[Stoves] Limiting factor for secondary burn?

[Kevin Chisholm]

Dear Paul

psanders at ilstu.edu wrote:
> Dear Frank,
> 
> We are like trains on different tracks and headed in different directions.  I
> deal with TLUD and I also work with my own special variation of up 
> draft that I
> call AVUD (Another Variation UpDraft) to distinguish it from any common old
> updraft gasifier.  Both have specific definitions.
> 
> But there is no clear meaning in the expression "BLUD" because all STANDARD
> regular fires are bottom lit and have up-draft, but they are not 
> gasifiers. Nobody that I know of has an updraft gasifier that they can 
> defend as meriting
> a special name of BLUD.  What you are making is not working and is not a
> gasifier.

It would seem clear to me that:
* If the fuel flows down and the air flows up, then it is an Up Draft.
* If it is lit on the top, it is a Top Lit Up Draft (TLUD) Gasifier.
* If it is lit below the fuel, then it is a Bottom Lit Up Draft 
(BLUD)Gasifier.

Am I missing something?

If you started a TLUD Gasifier and then continuously fed fresh fuel to 
it, you could get continuous evolution of pyrolysis gases. You could 
then continuously withdraw the char, and the top of the fuel bed would 
remain at a constant level even with continuous operation, continuous 
pyrolysis gas production and continuous char production. Since the 
reaction zone is below the fuel, this would be a "BLUD" also, even 
though it had char below it, and even though it was started up in the 
"TLUD mode".

Such a system would get around the problem of the need to dump the char 
out of a TLUD and restart with fresh biomass.
> 
> TLUD is a SPECIAL AND SPECIFIC NAME that refers to the top-lit updraft
> combustion originated by Tom Reed.

Actually, when you think about it, Tom Reed's System should properly be 
called a "TLUD Batch Pyrolyser Stove", in that it does not fully gasify 
the biomass fed to it and cannot operate continuously. The device I 
described above would properly be called a "BLUD Continuous Pyrolyser". 
  If secondary air was introduced just above the bed, then the device 
would be a "BLUD Continuous Pyrolyser with a Close Coupled Stove."


> 
> Specific comments below:
> 
> Quoting frank <frank at compostlab.com>:
> 
>> Dear Paul and stovers,
>>
>> I am thinking with a few simple tests we can determine the optimum 
>> conditions necessary to burn a 'small fuel'. Optimum conditions means 
>> air flow per square cm to keep the pyrolysis  of the low temperature 
>> volatiles optimized and not  having the CO oxidized to CO2 before the 
>> secondary combustion. (hope I am using the terms correctly!).
> 
> Even using the terms correctly does not mean that things happen that 
> way. Pyrolysis (as far as I know) does NOT create CO nor CO2.  Mainly 
> pyrolysis
> results in the release of the long-chain hydrocarbons (tars, smoke, junk,
> etc.), leaving much of the carbon behind. 

An "air fired pyrolyser" such as a TLUD pyrolyser will definitely have 
CO and CO2 mixed in with the gaseous products driven off the byomass by 
the heat generated from partial combustion.


> Again, this is NOT what can be done with a TLUD.  Downdraft gasifiers try to
> destroy the tars, etc. or filter them out.  But the TLUD is based on burning
> the tars, etc in the secondary combustion.

??? If the TLUD is "based on burning", then isn't it thus a stove system 
and not a pyrolyser?

I hope you find my suggestion for continuous feed and continuous char 
removal helpful. Please let us know if you try it.

Best wishes,

Kevin