[Stoves] Technical about TLUDs (was Re: GLASS for stoves .)

[Crispin Pemberton-Pigott]

Dear Paul

I am preparing a long message dealing with the earlier question about what happens when biomass is heated in the absence of oxygen. The 550 C comes from that investigation.

"I do not know of any studies specifically analyzing the TLUD gases while passing through the char layer or in the area between the char and the secondary combustion zone.  Probably has been looked at somewhere."

Riaz Ahmad  a rare contributor to this list, is looking into this. He is ‎a PhD candidate in the Biomass Key Laboratory at CAU. He has built a gasifier that can operate as a TLUD with an ascending or descending oxidation zone, at any oxygen level of choice. He is going to apply the decombustion theory to reverse engineer the gases produced to determine what fraction of the available solid fuel just got consumed. This entails analysing the gases before they are burned instead of after.

I have a book recommended by 'my gasification expert' which I will pass along in that message.

The mix of gases produced under different conditions is well know, actually, and forms the basis of the distillation of biomass and coal industry.

A precondition for getting a smokeless end to a TLUD burn is that the temperature must be above 550 so no tarry gases are formed. We must carefully define 'smoke'. There will be CO, possibly a lot, but no visible condensed smoke. It is obviously a subjective assessment, but I was pleasantly surprised to see at least some of the fires burn out very nicely.

Regards
Crispin


Chrispin's message below is very useful and confirms that there are TLUDs that can end without smoke (and some are smokey).

1.  It would be useful if we could get more info from the Indonesian testing.  Which of the tested TLUDs were ending with smoke?  Not so important to know the brand names, but to study the stove characteristics so that the causes of the smoke can be determined and then corrected.

At this point I will disagree with Crispin's explanation.  This difference of thought can be settled by science, and I am happy if he is correct.  But I offer a different PART of the explanation.

It is easy for all of us to agree that smoke from TLUDs at the end (or at other times) is mainly because of loss of the secondary flame.   Issues are 1)  insufficient gases, 2) loss of the "pilot" or sustaining flame/spark, and factors (gust of wind, some difference in the fuel for a moment) that cause those situations.

My scientific disagreement relates to this comment (empahsis added):
they [TLUD stoves] have produced all the tarry gases they will, and it has been cracked in the hot char.
That cracking situation occurs in downdraft gasifiers that have a hot bed of char through which the pyrlolytic gases must past.   Check those resultant (post -charcoal) gases and see that they are quite clean and (with some filter, cooking and maybe scrubbing) they can go to internal combustion (IC) engines.   These are clear gases, even when cooled for use in IC engines.

But the hot TLUD gases are never that clean.   They are transparent while still hot in the TLUD chamber above the created char, but if allowed to cool, they will become visible and will be called "smoke".   Without the fire of the secondary combustion, smoke will be emitted.

The cracking of the pyrolytic gases ("smoke") requires passing throught a much hotter bed of charcoal than is found in TLUD stoves.  (Tom Miles and probably some others can comment on the temperatures in the char-bed of downdraft gasifiers where some air for O2 is entering to burn (oxidize or char-gasifiy) the char.)

I do not know of any studies specifically analyzing the TLUD gases while passing through the char layer or in the area between the char and the secondary combustion zone.  Probably has been looked at somewhere.

Quick proof of the smokey gases in a WELL-FUNCTIONING TLUD (which will end without any released smoke) is to extinquish the secondary flame and see the billowing smoke.   Be ready to relight it quickly !!!!

So, I am delighted with Crispin's observation about some TLUD stove models being consistently functional without smoky incidents at the end.  Those are the vast majority of the TLUD stoves in use.  (Poorly functioning stoves do not get used or accepted.)  We are expecting TLUD stoves to have a great year in 2018 as more and more Stovers join these efforts.

Season's Greetings to all !!!

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu<mailto:psanders at ilstu.edu>
Skype:   paultlud    Phone: +1-309-452-7072
Website:  www.drtlud.com<https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.drtlud.com&data=02%7C01%7C%7Cfd33f7a3b92744d257e008d54c82e3a5%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636499047400175182&sdata=oKlJ1nNKoWMOt6zff%2Fi6CTYObi2hv7YNpODFZThqvEk%3D&reserved=0>

On 12/25/2017 6:21 PM, Crispin Pemberton-Pigott wrote:
Dear IH

Some TLUD’s have a smokeless conclusion to their combustion cycle. I found it interesting to see the difference. We were testing a lot of stoves (30?) for the Central Java Pilot and there are definitely two groups of TLUD’s: those that end in a cloud of smoke that require one to jump and run, and the others which have no smoke surge at the end at all.

It is the latter category that are processing the biomass at a temperature above 500C. That is the secret. When that is done, they have produced all the tarry gases they will, and it has been cracked in the hot char. The distillation gases are produced immediately below the red hot char so the processing can be above 550 at all times once it is lit well.

This clean ending permits the TLUD to be used indoors with ease. Many thousands are being used following the success of the pilot project.

Regards
Crispin

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