flash carbonization

["Michael J. Antal, Jr." <mantal@hawaii.edu>]

I returned from the Thermonet meeting in Graz, Austria earlier this week.
This meeting included a technical workshop on technologies for charcoal
production.  To the best of my knowledge, this was the first such technical
workshop on charcoal production to occur in the past 30 years.  After 3
decades of heavily funded international research aimed at the production of
ethanol, hydrogen, low and medium BTU gas, biocrude, and biodiesel from
biomass, I’m excited to see charcoal finally getting some attention!

I will try to summarize and answer the questions on flash carbonization that
appeared during my trip.

1.	“Are the yields I mention on a dry or wet weight basis?”  I only present
yields on a dry basis.  Detailed definitions of the various yields that we
measure are given in our technical publications (see the HNEI website).
2.	“How will equipment, which operates at elevated pressures, be safely and
economically employed in Third World countries?”  I respond with the
question: “How are oil wells safely and economically employed in Third World
countries?”  If the production of charcoal is profitable, it will not be
hard to operate the equipment in Third World countries or otherwise remote
locations.
3.	“Is my work relevant to the design of cookstoves?”  I do not believe
pressurized cookstoves that produce charcoal can be practical or cost
effective.  I believe that in the future charcoal will be produced
efficiently (without noxious effluents) and cheaply in centralized
facilities, and this charcoal will be sold to consumers who will burn it in
simple (i.e. not pressurized!), inexpensive, efficient cookstoves.
4.	“Can the “waste energy” of flash carbonization be used?”  Flash
carbonization produces virtually no tars.  The gas effluent contains mainly
steam, carbon dioxide, nitrogen, and traces of methane, oxygen, hydrogen,
and some heavier hydrocarbons.  This gas should not be vented directly to
the atmosphere!  Unfortunately, because of its low calorific value, it does
not burn easily.  In some ways the problem is similar to that of the exhaust
of a car engine.  We plan to explore the use of catalysts to oxidize the
combustible species in the effluent.  Since the gas leaves the reactor at
elevated pressure, it can be fed to a steam turbine (or perhaps a gas
microturbine) to generate power.  Note that the capital costs associated
with power production are high!  Alternatively, the sensible heat of the gas
may find uses in brick kilns, etc.
5.	“Why does pressure favor the formation of charcoal (carbon)?”  Tom Reed
and Peter Verhaart have given good partial answers to this question.  We
have spoken to the question in numerous archival journal publications and
theses over the past 20 years.  Dr. Morten Gronli with SINTEF in Norway and
I are preparing a major review of charcoal production and charcoal
properties that will be submitted for publication in the next few months.
This review will detail everything that is known about the subject.  I mail
reprints of my publications to anyone who sends me a request by mail (not
e-mail) on a University or Company letterhead.  Unfortunately, because of
copyright laws, these reprints are not available on the web.
6.	“What are the chief advantages of flash carbonization?”  The chief
advantages are i) high yields (approaching the theoretical limit); ii) very
short processing times (30 min or less); iii) homogeneous charcoal product
(few or no brands); iv) accepts virtually any biomass feedstock (e.g. wood
logs, sawdust, corn cobs, rice hulls, etc.) without preprocessing; v) very
low capital costs in comparison with other “high-tech” biomass conversion
processes (e.g. ethanol production from wood).  I remark that in our earlier
work we fully carbonized a moist Eucalyptus wood log as big as my thigh in
less than one hour.  Afterwards, I was easily able to break the carbon
(charcoal) log into two pieces with my bare hands.  I expect to repeat this
feat with a reaction time below 30 min in our new demonstration reactor.
Perhaps this illustration best explains my enthusiasm for flash
carbonization.

Please accept my thanks for your interest.  As Tom Reed has pointed out in
earlier messages, we are nearing the Hubbert peak.  Life will change
considerably when we pass from a buyer’s market for oil to a seller’s
market.  We need some cost-effective alternatives to fossil fuels.
Increasingly I think that charcoal soon will be recognized as the renewable
fuel of choice.

Best regards,
Michael.


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