Design and Operational Review of Three-Phase Gas-Oil-Water Separator Treatment of Natural Gas Processing Closed Drain Wastewater Stream
The liquid carried by the combined drain system mainly contains water, heavy liquid hydrocarbons and mixed light end hydrocarbon gas (VOC)/Acid Gas (e.g. H2S mixture). The liquid was routed to a small horizontal pressure vessel to flash-off trapped gas and carryover oil is skimmed in an open sump downstream of the vessel. Increased flow rate to the close drain flash system has decreased the retention time and thus results in adequate flashing of lighter hydrocarbons and acid gas from the closed drain influent coming into the old vessel. This has created a potential environment and safety hazard for the people working around that vessel when the flashing of residual hydrocarbon and acid gas occurs in the sump, which is open to atmosphere. The mitigation of the problem involved designing a large horizontal tank with a heating coil and oil separation chamber, which can provide adequate retention time for the VOC/acid gas to flash off from the influent liquid. The oil chamber will collect hydrocarbon-oil after the de-emulsification process. Mechanical agitation, by using the desanding nozzle, prevents accumulation of sand at the bottom of the vessel. The project aims at the prevention of the carryover oil with outlet water into the biological process reactor downstream of the new tank. The accumulated oil is analyzed. The oil sample contains species similar to light crude oil. Economic analysis is performed to estimate the revenue obtained from the disposal of spent oil to a third party carrier.