Experimental Research On NO_x Removal From Marine Diesel Engine Exhaust Gas Based On NaClO₂-Seawater Solution

With the rapid development of the world’s trade and marine transportation, the number of ships has been increased dramatically. The air pollution caused by marine diesel emissions becomes more and more serious, which much more concern worldwide. Thus, International Maritime Organization (IMO) released MARPOL Convention Annex VI, which aims to reduce air pollution caused by ships. In 2016, a more stringent standard for NOx emission control, Tier III, will be enforced into accomplice. For implementation of the convection, the international research institutions raised a variety of techniques to reduce NOx.Based on the comprehensive analysis of the characteristics of the existing NOx removal technology, this paper proposed NaClO2-seawater wet NOx removal technology. That is, using seawater as solvent to prepare NaC102 solutions. The application of this technology is expected to achieve comprehensive processing of marine diesel emissions.Firstly, this paper investigated the effect of HCl addition on the properties of NaC102 seawater and NaClO2 fresh water solution. It turned out that NaClO2 seawater solution exhibits good alkalinity-keeping ability. When the pH value drops to about 4, a greenish yellow color was observed in both solutions, which ClO2 forming is confirmed. The formation of ClO2 can be suppressed successfully by using seawater at the pH range of 5-8. Moreover, experiments were performed to study NOx removal performance of NaClO2 seawater and NaClO2 freshwater. The results showed that the rate of NOx removal in NaC102 seawater is slightly lower than that in NaC102 fresh water, but the duration of NOx removal in NaC102 seawater is about twice.Then, this paper studied the effect of concentration of NaC102, NO, and SO2, and the effect of solution temperature on NOx removal rate. The results showed that the removal rate will be increased by increasing the concentration of NaClO2, SO2, solution temperature and plus reducing the concentration of NO. On the other hand, the removal duration will be reduced by increasing SO2 concentration and solution temperature.Finally, according to the experimental results, this paper designed the two-stage marine diesel emissions integrated processing system and calculated the operating cost based on real diesel engine. The results showed that the NaClO2 cost was17.9 yuan/kgNO, close to the operating cost of SCR system and ozone oxidation NOx removal system. But the NaClO2 seawater NOx removal system has many advantages, such as the seawater was easy to get, SO2 can be removed simultaneously and so on. Besides, the operating cost can be further reduced by optimize the reaction conditions and add catalyst. Hence, the NaClO2 seawater suits for NOx removal in marine diesel emissions.