Application of electromagnetic flowmeter in strong corrosive environment
Henan Province Zhongyuan Dahua Group's urea production plant uses two electromagnetic flowmeters. One is used to measure the inlet flow rate of the high-pressure ammonium pump; the other is to measure the flow rate of the hydrolyzed waste liquid. In practical applications, both the response speed and other characteristics can meet the needs of process production. But there have also been some problems that we did not expect. Since it was completed and put into production in October of the same year, only two electromagnetic flowmeters measuring the inlet flow rate of the high-pressure ammonium forma- tion pump have been destroyed. In addition, one electromagnetic flowmeter for measuring the hydrolyzed waste liquid has also been damaged. The emergence of these problems has increased our factory's burden no matter from the process operation, or from the cost of production. This article will discuss the application of this plant.
The working principle and characteristics of the electromagnetic flowmeter 1. Working principle The electromagnetic flowmeter system is composed of a transmitter and a converter. The two are connected by two cables with double shielded cables. The transmitter is installed on the pipe system. The converter can be installed on site or in a central room. The measurement principle of the meter is based on Faraday's Law of Electromagnetic Induction: When a conductor is moved in a magnetic field to cut magnetic lines of force, induced electromotive force is generated at both ends of the conductor.
The same applies to the application of a conductive fluid. If it is assumed that the magnetic field strength is B, the pipe diameter is D, and the induced potential is E, then the volumetric flow rate of the pipe can be proved to be Qv=D/4×(E/B).
In the formula, B and D are set in the table. E is measured by a pair of electrodes on the measuring pipe of the transmitter. The actual electromagnetic flowmeter works according to this principle. It can be seen that the electromagnetic flowmeter is an instrument for measuring the volume flow, which has nothing to do with the physical properties such as temperature, pressure, density, viscosity, and conductivity of the fluid.
2, the characteristics of electromagnetic flowmeter Electromagnetic flowmeter has the following characteristics:
(1) The sensing element is not in contact with the measuring medium and can be used for the measurement of corrosive conductive medium flow;
(2) Wide range, the electromagnetic flowmeter with the same ratio up to 1:100;
(3) No pressure loss;
(4) The detection part has no movable parts:
(5) The flow of positive and negative fluids can be measured;
(6) Fast response.
The above are the advantages of the electromagnetic flowmeter, but it also has certain limitations and deficiencies.
(1) The measured medium must be conductive:
(2) Due to the limitation of the material of the lining of the measuring tube, the general use temperature range is 0-200°C, and because the electrode is embedded on the catheter, the working pressure of the electromagnetic flowmeter is also limited.
(3) The electromagnetic flowmeter has a complex structure and a high price.
3, the application of electromagnetic flowmeter I plant ammonium pump inlet flowmeter FT-09101 Germany's FISCHER & POTER's products, since it was put into operation in October 89, has replaced two, the initial use of DX1221 type, this electromagnetic flow meter with In stainless steel, the inner wall of the measuring tube is made of Teflon. The converter is enclosed in a cuboidal metal shell. The internal circuit board has a four-digit data disk and can be used as an indicator of the measured value. The transmitter and the converter are connected by two cables. The transmitter is installed on the pipeline and the converter is fixed on the frame next to it. This kind of flow meter can't adjust by itself regardless of zero or range, can only be calibrated at the appointed factory, it is very inconvenient to use. The flowmeter has not yet been used for one year and the indication has failed. After inspection, it was found that the circuit board of the transmitter has been corroded and several transistors have been rusted. This has not caused us enough attention. Only a few triodes were replaced and reinstalled. After repairing, the watch operated for several months and then lost its instructions. When we checked the watch again, we found that the circuit board and seven-core cable of the transmitter had all been corroded, and the watch was scrapped. This caused us to be vigilant. The original place where the watch was installed was too close to the high-pressure ammonia pump and the high-pressure ammonia pump. The ammonia that was emitted during the stoppage and leaked normally, and the ammonia gas attached to the ammonia, were often wrapped around the watch. As a result, the watch has been working in a corrosive environment, plus we have only paid attention to the corrosion resistance of the watch, and neglected the fragility of the watch, eventually leading to damage to the watch.
