[Stoves] [biochar-policy] More on briquettes and pellets

Sun Dec 5 15:00:53 CST 2010

Crispin, Jock, lists 

I think some of the ideas here may be counterproductive. See below. 

----- Original Message ----- 
From: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com> 
To: "Jock Gill" <jg45 at me.com>, biochar-policy at yahoogroups.com, "Stanley Richard" <rstanley at mind.net> 
Cc: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
Sent: Sunday, December 5, 2010 8:03:44 AM 
Subject: Re: [Stoves] [biochar-policy] More on briquettes and pellets 

Dear Jock 

Very nice web pages and a well presented instructions provided by the link. 

I have a question relating to the iCan. 

Have you tried elevating the primary air holes in the outer can above the bottom? I understand from the photos that the elevated holes are only on the inner cans. 

[RWL: I would go in the opposite direction - put all primary air holes on the bottom inner can surface - to get more uniform (vertical only) air flow] 

The reason I ask is that I have found benefit from making the primary air travel downwards at least part of the vertical height. The preheats the air slightly and provides negative buoyancy reducing draft. As the inner can starts to heat up, it increases the negative buoyancy because the inner can is hotter and this interaction tend to self-regulate the power. 

[RWL: I don's see the value in reducing draft anywhere - we work hard usually to achieve it. Re regulating power, I have always been amazed that with a fixed primary air supply, the power level (as indicated by the apparent rate of steam bubble formation) was amazingly uniform - over a full hour. It is easy and cheap to control power levels through controlling (only) the amount of primary air. I think turn-down ratio is a very important parameter that needs a lot more work. No gas or electric stove (I presume propane, ethanol, etc) manufacturer would give you less than about 3:1 for turn-down ratio. This parameter I think is one of the main reasons we are going to see increased stove use of the discarded fans used for cooling computers. 

If you get a significant preheat (I would make the gap between the cans no more than 10mm) you can burn harder, denser fuels that will not pyrolyse with a normal preheat. 

[RWL: I don't know if the use of " burn harder, denser fuels" was intentional. I believe Jock is only attempting pyrolysis - being interested in the resultant char for sequestration and soil improvement. 

Re "preheat", there is plenty of opportunity to use the outer gap for upward flowing preheat of secondary air. Lots of stoves doing that. The downward flow of primary air will supply not much heat for the already pretty darn hot pyrolysis front. 

Nat Mulcahy's Lucia stove does have [O=Opposite] downward flowing "primary" (sort of a misnomer) air - but it is in the inner chamber and carries no oxygen. The outer chamber does a wonderful job of both preheating and premixing his pyrolysis gases and secondary air so as to avoid the extra height needed to completely combust a diffusion flame. 

I can't remember what fuels I have ever had trouble pyrolyzing - but the only one I never had success with is dung - the extreme other end in density/hardness. I can imagine however that dense fuels might be harder to get started. In part this is because you need optical energy from the pyrolysis process to heat neighboring/adjacent particles - and near the top surface, much of that optical energy is directed upwards. This is a good reason to use starter/lighter fluids or easy to start fuels (maybe oily material like peanuts? - which I have never tried in a stove, but peanuts are easy to light with a match and pincers.) 

But another thing I learned early was that there is an enormous (factor of 10?) difference in interior biomass particle gas flow radially vs longitudinally. This helps explain why chips and disk shapes light more easily than logs. 

In any case, I'd like more data to prove that hard, dense fuels are a problem for Jock's (or any) type of pyrolysis stove. Not a problem for most pellets or briquettes I guess. 

Ron 

Give it a try! IT is really easy. 

Best regards 

Crispin 

From: Jock Gill [mailto:jg45 at me.com] 

Ron, 

I have been able to make very good char, as tested by Hugh McLaughlin, from grass tablets. These have a diameter of about 1.5 inches and I break them into wafers about 1/2 CM thick. My first batch of grass tablet biochar was actually made by Paul Anderson in one of his TLUDs. 

Please see this post from Nov. 2009: http://www.greaterdemocracy.org/archives/931 

I also find that quenching the biochar at the end of the pyrolysis is not critical at all. If I leave one of my iCans overnight, I lose less than half the charcoal. My guess is that this is the result of tuning the iCan for the least amount of primary air. I have noted that when the pyrolysis is over, the bed of charcoal emits "smoke". My goal is for zero smoke, but find that I can still get god biochar if the smoke is essentially gone in less than two minutes. My practice is to only quench after the smoke has essentially finished f within in about 3 minutes after the pyrolysis flames extinguish themselves. 

Cheers, 

Jock 

Jock Gill 

P.O. Box 3 

Peacham, VT 05862 

Carbon Negative Solutions 

(G) (802) 503-1258 

On Dec 5, 2010, at 1:42 AM, rongretlarson at comcast.net wrote: 

Richard and 2 lists: 

Thanks for the complete response. I conclude that pellets and briquettes are possibly able to act similarly in char-making stoves, but briquettes look better in traditional stoves. Apparently not much comparative work done yet for advantages of production of one vs the other. 

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