[Stoves] Simmering
Philip Lloyd
plloyd at mweb.co.za
Thu Oct 14 01:34:43 CDT 2010
It is rarely that I have to take issue with Crispin, but his recent
statement "Please note that one cannot easily state the thermal efficiency
of 'simmering' because no work is done. If the pot is as hot at the end as
in the beginning of the simmer, the efficiency is zero%" is, I believe,
wrong.
During simmering, some heat is lost from the pot by evaporation of water.
The object of simmering is to keep the contents as close to local boiling
temperature as possible while minimising the water loss, but you cannot do
both unless you completely seal the pot or use quite sophisticated control
technology - in the real world of cookstoves, the latter is not possible.
The loss of water can quite readily be measured, and converted to an energy
output via the heat of evaporation. So you can measure the heat out as
steam, and measure the heat in by the usual methods, and so come up with an
efficiency.
In the same way we measure the efficiency of heating from the rate of loss
of steam from a boiling pot. That tells you just how much heat is actually
going from the fuel into the water. Because the water is boiling, the
temperature is constant, and radiant, convective and conductive heat losses
are constant. The efficiency is slightly different from that determined by
the time to boil, but in the time to boil test, radiant, convective and
conductive heat losses vary, so it is significantly less reproducible than
efficiency determined by measuring mass loss once boiling.
Philip Lloyd
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Today's Topics:
1. Re: MUST CHARCOAL BE A CAUSE FOR CONCERN? (Otto Formo)
2. Re: MUST CHARCOAL BE A CAUSE FOR CONCERN?
(Crispin Pemberton-Pigott)
3. Re: MUST CHARCOAL BE A CAUSE FOR CONCERN?
(Crispin Pemberton-Pigott)
4. Re: MUST CHARCOAL BE A CAUSE FOR CONCERN? (Kevin)
----------------------------------------------------------------------
Message: 1
Date: Wed, 13 Oct 2010 23:56:09 +0200 (MEST)
From: Otto Formo <formo-o at online.no>
To: Kevin <kchisholm at ca.inter.net>, Discussion of biomass cooking
stoves <stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] MUST CHARCOAL BE A CAUSE FOR CONCERN?
Message-ID:
<29491408.10105.1287006969513.JavaMail.adm-moff at moffice6.nsc.no>
Content-Type: text/plain; charset="iso-8859-1"
Dear Kevin,
what you actually are "saying" is that people in developing countries have
no common sense and knowledge about polution from open fires.............
Why do they use open fires for cooking?
The most ovious reason is that they have no choice or options.
Secondly, this is how it has been done for centuries.
It "works", why change?
The women do the collecting of wood and the cooking, so why bather........
There is also no question about that even the best and most efficient
charcoal stoves (without a chimmny) emitts far more CO than any TLUD
gasifier stove.
The other fact is that CO also kills people in the "western" world as well
by "missuse" of gas for heating and cooking, but it does not mean that we
should stop using it!
BUT we should be VERY carefull by using open flames indoors without good
ventilation.
This is something we learn in school at early age.
If any positive progress should be "stoped" by missuse of just a few there
is no way the "World" are going to move "forward", ever.
Otto
> From: Kevin [kchisholm at ca.inter.net]
> Sent: 2010-10-13 16:33:52 MEST
> To: Discussion of biomass cooking stoves
> [stoves at lists.bioenergylists.org]
> Subject: Re: [Stoves] MUST CHARCOAL BE A CAUSE FOR CONCERN?
>
> Dear Rogerio
>
> I think that the wrong question is being asked. One can also ask the
> question: "Must wood be a cause for concern?"
>
> 1: If the ultimate concern is simply availability of fuel, then both
> primitive wood stoves and primitive charcoal systems are indeed a concern.
>
> 2: If health, as a result of products of combustion considerations is
> the ultimate concern, then both primitive cooking systems are a concern.
