Optimization Study Of Structure And Dimension For Diesel Engine SCR Catalyst

Shipping industry has been seeking for applicable technologies for NOx emission reduction to meet the MARPOL Tier Ⅲ, which sets strict NOx emission limits. Among various NOx reduction techniques, SCR is the one of the most effective measures recognized by the industry. As the key element of SCR system, catalyst is directly related to the NOx conversion capability, therefore, dimension design of the catalyst becomes an important research subject.Targeted on the 6105AZLD marine diesel engine, the SCR experimental platform is established and catalyst performance test carried out. Experimental results show that NOx conversion is less than 50% under all loads. Causes analysis indicates that inappropriate catalyst dimension leads to low NOx conversion. In this case, optimization design of SCR catalyst dimension is conducted in this paper.Firstly, the design scheme, key points and detailed design process are summaried by referencing to relevant literature. On this basis, the volume, section area and combination form of the SCR catalyst are preliminarily designed for the 6105AZLD diesel engine.Then, SCR catalyst model is established with AVL BOOST and its boundary conditions are set and calculated based on experimental data. To narrow the gap of catalyst activity between the model and the actual system, genetic algorithm is used to optimize the 13 kinetic parameters.Optimization result shows that the catalyst in the model and the actual catalyst have similar activity.Finally, the SCR model is utilized to analyze the effects of different structural parameters on catalyst performance. On the one hand, the different cell densities are modeled for the catalyst of fixed volume and the simulation results show that SCR performance indexes are not reached under distinct cell densities.On the other hand, optimal volume of the catalyst is initially explored and later other parameters are simulated and determined. Optimization results of the catalyst are 0.072 m3 in volume, 2×2 in section layout,30×30 in cell density and layer number is 2. Each layer is 0.4m in length. The NOx conversion, pressure drop and ammonia slip of the optimized catalyst are respectively 81%,237Pa and 7.5ppm, and the results comply with the design requirements.