Study On Modeling And Control Of Low Temperature Multi-effect Distillation Seawater Desalination System

With the world population growth,economic development and environmental pollution,the global total amount of fresh water is decreasing.The earth is rich in seawater resources,which is convenient for development.Therefore,seawater desalination is one of the effective solutions to solve the crisis of water resources.In order to improve the performance of seawater desalination system and better guide the actual factory to produce fresh water,it is necessary to study the low-temperature multi effect seawater desalination system.The main contents of this paper are as follows:(1)The steady-state model of the low-temperature multi effect seawater desalination system is established,and three different process flows,i.e.forward flow,horizontal flow and reverse flow,are constructed.The effects of system efficiency,feed seawater temperature,heating steam temperature and steam ejector extraction position on the system performance are analyzed by using Aspen software.(2)Considering the instability of the system when it just starts or encounters external interference,the dynamic model of the system is established based on the established steady-state model of the system.By adding external interference to the system,the dynamic response of the system with time is analyzed.The results show that the controller in Aspen software has poor anti-interference performance.Therefore,this paper uses aspen and MATLAB to improve the joint simulation method,and designs a model predictive controller in MATLAB to replace PID to achieve more stable control of the system.The results show that the joint simulation shortens the adjustment time of system response and improves the defect of poor anti-interference of Aspen controller.(3)Aiming at the inaccuracy of the evaporator model in Aspen software,the temperature model of the first effect evaporator is established separately,and the L1 adaptive state feedback controller is designed for local optimization and control.At the same time,considering that the evaporator temperature model may have parameter changes in the actual operation process,the identification effect of L1 adaptive controller for model parameters is analyzed.The analysis results show that the controller has excellent anti-interference and robustness,and can effectively resist external disturbances and model parameter changes.(4)According to the previous system modeling and control research,the software and hardware of the low-temperature multi effect seawater desalination control system are designed.At the same time,a remote monitoring software for the low-temperature multi effect seawater desalination system is developed using QT software based on the wireless communication mode of 4G network and c/s mode,aiming at the disadvantages of the poor on-site monitoring environment,difficult conditions and high labor cost of seawater desalination,It is used to display the data collected by the field sensor on the PC monitoring software,which can facilitate the staff to view the running status of the field equipment in real time and remotely.In this paper,for the low-temperature multi effect distillation seawater desalination system,the steady-state and dynamic models of the system are established,and the joint simulation and the temperature control of the first effect evaporator are realized.Based on this,the overall design of the system is carried out,which has guiding significance for the actual seawater desalination plant to produce fresh water.