Application of PROFIBUS in sewage treatment contro

Application of PROFIBUS Fieldbus in sewage treatment control system

taking the software redundant fieldbus control system of Haining sewage treatment plant as an example, this paper discusses the application of bus and redundancy technology in the field of sewage treatment. The hardware, software structure and working principle of the system are described. The application shows that the system can meet the automatic control requirements of sewage treatment, and has the advantages of advanced, reliable and good control performance

profibus is the national industrial fieldbus protocol standard formulated by Germany in the early 1990s, code din19245. It is an international open fieldbus standard, namely en50170 European fieldbus standard. This standard provides the best protection for the investment of suppliers and users and ensures the independence of suppliers. PROFIBUS specifies the technical and functional characteristics of serial fieldbus, which can make the decentralized digital controller from the bottom of the field to the workshop and networking. PROFIBUS is divided into master device (master station) and slave device (slave station). The master station determines the data communication on the bus. When the master station gets the bus control right, it can actively send information without external requests. The slave station is peripheral equipment. Typical slave stations include input/output devices, valves, drivers and measurement transmitters. They have no bus control, and only confirm the received information or send information to the master station when it sends a request

1 process introduction

the traditional activated sludge treatment process has the problems of high capital investment, high operating costs, realization of value-added services such as spot storage, logistics distribution and warehouse unit pledge, as well as high power consumption. SBR (sequence batch reactor) sequential batch process is a relatively advanced sewage treatment method in the world in recent years. Although this process has been developed abroad at the beginning of last century, it has not been really adopted by major domestic sewage treatment plants so far. The main reason is that it has strict requirements on time and self-control. The sewage treatment plants using SBR process are scattered, with a large number of equipment. Each working segment requires close connection and close cooperation between equipment, which is providing a place for Profibus fieldbus

Figure 1 SBR Sewage treatment process

sbr sewage treatment control system mainly includes: inlet pump room control system, swirl grit chamber control system, main reaction tank control system, outlet pump room control system, blower room control system, dehydration machine room control system, etc

the sewage collected by the urban sewage pipe is pressurized by the pump station to the intake pump room, where large solid impurities are filtered by the grid machine, and then the thinner sewage is pumped by the lift pump to the cyclone grit chamber. Here, the solid particles in sewage are removed due to the action of mixer and sand suction machine. The next process is that the sewage is first sent to the anaerobic tank of SBR tank for phosphorus and nitrogen removal, and then flows into the aerobic tank, where there are corresponding bacteria to decompose and purify the sewage. One of the main conditions for the survival of the sludge bacterial ecosystem in the reaction tank is the organic impurities in the sewage, and the other is the supply of oxygen. Therefore, the sewage treatment plant is specially equipped with a blower room, which directly aerates the sewage through the pipeline at the bottom of the tank. After treatment, the sewage that meets the standard can be directly discharged, and the excess sludge is pumped to the dehydration machine room. Through dehydration, the sludge is dried into cakes and used as fertilizer

2 system configuration and description

2.1 overall control requirements and functions

the requirements of the automatic control system of the sewage treatment plant are to automatically control and adjust the sewage treatment process, so that the treated water quality index can meet the required range. When the central control room of the company sends the upload instruction, the main working parameters (water quality parameters, flow, liquid level, etc.), operation status and main process curves in a certain period of time in the current operation process are uploaded to the central control room of the company

functions are as follows:

(1) control operation: the controlled equipment can be controlled in real time in the central control room, such as starting and stopping a certain equipment, adjusting the size of some analog output, setting some parameters of PLC, etc

(2) display function: use graphics to display the operating conditions of each field controlled equipment and the status parameters of each field in real time

(3) data management: according to the change speed and importance of different operating parameters, establish a production history database to store the original production data for statistical analysis. By comparing and analyzing the data in real-time database and historical database, some useful empirical parameters are obtained, which is conducive to optimizing the quasi closed-loop control of SBR pool, and some necessary parameters and results are displayed in real-time pictures and reports

(4) alarm function: when the measured value of an analog quantity (such as current, pressure, water level, etc.) exceeds the given range or the valve of a certain switching quantity (such as motor start and stop, valve switch) changes position, different levels of alarm can be sent according to different needs

(5) printing function: it can realize the printing of reports and graphics, as well as the real-time printing of various events and alarms. Printing methods can be divided into: scheduled printing and event triggered printing

2.2 control system network structure

if the conventional PLC centralized control mode is adopted, the on-site signal is connected to the PLC in the centralized control room through cable. Due to the long process line and the wide distribution range of on-site control points, a large number of cables and bridges need to be laid, and the on-site environment is bad, so its construction is very difficult. In view of this, the key technology and industrialization project of Pro in-situ nano synergistic high flame retardant polyurethane foam insulation material are adopted, and the evaluation results are publicized. According to the process division, the system has three master stations, five sub stations and two operator stations. Siemens's series PLC is adopted, and the main station adopts cpudp, which is equipped with a DP communication port and an MPI port. The substation adopts et200m field module with good versatility, which is used for field data acquisition and control. With the help of PROFIBUS (industrial field bus), it is convenient to establish the control network system

the control system is divided into three levels, namely, site level, control level and management level

2.2.1 management level

management level centrally monitors the operation status of each substation equipment. PROFIBUS FMS bus is selected as the management level fieldbus, and two redundant servers installed with configuration software are installed in the control room as the master station of PROFIBUS FMS fieldbus, which can collect field data at the same time. The server adopts WinCC configuration software and is equipped with server software package options

simatic s and mds2701 radio stations are responsible for wireless data communication with the company

2.2.2 control level

the main function of the control level is to receive the parameters or commands set by the management, control the production process of sewage treatment, and transmit the on-site status to the management. Plc1 and plc2 are respectively composed of a power module PS 307 and a CPU DP module. They are hot standby for each other and collectively handle all control algorithms and automatic operation of monitoring equipment. Centralized control enables all parts of the whole sewage plant control system to work in complete coordination

2.2.3 field level

Profibus-DP Field bus is used for field level control, which is very simple to realize the redundancy of the control system. Et200m remote unit is connected to two PROFIBUS-DP buses through two im bus interface modules. The sewage plant is equipped with six et200m remote units, two of which are in the SBR tank, and the other four are in the inlet pump room, outlet pump room, blower room and sludge dewatering room respectively. Each et200m unit is composed of two im bus interface modules and several other digital and analog input and output modules. The im bus interface module receives the commands from the master control station through the bus to realize data acquisition and equipment control. Only the commands of the master PLC are effective, while the commands of the hot standby PLC are ignored. The number and configuration of digital and analog input and output modules are determined by the local control and acquisition points

Figure 2 control system structure diagram

3 system software

the control program of the main control unit SPLC greatly exceeds the global demand. STEP7 is a programming software developed by Siemens and applied to s/s7400plc. It runs in WindowsNT or Windows98 operating system and has friendly user functions in all aspects of automation engineering. The program adopts modular programming structure, which is convenient for system maintenance and expansion

Figure 3 software flow chart

4 conclusion

the control system was debugged in September 2002, and the system has been stable and reliable since its operation. The labor productivity is greatly improved. The system effectively solves many problems in production, such as reducing sudden failures in the production process, shortening the production preparation time, such graphene materials and rush repair time developed by Professor Chen Yongsheng's team, reducing the labor intensity of workers, creating considerable economic and social benefits for the sewage treatment plant, and achieving the purpose of energy conservation and consumption reduction. It has reached a new level in production management. (end)