[Stoves] ***SPAM*** Re: Clean burning with a bit of moisture

[neiltm at uwclub.net]

Thanks Crispin,

I think for a year or two I wasn't receiving posts from the list, but 
then they resumed a while back.

If I have understood you correctly, the heat energy available to 
gasify the wood is offset by driving off the moisture as steam, thus 
reducing the quantity of gas?  

and

It is easier to control the combustion of less volatile wood, than 
totally dry wood?

I suppose this is what makes the TLUD such a good way to burn wood, 
since it so well controls the rate of gasification, plus of course 
the neat way in which the secondary air can be jetted across the top 
of the pyrolising mass.  I knew this of course, and that moisture 
content could be used to regulate the fire, but hadn't seen why quite 
so clearly as you describe.

I'm not sure I understand your comment in reference to rocket stoves 
though:

"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."

I'm wondering, if this is so, how it helps to increase the air flow 
through Aprovecho's 'Jet Flame' electric fan base for fires including 
rocket stoves?

Since this device as far as I can ascertain is not available on my 
side of the pond, or for sale generally?, I thought to experiment 
more with what I had got, and discovered how neat a solution my large 
hand crank BBQ fan turned out to be, held by a foot on the handle 
aiming underneath the stick pile from six or so inches back, and 
turning very slowly, with a free hand left for attending to the pot.  
Since most of the time I don't need it to achieve a smoke free fire, 
and turn down is by removing or not replacing sticks, and vice versa, 
this has left me wondering about the integrity of such a device 
turned off when not needed, with no air being forced through it, but 
presumably allowed to glow the stainless steel perforated base red?  
Would it not burn out, and/or conduct destructive heat to the fan?  
If so, then presumably the device is intended never to be switched 
off under a fire?  Questions more for Aprovecho than you I suppose, 
but I imagine you probably have a better understanding about this?

According to the Chinese/English label on my hand crank "hand 
barbeque hairdryer", it is power rated at 40W, LOL!

Best wishes,    Neil

On 12 Oct 2022 at 21:20, Crispin Pemberton-Pigott 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.)
> 
> _______________________________________________