Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Chemical and Biochemical Engineering


Dr. Hugo I. de Lasa


Gas–solid concurrent downers possess unique features when compared to other gas–solid systems. Establishing their fluid dynamic properties requires both experimental measurements of gas-solid flow properties and computational modeling.

Measuring gas-solid flow properties such as cluster solid concentrations, individual cluster slip velocities, and cluster sizes, involves the use of specialized optical equipment, as well as a rigorous data analysis methodology. In addition, the modeling of the fluid dynamics of gas-solid flows in downer units offers special challenges such as establishing a proper drag model, cluster configuration and sizes, sphericity, boundary conditions, among other issues.

In this PhD dissertation, the fluid dynamics of gas-solid flows in downer reactor units are analyzed in the context of a wide range of operating conditions. To accomplish this, local cluster particle characteristics are determined for the first time, using two separate downer units and a significantly enhanced data analysis. This involves individual cluster signals recorded by the CREC-GS-Optiprobes and a method for setting the data baseline using solid mass balances. The proposed methodology allows the calculation of individual cluster slip velocities, agglomerate particle sizes, individual particle cluster size distributions, and cluster drag coefficients.

Gas-solid flows in downers are simulated in the present PhD dissertation, using a Computational Particle Fluid Dynamics (CPFD) Numerical Scheme. The CPFD model includes particles represented as clusters. This model is validated with experimental data obtained from the two independent downer units which have different downer-column internal diameters (a 1 inch ID and a 2 inch ID). CPFD simulations are implemented using average particle cluster sizes as obtained experimentally. Experimentally observed time-averaged axial and radial velocities, solid concentration profiles, and cluster particle acceleration regions are successfully simulated by a CFPD model. These findings support: a) a narrow distribution of particle cluster catalyst residences, b) the characteristic particle “forward” mixing, and c) the relatively flat radial solid concentrations and solid cluster velocities.

It is found that CPFD simulations agree well with experimentally determined particle cluster velocity and the solid void fraction in the downer core region, with this being the case for all the operating conditions studied.