The Numerical Simulation And Optimization Of SCR Reactor For Marine Diesel Engine

According to the MARPOL Annex VI，NOxemission limits of marine diesel engine arebecoming increasingly strict. SCR technology is one of the promising ways for reducing NOxemission of marine diesel engine，which has many advantages such as unchanging basic enginestructure，high denitration and economical efficiency，wide applicable temperature range and soon.In this paper，simulation model was established for the SCR system for a marine dieselengine，and simulation analysis was carried out by using AVL BOOST and FIRE softwares.Themain research contents included the design and optimization of SCR reactor，the performanceanalysis of SCR reactor under different working conditions and the performance matchinganalysis of the whole engine.Firstly，the exhaust gas data on E3and D2test cycles were measured on test bed and thebasic structure sizes of the SCR reactor were calculated on the basis of the correspondingexhaust gas data. The1D simulation model of SCR reactor was built by using BOOST softwareand the influence of different reaction conditions and the structure sizes on SCR reactor’sperformance were analyzed by simulation.Then the structure sizes of SCR reactor wereoptimized by RSM method.The optimization results show that the cross-sectional area of SCRreactor is0.069m2，the length is0.974m，CPSI is140/in2，the thickness of catalyst support wallis0.15mm and the thickness of washcoat is0.01mm.Secondly，the3D model of the SCR reactor was established by using FIRE software. Thenthe3D flow distributions within SCR reactor at different expansion angles were analyzed in thepaper.The results show that the distribution area of NH3in the reactor reaches the maximumvalue and the pressure drop reaches to the minimum value when the expansion angles is90o.Moreover，when the expansion angles is90o， the performance of SCR reactor under differentworking conditions of the engine were analyzed in this paper. The simulation results show thatthe reaction rate and NOxconversion efficiency is lower and the amount of NH3slip is higherunder low load condition comparing with those under high load condition，which is because theexhaust gas temperature and exhaust mass flow is lower and the catalytic activity is weakerunder low load condition of engine.Lastly，the simulation model of diesel engine with SCR reactor was established and the influence of SCR reactor on power and economy performance of marine diesel engine wereanalyzed by using BOOST software in the paper.The results show that after structuraloptimization，the deduction of power and the raise of fuel consumption brought from SCRreactor are both within5%of the correspondent values of the diesel engine without SCR reactorunder the whole working condition range，which proves that the optimized structure sizes of theSCR reactor basically meet the matching requirement of the diesel engine.