Automatic control system of the hottest sewage tre

2022-08-12
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Automatic control system of sewage treatment plant

Abstract: combined with the process requirements of sewage treatment plant, this paper analyzes the automation solutions in sewage treatment by using an actual implementation case of sewage treatment plant

key words: sewage treatment, PLC, fieldbus, monitoring software

I. Introduction

with the development of the city and the continuous improvement of people's living standards, the discharge of urban sewage is also increasing year by year, which has caused serious pollution to the urban environment. Based on this demand, all regions are actively building sewage treatment plants to realize the supportive development of the city, beautify and manage the urban environment. Taking a sewage treatment plant as an example, combined with the process flow, this paper introduces the solution of implementing automatic control in the sewage treatment plant. The sewage treatment plant adopts hydrolysis SBR (UNITANK) aerobic treatment process. The water distribution well, power transformation and distribution system, sludge collecting tank and concentration tank of the lifting pump station in the import pretreatment section of the phase I project can be relatively convenient to use according to the treatment capacity of 120000 cubic meters/day in the phase II project. The hydrolysis tank and SBR tank are the first group with a treatment capacity of 60000 cubic meters/day. Two blowers and two dehydrators are installed first. In the second phase of the project, a group of hydrolysis tanks, SBR tanks and two blowers and dehydrators with a processing capacity of 60000 cubic meters/day will be added

II. Process and system requirements

the whole system is composed of four parts: water distribution well of lifting pump station in inlet pretreatment section, hydrolysis tank and sludge treatment, SBR reaction tank and blower room, power transformation and distribution system and dehydration machine room, well room, etc

there are five stations that need automatic control, including pump room, hydrolysis tank, substation, SBR tank and blower room. The pump room is responsible for controlling the sludge inlet valve, sludge outlet valve, submersible sewage pump intake gate, desander, grille well and walking sand suction and sand water separation device. The North hydrolysis tank is responsible for controlling 14 sludge discharge valves. The substation is responsible for monitoring the relevant voltage, current, active and reactive power and other analog signals of high and low voltage systems, and conducting benefit accounting. SBR tank is responsible for controlling the whole aerobic process. The blower room is responsible for controlling the opening of the blower guide vane and monitoring various important parameters of the blower. At the same time, in the central control room, the upper computer software should reflect the specific situation of each section in real time, including various states of the equipment, data of various instruments and process setting parameters, etc., calculate and query various parameters, such as temperature, liquid level, pH value, mud level value, Doppler flowmeter, etc., which can allow the operator to analyze and control various equipment on the site

the topology is as follows:

III. The implementation of the automatic control system

considering making the whole system more flexible and safe, the whole system control is divided into three layers: the first layer is manual on site, the second layer is controlled by the monitoring software of the upper computer, and the third layer is automatically operated without PLC. On site manual -- it is convenient for the maintenance and debugging of the equipment. When a device is switched to the on-site manual mode, the device will not be controlled by PLC, but only accept the on-site operation commands; The upper computer monitoring software is manually controlled -- it is conducive to the operation of the dispatching room. For each device, it can be separated from the automatic operation state of PLC and operated directly by the computer in the central control room. PLC automatic operation - automatic control of all equipment on site. It is responsible for the control of the whole sewage treatment process and will respond to faults. Even if the PLC and the upper computer are separated from communication, it can work safely by itself

according to the above requirements, we choose Siemens's series PLC for hardware, frequency converter and soft starter, and general monitoring software for software. Considering that there are five control stations and a large amount of communication data, and there is a certain distance between each station, and the farthest station is 300 meters from the central control room, the fieldbus combining PROFIBUS DP and PROFIBUS FMS is adopted, which can not only ensure the high-speed transmission of data, but also realize the integrity of large capacity data. Use the combination of frequency converter and soft starter to drive the submersible sewage pump motor, track the liquid level, and ensure that the liquid level is constant and consistent with the set value

in the central control room, a PC is used to complete the tasks of the operator station and the engineer station. At ordinary times, the shift leader and the operator mainly operate in order to show the research results of raw and auxiliary materials and equipment technology. The operator can only enter the operation after authorization. The engineer can open the corresponding function setting interface, and others are not allowed to enter this level. The operator station adopts eight screen multi screen display, which can be arbitrarily adjusted into each operation diagram, and can automatically turn the screen. The time of turning the screen is adjustable (the default is 15 minutes). A remote monitoring station is set in the central dispatching room of the company, which uses the local telephone line to communicate with the central control room of the sewage plant by dialing. The station adopts four screen multi screen display, which can realize the setting of dialing time interval, can be arbitrarily adjusted into each running diagram, and can automatically turn the screen, and the time of turning the screen is adjustable

the user interface is mainly in the form of a plan, partially reflecting some sections and functions related to the corresponding screen (manual and automatic, operation state setting, time setting, parameter setting, upper and lower limits, alarm, etc.). The alarm information, whether the automatic operation conditions can be met and the analysis scheme can pop up immediately, with voice prompts. The operation status table reflects the switching status of main equipment, pump current and voltage, parameters of field instruments, cumulative values (electricity, water, sludge, gas, etc.), comprehensive operation parameters (power consumption per unit of water lifting, power consumption per unit of gas supply, power consumption per unit of water treatment in the whole plant, etc.). The interface mainly includes: the structure diagram of the automatic control system of the sewage treatment plant, the process flow diagram of the sewage treatment plant, the plan of the sewage treatment plant, the engine (dynamic) of the electromechanical control mechanical components, the operation plan of the inlet pretreatment section and pump room (dynamic), the operation plan of the hydrolysis tank and sludge treatment (dynamic), the operation plan of the SBR tank and blower (dynamic), the operation plan of the dehydration machine room and well room (dynamic), High and low voltage power distribution plan (dynamic), general table of operation status of sewage treatment plant (dynamic), table of operation status of inlet pretreatment section and pump room (dynamic), table of operation status of hydrolysis tank and sludge treatment (dynamic), table of operation status of SBR tank and blower (dynamic), table of operation status of substation, dehydration machine room and well room (dynamic)

IV. general introduction

the whole automatic control system has well realized the idea at the beginning of the establishment of the plant, has operated smoothly, and its stability and convenience have been tested. It can operate normally even if there is no one on duty. Because the international standard PROFIBUS bus bus and mature scheme technology are adopted, the convenience of system expansion and maintenance in the future is guaranteed. The above describes the whole system

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