Forwarding Shirish on Bachat or REDI stove

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

Stovers:   The following message gives a bit more information on work going
on in India on at stove being developed for the Bachat Cooker.



----- Original Message -----
From: Shirish B. Patel <shirish@spacpl.com>
To: Ron Larson <ronallarson@qwest.net>
Cc: Aniruddha B Pandit <abp@udct.ernet.in>; kishore Mariwala
<kishorem@bom3.vsnl.net.in>; G K Bhide <agb@vsnl.com>; R S Shah
<jaijui@bom8.vsnl.net.in>
Sent: Saturday, April 21, 2001 9:53 PM


> 22 April
>
> Dear Ron,
>
>
            <snip a paragraph on a list reception problem>
>
> We expect to soon receive a specimen of the stove developed by Prof H S
> Mukunda. They call it the REDI stove. RED stands for Reverse Downdraft and
> RED was what the stove was  initially called. The 'I' for the Indian
> Institute of Science was then added to make the name 'REDI', which had the
> merit of sounding like "Ready". Once we have that stove we will be
> starting trials. I did not describe the arrangement they have for
> controlling primary air flow. Let me see if I can explain that in words,
> without a diagram. Between the floor of the stove (a solid disk) and the
> grating that supports the wood chips is an air space about 4 cm high. The
> wall of this cylindrical air space is continuous with the wall of the fuel
> chamber above, but is  punctured at one place with a hole about 3 cm dia.
> Projecting outside from this hole is a short stub of pipe, open at both
> ends, with a number of radially drilled holes around the pipe. The pipe
has
> a cap, consisting of a sleeve that fits closely (but not tightly) over the
> pipe, with the outer end closed. The sleeve of the cap has similar
radially
> drilled holes which match the holes in the stub of pipe projecting from
the
> stove. By rotating the cap one can regulate the primary air flow, from
zero
> to the full aperture of all the holes combined. The cap is put on after
the
> stove has been lit and got properly going. Lighting is from below in this
> case, not from the top as in the case of wood chips and pyrolisis.
>
    (RWL) :   This sounds like a unique and fine means of primary air
control.  I do not recall any quite like this.
I believe it can be used for top lighting (charcoal making) as well.

    I do not have any experience with the combination of controllable air
and bottom lighting - as I have only been interested in the making of
charcoal - which requires top lighting.  If it works and you are not
interested in the process of making charcoal there is certanly no reason
not to do this.  Please let us know more about the success you have with
controlling power output by controlling air supply.  I have been assuming
that there would not be enough uniformity in power output - which somehow
miraculously occurs with the charcoal-making, top-lighting approach.

> Prof Mukunda showed me another stove, very similar to the description of
the
> Vivek stove, for burning any kind of pulverised fuel--he showed me the
stove
> working when packed with sawdust. I said sawdust was an uncommon and
> unlikely fuel, to which Prof Mukunda's response was that any pulverised
fuel
> would do, and up to 50% of it could be wood chips or other pieces mixed
in,
> as long as the mass could be properly compacted and would not collapse
when
> the dowels that form the L-shaped draft hole are removed after compaction.
> At the start of the L, near the base of the stove, he had the same kind of
> air regulator control as described above.

    (rwl):      I hope your team is aware of the master's thesis work of Dr.
Priyadarshini Karve in Pune on this stove.

>
> One of our problems is going to be the variety of biomass fuels that
people
> want to use. No doubt there will be a different optimal design for each
such
> fuel: wood chips, wood sticks as you suggest, sawdust, dried leaves or
> groundnut shells, perhaps even briquettes as Prof Grover suggests. From
the
> amount of work that is going on around the world on the design of stoves I
> would guess it is hard enough designing a cheap and efficient stove that
is
> acceptable to the housewife for any one fuel: are we asking for too much
if
> we say that the same design, with minor adjustments, should work for more
> than one fuel? If we start with Prof Mukunda's basic design of stove for
> burning wood chips, could we not just remove the grating and use the same
> stove shell for compacted pulverised fuel with an L-shaped draft hole? Or
> replace the grating and burn a briquette which is placed on the grating?
The
> air supply regulation mechanism would be common to all.
>
    (RWL):  This is a great question - and I do not have a great answer.  I
think that with a power source and controllable blower, one will have better
success with a range of fuel types - as one cannot have too much resistance
in the primary air path.  One inserts a lot of resistance (pressure drop)
with any air flow controller, so one can't have too much in the fuel
container.

    If you or Professor Grover or anyone know of any charcoal-making with
large briquettes with unusual air flow holes (as in some coal and charcoal
briquettes, I think this list would like to hear about that work.

    When I have tried a deep layer of small wood pellets - no success (too
much resistance for a  relatively short "chimney/combustion region", but
could get the right action with a thinner layer of bigger pellets.  I have
tried cow dung without charcoaling success ever.  Don't know the reason for
failure.

> We do realise that we are asking the housewife to have one stove for use
> with the Bachat cooker, and another for her other, regular cooking needs,
> such as frying or baking, for which the Bachat stove may be too small. All
> the more reason to have just the one design of Bachat stove, able to
> accommodate a range of biomass fuel types.
>
    Perhaps you can still have two stoves if they are not too expensive.  We
in the US feel cheated if we don't have at least four burners (plus many
other cooking devices).

> Incidentally, the flame size can be as small as you like. 7 cm dia we
would
> think is the outer limit. But the output needs to 0.5Kw. And on gas at
least
> we have found efficiencies improve if the tip of the flame just touches
the
> base of the cooker. On wood burning stoves I have no idea what would
happen
> as the flame level drops.
>
(rwl): This is my observation as well.  On your last comment, I presume that
we agree that efficiency drops as the flame tip moves away from the cook
pot.

> If you have any further thoughts concerning any of this please let me know
> as we would like to discuss this in our next regular Research Team meeting
> scheduled for Wed 25 morning. And many thanks for getting us on the stoves
> list, the enlarged discussion is extremely useful. For example, we now
begin
> our work with an awareness of the range of fuels for which we should
> provide. We expect that as we progress the continuing dialogue with a
wider
> group will help us evaluate options that others have already explored and
> which we would otherwise waste time going into. We will keep you regularly
> posted as to what we are doing, and look forward to everyone's comments. I
> hope this 0.5Kw stove development can be an example of how progress can be
> speeded up by a process of wider invovlement and participation (is
mentoring
> a good word to describe that process?).
>
        (rwl):  Yours is a good example of what those of us in the
industrial world (unfortunately still a majority of the "stoves" list
membership) are looking for - as a way to both share our knowledge and to
learn from you.  The whole sharing process is dependent on having the rapid
and cheap communication possible with the Internet.

    Mentoring is not quite the right word since we all learn from each
other.  Everyone can contribute with their own special knowledge.  Being
able to do any big cooking job with only 0.5 kW is really remarkable

       Please say good morning to all on your research team on the 25th.

Ron

> Regards,
>
> Shirish



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