>
> 3: The good thing about 3 stone wood fires is that they emit gross
> irritants that minimize the potential for users to be killed during
> the cooking session from CO poisoning. Good gharcoal stoves can be
> very efficient and not emit apparent poisons, but if used in a
> confined space, the much more efficient charcoal stove can kill the Family
before the meal is finished.
>
> 4: Charcoal gives a quality of cooking that cannot be duplicated by a
> wood fire.
>
> Obviously, a dreadfully inefficient "3 Stone Fire" can be much safer
> than an "Improved Cooking Stove" that has much higher efficiency.
> There is so much smoke and poisons coming off the 3 Stone Fire that
> people move upwind. An "Improved Cooking Stove" might be improved just
> enough that people move it inside a living space, and then they start
> dying from all sorts of disorders. Charcoal stoves could end up being
> superior, in that there might still be enough "residual irritants"
> emitted such that the Cook uses it in a well ventilated space.
>
> The "problem", whatever it is, must be clearly defined before one can
> arrive at a meaningful answer to the "problem." A better question
> might be along the lines of: "What is the best way for people to
> accomplish their desired cooking task, with a given quantity of wood
> fuel, while improving the health of the people using a particular "cooking
system?"
>
> Perhaps someone else can formulate a better question that is more
> relevant to whatever issue is of concern. There is no point in
> promoting an "improved stove system" that cuts wood usage in half, but
> doesn't cook the food the way the people want it, and then kills them
afterward.
>
> Best wishes,
>
> Kevin
>
> ----- Original Message -----
> From: "rogerio carneiro de miranda" <carneirodemiranda at gmail.com>
> To: "Discussion of biomass cooking stoves"
> <stoves at lists.bioenergylists.org>
> Sent: Wednesday, October 13, 2010 9:01 AM
> Subject: Re: [Stoves] MUST CHARCOAL BE A CAUSE FOR CONCERN?
>
>
> Dear Crispin and others who has responded.
>
> Making a simple calculation (see table below), I found the following
> numbers based on 1 kg of Eucalyptus grandis, with 4650 kcal/kg as
> fuelwood, or 7600 kcal/kg as charcoal.
>
> Considering the worst case scenarios, with woodstoves efficiency of 10
> to 15% one would get 450 to 698 kcal of energy into the pot, and to
> have the same amount of energy from charcoal into the pot, one would
> need to have either a relative medium charcoaling efficiency of 20%
> but with a charcoal stove with 30% efficiency, or charcoal stoves of
> normal efficiency around 20% but with higher charcoaling efficiencies
> of 30 or 40-%.
>
> Based on that, shouldn't be logical to assume that under "primitive"
> existing general conditions as seeing in the field today, that
> cooking with wood is more energy efficient than cooking with charcoal?
>
> Assuming that woodstoves can easily achieve 20% efficiency which
> delivers 900 kcal into the pot, and to do the same job with charcol
> one would need a 30% energy efficiency charcoal stove using charcoal
> produced at 40% charcoaling process, what is nearly impossible to
> achieve.
>
> Unless charcoal stoves of 40% are possible, so to use with charcoaling
> kilns of high 30% efficiency?
>
> Rogerio
>
>
>
> cooking with charcoal
> efficiency(%) 10%-20%-30%
> (kcal)
> charcoaling 10% (760) (76) (152) (22)
> 20% (1520) (152) (304) (456)
> 30% (2280) (228) (456) (684)
> 40% (3040) (304) (608) (912)
>
> cooking with fuelwood
> efficiency(%) 10% 15% 20% 30%
> (Kcal) (450) (698) (900) (1350)
>
>
>
>
> 2010/10/12 Crispin Pemberton-Pigott <crispinpigott at gmail.com>:
> > Dear Rogerio
> >
> > We discussed this a while back and I forwarded some example of the
> > energy balance.
> >
> > Yes, the fact is there is nearly no difference between the amount of
> > food cooked with wood or that same wood turned into charcoal. The
> > caveats are that I depends on the wood stove, the charcoaling method
> > and the charcoal stove.
> >
> > Those are three huge variables, but for 'medium quality' on all
> > three counts, the answers are about the same.
