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Dear gordon</div>
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You almost nailed it. Heating some small portion of the biomass and the temperature of the nearby fuel (not all of it) is sufficient to ignite a reaction that can continue indefinitely provided there is sufficient insulation and the oxygen content of the fuel
is sufficient. </div>
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There are two approaches that will work, as I understand it: the first is the charring of underground biomass (or coal) in the absence of additional oxygen. Once started, it will continue until the fuel is exhausted. </div>
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The other does not require heating, but uses compressed air (oxygen) to provide the necessary reaction oxygen rapidly enough to get the reaction to continue (the Hawaiian invention).</div>
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An MPF is the front at which the heat releasing reaction takes place. </div>
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You can also consider the way char is formed. In the initial stage the energy needed to drive off the endothermic volatiles is more than the energy released by oxidizing the gases using only the oxygen available in the fuel. As the system heats up, the energy
gap between evaporating volatiles and exothermic reactions decreases. At some point, the gap is small enough for the released oxygen to continue in the absence of additional air. </div>
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TLUDs are in general too small to see this take place. They cool off too easily so additional air much be provided to sustain the reaction, which burns the rest of the hydrogen and at least some of the carbon. </div>
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An underground fire can continue for centuries. All it has to do is get started. Prof Lloyd can explain how these fires can even auto-ignite. You have probably heard of stacks of hay setting themselves on fire by decomposition of the material in a large enough
pile to retain the heat. Once it reaches or exceeds about 290 C the reactions are exothermic and from there it is a short trip to charging temperatures. The whole haystack can turn to char save the cool exterior. </div>
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Burning coal seams manufacture their own oxygen from water. Coal doesn't have enough oxygen to sustain a pyrolytic front unless it is really hot. But burn they do. </div>
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You can determine if there is an MPF but putting in a set of thermocouples and watching the front pass by. A burning log in an open fire has an MPF inside working it's way to the centre. The whole log will be charred long before it splits open. </div>
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The interesting thing about a packed bed gasifier is that it can make gas predictably and controllable from ýsmall sized fuel generally considered a waste material. It is no small achievement. </div>
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Regards </div>
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Crispin </div>
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<div>I took a look at the Adams Retort design and watched a few videos. A couple of questions come to mind:
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<div class="">1) How does one determine that an MPF exists in an A-R?</div>
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<div class="">2) I am not much of a chemist, but I would be interested to see an explanation of the reaction sequence where O2 is released and then burned in the MPF of an Adams Retort. </div>
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<div class="">It seems to me that if the external heat source is raising the temperature to the gasification point of the volatile components, thereby causing gasification (duh…), what purpose is the MPF serving? </div>
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<div class="">In a TLUD the MPF is burning some of the volatile gases to generate the heat needed to gasify un-pyrolyzed biomass. </div>
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<div class="">Gordon<br class="">
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<blockquote type="cite" class="">
<div class="">On Dec 9, 2017, at 10:54 PM, Crispin Pemberton-Pigott <<a href="mailto:crispinpigott@outlook.com" class="">crispinpigott@outlook.com</a>> wrote:</div>
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<span class="" style="color:windowtext">Dear Paul</span></div>
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<span class="" style="color:windowtext"> </span></div>
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<b class=""><span lang="EN-US" class="" style="color:windowtext">></span></b>Some of what you wrote is correct, but you go too far or leave out some important distinctions, thereby implying that some things are equal, that is, some are not really as worthy
and distinctive as others (Ron and Paul) have stated. <span class="Apple-converted-space"> </span><span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">Of course there were things left out. I am happy you included below further refinements to the explanation.</span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>1. Pyrolysis progresses (migrates) through a piece or pile of biomass as heat is able to penetrate. True. The Adam retort (and other retorts) heat the biomass from many sides, but there is no flame (actual
combustion) inside. It is a stretch of language to say that the pyrolysis in the retort</div>
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<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">>></span>has an MPF [migrating pyrolytic front] proceeding in a roughly horizontal direction.</div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">Au contraire. The Adam Retort (which heats the biomass from under a portion of the bottom of the pile, not multiple sides) does indeed have a MPF and the combustion is fed by oxidation using oxygen liberated by the thermal
decomposition of the fuel. There is no<span class="Apple-converted-space"> </span><i class="">added</i><span class="Apple-converted-space"> </span>oxygen, but oxygen there definitely is. There is enough oxygen in biomass to almost completely combust the hydrogen
content. In practise the carbon and hydrogen are both involved in sustaining the MPF. Once the fuel is hot enough, the MPF can move through the pile without any additional heat required.</span></div>
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<span class="" style="color:windowtext">></span>Sorry, that should say "has external heating proceeding inward from several directions from the sides toward the center." <span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">That is an incorrect description of the Adam Retort. There are retorts that function in the manner you describe. His is not one of them.</span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>Furthermore, the processes in a retort are in sequential order during numerous minutes to 1) heat virtually all of the biomass to drive off the moisture, then 2) add more heat to virtually all of the biomass to
