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Acid gas compression and purification are an effective way for the treatment of NOxin oxy-fuel combustion flue gas due to the reduced volume flow rate of flue gas in oxy-fuel combustion in comparison with air combustion. The design of reactors for NOxremoval is particularly important for future CO2utilization and storage and is also rather challenging due to the impact of pressure on both kinetic as well as mass-transfer parameters. To obtain the sensitivity as well as pressure dependence of different parameters, NOxremoval in water under high pressure in both bubbling and film modes was investigated based on both experimental and modeling methods. Six uncertain parameters, including mass-transfer coefficients of NO and NO2(kNO and kNO2), NO oxidation rate constant k1, liquid surface area S1, liquid film surface area S2, and liquid film volume VL, were identified and optimized to minimize relative errors between measurements and simulations. Three most important parameters affecting the simulated NOxabsorption results are kNO2, k1, and S1, followed by kNO. While S2 and VL only affect NO2, these two parameters have little effect on NO, HNO3, and HNO2. In the gas bubbling reactor system, the liquid phase plays the main absorption role in NOxand the liquid film plays a supplementary absorption role. The effective removal of NOxin the high-pressure system can also be achieved by using only liquid film absorption rather than gas bubbling absorption as gas absorption by the liquid film can generate high concentrations of HNO3, which is beneficial for subsequent utilization.