> >
> > The overall difference that one might be inclined to ponder is the
> > amount of energy that is used to being the fuel to the cook. In the
> > case of charcoal, say in Mozambique, the distance that one can
> > profitably transport charcoal is far greater than that for wood
> > because it is so much more energy dense.
> > It is even better than coal because coal usually has a lot of ash in it.
> >
> > So, when considering what to criticise, replace and promote, one has
> > to look at the three main variables, what one could do to change
> > them, and what the transport implications are. It is pretty tempting
> > to think of charcoal making vehicles using wood gas for locomotion,
> > delivering charcoal to the cities. They would start off heavily
> > loaded and get lighter as they got closer to town!
> >
> > I recall Cecil Cook and I having fun with this equation some time ago.
> >
> > What is always good (as Richard Stanley recently point out) is to
> > make sure that all the chips and dust from the charcoal business end
> > up in briquettes of some form. Usually the review of charcoal is
> > made by a hostile agent and the 'waste' involved is emphasized, not
> > the methods by which it can easily be made very efficient, all
> > things considered.
> >
> > There is still a lot of this story to be told by someone with a
> > talent for integrating technologies and stove ideas.
> >
> > Regards
> > Crispin
> >
> >
> > +++++++++++++++
> >
> >>I found the following quote on a FAO publication
> > (http://www.fao.org/docrep/005/y4450e/y4450e10.htm), and I wonder if
> > this is a correct statement responding to the question :
> >
> > "Must charcoal be a cause for concern?
> >
> > The shift from fuelwood to charcoal, even if it lasts only a few
> > decades, could have major ecological consequences if it is not kept
under control.
> > However, since charcoal stoves are more efficient than wood stoves,
> > the ratio of primary energy to usable energy is almost the same as
> > with fuelwood. Thus with adequate supervision, management and
> > support, the shift does not need to disrupt present levels of
> > resource use."
> >
> > What do you think? Can at the end, with actual stoves and
> > charcoaling efficiencies, be the wood consumption the same?
> >
> > Rogerio
> >
> >
> >
> > _______________________________________________
> > Stoves mailing list
> > Stoves at lists.bioenergylists.org
> > http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioene
> > rgylists.org
> >
>
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------------------------------
Message: 2
Date: Wed, 13 Oct 2010 18:29:32 -0400
From: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com>
To: "'Discussion of biomass cooking stoves'"
<stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] MUST CHARCOAL BE A CAUSE FOR CONCERN?
Message-ID: <002801cb6b26$1eaf3800$5c0da800$@gmail.com>
Content-Type: text/plain; charset="us-ascii"
Dear Kevin
As always, the devil is in the detail. It shows that monomaniacal intent to
'save fuel' is not always the best solution to anything. As longer term
readers of this will have noted, little is said about increasing the supply
of fuel, rather it is about saving it (cooking a meal with less). If you
increase the fuel supply, you don't necessarily need to save it. Getting
people to understand that fuel supply is not a problem everywhere, it is a
serious problem in some places. Combining wood gas stoves with charcoal
burning is a way of increasing the fuel supply as I will show below.
It would probably not be a stretch to say that stove development has
focussed on fuel efficiency above all else for the past 40 years. There are
very good reasons for having done so. Fuel supply is an obvious one. Having
to buy it instead of getting it free is another.
Charcoal is invariably mentioned in old documents and some new ones as
'wasteful' in its use of energy, even though a reasonable assessment of the
system efficiency would show that it compares reasonably with an open fire.
This fact of life is unpalatable to some. The reason I say that is my own
efforts to show what Rogerio said is true are not greeted with enthusiasm
because it opens new agendas which may not be well understood.
I want again to go over Rogerio's recent post:
>Making a simple calculation (see table below), I found the following
>numbers based on 1 kg of Eucalyptus grandis, with 4650 kcal/kg as
>fuelwood, or 7600 kcal/kg as charcoal.
