THE COMBUSTION OF DUST CLOUDS: A SURVEY OF THE LITERATURE

Special Research Report SR-17 Knowledge of the details of combustion processes in the burning of pulverized fuels or dusts is of importance for two pr!'lctical reasons: one, because of the role of combustible dust in mine explosions; and two, because in a variety of devices finely divided fuels can be burned efficiently to produce useful power. The factors commonly considered to be of principal importance in the basic processes of pulverized coal combustion are: temperature, volatile matter content, character of gas flow (laminar or turbulent), composition (especially oxygen content) of the gaseous medium, particle size, radiation to or from the burning fuel suspension, and ash or mineral matter content. A survey of the published literature on combustion of dusts shows a quite strong theoretical development to be available but a relatively inadequate quantity of basic experimental work. In particular, as increasingly finely divided solid fuels find use in combustion devices, there seems to be a need for better understanding of the role of radiant energy transfer in the burning process. In an experimental study of this question, one must first of all be able to create a fuel dispersion in a combustionsupporting gas such as air, and create it in such a way that the properties of the cloud prior to combustion are known. In particular, the size distribution and concentration of the particles in the dispersion must be measurable and reproducible. On the theoretical side, for the interpretation of results one must bring to bear an understanding of laminar and turbulent heat and mass transfer in such systems and, insofar as possible, a know- · ledge of the physical and chemical processes taking place in and around the particles. In addition, knowledge of the optical properties of dust clouds is essential. The following review is an attempt to summarize the literature that is both available and pertinent to the experimental problem.