[Stoves] Bangladesh TLUD (was Re: No subsidies in TLUD char peoduction

[Andrew Heggie]

On 9 December 2017 at 04:30, Julien Winter <winter.julien at gmail.com> wrote:
> Hi All;

> The reactor bodies will be a heat sink.  I am not sure how big an issue that
> would be, becaue gas flame is a the top of the stove, and heat in the center
> of the char above the 'flaming pyrolysis' moves predominantly upwards and
> not sideways, because air movement is upwards, and char is a poor conductor
> of heat sideways.  (I have measured the horizontal profile of temperature in
> metal TLUD reactors, and the temperature only drops in the 1-2 cm near the
> reactor sidewalls.).

Also as the concrete is made with vermiculite it will be a poorer
conductor of heat the losses at the pyrolysis front should be lower
than a steel container cooled by the heating up of the secondary air,
although ultimately at the end of burn it will have more residual heat
in it.

How hot can portland cement get before it breaks down?

>
> For burning pieces of wood more than 1 cm thick, some holes in the sidewalls
> of the reactor would provide pilot lights to prevent accidental shut-down of
> the reaction.  I belive this is important for thicker pieces of fuel than 5
> mm pellets, because it takes longer to reach pyrolysis temperatures at the
> center of thick pieces of fuel.  That means that when the reaction is turned
> down, char combustion on the surface of particles becomes important to keep
> the primary pyrolysis reaction going.

I noticed this from the slight greying of the char in some of the
clips, even so the glowing char would need to be above the spontaneous
combustion temperature of the offgas before it would re establish a
flame.


>
> (Just a side comment.  I have observed that the thicker the fuel the more
> primary air is required for the primary pyrolysis reaction.  I believe that
> this is because of the time it takes for the center of thick pieces of wood
> to reach pyrolysis temperatures.  Because the time it takes to completely
> char the wood, the heat from flaming pyrosysis is not sufficient, and heat
> from char combustion becomes important.  Thus a higher flow rate of primary
> air is required for a TLUD loaded with chunks of wood than pellet fuel.  As
> fuel thickness increases, the yield of biochar decreases.)

I'd still like to see a video of  Tom Reed's work repeated, a gold
lined quartz tube as the reactor ( I have no Idea why this was chosen
over a similar transparent ceramic tube) so I could see the flaming
pyrolysis, in most of my experiments I suspect my primary air rate was
too high and the migrating front was propagated by the radiation and
conduction of burning nascent char.

Julien, that was an interesting techie post, a refreshing   respite
from the horde of esoteric posts on politics and attribution of
pollution.

Andrew