BioEnergy Lists: Improved Biomass Cooking Stoves

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October 1996 Biomass Cooking Stoves Archive

For more messages see our 1996-2004 Biomass Stoves Discussion List Archives.

From 73002.1213 at compuserve.com Sun Oct 6 11:48:43 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:34:59 2004
Subject: UpDownCoCounterInverted Gasifiers
Message-ID: <961006154541_73002.1213_FHM47-19@CompuServe.COM>

Dear Ron, STOVES and GASIFICATION all:

Since we are discussing GASIFIER STOVES, I presume we need to put it on both
lists. I spent Thursday afternoon and Friday morning with Prasad - he took his
cold home Friday after lunch. I spent the afternoon with Etienne Moerman
yesterday and he feted me to some exotic beers. We tested Piet Verhardt's stove
and an old Hottenroth in the lab in Eindhoven. See other postings.

The terms "updraft" (air/O2 going up) and downdraft (air going down and fuel
going down) are sort of silly - what would happen in space where there is no up
and down. An improved terminology is Counter-Flow and CO-Flow respectively. A
better name for our "inverted downdraft" would be "inverted co-flow" except that
the fuel only flows "up" if you add an auger under the fuel bed. There is a
larger gasifier operating this way for power generation.

The advantage of UPDRAFT is that the charcoal burning on the grate generates
PLENTY of heat and can use wet fuel. It also generates 10-20% pyrolysis oil. If
you want to put it in an engine, the cleanup train will cost much more than the
gasifier. However, at least two such are being used in Europe today. The high
heat from charcoal burning is sufficient to pyrolyse all the volatiles in the
first 10% of operation and then you have a charcoal stove. (This was the way
Fred Hottenroth operated his stoves until Harry and I turned him around.)

In a DOWNDRAFT gasifier the air contacts biomass in a flaming pyrolysis mode and
leaves less than 0.1% tar. While still requiring cleanup - maybe - it is MUCH
easier than for updraft, and this was the type used in over 1 million vehicles
during WW II. It is very efficient and generates 1 to 3 m3 of gas per m2 of
grate (a superficial velocity of 1 m/sec). If you try to design a stove using
these numbers, a 3 kW stove would have a cross section of 1/ 600 m2 or ....
(10% moisture wood has 16 mJ/kg. 1 m3 of stove gas has an energy content of
about 6 MJ. If you ;t;ry to operate at lower velocities the forced downward
convection loses to the natural updraft and it goes updraft.

In the INVERED DOWNDRAFT stove Air from below first contacts the fuel,
pyrolysing it and leaving the charcoal behind. The pyrolysis oil is not burned
up because the velocity is so much lower. The air flow is supplied by natural
convectin rather than by the draft from the engine.

Now think about what an inverted updraft gasifier would be. (Maybe useless, but
lets discuss it ).

I hope this clears up the terminology. I really need to (a) make a drawing and
(b) do my cigar demonstration to make it crystal clear.

Regards from Schipol Airport, on my way to Stockholm through Frankfurt.

TOM

 

 

From 73002.1213 at compuserve.com Sun Oct 6 11:45:14 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:34:59 2004
Subject: Rogerio's Plea
Message-ID: <961006154515_73002.1213_FHM47-12@CompuServe.COM>

Rogerio and All:

Right on, Rogerio. Biomass needs to be seen as the number 1 "renewable" energy
source, and supported and promoted as such.

Our Biomass Energy Foundation (a 501 3 C not for profit) stands ready to help
submit projects for grants.

Go for it, TOM REED

 

 

From 73002.1213 at compuserve.com Sun Oct 6 11:43:58 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:34:59 2004
Subject: Fuelwood Consumption/refugee energy
Message-ID: <961006154529_73002.1213_FHM47-16@CompuServe.COM>

Dear Grant Ballard:

You take rather an extreme position in opposing an improved 3 stone stove
without having made any measurements on it. The enclosure probably re-radiates
heat into the fire and contains the ashes. There is some indication that ashes
are catalytic in combustion.

In any case, when people don't have enough to eat and don't have fuel to cook it
on, the question of smoke and CO pollution is far down their list of priorities.
Smokers regularly subject themselves to high levels of tar and CO. So, when
your life expectancy is 40, your priorities are likely to be different.

That is not to say that we shouldn't make some measurements and be concerned.

Regards, TOM REED

 

 

From 73002.1213 at compuserve.com Sun Oct 6 11:44:29 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:34:59 2004
Subject: Paul Wendelbo Stove test in Denmark
Message-ID: <961006154547_73002.1213_FHM47-21@CompuServe.COM>

STOVIFIERS: (A hybred name for gasifier stoves)

Wednesday I had the privelege to visit the Danish Technical University and see
many interesting gasifiers. One of particular interest to me was a "tin can"
stove first developed in 1985 by the Norwegian Paal Wendelbo and used in
Adjumani refugee camps for burning grass.

The stove I saw tested in Denmark operated very well. They have made tests on
efficiency with wood chips and found 25-27% efficiency, 1 liter water boiling
times of 6-12 min using 250 g fuel. Full details in paper by Per S. Nielsen
"Efficiency Tests on the Pyrolysis Gasifier Stove Peko Pe", July 1996.

The following advantages were observed for the stove:
Stove burns ithout smoke when sufficient air is supplied
Emissions of CO are low when sufficient air is supplied
Stove is easy to ignite
Stove is rapid in achieving boiling temperature
When burning grass in Uganda the stove can provide heat enough to boil a meal
in 45 minutes after reaching the boiling temperature
Due to the reduced effect [after volatiles burned] it is possible for the cook
to leave the stove for making other things
Stove is relatively cheap to produce
Stove is esy to move and carry around

Disadvantages compared to three stone stove:
One needs metal for producing the stove
One needs tools and skills to produce the stove
The biomass needs some kind of treatment before it can be used in the stove
[??]
The stove needs sto be produced relatively precisely to obtain the pyrolysis
gases, and especially precisely to achieve teh charcoal effect.
The stove needs dry biomass for achieving the pyrolysis process

[I doubt if Ron Larson would agree about many of these disadvanatages. As in
all things, one can fail if one doesn't pay some attentin. Ron uses two tomato
cans to achieve the same results. I am sure "farmer Jones" found similar faults
with the automobile after he saw his first car.]

*****

I have called this type of stove an "inverted downdraft gasifier stove" and it
operates on the same principle as the one I first built at SERI/NREL in 1985
after seeing the dreadful cooking conditions in S. Africa. It was sold by
Hottenroth-LaFontaine (without my blessing) about 1988-89 after I showed it to
Harry.

This would seem to be a case of simultaneous or parallel invention and I
certainly hope to meet Paal Wendelbo to find out the history of his work. Does
anyone have an E-mail address for him? Can we get him on the net? I'll be in
Stockholm all next week and maybe I can find him.

Regards to all, TOM REED

 

 

From 73002.1213 at compuserve.com Sun Oct 6 11:44:39 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:35:00 2004
Subject: Premixed and diffusion flames
Message-ID: <961006154604_73002.1213_FHM47-23@CompuServe.COM>

Hi Rolland and Prasad, and Ron and Grant: Stoveland, The Netherlands

I spent yesterday at Twente University and will spend today with Prasad at
Eindhoven talking about stoves. I met Roland Siemons and saw some of the new
stoves he has and may test. I hope he will get involved in these discussions.

Let me say in different words what Ron said to Grant because I believe it is not
fully appreciated.

1) DIFFUSION FLAMES:

Until about 1840 all flames were diffusion flames (like a candle or match or
wood fire) in which a source of fuel makes vapor which mixes by natural
convection with the surrounding air. Such a flame is low intensity and dirty,
since the fuel is cracked to soot before the oxygen reaches it to generate the
heat.

This is useful in the candle, since we need it's light. Much of the soot may
burn (as in the candle flame), but if one places an object (spoon) in the flame
before combustion is complete, it quenches the combustion, allowing unburned
fuel and soot to escape. (Please examine a candle flame closely, then put a
teaspoon halfway up the flame and observe the soot and smell.)

A diffusion flame has some use for light (the candle) or space heating (the
fireplace and preferably the stove. But it is inherently wasteful for cooking,
since

1) the small visible and huge infra red radiation cools the flame.
2) the heat is only generated at the fuel-air interface envelope which has a
large area

The full combustion only occurs above the visible fire. In an attempt to get the
pot close to the fire, you quench much of the combustion. If there is water in
the pot, so much the worse. So, sad to say, I don't think there is much future
for improved wood stoves and I blame it all on the diffusion flame.

2) PREMIXED FLAMES:
A correctly premixed air-fuel flame (like a Bunsen burner, gas stove or a gas
furnace) burns all the fuel at the flame front in a layer <0.1 mm thick and
produces very little radiatin. All the heat is available above this point in
the cross section of the flame. For a century producer gas (CO+H2) and now
natural gas stoves have satisfactorily cooked meals with high intensity gas
flames. Wood fires don't compete. Wood-gas fires may have a future.

However, if one makes first the wood into a gas, and then mixes the gas with
air and then burns it, one can have the same advantages as natural gas, propane
or producer gas fires. This is what Ron and I are doing on a small scale.

I hope to visit Shandong Village in which a gasifier fills a gas holder with
wood-gas, the gas is distributed in plastic pipe to each house, and each house
then uses the gas for cooking, lighting (Wellsbach mantles) or refrigeration
(the Kelinator gas refrigerator). The gas can also be used to generate
electricity.

Incidenally, the Wellsbach who invented the beautiful gas mantle was a student
of Bunsen.

Regards to all, TOM REED

 

 

From 73002.1213 at compuserve.com Sun Oct 6 11:44:36 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:35:00 2004
Subject: Eindhoven Stoves
Message-ID: <961006154557_73002.1213_FHM47-22@CompuServe.COM>

Here's a puzzle: This week I visisted two sites showing gasifier stoves. Do I
post it in the GASIFICATION or the STOVE node? Until I hear otherwise, I'll
post in both places.

Prasad attended my lecture on gasifiers at Twente (Enschede), then we travelled
by train to Eindhoven (2 hours!) to visit his lab yesterday at Eindhoven
University. Nice to meet my "NETPALS" and talk of cabages and kings and a
thousand things as well as our offician interests. Prasad has a bad cough, so
left me in the capable hands of Ettienne Moerman yesterday afternoon.

There are a few dozen kerosene stoves at Einhoven and a dozen or so wood stoves
left from the stove program of the last decade. (Funding has stopped
(temporarily) and no active stove work (except yesterday).

We first set up a Hottenroth ZSMART stove, pre-gasifier and operated it in the
gasifier mode by lighting on top. It burned 275 g of (too dry) pine block fuel
in 20.0 min (13.7 g/min). Assuming 16 mJ/kg for the wood this is an average
power level of 3.7 kWth. Since there was no control on primary air, the fuel
volatiles burned too fast with too little air. After volatile combustion
stopped the charcoal continued to burn another 20 minutes at a level that
Ettienne thought would be sufficient for simmering.

This particular stove was not designed for this use and did not burn all the
volatiles below the pot. In 1988 Harry LaFontaine visited Hottenroth and they
made a few "GAS-I-FIRE"modified stoves that were much are a major advance over
any wood cooking stoves that I have seen, but don't satisfy my "blue flame"
criterion and wouldn't min my $1000 bet with Harry.

We then tested Piet Verhard's "J" gasifier stove. I discussed this concept in
Hawaii about 1985 with Antal and Smith. I believe it was the subject of a
thesis. Who made and operated the first one?

This stove uses a reservoir "pot" of fuel at ground level ignited on the bottom.
Beneath the reservoir there is a horizontal passage to a 1 m stove pipe (hence
the J name). When first lit it burns in an updraft gasifier mode. Then a quick
blast of air on top of the burning fuel convinces the gases to go down through
the fire and up the 1 m stove pipe, producing downdraft gasification in the pot.
The gas burns sort of in the horizontal section, heating a pot placed there;
then up the stove pipe.

Piet: There was a lot of unburned gas at the top of the pipe. A bundle of
inlet air tubes passing through the hot gas under the pot would have given good
combustion before the pot. Your welding is excellent, but the metal is too
heavy gauge and sucks heat from the fire. Same comment for cast ceramic stoves
- more heat to the stove than to the pot.

Insulation seems to be an afterthought with most stove makers, probably based on
the idea that it is "too expensive". (Riser sleeves are $3 each, retail.)

All stovers: It takes 3.3 times (5 kg air /kg biomass) as much secondary air
to burn the volatiles as primary (1.5 kg/kg) to make them. No one is paying
enough attention to providing secondary air. Furthermore, where cold secondary
air hits hot combustible gas the fire may extinguish. Preheating that air
helps. A hot chamber for the combustion also helps.

I was glad to see the J STOVE concept in action, and while not convenient for
cook stoves, it could be useful in brick kilns, bakeries etc.

It was a pleasure to visit Einhoven and Ettienne and Prasad and Piet's J stove.
On to Stockholm and back to gasification.

Regards to all, TOM REED

 

 

From B.Tremeer at mail1.remote.uva.nl Mon Oct 7 13:08:12 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:00 2004
Subject: Fuelwood Consumption/refugee energy
Message-ID: <1.5.4.32.19961007181146.0067fb74@mail.uva.nl>

Dear Tom and all

(snip)
>You take rather an extreme position in opposing an improved 3 stone stove
>without having made any measurements on it.
(snip)

A few comments (its a great pity we did not meet):
I do take an extreme view, but my thoughts are not 'raw' speculation (I
would be happy to see a study disproving my view. I have tested an
'improved' single pot metal stove - in my view a formalised version of an
enclosed 3 stone stove. CO emissions were 3 times that of an open fire (my
name for a traditional unadulterated 3 stone fire) and TSP (smoke) also
higher (about 1.2 times). CO and TSP were however reduced compared to the
open fire by *lifting* the fire onto a grate. Excess air is critical for
efficient combustion. I do not believe that a user built, mud enclosure
around an open fire is safe. The amount of air for combustion is strongly
dependant on the way the stove is built. Since the stove is 'fed' through
the same opening as is used for primary and secondary air, the more fuel,
the less air - such a stove is thus very sensitive to the way it is operated.

(snip)
>You take rather an extreme position in opposing an improved 3 stone stove
>without having made any measurements on it. The enclosure probably re-radiates
>heat into the fire and contains the ashes. There is some indication that ashes
>are catalytic in combustion.
(snip)

The enclosure will re-radiate energy, yes. Less will be lost to the
suroundings (although we can expect some to be lost in heating up the stove
itself, hence the overall efficiency will improve the longer the cooking
duration). The walls will 'focus' the fire onto the base of the pot. I
therefore would expect such a device to have an improved overall efficiency
when compared to an open fire (even though the combustion efficiency would
be lower, as opposed to the heat transfer efficiency). A 50% fuel saving (at
least in the laboratory) is in my opinion entirely realistic.