>Considering the worst case scenarios, with woodstoves efficiency of 10
>to 15% one would get 450 to 698 kcal of energy into the pot, and to
>have the same amount of energy from charcoal into the pot, one would
>need to have either a relative medium charcoaling efficiency of 20% but
>with a charcoal stove with 30% efficiency, or charcoal stoves of normal
>efficiency around 20% but with higher charcoaling efficiencies of 30
>or 40-%.
I would not take a worst case example to make the demonstration because it
is misleading. So is the best case example, though a best case could be a
development target for a project.
Open fires are about 15% thermally efficient, based on measurements of
thermal efficiency during heating. Please note that one cannot easily state
the thermal efficiency of 'simmering' because no work is done. If the pot is
as hot at the end as in the beginning of the simmer, the efficiency is
zero%. So let's talk about the net heat transfer efficiency. This can be
measured by heating water in a pot. It is not difficult. It can be done at a
low or high power. Usually the thermal efficiency on low power is higher
than on high power, but not always.
1 kg of Eucalyptus grandis could give 4650 kCal/kg (19.465 MJ/kg) but not
with normal moisture content at say 15%. In real terms it would be about
16.156 MJ/kg
Turning that 1 kg of 15% moisture Eucalyptus grandis into charcoal would
yield about 250 g in a reasonable low tech kiln and 33 g in a good one. The
heat content is perhaps 29.5 MJ/kg so it has 7.4 up to 9.7 MJ of heat
available, about 60% as much as the wood from which it came but in a very
different form. I am not including high yield modern kilns in this
comparison.
A 33% yield means that 9.7/166.156 = 60% of the original wood heat is
available from the charcoal. This is said in opposition to those who claim
that 3/4 (etc) of the heat is lost/wasted when making charcoal. There are
very poor operators of charcoal kiln operations and the cure is not ban
their trade, it is to help them improve their yield. We don't tell poor
farmers to stop farming because they are inefficient! We teach them.
>Based on that, shouldn't be logical to assume that under "primitive"
>existing general conditions as seeing in the field today, that cooking
>with wood is more energy efficient than cooking with charcoal?
Let's have a good look:
16.2 MJ delivered at a 15% efficiency = 2.423 MJ delivered to the pot. What
you do with it, heating of boiling or simmering is up to you, but that is
how much heat will get there.
The thermal efficiency of a charcoal stove varies a great deal because at a
high power it is low and at low power they are usually very efficient. A
traditional stove like the ones in Lusaka (see attached) are really poor
with a thermal efficiency of about 20% on high. They would deliver about 1.5
to 2.0 MJ to the pot from all the charcoal made from a kg of wood. However
on low power they are much better - about 40% if it is not windy. This
increase in efficiency changes things a lot. It is also the condition that
applies when cooking on low fuel. That would deliver 3.0 to 4.0 MJ to the
pot - much better than an open fire. So how much average cooking is done on
low power? Depends where you are.
As has been shown elsewhere, an open fire can also be operated well and the
efficiency doubled at the extreme. So a highly skilled and patient cook
might even get 4.8 MJ into a pot using wood. As you can see, this is a test
of the cook, not only of the fuel or the 'stove'. The advantage for the
charcoal stove is that it takes nearly no skill at all to get a high
efficiency at the low power stage. Not so with an open fire. Open fires are
extremely susceptible to wind.
Let's take improved stoves for both: a 35% efficient wood stove and a 55%
efficient charcoal stove. What then?
35% x 16.156 = 5.7 MJ delivered by the wood stove If the charcoal was made
at 25% yield, the improved charcoal stove delivers 4.0 MJ.
If there is more charcoal (33% yield) the same stove delivers 5.35 MJ to the
pot by the time the whole kg has disappeared.
So there is not much difference between good charcoal making, and good
stoves, is there? Not a lot. Operator variability will certainly cover the
small difference. If the wood stove cook leaves some of the wood burning
doing nothing nothing, say 5%, it is quite believable that the consumption
will be the same.
The point being made by the charcoal-making wood-gasifying stoves promoters
is that the wood gas can be used to cook and therefore the overall equation
is hard to beat: the wood gas stove cooking with a thermal efficiency of 40%
(quite possible) would deliver additional heat to pots. The equation looks
like this:
Original heat minus leftover charcoal heat = heat available to 'cook with
gas'.
