[Stoves] Pyrolysis: No Air?
Ronal W. Larson
rongretlarson at comcast.net
Tue May 26 19:20:24 CDT 2015
Stephen and list
Thanks and see inserts below. This is to try to focus not on “pyrolysis” or “charcoal [=biochar]” or “IBI definitions” - but on TLUD terminology. This is to get your (everyone’s) reaction.
On May 25, 2015, at 6:27 AM, Stephen Joseph <joey.stephen at gmail.com> wrote:
> HI Guys
>
> Read the terminology page Cordner Peacocke and I put together on the IBI web site.
[RWL1: I think this means the site: http://www.biochar-international.org/biochar/faqs#q24, where one can read “ Biochar is made by pyrolysing biomass “.
I am trying to avoid the term “gasification” for making char (as used by Dean Still below). I can find the word “gasification” in other places at the IBI site - but find “pyrolysis” a lot more - as here. But, as happy as I am with this selective quote, I think this needs more discussion in the stove world.
Clearly a lot of valuable biochar can be made with processes that we can call gasification (and different parts of the IBI site say that).
> Pyrolysis can take place in an atmosphere where there is a small amount of air. Usually at levels below .2% of the theoretical amount of air required to completely burn a biomass to CO2 and water.
>
[RWL2: No disagreement. But in a TLUD (not the only way to make charcoal), the upward flowing air has about 21% oxygen below the downward moving pyrolysis front and zero above it. So, it is hard to justify “pyrolysis” with a TLUD using your 0.2% value. So I am still looking for other definitions of pyrolysis (and there are many). In many of those definitions, the emphasis is on the term “solid product”.
> Albrecht Kaupp wrote a very good manuscript ion on gasification in the 80’s and explained this very well.
[RWL3: I could find no copy of his 1984 book, but at the top of this cite
http://link.springer.com/chapter/10.1007/978-3-663-06868-6_3#page-2
and after “Look Inside”
http://link.springer.com/chapter/10.1007/978-3-663-06868-6_3#page-1, you see a figure 6 which is BLUD, not TLUD. As I am not trying in this note to separate pyrolysis from gasification, but only concentrating on TLUDs and making char, I consider your Kaupp cite to also be supportive of saying a TLUD is pyrolysis - not gasification.
[RWL4: Trying to rephrase my 18 May note (below) differently: I am saying that the main purpose of a TLUD is NOT to make a gas (which it does well), but rather to make a charcoal; so therefore TLUDs should be called pyrolyzers. On the other hand, I believe that some stoves which are NOT designed or used to make and save charcoal but have a distinct char making phase — have every reason to be be called gasifiers. I don’t put TLUDs in this second category - since TLUDs in fact gasify/combust the char badly (at the bottom - a long way from the cook pot - and at an excessive temperature).
Since the earliest days of this list, emphasis for what are now called TLUDs has been on making charcoal. Initially (1995) the TLUD topic was introduced as a way of saving forests (where char is always made badly). Later (2005) emphasis was as a way of making biochar. In between, as a way of reducing emissions, making money, etc. Nowhere in those 20 years have we had consensus on the word “pyrolysis” - which I am attempting to gather with this note (and Stephen’s help - I think).
To answer Dean’s second question There is no pyrolysis in a Rocket or an open fire? - I would say it best to call what is going on in Rockets and open fires as combustion. In more detail, I think at least some experts would say that the combustion of an individual piece of biomass has an early stage of pyrolysis and a later stage of gasification, but that any one instant there is generally a mixture of both, with a majority of pyrolysis at first and gasification at the end of one new fuel insert.
I find no fault with Dean’s two quotes below - but note his first doesn’t mention making char. Googling can give us hundreds of definitions - none (I think) for TLUDs.
Your (anyone’s?) thoughts on this rationale to answer Dean’s questions? Again thanks to Stephen.
Ron
ps - my response on the 18th was one that got away, as I lost control of sending for a short time as I came back from a week away. Apologies.
>
> Regards
> Stephen
>
> On Mon, May 18, 2015 at 2:33 PM, Ronal W. Larson <rongretlarson at comcast.net> wrote:
> Dean and list:
>
> This follows other material from Kirk, Paul, Alex and Julien. I would put the emphasis in defining the difference between the two terms on the word “char”. Pyrolysis trying to achieve char and gasification trying to avoid it.
>
> Ron
>
> On May 16, 2015, at 6:10 PM, Dean Still <deankstill at gmail.com> wrote:
>
>> Hi All,
>>
>> Seems to me that the word gasification might fit the TLUD process better? The primary air controls the amount of oxygen, the rate of reaction?
>> There is no pyrolysis in a Rocket or an open fire?
>>
>> Gasification is a process that converts organic or fossil fuel based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high temperatures (>700 °C), without combustion, with a controlled amount of oxygen and/or steam.
>>
>> Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen (or any halogen). It involves the simultaneous change of chemical composition and physical phase, and is irreversible. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating".
>>
>> Best,
>>
>> Dean
>>
>> On Sat, May 16, 2015 at 4:58 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:
>> Dear Alex, Dean
>>
>> That Reed reference is a good one. As biomass is about 40% oxygen by mass, there is a real chance one can have some combustion without any air at all. There is almost enough oxygen to burn all the hydrogen in most biomass. That is a heat source that could leave all the carbon behind, in theory. In practise there will always be CO and H2 in the output from a retort.
>>
>> Regards
>> Crispin
>>
>>
>> Dean,
>> There being oxygen in the chemical structure of biomass and oxygen in the spaces and cracks, a strict abstinence is difficult. In one of the Reed/Das handbooks there is a graph of the pyrolysis-gasification-combustion continuum, where the x axis goes from say zero to %200 of stoichiometric oxygen/air. I think ( always roughly) gasification fit in the %20-%80 range with pyrolysis below and combustion above. The char and gas yield % was in there too. I'm sure folks could argue endlessly about where exactly to place the demarcations.
>> Alex
>>
>> On Sat, May 16, 2015 at 6:50 PM, Dean Still <deankstill at gmail.com> wrote:
>> Hi All,
>> When I look up the word pyrolysis I find the following:
>> Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen (or any halogen). It involves the simultaneous change of chemical composition and physical phase, and is irreversible. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating".
>> However, I think that folks use it to describe what happens in a TLUD, etc? Isn't that gasification not pyrolysis because of the presence of some air?
>> Best,
>>
>> Dean
>>
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