[AT] gasifiers

[Ken Knierim]

On Thu, Oct 15, 2009 at 6:57 AM, Gene Dotson <gdotsly at watchtv.net> wrote:

>    Wood and all biomass fuels burn in 2 stages. The first and most
> noticable is the gas burning that is driven out by the heat, this is the
> flame you like to see in the fireplace. The second stage is the ember or
> charcoal stage when the solid part of the wood is consumed.  A fuel heated
> or burned in a limited oxygen atmosphere will drive the gas from the fuel
> and when directed to a chamber with free oxygen will then be consumed with
> very little waste or smoke.
>
>    All biomass fuels contain gas as a normal product of growth, mostly
> methane. Gas can be rendered by using heat or pressure or a combination of
> both as nature does in the production and accomulation of natural gas.
>
>    Many have noticed that burning wood that has laid for many years in the
> woods will burn with less visible flame than fresh wood due to the loss to
> the atmosphere of the gases. The solid mass is still there and burns well
> in
> the ember stage. (I use ember stage as I don't know the actual term).
>
>    I have wondered how much gas could be extracted from sawdust and a
> system to pressurize it and capture the gas?
>
>                        Gene
>
>
>
Gene,
    I had a similar thought, but possibly using chipped wood instead of
sawdust (basically the same, just different particle size). Steve's
information that the gases are corrosive surprised me but after dealing
semiconductor processes for awhile, there are methods of handling corrosive
and toxic materials. It's good to know BEFORE you start building the system,
certainly. Thanks Steve.
    My armchair guess is that with good filtering the gases can be
compressed for storage. It would depend on the gas makeup but I suspect that
with enough pressure, fractions could be drawn off so that various different
portions of the gases could be separated and handled appropriately. I'm not
sure compression is the best idea for all though; possibly a centrifugal
separator would be easier for some gases (like H2). Compressing and storing
hydrogen has some issues but there are folks working those issues.
Personally I see hydrogen as an energy storage medium rather than a fuel per
se. I can't help but wonder if some of the CO and possibly other gases
couldn't be burned off or reused in the system cycle with the addition of
some water to optimize hydrogen production. I'm not a chemist so I don't
know the answers and it's possible things would bond back together inside
the system before it could be cooled and separated, for all I know. CO is a
potential fuel, along with having some negative affects on humans and
atmosphere but if it were up to me I'd use it in the reactor to get more
hydrogen fuel (if it made sense and could be made to work without gumming up
the system).
    Logically, having a gasifier is part of the picture. Doing something
with it is the next obvious step. Right now the simplest and easiest way to
handle the gas is for a heating application. That would give a baseline for
the amount of energy being released. How to separate the gas and compress it
becomes the next step but I see it as a more capital intensive phase.
Compressors aren't cheap unless you have one laying around and safe handling
of stored energy starts to get the interest of the fire marshals. What are
the gases, other than CO and H2? And how much do the concentrations vary,
depending upon the sawdust you're feeding it, the temperature and moisture
of the fuel bed, etc?

Very interesting topic.

Ken in AZ