BEHAVIOR OF IRON-BEARING MINERALS IN THE EARLY STAGES OF PULVERIZED COAL CONVERSION PROCESSES

Early stage transformations and deposition of iron-bearing coal minera ls, in particular pyrite (FeS2), were studied. An atmospheric laborato ry-scale facility was used to simulate the near burner environment in two different coal conversion processes: (i) low-NOx pulverised coal c ombustion and (ii) entrained-flow gasification. Particle sampling show ed that for both environments the pyrite transforms quickly to pyrrhot ite (FeS). In the deposition experiments, this liquid pyrrhotite was i mpacted on substrate surfaces. The chemical composition and the morpho logy of the deposits formed under the two conditions showed clear diff erences. It appeared that the final product for low-NOx combustion con ditions was Fe2O3, whereas for entrained-flow gasification conditions, Fe was the final product. The deposits collected under both simulated gaseous environments did not contain sulphur. Based on these experime ntal findings, a descriptive model for pyrite transformations under bo th conditions is proposed. (C) 1998 Elsevier Science B.V. All rights r eserved.