I have read publications on the catalytic effect of ash, but my information
is not extensive. I believe that small quantities of some minerals assist in
combustion, these trace quantities depend largely on the soil and growth
conditions of the fuel (I need to look this up again to get specifics). I
don't think this would be sufficient to justify the idea that ash is good
for combustion. The possibility of ash clogging primary and secondary air
inlets is a big problem however. The combustion characteristics of a stove
can change significantly as ash builds up, hence I believe it is an
important design (and education/training) issue.

(snip)
>In any case, when people don't have enough to eat and don't have fuel to
cook it
>on, the question of smoke and CO pollution is far down their list of
priorities.
>Smokers regularly subject themselves to high levels of tar and CO. So, when
>your life expectancy is 40, your priorities are likely to be different.
(snip)

A question of priorities: yes, basic day to day survival will come first. In
many communities, however, smoke reduction is seen as a VERY high priority
by users. "See how we suffer" one 'grandma' with streaming eyes (from the
smoke) once told me. Survival in emergency situations is different -
community cooking (with an alternative fuel perhaps) becomes essential, as
well as training in fuel conservation (eg. lids - although people in
S.Africs know this instinctively) I think. Still, people promoting improved
stoves need to realise the importance of promoting a better product than
currently being used, not a more dangerous one.

I personally believe that emissions are FAR more important than fuel savings
(naturally with a few exceptional situations).

The impact of exposure to smoke, on young children in particular, is
enormous. I believe respiratory related diseases have been identified as the
leading cause of death in developing communities, I believe - Kirk Smith is
the person to talk to.

(snip)
>That is not to say that we shouldn't make some measurements and be concerned.
(snip)

As I said above I believe our concern should be first emissions and second
(or perhaps third) fuel savings. (Second should be improved quality of life,
perhaps?!?)

 

For anyone who is atill reading down at the bottom of this letter: a
comparison of five cooking devices I have compared is forthcoming in the
next edition of the journal Biomass and Bioenergy (Pergamon); title:
"Comparison of five rural, wood-burning cooking devices: efficiencies and
emissions"; authors: G Ballard-Tremeer & HH Jawurek. I could email a version
of this paper in MS Word format (over 200KB, if I remember correctly, when
PKZIPed so only if you really want it).

>From a somewhat rambling Grant, farewell...

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From B.Tremeer at mail1.remote.uva.nl Mon Oct 7 13:29:16 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:00 2004
Subject: Efficiency?
Message-ID: <1.5.4.32.19961007183249.006988e0@mail.uva.nl>

In the stove world during the 1980s there was lots of debate about the
definition of efficiency. Then in 1985 VITA published aome 'international
standards'. But then what?

Are we talking about the same things when we mention efficiency? Internal
comparisons I can understand (for example I frequently state an open fire
efficiency of 14% compared to one of 21% for a one pot metal stove, both
measured by me in the same way). But is a statement of efficiency without
this comparison any use? A very small change in operating procedure can
change 'efficiencies' drastic. For example in Tom's contribution (quoted
below) we do not know whether pot lids were used (with lids, during
simmering an 'efficiency' over 30% can be measured for a traditional open
fire). Lids are just one of MANY parameters. That's briefly why I think only
*comparisons* under the same testing conditions (with the same tester) are
useful.

I'm being controversial intentionally - I would like comments...

(snip from Tom Reed's Contribution on Re: Paul Wendelbo Stove test in Denmark)
>The stove I saw tested in Denmark operated very well. They have made tests on
>efficiency with wood chips and found 25-27% efficiency, 1 liter water boiling
>times of 6-12 min using 250 g fuel. Full details in paper by Per S. Nielsen
>"Efficiency Tests on the Pyrolysis Gasifier Stove Peko Pe", July 1996.
(snip)

I would like to see this paper, Tom, where can I find it, in what journal or
report?

Until next time
Grant

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From verhaarp at janus.cqu.edu.au Mon Oct 7 18:27:50 1996
From: verhaarp at janus.cqu.edu.au (Peter Verhaart)
Date: Tue Aug 31 21:35:00 2004
Subject: Shoes, ships and sealing wax
Message-ID: <9610072231.AA20586@janus.cqu.edu.au>

Dear Stovers,

26 September 1996
Australian spring is bursting out all over! For a long time there has
not been so much activity on
stoves@crest.org

Last things first. Last night's Bacchanal was very enjoyable. We managed to
grill a number of King Prawns on
the downdraft BBQ but it was still slow, even though it put away about 2/3
of a bucketful of firewood. It turned
out to be a good bread toaster. For the other goodies we went back to the
propane burning permanent fixture.

To Tom Reed
About standard burners.
Prasad and Etienne will tell you all about it, I am sure. We have used
standards from TNO (the Government
Applied Research Organisation in the Netherlands) where heat output rates
are given, together with pan sizes
and their optimal fill.
For the World Bank we developed a multi-wick kerosene burner for Niger or
some other African country where
the living units (number of people meals are cooked for) are much larger
than in the Western World. If I
remember correctly we found the heat output rate would have to be 4.5 kW to
be optimal.

Kool en kattepies (how alike the Germanic languages are)
For space heating the downdraft stove is very good, an efficiency of 100 %
if the chimney is allowed to exhaust
in the space to be heated. It would break down cigarette smoke. I remember
thinking when used for burning
waste, it could well deal with PCB's because of the high temperatures
generated.
I also seem to remember that the CO percentage increased sharply when all
wood has pyrolysed and the fuelbed
consists of only charcoal. Something to do with the sudden absence of
catalysts, such as water vapour. We didn't
do a test with adding water vapour.
This generates a next question. How safe is a charcoal stove inside a house?
Can Grant Ballard-Tremeer tell
us anything about emissions from charcoal stoves. Welcome to the club, bye
the way, Grant.

To Ron Larson

More NOx
A goodluck wish for biomass burning stovers. Emissions of NOx are associated
with high combustion
temperatures and, for a biomass burning stove this suggest complete
combustion. To get NOx emissions from
a woodburning cookstove would be like getting a speeding ticket while riding
a pushbike, something almost
beyond reach and too good to be true. For years this has been an unspoken
thought in the back of my mind
when Tom Reed made it surface by a remark to the effect that for a woodstove
it would be a sign of advanced
design if it had emissions of NOx.

To Carol Cross
I don't believe in miracle fuel. If it is at all related to sorghum, it
will be in the shape of straw. The
best kind of straw, from a stove maker's point of view, would be one without
SiO2 so as not to produce a lot
of ash. So far as I know no good cookstoves have been developed for burning
straw. In principle it would be
good if we could burn agricultural waste such as chaff and straw. Most foods
of vegetable origin are associated
with at least an equal amount of waste (such as straw and/or husks). If the
waste could be burned in a halfway
efficient cookstove, all food could be cooked on the heat generated burning
by its own waste products.
In general a good fuel crop would be fast growing, producing wood with a low
ash content in a shape that is
easy to use. There is a book, Firewood Crops, published by the National
Academy of Sciences in Washington
DC in the late seventies or early Eighties, which lists a large number of
plants, trees and shrubs that can be
useful.

7 October 1996

To Tom Reed
How time flies. Just enjoyed your reports from Europe. Very sorry I
couldn't be there too.
The supply of secondary air from the bottom of the Downdraft stove has been
considered. The danger is its low
temperature. If it had been tried and if it had worked, it would probably
have given the operator a little more
tolerance in feeding fuel into the stove. As it was, the operator had to see
to it that the fuelbed let through
enough air unmolested to burn the volatiles downstream from the grate. It is
probably important to give the
volatiles and air below the grate some opportunity to react before exposing
the gases to the cold surface of a
pan. You mentioned volatiles being present in the flue gases from the
downdraft stove during the lab tests. The
fuelbed was probably too thick. If you make it thick enough you can light
the gases at the end of the chimney.
This is not a stable situation, the combustion zone travels upward until the
top of the fuelbed is reached. During
this procedure the chimney spews poison gas.

One thing all the experimental stoves had in common was not enough time to
try them out. Only the downdraft
stove has had a fair go. All the others, specially the charcoal producing
ones suffered from being only briefly
operated by students who had to do a short assignment, had no time to be
properly instructed (even if we knew
what we wanted to be measured and how to achieve the results) and who had
their mind on things far removed
from woodburning cookstoves such as exams, Rock concerts and members of the
other sex.
So Etienne took over Prasad's task of familiarising you with a selection of
the beers of the Low Countries, better
than Coor's?

Wet fuel. We tried our downdraft stove with wet fuel and it worked very
well. It could run with a high
percentage of freshly cut saplings mixed with oven dry wood. We attributed
it to the high thermal radiation of
the fuelbed which would dry out the layer immediately above the char. In
counter flow burning, of course, the
heat of combustion is absorbed by the whole of the fuelbed, generating water
vapour and volatiles and tar.
I hope you use your cigars for enjoyment as well as for tests! Did you buy a
decent supply at Schiphol?

About diffusion- and premixed flames.
I have said it before somewhere and probably better.
The task we set ourselves is designing a burner which can handle a varying
supply of more or less gaseous fuel
of varying composition (at times non-ignitable) and produce a blue, pre
mixed flame. Some assignment!

Which version of the downdraft stove did you see, Tom. The original one was
made from 1 mm thick Cor ten
A steel and insulated with some form of Al2 O3 fibre blanket. We have
pictures or slides of the stove burning
red hot over its whole length.

Tell us more about those riser sleeves. What are they made of and where used.
A heavy ceramic stove is not necessarily a bad thing. Depending on the heat
conductivity of the material (low)
a quasi-steady state would be achieved in quite a short time. This would
apply so long as the heating up of the
stove mass would require only a small portion of the heat generated in the
stove. This is a property one can
hope for from a ceramic stove, certainly not from a thick walles metal stove.

A good idea to remind people of the different priorities people have
depending on their life expectancy!

That will do for now. Enjoy Europe and don't catch a cold.

Piet Verhaart

 

 

From verhaarp at janus.cqu.edu.au Mon Oct 7 18:40:09 1996
From: verhaarp at janus.cqu.edu.au (Peter Verhaart)
Date: Tue Aug 31 21:35:00 2004
Subject: Fuelwood Consumption/refugee energy
Message-ID: <9610072243.AA08408@janus.cqu.edu.au>

Dear Grant,

Could you E-mail me a copy of your article? You can send it as an attached
file, do let me know what sort of file it is (preferably WordPerfect of RTF)

About efficiency of a cooking stove.
There are two efficiencies, one very straightforward. Heat delivered to the
pan, divided by the heat generated by the (assumed complete) combustion of
the fuel.
The second kind of efficiency is the heat needed to finish the cooking
process, divided by the heat generated by the fuel. An example is contained
in "Wood heat for Cooking", probably obtainable from Prasad.

Hartelijke groeten
Piet Verhaart

 

 

From krksmith at uclink4.berkeley.edu Tue Oct 8 03:54:12 1996
From: krksmith at uclink4.berkeley.edu (Kirk R. Smith)
Date: Tue Aug 31 21:35:00 2004
Subject: Fuelwood Consumption/refugee energy
Message-ID: <199610080757.AAA28528@uclink4.berkeley.edu>

 

It was written:
>
>About efficiency of a cooking stove.
>There are two efficiencies, one very straightforward. Heat delivered to the
>pan, divided by the heat generated by the (assumed complete) combustion of
>the fuel.

Just a quick reaction that it may not be a good idea to assume complete
combustion. Incomplete combustion (i.e., combustion efficiency) is the most
critical component of emission factors (most emissions being PIC - products
of incomplete combustion). Overall stove efficiency, therefore, is best
thought of as a combination of two internal efficiencies: combustion
efficiency and heat-transfer efficiency. Too often, improved stoves
increase the second in order to increase overall efficiency of fuel use, but
in the process reduce the first enough to actually increase overall
emissions at the same time.

Cheers/K

 

 

From B.Tremeer at mail1.remote.uva.nl Tue Oct 8 06:49:08 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:00 2004
Subject: Efficiency
Message-ID: <199610081045.LAA16291@mail.uva.nl>

>Just a quick reaction that it may not be a good idea to assume complete
>combustion. Incomplete combustion (i.e., combustion efficiency) is the most
>critical component of emission factors (most emissions being PIC - products
>of incomplete combustion). Overall stove efficiency, therefore, is best
>thought of as a combination of two internal efficiencies: combustion
>efficiency and heat-transfer efficiency. Too often, improved stoves
>increase the second in order to increase overall efficiency of fuel use, but
>in the process reduce the first enough to actually increase overall
>emissions at the same time.

This is the problem of an enclosed three stone fire as I have been saying.
Overall efficiency increases because the heat transfer efficiency increases
significantly, not combustion efficiency (which decreases). The only simple
way of getting a measure of the efficiency of combustion is to measure
emissions. In my view, more important than measuring overall efficiency.

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From E.Moerman at stud.tue.nl Tue Oct 8 07:09:23 1996
From: E.Moerman at stud.tue.nl (E.Moerman)
Date: Tue Aug 31 21:35:00 2004
Subject: Eindhoven Stoves
Message-ID: <47708.s335192@popserver.tue.nl>

I think I should clarify something Tom Reed send in sunday. I also would
like to thank him for the exchange of ideas which gave me a few new stove
ideas to try.

Tom Reed wrote:

<snip>
> Piet: There was a lot of unburned gas at the top of the pipe. A bundle of
> inlet air tubes passing through the hot gas under the pot would have given
> good combustion before the pot. Your welding is excellent, but the metal
> is too heavy gauge and sucks heat from the fire. Same comment for cast
> ceramic stoves - more heat to the stove than to the pot.
<snip>

About the J-stove (downdraft stove): Piet Verhaart should tell this story,
but I will tell what I heard about it. The original idea indeed was to
produce a pyrolysis gas and burn all of it just below the pan. Piet build a
special stove to get this done. During lab testing it was not possible to
keep the flames just below the pan all the time. Sometimes flames would
travel upstream and end up burning just below the fuelbed. During these
tests it was then noticed that the stove burnt very clean with the flame
just below the fuelbed. Another more appropriate stove was build for testing
this 'new' phenomena and this is virtually the same stove you saw in the
lab. All this occurred in 1986/1987, so it looks like the people at Hawaii
were the first to build it and Eindhoven discovered it independently a
little later. The first few downdraft stoves were build using thin metal
sheets, but due to the very high temperatures they corroded heavily and were
inoperable within a couple of weeks. Later we switched to stainless steel
with a thickness of 1.5mm. Also all our stoves were heavily insulated with
Al2O3 blankets. Later on when I was in charge and only wanted to try out a
new concept I left parts not insulated for quick changes and visual
observations. Of course a stove that is to be used in the field should be
well insulated if possible. We were not familiar with riser-sleeves, but all
other insulations appeared to be too expensive and too difficult to get in
developing countries. So in that case you are left to the choice between
heavy ceramic/mud stoves and metal stoves. For short cooking tasks the metal
stoves loose less heat and for long cooking tasks the ceramic/mud stoves
loose less heat. If insulation is locally available for an affordable price
it should be applied on metal stoves.

