[Stoves] AUTOCHAR VS CLASSICAL CHARCOAL PYROLYSIS

Tue Dec 17 12:22:19 CST 2013

Dear Otto and All

Moving into the 21st Century:

AUTOCHAR VS CLASSICAL CHARCOAL PYROLYSIS

Classical charcoal making requires external heating of a charge of wood isolated in an internal vessel.

The outer vessel heats (and mostly dries) the internal biomass to about 300C, at which temperature the reaction to charcoal becomes  exothermic and the charcoal heats itself to 400-450C.  It is not necessary for the kiln to be heated beyond ~ 300-350 C to get full conversion to LOW temperature charcoal, with lots of volatiles remaining.  Probably the easiest charcoal to light, but may be smokier. 

This method leaves a LOT of the volatiles in the wood.  

AUTOCHARING originated in the Toplit updraft stove developed by the Biomass Energy Foundation in 1985.  

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The dry chips or sticks or pellets are lit ON TOP, and this volatalizes the 80% cellulose in the wood, making a synthesis gas of sorts:

C6H10O5 + 1/2 O2(+ 2 N2) ===> 6 CO + 5 H2 (+ 2 N2) 

The cellulose volatalizes easily and burns at the surface of each piece, heating it to 500-600C.  Many more volatiles are driven off, leaving a purer charcoal. This is a MUCH higher energy content gas, about 240 Btu/SCF, compared to the 150Btu/SCF when you also convert the lignin to charcoal to CO.  

In WWII days, the charcoal was not as valuable as the energy for driving the car, so the Imbert gasifier ran very hot and converted all the lignin/charcoal as well as the cellulose.  But today we recognize the charcoal'a value for 

O making better soil

O reducing Global warming

O leaving a better gas.  

So convert the cellulose to a better gas for cooking (or travel) and keep the higher temperature charcoal as a superior soil amendment and global warming cure...
Biochar.  

Onward with less global warming,

Tom Reed

I should test the agricultural effectiveness of each in my garden grow boxes.  But i found a pic of plants grown in increasingly hi T Biochar, and highest (559 C ?) was best. 
Tom Reed

