Gas flow rate issues in pipelines
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I would like to ask: the gas flow rate in the pipeline, which is shown as NM3/H on the DCS, is it related to the flow velocity of the gas inside the pipeline? The higher the flow rate, the larger it will display, right? In our methanol synthesis process, the flow rate of the gas exiting the alcohol separation unit is 410,000 NM3/H. This gas is then divided into two streams: one stream is vented (with the valve set at 0%), while the other stream goes to the recycler. The anti-surge flow rate for the recycler is indicated as 540,000 NM3/H (with the anti-surge valve also set at 0%) Let’s analyze the reasons. Bonus: The gauge is good!
Could any friend help explain this? ? It’s urgent!
Is there a change in pressure? Changes in pressure cause changes in volume
Pressure and temperature both affect the readings; it’s best to perform temperature and pressure compensation
Flow meters are highly dependent on the flow characteristics and physical property parameters of the medium being measured. Physical properties include: density, pressure, temperature, viscosity, isentropic index, fluid sound speed, compressibility coefficient, etc. Additionally, it has strict requirements for installation on-site. Some types require long straight sections upstream and downstream, such as orifice plate and vortex flow meter types; whereas other types have lower requirements or no such requirements at all, such as positive displacement and float type meters. The factors to be considered in this regard generally include: upstream and downstream measurement sections, pipe diameter, whether the pipeline vibrates or not, ease of maintenance, valve location, pipeline direction, electrical wiring and the presence of electromagnetic interference, as well as protective accessories. The accuracy or basic error specified in the instruction manuals for general flow meters is determined under the design conditions of those products; however, field usage conditions can vary greatly. This inevitably leads to additional errors, and such errors can only differ in magnitude – they cannot be completely eliminated. The field accuracy of a flow meter is the combination of the basic error and the additional errors. It varies depending on different operating conditions. Therefore, flow meters are instruments that rely heavily on the conditions in which they are used. They may be highly precise and accurate under laboratory conditions, but once in the field, changes in those conditions can lead to significant errors, or even render the flow meter unusable; hence, special attention must be paid. In addition, factors such as the ambient temperature and humidity at the site, the need for explosion protection, and the presence of electrical interference all have a significant impact on its measurement values. This is because electrical cables, motors, electrical switches and other wiring systems as well as electrical equipment generate electromagnetic interference. Moreover, high ambient temperatures or high humidity can shorten the lifespan of electronic components, thereby affecting the accuracy of the measurement data. Please have the LZ make a judgment based on their own type of gauge and actual operating conditions; for differential pressure gauges, this generally relates to the selection of the orifice diameter, wear, and blockages in the positive and negative pressure chambers ； Vortex street type is generally related to operating conditions (changes in Reynolds number). If the operating conditions vary greatly, temperature and pressure compensation needs to be added for correction.
With such a high flow rate, it’s probably a constant-flow tube? Similar flowmeters often exhibit significant errors in measurement
It might be that the resistance loss in the main pipeline is too high, which could lead to such a problem.....
The temperature at the alcohol outlet is 32.3°C, and at the inlet of the circulation pump it is 32.8°C. Since it’s the same pipeline, there shouldn’t be any losses along this pipeline from the alcohol outlet to the inlet of the circulation pump!
Flow rate is related to flow velocity; the flow rate is the product of flow velocity and the cross-sectional area of the pipe. Therefore, a higher flow velocity results in a higher flow rate, provided that the diameter of the pipe remains constant
Personally, I think what you’re saying are two different things. The anti-surge flow rate displayed on the DCS is not the one at the site; temperature compensation or pressure compensation should be applied. If it is temperature compensation, the higher the temperature, the lower the flow rate ； And pressure compensation is the same. The actual measurements taken on-site are not under standard conditions (101.325 KPA, 273.15 K), so it is necessary to convert them to standard conditions; compensation is required for this purpose. Only after conversion to standard conditions can they be compared with the design specifications, as the anti-surge design was originally developed under standard conditions. As for 410,000 NM3/H, it depends on how it is measured on-site; it could be a orifice flow meter or something else? The 410,000 on DCS is also obtained after conversion. If I’m wrong, please correct me.
There are probably few cases of temperature compensation and pressure compensation; the key issue lies in the suction pressure at the compressor inlet, which causes an increase in the inlet flow velocity and thus an increase in flow rate. The outlet flow rate of the alcohol component does not change much, due to pipeline resistance. I’m not sure if this explanation is valid. I appreciate your advice!