Dry Benefication of Coal by Triboelectrostatic Separation-Phase 2

This proposal is a sequel to an earlier ICCI-funded proposal (project number: 11/4A-2), aiming to build a “digital” triboelectrostatic separator for dry beneficiation of Illinois coal. There, we developed a CFD modeling, which we validated and used to study separation of coal particles (comprising of carbon and ash) in the separation chamber of a triboelectrostatic separator. We performed several parametric studies to optimize the geometric design of the chamber and to increase the performance of the separator in accord with the “separation efficiency” or “combustible recovery” curves. The project led to a wealth of information about the interplay of parameters that control the separation efficiency. However, as the coal particles were considered having “preassigned” charges, the tribocharging process did not enter to the picture. The tribocharging process, however, is a critical step in the triboelectrostatic separation, as the magnitudes and the distribution of the charges (acquired by the particles) dramatically affect the performance of the unit. The phenomenon is complex and is not well understood. As such, a deterministic CFD modeling of the tribocharging process will be a major leap forward in aiding the commercialization and scale up of TES units to enhance the quality of Illinois coal. Here it is proposed to develop a CFD modeling of the tribocharging process, using a charge relaxation model in conjunction with impulse equations that accounts for electrification of coal particles due to multiple impacts and rebounds from the wall. We use commercial software package (FLUENT) along with own user-supplied codes and use an Eulerian/Lagrangian scheme to solve the fluid flow equations and particle motions. We simulate several different particle-charging strategies such as pneumatically driven motion of coal particles through a spiral-shaped tubes and impact of the particles with the surface of a rotary charged cylinder. We then compare the charging efficiency of these tribochargers as a function of the controlling parameters. The integrated TES unit will be used to produce the grade recovery curves as a function of the controlling parameters of the whole unit. The goal is to use the “digital” triboelectrostatic unit as a “predictive means” for design optimization and scale up of TES processes by providing detailed insight about the effect and interplay of various controlling parameters on the separation efficiency curves.