Experimental Study Of Simultaneous Desulfurization And Denitrification From CO₂-enriched Flue Gas

The flue gases from oxyfuel combustion still contain a higher concentration ofpollutants such as NOx and SO₂besides CO₂. It would be have a significant impact on thecompression and utilization of CO₂. In this paper, CO₂compression process is used for thesimultaneous desulfurization and denitrification according to the feature that NOx and SO₂are easy to react with water under pressurized conditions. Influencing factors such aspressure, temperature, residence time, and additive water amount is systematicallyresearched by the experiment during the pressurized absorption process of NO and SO₂,and preliminary analysis of the pressurized absorption mechanism is provided.Experimental studies of NO separate absorption and simultaneous absorption of NOand SO₂have shown that the NO absorption rate which can reach97.5%at1.6MPa, andconversion rate of nitric acid increases as the pressure increases. With the extension ofresidence time, the NO absorption rate and conversion rate of nitric acid are improved. TheO₂concentration and initial NO concentration in the flue gas is helpful to improve the NOabsorption rate and conversion rate of nitric acid. The absorption temperature rise willreduce absorption effect of NO and SO₂. SO₂is soluble in water which makes it completelyabsorbed by water. SO₂and NO, H₂O, O₂can produce a complex series of intermediatereactions and generate a lot of NOx and SOx or hydroxide ammonia sulfonate. NO can playa similar role of catalyst during SO₂oxidation absorption. Overall SO₂and NO play amutually reinforcing role in the absorption process.By comparison of the absorption effect of NO and SO₂in N2atmosphere and CO₂atmosphere, what they have in common is that SO₂can be completely absorbed by water. InN2atmosphere, the NO absorption rate is lower than in the CO₂atmosphere and the rate ofconversion of sulfuric acid and nitric acid are slightly higher than the conversion rate inCO₂atmosphere.Finally, a preliminary analysis of the absorption mechanism is conducted. Chemicalabsorption reaction is more violent than the physical absorption, which can be described byfive general steps. By comparing the size of the electrode potential of relevantoxidation-reduction reaction with each other, the direction of the chemical reaction isexplained. Using chemical thermodynamic principles, the chemical reaction Gibbs freeenergy and the formula of chemical equilibrium constants of simultaneous desulfurizationand denitrification are derived. SO₂and NO partial pressure are calculated at different temperature, and the results are in good agreement with the experiment.