Simulation Of Multiphase Flow In WPSD Fluidized Bed And Study Of Heat Transfer In Synthesis Of Organosilicon Monomer

A fluidized bed, which is applied in the synthesis of organosilicon monomer, is studied in theory, experiment and numerical simulation to investigate the fluidization characteristics and heat transfer of Wide Particle Size Distribution (abbr: WPSD) of fine silicon powders.This paper adopts CFD, Eulerian model of particle dynamics theory and PC-SIMPLE numerical method to set a model of gas-solid multiphase flow under considering the interaction between gas and particles, one particle component and another component, and particle and particle in one component, to ascertain the initial condition and boundary condition and evaluate the influence of the configuration of fluidized bed on efficiency. The results show that, for the fluidized bed with WPSD of fine particles, there are small bubbles size, little particle raising phenomenon and steady flow fields in the static bed layer located at the bottom of the enlargement section of the fluidized bed.Compared the fluidization characteristics of the free bed, the vertical immersion bed, the immersion bed with triangular level arrangement (abbr: IBTLA) and the immersion bed with square level arrangement (abbr: IBSLA) respectively, the results of the numerical simulation indicate that the minimum fluidization velocity substantially decreased for WPSD, and the smaller particles are easier to fluidize than the larger ones; that the bubbles are broken in bed because of the figure-pipes and raise slower, and the phenomenon of the bubble coalescence is weakened as well as the degree of radial back mixing. And the results also show that the solid fraction closed to the wall decrease with the increase of the space between the vertical pipes, the height of the dense phase section of the bed has the same trend. In addition, some pipes are surrounded by the cavitations in the level of immersion tube fluidized bed. While, the cavitations increase with the decrease of the distance between pipes. The height of the bed layer of IBTLA is lower than the one of IBSLA and the cavitations in IBTLA is also less than in IBSLA.The pressure pulsation method is applied to study the fluidization characteristic of WPSD of silicon powders, and to draw out the relationship function between the pressure pulsation Standard Deviation and the gas velocity. The results show that the value of the minimum fluidization velocity is in agreement with the theoretical value.In order to overcome the following disadvantages, such as, uneven heat absorption and uneven air distribution of inlet in the fluidized bed reactors which applied in synthesis of organosilicon monomer. A new thought, developing a new type of the fluidized bed with once-through flow and uniform heat absorption, is proposed based on the simulation and experiment results. In this reactor, the following technologies are applied: heat absorption through symmetrical once-through figure pipe; the air diversion distributor with double cones; silicon powders directly back to bed. The industrial application of the new type of reactor show that there exist the same temperature of dense phase section in the new type of fluidized bed, and this reactor realize the uniform heat absorption.The convective heat transfer coefficient of the synthesis of organosilicon monomer is calculated and verified. In addition, the model of the fluidized bed with inner heat source, which is suitable for strong heat transfer process, is set up and the calculation function about the thickness of gas film is also proposed. And the calculated value of gas film thickness is in good agreement with the experimental values in the relative literature, which shows that the function and model set up in this paper could be applied in the calculation of gas film thickness in dense phase section. It could be speculated from the function that Gas film thicknessδmainly is relevant with the ratio of the unit volume reaction heat q. to the thermal conductivityk . The conclusion should be beneficial to the research of heat transfer process in the strongly exothermic reaction and be significant for designing related industrial reactors.