Light industry repetitive cooling water meter selection and device

First, the selection of various commonly used instruments in circulating water treatment facilities 1. The level gauges commonly used in liquid level gauges include a flowmeter type, a float ball type, an ultrasonic level gauge, a radar level gauge, and a magnetic flip level gauge.

According to the characteristics of various level gauges, in the industrial circulating water treatment facilities, the selection of various level gauges is generally based on the following principles: 1 The connected level gauge is usually used in less important indoor areas or as The standby of other level gauges, for example, may be set on the safety Water Tank on the platform of the process master workshop, so as to facilitate the inspection by the inspection personnel, and also be used as a backup for the magnetic flip level gauge on the safety water tank. 2 The float level gauge can be mainly used to interlock with the submersible pump in the project, control the operation and stoppage of the submersible pump in the ordinary water collection well, and can output the water level signal of the water collection well. 3Ultrasonic liquid level gauge is applicable to various water treatment structures, such as cold water tank, hot water tank, sludge tank, sludge thickening tank, pure water or softened water replenishing pool. 4 Magnetic steel flap level gauge is suitable for indoor water tanks or pools which require both manual observation and signal output. For example, the level gauge is provided on the safety water tank in the main workshop of the process, and the safety water tank platform The environment is poor and manual observation is difficult, so this level gauge was used. 5 Radar level gauges are used in high-impact occasions, such as pools or tanks in main workshops, where serious spills can occur if water is spilled from the pool or tank.

2. There are two uses of flow meter flow measurement, one for flow detection, and participation in process control to test whether the water supply capacity of a water treatment facility meets the requirements for normal production of the main process; the other is used for flow measurement, metering The results are sent to the company's energy center as the basis for the calculation of the company's water consumption technical and economic indicators. In the current highly automated projects, electromagnetic flowmeters and ultrasonic flowmeters are used most frequently. Flow meter selection in Table 2.

In industrial circulating water systems, the primary condition for the use of electromagnetic flowmeters or ultrasonic flowmeters is water quality. Industrial circulating water includes industrial net circulating water, demineralized water circulating water, pure water circulating water, turbid circulating water, mud containing iron oxide skin powder particles. Water, in which the conductivity of demineralized water circulating water and pure water circulating water is extremely low, an ultrasonic flowmeter should be used, and the rest of the water circulating water can be used.

The nature of the medium itself, including temperature, turbidity, ph, and oil content, is relatively low for flow meters. In small-diameter pipes, ultrasonic flowmeters are more expensive than electromagnetic flowmeters, and the length of straight pipe sections installed is longer than that of electromagnetic flowmeters. In the current water treatment facilities, electromagnetic flowmeters are usually selected for small-diameter pipelines; it is difficult to dismount and disassemble the flowmeters on large-diameter pipelines, and the front and rear of the electromagnetic flowmeter must be installed with maintenance shut-off valves, and the large-diameter pipeline is usually a circulating water supply. The main trunk, so the choice of ultrasonic flow meter on the large diameter pipeline.

3. Thermometer temperature measurement instrument according to the temperature measurement method can be divided into contact and non-contact two major categories. In the industrial circulating cooling water treatment system, the water temperature is not high, and contact thermometers are used. The water temperature of the measured water is sent to the main control room for water quality testing, and sent to the energy center or feedback signal to control the cooling tower fan. Rotating speed. In general, the contact temperature measuring instrument is relatively simple and reliable, and the measurement accuracy is high. However, due to the need for sufficient heat exchange between the temperature measuring element and the measured medium, it takes a certain amount of time to reach thermal equilibrium. Therefore, there is a delay in temperature measurement.

