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Invited lecture-20170907

Title
Title: Fluidization of Irregular Biomass Particles in Pulsating Fluidized Beds
Reporter: Prof. Bi Xiaotao Department of Chemical and Biological Engineering & Clean Energy Research Centre  The University of British Columbia, 2360 East Mall, Vancouver, V6T 1Z3, Canada
Time: Sep.7, 2017, 14:30-16:30
Address: 308 Meeting Room
Abstract
Abstract
Fluidized bed reactors have been widely applied for the thermochemical conversion of biomass, including combustion, gasification and pyrolysis, taking the advantage of their excellent heat and mass transfer characteristics. Due to its irregular shape and broad size distribution of biomass particles, biomass could not be properly fluidized without the aid of inert bed materials (such as sands used in combustors and gasifiers) or the use of conical beds or conical spouted beds. In the biomass torrefaction and pyrolysis process with the solids (biochar) as a desired product, it is important to prevent the contamination of inert bed materials so as to control the ash content of biochar. The use of inert bed materials thus should be avoided. This work has demonstrated that pulsed gas flow in fluidized bed is highly effective in achieving stable fluidization of biomass particles by overcoming channeling, partial and complete defluidization, in the absence of inert bed particles. Both hydrodynamics and heat/mass transfer were investigated in a pulsed fluidized bed with 0.15 m by 0.10 m rectangular cross-section area, and a fluidized bed with tapered bottom to improve reactor performance. Hydrodynamics of the pulsed reactor was investigated based on pressure fluctuations and visual observation. Biomass used in this work included Douglas fir, pine and switchgrass. Batch drying was selected as an indirect indicator of gas-solid mixing, heat/mass transfer. An optimum operating condition was identified to correspond to the natural frequency of the fluidized bed system based on the relationship among pulsation frequency, gas flow rate and the pressure fluctuations. The optimal performance of both heat and mass transfer was found to be achieved when the gas pulsating frequency was around the natural frequency of the system.
 

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