New experimental results of NO removal from simulated marine engine exhaust gases by Na2S2O8/urea solutions

Abstract

NO is the main precursor of photochemical smog. Since the SCR system of marine diesel engines has many disadvantages, this paper proposes an effective wet method to remove NO from the exhaust gases of marine diesel engines. Experiments were performed in a bubble column reactor to study the absorption of NO using sodium persulfate (Na2S2O8)/urea ((NH2)2CO) solutions from a simulated gas stream. The effects of various operating parameters on NO removal were investigated, including reaction temperature, urea concentration, Na2S2O8 concentration and the initial pH value of Na2S2O8/urea solutions. The experimental results showed that the NO removal efficiency increased with increasing reaction temperature (25–80 °C) and increasing Na2S2O8 concentration (0.01–0.2 mol/L). When the concentration of urea was higher than 0.5 mol/L at 60 °C, 1 mol/L at 70 °C or 2 mol/L at 80 °C, the NO removal efficiency increased with the increase of urea concentration (0.1–4 mol/L). The highest NO removal efficiency was 99.7%, occurring at 80 °C when the concentrations of Na2S2O8 and urea were 0.1 mol/L and 4 mol/L, respectively, and the concentration of nitrate was 14.93 mg/L. The optimal urea conditions were well below the legal limit of 60 mg/L. The NO removal efficiency increased with the increase of initial pH value within the herein investigated range of 7–9. All the experimental data showed that the novel system not only achieved effective NO removal efficiency, but also reduced the nitrate in wastewater, which could thus be applied to denitrification of marine engine exhaust gases.