The table below lists the composition limits for both the Gross (Normal Range) and Detailed (Extended Range) methods.

Component | Extended Range | |
---|---|---|

Min.% | Max.% | |

Methane | 0 | 100 |

Ethane | 0 | 100 |

Propane | 0 | 12 |

iButane | 0 | 6 |

nButane | 0 | 6 |

iPentane | 0 | 4 |

nPentane | 0 | 4 |

neo-Pentane | 0 | 4 |

nHexane | 0 | 100 |

nHeptane | 0 | 100 |

nOctane | 0 | 100 |

nNonane | 0 | 0.2 |

nDecane | 0 | 100 |

Hydrogen | 0 | 100 |

Nitrogen | 0 | 100 |

Carbon Dioxide | 0 | 100 |

Hydrogen Sulphide | 0 | 100 |

Water | 0 | 100 |

Helium | 0 | 3 |

Oxygen | 0 | 21 |

Carbon Monoxide | 0 | 3 |

Argon | 0 | 1 |

The general procedure for computing the speed of sound at the flowing or operating conditions is as follows:

Step 1. Input the operating temperature (T), the operating pressure (P) and the gas composition

Step 2. Calculate the molar mass of the mixture

Step 3. Calculate the compression factor and density of the fluid at the operating conditions

Step 4. Calculate the ideal gas constant pressure heat capacity at the operating temperature

Step 5. Calculate the real gas constant volume heat capacity at the operating conditions

Step 6. Calculate the real gas constant pressure heat capacity at the operating conditions

Step 7. Calculate the ratio of heat capacities, cp/cv, at the operating conditions

Step 8. Calculate the speed of sound based on the results of the preceding steps

Step 9. Calculate the isentropic exponent, k.

The upstream density is determined from gas compression factor at upstream conditions for temperature and pressure. The compression factor is calculated using the detail characterisation method defined in American Gas Association Report No.10 2003.

The upstream density and gas compression factor are related as follows:

Symbol | Description | Units |
---|---|---|

ρ_{1} |
Density at the upstream pressure point P1 | kg/m^{3} |

m | Gas molar mass | kg/kmol |

p_{1} |
Upstream pressure | bar a |

z_{1} |
Compression factor at upstream conditions | - |

t_{1} |
Upstream temperature | K |

Constant | Description | Value | Units |
---|---|---|---|

R | Universal Gas Constant | 8.314510e-3 | kJ/mol/K |

The standard density is determined from gas compression factor at standard conditions for temperature and pressure. The compression factor is calculated ising the detail characterisation method defined in American Gas Association Report No.10 2003.

The standard density and gas compression factor are related as follows:

Symbol | Description | Units |
---|---|---|

ρ_{b} |
Density at standard conditions | kg/Sm^{3} |

m | Gas molar mass | kg/kmol |

p_{b} |
Standard pressure | bar a |

z_{1} |
Compression factor at standard conditions | - |

t_{b} |
Standard temperature | K |

Constant | Description | Value | Units |
---|---|---|---|

R | Universal Gas Constant | 8.314510e-3 | kJ/mol/K |

The speed of sound can be calculated as follows:

Symbol | Description | Units |
---|---|---|

W | Speed of sound | m/s |

C_{P} |
Constant pressure heat capacity | J/kg-mol.K |

C_{V} |
Constant volume heat capacity | J/kg-mol.K |

T | Stream temperature | K |

M_{r} |
Molar mass of the mixture | kg/kmol |

Z | Upstream compression factor | - |

ρ | Stream density | kg/m^{3} |

∂Z/∂ρ | Partial derivative of Z with respect to ρ | - |

Constant | Description | Value | Units |
---|---|---|---|

R | Universal Gas Constant | 8.314510e-3 | kJ/mol/K |

- American Gas Association Report Number 10 - Speed of Sound in Natural Gas and Other Related Hydrocarbon Gases, 2003