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[Brian]

Here is a picture of oak scraps from my sawmill that I ran through a slow speed grinder.  Could this particle size work in a gasifier?  A slow speed grinder has a lower hp requirement than a chipper.

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[jimmason]

Brian said:

Here is a picture of oak scraps from my sawmill that I ran through a slow speed grinder.  Could this particle size work in a gasifier?  A slow speed grinder has a lower hp requirement than a chipper.

sadly, these are too small brian.  a downdraft is very sensitive to fuels under about 1/2" in size.  the small pieces seem to easily become the fines that lead to reduction bell packing.  bell packing with fines prevents the purging of reduced char, and slowly fills us the hearth all the way to the restriction.  this will concentrate combustion and reduction in the top part of the hearth, above the restriction, ultimately leading to clinkers right at the nozzles.  this follows from the char reducing all the way to ash in the top of the hearth, and not being able to pass downward and out.

over long runs, preventing the packing of fines in the reduction bell is a real challenge.  the best method to prevent it is to eliminate the very small pieces from your fuel.  you don't have to go all the way to the big classic chunk fuels if you have a well considered reactor.  but you do need pices bigger than you are getting out of your grinder.

the chips we're using currently are made with a disk chipper.  we screen out the overs and the unders.  we use a 3/8 or 1/2 screen to eliminate the unders.  the bell packing problems go away when we do this.  if we use a 1/4 or 1/8 mesh for the small screen, the packing problems tend to start.


jim