January 2002 Gasification Archive

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From pverhaart at optusnet.com.au Tue Jan 1 03:06:36 2002
From: pverhaart at optusnet.com.au (Peter Verhaart)
Date: Tue Aug 31 21:37:31 2004
Subject: Down draft stoves are grate!
In-Reply-To: <001001c19103$c423e260$6c15210c@default>
Message-ID: <5.1.0.14.2.20020101173826.00a5f9b0@mail.optusnet.com.au>

Rogerio,

At 12:46 31/12/01 +0000, you wrote:
>Dean, Ron, Peter Verhaart and stoves,
>
>snip

>I wonder if we should move toward a down draft burner?
>
>from this discussion I understand that DDS it will be easier to operate,
>requiring less frequently fueling.

No, the DDS wil have to be fed frequently with small quantities of fuel.
The advantage will be no smoke, when it has attained operating temperature,
it can be operated indoors and when needed contribute toward space heating.

I hope to be able in the near future, to report on its performance as a
stove and about the composition of the flue gases.

Very best wishes for the New Year, we in Australia are already 18 hours
into it.

Peter Vehaart

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From crispin at newdawn.sz Tue Jan 1 06:54:18 2002
From: crispin at newdawn.sz (Crispin)
Date: Tue Aug 31 21:37:31 2004
Subject: Actual heat from the fuel re: African Stove Tests
Message-ID: <004d01c192ba$828dfbc0$7ee80fc4@home>

Dear Piet and Kevin

Piet
>In oven dry state the mix should have a combustion value of around 20
MJ./kg

Kevin
>The cellulostic fraction of wood runs about 8,400 BTU per pound, and the
>resins from pine are similar in heating value to oil. Very aproximately,
>consider 16,800 BTU per pound. Pine that may be as much as 10% resin
>would then be:
> 8400 x .9 + 16,800 x .1 = 9,240 BTU/Lb

I have found the following from_Mechanical Engineer's Handbook_ McGraw Hill,
N.Y. First Edition, "Materials of Engineering" section/Wood/General
Properties of Wood, by Hermann Von Schrenk, p.579

"Calorific Value. The specific heat of practically all kinds of wood when
oven dry is 0.327 (Dunlap, _Forest Service Bulletin_ No. 110, 1912). The
calorific value of wood depends on its specific gravity (dry), heavier woods
giving more heat than light woods. According to Schenck, 1 cord of green
wood contains 250 gal. of water and the heat required to evaporate this into
steam is not available for other purposes. According to German experiments,
wood with 45 per cent. moisture gives only 50% as much heat as dry wood.
Rosin increases the heating power by about 12 per cent. According to Roth,
100 lb. of wood, as sold in woodyards, contains 25 lb. of water, 74 lb. of
(dry) wood and 1 lb. of ashes. Thus 100 lb. of green wood (50 per cent.
moisture) furnish about 270,000 B.t.u., 100 lb. of air dry wood (10 per
cent. moisture) about 580,000 B.t.u. and 100 lb. of kiln-dry wood (2 per
cent. moisture) about 630,000 B.t.u."

========
Although the type of wood Roth used is not stated and the figures do not
give a straight line, they give a total of only 6500 BTU per lb (oven-dry)
as a realizeable maximum which perhaps means an efficiency of only 70% in
burning. Based on Kevin's figure of 9240 I get 389813, 837375 and 909563
BTU respectively per 100 lbs based on their 'curve'. The experiment is
correct in principle but had serious errors. - CPP
========

"Relative Values of Woods as Fuels
Best: Hickory, beech, hornbeam, locust, heart pine.
Good: Oak, ash, birch, maple.
Moderate: Spruce, fir, chestnut, hemlock, sap pine.
Poor: White pine, alder, linden, cottonwood."

Under "Fuels" by Ozni P. Hood, Table 7, p. 608, shows the ash content of
various woods from "Slippery Elm" (1.69%) to Tamarack (0.09%). Pine is
around 0.3%.

Part of Table 8, p.609, "Analyses of Various Woods (Dry)" are two columns of
interest:

"Name Calories B.t.u.
Oak 4620 8316
Ash 4711 8480
Elm 4728 8510
Beech 4774 8590
Birch 4771 8586
Fir 5035 9063
Pine 5085 9153"

========
Based on the figure 9153 for pine I can calculate that the resin content of
their sample must be about 9%, according to Kevin's formula. - CPP
========

Under "Other Solid Fuels", p. 609:
"Sawmill Refuse, consisting of saw dust, "hogged" or shredded wood chips,
etc., containing from 40 to 60 per cent. moisture. The calorific value of
redwood, pine fir, hemlock, spruce and cedar refuse is practically 9000
B.t.u. per lb."

Lastly, charcoal (allowed access to atmospheric moisture after cooling) is
considered to be "84 per cent. carbon, 12 per cent. water, 3 per cent. ash
and 1 per cent. hydrogen." with a heating value "of about 12,850 B.t.u. per
lb."

========

Piet's 20 MJ/Kg divided by Kevin's 9250 BTU/Lb = 981 Joules / BTU. That's
pretty close.
Piet's 20 MJ/Kg divided by the olden days figure of 9153 = 991 Joules/BTU.
Even closer.

Going with a bone dry 9153 BTU/Lb and 1054 Joules/BTU I get 21.27 MJ/Kg.
This is a far cry from my estimated actual 15 MJ/Kg yield from the fuel.

My interpolation from the Roth slope and the 9153 BTU figure is about 17.2
MJ/Kg for 15% moisture content and 14.1 KMJ/Kg for 25% moisture for pine.

Can anyone give us soemthing more accurate?

New Year's Greetings from
Crispin

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From kchishol at fox.nstn.ca Tue Jan 1 09:24:13 2002
From: kchishol at fox.nstn.ca (Kevin Chisholm)
Date: Tue Aug 31 21:37:31 2004
Subject: Actual heat from the fuel re: African Stove Tests
In-Reply-To: <004d01c192ba$828dfbc0$7ee80fc4@home>
Message-ID: <001501c192cf$73e29800$b919059a@kevin>

----- Original Message -----
From: "Crispin" <crispin@newdawn.sz>
To: "Stoves" <stoves@crest.org>
Sent: Tuesday, January 01, 2002 7:49 AM
Subject: Actual heat from the fuel re: African Stove Tests

> Dear Piet and Kevin
>
> Piet
> >In oven dry state the mix should have a combustion value of around 20
> MJ./kg
>
> Kevin
> >The cellulostic fraction of wood runs about 8,400 BTU per pound, and the
> >resins from pine are similar in heating value to oil. Very aproximately,
> >consider 16,800 BTU per pound. Pine that may be as much as 10% resin
> >would then be:
> > 8400 x .9 + 16,800 x .1 = 9,240 BTU/Lb
>
> I have found the following from_Mechanical Engineer's Handbook_ McGraw
Hill,
> N.Y. First Edition, "Materials of Engineering" section/Wood/General
> Properties of Wood, by Hermann Von Schrenk, p.579
>
> "Calorific Value. The specific heat of practically all kinds of wood when
> oven dry is 0.327 (Dunlap, _Forest Service Bulletin_ No. 110, 1912). The
> calorific value of wood depends on its specific gravity (dry), heavier
woods
> giving more heat than light woods. According to Schenck, 1 cord of green
> wood contains 250 gal. of water and the heat required to evaporate this
into
> steam is not available for other purposes. According to German
experiments,
> wood with 45 per cent. moisture gives only 50% as much heat as dry wood.
> Rosin increases the heating power by about 12 per cent. According to
Roth,
> 100 lb. of wood, as sold in woodyards, contains 25 lb. of water, 74 lb. of
> (dry) wood and 1 lb. of ashes. Thus 100 lb. of green wood (50 per cent.
> moisture) furnish about 270,000 B.t.u., 100 lb. of air dry wood (10 per
> cent. moisture) about 580,000 B.t.u. and 100 lb. of kiln-dry wood (2 per
> cent. moisture) about 630,000 B.t.u."
>
> ========
> Although the type of wood Roth used is not stated and the figures do not
> give a straight line, they give a total of only 6500 BTU per lb (oven-dry)
> as a realizeable maximum which perhaps means an efficiency of only 70% in
> burning. Based on Kevin's figure of 9240 I get 389813, 837375 and 909563
> BTU respectively per 100 lbs based on their 'curve'. The experiment is
> correct in principle but had serious errors. - CPP
> ========
>
> "Relative Values of Woods as Fuels
> Best: Hickory, beech, hornbeam, locust, heart pine.
> Good: Oak, ash, birch, maple.
> Moderate: Spruce, fir, chestnut, hemlock, sap pine.
> Poor: White pine, alder, linden, cottonwood."
>
> Under "Fuels" by Ozni P. Hood, Table 7, p. 608, shows the ash content of
> various woods from "Slippery Elm" (1.69%) to Tamarack (0.09%). Pine is
> around 0.3%.
>
> Part of Table 8, p.609, "Analyses of Various Woods (Dry)" are two columns
of
> interest:
>
> "Name Calories B.t.u.
> Oak 4620 8316
> Ash 4711 8480
> Elm 4728 8510
> Beech 4774 8590
> Birch 4771 8586
> Fir 5035 9063
> Pine 5085 9153"
>
> ========
> Based on the figure 9153 for pine I can calculate that the resin content
of
> their sample must be about 9%, according to Kevin's formula. - CPP
> ========
>
> Under "Other Solid Fuels", p. 609:
> "Sawmill Refuse, consisting of saw dust, "hogged" or shredded wood chips,
> etc., containing from 40 to 60 per cent. moisture. The calorific value of
> redwood, pine fir, hemlock, spruce and cedar refuse is practically 9000
> B.t.u. per lb."
>
> Lastly, charcoal (allowed access to atmospheric moisture after cooling) is
> considered to be "84 per cent. carbon, 12 per cent. water, 3 per cent. ash
> and 1 per cent. hydrogen." with a heating value "of about 12,850 B.t.u.
per
> lb."
>
> ========
>
> Piet's 20 MJ/Kg divided by Kevin's 9250 BTU/Lb = 981 Joules / BTU. That's
> pretty close.
> Piet's 20 MJ/Kg divided by the olden days figure of 9153 = 991 Joules/BTU.
> Even closer.
>
> Going with a bone dry 9153 BTU/Lb and 1054 Joules/BTU I get 21.27 MJ/Kg.
> This is a far cry from my estimated actual 15 MJ/Kg yield from the fuel.
>
> My interpolation from the Roth slope and the 9153 BTU figure is about 17.2
> MJ/Kg for 15% moisture content and 14.1 KMJ/Kg for 25% moisture for pine.
>
> Can anyone give us soemthing more accurate?
>
> New Year's Greetings from
> Crispin
>
>
> -
> Stoves List Archives and Website:
> http://www.crest.org/discussion/stoves/current/
> http://www.ikweb.com/enuff/public_html/Stoves.html
>
> Stoves List Moderators:
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> Alex English, english@adan.kingston.net
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> -
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> http://solstice.crest.org/renewables/biomass-info/
> http://solstice.crest.org/renewables/biomass-info/carbon.shtml
>
> For information about CHAMBERS STOVES
> http://www.ikweb.com/enuff/public_html/Chamber.htm
>
>
>
>

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From kchishol at fox.nstn.ca Tue Jan 1 09:29:24 2002
From: kchishol at fox.nstn.ca (Kevin Chisholm)
Date: Tue Aug 31 21:37:31 2004
Subject: Actual heat from the fuel re: African Stove Tests
In-Reply-To: <004d01c192ba$828dfbc0$7ee80fc4@home>
Message-ID: <001e01c192d0$152fedc0$b919059a@kevin>

Dear Stovers:
I inadvertently sent Crispins original message to the list, rather than the
following reply. Following is the reply I intendd to send. Sorry about he
confusion.

Kevin Chisholm
*********************************
Dear Crispin

----- Original Message -----
From: "Crispin" <crispin@newdawn.sz>
To: "Stoves" <stoves@crest.org>
Sent: Tuesday, January 01, 2002 7:49 AM
Subject: Actual heat from the fuel re: African Stove Tests

Thanks for your thoughtful ananysis and your "search for thruth" on the
calorific value of woods in general, and resionous woods in particular.
>
> Piet
> >In oven dry state the mix should have a combustion value of around 20
> MJ./kg
>
> Kevin
> >The cellulostic fraction of wood runs about 8,400 BTU per pound, and the
> >resins from pine are similar in heating value to oil. Very aproximately,
> >consider 16,800 BTU per pound. Pine that may be as much as 10% resin
> >would then be:
> > 8400 x .9 + 16,800 x .1 = 9,240 BTU/Lb
>
> I have found the following from_Mechanical Engineer's Handbook_ McGraw
Hill,
> N.Y. First Edition, "Materials of Engineering" section/Wood/General
> Properties of Wood, by Hermann Von Schrenk, p.579
>
> "Calorific Value. The specific heat of practically all kinds of wood when
> oven dry is 0.327 (Dunlap, _Forest Service Bulletin_ No. 110, 1912).

This is probably reasonably accurate. However, the precision is probably a
bit excessive.

The
> calorific value of wood depends on its specific gravity (dry), heavier
woods
> giving more heat than light woods.

I hate it when I have to say "The book is wrong." :It makes me look
arrogant. :-) However, in this case, it is wrong. Firstly, the statement was
made 90 years ago, when wood was generally bought and sold by the CORD, a
volume measure, and not by the POUND (or kG). It is unquestionably true that
"heavier woods give more heat per CORD" but it is unquestionably wrong that
wood of higher specific gravity has more heat per CORD than woods of lower s
pecific gravity.

According to Schrenck, 1 cord of green
> wood contains 250 gal. of water

Going by memory, a cord of "green softwood, as cut" weighs about 3000
pounds, and a cord of "green hardwood weighs about 4000 pounds. 250 gallons
of water, if Imperial Gallons, would weigh 2,500 pounds. This would suggest
that "green softwood" has a moisture content wet basis of:
2500/3000 = 83.3%

With all due respect, Schrenk is quite wrong here.

and the heat required to evaporate this into
> steam is not available for other purposes.

This statement was correct when he made it, but with condensing boilers it
is wrong.

According to German experiments,
> wood with 45 per cent. moisture gives only 50% as much heat as dry wood.

This is indeed approximately correct in that wood with 45% moisture has
approximately only 1/2 as much dry wood per pound.

> Rosin increases the heating power by about 12 per cent.

This is wrong. He makes no reference to the quantity of rosin or resin
present. Taking his statement to a silly extreme.... if I purchased a cord
of "non-resinous wood" and added 1 pound of resin, I could increase its
heating value by 12%. If he said "Resinous woods containing typically 10%
reson have a hearing value about 12% greater than non-resinous woods." then
he would be approximately correct.

According to Roth,
> 100 lb. of wood, as sold in woodyards, contains 25 lb. of water, 74 lb. of
> (dry) wood and 1 lb. of ashes.

This is about 25% moisture wet basis. This is close to reasonably well
seasoned fuel wood.

Thus 100 lb. of green wood (50 per cent.
> moisture) furnish about 270,000 B.t.u., 100 lb. of air dry wood (10 per
> cent. moisture) about 580,000 B.t.u. and 100 lb. of kiln-dry wood (2 per
> cent. moisture) about 630,000 B.t.u."
>
> ========
> Although the type of wood Roth used is not stated and the figures do not
> give a straight line, they give a total of only 6500 BTU per lb (oven-dry)
> as a realizeable maximum which perhaps means an efficiency of only 70% in
> burning.

There a number of "unclarities" in the Roth statment which can lead to this
confusion:

1: He doesn't state if this is "moisture content wet basis" or "moisture
content dry basis.

2: He does not state whether this is the "true heating value" of the fuel,
in the sense of the total heating energy contained, OR if htis is the "net
heat available from burning the wood in a typical boiler or furnace.

Based on Kevin's figure of 9240 I get 389813, 837375 and 909563
> BTU respectively per 100 lbs based on their 'curve'. The experiment is
> correct in principle but had serious errors. - CPP
> ========

Would you care to "revisit that statement? :-)
>
> "Relative Values of Woods as Fuels
> Best: Hickory, beech, hornbeam, locust, heart pine.
> Good: Oak, ash, birch, maple.
> Moderate: Spruce, fir, chestnut, hemlock, sap pine.
> Poor: White pine, alder, linden, cottonwood."
>
> Under "Fuels" by Ozni P. Hood, Table 7, p. 608, shows the ash content of
> various woods from "Slippery Elm" (1.69%) to Tamarack (0.09%). Pine is
> around 0.3%.
>
> Part of Table 8, p.609, "Analyses of Various Woods (Dry)" are two columns
of
> interest:
>
> "Name Calories B.t.u.
> Oak 4620 8316
> Ash 4711 8480
> Elm 4728 8510
> Beech 4774 8590
> Birch 4771 8586
> Fir 5035 9063
> Pine 5085 9153"
>
> ========

I would suggest that my 9240 BTU/pound estimate is in very close agreement
with the 9153 BTU per pound estimate given in this reference. My estimate is
in error by about

(9240-9153)/9240 = 0.9%

Note, however, my calculated estimate was based on ash free cellulose while
his wood had .3% ash. If my estimate is corrected for ash presence, then my
estimate is off by only about 0.6%

On this point, I would say that were quite close to being in violent
agreement. :-)

> Based on the figure 9153 for pine I can calculate that the resin content
of
> their sample must be about 9%, according to Kevin's formula. - CPP
> ========
>
I would suggest that my approximation for the heating value of pine wasn't
really all that bad.

> Under "Other Solid Fuels", p. 609:
> "Sawmill Refuse, consisting of saw dust, "hogged" or shredded wood chips,
> etc., containing from 40 to 60 per cent. moisture. The calorific value of
> redwood, pine fir, hemlock, spruce and cedar refuse is practically 9000
> B.t.u. per lb."
>
This is a very generalized statement. There is a huge difference in the
heating value of a given wood when it contains 40% or 60% moisture. He would
not be far off howevr, if his figures were "corrected for moisture content
present."

> Lastly, charcoal (allowed access to atmospheric moisture after cooling) is
> considered to be "84 per cent. carbon, 12 per cent. water, 3 per cent. ash
> and 1 per cent. hydrogen." with a heating value "of about 12,850 B.t.u.
per
> lb."
>
> ========
>
> Piet's 20 MJ/Kg divided by Kevin's 9250 BTU/Lb = 981 Joules / BTU. That's
> pretty close.
> Piet's 20 MJ/Kg divided by the olden days figure of 9153 = 991 Joules/BTU.
> Even closer.
>
> Going with a bone dry 9153 BTU/Lb and 1054 Joules/BTU I get 21.27 MJ/Kg.
> This is a far cry from my estimated actual 15 MJ/Kg yield from the fuel.
>
Would this be the explanation for your unexpectedly high indication of your
stove efficiency?

