[Stoves] biochar rocket stove
Tom Miles
tmiles at trmiles.com
Tue Sep 18 14:22:22 CDT 2012
Kevin,
Good point but we'll have to get you to spin it differently. You don't lose
it to the ash pit , you "recover it as biochar." :-/
Tom
-----Original Message-----
From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Kevin C
Sent: Tuesday, September 18, 2012 12:12 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] biochar rocket stove
Dear Nolbert
A TLUD can indeed be an impressive stove. However, when claims are made for
"efficiency", one has to be careful to understand just how the "efficiency"
is determined.
Very roughly, dry wood has a heating value of about 18,000 KJ/kG, and char
has roughly 26,000 KJ/kG. If you used 1 kG of wood to perform a desired
cooking task, and you produced say 300 grams of char, the energy content in
the char would be approximately .3 x 26,000 = 7,800 kJ. The consequence here
is that
7800/18000 = 43% of the incoming wood energy is "lost to the ashpit."
it would be difficult to rationally claim to have a "very efficient stove",
when 43% of the incoming energy is lost to the ashpit.
You mention that the char from a TLUD can be used in a charcoal stove.
If the charcoal from a TLUD run was then consumed in a "char burning stove",
and if the "cooking results of BOTH the TLUD and the charcoal stove were
used to calculate "wood utilizing efficiency", the results would be more
fair and representative of the impact such a "stove system" would have on
reducing deforestation.
Subtracting the energy content of TLUD char from the input wood energy gives
a good indication of the efficiency of pyrolysis gas utilization, but it is
grossly misleading with respect to wood utilization. A "Char Making Stove"
inherently is less efficient, in terms of wood utilization, than a stove
system that efficiently burns the pyrolysis gases AND the char.
Best wishes,
Kevin Chisholm
Quoting Nolbert Muhumuza <muhumuza at gmail.com>:
> Hello Chrispin,
>
> I have read with caution the email you have posted today.
>
> I am currently involved with projects along with Paul Anderson in
> Uganda and around East Africa. While I honestly can not verify the
> origin on TLUD stoves, i have experienced for the last 2+ years how
> economical in terms of wood consumption (therefore wood saving) TLUDs are
in this region.
>
> Lab tests at CREEC (Makerere University) have also proved that TLUD
> micro-gasifiers are efficient backed with statistical data, including
> PEMS tests and comparisons with other types of stoves like the classic
> charcoal burners, rocket stoves and of course the 3-stone.
>
> These stoves are using less wood, cooking faster which is a major
> reason for their acceptance in East Africa. Women in the kitchens have
> tried and experienced how they use less quantity of wood, are less
> smoky and also cook quicker than their current conventional stoves.
> The notion of making char is a plus for TLUDs because they use the
> char for other valuable purposes including cooking.
>
> If you think otherwise, then you should try personally using these
> stoves for a while to prove what we are experiencing here.
>
> Nolbert.
>
> 2012/9/18 Crispin Pemberton-Pigott <crispinpigott at gmail.com>
>
>> 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/bi
>> ochar-rocket-stoves/
>>
>>
>> Steve****
>>
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>>
>
>
> --
> Nolbert Muhumuza
> P.O. Box 40127, Nakawa
> Kampala - Uganda
> Mobile: +256-776-346724
> Skype: nolbertm
>
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