HYDRODYNAMICS OF FLUIDIZATION EFFECT OF PRESSURE

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Abstract
One of the largest concerns when using fluidized beds to commercialize many chemical processes, such as gasification of coal, is scale-up. We believe this is due to the absence of an experimentally verified hydrodynamic theory that can describe the complicated transient gas and solid motion in a fluid bed. During the past few years several organizations began to develop hydrodynamic computer models that promise to be predictive in many respects. Our present computer model calculates the pressure, the void fraction and the velocities of a single size solid and of the gas. Computed time averaged porosity distributions in two dimensional beds with a Jet at atmospheric pressure agreed with our measurements without the use of any fitted parameters. Photographically determined bubble sizes compared well with the predicted sizes. Calculated gas velocity distributions also agreed with the experimental values measured at westinghouse in a semi-circular bed with a Jet. In this paper the results of our measurements of time averaged porosities in a steel bed at elevated pressures are compared to our model predictions. We also show that the computed Jet penetrations are close to those reported by IGT in their high pressure fluidized bed. Our calculations also show that the amplitudes of pressure oscillations are much smaller at elevated pressures than at atmospheric pressure. In this sense, the fluidization is smoother at high pressures. An analytical examination of the equations of change in terms of a linearized hyperbolic diffusion equation supports this observation.