ABSTRACT
If a gas passes upward through a bed of particles, the bed is fi xed at low gas velocities, but when the velocity is increased further, the particles separate from each other and are supported by the gas, then the bed starts fl uidizing. In the fl uidized bed, the particles contact with the gas at high effi ciency, and temperature is kept uniform because of good mixing of the particles. The features have been utilized for industrial applications 1 ; the fi rst use of the fl uidized bed as a large-scale reactor was Winkler’s coal gasifi er in 1926. Since the 1940s the fl uidized bed had played an important role for fl uid catalytic cracking using a combination of a reactor and a catalyst regenerator. Recently a circulating fl uidized bed, as shown in Figure 20.1, has been widely used as a boiler for solid fuel and waste.
