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The input hydrostatic level transmitter is widely used in petrochemical, electric power, metallurgy, and environmental protection industries due to its simple use, high precision, and easy installation and maintenance. However, due to some reasons, the measurement error is too large during the actual use, which affects the use of this measuring principle instrument. This paper analyzes the error causes of the level of the fore pool in the six-phase circulating pump room of Taiyuan No. 1 Thermal Power Plant, and proposes solutions for peer reference.
First, the input static pressure level transmitter working principle The static pressure of the liquid medium directly or indirectly acts on the sensor diaphragm, the static pressure is proportional to the height of the liquid to be measured, the static pressure generated by the liquid level makes the measuring diaphragm Displacement occurs, capacitance changes due to displacement of the diaphragm, detection of electronic components directly connected to it, amplification and conversion to standard signal output.
The formula is:
H: The height of the medium P: The differential pressure of the medium height Ï: The density of the medium g: Gravity acceleration Second, the engineering overview The sixth phase of the Taiyuan No. 1 Thermal Power Plant is a heating extraction unit supporting a Polish boiler of 2×300MW domestic turbines. Four circulating water pumps are installed in the circulating pump room of this project. The circulating water is supplied from the Taiyuan No. 1 Thermal Power Plant's storage reservoir - Jinyang Lake bank pumping station to the wet cooling tower via an underground pipeline. The circulating water is then transferred from the wet cooling tower to the circulation pump room forecourt, through the filter, to the circulation pump inlet, and then The circulating pump boosts pressure to the unit condenser. A total of five input-type hydrostatic level transmitters were installed in the front tank and at the inlet of each circulation pump.
Third, the phenomenon of failure Since the official transfer of the project, the maintenance of the circulation pump room is handed over to the old factory thermal workshop. Although the unit is a newly built unit, the level of the front pool of the circulating water pump house and the level of the inlet of the circulating pump frequently shift periodically after the official handover. The measurement level is low. After several verifications, the measurement instrument itself has no problems, and the instrument error level, accuracy, and range have not changed. Due to the remoteness of the pump house, the emergence of these problems led to the difficulty of inspection and maintenance work and the increase of labor intensity, which caused maintenance personnel to rush.
Fourth, the reason analysis Because the circulating water of this project is water stock water, the water contains a large number of microorganisms, algae, and it is rich in a lot of gas. In the water circulation process, the gas in the water is released at all times. Since the engineering design unit uses the input-type static pressure level transmitter, the diaphragm is in the transmitter body, and only a piece of stainless steel pipe is used in the water. And the pressure tube, there is a large space for accumulated gas in the pipeline, when the gas in the water is released and enters the pipeline, and slowly accumulates, so that the pressure p of the gas in the tube slowly increases, offsetting the height of the water. The pressure causes the pressure P acting on the diaphragm to decrease, thereby reducing the output of the transmitter.
The formula is:
p: Air pressure in the pressure pipe. 5. Improvement measures We analyzed the cause of the error. Since the input static pressure level transmitter cannot completely eliminate the cause of the error, the principle of the liquid level measuring instrument is no longer used. We used a non-contact ultrasonic liquid level transmitter in the front pool of the circulating pump room. After prolonged trial operation, the level measurement in the forebay of the circulating pump room was accurate, and no periodic measurement deviation occurred. It can be considered that this improvement measure is feasible and successful. The replacement of the level measuring instrument at the inlet of the circulation pump will be implemented in subsequent improvements.
VI. Conclusion Through this improvement measure, we have found the cause of the deviation and adopted ultrasonic liquid level measuring instruments to solve the problem of water level deviation. Summing up the above improvement measures, we believe that the input hydrostatic level transmitter is simple in principle and easy to install, but if the selection is not good, it will also lead to measurement deviation problems during use. If the input hydrostatic level transmitter does not use a pressure tube or if there is no room for gas storage in the design, the level transmitter will be more accurate and reliable.
At the same time, according to our application experience, the use of ultrasonic liquid level transmitters in open spaces is completely feasible and reliable, but it is not advisable to use ultrasonic level transmitters in confined spaces such as chemical desalination tanks and other containers. Because in the north of winter, the water tank will produce water vapor condensation on the ultrasonic probe, causing the ultrasonic liquid level transmitter to measure deviations. Therefore, when designing the liquid level measuring instrument, the measured medium and the difference in the measured environment should be fully considered. Different measuring instruments are used to ensure the accuracy and reliability of the measurement.
