Fw: Verhart on "Efficiency vs health impacts (forward from Alex English)" (on downdraft stoves)

["Ron Larson" <ronallarson@qwest.net>]

Stovers:

    Background:    Part of the following has been OK'd for transmission to
our list by Piet  (with my apologies for some delay).  Piet is below
responding to my Nov. 23 query about Hasan Khan (whose name some of us have
screwed up).  My query was based on Alex saying on the 22nd to my query on
the 20th, where I asked (referring to optimum excess air ratios)

> 4.  Have you seen these or similar figures in print anywhere?

(and Alex replied:

"I think you will find similar stuff in
Clean Combustion of Wood by A.M. Hasan and R Khan (1991)
http://www.ikweb.com/enuff/public_html/cc/cc.htm
This is about Eindhoven U. work with their downdraft stove. It was
many times cleaner than any updraft configuration that the tested.")

So, having now read the Hasan Khan material, I insert a few more questions
about this down-draft stove and work by Piet:

----- Original Message -----
From: Peter Verhaart <pverhaart@optusnet.com.au>
To: Ron Larson <ronallarson@qwest.net>
Sent: Saturday, November 24, 2001 4:30 AM
Subject: Re: Fw: Efficiency vs health impacts (forward from Alex English)


> Hasan and Khan are a "Dinity" or "Twinity". His name is Hasan (one or more
> middle names) Khan. He worked with the WSG in 1988 and returned to his
> native Bangla Desh. The last I heard of him was in 1991 or 92, he was at
> that time working in a National Fuel or Energy institute.
> He has published about his work, an article describing his tests on a
> combination cookstove and Tandoori, working in downdraft mode. Due to the
> clean combustion, the resulting hot gas can be used in direct contact with
> the food. The result was a large reduction in fuel consumption.

    I looked Dr. Khan up using Google (finding ist@klbd.net) and hope this
message reaches him (as head of a Fuel/stove institute in Dhaka, Bangladesh)
and that he can introduce himself later to this list.  Piet - thanks for
this update.

    Before going further, let me describe the Khan geometry a bit more.  The
unit has a "J" shape with the short (wood-containing) arm being about 15 cm,
the long arm variable and up to 1 meter height. The minimum separation of
the arms is 25 cm.  The maximum outside dimension is about 54 cm.

    The minimum CO found was .009%.  (90 ppm ) - but the range of obtaining
this (by varying fuel loading rate and chimney height) is relatively narrow.
(an optimum rate was two blocks every 30 seconds).  When charcoal was
produced in this stove, CO levels were higher. The block size ws a little
bigger than 2 cm, I think.

    I had assumed that this downdraft stove was the inverse of the inverse
down draft (IDD).  This is not true - there is no separation of primary and
secondary air in this Khan test setup.  I still have not figured out why
there is this narrow range of low emissions.  But there are plenty of data
for different experimental setups - for O2, CO2, CO.   It would behoove us
all to understand this data - I have seen no other as complete (although I
better read more of Alex' material).  I think this may be the inverse of the
Approvecho design, in some ways - that is power output can be controlled by
fuel loading rates and chimney heights..

    The main point is that the Khan geometry is not an "inverse" (of the
charcoal making stove I have been describing).  Neither is the situation
described next by Piet (because there doesn't seem to be primary air control
there either.)

Piet said next:
> I have made several attempts at designing something that would produce
> charcoal while the flames from the volatiles provided heat for cooking as
> well as for the charring.
> We never had enough of the mix of student and time to produce quantitative
> results. The stove consisted of an inner cylinder containing the wood. It
> was loaded from the top and closed with a more or less gastight lid. At
the
> bottom it had an opening. This inner cylinder was centred in an outer
> cylinder. An opening in its bottom corresponded with the bottom opening of
> the inner cylinder. Through that opening the wood at the bottom of the
> inner cylinder could be lit. The corresponding opening in the outer
> cylinder could be closed while it had a secondary adjustable air port. The
> idea was that heat from the burning wood would produce volatiles which
> would burn with the secondary air in the space between the two cylinders.
> The flames were supposed to come out above the top of the inner cylinder
> enabling cooking on the suitable shaped top of the outer cylinder. As
> stated before, no exhaustive tests have been done on this stove. I have a
> collection of slides among which a number depicting this stove.
> I am in the process of scanning all my slides (more than 5000 already and
> the end is still some way off).

    Piet -  This is not downdraft - right ? (which I interpret to be air
flow downward through the fuel)?   (Although there is bottom lighting of the
fuel supply.)   Was there any possibility of air entering the top of the
inner cylinder?  (I don't believe that primary air through the top is
necessary for this to work - but it would help in power output control..  I
believe that Professor Grover developed a "toroid" system rather like this -
but with the flames on the inside. No primary air control.   I saw two in
operation in Zimbabwe in 1995 - making charcoal.  Do I have the correct
interpretation?

> When this is done I hope to be able to quickly find any slide I ever made,
> which will then be available as a .jpg attachment to any interested
stover.
>
    I wish I could say I could ever do the same.  The only things I can find
these days are on the computer.

> Prasad might have more specific comment.
> Piet

    Prasad?  Any comments - especially on how to minimize CO (and hopefully
to make charcoal)

Any one else have some ideas on how to explain this highly variable behavior
of CO production?

Ron


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