New Experimental Results of NO_x Removal from Marine Diesel Engines by the Ozone/Urea System: Removal Efficiency and the NO_x Conversion Ratio

Abstract

Ship exhaust gas greatly threatens human health and the environment. The ozone/urea system has the advantages of strong oxidability, excellent reducibility, and low reductant consumption. This paper thoroughly studied the effects of urea concentration, O3 concentration, initial pH, temperature, O2 concentration, SO2 concentration, and initial NO concentration on NO x removal efficiency using the ozone/urea system. Moreover, this paper conducted a systematic study on the conversion proportion of NO x into nitrate and nitrite, which is very important for the ship NO x wet method. Urea concentration and O3 concentration played important roles in NO x removal efficiency. Weak acid and weak alkali media could effectively improve NO x removal efficiency, but the reasons were completely different. As the temperature increased, the NO x removal efficiency initially decreased and subsequently increased. Besides, the increase of temperature and initial pH could decrease the conversion proportions of NO x into nitrate and nitrite. The increase of SO2 concentration could not only reduce the NO x removal efficiency but also increase the conversion proportion of NO x into nitrate. However, increasing SO2 could significantly decrease the conversion proportion of NO x into nitrite. Under the optimal conditions of this paper, the NO x removal efficiency reached 97.8% and the conversion proportion of NO x into nitrate was only 20.39%. In addition, the urea content was just 0.3 mol/L, which was far lower than that in the prior study. This illustrated that the ozone/urea system had excellent application potential in marine exhaust gas purification.

Recyclable Iron Reduction Denitration: A Strategy for Removal of Nitrogen Oxides

“…Nitrogen oxides (NO x ), comprising mainly NO, NO 2 , N 2 O 3 , N 2 O 5 , and N 2 O, have always been one of the major air pollutants around the world . Stationary sources including power plants and industrial boilers, as well as motor vehicles, aircraft, and other mobile sources, are generally major contributors to NO x emissions, which lead to a range of atmospheric pollution problems such as ozone depletion, acid deposition, and photochemical smog. , Various effective approaches of NO x abatement including the selective catalytic reduction (SCR), selective noncatalytic reduction (SNCR), nonthermal plasma, electrochemical reduction, and absorption method have been adopted to meet the stringent environmental regulation for NO x . − Among them, SCR is currently the most mature and widely used NO x removal technology due to its high denitration efficiency and preferable selectivity. , SCR technology allows the reducing agent to selectively react with NO x in the presence of catalysts . At 300–420 °C, NO is catalytically reduced to N 2 with the denitration efficiency of more than 90%. , With ammonia as the reducing agent, NH 3 –SCR reveals the advantages in the wider operating temperature window, high NO x removal efficiency, and high N 2 selectivity .…”