Study On The Flow Characteristics Of The Gas-partical Ejector For Ende Pulverized Coal Gasifier

The issues of high carbon content in fly ash as well as low carbon conversion ratio for Ende pulverized coal gasifiers with the amount of gas output being 20000Nm3/h are the foundation of this study. The solution of adding a gas-particle ejector inside the high temperature cyclone separator of Ende pulverized coal gasifier was first proposed. What’s more, theoretical design was carried out. Meanwhile, numerical simulation on the ejector was conducted with the aid of Fluent software package. The influence of varied operating conditions and structural parameters on the flow field and its characteristics was investigated, in order to provide theoretical guidance when it comes to the practical design and operation of the gas-particle ejector.The design method of the gas-particle ejector was sorted out based on Sokolov one-dimensional ejector design theory, combining gas dynamics function and the basic laws of thermodynamics. A program was compiled to complete the structural parameters of the ejector according to this method and the geometric model for Ende pulverized coal gasifier was built. A modeling method was selected after some study, and then results from numerical simulation and experiment are compared, turning to be that there is good agreement between each other, indicating the validity of selecting the right modeling method.One-dimensional theory was not sufficient to know well the flow condition due to the complexity of the internal flow inside the ejector. Due to the flexibility and repeatability of numerical methods, the single-phase numerical simulation was first carried out. The gas ejection coefficient was calculated by changing parameters such as vapor pressure, ejecting flue gas pressure, ejector outlet pressure and the length of the nozzles exit position. In addition, the influence of different parameters on the flow characteristics of the ejector was acquired by analyzing these results.Gas-particle numerical simulation was conducted based on that of the single-phase, and the conclusions were listed as follows:(1) The particle ejecting ratio is zero with vapor pressurepp being zero. Gas ejector coefficient is negative whenpp equals to 0.5MPa, and there exists recirculation around the ejector inlet, the particle ejecting ratio being 0.423. As vapor pressure varied from 0.6MPa to 1Mpa, the particle ejecting ratio remains constant, the value being 1, indicating that all particles return to the gasifier. In terms of the ejector in this study, the ejector can run without any problem with vapor pressure being at least 0.6MPa.(2)There occurred a recirculation zone with large size when the nozzles exit position lcl was-800 mm, leading to the particles not falling down. As the nozzle moved in the direction of right, the recirculation zone shrink. The ejector can still function well with lcl being-680.77 mm. However, energy loss was caused since some particles were brought back to the receiving chamber by the recirculating gas. The influence of vortex on particles was weak when the nozzles exit position lcl was-450 mm. As the nozzle kept moving right, particles can fall down successfully, and there is no vortex inside the receiving chamber with lcl being-200mm、0mm、100mm and 200 mm, respectively. The function length of the mixing tube, however, would get shorter, and it was not beneficial for the energy exchange. Taking all parameters into account, vapor pressurepp should not be below 0.6MPa and the nozzles exit position lcl should be selected in the range-450 mm to 0mm.