PLCbasedDCScontrolsystemofsewagetreatmentplant

1、PLC-based DCS control system of sewage treatment plantZHANG YuanWU Guofang（Rockwell Automation Chongqing Office，Chongqing 400010）Abstract：This paper introduces the application of DCS based on PLCCompared with the old DCS，this

2、 can meet the needs of automatic operation of the sewage plantBesides it is much more flexible and low costKey words：PLC；Industrial Ethernet；DCS；Sewage Treatment；CASS With the rapid development of the

3、 national economy, governments at all levels pay more attention to environmental protection, one after another across a large number of new sewage treatment plant. These new sewage treatment plant in accordance with their own characteristics, the control system performance and the price of the new r

4、equirements. Chongqing Municipal Wastewater Treatment Plant using the Fengjie CASS process of living sewage treatment, daily processing capacity of 3 million tons. The DCS system for cost-effective PLC for the control unit, using commercially available computer monitoring station. Automation of the

5、entire system of production circumstances, effectively reducing the system cost, operating since 2004 and put into good condition. 1 Production Process Introduction Sewage treatment is a continuous process of biochemical reactions, there is oxidation ditch process, AO, SBR, CASS, and many different

6、treatment processes. Fengjie sewage treatment plant the sewage treatment process used for new improvements CASS (Cyclic Activated Sludge System, Cyclic Activated Sludge) process, belongs to a kind of modified SBR process, from the coarse screen well, CASS pool, blower room, dosing, the storage basin

7、s, dewatering room, contact disinfectant pool composition. The process has the following characteristics: (1)May be taking off and landing Decanter drainage water to minimize the disturbance to the bottom of the sediment sludge. (2) Strong impact on the refractory organic removal efficiency, both ni

8、trogen and phosphorus removal capabilities. (3) Process is short, small footprint, the building of low-cost, running costs province. (4) Management of simple, reliable operation, water quality is good, no peculiar smell. (5) Sludge production is low, sludge stable, non-occurrence of sludge bulking.

9、2 DCS control system selection and hardware configurations 2.1 DCS System Selection Fengjie mouth Chongqing Three Gorges before the sewage treatment plant bond-financed projects in the reservoir area of the first sewage treatment plant, according to the actual process requirements and construction f

10、eatures of the control system of the project put forward the following demands: (1) The controlled device control points within 800 points. Control the process more complicated, but we need the algorithm is not complicated, the basic in order to time control and bit-type control-oriented. (2) Contro

11、l system shall be mature, reliable, easy to debug and maintain. (3) Take into account that there will be third-party products, network communication and protocols and standards must have an open nature. (4)Measuring devices and controlled devices are the traditional equipment, basic non-fieldbus com

12、munication capabilities, so the input and output control, or the traditional I / O-point basis. (5) As a bond investment projects, as far as possible under the premise of meeting the requirements of cost reduction. After comparison, the plant's automatic control system with PLC-based DCS control

13、 system to meet the production requirements of the system on the basis of its performance and price to achieve a good balance. 2.2 based on PLC, DCS system Traditional DCS is the instrument for the process industry control systems developed, the main function is to achieve a continuous monitoring an

14、d regulation of physical quantities. PLC against the traditional relay control system developed, the main function is to achieve switching capacity of the logic control. In general, PLC is a local controller, but with the application of scale, as well as the emergence of industrial Ethernet, multi-P

15、LC can interconnect together to form a larger control system. PLC compared with the single a few major changes: (1) Mount on the network's general-purpose computer online, and its role first, to achieve system configuration, programming and downloading, second-line monitoring has been control th

16、e process of state. In this way, a field control layer and the coordination control layer DCS prototype emerged. (2) Added in the PLC analog I / O interface, and numerical computing, so that, PLC logic control not only complete, you can also complete the monitoring and control of analog and mixed-co

17、ntrol functions. (3) An increasing number of PLC manufacturers to change it into a dedicated network of general-purpose network, thus making it conditional PLC and other various computer systems and equipment to achieve integration, to form large-scale control system. The above points makes the PLC

18、to change the composition of the system to possess a form of DCS. As the PLC products have entered the market for years, its I / O interfaces, programming, network communication have tended to be standardized and adapt to the requirements of open systems, while able to increase through the expansion

19、 of field bus communication Capabilities. Coupled with the advantages of PLC in the price, making the field of PLC in the distributed control system has a very important role in many applications with a considerable competitive advantage. 2.3 Fengjie sewage treatment plant DCS system configuration a

20、nd composition DCS control systems to industrial Ethernet network structure of this open-ended basis, consisting of three subordinate controllers PLC0 , PLC1, PLC2 station, an upper engineer station, an upper operator stations. The topology shown in Figure 1. Figure1 System Topology of Sewage Treatm

