[Gasification] Reducing tar production

[Daniel Chisholm]

On Tue, 2006-31-10 at 08:34 +0200, Zietsman, Rex wrote: 
> [[snip] The Danish Technical University (DTU) has
> developed a two stage gasifier [snip]

Rex, I agree with you, their work looks really good, and it looks like
they've really solved the problem of producing engine-grade gas from
wood.  I'm quite interested to see if their prototype can be made into
something commercially successful.

They do seem to have achieved a highly efficient (>90% cold gas
efficiency), effectively-tar free system (over 2000 hours of engine
operation, with good documentation of trouble-free operation).  Their
design is quite well integrated, too.

The one thing I wonder about the commercialization potential of their
prototype is that they heat the chips indirectly for the pyrolysis.
Necessarily, this makes their first stage quite large and bulky.  While
perfectly fine for a prototype or small scale research reactor, this
could keep costs per kW high.  I think they realize this too, for
example in other papers they discuss using direct heat transfer for the
first gasification stage too (e.g. using steam as the gasification agent
and heat carrier, in a much larger scale system).

(w.r.t. using a truck engine filter, I wonder if it could be kept clean
by back-pulsing it from time to time?  DTU was using a polyester bag,
which only needed cleaning every ~6 hrs or so, IIRC.  They used
compressed N2, but I am thinking that using compressed producer gas
might be a better way to go)


> The DTU have also developed a vortex gasifier that does not have a
> separate pyrolysis step but uses aerodynamic principles to draw
> pyrolysis products up the centre of the gasifier (straight sides, no
> throat) much like a cyclone does. The central upward flow brings the
> tars up into the high temperature combustion zone where they get cracked
> and converted. I do not know how far they have progressed with such a
> design but they have patented it.

I don't recall reading about that one, do they have any articles about
it on their site?


-- 
- Daniel
Fredericton, NB  Canada