Q & A > Question Details
On distillation unit, we have crude surge drum at the beginning of the unit. This surge drum has PZV open to the crude column flash zone. What is the effect if the PZV open for releasing high pressure to the flash zone? And how about transfer this PZV to open on the manifold of the crude tanks?
22/11/2011 A: Ming-Hua Yao, Powertec Energy Corp, mikeyao@powertecenergy.com
The relief materials from pressure relief valve in this case is heavier ones, during the design phase routine these to flash zone of main fractionator to prevent heavier materials condensed in flare header.
Since the design pressure of crude tanks is atmosphere or several inches water only, routine the relief to manifold of crude tanks is not acceptable or not a good design practice.
19/11/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
If you are thinking that, when the current configuration relieves, there could be internal damage to the atmospheric column, it has happened. However, the arrangement has always been considered safe in terms of avoiding rupturing the external skin of equipment or piping. As for discharging the relief valve to the crude tanks suction manifold, because there surely are valves in that arrangement to be able to switch tanks, that location would not be a valid place for the relief to go. I don’t think you are referring to a vapor space manifold connecting the crude tanks. But, if you are, that would be O.K. if there are no valves in the configuration, and the pipe diameters are adequate. In any case, most designers (and corporations), but not all, require PSV discharge lines to be free draining.
Since this is a safety question, my usual disclaimer applies. “My comments are in no way intended to be used as a basis for design, merely observations based on my experience.”