C220 – API Compressibility and Cpl
Description
This calculates the volume flow rate adjusted to take pressure and compressibility into account.
References
Measurement of Petroleum Measurement Standards Chapter 11.2.1 – Compressibility Factors for Hydrocarbons: 0-90° API Gravity Range (1984)
Measurement of Petroleum Measurement Standards Chapter 11.2.1M – Compressibility Factors for Hydrocarbons: 638-1074 Kilograms per Cubic Metre Range (First Edition August 1984)
Measurement of Petroleum Measurement Standards Chapter 11.2.2 – Compressibility Factors for Hydrocarbons: 0.350-0.637 Relative Density (60°F/60°F) and -50°F to 140°F Metering Temperature (First Edition October 1986)
Measurement of Petroleum Measurement Standards Chapter 11.2.2M – Compressibility Factors for Hydrocarbons: 350-637 Kilograms per Cubic Metre Density (15°C) and -46°C to 60°C Metering Temperature (First Edition October 1986)
Kelton calculation reference C220
This calculation is used by the following calculations:
F028/K211 – API/Table 54 Density Referral
F023/K212 – API Density Referral
K229- GPA TP-25/27 – NGL and LPG Density Referral Calculation
F091 – GPA TP-25 – NGL and LPG Density Referral Calculation
F092 – GPA TP-27 – NGL and LPG Density Referral Calculation
F103 – API Table 24:1952 Density Referral
Options
Units of standard
- Metric
This option uses the metric versions of the API standards i.e. API 11.2.1M or API 11.2.2M
- US Customary
This option uses the versions of the API standards which use US customary units i.e. API 11.2.1 or API 11.2.2
Density Range
- Auto
Automatically select the appropriate calculation
- 350 to 637 kg/m³
Calculate using Chapter 11.2.2M procedure
- 638 to 1074 kg/m³
Calculate using Chapter 11.2.1M procedure
Vapour Pressure
Select this option to include the vapour pressure – the equilibrium bubble point pressure
Rounding
The standard specifies the method of rounding used to generate the tables, You can either select to round as per the standard or use the full precision.
Constants
If the metric option is selected, for API 11.2.1M the following constants are used to calculate compressibility factor
A = -1.62080 B = 2.1592 x 10-4 C = 0.79392 D = 2.326 x 10-3
If the US customary option is selected, for API 11.2.1 the following constants are used to calculate compressibility factor
A = -1.9947 B = 1.3427x 10-4 C = 0.87096 D = 4.2092 x 10-3
Calculations
For 350 to 637 kg/m3 (with rounding)
The correction for the pressure of the liquid is calculated by
Where the compressibility factor (F) is calculated by
Where DP = The pressure above the equilibrium bubble point pressure (Pe)
The terms A and B are calculated as below
Note: the steps which are for the tabular display have been omitted and leaving only those pertaining to the calculation.
The temperature is converted to °C to use the same units as the standard.
Step 1: The temperature is converted to Rankine using the approximation described in the standard
Step 2: Convert density to g/cm3
Step 3: Obtain 3 significant figures
Step 4: If the metric option is selected convert the density (15°C) to density (60°F).
Step 5: Convert the calculated density (60°F) in grams per cubic centimetre to relative density using the density of water at 60°F
Step 6: Obtain three significant decimal figures
Step 7: Calculate 96% of the critical temperature
Step 8: If the temperature in degrees Rankine TR is more than the near critical limit (TC). void the calculation, output a message, and start the next density and temperature set
Step 9: If the temperature in degrees Rankine TR is less than or equal to the near critical limit (TC). then calculate the A and B factors using steps 12 to 18.
Step 10: Calculate the A Factor
Step 11: Convert the A Factor to kilopascals if metric is selected, to psi if US customary is selected.
Step 12: Round and scale the A factor to the nearest whole number
Step 13: Calculate the B Factor
Step 14: Round and scale the B factor to the nearest 0.001
For 638 to 1074 kg/m3 (with rounding)
The basic equation forcalculating the compressibility factor (F) is
| Where | ||
| A | = | Coefficient for compressibility factor |
| B | = | Coefficient for compressibility factor |
| C | = | Coefficient for compressibility factor |
| D | = | Coefficient for compressibility factor |
| T | = | Temperature in °C |
| ρ | = | Density at 15°C |