[Stoves] An Introduction

Mon Dec 5 09:35:29 CST 2011

Dear MaxT

>.fine charcoal powder has been considered for engines and tested for uses
in such... 

Didn't ITDG have such an engine in the 70's?

>but I was assuming here that the idea would be to direct part of the
pyrolysis gasses into sustaining the pyrolysis reaction and other part of
those gasses into condensing into tar like fluids... 

I see the problem as one of trying to scale it down while dealing with the
fact that in the very beginning of the burning of a piece of fuel, the gases
that come out are not combustible. Getting clean ignition is a difficult
problem for solid fuels. One approach is to put some liquid fuel on a pile
of solid fuel and burn it as a batch. The simplest is top lighting like the
packed bed coal gasifier by John Davies in South Africa. He uses small
pieces of wood soaked in paraffin, meaning left in a jar of paraffin, not
sprinkled with it just before ignition.

With wood chips or grasses the 'unburnable' effect can be seen by watching
the edges of the fire attacking new fuel: it smokes first and hopefully the
smoke is drawn into the existing fire. It is partly steam, partly gases with
negative heat yield, and partly heat yielding gases. In the (existing) fire
all are dealt with but getting it going is not so simple. In a piston engine
the process is re-started over and over (on each 4-stroke cycle). That means
whatever reactor you have must be producing combustible gases befit can be
fed into an engine, if the scale is small and non-continuous.

Dr Reddy http://biochar.bioenergylists.org/taxonomy/term/331 showed the Magh
Biochar retort 2 as an approach to trying to get a pretty clean process from
beginning to end. It is essentially an enormous TLUD stove. By that I mean
it does not separate the combustion of the gases from the charcoal making
process. The process is in my view quite different from the Adams Retort by
Chris Adams which is a self-heating retort.

I think you are talking about diverting some of the gases from a device more
like an Adams report. Unless it was pretty expensive (well made, metal etc)
I doubt there are gases to spare. It is already hard enough to keep it
going. Here is an expensive charcoal maker that seems to be running very
cleanly http://www.youtube.com/watch?feature=player_detailpage
<http://www.youtube.com/watch?feature=player_detailpage&v=WHU66mUGCbg>
&v=WHU66mUGCbg 

An example of an all metal self-heating retort is at
http://www.instructables.com/id/How-to-Make-some-Charcoal/ and you can see
that there is quite a bit of fuel needed to get it going and once it does,
it cannot be described as a very clean. It is a heck of a lot less smoky
than typical rural charcoal making (smudge piles) so I guess it is better.
It will have a high % yield as none of the biomass is burned during the
production, just the start-up fuel.

There is a video of it at http://www.youtube.com/watch?v=YsphDAFz1DA
<http://www.youtube.com/watch?v=YsphDAFz1DA&feature=player_embedded>
&feature=player_embedded See the 2 minute mark of the video. At that point
the ignition wood is mostly burned and the gases are sustaining the fire.
They could have used a lot less wood to get it going but I think there I no
shortage of wood in Portland.

This series of videos http://www.youtube.com/watch?v=PGiCUAMargY
<http://www.youtube.com/watch?v=PGiCUAMargY&feature=related>
&feature=related shows a kiln in which some of the wood is burned and the
gases are vented, ignited and wasted. After the gas is combustible, it is
pretty clean. Until then..? 

To do something useful for any decent length of time I think you need to
have continuous gas production like this
http://www.youtube.com/watch?v=7WSK2mknON4
<http://www.youtube.com/watch?v=7WSK2mknON4&feature=endscreen&NR=1>
&feature=endscreen&NR=1 and
http://www.youtube.com/watch?feature=player_detailpage
<http://www.youtube.com/watch?feature=player_detailpage&v=DI6Ebgi75Ys>
&v=DI6Ebgi75Ys 

This one http://www.youtube.com/watch?v=oUxy0w2Mpl0
<http://www.youtube.com/watch?v=oUxy0w2Mpl0&feature=player_detailpage>
&feature=player_detailpage shows a propane tank converted into a wood pellet
burner making enough gas to opeate a small tractor engine, for a while at
least.

This one http://www.youtube.com/watch?feature=player_detailpage
<http://www.youtube.com/watch?feature=player_detailpage&v=C1nUC1e07OU>
&v=C1nUC1e07OU is a downdraft gasifier that can be refuelled. It has the
possibility of running day and night.  He notes something very important
which is that the gas has a low flame speed and shows how to use that to
advantage. He obviously does not have combustion analysis (based on what he
says about the flame). The fire at 3:45 of the video looks really good.

There are a lot of people in the US working on up and down draft gasifiers.

Regards

Crispin

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