Effects of particle density and sulfur forms on pyrolysis desulfurization in rapid heating of coals

Four kinds of coal particles, having the same average diameter, ranging from 69 to 89% C daf were first pyrolyzed rapidly in a free-fall reactor at atmospheric pressure under a nitrogen stream at a terminal temperature of 1253 K in order to clarify pyrolysis desulfurization and volatilization behavior, The extent of organic sulfur removal in the rapid pyrolysis did not correlate well with carbon content of raw coal. Then, the same sample particles were separated into three groups by the difference of density with a sink-float method. In the rapid pyrolysis of each group, volatile yield and extent of organic sulfur removal increased linearly with decreasing average density of the group, with exception of a high-rank coal. X-ray absorption near-edge structure analysis indicated that the low-density group contained sulfide and sulfoxide, which could contribute to the high extent of organic sulfur removal. The efficient removal of organic sulfur from the densest group in a high-rank coal by rapid pyrolysis actually resulted in decomposition and/or vaporization of elemental sulfur which was apparently regarded as organic sulfur according to the ASTM-(D2492).