Talk:Gasification
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What is the air / steam flow co- and counter-current with, the motion of the fuel? If the fuel moves, why is it called "fixed-bed"? Thanks.
--- The final resting area of char, that is currently undergoing the gasification processes, resides at a fixed bed depth (downdraft) N/cm from the original (raw unburnt feedstock (before heat and air where applied)), this final resting area is where the said char is completely reformed to (A)gas (producer, or syn gas) and (B)mineral ash (ash). At this point, the spent ash simply falls through the final bed retainment, and is replaced by more char that will undergo the same reforming process. The consumption or reforming process retains this level N/cm from the raw fuel area, by means of mecanical or gravity retention. Therefore the fuel is constantly moving to the said fixed bed.
Side note: some "slipped char" also moves past the final bed area and is known as "spent char".
A31ford 12:12, 30 April 2006 (UTC)
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The optimal flow of the gasification agent (air/oxygen/steam) in a fixed bed gasifier depends on the reactivity of the fuel (how fast it reacts chemically with the gasification agent at the given temperature) and by the energy effect you need from the gasifier. A faster flow results in a faster conversion, but also in a thinner gas, eventually approaching the exhaust from pure combustion. The gas flow is much faster (several m/s) than the movement of the char (several cm/hour).
The fuel particles in the "fixed bed" is nearly fixed in space. It is a correct observation that it does move as the fuel is consumed. But as indicated above, this movement is very slow.
My visits to the UK left me wondering why there are so many abandoned gas works there. Why were they built (what was the advantage over using the fuels involved to generate electricity), why are so many of them still around, and what did they usually run on? The article explains how the process works very well, but since gasworks redirects here, it'd be nice to elaborate on the actual gas works themselves. Bz2
