[Stoves] re-kindling stoves

[Tom Miles]

Has anyone dampered the inlet air to control the air flow through the
briquette?

Or, has anyone used a ceramic insert to partially block the air flow and
still provide a radiating surface?

Has anyone put a fan on the air supply and given the air a spin to scrub the
exposed 
fuel on the inside of the briquette?

Or, damper the inflow to promote gasification and induce a draft with an
outflow eductor to provide secondary air mixing? 

Tom
Musing

-----Original Message-----
From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Crispin
Pemberton-Pigott
Sent: Tuesday, December 28, 2010 8:19 AM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] re-kindling stoves

Dear Richard and Andrew

I know we all quote the 6 kg of air for burning biomass please keep in mind
that to get an excess air ratio of about 100% it takes twice as much as 'it
seems'. 

With the gasifiers, the ratio between primary and secondary might be a 1:6
split, but the secondary needs to provide all the excess air as well so it
is more like 1:10 than 1:6, yes?

The primary side for the gasifiers needs to remain the same (which is based
on experience, really) but the theoretical need for air on the secondary
side is surely less than the real need?

So when it comes to the air moving through the hollow briquette, can we
treat the whole needed air supply as being present 100% (instead of a
separate secondary supply) and concentrate only on mixing and combustion
chamber temperature? It looks as if the hole is a means to sneak the whole
air supply past the light biomass fuel without increasing the burn rate
which is what happens in most ordinary fires. I think Paul made this point
clear when we were talking about getting secondary air through the coal bed
earlier in '10.

So, one big advantage of using hollow briquettes is that it is probably
possible to get the whole air supply through in one go and avoid having the
complexity of secondary admission.

This being the case, it should be possible to create a perfect hole size for
each briquette mix and compression/forming method. This means in practice
that for any consistent product, one should vary the hole diameter and test
them in a stove, measuring the excess air. A simple method to do that is to
look for visible smoke most of the time. That means the air supply is
inadequate.

On the briquette press side, it means having replaceable cores with many
diameters. Fully implemented, one could select briquettes with the
appropriate burn rate: denser probably needing smaller cores to have the
right air supply to burn slower and longer.

Got thoughts on this?

Regards
Crispin NOT in the snowstorm


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