Also from Tom:

<snip>
> All stovers: It takes 3.3 times (5 kg air /kg biomass) as much secondary
> air to burn the volatiles as primary (1.5 kg/kg) to make them. No one is
> paying enough attention to providing secondary air. Furthermore, where
> cold secondary air hits hot combustible gas the fire may extinguish.
> Preheating that air helps. A hot chamber for the combustion also helps.
<snip>

In the downdraft stove we tested secondary air supply. The lowest point of
the CO/CO2 ratio curve could not be lowered further using secondary air.
However it was possible to get the cleanest combustion over a larger range
of air supply. Unfortunately this was almost impossible to achieve without
the aid of a real-time CO/CO2 meter. Therefore a user would not be able to
operate it correctly and would probably deteriorate the overall combustion
quality, so we choose not to include secondary air for the moment. Some of
our more recent test models do include secondary air supply, but there is no
money available anymore so it looks like this one will stay untested and
disappear in the trash can.

<snip>
> It was a pleasure to visit Einhoven and Ettienne and Prasad and Piet's J
> stove. On to Stockholm and back to gasification.
<snip>

It was a pleasure to have you around. I hope you will enjoy Stockholm.

Greetings to all.

Etienne
---------------------------------------------
Mr. Etienne Moerman E.Moerman@stud.tue.nl
Joh. Buyslaan 71 tel. +31-40-2571491
5652 NJ EINDHOVEN The Netherlands

 

From B.Tremeer at mail1.remote.uva.nl Tue Oct 8 07:19:24 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:00 2004
Subject: Efficiency
Message-ID: <199610081116.MAA16799@mail.uva.nl>

About efficiency:
Your definition seems to me too vague for practical use and will yield very
different results depending on how it is applied. Either everyone uses
*exactly* the same procedure or we recognise that quoted efficiencies are
not too useful.

If we were to make a rigid procedure though, I question the applicablilty to
real life - and after all that is what interests us. This tension was
clearly evident in the 1985 VITA international standards, so its not new. In
these standards pot lids were not advised (but could be used if desired to
match local practice). Lids have a *marked* effect on efficiency (and also
on emissions since with lids a lower power is required to maintain
simmering). If I compare my measured efficiency with yours and I don't know
whether you use lids I could be badly misled. I use lids only as an example,
there are *many* other important factors (just one more example, the size of
the pieces of fuel).

One can compare values only if they have been measured in the same way (same
procedure, same task, same method of operation, by the same person perhaps?).

Why am I trying to stir this up?
There is much talk of the need to develop methods for measuring emissions. I
am trying to build a framework and so I am looking critically at efficiency
measurements - the efficiency arguments came to an end, rather than were
concluded, as far as I can see.

Piet, the article is in MS Word with losts of graphs and TIFF images. It
won't make too much sense without them. What do you suggest...

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From skip.hayden at cc2smtp.NRCan.gc.ca Tue Oct 8 07:33:59 1996
From: skip.hayden at cc2smtp.NRCan.gc.ca (Skip Hayden)
Date: Tue Aug 31 21:35:00 2004
Subject: Efficiency
Message-ID: <9609088447.AA844785460@cc2smtp.nrcan.gc.ca>

I have a concern about breaking efficiency down simply into
combustion efficiency and heat transfer efficiency. It
often makes people lose the sense of how you can actually
improve the efficiency of a combustion process.

Basically there are three factors
1. the degree of completeness of combustion, i.e.
"combustion efficiency".
2. the level of excess air which you require in order to
achieve that degree of completeness of combustion.
3. the ability of the system to extract heat from the flame
and the combustion gases.

2. and 3. often tend to get mixed in together in what people
often call "heat transfer efficiency" but they are quite
separate.

2. is a function of the combustion process and the better
you make the process, in terms of mixing, temperature and
residence time (for the first two), the lower the amount of
excess you need to get the same or even a lesser amount of
incomplete combustion products (PIC's, emissions, etc.,
depending on your terminology). For example, running at 50%
excess air rather than 100% excess air can give you a fuel
saving (i.e. efficiency gain/final efficiency) of some 15%.
Moving from 500% excess air to 100% excess air would give
you far more. To know your ability to improve in this area,
where the best gains can usually be achieved, you need to
know your excess air level, measured by CO2 or O2. Reducing
excess air also lowers mass flow through the system and
generally improves the ability of the system to extract heat
from the flue gases - hence the reason that it has been
mixed up with the heat transfer efficiency, although it is
better thought of as improving combustion.

3. is affected primarily by the design and amount of heat
transfer surfaces which take energy out of the flame and
flue gases, by radiation, conduction and conection. Hence
the pot design, location etc can become a driving force
here.

Hope this helps,

Skip Hayden
Advanced Combustion Technologies, CETC/ETB
Ottawa, Canada

 

 

From E.Moerman at stud.tue.nl Tue Oct 8 08:45:44 1996
From: E.Moerman at stud.tue.nl (E.Moerman)
Date: Tue Aug 31 21:35:00 2004
Subject: Efficiency?
Message-ID: <53488.s335192@popserver.tue.nl>

<snip>
> In the stove world during the 1980s there was lots of debate about the
> definition of efficiency. Then in 1985 VITA published aome 'international
> standards'. But then what?
<snip>

WSG in Eindhoven uses a slightly different method, which gives more stable
results. More about it later.

(snip)
> measured by me in the same way). But is a statement of efficiency without
> this comparison any use? A very small change in operating procedure can
> change 'efficiencies' drastic. For example in Tom's contribution (quoted
> below) we do not know whether pot lids were used (with lids, during
> simmering an 'efficiency' over 30% can be measured for a traditional open
> fire). Lids are just one of MANY parameters. That's briefly why I think only
> *comparisons* under the same testing conditions (with the same tester) are
> useful.
(snip)

In our method experiments with and without lids result in the same
efficiency. Of course operating the fire is very important, but one should
do several experiments to find the optimal way of charging the wood in the
fire. Of course this method has only a very limited meaning for the ultimate
user. As we at Eindhoven have been saying for a long time the turn-down
ratio is probably more important than the efficiency.

Etienne
---------------------------------------------
Mr. Etienne Moerman E.Moerman@stud.tue.nl
Joh. Buyslaan 71 tel. +31-40-2571491
5652 NJ EINDHOVEN The Netherlands

 

From E.Moerman at stud.tue.nl Tue Oct 8 08:45:36 1996
From: E.Moerman at stud.tue.nl (E.Moerman)
Date: Tue Aug 31 21:35:00 2004
Subject: Fuelwood Consumption/refugee energy
Message-ID: <53483.s335192@popserver.tue.nl>

Dear Grant,

I would like to give a few reactions on your last email.

<snip>
> be lower, as opposed to the heat transfer efficiency). A 50% fuel saving (at
> least in the laboratory) is in my opinion entirely realistic.
<snip>

For the shielded fire we measured a 50% efficiency for one type of shielded
fire in the lab and easily over 40% efficiency for other versions.

<snip>
> S.Africs know this instinctively) I think. Still, people promoting improved
> stoves need to realise the importance of promoting a better product than
> currently being used, not a more dangerous one.
<snip>

I fully agree, however I think it is possible to make stoves with far lower
smoke emissions than an open fire. I would like to invite you to have a
look at our downdraft stove. It has extremely low emissions, although it is
not yet possible to make a cheap and easy to operate version yet. I know
that Tom Reed et al. have a stove with low emissions too, however I have not
yet been able to build that one. It should be easier to operate, but would
not be very efficient.

Etienne

PS If you want to come to Eindhoven to have a look in our lab contact me at
the address at the bottom.
---------------------------------------------
Mr. Etienne Moerman E.Moerman@stud.tue.nl
Joh. Buyslaan 71 tel. +31-40-2571491
5652 NJ EINDHOVEN The Netherlands

 

From E.Moerman at stud.tue.nl Tue Oct 8 08:45:59 1996
From: E.Moerman at stud.tue.nl (E.Moerman)
Date: Tue Aug 31 21:35:00 2004
Subject: Fuelwood Consumption/refugee energy
Message-ID: <53505.s335192@popserver.tue.nl>

> There are two efficiencies, one very straightforward. Heat delivered to the
> pan, divided by the heat generated by the (assumed complete) combustion of
> the fuel.
> The second kind of efficiency is the heat needed to finish the cooking
> process, divided by the heat generated by the fuel. An example is contained
> in "Wood heat for Cooking", probably obtainable from Prasad.

Yes it is still available. Interested? Email prasad@tn7.phys.tue.nl

Saludos

Etienne
---------------------------------------------
Mr. Etienne Moerman E.Moerman@stud.tue.nl
Joh. Buyslaan 71 tel. +31-40-2571491
5652 NJ EINDHOVEN The Netherlands

 

From verhaarp at janus.cqu.edu.au Tue Oct 8 18:52:35 1996
From: verhaarp at janus.cqu.edu.au (Peter Verhaart)
Date: Tue Aug 31 21:35:00 2004
Subject: Fuelwood Consumption/refugee energy
Message-ID: <9610082256.AA30786@janus.cqu.edu.au>

8 October 1996

Dear Grant,
One paragraph of yours I couldn't resist replying to. About the open
fire and its derivatives.
Outside of our Internet Stove Group very many have written derogatory prose
about the open fire without ever
having tested it in the past decades. In the eighties it was only our great
friend Waclav Micuta, who had done
measurements on the open fire and actually had the temerity to compare
performance of "Improved" stoves to
that of the open fire. He was also a great promoter of the haybox, I presume
you know what that is. When you
use a haybox in the boiling process all you do is heat the pan and its
contents to boiling point and then place
it in the haybox, which keeps it hot enabling the cooking process to proceed
to completion. This obviates the
need of the stove to have sophisticated controls. It can burn at its peak
heat output rate and should be doused
as soon as the contents of the pan reach boiling point. It is a sad fact
that no wood burning cookstove can be
turned down to a reasonable simmering rate.
A grate makes a lot of difference, as you have noticed. It supplies air to
the fuelbed and enables a higher
combustion intensity. The Eindhoven Woodburning Stove Group has figures on
the number of kW/sq.m with
and without a grate for the open fire. Have you been in touch with them yet?
Have you noticed that when "Stove experts" from any industrialised country
test an "Improved" woodstove, they
consistently cram all the fuel they can into the fueling port, thereby
depriving the fire of much needed air. I
never found an explanation for this behaviour.

To Prasad
Thank you very much for sending me Cathy Smits' report "Metingen aan de
'trapvormige downdraft
stove' met betrekking tot vermogen en rendement", which I received about a
week ago.
I reported some improvement in my Downdraft BBQ after fitting a taller
chimney (1.5 m) and reducing the
number of obstacles in the passages leading to the chimney. Yes, bricks are
very rough.

To Kirk Smith
You suggest taking into account the actual completeness of the combustion
and use that for calculating the heat
transfer efficiency. Well, that has been thought of and dismissed by one
member of the WSG's Steering
Committee in the late seventies. This learned gentleman uttered words to the
effect that the difference between
heat output from complete and actual combustion was too small for us to
worry about, so we shouldn't spend
our costly time on it.
Personally I am happy I deviated from this straight and narrow path, being
obsessed with the vista of blue
flames (which I have yet to see but we keep muddling on)

To All
There is something about differences in efficiency by yes or not using
a lid on the pan. I don't see how
the fire can be conscious of there being a lid somewhere up above. There
must be some confusion.
With a lid on, the pan looses less heat through evaporation, e.g. can be
kept at boiling point with less fuel
expenditure.
Without a lid there is more evaporation, even below boiling point, giving
rise to a slightly higher heat transfer
efficiency, more water evaporated using the same amount of fuel.

That is all for now, before everybody else wakes up and logs in.

More NOx

Piet Verhaart

 

 

From 73002.1213 at compuserve.com Tue Oct 8 23:57:48 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:35:00 2004
Subject: Shoes, ships and sealing wax
Message-ID: <961009035938_73002.1213_FHM57-17@CompuServe.COM>

Dear Piet:

What a wonderful letter! Yes I am enjoying Europe, tonight in Stockholm in a
1st class hotel, working for NUTEK to evaluate Swedish fundamental research.
We went to Gothenberg today and returned on the Very Fast and Very Beautiful
train.

The J stove had a lot of fibre insulation, including where the pot would be. I
had the impression that, in addition to cooking on the horizontal channel, one
could heat quite well with another pot on top of the radiating gasification bed.
I would guess it was radiating about 1 kW.

The riser sleeves are made from similar spun alumino-silicate fibers, chopped
short and slurried with starch, then molded on a vacuum screen. (I don't think
yours were Al2O3.) John Tatom was actually in that business for a while. You
should be able to find them in any city large enough to have casting shops.
They will stand molten iron temperatures. Cost about $3 retail.

Supply of cigar-gasifiers holding up well.

Regards, TOM REED

 

 

From skarekezi at form-net.com Wed Oct 9 02:57:34 1996
From: skarekezi at form-net.com (skarekezi@form-net.com)
Date: Tue Aug 31 21:35:00 2004
Subject: Request to Re-route E-mail Messages to New Address
Message-ID: <TCPSMTP.16.10.9.9.48.30.3180191682.377044@formnet-svr.form-net.com>

 

Dear Sir/Madam,

Thank you for the previous e-mail messages we have been receiving on the
stoves bulletin. We kindly request that all our future messages are
re-routed to our new e-mail address: skarekezi@form-net.com

Once again thank you for keeping us informed of new developments.

Yours sincerely

Lugard Majoro
FWD/AFREPREN

 

 

From B.Tremeer at mail1.remote.uva.nl Wed Oct 9 03:11:55 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:00 2004
Subject: Pot lids
Message-ID: <199610090708.IAA02339@mail.uva.nl>

The operator is conscious that there is a lid and therefore s/he requires a
lower power to achieve the same task - hence the difference in emission
levels. The reduced losses through evaporation alter the efficiency if the
evaporated water is included in ones definition of efficiency. If it is not,
how does one determine the efficiency during simmering?

