[Gasification] Autopyrolysis Biochar

Ken Boak ken.boak at gmail.com
Thu Dec 26 12:07:09 CST 2013

Tom Reed and Tom Miles,

Thanks for a useful discussion about biochar, made using the top lit
updraft (now autochar) method.

I believe you use the term auto, because you are using the heat generated
by combusting some of the syn-gas to self-char the wood?

It would be interesting to explore the variation of different fuel types
which can be converted by this method, from woodchips to cordwood, and
everything in between?

There is an active online community for charcoal gasifier enthusiasts,  who
typically make a batch of char in one process, allow it to cool,
mechanically process it down to the right lump size and then load this into
a simple charcoal gasifier.  If the char-production and gasification
process could be combined to reduce the fuel handling and loss of energy,
and yield a useful quantity of high calorific value syngas, and 20%
biochar, in the form of fine material, then this would safe a lot of time,
labour and joules.

Minimising the mechanical processing of wood, and maximising the useful
yield of the size and grade required is a way of driving up the efficiency
of the wood fuel.  After all, how many litres of diesel fuel go into
processing a tonne of firewood or producing a tonne of woodchips?

Also, if you want biochar as an end product, you will have to reduce the
amount of energy extracted, either thermal or as syngas for running a
generator. To have a biochar processor, where you can specify the biochar
yield - at say 20%, and have the rest come out as usable energy would be
good. However, with downdraft style gasifiers, the emphasis has been to
maximise the syn gas production, at the expense of a minimal yield of char.

Regarding gasifier efficiency, I have recently being helping set up a 20kWe
All Power Labs Power Pallet, as part of a CHP system in the south of the
UK.  We have the means so far to capture the waste thermal energy from the
engine coolant and contribute it to a 2500 litre thermal store.  We can
also extract up to 18kW of electrical energy to a dump load of 3 x 6kW
immersion heaters - also located in the thermal store tank. These heaters
are useful for conducting constant load, extended hour run tests on the
gasifier and genset.

The fuel stock is hardwood woodchips sorted to "half to one inch" chips,
and we are seeing a fuel consumption of about 20kg per hour when running
 the gen-set at 90% full load (18kW).


Ken Boak

On 26 December 2013 17:10, Tom Miles <tmiles at trmiles.com> wrote:

> TR>However, if I had a trench 5X5 ft2 in cross section, the pile of dry
> "TreeBrush" could be thrown in, lit at one end, and it would burn
> horizontally end to end and make Biochar.  Saving the cutting up process.
> Tom,
> Would it make a difference to cover the pile, leaving it open at both ends?
> Tom Miles
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