Study on Ship Exhaust Gas Denitrification Technology Based on Vapor-Phase Oxidation and Liquid-Phase Impingement Absorption

Abstract

A system combining gas-phase oxidation and liquid-phase collision absorption for removing NO from marine diesel engine exhaust was proposed. This method was the first to utilize different physical states of the same mixed solution to achieve both pre-oxidation and impingement reduction absorption of exhaust gases. During the pre-oxidation stage, a mixture of (NH4)2S2O8 and urea solution was atomized into a spray using an ultrasonic nebulizer to increase the contact area between the oxidant and the exhaust gas, thereby efficiently pre-oxidizing the exhaust gas in the gas phase. In the liquid-phase absorption stage, the (NH4)2S2O8 and urea solution was used in an impingement absorption process, which not only enhanced gas–liquid mass transfer efficiency but also effectively inhibited the formation of nitrates. Experimental results showed that, without increasing the amount of absorbent used, the maximum NO removal efficiency of this method reached 97% (temperature, 343 K; (NH4)2S2O8 concentration, 0.1 mol/L; urea concentration, 1.5 mol/L; NO concentration, 1000 ppm; pH, 7; impinging stream velocity, 15 m/s), compared to 72% using the conventional liquid-phase oxidation absorption method. Additionally, this method required only the addition of a nebulizer and two opposing nozzles to the existing desulfurization tower to achieve simultaneous removal of sulfur and nitrogen oxides from the exhaust gas, with low retrofitting costs making it favorable for practical engineering applications.