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

[Jock Gill]

Ron,

Thanks for the encouragement.  

A few comments inserted below.

Best wishes for the Holidays.

Jock

Jock Gill
P.O. Box 3
Peacham,  VT  05862
Carbon Negative Solutions
(G) (802) 503-1258



On Dec 5, 2010, at 6:15 PM, rongretlarson at comcast.net wrote:

> Jock:  You are right - there was a misunderstanding - on my part.  Sorry.  See below.  
> 
> 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?

[JPG == 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).

[JPG: Yes. We are saying the same thing.  I have not yet seen "cones".]


>     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.]

[JPG:  I tune the primary air to control the period where gas formation is greater than the secondary air flow resulting in an fuel to air mixture that is "too rich".  This is the period of maximum soot production from incomplete combustion of, if I have this right, the carbon monoxide.  That is, in the beginning and end of the pyrolysis, the fuel are ratio is too lean.  But burns very cleanly with a lot of blue flame as is seen on a gas stove.  In the middle, the "shoulders" of the gas production curve, the f/a ration is "just right".  During peak gas production, the mix is too rich.  I call this the Goldilocks syndrome of pyrolysis.

Another way the pyrolysis can be stopped is if the fuel 'expands' when heated and thus blocks off the primary air from the pyrolysis zone.  I typically see this problem with grass wafers.  I have to allow for the way the wafers react when heated when I load the iCan.] 

> 
> 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.]

[JPG: The outer can does get hot.  A great deal of thermal energy is radiated laterally.  This is one reason I am able, with wood pellets at least, to have the inner retort face upwards so students can "see" the flames from the gas produced by the retort.  See: http://www.greaterdemocracy.org/archives/983 ]
> 
>  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.]

[JPG: I look forward to your design.  It might be a wonderful challenge for a high school class?  Please post your solutions as comments on the iCan pages on Greater Democracy.

Best,

Jock]
> 
> Jock - again - really glad you are driving this educational side of char-making.  A big difficult topic.
> 
> Ron
> 

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