LNG storage tank simulation

1 inlet -> stored liquid + boil-off gas (reports weathering)

Governing equations

The exact equations the solver works for a lng storage tank — the same math shown in the app's "Theory" panel, not a black box.

$\dot n_{BOG}$

boil-off gas rate [mol/s]

$\dot Q_{leak}$

heat leaking into the tank [W]

$\Delta h_{vap}$

enthalpy of the equilibrium vapour minus the liquid [J/mol]

$T_{tank}$

tank temperature = bubble point at tank pressure [K]

$T_{bub}$

bubble-point temperature [K]

$P$

tank pressure [Pa]

$x_i$

liquid mole fraction of component i [-]

$y_i$

boil-off vapour mole fraction of component i [-]

$K_i$

equilibrium K-value of component i [-]

$\dot n_{in}$

LNG fed to the tank [mol/s]

$x_i^{stored}$

mole fraction left in the stored liquid after weathering [-]

Parameters

storage tank whose boil-off rate comes from the heat leak ('heat_leak' [W], or a guaranteed 'boil_off_rate' [1/day]) and whose boil-off COMPOSITION comes from a real equilibrium flash -- N2 and methane leave first, so the BOG is light and the stored liquid weathers heavier. Outlets: stored liquid + BOG. Well-mixed and steady-state; the differential-vapour composition is capped (with a warning) once the boil-off cut gets large, and stratification is a different model -- see analysis/lng_rollover.py

Example flowsheets that use it