Simultaneous removal of NOx, SOx, and CO2 at elevated temperature using a plasma-chemical hybrid process

In previous studies, the authors confirmed that the plasma-chemical combined hybrid process for controlling NO flue gas emission was extremely effective and economical in comparison with the conventional selective catalytic reduction (SCR) system and other technologies. In the present study, we carried out experiments on the simultaneous removal of NO_x and SO_x at elevated temperature using the plasma-chemical hybrid process. A series of experiments was performed to quantify all the reaction byproducts such as N₂O, CO, HNO₂, HNO₃, NO₃^-, and SO₄^- to evaluate the simultaneous NO_x and SO_x removal efficiency. The oxidation from NO to NO₂ without decreasing NO_x concentration (i.e., minimum reaction byproducts) and with least power consumption is the key for the optimum operation of the plasma reactor. The produced NO₂ was totally converted to N₂ and Na₂SO₄ with Na₂SO₃ or Na₂S with and without NaOH using the barrier-type packed-bed plasma reactor followed by the packed-column chemical reactor. The NO₂ reduction was more effective for Na₂S than Na₂SO₃ but produces H₂S with Na₂S. For both cases at least five times the stoichiometric amount of chemicals were required for complete NO₂ reduction. Nearly 100% of NO_x and SO ₂ and 40% Of CO₂ simultaneous removal were achieved with less than 5 ppm of N₂O and CO. The operating cost was less than 1/4 the SCR process. The additional SO₂ treatment system can be eliminated.