> My interpolation from the Roth slope and the 9153 BTU figure is about 17.2
> MJ/Kg for 15% moisture content and 14.1 KMJ/Kg for 25% moisture for pine.
>
> Can anyone give us soemthing more accurate?
>
Piet and I seem to be in reasonably close agreement. Perhaps others could
bring some additional facts to the matter to confirm whether we are closer
to the truth or if Marks and Schrenk are closer.

> New Year's Greetings from
> Crispin
>
Thanks!! And the same to you.

Kindest regards,

Kevin Chisholm

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From kchishol at fox.nstn.ca Tue Jan 1 09:53:51 2002
From: kchishol at fox.nstn.ca (Kevin Chisholm)
Date: Tue Aug 31 21:37:31 2004
Subject: Correction: Re: Actual heat from the fuel re: African Stove Tests
In-Reply-To: <004d01c192ba$828dfbc0$7ee80fc4@home>
Message-ID: <000b01c192d3$828084e0$ed19059a@kevin>

Dear Stovers

I made a typo error in my previous message:

What I said was:
> "heavier woods give more heat per CORD" but it is unquestionably wrong
that
> wood of higher specific gravity has more heat per CORD than woods of lower
specific gravity.
>
What I intended to say was:
> "heavier woods give more heat per CORD" but it is unquestionably wrong
that
> wood of higher specific gravity has more heat per POUND than woods of
lower specific gravity.

Kindest regards,

Kevin Chisholm

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From crispin at newdawn.sz Tue Jan 1 14:32:53 2002
From: crispin at newdawn.sz (Crispin)
Date: Tue Aug 31 21:37:31 2004
Subject: Actual heat from the fuel re: African Stove Tests
Message-ID: <003601c192fa$90e52460$74e80fc4@home>

Dear Kevin

>It is unquestionably true that "heavier woods give more heat per
>CORD" but it is unquestionably wrong that wood of higher
>specific gravity has more heat per CORD than woods of lower
>specific gravity.

When I have lots of time I will copy out the comparison of heat content of
wood purchased by cord. It is going to be useful to find out what to burn
if you are buying wood, but it does not really get to the nitty gritty of
the math of real fires burning non-dry wood..

>>According to Schrenck, 1 cord of green
>> wood contains 250 gal. of water

>Going by memory, a cord of "green softwood, as cut" weighs about 3000
>pounds, and a cord of "green hardwood weighs about 4000 pounds. 250
gallons
>of water, if Imperial Gallons, would weigh 2,500 pounds. This would suggest
>that "green softwood" has a moisture content wet basis of:
>2500/3000 = 83.3%

Your memory may have let you down here as obviously 83% is impossible. On
page 454 the density of apple wood (for instance) is 44 lb/ft^3 = 5632
lbs/cord at avg 17.5% moisture. Long leafed yellow pine is the same.

Wet oak is 7552 lbs/cord. Air dried it is 5120 for a difference of 2432 lbs
of water. It does not have a figure for wet pine. I think the 250 gallons,
Imperial or not, is correct.

>> Rosin increases the heating power by about 12 per cent.

>He makes no reference to the quantity of rosin or resin present.

IT is taken to be 'ordinary' meaning what an average buyer would find.

>> Thus 100 lb. of green wood (50 per cent.
>> moisture) furnish about 270,000 B.t.u., 100 lb. of air dry wood (10 per
>> cent. moisture) about 580,000 B.t.u. and 100 lb. of kiln-dry wood (2 per
>> cent. moisture) about 630,000 B.t.u."

>1: He doesn't state if this is "moisture content wet basis" or
>"moisture content dry basis.

I went over the numbers and it is a moisture content wet basis.

>2: He does not state ...if this is the "net heat available from
>burning the wood in a typical boiler or furnace.

It is my belief that it is the yield from a particular or average furnace
because it is well below the actual heat content and these guys were no
slouches about something this important.

>>Based on Kevin's figure of 9240 I get 389813, 837375 and 909563
>> BTU respectively per 100 lbs based on their 'curve'. The experiment is
>> correct in principle but had serious errors. - CPP

>Would you care to "revisit that statement? :-)

The working out of the numbers shows correctly that wet basis wood burns
with a higher heat content when there is less water in it and more dry
matter per unit input mass. The error was that the lowest moisture content
wood (2%) yielded less total heat per kg of dry matter than the 10% moisture
wood (again, per kg of dry matter). If you plot the experiment there is a
curve, not a straight line which 'physics math' would say has to be seen.

>I would suggest that my 9240 BTU/pound estimate is in very close
>agreement with the 9153 BTU per pound estimate given in this reference.

That is what I was saying too.

>> Under "Other Solid Fuels", p. 609:
>> "Sawmill Refuse, consisting of saw dust, "hogged" or shredded wood chips,
>> etc., containing from 40 to 60 per cent. moisture. The calorific value
of
>> redwood, pine fir, hemlock, spruce and cedar refuse is practically 9000
>> B.t.u. per lb."

>This is a very generalized statement. There is a huge difference in the
>heating value of a given wood when it contains 40% or 60% moisture.

The figures are for BTU/lb dry mass.

Daniel wrote
>The plain fact is that there is more variance in wood
>than we can easily quantify here.

I have no problem understanding variations, but we can't have stoves tested
with a pelletized wood as a standard test, or rather THE standard test
because some stoves will not work with that fuel. It packs too densely for
enough air to travel through it to feed the flames properly.

Most of the things you mention as variables in the wood affect the YIELD not
the amount of HEAT per lb dry mass. The cellulose + resin formula is pretty
impressive on this account. It covers the two main fuels in correct
proportion.

For example"
>The base of the tree certainly has more ash and
>density than the top branches.

It makes no real difference if you are measuring fuel consumption by unit
mass.

It is probably worth our while to find out what the heat content is for the
pellets as it surely varies regionally.

To get an idea of how much these old guys knew about wood, listen to this
description of "Southern Yellow Pine" by H Von Schrenk (Ibid. p.577-8)

"Southern yellow pines (all pines of the Southern States manufactured into
lumber including longleaf, shortleaf, loblolly and Cuban pines. The lumber
is divided according quality into "dense southern yellow pine" and "sound
southern yellow pine;" dense southern yellow pine should show on either end
an average of at least six annual rings per inch and at least one-third
summerwood, or else the greater number of rings should show at least
one-third summerwood, all as measured over the third, fourth and fifth
inches on a radial line from the pith; wide-ringed material excluded by this
rule is acceptable, provided the amount of summerwood, as above measured, is
at least one-half; the contrast in colour between summerwood and springwood
should be sharp, and the summerwood should be dark in colour, except in
pieces having considerably above the minimum requirement for summerwood;
sound southern yellow pine includes pieces of southern yellow pine without
any ring or summerwood requirement);..."

Summerwood is about twice as strong as springwood and so nature demanded
this appropriate categorization.

The section on strength of timber includes calculations for all these sorts
of wood because most structures were mostly built of wood in those days.
They knew what to put where. I recall that Shaker chairs have 13 different
types of wood in them.

For your interest, conifers contain on average more wood per cord that
hardwoods because of better straightness. Black Oak with an average
diameter of 5 inches is 85 cubic feet per cord (66% volumetric efficiency).
Eight inch chestnut gives 95 cu ft/cord.

Ibid p.584 reads "One cord of first-class split wood obtained from sound
pieces 12 in. in diam. contains 102.4 cu. ft. of solid wood."

Wet chestnut with a density of 0.96 kiln dries to only 0.47. All in all
there is a lot of variability but the most important thing to have is a
working rule of thumb based on known heat content of dry mass and a factor
for moisture content that is good enough to rate stoves.

As to the question of how much the cordwood will shrink when it dries out, I
can quote from p. 589:

"
The volumetric shrinkage of wood from the green to the oven-dry state,
expressed in percentage of volume, is 26.5 times the specific gravity as
based on green volume. Thus, for white oak, shrinkage = 0.46 x 26.5 = 12.2
per cent., and consists almost entirely of lateral contraction."

The Basintuthu test showed an overall efficiency (wood to water) of 35%
based on 15 MJ/Kg. If it was only 14.1 because of the water content, then
the efficiency was 37%. If it was 18, then it was only 29%. That is a
significant difference and if I did not know what the fuel was giving me, I
might make a wrong decision about whether a modification to the stove was an
improvement or not.

Thanks for the feedback!
Crispin

PS In 1912 white pine structural timber sold for $27.70 per 1000 board feet
in New York.

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From hseaver at cybershamanix.com Tue Jan 1 17:24:21 2002
From: hseaver at cybershamanix.com (Harmon Seaver)
Date: Tue Aug 31 21:37:31 2004
Subject: Actual heat from the fuel re: African Stove Tests
In-Reply-To: <003601c192fa$90e52460$74e80fc4@home>
Message-ID: <3C3236F5.BCB9DC1A@cybershamanix.com>

I guess I'd have to weigh in here with Ken -- I don't think the book
Crispin is looking at is a reliable reference. For instance, it says:
>
> "Relative Values of Woods as Fuels
> Best: Hickory, beech, hornbeam, locust, heart pine.
> Good: Oak, ash, birch, maple.
> Moderate: Spruce, fir, chestnut, hemlock, sap pine.
> Poor: White pine, alder, linden, cottonwood."
>
Having burned many cords of oak, ash, birch, and maple, I can
testify that birch simply doesn't belong in the same category, and I'm
not sure ash really does either. Ash, in fact, varies greatly between
white, green, and black -- major diffences not only as fuel but also as
lumber, strengths, etc.
Further, in Crispin's last post, he says:
>
> Wet oak is 7552 lbs/cord. Air dried it is 5120 for a difference of 2432 lbs
> of water. It does not have a figure for wet pine. I think the 250 gallons,
> Imperial or not, is correct.

Which wet oak? There are a great many species of oak, and having
cut and hauled a bit of oak (red, white, and northern black), I know
none of those will go 7552 lbs/cord. White oak, the heaviest (and which,
btw, often has more btu's than hickory) runs about 5570 lbs/cord, green
weight, and about 4200 dry. Not sure what swamp oak or live oak weighs
green, although I can understand them weighing more due to a damper
environment. Likewise tropical hardwoods can weigh more. Live oak might
weigh quite a bit more than white oak, but most people down where live
oak grows don't burn much firewood.
If you do a web search on green wood weight, you'll find a good bit
of variety -- I suspect that even a specific species varies in weight
depending upon it's environment and time of year cut. Or even possibly
locale cultivars.

--
Harmon Seaver
CyberShamanix
http://www.cybershamanix.com

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From Carefreeland at aol.com Tue Jan 1 22:42:33 2002
From: Carefreeland at aol.com (Carefreeland@aol.com)
Date: Tue Aug 31 21:37:32 2004
Subject: The Mystery of heat variance in biomass
Message-ID: <54.20975210.2963dba3@aol.com>

Dear Bio-E friends,
There seems to be a lot of confusion about how to properly assess the
heat values of various woods and other biomass energy sources. This is quite
understandable when we consider the complexity of the physical organic
chemistry involved in the production of these fuels. Allow me to show one
landscapers view.
Woody tissue is not just pure cellulose. Although cellulose is the
largest component in most cases, it is anything but alone. We can take two
white oak trees for example of similar age and grown in similar locations and
have quite a bit of measurable variance in wood fuel components. Some can be
attributed to cultivar difference as there is a large number of genes which
can display within the white oak family.
I have walked in the native woods locally, and found "classic" Ohio white
oak tree leaves to be as varied as fingerprints. Most of the time a
particular tree is identifiable, although the leaves can vary slightly even
on a single tree. It is the individual tree that has a given group of genes
displaying. Only if a woods has a monoculture of cuttings, would the genes
displaying be the same, tree to tree.
Now lets look at the other side of the equation. What are the fuels
present in the wood which we have to judge heat value from? There is a wide
variety of tars, resins and oils, both volatile and non, which make up the
hydrocarbon mix. There are sugars, starches, and even proteins also involved
in plant biochemistry.
Just how a plants roots have grown with relationship to water, and
localized soil chemistry can alter metabolism. The presents of sun and
shadows can dramatically affect the makeup of chemistry in a given part of a
plant. Many of these hydrocarbon compounds are building blocks of various
tissue so what is needed at a given time and place on a plant can affect the
mix.
Many plants produce resins and other chemicals as a defense response
against predatory insects, fungi and bacteria. Other plants produce chemicals
for frost protection, or to balance less than optimum soil chemistry. Some
chemicals are produced to protect plant tissue from excess sun or wind
drying. Plants that are exposed to high winds grow completely different in
structure than the same plants in a calm location. Fruiting habits change
from year to year with the weather conditions and can greatly affect growth
and chemistry of the balance of the plant.
I wish I could wave a magic wand and say we could just look at the
hydrogen to carbon ratios of ash free, moisture free wood, and have a
formula. The problem here is how do you predict the bonding of the
hydrocarbons? Depending on the energy of a particular pattern of molecular
bonds in the hydrocarbons, the same hydrogen to carbon ratios can vary in
bond energy.
All is not lost. Although we can wastefully argue the fine points for
days, we do know the final result is with in a range. I am burning some 200
year old green ash heartwood tonight with a particular hardness, probably
related to the grain structure which is much more "squiggly" and therefore
harder than many green ash trees I have burned. I would predict that it still
has a chemistry within 10% Mj per Kg of most green ash. The density would
still be the biggest variance, maybe 30%?
When we switch tree species we can count on an even greater variance due
to the general makeup and quantity of the various hydrocarbons. Cherry and
hedge both produce gases which burn like acetylene from the cracking of
various sap oil components. The hedge however, produces a slightly hotter
version which seems to burn cleaner with less soot. The cherry needs more
mixing of the fuel with air to eliminate the soot, but the sap is mostly
located in the bark.
The reason I recommend pellets for testing, is to at least standardize
the density to a degree. With pellets from the same producer generally made
up of a similar mix of wood types grown within a given range of conditions,
the law of averages will dictate a narrowing variability.
When testing stoves side by side, let us at least narrow the variability
of fuel used in a given set of tests. Taking dry "clear" wood from the same
part of the same tree is about as good as it gets. If such resources are not
available, than we must allow for variance and use a larger number of tests
to average the performance.
Every fossil fuel has the same problem, it has just been averaged out and
compensated for by testing and compensating in the refining process. Why can
we not do the same? We are doing the equivalent of inventing a stove or
gasifier that burns CRUDE oil cleanly and consistently, well to well, field
to field. What a challenge. Have they ever invented such an animal?
My hat is off to all the guys who have tirelessly sought the truths in
natures complex puzzle, living now, or documenting work long ago. It is on
this work that we build our devises and attempt to seek standards which can
be tolerated by a less than perfect society. Only by adding our work to that
already documented long ago, can we struggle to find the constants and
averages within the gift of natural fuel mix.
Always Forward,
Daniel Dimiduk

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From ronallarson at qwest.net Tue Jan 1 23:33:26 2002
From: ronallarson at qwest.net (Ron Larson)
Date: Tue Aug 31 21:37:32 2004
Subject: Fw - Re: Aeration via biomass heat
In-Reply-To: <002001c19211$267b5200$f8e06641@computer>
Message-ID: <038e01c19346$693417e0$17e26641@computer>

Stovers:
The question raised by Cornelius about powering shrimp farms moved off
list for awhile. But Tom Duke noted privately to me the possible value of
Stirling pumps (no electricity needed) as a possible lower cost approach
that could be done with biomass. The following gives some leads on
Stirlings that this list might find useful.

Tom:
Thanks

Ron

----- Original Message -----
From: Thomas Duke <tduke@igc.org>
To: Ron Larson <ronallarson@qwest.net>
Sent: Tuesday, January 01, 2002 12:17 PM
Subject: Re: Aeration via biomass heat

> Ron,
>
> KOCKUMS of Sweden built the Stirling powered submarine.

> Dr. James R. Senft Professor of Mathematical Science of the University of
> Wisconsin, River Falls WI is one of the top men in this Stirling engine
> field.

> Sunpower Inc., USA designs free-piston engines made to do serious work
> e-mail: info@sunpower.com

> Bomin Solar Company, Germany has designed several low and medium
temperature
> Stirling engines. (info@bominsolar.com)

> Stirling Technology, Inc., USA has a 5 HP shaft power Stirling from Japan
at
> n-tezuka@net.ksp.or.jp. their US email: stirltec@stirling-tech.com

> Solo Kleinmotoren GMBH, Germany has a Stirling engine
> http://www.solo-germany.com/english/frames/frame_innovation2.html

> Cummins has a 6 Kw engine URL:
>
http://solstice.crest.org/renewables/dish-stirling/chapter7/free-piston.html

> There are a few engines. Price and availability are the questions I ask,
> because some of these engines they have, but they are not available to us.
> Ford had an engine they tested in some trucks and there was a bus also
> tested.

> The engine that was most available last time I checked was the ST-5 from
> Stirling Technology http://www.stirling-tech.com
> Bomin has a good engine, but last time I checked with them it was not
> available yet.
>
> I am starting to see if I can think of places where nitrogen fertilizer
can
> not be gotten any other way, or is very difficult to get any other way.
>
> Tom Duke
> Burlington Iowa
>
> ----- Original Message -----
> From: "Ron Larson" <ronallarson@qwest.net>
> To: <CAVM@aol.com>
> Cc: "Thomas Duke" <tduke@igc.org>
> Sent: Monday, December 31, 2001 7:37 AM
> Subject: Fw: Aeration via biomass heat
>
>
> > Hi Tom -
> >
> > Good to hear from you. I agree that the Stirling is potentially a
> good
> > one - but I haven't been following the Stirling's commercial
> availability.
> > I don't believe it is in use for any large solar or biomass application.
> Am
> > I wrong? Whose product would you suggest?
> >
> > Let me know of anything new on the fertilizer production issue.
> >
> > Cornelius:
> >
> > Tom is a good thinker on these issues - and one of the most
inventive
> on
> > all sorts of things including charcoal-making stoves. If wind is at all
> an
> > option in Mexico - you should bring Tom in on how to do it cheaply.
> >
> >
> > Ron
> >
> >
> > ----- Original Message -----
> > From: Thomas Duke <tduke@igc.org>
> > To: Ron Larson <ronallarson@qwest.net>
> > Sent: Monday, December 31, 2001 9:29 AM
> > Subject: Re: Aeration via biomass heat
> >
> >
> > > Ron,
> > >
> > > A Stirling engine will convert biomass heat into air pressure.
> > >
> > > Tom Duke
> > > Burlington, Iowa
> > >
> > >
> > > ----- Original Message -----
> > > From: "Ron Larson" <ronallarson@qwest.net>
> > > To: <CAVM@aol.com>
> > > Cc: <stoves@crest.org>
> > > Sent: Sunday, December 30, 2001 2:52 PM
> > > Subject: Re: Aeration via biomass heat
> >
> > <snip>
> >
>
>

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From ronallarson at qwest.net Tue Jan 1 23:34:07 2002
From: ronallarson at qwest.net (Ron Larson)
Date: Tue Aug 31 21:37:32 2004
Subject: Down draft stoves are grate!
In-Reply-To: <001001c19103$c423e260$6c15210c@default>
Message-ID: <039001c19346$6b11b180$17e26641@computer>

Rogerio, Piet, et al

I agree with Piet (not to promote the DDS) - if we limit ourselves to
the style of fuel feeding described by Piet and Khan.

