Study on efficient removal of SOx and NOx from marine exhaust gas by wet scrubbing method using urea peroxide solution

•A novel oxidation absorption process for removing NOx and SOx in marine exhaust gas.•Urea peroxide can reduce SOx and NOx by about 100% and 90% respectively.•Reaction temperature, liquid-gas ratio and urea peroxide concentration can control the removal efficiency of NOx.•Urea peroxide can efficiently remove NOx and inhibit the generation of nitrate. Marine exhaust gas is seriously harmful to the environment, and only using a single pollutant treatment device is difficult to meet the emission regulations. It is imperative to study integrated and efficient marine exhaust gas pollutant removal technology. This study proposes a novel process capable of removing NOx and SOx in marine exhaust gas, and this process can achieve higher NOx and SOx removal efficiency and lower nitrate concentration by using urea peroxide (CO(NH2)2·H2O2) combined with a countercurrent scrubber. The effects of reaction temperature, urea peroxide concentration, liquid-gas ratio (L/G), SO2 concentration and urea concentration in urea peroxide solutions on NO removal were investigated. The results showed that the temperature and liquid-gas ratio played the key role at a fixed urea peroxide concentration, and the NOx removal efficiency increased with the increase of temperature (from 23 ℃ to 80 ℃) and liquid-gas ratio (from 2 L/m3 to 6 L/m3). The NO removal efficiency of urea peroxide solution was really higher than that of mixed solution of urea and hydrogen peroxide. The NO removal efficiency can reach above 90% with proper operating parameters. The larger liquid-gas ratio can make the urea peroxide concentration decrease, and the NO removal efficiency still met the emission regulation. The use of onefold urea peroxide can not only achieve higher SOx and NOx removal efficiency, but keep lower nitrate concentration. This novel process can be applied in ships combined with exhaust gas cleaning (EGC) system.