Thomas B Reed 
280 Hardwick Rd
Barre, MA 01005
508 353 7841

> On Dec 15, 2011, at 8:19 AM, Otto Formo <formo-o at online.no> wrote:
> 
> Dear Tom and all,
> About the amount of Tar produced in any combustion situation, its common known that the moisture content of the fuel is an important factor.
> Either to reduce or increase the production of tar or black carbon in the fuel chamber or up in the chimney for most heating systems.
> If you combined high moisture content fuel with low acess of oxygen, you will most likely and for certain end up with tar or black carbon in your combustion chamber and chimney. This will end up in a layer of sticky tar which can easily catch fire and destroy your chimney and in a worst senario burn down your house and property.
> 
> Norway are on the top of fires in housing and appartments due to that fact that most people dont learn from the past, using high moisture content firewood and low acess to oxcygen in the combustion phase.
> New types of woodstoves using gasfication technics has reduced this problem, but still the fuel is a challange, like here in this Forum
> 
> To reduce such problems the Peko Pe gasifier is ignited from the top and burn off the gases in that sense the carbon remains at the bottom of the fuel chamber.
> 
> You can either use that char for further cooking in an locally made Mbawula like in Zambia or it can be used as biochar in small scale production of Corn or other stable foodcrops locally.
> 
> We will follow up with an report from the trials in Zambia on sandy Kalahari soils, using Corn cobs as fuel for cooking in the Peko Pe and to be used as a soil improvement remedie for small scale farmers.
> 
> Thanks for the attention
> 
> Have a nice weekend.
> 
> Otto
> 
> 
>> From: rongretlarson at comcast.net
>> Sent: 2011-12-12 18:33:00 MET
>> To: Discussion of biomass cooking stoves [stoves at lists.bioenergylists.org]
>> Cc: Thomas Reed [tombreed2010 at gmail.com]
>> Subject: Re: [Stoves] Tar in P-Gas
>> 
>> Dean, Tom, List: 
>> 
>> See few inserts below - in both Dean and Tom's notes.. 
>> 
>> ----- Original Message -----
>> From: "Dean Still" <deankstill at gmail.com> 
>> To: "Thomas Reed" <tombreed2010 at gmail.com>, "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
>> Sent: Saturday, December 10, 2011 12:51:06 PM 
>> Subject: Re: [Stoves] Tar in P-Gas 
>> 
>> Hi Tom! 
>> 
>> Miss you. Your experiment with tar brings up a question. 
>> 
>> So far I've been trying to get as clean as possible and as efficient heat transfer as possible in TLUDs tuned under the emission hood. So we add just enough secondary air for clean but not too much that cools gases contacting the pot. We add a lot of primary air to have the made charcoal burn hot enough to keep the pot simmering above 93C so all fuel is useful in the cooking task. That means we can see 50% heat transfer and clean combustion with a variety of fuels. 
>> 
>> [RWL: I hope also to hear something about saving of the char for application to soils. 
>> 
>> How are you determining the optimum amount of secondary air? Peak temperatures? 
>> 
>> It is not clear from this whether you have the ability to control (during a run) the primary air. I would guess that if you have enough primary air to ensure satisfactory combustion of the resultant char - that that amount of air is excessive during the char-making phase. True? 
>> 
>> Re the 50% value - can you provide more details? In particular are you doing this with or without a pot lid? What sort of efficiency number might be obtained if the produced char was combusted in a separate device?] 
>> 
>> I remember your experiments with taking made gas and burning in a separate burner. A team at Stove Camp got a continual flame for about an hour but we have a long way to go to get this kind of stove to really work. Lots of tar! 
>> 
>> [RWL: What would be the rationale for this mode? I am thinking of a few reports for partitioning off some gas for a lantern (maybe electrical production) - but it is not clear why one would do this for a stove. ] 
>> 
>> Do you think we should we continue or concentrate on a TLUD approach? Larry has found the made gas to burner to be too persnickety for home cooking. 
>> 
>> [RWL: I would certainly hope that you and Aprovecho continue work on TLUDs. The justification of course is your highest-ranking results reported by EPA (Jim Jetter) recently for your version of a TLUD. 
>> 
>> Do es Larry's comment refer to the immediately preceding paragraph and a separate burner? Can you explain the geometry some more? (Why "persnickety"?) I am hoping this is not a comment for all your TLUD operations. (As one of the main advantages of any TLUD would seem to be the constancy of the flame.] 
>> 
>> More below on Tom's note. Ron 
>> Best, 
>> 
>> Dean 
>> 
>> 
>> On Sat, Dec 10, 2011 at 9:00 AM, Thomas Reed < tombreed2010 at gmail.com > wrote: 
>> 
>> 
>> Dear Pyrolysers (P-Guys) 
>> 
>> Having defined the difference between Woodgas and pyrolysis gas this morning, I was inspired to measure the tar content of the gas. 
>> 
>> 
>> [RWL: I wll comment separately next on that (excellent) note. 
>> 
>> <blockquote>
>> 
>> In a 3 1/4 D X 5 1/2 High can, I drilled only four 3/32" primary air holes 1/2" above the bottom. I half filled it with dry wood chips which I then lit, giving a modest generation of P-gas, burning about 2.0 g/ min. 
>> 
>> I then held a weighed 200 ml Pyrex Becker filled with 150 ml of water down in the smoke for one minute. It collected 63 mg of yellow, sticky, smelly tar. This is 3.1% of the wood that burned during the minute. The tar level may be higher, since probably not all of the tar condensed. 
>> 
>> The P-Gasifier was operated at a low superficial velocity to avoid asphyxiation. It may well be that levels are lower in % at higher operating levels, though the magnitude will only increase. 
>> 
>> [RWL: Tom, can you clarify the phrase "in the smoke" . Was the beaker above the flames or in them? We have lots of YouTube showing little smoke for TLUDs. Would you say this was a non-standard TLUD test? 
>> </blockquote>
>> 
>> 
>> <blockquote>
>> Since you haven't described any secondary air holes, can you describe the flame more? Was there any attachment of flames to the topmost layer of char (with secondary air traveling downward inside the can?) How high were the flames? Might we expect something different in tar-collection in a more usual TLUD geometry, where the cookpot is above the flames/smoke? 
>> 
>> </blockquote>
>> 
>> Ron 
>> 
>> <blockquote>
>> 
>> 
>> Not much speculation here. 
>> 
>> Tom Reed 
>> 
>> Aka 
>> 
>> 
>> Dr Thomas B Reed 
>> The Biomass Energy Foundation 
>> www.Woodgas.co 
>> 
>> </blockquote>
>> 
>> 
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