Single-stage plasma-chemical process for particulates, NO/sub x/, and SO/sub x/ simultaneous removal

Abstract

In a previous study, we investigated the simultaneous removal of NO/sub x/ and SO/sub x/ using a plasma-chemical hybrid process and showed nearly 100% of NO/sub x/ and SO/sub x/ removal. In this study, we investigated simultaneous removal of NO/sub x/, SO/sub 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 Na/sub 2/SO/sub 3/ 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 NO/sub 2/, Na/sub 2/SO/sub 3/ solution to reduce NO/sub 2/ to N/sub 2/ and Na/sub 2/SO/sub 4/, and NaOH solution to neutralize nitric and sulfuric acids in the solutions. Without Na/sub 2/SO/sub 3/ and NaOH solutions, 95% of NO removal and no SO/sub 2/ conversion were achieved at 2.5 W. With water, 97% of NO and 64% of NO/sub x/ removal were achieved at 2.6 W, and more than 95% of SO/sub 2/ removal was achieved regardless of the discharge power. With Na/sub 2/SO/sub 3/ and NaOH solutions, 98% of NO and 75% of NO/sub x/ removal were achieved at 2.9 W, and more than 93% of SO/sub 2/ removal was achieved regardless of the discharge power. For the purpose of enhancement of surface reaction on NO/sub 2/ reduction with Na/sub 2/SO/sub 3/, Raschig rings were placed beneath the plasma section with the effective lengths of 5, 10, and 15 cm. As a result, no significant NO/sub 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.