[Stoves] 2 KW Woodgas generator with turbine

[andrew]

On Sunday 18 March 2007 10:24, Crispin Pemberton-Pigott wrote:

>
> This guy speaks as if it is normal to generate 2 KW worth of
> electricity from wood gas using his burner.

Firstly this topic is better at [gasification] rather than [stoves], 
complication, safety and capital expense means the waste heat is 
never likely to be a prime use of the technology, least of all for 
cooking.

He may generate 2kW(e) but what is the cost in input kW(t)? My guess 
is around the 5% mark, probably no better than a modern TEG. I say 
this because we built a pyrolyser with a bit more sophistication 
than this. it ran at 2bar above atmospheric. Now think about this 
the next time you pump up a car tyre, it's a non insignificant 
pressure. So the containment has to be internally insulated and 
pressurised, the "skin" has to withstand this and to do so must leak 
a bit of heat.

Why do I compare it with a pyrolyser? It's because there are 
difficulties with complete gasification such that for this use it is 
actually quite a bit easier just to deal with pyrolysis offgas and 
discard the char. I think even fairly successful gasifiers running 
reciprocating ic engines have tended to leave a lot of char with the 
ash.

Terra Preta enthusiasts will see an opportunity similar to that 
presented by a TLUD stove once carbon trading/offsets work at the 
micro level.

There are a number of means of pushing up the conversion from these 
low pressure "agricultural" gas turbines but they involve 
significant cost. An increase from 11% to 20% was mooted for a 250kW 
output with a pressure ratio of 2.9:1.

> There is quite a lot to see (including a 120,000 RPM turbine) at

Maybe but how safe is a turbine with an inlet temperature of ~1000C 
running continuously, when it was designed to operate at an inlet 
temperature of 500C for a vehicle life of a few thousand running 
hours?
>
> My simplest interpretation of it is that he is using a vehicle
> turbocharger to compress the gasifier...yes?  

Most likely the compressor provides compressed air for both the 
combustion and the gasification, the containment all running under 
pressure.

> Or is it burning the 
> gas to drive the turbine and get electric power from the shaft? 

He'll be burning the gas in a separate combustion region and then 
expanding the products through the turbine, even with wood the thing 
will need quite a lot of dilution air to get the turbine inlet 
temperature low enough (you might be able to do this with the water 
from green wood but it would likely interfere with the gasification 
part too badly).

> Either way there is a lot of heat to cook with left over.

Definitelyy probably about 600C, but the food would fly and the cook 
would go deaf.

Should anyone in UK want to further the concept I may know a man that 
could find the bits still, unless they're already en route to a 
smelter in China.

Andrew Heggi