Air flow and particle transport in a triboelectric coal/ash cleaning system-counter flowing straight duct design

The process of triboelectric coal/ash cleaning is outlined and a new design for scale-up to industrial systems is described. A straight rectangular du ct forms the mixing chamber and the main body of this triboelectric separat or. To improve mixing and to generate a uniform concentration in the main e lectrostatic separator duct, the mixture enters the mixing box in the form of two opposing jets. The stress transport model of the FLUENT code is used for simulating the me an gas flow and to guide the overall design of the electrostatic coal/ash s eparator. The three-dimensional computational grid covers the mixing chambe r with the opposing inlets and the upper part of the main separator duct. T he gas flow field conditions including the directional intensities of turbu lence are evaluated. The instantaneous fluctuating velocity field was simul ated by a Gaussian filtered white noise model. A recently developed computa tional model for Lagrangian particle tracking is used to study the transpor t of particles from the inlets to the main body of the separator duct. The model accounts for the drag and lift forces acting on the particle, in addi tion to the Brownian motion and gravitational sedimentation effects. The pa rticles are also dispersed by the action of the high level of turbulence th at is generated in the mixing chamber. The computational results show that the new design generates roughly uniform flow conditions in the triboelectr ic separator duct. Furthermore, the larger 100 mum particles will have a mo re uniform distribution when compared with the smaller (40 mum) particles. The effect of the presence of an electric field perpendicular to the flow d irection is also studied. It is shown that the charged particles are signif icantly deflected by the action of the electrostatic forces. As a result, t he system could separate coal and ash particles that carry different charge s. The simplicity and effectiveness of the straight duct separator makes it a prime candidate for scale-up for use in industrial applications for onli ne coal beneficiation and separation of minerals from ash in combustion pro duct.