[Stoves] Comparing the fate of fuel energy between stoves -- a simple table?

[Crispin Pemberton-Pigott]

Dear Julien

I think it is a mistake (or a poor assumption) to assume that a 'small char
fire' is a) at the bottom, b) is not an effective heat source and c)
represents a loss of some kind.

The distance between a heat source and a pot is not as indicative of
anything significant. 

My rule is: Never Assume Anything.

Calculate first, then observe, as appropriate.

The simmering that is sometimes done in a cooking event is often well
supplied with heat with a low power char fire at the end.

Convective heat transfer can be very efficient. Basically the argument that
distance matters is an assumption that most heat transfer from burning char
is from radiant. This is nearly never true in a real fire. If the convective
heat transfer is done with a low excess air level, it can be very good.

Regards
Crispin


-----Original Message-----
From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
Julien Winter
Sent: Friday, July 19, 2013 9:08 PM
To: Discussion of biomass cooking stoves
Subject: [Stoves] Comparing the fate of fuel energy between stoves -- a
simple table?

Hello Stovers;

I am in Dhaka, Bangladesh, and I am going into a meeting in a couple of days
to talk about biochar production through cookstoves.  I have already been
asked a question about whether biochar-making is a cost (in fuel) that
stove-user may not want to make.  For example, "why not burn the fuel to ash
and not save the biochar?"  ... to which I reply that for a ND-TLUD, 70% of
the fuel energy was in the gas fire, and the carbon fire is a long way from
the pot, and a TLUD is a great deal more efficient that a traditional stove,
and who would want a high temperature carbon fire at the bottom of one's
cherished stove anyway.

I realize that there are some huge ceteris paribus assumptions to be made
about standard conditions for comparing different stove types and fuels, but
can anybody have a crack at filling in this "simple" table?
 I just want some ballpark figures to help justify biocharmakery.

FATE OF THE ENERGY CONTAINED IN A WOOD FUEL

STOVE_TYPE        COOKING          BIOCHAR          LOST
============================================
                             ----------------------- (%)
-----------------------------
1) ND-TLUD
2) 3-stone
3) Anila
4) Chula
5) etc.

I have just put in some stove names as examples.  The value for %energy in
biochar is zero for many stoves, so many comparisons amounts to a comparison
of stove efficiencies.

As must be the case for many less well off countries, the most ecologically
sound method of making biochar in Bangladesh will be through their
cookstoves, and the biggest, most immediate impact of biochar on people's
lives will be to improve the fertility of homestead gardens.  That is easy
to say; it will be a lot harder to do.

Thanks,
Julien.

--
Julien Winter
Cobourg, ON, CANADA

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