[Stoves] RE: Henson Center Fiure Burner System; Was: Re: improving charcoal stoves

[Paul S. Anderson]

Stovers,

The topic is now the New Lao stove, but everyone seems reluctant to change the
Subject line, so I have not changed it either.

On the New Lao stove, an easy way to provide secondary air at the top 
of the bed
of charcoal would be to have an air inlet pipe with elbow bring in 
secondary air
from the side and up under the fuel area along side of the holes for 
the primary
air.  The pipe would project upward to the height of the top of the charcoal,
thereby protecting the secondary air from being pre-maturely combusted 
and also
provide some pre-heating of the secondary air.

I am not sure how the secondary air should be spread out somewhat at 
the top of
the pipe (lateral holes or an "air spreader" or what), but some 
experimentation
would indicate (1) if there was any advantage from the pipe, and (2) what
spreading method would be best.

The same secondary air pipe (above) might also provide a nice advantage to the
central channel grate (the Henson innovation).  The diameter of the channel
might need to be greater to allow for the pipe as well as the primary air.  IF
THIS combination of separate primary air and separate secondary air is
functional, THEN this device could qualify as a "gasifier" because the device
is separating in time and place the making of the gases from the combustion of
the gases.

Similarly, if the above paragraph proves workable in a Henson-style 
device, then
transfer that back to the New Lao stove.  Make the addition of a 
central channel
plus secondary air pipe.  That would occupy part of the diameter of the 
New Lao
charcoal container, which would be desirable because a taller (and not spread
out) pile of charcoal would enhance the central channel effect.

JFR, what do you think?

Paul

Quoting AJH <list at sylva.icuklive.co.uk>:

> On Fri, 2 Jun 2006 22:21:02 -0700, Tom Miles wrote:
>
>> If you look at the (Ashden Awards Finalist) CFSP New Lao Bucket stove (
>> www.bioenergylists.org ) and follow the links (CFSP Stove Designs) to
>> compare it with the traditional Lao bucket stove on the CFSP site, it looks
>> like combustion was improved by using larger holes, a deeper combustion
>> chamber, better insulation, and a better fitting gap at the pot rests.
>
> I've looked at this and the GYAPA via your site. The movie of the
> GYAPA shows just over a single layer of coals. We have previously
> discussed gasification of charcoal where the necessary depth of hot
> char bed has been mooted as >5" and/or >20 particle diameters. So in
> the instance of the GYAPA it looks like the aim is not to produce CO.
>
> On the other hand you mention the New Lao as being deeper (more depth
> of bed increasing CO production) and better insulated (less energy
> loss from char bed thus higher temperature favouring CO production),
> The larger holes indicate higher primary air (but not excess because
> the deeper bed ensures a reduction zone??) and thus higher power. The
> trouble is that there is no provision for secondary air, which points
> to the charcoal being in largish chunks so that the primary air is
> that air that attaches to the coals and secondary air is that air that
> passes straight through the gaps and is available to react with CO
> generated by the primary air just above the coals. In this case I
> would expect a short blue flame above the coals.
>
> Personally I would have thought the shallow bed and no CO was a better
> route for charcoal burning, the deeper bed and gasification offers no
> advantage over wood burning but achieves higher temperatures, from
> simple mass flow considerations. I also think under natural draught
> and no chimney there wouldn't be good gasification.
>
> The easy test would be to set one up with a pot and sample the gases
> from under the pot and down to see how much and where CO was being
> produced, compared with CO2. I've done this for CO with hot flue gas
> by sampling via a very long steel tube but most flue gas testers only
> cope with small percentages of CO. Also I have no access to a flue gas
> tester at home.
>
> Either way it looks like both designs would benefit by the pot having
> a skirt but it is difficult to say if the pot gap may be providing
> some secondary air.
>
> If the deeper bucket were to be run as an updraught gasifier then
> loading it with smaller graded coals would increase CO production but
> I think better provision for secondary air (possibly preheated by
> rising up the outside of the bucket) would be required. I consider
> this would be unsafe for household use.
>
> AJH
>
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-- 
Paul S. Anderson, Ph.D., Geography professor - Emeritus
Telephone:  USA-309-452-7072 (residence and office)
Internet site:  www.ilstu.edu/~psanders
For my gasifier stoves info, go to (below) and click on my name:
http://www.repp.org/discussiongroups/resources/stoves/contributions.html

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