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Boil off gas pressure build-up

Boil off gas pressure build-up

There is an insulated container of 100 m3 capacity which is 95% full with LNG (MM 16.4 kg/kmole) at -160 degC, saturated and at near ambient pressure (~0.2 barg). The heat ingress to the container develops 0.3 vol%/day of boil-off gas, resulting in the pressure inside the container to increase over time.

How do I calculate the pressure build-up after 1 day, 2 days, after x days, etc. before it reaches the PSV set point of 10 barg? Assume that no LNG is transfered out of / into the container during this time.

Thank you!

RE: Boil off gas pressure build-up

Student post / question?

For starters just use the ideal gas law, just remember to work in absolute pressure and absolute temperature. You can prob assume gass temp is close to -160. Volume of gas to vol of liquid use 600:1.

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RE: Boil off gas pressure build-up

You can model this easily on the Depressure routine in Hysis or Simsci - Pro II.

RE: Boil off gas pressure build-up

this heat & mass balance can be solved by hand calculation or in Excel...
For fluid properties look in tables (as suggested by LittleInch) or use some process library or maybe Nist database...

RE: Boil off gas pressure build-up

Yet another first time poster who vanishes into the ether.....

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