Combustion kinetics of H2S and other sulfurous species with relevance to industrial processes

Abstract Raw natural gas and crude oil contain a variety of sulfurous species such as H2S, COS, CS2, mercaptans, and organosulfur complexes that lead to the formation of SO2 and other sulfurous compounds during combustion. The strict regulation on their emission has motivated the development of oil and gas sweetening processes, where such species are removed from fuels, and a sulfur-rich stream is generated. Many industries and plants such as cement industry, smelters, and power plants, involving the combustion of sulfur-bearing fuels, also generate gas streams rich in sulfur compounds. Such gas streams are mainly treated using sulfur recovery units (SRUs). To understand combustion occurring in SRUs, various studies on exploring the mechanism and the kinetics of sulfur-related reactions have been conducted. This review highlights the advancements in the kinetic models and the experiments on the combustion of sulfurous species and their interaction with hydrocarbons. The operational and the pilot plant data on H2S combustion in furnaces and the lab-scale experiments on sulfur oxidation, reduction, and sulfur-hydrocarbon reactions are discussed that have provided valuable data to validate combustion models. Due to the complex nature of sulfur chemistry, the quantum calculations on sulfur reactions have helped tremendously in improving the kinetic models. The findings of the potential energy surface studies with different spin multiplicities for major reactions affecting the combustion of sulfurous species such as the reactions of H2S and HS with oxidants (e.g., O2 and SO2), sulfur-hydrogen reaction leading to disulfur species, and the hydrocarbon-sulfur interactions leading to COS, CS2, mercaptan, and S-PAH formation are discussed. The combination of quantum calculations, reactor modeling, and experimental studies have improved our understanding on the role of various intermediates such as disulfur species in the combustion of H2S that was not known before. The detailed models have also helped in predicting the formation of large PAHs in the furnace that possibly explain the carbon-sulfur complexes found in the downstream catalytic units and in the process optimization to reduce the sulfur production cost. The recent developments on the innovation utilization of acid gas to produce hydrogen or syngas, SO2 to produce sulfur, and sulfur as an energy vector in thermochemical cycles for electricity generation are discussed.