[Gasification] Homemade gas turbines

[Daniel Chisholm]

On Sun, 2007-15-07 at 16:27 -0600, Bob Stuart wrote:
> On 15-Jul-07, at 4:14 PM, Ian Vincent wrote:
> 
> > Hi
> >
> > I was googling about over the weekend and found that there are designs for
> > making a gas turbines from vehicle turbochargers yet I never heard  mention

e.g. (though it hasn't been updated in a long time):

http://www.gas-turbines.com/t98ntxx/index.html
http://www.gas-turbines.com/nt6/index.html


IMO, there are few projects whose nifty-o-matic factor exceeds that of a
homemade gas turbine...


> > of such on this list. In fact I never saw much about using gas  
> > turbines on
> > this list at all. Yet it seems like an obvious combination,  
> > gasifier + gas
> > turbine + alternator = electricity. Is there some basic problem  
> > with this
> > that is not immediately obvious?
> 
> The only problem I've thought of is that you need two compressor  
> sections, one for the air and one for the fuel gas.

That is if your gasifier runs at atmospheric pressure.

If your gasifier is pressurized (i.e. located between the compressor and
turbine sections), you don't need to do this.  Your engine layout is
then pretty much the same as a conventional liquid fueled turbine,
except that you are using a solid fuel instead of a liquid one.  You
will need to have a method to to reliably feed wood into the pressurized
gasifier/combustor (e.g. fuel lock hopper).


Practical pressure ratios for a single stage gas turbine built from an
automotive turbocharger are 2.5-3, which is relatively low.  Compressor
and turbine efficiencies are in the 70-80% neighbourhood.  Reasonable
turbine inlet temperatures are in the ~1600F neighbourhood.  This will
result in a thermal efficiency in the mid to high single digits.

If you have a productive use for a waste heat stream that is ~1000F (I'd
have to look up my spreadsheet to be more specific), consisting of
90-95% of the heat from your fuel input, then you could have a real
winner of an application.

Using automotive turbocharger(s), if you want to capture shaft power,
you will have to make some sort of mechanical modification to connect to
the turbine shaft (ordinarily there is no power take off).  Or you can
use a second turbocharger, cut it in half, and use its turbine as a free
turbine wheel.

If you don't have an economical use for your waste heat, your <10%
efficiency may well override the benefits of the turbine's low capital
cost, simplicity, and (relatively) cheap fuel.

If you need to increase your thermal efficiency, you can:

- increase the pressure ratio.  E.g. go to a multi stage compressor
and/or turbine

- add a recuperator (a heat exchanger to capture some of the exhaust
heat into the compressed air)

- use a more efficient compressor and/or turbine.  As you increase your
pressure ratio, this becomes ever more significant.

- increase the turbine inlet temperature (though you quickly run into
materials problems that exceed the state of the art!)


-- 
- Daniel
Fredericton, NB  Canada