Simultaneous Desulfurization And Denitration By Seawater Mixed With Persulfate

Sulfur oxides(SOX) and nitrogen oxides(NOX) from ship emissions are being strictly regulated due to implementation of the new emission standards for ship emissions. However, conventional pollutants control systems, generally consisting of desulphurization and denitration facilities in series, show many shortcomings such as complex processes, high operating cost, and large cover area, etc. Hence, a new method has been proposed in current work to simultaneously capture SOX and NOX. Persulfates were added into seawater to enhance the uptake of SOX and NOX in seawater. Effects of reaction temperature, retention time, pH value, concentrations of persulfates, and types of persulfates on the simultaneous removal of SOX and NOX were analyzed. Moreover, technical feasibility was discussed and optimal operation conditions were obtained accordingly. Conclusions can be drawn as below.Seawater can remove SO2 of low concentration at low temperatures while show a sharply decreased efficiency at high temperatures. Meanwhile, seawater shows no obvious effect on the uptake of NO. The addition of persulfates in the seawater shows a promotion effect on the capture of NO. Simultaneously, the adsorption efficiency of NO in seawater is associated with reaction temperature, initial gas concentration, concentrations and types of persulfates. To be specific, the uptake efficiency of NO in the seawater is reversely related to the reaction temperature and initial NO concentraion while positively correlated with the concentration of persulfates. SO2 shows dual effects on the uptake of NO in seawater. The presence of low concentration SO2 can enhance the capture of NO while high concentration of SO2 will inhibit the adsorption of NO in the seawater due to the competitive adsorption. Among the three types of persulfates, potassium persulfate shows slightly higher prompting effects on the uptake of NO than the other two persulfates.Further mechanism analysis indicated that S2O82- ions from persulfates could produce radicals OH· and SO4-·. The generated radicals, as well as the S2O82- ions, can oxidize captured NO and SO2 to NO2- and SO42-. Moreover, NO2- can be further oxidized to NO3-with the presence of OH·, SO4-· and S2O82- ions. Hence, how to effectively activate S2O82-to form OH· and SO4-· become the key issue. According to the experiment results, SO2 can be totally removed and 80 % of NO can be captured even after 30 min when the temperature is around 90 °C and concentration of persulfates is no lower than 0.3mol/L.