Fluidization characteristics of gas fluidized beds at elevated temperatures

Abstract

The hydrodynamic behavior of a gas-fluidized bed has been investigated at ambient and elevated temperatures. Beds of two mean sizes of sands, 641 and 1312 μm, at temperatures of 298 K and also in the range 913–1173 K have been examined over a wide range of air velocities up to 4 m/s. The bed-pressure drop and its fluctuation over a time period of 18 s were measured as a function of air velocity and bed temperature. Variable temperatures were obtained by burning either coal or propane-air mixtures of different compositions. These data were analyzed to obtain values for the minimum fluidization velocity as a function of temperature, bed voidage as a function of bed height, bed temperature and air velocity, and the time-averaged amplitudes of the fluctuations in the pressure drop, bubble or void-renewal frequency and solids concentration as functions of bed temperature and air velocity. It is shown that the hydrodynamic behavior is in accordance with the powder-classification scheme of Saxena and Ganzha. Furthermore, this work has highlight ed the importance of particle size and bed temperature in the operation of fluidized-bed reactors in general and coal combustors in particular. This work has also pointed to the need for further investigations that will improve our understanding of such two-phase reactors.