[Gasification] Pellet Fluffing and axial/rotary screw

[jim mason]

On 3/1/07, drew <drew at artforging.com> wrote:
> I have used pellets in my tlud variant and found the swelling action to
> be extremely challengingly.   So much so that I gave up on pellets
> unless mixed with other fuel.   They seem to swell in reaction to heat,
> but perhaps more to the resultant steam?   My system was a pressurized
> low volume flow and it resulted some times in a hopper so packed that a
> chisel was necessary to clear it.   The pellets I used were Fir sawdust
> with low moisture content (< 10%).


well, this would make some sense, as with an updraft you are going to
be passing lots of steam over the pellets, and such will make them
swell.  the end part of your fuel bed in an updraft design, even the
top lit varieties, is seeing all the steam and tar from everything
before it.  with a large fuel hopper, this will be a significant
amount of steam.

using them in a downdraft, the vapor is tending to go down to the
fire.  well, some is going up out the top and some goes to the fire,
depending on flow rate.  but at least where the heat is is close to
the fire and most of the steam is not travelling through tons of fuel
before the fire.

yes, i now remember that  i had pellets swell, but it was in the
crossdraft "gas-can-i-fier" i made.  see bottom of page here:
http://whatiamupto.com/Gasification/quadrafier/index.html.  this
crossdraft had a completely sealed hopper.  here i learned the
sensitivity of a sealed hopper to moist fuels, as well as not properly
starting it with charcoal in the bottom.  i tried to just fill it with
pellets and run.  it steamed out quickly, as would be expected.

it seems the updraft would have a similar effect on pellets, but
admitedly smaller.

again, i would really encourage others to try building stupid simple
versions of each gasifier type and see what they do.  there is tons of
learning to be had in watching them.  much more learning than watching
the perfect one work in the end.

if you give up the notion that you are building a real one for a real
application, you can build a gasifier in one day, from stuff lying
around your shop. watching a  junk one work is much stronger
motivation towards actually building your "real" one than just
continuing to mull over the perfect one you are just about to build.

j






>
> I was not aware of the dual motion in the injection molding machines
> makes great sense to me.  Perhaps John F.   JBF biofuels uses them in
> his system, if not they might be worth while?
>
> All the best
> Drew
>
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