But I think there is plenty of evidence from the gasifier community
(Reed, Das,....) that downdraft works well for pellets and gas production.
I also think that we should heed the good words offered by Dean Still on
some advantages they have found with DD.

But my main point is that I can find no-one doing stove R&D
incorporating both DD and air control (implying a closed batch load of fuel)
with a small controllable port for primary air control). This looks
potentially attractive and I hope someone can report on whether it has some
advantages.

Perhaps yours is the group to give it a try, since the DD stove
described by Piet is rather close to your own designs as I understand them
(meaning a large metal plate and a chimney).

Ron

----- Original Message -----
From: Peter Verhaart <pverhaart@optusnet.com.au>
To: Rogerio Miranda <rmiranda@sdnnic.org.ni>
Cc: <stoves@crest.org>
Sent: Tuesday, January 01, 2002 12:45 AM
Subject: Re: Down draft stoves are grate!

> Rogerio,
>
>
> At 12:46 31/12/01 +0000, you wrote:
> >Dean, Ron, Peter Verhaart and stoves,
> >
> >snip
>
>
> >I wonder if we should move toward a down draft burner?
> >
> >from this discussion I understand that DDS it will be easier to operate,
> >requiring less frequently fueling.
>
> No, the DDS wil have to be fed frequently with small quantities of fuel.
> The advantage will be no smoke, when it has attained operating
temperature,
> it can be operated indoors and when needed contribute toward space
heating.
>
> I hope to be able in the near future, to report on its performance as a
> stove and about the composition of the flue gases.
>
> Very best wishes for the New Year, we in Australia are already 18 hours
> into it.
>
> Peter Vehaart
>
>
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From ronallarson at qwest.net Tue Jan 1 23:34:39 2002
From: ronallarson at qwest.net (Ron Larson)
Date: Tue Aug 31 21:37:32 2004
Subject: Down draft stoves are grate!
In-Reply-To: <3.0.5.32.20011231124604.00e663d0@205.218.248.130>
Message-ID: <039101c19346$6c044ee0$17e26641@computer>

Harmon

I am not sure to which thread you refer. I am quite convinced that no
one has done any work on down draft stoves where there is separate primary
air control. Because our up-draft stove work with pyrolysis gets away with
only primary air control, I do not know if it is necessary or desirable to
also have secondary air control.

The only diagram I remember was one for the "Dasifier" sent in by Tom
Reed on November 5 (can be found in the archives fairly easily (I haven't
looked and assume it is there).

I also suppose you or others might have looked at Piet Verhaart's photos
on Alex' site:
(http://www.ikweb.com/enuff/public_html/DDBbq/DDB.htm)
I am forwarding separately a response from Piet to me (that I
believe inadvertently left out "stoves") that may give you some leads.

I hope others can add more suggestions that I have forgotten.

I look forward to hearing of your new expanded research program -
especially as to your need for increased draft.

Ron

----- Original Message -----
From: Harmon Seaver <hseaver@cybershamanix.com>
To: <stoves@crest.org>
Sent: Monday, December 31, 2001 5:23 PM
Subject: Re: Down draft stoves are grate!

> Arrrgghh! I've been trying to find the info about the "downdraft"
> cookstove that was posted here awhile back. It was rather unique, had a
> small "hopper" on one end for wood chips, pellets, etc. then a flat
> cooking section leading to a chimney. There was some discussion on
> whether or not it was actually a gasifier, and, I think, the consensus
> was that it wasn't, since it had no secondary air port.
> Can anyone point me to that thread or the name?
>
> At the moment, I'm reeking of wood smoke, having fired up a new double
> barrel woodstove which is in serious need of induced draft! Also just
> bought a new MIG welder and a drill press so I can have more fun playing
> with stoves and gasifiers.
>
>
> --
> Harmon Seaver
> CyberShamanix
> http://www.cybershamanix.com
>
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From ronallarson at qwest.net Tue Jan 1 23:35:11 2002
From: ronallarson at qwest.net (Ron Larson)
Date: Tue Aug 31 21:37:32 2004
Subject: Fw: Verhaart response on DD questions
Message-ID: <039201c19346$6d001400$17e26641@computer>

Stovers:

In my response today to Harmon,
I went looking for the web site given below and realized for the first time that
Piet's response below had not gone to the full list. As I am pretty sure
that Piet wanted it fully out and because it contains such good new information,
I am forwarding it without comment (and not much would be given anyway - this
response is very good).

Ron

----- Original Message -----
From: <A
href="mailto:pverhaart@optusnet.com.au" title=pverhaart@optusnet.com.au>Peter
Verhaart
To: <A href="mailto:ronallarson@qwest.net"
title=ronallarson@qwest.net>Ron Larson
Sent: Saturday, December 29, 2001 12:19 AM
Subject: Re: Continuing on stove nomenclature and descriptions
(Faemus??)
At 08:48 28/12/01 -0700, you wrote:
Peter (cc
stoves): Thanks
for the correction. I visited the stoves site maintained by Alex (<A
href="http://www.ikweb.com/enuff/public_html/DDBbq/DDB.htm">http://www.ikweb.com/enuff/public_html/DDBbq/DDB.htm) Yours is a nice looking unit - I only vaguely
remember seeing it earlier (which is dated Feb. 7, 1999). The design is
somewhat similar to what I described in my following note of yesterday - but I
like better your lower placement of the fuel-air
sources. A few
questions - 1. Can you expand on
the use of "cheat holes in the riser pipe". I can't spy them. How
large? How far up? How does their existence help start the updraft
mode?There are 3 holes of 12 mm in the riser pipe, about
20 mm above the grate. A 30 mm wide strip of steel, 30 mm above the grate is
welded on the riser pipe. When the fire is started it burns in updraft mode,
very weakly so as there is no chimney draft.Some of the time some of the
flames will enter the 'cheat holes' and so create the beginning of chimney
draft. As the average temperature of the gases downstream from the fire
increases, so will the chimney draft and in a typical case it takes about 12
minutes to establish full downdraft mode.
 2. Can you tell us
more about the "slide to adjust the active grate area." Does this
change the amount of air flow? I can't figure out the
location. Is it right below the visible grate - or further down?
How far down? What range of areas are possible?The
slide covers the grate from fully open (about 120 * 120 mm) to fully closed. It
is on top of the grate, when activated it pushes the burning fuel closer
together. I use it about 1/3 closed for my one or two steaks. The available
grate area can vary from 14400 mm^2 to zero.
 3. What is the
mechanism for removing ash?The ash collects (mainly) in
the dead end at the bottom of the riser pipe. A lid which doubles as a third pod
can be detached to remove the ash.
 4. In the Khan paper,
wood blocks were added at rates like two small blocks every thirty
seconds. What is your typical fuel feed rate? Have you
calculated maximum and minimum power levels in kW? Is there a
"sweet spot"? Have you ever measured CO or other
emissions?I probably add them at a similar rate. The
procedure is to cover any hole in the burning fuelbed with a piece of wood. I
did not experiment, as Hasan has done, with chimney height, I just took about
1.2 m (just guessing) because I knew from earlier experiments (with Hasan) that
this would be sufficient.I have not had the opportunity to measure CO or
other emissions other than by nose. Things might look up in the near future
though, a lecturer from Biology at the Central Queensland University has
developed a process to convert (?) shrub and tree cuttings into fuel and
even briquettes, if I am informed correctly, not charcoal. The idea is, if I am
not mistaken, to provide a fuel which contains no harmful bacteria or
fungi.
 5. Is there any
insulation? (all metal?) Any estimate of
efficiency?Yes, a 1 cm thick layer of Kaowool on the
bottom and sides of the body that carries the steel plate. The efficiency of a
barbecue? kg of steak/kg of wood. Might be less than unity, certainly if you
like your steak rare.
 6. In the US, our
barbecues are always (? - at least usually) open grates - not solid plates
like yours (which is of course needed to maintain draft). Is it typical
in other locations where you have lived to have barbecues with solid
surfaces?In Australia most gas barbecues have both a
solid surface as well as a grate over lumps of pumice or such. In my experience
the solid surface is used predominantly.
 7. I can see using
your design as a "griddle", but also as a "plancha-type" - with ordinary cook
pots and a maximum temperature need only of that for boiling water. Do
you have any experience or data on how the stove works that way?
No, but I have been thinking of doing an experiment. I
have even started making a stove with a hot plate, I might take it up again when
the weather cools down a little, we are now regularly having temperatures of 40+
C.
 8. How uniform is the
temperature on the cooking surface? Did you ever (or could you)
try putting a large square basting pan on the cook surface and observe where
boiling is occurring? I'd like to know the max "Figure of Merit" (ratio
of weight of water evaporated to the weight of fuel) you could obtain (and
whether this changes much with the vigor of the
boil).The temperature is not uniform, it is highest
right above the riser pipe. The plate is 10 mm steel. Aluminium of the same
thickness would give a more uniform distribution and the steel plate would
probably have a more uniform temperature if I welded fins on the downstream end
of it. As it is, however, it has its advantages, the hot end is good for steaks,
the downstream part better suited for sausages.
 9. The plate thickness
of 10 mm seems a bit large. Any particular reason for that
thickness? How about side thicknesses?See 8. It
makes the stove quite heavy, reason more uniform temperature. Sides are 3 mm
steel, being the only available material at the time.
 10. I am wondering
about your statement that it takes about 12 minutes to settle
down. What is happening during this period? Are you building
up a layer of charcoal below the grate?The 12 minutes
are used both to let the fire spread and to create hot gases in the chimney.
During this period it has all the earmarks of a classical wood fire, flames,
glow and smoke. There is only volatiles and air and flames below the grate, all
the charcoal burns (sorry) up on the grate. It is a more or less stationary
process with a (more or less) constant rate of burning charcoal, pyrolysis and
combustion of volatiles. Our explanation of the clean combustion is a mix of
high temperature, turbulence and short residence time resulting in clean
combustion. We noticed at Eindhoven that the CO tends to increase the moment all
wood is carbonised and no more volatiles are produced.
 11. It looks like your
design could be readily modified to achieve power control through air flow
rather than fuel metering (which offers also the possibility of
charcoal-making). Have you ever seen such a design - and can you supply
references? Does your own work at Eindhoven exist on the web
anywhere? Published in a journal anywhere?I
don't see how that could be achieved. The air control is through the
permeability of the fuelbed and, to some extent by the size and height of the
chimney. For a charcoal making stove you would preferably have a process where
you have a constant composition of the volatiles so you can design a burner for
it. To achieve that you need a more or less stationary process (like in
the downdraft stove). It smells like mechanisation to me.There is or should
be one article: "Making do with the open fire", many aspects of which have been
rediscovered by Dean Stil, for whom I have great respect for opening up this
topic which 20 years ago was almost lethal. Then there is the collection of
articles "Wood heat for cooking". Apart from that there is little. I didn't
publish, so I perished.
Again my
apologies for having not remembered your prior positive statements about your
down-draft barbecue. Besides the major advantage of getting the smoke
out of one's eyes - are there any other benefits or disadvantages we should
know about?Yes, no smoke, just clean gas, mainly N2; CO2
and H2O and the merest traces of CO, which make it suitable for baking in direct
contact with the clean gases, like described by Hasan Khan.No apologies,
Ron, thank you again for doing a great job over the (almost) past year and best
wishes for the next

From kenboak at stirlingservice.freeserve.co.uk Wed Jan 2 03:25:13 2002
From: kenboak at stirlingservice.freeserve.co.uk (kenboak@stirlingservice.freeserve.co.uk)
Date: Tue Aug 31 21:37:32 2004
Subject: Stirling Engines
Message-ID: <20020102082420.NLZO22946.fep04-svc.ttyl.com@localhost>

Listers,

Firstly I would like wish you all a Happy New Year, and say that I have appreciated hearing about the various stove developments that have created much interest over the Christmas period.

Secondly I would like to say that the Stirling engine does not currently stand in a good commercial position - I have been following its progress since 1990 and I have seen little evidence of anything other than over-priced laboratory prototypes, and a series of failed commercial ventures.

There are however 3 exceptions:

1. Build your own from a Viebach Kit of castings. This will produce about 350W of electricity or 500W of mechanical power from biomass - cost about $4000. Multi cylinder designs are possible to add power in 1/2 hp increments.

http://www.uwemoch.de/english.htm

http://www.geocities.com/Viebachstirling/ - german language only

2. Buy a Whispergen 750W combined heat and power system from Whispergen New Zealand or Victron Energies (Netherlands & Europe) The cost is $11000.

http://www.victronenergie.com/Products/whispergen/whispergen.htm

3. Commission an amateur Stirling engine builder, such as Jim Symanski of Pescadero CA, to make a custom engine to suit your requirements. Jim is building wood fired engines in the 2hp to 5hp range

http://www.symanski.net/stirlings/jimd6.html

None of the other organisations named in the previous emails have anything to offer at a remotely viable price.

Ken Boak,

Chairman, Stirling Engine Society

_______________________________________________________________________
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From pverhaart at optusnet.com.au Wed Jan 2 05:22:14 2002
From: pverhaart at optusnet.com.au (Peter Verhaart)
Date: Tue Aug 31 21:37:32 2004
Subject: Actual heat from the fuel re: African Stove Tests
In-Reply-To: <004d01c192ba$828dfbc0$7ee80fc4@home>
Message-ID: <5.1.0.14.2.20020102153409.00a6cec0@mail.optusnet.com.au>

At 10:24 1/01/02 -0400, you wrote:
>Dear Stovers:
>I inadvertently sent Crispins original message to the list, rather than the
>following reply. Following is the reply I intendd to send. Sorry about he
>confusion.
>
>Kevin Chisholm
>*********************************
>Dear Crispin
>
>
>I hate it when I have to say "The book is wrong." :It makes me look
>arrogant. :-) However, in this case, it is wrong. Firstly, the statement was
>made 90 years ago, when wood was generally bought and sold by the CORD, a
>volume measure, and not by the POUND (or kG). It is unquestionably true that
>"heavier woods give more heat per CORD" but it is unquestionably wrong that
>wood of higher specific gravity has more heat per CORD than woods of lower s
>pecific gravity.

The book is wrong, I love saying that, the book is wrong. Resinous woods
have a rather low density but a high combustion value, probably much higher
than much denser woods not containing resin.
What kind of accuracy do you think you need?

Peter Verhaart

Snip

Kindest regards,

>Kevin Chisholm

And my compliments to Kevin for his exhausive analysis, which I enjoyed
reading.
Happy New Year

Peter Verhaart

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From dglickd at pipeline.com Wed Jan 2 09:10:48 2002
From: dglickd at pipeline.com (Dick Glick)
Date: Tue Aug 31 21:37:32 2004
Subject: GAS-L: The Mystery of heat variance in biomass
In-Reply-To: <54.20975210.2963dba3@aol.com>
Message-ID: <087c01c19397$48749830$0100a8c0@cframcomp>

Hello Carefreeland and others -

As a starting point on a dry mass basis -- biomass has an ultimate-like
compositional
formula, providing the ratios of the CHO components -- that may be viewed as
an approximation because of variations in the CHO composition of components;
cellulose, hemicellulose and lignin. Inorganics need to be subtracted to
provide the biomass mass fraction of interest.

A representative component analysis is found in, for example;
www.mluri.sari.ac.uk/IFRU/thesis/phd_castro.pdf

Cellulose (pure cotton) formula is (C6H10O5)x where x is the number of
monomer units in the polymer -- x is a variable and large. Hemicellulose is
generally less well defined, but may be represented to a reasonable
approximation by a combination of 5 and 6 carbon sugars as the basic units;
perhaps something like (C11H18O9)x. For lignin, (C10H1603)x -- see;
http://www.agen.ufl.edu/~chyn/age4660/lect/lect_2b/lect_02.htm

The low heat values for cellulose is near 7000 BTU per pound and that for
lignin, closer to 10,000 BTU/pound. There are estimates, particularly for
biomass used as rumen feeds, of the relative biomass component compositions.

The rest is arithmetic -- if the heat content you requested is to be
obtained.

Best, Dick

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From ronallarson at qwest.net Wed Jan 2 10:17:59 2002
From: ronallarson at qwest.net (Ron Larson)
Date: Tue Aug 31 21:37:32 2004
Subject: Fw: - an expert (Boak) on Stirlings
Message-ID: <003001c193a0$f2fe7f60$8ee56641@computer>

Ken (cc stovers):
Thanks for sending this on - which by its salutation I assume was
intended for general distribution. Your position as President of the
Stirling Engine Society, with such a quick response to "stoves" is indeed
gratifying.

Several questions:
1. Can we assume that the relatively high costs given below are due to
small sales volume? That with volumes like those for small portable IC
engines, the costs would be comparable? That there is nothing inherently
costly about the Stirling?
2. To be active in your society, you must personally be sold on the
long-term viability of the Stirling. Is it because of something more than
the external combustion aspects? Efficiency? Life time? Serviceability?
Applicability to solar? (my reason)
3. I send this to the full list because I can see an eventual market
for very small Stirlings (smaller than your products below) as part of a
hybrid system - solar during the (sunny) day and biomass in the evenings.
Even at your relatively high costs below, a biomass-fueled approach might be
(or soon could be) competitive to PV, which is now seen to be the least-cost
option in most remote markets - but whose costs are dominated by storage
requirements. If such were to come about, I presume that the energy source
would look a lot like the stoves we talk about (except smaller, as we
generally deal with many kW). Do you listen in to "stoves" dialog for this
reason? Any guidance to give those on this list who might want to develop a
simple rural-suitable heat source for Stirlings? Are there manufacturers
interested in such a market?
4. Thanks also for the Holiday greetings.

