Dear PaulAgain I feel you are imposing restrictions on how products should work. Recycled char can definitely be burned. If you have pellets that yield 15-20″% of initial fuel mass then definitely some of the char burned. That establishes the principle that TLUDs can burn char.
No. The char yield is associated with some char combustion during the time of the pyrolysis, but that is not the same as having the char as the input fuel.
The stoves that recycle char to the next cooking session burn a large amount of the total char such that the mass ‘carried forward’ is about the same each time. This establishes that the total char produced, net, each replication is completely combusted.
That is “burning char” during the pyrolysis process, not the burning of char as the input fuel (100% of the input being charcoal).
All that is needed is to increase the gasification rate until there is significant char gasification. This does not hold for all models nor all fire powers. Some produce more than they can recycle so a portion is lost, or retained for other purposes. In the fuel consumption calculation that is fuel fed, meaning more is needed next time. For example a stove may produce 20% char from a mix that was 90% fresh pellets and 10% old char. In that case half the remaining char is not used next time.
Tom Reed showed years ago that the amount of char produced is inversely impacted by the amount of primary air. Expect that to be the case.
Stoves that do this have been made and sold in Indonesia for several years.
Please send details about those stoves, numbers, how they are used, photos, videos, etc.. I do not dispute that statement. But it would be nice to have some supportive info so we all can interpret what you says you have (measured or seen or been told or believe).
While there is a ‘purist’ group holding that char is produced and not burned,
I said above that some char is burned during the pyrolysis stage. TLUD processes have OXIC pyrolysis (oxygen present, but in limited amount), also called “flaming pyrolysis”, but I prefer the term “glowing pyrolysis.” So some char will be consumed. ANOXIC pyrolysis (no entrance of oxygen) is what occurs in a retort. Expect some char to be consumed during the pyrolysis
and there are stoves like that, it is not a general case. It is particular to those products with a low temperature gas production rate. The cleanest stove we tested was like that. The most efficient was like the case above, in the high 30’s, assessed on the Central Java cooking sequence.
Efficient. As in heat transfer efficiency, I assume. And what you describe is logical. that is, turn up the heat (more primary air) and the stronger fire moves the hot gases better and that improves the efficiency.
The Rocketworks stove from South is in the same efficiency range. It is a stick burner with a novel grate and both preheated secondary and tertiary air, i.e. not a gasifier nor semi-gasifier.
I am not familier yet with that stove. Interesting. Do you have a definition for “tertiary air?” Please let us know.
Crispin, referring to your initial sentence, I do not IMPOSE restrictions on TLUD usage. I point out (to the best of my ability) what I believe (know in some cases) to be true and the best practices. But just suggestions. I have seen so many different methods and materials and designs about TLUD stoves for over 16 years. SOMETIMES THERE ARE SOME REAL GOOD INNOVATIONS (witness Kirk Harris and Alexis Belonio). I try to call attention to the innovations that seem to have strong merit.
And sometimes the differences are (be nice, use soft words) less than stellar. Some people totally disregard what is clearly established. Maybe they do not read the materials. Or maybe the “not invented here” complex takes over. Or they like reinventing the wheel. They are welcome to do all of that and more. (But not with my time nor with my funding.)
To me, the burning of charcoal as charcoal (not during the migratory pyrolytic front stage) inside a TLUD stove is to be avoided. Reasons include:
a. overheats the metal, shortening the life of the fuel chamber,
b. The air enters at the bottom, and the char is burning there, and it is underneath the layers of relatively cooler char (that looks black, not glowing), which blocks the radient heat from reaching the pot,, and
c. the hot char at the bottom is relatively far away from the bottom of the pot (and everyone knows that proper charcoal stoves have the pot very close to the hot char.)
