Bubble control in gas-fluidized beds with applied electric fields

Abstract

In some gas-fluidized bed applications the presence of bubbles and channeling is undesirable due to gas bypassing. The partial or total dissipation of such bubbles will contribute to improved fluidized bed performance in applications, such as combustion and catalytic reactors, where intimate gas—particle contact is important. Preliminary studies in this laboratory over the past two years demonstrate that, in laboratory size gas-fluidized beds, bubbles can be controlled in size and intensity by the application of suitably applied electric fields. The electric fields are shown to be effective at a gas—solid particulate interface and therefore “seek out” any existing bubbles within the bed. The required electric fields are of the order kV/cm in strength and are found to be influential on a variety of particulate materials including both good conductors ( e.g. copper) and semi-insulators ( e.g. coal, glass, limestone). Both a.c. and d.c. electric fields, applied with and without electrode—particle contact, are discussed on two bed geometries: rectangular and cylindrical. Data are presented for the case of a.c. electric fields with the electrodes placed externally to the bed. In a separate experiment, data collected on various kinds of particles by “gravity lifting tests” suggest that larger particles (and beds) than those fluidized here (29 – 390 μm) can also be so controlled.