[Stoves] stoves and credits again

[Crispin Pemberton-Pigott]

Dear Persistent Paul

I appreciate the way in which you have stuck to the promotion of TLUD’s and show no signs of skacking.

>>…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.

Well I just showed that char can be an input to a TLUD. I can burn charcoal only as an input fuel to a TLUD.  I have a set of cooking photos used for promotion showing a Vesto operating as a TLUD charcoal burner with a cooking plate in place of the pot. Charcoal stoves operate much better, cleaner and longer when operated in TLUD mode. TLUD was the standard operating method for the POCA which is a charcoal-only stove.

“TLUD” is a way to light and burn fuel, not a type of stove. For example the SDC-1 TLUD gasifier which recently passed an emission test at the SET Lab in Ulaanbaatar can be operated in three distinctly different modes, only one of which is TLUD. You usually attach a long string of qualifiers on the TLUD description which I have no problem with, as it describes a sub-set of all TLUDs: A TLLUD with a downward-migrating pyrolytic front. Operated in that mode it will indeed produce biochar from a biofuel. It will also produce coke from coal because it is a particular method of combusting 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).

I disagree. If I put in 150g of char from a previous burn and end up with 150 f for the next fire, then all the char produced (if any) during the burn was consumed. I didn’t say it was a pyrolytic fire only, just noted that there is char produced and burned and that on a net basis, the fuel carried forward remains about constant. It is of course, not the same pieces of char that were put in.

>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.

Agreed. If you want to burn the char and yield the heat instead of recover the char, change the air flow.

>>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.

They look exactly like the TLUD’s you are used to from Dr Nurhuda, among others. It seems the producers are quite aware of the possibilities. Some fuels tend to burn most or all of the char, for example pistachio shells, and I conclude that the fuel in those stoves is being used as a form of primary air control. When this is the case, changing the fuel changes the packing which changes the air flow and results in a different air-fuel ratio in the primary combustion zone.

>>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

That describes two of all possible conditions. Other conditions exist.

>>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.

We do not measure and report the heat transfer efficiency as it is a performance test, not a design test. We can make assumptions about the heat transfer efficiency but I was referring to the fuel efficiency. The heat transfer efficiency of a TLUD gasifier that does not burn the char is similar to a low-end LPG stove. Above 45% the number is highly dependent on the excess air level, as a general rule.

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.

Tertiary air means a third air entrance zone above the secondary zone.

The website is http://www.rocketworks.org/

>To me, the burning of charcoal as charcoal (not during the migratory pyrolytic front stage) inside a TLUD stove is to be avoided.

That is OK, in terms of an opinion, but it is not what people are doing and I expect the main reason is fuel efficiency.

>Reasons include:
>a.  overheats the metal, shortening the life of the fuel chamber,

That is one choice we could make.

>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,

Oh, no that would not be a TLUD. That is a BLUD.  You can also light the char (100% of the fuel load) on top and operate it as a TLUD. The primary/secondary split is different. In at least one case I have used a stove that had a level to shift from one condition to the other.

>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.)

There are a couple of assumptions in that statement which may not hold true for everyone. High heat transfer efficiency may not be the target, the excess air level is dominant in heat transfer, and when operating in a TLUD mode (recall John Davies’ stove in Secunda) the only thing on top is ash, not fuel.

A stove burning fuel with little to no ash has little to nothing on top of the fuel being burned.

Regards
Crispin

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