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Abstract: The penetration lengths of a jet issuing from upward and downward injection nozzles were measured in a dense fluidized bed of Geldart A to Geldart B particles, operated at superficial velocity well beyond the minimum bubbling velocity. Nozzle orientation, injection velocity and injected gas density were found to be the parameters having the most influence on the jet penetration lengths. Three distinct jet penetration lengths were determined for the upward nozzle: L min , L max and L b , in accordance with Knowlton and Hirsan''s (1980) definition [1], while for the downward nozzle, only L min and L max were observed. The jet penetration lengths were correlated with respect to dimensionless groups in a systematic approach in an effort to identify the most important terms. For each nozzle orientation, the analysis yielded unique correlation format which could be applied to each characteristic jet length by changing the correlation parameters. Fundamental distinctions between the upward and downward nozzles were uncovered. The mechanism responsible for the jet momentum dissipation was found to be gravitational forces acting on the jet volume for the upward nozzle and drag forces exerted on the entrained particles for the downward nozzle. Five new correlations were derived for the prediction of the characteristic jet lengths for upward and downward nozzles. The correlations retained for the upward nozzle were also found to be in good agreement with data from a high pressure fluidized bed. [Copyright &y& Elsevier]

Abstract: Biomass is important in energy conversion processes due to their favourable status with respect to greenhouse gas emissions. However, biomass particles have unusual properties which make them difficult to fluidize and handle. This paper reviews recent research on the hydrodynamics and mixing of biomass particles in fluidized beds. Whereas there has been considerable effort to develop new biomass gasification, combustion, pyrolysis and bio-conversion processes, relatively few authors have characterized the relevant flow characteristics of biomass particles in fluidized beds or investigated measures that could assist in resolving flow issues. The limited work that has been reported on biomass fluidization primarily treats means of achieving fluidization, mixing and segregation. Most of the work has been in low-velocity fluidized beds, although circulating fluidized beds are also important. Further research is needed to provide general understanding of interactions among heterogeneous particles and guidance on conditions that can lead to viable and sustainable processes. [Copyright &y& Elsevier]

Abstract: Experiments were conducted in the geometrically- and dynamically-scaled UBC half-column to test different configurations that might significantly reduce stripper shed fouling and increase run length, while providing little or no decrease in stripping efficiency in two commercial fluid cokers. The results showed that a series of horizontal gas jets, without baffles, constrained to use no more steam than in the existing commercial operations, were unable to fully match the stripping efficiency of the strippers with shed internals. Wall baffles were also of little assistance. However, relatively large crossed-sheds, called “mega-sheds,” combined with a limited number of staggered gas jets, provide a promising geometry, with more tolerance to fouling and stripping efficiency equivalent to that of the existing commercial units. [Copyright &y& Elsevier]

A novel high temperature optical fiber probe has been developed to study the effects of bed temperature on the local two-phase flow structure in a pilot scale fluidized bed of the FCC particles with bed temperatures ranging from 25°C to 420°C, covering both the bubbling and turbulent fluidization regimes. The results show that fluidization is enhanced and fluctuations of the local two-phase flow structure become more intense with increasing bed temperature. At constant superficial gas velocities, the averaged local particle concentration, the dense phase fraction and particle concentration in the dense phase decrease with increasing bed temperature, whereas both the frequency of the dilute/dense phase cycle and the ratio of the dilute phase duration to the dense phase duration increase. In addition, the effects of temperature on the dilute phase depend on superficial gas velocity. The conventional two-phase models fail to predict these changes of the local flow structure with temperature, which may be explained by the fact that the role of interparticle forces is neglected at different bed temperatures. Indeed, fluidization behaviors of the FCC particles tested increasingly shift from typical Geldart A towards B with increasing temperature due to a decrease of the interparticle attractive forces and a simultaneous increase of interparticle repulsive forces. [Copyright &y& Elsevier]

This paper was made possible through the development of a novel high temperature optical fiber probe to study the hydrodynamics of a high temperature fluidized bed reactor. The experimental results show that the hydrodynamic parameters considerably change with bed temperature when fluidizing FCC particles. For a given superficial gas velocity, the average local particle concentration, the dense phase fraction and the particle concentration in the dense phase decrease with increasing bed temperature. As a result of an increase in temperature, the fluidized behavior of the FCC particles progressively shifts from typical Geldart A towards B. Consequently, a modified two-phase model, based on the simple two-phase model, integrating the effects of temperature and superficial gas velocity on the hydrodynamics, is proposed. Simulation of a reactive catalytic system using a conventional simple two-phase model and the modified model is achieved. The predicted reactor performances strongly differ for each model. In the present case, the simple two-phase model underestimates the reactor performance by inadequately accounting for the solid fractions in the bubble and dense phases and their dependence on temperature and superficial gas velocity. This suggests that the hydrodynamic models should take into account the effects of temperature and superficial gas velocity when simulating the performance of a high temperature fluidized bed reactor. [Copyright &y& Elsevier]