Removal of NOₓ from oxyfuel derived CO₂ by reaction with water condensate formed during compression

Oxyfuel is a carbon capture and storage technology that reduces carbon dioxide emissions from coal fired power plants. However, CO₂ derived from oxyfuel combustion has impurities that cause corrosion to plant, transport lines and sequestration site. The use of the CO₂ compression system in an oxyfuel power plant to remove these impurities has been proposed and tested by international gas vendors both at laboratory and power-plant scale; however the extent of the compression system in potentially removing the impurities is unknown. The current research uses laboratory experiments to study the reactions of nitrogen oxides in the compression system, from the oxidation of NO to NO₂ in the gas phase to the absorption in liquid water and also reactions with water vapour from ambient conditions to pressures of 30 bar. The reactor used was a bubble column that was preloaded with liquid water. Results show that nitric oxide is readily oxidised to water-soluble nitrogen dioxide at elevated pressures, that this reaction is kinetically-controlled and can be predicted using an equation derived for atmospheric pressure conditions. The resulting nitrogen dioxide is shown to react with liquid water to form nitrous and nitric acid. Single experiments also showed the potential for gas phase acid formation and condensation. Overall mass balances across the gas-liquid system was complicated by the stability of the absorbed NOₓ species in the liquid.