HYDRODYNAMIC ANALYSIS OF GAS-SOLID FLUIDIZED BEDS

The object of this investigation is to develop an experimentally verified hydrodynamic model to predict solids circulation around a jet in a fluidized bed gasifier. Hydrodynamic models of fluidization use the principles of conservation of mass, momentum and energy. To account for unequal velocities of solid and fluid phases, separate phase momentum balances are developed. Other fluid bed models used in the scale-up of gasifiers do not employ the principles of conservation of momentum. Therefore, these models cannot predict fluid and particle motion. In such models solids mixing is described by means of empirical transfer coefficients.;Pressure and density fluctuations are a common characteristics of gas-solid fluidized beds. A one dimensional study of pressure fluctuations was performed to study the effect of changing gas flow and static bed height on frequency and amplitude of oscillations. Oscillatory behavior of two different hydrodynamic models was compared to each other and to data.;A two dimensional unsteady computer code was used and modified to give gas and solid velocities, void fractions and pressure in a fluid bed with a jet. The growth, propagation and collapse of bubbles was calculated. Time averaged void fractions were calculated that showed good agreement with void fractions measured with a gamma ray densitometer. Calculated gas and solid velocities in the jet appeared to be reasonable.