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

[Frank Shields]

Ron and stovers,

 

< snip >

 

If not we need
more terms for fractions not filled in by torrefied biomass. I prefer having
several degrees of torrefaction. That because the curve is steep for weight
loss and structural changes between 250c and 450c. Stable below 250 and
above 450c. 
     [RWL:  Agree with all. ]




[*]Do we really want more terms? I think we do but suggest to save a big battle we just lump all between wood and biochar to be terrefied and work on subclasses.  

 

Not sure how to group the lower, middle and upper values of torrefied
biomass. Lower could be up to when the biomass snaps meaning structure is
broken, Upper is when the volume is 25% reduced to biochar.
    [RWL:   A said above, I only can agree on the "lower" being torrefaction.   I think/hope the definition includes the concept of hydrophobicity. ] 



[*]However we subclass it needs to be a measureable constituent. Easily measured using inexpensive tests  is best. Can be done measuring the gas changes (perhaps when they support combustion) or some kind of biomass measurements. 


The TD sticks start at 0.69 cm wide and 15 cm long ( 10.35 cm sq)and end up
at 650c to be 0.42 wide and 13 cm long (5.46 cm sq).

   [RWL:   It would be very helpful to have other reduction numbers at (any) other T's.  At 650 0C, the two dimensional changes are to 87 and 61%  (not surprising - the literature is full of references to shrinkage being different with and against the grain).  Your area change is to about 53%.  Assuming thickness varies as width, the volume change is to 32%.  I have never measured in this way, but guess that my previous tests were not so extreme - and therefore unlikely that my char-beds reached 650 oC.   Any others have any similar data?   Needed because I presume this is wood species dependent.   I have seen shrinkage data before - and will go look for it again.   In your case,  they probably strive hard to keep the raw wood material the same - but there could be some additional start-off dimensional changes in rooms with different humidity.



[*] Easy to measure width, harder length because the sticks are so easily broken when beyond a certain point. Up to a point it is easily measured both width and length. To deal with the different types of wood used I suggest a measure at zero torrefication and another at max, ~600 deg, to get the max reduction. Then split that into three classes to base on ”Percent  of torrefaction.”   That will take care of any type of wood used in calibration (I think). 

I just mention these test methods because to answer about using torrefied biomass to ship for pellets and fuel we need data. Starting with the end user we need to know what amount of torrefraction will be acceptable. Then working back we need to know what savings that will amount to in shipping lighter and smaller loads and then in production we need to know the cost of producing and, my main concern, is can it be done resulting in a consistent product (needed by all) on such a steep slope of change. And my small part in all this is test methods. 

Great topic – by the way.

 

Regards

 

Frank

 

Frank Shields

42 Hangar Way

Watsonville,  CA  95076

(831) 724-5244 tel

(831) 724-3188 fax

frank at bioCharlab.com

 

 

 

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