The wastewater treatment system plan should fully consider the narrow living characteristics of campus life in real life, and strive to achieve the purpose of small equipment, stable performance, and less investment in projects. The effect of ambient temperature on bacterial metabolism during the wastewater treatment process directly affects the wastewater treatment effect. Therefore, a buried brick-concrete structure treatment tank is used to reduce the effect of temperature on the treatment effect. At the same time, the wastewater treatment technology changes greatly in process parameters, and the hardware design selection and equipment debugging are more complex. The use of advanced PLC control technology can improve the efficiency of wastewater treatment and facilitate the operation and use.
The waste water treatment system consists of a sewage treatment tank, a clear water tank, a reclaimed water tank, an electric control box, a water pump, a Roots blower, an electric valve, and a solenoid valve. The liquids are set in the sewage treatment tank, clear water tank, and middle water tank respectively. The position switch detects the water level in the tank and the tank. Wastewater treatment system schematic shown in Figure 1.
The first stage of the sewage treatment: When the water level in the sewage pool is at a low water level or is not in the water-free state, the electric valve will automatically start to enter the sewage. When the wastewater contained in the sewage pool reaches a normal high water level, the electric valve is automatically closed and the sewage in the wastewater pool is in a state of slight oxygen and anaerobic.
The second stage of sewage treatment: using the aeration method that can degrade macromolecule pollutants, can decolorize and deodorize the wastewater, balance the pH of the flora, and efficiently decontaminate the pollutants, ie the aerobic treatment process. The entire aerobic (aeration) time generally takes 6 to 8 hours. An emptying solenoid valve is installed on the aeration line. When the electric valve is automatically closed, the emptying solenoid valve is opened and the Roots blower is started with no load, then the emptying solenoid valve is closed and the sewage tank starts to aerate. When the aeration treatment is finished, the emptying solenoid valve is opened again and the Roots blower is stopped without load, and then the solenoid valve is closed and closed. The aeration fan starts and stops under no-load conditions and can protect the motor and fan. After 0.5 hours of water quality precipitation, PLC issued the 1# clean water pump command and the precipitated water pump was pumped into the clean water tank. When the water level in the clear water tank rises to a normal high water level, the 1# clear water pump will automatically stop running. At this time, the 2# clean water pump will automatically start pumping water to the middle water tank. When the water tank reaches a normal high water level, the 2# clean water pump will automatically stop running. At this time, the water in the medium water tank will completely complete the treatment process.
As shown above, when the water level in the water tank drops to a low water level, the 2# water pump automatically starts pumping water to the water tank. When the water level in the cesspool falls to a low level, the electric valve will automatically open and continue to incorporate sewage into the lagoon. This cycle.
Wastewater treatment technology Different selection of biological flora for different wastewater quality requires different process requirements. Electrical control systems should have parameters that can be modified to meet wastewater treatment requirements.
2. The power equipment (water pump, Roots blower, electric valve) used in the wastewater treatment system of the SBR wastewater treatment system adopts a three-phase AC asynchronous motor, and the motor and solenoid valve (AC220V matching) are matched with waterproof and moisture-proof type.
1# water pump: vertical centrifugal pump LS50-10-A, head 10m, flow rate 29m3/h, 1kW.
2 # clean water pump: vertical centrifugal pump LS40-32.1, head 30m, flow rate 16m3/h, 3kW.
Aeration Roots blower: TSA-40, 0.7m3/min, 1.1kW.
Electric valve: Body D97A1X5-10ZB-125mm, electric device LQ20-1, AC380V, 60W.
3. SBR wastewater treatment electrical control system design requirements 1) Control device selection PLC as the system's control core, according to process requirements a reasonable choice of PLC models and I / O interface.
2) The manual/automatic mode can be performed. The program can be edited according to the process requirements and the parameters can be set in real time.
3) The drive motor on the electric valve is a two-way operation of positive and reverse rotation. Therefore, an interlock function must be added to the PLC control circuit.
