(622b) Improving Performance of a Spouted Bed Based on Distribution of Solid Particles
AIChE Annual Meeting
Thursday, November 20, 2014 - 8:50am to 9:10am
The present work is a part of scale-up methodology in the Multiphase and Multiscale processes Laboratory (MMPL) of Chemical and Biological Engineering Department, Missouri University of Science and Technology, MO, USA. A spouted bed is a special case of fluidization. It is an effective means of contacting gas with coarse solid particles .Gas-solid spouted beds are either cylindrical bed with cone base or the whole bed is in a cone shape where the gas enters as a jet. The gas forms a spout region that carries the solids upward in a diluted phase that forms a fountain at the top of the bed where the solids fall down and move downward in the annular region. Improving operability of the spouted bed could be obtained via uniform solids' distribution and overcome the instability of operation. Steady-state solids concentration measurements were carried out in a narrow (0.076 m ID ) cylindrical spouted bed made of Plexiglas that used 60° conical shape spouted bed. Radial concentration of particles (glass and steel beads) at various bed heights under different flow patterns were measured using sophisticated optical probes. High accuracy pressure transducers monitored the pressure drop across the bed. Various operating variables could affect the distribution of solids across the bed. Genetic optimization technique is a powerful tool to obtain the desired design parameters and set of operating conditions. This would guide the experimental work and reduce the risk and cost of the design and operation. The selected critical variables are: gas velocity, particles' density and particles' diameter. At different superficial velocities of air ranging from 0.74 to 1.0 m/s, the solids concentration profile at low velocity of 0.74 m/s is higher than that of 0.95 and 1.0 m/s. The concentration of high-density particles is greater than that of low-density particles for all positions of the bed. It has been found that the gas velocity is the effective variable of solids' distribution. Density of solid particles has positive effect on solids hold up, while size of beads has negative effect.Concentration of solid particles was higher at the wall and it decreased towards the center of the bed. The profile curves of beads have triangular pulse shapes and non-uniform at fountain region for different velocities of gas. The spouted bed becomes highly interactive nonlinear process at instable conditions. Efficiency of the bed would be dropped at instable conditions. Solids' profiles have uniform shapes at the annular region. The stability was observed when the solid particles were distributed homogenously across the bed at different velocities of gas. Linear spouted process could be obtained at stable conditions. The solids' distribution is found to be a key parameter in the scale-up methodology of the present spouted bedUniformity of solid particles enhances hydrodynamic parameters, heat and mass transfer in addition to conversion of reactants in the spouted bed.
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