THIS PAPER reports the outcomes from a PhD study into the pressurised flow
gasification of sugarcane processing wastes (bagasse and cane harvesting trash).
Pressurised gasification has been proposed as a means to improve the
cogeneration cycle efficiency of sugarcane factories. The primary objective of
this study was to determine the gasification reactivity of bagasse and cane trash,
to provide data for the design of commercial pressurised gasifiers. For design
purposes, gasification reactivity is defined by (a) the amount of initial
conversion by pyrolysis and (b) the reaction rate of the resulting char residual. In
this study these two parameters were measured by a combination of
conventional techniques and in a purpose designed reactor. The char and ash
residues were also characterised by optical microscope, electron microscope, gas
adsorption and x-ray analytical techniques, to gain a better understanding of the
processes occurring during gasification. The key findings were: 1. Pressurised
gasification processes are at a significant disadvantage to un-pressurised designs,
due to significant inhibition of the initial pyrolysis (fuel conversion) step at
elevated pressures. 2. Within the range of temperatures and residence times
expected in commercial biomass gasifiers, the rate of char gasification was so
low as to not contribute significantly to overall fuel conversion. 3. Char
gasification showed a significant time dependent loss of reactivity in entrained
flow experiments, which was attributed to coke formation and trapping of
carbonaceous material by the silicate species derived from the original biomass.
The findings highlight significant issues with regards to proper fuel conversion
in biomass gasifiers, particularly pressurised systems. The implications of the
findings to the selection and design of advanced cogeneration cycles are
discussed.