Ron

----- Original Message -----
From: <kenboak@stirlingservice.freeserve.co.uk>
To: Ron Larson <ronallarson@qwest.net>
Sent: Wednesday, January 02, 2002 1:20 AM
Subject: Re: Fw - Re: Aeration via biomass heat

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From Carefreeland at aol.com Wed Jan 2 11:56:44 2002
From: Carefreeland at aol.com (Carefreeland@aol.com)
Date: Tue Aug 31 21:37:32 2004
Subject: GAS-L: The Mystery of heat variance in biomass
Message-ID: <17c.1a03593.296495c5@aol.com>

Dear dglickd,
This is exactly what we need every now and then, a good organic chemist.
This formula is a great way to determine by analysis, what a plant is
producing for the purpose of converting chemistry to physics.
What I am deriving from this formula is the way in which some plants
produce higher caloric value per mass. If one is to take a chart of local
firewood's we can see a very direct correlation between strength/weight of
fiber and heat value. This could easily be explained by the presents of more
high energy lignin, which is a bonding agent in the fibers. Lignin has less
percentage oxygen than cellulose.
Osage orange (hedge) comes out near the top by my chart, at 7073 Btu per
pound. It is indeed one of the strongest woods known to man hence it's name
Boise, DE Ark or "wood of the bow." This is from figures from Firewood for
your Fireplace by Warren Donnelly, 1974. Probably air dry wood.
How do we explain the high figure for Black cherry at 7142 Btu/pound, or
Cottonwood at 7142? I would say that the raw sugars present in cherry sap
must be very high energy. Any clue as to what their formula is? Cottonwood
may be low strength because of the light density of fibers lacking a good
"weave." Cottonwood also has so many large pores that it tends to rot fast.
The high heat here may also come somewhat from low ash content.
Pine is much lower at 6190 Btu/pound, but again are we talking split
heartwood or small stock with a high bark to weight ratio? I would venture
to say that the resin here, which is more hydrocarbon in nature, would be
very high in heat, but present less in the core than in the bark. Again,
what variety of pine, and growing where?
Silver maple comes out lower at 5937 Btu/pound, probably due to simpler
cellulose and ash. Box elder is very low at 4783 Btu/pound but it is very
high in ash.
I will say that all of this indicates that the usual ways that trees
repair damage and add strength for wind resistance all seem to add heat
density to the wood. I cannot make this a rule though.
Cork bark elm is no higher heat than Siberian elm, yet it makes stronger
wood. Why? The woven grain of the cork bark gives it it's strength. The
open grain of Siberian elm makes an excellent charcoal though because of it's
porosity and lower apparent ash.
I suppose we could do this complex analysis of compounds which change
with the weather. This is of great use to botanists who are unlocking the
secrets of Btu. production.
The simpler way for most folks, is just to test raw heat value of what
material you have, with an understanding of the processes by which those
values vary. Start with dry wood and subtract the ash. Just don't be upset
by a 2% variation from your neighbors experiments, it's not worth the trouble
to track it down.
If 2% is the difference for you, than pay for good feedstock analysis,
with a very consistent material. F 1 Hybrid or cutting produced trees grown
on plantations, wheat or other grain crops, sugarcane and grasses, all tend
to be much more similar in final make up due to the trouble farmers have gone
through to make a consistent product. Just use test samples from the same
crop to compare apples to apples.
Any good chemical analysis avalible of saps and resins? What is cherry
sap Vs maple sap? How about pine sap Vs spruce? What is in the high energy
sap in locust wood?
This will expand the range of chemistry for analysis.
Daniel Carefreeland(scape) Dimiduk

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From willing at mb.sympatico.ca Wed Jan 2 11:58:15 2002
From: willing at mb.sympatico.ca (Scott Willing)
Date: Tue Aug 31 21:37:32 2004
Subject: Stirling Engines
In-Reply-To: <20020102082420.NLZO22946.fep04-svc.ttyl.com@localhost>
Message-ID: <3C32E829.21269.30E0F5@localhost>

Ken,

I've been casually investigating the Stirling technology. I've checked
out the Viebach stuff, and now (thanks to your post) the
Whispergen.

But it is not at all clear from the limited information available on the
Viebach engine (at least in English) how heat is to be supplied to
the unit. Does anyone know this? Something tells me I can't just
set it on top of my wood stove, hook up an alternator and start
charging my batteries.

In the case of the Whispergen, the intended fuel is liquid kerosine,
diesel or natural gas... all things that can be stuffed through a tube.

The Symanski is the only wood-fired unit of the three.

I'd like to echo Ron's questions about inherent cost etc. I have a
feeling that the Stirling isn't going to come into its own until the end
of cheap and available fossil fuels seems closer to most people than
it does now, creating sufficient demand from those with the
resources to buy in.

As a rural resident of central Canada, I would pay a pretty good
buck for something of very modest capabilities to supplement my
PV electrical generation in the winter - when sun can be scarce and
I'm burning wood for heat anyway. Stirling seems a perfect match.
But I think my priorities are out of whack with the most of the rest of
the planet, which I would divide roughly into two groups - those who
think the status-quo (IC gas or diesel-powered generators) is just
swell, and those for whom the conversation is basically moot since,
for them, both technologies are stratospherically out of reach.

-smw

From: kenboak@stirlingservice.freeserve.co.uk
To: stoves@crest.org
Subject: Stirling Engines
Date sent: Wed, 2 Jan 2002 8:24:20 +0000

> Listers,
>
> Firstly I would like wish you all a Happy New Year, and say that I have appreciated hearing about the various stove developments that have created much interest over the Christmas period.
>
> Secondly I would like to say that the Stirling engine does not currently stand in a good commercial position - I have been following its progress since 1990 and I have seen little evidence of anything other than over-priced laboratory prototypes, and a series of failed commercial ventures.
>
> There are however 3 exceptions:
>
> 1. Build your own from a Viebach Kit of castings. This will produce about 350W of electricity or 500W of mechanical power from biomass - cost about $4000. Multi cylinder designs are possible to add power in 1/2 hp increments.
>
> http://www.uwemoch.de/english.htm
>
> http://www.geocities.com/Viebachstirling/ - german language only
>
> 2. Buy a Whispergen 750W combined heat and power system from Whispergen New Zealand or Victron Energies (Netherlands & Europe) The cost is $11000.
>
> http://www.victronenergie.com/Products/whispergen/whispergen.htm
>
> 3. Commission an amateur Stirling engine builder, such as Jim Symanski of Pescadero CA, to make a custom engine to suit your requirements. Jim is building wood fired engines in the 2hp to 5hp range
>
> http://www.symanski.net/stirlings/jimd6.html
>
>
> None of the other organisations named in the previous emails have anything to offer at a remotely viable price.
>
>
>
> Ken Boak,
>
>
> Chairman, Stirling Engine Society
>
>
>
>
> _______________________________________________________________________
> Never pay another Internet phone bill!
> Freeserve AnyTime, for all the Internet access you want, day and night, only £12.99 per month.
> Sign-up at http://www.freeserve.com/time/anytime
>
>
>
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>
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>
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From dglickd at pipeline.com Wed Jan 2 13:04:59 2002
From: dglickd at pipeline.com (Dick Glick)
Date: Tue Aug 31 21:37:32 2004
Subject: GAS-L: The Mystery of heat variance in biomass
In-Reply-To: <17c.1a03593.296495c5@aol.com>
Message-ID: <08a801c193b8$0001fb80$0100a8c0@cframcomp>

Hello Carefreeland and All --

Plant initial chemistry -- photosynthesis -- is the light catalyzed reaction
of carbon dioxide and water to form carbohydrates. As is true for both
animals as well as for plants -- respiration accounts for further reactions.
Photosynthesis provides the mechanism for formation of carbohydrates and
then respiration in plants is the reaction of carbohydrates with oxygen to
yield carbon dioxide and oxygen depleted organic plant substances. Examples
of interest is the plant progeny mechanism -- the seed producing process --
as well as the formation of lignin, plant oils, etc.

Best, Dick

----- Original Message -----
From: <Carefreeland@aol.com>
To: <dglickd@pipeline.com>; <stoves@crest.org>; <gasification@crest.org>;
<wastewatts@yahoogroups.com>
Sent: Wednesday, January 02, 2002 11:56 AM
Subject: Re: GAS-L: The Mystery of heat variance in biomass

> Dear dglickd,
> This is exactly what we need every now and then, a good organic
chemist.
> This formula is a great way to determine by analysis, what a plant is
> producing for the purpose of converting chemistry to physics.
> What I am deriving from this formula is the way in which some plants
> produce higher caloric value per mass. If one is to take a chart of local
> firewood's we can see a very direct correlation between strength/weight of
> fiber and heat value. This could easily be explained by the presents of
more
> high energy lignin, which is a bonding agent in the fibers. Lignin has
less
> percentage oxygen than cellulose.
> Osage orange (hedge) comes out near the top by my chart, at 7073 Btu
per
> pound. It is indeed one of the strongest woods known to man hence it's
name
> Boise, DE Ark or "wood of the bow." This is from figures from Firewood
for
> your Fireplace by Warren Donnelly, 1974. Probably air dry wood.
> How do we explain the high figure for Black cherry at 7142 Btu/pound,
or
> Cottonwood at 7142? I would say that the raw sugars present in cherry sap
> must be very high energy. Any clue as to what their formula is?
Cottonwood
> may be low strength because of the light density of fibers lacking a good
> "weave." Cottonwood also has so many large pores that it tends to rot
fast.
> The high heat here may also come somewhat from low ash content.
> Pine is much lower at 6190 Btu/pound, but again are we talking split
> heartwood or small stock with a high bark to weight ratio? I would
venture
> to say that the resin here, which is more hydrocarbon in nature, would be
> very high in heat, but present less in the core than in the bark. Again,
> what variety of pine, and growing where?
> Silver maple comes out lower at 5937 Btu/pound, probably due to
simpler
> cellulose and ash. Box elder is very low at 4783 Btu/pound but it is very
> high in ash.
> I will say that all of this indicates that the usual ways that trees
> repair damage and add strength for wind resistance all seem to add heat
> density to the wood. I cannot make this a rule though.
> Cork bark elm is no higher heat than Siberian elm, yet it makes
stronger
> wood. Why? The woven grain of the cork bark gives it it's strength. The
> open grain of Siberian elm makes an excellent charcoal though because of
it's
> porosity and lower apparent ash.
> I suppose we could do this complex analysis of compounds which change
> with the weather. This is of great use to botanists who are unlocking the
> secrets of Btu. production.
> The simpler way for most folks, is just to test raw heat value of
what
> material you have, with an understanding of the processes by which those
> values vary. Start with dry wood and subtract the ash. Just don't be
upset
> by a 2% variation from your neighbors experiments, it's not worth the
trouble
> to track it down.
> If 2% is the difference for you, than pay for good feedstock analysis,
> with a very consistent material. F 1 Hybrid or cutting produced trees
grown
> on plantations, wheat or other grain crops, sugarcane and grasses, all
tend
> to be much more similar in final make up due to the trouble farmers have
gone
> through to make a consistent product. Just use test samples from the same
> crop to compare apples to apples.
> Any good chemical analysis avalible of saps and resins? What is
cherry
> sap Vs maple sap? How about pine sap Vs spruce? What is in the high
energy
> sap in locust wood?
> This will expand the range of chemistry for analysis.
> Daniel Carefreeland(scape) Dimiduk

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From kenboak at stirlingservice.freeserve.co.uk Wed Jan 2 13:47:47 2002
From: kenboak at stirlingservice.freeserve.co.uk (kenboak@stirlingservice.freeserve.co.uk)
Date: Tue Aug 31 21:37:32 2004
Subject: Stirlings
Message-ID: <20020102184709.OFLN22946.fep04-svc.ttyl.com@localhost>

Ron and Stovers,

Thanks for your series of questions.

1. High costs are solely down to very low volume production - eg. Whistpertech are only making 10 units a week. There is nothing complex about the Stirling, amateurs can build models from tin cans with power output between 1 and 10W. These would be ideal for stove applications.

Omachron of Ontario are expected to start producing cheap engines this year in China. After all, China can produce a complete 125cc motorbike and sell it for under $450, the sooner they start building Stirlings in mass production, the better.

Check Out: http://www.omachron.com/papers.html

1b. The Stirling can be over-engineered. This was the case with the Philips 10-2C engine of 1951, but of the estimated 150 manufactured, about 75 are still known to be in working order. Modern manufacturing methods and extensive use of cheap stainless steel stampings/pressings will help to keep the costs down.

2. The Stirling is one of the simplest, most elegant ways of turning heat into mechanical power. A friend has a self-built solar engine with a 18" parabolic dish. Yesterday (New Year's day) at 2pm in London, behind a double glazed window he still got 10W of shaft power, from an engine with a 1" bore and a 7/8" stroke.

3. I have written an article on medium temperture difference engines suitable for domestic scale combined heat and power running on biomass. They use stainless steel cooking pots for the heat exchangers and salvaged automotive pistons and liners for the power piston. Estimated power output in the 50 to 100W range. I will forward this article to those who are interested.

4. I listen in to the stoves discussions, as I see a very viable source of heat from wood and other biomass. (I also like playing with fires ;-) I aim to show how cheap Stirlings can be made using existing metal working methods and readily available scrap materials in developing countries.

Ken

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From kenboak at stirlingservice.freeserve.co.uk Wed Jan 2 14:00:09 2002
From: kenboak at stirlingservice.freeserve.co.uk (kenboak@stirlingservice.freeserve.co.uk)
Date: Tue Aug 31 21:37:32 2004
Subject: Stirling Engines
Message-ID: <20020102185936.OFVT22946.fep04-svc.ttyl.com@localhost>

Scott & Stovers,

The Viebach engine can readily be inverted over a conventional wood burning stove run an alternator via a belt drive and start charging batteries. Viebach has done this in a demo model:

See the bottom of this site for a photo:

http://www.geocities.com/wastewatts/index.html

You can make out the nest of heat exchanger tubes sitting in the space at the top of the stove next to the flue outlet.

In Winter 1995 I demonstrated one of the early Viebach engines in London. We ran it for a week, 8 hours a day at an engineering exhibition. We used a 3kW propane burner to supply the heat. The mean electrical power output was 350W or about 8kWh per 24hrs.

If you go back 100 years - almost all hot-air and Stirling engines were solid fuel fired, Rider, Ericsson, Robinson etc. The problem was that they were big and heavy made from cast iron - Viebach engine weighs 50lbs and benefits from much more efficient heater and cooler.

Viebach has sold at least 100 systems to amateur enthusiasts, and is now offering an integral generator.

Look at the Uwe Moch site for the prices

Ken

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From pverhaart at optusnet.com.au Wed Jan 2 18:47:01 2002
From: pverhaart at optusnet.com.au (Peter Verhaart)
Date: Tue Aug 31 21:37:32 2004
Subject: Stirling Engines
In-Reply-To: <20020102185936.OFVT22946.fep04-svc.ttyl.com@localhost>
Message-ID: <5.1.0.14.2.20020103091052.00a352b0@mail.optusnet.com.au>

At 18:59 2/01/02 +0000, you wrote:
>Scott & Stovers,
>
>The Viebach engine can readily be inverted over a conventional wood
>burning stove run an alternator via a belt drive and start charging
>batteries. Viebach has done this in a demo model:
>
>See the bottom of this site for a photo:
>
>http://www.geocities.com/wastewatts/index.html
>
>You can make out the nest of heat exchanger tubes sitting in the space at
>the top of the stove next to the flue outlet.
>
>In Winter 1995 I demonstrated one of the early Viebach engines in
>London. We ran it for a week, 8 hours a day at an engineering exhibition.
>We used a 3kW propane burner to supply the heat. The mean electrical power
>output was 350W or about 8kWh per 24hrs.

So the conversion efficiency was less than 12 %?

Peter Verhaart

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From krksmith at uclink4.berkeley.edu Wed Jan 2 19:56:29 2002
From: krksmith at uclink4.berkeley.edu (Kirk R. Smith)
Date: Tue Aug 31 21:37:32 2004
Subject: Wood energy contents
In-Reply-To: <001e01c192d0$152fedc0$b919059a@kevin>
Message-ID: <4.2.0.58.20020102100933.01578b28@128.32.25.39>

According to an authoritative report by the Tropical Products Institute
in London (Report G-162, 1982), there is actually little difference in
gross energy content among wood types by mass. This can be seen
below (and attached) where the coefficients of variation (standard
deviation divided by the mean) of all woods tested is only 5%.
Although it would be great to know everything about all aspects of the
system, it seems to me that, given the range of uncertainties we must
accomodate in wood stove work, intrinsic differences in energy content
among wood species is in most circumstances a relatively small
contributor to system uncertainties. Usually of much greater
practical importance, for example, is the moisture content, which changes
lower heating value (and perhaps pollutant emissions) dramatically.

What do you think? Cheers for the new year/k

Gross Energy Contents of Hardwoods and
Softwoods

Numbers
of
Samples Range(MJ/kg) Mean(MJ/kg) Coefficient
of variation (percent)

Hardwood                268                     15.58-23.72     19.7            5
Softwood                70                      18.61-28.45     20.8            7
All
Woods               338                     15.58-28.45     20.0            5
Hardwood
Bark   72                      15.75-24.03     19.3            9
Softwood
Bark   56                      17.77-25.10     21.4            6
All
Barks               128                     15.75-25.10     20.2            9
Hardwood
sapwood        111                     18.11-21.98     20.4            4
Hardwood
heartwood      111                     18.51-23.66     20.7            5
Softwood
sapwood        3                       17.19-22.93     20.2            -
Softwood
heartwood      3                       17.19-21.16     19.6            -

From: TPI, G 162, 1982, Calorific Values for Wood and Bark.

At 03:43 PM 1/2/2002 +1000, Peter Verhaart wrote:
At 10:24 1/01/02 -0400, you wrote:
Dear Stovers:
I inadvertently sent Crispins original message to the list, rather than
the
following reply. Following is the reply I intendd to send. Sorry about
he
confusion.

Kevin Chisholm
*********************************
Dear Crispin

I hate it when I have to say "The book is wrong." :It makes me
look
arrogant. :-) However, in this case, it is wrong. Firstly, the statement
was
made 90 years ago, when wood was generally bought and sold by the CORD,
a
volume measure, and not by the POUND (or kG). It is unquestionably true
that
"heavier woods give more heat per CORD" but it is
unquestionably wrong that
wood of higher specific gravity has more heat per CORD than woods of
lower s
pecific gravity.

The book is wrong, I love saying that, the book is wrong. Resinous woods
have a rather low density but a high combustion value, probably much
higher than much denser woods not containing resin.
What kind of accuracy do you think you need?

Peter Verhaart

Snip

Kindest regards,

Kevin Chisholm
And my compliments to Kevin for his exhausive analysis, which I enjoyed
reading.
Happy New Year

Peter Verhaart

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gross_energy_hard_softwoods_table.doc

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From kenboak at stirlingservice.freeserve.co.uk Wed Jan 2 20:25:56 2002
From: kenboak at stirlingservice.freeserve.co.uk (Ken Boak)
Date: Tue Aug 31 21:37:32 2004
Subject: Stirling Engines
In-Reply-To: <5.1.0.14.2.20020103091052.00a352b0@mail.optusnet.com.au>
Message-ID: <00a701c193f5$8d640ee0$81b4883e@boakk>

Peter & Stovers,

The Viebach Stirling will produce about 500W of shaft power, making its
thermomechanical efficiency about 16.6%.

As it is designed for combined heat and power operation, where fuel would
have to be burned for heating anyway (say a wood stove in winter) the fact
that it can convert more than 10% of the heta energy in the wood into
electricity should not be dismissed as being inefficient.

All this is done by a unit in a box 30" x 24" x 24" which makes no more
noise than a domestic washing machine.

