Fluctuations in the measurement of cryogenic liquids
Thread Content
For liquid level measurement in LNG storage tanks, pressure transmitters with differential pressure sensors are commonly used; during operation, peak levels occur in the morning and evening, following a fairly regular pattern. Besides switching to a top-mounted servo level gauge, what other ways are there to eliminate wave peaks?
By making changes to the piping, the morning and evening peaks can be eliminated. . . A servo is necessary.
Is it in the north? The temperature difference between day and night is large. If it has no impact on the medium, it’s fine to use a pressure guide pipe with heating to maintain a constant temperature for the medium
Under normal circumstances, the medium in the pressure guide tube vaporizes; when the temperature is low, it condenses back. Such a situation occurs when the temperature is not constant.
1. The operation of the process has an impact on the liquid level in the storage tank; search for “Research on the Stability of Differential Pressure Level Measurement for Cryogenic Liquids””； 2. For measuring the liquid level differential pressure in low-temperature storage tanks, a short section of pressure guide tube is necessary for the vaporization of the liquid, thereby preventing damage to the diaphragm used in the positive-pressure measurement. Temperature affects the height of the liquid accumulation on the positive-pressure side, which can result in slight variations in the liquid level reading ； 3. Replacing the servo requires modifying the pressure vessel, and the cost is not low. While liquid level measurement becomes more accurate, this approach is not convenient for trade handovers. The capacity of the tank also needs to be regularly calibrated; generally, flow meters or weighing systems are used for such handovers ； 4. It is not known what the range of fluctuations is; if it is within a reasonable range, it is suitable for use in level alarms and interlocks ； Overall, the differential pressure method is a commonly used level measurement technique for low-temperature storage tanks; it features high reliability and simple maintenance. By strengthening the maintenance of these instruments, it is possible to reduce the fluctuations in level measurements.
Thank you for the advice. For 5000 m3 LNG storage tanks, fluctuations of several dozen centimeters affect the measurement reports; therefore, there is a requirement to improve accuracy.
What was said on the 4th floor is correct; this situation is caused by the temperature difference between day and night, and it is necessary to add heat mixing to the pressure measurement pipeline. The problem can be solved.
If increasing the heat tracing does not solve the problem, a bypass pipe can be added to use guided-wave radar for measurement
The pressure transmission in the root diaphragm box may be affected under low-temperature conditions. If the level gauge is exposed to air, condensation due to the air dew point will occur after it is reinstalled, which can have an impact on the root section