Design And Research Of Automatic Monitoring And Control System In 40, 000 Tons Sewage Treatment Plant

With the improvement of living standards and the needs of sustainable development, sewage treatment has aroused much attention of the society. It can play a role in environmental protection, and can deal with water reuse to conserve water resources. In order to improve the quality and efficiency of sewage treatment, and save manpower and raw materials, designing an automatic monitoring system is very necessary. This thesis takes Yuncheng County Sewage treatment plant as an example, introducing the overall design plan of middle and small scale Sewage treatment plants' automatic monitoring systems.Yuncheng County Sewage treatment plant uses invert A~2/O processing technique and conducts sewage treatment 40,000 tons per day. The whole supervisory system consists of three parts. The first part is field data collection, which completes the data acquisition function. The second part is scene control unit. It is divided into two parts—scene control cubicle and the PLC station. Scene control cubicle mainly completes the task of hand control; PLC stands mainly competes the tasks of data processing, automatic control and communication. The third part is superior monitoring. The main function of it is to monitor the operation of various technical processes and implement remote control.This system takes OMRON Corporation's PLC, CJ1M and SIEMENS Corporation's PLC, and S7-300 and S7-200 as data acquisition and the control unit, coordinating each kind of examination measuring appliance and the control device to collect the data of several control quantities—sewage fluid position, current capacity, pH, temperature and dissolved oxygen concentration. At the same time, according to the request of the control, every field apparatuses like coarse and fine grids, lift pump, air blower carries are on corresponding control. According to technical process and control request, five stations which are connected with senior PC by Ethernet are established. Senior PC exchanges data with each station through Kingview of Asia-control, thus centralized-control are realized. This thesis introduced the overall project design, the design of each PLC station, the monitor of key parameter, the sequence of technical process, communication network and PC monitoring software.The dissolved oxygen (DO) which is an important parameter of attribute water quality in the process of sewage treatment is the focus of control. But because the volatility of sewage components is quite big, the dissolved oxygen is also the difficult in the process of control. Based on the massive researches on control objects and combining with the DO control experience of other sewage treatment projects, this thesis decides to use fuzzy PID control algorithm which combines fuzzy control with commonly used PID control to control the process of air blower's opening so that the content of DO is controlled in certain scope.This system has been adopted by the Yuncheng County Sewage treatment plant and has served the anticipated control purpose and effect. It is economically and socially significant.