The role of radiation absorption in defining explosibility of coal/rock dust mixtures

Abstract

This paper presents a theory and supporting data that coal dust explosibility and inerting requirements by powdered inhibitors such as rock dust depend upon a material property called the specific absorption which, in turn, relates to the ability of the coal and inert dusts to compete for absorption of the radiant energy from a source of ignition (or propagation) of explosion. The theory explains the experimental observation that at the lower explosion limit, the product of specific absorption and mass concentration of coal dust is constant for a fixed coal volatility. Theory and data also support the suggestion that a “rock dust meter” (RDM), which was previously developed at the Bureau of Mines to determine rock dust concentration in a coal/rock dust mixture, may also serve directly as an “explosibility meter” to determine the explosion potential of the dust mixture. The RDM is a simple optical device that measures the relative reflectance (at λ =0.94 μ m) from bulk mixtures of coal/rock dust. The ratio of the coal to rock dust specific absorption parameters, as determined by the RDM, allows for an a priori prediction of the mass fraction of rock dust necessary to inert a particular coal dust. It is also significant that, for coal of a fixed volatility, the relative reflectance measured by the RDM at the inert limit is a constant, independent of the particle sizes of the coal dust and rock dust.