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Application of sewage treatment control system

Application of sewage treatment control system

ABSTRACT: According to the characteristics of sewage treatment control system in environmental protection, a distributed I/O system composed of S7-300 CPU and UniMAT I/O module is adopted to monitor and control the instruments and equipments on the spot. The results show that this way not only reduces the cost, but also achieves the desired effect.


Keywords: sewage treatment control system, UniMAT PLC



I. General Situation of the project


XX County Sewage Treatment Project is a municipal key project approved by the Development and Reform Commission. The design scale of the project is 100,000 tons of sewage per day. The control system of the sewage treatment project adopts UniMAT PLC module and Siemens S7-300 CPU control system. The upper control system adopts Siemens WINCC upper control system to feed the equipment of the sewage treatment plant. Line monitoring.


2. Control objects


This project mainly controls the opening, closing, stopping and running of field equipment (pumps, valves, etc.); the opening and closing of electric valves; the interlocking of key equipment; and realizes the automation of the whole sewage treatment process of sewage / coarse grille / fine grille / CASS tank / dosing room / sewage desliming room / landfill.


3. System configuration


The CPU 315-2DP and CP343-1 Lean modules of Siemens are adopted. The distributed I/O modules are all made up of UniMAT 300 series modules. The field control station and sludge dewatering room are connected by DP mode through EM277, and the field control station and dosing room are connected by MODBUS to DP mode. The whole system consists of 1 PLC field control stations, 1 operator stations and 1 engineer stations. The central control room and the field control station are connected by Ethernet. The operator station of the central control room provides the real-time information of the production process and all the alarm functions. The central control room monitoring system adopts Siemens WINCC configuration software. WINCC is the configuration software platform introduced by Siemens. It is easy to use, can construct flexible interface and strong function, and can develop strong combination picture with WINCC configuration software.

4. System functions and Implementation


1). system process

Total process screen


After the sewage is filtered through coarse grille, it enters the sewage regulating pool, then rises through the sewage lifting pump, passes through fine grille, then enters the sand sink, then enters the CASS pool for aeration treatment, then carries on the sedimentation, after the sedimentation, discharges the sludge to the sludge storage pool, and then carries on the sludge dewatering. The sewage from CASS pool is deposited and discharged to contact disinfection pool. Chemical treatment is carried out in the dosing room to reach the discharge standard. There are other reports, handover and other auxiliary interfaces.


2). system functions


The lowest layer of the system is the equipment control layer, which mainly completes the field control and monitoring of the equipment; the second layer is the monitoring layer, which mainly completes the on-line monitoring of the sewage treatment system in the whole plant and sends control instructions to the equipment control layer. The system includes monitoring the main interface and multiple sub interfaces. The main interface reflects the total process of sewage treatment, and the sub-interface monitors and controls each sub-process.

CASS pool control screen


The system is mainly controlled by the operator in the central control room, which has a server, two clients and UPS. The central control room uses WinCC to configure the upper computer system to generate the upper computer monitoring system, and processes the data collected by PLC. It is responsible for data management, data acquisition, alarm, fault, trend chart, data recording and report forms, and real-time display of equipment running status, running time, fault alarm processing, report output, etc., to achieve the monitoring of all equipment in the plant.


Its main functions are as follows:


A.Control operation: In the central control room, the system can be controlled on-line, such as starting and stopping a certain equipment, manual or automatic sequential control, PLC control mode switching and field PLC parameter setting value modification.


B. Display function: the real-time display of the operating conditions of the controlled equipment of each PLC station by graphics; dynamic display of various analog signals, switching signals, various cumulative signals and other values, through buttons, switches, signal lights, colors, percentages, filling and other means vividly expressed. management: it can set up information base such as runtime, alarm, fault, trend chart, system parameters and so on.

D.Data processing: Processing the digital and analog data uploaded by PLC and displaying them on the PC system as required.

E. alarm function: monitoring the status of all control equipment in sewage treatment plant, beyond the allowable range, that is, listed in the alarm table, and display the location and alarm level.

F. Fault Function: To monitor all the control equipment units in the sewage treatment plant. If there is a fault, it is listed in the fault table and the name and location of the equipment are displayed.

G. report function: generating runtime reports, influent / effluent flow reports, online COD reports, etc.


3)PLC control statio


According to the process requirements, after PLC power-on self-check, according to the signal of the host computer monitoring system to control the plant equipment start-stop, forward and reverse action. PLC completes the data acquisition of all the equipment of sewage treatment plant, such as water pump, coarse grille, fine grille, etc. After simple operation, it is uploaded to the upper computer monitoring system. When circuit breaks, short circuit or overload occurs, the data collected by PLC will exceed the set threshold, and the PLC will stop the control equipment and send an alarm signal to the upper computer monitoring system. All sensors adopt on-line instruments. The sampled data are converted into 4-20m standard current signal by the transmitter. The sampled data are directly transmitted to SM331 and 332 (analog input and output module), and converted to 0-27648 digital quantity by analog/digital conversion. The input and output of switch input is SM321 and 322 (digital input and output module). Among them, digital input (321-1BL00), output module (322-1BL00), analog input (331-7KF02), output module (332-5HF00), interface module (153-1AA03) all adopt domestic UniMAT series modules, which are stable in use, accurate in measurement and meet the requirements of the system.

4) data communication


This system connects the central control room and PLC control station into a network through industrial Ethernet, and realizes the data communication between PLC and WinCC. Separate 1 sets of S7-200 PLC systems are used for sludge dewatering. The system is connected with the EM277 of S7-200 in the sludge dewatering room, and the EM277 is hung on the DP sub-network of the system to communicate, thus controlling the start-up and stop of the equipment in the sludge dewatering room. The start and stop of the pump in the dispensing room is connected to the system DP network through the MODBUS to DP module, which is controlled in the central control room.


5. Use effect analysis

This PLC system adopts Siemens CPU and remote I/O station of Uygur UniMAT to form a centralized-distributed network structure control system, which not only ensures the stability of the control system, but also greatly saves the hardware investment and related construction costs. Since its completion and commissioning, the operation has been stable and reliable, and the control accuracy fully meets the design requirements, which not only saves costs, but also reduces energy consumption, improves efficiency, fully achieves the desired goal, and meets the requirements of environmental protection.

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