Laboratory investigation of high pressure NO oxidation to NO2 and capture with liquid and gaseous water under oxy-fuel CO2 compression conditions

• Dry gas compression of NO to NO2 and absorption into water at pressures up to 30 bar.
• Validation of atmospheric kinetic model for the oxidation of NO to NO2 up to 30 bar.
• Demonstration of possibility of gas phase reactions involving NOx and water vapour.
• Investigation of the stability of NOx in liquids.
• Mass balance closure of the gas/liquid system.

Oxyfuel combustion enables carbon dioxide capture for storage and can therefore significantly reduce carbon dioxide emissions from coal fired power plants. However, CO2 derived from oxyfuel combustion has impurities that cause corrosion to plant equipment and transport lines and may be subjected to certain storage and end user requirements. 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 quantitative removal of these impurities by the compression system is unknown. The current research uses laboratory experiments to study the reactions of nitrogen oxides in the compression system. These include the oxidation of NO to NO2 in the gas phase, the absorption in liquid water and also reactions with water vapour in conditions 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. 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 were complicated by the stability of the absorbed NOx species in the liquid.