[Stoves] Re: Distillation and oxidation Re: Understanding TLUDs, MPF and more. (was Re: Bangladesh TLUD )

Some clarification,

1.  This message is to the Stoves Listserv.   There have been perhaps 20 other messages with the exact same Subject title that have gone to only 3 to 5 people, even with the    RE:[Stoves] start to the title.   There were some good exchanges and I learned so infom but (in my opinion) most Stovers should be glad that they were spared from reading those messages. 

2.  The topic is actually of more potential interest to those who are keen about Gasification (broadest definition).   And those readers are on their own listserv, of which I have been a subscriber since about 2001-02.   That Gasification List has shown MINIMAL interest in the topic of TLUD stoves and other micro-gasification devices, and I almost totally agree with them about that Gasification Listserve to be dealing with larger systems, not stoves.   So the dialog about TLUDs etc has been on the Stoves LIstserv.  

3.  I will NOT be posting this discussion of distillation and oxidation to the Gasification Listserv.  But on that list are the experts about pyrolysis and gasification and all the related processes.   Tom Miles is on both listservs but did not direct the past messages to that group.   The Gasification group can also be very good at “verbal wars” and “definitions” debates. 

4.  Crispin has written one thing that I do need to address.   He wrote:

I see now that the two different approaches described by Hirendra will probably give different results:

It has been acknowledged that Hirendra is a gasification expert (in his 80s) who had not heard for TLUD stoves prior to Crispin bringing him in as a expert.   I suspect that MANY true experts on the formal and longstanding science of gasification have not heard of TLUD or other micro-gasifier devices, and have not studied them.   That is fine, but does not mean that their comments are correct about gasification topics that are new to them.   The next sentence is NOT correct, whether stated by Hirendra or Crispin: 

the ‎TLUD with a glowing bed through which the distilled gases immediately under it have to pass in one type,

How are there distilled gases (pyrolytic gases, combustible gases) ever getting to be UNDER the the glowing bed, even if “immediately under” means a millimeter or less.   It is possible that some of the gases that are coming out of a pyrolyzing piece of biomass could be exiting downward, which would be directly into the glowing bed (or any very thin layer that is glowing red hot.)    Expect those gases to be combusted IF there is sufficient primary air reaching that area.  If surplus gases are there, they would move upward, NOT THROUGH ANY GLOWING BED.

Also consider the pyrolytic gases coming out of the upper side of the pieces of biomass.   There is no glowing area at all on that side, and the gases move awary from the glowing hot zone that is beneath the pieces of biomass. 

The pyrolytic (“destructively dry distilled”) combustible gases that move upward inside a TLUD stove are tarry, smoky, long-chain hydrocarbons.  

I thank Andrew and Alex for their comments and clarifications, some of which are found below.


On 1/7/2018 5:27 AM, Crispin Pemberton-Pigott wrote:


Dear Andrew    I have been looking into the combustion of hydrogen and I think the idea that hydrogen does not make water vapour in a small gasifier at all is not going to hold up. Let's keep looking.    According to the hydrogen promoting guys the ignition energy is SO LOW just about anything will make it react. In other words the gas doesn't have to reach 570 C to auto-ignite‎. It will accept any input above 0.05 MJ.    The TLUD experiments from Julien report temperatures above 600 and I suspect the thermocouples are all under-reporting.    I see now that the two different approaches described by Hirendra will probably give different results: the ‎TLUD with a glowing bed through which the distilled gases immediately under it have to pass in one type, and the continuous updraft where the oxidation layer is always under the distillation zone is the other.  In the latter case the hydrogen will not pass through a 'fire' in any sense and if it remains under 570 it will not auto-ignite.    Some gasifiers are run up to 1100 C so I am not including them. Just the ones we have been calling 'pyrolysers' for some reason that is not nearly as clear now that we have discussed it more.    Back in the land of real and small gasifiers, the reactions in the little TLUD's take place in the presence of air so the availability of oxygen is not the limitation, right? At the moment, from what I have read, that if I fed hydrogen into the primary air supply of a TLUD it would all emerge in the gas stream above. If you try it, stand well back.    Regards  Crispin            On 7 January 2018 at 02:31, alex english <aenglish444@gmail.com>; wrote:  
Destructive distillation of wood was the term back in the 1930s when my  grandfather wrote a high school text book.  Attached;   is a slide on pyrolysis stages from our national labs senior scientist  responsible for bioenergy and the tar sands pyrolysis.  and two images of google word use search between 1800-2000 for pyrolysis and  destructive distillation.  
    Good graphs of the change in terminology from destructive distillation  toward pyrolysis. I knew the term but considered it more to do with  the making of simple organic compounds from wood before organic  chemistry really took off with the petrochemical industry.    The wood gas distillation produced acetic acid and methanol amongst  many other chemicals. I have posted in the past about an acetic acid  plant in Germany which pyrolysed beech logs, distilled vinegar and  used the other gasous products in a spark ignition engine to power the  plant. charcoal was a less valuable by product.    There have been a flurry of offlist e-mails which I have replied to  without realising they will not be seen on stoves.    Anyway your slide clearly shows agreement with what Tom Reed said all  those years ago, there is an exothermic stage and here the range is  given a bit wider as 280-500C but the salient point is that the oxygen  bearing compounds given off do not include water beyond the drying  phase. So in the final stages the  gases CO and H2 are favoured as I  have said earlier.    Whilst acknowledging there may be a means for disociating all the  elements in wood and recombining the oxygen with the hydrogen it does  not happen in simple stoves or gasification.    Andrew    _______________________________________________  Stoves mailing list