Effect of elevated pressure on fluidization phenomena. Final report

Critical comparison of hydrodynamic models for gas–solid fluidized beds—Part I : bubbling gas–solid fluidized beds operated with a jet

“…by Harrison and Leung (1961), that assumes no gas leakage over the bubble interface, over-predicts the bubble diameter during the entire bubble formation process for both particle sizes. The model by Yang et al (1984), that assumes gas leakage to the emulsion phase with the minimum fluidization velocity, also over-predicts the bubble diameter during the entire bubble formation process for the smaller particles, but for the larger particles, the bubble diameter is initially over-predicted, but under-predicted in a later stage of the bubble formation process. From this it can be concluded that the gas leakage from a bubble in a bed with 500 m particles is initially larger than minimum fluidization velocity, but in a later stage smaller than the minimum fluidization velocity.…”

“…Several phenomenological models have been proposed in the literature to describe the initial bubble growth of the startup bubble at a single orifice. The models proposed by Harrison and Leung (1961), Yang (1984) and Caram and Hsu (1986) are based on the assumption that spherical bubbles are formed at the orifice, which grow due to gas injection through the orifice, while gas is exchanged with the surrounding emulsion phase through the bubble boundary. In these models the injection flow rate Q is considered to be constant during the entire bubble formation process, and the exchange velocity u ex is assumed to be uniform over the bubble interface.…”

“…approaches used in the description of bubble formation at a single orificeAuthorsExchange velocityHarrison and Leung (1961) u ex = 0Yang et al (1984) u ex = u mf…”

Experimental Observations of Fluidized Beds at Elevated Pressures

“…It is important for the design of fluidized-bed reactors to know to what extent pressure influences such important parameters as gas-solid contacting, bed-to-surface heat transfer and solids elutriation, while theoretical interest centres on the fluid-dynamic reasons for these influences. A comprehensive summary of reported experimental work in this area is given in Table I which is an extended and updated version of a compilation prepared by Yang and Keairns (1983). Table 1 shows that experimental studies have tended to concentrate on the behaviour of solid materials falling in Groups A and B of the Geldart (1973) classification, and have been concerned mainly with the effect of pressure on such hydrodynamic features as minimum fluidization velocity, U,,, minimum bubbling velocity, U,,,, bubble volume, bubble shape etc.…”