That is, 16,156 - 7.38 MJ (assuming a 25% yield from the stove) = 8.78 MJ is
available to cook with. At a cooking efficiency of 40% (improved wood
gasifying stove) 8.78 x 0.4 = 3.51 MJ delivered to the pot while leaving the
charcoal behind.
If the charcoal thus produced were to be burned in a charcoal stove (this is
theoretical - I have never heard of someone doing this) the total heat into
the pots would be, best case:
8.78 x 40% gas stove efficiency + 7.38 x 55% charcoal stove efficiency =
7.57 MJ delivered to the pot for a system efficiency of 7.57/16.156 = 47%.
>Assuming that woodstoves can easily achieve 20% efficiency which
>delivers 900 kcal into the pot, and to do the same job with charcoal
delivers 3.52 MJ
>one would need a 30% energy efficiency charcoal stove using charcoal
>produced at 40% charcoaling process, what is nearly impossible to
>achieve.
Well, not quite impossible. Charcoal stoves can easily be more than 40%
efficient and 35% charcoal production is not difficult at all. Charcoal
stoves designed to run at low power are more than 60% efficient. The reason
for this is that charcoal burning is inherently more efficient than wood
burning. The reason is that the Hydrogen content of the charcoal is very
low. The air demand for wood is higher per MJ than for high carbon fuels.
That is why coal is inherently more efficient than biomass. High energy coal
needs even less. Less air is required when there is less H2 so the cooling
effect is reduced. For any given quantity of excess air, carbon fires
outperform Hydrogen fires.
For this reason charcoal is always more efficient than wood, just as diesel
engines are always more efficient that gasoline ones (because the higher the
compression ratio, the higher the efficiency).
>Unless charcoal stoves of 40% are possible, so to use with charcoaling
>kilns of high 30% efficiency?
If a charcoal stove is 45% efficient on High and 60% efficient on Low
(average 52.5%), combined with charcoal made at 35% efficiency, the
delivered heat is 5.42 MJ (33.6%). That is about twice as good as an open
fire. It is about the same as a good, improved wood stove. The gas-charcoal
combination would be 40% better (47% total).
One problem is that charcoal produce stove promoters have gone strarry-eyed
over producing char and burying it. In my view there are two camps calling
for this: those promoting agriculture (with spotty, in encouraging results)
and those with a prospect for plunder (carbon credits paying for
unaffordable stoves). The math then looks very different. Taking the char
and burying it and to do the same job with charcoal delivers 3.52 MJ
(assuming a really good gasifier at 40% efficiency). That is 22% - not as
good as any rubbishy improved stove or even a well-run open fire. It means
marginal feedstock savings, plus the inconvenience of managing the fuel,
ignition, and char.
You can see why people are confused about the subject.
Regards
Crispin
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Message: 3
Date: Wed, 13 Oct 2010 19:16:09 -0400
From: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com>
To: "'Discussion of biomass cooking stoves'"
<stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] MUST CHARCOAL BE A CAUSE FOR CONCERN?
Message-ID: <003d01cb6b2c$9f9bec00$ded3c400$@gmail.com>
Content-Type: text/plain; charset="us-ascii"
Dear Otto
You certainly have a way with words.
Before criticising Kevin you should learn more about people in 'poor'
countries. We in the oh-so-superior West think that smoke is a bad thing,
that anyone with 'common sense' would know that.
Read and learn:
In Moto Grosso in Brazil, people are VERY aware that fires can create smoke
and that it is very beneficial. This is diametric opposition to the Western
medical view. Without it the Nambiquara would die younger. Dying young from
malaria or any of numerous other diseases carried by mosquitoes is not
preferable to learning how to creatively use something as useful as biomass
smoke.