If you want to burn logs to make power, you can, or if you want to burn used
sump oil, or waste veg oil, or wood pellets or LPG or natural gas these
will all run the sam ebasic Stirling driven alternator.

This is a niche application for a very simple prime mover - a very elegant
heat engine. The problem is that the Stirling is too frequently applied as
a replacement to an IC engine, and this is its failing. Instead you should
use the Stirling in applications where you cannot use an IC engine for
reasons of noise, pollution or fuel restrictions - or where you just do not
need many horsepower.

Ken

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From kchishol at fox.nstn.ca Thu Jan 3 01:56:53 2002
From: kchishol at fox.nstn.ca (Kevin Chisholm)
Date: Tue Aug 31 21:37:32 2004
Subject: Actual heat from the fuel re: African Stove Tests
In-Reply-To: <003601c192fa$90e52460$74e80fc4@home>
Message-ID: <016901c19423$2e6016e0$b319059a@kevin>

Dear Crispin
----- Original Message -----
From: "Crispin" <crispin@newdawn.sz>
To: "Stoves" <stoves@crest.org>
Sent: Tuesday, January 01, 2002 3:20 PM
Subject: RE: Actual heat from the fuel re: African Stove Tests

> Dear Kevin
>
> >It is unquestionably true that "heavier woods give more heat per
> >CORD" but it is unquestionably wrong that wood of higher
> >specific gravity has more heat per CORD than woods of lower
> >specific gravity.

The above is the statement I made with a typo error... the correct statement
should have been:

> >It is unquestionably true that "heavier woods give more heat per
> >CORD" but it is unquestionably wrong that wood of higher
> >specific gravity has more heat per POUND than woods of lower
> >specific gravity.

>
> When I have lots of time I will copy out the comparison of heat content of
> wood purchased by cord. It is going to be useful to find out what to burn
> if you are buying wood, but it does not really get to the nitty gritty of
> the math of real fires burning non-dry wood..

There is no question that when you buy by the CORD, you get the best deal
with wood that has the higher specific gravity, simply because you are
getting more pounds per cord with the more dense woods.
>
> >>According to Schrenck, 1 cord of green
> >> wood contains 250 gal. of water
>
> >Going by memory, a cord of "green softwood, as cut" weighs about 3000
> >pounds, and a cord of "green hardwood weighs about 4000 pounds. 250
> gallons
> >of water, if Imperial Gallons, would weigh 2,500 pounds. This would
suggest
> >that "green softwood" has a moisture content wet basis of:
> >2500/3000 = 83.3%
>
> Your memory may have let you down here as obviously 83% is impossible.

Another possibility is that green wood does not contain 250 gallons of water
per cordand that Schrenk was wrong!! :-)
On
> page 454 the density of apple wood (for instance) is 44 lb/ft^3 = 5632
> lbs/cord at avg 17.5% moisture.

This would be the correct number if you had 128 cubic feet of this wood in a
cord. To do this, you would need planed wood. The reality is that typical
"as stacked round wood" contains about 85 actual cubic feet of wood per
cord. This calculates out to 3740 pounds per cord. Not far off my 4000 pound
estimate.

Long leafed yellow pine is the same.
>
> Wet oak is 7552 lbs/cord. Air dried it is 5120 for a difference of 2432
lbs
> of water. It does not have a figure for wet pine. I think the 250
gallons,
> Imperial or not, is correct.
>
I would respectfully suggest that you are wrong here. If we assume that the
average cord of wet oak is in the round form, and that it is carefully
stacked to maximize the wood content, then it is unlikely that it would
contain more than 100 cubic feet of solid wood per cord. This would give a
wood density of 75.52 pounds per cubic foot. This wood would not float.

If you take a piece of wet oak and drop it in the water, does it sink or
float?

If the "bone dry" wood has a specific gravity of less than 1.000, then it is
inherently impossible to add enough water to make the wood sink in water.
Some tropical woods such as purple heart, and lignum vitae, are "sinkers."

> >> Rosin increases the heating power by about 12 per cent.
>
> >He makes no reference to the quantity of rosin or resin present.
>
> IT is taken to be 'ordinary' meaning what an average buyer would find.
>
> >> Thus 100 lb. of green wood (50 per cent.
> >> moisture) furnish about 270,000 B.t.u., 100 lb. of air dry wood (10 per
> >> cent. moisture) about 580,000 B.t.u. and 100 lb. of kiln-dry wood (2
per
> >> cent. moisture) about 630,000 B.t.u."
>
> >1: He doesn't state if this is "moisture content wet basis" or
> >"moisture content dry basis.
>
> I went over the numbers and it is a moisture content wet basis.
>
> >2: He does not state ...if this is the "net heat available from
> >burning the wood in a typical boiler or furnace.
>
> It is my belief that it is the yield from a particular or average furnace
> because it is well below the actual heat content and these guys were no
> slouches about something this important.
>
With all due respect, he was a slouch. He left too many areas for ambiguity.
Thats what slouches do. What he said may have been appropriate for a given
context, but it is quite inappropriate to take his work out of context, and
to rely seriously on it, to deduce what he did not intend to convey. What
you quoted of his work was definitely sloppy.

> >>Based on Kevin's figure of 9240 I get 389813, 837375 and 909563
> >> BTU respectively per 100 lbs based on their 'curve'. The experiment is
> >> correct in principle but had serious errors. - CPP
>
> >Would you care to "revisit that statement? :-)
>
> The working out of the numbers shows correctly that wet basis wood burns
> with a higher heat content when there is less water in it and more dry
> matter per unit input mass. The error was that the lowest moisture
content
> wood (2%) yielded less total heat per kg of dry matter than the 10%
moisture
> wood (again, per kg of dry matter). If you plot the experiment there is a
> curve, not a straight line which 'physics math' would say has to be seen.
>
I don't know if you answered the question or not..... I maintain that what I
stated was indeed correct. Would you please clearly state whether you feel I
am correct or incorrect. If you feel I am wrong, please show me specifically
where I am wrong.

> >I would suggest that my 9240 BTU/pound estimate is in very close
> >agreement with the 9153 BTU per pound estimate given in this reference.
>
> That is what I was saying too.
>
So, I was not incorrect after all? :-)

> >> Under "Other Solid Fuels", p. 609:
> >> "Sawmill Refuse, consisting of saw dust, "hogged" or shredded wood
chips,
> >> etc., containing from 40 to 60 per cent. moisture. The calorific value
> of
> >> redwood, pine fir, hemlock, spruce and cedar refuse is practically 9000
> >> B.t.u. per lb."
>
> >This is a very generalized statement. There is a huge difference in the
> >heating value of a given wood when it contains 40% or 60% moisture.
>
> The figures are for BTU/lb dry mass.
>
OK... if it is "dry wood, then this is quite close to my estimate of 9,240
BTU/pound assuming "as much as 10% resin." However, as originally presented,
the statement was anything but clear.

...del...
> Most of the things you mention as variables in the wood affect the YIELD
not
> the amount of HEAT per lb dry mass. The cellulose + resin formula is
pretty
> impressive on this account. It covers the two main fuels in correct
> proportion.

I do not understand what you mean by YIELD. Could you please clarify?
>
> For example"
> >The base of the tree certainly has more ash and
> >density than the top branches.
>
This is questionable, for the simple reason that the ramial wood has a
higher percentage of bark, and bark generally tends to have more ash than
wood. Alternatively, if the wood was harvested by a skidder rather than a
porter, it would have MORE ash due to the mud content picked up in skidding.

> It makes no real difference if you are measuring fuel consumption by unit
> mass.
>
Agreed. This is where Schrenk went wrong, with his contention that density
was an important factor in determination of heating values.

> It is probably worth our while to find out what the heat content is for
the
> pellets as it surely varies regionally.
>
If we go on a "per pound basis" and correct for resin content, it should not
be much of a problem. All you have to do is ask the pellet manufacturer
"What is the typical heat content of your pellets, and how much do you
expect the heat content to vary from batch to batch?"

> To get an idea of how much these old guys knew about wood, listen to this
> description of "Southern Yellow Pine" by H Von Schrenk (Ibid. p.577-8)
>
> "Southern yellow pines (all pines of the Southern States manufactured into
> lumber including longleaf, shortleaf, loblolly and Cuban pines. The
lumber
> is divided according quality into "dense southern yellow pine" and "sound
> southern yellow pine;" dense southern yellow pine should show on either
end
> an average of at least six annual rings per inch and at least one-third
> summerwood, or else the greater number of rings should show at least
> one-third summerwood, all as measured over the third, fourth and fifth
> inches on a radial line from the pith; wide-ringed material excluded by
this
> rule is acceptable, provided the amount of summerwood, as above measured,
is
> at least one-half; the contrast in colour between summerwood and
springwood
> should be sharp, and the summerwood should be dark in colour, except in
> pieces having considerably above the minimum requirement for summerwood;
> sound southern yellow pine includes pieces of southern yellow pine without
> any ring or summerwood requirement);..."
>
> Summerwood is about twice as strong as springwood and so nature demanded
> this appropriate categorization.
>
With all due respect to the good Mr. Schrenk, this is a lot of fluff and is
not at all relevant to the present discussion.

> The section on strength of timber includes calculations for all these
sorts
> of wood because most structures were mostly built of wood in those days.
> They knew what to put where. I recall that Shaker chairs have 13
different
> types of wood in them.
>
Thats a Carpentry consideration, not a biomass energy consideration.

> For your interest, conifers contain on average more wood per cord that
> hardwoods because of better straightness. Black Oak with an average
> diameter of 5 inches is 85 cubic feet per cord (66% volumetric
efficiency).
> Eight inch chestnut gives 95 cu ft/cord.
>
With all due respect, this data is meaningless because of its generality.
Firstly, the diameter is totally irrelevant: Secondly, the species is
totally irrelevant. Thirdly, it is irrelevant whether the wood is coniferous
or deciduous. Fourthly, the "physical size of the actual cord" is important.
("Whle tree harvesting " of trees, giving a measure of 128 cubic feet of
stacked wood volume wil give a very much different "stacking efficiency"
than if the wood was blocked up as firewood in stove lengths.The art of
bucking a tree into logs determines how much yield a sawyer will get from a
"cord" of logs. Well bucked logs will stack well, and will give a relatively
high stacking efficiency because they are straight. Wood that is cut for
firewood has little to no concern for straightness, and as a consequence,
the "stacking efficiency" of wood for firewood is invariably less than for
wood that was cut for logs. Indeed, it is to the direct advantage of the
firewood seller to produce "less efficiently stacked wood"

> Ibid p.584 reads "One cord of first-class split wood obtained from sound
> pieces 12 in. in diam. contains 102.4 cu. ft. of solid wood."
>
The key thing here is the skill employed in stacking the split wood. Well
stacked wood will have few gaps or voids.

There are many variables associate with colume measures of wood. The "102.4
cubic feet of solid wood per cord" is unrealistically precise. This number
was undoubtedly calculated from a "face cord", and then projected as though
it would hold true for a "full cord." One problem is butting the wood
together.... if the wood was cut into stove lengths of approximately 16" and
split, it would be extremely unlikely the "three sticks per 4' width" would
butt perfectly. Three "face cords" would thus appear in reality to be
significantly more than one "full cord."

Hexagonal close packed wood of uniform size would have a maximum solid wood
content of approximately 116.0865 cubic feet per cord. However, that assumes
perfectly straight cylindrical stciks, with no knot lumps, sweep, bend,
hollow center, crooks or taper, which never occurs in real life. Especially
so, for wood cut for the heating trade.

> Wet chestnut with a density of 0.96 kiln dries to only 0.47.

I presume you mean "specific gravity."

All in all
> there is a lot of variability but the most important thing to have is a
> working rule of thumb based on known heat content of dry mass and a factor
> for moisture content that is good enough to rate stoves.
>
I would suggest that a good "base point" is "air dried wood" which would
typically have in the range of 20% moisture content.. However, even this can
be a big variable. When accuracy is important, then the "general rules" or
"rules of thumb" are not necessarily dependable. When accuracy is important,
then the best way by far is to dry representative samples, and correct for
moisture on a "bone dry basis."

I would indeed appreciate a confirmation of where specifically you feel I am
wrong and an explanation of why you feel I am in error, so that, in the
event I am actually in error, I can learn from it.

I look forward to your helpful reply.

Kindest regards,

Kevin Chisholm

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From pverhaart at optusnet.com.au Thu Jan 3 05:57:43 2002
From: pverhaart at optusnet.com.au (Peter Verhaart)
Date: Tue Aug 31 21:37:32 2004
Subject: Wood energy contents
In-Reply-To: <5.1.0.14.2.20020102153409.00a6cec0@mail.optusnet.com.au>
Message-ID: <5.1.0.14.2.20020103201225.00a09160@mail.optusnet.com.au>

At 16:56 2/01/02 -0800, you wrote:
>According to an authoritative report by the Tropical Products Institute in
>London (Report G-162, 1982), there is actually little difference in gross
>energy content among wood types by mass. This can be seen below (and
>attached) where the coefficients of variation (standard deviation divided
>by the mean) of all woods tested is only 5%. Although it would be great
>to know everything about all aspects of the system, it seems to me that,
>given the range of uncertainties we must accomodate in wood stove work,
>intrinsic differences in energy content among wood species is in most
>circumstances a relatively small contributor to system
>uncertainties. Usually of much greater practical importance, for example,
>is the moisture content, which changes lower heating value (and perhaps
>pollutant emissions) dramatically.
>
>What do you think? Cheers for the new year/k

In complete accord, happy New Year, Kirk.

Peter Verhaart

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From pverhaart at optusnet.com.au Thu Jan 3 05:58:42 2002
From: pverhaart at optusnet.com.au (Peter Verhaart)
Date: Tue Aug 31 21:37:32 2004
Subject: Stirling Engines
In-Reply-To: <5.1.0.14.2.20020103091052.00a352b0@mail.optusnet.com.au>
Message-ID: <5.1.0.14.2.20020103201935.00a3f610@mail.optusnet.com.au>

Thank you Ken. What kind of temperature can the head stand? How is the low
temperature heat discharged?
If a downdraft system were used, you could get at least 700 C in the head.
Designing a mechanical stoker would not be that hard since we then have
mechanical power available.

Peter Verhaart

At 01:25 3/01/02 +0000, you wrote:
>Peter & Stovers,
>
>The Viebach Stirling will produce about 500W of shaft power, making its
>thermomechanical efficiency about 16.6%.

Snip

>Ken

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From Reedtb2 at cs.com Thu Jan 3 07:19:27 2002
From: Reedtb2 at cs.com (Reedtb2@cs.com)
Date: Tue Aug 31 21:37:32 2004
Subject: Juntos (together) stove !!! This works!!
Message-ID: <7c.20b3817a.2965a5b3@cs.com>

Dear Paul and All:

Sounds great! I love the name. I love the "minch". I love the fact that
you have only been working in stoves for 8 months, but have a potentially
saleable stove COMBINING the best efforts of many on this list. There's no
substitute for DOING. I hope you will have your 10 stoves ready for Spring.

You might consider "beta testing" the stoves by selling them (at cost?) to
members on the STOVE list for them to test under their other conditions.

I hope you will get a drawing program (I use Corel Draw) and draw a pretty
picture of the concept complete with schematic raw fuel, pyrolysing fuel and
charcoal and flames, even though I'm beginning to get the idea.

It would be nice to see a stove commercialized (US) or deployed (the world)
from this list to pay for all the talk we've had.

Onward, TOM REED THE BEF STOVEWORKS

In a message dated 12/31/01 7:58:14 AM Pacific Standard Time,
psanders@ilstu.edu writes:

<<
Juntos ("together") Stove report.

This is a new design and it works in initial trials.

After my December Africa trip, I am back in frozen Illinois doing stove
design work.

Ambient temperature 20 F ( -5 C), snow fluries, light wind,
unprotected/unshielded stove and aluminum pot, and I boiled a liter of water
in 5 minutes. I am happy (but also glad to get indoors to write the report.)

I have already named my new stove. “Juntos” means
“together” in Portuguese (with a soft “j” sound like
the “ge” in protégé. Or in Spanish with the “h”
sound like in a political junta, making it sound like: “hoontos”
but not “hunt-tos”. In either language, it still means
“together” and is understandable by English speakers because of
the “junta” term.

Components of the Juntos stove:

1. Basket-shaped metal grate ala New Dawn – Crispin PP
2. Rocket stove (small version) ala Aprovecho – Dean Stills
3. True gasification unit ala Reed-Larson
4. Can burn briquettes ala Legacy – Richard Stanley
5. Air-pipe ala Paul Anderson

Includes pre-heated secondary air,
TOP lighting AND BOTTOM lighting sections,
Fast initial heat,
Long-term slow heat
Smoke-less when operational, almost smokeless at start-up.
Tincanium materials with probable mud and brick options,
Projected cost to be under $10 per unit, maybe under $3 if not counting
local labor and materials
But we could also have the “top of the line model” with $100
value (chrome plated and nice handles, etc??)
Burns most biomass fuels

And this is NOT an April Fools joke. It really does work. I have made and
tested two of them.

Think of layers of tin cans, each can has about a 6 minch diameter and a 7
minch height.

(Oh, by the way, I like the metric system, so I have invented the
“minch” unit, which is a
METRIC inch.).
One minch is exactly 2.50000 centimeters (not the 2.5415…..cm in the
English inch, which probably should be called an “einch” )

So multiply the minch measurements by 2.5 and you have the centimeter sizes.

4 minch = 10 cm
5 minch = 12.5 cm
6 minch = 15 cm
7 minch = 17.5 cm
8 minch = 20 cm
40 minch = 1 meter
and 0.4 minch = 1 cm.

Anyway, back to the stove
1. The lower or bottom unit is a tin can (I prefer a “gallon paint
can” because it comes with a lip at the top edge) with about 6 minch
diameter, open at the top, and with plenty of air holes at bottom or around
the lower outside edge. It would be nice if this lower can could be about
10 minch tall (see #2 below)

2. Insert a “basket grate” (ala Crispin) that is open at the
top (diameter just under 6 minch) and has a lip that seals reasonably well
with the top of the lower can (#1). The bucket height needs to match
– ( that is, fit inside) - the lower can. I like Crispin’s
basket grate that is about 9 minch high, so I needed to have an elongated
lower tin can for one of my initial stoves. I made a longer can by taping a
second can underneath.

3. The basket gate is sealed in its lower ¾ of length, and only the top
quarter has air holes in the side walls. This means that air that enters the
bottom of the tincan is able to rise up the outside of the basket (thereby
being warmed) and then that air enters into the upper part of the basket as
SECONDARY air to be mixed with the gasification gases that are being
generated below in the basket.

4. At the bottom of the basket grate is an airpipe the allows primary air
to enter at the bottom of the biomass fuel supply. The air goes upward to
the gasification (pyrolysis) zone that is gradually burning downward after
being TOP LIGHTED. All of this is ala Reed-Larson and their IDD unit, except
that the holes for the secondary air are in this lower unit, not provided by
a gap between the gasifier and the burner. In other words, the gases are
burned in the upper part of the basket grate.

