[Stoves] Adding value to charcoal from TLUD stoves

[Philip Lloyd]

How recalcitrant is tar to decomposition in soil? There is tar and tar.  The tar that is present in crude oil soon gets chewed up – think of the slight effect of the Gulf of Mexico oil spill, and how fouled areas were quite quickly cleaned naturally.  But do a bit of heat treatment/oxidation, and the tar becomes really stable.  Our roads don’t generally disappear. So I would guess that the tar in a charcoal would be resistant to biological attack.

 

Hope that helps.

 

Philip[

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Crispin Pemberton-Pigott
Sent: 02 April 2014 06:56
To: stoves at lists.bioenergylists.org; Phillip Lloyd
Subject: Re: [Stoves] Adding value to charcoal from TLUD stoves

 

‎Thanks Julien

That was very helpful. 

 

Prof Lloyd, can you assist us answering Question 3 below?

 

‎Regards 

Crispin 

 

 

 

Hello Rajan and all;

 

The point you raise about allowing for a few minutes of the char-burning phase to heat the charred fuel and drive off any left over volatiles is a good one.

 

The height of the TLUD combustion chamber is likely to be important, because the top of a tall column of charcoal may not get hot enough to drive off volatiles by char-burning. In addition, the top of a tall column will have experienced a longer time for tars to condense during the flaming-pyrolysis phases than a shorter column.  I have made some grimy wood-pellet biochar in a stove pipe TLUD.

 

Not driving off the volatiles will result in fine pore space of the biochar being occluded.  Perhaps that is what was going on with the following research: 

Peterson, S. 2013.  Comparison of gasification and pyrolysis methods for preparing biochar from corn stover and wheat straw. 

http://biochar.illinois.edu/Peterson.pdf

In this Powerpoint presentation, he shows that TLUD biochar had a lower surface area than biochar made by pyrolysis.

I think there are some questions to answer:

1)  Is it commonly the case the a short period of char-burning will raise the temperature of the bed of char sufficiently to drive off all condensed volatiles?

2)  Is there any difference between forced and natural draft TLUDs?

3)  How recalcitrant to decomposition is tar in soil, and in particular, tar embedded on biochar?  Is the occlusion of pore space long-term?

And a final comment.  Users of TLUDs will have to learn how to drive them properly if they want to make good quality biochar.

Thanks, Rajan, for your observations.

Cheers,

Julien.



-- 

Julien Winter
Cobourg, ON, CANADA

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