Jock: You are right - there was a misunderstanding - on my part. Sorry. See below.
----- Original Message ----- From: "Jock Gill" <[email protected]> To: [email protected] Cc: "Jock Gill" <[email protected]>, "Discussion of biomass cooking stoves" <[email protected]>, [email protected], "Stanley Richard" <[email protected]> Sent: Sunday, December 5, 2010 2:59:46 PM Subject: Re: [Stoves] [biochar-policy] More on briquettes and pellets Ron, I think there is a mis-understanding. My iCans ONLY have primary air air holes in the bottom of the iCan. I start with fewer and smaller until I get a distribution pattern, number of holes, and hole size that is well tuned to the fuel type, size, form factor, and other stove parameters - such as surface area of the pyrolysis zone. [RWL: I had not picked up that the term "ican" refers to the inner (smaller, fuel-containing) can only. True? But new question on last few words. I have found that the "surface area of the pyrolysis zone" is identical to the cross-sectional area of the inner can. I guess that is what you meant - have you ever seen that moving "pyrolysis zone" be other than "flat-disk- like"? [Your "surface area" phrase made me think of something conical). Certainly larger inner can diameters require more primary air - at least to get the max possible power output. It is also possible that too dense and/or too deep a fuel may kill the operation no matter how much primary air hole total area. (This being the question of how large a turn-down ratio can be achieved.] I place the iCan inside a second, larger, can for 1] wind protection; lateral heat loss mitigation; safely contain loose bits of red hot charcoal; and so forth. [RWL: I like it.] The question is to "vent" this outer can to allow primary air access or not. If the choice is to vent, then where to place the holes for the primary air to enter? These holes in the OUTER can, are NOT on the bottom of the outer can so as to allow it to safely contain any hot bits. So the question is simple, how much venting do you create and where on the side of the outer can do you put the vents. [RWL: Understood now - but also believe that the majority of that air will travel upward to serve as secondary air.. OK? My preference at the moment is to place those primary air entry holes at the bottom the outer can - and let some leak around for secondary air. In this regard, want to warn that the bottom of the "package" can get pretty hot - and there needs to be a standoff arrangement of some type.] I agree that the ability to regulate the primary air flow into the iCan, the air flow to sustain the pyrolysis, would be very useful. My design goal is simply to create the easiest, and least expensive, introduction into the world of pyrolysis and biochar for young people. Sometimes good enough is just right. [RWL: Understood also - but I am still going to push for variable primary air as a key design feature - and maybe one that is acceptable/useful/important for classroom pedagogical purposes as well. I won't push this point until I have a simple solution you like. Having that flexibility can allow any TLUD to be used for multiple feedstocks without "retuning". As you point out, there is value for the teacher/student in seeing more directly/clearly how primary air supply magnitude changes the performance.] Jock - again - really glad you are driving this educational side of char-making. A big difficult topic. Ron I also agree with and second your comments about Nat at World Stove. Cheers, Jock Jock Gill P.O. Box 3 Peacham, VT 05862 Carbon Negative Solutions (G) (802) 503-1258 On Dec 5, 2010, at 4:00 PM, [email protected] wrote: Crispin, Jock, lists I think some of the ideas here may be counterproductive. See below. ----- Original Message ----- From: "Crispin Pemberton-Pigott" < [email protected] > To: "Jock Gill" < [email protected] >, [email protected] , "Stanley Richard" < [email protected] > Cc: "Discussion of biomass cooking stoves" < [email protected] > 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.
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