Maintaining the low pressure separator at too high a pressure can cause the natural gasoline condensate holding tank to over-pressure. As a rough approximation, about half a mole of gas is vented from a condensate tank for each barrel of condensate collected. This gas evolution rate is based on a 65 psig low pressure separator pressure and an average vapor molecular weight approximating propane.
Most often, roofs on condensate collection tanks are ruptured when the upper liquid dump valve on the low pressure separator sticks open. This permits all the low pressure separator flash gas to blow into the condensate tank. On one occasion, I observed an operator by-pass liquid from the high pressure separator around the low pressure separator and directly to the condensate tank. He explained that the upper liquid level dump valve was stuck closed, and that consequently gasoline was blowing out of the low pressure separator’s vent. While I agreed that spewing gasoline over a nearby road was dangerous, I also correctly predicted that bypassing the low pressure separator would blow a hole in the roof of the condensate collection tank.