[Gasification] the most important thing (quite possibly) i've learned to date
jim at allpowerlabs.org
Mon Oct 18 00:08:20 CDT 2010
there are many variables to move around in a gasifier, and all of them are
important. but once the basics are in order, i'm coming to the conclusion
the most impactful thing one can do/add/fix to the basic imbert design is to
the ic engine exhaust to heat the incoming fuel.
no, i don't have any numbers on this yet (we hope to get these soon), but
anecdotal experiences keep piling up. the biggest flexibility gains i'm
both in poor fuel shape/size and moisture tolerance, as well as gas turndown
are from the ic exhaust heat exchanger. on our rig, this is called the
rigs call this something else.
this is not terribly surprising. the ic exhaust is the biggest waste heat
source we have around a gasifier. in principle, the ic exhaust has about
3x or 4x the heat available as the outgoing syngas. the incoming fuel
has much more heating capacity than the incoming air (the multiple i forget
the moment, but i do know the incoming air can only take up about 1/2 of the
heat available in the outgoing syngas).
also, the ic exhaust is much hotter than the outgoing syngas after
the incoming air. thus you can use the ic exhaust to do much more than dry
fuel. you can it to drive the fuel through pyrolysis, and really, get it up
about 4-500c before it falls into the hearth proper. this is a big
from the typical situation of still moist fuel falling into the hearth.
not only can you use the ic exhaust to add a very significant amount of heat
the system, you can also use it to change the character of pyrolysis in the
reactor. a typical downdraft has very high temp short residence time
right on top of the nozzles. this high temp pyrolysis optimizes the creation
teritary tars, or refractory tars, which are difficult to crack again (given
lots of double carbon bonds). if you externally drive pyrolysis at lower
over longer time, you get more primary and secondary tars, which are easier
crack downstream (fewer double carbon bonds). this seems to allow hearth
conditions to be less perfect and still get good gas out.
using ic exhaust to heat incoming fuel is not a complete get out of jail
card. but to me it seems the most impactful new thing one can do on these
it seems to have more of an impact than any other single thing we've done to
date on the gek.
yes, all of it is important, and all of it should be tended to, but the
my current vote for the biggest bang for the effort. hopefully we can get
proper numbers on this soon (and prove or disprove the above conjecture).
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