SULFUR TRANSFORMATIONS DURING PYROLYSIS OF A HIGH-SULFUR POLISH COKING COAL

A coking coal containing 4.9 wt%, db, of sulfur was subjected to pyrolysis at 330-1700 degrees C in an atmosphere of evolved gases. The changes in the forms of sulfur were determined by wet chemical analysis. Scanning electron microscopy (SEM) combined with X-ray microanalysis were used to monitor the reduction of pyrite during coal pyrolysis and the retention of sulfur by the alkali constituents of the coal mineral matter. It was found that between 360 and 700 degrees C the conversion of pyrite to ferrous sulfide occurred. This was accompanied by a high accumulation of organic sulfur in the char. Calcite and siderite present in the mineral matter of the coal were responsible for a further increase in sulfide sulfur. Spherical agglomerates composed of calcium and iron sulfides were detected. Above 1000 degrees C sulfur re-enrichment on the surface of ferrous sulfide particles was observed. Pyrolysis conducted at 1700 degrees C did not re:move the sulfide sulfur completely. Organic sulfur was also present in a significant amount. The roles of alkali components and an environment rich in volatile sulfur compounds in sulfur retention during coal pyrolysis are discussed.