Research And Application On Control System Of Low Temperature Multi-effect Distillation Seawater Desalination With Thermal Vapor Compression

At present,25% of the world population is lack of fresh water supplies, more than 80% countries have serious water problems. Seawater desalination has become an important means to offer water shortages in the world. From the point of economic benefit and water quality, low temperature multi-effect desalination technology is one of the main desalination method, especially suitable for power plants and iron and steel enterprises.The research object of this dissertation is low temperature multi-effect distillation seawater desalination system with thermal vapor compression. According to the characteristics of the seawater desalination system, the concentrated salt water level control defects of the existing system was discussed, a fuzzy-PID controller was designed to realize the effective control of concentrated salt water level, which helped to improve the stability of the operation of seawater desalination system.The main works in this dissertation are as followings:(1)Introduced the process of low-temperature multi-effect seawater desalination (LT-MED) with thermal vapor compression desalination in Shougang Jingtang, analyzed the working principle and function of the thermal vapor compressor(TVC), studied the thermal performance index of the seawater desalination system;(2) Analyzed the characteristics of the seawater desalination system controlled process, the history data including the main inlet temperature, pressure of seawater desalination, feed water flow, condensate water, distilled water and concentrated salt water level was collected, the trend of the above data and the relative factors affecting the stability of concentrated salt water level was studied.(3) Studied the concentrate salt water control strategy and experimental scheme, proposed a fuzzy PID controller based on the analysis of the defects existing in level control method.(4) The tuning rules of fuzzy PID parameters and the fuzzy inference rules was established, and the fuzzy controller for concentrated salt water was designed according to the collected data from the industrial field and expert control experience.(5) Designed hardware architecture and software program of the automatic control system of the seawater desalination procedure, developed the man-machine monitoring interface on the platform of siemens s7-400 PLC according to the design principle of the control strategy, interlock and alarm was set based on the control logic requirements, and realized the monitoring and control of seawater desalination.The design and optimization of the above control system in this dissertation realized the effective concentrated salt water level control, improved the water generation ratio of low temperature multi-effect distillation seawater desalination system with thermal vapor compression in shougang Jingtang.The applications of the system shows that the concentrated salt water level fuzzy PID control helps to improve the response time, optimize the dynamic response performance, reduces the steady-state error of the system, and meet the concentrated salt water level control requirements, which provides a guarantee for the stable operation of seawater desalination system and has a strong practical application.