Research On Key Technology Of SCR DeNO_x System For Small And Medium-sized Ships

As the MARPOL convention continues to advance,all countries must adopt advanced NOx emission control technologies to meet the requirements of emission regulations.Selective catalytic reduction technology is one of the mature and reliable post-treatment technologies,so it is of great significance to develop the key technology related to marine SCR system for energy conservation and emission reduction.In this paper,the physical and chemical properties of the SCR catalyst was firstly characterized via N₂ adsorption-desorption,SEM-EDS,XPS and XRF,through which element distribution,pore size distribution and morphology were discovered.It was found that the active component is V₂O₅,and Al₂O₃is the support.Moreover,the distribution of V₂O₅in Al₂O₃ isn’t uniform,with the content descending from the core to the surface.In-situ IR was used to investigate the SCR mechanism over the catalyst via transient response methods,such as NH₃-TPD,NO+O₂-TPD,NH₃-TPSR and NO+O₂-TPSR.The Eley-Rideal mechanism was recognized.Based on the activity test,the kinetics model was derived.The results show that the SCR activation energy is 36.5k J/mol,while the NH₃oxidation one is 78 k J/mol.The effect of internal diffusion was also found,and the effective coefficient for SCR is 0.324,while for NH₃ oxidation is 0.636.Since the effective coefficient of NH₃ oxidation is higher than that of SCR,the NH₃ oxidation is a body reaction while SCR is a surface reaction.Based on the standard catalyst module,the SCR reactor structure was initially designed,and the three-dimensional structure model of the reactor was established.The flow uniformity and pressure loss inside the reactor were analyzed by numerical simulation with FLUENT software.On the basis of the original model,the inlet velocity,catalyst layer spacing,catalyst module length and the number of catalyst layers were changed to analyze and compare the variation law of velocity distribution uniformity and pressure loss in the reactor.The results show that with the decrease of the reactor inlet velocity,the velocity distribution uniformity increases gradually,and the pressure loss at the reactor inlet and outlet and the front and rear end faces of the catalyst decreases gradually.With the increase of the catalyst layer spacing,the smaller the velocity relative standard deviation is,the better the flow uniformity is.Compared with the catalyst module with a length of 450mm,the catalyst with a length of300mm has a poor uniformity of velocity distribution,but a small pressure loss.Compared with two-layer catalyst,three-layer catalysthas higher velocity distribution uniformity,but larger pressure loss.With the decrease of loads,the conversion rates of NO and NH₃ were gradually reduced,and the conversion rates of NH₃ were greater than that of NO.Meanwhile,the conversion rates of reactants of three-layer catalysts were slightly greater than those of reactants of two-layer catalysts.