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

Sat Jan 6 15:39:47 CST 2018

Dear Andrew and Paul

This is a most interesting and foundational subject and I have been overwhelmed for days so I am tardy in replying.

The evidence from the distillation of biomass to produce liquids and ‎gases shows that there is a conversion of biomass to CO2. Paul asks if the C is completely separated from the OH. It probably does now and then but it is not material. If it happens the heat is lost then regained, lost again and regained as the chemistry rapidly changes. What we do know is that in the end, there is only a net heat released from the biomass at 360C, and that the rest of the time the chemical changes leading to the gaseous products are energy-neutral. This of course is in the absence of air.

‎In the presence of air anything goes. There are about 450 different reactions taking place and 150 chemical species witnessed.

It should be possible to calculate the heat available from the distillation of biomass in the absence of air, and based on the chemistry of the combustion gases, the same can be done when air is present.

The big take away I have from this investigation is that the term ‎'pyrolysis' is too broad to usefully describe the processes of drying, distillation, oxidation and reforming of gases and liquids. Yes they all involve heat but we need a much clearer analysis using additional terms.

Paul, I have been thinking this week that you are probably not going to have much success trying to change the standard terms used in the professional gasification sector. These people have been talking about this subject for a very long time‎.

Some of the things you wrote carry the implication that they are 'generally true' but when I reflect on them, they are really only applicable to particular devices working in a particular. I won't take your time with examples. I am just cautioning that something may be true but only in certain cases and therefore doesn't represent something generally true.

You have seen enough cases of such claims for 'how stoves work'. Larry Winiarsky's ten rules for Rocket Stoves are pretty good, for Rocket Stoves.

Samer Abdelnour was visiting Waterloo this week speaking at the Balsille School of Management on the stove wars of Darfur. He asked me to take a stove along so I took two: one from Yogyakarta (what I once called the cleanest stove in the world) and a Vesto with a big pot on top.

I ran it the night before in TLUD char-making mode using 6mm wood pellets. It made 310 g of charcoal pellets. ‎So his presentation was made with two TLUD ND gasifiers on display, including a large ziplock bag of biochar produced with the larger one. I thought you'd like to know that.

Regards
Crispin

On 4 January 2018 at 01:10, Paul Anderson <psanders at ilstu.edu> wrote:

> Oxidation during pyrolysis:
>
> Not a reference, but a statement and question:   When a carbohydrate
> molecule (containing O and H and C) is broken apart by heat (which is the
> process of pyrolysis), what happens inside the molecule is not totally
> understood.  Is it not possible that a carbon atom that is linked to an
> oxygen atom (and to many other atoms) could not be shedding the other atoms
> and the C + O are never separated?   That would result in a molecule of CO
> that is NOT from the combination of C with O, and therefore the C was not
> oxidized.   The C was already with the O.
>
> The "atomic scientists" can discuss that possibility.   I leave it as CO
> being present as a result of pyrolysis, and not necessarily because some
> "free standing" "liberated" atom of O was then joined with an atom of C.

Paul  did you get any further with this?

I suspect you narrowed the field a bit by qualifying who should reply.

There are two separate points here

1) It is probably known which bonds are broken and new ones remade
during pyrolysis as nuclear magnetic resonance enables a lab to
estimate types and  the frequency of occurrence of different bonds,
each bond C-C C=C C-O -OH re radiates the energy at different
frequencies. More importantly is whether there is enough energy is
available to break the bond. and this leads to point 2

2) Crispin seems to be saying that, given knowledge of all the bonds
in a piece of wood, there is net energy available  to reform all the
hydrogen with the oxygen in the wood  to give water and carbon as the
outputs? Have I got that right Crispin?

It may be so but for the purposes of burning fuel in cookstoves we are
just going to have to supply air and enough initial heat for oxygen
molecules to dissociate and react with the fuel.

Andrew

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