Ask about the relationship between flow rate and pressure
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This post was last edited by batawfn on 2017-6-2 at 10:25. The current installation location is in front of our control valve; the flow meter has a diameter of 150, and the operating pressure is 0.4–0.5 bar, with the actual pressure being around 0.45 bar. My requirement is for a maximum flow rate of 2800 m3/h of natural gas. I want to work downstream of the control valve, that is, downstream of the pressure regulator, in order to avoid the effects of fluctuations in the pressure of the air supply upstream. The working pressure downstream is 0.2 bar, and it remains relatively stable within this range. I’m wondering whether the flow measurement range is sufficient, and by how much will the value decrease! Is there a specific conversion formula? Even knowing an approximate range would be fine for control instruments
There is basically no impact; note that the flow meter requires straight pipelines before and after it, and it should not be too close to the control valve, as this could affect flow stability.
If it is a flow control valve, it is best to place the flow meter upstream of the control valve; otherwise, the fluctuations will be greater. If you really want to test the flow meter, ensure that there is as long a straight pipe section as possible ahead of it
Is the 2800 m3/h natural gas flow rate mentioned by the poster the flow rate under standard conditions or under actual operating conditions? What is the measurement range of the flow meter (usually the operating flow range)? Assuming that 2800 m3/h is the flow rate under standard conditions, and the flow meter is installed in front of the control valve with a medium pressure of 0.45 bar (gauge pressure, which needs to be converted to absolute pressure for calculation), the flow rate under actual operating conditions can be estimated as: 2800/(0.45+1) = 1931 m3/h ； Similarly, when the flow meter is installed after the control valve and the medium pressure is 0.2 bar, the operating flow rate is estimated to be: 2800/(0.2+1) = 2333 m3/h. In other words, if the flow meter’s measurement range covers the values of 1931 and 2333, it means that the flow rate can be measured whether the meter is installed before or after the control valve. The above calculation formulas take into account only the effect of pressure, representing the most rough estimate ； The conversion formula between the actual flow rate under standard conditions and the flow rate under operating conditions also needs to take into account the effects of temperature and the gas compressibility factor (factors that must be considered due to the difference in compressibility between real gases and ideal gases). However, such rough estimates do not affect the interpretation of the results, unless the calculated values correspond to the extreme limits of the flow meter’s measurement range (the maximum and minimum flow rates that can be measured).
Don’t count it; think about it – everything goes through a flow meter, and before and after installation there is only a change in pressure. If it is installed at the back, the pressure behind the valve that can be controlled may not be 0.2; to achieve the same flow rate, the control valve will need to be opened a little more.