Experimental and theoretical investigation into the ignition and combustion processes of single coal particles under zero and normal gravity conditions

Abstract

The results of research and numerical calculation of ignition and burning process of single dust particles arranged in a row are presented. The influence of particle diameter (0.3–1.2 mm), coal volatile content (2–48%), and oxygen concentration in the gas (21–100%) on the ignition process and the rate of flame propagation were tested. Also the temperature was measured around the particles in the course of ignition and burning processes. Experiments under zero gravity conditions were performed to investigate the process mechanism and to observe ignition which is only controlled by heat radiation and conduction. Comparison of the obtained results with those obtained in normal gravity conditions makes it possible to determine the free convection influence on the investigated process. With the investigated particle diameters ignition occurs on the particle surface and further flame development around the particle depends mainly on the volatile content in the coal. Discrete and continuous flame propagation was observed depending on condition in which the process was carried out. There is an optimal distance between the particles where the maximum flame propagation velocity is obtained. A physical model of the process is presented which explains the flame propagation mechanism and determines the ignition requirements. On the basis of this model, a mathematical model of the process was formulated which enables one to predict the influence of different heat transfer mechanisms on particle ignition and flame propagation.