Effect of solid loading and inlet aspect ratio on cyclone efficiency and pressure drop: Experimental study and CFD simulations

Abstract

This work presents both an experimental and a numerical study on the effect of solid loading and inlet aspect ratio on cyclone performances in a circulating fluidized bed process (CFB). The unit operates at ambient temperature, atmospheric pressure with air and Geldart Group A glass bead particles of median diameter of 42.2 μm. The experimental study investigates the effect of solid loading (i.e. normalized solid loading C/Cmax from 0.014 to 0.41) and inlet aspect ratio (from 3 to 7, keeping the inlet area constant) on both gas separation and solid collection efficiencies (fractional and global) and pressure drop. Experimental results showed that cyclone pressure drop is primarily affected by solid loading. This parameter first decreases for normalized loadings up to about 0.127 before increasing for higher values. It was also found that global solid efficiency increases with solid loadings and is strongly favored by increasing the inlet aspect ratio. The numerical study was carried out with the software Barracuda VR®. It first consists on establishing a methodology on how to simulate cyclones, especially regarding the type of dipleg boundary conditions (BC). The gas flow within the cyclone dipleg, either upward or downward, was found to be a key information for the simulation. For normalized solid loadings up to 0.127, CFD results showed that the gas flows upward in the dipleg with a gas flow rate equal to the loop seal aeration of the CFB while for higher values, the gas flow is downward corresponding to a certain amount of gas underflow. The most appropriate boundary condition to employ in the cyclone dipleg outlet in order to represent the gas flow behavior was found to be a pressure BC whose value leads to either an upward or a downward gas flow. Considering this pressure BC and adapting its value to match the experimental dipleg aeration or gas underflow, the CFD results were found to be in very good agreement compared to experimental data.