Re: GAS-L: maximum pressure

["Dick Glick" <dglickd@pipeline.com>]

Hello -- Your assuming equilibrium thermodynamics-- the reaction in question
is not run under equilibrium conditions!  Dick
----- Original Message -----
From: <JackProot@aol.com>
To: <gasification@crest.org>
Sent: Tuesday, February 05, 2002 10:36 PM
Subject: Re: GAS-L: maximum pressure


> In a message dated 02-02-01 14:25:07 EST, LINVENT@aol.com writes:
>
> << The major benefit to high pressure is not having to compress the gas to
>  feed into a turbine which operates at 150-350 psi. Compressing the gas
after
>  gasification is a significant parasitic load. >>
>
> I am still trying to understand the advantages of working under pressure
> in a hot gasifier. Reflections :
>
> - compressing the gas after gasification requires energy, OK. But so does
> the compression of air before gasification. Slightly smaller volume maybe
> but then consider the unavoidable leaks ...
>
> - I keep thinking something is missing in the reasoning. Or why would
> people spend so much money in Hawai to replace a stupid compressor
> after the gasifier ?
>
> - In a first message, I wrote that Le Chatelier was pushing the reactions
> the wrong way : when pressure goes up, the reactions are displaced
> towards the least volume.   Ex : 2CO <-> CO2 + C goes to the right.
> Not exactly what we want.
> Well, actually, I didn't get the whole picture : we can also see something
> like   C + 2H2 <-> CH4    which is favored by an increase in pressure.
> Generating methane is quite exciting !
> I ran a quick thermodynamic model with a 20% moisture wood at 800°C.
> No methane at atmospheric pressure of course, it is largely decomposed
> above 600°C. But at 15 bar, I had about 5% in the gas. (Could not go any
> higher as the wood began leaving an important carbon residue in the
> vessel. Need more moisture to increase the pressure.)
> Interestingly enough, the yield increases slowly with the pressure.
> (I mean the ratio of heat capacity in the gas vs. the wood used.)
>
> - If we take the gas produced at one atmosphere and we compress it
> to 15 bar at the same temperature, we get approximately the same
> composition as the gas produced at 15 bar in the furnace. This latter
> operation is of course a lot easier. (A heat exchanger could cool down
> the gas before the blower and reheat it after, to soften the cost.)
>
> Ain't that fun, to run a furnace on paper ?
> We can still burn the paper when we are done   :-)
>
> Still suspicious : rich idea in hiding or mad scientist ?
>
> Jacques Proot
> (metallurgical process - and gas amateur after hours)
>
> -
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