[Stoves] Biomass stoves v. PV-induction cooking (re: Frank)

[Ronal W. Larson]

Andrew:  cc List and Norm

	1.  Thanks for this message - which I am presuming was also intended to go to the list.

	2.  Googling for his name and stoves and pyrolysis I found quite a few, of which this was the first.

http://cgpl.iisc.ernet.in/dasappa/img/pdf/thesis/Sadhan_Thesis_July16.pdf <http://cgpl.iisc.ernet.in/dasappa/img/pdf/thesis/Sadhan_Thesis_July16.pdf>

	This all seems to be BLDD as opposed to TLUD - or is there some of both?

	Regardless, it would be wonderful to see more on stoves producing char with BLDD - which have the possibility of continuous feeding.

	3.  I need a few days to catch up after a week away - before getting into this in detail.  Could you or anyone give more of a lead on the topics you mention further below.  Your ideas there are top notch.


> On Feb 1, 2017, at 9:41 AM, Andrew Heggie <aj.heggie at gmail.com> wrote:
> 
> On 1 February 2017 at 15:13, Ronal W. Larson <rongretlarson at comcast.net> wrote:
>> Andrew:  cc list and Norm
>> 
>>        As Norm and I talked, we came to the same conclusion.  But it is and was a remarkable video to see ANY downward flowing gases.  I’d like to know if anyone with computational fluid dynamic simulation capability can report on this being observed as well - and whether they can report any negative implications, etc.
>> 
>>        Presumably this could suggest that larger is either better or worse.
> 
> Interesting last question, I would like to know if one could see these
> pyrolysis products passing back through the front as it descends past
> the pyrex.
	[RWL:  Not sure of your question.  One has a very limited view of what is going on - because the pyrex gets “tarred-up” quickly (by these downward flowing gases).  It also might be that this is periodic in the circumferential direction - as the tarring was only over part of the pyrex.

	Norm also mentioned some possible upward flowing hot channels - well below the front.  Again.  Not enough know yet on that.  And is this only for larger systems?
	But briefly,  I think the answer is “Yes” - as I think I saw the downward flowing “smoke” both before and after the front passed the pyrex.  Norm?

> Tom Reed talked about using a quartz?? tube lined with a
> transparent layer of gold IIRC to observe the pyrolysis front
> descending.  We know from him and S Varunkumar's thesis that at low
> superficial velocities  a flame can be seen.
	[RWL:  My recollection of the tests with the thin gold layer was that we could easily see a small flame at the front.  I believe the flame energy that is directed downward is critical in heating up the outer layers of the next lower level the front will shortly reach.  
	With Norm’s video we could see flamelets - I believe preceding the main pyrolysis front.  I think we say flamelet propagation inward as well as downward.  ll this obviously dependent on pressure variations in the fuel bed.   Again - Norm?

> As velocity increases I
> think the offgas rises away too quickly to meet oxygen in the primary
> air but if there is a recirculation then  gas may ignite as it meets
> primary air at the hot front.
	[RWL:  Yup.  

	Others may not understand the complex nature of this front.  A minimum amount of CO2 is normally produced at the front.  Andrew is here saying that these unusual smoke (combustible) particles when they progress inward may be producing CO2 - which we don’t want.   Such produced CO2 is probably largely converted back to CO when it meets the hot char - but then you are losing char (and energy).
	Andrew - I don’t understand your first phrase (“As velocity increases”).  Are you referring to the presumed normal situation, or this “new” case in Norm’s geometry.   
	If anyone has formulae for the change in pressure and velocities at the pyrolysis front (of any type), I think that would help us design better stoves.  Andrew is correct here I believe re “too quickly”.    This is great - as we get the valuable CO and H2, rather than the non-valuable CO2.  
	If anyone has any chemistry showing the amounts of more complex molecules above the pyrolysis front, that would be a help.

	Are these topics discussed in the Varunkumar thesis?  Could be very valuable.
	

>> 
>>        Thanks for the feedback.   Your own char-making was with very large diameters.  Might you have seen anything similar?
> 
> Not seen it but I did propose a simple feedback mechanism to burn
> offgas and feed the hot products back under the wood to increase char
> yield.
	[RWL:  It has been decades since you described that (if ever) on this list. (I learned about your work mostly while visiting you in the UK.)   Can you repeat that description - and anything that might help in drying wet wood - which was a big topic at the recent ETHOS meeting.
	I’m not sure if this is pertinent, but Nat Mulcahy has a very different approach to char making in his World Stove.  He has a clever (patented) use of Venturi effects to draw hot N2 down (NOT up) through his fuel bed.  So there is nothing like a front or flames anywhere in the fuel bed as it slowly pyrolyzes - carrying along the pyrolysis gases (whose makeup certainly has CO and H2 - but I don’t know what else).
	Andrew - might you say that what you described here was similar to Nat’s use of hot N2?  I think you both had some CO2.  You (nd NAT) did NOT have O2 being re-directed downward.  Your emphasis was presumably on maximizing the energy in the hot gases for further pyrolyzation?  This would not be called gasification (no consumption of char)?
	Another question - were you ever in those days with your large systems, attempting to also get useful energy output - or just char?
	Anything to add about any of this for small cookstove design?

	Again thanks for these additional thoughts on what Norm was able to observe with his clever pyrex window.  (Our list Moderator - Andrew - is enormously knowledgable on all of the technical aspects of char-making.  We don’t hear enough from Andrew.  Andrew - thanks again for moderating.)

Ron


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