Study On The Simulation Of Urea Injection And Mixing Uniformity Of Marine SCR System

Annex VI of MARPOL Convention and the establishment of the emission control zone make the existing NOx emission control technology difficult to meet the requirements.In several commonly used emission reduction technologies of NOx for ship,the SCR technology can meet Tier III standards alone.In SCR,the more uniform the urea solution and the exhaust gas mixture,the more uniform the distribution of NH3 and the higher the denitration efficiency.The distribution uniformity of urea solution and exhaust gas is mainly influenced by the atomization characteristics of urea and the structureoe the SCR system.This article selects a certain Marine SCR jet mixing system as the research object,and through simulating the process of urea water mixed with the diesel engine exhaust to determine the optimal nozzle scheme.At last the mixer of the SCR system is designed and analyzed.The main contents are as follows(1)Establishment of numerical model of jet mixing system.The corresponding computational model is chosen to solve the problem based on SCR working principle and the numerical simulation of jet mixing process by Fluent,then,3d modeling and grid division of the SCR jet mixing system are conducted,the initial conditions and boundary conditions are determined according to the parameters of diesel engine,which provides theoretical support for the simulation work below(2)Simulation research of nozzle parameters and layout plan.Factors such as distance of the injection point and the inlet of expansion pipe,height of nozzle,pore diameter and number of holes that influence the atomization quality of urea spray were studied by using Fluent to obtain the optimal nozzle scheme.(3)The design and effect verification of the mixer.According to the relevant parameters of the diesel engine,the working principle of the mixer and on the basis of the nozzle parameter,a new type of mixer is designed.In order to verify the effect of the designed mixer,Fluent is used to simulate different circumstances with mixers and without mixer.The simulation results show that mixer can effectively improve the mixing degree of urea water and exhaust gas,and the designed mixer has better effect.(4)Simulation research of the installation position and the structural parameters of the mixer.Based on the verified effect of mixer,the installation position and two structural parameters of the mixer were simulated and determined.According to the simulation results,the optimal installation location and structural parameters of the mixer determined in this paper are:C=1000mm,R1=30° and ?=45mm.