4) The grounding of the PLC should be designed according to the requirements in the manual and shown or described in the figure.
5) For the safe operation of the equipment, consider necessary protective measures, such as motor overheating protection, control system short circuit protection and so on.
6) Drawing the electrical schematic: including the main circuit, control circuit, PLC hardware circuit, and programming the PLC I/O interface function table.
7) Select electrical components and compile the component list.
8) Drawing wiring diagrams, electrical cabinet layout and wiring diagrams, control panel layout drawings and wiring diagrams.
9) Use ladder diagrams or instruction tables to program PLC control programs.
Second, SBR wastewater treatment electrical control system overall design process 1. Overall solution description 1) The control target motor of SBR wastewater treatment system is completed and stopped by the AC contactor, and the motor of the electric valve should adopt positive and negative control.
2) The water level detection switch of the sewage pool, clear water tank, and middle water tank should consider the anti-interference performance when selecting the type, and consider the corrosion resistance of the electrode.
3) The electric motor is driven on the electric valve, and its internal overload protection switch is normally closed contact. As the electric valve overload protection signal, PLC control circuit considers the logical relationship of the signal.
4) 1# clean water pump, 2# clean water pump, Roots blower motor and electric valve motor adopt thermal relay to realize overload protection respectively. The normally open contact of the thermal relay is converted by the intermediate relay and used as PLC input signal to Complete overload protection for each motor system.
5) The control of the Roots blower is required to start or stop under no load conditions, and an aeration solenoid valve needs to be provided on the aeration line.
6) The main circuit breaker, each load circuit and control circuit and PLC control circuit using fuses to achieve short circuit protection.
7) The electric control box is set in the control room. The control panel and the electrical board in the electric control box are connected with a BVR-type copper wire, and the terminal box is connected between the electric control box and the execution device.
8) PLC selects relay output type.
9) The PLC itself is equipped with a 24V DC power supply, taking into account its power supply capacity when external loads are applied. PLC grounding adopts the third grounding method to improve the anti-interference ability.
2. SBR wastewater treatment electrical control schematic design (1) main circuit design wastewater treatment electrical control system main circuit shown in Figure 2.
1) AC contactors KM1, KM2, and KM3 in the main circuit control 1# clean water pump M1, 2# clean water pump M2, and aeration blower M3; AC contactors KM4 and KM5 control electric valve motor M4, and are completed through positive and negative rotation. The function of opening the valve and closing the valve.
2) Motors M1, M2, M3, M4 are overloaded by thermal relays FR1, FR2, FR3, FR4. The electric valve motor M4 controller is also equipped with a normally closed thermal protection switch to achieve double protection of the valve motor M4.
3) QF is the main power switch, which can not only complete the short circuit protection of the main circuit, but also play the role of breaking the three-phase AC power supply. It is convenient to use and maintain.
4) The fuses FU1, FU2, FU3, and FU4 realize the short circuit protection of each load circuit. FU5 and FU6 complete the short-circuit protection of the AC control loop and the PLC control loop, respectively.
(2) AC control circuit design Wastewater treatment system AC control circuit is shown in Figure 3.
1) The control circuit has a power indication HL. PLC power supply circuit uses isolation transformer TC to prevent power supply interference.
2) Selection of the isolation transformer TC According to the PLC power consumption configuration, a standard type, ratio 1:1, and 100VA isolation transformer can be configured.
3) 1# clean water pump M1, 2# clean water pump M2, aeration blower M3 have running lights HL1, HL2, and HL3, respectively, controlled by KM1, KM2, and KM3 contactor normally open auxiliary contacts.
4) Overload protection of 4 motors M1, M2, M3 and M4 is realized by 4 thermal relays FR1, FR2, FR3, and FR4 respectively. After the normally closed contact is connected in parallel, it is connected with the intermediate relay KA1 to form an overload protection signal. KA1 Also play a role in voltage conversion, the 220V AC signal into a DC 24V signal into the PLC to complete the overload protection control function.