drive off the low-temperature volatiles to create torrified material, and than 3) to finally get the temperature hot enough to have actual pryrolysis, first in the 400 deg C range and then at higher temperatures if the external heating is continued.<span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">That is true for some retorts, not the Adams Retort.</span></div>
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<span class="" style="color:windowtext">></span>In sharp contrast, in a TLUD there is a distinctive zone of a few cm depth with actual small amounts of combustion (of some of the initial offgases). That zone migrates through the pile of biomass, heating mainly
by radiation a small layer of biomass below the MPF, then with pyrolysis at a rather uniform temperature (generally from 450 to 700 C, depending on USER CONTROLED<span class="Apple-converted-space"> </span><span class="" style="color:windowtext">[<i class="">sic</i>]<span class="Apple-converted-space"> </span></span>flow
of primary air) to create the char as the gases move upward.<span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">The same also happens in a downdraft pyrolyser, and a bottom-pit updraft pyrolyser such as those produce by Hirendra Chakrabarti in India.</span></div>
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<span class="" style="color:windowtext">The addition of a control feature makes the process variable, however it does not fundamentally change how the system works.</span></div>
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<span class="" style="color:windowtext">></span>You may choose to try to equate the two descriptions above, but that would diminish your credibility as a precision-seeking scientist. <span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">There is no need for that kind of talk. First familiarise yourself with the systems under discussion. Seen from the side, an Adam Retort starts the MPF on the bottom right and it moves over a period of about 2 hours to
the top left. Prof Lloyd can provide examples of sustained MPF’s moving horizontally underground in the Witbank area of South Africa without any addition of primary air. There are conditions where primary is required, and others when it is not. Tiny stoves
require it.</span></div>
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<span class="" style="color:windowtext">></span>And to equate a smouldering tree stump to MPF is a stretch beyond a stretch. Yes, there is fire there, and yes there is pyrolysis occuring. But such comparison is akin to saying that a ladybug and a moose are
the same because both are living creatures; and in fact both are animals. Even a petunia and a whale are both living organisms. Scientific comparisons need precision and detail.<span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">That is why the discussion is on principles not ladybugs. A dry tree stump can be ignited to char the stump and the roots underground, and in the 1800’s one could buy a kit for doing so. I was told of a different method
when I was young involving a steel pipe and kerosene. The point was to get the stump hot enough so that the pyrolysis would continue into the ground. The TLUD stove with an MPF is no more than a containerised version with controllable primary air.</span></div>
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2. Ron correctly pointed out that in normal operation of TLUD stoves, there is zero O2 that gets past the MPF. That is vastly different from having so much primary air enter (as in Rocket stoves and other burners) that there is O2 moving upward above the
fuel (where the gases were created). <span class="Apple-converted-space"> </span><span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">Ron is correct about the O<sub class="">2</sub>. It is indeed different (I don’t know about ‘vastly’ from stoves where the fuel and flames are ‘attached’ to the solid fuel and the gases oxidise as and when they can. it
is also true (but I didn’t expound on it) that within a fuel bed there are zones without no available O<sub class="">2</sub>, just as in the zone above the char.</span></div>
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<span class="" style="color:windowtext">></span>You are saying that is good as preheated secondary O2. <span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">Functionally that is secondary air provided simultaneously, at least in some cases. My definitions are general cases and can be applied to the situation you describe.</span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">></span>Maybe, but not really. It is simply inadequate combustion, with the results of undesirable emissions. <span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">That is speculation and cannot be true in all cases.</span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>The excessive primary air (which you state should be secondary air)<span class="" style="color:windowtext">...</span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">Which I state has the function of providing secondary air…</span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">>…</span>has had a cooling effect on the raw fuel that the combustion is trying to get hot enough to give off the pyrolytic gases. <span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">That is not a general case. It could happen.</span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>In other words, that secondary air that has passed over the fuel is part of the problem, not part of a solution because it has taken heat away from the fuel.<br class="">
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<span class="" style="color:windowtext"></span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">That is not the case. What ‘problem’? Heat passed through a metal wall to secondary air is not ‘different heat’ from that gained by air passing through a fuel bed, or along a hot combustion chamber wall. There are many
roads to Rome. Air that is consumed after preheating is indifferent to hwo the heat was gained.</span></div>
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<span class="" style="color:windowtext">></span>3. Tertiary air: Defined as either 1) the needed secondary air that did not get into the combustion zone soon enough (meaning that there was poor stove design)<span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">I see this as inaccurate on two counts: 1) the secondary air may be added in a way that decomposes complex gases further before final combustion, and 2) the bit about poor design is unfair comment. There are many good
designs you may not know about.</span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">>…</span>or 2) excess air that will lower the temperature of the hot gases (meaning that this "tertiary air" was NOT needed nor part of the combustion process). <span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
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<span class="" style="color:windowtext">Tertiary air may be provided for a number of reasons, but normally to provide the oxygen needed to complete combustion with a desirable level of free O<sub class="">2</sub><span class="Apple-converted-space"> </span>in
the gases. Under certain circumstances, for example natural gas boilers, the level of free O<sub class="">2</sub><span class="Apple-converted-space"> </span>is very low (1% by volume). To maintain such a low level of excess air it may be necessary to have
tertiary or even more air injection points.</span></div>
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<br class="">
