Single-droplet combustion of coal slurry fuels

Abstract

The combustion characteristics of single droplets of coal slurry fuels were experimentally investigated using both spontaneous and forced ignition. Results showed that the combustion is a sequential two-staged process, consisting of gas-phase combusion of the volatiles followed by combusion of the solid residue, which is mostly carbon. A splashing combustion phenomenon, which corresponds to the outgassing of the thermally cracked fuel gas from the droplet interior, occurred during the later period of gas-phase combustion in the same way as for residual heavy fuel oils. However, no disintegration or disruption of the droplet was observed. The duration of combustion of the solid residue agglomerate was several times longer than that of the volatiles, and therefore constituted a major part of the total burning time. The gas-phase burning time as well as the total burning time were found to vary linearly with the square of the initial droplet diameter, thus obeying the “square law of initial droplet diameter.” The overall burning rate coefficients of coal slurry fuels were about 1 2 to 1 4 times those of residual heavy fuel oils because of the long solid combustion time. The overall burning rate coefficient was found to depend mainly on the residual carbon content of the coal slurry fuel.