Fluidised bed gasification and pyrolysis of woodchips.

The work presented in this thesis includes
experimental investigation using a basic fluidised bed to
gasify woodchips and cold modelling studies to improve the
fluid bed reactor dynamics incorporating bed internals,
such as draft tubes and jets.
Low grade fuel gas was produced from woodchips as
feedstock, in a 154 mm i/d fluidised bed as the main
experimental part of the project using air as the gasifying
medium. The influence of a number of process variables on
the gasification process were studied including fuel
feedrates, temperatures and bed heights, with respect to
their effects on quality and quantity of the fuel gas
produced. It was found that fuel gas of about 6 MJ/Nm3 can
be obtained with temperatures in excess of 700 °c and
with fuel feedrates in excess of 3.5 times stoichiometric.
The process also benefitted from increasing the static bed
heights of the fluidised bed, which was due to the better
separation of the combustion and gasification zones.
The cold modelling studies coducted using a 2-D
glass model employing a draft tube a nd jet system, and
using a novel photographic technique produced more
realistic data. This showed that both the systems in
question produced induced recirculation rates which can be
controlled by the process variables such as bed height, bed and jet velocities. Further studies employing these
systems for biomass conversion should prove that a better
fuel gas quality and quantity can be achieved. In addition
a variety of feedstocks can be utilised using the same
reactor configuration.