Numerical Simulation Of Gas-solids Multiphase Flow In FCC Riser Reactor

The concentration and velocity distribution of catalyst particles in the riser of fluidized catalytic cracking(FCC) play an important role in the cracking reaction. Therefore, it is especially important to study the flow behavior of the catalyst particles in the riser. This work based on the rule of gas-solid flow in the riser, used the experimental data of the cold flow laboratory scale riser, analyzed the flow behavior of gas and single sized particles in the riser of FCC with the theory of fluid dynamics, and developed a mathematic model for the single sized particles fluidization in the mini-type riser. By comparing and analyzing the simulated results for different models(the kinetic theory of particulate flow, gas-solid drag model, solid viscosity model) and the experimental data, the optimized model for experiment-scope riser was obtained. Making use of the model developed above, the effect of inlet configuration of the riser, riser length and catalyst property on the catalyst distribution in the riser was investigated. Simulation results show that, in order to make the simulation conditions coincide with the experiment, it is realistic to choose side-inlet in 3-D simulation. The radial and axial distribution of catalyst particles concentration become more uniform with the riser length increasing and the particle diameter decreasing.With the feedstock of FCC becoming more and more heavier, environment protection demanding for the friend fuel and society wanting for the multi-product of FCC, the catalysts of FCC have also changed quickly. Moreover, in order to realize integrated utilization of energy, mixing fluidization and heat transfer of catalysts of different processes was studied, and this is also related to the mixing/segregation fluidization behavior of solid mixtures. Therefore, it is necessary to investigate fluidization behavior of multi-solids in the riser. This work based upon the model for the single sized particles fluidization in the mini-type riser, modified gas momentum equation, solid continuum equation, solid momentum equation and constitution equation properly, and developed a mathematic model for the multi-solids fluidization. Utilizing the multi-solids fluidization model and the Multiphase Flow with Interphase eXchange(MFIX) code, flow behavior of binary mixture in the riser was simulated. The distribution of concentration, velocity, mean particle diameter and granular temperature of the binary mixture in the riser was obtained, and compared with Mathiesen et al experimental data. By comparing the simulated results for different solid-solid drag models and different particle restitution coefficients with the experimental data, the optimized model for the gas and binary solids fluidization was obtained. Making use of the multi-solids fluidization model, the effect of particle composition and superficial gas velocity on bed density was investigated. Simulation results show that, when the particles are too large to be fluidized, adding small particles can improve fluidization and make particles distribution in the riser become more uniform. Moreover, since adding small particles, the uniformity of axial bed density distribution increased with superficial gas velocity increasing for the given initial bed height.