[Stoves] Clean burning with a bit of moisture

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On Wed, Oct 12, 2022 at 11:26 PM Crispin Pemberton-Pigott <
crispinpigott at outlook.com> wrote:

> Dear Neil
>
> Hey! Long time. My theory which is only informed by way too much time
> spent trying to burn everything under the sun is this:
>
> Fuel moisture moderates the rate at which gases evolve from biomass, with
> other factors being the oil content (gummy wood), density, porosity, ash
> content and the volatile fraction of the total mass (which is to say, the
> ash-free carbon content in reverse.
>
> If you want to make smoke, you heat a mass of fuel all at once and starve
> it of sufficient air. This is easy to demonstrate - toss a big pile of
> leaves onto a fire making sure to cover all visible flame. It will smoke
> like crazy.
>
> Set the same pile of leaves in a long "chain" on the ground and light it
> one end. It will burn rather cleanly to the other end.  What is the
> difference?  In case one you have a lot of fuel being heated underneath by
> char and hot fuel with hardly any air to complete the combustion of gases
> generated.
>
> Take a cylindrical stove and put in wood with a fire, and slow keep adding
> fuel until at some point, the flames are heating enough wood to produce
> more gases than there is air to burn it properly. Now it is smoking.
> Whatever amount that is, instead of putting in less fuel, use wetter wood,
> say 3% more moisture. This will moderate the burn and it will be clean(er).
>
> If you have a really decent fire  burning away in a fireplace or stove,
> and add totally dry wood, it will nearly explode into gases as fast as it
> can, with big self-accelerating flames pushing out combustible gases.
>
> One can build a stove to handle very dry material, but most are not tuned
> to that. So they work best with 12% Denver dry wood.
>
> I have observed that to burn wood grown in a desert, like Chad or Niger,
> the designed has to treat it as dry: limited fuel heating by having no
> primary air preheating, preheated secondary air. That fuel is gummy and
> dry. Terrible stuff to burn clean.
>
> If you know it is green and damp like an EPA wood stove test, you preheat
> the fuel and air well, then try to limit the power by total air
> restriction/control. Retain the heat, roast the fuel slowly and have
> adequate secondary air. But not too much. Most stoves have way too much air
> going through them, a rocket stove on medium power, for example. They have
> 6 to 10 times too much air going in.
>
> The hot water vapour has an effect on the particle agglomeration somehow.
> Smaller particles are easier to burn out - acting more like gases.
>
> Somehow it all adds up.
> Crispin
>
>
> *From:* neiltm at uwclub.net
> *Sent:* October 12, 2022 2:06 PM
> *To:* stoves at lists.bioenergylists.org
> *Reply to:* stoves at lists.bioenergylists.org
> *Subject:* [Stoves] ***SPAM*** Re: ***SPAM*** Re: ***SPAM*** Re:
> ***SPAM*** Re: Stoves Digest, Vol 146, Issue 3
>
> On 12 Oct 2022 at 0:46, Crispin Pemberton-Pigott wrote:
>
> > There is a general rule which that biomass burns best (most cleanly and
> > completely) when it is NOT completely dry, unless you have a special
> > combustor.
>
> Can you explain why that should be so Crispin?
>
> I feel this is right from my own experience, but also remember those
> running internal combustion engines from woodgas said the same thing.
>  Their theory was that they were 'cracking' the water into hydrogen
> and oxygen, and got better performance than with totally dry wood.
>
> Best wishes,   Neil Taylor, (still regularly cooking with wood, but
> mostly these days with my original StoveTec rocket stove when not
> camping, and utilising a large BBQ hand crank fan for forced air,
> turned slowly in the early stages to avoid smoke.)
>
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