Experimental Research On Particle Flow Characteristics In Thermal Plasma Downer Reactior At Cold Mode State

The key problem of coking seriously restricts the stable and continuous operation in thermal plasma downer reactor for the coal cracking process to produce acetylene production. When injecting appropriate amount of inertia particles and coal into downer, the problem of coking could be prohibited or alleviated since the inert particles can carry the coking precursor of coal and also will continually scour the downer wall to draw the coking matter off. However, a binary particle mixture system composed of inert and reaction particles will occur in downer and cause some changes in flow behavior, which become a new unclear problem. Unfortunately almost the past studies were focused mostly on single particle and gas mixing flow behavior in downers. Therefore in order to expand the industrial application scope of downer and resolve the coking problem for the process of acetylene production from coal cracking in thermal plasma downer, It is necessary to have a special and systematic study on the solid flow behavior, redial and axial distributions of local particle velocity and flow development along the downer for the binary particle mixture system.The axial and radial distributions of the local particle velocity at different radial positions on various axial levels along a downer were systematically measured by using a PV-4A fiber-optic particle velocity probe in a half-column downer of 2m-height and Φ30 mm I.D. The approximate particles settling velocities were measured and predicted, and also compared with theoretically calculated ones. Then the flow regions in downer were determined and the flow patterns of gas and solids were examined. Four kinds of solid materials with different physical properties were used to study the effects of particle properties on the axial and radial distributions of the local particle velocity. And the influences of distributor geometry configuration, dealing with both orthogonal tube and annular styles, and operation conditions on radial distributions of the local particle velocity were also investigated in this paper. Based on the concept of dimensionless local particle velocity, a new correlations for predicting the local particle velocity distribution was developed by regressing experimental data from different geometrical downers and different material systems in both present work and literatures, which can be used in a relatively wider range. Finally, the radial distributions of binary mixture particle velocity,formed by respectively and simultaneously injecting fine-FCC catalysts and coarse-glass beads in downers,were examined at different composition ratios of FCC catalysts to glass beads. The main results are shown as below:(1) The approximate particles settling velocities determined by experiments appear in the similar variation rule as the calculated ones, i.e. these velocities are increased with the increasing of particle sizes; In this study, the local particle and mean particle velocities, measured at very low gas flow-rate, can be taken as the approximate particles settling velocities.(2) The gas and solids flow development in downer and the radial distributions of local particle velocity are varied significantly with the physical properties of particle. In the first acceleration region, the radial distributions of local particle velocity fluctuate more often and are more steeped, while in the second acceleration region they are more stable and uniform. The key factor for the great change of radial distributions of local particle velocity is the particle properties, and at the same operation conditions, the large the particle size and the high the particle density, the more even the radial distributions of local particle velocity.(3) The reduced particle velocity () can reflect the even level of the radial distributions of local particle velocity. Five dimensionless numbers, standing for the bed geometrical characteristics, physical properties of particle, and others, i.e., H/D,vp*,Re0,Cds and were employed to develop a new correlation for predicting the...