At night when the mozzies are particularly bad, people light a smoky fire
using damp wood in the room (open fire). They lower a woven cloth over the
doorway so the entire room fills up with smoke until it reaches the lowest
edge of the cloth, then escapes outside. In Swaziland the same technology
was traditionally used in their 'guqa na thandaza' beehive grass huts so it
is probably widely known.
The level of the bottom of the cloth is secured about 25mm vertically above
the nose of the people sleeping on the floor. The whole room fills with
smoke down to that level and kills the mosquitoes as they enter the room.
The people sleeping on the floor are protected throughout the night or as
long as the smoke lasts. You already knew this, right?
If you brought a nice clean-burning gasifier with low CO into these homes,
they would ask, "What foreign idiot invented a stove that can't make smoke!?
Duh! Have they no common sense??"
Replacing open indoor fires in Mozambique will definitely increase the
incidence malaria and probably other diseases born by roof-dwelling insects.
"He died young from malaria, but at least he didn't die of black carbon
smoke inhalation as an old man!"
Stoves function in a complex medical and environmental and economic matrix.
Reducing fuel consumption reduces prices and puts people out of work - often
the only paid work available. Food prices are depressed internationally
because of vast US and EU dumping of subsidised production. Growing food is
therefore not usually a viable option, though it would be the obvious
alternative.
People who buy fuel, and who buy less when they have an improved stove, will
spend the money on other things - usually not things provided by the fuel
industry workers.
Stove producers, often cited as providing employment, have other products
they can sell and rapidly switch if their stove making business drops off.
And there are not many of them compared with fuel suppliers.
Stove and fuel promoting requires tough decisions made after considering
many implications. Some efforts are misplaced. Look at the efforts made to
ban or suppress paraffin on the basis that it is a 'dangerous, smelly, smoky
fuel' responsible for 'burning thousands to death'. Jet aircraft burn
paraffin very cleanly. It is the STOVE not the FUEL! Crikey. Get a grip.
Let's elevate the quality of discussion to the point where the content
provides useful guidance.
Regards
Crispin
------------------------------
Message: 4
Date: Wed, 13 Oct 2010 23:53:32 -0300
From: "Kevin" <kchisholm at ca.inter.net>
To: "Otto Formo" <formo-o at online.no>, "Discussion of biomass cooking
stoves" <stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] MUST CHARCOAL BE A CAUSE FOR CONCERN?
Message-ID: <649A3A93783A4C72A7D20233C8FFCC64 at usera594fda0bf>
Content-Type: text/plain; charset="iso-8859-1"
Dear Otto
----- Original Message -----
From: Otto Formo
Subject: SV: [Stoves] MUST CHARCOAL BE A CAUSE FOR CONCERN?
Dear Kevin,
what you actually are "saying" is that people in developing countries have
no common sense and knowledge about polution from open fires.............
# Not at all!! They work with what they have to accomplish what they
want.My comments were directed more at the FAO who put prime focus on simply
saving trees, rather than helping improving the lifestyle and health of the
people.
Why do they use open fires for cooking?
The most ovious reason is that they have no choice or options.
Secondly, this is how it has been done for centuries.
It "works", why change?
The women do the collecting of wood and the cooking, so why bather........
# It is certainly misdirected to put the focus on saving trees at the
expense of harming people. Hopefully, it will be a "win-win-win" situation
where more efficient (less wood) and more effective (do a better job of
cooking the way they want to cook) and cleaner (less harmful pollution)
stoves can be configured.
Best wishes,
Kevin
Inferring that "charcoal is bad" overlooks part of the function of some
cooking systems. Some cooking styles must have the intense heat that
charcoal can produce. The point of my posting was to address the whole
problem, not just part of it.
There is also no question about that even the best and most efficient
charcoal stoves (without a chimmny) emitts far more CO than any TLUD
gasifier stove.
# Charcoal stoves permit a unique cooking capability that a TLUD cannot
duplicate. There is probably a place for both stove systems. Much work has
been done on TLUD stoves in the past few years, and they are working better
now than ever. Less work has been done on charcoal stoves... no doubt that
they can also be greatly improved also.
