Measurement and modeling of nitrogen oxides absorption in a pressurized reactor relevant to CO2 compression and purification process

Abstract The removal of nitrogen oxides under a high pressure has been widely accepted as an effective method for the treatment of oxy-fuel combustion flue gas. The high pressure promotes the oxidation of NO to NO2, subsequently removed by water to form nitric acid. However, both the measurement and modeling of nitrogen oxides absorption shows uncertainties. To quantify the nitrogen mass balance, gas-phase NO/NO2 and HNO2 were measured online, whereas liquid-phase HNO2 and HNO3 were analyzed offline. Nitrogen mass balance was achieved with a relative error within ±8%. To improve modeling accuracy, a novel multiparameter optimization method was proposed. Mass transfer coefficients of NO2/NO, rate constant of NO oxidation, surface area, and volume of liquid were optimized. The absorption of NO2 into a liquid was dominated by gas-phase mass transfer with the mass transfer coefficient decreasing from 1.77 × 10−4 mol m−2 s−1 Kpa−1 to 1.26 × 10−4 mol m−2 s−1 Kpa−1 with the increase of reactor pressure from 5 bar to 20 bar. The pressure dependent rate constant for NO oxidation agreed with gas-phase NO oxidation experimental measurement. It first decreased with the reactor pressure from 5 bar to 15 bar followed by an increase from 15 bar to 20 bar. The surface area of liquid decreased while the liquid volume increased with the rising reactor pressure indicating that liquid droplets were formed by gas bubbling and attached onto the inner surface of the reactor. This study resolved the uncertainties in measurement and modeling of the nitrogen oxides absorption process.