Dear Steve****
** **
That was an interesting excursion. To be brief, there are a great number
of technical misconceptions contained in the document
http://www.soil-carbon-regeneration.co.uk/biochar/wp-content/uploads/2012/05/Biochar-Rocket-Stove-building-instructions.pdf
so
my advice is to try to gain some knowledge from the general approach and
from the unusual layout of the product but not take it all as literally
true. ****
** **
It is interesting that anything with a side feed is being termed a Rocket
Stove. That rather undermines the actual Rocket Stove as a unique design,
in my view. I guess people will call it what they want.****
** **
I have copied here a paragraph from a the document:****
** **
*The tlud*****
Designed by Paul Anderson, the top light upward draught (tlud) gasifying
cook stove works on more than just one level. It is a very efficient cook
stove, producing a lot of heat from a small amount of wood. It is smokeless
and it produces biochar. Paul Anderson has also been instrumental in
getting these stoves distributed and used in developing countries where
wood or charcoal is otherwise used in conventional fires for cooking. By
being more efficient, less wood is needed. By being smokeless, diseases and
deaths caused by smoke in living spaces are reduced. By producing biochar,
subsistence growers are able to [maintain] soil fertility and improve soil
structure, biological activity and moisture holding capacity. Atmospheric
carbon is also being sequestered by the use of these stoves.****
** **
So, I have some issues with some of this and because the whole list was
referred to it there is merit in correcting some of the impressions given.
****
** **
The TLUD was invented centuries ago as a way to burning with little smoke.
The Romans used TLUD fires. A TLUD cooking stove may or may not be
?efficient? depending entirely on how well it transfers heat from the flame
to the pot and whether or not the remaining char( if any) is counted as
?consumed by the stove? or not. ****
** **
The heat produced by a TLUD is no greater than the heat released by
burning the same amount of fuel to the same extent in any other stove. That
is, if you gasify wood in some other device the heat is exactly the same.
TLUD?s are renowned for making lots of smoke when things are not working
properly, like in the beginning and at the end of a burn there can be lots
of smoke. Mitigation of this involves timely intervention by the cook. They
are, after all, smoke producing devices that then burn the smoke. ****
** **
You have no doubt seen Paul Anderson throwing a lit match into a smoke
bomb of a stove re-lighting the fire when it has blown out. I have done it
myself dozens of times. When they are running well, especially during the
main part of the burn, they are amazingly smokeless, like any other really
good biomass stove. I hope that the products evolve to the extent that they
really are smokeless.****
** **
Now, about ?being more efficient? and ?using less wood?. I have been
reading a range of documents/comments on this matter and it is not at all
clear what is being claimed rather than inferred. If a stove is ?more
efficient? then we expect that it will use less input of raw fuel (fewer
trees chopped). If a stove uses the same amount of fuel and cooks while
also producing char, it is not ?more efficient? and it is not ?using less
wood?. Only by ?actually using less wood? can a stove claim to be using
less fuel, as far as I can understand it, looking at the forest and
counting the trees. We have had several conversations here about whether a
char making stove saves fuel, and so far there are no clear indications
that they do. There is no shortage of *claims* that they do. They *cook
with* *less energy*, but the input of fuel is about the same because a
lot of the energy in the original fuel is still in the unburned char.****
** **
To put some numbers on it (so it is not just a matter of opinion or
prejudice) if a stove produces 20% char, and cooks with the same thermal
efficiency as the baseline stove, then it definitely is using more fuel
because it will consume raw wood to make the char plus the same amount of
fuel to do the cooking.****
** **
If a stove uses less energy to do the cooking (because it has a better
heat transfer efficiency) then the fuel saved might equal the fuel needed
to produce the char. If the fuel saved (through better energy delivery
efficiency) is least 40%, and 20% char is produced, that is *more
efficient cooking* but there is still no fuel saving at all.****
** **
If the stove?s cooking efficiency was doubled compared with the baseline
stove, there is some 50% of the fuel left to turn into charcoal. How much?
At the most 45% of the mass. That would be remarkably good. So if half as
much fuel was used to cook and the remainder was turned into char, let?s
say ½ of the remaining fuel emerges as char, how much fuel is saved? Zero
%. ****
** **
Why? Because ½ of the baseline amount of fuel is being used to cook, and
the other ½ is being turned into char. That is not a saving of fuel. It is
clever, it is cooking while making char, but it is not saving fuel.****
** **
So how does a TLUD save fuel and produce char at the *same* time? What
are the real numbers? I think the biochar promoters should lead on this
point. They must marshal their facts put numbers to the claims. If they
don?t lead the field, then those stoves and the char industry will be
discredited by these exaggerated claims.****
** **
Suppose a really well designed stove saved 75% of the fuel over a baseline
product. Suppose it also produced 25% char (based on the original dry mass
of fuel). How much fuel, chopped trees or grassy biomass, would be saved
(actual reduction in consumption)? ****
** **
If you can calculate the answer to this question you are well on your way
to promoting a ?fuel saving char making TLUD? that will be believed. I, for
one, look forward to seeing such a stove.****
** **
Best regards****
Crispin****
** **
HI,
with regard the quoted exchange in post ****
Stoves Digest, Vol 25, Issue 21****
"Aron:
>
> Can you clarify your intended design? I know of no way that
> you can turn a rocket stove into a char-making stove (but would
> love to hear differently).
>
> Ron."
>
The following link is to an acquaintances site who has adapted the rocket
stove to gasify woody particles within the insulating jacket of the
combustion rocket elbow.
I would be very interested to hear responses to this design approach.
http://www.soil-carbon-regeneration.co.uk/biochar/biochar-stoves-2/biochar-rocket-stoves/
Steve****
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