Simultaneous removal of SO₂ and NO_x from flue gas by low-temperature adsorption over activated carbon

An exceptional phenomenon has been observed that SO₂ and NO_x in flue gas can be effectively adsorbed over activated carbon with a surprising capacity at cold temperatures with the presence of oxygen. In this study, the adsorption characteristics of NO and SO₂ over activated carbon at 80, 20, 0, and - 20 is experimentally investigated. Without the presence of oxygen, adsorption of NO is negligible. In the presence of oxygen, NO can be oxidized to NO₂ over activated carbon which leads to the co-adsorption of NO/NO₂ within the adsorption bed. Catalytic oxidation of NO over activated carbon can be significantly enhanced at cold temperatures, leading to an extraordinary increase of adsorption capacity of NO. With an initial concentration of NO = 200 ppmv and a space velocity of 5000 h^-1, the average specific capacity increases from 3.8 to 169.1 mg/g when the temperature decreases from 80 to - 20 ℃. For NO-O₂ co-adsorption, the specific capacity increases along the adsorption bed due to the increasing NO₂ concentrations. The adsorption capacity of SO₂ is also significantly enhanced at cold temperatures. With an initial concentration of SO₂ = 1000 ppmv, the specific capacity increases from 12.9 to 123.1 mg/g when the temperature decreases from 80 to - 20 ℃. A novel low-temperature adsorption (LAS) process is developed to simultaneously remove SO₂ and NO_x from flue gas with a target of near-zero emission. A pilot-scale testing platform with a flue gas flowrate of 3600 Nm³/h is developed and tested. Emission of both SO₂ and NO_x is less than 1 ppmv, and the predicted energy penalty is about 3% of the net generation.