The Anatomy of Liquid Displacement and Vapor Breakthrough

The loss of High Pressure (HP) / Low Pressure (LP) interface has to be evaluated in order to (a) ensure that the downstream equipment can handle the energy and/or mass accumulation and (b) to also ensure that the upstream equipment can handle the rapid depressurization. The loss of the HP/LP interface can occur as a result of automatic controls failure/malfunction, and/or inadvertent valve opening / human error as seen in Figure 1. Potential outcomes of the loss of the HP/LP interface include but may not necessarily be limited to:

1. Overfilling of the downstream equipment, i.e. as the liquid is displaced from the upstream equipment into the downstream equipment.

2. High temperatures associated with the rapid compression of the vapor space of the downstream equipment associated with liquid displacement.

3. Multiphase flow associated with increasing liquid level, liquid entrainment, and/or high superficial vapor velocities caused by pressure relief device actuation in the downstream equipment.

4. Low temperatures caused by rapid depressurization in the upstream equipment and ultimately in the downstream equipment as pressure is further reduced when the gas breaks through to the downstream equipment.

5. Possible hydrate formation in the upstream and / or downstream equipment.

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