[Stoves] Misuderstanding of TLUD stoves Re: Refuelable TLUD Coal Stove developed in Mongolia that is not a batch process.

Sat Mar 5 22:43:16 CST 2011

Go to the bottom of Crispin's message for my reply.
-- 
Paul S. Anderson, PhD
Known to some as:  Dr. TLUD    Doc    Professor
Phone (USA): 309-452-7072   SKYPE: paultlud   Email: psanders at ilstu.edu

Quoting Crispin Pemberton-Pigott <crispinpigott at gmail.com>:

> Dear Paul
>
> I am still not convinced you agree that it is possible to make an upside
> down TLUD. The description you have provided (several times) can be
> inverted.
>
> Let me see if I can follow this closely enough to satisfy you. I t is my
> view that you are ascribing to all devices something that happens with some
> fuels and not others. Your descriptions may apply to chopped biomass, or
> some chopped biomass, but it does not apply to all fuels in all
> configurations running at all air flow rates in all directions. I think you
> are attempting to classify all stove or fire configurations and you reserve
> a special case for TLUD's as being essentially different from an inverted
> TLUD. While I do not understand why you want to do that, I will try to
> assist because I find your conclusions mostly correct.
>
> "In a true downdraft gasifier, there is a hot zone that stays at the bottom
> all the time, and the fuel moves downward to it, becomes char and is later
> subjected to char gasification.  The air flow is also downward."
>
> This only true is some cases. A downdraft gasifier can gasify all the fuel.
> I don't think we can say 'a true downdraft gasifier'. What's that? You
> describe a situation in which the fuel moves down all the time. Well, some
> gasifiers work like that but I would not call that a gasifier at all unless
> there was a limited air supply that produced a combustible gas. Increasing
> the air supply would make it a fire, not a gasifier.
>
>  Then there is the case I described (which I have built and run many times)
> in which the fuel is NOT falling continuously into the hot zone. There is a
> pyrolysis front that moves upwards through the fuel, just as you describe
> one moving downwards through the fuel, reaching the 'end' of the furl
> charge. That is on top in the downdraft and the bottom in the updraft.
>
> They are literally identical in operation save for the 'down-ness' of the
> construction. In the case of a downdraft, more fuel can be added on top of
> the pyrolysed fuel and the reaction can continue. In the case of a TLUD fuel
> can be pumped under the pile to achieve the same result. There are large
> Russian coal burners that work this way. They can make gas or burn
> everything completely, and/or make coke depending on what you want. I have
> seen drawings for a 320 kW one here in Ulaanbaatar.
>
> "In a TLUD, the hot zone starts at the top, but then the hot pyrolysis
> front migrates downward until reaching the bottom of the fuel pile.
> That is FUNDAMENTALLY DIFFERENT from the downdraft gasifiers."
>
> Well, it is different from the one you described above, but it is identical
> to the ones I have built. It is identical to a downdraft gasifier that
> operates in a char producing mode. You described a downdraft fire that burns
> the char and which has more fuel falling into the hot zone. I have built
> those too. Depends on what you want! If you choke the air passing through
> the fuel in a downdraft stove, just as you choke the under-air in a TLUD,
> the result is the same: same fire, same gases, same pyrolysis front, same
> char. The difference is that you can toss a little fuel on top of the hot
> zone. I can toss fuel on top of the pyrolysis done. Both have the effect of
> continuation of the fire.
>
> This continuation is however slightly different in nature. Tossing small
> amount of fuel on top of TLUD is not continuing a TLUD gasifier operation as
> there is now no moving pyrolysis front. Opening the cover of a DD gasifier
> and tossing on some fuel on top of the still reacting pyrolysis front lets
> the 'true gasification' continue. You could in fact add a 1 foot deep pile
> of fuel on top of the fuel and the pyrolysis zone would move into it as it
> did before. If the air supply remained controlled (limited) it would
> continue to produce gases below the grate at the bottom.
>
> If you like I can demonstrate this to you.
>
>> Note:  In the case of the Chip Energy Biomass Furnace (www.chipenergy.com)
> which is a true updraft gasifier with continuous operation (and the hot zone
> is at the bottom where the air is entering), the new fuel enters in small
> amounts, avoiding the problem mentioned in the above paragraph about water
> vapor."
>
> This does not sound like a TLUD, it sounds like a gasifier that has fuel
> dropped onto a burning layer in a restricted air environment (which
> automatically produces a combustible gas). I agree that it is updraft. I
> agree that it is a gasifier. It is of course no longer 'top-lit' as the hot
> zone is under the new fuel, right?

Crispin.  Correct.  The Chip Energy Biomass Furnace is NOT a TLUD.   
That is what I have said.

Concerning your other comments, the problem is that the term  
"downdraft" is being used as the SINGLE descriptor of several  
strikingly different types of gasifiers.  I have used the term "true"  
when maybe I should have said "traditional, as seen in the textbooks  
descriptions."  OTHER modifier words would be useful to describe the  
different variations of downdraft devices with which you are working.   
But you need to do that, not me.  You need to be clear about what  
variation of downdraft gasifier you are referring.

And I will try to do likewise.

Paul
>
> Interesting.
>
> Regards
> Crispin
>
>
>
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