Research And Design Of SCR Control System

With the development of the international marine shipping industry,the problem of exhaust pollution of large-scale marine diesel engines has become more and more serious,and NO_x in exhaust gas has caused great harm to the environment and human health.The Tier III standard for more stringent emission regulations has been introduced and implemented,and research on marine diesel engine emission reduction control technology has become a hot topic today.Among them,SCR is the most promising technical means,with the advantages of high NO_x conversion rate,easy realization of reaction process and no pollution to the environment.However,the core technology and product market of SCR are now occupied by foreign manufacturers.This paper studies the principle and working mode of SCR technology,designs and implements an SCR control system,and verifies the system function and emission reduction effect through experiments to ensure that Tier III emission indicator is satisfied.Based on the analysis of the research status of SCR technology at home and abroad,the overall design of the marine SCR system is carried out,clarify the working principle and composition of the system,propose the design plan,and carry out the selection of related components.SIEMENS PLC is selected as the system controller based on system function requirements,complete serial RS-422 communication with CAN network,design control system for the main actuator urea pump of the system.Perform PLC hardware configuration and programming to realize automatic system control.LabVIEW is selected as the PC development software,and the communication network between the PLC and the host computer is built through the S7 protocol to complete the SCR system monitoring interface.For the traditional SCR system PID parameters can not be set online,the catalyst model is established in Matlab,the urea injection amount is calculated,and the particle swarm optimization fuzzy PID controller is proposed.Through simulation comparison,the control performance is obviously superior to the traditional closed-loop control in terms of adjustment time,overshoot,anti-disturbance,etc.,and Simulink and LabVIEW co-simulation are designed to realize online self-tuning of PID parameters.Finally,the experimental verification of the designed SCR system function,test and verification system communication network,can realize the exchange of RS-422 and CAN communication modes.The function of the urea pump control system is normal.When the injection precision is below 2000ml/h,the relative error is less than 5%.Above 2000ml/h,the relative error is reduced to less than 2%,which meets the experimental requirements.The SCR system bench test was carried out.The results show that the NO_x conversion rate of the SCR control system can reach more than 80%when the reaction temperature reaches the optimal temperature of the catalyst,and the escape amount of NH₃ is less than 10ppm,which meets the marine SCR system standard and meets the IMO Tier III emission indicator requirements.