>From Piet
>To All
> There is something about differences in efficiency by yes or not using
>a lid on the pan. I don't see how
>the fire can be conscious of there being a lid somewhere up above. There
>must be some confusion.
>With a lid on, the pan looses less heat through evaporation, e.g. can be
>kept at boiling point with less fuel expenditure.
>Without a lid there is more evaporation, even below boiling point, giving
>rise to a slightly higher heat transfer efficiency, more water evaporated using
>the same amount of fuel.
>
>That is all for now, before everybody else wakes up and logs in.
>

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From B.Tremeer at mail1.remote.uva.nl Wed Oct 9 03:23:33 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:00 2004
Subject: The open fire
Message-ID: <199610090720.IAA02414@mail.uva.nl>

At 08:56 9-10-96 +1000, Piet wrote:
> 8 October 1996
>
>Dear Grant,
> One paragraph of yours I couldn't resist replying to. About the open
>fire and its derivatives.

Yes, I believe the open fire can be very efficient. One of its chief
advantages is that the user can see what is happening and adjust it
accordingly. Operating it in a very low power mode is also easy.

Has anyone measured an open fire as operated by a rural cook? It took me
about 15 fires before I learned some of the tricks of operation - not as
straightforward as it seems at first to run it well (although its easy to
build a bonfire which will be very inefficient). I am sure there are many
other skills to learn...

>Have you noticed that when "Stove experts" from any industrialised country
>test an "Improved" woodstove, they
>consistently cram all the fuel they can into the fueling port, thereby
>depriving the fire of much needed air. I
>never found an explanation for this behaviour.

Odd isn't it. I have seen people in less developed countries do this too,
perhaps it is human nature? Therefore I think this tendancy should be
'designed in'.

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From B.Tremeer at mail1.remote.uva.nl Wed Oct 9 07:53:28 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:00 2004
Subject: Efficiency?
Message-ID: <199610091150.MAA05906@mail.uva.nl>

Etienne wrote:
(snip)
>WSG in Eindhoven uses a slightly different method, which gives more stable
>results. More about it later.
(snip)

Yes more info please Etienne.

(snip)
>As we at Eindhoven have been saying for a long time the turn-down
>ratio is probably more important than the efficiency.
(snip)

Which is one of the distinct advantages of an open fire...

(snip)
>For the shielded fire we measured a 50% efficiency for one type of shielded
>fire in the lab and easily over 40% efficiency for other versions.
(snip)

Remember you use a different definition of efficiency from me? How does it
compare to an open fire measured in the same way - that, I think, is what
counts.

(snip)
>... I think it is possible to make stoves with far lower
>smoke emissions than an open fire. I would like to invite you to have a
>look at our downdraft stove. It has extremely low emissions, although it is
>not yet possible to make a cheap and easy to operate version yet. I know
>that Tom Reed et al. have a stove with low emissions too, however I have not
>yet been able to build that one. It should be easier to operate, but would
>not be very efficient.
(snip)

Yes, I like these ideas and would like to see them. I will only be able to
visit you much later in the year though. This type of stove is possibly part
of what I was calling a 'technology jump' - an improved stove which is
substantially better.

All the best
Grant

 

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From prasad at tn7.phys.tue.nl Wed Oct 9 08:34:47 1996
From: prasad at tn7.phys.tue.nl (prasad)
Date: Tue Aug 31 21:35:00 2004
Subject: Shoes, ships and sealing wax
In-Reply-To: <9610072231.AA20586@janus.cqu.edu.au>
Message-ID: <9610091229.AA17511@tn7.phys.tue.nl>

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From prasad at tn7.phys.tue.nl Wed Oct 9 09:38:35 1996
From: prasad at tn7.phys.tue.nl (prasad)
Date: Tue Aug 31 21:35:00 2004
Subject: Efficiency?
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From prasad at tn7.phys.tue.nl Wed Oct 9 13:11:03 1996
From: prasad at tn7.phys.tue.nl (prasad@tn7.phys.tue.nl)
Date: Tue Aug 31 21:35:00 2004
Subject: Efficiency
Message-ID: <199610091711.NAA18142@solstice.crest.org>

From: Prasad

Date:9 October 1996

Sub: The Great Efficiency debate

Dear Stovers

I thought nobody was interested in efficiencies of such mundane things as
cookstoves anymore. It is great to hear the discussion start again. The
problem is that when one grows older, one gets somehow the feeling that we
have gone through this business and is it necessary to rehash things all
over again? As the discussion has shown, there is recognition of the earlier
argument but there was no resolution of the differences. As far as I am
concerned the argument died because woodstoves are no longer on the priority
list of donor community. If this sounds somewhat denigrating to the efforts
in developing countries on behalf of the poor and deprived, that at least is
not the intention. There have been many efforts not only at defining
efficiency but also at developing standards for measuring them. Apart from
VITA I can name four other standards at least: The Sahel Standard; there is
an East
African (?) standard; there is the Chinese one; and there is the Indian one.
To be frank the differences among these are not based upon any profound new
thoughts about either the stove science or the measurement techniques. Piet
Visser and I are preparing a paper which provides an up-to-date review on
the subject.

Turning now to the points of discussion, there apparently are two broad
issues. The first concerns the distiction between combustion and heat
transfer efficiencies. As far as I could gather the second one runs
something like this: there aint no point in prescribing beautiful tests on
the basis of laboratory experience; life in the real world does not conform
to this and as such ignore the former. Both these arguments have been heard
by Piet Verhaart and me since we ran into the woodstove problem way back in
the year of our Lord 1979. As far as I am concerned the argument arises
because we have never agreed on a set of ground rules. If in fact we did
agree on a set of ground rules, there apparently is no refereeing system to
enforce these rules.

Without getting too involved I shall look at two statements which were heard
before and are heard again. An improved stove did improve the heat transfer
efficiency, but this was achieved at the expense of combustion efficiency.
Here is a caricatural calculation to show the less than satisfactory nature
of this discussion. Consider the traditional three stone fire. One such fire
shows a heat transfer efficiency of 15% and a combustion efficiency of 85%
(this is not a spare afternnon's exercise to determine; to put it mildly, it
is a pain in the you know where). A new stove produced a heat transfer
efficiency of 30%. What happened to its combustion efficiency. A careless
user of the above argument might be tempted to conclude that the combustion
efficiency dropped to 70%. I'm sure that was not the way the argument was
intended to be used.

Turning next to the dichotomy between the lab and the field. I simply think
that people who talk of these differences are not interested in stoves
designed to perform well but are looking for a device to cook food with
whatever species of fuel in whatever form it is available with arbitrary
amounts of moisture content. More power to them.

But should you guys be interested in pushing the discussion any further,
maybe you should read our earlier writings, find holes and set up new ground
rules etc.

Prasad

 

 

From aellegaard at nn.apc.org Wed Oct 9 15:35:43 1996
From: aellegaard at nn.apc.org (aellegaard@nn.apc.org)
Date: Tue Aug 31 21:35:00 2004
Subject: Emissions
Message-ID: <199610092039.UAA08840@nn.apc.org>

I have been following the "efficiency" discussion with some interest, but
what interests me most is what Grant Ballard wrote:
"Why am I trying to stir this up?
There is much talk of the need to develop methods for measuring emissions."

I think there may be some value in turning to emissions, then. But I fear that
we shall see that emissions are almost as difficult to capture as efficiencey,
or probably more. Together with the National Council for Scientific
Research (Drs Kaoma and Kasali) we tried to determine emissions from a
number of stoves, both traditional and improved, with charcoal, coal brique
ttes and coal as fuels. We used a method based on a paper by Ahuja et al
from 1987 (I think). This was based on work done by Kirk's groups in
Hawaii if I am not mistaken. We did get some figures, but it is somewhat
difficult to tell how solid they were. What methods have you been using
for chimneyless stoves?

On the other hand, it may be that we should discuss exposure rather than
emissions. After all, the emissions are chiefly a problem when somebody
is there to be exposed to them. This opens up yet another degree of
freedom in the equation, since people have an activity pattern that is
not easily replicated.

So if you have, please some information about emissions.

Regards
Anders Ellegard

 

From larcon at csn.net Wed Oct 9 20:01:56 1996
From: larcon at csn.net (Ronal Larson)
Date: Tue Aug 31 21:35:01 2004
Subject: Multiple topics
Message-ID: <Pine.3.89.9610091700.A29452-0100000@teal.csn.net>

 

This is a 12-part response. Sorry. Too many good communications
recently. Ron

1. First on GrantÕs observations today. Re ÒThe open fireÓ. He said:
ÒHas anyone measured an open fire as operated by a rural cook? It took me
about 15 fires before I learned some of the tricks of operation - Ò
Response: Grant - I hope you will transmit some of these tricks.
I am very weak on this topic; I donÕt know how they do so well.

2. Same message, Grant: Ò. I have seen people in less developed countries
do this (cram fuel) too, perhaps it is human nature? Therefore I think
this tendency should be 'designed in'. Ò
Response: I believe this is exactly what one must do in any
charcoal-making cookstove (to an extent - the primary air must still get
through). There should be no obvious place to put another (vertical, in
my opinion) branch.

3. From Prasad on ÒThe Great Efficiency debateÓ. Prasad : ÒApart from
VITA I can name four other standards at least: ... Piet Visser and I
are preparing a paper which provides an up-to-date review on the subject.Ó
Response - All the standards I have studied seem to have handled
co production of charcoal incorrectly. I think the effect of charcoal
production should appear in the numerator - not the denominator - of an
efficiency definition.
The difference is substantial. If 1/3 of the energy remains in
the form of charcoal, 1/3 is lost, and 1/3 is useful, the existing
definitions will either give 1/3 (ignoring the charcoal value) or 1/2
(subtracting the charcoal value in the denominator) as the efficiency. I
think the right answer is 1/3+1/3 = 2/3.
Prasad - I look forward to seeing how your article covers this co
product efficiency issue.

4. From GrantÕs: Ò RE: Efficiency?Ó today. Grant was responding to
Etienne who wrote: ÒI think it is possible to make stoves with far lower
smoke emissions than an open fire. I would like to invite you to have a
look at our downdraft stove. It has extremely low emissions, although it
is not yet possible to make a cheap and easy to operate version yet. I
know that Tom Reed et al. have a stove with low emissions too, however I
have not yet been able to build that one. It should be easier to operate,
but would not be very efficient.Ó
Response to Etienne: Our charcoal-making stove is relatively
cheap (I mostly use thrown-away cans, but also have used clay and
bricks. Tom Duke has constructed one using a hole in the ground.
I find it easy to operate, but if built without understanding the
basic principles, it probably wonÕt work at all.
I especially would like to hear why you think a charcoal-making
stove should Ònot be very efficientÓ. It has a fairly large and
controllable turn-down ratio, the chimney is quite short, insulation and
reflectors can reduce radiative losses, convective heat transfer shields
can be added around the cookpot, the excess air ratio seems about right,
and combustion efficiency is very close to 100%.

5. Grant continued: Ò Yes, I like these ideas and would like to see
them. ...... This type of stove is possibly part of what I was calling a
'technology jump' - an improved stove which is substantially better.Ó
Response: As Kirk pointed out, the downdraft gasifier (heating)
stove goes back at least to the 17th century - but as near as I tell
no-one has yet claimed such a downdraft stoveÕs high value for cooking.
Especially with this group, I hesitate to claim that a charcoal-making
stove is a technology jump (or the final answer), but I have yet to see
any mention of charcoal co-production in print prior to this groupÕs
discussion in 1996 (and I have looked at many hundreds of pages of stoves
literature).
Making charcoal (i.e. controlling air flow in pyrolysis) is not a
technology jump, nor is separating primary from secondary air (but I
havenÕt seen it in any other small cheap cookstove), nor should be the
use of the waste heat from traditional charcoal making (which I also have
never seen developed). Moreover, all the few persons who have seen it
work says that charcoal-making cookstoves should be further developed -
so I believe it is both relatively new and worth doing. This stoves list
group is the one to do so.
The basic idea is simple - make charcoal and use the waste gases
for cooking. But my first 10 stoves didnÕt work at all. Anyone
desiring further design hints to increase their learning curve slope is
certainly welcome to last JanuaryÕs (still too) brief descriptions.

6. From a brief Grant note yesterday entitled ÒRe: Fuelwood Consumption
/refugee energyÓ: ÒThe combustion characteristics of a stove can change
significantly as ash builds up, hence I believe it is an important design
(and education/training) issue.Ó
Response: There is no ash production in a charcoal-making stove
(the problem being sent to the userÕs stove). But plenty of
education/training issues remain.

7. Grant from the same: ÒStill, people promoting improved stoves need to
realise the importance of promoting a better product than currently being
used, not a more dangerous one. I personally believe that emissions are
FAR more important than fuel savings (naturally with a few exceptional
situations).Ó
Response: I agree - and only recently came to realize this after
reading Kirk Smith. I believe charcoal making stoves properly operated
can do this. My one shot thus far at a laboratory test found CO below
the measurement limit (of 0.1%) available then. Tom Reed and I only
rarely see or smell smoke. Your and KirkÕs stove health-impact testing
must be expanded to help reduce this serious health problem.
A charcoal-making stove that could replace the current very
wasteful charcoal production processes would also have a major impact on
production of global-warming gases (other than CO2) - an effect probably
larger than that from unburned gases from 3-stone fires.
And several times more trees are felled than theoretically needed
to make charcoal.

8. Responding to yesterdayÕ s Peter Verhaart comments in ÒShoes,
ships and sealing waxÓ, in talking about my comments a while back on
desiring high temperature, Piet said: ....Ó ..it would be a sign of
advanced design if it (ANY STOVE) had emissions of NOx.Ó
Response: I know almost nothing on this subject. If I am able to
get more testing accomplished, should NOx be one of the important tests?
At what Nox levels do problems begin?

9. Responding to Skip Hayden in his Ò Re[2]: EfficiencyÓ. Skip
noted: Ò........ Reducing excess air also lowers mass flow through the
system and generally improves the ability of the system to extract heat
from the flue gases - hence the reason that it has been mixed up with the
heat transfer efficiency, although it is better thought of as improving
combustion.Ó
Response: This suggestion is very helpful (and almost never
measured or discussed). Based on Eindhoven comments on CO production, I
have been assuming that an exhaust plume with about equal parts O2 and
CO2 would be correct - and I found approximately this in our only such
test so far. Any disagreement that 10-11% each would be a desirable
goal (assuming this is accompanied by negligible CO and particulates)?
Skip - In large systems, where excess air may be worth
monitoring, what do they strive for? How do they measure it?
In several of his papers, Kirk Smith cites work by Jay Shelton
showing measurements of the (only 2) efficiency components that Skip is
questioning - as a function of fuel moisture content. After reading the
original Shelton (heating stove) paper, Ron West and I have recently
decided that the Shelton results are highly suspect (which showed a peak
overall efficiency at about 15% moisture content, but a peak in the Òheat
transferÓ efficiency at a higher moisture content). Shelton also noted
how difficult it was to determine his two separate efficiency effects
(involving deductions of the two efficiencies by finding the differences
of large quantities.)
I hope that both Kirk and Skip and others can recommend the best
ways for the stove community to measure three (or even two) separate
effects (and also comment on the reasonableness of the Shelton results)
. Shelton kept his power level constant - with a constant single air
supply opening in a his enclosed heating stove - by using a variable wood
supply - as the moisture content changed - not the way that a cookstove
should be operated.

