[Gasification] drying fuel

[Adam Carr, Renergy]

Toby,

Thank you for this, and I can see exactly where you are coming from. I guess I am just going to have to go over to Germany and check the bloody thing out. I have a suspicion that (as suggested by Doug Williams) that the secret to all this may turn out to be drying the "chunks" outside under cover before "finishing" them on a walking floor or similar, however there are clearly material handling issues here - not to mention working out how much storage/drying space this under cover ambient drying phase will involve, and how to optimise the process/circulation of air. I suspect the size of heap/depth of the bed will prove important, and that the difference between chunks and chips in terms of the interstices allowing natural convection will also be significant.

Regards

Adam Carr.
  ----- Original Message ----- 
  From: Toby Seiler 
  To: acarr at fhsinternet.com 
  Cc: gasification at listserv.repp.org 
  Sent: Friday, December 15, 2006 12:47 PM
  Subject: drying fuel


  Adam; 

  Drying chips on a walking floor has the disadvantage that the incoming hot air always drys the same chips near the air opening, but that vapor can re-condense on the downstream (in the air flow) chips and bring them to a higher MC.  The moisture content will vary significantly from the bottom to the top

  If the heated air were recirculated several times in stages, the chips entering this final stage may be above the dew point (assuming enough energy input) .  If the air exiting is below the dew point, drying is not complete and some moisture is condensing back onto the chips causing that portion to go to as high as 100% MC, higher than the 50% in. Without enough thermal energy, you are redistributing moisture, I believe.

  If you have indirect heat transfer (so the moisture cannot condense back into the wood), you may recover enough heat.  At 1000 btu/ lb of water to evaporate, 970 is returned in condensation, as long as it's not the wood chip that receives the condensing water.


  Regards,   Toby Seiler
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