5. Enter the Rocket Stove. Basically I made an OPEN-BOTTOM small rocket
stove to place on top of the lower unit (#1-3). I used a same-size tin can
and placed a wire grid at the bottom (top keep the chunky fuel from falling
through the bottom) and a side hole for inserting fuel pieces. (My
experiment had NO insulation or second layer or shield around the rocket
unit, so in my -5 degree C environment, you can imagine how much efficiency
I was loosing !!!! )

6. ABOVE the top of the rocket stove I could place an additional ring (for
more chimney effect) or place a holder for the pot of water. That holder is
want I will call the “cooking spot” or the “cooking
level”. I envision that in a real stove, the cooking spot will be
independently supported by bricks or metal or whatever, and could look like
the top of a stove with “burners” coming from underneath and/or
with a hot metal plate and a hot-water tank and whatever else the cook wants.
In other words, the heat generation containers would NOT be required to
support the weight of the cooking pots. And therefore the heat generation
containers can be inserted and removed from the area (a chamber?) that is
below the cooking spot.

7. And an extra: I rigged up a bicycle tire pump to be able to force air
into the air pipe that provides the primary air to the gasifier. I did not
need it, but it let me play with some “forced convection” options.

8. I could give more details on how I made one “basket grate”
that fit into a gallon paint can. I rolled some sheet metal, closed off the
bottom, punched some holes for the secondary air passages, added an air-pipe,
and stuck it into the paint can, sealing for air leaks as best as possible.

9. Fire dynamics observed:
a. By itself, the lower unit (the gasifier) has the characteristics of the
NC (natural convection) IDD unit of Reed-Larson. Not much draft.
Languishing flames. Nice but not sufficient to cook a real meal as currently
configured by itself.

b. The gasifier was loaded several times, mainly with the wood pellets
commercially available in the USA for pellet stoves. I consider those
pellets (diameter 0.5 cm and variable lengths of 1 to 2 cm) to be too small.
I think they block too much the flow of the air in the NC gasifier. I am
seeking some more “chunky” fuel, maybe 1 x 1 cm to 2 x 2 cm
sizes). I did sometimes mix in some sticks and some locust tree seed-pods
and some birch-bark (wow! for b-b) just for seeing some impact. I am NOT
measureing fuel quantities. I just want to get an acceptable fire, then we
can measure the heck out of it.

c. Into the Rocket unit, I placed various stuff. Mainly twigs and broken
pieces of briquettes, and once a full Legacy briquette with center hole.
Everything burned VERY well.

d. Imagine the secondary flames for the gasifier unit licking at the bottom
of the fuel in the Rocket stove. I hardly needed to think of lighting the
rocket area. The fire quickly went to minimal smoke, with shooting flames
that would make any cook-in-a-hurry a happy person. In fact, I was more
concerned about cutting back the fire!! I noticed great action in the
gasifier unit. The flames above must have been pulling in a draft of primary
air. I only played a little with trying to limit the primary air via the
air-pipe.

e. After the initial blaze with the rocket unit working great, those rocket
flames could be continued via the side-feeder hole, or allowed to extinguish
themselves. Then the gasifier continued to put out nice moderate heat that
could keep a slow boil going. (Remember that I was outside, below freezing,
and snowing slightly, and with no insulation on my stove, so do not ask me
for more than these “impressions” of what is
“moderate”, etc.)

f. When flames were gone from the gasifier, I tried the air pump. I had a
virtual forge in operation with glowing coals that eventually burned through
some of my makeshift metal materials! To consume in the stove or remove the
charcoal is an open option.

10. Discussion:

It seems to work very well as a combination of our various technologies.

Cheap at twice the price.

Subject to MANY variations and refinements, including issues such as
diameter of unit, and nature of the basket-grate, and control of air in the
air-pipe.

The stove really does bring together stove components from several people.
And that is why I chose the name “Juntos”. I can imagine seeing
variations to be called Juntos-2 and Juntos-3 and Juntos-3.C.7. I
consider the “Juntos” name to be copyrighted for this style of
stoves because the stove has potential to make it into production. If you
want a generic name, call them “combination stoves.”

Likewise, I and we all must respect that the “Rocket Stove” is
an Aprovecho name and product, so I should be referring to a
“lower-side loading stove” or whatever.

I invite everyone to participate with this stove design work.

Crispin, I will probably be making an order for some basket grates to my
specifications, so you can start thinking of what the prices could be and
what materials you recommend.

I hope to have enough refinements by February to seriously consider
production of 10 or 100 for my March trip to southern Africa.

Pictures? Not needed. Crispin and Dean and Richard and Tom+Ron all have
their websites to see the component parts. All I had in the back yard
looked like 2 or 3 paint cans stacked on top of each other, with flames at
the top.

Sincerely,

Paul
>>

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From Reedtb2 at cs.com Thu Jan 3 07:20:21 2002
From: Reedtb2 at cs.com (Reedtb2@cs.com)
Date: Tue Aug 31 21:37:32 2004
Subject: Stoves plans for Jo-burg world conference
Message-ID: <a5.208914fe.2965a5c0@cs.com>

Dear All:

In my experience these big general topic conferences are fun but not very
useful. Bureaucrats talking to bureaucrats mostly. We'll need them at the
right time, but I doubt if I want to spend a week an $5000 hearing them
repeat the half truths of yesteryear.

TOM REED

In a message dated 12/31/01 8:03:28 AM Pacific Standard Time,
psanders@ilstu.edu writes:

<<
Stovers,

We need to discuss who is going to the big UN conference in Jo-burg, South
Africa in the first week of September 2002 (THIS year).

I expect to be there, and I would certainly like to have some "stoves"
representation. I imagine that "booths" in the NGO area are already being
planned. Anyone have any info on that?

Can "stoves" join in with some other entity? Is Crest going to be there?
People, booth, both??

Happy new year to you all.

Paul
>>

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From Reedtb2 at cs.com Thu Jan 3 07:22:03 2002
From: Reedtb2 at cs.com (Reedtb2@cs.com)
Date: Tue Aug 31 21:37:33 2004
Subject: Down draft stoves are grate!
Message-ID: <138.726c07c.2965a5a5@cs.com>

Dear Ron:

You said " But my main point is that I can find no-one doing stove R&D
incorporating both DD and air control (implying a closed batch load of fuel)
with a small controllable port for primary air control). This looks
potentially attractive and I hope someone can report on whether it has some
advantages."

You might remember that the Turbo Stove we showed you at CPC had both
control over the fraction of primary air (to adjust the Air/Fuel ratio to
various fuels or limit power) and over the overall air supply (a gate on the
blower) to control total power once the correct air/fuel ratio was arrived at.
OOOOOOOOO
Are you going to ETHOS? I plan to go but haven't got my ticket yet. Let me
know what plane you are taking and maybe we can share a cab to U. Seattle....

Cheers, TOM REED BEF STOVEWORKS

In a message dated 1/1/02 8:34:25 PM Pacific Standard Time,
ronallarson@qwest.net writes:

<<
Rogerio, Piet, et al

I agree with Piet (not to promote the DDS) - if we limit ourselves to
the style of fuel feeding described by Piet and Khan.

But I think there is plenty of evidence from the gasifier community
(Reed, Das,....) that downdraft works well for pellets and gas production.
I also think that we should heed the good words offered by Dean Still on
some advantages they have found with DD.

But my main point is that I can find no-one doing stove R&D
incorporating both DD and air control (implying a closed batch load of fuel)
with a small controllable port for primary air control). This looks
potentially attractive and I hope someone can report on whether it has some
advantages.

Perhaps yours is the group to give it a try, since the DD stove
described by Piet is rather close to your own designs as I understand them
(meaning a large metal plate and a chimney).

Ron
>>

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From crispin at newdawn.sz Thu Jan 3 07:52:51 2002
From: crispin at newdawn.sz (New Dawn Engineering /ATEX)
Date: Tue Aug 31 21:37:33 2004
Subject: Actual heat from the fuel re: African Stove Tests
Message-ID: <001401c19457$07dbde80$2a47fea9@md>

Dear Kevin

I am not sure I ma in a position to judge which figures are correct or not.
I can only report on what my eyes have seen and my spreadsheets tell me. I
have tried to show that the figures reported for things like wet weight hnd
heat content are sensibly described, even if they are not couched using
modern technical forms.

I can forward the view of 100 years ago (for those interested in buying wood
by the cord which certainly happens in the US and probably Canada) that the
volume of solid wood in a stacked cord does depend on the diameter of the
wod stock. The 'efficiency' as I described it varies from 62 cubic feet of
solid wood for 1 inch diameter material to 85 cubic feet in and about the 5
inch range. Above that in diameter the solid wood component drops very
slightly. The table give expectable volumes up to 12 inch stock.

I do not know about 'stove' cut lengths and what the stacking would be. 100
years ago standard ratings of stacking wood were done with 48 long inch
pieces which were then stacked as best could be done in a cord-sized box 4 x
4 x 8 feet.

The efficiency is affected by the species as some grow very straight and
many do not. All the conifers tend to have very straight 48 inch lengths
and things like beech of maple are bent here and there affecting the stack.

I would expect that short split wood carefully stacked would reach very high
packing.

Your point about the density of the wet oak is well taken. Perhaps the
authors were refering to 128 cubic feet of green oak, not a cord, but the
figures given were listed as the weight of green wood stacked in cords. I
know that some woods sink in water when cut, others sink when soaked in
water (even in seawater!) and some never do. I am not sure the answer will
affect stove list subscribers. As we have no oak here to measure I will not
be able to verify anything for you.

>It is unquestionably true that "heavier woods give more heat per
>CORD" but it is unquestionably wrong that wood of higher
>specific gravity has more heat per POUND than woods of lower
>specific gravity.

This is very true and the example you gave was quite helpful to
understanding this.

I cited
>>Thus 100 lb. of green wood (50 per cent. moisture) furnish
>>about 270,000 B.t.u., 100 lb. of air dry wood (10 per
>>cent. moisture) about 580,000 B.t.u. and 100 lb. of kiln-dry
>>wood (2 per cent. moisture) about 630,000 B.t.u."

I feel the figure of 580,000 should be lower by a few percent, and that this
was a stove-based test not a thermal lab evaluation.

You gave me a figure for a pine with a certain level of resin in it (10%).
Perhaps they used a pine with a different resin level. I calculated that to
be 9%, and I assumed you were prefectly correct.

>> Most of the things you mention as variables in the wood affect the
>>YIELD not the amount of HEAT per lb dry mass.
>>The cellulose + resin formula is pretty impressive on
>>this account. It covers the two main fuels in correct
>> proportion.

>I do not understand what you mean by YIELD. Could you please clarify?

Well, things like soil conditions, rainfall, insolation etc affect the
amount of wood the forest yeilds per acre, not the amount of heat one gets
from burning dry cellulose. I meant yield in the agricultural sense. If
the wood growing conditions affects the heat produced by the dry mass of the
cellulose I would like to hear about that because it would be important to
species selection for woodlots.

>There are many variables associate with colume measures of wood.
>The "102.4 cubic feet of solid wood per cord" is unrealistically precise.
>This number was undoubtedly calculated from a "face cord", and then
>projected as though it would hold true for a "full cord."

I can't make that assumption. It is my belief that they based it on a large
number of cords, averaged. A great deal of timber was loaded into "standard
old" boxcars, whatever that means for transport over long distances. People
used huge amounts of firewood 100 years ago.

>>...the most important thing to have is a working rule
>>of thumb based on known heat content of dry mass
>>and a factor for moisture content that is good enough
>>to rate stoves.

>I would suggest that a good "base point" is "air dried wood"
>which would typically have in the range of 20% moisture content.

I can be most agreeable with that. The thing I need is a standard method of
calculating the actual heat available from burning it, compared with burning
oven-dried material. There is practically no point in us establishing an
internation gentlemen's (or woman's) agreement on testing stove efficiency
if we cannot establish how much heat a fuel charge contains. This is my
motivation in writing all this.

It would appear from all I have read that our air-dried briquettes have
between 14.1 and 17 MJ/Kg.

I think I remember someone writing in a few months ago giving a method of
calculating the heat loss due to moisture content. Could they please speak
up? We should be able to confirm the theory in a stove by doing identical
tests with briquettes of a known moisture content and with zero moisture
content. The performance difference should gives a close approximation of
the theoretical difference.

Many thanks to everyone.
Crispin

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From crispin at newdawn.sz Thu Jan 3 07:53:26 2002
From: crispin at newdawn.sz (New Dawn Engineering /ATEX)
Date: Tue Aug 31 21:37:33 2004
Subject: Kirks graphic
Message-ID: <001501c19457$09119f60$2a47fea9@md>

Dear Kirk

Could you please send me that graphic image directly as I only got a large
number of letters in the stoves digest. I still haven't found out how to
get the messages as they arrive at the discussion list. I only get the
digest.

Also there appears to have been a photo sent but I couldn't see that either.
I dn't know who sent it.

Thanks
Crispin

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From crispin at newdawn.sz Thu Jan 3 07:54:18 2002
From: crispin at newdawn.sz (New Dawn Engineering /ATEX)
Date: Tue Aug 31 21:37:33 2004
Subject: Stirlings in developing countries
Message-ID: <001601c19457$09ebd2c0$2a47fea9@md>

Dear Ken and other Stirling enthusiasts

I am offering to have a go at producing a small 250 watt (electrical) output
biomass fired engine on condition it is a public design (unencumbered by
intellectual property rights). We at New Dawn have been looking for years
for a suitable design but lacked the contacts.

Perhaps a member of the association would be willing to assist a developing
country like ours have a go at making an appropriate example of alternative
power. The Renewable Energy Association of Swaziland (REASWA) would also
like to be involved in dissemination.

We need 250 to 500 watts to compete with PV on remote pumping applications.
The PV systems are also 'out of reach' on generally only installed when a
grant is made.

The use of preheated primary and secondary air in our stoves may well be
applied to Stirling engines to good effect.

Regards
Crispin

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From kenboak at stirlingservice.freeserve.co.uk Thu Jan 3 13:51:14 2002
From: kenboak at stirlingservice.freeserve.co.uk (kenboak@stirlingservice.freeserve.co.uk)
Date: Tue Aug 31 21:37:33 2004
Subject: Stirling Engines
Message-ID: <20020103185040.QMPZ22946.fep04-svc.ttyl.com@localhost>

Peter & Stovers

The heater head is rated at 650 C max, but should be alright for short times at 700C. Heat is continuously being removed from the head by the working gas so it shouldn't overheat if the engine is running.

Viebach also tried a "super-alloy" stainless steel for use at 700C.

Viebach does a set of plans for the amateur to construct his engine

Look at Bernd Kammerich's site for details of hios wood fired Viebach configured as an alpha engine.

http://members.aol.com/BKammerich/mainengl.htm

Here is a whole page of links on Stirling Engines - too many to mention.

http://www.ucolick.org/~de/StirlingEngines.html

Technical data - translation from german

Dimensions:Height: approx. 600 mm Heating: arbitrary (prototype with propane gas)
Surface area: approx. 350 x 300 mm
Cooling: Water cooling
Weight, execution in aluminum casting: approx. 20 kg
Gas consumption without 225 gram/hour with 300 W mechanical
With generator ST 05 g-g approx..30 kg
Combustion air preheater
Flywheel mass 7.5 kg of diameter: 280 mm Working piston diameter: 85 mm
Idling speed: approx. 800 Umdr/min
Displacer piston diameter: 96 mm
Torque: 8 Nm
Stroke: 75 mm
Power Output - predicted: 300 - 500W
Working medium: Air or nitrogen

Power achieved so far measured with 10 bar: 505 Watts
Operating pressure: up to 10 bar
Achievement with generator: 450 Watts el.
Thermomechanical efficiency(with burner) 22%
Necessary temperature at the heater head:
The engine runs starting from 200°C, for 500W max. 650°C <
As refridgerator with air as work gas -100°C

Ken Boak

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From psanders at ilstu.edu Thu Jan 3 17:01:41 2002
From: psanders at ilstu.edu (Paul S. Anderson)
Date: Tue Aug 31 21:37:33 2004
Subject: Down draft stoves are grate!
In-Reply-To: <001001c19103$c423e260$6c15210c@default>
Message-ID: <4.3.1.2.20020103160122.00c39e70@mail.ilstu.edu>

Hi,

the shown DD BBQ did NOT have much of a hopper to hold the fuel, and, as
pointed out by Ron, does NOT have much control over the primary air supply
(except some adjustable grate that did not sound like much control, but I
might be wrong.)

ALL of my work with the IDD gasifier focuses attention to the need to
control the primary air supply.

Also, is it not possible that the generated gases are too far from the
flame to be continually ignited? A concern with the IDD is a "flare-out"
loss of flame to ignite the gases, thus resulting in smoke that should be
consumed in the flames. Is there an ignition method for the BBQ with the
DD fuel supply?

Paul
Paul S. Anderson, Ph.D., Fulbright Prof. to Mozambique 8/99 - 7/00
Dept of Geography - Geology (Box 4400), Illinois State University
Normal, IL 61790-4400 Voice: 309-438-7360; FAX: 309-438-5310
E-mail: psanders@ilstu.edu - Internet items: www.ilstu.edu/~psanders

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From larch at kootenay.com Thu Jan 3 18:26:59 2002
From: larch at kootenay.com (David & Laura Strom)
Date: Tue Aug 31 21:37:33 2004
Subject: Actual heat from the fuel re: African Stove Tests
In-Reply-To: <003601c192fa$90e52460$74e80fc4@home>
Message-ID: <3C340652.354B8950@kootenay.com>

The factors we log scalers use in British Columbia are:

For tightly-stacked gymnosperm cordwood, 1 cord = 2.3 cubic metres solid
volume.

Tightly-stacked rounds with bark ("average" bark?) = .65 of solid volume
(xylem)

Chemical composition and density can vary greatly by site conditions, age, and
where on the stem the wood grew. Larch butts, for example, can be up 23% (by
weight) arabinogalactan. One board can be as light as pine and the next would
have been a "sinker" log, if logs were still transported by boom or river
drive.

Best to do measurements on some trial batches from a source as typical as you
can get to real life.

Greetings,
David Strom

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From pverhaart at optusnet.com.au Fri Jan 4 01:21:26 2002
From: pverhaart at optusnet.com.au (Peter Verhaart)
Date: Tue Aug 31 21:37:33 2004
Subject: Down draft stoves are grate!
In-Reply-To: <039001c19346$6b11b180$17e26641@computer>
Message-ID: <5.1.0.14.2.20020104160855.00a3eae0@mail.optusnet.com.au>

At 16:07 3/01/02 -0600, you wrote:
>Hi,
>
>the shown DD BBQ did NOT have much of a hopper to hold the fuel, and, as
>pointed out by Ron, does NOT have much control over the primary air supply
>(except some adjustable grate that did not sound like much control, but I
>might be wrong.)