After learning lessons, we replaced another instrument of the same type in the overhaul of the year 92. However, this time we have paid special attention to the problem of corrosion. In order to prevent corrosive gases from intruding into the electronic room, we are at the edge of the junction box cover and cables. The joints are all sealed with silicone rubber and sealed with water and electricity dual-purpose tape in order to achieve the purpose of anti-corrosion. After the watch was put into operation for more than one year, the same failure occurred again, and the transmitter circuit board and cable were corroded and the watch was damaged.
When the accident happened again, we had to think carefully about the problem of corrosion. Why did the transmitter seal so well and erode? The converter that was only half a meter away from the transmitter was safe and sound. After careful observation and analysis, The answer has finally been found. The original installation of the transmitter's pipe was due to the high flow rate, and it was constantly vibrating. The sealant was easy to loosen and fall off. The continuous vibration increased the assisting power for the intrusion of ammonia gas. The converters on the frame have no vibration and the seals are intact, so there is no corrosion.
Find the cause of the failure, naturally find the troubleshooting measures. In the 1994 overhaul, we replaced this watch again. This time, we used an electromagnetic flowmeter from Jiangsu Jiujiu Instrument Co., Ltd. This electromagnetic flowmeter is much more advanced than the former two. It uses microprocessor technology. There is a double row of liquid crystal display on the converter, there are three buttons below the display, through which you can configure the parameters of the flowmeter, and you can look up the relevant parameter setting of the flowmeter. The table has a strong external communication interface capabilities, can communicate with other peripherals in analog and digital manner, and with a strong self-diagnostic function, the input and selection of parameters to direct data input and main sub-menu selection mode, The zero adjustment and range setting can be easily performed and the operation is very convenient. In order to ensure the safe operation of this watch, we have adopted another anti-corrosion measure based on the lessons of the first two lessons - the air blow and antiseptic method. The principle of this method is to increase the pressure of pure gas in the transmitter junction box, so that harmful gases cannot invade the junction box, so as to achieve anti-corrosion purposes. The specific method is to make two small holes in the electronic chamber of the electromagnetic flowmeter transmitter, an air intake, an exhaust, and then connected to the instrument air, so that the air maintains a small flow, then the pressure of pure air in the electronic room is increased, Air flow can only flow from the inside to the outside of the pores, thus preventing the intrusion of harmful gases and playing a role in preservation. After the watch was put into operation, the effect has been very good. In the 2001 overhaul that took 7 years, we had opened the electronic room inspection and found no corrosion. It can be seen that blowing and antisepticizing really played a role.
Just in case, we also pay attention to the usual maintenance, regular replacement of the insulating tape and sealant on the converter and the transmitter cable to prevent seal damage caused by aging. In order to protect the LCD monitor, we added a sun visor to the monitor to prevent the LCD monitor from being exposed to direct sunlight for a long time. There was also a failure of the small-diameter flowmeter FT-09701 for the measurement of hydrolyzed waste liquid. This watch is also a product of FISCH&POTER. It is an integrated device. The converter and the transmitter are fixed together and transmitted by the communication cable. To the main control room, the fault phenomenon is measuring the lining of the tube bulge, so that the eddy current flow lines become bent, destroying the axial symmetry of the fluid flow rate, causing great errors in the measurement, the instrument failure, the specific cause of the bulging in the end is Over-temperature and over-pressure, or product quality issues are still not clear. At the time of overhaul in 1993, we replaced a new model with the same model. The results showed that the circuit board corrosion phenomenon occurred after not running for a long time. In 1995 and 1998, we updated this watch, and the main causes of damage were also It is the corrosion of the circuit board. In 1998, we improved the meter by blowing the meter air. Until now, there was no abnormal phenomenon on this watch. The operation has been good.
