Effect of solids loading method on bed porosity and gas flux distribution in a fixed-bed reactor

Abstract

We examine the effect of the method of loading particulate solids into a commercial fixed-bed reactor on porosity distribution through the resulting bed. Cylindrical extrudates were released into a vertical vessel through a loading chute at the top center with a single hollow cone as a distributor device. Bed porosity and gas flow variations through the solids were deduced using a temperature response analysis recognizing axial convection as the dominant heat transfer mode. Porosity distribution was extremely sensitive to the position of a circular orifice in the chute above the distributor cone. With the orifice just above the distributor, particles slid off the cone in a well-defined sheet landing at about one-third the vessel radius, from which solids spread into the vessel by sliding down the rising-bed surface at the angle of repose. This produced a radially non-uniform porosity resulting in a gas flux at the bed center, roughly half that at the reactor wall. Much more uniform porosity was obtained by raising the orifice in the loading chute such that falling particles approached terminal velocity before striking the cone, dispersing more broadly over the vessel cross-section.