Reasons for fluctuations in gas flow measurement in large-diameter pipelines
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An air separation unit with a capacity of 60,000 units; a Shengyu series two-in-one compressor set. The flow rate at the compressor outlet is measured using Wilo sensors. The pipe diameter is 1.2 meters, with a maximum measurement range of 250,000 units; during normal operation the flow rate is around 200,000 units, while in actual use it fluctuates around 20,000 units. This variation has a significant impact on surge control. The measures taken include the following: 1. The original pressure guide pipe was too long, resulting in significant vibration. Its length was originally about 15 meters, but it has now been reduced to around 5 meters, which has basically eliminated the pipeline vibration; however, fluctuations still occur. 2. Check all connections to ensure there is no gas leakage. 3. Another target flowmeter was added, with both meters in use, but the readings still showed significant fluctuations. 4. The differential pressure transmitter uses Rosemount products; the damping has been set to its maximum level, but it has no effect. 5. The straight pipe sections before and after installation fully meet the requirements. There are several possible explanations: 1. The gas at the outlet of the unit is unstable, resulting in fluctuations in flow rate, but this cannot be verified. 2. When insert-type flow meters are used for measurement in large-diameter pipelines, the large length of the meter itself causes slight vibrations, which leads to fluctuations in the measurement results. If possible, it is planned to secure the lower end of the Velviba to see if that improves the situation. 3. Due to issues with the accuracy of the component itself during measurement, it is planned to switch to a perforated plate; however, it is unknown whether large-diameter perforated plates will have a significant impact on the resistance of the manufacturing process. I would be very grateful if all fellow sailors could share their insights!
It’s so long – why isn’t the lower end fixed?
1: Measure the current of the unit to see if there is a correlation between fluctuations in current and fluctuations in flow rate. 2: The pressure flow meters for pipes with a diameter of 1200 don’t have fixed slots; over time, once they bend, it might become impossible to remove them. 3: The advantage of pressure-based flow meters is their ease of installation, but their accuracy is lower. Additionally, if you set the damping to its maximum level, data distortion becomes quite severe. The pressure at the outlet of the air compressor should be at least a few kilograms to over a dozen kilograms, or even higher; the pressure loss caused by the orifice plate is practically negligible. By the way, what is the differential pressure range?
In the situation you described, when using pressure transmitters of the Ba type, it is necessary to install them with both ends fixed. If the airflow at that location is unstable, then you should consider choosing another location, such as further back or on the pipeline downstream from the pressure stabilizing tank. As for measuring the gas pressure, it’s better to connect the transmitter directly rather than using a pressure guide tube; the gas inside the guide tube can be compressed, and the shorter it is, the better. You could also consider using capillaries to transmit pressure – that’s about it
It uses a steam turbine instead of an electric drive, so it’s not possible to measure the current. Consider also the possibility that no vibration is generated at the lower end; then why does the target flow meter still experience fluctuations? Additionally, the damping was adjusted for testing; if it wasn’t effective, it was changed back. Thank you
The installation location is the best option, as it provides the longest straight pipe section; other locations do not meet the requirements for a straight pipe section. Furthermore, since both the flow rate and the target value fluctuate, it is suspected that the airflow itself is unstable, but this cannot be verified. I’m considering changing to an orifice plate.
Since there is doubt about the instability of the airflow itself, it indicates that this installation location is not necessarily the best choice (just because the straight pipe section is the longest does not mean it is the best location; it is merely one of the requirements specified for the flow meter). It is likely the \"unstable airflow\" caused by the pulsating flow at the compressor outlet; such pulsating flow can travel over long distances. Therefore, it is suspected that the installation location may not be the optimal spot – it would be better to choose a point on the pipeline after the pressure stabilizing tank.
Is the compressor outlet pressure stable? If both different instruments show fluctuations, I will inform the process team that it is the flow rate itself that is fluctuating, and it’s not a problem with the instruments.
What does a fluctuation of 20,000 mean? What is the unit for 20,000? Is it 20,000 fluctuations per second?, or 20,000 fluctuations per minute? Or 20,000 fluctuations in 1 hour or 10,000,000 hours? :P
It is necessary to describe clearly the temporal characteristics of the fluctuations in order to determine whether it is due to air flow or an inappropriate filtering and damping method for the differential pressure gauge.