5) Sheung Shui solenoid valve YA1 and indicator light HL1, empty solenoid valve YA2, respectively, by the intermediate relay KA2 and KA3 contact control.
(3) Main parameter calculation 1) Breaker QF trip current. The circuit breaker is the power system power switch. The main loop control object is an inductive load AC motor. The overcurrent tripping value of the circuit breaker is set at 1.7 times the motor starting current. Wastewater treatment system has a 3kW load motor, a larger starting current, the remaining three are less than 1.1kW, starting current is small, and the process requires 4 motors to start separately, so you can automatically switch the QF trip current according to 3kW motor selection IQF:
IQF = 1.7IN = 1.7 × 6A = 10.2A ≈ 10A, the choice of circuit breakers IQF = 10A.
2) Fusible FU melt rated current IFU. Taking an aeration fan as an example, IFU≥2IN=2*2.5A=5A, and a 5A melt is selected. The remaining melt rated current is selected according to the above method. The control circuit melt rated current is 2A.
3) For the selection of thermal relay, refer to the relevant technical manual and calculate the parameters by yourself. At the same time, you can view more technical documents of China Sewage Treatment Engineering Network.
(4) PLC control circuit design includes PLC hardware structure configuration and PLC control principle circuit design.
1) Hardware structure design. Understand the drive requirements of each control object, such as: the level of the drive voltage, the nature of the load, etc.; analyze the control requirements of the object, determine the number of input/output interfaces (I/O); determine the accuracy and type of the control parameters, such as: Switch quantity, analog quantity control, storage capacity of user's program memory,etc., choose suitable PLC model and peripheral hardware, finish PLC hardware structural configuration.
2) According to the above hardware selection and process requirements, draw the PLC control circuit schematic, draw the PLC control circuit, and compile the I/O interface function table. Figure 4 shows the schematic diagram of the PLC control circuit of the SBR wastewater treatment system. L6 is used as the power supply of the PLC output loop and supplies power to the load of the output loop. All COM terminals of the output loop are shorted and then connected to the power supply N terminal.
3) The KM4 and KM5 contactor coil branches are designed with an interlock circuit to prevent malfunctions.
4) In the PLC input loop, the signal power is provided by the PLC's own 24V DC power supply, and all input COM terminals are shorted and then connected to the (+) terminal of the PLC power supply DC24V. If there is an active signal device at the input port, it is necessary to consider the power supply level and capacity of the signal device. It is better not to use the PLC's own 24V DC power supply to prevent the power supply from being damaged or affecting the signal quality of other input ports.
5) PLC adopts relay output. The rated control capacity of each output point is AC250V, 2A.
1) Programming. According to the control requirements, a wastewater treatment system control flow chart is set up, as shown in Figure 11-5. The sequence of actions of each control object and the relationship between them are expressed. Based on the clear allocation of PLC register space and the determination of special registers, the program design of the control system is carried out, including the main program preparation, the preparation of each function subroutine, and the preparation of other auxiliary programs.
2) Static debugging of the system. During no-load static debugging, check whether the logic in the hardware interface circuit is correct for the running program. Then debug the subroutine or function module program first, then debug the initialization program, and finally debug the main program. The debugging process is as close to the actual system as possible, taking into consideration various possible situations, making repeated debugging, and analyzing the problems and adjusting the procedures or parameters in time.
3) System dynamic debugging and operation. In the dynamic load state debugging, close observation of the system's operating state, using manual and then automatic debugging method, and gradually. In case of problems, stop in time, analyze the causes of the problems, and propose solutions to the problems. At the same time, make detailed records for analysis and improvement.
Small SBR Wastewater Treatment PLC Electrical Control System Course Design
Wastewater treatment technology is a kind of high-efficiency waste water recycling treatment technology. The dominant bacteria technology is used to treat the domestic sewage of the campus. The treated reclaimed water can be used to water green areas, flowers and trees, flush toilets and vehicles, etc., thereby saving water resources. the goal of.