[Gasification] the most important thing (quite possibly) i'velearned to date

Kevin kchisholm at ca.inter.net
Mon Oct 18 00:43:27 CDT 2010

Dear Jim

Interesting thoughts!

What are your thoughts on the optimum moisture content of biomass feed to a gasifier? On the one hand, with low fuel moisture content, there is a low endothermic load on teh reaction. On the other hand, a high moisture content could yield greater hydrogen content in the output gas.

To take things to the limit, what are your thoughts on feeding a gasifier with torrified wood?


  ----- Original Message ----- 
  From: jim mason 
  To: gasification at bioenergylists.org 
  Sent: Monday, October 18, 2010 2:08 AM
  Subject: [Gasification] the most important thing (quite possibly) i'velearned to date

  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 that
  the most impactful thing one can do/add/fix to the basic imbert design is to use 
  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 the
  anecdotal experiences keep piling up. the biggest flexibility gains i'm finding
  both in poor fuel shape/size and moisture tolerance, as well as gas turndown ratio, 
  are from the ic exhaust heat exchanger. on our rig, this is called the pyrocoil. other
  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 about
  3x or 4x the heat available as the outgoing syngas. the incoming fuel similarly
  has much more heating capacity than the incoming air (the multiple i forget at
  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 preheating
  the incoming air. thus you can use the ic exhaust to do much more than dry the
  fuel. you can it to drive the fuel through pyrolysis, and really, get it up to
  about 4-500c before it falls into the hearth proper. this is a big difference
  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 to
  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 pyrolysis
  right on top of the nozzles. this high temp pyrolysis optimizes the creation of
  teritary tars, or refractory tars, which are difficult to crack again (given
  lots of double carbon bonds). if you externally drive pyrolysis at lower temp
  over longer time, you get more primary and secondary tars, which are easier to
  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 free
  card. but to me it seems the most impactful new thing one can do on these rigs.
  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 above is
  my current vote for the biggest bang for the effort. hopefully we can get some
  proper numbers on this soon (and prove or disprove the above conjecture).


  Jim Mason
  Website: http://www.whatiamupto.com
  Current Projects: 
     - Gasifier Experimenters Kit (the GEK): http://www.gekgasifier.com
     - Escape from Berkeley alt fuels vehicle race: www.escapefromberkeley.com
     - ALL Power Labs on Twitter: http://twitter.com/allpowerlabs
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