Simultaneous removal of nitrogen oxide/nitrogen dioxide/sulfur dioxide from gas streams by combined plasma scrubbing technology

Oxides of nitrogen (NO_x) [nitrogen oxide (NO) + nitrogen dioxide (NO₂)] and sulfur dioxide (SO₂) are removed individually in traditional air pollution control technologies. This study proposes a combined plasma scrubbing (CPS) system for simultaneous removal of SO₂ and NO_x. CPS consists of a dielectric barrier discharge (DBD) and wet scrubbing in series. DBD is used to generate nonther-mal plasmas for converting NO to NO₂. The water-soluble NO₂ then can be removed by wet scrubbing accompanied with SO₂ removal. In this work, CPS was tested with simulated exhausts in the laboratory and with diesel-generator exhausts in the field. Experimental results indicate that DBD is very efficient in converting NO to NO₂. More than 90% removal of NO, NO_x, and SO₂ can be simultaneously achieved with CPS. Both sodium sulfide (Na₂S) and sodium sulfite (Na₂SO₃) scrubbing solutions are good for NO₂ and SO₂ absorption. Energy efficiencies for NO_x and SO₂ removal are 17 and 18 g/kWh, respectively. The technical feasibility of CPS for simultaneous removal of NO, NO₂, and SO₂ from gas streams is successfully demonstrated in this study. However, production of carbon monoxide as a side-product (∼100 ppm) is found and should be considered.