(169f) Evolution of the Morphology of Chars From Pyrolysis of Sugarcane Bagasse

Evolution
of the Morphology of Chars from Pyrolysis of Bagasse

Pradeep
K. Agrawal¹, Carsten Sievers¹, John D. Muzzy¹,
Pranjal Kalita¹, Gautami M. Newalkar¹, Steven Lien²,
Scott A. Sinquefield², John P. Henley³, Derrick W. Flick³,
and Brien A. Stears³

¹School
of Chemical & Biomolecular Engineering,²Institute of Paper
Science & Technology, Georgia Institute of Technology, Atlanta, Georgia
30332; ³Dow Chemical Company, Midland, Michigan

A major advantage of biomass gasification in
thermochemical platform for biomass utilization is that any type of biomass can
be converted to syngas, making it attractive for unmerchantable wood, harvest
residue, and waste from forest and paper industry. The mechanism of biomass
gasification is complicated and can be considered as two processes in series ? biomass
pyrolysis and char gasification. The morphology of char from biomass pyrolysis
is affected by a number of variables, e.g., ash content and composition, pressure,
temperature, and heating rates. This, in turn, would affect the char
gasification kinetics. A combination of two complementary techniques is being
utilized in this study: (i) pressurized entrained flow reactor (PEFR) provides
high heating rates (≥ 10^3oC/sec) and short
residence times (1-20 sec), and (ii) thermo-gravimetric analyzer (TGA) provides
lower heating rates (0.1-1 ^oC/sec), but larger residence times
(5-100 min).

We present here the results on char morphology
obtained during the pyrolysis of sugarcane bagasse at several pressures and
temperatures. The ash content of bagasse stalk differs greatly from the bagasse
leaves, which affects the char morphology and subsequent gasification rates.
Pyrolysis studies were carried out at pressures between 1-20 bars and at
temperatures between 600-1000 ^oC. High ash content, particularly
silica, appears to impact on the char morphology. Nitrogen physisorption
studies show nearly two orders of magnitude increase in the char surface area,
indicating a significant role of pyrolysis temperature and pressure on the
surface area at high heating rates, such as those inherent in an entrained flow
reactor. CO₂ adsorption studies at 0 ^oC, on the other
hand, present a very different trend for the same chars.

Lower heating rates (0.1-1 ^oC/sec) as
typical of TGA pyrolysis yield different char morphology which is not
representative of what one would expect in a commercial pyrolysis/gasification
set-up. Approaches to obtain industrially meaningful kinetic rate data are
discussed.