Modeling of a fluidized bed combustor with immersed tubes. Quarterly report, March--May 1976

Abstract

A mechanistic model for non-catalytic solid-gas reactions in fluidized beds has been developed in which the gas flow and solids circulation are described by accounting for (1) the presence of the cloud-wake phase, (2) decrease in solids by elutriation and chemical reaction, and (3) the solids feed and overflow rates. This model considers a general population balance in which both solids size and density vary as a result of reaction. The solids in the emulsion phase may have a net downward. stationary, or upward movement depending on the rate of solids feed. A computer simulation is presented for a representative system which considers a shrinking-core solid-gas reaction and an elutriation constant inversely proportional to particle size and density. Numerical calculations have been performed to evaluate the effect of continuous solids feed rate on circulation patterns and conversions of gas and solids in the bed. The results show that the extent of gas bypassing through bubbles is reduced when the solids feed rate is increased. This is particularly significant to a fast reacting system such as high-pressure coal combustion where the solids feed rate is high. A review of the literature on heat transfer to horizontal tubes in fluidized beds is underway.