Study On Fluid Dynamics Of Draft Tube Spout-fluid Bed For Silicon Tetrachloride Hydrogenation

The modified Siemens Process will produce large amounts of silicontetrachloride, and the conventional treatment method of silicon tetrachloride has theproblem of low conversion and high consumption. So it is necessary to develop a newmethod to improve the hydrogenating reduction process of silicon tetrachloride. Thespout-fluid bed with a draft tube (DTSFB), combining the favorable properties of bothspouted and fluidized beds, is widely applied in chemical engeering processes.However, few reports focus on the field of draft tube spout-fluid bed with finerparticles, such as sub-millimeter grade silicon particles, which are important rawmaterials using in the silicon tetrachloride reaction process. Therefore, the presentwork is devoted to research the gas-solid flow characteristics by experimental andsimulated approaches for developing an industry-scale draft tube spout-fluid bed.An experimental study in a draft tube spout-fluid bed was performed in a182mm diameter cylindrical column with a flat distributor. Different flow patterns weredistinguished and identified, and described the main characteristics of flow patterns.According to the bed pressure drop and its standard deviation, typical flow regimemaps were plotted by changing the spout gas and fluid gas velocity, and the transltionlaw between flow pattems was summarized. Furthermore, the effect of bedgeometrical parameter on flow regime map was also investigated.The relations of hydrokinetics parameters, such as pressure drop and its standarddeviation, the maximum spouting pressure, the minimum spout-fluidizing velocityand the solids circulation rate to the geometrical parameters and operating parameterswere presented. In addition, new correlations of maximum spouting pressure andminimum spout-fluidizing velocity were also developed. Moreover, the geometricalparameters and operating parameters which had influence on solids circulation rateswere analyzed, and the solids circulation rates were controlled by both verticalentrainment ability and lateral entrainment ability.When the annular reigon was not fluidized, the gas bypassing fraction ofspouting gas was calculated by Ergun equation. And the above calculation methodwhich was proved correct by the relationship between CD region pressure drop andgas velocity.The relations of hydrokinetics parameters to the geometrical parameters and operating parameters were discsussed. The results showed that gas bypassing wasnot only associated with parameters, but also affected by jet flow and gas mixingcharacteristics, and they restricted and influenced each other.A mathematical model about draft tube spout-fluid bed was established based onthe Eulerian multiphase model according to the kinetic theary of granular flow.Effects of related parameters on simulation results were investigated. The resultsshowed that the bed pressure drop was similar to the experimental result and flowfields showed agreement with the experimental result. The applicability and reliabilityof the model were validated, and the simulation results could be an effective way topredict the experimental results.