[Stoves] Gasifying coal?

[IPC]

Dear All

I'm just a little concerned that some of the questions I don't understand
because I don't understand the language.  

In much of the literature "gasification" means the turning of a combustible
fuel into  blend of carbon monoxide and hydrogen by, for instance, the
reaction of the fuel with oxygen and, typically, steam, although there may
be enough water present in the fuel to provide the necessary H2O.  Both
exothermic and endothermic reactions take place simultaneously and the end
result is an essentially carbon-free inert residue or "ash". Wikipedia, for
instance, defines gasification as "a process that converts carbonaceous
materials, such as coal, petroleum, or biomass, into carbon monoxide and
hydrogen by reacting the raw material at high temperatures with a controlled
amount of oxygen."

But Thomas is talking about a process that yields a "stove coke" from coal.
I think of this as either "carbonisation" or "devolatilisation" depending on
whether I am focusing on the char or the gas.  Its the same process in both
cases, just that slightly different optimum operating conditions apply,
depending on whether I want to optimise char or gas production. Basically
heating the fuel in the absence of air breaks the fuel apart, producing a
fuel-rich gaseous fraction and leaving a carbon-rich char.  You can get the
heat for pyrolysing much of the mass by burning a little of the mass and
restricting the flow of air. Its a much simpler process than gasification,
and yields pyrolysis gases that are fairly rich in things like methane,
methanol, and a range of alcohols, ketones and the like.  In contrast,
gasification produces primarily hydrogen and carbon monoxide, which burn
very differently from the pyrolysis gases. 

The reason I am concerned is because if you use the 'wrong' name you can
miss an awful lot of information.  The literature on devolatilizing or
coking coal is so huge and ancient it is difficult to know where to start;
in contrast the literature on gasifying coal gives you 'only' about 1
million Google references. 

Trust this assists in the debate.

(Dr)Philip Lloyd
Energy Research Centre
University of Cape Town
Private Bag Rondebosch 7701
South Africa
Tel +27 (0)21 650 3896
Fax +27 (0)21 650 2830
 

    
 

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Thomas Reed
Sent: 12 December 2007 04:23
To: Discussion of biomass cooking stoves; gasifICATION
Subject: Re: [Stoves] Gasifying coal?

Dear Crispin and All:

In 1998 Robb Walt of CPC asked me the same question:  Can the WoodGas stove
gasify coal.  Since coal is only 20% volatile while wood is 80%, I didn't
think so, but having discovered that my opinions are often wrong, I got a
few chunks of Western Coal from Coors.  (There are long supply trains here
in Golden, and sometimes pieces fall off - or are helped off.  It takes a
LOT of coal to make beer.) 

I crushed the coal and pea sized it, put it in the stove, ignited it with
chips/sawdust pellets/coal.  (Coal is hard to ignite) and was delighted to
find that it burned longer even than wood pellets, being so 
dense.  It yielded about 50% of  "stove coke".   Experiment trumps 
opinion again!  (Some of my best inventions have come from ignoring my
instincts.)
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The charcoal from our woodgas stove can be a useful byproduct.  Any
suggestions for the "stovecoke"?

Yours truly,

Tom Reed

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