Modeling the hydrodynamics in a coupled high-density downer-to-riser reactor

A coupled high-density downer-to-riser (DtoR) reactor is proposed for the controlled reaction pathway in the fluid catalytic cracking (FCC) process with the desired products distribution, e.g., clean gasoline with less olefin content. Hydrodynamics in such a reactor coupling system is studied using a compressive model that considers the pressure balances around all the sub-units in the prototype. The continuity closure condition is used to determine the material balance of the solid particles flowing in the circulating fluidized bed system. The model predictions have good agreement with the experimental data in rather wide operating conditions, e.g., when the solids circulation rate goes to more than 400 kg/m² s. The effects of the solids inventory, the superficial gas velocity, the particle diameter and density, the inside diameter of risers, and the fractional opening of the control valve for the solids flow on the operation of the DtoR system, are investigated and discussed in detail. It is demonstrated that the model offers appropriate guidance for the design and the operation of the coupled circulating fluidized bed system.