Clarifying the decomposition process of pyrite and SO2 release in the cyclone preheater of a dry rotary cement kiln system

Abstract

Abstract SO2 emissions in the cement industry are mainly caused by the decomposition/oxidization of pyrite at 300–600 °C in a cyclone preheater, which is a multistage suspension heating apparatus normally consisting of 5-stage cyclones and totally differentiated from the fixed bed, fluidized bed, and circulating fluidized bed. Therefore, clarifying the decomposition process of pyrite in the preheater environment is very important prior to flue gas desulfurization. In the present study, a multistage entrained flow reactor was designed to simulate the cyclone preheater, and then the effects of heating stage and temperature, O2 concentration, residence time and particle size on the decomposition process of pyrite were investigated. The results show that pyrite was transformed to a metastable crystalline state after first-stage heating, and then oxidized to pyrrhotine and magnetite/hematite after second-stage heating and third-stage heating step by step accompanied with SO2 release. The decomposition process of pyrite was controlled by the diffusion rate of sulfur gas and O2 in the product layer and accelerated by the radial cracks due to the volume shrinkage during decomposition. The results will give deeper insight into the decomposition of pyrite, release and capture of SO2, and sulfur flow of the kiln system, which are the fundamental to design process-compatible flue gas desulfurization technology for the cement industry.