Study on the Alkali Release from the Combustion Products of a Single Coal Particle by Laser Ignition

This work concerned the measurement of alkali metal (Na and K) release during the combustion process of three different types of coal at atmospheric pressure. Measurements were performed from the CO2 laser ignition of a single coal particle in different oxygen concentrations of O2/N2 and O2/CO2 atmospheres. An atomic emission spectrum of alkali metals was directly collected by the slit of the spectrometer with an intensified charge-coupled device (ICCD) detector to obtain the temporal and spatial release behaviors of alkalis. The results indicated that the type of coals would influence the release process of alkali metals, whose release duration would be longer for the coals with a higher carbonization level. With the increase of the oxygen concentration, the intergal intensity of Na and K during combustion was found to be enhanced and the release amount increased with obvious exponential growth. In comparison to the O2/N2 atmosphere, CO2 in the oxygen-rich atmosphere had an obvious inhibitory effect on alkali metal release, which was most notable for anthracite. The release processes of alkali metals in different types of coal were also related with the flame temperature, which have little correlation with the spatial distribution of alkali metals, probably as a result of the diffusion effects.