Three-dimensional multi-phase simulation of the mixing and segregation of binary particle mixtures in a two-jet spout fluidized bed

This study presents a three-dimensional numerical study of the mixing and segregation of binary particle mixtures in a two-jet spout fluidized bed based on an Eulerian-Eulerian three-fluid model. Initially, the particle mixtures were premixed and packed in a rectangular fluidized bed. As the calculation began, the gas stream was injected into the bed from the distributor and jet nozzles. The model was validated by comparing the simulated jet penetration depths with corresponding experimental data. The main features of the complex gas-solid flow behaviors and the mechanism of mixing and segregation of the binary mixtures were analyzed, Moreover, further simulations were carried out to evaluate the effects of operating conditions on the mixing and segregation of binary particle mixtures. The results illustrate that mixing can be enhanced by increasing the jet velocity or enlarging the difference of initial proportions of binary particle mixtures.

Three-dimensional multiphase full-loop simulation of directional separation of binary particle mixtures in high-flux coal-direct chemical-looping combustion system

Coal-direct chemical-looping combustion(CDCLC)is a promising coal combustion technique that provides CO2 capture with a low energy penalty.In this study,we developed a three-dimensional Eulerian-Eulerian multiphase full-loop model for simulating the circulation and separation of binary particle mixtures in a novel high-flux CDCLC system.This model comprised a high-flux circulating fluidized bed as the fuel reactor(FR),a counter-flow moving bed as the air reactor(AR),a high-flux carbon stripper,two downcomers,and two J-valves.This model predicted the main features of complex gas-solid flow behaviors in the system.The simulation results showed that quasi-stable solid circulation in the whole system could be achieved,and the FR,AR,and J-valves operated in a dense suspension upflow regime,a near-plug-flow regime,and a bubbling fluidization regime,respectively.The multiphase flow model of binary particle mixtures was used to predict the mechanisms of directional separation of binary particle mixtures of an oxygen carrier(OC)and coal throughout the system.A decrease in the baffle aspect ratio of the inertial separator improved the coal selective separation efficiency but resulted in a slight decline in the OC selective separation;this is believed to be the result of weakening of particle collisions with the baffle.A higher FR gas velocity had a slightly negative effect on the OC selective separation efficiency,but improved the coal selective separation efficiency;this can be attributed to an increase in the particle-carrying capacity of the gas stream.A decrease in the coal particle size led to better entrainment of the coal particles by the gas stream and this increased the coal selective separation efficiency.In real CDCLC applications,the operating variables for separation of binary particle mixtures should be comprehensively assessed to determine their positive and negative effects on the carbon capture efficiency,OC regeneration efficiency,gas leakage restraint,energy consumption,and fuel conversion.

Rotation characteristic and granular temperature analysis in a bubbling fluidized bed of binary particles

In this work, a discrete particle model （DPM） was applied to investigate the dynamic characteristics in a gas-solid bubbling fluidized bed of binary solid particles. The solid phase was simulated by the hard- sphere discrete particle model. The large eddy simulation （LES） method was used to simulate the gas phase. To improve the accuracy of the simulation, an improved sub-grid scale （SGS） model in the LES method was also applied. The mutative Smagorinsky constant case was compared with the previously published experimental data. The simulation by the mutative Smagorinsky constant model exhibited better agreement with the experimental data than that by the common invariant Smagorinsky constant model. Various restitution coefficients and different compositions of binary solids were investigated to determine their influences on the rotation characteristics and granular temperatures of the particles. The particle translational and rotational characteristic distributions were related to certain simulation parameters.

Experimental study on the 3D vibrated packing densification of binary sphere mixtures

The packing densification of binary spherical mixtures under 3D mechanical vibration was studied experimentally. The influences of vibration frequency （ω）, volume fraction of large spheres （XL）, sphere size ratio （r, diameter ratio of small to large spheres）, and container size （D） on the random binary packing density （p） were systematically analyzed. For any given set of conditions, there exist optimal ω and XL to realize the densest random binary packing; too large or small ω and XL is not helpful for densification. The influences of both r and D on p are monotonic; either reducing r or increasing D leads to a high value of p. With all other parameters held constant, the densest random packing occurs when XL is dominant, which is in good agreement with the Furnas relation. Moreover, the highest random binary packing density obtained in our work agrees well with corresponding numerical and analytical results in the literature.