10. From Peter Verhaart on yesterdayÕs Ò Re: Fuelwood
Consumption/refugee energyÓ. Piet stated: ÒPersonally ... being
obsessed with the vista of blue flames (which I have yet to see but we
keep muddling on)Ó.
Response: I also have not seen a real blue flame. This opening
by Piet allows me to comment on Tom ReedÕs earlier comment on ÒPremixed
and diffusion flamesÓ where Tom said Ò However, if one makes first the
wood into a gas, and then mixes the gas with air and then burns it, one
can have the same advantages as natural gas, propane
or producer gas fires. This is what Ron and I are doing on a small scale.Ó
To clarify - I certainly endorse making the wood gas. However,I
have tried to achieve pre-mixing and have thus far (unfortunately) been
unsuccessful. The only difference I see from a normal candle diffusion
flame is an inversion - the central part of our stoveÕs flame is
secondary air rather than gas. I am afraid that premixing requires
either a pressurized air or fuel source or a very tall mixing tube with
subsequent heat loss.
It would be nice to have pre-mixing and I hope someone in this
audience will find a solution for achieving it. Note however, that one
needs a certain natural draft to bring in both the necessary primary and
secondary air and so the relatively small height (about 1.5 * diameter)
needed to achieve complete combustion of the diffusion flame is not too
much of a hardship. For large diameters it is also necessary to bring in
central secondary air to keep this chimney height low.

11. Tom Reed also had a Sunday message on nomenclature. After a
considerable effort at a more lengthy response I have decided that my
central stove issue is the co-production of charcoal. I canÕt see that
the terms ÒinversionÓ or Òco-currentÓ help stove users to visualize what
is happening in a batch charcoal-making operation. I must therefore for
awhile longer use the term Òcharcoal-making cookstoveÓ when referring to
what I am trying to do.
Gasification is possibly helpful; certainly it has a charcoal
phase or charcoal (physical) level - but consuming that charcoal (is this
a part of all gasification?) in the same stove envelope doesnÕt seem to
me to be the best approach to solving the noxious gas problem -
especially when done with a single air supply.

12. Re the Hottenroth stoves. There are several aspects of these worth
noting. The air supply is controlled in all models through several types
of clever flaps or rotating shutters. This (controllable) volume of air
is circulated (fan-forced or natural convection) all the way upwards
through an outermost cylindrical channel and then back downward through
an immediately interior cylindrical channel to a thin cylindrical
lowermost entry slit. Fuelwood can be entered only from the top, after
removing the cookpot.
This set of three concentric metal layers reduces radiative
losses and the double air pass pre-heats the combustion air and reduces
losses. Although this air is not separated into primary and secondary
components, top lighting can achieve some charcoal making - with
secondary air sneaking in over the top. No mention is made in the
Z-Stove patent or literature of charcoal-making.

13. Sorry for mixing so many thoughts together. I tried to be
succinct. This is as tough a topic to understand as any I have ever
worked on. We should expect to spend some time understanding each
otherÕs views and concerns and backgrounds that will be helpful.
Cheers. Ron

ps - please excuse the (Mac?) replacement of " with R or S.

 

From 73002.1213 at compuserve.com Thu Oct 10 00:43:17 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:35:01 2004
Subject: Efficiency?
Message-ID: <961010044505_73002.1213_FHM53-4@CompuServe.COM>

Grant, Etiaenne et al:

Last week Etienne and I agreed that if we can't make one quantum jump in stoves
we should pack it in and do something more useful. We did not completely define
this, but it should included cooking in my wife's kitchen without smell. (Did
this once.)

We also agreed that 2 quantum leaps would be better. Maybe this would require
that my wife throw out her electric stove and use the new stove forever. We
havn't reached this stage. Maybe this is too severe a test.

Cheers, TOM REED

 

 

From rmiranda at sdnnic.org.ni Thu Oct 10 10:48:44 1996
From: rmiranda at sdnnic.org.ni (Rogerio Carneiro de Miranda)
Date: Tue Aug 31 21:35:01 2004
Subject: Efficiency
Message-ID: <199610100853.IAA02786@ns.sdnnic.org.ni>

Hi stovers:

sorry for the dummy question. I am just a forester with no background in
combustion, et al. But I am trying to understand what you all mean, when you
are saying that improved stoves are less efficient in combustion, but more
in heat transfer. why?
I would assume that it happens because when you enclose the fire, there is
less O2, what results in an unperfect combustion. is that right ?

If in an improved stove you get more heat transfer, it means that you will
demand less fuel, and so less fuelwood ?

In PROLENA's project of promoting improved stoves in Tegucigalpa, we just
did a literature review of woodstoves models and decide for one model that
claimed 30% fuel reduction and was easy and cheap to build. So, with the
community we are telling them that the stove wich we promote will save them
money (buying less fuel) and also contaminate less inside their home with
the use of a chimney. I wonder now (from what you are saying) if the air
quality in the community is worse now than before, and if at least we
reduced individuals exposure to woodsmoke?

DUMMY's TABLE

STOVE COMBUSTION EFFICIENCY HEAT TRANSFER AIR POLUTION kg/kj

traditional 85% 15% x z

improved <85% 30% >x <z

 

Is there any book titled WOODSTOVE FOR DUMMIES ?

thanks

rogerio
--------------------------------------------------------------------------
Rogerio Carneiro de Miranda Telefax: (505) 276 0555
PROLENA(Nicaragua) Managua Nicaragua
E-mail: rmiranda@sdnnic.org.ni
-------------------------------------------------------------------------

 

 

From E.Moerman at stud.tue.nl Thu Oct 10 14:30:26 1996
From: E.Moerman at stud.tue.nl (E.Moerman)
Date: Tue Aug 31 21:35:01 2004
Subject: Efficiency?
Message-ID: <74166.s335192@popserver.tue.nl>

A few answers and comments to Grant:

(snip)
> Etienne wrote:
> (snip)
>
>>WSG in Eindhoven uses a slightly different method, which gives more stable
>> results. More about it later.
>>
> (snip)
>
> Yes more info please Etienne.

(snip)

Ok. In our efficiency determination the reasoning is that we try to improve
the heat transfer to the pan. The fact that part of the water in the pan
evaporates is of no consequence to the heat transfer to the pan (of course
in the actual cooking process it would be a loss and a lid should be used).
The advantage of not considering the evaporation as water is that there is a
negligible difference between a test with and without a lid, see Bussmann's
thesis. Of course this is a lab test and only determines the heat transfer
efficiency to the pan. For the actual cooking task simmering periods often
occur and different types of food (preparation) require different cooking
operations. Since these vary greatly Specific Consumption figures should be
determined for different types of food. However even than large differences
occur since some people like to overcook their meals and others like to
undercook them. Also fuel, moisture content, charging habits, etc. have an
influence. To conclude our lab test is about the only one that leads to more
or less reproducable results.

Yesterday I saw a program on the determination of exhaust levels of cars and
this made me think. The situation between cars and stoves is very similar in
both cases there is a discrepency between lab and field results. The way
they solve this in cars is to let a car in the lab perform according to a
fixed plan. Say go from 0 to 40 in 10 sec. than change to 2nd gear. Go to 60
go to 3rd gear after 80 sec. Go stationary for 2 min. etc. This would be
more or less representative for an average commuter and could give some
indications for the actual performance. I think we should do something like
this for stoves for both efficiency and emissions. It would be far more
detailed than any existing stove efficiency measurement. I would suggest
that 3 or 4 people come up with a suggested test programme. Of course others
could forward any views on it before hand and when the suggested test
programme is presented.

> (snip)
>
>>As we at Eindhoven have been saying for a long time the turn-down
>> ratio is probably more important than the efficiency.
>>
> (snip)
>
> Which is one of the distinct advantages of an open fire...
>
(snip)

I agree with Grant here. The open fire is so versatile and cheap that most
if not all stove dissimenation programs failed.

> (snip)
>
>>For the shielded fire we measured a 50% efficiency for one type of shielded
>> fire in the lab and easily over 40% efficiency for other versions.
>>
> (snip)
>
> Remember you use a different definition of efficiency from me? How does it
> compare to an open fire measured in the same way - that, I think, is what
> counts.
>
> (snip)

Open fire, with well tended fire. Around 25%.

> Yes, I like these ideas and would like to see them. I will only be able to
> visit you much later in the year though. This type of stove is possibly part

You are welcome any time.

Etienne
---------------------------------------------
Mr. Etienne Moerman E.Moerman@stud.tue.nl
Joh. Buyslaan 71 tel. +31-40-2571491
5652 NJ EINDHOVEN The Netherlands

 

From E.Moerman at stud.tue.nl Thu Oct 10 14:30:18 1996
From: E.Moerman at stud.tue.nl (E.Moerman)
Date: Tue Aug 31 21:35:01 2004
Subject: Shoes, ships and sealing wax
Message-ID: <74163.s335192@popserver.tue.nl>

Dear Tom

> The riser sleeves are made from similar spun alumino-silicate fibers,
> chopped short and slurried with starch, then molded on a vacuum screen. (I
> don't think yours were Al2O3.) John Tatom was actually in that business

I am sure ours were Al2O3, since I ordered them myself and they had nothing
else available at that time and place.

> for a while. You should be able to find them in any city large enough to
> have casting shops. They will stand molten iron temperatures. Cost about
> $3 retail.

I still did not have the time to look for the riser sleeves. Maybe later.

Greeting

Etienne
---------------------------------------------
Mr. Etienne Moerman E.Moerman@stud.tue.nl
Joh. Buyslaan 71 tel. +31-40-2571491
5652 NJ EINDHOVEN The Netherlands

 

From larcon at csn.net Thu Oct 10 17:34:41 1996
From: larcon at csn.net (Ronal Larson)
Date: Tue Aug 31 21:35:01 2004
Subject: Shoes, ships and sealing wax
In-Reply-To: <74163.s335192@popserver.tue.nl>
Message-ID: <Pine.3.89.9610101525.A20457-0100000@teal.csn.net>

 

I have had a little experience with these riser sleeves that may be of
some help. They are excellent at low temperatures but the organic binder
can outgas and burn at elevated temperatures. They then are quite soft
and I fear will not have much life in a rural situation. If used in a
high temperature application, I think they will have to be coated in some
other high temperature way. I tried but my first test didn't work.

Ron Larson

On Thu, 10 Oct 1996, E.Moerman wrote:

> Dear Tom
>
> > The riser sleeves are made from similar spun alumino-silicate fibers,
> > chopped short and slurried with starch, then molded on a vacuum screen. (I
> > don't think yours were Al2O3.) John Tatom was actually in that business
>
> I am sure ours were Al2O3, since I ordered them myself and they had nothing
> else available at that time and place.
>
>
> > for a while. You should be able to find them in any city large enough to
> > have casting shops. They will stand molten iron temperatures. Cost about
> > $3 retail.
>
> I still did not have the time to look for the riser sleeves. Maybe later.
>
>
> Greeting
>
> Etienne
> ---------------------------------------------
> Mr. Etienne Moerman E.Moerman@stud.tue.nl
> Joh. Buyslaan 71 tel. +31-40-2571491
> 5652 NJ EINDHOVEN The Netherlands
>

 

 

From verhaarp at janus.cqu.edu.au Thu Oct 10 18:01:11 1996
From: verhaarp at janus.cqu.edu.au (Peter Verhaart)
Date: Tue Aug 31 21:35:01 2004
Subject: Future of stoves
Message-ID: <9610102204.AA05146@janus.cqu.edu.au>

 

To all stovers,

We have been talking about woodburning cookstoves for decades and where has
it got us? Smoke and tar and
soot and heat transfer efficiencies in the 20's (percent).
What did we do wrong?
Not enough irreverence?
We talk about pre-mixed flames but how can we realise that? No constant
supply of gas, no constant
composition of gas and no means of supplying the air where we want it.
The great charm of the downdraft or J-stove is that we went against nature
and against tradition.
What is wrong with it? Plenty, it needs great care in tending and the
problem is where to tap the heat.
It has however proved a point. You get good combustion and high tempertures
if you can keep the combustion
confined to a thin layer of fuel.
That is probably what happens in the Jet stove (or some other name), in
which a single log is burned. From the
description I gathered that the log is in a more or less vertical position
and rests on a porous ceramic base. It
is not clear where the air comes from. It could come from above and pass
along the log, its velocity preventing
the combustion zone from travelling upward faster than the bottom end is
consumed.
Having the combustion at the bottom end provides a simple means to feed the
fuel. The bad news is that hot
gases tend to rise and may cause premature pyrolysis of the fuel.
One could think of feeding the combustion air through the base where it
contacts the burning char before
wending its way downward where volatiles mix with it and burn up. We have
discussed this idea in Eindhoven
under the title "Quick dip stove", or "Blowing grate stove", but it didn't
get beyond talk. During part of our trip
to Tasmania May last year, we had the good luck to stay in a cottage owned
by a stove builder. With thus my
interest in stoves rekindled, I have started to build a ventilated grate
stove, but the work progresses very slowly.
The idea is to use it outside during the winter as a source of heat and a
barbecue. If it works!
Another way would be to feed the fuel in an upward direction to where air
flows over the burning layer of fuel,
this happens to some extent in Fred Hottenroth's Sierra stove and, in a
slightly more controlled way in my
recently finished Jak stove. With this arrangement convective heat transfer
to unburnt fuel would be less of a
problem.

Diffusion flames aren't all bad. Look at the match and the candle. What do
they have in common? They are both
very small so that in the end enough air can get through to the gases to
burn them. In larger diffusion flames
there is too little relative surface area for timely diffusion of air to
where it is needed and the result is soot and
smoke. So, if we must live with diffusion flames, then let them be small in
size and great in number. If you
make the flames small enough they won't even be luminous.

I think the only way we can make any progress is by coming up with something
radically different, something
nobody has yet thought of. Wild, scientific analysis comes later.
Thermocouples for generating electricity for driving a tiny ventilator
(cooling fans for computer chips are sold
for 8 A$ here). Once we have something that works we can think of ways to
reduce costs.

