Re: GAS-L: Cheap charcoal gasifiers

[Andrew Heggie <andrew.heggie@dtn.ntl.com>]

On Fri, 14 Apr 2000 19:45:52 +1200, Doug Williams wrote:

>Dear Andrew and gasification colleagues.
>
>My apologies for replying to earlier postings at this late date, but I am
>disappointed that so many good questions and statements are unanswered or
>challenged.  Is our knowledge so insecure we fear to present it, or do we
>think its too commercially valuable to share?

It is unfortunate the group has gone so quiet on this, I guess a lot
of the reason is commercial confidentiality. The industry here in UK
is beginning to look very optimistic for biomass with one combined
cycle gas turbine in construction and two more at planning. On the
small scale it remains quiet with the exception of pre-commercial and
research projects.
>
>Andrew, your questions about charcoal gasifiers and their cost compared to
>wood gasifiers is you could say, a trick question.  You still need the same
>amount of components gasifier (simpler), cyclone, coolers and filter, with
>the only real difference being in the lack of condensate.  The more gas you
>need, the bigger they become, and they do need to move away from the single
>big nozzle to achieve the increase in size.  It would not be necessary to do
>this if charcoal quality was consistent, but in the real world, its more
>often torrified wood than charcoal.

May I infer from this that if the charcoal is low in volatiles and the
engine small then the gasifier for charcoal could be smaller (cv of
charcoal is 30MJ/kg compared to seasoned wood 15MJ/kg) superficial
velocity will be high (as cv of off gas is reduced from 5MJ/kg to
about 4MJ/kg)?

For complete gasification the ash must be entrained by the offgas. The
ash content has increased as it was all retained in the char matrix so
it is a bigger problem than a wood gasifier. However is there any good
reason why the coolant could not also be a primary filter, the ash
being removed as a sludge from the filter?
>
>As to the cost of these charcoal gasifiers, why does anyone expect them to
>be cheap, work for 10 years and come complete with commercial warranties
>There is also an expectancy that you the owner, can ignore the need for
>operational training, servicing, and maintaining safety standards, all
>issues that a responsible manufacturer has to resolve, in order to sell you
>a gasifier.

Point taken, however I was still thinking on the lines of something a
local blacksmith could assemble rather than a turnkey package.
>
>The interest in charcoal gasifiers of course comes from the simplistic
>pictures you see in historical literature, the Kalle for instance.  Its
>actually a very crude example of gas making principles and far less reliable
>than a cross draught system.  They all worked of course, but in the end the

Any idea why? Joacim, the thread originator, fed back some thoughts on
improving the design, I still have not quite grasped why, using a good
charcoal, a simple updraught design has any disadvantages. I admit I
have not built anything other than an updraught gasifier ( and this
for not for engine use)!

>reliability and durability of components came back to the individual
>manufacturers skill and understanding of the gas making phenomena.

Yes I understand that gasifiers remain a black art! I had always
assumed this was due to variables in the feedstock.
>
>Simple charcoal gasifiers for developing countries were developed at AIT in
>Thailand using Ferro cement and chicken wire.  These were further developed
>at Bremen University in Germany (1989) and BTG in the Netherlands.  I
>participated in the Bremen project supervising "cheap" steel gasifiers.

Any pointers to the 1989 design?
>
>I'd like to suggest that it be kept in mind, that we cannot impose our
>ideals on rural populations in far away places.  Our choice of technologies

This is the point Vernon made.
>is not simple or cheap, but it can be reliable if the gas making phenomena
>is understood.
>
>Finally, don't believe all you read in historical literature, for even with
>all the dimensions they supply to copy, you will have a hard time making
>them work.
Which is why I have not rushed to build one, I was hoping someone
would post a better analysis of likely costs and efficiencies at the
40kW scale. ( his being what I considered a typical large V8 would be
derated to, running on CO)
AJH


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