A technique in which a finely divided solid is caused to behave like a fluid by suspending it in a moving gas or liquid. The solids so treated are frequently catalysts, hence the term fluid catalysis. The fluidized catalyst, e.g., alumina-silica gel, is brought into intimate contact with the suspending liquid or gas mix, usually a petroleum fraction. Local overheating of the catalyst is greatly reduced, and portions of catalyst can be easily removed for regeneration without shutting down the unit. There are also noncatalytic applications of fluidization, e.g., reduction of iron ore. Important uses of the fluidized bed process are (1) cracking of petroleum fractions, (2) gasification of coal, (3) application of organic coatings to metals (fusion bond method), (4) coal combustion, in which sulfur-bearing coal (1.33-inch diameter) is fed into a fluidized bed of limestone. Combustion occurs at 1600F, at which temperature the limestone is reduced to lime, which reacts with the sulfur in the coal to form gypsum. This technique makes possible the use of high-sulfur coal without necessity of scrubbers. The bed material is approximately 5% coal and 95% limestone products.
