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Marine diesel engines produce exhaust gas including a lot of SO2 and NOx. This paper proposes a process that is capable of removing NOx and SO2 simultaneously; this process utilizes ozone oxidation and an alkaline countercurrent packed scrubber. Ozone decomposition, oxidation properties of NOx, and removal efficiency of NOx and SO2 were investigated, and the optimal factors were established. The reaction mechanism and products for simultaneous desulfurization and denitration were deduced. Results show that the ozone decomposition rate depends on exhaust gas temperature and initial concentration of ozone. Oxidation efficiency of NOx decreases as temperature rose and initial concentration of ozone reduced. The presence of SO2 has little influence on NO conversion process. CO­(NH2)2 is the best reducing additive to reduce the consumption of ozone. The optimal factors for SO2-reduction and NOx-reduction were achieved, such as temperature of 150 °C, stoichiometric ratio between ozone and NO of 0.6, and pH about of 8 by alkaline absorption. With this method, about 93% NOx and close to 100% SO2 can be removed at same time and regulations of the international maritime organization (IMO) can be met.

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Marine diesel engines produce exhaust gas including a lot of SO x and particulate matter (PM), and laws have been promulgated to regulate ship exhaust emissions. This paper proposes a U-type exhaust gas cleaning (EGC) system that is capable of removing SO 2 and particulate matter (PM) simultaneously. The purpose of this study was to find the relationships between removing efficiency and parameters of EGC system, then get the optimal structural and operational parameters. The experimental results show that the SO 2 absorption rate in the scrubber was mainly influenced by liquid−gas ratio, pH value, and temperature in the range of experimental operating conditions. With the system stable running, when the liquid−gas ratio and temperature were determined, the pH value must be in a fixed range of 6.5−7.5. The further research was also carried on for the EGC system applicable to ships. On the basis of SO 2 removal efficiency, the prediction and experimental validation of particulate matter (PM) were studied. When comparing the results of prediction and experiment, the data show good agreement. PM removal efficiency was related to liquid−gas ratio, droplet size, and height of chamber. The height of spray chamber was the key structure factor, and the droplet size was the operational parameter affecting PM removing efficiency. The increasing of liquid−gas ratio both could lead to an increase in the SO 2 and PM removal efficiencies. Thus, according to this study, the usage of EGC system can removed SO 2 and PM at same time, and it can satisfy future ships emissions regulations. The theoretical analysis and experimental results of scrubber can be extended to apply in marine exhaust gas after-treatment technologies.

Abstract:The International Maritime Organization (IMO) Marine Environment Protection Committee (MEPC) and some countries have gradually strengthened the laws regulating ship exhaust emissions. The aim of this paper is to estimate the impact of an after-treatment technology exhaust gas cleaning (EGC) system on marine diesel engine emissions and the cost advantage compared to using low-sulfur fuel oil. The emission characteristics of SO 2 and particulate matter (PM) produced from high sulfur oil and low sulfur oil in a low-speed two-stroke marine diesel engine were also presented. The removal efficiency of SO 2 has been tested and the PM removal efficiency was also predicted in this study. When using high sulfur oil, the emission factor of SO 2 and PM were from 8.73 g/kWh to 11.6 g/kWh and 2.0 g/kWh to 2.7 g/kWh, respectively. These values are significantly higher than the emission values from using low sulfur oil. The fuel sulfur content (FSC) was the key factor affecting the emission factors of SO 2 and PM. The fuel change could reduce the mass emission factor of PM, which is above 90% for the total particle emission with the two fuels. When using the EGC system, the desulfurization efficiencies were above 99%. The pH values at a 25, 39, 53, and 67% load were also stabilized to be around 7.5, 7.6, 7.7, and 8, respectively. The EGC system can also capture part of the primary PM and secondary PM formed from SO 2 . The EGC system was more effective for PM of the size larger than 1 µm. Thus, according to this study, the usage of low sulfur oil and EGC will also substantially decrease the emission of currently unregulated hazardous chemical species in the exhaust gas of ships in addition to satisfying future emissions regulations of ship. Furthermore, the EGC system also had a significant cost advantage compared to using low-sulfur fuel oil.