Nitrogen volume required to dilute an LNG cargo tank from initial O₂/HC concentration down to the target using a dilution (well-mixed) purge - the baseline method when displacement cannot be guaranteed.
Formula
$$ V_{purge} = V_{tank} \cdot \ln\left(\frac{c_0 - c_p}{c_t - c_p}\right) $$Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $V_{tank}$ | Tank gross volume | m³ | capacity plan |
| $c_0$ | Initial impurity concentration | %vol | gas analyser |
| $c_t$ | Target concentration | %vol | IGC/SIGTTO |
| $c_p$ | Purge-gas impurity | %vol | N₂ generator spec |
Sources
- SIGTTO - Liquefied Gas Handling Principles 4th ed..
- IGC Code Ch. 9.