[Stoves] ***SPAM*** Re: ***SPAM*** Re: [Biochar] Charcoal producing electrical power plant

[ajheggie at gmail.com]

Dear Kirk

I was long ago appalled at the waste and pollution making charcoal in ring
kilns and while researching the problem I came across this list and the
early mentions of the Reed-Larson inverted downdraught stove, now renamed
TLUD by Paul. Twenty years ago I devised a method of making lumpwood
charcoal from freshly cut wood cleanly. It had a dryer stage, a carboniser
stage and for the sake of making it attractive  a chap I met on the list
who was into gas turbines suggested producing power. It all worked but the
power side of things grew like topsy in expense and we failed to
commercialise anything other than the dryer section.

The thing is power generation benefits from scale so for small generation a
5hp petrol engine does it at low efficiency and the running costs are
largely disregarded, next up are the large diesel generators in the 100hp
class, they  are competitive for peak and emergency use  but their
operating costs are considerably more than steam turbines. Ordinary steam
turbines are not as efficient, at about 35% conversion, as big diesel
engines but they score in very low operating and maintenance costs.
Nowadays in the UK we generate most of our non-renewable  electricity in
GigaWatt sized combined cycle gas fueled plants and these demonstrate how
the best can be gotten out of the heat by burning the gas in a gas turbine
and then raising steam with the exhaust passing that through a turbine.
There is scope for running a lot of district heating from them but I don't
think that is done here.

One of the reasons they are efficient is that the pressure at which the
turbines work is high, so as not to leak air,  and tolerances between the
turbine and case are very low. These tolerances are similar as you go down
in size so a smaller turbine has higher leakage  losses and must operate at
lower pressure. We reckoned you might get down to around 300kW with a low
pressure (about 4bar if I remember) gas turbine with reheat but it would
only convert 16% of the heat to power.

Anyway my point is I don't think you can compete with grid power using the
heat from a small biomass plant and as biochar is not mainstream yet it is
mostly taking place at the smaller scale.

I DO believe biochar excess heat should be used but to avoid the cost and
complication of electric production ( the Philips type stove with its TEG
being a notable exception for off grid situations). I still have hopes for
domestic combined heat and power and TEGs but put my money on PV on my roof.

It is getting a bit far from the purpose of this list  to discuss either
biochar production or home heating with the excess but I have a few ideas
if you want to discuss.

Andrew
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