[Gasification] catalyst

[Daniel Chisholm]

On Thu, 2007-03-05 at 06:13 -0700, Toby Seiler wrote:

>  ...I'm asking about is for a downdraft gasifier that has only enough
> oxygen to complete the burn after the grate, being fed into a second
> stage catalytic unit (close coupled) thus supplying the thermal energy
> for a second stage that is oxygen starved.  Not a batch process with
> excess oxygen but a controlled continuous feed of several feed stocks
> in a second chamber (my proposed design being cross flow in that
> section).  

and from your earlier email:

> ...a two stage system where the first stage is firing into a catalytic
> unit (made of high temp ceramics), the second is fueled with water
> saturated fuel and/or dry fuel and oxygen starved.  Steam being added,
> but only as a supplement to the wetted fuel, if required.  Because of
> the ongoing/never-ending off topic discussion, I have received almost
> no response to reasonable questions about gasification.

Toby, could you elaborate on your description a bit?  You are proposing
to start with a downdraft gasifier, but I don't understand the purpose
of the catalytic unit.

Are you trying to produce engine-grade gas, and the purpose of the
catalytic unit etc is to reduce tars?

If you are after engine-grade gas, are you familiar with the DTU (Danish
Technical University) design?  Theirs is a two-stage gasification
process, which generates engine-grade gas.  The key details of their
system:

- a gasifier (it is an indirectly-heated pyrolizer, though this detail
is unimportant)
- a partial combustor (a small amount of air is added, producing 1200C;
tars are destroyed both by partial oxidation and by temperature).
- the hot 1200C gas then passes through a char bed, reducing some of the
hot CO2 to CO + H2, and dropping the temperature to 800C

Because the char bed is essentially tar-free, and the gas from the
partial combustor is essentially tar-free, their product gas is also
essentially tar-free.

They also do a lot of detail engineering to produce an efficient system,
the usual sorts of tricks you would expect, but the above are the key
details.





-- 
- Daniel
Fredericton, NB  Canada