# TLUD's are a neat stove for some applications, but they are far from
being a cooking panacea. They require a highly prepared fuel, that they
don't burn to completion, and they are basically a "batch stove". They are
not really a "gasifier stove" but rather a "pyrolysis gas stove", that wants
to leave charcoal behind. For some applications, the production of charcoal
can be a disadvantage, while for others, it can be very advantageous.
# So, getting back to my basic point... just what is the set of problems
that need to be addressed? Why is charcoal a problem? What can be done to
reduce the problems with charcoal? What other factors should be dealt with
as part of the problem?
The other fact is that CO also kills people in the "western" world as well
by "missuse" of gas for heating and cooking, but it does not mean that we
should stop using it!
BUT we should be VERY carefull by using open flames indoors without good
ventilation.
This is something we learn in school at early age.
If any positive progress should be "stoped" by missuse of just a few there
is no way the "World" are going to move "forward", ever.
Otto
> From: Kevin [kchisholm at ca.inter.net]
> Sent: 2010-10-13 16:33:52 MEST
> To: Discussion of biomass cooking stoves
[stoves at lists.bioenergylists.org]
> Subject: Re: [Stoves] MUST CHARCOAL BE A CAUSE FOR CONCERN?
>
> Dear Rogerio
>
> I think that the wrong question is being asked. One can also ask the
> question: "Must wood be a cause for concern?"
>
> 1: If the ultimate concern is simply availability of fuel, then both
> primitive wood stoves and primitive charcoal systems are indeed a
concern.
>
> 2: If health, as a result of products of combustion considerations is
the
> ultimate concern, then both primitive cooking systems are a concern.
>
> 3: The good thing about 3 stone wood fires is that they emit gross
irritants
> that minimize the potential for users to be killed during the cooking
> session from CO poisoning. Good gharcoal stoves can be very efficient
and
> not emit apparent poisons, but if used in a confined space, the much
more
> efficient charcoal stove can kill the Family before the meal is
finished.
>
> 4: Charcoal gives a quality of cooking that cannot be duplicated by a
wood
> fire.
>
> Obviously, a dreadfully inefficient "3 Stone Fire" can be much safer
than an
> "Improved Cooking Stove" that has much higher efficiency. There is so
much
> smoke and poisons coming off the 3 Stone Fire that people move upwind.
An
> "Improved Cooking Stove" might be improved just enough that people move
it
> inside a living space, and then they start dying from all sorts of
> disorders. Charcoal stoves could end up being superior, in that there
might
> still be enough "residual irritants" emitted such that the Cook uses it
in a
> well ventilated space.
>
> The "problem", whatever it is, must be clearly defined before one can
arrive
> at a meaningful answer to the "problem." A better question might be
along
> the lines of: "What is the best way for people to accomplish their
desired
> cooking task, with a given quantity of wood fuel, while improving the
health
> of the people using a particular "cooking system?"
>
> Perhaps someone else can formulate a better question that is more
relevant
> to whatever issue is of concern. There is no point in promoting an
"improved
> stove system" that cuts wood usage in half, but doesn't cook the food
the
> way the people want it, and then kills them afterward.
>
> Best wishes,
>
> Kevin
>
> ----- Original Message -----
> From: "rogerio carneiro de miranda" <carneirodemiranda at gmail.com>
> To: "Discussion of biomass cooking stoves"
<stoves at lists.bioenergylists.org>
> Sent: Wednesday, October 13, 2010 9:01 AM
> Subject: Re: [Stoves] MUST CHARCOAL BE A CAUSE FOR CONCERN?
>
>
> Dear Crispin and others who has responded.
>
> Making a simple calculation (see table below), I found the following
> numbers based on 1 kg of Eucalyptus grandis, with 4650 kcal/kg as
> fuelwood, or 7600 kcal/kg as charcoal.
>
> Considering the worst case scenarios, with woodstoves efficiency of 10
> to 15% one would get 450 to 698 kcal of energy into the pot, and to
> have the same amount of energy from charcoal into the pot, one would
> need to have either a relative medium charcoaling efficiency of 20%
> but with a charcoal stove with 30% efficiency, or charcoal stoves of
> normal efficiency around 20% but with higher charcoaling efficiencies
> of 30 or 40-%.
