Solving Oil Water Separator Problems

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Oil Production and Refining

MSR Introduces High Efficiency Separation Systems for Oil Production and Refining

Many separation devices currently used in the oil production and refining industries are similar or identical to those used a hundred years ago. This technology was adequate at that time, but much oil better recovery is now possible.   It is no longer acceptable to lose hydrocarbons to the environment instead of make them into salable products.  The reason a barrel of oil is 42 gallons is that 8 were lost from barrels being shipped from the production field to the refineries.  The old technology is also no longer adequate for environmental purposes to meet the Clean Water Act or to recover the last amount of oil present in refinery outfall water to reduce the oil content to less than 10 or 15 mg/l.  MSR’s coalescing plate separators can be used to separate oil and water for enhanced resource recovery and to meet legal requirements.

Click HERE to read our Oil Refinery Wastewater Management paper

Separations in the oil industry:

There are numerous places in the process of extracting crude oil from the ground and converting it into gasoline, diesel fuel, and other useful hydrocarbons. In many of these places, the oil becomes mixed with at least some water – often a lot of water – and the two phases need to be separated.

Some typical places where separation technology is useful:

  • In the oil production system where water, oil, and gas are jointly produced together.
  • In the oil refinery or water and steam are often used as part of the refining process.
  • In the oil refinery or tank farm where there may be either rainwater or processed water contaminated with hydrocarbons.

Please note coalescing plate separation technology is mostly useful for removing small quantities of oil from large quantities of water. This is because the oil often has a relatively high viscosity and that makes it difficult for water droplets to move within the oil according to Stokes law. In most cases in the oil industry, other coalescing technologies including electrostatic desalters are used if the flow is primarily hydrocarbons.

Production Separators:

Production separators are traditionally pressurized horizontal or vertical three-phase separators intended to split the oil, gas, and water into three streams. The gas is much, much lighter than the other two phases and separates readily, especially with the use of a vane pack for capturing any droplets that might be present in the gas stream. Coalescing media can be used to improve the separation of the oil and water to give better separation in a small unit.

Large MSR Separator installed at a gas processing facility in Wyoming

Downstream of the typical pressurized separator, there would often be a gunbarrel or battery of gunbarrels which performs further separation. These can be readily replaced with a relatively small separator.

Common separations systems used in the oilfield include gunbarrel separators and horizontal separators. The gunbarrel separator systems as illustrated below are simple gravity systems where the oil gas and water mixture comes to a preseparation system and the gas is supposed to separate out in the preseparation system and joined the gas which eventually separates out of the oil water mixture at the top of the gunbarrel. The oil and water mixture flows into the distributor near the bottom of the separator where the oil droplets are supposed to collect under the umbrella style distributor and weep upward into the oil layer water droplets are supposed to coalesce and come downward. Any water drops in trained in the rising oil will migrate into the oil layer above the water layer, and from there must fall back down through the oil layer to rejoin the water.

These systems are simple, easy to operate, and tolerant of solids but the flow pattern and lack of properly designed internals keeps them from being very efficient at removing smaller droplet sizes. This is because the design of the gunbarrel does not meet the laminar flow criteria for Stokes law to apply.

Typical Gunbarrel Separator

Process Separators:

There are numerous places in the processing scheme of an oil refinery where the steam condensate from steam used in processes must be separated from the hydrocarbons in the condensate water flow may contain substantial amounts of hydrocarbons. Coalescing technology can be used at this point of the processing scheme to improve efficiency of the process.

Refinery Effluent Separators:

In 1947, the API commissioned a study from the University of Wisconsin to determine the design method that could be used to design separators for removing the oil from water in refinery effluent water. The purpose of this design method was primarily for resource recovery although it also helped with mitigating the nuisance effect of oil exiting the refineries and entering streams and lakes.

API separators are extensively used in oil refineries and chemical processing facilities where waters containing relatively large amounts of oil are present and need to be processed to meet the requirements of NPDES permits.

Advantages of the API and API type separators are simplicity of design, low cost, low maintenance, and resistance to plugging with solids. The primary disadvantage of these simple gravity separators is the poor quality of separation that they provide.  The API’s own survey indicates it is common for API separator effluent streams to exceed 100 mg/l, which would NOT meet the requirements of the Clean Water Act for “no sheen” or the Canadian Fisheries Act.Systems are also sold as “API type separators”, which commonly means that they have the same general baffle arrangement as a regular API separator, but do not conform to the design criteria established by the API. Separators which have a lesser residence time (and are therefore smaller and less expensive than rigorously designed API separators) do not meet the API design criteria and, therefore, cannot be expected to meet the API’s modest effluent expectations.

The photo below shows one of a set of four separators installed at a US oil refinery.  Total capacity of the set is 20,000 US gpm (4600 m3/hr or 685,000 barrels per day).  The usual effluent from this separation system is less than 10 mg/l.

MSR has designed units for use up to 685,000 BPD, and can construct any size unit, small or large.  Please call or email MSR for information on how to improve separation of oil at your facility and capture virtually of the oil in the water streams.