[Gasification] Gasifier construction question

[doug.williams]

Hello David,

You ask:
> In most systems I have seen, the reaction vessel is metal, usually
> stainless steel.  Has anyone looked at refractory ceramics for this area?

I assume you are referring to the gasifier casing, which can be built out of 
ordinary steel plate or sheet. Stainless steel is only a non corrosive 
material, and not a specifification for producer gas systems. Some old time 
gasifiers were built out of brick, but the gas quality created major toxic 
pollution. With the high quality refractories available today, it should be 
possible to build a reasonably reliable gasifier. You can see a line drawing 
of an open core gasifier built out of cement on the Fluidyne Archive 
www.fluidynenz.250x.com   This was a charcoal gasifier, and has galvanized 
bird wire, tied to fencing wire as an armature. They were built on site by 
the operators in developing countries.

> Looking at the refractories on the web, I see that they need internal
> reinforcement (i.e. a wire mesh to hold them) and a fairly difficult
> cure cycle.

If using refractory, the reinforcing can actually create a problem if it is 
steel. Of course it depends on where the refractory is used, but reinforcing 
is not always required, in every instance.

> However they tend to have lower thermal conductivity
> (especially when backed with pearlite filled refractories) but are
> more susceptible to abrasion than stainless steel.

What ever the material in a gasifier, it all has to reach an equilibrium of 
operational temperature. Depending on how you design the actual high 
temperature zone, the outer wall refractory will have a layer of non 
oxidizing charcoal against it, and this forms an insulation in itself, and 
makes the refractory redundant, unless the gasifier is all ceramic.

I have never seen abrasion of ceramic caused by the flow of wood and 
charcoal, mainly because the fuel flows are vertical to the surfaces.

> Anyone else have thoughts on this as a throat material?

Castable refractory is a choice available to you if cannot obtain the right 
Austentic high nickel metals ( Avesta 253MA).
You should select a mix that has a resistance to expansion when heated, and 
be able to accept thermal shock. As a throat tube, you can expect 1,200C+ 
within minutes of ignition, so get the best available. We have discussed 
this previously, and cheap DIY experimental refractory had some good 
suggestions from list members. Check the Gasification Archives.

Doug Williams,
Fluidyne Gasification.