LPG vehicles have a large amount of residual liquid left after loading, which cannot be emptied
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I’m new here. I would like to ask my colleagues: after filling a liquefied petroleum gas vehicle, when liquid-phase transfer piping is used for venting, it remains a considerable amount of residual liquid even after prolonged venting. Is this normal? Is it still a problem with the components of the liquefied gas? Is it a problem with the flexible hose or the pipeline? Please help answer this question; thank you all!
The vent pipe of the flexible hose is usually connected to the vapor equilibrium pipe of the storage tank, allowing residual liquid to be vented back into the tank. If the pressure in the vapor equilibrium tube reaches the saturation vapor pressure, the residual liquid cannot be completely vaporized.
For occasional unloading operations, it is best to complete loading first, then purge the remaining material in the transfer hose with nitrogen and transfer it into the tank truck; afterwards, it can be connected to the gas pipeline； Frequent unloading ensures that the valve remains closed without causing a liquid seal. Furthermore, if both the liquid phase and the gas phase are in communication with each other, vaporization of the liquid phase requires heat absorption; therefore, the vaporization rate will not be very fast.