Formation and Techniques for Control of Sulfur Dioxide and Other Sulfur Compounds in Portland Cement Kiln Systems

This report presents the chemical and physical factors governing the generation of sulfur dioxide (SO2), its transformation into other sulfur compounds, and the removal of sulfur oxides within the cement kiln system. Sulfur in cement kilns is derived from both kiln feed and from the kiln fuel. The form of the sulfur dictates the location in the kiln where the SO2 generation takes place. Sulfur in the fuel is oxidized in the burning zone or calciner, and is easily removed by reactive lime present in the kiln. Kiln feed sulfur may be in the form of elemental sulfur, organic sulfur compounds, sulfides (either simple sulfides or polysulfides, such as pyrites), or sulfates. When present in the form of sulfate, it usually does not form SO2 but rather leaves the kiln system with the clinker. When present in any of the other forms, it may be oxidized to SO2. Several control techniques were evaluated including: inherent SO2 removal in rotary kilns, inherent SO2 removal by in-line raw mills, process alterations, dry reagent injection, hot meal injection, spray dryer absorber, and wet SO2 scrubber.