flash carbonization of biomass

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

Dear friends: probably you recall that our fundamental research concerning
the effects of pressure on biomass pyrolysis led us to the discovery that
near-theoretical yields of carbon (charcoal) can be obtained from all sorts
of biomass with short reaction times (ca. 60 min) when pyrolysis is
conducted at elevated pressure (ca. 100 psig).  Although the energy input to
our pilot plant was small, last March an engineer expressed concerns about
it to us.  Consequently, we began to explore new ways of operating our
equipment in order to reduce the energy input.  Not long thereafter we
learned how to deliver very small amounts of air to the reactor and burn the
combustible pyrolytic vapors while retaining a high yield of charcoal.  Our
data indicates that charcoal can be produced from all sorts of biomass at
elevated pressures in near-theoretical yields with cooking times of less
than 30 min and negligible energy input.  For some feedstocks a processing
time of 15 to 20 min appears to be practical.  The yield of tar is
negligible.  In light of the incredibly short reaction times that we now
employ, we refer to our new process as “flash carbonization”.  A summary of
some of our results is now posted on the HNEI web site (see below).  I
emphasize that these early results have not been optimized, and that we
expect to realize some further improvements in the fixed-carbon yield and
reductions in the reaction time in the near future.  In summary, it is now
possible to convert a one ton (or a ten ton) batch of wood (or sawdust or
rice hulls or corn cobs) into high-yield charcoal with a processing time of
less than 30 min and negligible energy input.

As a result of this progress, the University of Hawaii has given me a grant
to build a demonstration scale reactor that will be used to convert the
University’s green wastes into marketable charcoal.  Here in Hawaii the
markets for charcoal include potting media for orchids and ornamental
plants, barbeque charcoal for our restaurants, and charcoal as a clean
renewable substitute for imported coal.  The capital cost of the
demonstration reactor will be less than $50,000.  The capital cost of a
commercial reactor that produces ca. 50 tons per day of charcoal should not
exceed $100,000.

I will give our first technical presentation on this work at the ThermoNet
meeting in Graz on 10 January.  Consequently, I will be away from my office
until mid-January.  I expect that we will publish these findings in about
six months.  When this occurs, I will post a summary on the HNEI web site.

Thanks for your interest.  I give you my best wishes for the holidays.

Michael J. Antal, Jr.
Coral Industries Distinguished Professor of Renewable Energy Resources
Hawaii Natural Energy Institute
University of Hawaii at Manoa
Honolulu, HI 96822

Phone: 808/956-7267
Fax: 808/956-2336
http://www.soest.hawaii.edu./HNEI/
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