[Gasification] Why dry gasification fuel?

Sat Dec 16 00:21:13 CST 2006

Dear List,

I'm a student here, but am always trying to apply general principles that I
rely on for generic chemical synthesis to the reactions of gasification as
discussed by the List and provided by references supplied by Greg and many
other practitioners.

I think that it would be grand if wet fuel could somehow be gasified to an
ideal end state in a single homogeneous reaction, but I think that it is
unlikely. Most of the processes that I have worked with (admittedly not
gasification) resolve to several connected reactions occurring in step-wise
fashion.

The beauty of gasification-as it is commonly discussed on the List-is it's
ability to adapt itself to varying feedstocks. Perhaps, if a single
feedstock of consistent quality were considered, a single-vessel reaction
could be devised that would yield optimal products; both the
H2/carbonization and water-gas reactions would occur between inlet and
outlet. But most often, optimization will require constraints on the quality
of feedstock in addition to specific reaction zone control. Moisture content
is one of these constraints (perhaps mineral content is another practical
consideration).

Drying fuel is a no-brainer. Recovering energy from the drying process in
the form of vapor->liquid enthalpy is also mundane. Designing a system that
functions efficiently regardless of whatever we toss at it is a much more
complex challenge.

Progress is most evident when looking at outcomes, i.e. what works:
gasifier-powered trucks, cook-stoves and stationary generators. From there,
the challenge is optimization and generalization.

Nearly all of the seminal technological achievements of mankind have
occurred outside of the academic environment.

Mark Ludlow, P.E.

-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] On Behalf Of Greg Manning
Sent: Friday, December 15, 2006 3:20 PM
To: A Gasification
Subject: Re: [Gasification] Why dry gasification fuel?

 Sorry Steve, it is C.....

it's not pyrolysis that is the concern, rather the area farther down the
reactor, we call this the "Reduction Zone" (zones from the top down, hopper
(Bunker),  Pyrolysis, Oxidation, Reduction). side note: reduction being
chemical NOT physical.

Here, this will be a bit of reading... BUT, for the condensed version, go to
section 2.5.1 Processes occurring in a downdraught gasifier (About the
internal workings), This "Net Book" is so to speak... my bible....
http://www.fao.org/docrep/t0512e/t0512e00.htm

As far as process heat, the screen cased auger, has air from the gas output
section condenser, piped to it (about 50c or so)

Greg

BTW (By The Way) Downdraft gasifiers use charcoal as insulation, as to not
melt the steel casing within the oxidation section (where we get our needed
heat, for thermalitic chemical reduction).

-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org]On Behalf Of Steve Redmond
Sent: Friday, December 15, 2006 4:58 PM
To: gasification at listserv.repp.org
Subject: [Gasification] Why dry gassification fuel?

Hi Greg,

Yes I do subscribe now. No need to send twice.

I doubt that the 700 to 900 (F, I believe, not C) needed to thermally
sustain pyrolisis is unattainable with 50% mc chips in a self (charcoal)
consuming reactor.

In fact I'm certain it is attainable.

Excess heat and steam can be condensed from the gas flow and made to give up
heat to the reactor. The air intake is one area to look at.

In fact by drying chips with process heat, the energy balance is the same.
The question is, where do you want to spend your energy to evaporate water
from the chip, before pyrolisis or during it? No free rides.

I'm suggesting not separating these processes.

Unless naturally air dried chips are used, heat input to dry the chips comes
from the chips, at one stage or another. Even the engine exhaust manifold
heat derives from the chips. It also could raise reactor temperature, rather
than drying chips pre-pyrolisis.

The advantage is to eliminate a separate stage of chip handling: drying.

--Steve

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