Validation and application of CPFD models in simulating hydrodynamics and reactions in riser reactor with Geldart A particles

3D virtual full-loop CFD simulation of industrial two-stage FCC reaction–regeneration system

The 3D virtual full-loop CFD simulation method with two-fluid model (TFM) was developed to model an industrial two-stage FCC reaction–regeneration system. The virtual connections (mass, species, and energy) between riser reactors, disengager, stripper, and regenerator were realized by defining user-defined functions (UDFs) for boundary conditions according to the reality. Five correction factors were used to correct the reaction rates in the 14-lump FCC reaction kinetics, and two correction factors were used to correct the FCC reaction heat in the first and second riser reactors. As a result, the whole FCC reaction–regeneration system was successfully modeled in one single CFD case. A thorough and comprehensive view of the performance of reaction–regeneration system was obtained by the 3D virtual full-loop CFD simulation, which is helpful for the operating and optimization of FCC unit. The major predicted results were in a good agreement with the industrial data. The effects of operating conditions were also investigated by changing regenerated temperature, catalyst to oil (CTO) ratio, and process capacity.

Numerical Simulation of the Gas-Solid Two-Phase Flow-Reaction Process in a Maximizing Isoparaffin Process Reactor

The process of the fluid catalytic cracking (FCC) is accompanied by complex physical and chemical reactions and phase transition processes. For the FCC process-maximizing isoparaffin process (MIP), coupled simulation and optimization of flow reaction can meet the requirements for the design and operation of high efficiency, low energy consumption, low pollution, and low cost in the catalytic device. A combination of Eulerian-Eulerian model and 11-lump kinetic model is adopted to simulate the flow-reaction process of gas-solid two-phase of an industrial MIP riser reactor. A drag model based on the energy-minimization multiscale model established by Yang is incorporated into FLUENT through a user-defined function (UDF). The temperature distribution of the catalyst and the concentration of each product component at the outlet are in good agreement with the industrial measured data, which indicates that the established coupling model of flow reaction and drag model are reliable and effective. The two operating variables of the catalyst-to-oil ratio and catalyst inlet temperature are explored their effects on the flow-reaction process of FCC gas-solid two-phase. In the prelifting zone, the velocity of catalyst particles presents parabolic distribution. In the first reaction zone, the maximum velocity of catalyst particles is about 1/2 of the radius of the riser. In the second reaction zone, the maximum particle velocity of catalyst is located in the central region, with a slight increase in about 1/2 of the radius of the riser. The increase in catalyst-to-oil ratio leads to the decrease in the yield of diesel oil and the increase in yields of gasoline, liquefied petroleum gas, propylene, and dry gas. The changes in the catalyst inlet temperature affect the product distribution of the outlet component, which can provide an important guiding significance.

3D CPFD Simulation of Circulating Fluidized Bed Downer and Riser: Comparisons of Flow Structure and Solids Back-Mixing Behavior

The difference of gas-solids flow between a circulating fluidized bed (CFB) downer and riser was compared by computational particle fluid dynamics (CPFD) approach. The comparison was conducted under the same operating conditions. Simulation results demonstrated that the downer showed much more uniform solids holdup and solids velocity distribution compared with the riser. The radial non-uniformity index of the solids holdup in the riser was over 10 times than that in the downer. In addition, small clusters tended to be present in the whole downer, large clusters tended to be present near the wall in riser. It was found that the different cluster behavior is important in determining the different flow behaviors of solids in the downer and riser. While the particle residence time increased evenly along the downward direction in the downer, particles with both shorter and longer residence time were predicted in the whole riser. The nearly vertical cumulative residence time distribution (RTD) curve in the downer further demonstrated that the solids back-mixing in the downer is limited while that in the riser is severe. Solids turbulence in the downer was much weaker compared with the riser, while the large clusters formation near the wall in the riser would hinder solids transportation ability.