| With the intensification of urbanization and industrialization,risers have gradually become the object of attention in the gas-solid processing industry.The typical ’ ring-core ’ flow structure in the riser greatly reduces the conversion rate of raw materials during gas-solid mixing and cracking.Interphase interaction,particle collision and agglomeration make gas-solid flow and reaction more complex.The continuous improvement of numerical simulation methods makes the accurate modeling of fluidized beds more important.In this paper,based on the energy minimum multi-scale method,combined with the two-fluid model and the theory of particle dynamics,the method of calculating the bubble size is extended to the riser,and a multi-stage drag model suitable for the simulation of gas-solid flow in riser with internals is proposed.The flow-reaction coupling calculation method is also established.The piecewise drag model was used to simulate the gas-solid flow in the riser with internals under two-dimensional and three-dimensional different structural and physical parameters,and compared with the simulation results of the free bed flow under the Yang drag model.The simulation captured the non-uniform flow structure of the riser and described the improvement of gas-solid mixing by the internals.It is found that the internals change the axial particle concentration partition in the riser and reduce the particle concentration in the dense phase region.gas acceleration increases the turbulence of the system,improves the gas phase vortex diffusion,and improves the contact and mass transfer ability between the radial gas-solid phases.The increase of system pulsation and the diversion of components weaken the formation of particle aggregates,and the interception increases the pressure drop in the bed.The effect of spatial variation on voidage fluctuation is more significant than that of time variation.The results show that the multi-row internals further increase the turbulence of the system,and the multistage drag model can well simulate the flow in the non-free bed.The piecewise drag model was used to simulate the catalytic cracking process of crude oil,and the influence of internals on the distribution of parameters such as porosity,pressure drop and heat exchange intensity was analyzed.The results show that the residence time of the catalyst at the bottom of the riser in the non-free bed is longer,the pseudo-particle temperature lags behind that in the free bed,and the heat exchange between the gas phase and the catalyst is more intense.At the same time,the weakening of agglomeration behavior reduces the adhesion of coke on the catalyst surface,improves the activity of the catalyst in the system,and changes the depth of the catalytic cracking reaction.The yield of gasoline is the highest and the yield of non-condensable light gas is the lowest.The flow reaction-coupling calculation method can be used to calculate the cracking process. |
