[Terrapreta] biochar and sugarcane growth (reply to AD Karve)

[Sean K. Barry]

Hi Jeff, Tom, and All,

Regardless of the biomass feedstock, it is not possible to harvest all of the available chemical energy in the biomass entirely as sensible heat, fuel gas, or energy containing charcoal.  When biomass is pyrolyzed, the chemical makeup of the feedstock, its moisture content, the amount of air (oxygen) flow, reactor pressure, and temperature during pyrolysis, and the speed of the pyrolysis all come into to play to determine which fraction of the biomass energy goes to what resultant product or energy flow.

Tom is right, the sugar mills need heat energy more than they need to produce charcoal to put back onto sugarcane fields.  Jeff is right too, that one cannot do ALL of both at the same time (harvest the ALL of the heat and at the same time convert ALL of the biomass carbon to charcoal).  But, Jeff, you cannot do that anymore with switchgrass, wood, or house trash, either.

There is only a finite amount of chemical energy in any biomass.  Conversion to char through pyrolysis necessarily requires loss of carbon to off gases; like CO2, CO, and CH4.  So, not all of the carbon can be left in the charcoal.  Not all of the heat is sensible heat (heat which has a usable thermo-grade down to the surrounding environmental temperature).  Some heat is just lost.  It's temperature is too low compared to the surroundings to be useful.  When there is no more oxygen in the reactor, either coming into the pyrolysis reaction or coming out of the remaining un-pyrolyzed biomass from water (H2O) content or oxygen atoms in the carbohydrate molecules, then even the partial combustion stops.  The production of fuel gases will also stop.  But the carbon in the remaining charcoal retains some (up to a large fraction actually, like ~60%) of the original energy in the biomass chemical bonds.

It is actually possible to control a pyrolysis reaction, capture the useful heat, capture the useful fuel gases, and retain some char from the reaction.  It is possible to produce some sensible heat, some fuel gas, and some charcoal from ALL of the chemical energy that is in the biomass feedstock.  The economics of doing any of such is primarily about the application that the biomass is being used in.

So, sugar mills can harvest as much heat as they want from cane trash.  Sugarcane growers can harvest charcoal from cane trash.
And, either party could do some of both, it they had a use for it which made economic sense for them to do it that way.

Regards,

SKB


  ----- Original Message ----- 
  From: Jeff Davis<mailto:jeff0124 at velocity.net> 
  To: terrapreta at bioenergylists.org<mailto:terrapreta at bioenergylists.org> 
  Sent: Friday, May 18, 2007 8:41 PM
  Subject: Re: [Terrapreta] biochar and sugarcane growth (reply to AD Karve)


  Tom wrote:
  > Initially there may be more incentive for a sugar mill to make heat and
  > power from bagasse than to make charcoal.

  But Tom, is it not possible to make heat for the mill AND charcoal?

  My Mr. Charcoal can do this with feedstock such as switchgrass, wood and
  house trash.



  You friend and reader,

  Jeff





  -- 
  Jeff Davis

  Some where 20 miles south of Lake Erie, USA

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