>
> Based on that, shouldn't be logical to assume that under "primitive"
> existing general conditions as seeing in the field today, that
> cooking with wood is more energy efficient than cooking with charcoal?
>
> Assuming that woodstoves can easily achieve 20% efficiency which
> delivers 900 kcal into the pot, and to do the same job with charcol
> one would need a 30% energy efficiency charcoal stove using charcoal
> produced at 40% charcoaling process, what is nearly impossible to
> achieve.
>
> Unless charcoal stoves of 40% are possible, so to use with charcoaling
> kilns of high 30% efficiency?
>
> Rogerio
>
>
>
> cooking with charcoal
> efficiency(%) 10%-20%-30%
> (kcal)
> charcoaling 10% (760) (76) (152) (22)
> 20% (1520) (152) (304) (456)
> 30% (2280) (228) (456) (684)
> 40% (3040) (304) (608) (912)
>
> cooking with fuelwood
> efficiency(%) 10% 15% 20% 30%
> (Kcal) (450) (698) (900) (1350)
>
>
>
>
> 2010/10/12 Crispin Pemberton-Pigott <crispinpigott at gmail.com>:
> > Dear Rogerio
> >
> > We discussed this a while back and I forwarded some example of the
energy
> > balance.
> >
> > Yes, the fact is there is nearly no difference between the amount of
food
> > cooked with wood or that same wood turned into charcoal. The caveats
are
> > that I depends on the wood stove, the charcoaling method and the
charcoal
> > stove.
> >
> > Those are three huge variables, but for 'medium quality' on all three
> > counts, the answers are about the same.
> >
> > The overall difference that one might be inclined to ponder is the
amount
> > of
> > energy that is used to being the fuel to the cook. In the case of
> > charcoal,
> > say in Mozambique, the distance that one can profitably transport
charcoal
> > is far greater than that for wood because it is so much more energy
dense.
> > It is even better than coal because coal usually has a lot of ash in
it.
> >
> > So, when considering what to criticise, replace and promote, one has
to
> > look
> > at the three main variables, what one could do to change them, and
what
> > the
> > transport implications are. It is pretty tempting to think of charcoal
> > making vehicles using wood gas for locomotion, delivering charcoal to
the
> > cities. They would start off heavily loaded and get lighter as they
got
> > closer to town!
> >
> > I recall Cecil Cook and I having fun with this equation some time ago.
> >
> > What is always good (as Richard Stanley recently point out) is to make
> > sure
> > that all the chips and dust from the charcoal business end up in
> > briquettes
> > of some form. Usually the review of charcoal is made by a hostile
agent
> > and
> > the 'waste' involved is emphasized, not the methods by which it can
easily
> > be made very efficient, all things considered.
> >
> > There is still a lot of this story to be told by someone with a talent
for
> > integrating technologies and stove ideas.
> >
> > Regards
> > Crispin
> >
> >
> > +++++++++++++++
> >
> >>I found the following quote on a FAO publication
> > (http://www.fao.org/docrep/005/y4450e/y4450e10.htm), and I wonder if
this
> > is
> > a correct statement responding to the question :
> >
> > "Must charcoal be a cause for concern?
> >
> > The shift from fuelwood to charcoal, even if it lasts only a few
decades,
> > could have major ecological consequences if it is not kept under
control.
> > However, since charcoal stoves are more efficient than wood stoves,
the
> > ratio of primary energy to usable energy is almost the same as with
> > fuelwood. Thus with adequate supervision, management and support, the
> > shift
> > does not need to disrupt present levels of resource use."
> >
> > What do you think? Can at the end, with actual stoves and charcoaling
> > efficiencies, be the wood consumption the same?
> >
> > Rogerio
> >
> >
> >
> > _______________________________________________
> > Stoves mailing list
> > Stoves at lists.bioenergylists.org
> >
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists
.org
> >
>
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