In producing operations it is often necessary to handle waste water that may include water produced with crude oil, rain water, and washdown water. The water must be separated from the crude oil and disposed of in a manner that does not violate established environmental regulations. In offshore areas where discharge to the sea is allowed, the governing regulatory body specifies the maximum hydrocarbon content in the water that may be discharged overboard. The range is currently 15 mg/1 to 50 mg/1 depending on the specific location. In most onshore locations the water cannot be disposed of on the surface, due to possible salt contamination, and must be injected into an acceptable disposal formation or disposed of by evaporation. In either case it will probably be necessary to treat the produced water to lower its hydrocarbon content below that normally obtained from free-water knockouts and oil treaters. The purpose of this article is to present the engineer with a procedure for selecting the appropriate type of equipment for treating oil from produced water and to provide the theoretical equations and empirical rules necessary to size the equipment. When this design procedure is followed, the engineer will be able to develop a process flowsheet, determine equipment sizes, and evaluate vendor proposals for any waste water treating system.
