProp, which is a thermodynamic software that can be used to design the cycle.

Also, for those HVAC guys interested, Carrier built some small ORC's (~200 kW) using chiller parts. They are now built by UTC under the brand Pratt and Whitney (the power division). The marketing geniuses came up with the name "purecycle".

Turbine would be easier. And then why not just use water rather than refrigerant. But first, do the math and you'll find because of losses due to efficiency you'll have a net loss. Our electrical grid is only 32% efficient.
Now, if you had a fast moving stream in your backyard you'd have something.

Condensing back to liquid, wouldn't be that much of a problem.
Finding a suitable compressor could be the main problem.

But, as Stamas said, We can't help you.

I did a little searching around and found that such "reverse compressors" already exist and are used extensively in industry. They're called "turboexpanders".

Check out what Wikipedia says about their use in power generation applications.

http://en.wikipedia.org/wiki/Turboexpander

More interesting to us refrigeration guys though is how turboexpanders can also be used to replace expansion valves in a system...and generate power in the process.

I read where a turboexpander connected to the compressor shaft can generate around 15% of the power required by the compressor.

Cool stuff.

Honestly, I doubt a compressor as manufactured today would do it. There is too much restriction to be efficient, think discharge and suction valves. What you would need is one with no valve plates, and a way to control the "steam" flow. the least amount of resistance to flow would be best to spin your generator. to me, a centrifugal type arrangement might be best as the wheels dont have high lift and spin rather freely in comparison. but then again WTF do i know?

Google "Refrigerant Steam Engines". Surprisingly, there's a lot of discussion going on out there. Mostly "pie in the sky" stuff, but a few thought provoking ones.

I particularly like this one where it talks about using scroll compressors:
http://www.redrok.com/engine.htm

Theoretically, I suppose it's possible. Using a refrigerant instead of water allows for the the boiling of the refrigerant to create high pressure "steam" utilizing a relative low temperature heat source and condensing it with a cool medium as a heat sink.

However, to attempt to build such a machine using a device designed as a refrigeration compressor would appear to have far too many stumbling block to be even remotely practical.

In any case, you won't get much detailed help here...even if there is someone familiar with such applications...because this site doesn't allow such discussion in an open forum.

Originally Posted by clockou

I want to use high pressure refrigerant as steam, to run a compressor (backwards) to run a generator. (to run my house, or charge a battery pack)
Is there anyway to match all of this together? What rating on the compressor would tell me that its strong enough to run a (say) 20hp generator?
I want to put the refrigerant steam into the drive side of the compressor to subsequently run the generator. How much pressure out of how large a line will turn the right size compressor.
I'm sure this is not a normal question. Its diffinently in the DIY area. And, probably no one has all the answers, but I would appreciate any answer, even a pretty good guess, to help me get started.
Thank you,
Clockou

Instead of reinventing the wheel, why not get a Solar PV Panel to charge your batteries and a generator?

I'm not sure what refrigerant you are planning to use as the "steam", or how you would go about modifying a compressor to act as a "steam" engine to drive your generator, but if you are planning on driving a 20 hp load with it, the quantity of refrigerant "steam" needed would be huge, as would the size of the compressor.

Even if you somehow managed to create a device that is fairly mechanically efficient, with a closed loop system, the energy requirement to cool and condense the refrigerant "steam" back to a liquid for reuse would exceed the output of the generator. No free lunch in the cold harsh reality of physics.

If your idea is to operate the refrigerant "steam" side as an open loop system, that would be highly illegal with most chemicals used as refrigerants. The refrigerant cost would also greatly exceed the fuel cost of a conventional generator.

Not a DIY site, especially not for a wonderment like this idea.

I'm not a Hvac guy, but,

I want to use high pressure refrigerant as steam, to run a compressor (backwards) to run a generator. (to run my house, or charge a battery pack)
Is there anyway to match all of this together? What rating on the compressor would tell me that its strong enough to run a (say) 20hp generator?
I want to put the refrigerant steam into the drive side of the compressor to subsequently run the generator. How much pressure out of how large a line will turn the right size compressor.
I'm sure this is not a normal question. Its diffinently in the DIY area. And, probably no one has all the answers, but I would appreciate any answer, even a pretty good guess, to help me get started.
Thank you,
Clockou