Yes, you are. This is not a gasifier, it burns wood. I never mentioned a
hopper, I did mention the fact that wood had to be added (almost)
continuously in small quantities.
Being (used as) a barbecue, it is no great inconvenience to feed it.

The generated gases burn downstream from the grate, having just negotiated
the brightly burning char, the excess air as well as the volatiles are
fresh and hot and eager to burn which they do on their way from the grate
to the box carrying the hot plate.

I have at times wondered if it would be useful to upload some more detailed
pictures of the stove, any comment?

Peter Verhaart

>ALL of my work with the IDD gasifier focuses attention to the need to
>control the primary air supply.
>
>Also, is it not possible that the generated gases are too far from the
>flame to be continually ignited? A concern with the IDD is a "flare-out"
>loss of flame to ignite the gases, thus resulting in smoke that should be
>consumed in the flames. Is there an ignition method for the BBQ with the
>DD fuel supply?
>
>Paul
>Paul S. Anderson, Ph.D., Fulbright Prof. to Mozambique 8/99 - 7/00
>Dept of Geography - Geology (Box 4400), Illinois State University
>Normal, IL 61790-4400 Voice: 309-438-7360; FAX: 309-438-5310
>E-mail: psanders@ilstu.edu - Internet items: www.ilstu.edu/~psanders

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From pverhaart at optusnet.com.au Fri Jan 4 01:22:31 2002
From: pverhaart at optusnet.com.au (Peter Verhaart)
Date: Tue Aug 31 21:37:33 2004
Subject: GAS-L: The Mystery of heat variance in biomass
In-Reply-To: <183.1a99c0e.2965a5a4@cs.com>
Message-ID: <5.1.0.14.2.20020104155020.00a3f380@mail.optusnet.com.au>

Stove dried wood contains about 50% carbon (at least I think that was the
rule of thumb we adopted). Next we assumed the rest was H and O in the
proportion of water. This gives C3 H4O2.
Nobody suggests this is accurate but works in the world of stovers.
There was a staff member at Eindhoven (not in our faculty, I am happy to
say), who explained the charcoal making process as driving off the water.
If things were only that simple.

Piet

At 07:16 3/01/02 -0500, you wrote:
>Dear All:
>
>Actually, not much mystery here.
>
>If you examine the heating value of "fresh" biomass it can vary from 5 to 22
>MJ/kg due to variations in WATER CONTENT, ASH CONTENT, and possibly
>composition. If however you look at the 100 or so samples on our website,
>www.woodgas.com , www.Phyllis.ne or others, you will see that the heating
>values vary from 18 to 22 MJ/kg based on BONE DRY, ASH free analysis.
>
>I use the average composition
>
>C H(1.4) O (0.six) to represent ALL biomass, knowing that it all varies a
>little. THere is also a formula at the site that predicts heating value from
>the ultimate analysis within about 1.5%.
>
>So, no great mystery if properly approached....
>
>Yours truly, TOM REED BEF STOVEWORKS

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From Carefreeland at aol.com Fri Jan 4 09:28:44 2002
From: Carefreeland at aol.com (Carefreeland@aol.com)
Date: Tue Aug 31 21:37:33 2004
Subject: Actual heat from the fuel re: African Stove Tests
Message-ID: <e6.20e8aebd.29671612@aol.com>

David writes:
Chemical composition and density can vary greatly by site conditions,
age, and
where on the stem the wood grew. Larch butts, for example, can be up 23% (by
weight) arabinogalactan. One board can be as light as pine and the next would
have been a "sinker" log, if logs were still transported by boom or river
drive.

Dan replies:
Thanks for backing me up on this observation of variation in wood density
and chemistry within a tree trunk. Another good example is the effect that
tree base wood dulls a chainsaw so quick. The reason here is "splash up" of
soil from the rain as the tree is growing. The bark grows around so much
dirt, that it acts like polishing grit on a cutting chain.
Lower on a plant, there is also less filtering of salts picked up by the
roots through cellular membrane osmosis. An example of this, is the reason
why we take cuttings of vegetative plants to renew the tissue. It's like
changing the filter cartridge.
This all makes higher ash content in the tree base.
The base of a tree also is stiffened the most by reaction to the wind,
producing buttresses in large trees. I am sure that this wood is of the
stiffer variety from more carbon bonding. This wouldn't make a huge
difference, but a measurable one chemically. Density is more affected.
Question, what is ARABINOGALACTAN ? What is it used for?
Thanks,
Dan Dimiduk

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From ronallarson at qwest.net Sat Jan 5 01:14:38 2002
From: ronallarson at qwest.net (Ron Larson)
Date: Tue Aug 31 21:37:33 2004
Subject: Down draft stoves are grate!
In-Reply-To: <001001c19103$c423e260$6c15210c@default>
Message-ID: <01e501c195b0$7b15e620$184be73f@computer>

Piet:

Thanks for your answer (later) to the first question below from Paul.
But you didn't answer the second question on flame holding. Could you
describe something more about what happens when the fuel loading is either
too fast or slow? Is there any difference between your design and the work
described by Khan? (In other words, could you say more about the operation
on each side of the "sweet spot". Length of flame, where the flame seems to
attach, etc.)
I would like to believe that, under all conditions, the flame is
attached to the burning wood. Paul seems to believe there is a large
separation between the wooden blocks and the flame - not true?
Could you also address anything special about best ways for start up?
And what conditions lead to flame out (due to wind? due to too much fuel?
too little?) and what you then need to do to re-ignite)

Thanks in advance.

----- Original Message -----
From: Paul S. Anderson <psanders@ilstu.edu>
To: Ron Larson <ronallarson@qwest.net>; Peter Verhaart
<pverhaart@optusnet.com.au>; Rogerio Miranda <rmiranda@sdnnic.org.ni>
Cc: <stoves@crest.org>
Sent: Thursday, January 03, 2002 3:07 PM
Subject: Re: Down draft stoves are grate!

> Hi,
>
> the shown DD BBQ did NOT have much of a hopper to hold the fuel, and, as
> pointed out by Ron, does NOT have much control over the primary air supply
> (except some adjustable grate that did not sound like much control, but I
> might be wrong.)
>
> ALL of my work with the IDD gasifier focuses attention to the need to
> control the primary air supply.
>
> Also, is it not possible that the generated gases are too far from the
> flame to be continually ignited? A concern with the IDD is a "flare-out"
> loss of flame to ignite the gases, thus resulting in smoke that should be
> consumed in the flames. Is there an ignition method for the BBQ with the
> DD fuel supply?
>
> Paul

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From ronallarson at qwest.net Sat Jan 5 01:15:30 2002
From: ronallarson at qwest.net (Ron Larson)
Date: Tue Aug 31 21:37:33 2004
Subject: Down draft stoves are grate!
In-Reply-To: <138.726c07c.2965a5a5@cs.com>
Message-ID: <01e601c195b0$7c2a1540$184be73f@computer>

Tom
You didn't catch the distinction I was making between DD and IDD (or
UD). To the best of my knowledge all of your turbo stove work has been with
IDD (UD). Please advise whether you have done any DD stove work (not DD
gasifiers) or know anyone who has done DD stove work with air control (not
fuel level control). Either forced or natural down draft. Thanks.

Ron

----- Original Message -----
From: <Reedtb2@cs.com>
To: <ronallarson@qwest.net>; <pverhaart@optusnet.com.au>;
<rmiranda@sdnnic.org.ni>
Cc: <stoves@crest.org>
Sent: Thursday, January 03, 2002 5:16 AM
Subject: Re: Down draft stoves are grate!

> Dear Ron:
>
> You said " But my main point is that I can find no-one doing stove R&D
> incorporating both DD and air control (implying a closed batch load of
fuel)
> with a small controllable port for primary air control). This looks
> potentially attractive and I hope someone can report on whether it has
some
> advantages."
>
> You might remember that the Turbo Stove we showed you at CPC had both
> control over the fraction of primary air (to adjust the Air/Fuel ratio to
> various fuels or limit power) and over the overall air supply (a gate on
the
> blower) to control total power once the correct air/fuel ratio was arrived
at.
> OOOOOOOOO
> Are you going to ETHOS? I plan to go but haven't got my ticket yet. Let
me
> know what plane you are taking and maybe we can share a cab to U.
Seattle....
>
> Cheers, TOM REED BEF STOVEWORKS
>
>
> In a message dated 1/1/02 8:34:25 PM Pacific Standard Time,
> ronallarson@qwest.net writes:
>
> <<
> Rogerio, Piet, et al
>
> I agree with Piet (not to promote the DDS) - if we limit ourselves to
> the style of fuel feeding described by Piet and Khan.
>
> But I think there is plenty of evidence from the gasifier community
> (Reed, Das,....) that downdraft works well for pellets and gas production
.
> I also think that we should heed the good words offered by Dean Still on
> some advantages they have found with DD.
>
> But my main point is that I can find no-one doing stove R&D
> incorporating both DD and air control (implying a closed batch load of
fuel)
> with a small controllable port for primary air control). This looks
> potentially attractive and I hope someone can report on whether it has
some
> advantages.
>
> Perhaps yours is the group to give it a try, since the DD stove
> described by Piet is rather close to your own designs as I understand
them
> (meaning a large metal plate and a chimney).
>
>
> Ron
> >>
>
> -
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From ronallarson at qwest.net Sat Jan 5 01:16:17 2002
From: ronallarson at qwest.net (Ron Larson)
Date: Tue Aug 31 21:37:33 2004
Subject: Juntos (together) stove !!! This works!!
In-Reply-To: <530055645.1009814289856.JavaMail.root@mail.ilstu.edu>
Message-ID: <01e801c195b0$7e4ad260$184be73f@computer>

Paul:

Like Tom Reed, I congratulate you on coming up with your new "juntos"
design reported on 12/31. Some questions below. (Like others, I hope for a
diagram when you can get to it. Maybe my issues will help).

You said:

<snip>

a. " I boiled a liter of water in 5 minutes."

This is indeed a good value - but I can't even remember others. I
vaguely recall that the Japanese liquid fuel camping stove Physician had
around 3 minutes as his lower limit (I think also for a liter). Anyone
able
to beat Paul's number? I am sure I never did so well. Was there shielding
around the pot - what size and shape pot? Can you estimate anything about
the power output (kW) or fuel consumption rate (grams per minute?).

b. I like your "juntos" name and explanation. Also "tincanium". However,
I hope the "minch" will be dropped - even more than I hope we can drop
inches, BTUs, and horsepower on this list. Metric units need to and can
come to the US - and maybe the stoves list can lead the way. Every US
stover I know can handle the metric system and usually does.
To the accuracy we achieve on this list, the minch is an inch anyway.

c. You coupled the terms: "Fast initial heat, Long-term slow heat" Can
you (now or later) couple this with an estimate in kW (or grams per minute).
Also helpful would be this only as a (turn-down) ratio.

d. You said "Projected cost to be under $10 per unit, maybe under $3 if not
counting local labor and materials"
Was this an estimate using cans or starting from scratch? Village artisans
or factories? I think it important to emphasize to this list that
controlling air flow does not have to be expensive. Congratulations

e. You said: <snip>
"1. The lower or bottom unit ...... with plenty of air holes at bottom or
around the lower outside edge."
(RWL): Could you better define the number and size of air holes - Do
you think there might be any advantage to making these secondary air holes
controllable? (So as to control the excess air ratio?)

f. In (2), you used the terms "basket grate" and "bucket" which I like
much better than "grate" as used by Crispin. Having seen the predecessor
stove in Zimbabwe, I have a clearer picture of this than most - but think we
should use the "bucket grate" term when there are not many holes, and
"basket grate" otherwise..

g. In (3) you note that for the basket grate "...only the top quarter has
air holes in the side walls" I think this is critical and glad to see that
you are planning to test with other configurations of holes. My work has
never had any holes in the fuel container, and I think the Zimbabwe
equivalent (name forgotten) had holes everywhere (no air control)
My (poor) recollection is that someone 3-4 years ago reported on a "basket
grate" with a top lit, air controlled, updraft charcoal-making,
natural-draft stove (I am intentionally trying to avoid the term IDD). which
had several (many?) holes per square cm ( perforated metal - rather like a
screen). It surprised me then and still does that this seemed to work.
Anyone on the list remember that stove developer? I do like this approach
for preheating the secondary air.

h. In (4) You introduce the controllable "Anderson air pipe" which I
believe has not been previously reported. Tom Reed does employ a blower
this way. Could you describe how you control the primary air - and how you
ensure a tight coupling?

i. Also in (4) You talk about the ".... gasification (pyrolysis) zone that
is gradually burning downward after being TOP LIGHTED." I would prefer to
drop the term "gasification" in this mode and say instead " .. the pyrolysis
zone is moving downward". We often hear of "charcoal burning" - which can
mean two very different things - either consuming or making charcoal (by
pyrolysis, not gasification). Small point, but I predict some list members
just starting up in later years will go off in the wrong direction with
these uses of "gasification" and "burning".

j. Re "5. Enter the Rocket Stove." I like this!! Could you add
more on the nature of the grid (a grate) you have employed? Any
deterioration? Will this have to be stainless? Etc (We had one report on
using locally made ceramic rods successfully as a grate.)

k. You said Re "6. [you] .... could place an additional ring (for more
chimney effect) or place a holder for the pot of water." Could you clarify
which you did in the test reported - and what the combustion area height was
for the Rocket Stove alone?

l. Also in (6) you said: "... the heat generation containers would NOT be
required to support the weight of the cooking pots. And therefore the heat
generation containers can be inserted and removed from the area (a chamber?)
that is below the cooking spot." I think this is a very important point
that we need to discuss more. The alterative is too often quite tippy, and
as you say not amenable to change-out. In Ethiopia, I tried a tripod
arrangement for the burner surface support - with mixed results. (hard to
get level)

m. Re (7). "....: I rigged up a bicycle tire pump..." Anything to report
(beyond that below)? Is "puffiness" a problem? Would a homeowner be
willing to do?

n. Re (9a) , you said: " By itself, the lower unit (the gasifier) .....
Not much draft. Languishing flames." (Again - I would prefer "pyrolyzer"
over "gasifier") Was there any combustion chamber height (to attain a
better draft) above the lower pyrolyzing chamber? I am surprised that it
worked at all, if there was no upper cylinder. What was the depth of the
fuel below the uppermost lip surface in this test?

o. Re (9d) You said: " The flames above must have been pulling in a draft
of primary air. I only played a little with trying to limit the primary air
via the air-pipe." Others who have not tried this will not appreciate the
"tremendous" (loosely speaking) draft available from chimney heights even as
little as 15 cm. Some control mechanisms I have tried, that looked visually
like they were tightly closed, still let in too much primary air. Again, I
am interested in how you were controlling the primary air through the tube
(rotating valves, flaps, plugs, etc)

p Re (9e). You said: ".... Then the gasifier continued to put out nice
moderate heat that could keep a slow boil going." I think the added fuel
input port above (part of the bottomless "Rocket") has many nice potential
features - but I worry about not being able to control its air flow. Maybe
you can see a way to put a closeable door there - to keep the excess air
ratio down - and keep efficiencies up.

q. re (9f) You said: .".... To consume in the stove or remove the
charcoal is an open option." Did you mean this last sentence to apply in
all cases or in only the case with the "forge" operation obtainable with the
air pump? I wonder if Dan Diminiuk or Das or other stove-list metal working
experts could say something about the modern blacksmith's use of a forge air
blower that has a large enough angular momentum to keep rotating and pumping
air for a minute or so (a guess) before being cranked up again. Can these
be produced at sufficiently low cost to be used to help consume the
charcoal? Should we stick with electrically powered blowers?

Re your "10. Discussion" No comments nor questions. We will all benefit
from diagrams, but your description was excellent. Hope my questions might
spark some discussion (and further experiments) of the type you:are urging.

Your "togetherness" approach is also reminiscent of the "Dasifier"
developed by our new "stoves" member Das (and introduced by Tom Reed on Nov.
5). Das also was coupling two very different (in his case, UD and DD)
approaches in a single device - with nice consequences.

Your submission has also asked me to ask myself whether the proposed DD
pyrolysis stove of the type I described on 27 December (that I still think
has not been constructed) has a parallel along the lines you are
investigating. That is - what does a "DD Rocket" look like and does it
operate with the advantages you have given? Tis late, so I'll see if I have
an answer after sleeping on it. Offhand, your combined UD approach looks
much better (ability to add fuel late in the process, get higher output
power (turn-up ratio) when starting or otherwise needed). The main
advantage of the DD pyrolyzer stove concept is that the required draft gets
all emissions out of the room - so maybe the added feature of another
down-stream fuel port may also be worth considering.

Anyone else have a comparable "juntos" ("together") stove idea?

Lastly, Paul - any negatives that you have thought of? Would you guess
that the extra cost of combining types will generally be found valuable
for/by users? Any concerns about being able to teach users?

Again, thanks for providing this early report. I look forward to
hearing more - especially on your results with different types of fuels. It
is great to hear that the juntos is so tolerant of fuel type. It will be
interesting to see the juntos subjected to laboratory-type emissions and
efficiency testing. Maybe with support from the Shell Foundation.

Ron

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From lanny at roman.net Sat Jan 5 11:07:47 2002
From: lanny at roman.net (Lanny Henson)
Date: Tue Aug 31 21:37:33 2004
Subject: Pot jacket with beaded spacer
Message-ID: <003101c19602$bf3f9240$44ba3cd0@default>

How about using a bead to space and form a spiral channel pathway around the
pot to maximize the time hot gas spends on the pot. Here are two photos
about 50kb each of a first attempt at building one. I only have about 1.5 sq
in of channel space with this first test piece, not enough.
http://www.roman.net/~lanny/pj1.jpg
http://www.roman.net/~lanny/pj2.jpg
Lanny

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From kchishol at fox.nstn.ca Sat Jan 5 11:58:37 2002
From: kchishol at fox.nstn.ca (Kevin Chisholm)
Date: Tue Aug 31 21:37:33 2004
Subject: Pot jacket with beaded spacer
In-Reply-To: <003101c19602$bf3f9240$44ba3cd0@default>
Message-ID: <000c01c19609$9887e740$a119059a@kevin>

Dear Lanny

I think you have quite a neat idea here in concept. It would certainly work
well to improve heat transfer.

However, I would anticipate the following problems:

1: Pressure losses would require increased draft to ensure that all the
products of combustion were drawn through the passages.

2: The sidewalls of the pot would be sure to find any soot components in the
products of combustion

3: This system may end up being so effective as a heat transfer device that
it becomes self defeating. Specifically, it may extract so much heat from
the products of combustion that there is insufficient "waste heat" in the
off gas to create draft sufficient to run the stove at its original power
level.

It is possible that with the rolled bead, you may have "too much of a good
thing." Possibly you would get better net results if you simply used a
similar jacket, but with 4 centering dimples, to center the jacket around
the pot. Your effective "gas passage area" would be much larger, and
pressure drop would be correspondingly much smaller.