In baseball, “three strikes and you’re out.” But this isn’t baseball, and I am not the umpire. But the ballgame is more fun if the players learn good techniques so that they have better chances to hit the ball (or cook the meal). But I would rather have many people playing ball with suboptimal skills (or using TLUD stoves in less than optimal ways) than to not have the ballgame or TLUD cooking taking place.
Paul
RegardsCrispin
Crispin,I am sure that Bill and Gordon in New Mexico (and others including myself) will appreciate more info (details, photos, sizes, etc) about the continuous TLUDs with bottom feeding. Please try to provide.
When mixing in the previously made char into the future batches of fuel, there are two concerns:
1. Cannot mix in hot, glowing char (which would ignite low into the columnof fuel), Therefore must be extinquished, which is an extra step.
2. Char from a TLUD at whatever temperature of pyrolysis will essentially be “inert” material into a next batch to be pyrolyzed at the same temperature. No gain. Just filling space. [[ But one exception: created char can pick up some of the volatiles that are rising through it. Those volatiles would be elegible to be released for making energy in the second round. As far as I know, those volatiles would be a very very small percentage of the energy in the processes. }} So why bother to do it, UNLESS the intention is to burn the created char (which should not be done in a TLUD).
I agree that anyone is allowed to test and experiment with any methods and materials. What we are awaiting are reports of adoption of methods etc by significant numbers of appropriate users.
Paul
On 9/28/2017 10:29 AM, Crispin Pemberton-Pigott wrote:
Dear Paul
Thanks for the ideas about char. I want to correct a couple of impressions.
>And users can continually drop in more fuel, which is “trickle feeding”and requires user attention. TLUDs are batch units.
This is only true some of the time. TLUD burners are frequently (often, not rarely) built at small industrial scale using batch-push feeding from below. I was surprised to find that the Stove Development Centre in Ulaanbaatar has been making a number of these units – the surprise coming from the fact that none of the domestic candidate stoves had used this system. I saw one being repaired in August. Being a TLUD does not mean it has to be a single batch unit.
The char or charred fuel is not placed on top of the fresh fuel – it is mixed in and forms part of the fuel. I don’t know what the upper limits of content are, I believe for different stoves there are different limits. The HTP spreadsheet was modified in 2013 or so to accommodate this sort of ‘limited ability to recycle processed fuel’ and still produce the correct ‘as burned’ (AB) fuel analysis that forms the basis of the chemical mass balance calculation.
Next, with reference to the recycling of fuel from one burn to the next:
>Also, apart from the lab testing, is there evidence that the Indonesian cooks are actually using the stove as it was being used in the lab?
That is not up to the lab performing the test. If a manufacturer comes out with a novel method of construction and operation, it is up to the lab to test it as designed, not to speculate about home someone in future might use it.
For a project it makes a difference and a project might not adopt a stove for promotion if the cultural conflicts with how it works. In short, the testing does not stand in the way of innovation. There is a clear separation between the invention and testing of products from the projects that may or may not use them. I realise that there has been a confabulation of projects and test protocols in the past. That should end. A test method should be technology neutral.
That said, a test protocol specific to a project is also valid. On project I was associated with required that the stoves be mis-operated and the performance reported because ‘obvious misuse’ is an accepted risk and we wanted to know the implications.
>These stoves can be operated in different ways.
Yes, but it would be good if you did not limit the operation of a TLUD to a batch or trickle-feed mode. There are other products around. TLUD coal and pellet and briquette burners are quite common. I expect one day the TLUD promoters will accept this as a standard operating technique because it overcomes several of the attested shortcomings of batch-loaded stoves.
>How many of each of those units (Todd’s or the Indonesian ones) are in daily use in households? I hope that the numbers of users are VERY high. Please send details.
I am not sure stoves are listed by operating mode. Those that are claimed to be operating as TLUDs with recycled fuel could be identified by brand and the numbers (probably) extracted from the CSI Indonesia aggregated sales numbers. It is in the thousands I suppose. I am not the one to ask.
Regards
Crispin