Pilot Plant NO2 Removal with Aqueous Sulfite

Abstract A novel method to remove nitrogen dioxide (NO2) from the flue gas of coal-fired power plants with CO2 capture has been advanced for commercial implementation. The technology leverages the equipment and chemistry in an existing (sulfur dioxide) SO2 polishing scrubber upstream of the main CO2 capture unit to remove the NO2, preventing degradation of the CO2 capture solvent and formation of nitrosamines. The report focuses on further evaluation of the chemical additives and operating conditions associated with the NO2 removal process to define conditions for commercial scale testing and deployment. Experimental work systematically evaluated a series of potential additives to minimize the oxidation of sulfite in a representative SO2 pre-scrubber solution. The additive combinations and concentrations were varied alongside important process conditions such as temperature, oxygen concentration, and metals present in solution to mimic the conditions expected in a commercial system. Important results of the parametric experimental work include identifying a new, potent sulfite oxidation inhibitor, revealing the importance of combining inhibitors with metal chelating agents, validation of a low-cost additive process, and development of a new semi-empirical model to represent mechanisms associated with sulfite oxidation. In addition, the experimental work revealed the impact of operating at higher temperatures (representative of a field test unit), which will guide the selection and concertation of additives as well. Techno-economic analysis identified potential net savings as large as $1.30/tonne CO2 captured and quantified the potential benefit of low cost additive options actively being pursued by the development team. Finally, the experimental results and engineering analysis supported the development of a detailed field testing plan and protocol to evaluate the technology at near-commercial scale. The field test preparation included development of procedures to introduce chemical additives to an existing SO2 polishing unit and identification of representative flue gas conditions based on a review of existing plants. These activities will have direct bearing on operation and design of commercial units.