A prospective absorption system for marine NOx removal from simulated gas using Na2SO3/urea composite absorbents in bubble reactor

Abstract The large amount of NOx emitted from ships causes great harm to the environment and to health. Due to the strict regulations on NOx emission, it is urgent to develop a marine NOx absorption technology with efficient NOx removal and less nitrate residue in scrubber water. This paper proposed a novel composite Na2SO3/(NH2)2CO absorption system that could efficiently absorb NOx from ships. The NOx absorption process was studied in combination with a bubble reactor. Na2SO3 could react with NOx to convert the N into nitrite and N2, and (NH2)2CO could reduce the nitrate, nitrite, and NOx to N2. The main key parameters such as Na2SO3 concentration, (NH2)2CO concentration, SO2 concentration, oxygen concentration, NOx oxidation degree, initial NOx concentration, initial pH, and temperature were investigated experimentally. The Na2SO3 concentration had great effects on the NOx absorption efficiency. The nitrate concentration was significantly affected by the absorbents concentration, the NOx oxidation degree, the temperature, and the O2 concentration (0%–8%). Acid condition was not conducive to NOx absorption. A NOx absorption efficiency of 92.3%, a nitrate content of 13.1 mg/L, and the nitrite content of 21.3 mg/L were achieved under the optimal conditions in which, Na2SO3 was 0.25 mol/L, (NH2)2CO was 0.4 mol/L, SO2 was 700 ppm, NOx oxidation degree was 20%, initial NOx was 1000 ppm, and O2 was 12%. The Na2SO3/(NH2)2CO absorption system satisfied the regulations on NOx removal efficiency and nitrate concentration of scrubber water and therefore showed excellent application prospects on ships.