[Terrapreta] Farm Scale Batch Charcoal Furnace for Homestead or Farm

[andrew]

On Sunday 06 April 2008 11:05, David Stewart wrote:
>  My interest runs to using wood as a biomass source
> (I am located in the Northeast US) both for heat and for agrichar
> and biogas.

It's a shame you're about 4000 miles away, charcoal heat and power is 
something I've been interested in for a few years, my colleague 
managed to get as far as running a gas turbine (with support fuel) 
off the offgas (biogas tends to be interpreted as the gas given off 
by the anaerobic digestion of volatile solids and is a mixture of 
CO2 and methane).

> The primary attribute of
> this furnace would be to create the biochar in a chamber separate
> from the heat creation chamber.  This would allow for easy
> extraction of biogas and efficient use of the wood being burned in
> the combustion chamber when not being used to heat the house...

The thing about the offgas from a retort/kiln is that it is 
quite "dirty" being a mixture of tarry vapours as well as gases like 
methane and CO, so piping it any distance is problematical. 

If you use a wet (hydronic) system then you can take this heat after 
it has done some work for you in pyrolysisng the wood, which is 
happening at between 270C and 500C, depending on what sort of char 
you're after, so taking heat out at 95C makes a later call on it. 
This hot water can be a fairly inexpensive thermal store to even out 
fluctuation between batches.

The trouble with a batch system will be in reconciling the heat from 
the flaring of offgas with the earlier need for it to heat the 
retort. A Russian chap, Yury, from the [stoves] list gets around 
this by loading large cassettes of prepared logs sequentially into a 
kiln, so that the heat from a pyrolysing batch initiates pyrolysis 
in the new batch.

I cannot see any real need for running as a batch, especially as 
there is no need for the char to be large particles or dry. Why not 
a simple downdraught chip burner but with the char withdrawn before 
it gets oxidised to CO?

How about some figures for heating requirements and an idea of the 
raw material you are considering?

AJH