Design Theoretical And Experimental Research On The Denitrification Reactor Of Hydrolysis Ammonia Production For Diesel Engine

According to the selective catalytic reduction(SCR)and the analysis of the characteristics of mobile source urea hydrolysis mechanism of aunonia technology,a urea reactor based on map for urea hydrolysis of SCR was developed.Through the simulation of urea hydrolysis device,the optimization model of the approximate model of denitration catalyst,the design of the software and hardware of the control system and the performance test of the platform,the influence of urea hydrolysis unit denitration catalyst and its control system on the denitrification process was studied systematically under different structures.In order to achieve the goal of high efficiency denitrification,an effective way to control urea hydrolysis ammonia production and selective catalytic reduction process of urea from mobile source was explored.It lays a theoretical foundation for engineering application of mobile source urea hydrolysis SCR technology.As the main emission source of nitrogen oxides(NOx,commonly known as nitrate)in China,it is urgent to reduce NOx emissions from diesel engines.SCR system,which mainly uses urea pyrolysis to produce ammonia,has been widely used to remove nitrogen oxides from diesel engine because of its better denitrification efficiency and resistance to sulfur dioxide poisoning.However,there are some disadvantages in this technology,for example,urea droplets are easy to form deposits,urea water spray,evaporation,decomposition and mixing affect ammonia conversion efficiency,ammonia leakage is difficult to control and so on.And the core technology is in the hands of foreign companies.Therefore,it is urgent to develop SCR denitrification technology with high efficiency and low denitration cost and independent intellectual propety rights suitable for China's national conditions.Compared with urea pyrolysis SCR,urea hydrolysis SCR has the advantages of simple mechanism,no deposition,low denitrification cost and so on.It is a kind of SCR denitrification reactor with great development potential.In this paper,a urea hydrolysis SCR denitrification reactor based on map is designed.The reactor consists of two parts in series,urea hydrolyser(producing ammonia)and denitration catalyst(removal of NOx).First,on the basis of the urea hydrolysis mechanism studying a method of urea hydrolysis ammonia for vehicle was put forward.The structure design of SCR urea hydrolysate for vehicle was carried out.The solid model was established by CATIA,and the three-dimensional structure model of SCR urea hydrolyser was established by FLUENT software.The temperature field,pressure field and exhaust flow field were simulated and tested.According to the NOx emission concentration,exhaust temperature and other exhaust parameters map of JX493ZLQ3 diesel engine,as well as the denitrification capacity and ammonia escape rate of the reactor,the structure parameters of SCR urea hydrolyser were obtained,and the SCR urea hydrolyser was simulated and optimized.The reactor structure is optimized according to the result,and the reactor structure is designed to meet the demand of velocity uniformity.Secondly,on the basis of the study of the mechanism of ammonia catalytic reduction reaction,the structure of the SCR denitrification catalyst was designed by simulation and genetic algorithm.Asingle channel model is used to simulate the catalyst and a catalyst calculation model is established in the AVL BOOST platform to study the related factors of the catalyst.The Kriging approximation model is established on the basis of Latin hypercube sampling points,and the NSGA-II(Non-dominated,Sorting,Genetic,Algorithm)algorithm is used to optimize the structure parameters of the catalyst.The structure design of catalyst is carried out by this calculation result.Considering the universality,applicability and cost of catalyst,catalyst was chosen,and then the catalyst was loaded onto cordierite carriers by dipping method.Thirdly,a two level control method is proposed to adjust ammonia and urea.The control system of ammonia hydrolysis denitrification reactor for vehicle is developed,and the process control of selective catalytic reduction is realized.Through the analysis of the hydrolysis mechanism and catalytic mechanism,the design of SCR control strategy for urea hydrolysis was carred out.The basic structure of the control strategy of urea hydrolysis SCR includes the basic parameter module,the solution mass concentration detection module,the product gas demand module and the urea hydrolysis module.On this basis,Renesas UPD70F3380 microcontroller is used to design control circuit.After the initial completion of the core design of the electronic control system,through the careful analysis of the program software requirements,formulate a reasonable software architecture has been formulated.Then,the main program design,CAN communication program design and AD acquisition program design are carried out respectively.Finally,a urea hydrolysis SCR denitrification reactor test bench was set up.The structure and property of urea hydrolyser test were carried out,and the influence of heating temperature and initial concentration of urea solution on hydrolysis ammonia prodution process was studied by the test.On this basis,the material balance check test was carried out.Through the ESC experiment which is the experiment of the thirteen operating point and its intermediate operating point,the basic steady hydrolysis ammonia control map was obtained.Through the ETC experiment,the transient urea slow control rate was calibrated to achieve the target value of ammonia gas and NOx and meet the requirements of steady-state transient.