<span class="" style="color:windowtext">></span>Either way, the concept of "tertiary air" is bogus in the context of cookstove combustion. <span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">That is opinion only, contradicted by existing technologies that use it. One of the highest performing stick-burning stoves available has tertiary air injection – the Rocketworks stoves from Adrian Padt in Durban, tens
of thousands of which are sold each year.</span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>The objective is to get the combustion to be complete with the proper amounts of primary and secondary air at the correct times and places.<span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">That is true in some cases and not in others. Most Rocket stoves (per Aprovecho design guides) have only a single air entrance. The Rocketworks stoves have three distinct times and places.</span></div>
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<br class="">
<span class="" style="color:windowtext">></span>4. You wrote:<span class="Apple-converted-space"> </span><span class="" style="color:windowtext"></span></div>
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<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">>></span>This [MPF} process is ... how the Terra Preta soils in the Amazon were created over 20,000 years of slash and burn agriculture.</div>
</blockquote>
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<span class="" style="color:windowtext">></span>The origins of Terra Preta are still being debated by the experts in that field, which is certainly not your claimed field of expertise.<span class="" style="color:windowtext"></span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">I am sorry to hear you talk about ‘fields of expertise’. Facts in evidence speak for themselves and are not invalidated by any messenger claims.</span></div>
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</div>
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<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">>></span>The Amerindians cultivated land that was already productive, they did not create it<span class="Apple-converted-space"> </span><i class="">de novo</i>. Cecil confirms they farm patches of land that are already
productive, not random areas. He observed this when he was doing PhD field research while at Harvard.<span class="Apple-converted-space"> </span><br class="">
<br class="">
</div>
</blockquote>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>I have great respect for Cecil Cook. But somehow what you have attributed to him and his work has not reach my attention previously. <span class="" style="color:windowtext"></span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">So what?<span class="Apple-converted-space"> </span></span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>And I do not accept your statements. <span class="" style="color:windowtext"></span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">I don’t care. I cared to know, by interviewing him, how the Amerindians farmed and what role char had in their agriculture. I reported this previously to this list. Maybe you forgot. It is in the archives. At the time
Ron replied that did didn’t accept the observational reports from Cecil who lived in the jungle for 4 years learning how their agricultural society functions.</span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>What happened thousands of years ago was not witnessed by Cecil. He could only observe the current day activities on lands that somehow became fertile. <span class="" style="color:windowtext"></span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">He reported observations, the most important of which is that they do not practise slash and burn farming over whole areas, but only the fertile bits. The practice of slash and burning creates a lot of char in the ground,
something contested by Ron at that time and diminished by your message regarding the tree stumps burning in California. If you don’t believe me, you can visit the area right now and witness the MPFs moving into the ground to charcoal the root systems. A major
part of the work of firefighters is extinguishing these MPFs. This is sufficient to convince me they exist. If they exist, they are producing biochar in the ground.</span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>You can take that topic to the Biochar Listserv, if you want to discuss it further. <span class="" style="color:windowtext"></span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">I have no interest in discussions on another list. I receive information from the Biochar-Ontario group.</span></div>
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<br class="">
<span class="" style="color:windowtext">></span>Sorry, I reject much of what you wrote. <span class="Apple-converted-space"> </span><span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">Don’t be sorry. Learn and be happy! We are sharing perspectives here.</span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>I would not want you to be instructing people about TLUD stoves and char making and Terra Preta. <span class="" style="color:windowtext"></span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">That is none of your business over which you have no control.</span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">></span>IMHO, your comments about pyrolysis in different devices reflect poorly on your credibikity<span class="Apple-converted-space"> </span><span class="" style="color:windowtext">[<i class="">sic</i>]<span class="Apple-converted-space"> </span></span>regarding
your other strongly expressed positions, but that is a topic for others to discuss.<span class="" style="color:windowtext"></span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">And I feel sometimes you could learn a thing or two before posting comments about other technologies. Like everyone else, I find your contributions worthy and partially correct.</span></div>
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<br class="">
<span class="" style="color:windowtext">Perhaps there is something you could answer: Is there something about char making that requires or drives their proponents to make completely unnecessary personal attacks and derisive, inaccurate speculations about motives?
Outside the agricultural sector and the production of char-enhanced fertilisers, I find the biochar enthusiasts as a group to be cloistered and fanatical, frequently engaging in divisive speech about something they have recently discovered.</span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">I should take a minute to compliment you, Xavier, Julien, Jonas Haller and Dr Nurhuda for being very open to exchange with me advice, explanations and observations without reservations about how or where the information
originates. All of you have produced very interesting and effective products suited to certain communities.</span></div>
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<span class="" style="color:windowtext"> </span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">Best regards for a better burn</span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext">Crispin</span></div>
<div class="" style="margin:0cm 0cm 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<span class="" style="color:windowtext"> </span></div>
</div>
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