Small Scale Turbine Compression Question

[buddyswift]

Hi there,

I'm working on some concepts for a clean solar energy collection and storage facility (enough to power a 3rd world village daily). A particular idea of interest is that of compressed air (150-200bar).

How viable would turbine compression be for this application? What sort of efficiency could I expect from the compression stage, and what sort of effciency could I expect using the compressed air to drive a fan/turbine at a later stage?

Help is greatly appreciated! Thanks.

 

[BigInch]

That's very high pressure for a 3rd world village. Probably quite dangerous considering a typical lack of skilled operators and money for maintenance. High pressures have high energy costs of compression and leakage rates much greater than low pressure alternatives. Compressing to 100 psig you will need somewhere between 15 and 25 kW/100 SCFM, depending on actual compressor and site conditions. Can you get that much from your solar system? Must be a hot place there. Higher pressures will require considerably more power.

As for your specific question, assuming scale factors are towards the smaller side, you should expect to have overall efficiencies of no more than 15% from compressor input power to power delivered to moving air by the fan.

At 100 psig, specific power is approximately 16 kW/100 cfm to 18 kW/100 cfm.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[zdas04]

Interesting idea, but doing it with compressed air has even more skill factors than BigInch brought up. The air has humidity in it, at elevated pressure this water is liquid and a big corrosion risk. The storage vessel has a big risk of failing with shrapnel when the PSV gets wired shut because it is making noise.

Why not look at doing it with water? Use the solar to pump the water into a water tower, then run a water wheel powered generator. If the water tower springs a leak, stopping the leak can be pretty low tech (a stick and a rubber patch). Buying a tank that you can put in an elevated location (either on a hill, on a pedestal, or on a support structure) is a lot less expensive than getting pressure vessel rated for 150-200 bar. I don't have the efficiency numbers on a pump/water wheel/generator lash up but my bet is that it is better than you'd get with a compressor and gas turbine.



David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

"It is always a poor idea to ask your Bridge Club for medical advice or a collection of geek engineers for legal advice"

 

[BigInch]

I think you could probably get something straight away of 20% of the solar panel's output back. Pump efficiency of 0.6 and a well designed water wheel 0.4 and some reasonable generator 0.8 maybe 30% with a decent pump and water power turbine, but costs just went up. And as much as 35% for high quality equipment and line losses to load point could be contained. But now you're talking real money.

Then you've still got to account for motor and fan efficiency to get to actual power delivered to move the air. If that's 0.9 x 0.6, you'd be back to 12% overall (100 psig pressure system) again.

Working with high pressure air, it probably wouldn't be much more than 6% with a throw-together system ... and dangerous. I imagine that you'd probably wind up just using the air to fill tires really fast ... for awhile.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch

http://virtualpipeline.spaces.live.com/