(585b) The Use of Gas Pressure Profiles to Enhance Blending in Conical Hoppers and Cone-in-Cone Blenders

In traditional mass flow theory the velocity in hoppers and bins depends in part on the wall friction angle in the hopper and the internal friction angle of the solid. The radial stress theory pioneered by Dr. Jerry Johanson can be used to compute the expected solids velocity profiles in conical hoppers and plane flow hoppers, as well as hoppers that have internal structures such as the cone-in-cone. However, stress gradients, gas pressure gradients, and changes in the flow direction relative to the direction of gravity all induce flow patterns that are different from the traditional radial flow patterns which generally exist in normal gravity flow. The focus of this paper is to relate these external forces to the expected velocity in bins and hoppers, and then relate the velocity profiles to residence time distribution, combining the Danckwerts’ theory with a modified version of the radial stress theory to quantify continuous blending in process equipment. We will present work that highlights a parametric study of various mass flow devices used as blending devices including the cone-in-cone, the Diamondback® hopper, traditional conical hopper, and offset conical hoppers. The parameters studied will include wall friction angle, gas pressure gradient, stress gradient, hopper geometry and gravitational direction. Each of these mass flow devices will have, associated with it, a characteristic residence time distribution that can be used with incoming concentration distributions to blend a bulk solid material. The question to be answered is: what, friction angles, gas pressure gradients, solid stress gradients and hopper configurations will optimize the continuous blending from these mass flow devices?