[Gasification] r.e. What is the difference between a Gasifier & Charcoal Retort

[Mark & Elena Gallmeier]

Dear Neal, Harmon & All,

DISCLAIMER:  The following pertains to smaller scale gasification in the 
USA.

> Doesn't the gas from the flue of a charcoal retort also contain
> combustibes?<

Yes.  Dr. Reed answered this, mostly.  The other volatiles include a tiny
percentage of methanol vapor and numerous other chemicals.  Charring yields:

1.  H2 & CO fuel gasses.
2.  Solid mostly carbon char fuel.
3.  A very small percentage of methanol, around 2%.
4.  Other chemically useful tars.

> Couldn't it also be piped to an IC engine for fuel?<

The H2 & CO could after condensing out or fractionating the other
volatiles, and the water vapor.

>>What's going to be used then to heat the retort?  Normally that gas would
>>be burned to help heat  the retort.<<

Depends on what your available fuels are and what you want from the process.
'Bridging' and proper fuel sizing is not a critical issue (translation: 
tight tolerances on fuel prep and expensive
fuel prep equipment) either for char process fuel or for char feedstock.

Sustained testimony on this list over the years says gasifier fuel problems 
are the leading failure point for modern gasifier projects.

It is true that 'thermal efficiency' and other efficiencies are far greater 
for more advanced gasifier designs.  The fine print that comes along with 
these greater operating efficiencies
demands fairly exacting fuel preparation and gasifiers designed around 
specific fuel types and sizes.   For wood this translates into wood chip 
sizes larger than what is usually produced by the wood chippers now in 
common service in the USA.   Now you have to purchase 'special' chippers 
whose cost will probably exceed the rest of the installation, whether for 
yourself or to reequip existing tree cutters.

And it excludes other abundant forms of waste biomass.   These forms include 
wood construction waste (too many nails to chip), scrap cargo pallets 
(ditto) and mulch which is usually too small and always too irregular in the 
size of particles.

In my own field research here in SW Florida I determined THE BIOMASS FUELS 
THAT ARE LEAST DESIRABLE FOR GASIFICATION ARE ALSO THE MOST READILY 
AVAILABLE.  Least desirable according to current small gasifier design 
approaches, anyway.  This has profound implications for gasification and 
especially smaller scale gasification.

These biomass fuels include wood construction scrap, scrap wood cargo 
pallets, mulch and tree cutting service wood chips averaging 3/4" x 1/2" x 
1/4".  All of these fuels are far more easily 'charred'.

'Charcoal' was also widely used as a gasifier fuel in the 1930s and 1940s. 
GENGAS and "State
of the Art" by Ali Kaupp (both from BEF Press) report that 1940s gasifier 
operators
actually preferred charcoal gasifiers.    Incidentally, both these books 
also document the growth of extensive gasifier fuel preparation and 
distribution industries in Sweden, Germany, France, Switzerland, all 
producing 'ideal' gasifier fuels to exacting standards.  We are currently 
lacking this sort of production and distribution infrastructure in North 
America...

With charcoaling, the fuel prep cycle can be entirely done with available 
low cost chainsaws and log
splitters, rather than still rare and expensive 'block size' wood chippers.

So little has been done with charcoal gasifiers in the modern era that 
knowledge is effectively limited to 1940s era literature.  I'd also add that 
little research appears to have been conducted into improving the thermal 
efficiency of charcoal retorts.    There have been two embedded assumptions 
in charcoaling and retort installation designs to date.  First, one has an 
effectively unlimited supply of wood fuel to drive the process.  Second, the 
resulting char is the objective product goal and will be used elsewhere, 
rather than char being an intermediate step.

>> What's going to be used then to heat the retort?...<<

Something else.  If you started with a wood fire, then more wood,
obviously.    If you began with other heat sources...   Incidentally, some 
other candidate heat sources look like they might lead to more thermally 
efficient retort designs, especially if they are the only heat source used 
for the entire process.

Several circumstances have changed since the late 1940s when the appearance
of cheap natural gas killed off widespread commercial charring in the USA. 
First,
natural gas is not so cheap anymore, and it looks set to get less cheap all 
the
time.  Second, coke made from coal has soared in price.  And coke
availability is disappearing because the EPA is determined to exterminate
all U.S.A. coal coking batteries.   For metallurgical purposes, high quality 
char is the
only feasible substitute fuel for smaller cupola furnaces.

All these are reasons that made 'charcoaling' my own hardware entry point 
into 'biomass
gasification'.

Regards,

Mark

Message: 6
Date: Wed, 31 May 2006 07:56:27 -0500
From: "Harmon Seaver" <hseaver at gmail.com>
Subject: Re: [Gasification] Re: r.e. What is the difference between a
gasifier and a charcoal kiln?
To: Gasification <GASIFICATION at listserv.repp.org>
Message-ID:
<22acb24d0605310556m2204b302h48cafbce9a4e9f21 at mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed

On 5/30/06, CAVM at aol.com <CAVM at aol.com> wrote:
>
> Mark et al,
>
> Doesn't the gas from the flue of a charcoal retort also contain
> combustibes?
> Couldn't it also be piped to an IC engine for fuel?  Charcoal  would be a
> byproduct.


     What's going to be used then to heat the retort? Normally that
gas would be burned to help heat  the retort. I doubt the energy
efficiency of trying to make charcoal AND run an engine is going to
compute very well, even if, as Daniel said, the tar problem wasn't a
serious issue.