Reclaimed water automatic control system
The water pollution situation in our country is severe, and the problem of water scarcity is very prominent. Reclaimed water is one of the effective ways to alleviate the water crisis in our country. The term 'reclaimed water' originated in Japan. It is a non potable water that is used to flush toilets, clean cars, green spaces, or supplement cooling water after appropriate treatment of miscellaneous drainage generated in urban and residential areas to meet certain water quality standards. It is named "Zhongshui" because its water quality is between upper and lower water.
Reclaimed water is internationally recognized as the 'second source of urban water'. Reclaimed water can not only solve the impact of sewage on urban environment, but also increase the total available water resources, which is an important source of water and water-saving measure in cities. According to analysis, with the gradual adjustment and rationalization of water supply prices, the value advantage of reclaimed water as the "second water source" in cities is further highlighted.
1、 Project Process Introduction:
The project adopts a MBR water treatment process that combines traditional activated sludge biological treatment technology with immersion type hollow fiber membrane physical filtration technology. This technology is recognized by the international community as one of the most promising and practical technologies for development and promotion, and is also a key and mature practical technology developed in developed countries. After the operation of the reclaimed water reuse project, significant benefits have been generated:
1、Reduce water consumption by 360000 tons annually;
2、Reduce sewage discharge by 360000 tons annually;
3、Reduce COD emissions by 140 tons annually.
2、System network topology diagram:
DCS monitoring equipment is the bridge link between industrial sites and testing centers. On the one hand, it collects signals such as on-site instruments, transmitters, and equipment operating status, and on the other hand, it communicates with the testing center to execute relevant commands. Monitoring equipment is generally unmanned. In this control system, Siemens S7-414H is used as the central controller, with dual power redundancy and dual CPU hot standby. The IPO template adopts ET200M extension connection. The use of active bus modules and rails enables the system to support hot swapping of IPO modules; Redundant design of communication module. The communication protocol adopts Profibus protocol, with a data transmission rate of up to 12MPs, fully ensuring high reliability and speed of data communication. The DCS system adopts true redundancy except for IPO cards.
3、The main functions completed by the control system are:
(1) Monitor every analog and digital quantity in the monitoring system: detect and display the flow rate, pressure, water temperature, conductivity, turbidity, pH value, etc. of raw water, concentrated water, and product water; Monitoring of pump motor start stop, operating status, voltage and current; Automatic valve switch status, condition interlock; The automatic operation of the system's startup, running, and shutdown processes does not require manual intervention under normal conditions, avoiding operational errors.
(2) Display abnormal data and automatically pop up an alarm screen to confirm the alarm. For all abnormal data in the system, there are alarm screens and flashing prompts for data; The abnormal operation status of the pump motor and the fault status of the process equipment can trigger alarm screens and fault confirmation alarm screens.
(3) Establish trend images and obtain trend information. All flow, pressure, temperature, turbidity, and pH analog displays can be established as vertical and trend screens, and stored in the upper computer for a long time, which can be accessed and viewed at any time, facilitating production management and operation maintenance
(4) Adjust process settings and biases, etc. All process values, such as raw water inlet volume, fresh water outlet temperature, high-pressure inlet pressure, etc., can be manually or automatically adjusted online. The formula of the added medication can be saved in the computer as needed and automatically added in proportion according to the formula.
4、The main features of the control system are:
(1) The redundant system of controller S7-414H can achieve dual controller redundant automatic switching function. When the main control CPU fails, the other CPU automatically takes over the work of the main control CPU, with a switching time of milliseconds. Fully ensuring the safe operation of the system.
(2) The redundant communication interface and cable of ET200MIPO station using PROFIBUS-DP protocol are used for communication redundancy, achieving redundant communication with dual controllers (CPUs) and providing assurance for signal acquisition and transmission.
(3) Power redundancy, 10A DC power redundancy configuration, used for CPU and template power supply to ensure power supply reliability.
(4) During the debugging process of the system, due to significant changes in process requirements, program modifications are frequent. However, Siemens STEP7 programming software provides comprehensive programming tools that comply with the IEC1131 standard, including ladder diagrams (LAD2ER), statement tables (STL), continuous function diagrams (CFC), sequential function diagrams (SFC), structured language (SCL), and various programming tools can be mixed and cross referenced conveniently and quickly. In addition, the system's standard function block library improves programming efficiency and shortens the engineering cycle.
(5) The screen monitoring software WINCC6.0 (Window Monitoring Center) is an open full graphic human-machine interface based on the WINDOWS 2000PXP operating system. It has the characteristics of easy configuration and simple operation, and has a complete industrial graphics library, such as valves, water storage tanks, simulated traditional display instruments, pipelines, etc., which facilitates the design of monitoring system process screens.
5、Application experience
（1）The automatic control system for water treatment adopts redundancy, which not only meets the requirements of process control but also improves the operational safety and reliability of the system. It is worth promoting and applying in large-scale reclaimed water reuse and seawater desalination systems
（2）The CPU adopts hardware redundancy, and programming is no different from a single PLC, so there is no need to consider too much in project design and debugging. Therefore, more and more energy can be focused on understanding the process, greatly saving time and effort;
（3）The programmable controller and configuration software of the control system are both selected from the same product, which can fully utilize its internal protocols, has good data resource sharing, high compatibility, complete functions, and friendly configuration interface.
