Granular Flow and Heat Transfer in a Screw Conveyor Heater: A Discrete Element Modeling Study

Abstract

The current work is driven by the need to dry low-rank coals (LRC) in a cost-effective, safe and energy efficient process. Although a number of technologies exist to dry LRC satisfactorily, none can yet claim the capability to continuously process a large amount of coal safely and economically. The screw conveyor heater/dryer is a promising technology that can potentially achieve the said requirements. Currently there is no published work reported on simultaneous modeling of flow and heat transfer of granular beds in a screw conveyor configuration using Discrete Element Method (DEM). As a pioneering work in this subject area, the thesis uses DEM to investigate the influence of operating and geometrical parameters on the hydrodynamic and thermal performance of a screw conveyor heater. The execution of `virtual experiments? via DEM enable system-scale predictions using particle-scale simulation data, while reducing prototyping and testing costs associated with the development of the heater. For the basic screw study, parameters studied include: screw speed (7-19 rpm), mass flow rate (15-300 kg h-1), angle of inclination (0-15 ?), and screw pitch-to-diameter ratio (0.25-1.0). This work aims to provide useful insights for future improvements to the designs of screw conveyor heat exchangers.