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

[Paul Olivier]

Ron,

There are many papers explaining the benefits of the torrefaction of
certain types of biomass.
Moisture is removed, and biomass is no longer hygroscopic.
Once torrefied, the biomass can be so easily pelleted.
Once pelleted, it can be so easily transported and gasified.

Here in Vietnam we have about 8.2 million metric tons of rice hulls each
year.
This material does not have to be torrefied.
But Vietnam also has 54 million tons of rice straw
 - a type of biomass does not have a uniform grain size
 - and a type of biomass that is hygroscopic.
If torrefied and pelleted, it should gasify quite well.


Thanks.
Paul


On Fri, Feb 24, 2012 at 5:27 AM, <rongretlarson at comcast.net> wrote:

> 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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-- 
Paul A. Olivier PhD
27C Pham Hong Thai Street
Dalat
Vietnam

Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
http://www.esrla.com/
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