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# NX-19 Calculations for Compressibility

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 anicefob (Chemical) 18 Jun 12 17:14
 thread1036-309842: Need Excel Calc for Linepack Calculation 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 (Chemical) 18 Jun 12 17:17
 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 (Chemical) 21 Jun 12 14:09
 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 (Petroleum) 21 Jun 12 16:59
 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 (Petroleum) 21 Jun 12 17:00
 No offense meant. If it ain't broke, don't fix it. If it's not safe ... make it that way.
 dcasto (Chemical) 22 Jun 12 9:26
 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 (Petroleum) 23 Jun 12 11:10
 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.

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