Simulation Study On Structure Downsizing Of SCR Reactor Of Marine Diesel Engine

With the emission regulations of marine diesel engines becoming increasingly stringent,it is an inevitable trend to configure exhaust after-treatment device on marine diesel engines.In particular,with TIER?emission regulations putting into effect,the selective catalytic reduction(SCR)plays an increasingly important role in reducing NOx emissions from marine diesel engines.However,due to the bulky SCR system of marine diesel engine,it is very indispensable to carry out the study about the downsizing of SCR system.The structure of the reactor was systematically optimized.First,a 1D model of an SCR reactor containing inlet,urea nozzles,SCR reactors and outlet was established using the AVL BOOST software,the chemical reaction kinetic parameters appeared in the reactor were calibrated.The results show that,the NOx conversion rate obtained by the simulation is closer to the experimental data.Then the effects of structural parameters such as catalyst length,cross-sectional area,CPSI,coating thickness and substrate wall thickness,et al,on NOx conversion rate and pressure drop were studied under different loads of diesel engine.The structural parameters that have a great influence on NOx conversion rate and pressure drop were obtained.Next,using the RSM(response surface method)to optimize the structural parameters of the catalyst,the optimized structural parameters are:catalyst cross-sectional area is59612 mm~2,length is 190 mm,CPSI is 350,coating thickness is 0.01 mm,substrate wall thickness is 0.21 mm.When using the optimal structural parameters,the NOx conversion rate of the SCR reactor is 94%,the pressure drop is 733.9 Pa,the catalyst volume is 11.4 L.The total volume of catalyst was reduced by 31.3%compared to before optimization.Based on the above research,a 3D model of SCR reactor with single branch was established by using the AVL FIRE software,the number of layout layer and layer spacing of catalyst were studied by simulation.It was concluded that appropriate increase of the catalyst layer number and layer spacing can improve the performance of the reactor.When the number of layout layer was 2 and layer spacing of catalyst was 24 mm,the performance of the SCR system was best.Finally,3D models of SCR reactor with multiple branches were established by using the AVL FIRE software.As the number of the branch increased,NOx conversion rate tended to increase and reached the maximum when the number was 3.With the increase of branch road,the change of pressure drop was not obvious,in 995~1050 Pa.