Experiment Study And Numerical Simulation Of Gas-Solid Flow In Dense Transport Bed

In view of developing coal-based poly-generation and the requirements of IGCC to coal gasification technology, the pulverized coal pressurized dense transport bed gasification technology, proposed by Institute of Engineering Thermophysics Chinese Academy of Sciences, can deal with coal of high sulfur, high ash, high ash melting point and also has excellent peak load regulation performance. The experiment and simulation study on gas-solid flow in a transport bed is made in the thesis.An experiment study is carried out in a square cross-section transport bed with 10m high and cross-sectional area of 0.27×0.27 m~2. The effects of superficial gas velocity, circulation rate and exit structure on axis solids concentration distributions have been obtained. The cold experiment results indicate that the axis solids concentration distributions contain a dilute region towards the top and a dense region near the bottom giving a exponential shape profile; Solids concentration minishes with increasing superficial gas velocity, and rises with increasing circulation rate in the same height position; Exit structure mainly affects the solids concentration near the exit of bed, under abrupt exit, the bed solids concentration contain a dilute region in the middle and a dense region near the bottom and top giving a C-shape profile. Based on the square cross-section transport bed cold experiment results, in accordance with the test requirements, a circular transport bed test rig with a riser of 0.187 m in diameter and 10 m in high has been built. Some preliminary experiments have been made, its circulation rate reaches 222 kg/m~2s, and the dense region (ε_s> 0.1) reaches 3.5 meters height of the bed.The factors which impact bed pressure drop in the cold test are analyzed, and the nondimensional criterion number equation of bed pressure drop has been obtained. According to test results, the correlations for calculating bed pressure distribution, solids concentration distribution and the total bed pressure drop were presented respectively, and the calculations are agreed well with experimental data. This paper simulates and examines the fluid dynamical characteristics of the gas-solid flow in a transport bed by using the computational fluid dynamics commercial software Fluent, which adoptes the Eulerian two-fluid model. By taking cluster effects into account, it uses the energy-minimization multi-scale model to improve the drag force between gas and solid. The simulation result well accord with the experiment result, and can well describle the actual status in the transport bed. This implies that the gas-solid drag model considering the cluster effects can well describle the dense gas-solid two-phase heterogeneous flow.