How to simulate lng front end and storage: guard beds, tank boil-off, driver limit

The parts of a **5.2 Mtpa LNG train** that are not the cold box, and the four questions they answer that no bulk unit can — at real capacity, so the vessel sizes and duties are ones an engineer can check against their own plant. **Guard beds:** a sulfur-carbon bed takes mercury from 200 to 0.01 µg/Nm³ — the brazed-aluminium limit, because mercury attacks the plate-fin cold box by liquid-metal embrittlement — on a 4.8 m x 6.6 m bed with **4.2 years** of life from a capacity balance — inside the 3-5 year window these non-regenerable beds are actually replaced on, which is what a turnaround plan needs. A 4A molecular sieve then dries the gas to 0.1 ppmv, the only route to a cryogenic water spec (a glycol contactor tops out near a −30 °C dew point), on a 4.9 m x 5.1 m bed running a **13.8 h cycle** for 1.3 MW of regeneration duty. **Storage:** the LNG goes to a tank whose boil-off rate comes from a 0.05%/day guarantee but whose boil-off *composition* comes from a real equilibrium flash — and that is the interesting part, because the vapour leaves at ~11 mol% nitrogen against 1.1% in the feed. Nitrogen and methane are far more volatile at 113 K, so the boil-off is light and the stored liquid weathers heavier: nobody specified that, the flash found it. **Recondensing:** the boil-off goes back into the send-out LNG rather than to a flare, and the unit reports the LNG:BOG ratio (1999) against the minimum the energy balance demands (3.8), which is the constraint a terminal is actually operated against. **The driver:** a gas turbine burning plant fuel gas, rated **97.5 MW** at ISO conditions, delivers only **84.5 MW at 35 °C** — 5.5 MW short of its 90 MW refrigeration load, and flagged as such. That derate is computed from two physical effects (a fixed-geometry compressor swallows a fixed volume so mass flow follows air density, and hotter air costs more to compress), not from a vendor curve, and it comes out at 0.66%/K — mid-band for industrial machines. It is why a tropical LNG train makes less product in summer.

Frequently asked questions

What does the LNG front end and storage: guard beds, tank boil-off, driver limit model simulate?

The parts of a **5.2 Mtpa LNG train** that are not the cold box, and the four questions they answer that no bulk unit can — at real capacity, so the vessel sizes and duties are ones an engineer can check against their own plant. **Guard beds:** a sulfur-carbon bed takes mercury from 200 to 0.01 µg/Nm³ — the brazed-aluminium limit, because mercury attacks the plate-fin cold box by liquid-metal embrittlement — on a 4.8 m x 6.6 m bed with **4.2 years** of life from a capacity balance — inside the 3-5 year window these non-regenerable beds are actually replaced on, which is what a turnaround plan needs. A 4A molecular sieve then dries the gas to 0.1 ppmv, the only route to a cryogenic water spec (a glycol contactor tops out near a −30 °C dew point), on a 4.9 m x 5.1 m bed running a **13.8 h cycle** for 1.3 MW of regeneration duty. **Storage:** the LNG goes to a tank whose boil-off rate comes from a 0.05%/day guarantee but whose boil-off *composition* comes from a real equilibrium flash — and that is the interesting part, because the vapour leaves at ~11 mol% nitrogen against 1.1% in the feed. Nitrogen and methane are far more volatile at 113 K, so the boil-off is light and the stored liquid weathers heavier: nobody specified that, the flash found it. **Recondensing:** the boil-off goes back into the send-out LNG rather than to a flare, and the unit reports the LNG:BOG ratio (1999) against the minimum the energy balance demands (3.8), which is the constraint a terminal is actually operated against. **The driver:** a gas turbine burning plant fuel gas, rated **97.5 MW** at ISO conditions, delivers only **84.5 MW at 35 °C** — 5.5 MW short of its 90 MW refrigeration load, and flagged as such. That derate is computed from two physical effects (a fixed-geometry compressor swallows a fixed volume so mass flow follows air density, and hotter air costs more to compress), not from a vendor curve, and it comes out at 0.66%/K — mid-band for industrial machines. It is why a tropical LNG train makes less product in summer.

Which thermodynamic method does it use?

The PENG-ROBINSON property package, over n2, methane, ethane, propane, water — already selected. You can switch the method on the canvas before running.

Which unit operations are in the flowsheet?

It chains MRU, DEHY, 2× Liquefy, JT, DRUM, TANK, Sendout PUMP, BOG COMP, Recon, GT. Every block is a real, solvable unit operation you can reconfigure, add to, or remove.

Do I need to install software or buy a license?

No. LNG front end and storage: guard beds, tank boil-off, driver limit runs entirely in your browser on MaximaLabs — free, no install, no license. Open the model to load it live and run the deterministic solver.