[Stoves] Is there a role for combining torrefaction and char-making stoves?

[Frank Shields]

Dear Stovers and Ron,

 

Interesting idea. Torrefied wood is on a steep slope starting at 250 and ending at 450 from the info I have. Going from 100 unit weight to 20 so you are talking about a system that will be hard to control IMO and the result will be a wide variation of quality. With just enough heat the wood is easily broken with a snap so could save on size reduction for the stove and lighter in weight. If heating to, say 350, why not just go to completion(?) rather than start over. 

 

Look forward to hearing what others say.

 

Regards

Frank

 

 

Frank Shields

42 Hangar Way

Watsonville,  CA  95076

(831) 724-5244 tel

(831) 724-3188 fax

frank at bioCharlab.com

 

 

 

 

 

 

 

 

From: stoves-bounces at lists.bioenergylists.org [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of rongretlarson at comcast.net
Sent: Thursday, February 23, 2012 2:27 PM
To: Discussion of biomass; Biochar-production; biochar-policy
Subject: [Stoves] Is there a role for combining torrefaction and char-making stoves?

 

Lists:

   Q1a.   This is to get anyone's/everyone's reaction to a concept I have not yet seen in stove literature.  Briefly, if torrefied biomass is supplied to charcoal-making stoves, might it be worth the extra expense over biomass which has seen no prior thermal processing.

   Q1b.   Is it a new idea?   I don't see anything patentable here - as torrefaction is an old concept, and char-making in stoves should not change at all.

   Q1c.  Has anyone actually tried the idea already?

   Q2.  On the negative side will be:
      a.   Added expense.    The key question is not if - but how much added expense might be tolerable?
      b.   Some energy is lost - maybe even extra energy will be needed  - certainly some for start-up. 
      c.   There may have to be pelletizing costs as well  (but maybe not.)  A key question is whether pelletizing can do the same thing.
      d.   We have heard that some moisture is valuable.  Maybe torrefied fuel could become too dry?
      e.  I think BFW and others will (in some cases appropriately) claim foul for ruining the local soils through export of a valuable source compost product - which may not end up as a Biochar (which alternative should offset any soil degradation disadvantage)
   
 Q.   Can anyone think of other negatives - just when comparing to "raw" biomass or pellets headed for char-making stoves?   

   Q3.. On the positive side are 
     a.   All the positives of making a char that can be later termed Biochar if placed in soil (atmospheric and soil improvement, conservation of water, retention of nutrients, etc).   Making, rather than expending, money while cooking would still be possible if the char is worth more than the lost energy..
     a.   The fuel may be very dry - maybe even bone dry.  It could be a positive in terms of starting and fewer released noxious gases.  
     b.    The energy content is appreciably enhanced - possibly from below 15 MJ/kg  (low because of water content) to above 25 MJ/kg.
     c.   There are reduced costs in transporting the fuel (per unit energy, same transport costs per ton).
     d.   Its character should be more consistent from batch to batch and therefore helpful to the cook in timing events.
     e.   Torrefaction might produce fewer harmful emissions when actually used.  Processing and pelletizing ives an opportunity for adding favorable odors.
     f.   Torrefaction might significantly increase the total supply of biomass available for Biochar.
    g.   This sort of pre-processing can significantly add to local job opportunities - and reduce illegal char-making with its (often illegal) waste of energy.
    h.   This pre-processing will take less time in the kiln than conversion to char.  Hence less needed hardware. 
    i.     Lower temperatures should mean longer life for the metal hardware than if we were producing char.
    j.    The material might (also might not) have better handling characteristics than char.  Still friable, but not overly so.
    k.   Provides needed jobs in ag areas.  Maybe can be carried out at most any time of the year, as long as there is a place to store the raw wastes.
   l.    Torrefaction might allow productive use of waste material that otherwise has no apparent use.  

  4.  I have some ideas on how to control the torrefaction without power - available to anyone wishing to carry this further.  I see no patent issues here.  The basic idea I have in mind is something like 8 or 10 (200 liter, low cost, no-longer useable steel) barrels rolling down a slight incline in a small linear kiln.   I broached this rolling drum idea a few months ago as a way to make char.  Torrefying seems harder than making char, as we are likely working in an exothermic temperature regime where there could be runaway to higher-than-desired temperatures.   I'd be glad to talk further with anyone interested on how to carry this out in remote areas.  But mostly I am asking whether there is a fatal flaw in going further down this route - just for char-making stoves where we can be sure we are productively using the (later) valuable energy used for cooking.

5.  The reason for raising this is the large interest we read about in torrefaction - to replace coal in large electric power plants.  Why don't we see it in biochar and stove literature?

Thoughts?

Ron

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