Ultrasonic liquid level meter for liquid level measurement in sewage treatment

Project Overview

With the improvement of urbanization level and the increase of urban population, sewage treatment is an important issue faced by every city. In order to treat sewage in a timely manner, various cities have established sewage treatment systems such as sewage pumping stations. With the continuous strengthening of environmental protection and the daily processing volume of sewage treatment, it is necessary to purchase a certain amount of instrument equipment, such as liquid level switches, liquid level meters, flow meters, pressure switches, etc., to maintain the maintenance of water treatment plants. Safe, efficient and reliable operation is essential. Among these instruments, this article mainly talks about how ultrasonic liquid level meters are used for liquid level measurement in sewage treatment to realize the automated operation of the entire sewage treatment plant.

  1. Sewage treatment process

  Sewage treatment operations generally adopt a three-level treatment process. The specific process is as follows:

1. The primary treatment (i.e. physical treatment) is that the raw sewage that passes through the coarse grid is lifted by the sewage lifting pump, passes through the grid or sand filter, and then enters the grit settling tank. The sewage that has been separated from sand and water enters the primary sedimentation tank.

2. Secondary treatment is when the effluent from the primary sedimentation tank enters the SW treatment equipment, which includes the activated sludge method and the SW membrane method (the reactors of the activated sludge method include aeration tanks, oxidation ditches, etc., and the SW membrane method includes SW filters, SW Turntable, SW contact oxidation method and SW fluidized bed), the effluent from the SW treatment equipment enters the secondary sedimentation tank, and the effluent from the secondary sedimentation tank is safely discharged or enters the third-level treatment.

3. The three-level treatment includes SW denitrification and phosphorus removal, coagulation and sedimentation, sand filtration, and activated carbon adsorption. Part of the sludge from the secondary sedimentation tank flows back to the primary sedimentation tank or SW treatment equipment, and part enters the sludge concentration tank, and then enters the sludge digestion tank. After dehydration and drying equipment, the sludge is reused later.

  2. Main problems in liquid level measurement

  In every environment of sewage treatment, liquid level meters are indispensable, used to measure and monitor wastewater and chemicals such as XD agents. To ensure the orderly injection of chemical solutions such as sewage and XD agents and the smooth discharge after three-level chemical treatment, the importance of the liquid level gauge for the automatic operation of the sewage treatment system can be seen.

The user has used a float switch to maintain the water level before, but due to the fact that the cable is easily entangled during the use of the liquid level switch, and repeated movements for a long time, the cable is aging and thick, and the cable is prone to breakage and cable sheathing. Problems such as rupture and damage, frequent instrument failures, etc. often require the pump to be stopped for maintenance, and manual supervision has to be carried out, which increases the inspection cycle, resulting in reduced work efficiency and causing great distress to users.

In addition, because sewage is corrosive to a certain extent and is accompanied by certain toxic gases, and the measurement space is limited, and there are stirring, foam, steam and condensation, etc., the requirements for the liquid level meter are relatively high.

  3. What are the advantages of ultrasonic liquid level gauges

  Based on the understanding of the user’s working condition characteristics and problems encountered in measurement, the main reasons for using explosion-proof ultrasonic liquid level meters are: For automatic control of lift pumps.

Specifically, one flameproof ultrasonic liquid level meter is installed in each of the sewage lifting well and the anaerobic water supply well (inlet pump well) in the primary treatment process to measure the water level in the pump well. Real-time transmission to the PLC operator and host computer for system analysis. According to the control program corresponding to the measured value, the operation of the lift pump is automatically controlled to start and stop. In this way, the operating status of the pump can be adjusted accurately and timely according to the amount of external water in the sewage treatment plant, reducing equipment fatigue; at the same time, the human resource consumption of three shifts of traditional pumping stations can be eliminated.

 Why is it recommended to users to use explosion-proof ultrasonic liquid level gauge? This is because the ultrasonic liquid level meter has many advantages in measuring liquid level. For example, it has no mechanical movable parts, is a non-contact measurement, has high reliability, is easy to install and use, and is not affected by the viscosity and density of the liquid. It is very Suitable for liquid level measurement in open tanks. While operating stably and reliably, its low price and simple installation, debugging and maintenance greatly reduce the user's expenditure during the application process and achieve low-cost operation and maintenance.

(1) Precautions for purchase and selection

  In order to make the ultrasonic liquid level meter better adapt to the needs of on-site working condition measurement, when selecting the ultrasonic liquid level meter, attention should be paid to The following matters:

  1. Choose a reasonable range according to the on-site working conditions, but if there is a lot of steam or foam on site, an instrument with a larger range should be selected.

2. In general weak acid and weak alkali environments, ordinary probes (such as ABS) can be used. However, when used in highly corrosive situations, instruments with anti-corrosion probes (such as PVDF) should be used.

3. In places with explosive gases such as urban drainage pump stations, water collection wells, biochemical reaction tanks, and sedimentation tanks, for safety reasons, it is necessary to choose an ultrasonic liquid level meter with explosion-proof function.

(2) How to use ultrasonic liquid level gauge

  Whether the selection is reasonable depends on whether the instrument matches the working conditions, and the standardized use of ultrasonic liquid level gauge will directly affect its function. play. Specifically, when using the ultrasonic liquid level meter, it needs to be used correctly according to the following methods:

  1. Adjust the height of the ultrasonic liquid level meter sensor from the liquid level. Not too far, not too close. If it is too far, the signal received by the probe is too weak; if it is too close, it enters the blind zone of the probe and cannot be detected.

2. Ensure that the probe surface is vertically facing the liquid surface to be measured, and the horizontality is maintained at 2°. At the same time, ensure that there are no obstacles in the area covered by the ultrasonic beam emitted by the probe, especially ladders, pipes, limit switches, etc. in the tank. Under normal circumstances, the transmitter diode will flash, and when an echo is received, clicking and clicking sounds can be heard near the sensor.

3. The anti-electromagnetic interference performance of ultrasonic waves is not good, and nearby electrical equipment can easily affect it. Signal lines should be in separate conduits, away from power lines and lighting lines. To ensure that the signal PB is good, conductive steel pipes should be used for wiring pipes, and the PB layer should be grounded at a single point to prevent the instrument from being interfered by the potential difference of the circuit.disturb.

4. In order to prevent poor contact of the signal line, try to leave no joints in the middle of the signal line, and there should not be any looseness in the crimping area of ​​the terminals, otherwise the contact resistance will be large. If there must be a joint, it needs to be welded to reduce the occurrence of bad things.

5. If the signal line, especially the connector, gets damp, it will cause signal disorder. When cable trenches are required, signal lines should be laid on the cable trench supports.

The ultrasonic liquid level meter can reflect the water level in a timely manner and accurately and timely adjust the operating status of the pump according to the amount of external water in the sewage treatment plant. This not only reduces equipment fatigue, but also facilitates the dispatching room to make real-time and reasonable adjustments based on the water level. Management and control solves the problem of data deviation caused by inaccurate measurement data. Together with other instruments and equipment, it realizes the automated operation of the entire sewage treatment plant, ensuring the smooth progress of the operation and improving the overall benefits of the enterprise.