I am not against making charcoal but it is not a great priority of mine.
None of a stove's performance should
be sacrificed for making charcoal. If the only way a stove can work properly
is when making charcoal, well and
good. So far I haven't seen a performance of a charcoal making stove that is
superior to the downdraft stove
for attainable high temperatures and clean combustion. I think the idea of
confining combustion to a thin layer
of fuel is a sound one. The hard part is to implement it.

So much for now. It is said progress is born from dissatisfacion with
existing conditions. Of that there is plenty.
Looking forward in anger.
Cheers
Piet Verhaart

 

 

From B.Tremeer at mail1.remote.uva.nl Fri Oct 11 03:24:51 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:01 2004
Subject: Efficiency
Message-ID: <199610110721.IAA07923@mail.uva.nl>

Dear Rogerio

Your question isn't a 'dummy' question at all. You have understood exactly
what we have been saying (or trying to say).

Yes, there is a danger that an improved stove will have greater emissions
than an open fire. I have not been saying that *all* improved stoves will
have greater emissions, though. Your stove may increase or decrease
emissions but the only way to tell is to measure them. You say it has a
chimney, which is good - at least the combustion gases are being removed
from the dwelling, but, depending on the climate these gases may be trapped
in a temperature inversion and so people may still be exposed to them.

Your table is almost right - but the column "Heat transfer" should be
relabelled "Overall efficiency" (and take care not to confuse fuel saving
with efficiency). The value most people use for efficiency (if they claim a
25% efficiency say) is combined heat transfer and combustion efficiency
because it is *VERY* difficult to measure them separately.

If anyone finds that book, I would like a copy too.
Grant

At 08:53 10-10-96 GMT, you wrote:
>Hi stovers:
>
>sorry for the dummy question. I am just a forester with no background in
>combustion, et al. But I am trying to understand what you all mean, when you
>are saying that improved stoves are less efficient in combustion, but more
>in heat transfer. why?
>I would assume that it happens because when you enclose the fire, there is
>less O2, what results in an unperfect combustion. is that right ?
>
>If in an improved stove you get more heat transfer, it means that you will
>demand less fuel, and so less fuelwood ?
>
>In PROLENA's project of promoting improved stoves in Tegucigalpa, we just
>did a literature review of woodstoves models and decide for one model that
>claimed 30% fuel reduction and was easy and cheap to build. So, with the
>community we are telling them that the stove wich we promote will save them
>money (buying less fuel) and also contaminate less inside their home with
>the use of a chimney. I wonder now (from what you are saying) if the air
>quality in the community is worse now than before, and if at least we
>reduced individuals exposure to woodsmoke?
>
>
>DUMMY's TABLE
>
>STOVE COMBUSTION EFFICIENCY HEAT TRANSFER AIR POLUTION kg/kj
>
>traditional 85% 15% x z
>
>improved <85% 30% >x <z
>
>
>
>Is there any book titled WOODSTOVE FOR DUMMIES ?
>
>thanks
>
>
>rogerio
>--------------------------------------------------------------------------
>Rogerio Carneiro de Miranda Telefax: (505) 276 0555
>PROLENA(Nicaragua) Managua Nicaragua
>E-mail: rmiranda@sdnnic.org.ni
>-------------------------------------------------------------------------
>
>
>

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From E.Moerman at stud.tue.nl Fri Oct 11 07:55:57 1996
From: E.Moerman at stud.tue.nl (E.Moerman)
Date: Tue Aug 31 21:35:01 2004
Subject: Multiple topics
Message-ID: <50502.s335192@popserver.tue.nl>

Ron Larson- Your message came through quite battered and hard to read.
However an answer to question =099.

> =099. Responding to Skip Hayden in his =D2 Re[2]: Efficiency=D3. Skip=20
> noted: =D2........ Reducing excess air also lowers mass flow through the=20
> system and generally improves the ability of the system to extract heat=20
> from the flue gases - hence the reason that it has been mixed up with the=
> =20
> heat transfer efficiency, although it is better thought of as improving=20
> combustion.=D3
> =09Response: This suggestion is very helpful (and almost never=20
> measured or discussed). Based on Eindhoven comments on CO production, I=20
> have been assuming that an exhaust plume with about equal parts O2 and=20
> CO2 would be correct - and I found approximately this in our only such=20
> test so far. Any disagreement that 10-11% each would be a desirable=20
> goal (assuming this is accompanied by negligible CO and particulates)? =20
> =09Skip - In large systems, where excess air may be worth=20
> monitoring, what do they strive for? How do they measure it?

I don't know how you came up with the suggestion from Eindhoven. Assuming
good combustion quality is desired we would want a O2% between 5-9% in the
downdraft stove. Obviously for efficiency reasons you would want to be
between 5-6%. Translating this into excess air 1.3-2.3 with an optimum
around 1.8 for combustion quality and 1.5 still very good and more
efficient.

Etienne
---------------------------------------------
Mr. Etienne Moerman E.Moerman@stud.tue.nl
Joh. Buyslaan 71 tel. +31-40-2571491
5652 NJ EINDHOVEN The Netherlands

 

From B.Tremeer at mail1.remote.uva.nl Fri Oct 11 08:00:35 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:01 2004
Subject: Open fire turn down ratio
Message-ID: <199610111157.MAA11030@mail.uva.nl>

I was discussing earlier:
>(snip)
>
>>As we at Eindhoven have been saying for a long time the turn-down
>> ratio is probably more important than the efficiency.
>>
>(snip)
>
> Which is one of the distinct advantages of an open fire...
>
>(snip)

Actually I must correct myself about the open fire. I found in my tests that
an open fire can indeed be operated at a very low power, but it was
ineffective for cooking (or maintaining a water temperature) at these
powers. The effective turn-down ratio was infact quite small. A stove on the
other hand could be operated at lower powers and still be effective (only
once it was hot, though).

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From bhatta at ait.ac.th Fri Oct 11 08:05:56 1996
From: bhatta at ait.ac.th (Prof. S.C. Bhattacharya)
Date: Tue Aug 31 21:35:01 2004
Subject: Hampton Jetstream
Message-ID: <Pine.GSO.3.94.961011185854.24651A-100000@rccsun>

 

Can any body provide the address (Postal, fax or email) of Parrsboro
Metals, Nova Scotia who are supposed to be producing the clean wood
burning systems? We need the address rather urgently.

S.C. Bhattacharya

-------------------------------------------------------------------
S. C. Bhattacharya Voice : (66-2) 524 5403 (Off)
Professor 524 5913 (Res)
Asian Institute of Technology Fax : (66-2) 524 5439
GPO Box 2754, Bangkok 10501 516 2126
Thailand e-mail: bhatta@ait.ac.th
-------------------------------------------------------------------

 

 

From tmiles at teleport.com Fri Oct 11 11:18:22 1996
From: tmiles at teleport.com (Tom Miles)
Date: Tue Aug 31 21:35:01 2004
Subject: WWW archive
Message-ID: <2.2.32.19961011152017.0074103c@mail.teleport.com>

Stovers,

While you may not realize it Stoves@crest.org is archived at CREST at

http://solstice.crest.org/renewables/stoves-list-archive/index.html

We just need to add the link to the CREST homepage and other related sites.
We should make a Stoves topical homepage that links to the archive and other
sites. IF someone would like to provide a reasonably orgnized content I can
do the HTML. We can use it to present images of stove designs or ftp
reference files. It might be especially useful to refer people to to cover
topics that we have already worked over on the list.

Tom


----------------------------------------------------------------------------
-------
Tom Miles, Jr. Thomas R. Miles
tmiles@teleport.com, tmiles@ortel.org Consulting Design Engineer
http://www.teleport.com/~tmiles/ 5475 SW Arrowwood Lane
Tel (503) 591-1947 Fax (503) 292-2919 Portland, Oregon, USA 97225-1353

 

 

From gayathri at aero.iisc.ernet.in Fri Oct 11 11:37:40 1996
From: gayathri at aero.iisc.ernet.in (Gayathri)
Date: Tue Aug 31 21:35:01 2004
Subject: Hampton Jetstream
Message-ID: <9610120208.AA29447@aero.iisc.ernet.in>

 

 

From verhaarp at janus.cqu.edu.au Fri Oct 11 17:46:27 1996
From: verhaarp at janus.cqu.edu.au (Peter Verhaart)
Date: Tue Aug 31 21:35:01 2004
Subject: Hampton Jetstream
Message-ID: <9610112150.AA19487@janus.cqu.edu.au>

There might be something wrong. I only received the heading Re: Hampton
Jetstream. Was there more?
Piet Verhaart

 

 

From skip.hayden at cc2smtp.NRCan.gc.ca Fri Oct 11 18:26:50 1996
From: skip.hayden at cc2smtp.NRCan.gc.ca (Skip Hayden)
Date: Tue Aug 31 21:35:01 2004
Subject: Hampton Jetstream
Message-ID: <9609118450.AA845083822@cc2smtp.nrcan.gc.ca>

Kerr Controls or Parrsboro Metals (their manufacturing arm)
are located in Parrsboro Nova Scotia.

I'll send you their telephone number and address when I get
back to the lab next Tuesday.

Skip Hayden

 

 

From E.Moerman at stud.tue.nl Sat Oct 12 08:54:09 1996
From: E.Moerman at stud.tue.nl (E.Moerman)
Date: Tue Aug 31 21:35:01 2004
Subject: Efficiency
Message-ID: <53990.s335192@popserver.tue.nl>

To all who want a book which covers the basics of a woodstove.

At Eindhoven we have written a book called

A Woodstove Compendium

We still have plenty of copies available, so if anybody is interested let me
know. I think Prasad will not mind if I say that copies are available for
free.

Etienne
---------------------------------------------
Mr. Etienne Moerman E.Moerman@stud.tue.nl
Joh. Buyslaan 71 tel. +31-40-2571491
5652 NJ EINDHOVEN The Netherlands

 

From prasad at tn7.phys.tue.nl Sun Oct 13 12:52:10 1996
From: prasad at tn7.phys.tue.nl (prasad)
Date: Tue Aug 31 21:35:01 2004
Subject: Efficiency
In-Reply-To: <53990.s335192@popserver.tue.nl>
Message-ID: <9610131646.AA21687@tn7.phys.tue.nl>

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From 73002.1213 at compuserve.com Thu Oct 17 03:32:01 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:35:01 2004
Subject: Charcoal, yes or no?
Message-ID: <961017073143_73002.1213_FHM31-11@CompuServe.COM>

Stovers &Gasifiers all: (Strassburg station, 2
AM, Tues. 10/15/96)

Charcoal is the oldest "synthetic fuel" developed by humans and has been made
for at least 10,000 years. No charcoal = no bronze or iron age, no civilization
as we know it. However, it's use in industrial countries has slipped primarily
to recreational use in barbecues and chemical uses. In many developing
countries it is still the fuel of choice.

The classical manufacture of charcoal is very inefficient. The typical yield,
energy basis is 20-40% of the value of the wood or biomass. The rest goes up in
polluting smoke. In special units the "smoke" was condensed to give methanol,
acetic acid, acetone and many other chemicals up to about 1950. However, these
are all made much more cheaply now from petroleum. So a Developing Country*
charcoal kiln is also a major source of pollution.

It is easy to make a gasifier to operate on charcoal, and at the beginning of
World War II most gas generators used charcoal. However, the forest was
disappearing so fast that techniques were developed to use whole (<20% moisture)
wood. Our inverted downdraft stove cooks with the vapor and makes charcoal.

Speaking personally, I find cooking with charcoal a great nuisance. It is hard
to light, hard to control once lit, and continues to burn many hours after the
food is cooked. So, when we developed the inverted downdraft gasifier that
produces 25% charcoal, I considered that feature to be a drawback. But my
partner, Harry LaFontaine, considered it to be a positive feature and now Ron
Larson also thinks so.

Visiting Prasd and Moerman last week, they both expressed the opinion that
making charcoal was dirty and wasteful and should not be encouraged.

SO MUCH FOR DEVELOPED COUNTRIES*

In many developing countries, charcoal is the fuel of choice. Ron Larson
contacted me in 1993 and asked if I knew any way to cook with the volatiles and
make charcoal. I said, unfortunately yes. We have continued to develop this
stove and it is an excellent charcoal producer. (Most third world charcoal
making is lucky to reach 20% efficiency.) In larger size it could be good for
baking, brickmaking etc. with charcoal as the byproduct.

And Mike Antal now has a process that makes 40-45% charcoal. I think it could
be practical.

So we have here the making of a fine debate - should be proceed to help make
charcoal in developing countries in our more efficient fashion or should we try
to modify the stove to use ALL the fuel for cooking.

Opinions? TOM REED

* I hate the term "Developing Countries". It sounds somewhat patronizing. It
also seems to imply that Europe and the US are "Developed" and won't change. In
fact, I suspect India will "pass up" the developed countries in 2096 - they are
smarter and work harder and are more democratic - and bigger. China will follow
a few generations later. Does anyone have a better term?

Mike: Where are you? Where is your charcoal process?

 

 

From antal at wiliki.eng.hawaii.edu Thu Oct 17 14:00:28 1996
From: antal at wiliki.eng.hawaii.edu (Michael Antal)
Date: Tue Aug 31 21:35:01 2004
Subject: Charcoal, yes or no?
In-Reply-To: <961017073143_73002.1213_FHM31-11@CompuServe.COM>
Message-ID: <Pine.HPP.3.95.961017075721.22032B-100000@wiliki.eng.hawaii.edu>

Dear Tom: thanks for your message. Actually, we achieve yields of 41 to
62% charcoal, depending on the feedstock. We have recently learned how to
make high-yield activated carbons from biomass and realize yields of 25 to
30% of a good quality activated carbon based on the dry weight of the raw
biomass feedstock. So we get higher yields of activated carbon than
industry usually gets of charcoal. The charcoal you cook with must be the
cheap Kingsford variety made from coal. Real charcoal burns vigorously in
a good grill with underfire air. Concerning our status: I have a business
plan and am prepared to invest $25,000 of my own money in the production
of macadamia nut shell charcoal (and activated carbons). We are operating
our pilot plant to test the market. I hope that once the market is
established, a macadamia nut factory will partner with me. Maybe you'd
like to invest in a good cause? Have a safe journey. Best regards,
Michael.

 

 

From larcon at csn.net Fri Oct 18 23:42:04 1996
From: larcon at csn.net (Ronal Larson)
Date: Tue Aug 31 21:35:01 2004
Subject: Charcoal, yes or no?
In-Reply-To: <961017073143_73002.1213_FHM31-11@CompuServe.COM>
Message-ID: <Pine.3.89.9610182105.A14081-0100000@teal.csn.net>

 

Following up on Tom Reed's request yesterday to further discuss charcoal.

