Studies Towards Development of Improved Modelling and Scale-Up Procedures for Dense-Phase Pneumatic Conveying of Fine Powders

Abstract

This thesis aims to provide an improved model for solids friction factor and particle velocity for fluidized dense-phase pneumatic conveying of fine powders. Due to the highly turbulent and concentrated moving dunes, only limited progress has been attained so far towards understanding the flow mechanism of fluidized dense-phase pneumatic conveying of fine powders. A new test facility has been developed for the pneumatic conveying of fine powders. Fine powders such as cement and fly ash were tested for their apparent rheology in a rotational powder rheology tester. Tests were carried out with different rotational speeds and fluidization air quantities. Governing equations for solids-gas flow for fluidized dense-phase pneumatic conveying of powders have been developed considering one-directional steady-state flow, and the same were solved by using Fourth-fifth-order Runge-Kutta-Fehlberg (RKF45) method for various solids flow and airflow rates for constant and variable fluidized bulk densities to determine particle and actual gas velocities. The results have shown an increasing trend of particle and actual gas velocities and decreasing trend of solids volumetric concentration in the direction of flow. From the numerically obtained values, a model for particle velocity has been obtained using solids loading ratio, dimensionless velocity, dimensionless diameter and dimensionless density terms covering flow, pipe and particle properties. An improved model for solids friction factor has been developed by incorporating an additional collision term representing energy loss due to particle-particle impact during conveying. The new solids friction factor model has been validated by using it to predict total pipeline pressure drop for length and diameter scale-up conditions and comparing the predicted pneumatic conveying characteristics against the experimental plots. The results confirm the improved prediction capability of the new solids friction factor model. The model has been further improved by incorporating apparent powder rheology terms in the expression for solidsv friction factor model. Two different formats for modelling solids friction factor were evaluated; one format is scientifically more appropriate, whereas the other format provides practical convenience of testing and modelling. A comprehensive scale-up evaluation has shown that the format with convenience can provide satisfactory results from an industrial design point of view.