| Shipping transportation is a global trade,SO2 and other pollutants in the exhaust gases from operating emissions will adversely affect the atmosphere and the marine environment.To prevent air pollutions from SO2 in marine emissions,the International Maritime Organization(IMO)legislation stipulates that the sulfur content of vessels sailing within the Sulfur Emissions Control Zone(SECA)shall be not more than 0.1%wt since 2015;the sulfur content of vessels shall be not exceed 0.5%wt outside the SEC A,since 2020.In order to meet the requirements of the regulations,the marine exhaust gas desulfurization technology is the most feasible.In this paper,the combination of theoretical and experimental methods are used to research the SO2 absorption,the oxidation of sulfite and the comprehensive treatment of waste water in the exhaust gas scrubbing technology of sodium-alkali ship.Then,the verification study of the related engine matching of exhaust gas desulfurization system and the conprehensive evaluation about index system of exhaust gas desulfurization technology are established,and aim to provide reference for the research of related technology.In this paper,the mechanisms of SO2 absorption by using sodium-alkali are studied,and the main factors influencing the absorption process of SO2 are confirmed.The influence of SO2 absorption rate and efficiency are obtained by decreasing the equilibrium concentration of SO2 in absorbent solution,and increasing the partial pressure of main gas-phase.Priority is given to the presence of a chemical absorption process.The parameters of the internal and the 3D flow field in the scrubber are optimized to improve the total mass transfer coefficient of the gas phase and increase the effective area of the gas-liquid contact.The influence of parameters such as liquid-gas ratio,inlet parameters,absorbent parameters and operating pH values on desulfurization efficiency are studied by diesel engine exhaust gas desulfurization experiment system The results shows that the desulfurization efficiency increases with the increasing liquid-gas ratio,the higher pH value of the scrubbing solution and the concentration of Na+,the lower SO2 concentration of inlet and ratio of sulfate radical,and the decreasing exhaust gas temperature.The effect of CO2 concentration on the desulfurization efficiency is negligible.In this paper,the desulfurization efficiency model of sodium scrubbing was established.The ratio of liquid to gas,Na+ concentration,pH of absorption solution,ratio of sulfate ion and SO2 concentration of exhaust gas were integrated into a dimensionless parameter which is e.The relationship between desulfurization efficiency and the comprehensive influencing factors is given,which provides a new method for the design and optimization of the scrubbing system.In this paper,the oxidation process of sulfite is investigated experimentally.The effects of different factors were compared.The optimum parameters shows as follows:the initial concentration of sulfite 1.5 mol/L,the initial pH 5.5,the oxidation temperature 25?,air flow rate 0.4 m3/h,sulfate concentration 0.12mol/L.Comnpared with the main factors influencing the coagulation process,flotation process and adsorption process of desulfurization waste water comprehensive treatment,the results of the research indicated that factors affecting coagulation process of waste water treatment follows the order:the dosing of coagulant concentration,pH value,reaction temperature,mixing speed,mixing time and precipitate time.The influence factors on flotation process are respectively as follows:reflux ratio,dissolved air pressure,flotation time,treated water quality,pH value and coagulant dosing quantity.In addition,the activated carbon dosage,activated carbon adsorption time and pH value have the diminishing influence on activated carbon adsorption process.A pilot-scale 4.2MW exhaust gas desulfurization system is built up to study matching experiments,and the experimental engine is MAN 5S50ME diesel engine.The results show that:in the case that the fuel sulfur content was 3.5%(m/m),the SO2 bulk concentration of the exhaust gas under various operating conditions is less than 6.0 ppm,and the data has a good stability.The pH value,turbidity and PAH contents in the desulfurized waste water treated by the waste water treatment system can fuly satisfied MEPC184(59)regulations.All index of proposed 4.2MW marine exhaust gas desulfurization study system meet the relevant regulations of the IMO regulations.The results of the theoretical analysis and laboratory studies are verified.Finally,based on the data obtained,economical efficiency of the marine exhaust gas desulfurization technology by using the sodium-alkali is analyzed,the system investments,operating costs and payback period were obtained.Based on the economic analysis,the research focuses on a comprehensive evaluation model,which includes four categories:environmental performance,technical performance,economic performance and system adaptability was established.A conprehensive evaluation has been investigated about three kinds of marine desulfurization technologies(sodium-alkali method,seawater method and calcium base dry method).When the marine exhaust gas scrubbing system was installed to meet the IMO regulations on the sulfur content of fuel oil,the sodium-alkali method is optimal,and the seawater method is superior to the calcium base dry method.The above-mentioned research in this paper reveals the law characteristics of the SO2 absorption,oxidation of sulfite and the cornprehensive treatment of waste water.The researches provides references for the research and development of marine exhaust gas desulfurization technology. |
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