X-Ray Absorption Study of the Interaction of Coal Combustion Gases with Calcium Oxide

X-ray absorption measurements were performed on coal samples at beamline X18B at the National Synchrotron Light Source. The coal samples were probed at both the calcium and sulfur environments. Also in-situ measurements were made on the coal sample to study the evolution of sulfur on heating. The reaction of sulfur dioxide, evolved from the coal, with calcium oxide was studied in various environments. Both XANES and EXAFS techniques were employed at the calcium and sulfur K edges. Based on these measurements, it was observed that the traces of calcium present in the coal were in the form of calcite. The sulfur content in the coal was of organic and pyritic form. Some of the organic sulfur present in the coal was in the form of weakly bound sulfur. There were also traces of sulfates in the coal. The evolution of sulfur from the coal during heating under vacuum and during combustion were traced. Heating the coal under vacuum results in the weakly bound sulfur decomposition to form sulfur dioxide and were evolved. In the presence of calcium oxide even under vacuum the evolved gas, sulfur dioxide, was trapped by calcium oxide. Heating the coal with calcium oxide in the presence of oxygen resulted in complete conversion of sulfur in the coal into sulfur dioxide, which in turn was trapped completely by calcium oxide to form calcium sulfate. Based on these results it was clear that calcium oxide is a very effective sorbent for the removal of sulfur dioxide during combustion of coal.