Abstract
Suspensions of pulverised coal particles in shock-heated gases have been studied under conditions of non-ignition to high intensity combustion. In order to study separately the various stages of particle combustion pyrometric methods of measuring particle surface temperatures have been developed. In general three classes of particle temperature history have been obtained according to the composition of test gas used. In shock-heated nitrogen coal particles heatod to gas temperature in times dependent on particle size and their moisture content. The influence of moisture on heating rates was to cause a temperature arrest some 60 to 100°k below gas temperature. Gas to particle heat transfer coefficients are deduced for various coal sizes between 15 and 35microns. In gas mixtures with low oxygen concentrations, slow oxidation of the particle surface was observed which led to their heating to a steady temperature in excess of gas temperature by as much as 160°K. At this point, a heat balance was achieved and no flame occured. With higher oxygen concentrations, or initial has temperature no such steady temperature was reached, the particles heating at an exponentially increasing rate to around 1800°K at which temperature volatile ignition occured and the particle suspension rapidly reached its maximum temperature of around 2800°K. Calculation showed that this temperature was reached only on complete burnout of the particles. Particle heating rates up to volatile ignition were strongly influenced by oxygen concentration and particle size and type whilst after volatile ignition burnout was independent of type but dependent on size. Consequently, mathematical analyses of the results were based on 'chemically controlled' heat release rates below particle temperatures of 1800°K and 'diffusional controlled' rates above.