# C183 – ISO 6578 Klosek-McKinley LNG Density

## Description

This equation is used to calculate the saturated liquid density of LNG mixtures from composition. The equation is valid at temperatures between -180°C and -140°C, and only for LNG mixtures with:

- an average molecular mass of less than 20.0 kg/kmol,
- mole fractions of N2 less than 5%,
- mole fractions of total C4 less than 5%,
- mole fractions of C5+ less than 1%,
- and no more than a “trace” of O2.

## References

ISO 6578:1991 (BS 7577:1992) – Calculation procedures for static measurement of refrigerated light hydrocarbon fluids

KELTON calculation reference C183

FLOCALC calculation reference F054

KIMS calculation references K187

## Inputs

The required inputs for this calculation are:

- LNG mixture composition
- Temperature at which the saturated density is required

## Calculations

The LNG density is calculated from the following equation:

Where | ||

ρ_{t} |
= | LNG mixture density at temperature t in °C |

x_{i} |
= | Mole fraction of component i |

M_{i} |
= | Molar mass of component i |

V_{i} |
= | Molar volume of component i at temperature t in °C |

V_{c} |
= | Reduction in volume due to mixing of components at temperature t in °C |

The molar mass and volume values are obtained from the relevant tables in ISO 6578:1991.

The reduction in volume due to mixing, Vc, is calculated from:

Where | ||

k_{1} |
= | Correction factor due to presence of hydrocarbons |

k_{2} |
= | Correction factor due to presence of nitrogen |

x_{1} |
= | Mole fraction of methane |

x_{2} |
= | Mole fraction of nitrogen |

The correction factors k_{1} and k_{2} are obtained from the relevant tables in ISO 6578:1991, as a function of temperature and average molecular weight of the LNG mixture.