Computational study of particle distribution development in a cold-flow laboratory scale downer reactor

The use of downer reactors (gas-solid co-current downward flow) in the FCC process for the upgrading of heavy crude oil into more valuable products has gradually become more common in the last decades. This kind of reactor is characterized by having homogeneous axial and radial flow structures, no back mixing, and shorter residence times as compared with the riser reactor type. The Computational Fluids Dynamics software, Ansys Fluent, was used to study two-dimensional gas (air) and solid (catalyst particle) flow in a downer section of a cold-flow circulation fluidized bed (CFB) system at laboratory scale. The implemented computational model was validated by comparing numerical results for solid velocity and volume fraction with measurements carried out on a CFB system using a fiber-optic probe laser velocimeter. According to numerical results obtained for different gas velocity and solid flux, flow development could only be estimated by considering solid axial velocity changes along the reactor. It is also necessary to consider solid volume fraction axial variations as radial profiles can change even when velocity profiles are developed.