[Stoves] response to Dr. A.D. Karve

[Michael J. Antal, Jr.]

Dear friends: our publications concerning charcoal report fixed-carbon
yields ranging from 25% to 41%.  In addition to the process conditions, the
chemical composition of the feedstock strongly affects the fixed-carbon
yield, as reflected in the wide range of fixed-carbon yields that we have
measured in our work.

Chemical and mechanical engineers with experience in fuel science know that
charcoal always contains volatile matter.  It is a rare charcoal that
contains less than 10% volatile matter.  In light of this fact, Dr. Karve's
claim (below) that his charcoal "is free from volatiles" is simply wishful
thinking.  I urge Dr. Karve to actually complete a proximate analysis of his
charcoal, and to measure the ash content and moisture content of his
feedstock.  With this additional data, he can calculate for himself his
fixed-carbon yield without guesswork.

Even if Dr. Karve calculates his fixed-carbon yield, it will not be possible
for us to easily compare our results.  Why?  Because as I mentioned above,
the fixed-carbon yield depends strongly upon the composition of the
feedstock.  Thus the fixed carbon yield of a corncob charcoal cannnot be
compared with the fixed-carbon yield of charcoal from banagrass.  In light
of these facts, I urge Dr. Karve to obtain an elemental analysis of his
feedstock, and use a thermochemical equilibrium program (e.g. StanJan) to
calculate the yield of carbon that can be obtained from his feedstock when
thermochemical equilibrium is achieved in a pyrolytic environment.  This
"limiting theoretical yield" of fixed-carbon provides an absolute basis for
judging the efficiency of a carbonization process.  In our work we often
realize 90% to 100% of the limiting theroretical yield of fixed carbon from
biomass feedstocks.  But in a few cases our yields are lower.  For example,
using sunflower shells we are unable to achieve 90% of the theoretical
yield.  On the other, with corncobs we easily achieve 100% of the
theoretical yield over a wide range of conditions.  All our results are
available in a series of peer-reviewed, archival journal publications.

In closing I want to express my sincere congratulations to Dr. Karve for his
success in capturing the attention of the steel industry.  The use of coking
coals to reduce metal ores is among the worst contributors to CO2 emissions
and climate change.  A shift by the steel industry to charcoal will benefit
all of us.

Best wishes, Michael.

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org]On Behalf Of adkarve
Sent: Saturday, June 09, 2007 7:23 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] response to Dr. A.D. Karve


Dear Stovers,
I wish to express my regrets about the wrong concept that I had about Prof.
Antal's process.  I should have contacted him to get more information. I was
only reporting what a chemical technologist colleague told me, which is
however valid for the processes he was refering to, namely natural coal
formation and conversion of wet biomass into charcoal by heating it in a
pressure
vessel.
However, I wish to point out that Prof. Antal has conceded that the charcoal
produced by him has typically less than 25% volatile matter.  Assuming that
his process yields charcoal containing, on an average, 20% volatile matter,
it explains the high charcoal yield. If a fifth of the weight is deducted
from his 40% char yield, one gets a figure of 32% pure carbon. The
oven-and -retort process yields about 33% char. It is free from volatiles
and comparable to high quality coke. Industries using coke are willing to
use our charcoal as a substitute for coke.
Yours
A.D.Karve