Doctor of Philosophy
Chemical and Biochemical Engineering
Dr. Franco Berruti & Dr. Cedric Briens
An integrated gas-solids separator and stripper was developed, tested, and optimized for a circulating fluidized bed (CFB) downer at the Institute for Chemicals and Fuels from Alternative Resources (ICFAR) at Western University. The downer, designed for pyrolytic co-processing of heavy oil and biomass to valuable liquid fuels and chemicals, capitalizes on the plug flow behavior of gravity-assisted downward gas-solids flow, which has been proven in previous work. However, the effect of the reactor exit on unit performance has not been studied. Therefore, a comprehensive assessment of the gas-solids separator performance in a 0.07 m diameter, 1.34 m tall cold model downer was done in this thesis.
A novel, fast and cost effective pressure-response-based gas RTD measurement technique was developed that was able to screen potential separator designs. Several other conventional experimental methods, including solids RTD measurement using phosphorescent tracer and stripping efficiency measurement using CO2 tracer, were used to further assess the separator performance. The separator performance was found to be strongly dependent on the separator cone diameter. A novel, objective Separator Performance Index (SPI) was developed to assess separator performance in a comprehensive manner. Separator performance was shown to increase dramatically with the separator cone size.
A 6.3 cm diameter, 60° internal angle cone-shaped separator performed best among several tested separator designs in terms of maximum solids collection efficiency (> 99.9%), good control of mean residence time (~ 0.5 s), and least gas backmixing. The cone-shaped separator performance was maximized with fully turbulent superficial gas velocities greater than 0.85 m/s, high solids-to-gas mass loading ratios greater than 10 kg/kg, and with stripping gas injected 30 cm below the gas outlet in the range of 6 % to 15 % by volume of the downer gas flowrate, which are preferred conditions for process intensification. Separator performance was shown to decrease with particle size. However, enhanced heat and mass transfer result with smaller particles. Therefore, the use of stripping gas is essential to minimize gas backmixing in the separator when using small particles to achieve favorable pyrolysis reaction kinetics.
Huard, Martin, "Residence Time Distribution Measurements in a Downer Reactor & Gas-Solids Separator" (2015). Electronic Thesis and Dissertation Repository. 2785.