4. Concluding Remarks We just discussed the anti-corrosion problem of the electromagnetic flowmeter in combination with the application of our plant. Of course, there are many better ways to prevent corrosion. This depends on the conditions. In fact, the electromagnetic flowmeter should also be used in applications. Considering electromagnetic interference, vibration, and other factors that affect the accuracy of the measurement, we must consider its advantages as well as its limitations. Only a comprehensive study of the analysis and rule out all the adverse factors in order to make better use of electromagnetic flowmeter.
The working principle and characteristics of the electromagnetic flowmeter 1. Working principle The electromagnetic flowmeter system is composed of a transmitter and a converter. The two are connected by two cables with double shielded cables. The transmitter is installed on the pipe system. The converter can be installed on site or in a central room. The measurement principle of the meter is based on Faraday's Law of Electromagnetic Induction: When a conductor is moved in a magnetic field to cut magnetic lines of force, induced electromotive force is generated at both ends of the conductor.
The same applies to the application of a conductive fluid. If it is assumed that the magnetic field strength is B, the pipe diameter is D, and the induced potential is E, then the volumetric flow rate of the pipe can be proved to be Qv=D/4×(E/B).
In the formula, B and D are set in the table. E is measured by a pair of electrodes on the measuring pipe of the transmitter. The actual electromagnetic flowmeter works according to this principle. It can be seen that the electromagnetic flowmeter is an instrument for measuring the volume flow, which has nothing to do with the physical properties such as temperature, pressure, density, viscosity, and conductivity of the fluid.
2, the characteristics of electromagnetic flowmeter Electromagnetic flowmeter has the following characteristics:
(1) The sensing element is not in contact with the measuring medium and can be used for the measurement of corrosive conductive medium flow;
(2) Wide range, the electromagnetic flowmeter with the same ratio up to 1:100;
(3) No pressure loss;
(4) The detection part has no movable parts:
(5) The flow of positive and negative fluids can be measured;
(6) Fast response.
The above are the advantages of the electromagnetic flowmeter, but it also has certain limitations and deficiencies.
(1) The measured medium must be conductive:
(2) Due to the limitation of the material of the lining of the measuring tube, the general use temperature range is 0-200°C, and because the electrode is embedded on the catheter, the working pressure of the electromagnetic flowmeter is also limited.
(3) The electromagnetic flowmeter has a complex structure and a high price.
3, the application of electromagnetic flowmeter I plant ammonium pump inlet flowmeter FT-09101 Germany's FISCHER & POTER's products, since it was put into operation in October 89, has replaced two, the initial use of DX1221 type, this electromagnetic flow meter with In stainless steel, the inner wall of the measuring tube is made of Teflon. The converter is enclosed in a cuboidal metal shell. The internal circuit board has a four-digit data disk and can be used as an indicator of the measured value. The transmitter and the converter are connected by two cables. The transmitter is installed on the pipeline and the converter is fixed on the frame next to it. This kind of flow meter can't adjust by itself regardless of zero or range, can only be calibrated at the appointed factory, it is very inconvenient to use. The flowmeter has not yet been used for one year and the indication has failed. After inspection, it was found that the circuit board of the transmitter has been corroded and several transistors have been rusted. This has not caused us enough attention. Only a few triodes were replaced and reinstalled. After repairing, the watch operated for several months and then lost its instructions. When we checked the watch again, we found that the circuit board and seven-core cable of the transmitter had all been corroded, and the watch was scrapped. This caused us to be vigilant. The original place where the watch was installed was too close to the high-pressure ammonia pump and the high-pressure ammonia pump. The ammonia that was emitted during the stoppage and leaked normally, and the ammonia gas attached to the ammonia, were often wrapped around the watch. As a result, the watch has been working in a corrosive environment, plus we have only paid attention to the corrosion resistance of the watch, and neglected the fragility of the watch, eventually leading to damage to the watch.
