ChemProCal • Thermodynamics • LNG Storage Tank Boil-Off Gas (BOG) & Stratification Rollover Predictor

THERMODYNAMICS

LNG Storage Tank Boil-Off Gas (BOG) & Stratification Rollover Predictor

Calculates conductive and convective heat leak (BOR %/day) for full-containment cryogenic LNG tanks, predicting double-diffusive stratification and dormant time to hazardous tank rollover.

Full-Containment LNG Tank Geometry & Insulation

Tank Gross Storage Capacity

$\text{m}^3$ (Gross)

Current Liquid Fill Level

% Full

Inner Tank Diameter ($D_{\text{in}}$)

meters (9% Ni)

Tank Shell Height ($H_{\text{shell}}$)

meters

Perlite Annular Insulation Thickness

mm (Annular Space)

Ambient Air Temperature

°C

LNG Fluid Properties & Cargo Transfer Mode

LNG Bulk Storage Temperature

°C

Stored LNG Density ($\rho_{\text{LNG}}$)

$\text{kg/m}^3$

Ship Cargo Unloading Flow Rate

$\text{m}^3/\text{h}$

Bottom Heel Layer Density

$\text{kg/m}^3$ (Heavy Heel)

Top Cargo Layer Density

$\text{kg/m}^3$ (Light LNG)

Cargo Transfer Active?

NFPA 59A EN 1473 Rollover

LNG Tank Thermodynamics & Rollover Danger

Atmospheric LNG storage tanks operate at $-161.5^\circ\text{C}$ and $1.05\text{--}1.15\ \text{bara}$. Ambient heat ingress constantly boils the liquid:

Boil-Off Rate (BOR): Typically $0.04\text{--}0.08\%$ of tank inventory per day in modern full-containment tanks. Must be captured via recondensation or fuel gas compression.
Stratification Hazard: When fresh cargo of different density is loaded over an existing heel without thorough mixing, two stratified convective layers develop. The bottom layer heats up under hydrostatic pressure without boiling, becoming superheated.
Spontaneous Rollover: As bottom density falls to match the top layer, rapid buoyancy inversion releases trapped superheat, triggering sudden vapor surges up to $20\times$ normal boil-off that can overpressure tanks and lift relief valves.

LNG Tank Boil-Off & Rollover Theory

Atmospheric cryogenic tanks are protected by multiple barrier layers. Sizing is governed by NFPA 59A and European standard EN 1473.

1. Static Boil-Off Rate (BOR)

Heat ingress through the annular perlite space, cellular glass bottom slab, and suspended insulation deck causes continuous vaporization of stored liquid:

$$\text{BOR} = \frac{\dot{m}_{\text{BOG}} \cdot 24 \cdot 100}{M_{\text{LNG}}} = \frac{(Q_{\text{total}} / \Delta H_{\text{vap}}) \cdot 24 \cdot 100}{M_{\text{LNG}}} \quad [\%/\text{day}]$$

2. Double-Diffusive Rollover Dynamics (Turner Model)

When two layers of different density form, heat diffuses across the interface approximately $100\times$ faster than mass ($Le \approx 100$). The bottom layer cannot boil due to liquid hydrostatic head and accumulates superheat. When the densities equilibrate, catastrophic mixing occurs, flashing up to $20\times$ normal boil-off into the vapor space within hours.

Tool Units

Input / Output Units

Configure global unit system preset or individual parameter dimensions.

LNG Storage Tank Boil-Off Gas (BOG) & Stratification Rollover Predictor

Full-Containment LNG Tank Geometry & Insulation

LNG Fluid Properties & Cargo Transfer Mode

Boil-Off Gas (BOG) & Rollover Prediction

Tank Inventory & Cargo Transfer Mode

Stratification & Rollover Dynamics

Cryogenic Storage Alerts & Rollover Mitigation

LNG Tank Boil-Off & Rollover Theory

1. Static Boil-Off Rate (BOR)

2. Double-Diffusive Rollover Dynamics (Turner Model)

Input / Output Units