Does natural gas flow need to be density compensated if it is already pressure and temperature compensated . . .
. . . or does pressure and temperature compensation account for density changes?

What is the formula to pressure, temperature, and density compensate a natural gas flow calculation.

 

Assuming your flowmeter is turbine based, AGA 7 (2002) says the flow needs to be corrected to P (pressure), T (temperature) and Z (compressibility).

P and T is direct measured from sensor, but Z is calculated based on AGA 8 (1994) standard.

i'm giving an example based on industry practice.

<i>* AGA = American Gas Association</i>

 

It is a dP transmitter, measuring natural gas flow across an orifice plate. Hoping that Pressure and Temperature compensation is sufficient, without the need to density compensate. Also interested in AGA or ASME standard associated with said gas flow compensation.

 

The pressure and temperature compensation is the density compensation!

 

Gromit,

Provided your gas composition does not change and the molecular weight or SG is constant, pressure and temperature compensation is all you need to compute the correct density. If gas composition varies, then this is a separate issue and a gas analyzer would be required unless the variances are minimal and you can live with the error. Selecting a mean density can cut this error in half if you don't want to shell out $$ for an analyzer.

 

ok, since it is based on orifice plate - then AGA 3(1995) is applicable for your case. As per the said standard, the following input is required:

1. dP
2. actual, P
3. actual, T
4. actual, Z
5. corrected, Z
6. actual, Density
7. corrected, Density

pls note that item 4 to 7 is an output of AGA 8 calculation.

below is a very GOOD explanation of your application. pls take a look.

http://www.xivix.ca/AGA_ALL/AGA/ENG/AGA3.htm

cheers