Regarding the issue of mixing gas metering (not sure if this is the right place to post it)
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This post was last edited by Petrochemical Engineer on 2016-9-8 at 12:35. I have a question: There is a mixed gas whose flow rate needs to be measured. Orifice flow meters measure volumetric flow rate, and to determine the mass flow rate of the mixture, it is necessary to first find out the density of the mixed gas. After sampling and analysis, the average molecular weight M of the gas mixture is calculated based on its volume composition (it is obtained by multiplying the volume fractions of each component as determined by chromatographic analysis by their respective molecular weights). Using the gas law: density = PM (average molecular weight) / RT, where P and T are the parameters under which the gas is present in the pipeline, the density of the gas mixture in the pipeline can be calculated. I’m not sure if this method of calculation is correct
This post was last edited by ssln123 on 2016-9-8 at 10:53. I didn’t understand what the original poster meant; if measurement is necessary, it comes down to choosing a flow meter. If the density is difficult to determine, then a mass flow meter could be considered.
I’ve revised the post again; it should be clear now. It’s not a problem of choosing a flow meter; one already exists.
OP, what are the actual pressure and temperature?
What is the operating pressure? The ideal gas law is only applicable to gases at low pressures; the lower the pressure, the smaller the deviation.
The following are my personal opinions; please feel free to correct me if I’m wrong. What needs to be measured here is the mass flow rate. Currently, the data available includes the volume flow rate measured by the orifice flow meter, as well as the density determined based on the gas composition. The mass flow rate is then calculated from these values of volume flow rate and density. However, this method yields inaccurate results. Setting aside for now the error in the density value calculated, the volume flow rate measured by the orifice flow meter (which is determined by the pressure difference created by the throttling element) is itself related to density; therefore, this volume flow rate also needs to be corrected. M_actual = Q_measured * sqrt(ρ_design/ρ_actual) * ρ_actual. It’s quite a complicated process that results in not very accurate data. Why not use a mass flow meter instead?
The simplest method is to install a gas densitometer on the gas pipeline, integrate the actual density value provided by the densitometer with the volumetric flow rate; this should work.
I just think that a mass flow meter might be a more reasonable choice than an orifice plate... As for whether it’s easy to measure, I’m not sure either...
When measuring gases, it’s not possible to simply apply the ideal gas law; for real gases, the compressibility factor must be taken into account.
This method does not provide accurate measurements; it is best to use a mass flow meter.