The temperature measuring instrument can be divided into two types: integrated and split type according to the integrated mode of the device. Integrated thermometers are generally used in circulating water treatment systems. Integrated thermometers generally consist of a temperature probe (thermocouple or RTD sensor) and a two-wire solid electronic unit. The solid-state module is used to mount the temperature probe directly in the junction box to form an integrated transmitter. Integrated thermometers are generally divided into thermal resistance and thermocouple type. The integrated thermometer has the advantages of simple structure, saving lead, large output signal, strong anti-interference ability, good linearity, simple display instrument, solid-state module anti-vibration and moisture proof, reverse connection protection and current limiting protection, and reliable work. The output of the integrated thermometer is a unified 4-20mA signal; it can be used with a computer system or other conventional instruments. Can also be made according to user requirements explosion-proof or fire-proof measuring instruments.

4. Pressure gauges In industrial circulating water treatment facilities, pressure gauges are provided on the inlet and outlet pipes of circulating water supply, return water mains, pump outlet pipes, and filters, heat exchangers, and other equipment. Pressure gauge is mainly composed of load cell sensor, module circuit, display meter, case and process connector. It can convert the received liquid and other pressure signals into standard current and voltage signals to provide secondary instruments such as alarms, recorders, and regulators for measurement, indication, and process adjustment.

The principle of pressure gauge measurement is that the process pressure and the reference pressure act on the two ends of the integrated silicon pressure sensitive element, respectively, and the differential pressure causes the silicon wafer to deform (the displacement is very small, only in the micrometer range), so that the silicon wafer is made of semiconductor technology. The full dynamic single-arm bridge outputs a millivolt-level voltage signal proportional to pressure driven by an external current source. Since the silicon material has excellent strength, the linearity and variation index of the output signal are both high. During operation, the gauge converts the measured physical quantity into a millivolt-level voltage signal and sends it to a differential amplifier that has a high amplification and cancels temperature drift. The amplified signal is converted into a corresponding current signal by voltage-current conversion, and then subjected to a non-linear correction. Finally, a standard current-voltage signal having a linear relationship with the input pressure is generated.

The pressure gauge outputs the signal to the water treatment control room, and the pressure signal on the main process circulation water supply pipe is also sent directly to the main process's operation room.

5. Conductivity meter Conductivity meter is a process meter (integrated transmitter) that measures the ion concentration indirectly by measuring the conductivity value of a solution, and can continuously detect the conductivity of an aqueous solution in an industrial process on-line. The conductivity meter is mainly composed of a conductivity cell, an electronic module, a display meter and a housing. The electronic module circuit is composed of excitation power supply, conductivity cell, conductance amplifier, phase sensitive rectifier, demodulator, temperature compensation, overload protection and current conversion. Since the electrolyte solution is a good conductor of electricity as well as the metal conductor, the current must flow through the electrolyte solution and must have an electrical resistance and comply with Ohm's law. However, the resistance temperature characteristics of liquids are contrary to those of metal conductors and have negative temperature characteristics. In order to distinguish from the metal conductor, the conductivity of the electrolyte solution is represented by conductance (reciprocal of resistance) or conductivity (reciprocal of resistivity). When two electrodes that are insulated from each other form a conductivity cell, a current loop is formed if the solution to be measured is placed in between, and a constant voltage alternating current is passed through. If the voltage size and the electrode size are fixed, the loop current and the conductivity have a certain function. In this way, measuring the current flowing in the solution to be measured, the conductivity of the solution to be measured can be measured.

In the industrial circulating water treatment system, the output signal of the conductivity meter is interlocked with the forced-discharge electric valve of the cold water tank of the net circulation and turbid circulation system. When the conductivity of the water in the cold water tank reaches a certain value, the forced-discharge electric valve is opened. The pool began to force sewage.

Second, the installation of various commonly used instruments in circulating water treatment facilities 1. There is no special installation requirement for installation of level gauges, float ball level gauges, magnetic steel flap level gauges.

Ultrasonic and radar level gauges shall be installed above the highest water surface. There shall be no obstructions (including the wall of the pool) down to the surface of the water within a certain range to prevent obstructions from reflecting sound waves to interfere with the measured values. Ultrasonic and radar level gauges are generally installed above structures such as hot and cold water tanks, sludge tanks, or sludge thickening tanks. Installation should be considered for ease of maintenance, and maintenance platforms should be provided when necessary.

