Single-stage plasma-chemical process for particulates, NOx, and SOx simultaneous removal

In a previous study, we investigated the simultaneous removal of NO_x and SO_x using a plasma-chemical hybrid process and showed nearly 100% of NO_x and SO_x removal. In this study, we investigated simultaneous removal of NO_x, SO_x, and particulates using a single-stage wet-type plasma reactor. This reactor consists of a discharge wire and pyrex cylinder, wrapped by the copper mesh where Na₂SO₃ and NaOH solutions flow along the inner wall of the cylinder from the top to the bottom of the reactor. Particulates are charged by pulse corona and collected on the inner wall, and then removed by solutions flow. This method is effective for extremely low. and high-resistivity particles to cause reentrainment or back corona. The plasma was used to oxidize NO to NO₂, Na₂SO₃ solution to reduce NO₂ to N₂ and Na₂SO₄, and NaOH solution to neutralize nitric and sulfuric acids in the solutions. Without Na₂SO₃ and NaOH solutions, 95% of NO removal and no SO₂ conversion were achieved at 2.5 W. With water, 97% of NO and 64% of NO_x removal were achieved at 2.6 W, and more than 95% of SO₂ removal was achieved regardless of the discharge power. With Na₂SO₃ and NaOH solutions, 98% of NO and 75% of NO_x removal were achieved at 2.9 W, and more than 93% of SO₂ removal was achieved regardless of the discharge power. For the purpose of enhancement of surface reaction on NO₂ reduction with Na₂SO₃, Raschig rings were placed beneath the plasma section with the effective lengths of 5, 10, and 15 cm. As a result, no significant NO_x removal was obtained in comparison with no Raschig rings. Regarding the removal efficiency of diesel soots using the plasma-chemical hybrid reactor, more than 90% of particulate removal efficiency was obtained.