[Stoves] cook stoves for Cameroon

Wed Sep 17 22:38:37 CDT 2014

Dear Huck

The last question first:

How much 'tree' do you need to cook?

That is the question. If you are cooking on multiple stoves one that makes
charcoal and one that burns it, you can analyse that as a 'system' but
remember that to evaluate them you have to do them separately.  A lot of
conflict, actually, has emerged over this question because those who want to
make charcoal-making stoves don't want them penalised for being inefficient,
even if they are. They bring a lot of arguments in favour of this or that
aspect of a system of which the stove is a port. No problem - such arguments
are reasonable when discussing systems, however your question is strictly
about stove performance.

The way you phrased the question is the same as the way the UNFCCC phrases
it - how much tree for how much cooking. The assumption is that less trees
used for the same amount of cooking is more efficient.

When calculations are made, however, people frequently calculate the energy
released, not the amount of fuel consumed and the two numbers are nearly
always different. We are not burning gasoline. Cars do not make charcoal.
'Leftovers' can be a significant portion of the energy available, 

As Prof Lloyd just remarked a couple of days ago, it takes a lot of work to
get fuel and people are not crazy - they want to burn it before going out to
get more.

It is for these reasons that het Clean Stove Initiative Indonesia
(CSI-Indonesia) uses a calculation method that captures the amount of raw
fuel needed to complete another test burn cycle. The energy in that 'fuel
consumed' is determined. That is the energy available. The energy gained by
the pot (including the heat gained by the pot material as it can be
substantial) is determined over a cooking simulation. In the case of the
CSI-Indonesia pilot the determination is made using the CSI-WHT ('Water
Heating Test'). This is an accurate measure of the energy gained by the pot
- to within a few Joules.

Energy applied divided by energy drawn from the forest is the system
efficiency, or 'overall efficiency'.

Regards

Crispin

Hi All,

I found myself a little confused by the discussion.  

Not being expert in the field, this is how I would pose my questions:

1.	There is a certain amount of energy per kilogram of wood (I'm going
to stick with wood for the moment rather than all biomass).
2.	When burned, some of that energy is realized and some is not, i.e.
there is not complete combustion.  How complete is the combustion?  How much
energy is released?  That would be the first measure.  I want this because
it tells me about one component of the system and is useful for design.  It
does not tell me the net result for the user.
3.	How much of the released energy goes into cooking?  That would be my
next measure.  That should tell me what weight of wood people have to
collect to cook their food.  It is worth noting that the amount of energy
that goes into cooking is also affected by the pots and lids used as well as
how they fit onto the stove.
4.	It is also important to know how much energy was expended to get the
fuel and prepare it for use.  Some of that energy is human energy so it gets
treated a bit differently and has a different impact.  For example, it
doesn't convert simply to climate impact (are humans low global warming gas
emitters?).  If you cut up the fuel a lot and process it a lot there is a
cost there.  I don't know how that stacks up for gasifiers vs other stoves.
5.	Regarding charcoal.  I am presuming you can still use the charcoal.
I was, apparently erroneously, under the impression that gasifier stoves
could continue to receive primary air and therefore burn the charcoal.  I
actually liked that idea because it was simple and used most of the energy
in the stove.  If you take the charcoal out of the stove you then have a
couple of options for using it.  You can burn it in another stove, which has
some appeal as you can do a different kind of cooking with it (e.g. BBQ, or
?).  But also seems like quite a bit of work and complication for a small
amount of charcoal.  Or, you can use it in the soil. So another question:
6.	Is a gasifier stove with charcoal (biochar) buried actually carbon
negative?
7.	Then the other important measure: what are the emissions?

And, a kind of crude question: with the ins and outs of this discussion is
it the case that rocket stoves or some other stove is more efficient than
the gasifiers?  In my question by efficiency I mean kg of wood required for
a Cameroonian to cook their meals?

Which stove do they have to carry more wood for and do more fuel preparation
for?  (I'm not sure how you measure the combined work for those tasks).

Huck

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