21、entPLC0 controllers installed in the central management center, large-screen mosaic analog display, through acquisition of various equipment over Ethernet Status signals and means of communication with the RS232 and the mosaic screen communication, will produce the entire process as well as the devi

22、ce status is displayed. PLC1 installed in the transformer substation, responsible for controlling the grid wells and sewage lifting pumps, grit chamber, No. 1, CASS pool, 2 CASS pool, 3 CASS pool, blower room, storage basins, and flow well flow detection, exposure measurement and control part of the

23、 disinfection tank, part of the electrical distribution room parameter monitoring. PLC2 installed in the inter-dosing. Used to control the dosing between the electromagnetic valves, mixers, diaphragm pumps, including a full set of dosing devices. Central management center, two monitoring computers u

24、sing the company's OptiPlex series of DELL desktop. OptiPlex line of desktop targeted at the primary server applications, in high-performance under the premise of their specially designed wire shield structure and the cooling system to ensure the system's high reliability and stability. The

25、monitoring software used is based on Microsoft Windows2000 platform, commercial machine to the operating system compatibility slightly better than the IPC. The plant control system for the exchange of information throughout the layer and control layer two-one. The use of advanced industrial Ethernet

26、, with fast and reliable. Industrial Ethernet is based on the traditional Ethernet-based, the requirements for industrial control, improved as a form of information and control network, with a net in the end, and reduce network cost characteristics. 3 automation system features 3.1 monitoring softwa

27、re Monitoring software using Kai 2000 software, Kai for Beijing 2000 Fu Hui Tong development of a universal monitoring software, the software on the OPC to support better communication. OPC (OLEforProcessContro1) is based on COM (ComponentObjectMode1) and DCOM (DistributedComponentObjectMode1) techn

28、ology, object-oriented software protocol. OPC as the on-site equipment, automation applications and enterprise management applications provided between an open and consistent interface specifications from different suppliers of software and hardware to provide plug and play connectivity. The system

29、monitoring software and DCS hardware, communication protocol used between the OPC method, ROCKWELL's RSLINX software OPCSEVER software as OPCCLIENT monitor side and read the data, using this to communicate to avoid DCS system monitoring software drivers support inadequate to happen. 3.2 Control

30、Mode In order to facilitate operation of debugging and accident emergency management, system control mode is divided into three types: (1) In-place manually. Through the local control box or the MCC on the button, switch handling equipment. (2) Remote control. Through central management center, two

31、computers in manual mode, control equipment. (3) Automatic. System based on auto-complete working condition of equipment start-stop, adjust control. Remote and local control mode switching from the MCC cabinet or local control box complete; automated and remote control mode switching from the comput

32、er to complete the two monitors. 3.3 monitoring capabilities Two computers and engineers, respectively, as the operator station alternate with each other, set at the central management center, the whole factory process equipment operating conditions, operating parameters for centralized monitoring o

33、f , remote field devices. Monitor your computer via the integrated 1000M card via Industrial Ethernet and PLC system for data exchange. Main functions: (1) Process monitoring. Systems according to technical requirements of the various aspects of wastewater treatment parameters and equipment status m

34、onitoring, but also with process asked to choose automatic, the order, timing and other control mode. (2) Alarm and alarm logging. When the device is an accident, the system will be in the computer, mosaic big screen, local control box on the alarm indicator. At the same time the computer will have

35、taken place in the contents of the alarm time and to confirm the time recorded. On the computer can carry out voice alarm. (3) Interlock protection. When the system detects the start of partial failure of the corresponding interlock protection program. (4) Parameter setting function. Available at a

36、central management center monitor of any one computer or on-site control station on the man-machine interface, alarm upper and lower limits, adjust parameters, run-time parameters such as set-up. (5) Data recording storage. System can access to important data such as process parameters, operating co

37、nditions, equipment, records storage, running time etc. to prepare for calls. (6) Operation record. Automatically preserve an important operational records, such as changes in parameters, operation of equipment, operator code, time and content. (7) Real-time data curve and the curve of historical da

38、ta. Of important process parameters can be real-time curve display and record historical data curve. (8) Multi-level password protection. Management Center at the central monitoring computer of any one operation can be set different permissions, permission to operate only the corresponding operators

39、, entering the correct password before they can access the class picture. (9) Printing functions. Reports can be printed, curve printing, graphic printing. 4 Engineering Effect The project was launched in May 2003, in April 2004 to run the factory equipment, the transfer of its DCS system is stable

40、and reliable operation without damage. System put into use, the operator at the central management center will be able to fully understand the operation of intelligence throughout the plant, DCS system to pump and water decanter and other major equipment can be based on pre-configured parameter auto

41、mation. Just the whole system of central management center operators will be able to ensure the normal operation of the system greatly reduces the labor intensity of Attendant. The system put into operation in the past, sewage treatment plants solved the degree of automation is low, all devices need to be manually operated, on duty labor-intensive