1. Field of the Invention
The invention relates to an apparatus and process for the separation and removal of oil from mixtures of oil and water. In a more particular aspect, it relates to separation of oil and particulate solids from oily and dirty water mixtures produced concurrently with oil on offshore platforms.
2. Brief Description of the Prior Art
Commonly called skimmers or settling tanks, most separators employed to remove oil from oil and water mixtures produced in association with the production of petroleum are of either a horizontal or vertical cylindrical configuration and are often installed upstream of a final water polishing apparatus, particularly on offshore platforms.
Such skimmers are essential to remove oil from the produced water for environmental and conservation reasons. For example, if the produced water is to be discharged in the sea, environmental and conservation considerations dictate that the oil entrained therein be removed. It is essential that a substantial portion of the oil be removed from such oil and water mixtures to avoid overloading polishing apparatus which further purifies the water.
Presently available skimmers have horizontal flow in horizontal vessels with few or no internal devices, or they have vertical downflow in vertical vessels. Horizontal flow vessels are more effective than the vertical flow vessels since the flow of the fluids is perpendicular to the oil droplet rise, and does not counteract it. However, particularly for offshore use, the horizontal vessel requires considerably more of extremely scarce and expensive deck space than the vertical designs, and is more prone to internal mixing due to movement of the production vessel or platform.
Presently available vertical skimmer vessels generally have the inlet near the top and the water outlet near the bottom. The downward flow in such vessels results in a water velocity which directly opposes oil droplet flotation tendency, consequently requiring more retention time and a much larger vessel which in turn takes up more space than if the flow were horizontal.
The oil and water mixtures requiring separation in association with the production of oil also will often have heavy loads of particulate solids such as dirt and sand of various sizes. With the presently available vertical vessels, the solids entering at the top fall through the vessel's contents to the bottom, stirring the contents and carrying oil droplets back into suspension or carrying the oil droplets near or through the water outlet.
One advantageous approach to the problems with presently available equipment hereinabove outlined is disclosed in U.S. Pat. No. 3,933,654 which discloses an oil separator wherein the inlet flows the oil-water mixture into a quiescent zone with upwardly and horizontally diagonal flow through a coalescing section with recovery of the oil through an outlet and recovery of the water after passing through a vertically circuitous route defined by baffles and then through an outlet. However, though the disclosure of U.S. Pat. No. 3,933,654 offers some advantage over conventional horizontal skimmer design or over conventional vertical skimmer design, it does not anticipate nor suggest the unexpectedly superior results obtained in accordance with the present invention.