Ronal and all, ( I do not know if other Listservs should be sent a copy.)
Great topic. I have a little different twist to it.
TLUD stoves do much better when fuel is dry (under 20% MC, and better
if under 10%, but that often is not common.). So, in hot humid
places, finding fuel that is sufficiently dry can be a real challenge.
So, I and others are seeking ways to dry the moist fuels, including
recently cut green wood. The key idea is to somehow utilize the
"waste" heat of the TLUD cookstoves (that is the heat where it is
AFTER passing the pot.)
I really like Ron's barrels rolling on an slight incline. Nothing
better than having gravity do much of the work. So, count me in on
any discussions of mechanisms for drying fuels. I am designing some
other ways that we can also discuss later. I think that the drums
would need to be well perforated to allow the moisture and other gases
to escape easily. Otherwise, it is just steaming itself.
About torrification. I am not very interested in heating the biomass
that much. After all, if it is going to be pyrolyzed later (and I am
thinking of inside of TLUDs large and small where the issue is fuel
dryness), the degree of heat treatment does not need to be very much.
By "degree", I mean "the extent of" and also "the upper temperature of".
Can someone please provide a "sub-classifications of torrification" summary?
What is "torrified" to one person might not be the same as to another person.
"Drying" is also subject to "degrees"
Dried to less than 10% MC might be at only 90 deg C.
Seriously dried at 110 to 120 C is probably "kiln dried"
From 150 to perhaps 220 C we start driving off other "substances"
besides water.
And somewhere (temperature wise) we obtain combustible gases and are
entering into the realms of pyrolysis.
Because of my interest in "dry" which is at far lower temperatures
than "torrified", I have no concerns about the mainly-water-vapor ever
catching on fire. And if a few chips really get hot and are blackened
(becoming torrified?), they are still overwhelmed with the much larger
quantities of biomass nearby inside the barrel or in some chute.
So, I raise the question: Why go all the way to torrification unless
significant transportation or shape modifications are in the next steps?
If the objective is biochar and if the pyrolysis process is TLUD (and
perhaps others as well), why not just make the fuels "dry"???
Paul
--
Paul S. Anderson, PhD
Known to some as: Dr TLUD Doc Professor
Phone (USA): 309-452-7072 SKYPE: paultlud Email: [email protected]
www.gtz.de/de/dokumente/giz2011-en-micro-gasification.pdf (excellent ref.)
My website specific for TLUD information: www.drtlud.com = www.DrTLUD.com
On Fri, Feb 24, 2012 at 5:27 AM, <[email protected]> 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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