After learning lessons, we replaced another instrument of the same type in the overhaul of the year 92. However, this time we have paid special attention to the problem of corrosion. In order to prevent corrosive gases from intruding into the electronic room, we are at the edge of the junction box cover and cables. The joints are all sealed with silicone rubber and sealed with water and electricity dual-purpose tape in order to achieve the purpose of anti-corrosion. After the watch was put into operation for more than one year, the same failure occurred again, and the transmitter circuit board and cable were corroded and the watch was damaged.
When the accident happened again, we had to think carefully about the problem of corrosion. Why did the transmitter seal so well and erode? The converter that was only half a meter away from the transmitter was safe and sound. After careful observation and analysis, The answer has finally been found. The original installation of the transmitter's pipe was due to the high flow rate, and it was constantly vibrating. The sealant was easy to loosen and fall off. The continuous vibration increased the assisting power for the intrusion of ammonia gas. The converters on the frame have no vibration and the seals are intact, so there is no corrosion.
Find the cause of the failure, naturally find the troubleshooting measures. In the 1994 overhaul, we replaced this watch again. This time, we used an electromagnetic flowmeter from Jiangsu Jiujiu Instrument Co., Ltd. This electromagnetic flowmeter is much more advanced than the former two. It uses microprocessor technology. There is a double row of liquid crystal display on the converter, there are three buttons below the display, through which you can configure the parameters of the flowmeter, and you can look up the relevant parameter setting of the flowmeter. The table has a strong external communication interface capabilities, can communicate with other peripherals in analog and digital manner, and with a strong self-diagnostic function, the input and selection of parameters to direct data input and main sub-menu selection mode, The zero adjustment and range setting can be easily performed and the operation is very convenient. In order to ensure the safe operation of this watch, we have adopted another anti-corrosion measure based on the lessons of the first two lessons - the air blow and antiseptic method. The principle of this method is to increase the pressure of pure gas in the transmitter junction box, so that harmful gases cannot invade the junction box, so as to achieve anti-corrosion purposes. The specific method is to make two small holes in the electronic chamber of the electromagnetic flowmeter transmitter, an air intake, an exhaust, and then connected to the instrument air, so that the air maintains a small flow, then the pressure of pure air in the electronic room is increased, Air flow can only flow from the inside to the outside of the pores, thus preventing the intrusion of harmful gases and playing a role in preservation. After the watch was put into operation, the effect has been very good. In the 2001 overhaul that took 7 years, we had opened the electronic room inspection and found no corrosion. It can be seen that blowing and antisepticizing really played a role.
Just in case, we also pay attention to the usual maintenance, regular replacement of the insulating tape and sealant on the converter and the transmitter cable to prevent seal damage caused by aging. In order to protect the LCD monitor, we added a sun visor to the monitor to prevent the LCD monitor from being exposed to direct sunlight for a long time. There was also a failure of the small-diameter flowmeter FT-09701 for the measurement of hydrolyzed waste liquid. This watch is also a product of FISCH&POTER. It is an integrated device. The converter and the transmitter are fixed together and transmitted by the communication cable. To the main control room, the fault phenomenon is measuring the lining of the tube bulge, so that the eddy current flow lines become bent, destroying the axial symmetry of the fluid flow rate, causing great errors in the measurement, the instrument failure, the specific cause of the bulging in the end is Over-temperature and over-pressure, or product quality issues are still not clear. At the time of overhaul in 1993, we replaced a new model with the same model. The results showed that the circuit board corrosion phenomenon occurred after not running for a long time. In 1995 and 1998, we updated this watch, and the main causes of damage were also It is the corrosion of the circuit board. In 1998, we improved the meter by blowing the meter air. Until now, there was no abnormal phenomenon on this watch. The operation has been good.
4. Concluding Remarks We just discussed the anti-corrosion problem of the electromagnetic flowmeter in combination with the application of our plant. Of course, there are many better ways to prevent corrosion. This depends on the conditions. In fact, the electromagnetic flowmeter should also be used in applications. Considering electromagnetic interference, vibration, and other factors that affect the accuracy of the measurement, we must consider its advantages as well as its limitations. Only a comprehensive study of the analysis and rule out all the adverse factors in order to make better use of electromagnetic flowmeter.
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