Propane Calculation of Gas Volume VCF
This routine calculates the vapor VCF of a fluid containing mostly propane. The vapor pressure is later used as the pressure inside the vessel. The VCF converts vapor volume at a temperature to an equivalent liquid volume at 60°F. Note that the current RD60 of pure propane is 0.50738.
Inputs
| Input | Description |
|---|---|
| RD60 | The Relative Density of fluid at 60°F (must be between 0.500 and 0.525). |
| Temperature | The Temperature of vapor (must be between -40 and 140°F). |
Immediate Variables
P = Pressure (psia)
Outputs
| Output | Description |
|---|---|
| VCF_vap | The Volume correction factor that converts a vapor volume at an actual temperature to an equivalent liquid volume at 60°F. |
Vapor VCF Implementation Procedure (60°F base temp)
- Check inputs:
- If RD60 < 0.500 Stop
- If RD60 > 0.525 Stop
- If Temp < -40.0 Stop
- If Temp > 140.0 Stop
Compute vapor pressures per API published Manual of Petroleum Measurement Standards [2]:
A and B Factor Equations:
- If (0.490 ≤ RD60 < 0.510) then
- A = -6.4747 + (37.083 * RD60) + 0.0 * (RD60)2
- B = 12038.0 – (31296.5 * RD60) + 0.0 * (RD60)2
- Else If (0.510 ≤ RD60 < 0.560) then
- A = 11.5454 + (1.749 * RD60) + 0.0 * (RD60)2
- B = 1378.8 – (10396.1 * RD60) + 0.0 * (RD60)2
- Else
- STOP
- End
- Calculate Pressure using Natural Logarithm:
- C = 443.0
- XX = A + (B / (Temp + C))
- P = exp (XX)
Compute VCF using GPA Standard 8195-905 [3]:
Interpolation Factor:
Factor = (RD60 – 0.500 ) / ( 0.525 – 0.500 )
Convert temperature to Rankine:
TempR = Temp + 460.67
B and F Factor Equations:
B525 = 4.015E-5 * (TempR)2 – 0.05046592 * TempR + 16.66506687
B500 = 2.784E-5 * (TempR)2 – 0.03572594 * TempR + 12.09183298
F525 = 0.975E-5 * (TempR)2 – 0.01502254 * TempR + 7.66774254
F500 = 1.023E-5 * (TempR)2 – 0.01522734 * TempR + 7.49328864
B2 = ((B525 – B500) * Factor + B500) / 1000.
F2 = ((F525 – F500) * Factor + F500) / 10000.
Calculate VCF:
VCF_vap = P * F2 / (1 – B2 * P)
Example: Propane Vapor VCF Calculation
| Name | Units | Value |
|---|---|---|
| RD60 | SG | 0.50738 |
| Temp | °F | 60 |
| A | Dimensionless | 12.34047 |
| B | °F | -3841.22 |
| C | °F | 443 |
| XX | Dimensionless | 4.703856 |
| Pressure | psia | 110.3719 |
| Temp in R | °R | 520.67 |
| B525 | Dimensionless | 1.273531 |
| B500 | Dimensionless | 1.037755 |
| F525 | Dimensionless | 2.489155 |
| F500 | Dimensionless | 2.338194 |
| Factor | Dimensionless | 0.2952 |
| B2 term | Dimensionless | 0.001107 |
| F2 term | Dimensionless | 0.000238 |
| VCF_vap | Dimensionless | 0.029961 |