Regardless of its initiating contingency, the largest sustainable liquid release to the disposal system should be identified to evaluate the adequacy of liquid separation and collection equipment (e.g., knockout drums) within the disposal system.
Determination of Credibility
Blockage of any liquid stream within the process can result in a liquid discharge to the relief header. The most common contingency resulting in a large liquid discharge to the relief header is overfilling of unit feed surge drums. See Item 3, “Overfilling of Vessel” on page 1200-19 for a discussion of the applicability of the overfilling contingency for individual pieces of equipment.
Determination of Impact on the Collection and Disposal System
A large liquid release rarely leads to a hydraulic (i.e., back pressure) concern. However, such releases should be considered when evaluating or specifying the capacity of any liquid collection equipment within the disposal system. In cases in which the source of the liquid may be limited, consideration should be given to the volume of the liquid source compared to the volume of the liquid collection equipment.