First, the input static pressure level transmitter working principle The static pressure of the liquid medium directly or indirectly acts on the sensor diaphragm, the static pressure is proportional to the height of the liquid to be measured, the static pressure generated by the liquid level makes the measuring diaphragm Displacement occurs, capacitance changes due to displacement of the diaphragm, detection of electronic components directly connected to it, amplification and conversion to standard signal output.
The formula is:
H: The height of the medium P: The differential pressure of the medium height Ï: The density of the medium g: Gravity acceleration Second, the engineering overview The sixth phase of the Taiyuan No. 1 Thermal Power Plant is a heating extraction unit supporting a Polish boiler of 2×300MW domestic turbines. Four circulating water pumps are installed in the circulating pump room of this project. The circulating water is supplied from the Taiyuan No. 1 Thermal Power Plant's storage reservoir - Jinyang Lake bank pumping station to the wet cooling tower via an underground pipeline. The circulating water is then transferred from the wet cooling tower to the circulation pump room forecourt, through the filter, to the circulation pump inlet, and then The circulating pump boosts pressure to the unit condenser. A total of five input-type hydrostatic level transmitters were installed in the front tank and at the inlet of each circulation pump.
Third, the phenomenon of failure Since the official transfer of the project, the maintenance of the circulation pump room is handed over to the old factory thermal workshop. Although the unit is a newly built unit, the level of the front pool of the circulating water pump house and the level of the inlet of the circulating pump frequently shift periodically after the official handover. The measurement level is low. After several verifications, the measurement instrument itself has no problems, and the instrument error level, accuracy, and range have not changed. Due to the remoteness of the pump house, the emergence of these problems led to the difficulty of inspection and maintenance work and the increase of labor intensity, which caused maintenance personnel to rush.
Fourth, the reason analysis Because the circulating water of this project is water stock water, the water contains a large number of microorganisms, algae, and it is rich in a lot of gas. In the water circulation process, the gas in the water is released at all times. Since the engineering design unit uses the input-type static pressure level transmitter, the diaphragm is in the transmitter body, and only a piece of stainless steel pipe is used in the water. And the pressure tube, there is a large space for accumulated gas in the pipeline, when the gas in the water is released and enters the pipeline, and slowly accumulates, so that the pressure p of the gas in the tube slowly increases, offsetting the height of the water. The pressure causes the pressure P acting on the diaphragm to decrease, thereby reducing the output of the transmitter.
The formula is:
p: Air pressure in the pressure pipe. 5. Improvement measures We analyzed the cause of the error. Since the input static pressure level transmitter cannot completely eliminate the cause of the error, the principle of the liquid level measuring instrument is no longer used. We used a non-contact ultrasonic liquid level transmitter in the front pool of the circulating pump room. After prolonged trial operation, the level measurement in the forebay of the circulating pump room was accurate, and no periodic measurement deviation occurred. It can be considered that this improvement measure is feasible and successful. The replacement of the level measuring instrument at the inlet of the circulation pump will be implemented in subsequent improvements.
VI. Conclusion Through this improvement measure, we have found the cause of the deviation and adopted ultrasonic liquid level measuring instruments to solve the problem of water level deviation. Summing up the above improvement measures, we believe that the input hydrostatic level transmitter is simple in principle and easy to install, but if the selection is not good, it will also lead to measurement deviation problems during use. If the input hydrostatic level transmitter does not use a pressure tube or if there is no room for gas storage in the design, the level transmitter will be more accurate and reliable.
At the same time, according to our application experience, the use of ultrasonic liquid level transmitters in open spaces is completely feasible and reliable, but it is not advisable to use ultrasonic level transmitters in confined spaces such as chemical desalination tanks and other containers. Because in the north of winter, the water tank will produce water vapor condensation on the ultrasonic probe, causing the ultrasonic liquid level transmitter to measure deviations. Therefore, when designing the liquid level measuring instrument, the measured medium and the difference in the measured environment should be fully considered. Different measuring instruments are used to ensure the accuracy and reliability of the measurement.
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