2. The flowmeter installation flowmeter should be set up as far as possible on the surface mounted pipeline. Large diameter flowmeters are generally installed underground, so it is necessary to set up the instrumentation well. Wells are usually reinforced concrete structures and should not leak. The outdoor instrument wells must also be covered and should prevent rainwater or other water from entering the well from the lid. If necessary, the instrument wells should be equipped with automatic drainage facilities. When designing the instrument well, it should also be noted that the size of the manhole inspection hole must meet the instrument lifting requirements. The transmitter should be located in a location free of water-vapor erosion. For example, if the flowmeter leads to a sufficient length, it is best to set the transmitter in a room with good environment. Leads connected to the transmitter must not have any form of connector. The shielded wire should be well grounded.

The lining material of the electromagnetic flowmeter is mostly made of neoprene, because it has good wear resistance, especially when it is applied to turbid water. Installation should pay attention to the source of the electromagnetic field away from the outside world, so as not to affect the sensor's working magnetic field and flow signal, the sensor is installed horizontally, the central axis of the two electrodes is required to be in the horizontal state, to prevent the deposition of particulate impurities, affecting the electrode work. The measuring tube should be full of tubes and not allow a lot of air bubbles to pass through the sensor. When the conditions cannot be met, appropriate measures should be taken. In order to make the instrument work reliably and improve the measurement accuracy without interference from external parasitic potentials, the sensor should have a good separate grounding wire, and the grounding resistance should be less than 10Ω, especially when it is installed on the cathodic protection pipeline. The converter shall be installed in a place that meets the requirements of its degree of protection. Under the premise of meeting the installation environment and the requirements for use, the distance between the converter and the sensor and the connecting cable should be as short as possible to save investment and reduce the potential for strong electricity. Signal interference.

If the ultrasonic flowmeter is selected, special attention should be paid to the installation error of the sensor, the fouling of the inner wall of the pipeline, and the uniformity of the anticorrosion layer. These factors have a great influence on the measurement results. According to the measurement principle of the ultrasonic flowmeter, the accuracy of the measurement can only be guaranteed when the flow velocity distribution is uniform. Therefore, the ultrasonic flowmeter should not be set where the pipeline changes.

3. The installation of the thermometer Because the temperature difference between different water levels or different plane positions in the hot and cold water tanks of industrial circulating water treatment facilities is relatively large, it is recommended that the thermometers be installed in the circulating cooling water supply pipe and the water inlet main pipe of the cooling tower. Ensure the accuracy of the temperature measurement of the circulating water system. The thermometer on the buried pipeline can also be located in the underground meter well.

4. When installing the pressure gauge during installation, the pressure measuring tube should be provided with a damping device before entering the sensor to facilitate measuring the stable pressure value; the effect of the sensor installation height on the measured value should also be taken into account and the displayed value should be added. The pressure difference between the sensor and the pressure measurement point.

5. Installation of the conductivity meter The conductance meter's conductivity cell is located in the pool and the rest of the conductivity cell is located in the sink. Conductivity meter conductance pool should be set away from the hot and cold pool make-up water pipe, near the place where the water pipe is relatively good, the conductivity value is low. The location of the conductivity cell close to the cold water reservoir supplement pipe will cause inaccuracy in the judgment of the entire circulating water system quality, thus affecting the water quality stabilization of the circulating water system, such as dosing and forced drainage.

III. Conclusion The quality of the instrumentation is directly related to the normal operation of the industrial circulating cooling water system. When selecting the instrument, it is necessary to repeatedly compare the performance, quality, price, spare parts and after-sales service of the instrument. High accuracy; fast response time; output signal can be analog or digital (according to actual requirements); instrument protection level should meet the requirements of the environment, generally should not be less than IP65; field monitoring instrument should use digital display Instrument; the power supply of the instrument should be independent, and should not share the power supply with the computer, so as to ensure that the power supply does not interfere with each other during faults and maintenance, so that each can operate stably and reliably; should choose the instrument that can provide reliable service and have rich experience in production Manufacturers.