pyResToolbox MCP Server

Calculate gas pseudo-critical properties (Tc and Pc).

CRITICAL GAS PROPERTY CALCULATION - Computes pseudo-critical temperature and pressure for real gas mixtures. Required for Z-factor calculations and all gas property correlations. Pseudo-critical properties are weighted averages of pure component critical properties, adjusted for non-hydrocarbon components.

Parameters:

• sg (float, required): Gas specific gravity (air=1.0). Valid: 0.55-3.0. Typical: 0.6-1.2. Example: 0.7 for dry gas.

• h2s (float, optional, default=0.0): H2S mole fraction (0-1). Typical: 0-0.05. Example: 0.02 for 2% H2S. High H2S significantly affects Tc/Pc.

• co2 (float, optional, default=0.0): CO2 mole fraction (0-1). Typical: 0-0.20. Example: 0.05 for 5% CO2.

• n2 (float, optional, default=0.0): N2 mole fraction (0-1). Typical: 0-0.10. Example: 0.01 for 1% N2.

• method (str, optional, default="PMC"): Correlation method. Options: "PMC", "SUT", "BUR". PMC recommended.

Pseudo-Critical Properties:

• Tc (Pseudo-critical Temperature): Temperature above which gas cannot be liquefied regardless of pressure. Typical: 300-500°R for natural gas.

• Pc (Pseudo-critical Pressure): Pressure at critical temperature. Typical: 600-800 psia for natural gas.

Method Selection:

• PMC (Piper, McCain & Corredor 1993): RECOMMENDED. Most accurate for wide range of gas compositions. Accounts for non-hydrocarbon effects.

• SUT (Sutton 1985): Classic method. Use for compatibility with older methods.

• BUR (Burrows 1981): Alternative method. Use for specific applications.

Non-Hydrocarbon Effects:

• H2S: Increases both Tc and Pc significantly

• CO2: Increases Tc, decreases Pc slightly

• N2: Increases Pc, decreases Tc slightly

• Always account for non-hydrocarbons for accurate Z-factor calculations

Returns: Dictionary with:

• value (dict): Contains "tc" (degR) and "pc" (psia)

• method (str): Method used

• units (dict): {"tc": "degR", "pc": "psia"}

• inputs (dict): Echo of input parameters

Common Mistakes:

• Not accounting for non-hydrocarbon fractions (H2S, CO2, N2)

• Using wrong gas gravity (must be separator gas, not sales gas)

• Confusing pseudo-critical with true critical properties

• Using critical properties for pure components instead of mixtures

Example Usage:

Result: Tc ≈ 380-420°R, Pc ≈ 650-750 psia for typical natural gas.

Note: Critical properties are used internally by gas_z_factor and other gas property tools. Always use PMC method unless specific compatibility required. Account for all non-hydrocarbon components - even small amounts affect results.