Study on removing NO from simulated marine diesel engine exhaust gas using the novel composite system of Ozone-Na2SO3/(NH2)2CO

Kinetic Study on the Reduction of Room-Temperature NOx in Etching Waste Gas by Na2S2O5 and Urea in Alkaline Pretreatment

“…After 2 h of treatment, the removal rates of NO 2 and NO x decreased from 85 to 68% and from 80 to 58%, respectively. Owing to the large consumption of Na 2 S 2 O 5 and the reduction in the SO 3 2– concentration, eqs and shifted to the left, and the removal rates of NO x and NO 2 were markedly reduced Na 2 normalS 2 normalO 5 + normalH 2 normalO → 2 Na normalH normalS normalO 3 2 Na normalH normalS normalO 3 → Na 2 SO 3 + normalH 2 normalO + SO 2 2 normalN O 2 + SO 3 2 − + normalH 2 normalO → SO 4 2 − + 2 normalN normalO 2 − + 2 normalH + 2 normalN normalO 2 + 4 normalS normalO 3 2 − → …”

“…This is because, in addition to Na 2 S 2 O 5 that needs to be consumed to remove NO 2 and NO x , the etching waste gas contains a large amount of O 2 , Cl 2 , and acidic waste gases such as HF, which can also oxidize SO 3 2– to SO 4 2– . This may explain why the SO 3 2– concentration required to reduce marine exhaust gas is high . The oxidation–reduction potential (ORP) of E SO 4 2– /SO 3 2– is −0.94 mV, and the ORP of the Na 2 S used for current etching waste gas treatment is −0.48 mV higher than that of E SO 4 2– /SO 3 2– .…”

“…After 2 h of treatment, the removal rates of NO 2 and NO x decreased from 85 to 68% and from 80 to 58%, respectively. Owing to the large consumption of Na 2 S 2 O 5 and the reduction in the SO 3 2– concentration, eqs and shifted to the left, and the removal rates of NO x and NO 2 were markedly reduced …”

“…Research on wet NO x oxidation–reduction methods has mainly focused on controlling the removal conditions; however, the mechanism of the reactions in these methods is still poorly understood . In addition, sulfites are inevitably oxidized by air during use, and transition metals such as Co 2+ , Mn 2+ , and Cu 2+ in exhaust gas have undesired effects on the oxidation reaction rate of sulfites.…”

“…The difficulty in dissolving NO results in the low denitrification effect of these methods. With oxidation–reduction absorption, NO is first oxidized to NO 2 , and then NO 2 is reduced to N 2 , thereby efficiently removing NO x with low residual amounts of nitrate. − …”