FLUIDIZATION AND MULTHIPHASE REACTORS

Fluidized bed reactors have been widely used in industrial processes for conducting both catalytic and non-catalytic reactions, fuel combustion, particulate drying, powder coating and granulation, electrolysis etc. I started my research career on fluidization in 1985, and have conducted research over many areas of fluidization research, including hydrodynamics, flow patterns and flow regimes, heat transfer, mass transfer, reactor performance testing, modeling and simulation, scaling and scale-up, commercial reactor trouble-shooting etc. covering gas-solids, liquid-solids, gas-liquid-solids bubbling, turbulent and circulating fluidized beds. Recently we have also been working on conical spouted beds and downer reactors. My current fluidization research is focused on electrostatic charging in gas-solids fluidized beds with dielectric materials, multiscale reactor modeling and analysis, high-density circulating fluidized beds, turbulent fluidized beds, and novel fluidized bed catalytic reactors for air pollutant control.

ELECTROSTATICS

Electrostatic charges generated during particle handling, transport, and processing due to particle-particle contact and gas-particle and particle-wall frictions by frictional charging, tribo-electrification and contact charging can cause harmful electrostatic phenomena. Electrostatic adhesion due to highly charged particles can cause the formation of undesired polymer chunks in polymerization reactors, or the formation of polymer sheets on the reactor wall, leading to the generation of waste/byproduct. Electrostatic charges can also cause electrical interferences to internal sensors and thus disrupt process instrumentation. Electrostatic discharge can result in harmful electrical shocks to operating personnel and, in the worst case, can result fires or explosions in commercial power-handling equipment and manufacturing facilities. While there is an understanding of charge generation from particle-to-gas friction and particle-wall-collision, charge generation from the contact between insulating particles is still poorly understood. Local charge generation and distribution in fluidized beds, the role of bubble motion in enhancing charge generation and the resulting charge distribution around rising bubbles have not been studied until recently.

Since 1997, we have been developing experimental techniques for characterizing electrostatic charges in gas-solids fluidized beds with polymeric particles in order to reduce the charge generation and charge buildup in gas-solids fluidized bed reactors in collaboration with Nova Chemicals Inc., Mitsubishi Chemicals Inc. and Japan Polychem. So far we have, for the first time, developed a model to interpret the charge induction and transfer from the fluidized bed to an immersed ball probe based on both charge induction from passing bubbles and charge transfer due to particle-probe collisions. The model simulation has been primarily validated using data collected from cold model fluidized bed data. Since 2002, we have been studying the charge distribution around gas bubbles using image reconstruction method, and charge generation mechanisms using an in-line Faraday cup fluidized bed, with the support of a NSERC Strategic grant. So far we have made significant progress on this field, with one patent application in preparation on a novel charge monitoring technique and 8 papers published. Currently we continue our work on fundamental understanding of electrostatic charges, and also planning to apply the knowledge we have gained to help the industry to solve static charge problems in commercial gas-phase polymerization reactors and other particulate processing and handling processes.

GREEN ENGINEERING, CLEAN ENERGY, AND SUSTAINABILITY

Green engineering is the design, commercialization and use of processes and products, which are feasible and economical while minimizing impacts on ecosystems over the full life-cycle. In contrary to traditional engineering approaches in which both technical and economical aspects of a technology are the focal point, green engineering extends our research and development beyond the manufacturing of the material and product to include the ecological impacts of a process/product or a technology on the renewability and sustainability of the raw materials, the toxicity and health risks during the product use, and the recycleability and degradability at the end of the product use. In recent years, I have developed strong interest on the green engineering, a multidisciplinary multiscale approach toward sustainable development. We have been developing environmental systems analysis and life cycle analysis tools to model and evaluate the biomass collection and processing process, as well as conducted experimental studies on the fluidized bed biomass combustion to minimize the dioxin/furan formation from biomass combustion by system optimization. Collaborating with Ballard Power Systems, we have been applying our two-phase flow expertise to the water management in PEM fuel cells. So far we have made a few presentations at both national and international conferences and invited seminars on the concepts of multiscale approaches, clean and renewable energy development, fuel cells and prevention of air pollution and agricultural waste management. Meanwhile, we have been incorporating green engineering principles into the teaching, with the first green engineering course (CHBE484) introduced in 2004 at UBC. Currently, we work on PEM fuel cells, biomass processing, life cycle analysis and industrial ecology for pollution prevention and waste management. Both clean energy and green engineering will be a key area of our research and teaching in the near future.