Dear Ron and Everyone
There are some really good points here which bear a little analysis.
4. On p 50, we read (emphasis added):
"Biomass is generally considered to be a renewable
fuel. When it is burnt any CO2 released is
assumed to be reabsorbed through re-growth of
biomass. If biomass is not re-grown, then the
emissions from biomass can be considered to be
a non-renewable fuel. Therefore, cooking stove
projects can only generate emission reductions
where it can be shown that the biomass used is
non-renewable."
For a list of rules on what constitutes fundable biomass use reduction you
could see the UNFCCC documents on calculating it.
> c. But we got a fair amount of cooking out of that 28 cent investment. We
> started out with about 4 kg * 18 MJ/kg = 72 MJ, and ended up with 1 kg * 30
> MJ /kg in char - a difference of 42 MJ.
This needs slight editing. It is a tropical, humid country and drying fuel is a
difficult business. Assume 15 MJ/kg and that is probably the best you are going
to get. That is 60 MJ. It is unlikely you will get 1 kg of char – more likely
25% of the dry mass . There is often confusion about the initial fuel dry mass
and the charcoal dry mass yield. Just be careful about the units.
> f. Since char-making stoves are reported by EPA (and others) to be the
> highest efficiency reported (in part because the power level is
> controllable), maybe the economic argument is even more in favor of the
> char-maker.
The tests you refer to used a WBT that credits the unburned char as ‘fuel not
consumed’ then calculates backwards to get a ‘dry mas fuel equivalent of the
energy released during the burn. This ‘dry mass fuel equivalent’ is
considerably less than the actual fuel consumed. Thus the ‘fuel efficiency’ is
not the stated final number. This was discussed in detail here where after Jim
Jetter and I agreed that if the char is not ‘fuel’ to the stove it was created
in, it has to be considered ‘lost’ with the ash. As the thermal efficiency is
determined from the heat released, not the fuel consumed, the overall
efficiency is somewhat misrepresented by the test method.
In short, char making TLUD’s have been given efficiency ratings and fuel
consumptions numbers that far exceed their actual performance as viewed from
the fuel pile’s and fuel buyer’s points of view. A pretty comprehensive
restatement of stove performance is required to get a realistic picture of
stove performance comparisons as the issue of wasted charcoal affects stoves
differently. The more they create charcoal during cooking, the greater has been
the padding of their fuel performance numbers.
Regards
Crispin
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