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

[Andrew Heggie]

 On Wed, 13 Dec 2017 02:27:00 +0000,Crispin Pemberton-Pigott <
crispinpigott at outlook.com> wrote:

>Dear Andrew and All
>
>Now that everyone is or is not a chemist, it is time to end the fun.
>
>This is the major point made by you and Paul.
>
>>My point remaining that to release heat from wood you need to add oxygen
and the fact the wood already has oxygen containing molecules within it is
irrelevant.
>
>I am suggesting that this is incorrect. Whether one can do it in tin cans
on a small scale is a different matter.

As Paul has said that's a different can of worms

>
>There are two possible processes that can take place without oxygen
(heating fuel without the addition of any air at all). They are
>
>Auto-catalysis
>Auto-pyrolysis


Okay I shall snip the rest as I see where you are coming from. There have
been a number of processes proposed for gasifying organic matter, some
involve establising a plasma an in these conditions all the biomass will
decompose  with all the molecules separating into radicals. I imaginne the
conditions could be tuned to end up with the oxgen atoms recombining with
hydrogen atoms.

In practice we see something different even with high temperature flash
pyrolysers, at the high rate of pyrolysis and high temperature the gases CO
and H2 are favoured.

We see this with simple retorts, as the temperature is raised the initial
pyrolysis products are ones containing multiples of oxygen atoms, acetic
acid springs to mind then ketones etc. As things heat up some
recombinations occur within the pieces of char but the at high temperatures
and low pressures the reactions still favour the formation of gases, CO,
CH4 and H2  rather than more solid char and water. So to imply the oxygen
in the wood is available to combine with hydrogen in the wood is misleading.


Long ago my brother warned me against trying to work out heat released from
biomass by working out the bond energies before and after because it didn't
account for the externalities like temperature and pressure.

Andrew
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