Design Variables of Pilot Scale Electrostatic Separator for Removing Unburned Carbon from Coal Fly Ash

Abstract

A pilot scale beneficiation system for removing unburned carbon from coal fly ash was developed and has tested using a continuous triboelectrostatic separator composed of two vertical electrodes and an ejector tribocharger. Tests were conducted to evaluate the charge density and the separation efficiency at various operating conditions. With a stainless steel tribocharger, the optimum conditions for achieving maximum charge density were as follows: air flow rate, 3.4 m³/min; feed rate, <300 kg/h; relative humidity, <30%. Under these optimum conditions, clean ash with an LOI (loss on ignition) of less than 4.5% could be recovered (yield: >70%). The electrostatic separator was operated under the following conditions: width of the diffuser slit, 4 mm; air velocity at the diffuser outlet, 16.7 m/s; distance between the diffuser slit and the splitter, 15 cm. The optimum feed rate was found to be 830 kg/h per square meters of the electrode surface area, which can be used as the scale-up factor for the electroseparator.