Best wishes with your tests!! Please keep us posted on your results.

Kindest regards,

Kevin Chisholm
----- Original Message -----
From: "Lanny Henson" <lanny@roman.net>
To: <stoves@crest.org>
Sent: Saturday, January 05, 2002 12:04 PM
Subject: Pot jacket with beaded spacer

> How about using a bead to space and form a spiral channel pathway around
the
> pot to maximize the time hot gas spends on the pot. Here are two photos
> about 50kb each of a first attempt at building one. I only have about 1.5
sq
> in of channel space with this first test piece, not enough.
> http://www.roman.net/~lanny/pj1.jpg
> http://www.roman.net/~lanny/pj2.jpg
> Lanny
>
>
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From andrew.heggie at dtn.ntl.com Sat Jan 5 12:30:57 2002
From: andrew.heggie at dtn.ntl.com (AJH)
Date: Tue Aug 31 21:37:33 2004
Subject: Pot jacket with beaded spacer
In-Reply-To: <003101c19602$bf3f9240$44ba3cd0@default>
Message-ID: <t6de3u8vblh15dg1qfkrm43p8vp1ntod58@4ax.com>

On Sat, 5 Jan 2002 12:54:03 -0400, "Kevin Chisholm"
<kchishol@fox.nstn.ca> wrote:

>Dear Lanny
>
>I think you have quite a neat idea here in concept. It would certainly work
>well to improve heat transfer.
>
>However, I would anticipate the following problems:
>
>1: Pressure losses would require increased draft to ensure that all the
>products of combustion were drawn through the passages.

I agree from the pictures the drag of the surfaces would be high, in
my attempts at implementation I brazed on 50mm "flights" to maintain a
50mm by ~100mm flue path. I actually had concluded the helical flights
would best be formed in the stove rather than the pot to keep the pot
price low. I can provide pictures of my attempt but have never
fathomed out how to upload to my webspace. I have set this aside as it
was rather more complex and involved a concept more similar to the
storm kettle but with the flue gases making passes over both inner and
outer surfaces, I failed to make it well enough to be watertight.
>
>2: The sidewalls of the pot would be sure to find any soot components in the
>products of combustion

As would any cold surface, pot included. Hence ensure more complete
combustion.
>
>3: This system may end up being so effective as a heat transfer device that
>it becomes self defeating. Specifically, it may extract so much heat from
>the products of combustion that there is insufficient "waste heat" in the
>off gas to create draft sufficient to run the stove at its original power
>level.

Which is yet another reason to look at forced draught.

AJH With a belated Happy New Year to all stovers

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From crispin at newdawn.sz Sat Jan 5 13:03:22 2002
From: crispin at newdawn.sz (Crispin)
Date: Tue Aug 31 21:37:33 2004
Subject: Truncated cone basket grates
Message-ID: <009a01c19612$b6d3dc00$4be80fc4@home>

Dear Stovers

The nomenclature problem for the grate is recognized. I have no real
opinion on it. What is clear to you?

If you want to make a basket grate and try it out, make a truncated cone
with a large diameter (the top) of about 135-140mm and a bottom of about
115mm. The height should be about 250-275mm. Space the holes in it so that
the are approximately evenly distributed. Make 60-80 holes with a diameter
of 7.5mm (a-la-Hancock) or 10.5 (a-la-New Dawn). The bottom is completely
open with just enough wire or grate or expanded steel sheet to hold the fuel
while it is burning.

It has to sit inside a secondary air tube that is very loose, about 145mm in
diameter and similar height. Hold it as you will, fill with about 150-250
grams of small wood and bottom light! Once it is heated up, it should boil
a litre of water in under 3 minutes depending on the pot's mass
size/colour/finish.

You can create a charcoaling grate by placing a large washer cut from sheet
metal so the bottom hole is reduced to 25-40 in diameter and then drop in a
sleeve made from a rolled up sheet so that it blocks half or more of the
holes.

Paul, you might try this so you can block secondary air in portions of the
grate in an experimental fashion. The fuel at the bottom, though
bottom-burning not top-burning, is starved of air and smokes excessively.
This smoke is burned in the upper section of the grate when mixed with
pre-heated secondary air. Substantial charcoal is produced because of a
lack of primary air. I do not find this useful.

You can continue to add fuel from the top as long as you only add it up to
the top of the inner sleeve. More charcoal can be made in this way.
Removing the sleeve and washer turns it into a regular stove again. The
washer will block the ash from falling out so it will not clear itself like
a Tsotso or Basintuthu.

One problem I have had with the choked stoves is that if the primary air is
preheated it is difficult to turn the power down without continuing to
generate so much wood gas that it lights up when it has left the stove/pot
area and flames off like an oil rig. It is impressive but it is not very
efficient when doing that. The immediate cause appears to be that heat
stored in the steel work drives the gassing and as the temperature of the
incoming air rises significantly due to its decreased velocity, the process
may even accelerate! Not what I have in mind. My cure is to limit the fuel
content as the main power control mechanism on that layout.

Regards
Crispin

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From ronallarson at qwest.net Sat Jan 5 14:20:32 2002
From: ronallarson at qwest.net (Ron Larson)
Date: Tue Aug 31 21:37:33 2004
Subject: flash carbonization of biomass
In-Reply-To: <DKEKJFDEBAHEFLPFIOFOIENICBAA.mantal@hawaii.edu>
Message-ID: <00b001c1961e$4f29a880$06f66641@computer>

Andrew: Sorry for the long delay in responding to your very thoughtful
response of Dec. 29 (to mine of 12/25) on charcoal-making (including CM
stoves).

1. You said (after quoting me on Antal's new discovery):
".... I thought the major achievement of his process was the
high yield of carbon as opposed to high volatiles charcoal. This
should have good implications for low ash charcoal for use in high
grade metal refining......"
(RWL1): I need help on this from both yourself and Mike. Are you
suggesting 1) that Mike does not have high volatiles and 2) that high carbon
means low ash, and/or 3) that high grade metal refining requires low ash.
My confusion comes from not knowing enough about different grades of
charcoal and their uses - which I am sure both you and Mike do.
I once gave some stove-produced charcoal to a woman using it for burning
incense - she didn't like it as it (I think) had too much "high volatiles".
On the other hand, I have heard others on this list say that high volatiles
was an advantage in lighting charcoal for cooking. Could you give us a
tutorial on charcoal - especially as desired in rural areas for cooking?

2. After another quote from me asking Mike about small scale pressurization
for cooking, you said: "
"High pressure is very limiting as the vessel size increases, which has
implications for mechanised loading. What a lot of people seem to fail
to appreciate is that charring even at low pressures can be a quick
process."

(RWL2): Your response is (naturally) dictated by the very impressive
large scale (one person operation but megascale compared to a cook stove)
work that I had the privilege to see in operation in October - including
mechanised loading. But my view of a "pressurized cook stove" is one that
is of course hand-loaded and is smaller than the usual pressure cookers I
see. While agreeing with you completely, I'd like your opinion on whether
there is some fundamental reason to forget working on pressurized
small-scale cook stoves.
On your second point, I guess I agree - but need clarification. First,
we are generally not interested in speed of charcoal-making with a CM stove.
My interest in pressurization is more in being able to get a superior and
higher quantity of charcoal. Maybe to also use the pressure productively
(perhaps).

3a. The third quote of mine you used was directed to "waste" heat
utilization. You referred to our "cocoa tin" discussion and said:
"The drawback of this retort heated from outside approach is that the
heat
transfer can only take place through the walls of the vessel and
thence from char particle to unreacted biomass, but it does make use
of the offgas being flared in a supporting fire. There is likely to be
gradation of the extent of charring from outside to middle."
(RWL3a) This also was the case with the similar CM stove developed by
Professor Grover in India. It was not rapidly controllable either. The
retort's principal advantage is that it effectively prevents air entry.
(but not so easy to obtain complete closure.)

3b. You continued: " Traditionally char was made in kilns, basically an
air starved fire in
a container, I believe the idd stove is a kiln in this respect. The
kiln has a heat transfer advantage in that the offgas and combustion
products circulate around as yet unreacted biomass. The disadvantage
is that valuable char is consumed preferentially to offgas to achieve
this."
(RWL3b): Again, a need for further discussion. 1.) I don't see the
"heat transfer advantage". The CM UD (or should I say UD CM? I choose the
former only because it is eawier to say) stove puts about the same about of
hot gas past about the same amount of unreacted wood, it would seem (albeit
a much longer path in a large kiln. In the CM UD stove, there is a
continued similar parallel gas flow path whereas in most kilns they seem to
be mostly bottom lit (my reading of the charcoal kiln literature) - and the
air flow is dictated either by moving a number of chimneys or by air holes
that appear as the dirt-covered pit kiln collapses.
[Oops - after rereading, I realized your comparison was not between a
kiln and a CM UD, but rather between a retort and a kiln. But I decided to
leave my comment, since it might help someone.)

2) There is a charcoal loss in both kilns and the CM UD by combustion -
but I don't believe this is intentional. Rather, I believe that a
well-managed kiln (and CM UD) continues in operation by virtue of the
pyrolysis reaction being exothermal. My "proof" of lack of combustion is
that the charcoal from a CM UD is rarely white (except where near the
secondary air source) - no ash.

3c. You said: "So one needs to combine the attributes of a kiln's good
heat transfer,
with those of a retort's high char yield. This is the approach Lurgi
used in coal retorts and I believe the Simcoa plant. Mike appears to
be taking the same route and it is also my preferred approach.
....."
(RWL3c): I think we probably have a lot to learn from the world of coke
making. Can you provide some references to the Lurgi/Simcoa processes? As
I interpret this, you are saying that you prefer the retort to the kiln -
and probably even at the small CM UD stove level. My reaction is that I
don't know enough about the retort approach to make a choice at the large
scale level (except that most charcoal kilns are venting only - no flaring -
horrible!). I am bothered by Mkie Antal's response that his approach does
not release a combustible gas - presumably too moist, maybe because he (like
many charcoal makers, including yourself) wants to utilize material of any
moisture content. I am not willing to accept that the retort approach is
better for cookstove operations - it has a very slow response time. Do you
agree? Should I be taking most of your comments in this message as not
applying to cookstoves?

3d. You said next: "This is why I am not keen on promoting IDD as a means
of making
charcoal, though I am happy to accept its by product is charcoal that
is produced with little pollution and as such is better than much
charcoal making. I think Tom Reed agrees with me the IDD pyrolysis
front is powered by charcoal burning, plainly this detracts from
charcoal yield. With the advanced clean charcoal making I, and Mike
Antal, are playing with any heat necessary for maintaining pyrolysis
comes from burning some of the offgas and recirculating this hot gas
stream through the char. There are a number of ways of configuring
this, none patentable IMO but nonetheless the actual designs will be
proprietary and subject to confidentiality."
(RWL3d): I like your first sentence. I also believe that rapid
controllability of power output is of high value - as is having a saleable
co-product.
I invite Tom and others to comment on the second, which I don't believe
is true - but
I am of course willing to give up some charcoal, even if true. The CM UD
stove charcoal yield (25%?) is about equal to that from the best of (heavily
polluting) rural charcoal makers.
There is no single optimization demand on processes with co-products.
So far, the only big drawback I hear is that education is required. You,
Mike, and I (but not everyone) agree that we should be trying to get rid of
the traditional kiln approach. Which approach will end up being successful
will depend on faactors we can now probably not even guess. We have to
fight thousands of years of traditional charcoal making (and my concerns
are not only that the gases are un-healthy, but also global warming
concerns, and desertifications and deforestation from something that is so
wasteful.
I understand your and Mike's concerns about confidentiality - and
appreciate all that you do help us with good ideas.

(3e) The implementation I am looking at uses quite basic technology and
should be possible to deploy in the sort of situations envisaged by
the Karves' project. A benefit to my mind is that this method can
control the temperature and cook time of the biomass to vary the
resulting char from post torrefied wood through Tom's seasweep and up
to metallurgical grades. My interest is in high volatiles charcoal and
I have made material which is friable like charcoal but retains 45% of
the mass of the original dry matter.
(RWL3e): Having seen your work up close, I can attest that your steam
drying technology is quite exciting to me - and I understand you know how
to control temperature - which I don't think we will get to for the rural
stove market. I would like to hear more about your reason for interest in
the high volatiles market - and whether there is a lesson there for the
rural stove area - both for those producing charcoal briquettes and for
those of us interested in CM stoves (either UD or DD).

Summary - Andrew. Thanks for these valuable inputs on charcoal. Always fun
to correspond with you.

I would still like to hear more from anyone on the subject of higher
pressure as applied to small (order of 1 kg per hour?) CM operations. I am
leaning against pressurization and retorts, but for reasons of poor
controllability. Can a retort approach be done at very small scale with
rapid control response and low cost?

Ron

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From dstill at epud.net Sat Jan 5 14:25:11 2002
From: dstill at epud.net (Dean Still)
Date: Tue Aug 31 21:37:33 2004
Subject: LETS ADOPT A UNIVERSAL POT
Message-ID: <001c01c1963f$d1273c00$0915210c@default>

Dear Lanny,

Glad to hear that you want to continue the Rocket Wok project. I'll try from
my end to use the stove as much as possible, get the students to use it and
give it a real try out. And I'll get you all the feedback. Also inform the
List.

I looked at your improved pot skirt and my two cents worth would be that
using a insulated Rocket combustion chamber under the pot gives us a lot of
draft so I wouldn't think that diminished draft would be a problem. Mark
Bryden who advises me about stoves, has the idea that increasing the force
with which hot flue gases contact the pot helps to punch through a still air
boundry layer so I wonder about the value of increasing dwell time, slowing
hot gases, as a big determinant of heat transfer. I don't know and the
perfect test might be to compare results from a straight skirt and your
spiral. I do know that the right sized gap has a tremendous effect on heat
transfer and that this gap is very small. Larry uses as a rule of thumb
keeping the same cross sectional area all through the stove so bigger pots
use smaller gaps.

Of course, the pot shape is a huge factor. A pot that touches more water
inside is better, therefore a large diameter pot with a little water in it
boils quickly. In our tests, big pots generally score higher than small
pots.

Could I then take this opportunity to forward a suggestion which Ron and I
tossed about on a train heading from Rugby to London? Let's form one center
of sanity in the bigger stove world here on the CREST list and all agree on
a pot size/amount of water that we all use in our tests! Then we can compare
results of tests. Until we do so, this factor will confound comparisons.

At Aprovecho we now use a nine inch in diameter steel pot that is five
inches high. We use five pounds of water in it. But I'm perfectly happy to
switch to liters!!

If we establish the UNIVERSAL POT SIZE FOR TESTING/AMOUNT OF WATER we will
have done something that the befuddled stove world has not accomplished in
decades! Let's do it and maybe we'll force the rest of the stove world to
follow...

Best,

Dean

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From dstill at epud.net Sat Jan 5 19:42:36 2002
From: dstill at epud.net (Dean Still)
Date: Tue Aug 31 21:37:33 2004
Subject: UNIVERSAL POT
Message-ID: <001101c1964a$dec6c780$1615210c@default>

Dear Don,

I agree that a bigger pot and one and a half gallons of water is a better
size as it is more like what folks are using in Central America.

Best,

Dean

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From Carefreeland at aol.com Sat Jan 5 19:51:09 2002
From: Carefreeland at aol.com (Carefreeland@aol.com)
Date: Tue Aug 31 21:37:33 2004
Subject: flash carbonization of biomass
Message-ID: <ca.47b5fa3.2968f93c@aol.com>

Ron says:
I would still like to hear more from anyone on the subject of higher
pressure as applied to small (order of 1 kg per hour)? CM operations. I am
leaning against pressurization and retorts, but for reasons of poor
controllability. Can a retort approach be done at very small scale with
rapid control response and low cost?

Ron

Dan's reply:
I've been building up a supply of "tincanium" for experiments. My first
was going to be a idd stove with the aluminum base experiment. I like this
challenge even better, and have a couple of empty 16oz. disposable propane
cylinders for small retorts.
I could use any ideas on how to configure this. Right now my first
instinct is to make the cylinder upside down and vertical suspended within a
large tin can. The top (bottom) of the cylinder would be cut and open like a
hinged pot lid. The bottom (top) would have a drilled out valve with some
kind of burner to heat the retort first, then residual heat would go to the
pot on top of the retort.
The devise would need a pressure relief system, probably in the loading
door latch. I wood imagine that any wood that fit in the retort could be
used.
The bottom of the can would need a small combustion area to prime the
retort. possibly using a small measured amount of kindling. Could we idd
this part too? By having two parts that produced heat, the charcoal from the
first process would help the second ignite and reach combustion temp. The
burner could be designed to receive gas from both bottom or top.
Complex, but could be an efficient charcoal producer. This is what I
call "cutting edge research" or maybe just a "shot in the dark."
Well, just a few stray thoughts on a way to approach this.
Comments?
Daniel Dimiduk

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From Reedtb2 at cs.com Sat Jan 5 19:51:36 2002
From: Reedtb2 at cs.com (Reedtb2@cs.com)
Date: Tue Aug 31 21:37:33 2004
Subject: LETS ADOPT A UNIVERSAL POT
Message-ID: <138.74460f9.2968f98d@cs.com>

I like the idea of a universal stove test with a prescribed pot size. However, I was puzzled during my visit that you boiled 5 lb of water when so many other people (and therefore we do it) seem to use 1 liter.

I vote for 1 liter because

The test is faster
It is enough to do most cooking since the steam condenses on the food (when there is a lid)
It is easier to divide by 1,000 cm3 than 5 lb or 2.72 liters.

Ron asked this morning whether 3 minutes to boil 1 liter was a record. Possibly. We most always boil in less than 7 minutes, sometimes 5 minutes on the various forced draft stoves. FOr water at 20 C boiling at 100 C, 5 minutes to boiling implies a heat transfer rate of (1 liter X 4.18 kJ/liter-degreeX80degrees/300 sec) 1.11 kJ/s = 1.11 kW, a respectable heat transfer. (The small element on an electric stove consumes 1.5 kW, the large 2.5 kW).

I hope you are taking a census on the answers, having asked a good question.

Yours truly, TOM REED BEF STOVEWORKS

In a message dated 1/5/02 12:25:15 PM Mountain Standard Time, dstill@epud.net writes:

Dear Lanny,

At Aprovecho we now use a nine inch in diameter steel pot that is five
inches high. We use five pounds of water in it. But I'm perfectly happy to
switch to liters!!

Best,

Dean

From Reedtb2 at cs.com Sat Jan 5 19:52:01 2002
From: Reedtb2 at cs.com (Reedtb2@cs.com)
Date: Tue Aug 31 21:37:33 2004
Subject: "Formula for Biomass" and Charcoaling....
Message-ID: <b7.19819873.2968f99b@cs.com>

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BioEnergy Lists: Improved Biomass Cooking Stoves

January 2002 Biomass Cooking Stoves Archive