The Influence of Volatiles on Combustion Rate of Loy Yang Coal Char in a Fluidised Bed Combustor

Abstract

AbstractAn experimental investigation into the influence of volatiles as simulated by propane on the combustion rate of Loy Yang coal char in a bubbling fluidised bed combustor has been conducted. The weight loss and burn‐out times for a batch of +3.35‐3.175 mm sized coal particles were examined at temperatures of 700°C, 800°C and 900° C. Silica sand (+250–180μm) as the bed material was fluidised either by a 10% v/v oxygen stream or 10% v/v oxygen and 3% v/v propane mixture, both balanced with nitrogen. Samples were retrieved at various time increments by means of a movable gauze basket and quenched in a nitrogen stream. It was observed that burnout times of char particles at 700°C, 800°C and 900°C in a propane/air environment were 13%, 39% and 88% greater respectively, than those at the same temperatures but in the 10% v/v oxygen stream. At the lower combustion temperature of 70O°C, minimal effect of extended char combustion times is concordant with observations of particles spending a small proportion of time at the bed surface, where oxygen concentration is lower due to over‐bed burning of propane. At the higher bed temperatures, the reduction in the char combustion rate in the presence of propane is consistent with the transition from over‐bed to in‐bed combustion of propane. Consequently, there is competition between the propane and char for available oxygen, causing a substantial decrease in the char combustion rate with increasing temperature. The influence of propane on the burnout times observed compare favourably to that reported in literature. The rate of char combustion was found to correlate well to the simple diffusion‐controlled oxidation of a char particle in laminar flow.