Re: Gasifier fundamental question

["Paul S. Anderson" <psanders@ilstu.edu>]

At 12:04 PM 4/14/02 -0300, Kevin Chisholm wrote:
>Dear Dr. Karve
>I think Paul is asking the wrong question, when he asks if it makes any
>difference where the fuel is being burned.
>
>The answer to that question is, to me, in my blatant humble opinion, is very
>obvious: It must be burned where the stove design requires it to be burned.

Some observations from Paul:
1.  It is not "where the stove design requires...", but rather "where the 
stoveS designS require it to be burned."   We must think of multiple stoves 
(plural).  Even the very poor households generally have two or more places 
and arrangements for burning different fuels (and we all agree that 
charcoal is a different fuel than is wood or biomass) or for different 
conditions of weather, etc.

2.  The distance from the fuel to the pot is extremely important.  Kevin 
correctly points out the negative side of flames licking the bottom of the 
pot, and therefore advocates more height in the stove structure for that 
same heat level of fire.  But charcoal needs to be close to the pot if it 
is to be well used.  Therefore, SOMETHING must move.  Move the pot to a 
lower position close to the charcoal; or move the charcoal to a higher 
position close to the pot; or move the charcoal to a different stove (or 
save it for use later) where the correct distance can be 
maintained.  Almost always, something must move.

3.  I said "almost always" because of (at least) two situations:
       3.a.   The cook might be very happy with the low heat reaching the 
pot that is "too high in distance" from the charcoal, as in just wanting to 
simmer the pot after using the initial high heat to get the pot hot.
                       AND
       3.b     Tom Reed's turbo stove with blower can kick in the extra air 
to burn the charcoal after the pyrolysis gasification has ended, and the 
pot stays in the same place in relation to the fuel.  BUT:
         The BUT is that the extra air forced onto the charcoal essentially 
creates a forge (or some other name for a very high temperature forced-air 
stove).   I tried that with one of my "tincanium" Juntos stoves and 
promptly melted/vaporized/destroyed the aluminum air pipe in the bottom 
under the fuel grate through which the primary air was being 
forced.  Furthermore, the higher heat would take a major toll on the life 
span of the gasifier can.  (This is in contrast to the relatively lower 
temperatures in the can needed during the gasification stage.)  The 
alternative is to make a more-resistant-to-high-temperatures gasifier, and 
we know that such metals and thicknesses do exist.  But that raises the 
cost of the stove (and also the cost to provide some form of forced 
draft).  It also raises the question of added "mass" that needs to be 
heated, something that Dean and Larry do not favor (but they do recognize 
that some material is needed, and maybe this increase in mass is not very 
important.)

4.  Therefore, I have the current opinion that removing the charcoal after 
gasification of the biomass fuel is a highly appropriate procedure.

5.  Addendum concerning Ronal's earlier comment about smoke at the end of 
the gasification stage:  When I have a decent chimney in place, or when 
another combustion unit (such as an open-bottom rocket stove) is above the 
gasifier, the natural draft keeps the gasification going all the way to the 
end (I am using pellets and I was running at the not-quantified "plenty of 
air" setting).  I let it run 30 to 60 seconds extra, and when I pull out 
the gasifier, I have no smoke and only glowing coals that I dump into an 
old paint can and reseal.

6.  In my work I am doing almost nothing concerning charcoal except to 
witness that the gasifier does a nice job of creating the 
charcoal.  Basically, I have no difficulties with the ideas of charcoal 
production and I am glad that folks like Ron and AD and Dan D. are able to 
see justification in the charcoal side of things.

Paul

Paul S. Anderson, Ph.D.,  Fulbright Prof. to Mozambique 8/99 - 7/00
Rotary University Teacher Grantee to Mozambique >10 mo of 2001-2003
Dept of Geography - Geology (Box 4400), Illinois State University
Normal, IL  61790-4400   Voice:  309-438-7360;  FAX:  309-438-5310
E-mail: psanders@ilstu.edu - Internet items: www.ilstu.edu/~psanders


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