Fluidized bed biomass gasification

In this thesis, biomass gasification was studied in a bubbling fluidized bed reactor. Many chemical reactions are involved in gasification. Pyrolysis is the first step that takes place in gasification and combustion of solid fuels such as biomass and coal. In bubbling fluidized bed gasifiers (BFBG) of biomass materials, the products of pyrolysis are subject to further chemical reactions. This takes place in a bed that is at a high temperature of T≥800°C or in the freeboard area of the reactor. Two aspects of BFBGs, i.e. pyrolysis and hydrodynamics of a fluidized bed at high temperatures, are the main subjects of this study.; In the first step, pyrolysis of three biomass materials was studied. Thermogravimetry analysis (TGA) was employed alongside with gas chromatography (GC) technique. TGA provides the overall devolatilization of biomass and GC accounts for the individual gases released during pyrolysis. The ensemble use of these two techniques provides a complete picture of pyrolysis and the range of products in it. Different heating rates were used in the TGA experiments to investigate its effect on product distribution in pyrolysis. Experimental results show that yield of different gases depends on the heating rate that the biomass experiences during the pyrolysis in the thermobalance. Based on the obtained experimental results, kinetic models were developed for overall devolatilization and individual gas releases. The kinetic model for the individual gas release was then modified to account for the change in the yield of gases with heating rates.; In the second step, phase dynamics and solids mixing were studied in a fluidized bed at high temperatures (25--700°C). BFBGs are an example of reactors that operate at relatively high temperatures. For the first time, Radioactive Particle Tracking (RPT) was employed at high temperatures to study the hydrodynamics of a fluidized bed reactor. A single solid tracer was made of scandium oxide with density and size close to those of the bed particles. The tracer was placed in the fluidized bed at high temperature after being activated to 200--300 muCi in the SLOWPOKE nuclear reactor at the nuclear engineering department of the Ecole Polytechnique de Montreal. The gamma-rays emitted from the tracer were detected by eight NaI scintillation detectors located around the bed. The gamma-rays counts received by the arrays of detectors were used to locate the tracer in the fluidized bed. Larachi et al. (1995) have described the details of tracer position reconstruction in RPT. (Abstract shortened by UMI.)...