<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Andrew: cc List and Norm</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>1. Thanks for this message - which I am presuming was also intended to go to the list.</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>2. Googling for his name and stoves and pyrolysis I found quite a few, of which this was the first.</div><div class=""><br class=""></div><div class=""><a href="http://cgpl.iisc.ernet.in/dasappa/img/pdf/thesis/Sadhan_Thesis_July16.pdf" class="">http://cgpl.iisc.ernet.in/dasappa/img/pdf/thesis/Sadhan_Thesis_July16.pdf</a></div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>This all seems to be BLDD as opposed to TLUD - or is there some of both?</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>Regardless, it would be wonderful to see more on stoves producing char with BLDD - which have the possibility of continuous feeding.</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>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.</div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On Feb 1, 2017, at 9:41 AM, Andrew Heggie <<a href="mailto:aj.heggie@gmail.com" class="">aj.heggie@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">On 1 February 2017 at 15:13, Ronal W. Larson <<a href="mailto:rongretlarson@comcast.net" class="">rongretlarson@comcast.net</a>> wrote:<br class=""><blockquote type="cite" class="">Andrew: cc list and Norm<br class=""><br class=""> 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.<br class=""><br class=""> Presumably this could suggest that larger is either better or worse.<br class=""></blockquote><br class="">Interesting last question, I would like to know if one could see these<br class="">pyrolysis products passing back through the front as it descends past<br class="">the pyrex. </div></div></blockquote><div><span class="Apple-tab-span" style="white-space:pre"> </span><b class="">[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.</b></div><div><b class=""><br class=""></b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>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?</b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>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?</b></div><br class=""><blockquote type="cite" class=""><div class=""><div class="">Tom Reed talked about using a quartz?? tube lined with a<br class="">transparent layer of gold IIRC to observe the pyrolysis front<br class="">descending. We know from him and S Varunkumar's thesis that at low<br class="">superficial velocities a flame can be seen. </div></div></blockquote><div><span class="Apple-tab-span" style="white-space:pre"> </span><b class="">[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. </b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>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?</b></div><br class=""><blockquote type="cite" class=""><div class=""><div class="">As velocity increases I<br class="">think the offgas rises away too quickly to meet oxygen in the primary<br class="">air but if there is a recirculation then gas may ignite as it meets<br class="">primary air at the hot front.<br class=""></div></div></blockquote><div><span class="Apple-tab-span" style="white-space:pre"> </span><b class="">[RWL: Yup. </b></div><div><b class=""><br class=""></b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>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).</b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>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. </b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>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. </b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>If anyone has any chemistry showing the amounts of more complex molecules above the pyrolysis front, that would be a help.</b></div><div><b class=""><br class=""></b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>Are these topics discussed in the Varunkumar thesis? Could be very valuable.</b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span></b></div><br class=""><blockquote type="cite" class=""><div class=""><div class=""><blockquote type="cite" class=""><br class=""> Thanks for the feedback. Your own char-making was with very large diameters. Might you have seen anything similar?<br class=""></blockquote><br class="">Not seen it but I did propose a simple feedback mechanism to burn<br class="">offgas and feed the hot products back under the wood to increase char<br class="">yield.<br class=""></div></div></blockquote><span class="Apple-tab-span" style="white-space:pre"> </span><b class="">[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.</b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>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).</b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>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)?</b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>Another question - were you ever in those days with your large systems, attempting to also get useful energy output - or just char?</b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>Anything to add about any of this for small cookstove design?</b></div><div><b class=""><br class=""></b></div><div><b class=""><span class="Apple-tab-span" style="white-space:pre"> </span>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.)</b></div><div><b class=""><br class=""></b></div><div><b class="">Ron</b></div><div><b class=""><br class=""></b></div><br class=""></body></html>