First, thanks to Mike Antal for sticking up for charcoal. I am no
expert on using charcoal - but I have rarely seen smoke and fumes when I
use it or when watching it be used by skilled usrs. I have never seen
problems in starting it (by third world cooks) - but, like Tom, I also
have had problems. These are certainly true with the "Kingsford coal"
type - but also when using small pieces or my own home-made briquettes.

Mike - you have not (I think) heard the stoves list's recent
discussion on the health impacts of cookstoves. Do you have any special
information on this subject - perhaps especially relative to CO? My
perception is that there is a decided health improvement in charcoal
stoves over wood stoves.

I understand one reason why Prasad and Etienne should have an
aversion to charcoal - its present wasteful method of manufacture. But
if charcoal is captured as a byproduct of a cooking process that is much
more healthful, with high efficiency, then I don't understand this aversion.

The thousands of years of charcoal production and willlingness to
pay more than twice as much for cooking a meal should be a good
indication that charcoal has some merit. Can anyone explain it on any
basis other than reduced smoke and reduced time in tending?

One experiential caution and admission. I gave some of my old
scrap charcoal (including brands) to a needy local Ethiopian family -
thinking of barbecue use only. When they used it indoors for making
coffee, it was certainly not satisfactory - even setting off an alarm. I
now need to get the wife to try some that at least looks good to me.
Developing country (the World Bank uses this term - so I think we can
also) charcoal producers undoubtedly know how to get the right (on
average) amount of residual gases in the charcoal to balance off smoke
and ease of starting. Maybe when I have their experience, I'll know
also. Does anyone know of any simple tests that knowledgeable buyers use
to select pieces that fit their own cooking needs?

Ron Larson

 

From kammen at phoenix.Princeton.EDU Sat Oct 19 00:07:35 1996
From: kammen at phoenix.Princeton.EDU (Daniel M. Kammen)
Date: Tue Aug 31 21:35:01 2004
Subject: No Subject
Message-ID: <v01530535ae8dc9b72200@[128.112.44.150]>

In response to:

>Is there any book titled WOODSTOVE FOR DUMMIES ?
>
>thanks
>
>
>rogerio
>--------------------------------------------------------------------------
>Rogerio Carneiro de Miranda Telefax: (505) 276 0555
>PROLENA(Nicaragua) Managua Nicaragua
>E-mail: rmiranda@sdnnic.org.ni
>-------------------------------------------------------------------------

I would recommend:

S. Joseph, K. K. Prasad, and H. B. van der Zaan "Bringing stoves to the people"
(Foundation for Woodstove dissemination: Nairobi, Kenya).

KENGO (1991) "How to make and use the Kenya Ceramic Jiko (KCJ), (Nairobi,
Kenya).

Sam F. Bsldwin (1986) "Biomass stoves: Engineering desing, development, and
dissemination" (Volunteers in Technical Assistance: Arlington, VA USA) and
Center for Energy and Env. Studies: Princeton University, Report #224).

 

 

 

From E.Moerman at stud.tue.nl Mon Oct 21 10:15:36 1996
From: E.Moerman at stud.tue.nl (E.Moerman)
Date: Tue Aug 31 21:35:01 2004
Subject: Charcoal, yes or no?
Message-ID: <58835.s335192@popserver.tue.nl>

Following up Ron Larson's discussion of charcoal.

Ron writes:
> First, thanks to Mike Antal for sticking up for charcoal. I am no
> expert on using charcoal - but I have rarely seen smoke and fumes when I
> use it or when watching it be used by skilled usrs. I have never seen
--------

My comment:

This is very true. Smoke and fumes are generally not to be seen nor smelled.
However if you measure the CO emissions as we did, you notice that they are
very high. In fact higher than the CO emissions from ordinary wood. While
these CO emissions are not observable to the user, the user gets a false
sense of security. As far as charcoal is concerned this really is a silent
killer.

Regarding the charcoal production:
So far I have not heard how much wood you need for a specific cooking task
and how much charcoal is produced. Prasad and I have the impression that you
will use more wood, in fact so much so that your overall efficiensy is less
than an ordinary woodstove that burns the charcoal during the simmering
period.

Etienne
---------------------------------------------
Mr. Etienne Moerman E.Moerman@stud.tue.nl
Joh. Buyslaan 71 tel. +31-40-2571491
5652 NJ EINDHOVEN The Netherlands

 

From antal at wiliki.eng.hawaii.edu Mon Oct 21 13:57:02 1996
From: antal at wiliki.eng.hawaii.edu (Michael Antal)
Date: Tue Aug 31 21:35:01 2004
Subject: Charcoal, yes or no?
In-Reply-To: <Pine.3.89.9610182105.A14081-0100000@teal.csn.net>
Message-ID: <Pine.HPP.3.95.961021075832.5551C-100000@wiliki.eng.hawaii.edu>

Dear Ron: concerning emissions from stoves: I suppose that you know Kirk
Smith (formerly of the EWC, now Berkeley)? He is the expert on such
matters. Regards, Michael Antal.

 

 

From larcon at csn.net Mon Oct 21 21:27:30 1996
From: larcon at csn.net (Ronal Larson)
Date: Tue Aug 31 21:35:01 2004
Subject: Charcoal, yes or no?
In-Reply-To: <58835.s335192@popserver.tue.nl>
Message-ID: <Pine.3.89.9610211908.A10463-0100000@teal.csn.net>

 

Comments below -

On Mon, 21 Oct 1996, E.Moerman wrote:

> Following up Ron Larson's discussion of charcoal.
>
>
> Ron writes:
> > First, thanks to Mike Antal for sticking up for charcoal. I am no
> > expert on using charcoal - but I have rarely seen smoke and fumes when I
> > use it or when watching it be used by skilled usrs. I have never seen
> --------
>
> My comment:
>
> This is very true. Smoke and fumes are generally not to be seen nor smelled.
> However if you measure the CO emissions as we did, you notice that they are
> very high. In fact higher than the CO emissions from ordinary wood. While
> these CO emissions are not observable to the user, the user gets a false
> sense of security. As far as charcoal is concerned this really is a silent
> killer.
>
> I have to pass on this - I have made no measurements. I will
reread Kirk Smith's material - but believe that he has not found it to be
as bad.

Mike Antal - were you suggesting that CO should not be a problem
with adequate air flow?

Anyone -Is there a law of nature that says that CO production
must be high with a charcoal-burning stove.

> Regarding the charcoal production:
> So far I have not heard how much wood you need for a specific cooking task
> and how much charcoal is produced. Prasad and I have the impression that you
> will use more wood, in fact so much so that your overall efficiensy is less
> than an ordinary woodstove that burns the charcoal during the simmering
> period.
>
>
A few weeks ago, I suggested an overall efficiency of 2/3 from 1/3
energy in the charcoal, 1/3 captured, and 1/3 lost. I have not achieved
this, but believe it is possible with care in design. My efforts have so
far been directed in other directions. If this were possible, I believe
the efficiency would be higher than in the "ordinary stove that burns the
charcoal". There are several reasons for believing this. First, the
combustion efficiency should be much higher; Kirk Smith is finding about
11% loss due to poor combustion. Second, the control of the primary air
allows a large turn-down ratio - which you have pointed out is key to high
efficiency. Third, I have not found a way to get the burning charcoal as
close to the pot as is necessary for high efficiency. I believe the
charcoal must combust from the bottom and therefore radiation is very
inefficient.

Anyone else?

Ron

 

 

From 73002.1213 at compuserve.com Tue Oct 22 02:12:09 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:35:01 2004
Subject: Rumford, Altimira
Message-ID: <961022061359_73002.1213_FHM48-1@CompuServe.COM>

Hi!

All work and no play makes Tom a dull boy. I arrived in Munich at noon Sunday
and my plane wasn't until 7, so I looked at the map, what to do.

You may remember that Ron Larson and I recommended strongly the collected works
of Benjamin Thompson, Lord Rumford (Sandford Brown, Harvard Press?). He has
more understanding of stoves than anyone I have yet seen on the stove net. He
was the right hand man of the King of Bavaria 1790-1810 and made many changes
there and many of his most important discoveries there. I was delighted to find
the "Englische Gartens", founded by Rumford in walking distance of the station.

I was more delighted to find the Rumford Schloww (castle) there. The day before
I had visited the King Ludwig schlosses, Linderhof and Neuschwanstein. The
Rumford Schloss is very modest by comparison, but there it was in the Garten.

The largest technical museum in the world is the Deutsch museum, so I went there
next. A wonderful museum, too big to see in a week, let alone my 3 hours.
However, they have a full scale reproduction of the cave paintings at Altimira
that thrilled me. But I didn't find anything on gasifiers and not much on
stoves.

Put these on your list to see next time you are in Muensch.

Regards, TOM REED

 

 

From aellegaard at nn.apc.org Tue Oct 22 02:54:52 1996
From: aellegaard at nn.apc.org (aellegaard@nn.apc.org)
Date: Tue Aug 31 21:35:01 2004
Subject: Charcoal, yes or no?
Message-ID: <199610220758.HAA08310@nn.apc.org>

I have actually carried out surveys in two intensely charcoal-using
cities in Africa, Lusaka and Maputo. I found emission to particulates
for charcoal users to be intermediate between electricity and wood users,
but CO exposures reoughly the same. From the health point of view there
was no difference between electricity and charcoal users, but wood users
were worse off. It seems charcoal would be a viable medium-term alternative
from these points of view. Lusaka details were reported in Energy Policy
vol 23 (1993), Maputo results in Environmental Health Perspectives Sept.
issue this year.
Carbon monoxide from charcoal becomes a problem, I believe, especially
when it is used for heating in the night (See Energy for Sustainable
Development 2(2) July 1995). Exposure during cooking time is around the
tolerable limit of 25 ppmh (ppm times hours).
Regards
Anders

 

From B.Tremeer at mail1.remote.uva.nl Tue Oct 22 08:07:39 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:01 2004
Subject: Charcoal, yes or no?
Message-ID: <1.5.4.32.19961022131126.0069ddcc@mail.uva.nl>

At 07:31 PM 10/21/96 -0600, Ron wrote:
> I have to pass on this - I have made no measurements. I will
>reread Kirk Smith's material - but believe that he has not found it to be
>as bad.
>
> Mike Antal - were you suggesting that CO should not be a problem
>with adequate air flow?
>
> Anyone -Is there a law of nature that says that CO production
>must be high with a charcoal-burning stove.

In my tests, the char burning phase of combustion did not have significantly
greater CO formation than during the flaming stage (at the same burn rate).
The relationship between smoke and CO during any stage depends on the type
of stove: It is true that CO could be formed without much smoke and
visa-verse. Char can burn in a smoldering or glowing manner (depending on
the temperature and amount and 'access' of oxygen). With glowing combustion,
char combustion can occur with very low (potentially zero) CO and smoke, I
believe.

Ron, your comments about the efficiency sound reasonable, but remember that
we are all talking about something different when we say efficiency. When
you do measurements I suggest you test another stove (say an open 'three
stone' fire) in the same way, which you can use in comparison. This would
make your figure somewhat more useful (Besides the beneficial experience of
cooking the way most of the world does every day - I learned a lot!).

I would prefer burn rate control (hence fire power) to come from fuel feed
rate rather than primary air. Starving a fire of air could increase
emissions - this would need to be tested...

All the best,
Grant

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From larcon at csn.net Tue Oct 22 11:52:12 1996
From: larcon at csn.net (Ronal Larson)
Date: Tue Aug 31 21:35:01 2004
Subject: Charcoal, yes or no?
In-Reply-To: <1.5.4.32.19961022131126.0069ddcc@mail.uva.nl>
Message-ID: <Pine.3.89.9610220911.A22807-0100000@teal.csn.net>

 

Comments interspersed below (on just a part of the original)

On Tue, 22 Oct 1996, Grant Ballard-Tremeer wrote:

> At 07:31 PM 10/21/96 -0600, Ron wrote:

> In my tests, the char burning phase of combustion did not have significantly
> greater CO formation than during the flaming stage (at the same burn rate).
> The relationship between smoke and CO during any stage depends on the type
> of stove: It is true that CO could be formed without much smoke and
> visa-verse. Char can burn in a smoldering or glowing manner (depending on
> the temperature and amount and 'access' of oxygen). With glowing combustion,
> char combustion can occur with very low (potentially zero) CO and smoke, I
> believe.

Grant - could you describe a little more on the characteristics of the
stove that gave glowing combustion. What negative aspects come from
these tradeoffs?

>
> Ron, your comments about the efficiency sound reasonable, but remember that
> we are all talking about something different when we say efficiency. When
> you do measurements I suggest you test another stove (say an open 'three
> stone' fire) in the same way, which you can use in comparison. This would
> make your figure somewhat more useful (Besides the beneficial experience of
> cooking the way most of the world does every day - I learned a lot!).
>
I have tried a little - but I was hopeless. I think you still
owe the group some hints on how to do better.

> I would prefer burn rate control (hence fire power) to come from fuel feed
> rate rather than primary air. Starving a fire of air could increase
> emissions - this would need to be tested...
>
In our charcoal-making stove, there is always a fixed batch load-
so we need to define our terms a little more. The "fuel" is either the
batch dry biomass or it is the gas produced by pyrolysis. In any
pyrolysis process, "starving" is fundamental and absolutely required.
But it is not zero - although pretty close (remember there is a fair
amount of oxygen in the fuel itself). Thus a control of that air gives
control of the pyrolysis rate and a control of the resultant pyrolysis
gases - which now can be considered a "fuel". Now the secondary air must
of course not be "starved" or there will be terrible emissions.

So I am agreeing and strongly disagreeing. The operation of a
charcoal-making stove is nothing like the operation of an ordinary stove
- since the ordinary stove makes no effort to separate the air supply
into primary and secondary amounts - and does not operate in a batch mode.

All the best,

Ron

 

From verhaarp at janus.cqu.edu.au Tue Oct 22 20:58:44 1996
From: verhaarp at janus.cqu.edu.au (Peter Verhaart)
Date: Tue Aug 31 21:35:01 2004
Subject: Charcoal, yes or no?
Message-ID: <9610230102.AA30131@janus.cqu.edu.au>

>From Piet Verhaart
Re CO emissions from charcoal stoves.
One thing I seem to remember is a sharp rise in the CO percentage in the
downdraft stove when all wood has pyrolysed and only charcoal is left on
the grate. Somewhere I read that water vapour catalyses the oxydation of CO
to CO2, which could account for the sudden rise.

----------
> From: Ronal Larson <larcon@csn.net>
> To: stoves@crest.org
> Subject: Re: Charcoal, yes or no?
> Date: Tuesday, 22 October 1996 11:31
>

> Mike Antal - were you suggesting that CO should not be a problem
> with adequate air flow?
>
> Anyone -Is there a law of nature that says that CO production
> must be high with a charcoal-burning stove.

