NX-19 Calculations for Compressibility 1

[anicefob]

thread1036-309842

Thanks to linepacker for the VBA for calculating the supercompressibility factor. There are some minor errors in the VBA code & points for those wishing to use it.

1) You need to replace
nx19_Padj = (156.47 * nx19_Ppsia) / (160.8 - (7.22 * SG) + moleCO2 - (0.392 * moleN2))
with
nx19_Padj = (156.47 * Ppsig) / (160.8 - (7.22 * SG) + moleCO2 - (0.392 * moleN2))

This is because nx19_Padj is supposed to be in psig. Also, not doing it would result in double counting of the atmospheric pressure (14.7 psia) when computing the variable nx19_Pii

2) You need to replace
nx19_fpv = ((1 + (0.00132 / nx19_Tao ^ 3.25)) ^ -2) / (((1 / ((nx19_B / nx19_Dp) - nx19_Dp + (nx19_N / (3 * nx19_Pii))))) ^ 0.5)
with
nx19_fpv = ((1 + (0.00132 / nx19_Tao ^ 3.25)) ^ -2) / (((1 / ((nx19_B / nx19_Dp) - nx19_Dp + (nx19_N / (3 * nx19_Pii))))) ^ 0.5)

3) The VBA code provided is only valid for a certain range of temperature & pressure when the E equals E2 (and not when E equals E1, E3, E4, E5a, E5b, E5c, or E6). You will need to refer to the NX-19 document to incorporate these into the code.

Thanks again to Linepacker (errors notiwthstanding)

Enjoy!

 

[anicefob]

CORRECTION in above:

2) You need to replace
nx19_fpv = ((1 + (0.00132 / nx19_Tao ^ 3.25)) ^ -2) / (((1 / ((nx19_B / nx19_Dp) - nx19_Dp + (nx19_N / (3 * nx19_Pii))))) ^ 0.5)
with
nx19_fpv = ((1 + (0.00132 / nx19_Tao ^ 3.25)) ^ -1) / (((1 / ((nx19_B / nx19_Dp) - nx19_Dp + (nx19_N / (3 * nx19_Pii))))) ^ 0.5)

 

[dcasto]

here is a simpliar method for compressibility of natural gases with under 4% inerts

Tc (critical temperature) =169.01+314.001*Spgr where spgr is specific gravity
Pc (critical Pressure) = 708.75-57.5*Spgr

Pr = PSIA at conditions / Pc
Tr = T (rankin) at conditions / Tc
z = 1 + (0.0703 *Pr / Tr) * (1 - 6 / Tr ^ 2)

At 60F and 1000 psia on a .6 spgr gas, z = .8682

 

[BigInch]

If NX-19 is the subject, simpler methods are of no interest.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[BigInch]

No offense meant.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[dcasto]

the question was calculating zfactor to find LINE PACK. He found NX-19 and was having problems. Here is a simple way to get the same answer. Now, if the OP was trying to replicate API measurement, yeah the choice of z factor subroutines is limited.

 

[BigInch]

No, "linepacker" was the user name of the guy that asked the original question about NX-19 a long time ago. This post is a correction to the code that was posted in the referenced thread.

If it ain't broke, don't fix it. If it's not safe ... make it that way.