Fluid Beds: At Last, Challenging Two Entrenched Practices
Arthur M. Squires 1,
Mooson Kwauk 2, and
Amos A. Avidan 3
1 University Distinguished Professor, Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg 24061.
2 Member of the Chinese Academy of Sciences, is professor and director of the Academy's Institute of Chemical Metallurgy, Beijing, People's Republic of China.
3 Senior research engineer, Mobil Research and Development Corporation, Paulsboro, New Jersey 08066.
Originating in the 1920' s and 1930's, two distinct fluidization arts have emerged, one for treating coarse solids and the other for fine powders. Fluidization research has tended to focus on bubbling beds of coarse solids, but designers of such beds for burning coal have learned to appreciate the importance of combustion of fine char particles in the freeboard. Designers of successful processes for powders have focused on bubble suppression. Since about 1980, combustion fluid beds of both types are challenging the conventional pulverized-coal boiler; they provide better means for controlling emissions from the combustion of high-sulfur fuels. Progress in the "bubbleless" fluidization of fine powders is increasing the fluid bed's competitiveness with the fixed-bed catalytic reactor. Efforts to advance the fluid bed for catalysis, besides increasing gas velocities beyond levels that most researchers have used in the past, must include systematic study of the level of fine particles smaller than 40 micrometers.