 

 

From gayathri at aero.iisc.ernet.in Fri Oct 25 07:23:14 1996
From: gayathri at aero.iisc.ernet.in (Gayathri)
Date: Tue Aug 31 21:35:01 2004
Subject: FRom Tom Reed
Message-ID: <9610252154.AA08989@aero.iisc.ernet.in>

VIS000U
3;
`
3;
Grovers address, Tom's tripTom Reed
73002,1213 BIOENERGYINTERNET:bioenergy@crest.org
GASIFICATIONINTERNET:gasification@crest.org

There have been questions about P.D. Grover's whereabouts. I had lunch with Grover and Kishore Wednesday, and he sends his regards. He has just retired from IIT Delhi, but still has his lab there. Retired means still working at IIT and consulting for half a dozen companies and has an office at one. He looks great and is still a major major source of information on rice hull silica, stoves, pyrolysers, charcoal, gasifiers etc. He didn't know his internet number, but expects to soon. You can reach him at:@b

B-36, Gian Deep Apartment, 8, Mayur Vihar, Phase I, Delhi - 110 091; Tel: 225 2541 or CMS Energy Systems, Ltd., 44 Community Centre, East of Kallash, New Delhi 110 065, Tel: 623 5026, Fx: 6840159, 6218273. @b

Gayathri: You might send this message to others in India who would be interested. @b

Regards to all, TOM REED

 

From brr at cc.iitb.ernet.in Wed Oct 30 00:44:12 1996
From: brr at cc.iitb.ernet.in (b rajaram)
Date: Tue Aug 31 21:35:01 2004
Subject: charcoal, yes or no?
Message-ID: <Pine.OSF.3.95.961030110940.31478H-100000@tulsi.cc.iitb.ernet.in>

 

Yes, there is a law of nature that says that
when O2 passes up through a surplus of hot
(>700C) carbon, it will form CO in preference
to CO2. So charcoal stoves indoors are a potential hazard. @b

I believe I remember that in Korea the use of charcoal
braziers has religious strictures promoting putting
used ash on top of the charcoal. Is used ash catalytic to @b

CO + 1/2 O2 ===> CO2 ?@b

(Kirk - yesterday I visited the TREES project outside
Delhi and saw your NEW Test Kitchen hut.
Looks much better than the Hawaiin one! i hope you will
test charcoal heating in these huts with an without an ash cover. )@b

There is also concern about using producer (city)
gas in villages because of the high CO content.
However, no matter how clean the gas, there is a
STRONG odor from minor constituents that can warn
the housewife - if she will pay attention. No odorant ne
cessary. If this isn't enough, a dose of methyl
mercaptan in the gas will drive her out of the house.
In Shandong Province, there are three villages using
stored producer gas? Ralph - any concern about CO?
Any fatalities yet? How about a cheap CO
detertor/ smoke alarm? The first fatality will likely
be the end of all stove and gasifier programs.
Death from domestic devils (emphysema, glaucoma,...)
can be tolerated forever; death from foreign devils
is an excuse to throw them out. @b

Caution, TOM REED@b

Beware, TOM REED@b

 

 

From gayathri at aero.iisc.ernet.in Wed Oct 30 04:37:10 1996
From: gayathri at aero.iisc.ernet.in (Gayathri)
Date: Tue Aug 31 21:35:01 2004
Subject: charcoal, yes or no?
Message-ID: <9610302002.AA23495@aero.iisc.ernet.in>

 

 

 

From prasad at tn7.phys.tue.nl Thu Oct 31 06:57:28 1996
From: prasad at tn7.phys.tue.nl (prasad)
Date: Tue Aug 31 21:35:02 2004
Subject: On efficiency and co-production of charcoal
Message-ID: <9610311146.AA08914@tn7.phys.tue.nl>

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From B.Tremeer at mail1.remote.uva.nl Thu Oct 31 09:06:31 1996
From: B.Tremeer at mail1.remote.uva.nl (Grant Ballard-Tremeer)
Date: Tue Aug 31 21:35:02 2004
Subject: On efficiency...
Message-ID: <1.5.4.32.19961031140422.00686eb0@mail.uva.nl>

In my view we are in danger of getting our aims confused (loosing the wood
for the trees, perhaps) when we talk about efficiency.

I agree with Prasad that the test procedure should be simple to carry out
(for the same reasons). Such a "field laboratory" test is required. But what
is the aim of such a test - to measure efficiency or to determine whether
the proposed improved stove saves fuel for a relevant common task (or
phrased more correctly: uses less fuel than other stoves)? Is efficiency the
best tool to achieve this aim? I believe not.

* I believe "field laboratory" tests should be comparative not absolute.

* Calorific value and moisture content are immaterial - as long as they are
constant between tests. The same fuel, from the same batched, stored in the
same way should be used. Experimental method is vital: all parameters should
be randomised to minimise the effect of unmeasured variations (my hobby horse).

* I am proposing that the unit of comparison is "fuel used" to achieve the
task (as I believe emission mass per task is the best measure for emission
comparisons)

* I am not proposing a "specific fuel consumed" unit as recommended in the
VITA 'standards'. Such units are deceptive because they imply that apples
can be compared with oranges by dividing by a suitable factor (mass of water
heated in VITA's case).

* Why should high tech labs not use high tech equipment for their
comparisons? So long as apples are compared with apples I'm happy. And as
long as realistic methods for field laboratory studies are also available.

Prasad, I would like to get my hands on some of the work you describe - I
realise that I am being very vocal in an area I have not studied intensly (I
have immersed myself in emissions not efficiency). Could you send what you
consider the most important reading...

Farewell to all
Grant

-------------------------------------------------------------
Grant Ballard-Tremeer
fax: +31 20 525 6272 mark clearly c/o EPCEM
Weesperstraat 47 k.16; 1018DN; Amsterdam; The Netherlands
email: B.Tremeer@mail.uva.nl
btremeer@hagar.mech.wits.ac.za

 

 

From larcon at csn.net Thu Oct 31 10:57:58 1996
From: larcon at csn.net (Ronal Larson)
Date: Tue Aug 31 21:35:02 2004
Subject: On efficiency and co-production of charcoal
In-Reply-To: <9610311146.AA08914@tn7.phys.tue.nl>
Message-ID: <Pine.3.89.9610310818.A11425-0100000@teal.csn.net>

 

I am afraid Prasad has missed my point when I raised the subject of
accounting for charcoal in an efficiency computation. To repeat - I am
looking for agreement on the appropriate definition for efficiency when
the amount of energy in the charcoal is on the order of the useful or
lost energy. My point was that I believe ALL (repeat ALL) the existing
stove efficiency formulas that do include charcoal effects do so
incorrectly. I still hope someone will respond on this point - which is
not nitpicking when the different results differ by factors of two for a
charcoal-making stove.

Obviously, if you burn all the charcoal up there is no
definitional difficulty at all. I do not object to the Prasad approach
to measuring efficiency and fail to see any fundamental issues in his
approach. I also agree with Grant, however, that a comparison test is
certainly much more likely to be believable when comparing two stoves. I
believe this argues strongly for in-situ stove competitions.

But I think the efficiency issue also needs to be coupled with
the pollution issue. My two main reasons for wanting to develop a
charcoal producing stove are 1) to stop the terrible present charcoal
production processes and 2) to greatly reduce the present terrible
pollution from (I believe all) wood-burning stoves. I think a better
question then is what is the efficiency or fuel consumption comparison
(however defined) under conditions of equal pollution levels. I doubt
that any wood-burning stove can then compete with a wood-burning
charcoal-making stove. Has anyone any experience with a figure-of-merit
that combines wood consumption and wood pollution?

Ron Larson

 

From westr at magellan.Colorado.EDU Thu Oct 31 15:18:39 1996
From: westr at magellan.Colorado.EDU (Ronald E West)
Date: Tue Aug 31 21:35:02 2004
Subject: Charcoal, Yes or No?
Message-ID: <Pine.SUN.3.91.961031125019.19593A-100000@magellan.Colorado.EDU>

In response to the question, "Is there a law of nature that says when O2
passes through a surplus of hot carbon, it will form CO in preference to
CO2?", somewone wrote, "Yes, there is...."
This latter statement is partially correct. Thermodynamic equilibrium of
the reaction C + CO2 ----> 2 CO [or, equivalently, (C + 1/2 O2 -->
CO) - (CO + 1/2 O2 ----> CO2)] does indeed favor CO. However, it only
applies so long as CO, O2, and CO2 are in immediate, molecular contact
with carbon. As soon as the CO leaves the carbon surface and goes into
the gas phase, it will react as: CO + 1/2 O2 ---> CO2 (which highly
favors CO2) provided the temperature is high enough and there is
sufficient oxygen with reasonably good mixing. These conditions are
almost assured when charcoal is glowing ( T > 700 C) as oxygen must be
being transported to the carbon surface at a sufficiently high rate to
keep the carbon oxidation reaction going. Of course, mixing, heat
transfer, etc. are never perfect, and, if the CO2 contacts additional
carbon, the reaction C + CO2 ---> 2CO can occur again if that carbon is hot
enough (if it is, however, the gas phase oxidation of CO would again occur).
For these reasons, some CO will remain in the gas phase, as in
any combustion reaction. But the CO concentration need not be
significantly different than in other combustions.

Warm fires,
Ron West

 

From mheat at mha-net.org Thu Oct 31 18:23:48 1996
From: mheat at mha-net.org (Norbert Senf)
Date: Tue Aug 31 21:35:02 2004
Subject: Introduction
Message-ID: <199610312321.SAA06307@nic.ott.hookup.net>

I've been subscribed to this list for a couple of weeks and following it
with interest. My own field is designing, manufacturing, building and
testing masonry heating systems (high mass cordwood burning stoves used for
domestic heating, baking and hot water in Canada and the U.S.). My research
interest for the last 5 years has been emissions, prompted by US-EPA
regulations in the United States. We've been measuring particulates with
several different types of dilution tunnels.

The main issue in laboratory testing has turned out to be fueling protocol,
as one might expect with such a complicated and variable fuel as cordwood.
One thing we've developed is an elaborate descriptive method for the fuel
load: number of pieces, individual piece weight, individual piece moisture,
individual piece circumference (allows surface to volume ratio to be
calculated), pieces individually numbered and located in the pile,
photograph of fuel load spread out on floor, in order, and also stacked in
firebox. On a 2 hour laboratory test, the above procedure only adds about 10
minutes of work. It has turned out to be invaluable information, since fuel
load geometry appears to be one of the primary variables in reducing
emissions - something we only discovered in retrospect.

I look forward to meeting you all in print. We have a website at
www.mha-net.org/msb and one for our lab at www.mha-net.org/msb/lopez.htm.

Best Regards

Norbert Senf
----------------------------------------------------------
Norbert Senf email: mheat@mha-net.org
Masonry Stove Builders website: www.mha-net.org
RR 5 Shawville fax: 819.647.5092
Quebec J0X 2Y0

 

 

From 73002.1213 at compuserve.com Thu Oct 31 20:37:27 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:35:02 2004
Subject: Charcoal, yes or no?
Message-ID: <961101013224_73002.1213_FHM62-11@CompuServe.COM>

(You may have already received this - I'm not sure what transmissions I have
sent - sorry.)

Ron et al:

Yes, there is a law of nature that says that when O2 passes up through a surplus
of hot (>700C) carbon, it will form CO in preference to CO2. So charcoal stoves
indoors are a potential hazard.

I believe I remember that in Korea the use of charcoal braziers has religious
strictures promoting putting used ash on top of the charcoal. Is used ash
catalytic to

CO + 1/2 O2 ===> CO2 ?

(Kirk - yesterday I visited the TREES project outside Delhi and saw your NEW
Test Kitchen hut. Looks much better than the Hawaiin one! i hope you will test
charcoal heating in these huts with an without an ash cover. )

There is also concern about using producer (city) gas in villages because of the
high CO content. However, no matter how clean the gas, there is a STRONG odor
from minor constituents that can warn the housewife - if she will pay attention.
No odorant necessary. If this isn't enough, a dose of methyl mercaptan in the
gas will drive her out of the house. In Shandong Province, there are three
villages using stored producer gas? Ralph - any concern about CO? Any
fatalities yet? How about a cheap CO detertor/ smoke alarm? The first
fatality will likely be the end of all stove and gasifier programs. Death from
domestic devils (emphysema, glaucoma,...) can be tolerated forever; death from
foreign devils is an excuse to throw them out.

Caution, TOM REED

Beware, TOM REED

 

 

From 73002.1213 at compuserve.com Thu Oct 31 22:36:23 1996
From: 73002.1213 at compuserve.com (Tom Reed)
Date: Tue Aug 31 21:35:02 2004
Subject: Grovers address, Tom's trip
Message-ID: <961101013602_73002.1213_FHM62-23@CompuServe.COM>

I believe the following letter was sent by Gayathri in Bangalore when I couldn't
contact Compuserve. If you've seen it, sorry..

Hi eveyone:

There have been questions about P.D. Grover's whereabouts. I had lunch with
Grover and Kishore Wednesday, and he sends his regards. He has just retired
from IIT Delhi, but still has his lab there. Retired means still working at IIT
and consulting for half a dozen companies and has an office at one. He looks
great and is still a major major source of information on rice hull silica,
stoves, pyrolysers, charcoal, gasifiers etc. He didn't know his internet
number, but expects to soon. You can reach him at:

B-36, Gian Deep Apartment, 8, Mayur Vihar, Phase I, Delhi - 110 091; Tel: 225
2541 or CMS Energy Systems, Ltd., 44 Community Centre, East of Kallash, New
Delhi 110 065, Tel: 623 5026, Fx: 6840159, 6218273.

Gayathri: You might send this message to others in India who would be
interested.

Regards to all,
TOM REED

 

 

From larcon at csn.net Thu Oct 31 22:50:55 1996
From: larcon at csn.net (Ronal Larson)
Date: Tue Aug 31 21:35:02 2004
Subject: Introduction
In-Reply-To: <199610312321.SAA06307@nic.ott.hookup.net>
Message-ID: <Pine.3.89.9610311933.A8472-0100000@teal.csn.net>

 

On Thu, 31 Oct 1996, Norbert Senf wrote:

(in part)

> minutes of work. It has turned out to be invaluable information, since fuel
> load geometry appears to be one of the primary variables in reducing
> emissions - something we only discovered in retrospect.
>
> I look forward to meeting you all in print. We have a website at
> www.mha-net.org/msb and one for our lab at www.mha-net.org/msb/lopez.htm.
>

Norbert - welcome to our group. Yours was a helpful contribution.

Could you describe what the loading pattern is to achieve low emissions
(and alternatively high emissions).

Ron Larson