Fact Sheet - Coalescence

Intro to Produced Water
Technology Descriptions
Fed & State Regulations
Technology Identification

This fact sheet describes technologies for joining or coalescing small oil droplets into larger ones that are more amenable to removal. According to Stokes Law, oil rises at a rate dependent on the droplet diameter and the fluid viscosity. Smaller diameter droplets rise more slowly. One way of increasing the rate at which droplets rise is to increase the droplet diameter.

ACS Industries provides a thorough reference on liquid/liquid coalescers (ACS Industries undated). Coalescers provide surfaces on which oil droplets can congregate and merge. Most coalescers use fiberglass, polyester, metal, or Teflon media, which are arranged in a mesh, co-knit, or irregular "wool" format. ACS (undated) shows photographs of the different media types. Finer meshed media are more capable of capturing and coalescing smaller droplets. However, tighter mesh becomes more vulnerable to fouling with solids. If solids are likely to pose a problem, filtering devices or other solids-removal equipment should be employed before running the coalescer.

Tulloch (2003) reviews a pre-coalescer device that consists of a bundle of oleophilic polypropylene fibers inside a cartridge positioned along a flow line just upstream of another separation device (e.g., hydrocyclone, filter). The fibers serve to aggregate small oil droplets for easier downstream removal. The coalescence occurs rapidly (within two seconds). The appearance of the fiber bundle looks somewhat like the tail of a horse, giving rise to the device's name "Mare's Tail." Tulloch (2003) reports that oil droplet growth was enhanced by increasing either the length of the fibers or the number of fibers packed into the cartridge.

Mare's Tail Coalescer showing bundle of fibers.
Mare's Tail Coalescer 
showing bundle of fibers; 
Source: Opus.
  Closeup of Mare's Tail Coalescer showing bundle of fibers.Source: Opus.
Closeup of Mare's Tail Coalescer showing bundle of fibers; Source: Opus.

Recently, controlled application of ultrasound has been shown to coalesce oil droplets. The technology is still under development (Sinker 2007).

The Total Oil Remediation and Recovery (TORR) process technology is based on a multistage adsorption and separation system with the capacity of multiphase separation of large and small (free-floating and emulsified) oil droplets in produced water (Plebon et al. 2005, Saad et al. 2006). This is accomplished by means of a patented reusable petroleum adsorbent media coalescing agent, which is polyurethane-based, oleophilic, hydrophobic, and non-toxic.

The oily water passes through multiple vessels containing the media and a recovery chamber. The media continuously adsorb, coalesce, and desorb the very small droplets in oil emulsions. This process creates larger oil droplets. In the recovery chamber, oil droplets float to the top where the final separation of oil, gas, and the water occurs.

Schematic of TORR process.
Schematic of TORR process; Source: TORR Canada.
  Photo of TORR to view larger image
TORR vessels; Source: TORR Canada.

Limited performance data from the pilot-scale tests and trials are available (Plebon et al. 2005, Saad et al. 2006):

  • A trial on North Sea floating production, storage, and offloading vessel (FPSO) gave oil and grease of <5 mg/l.
  • A trial on North Sea platform gave oil and grease of <15mg/l.
  • A trial on North Sea semi-submersible rig gave oil and grease of <10 mg/l.


ACS Industries, undated, "Liquid-Liquid Coalescer Design Manual," 18 pp. Available at [PDF - external site].

Plebon, et al., 2005, "Further Advances in Produced Water De-Oiling Utilizing A Technology That Removes and Recovers Dispersed Oil in Produced Water 2 Microns and Larger," presented at the 12th International Petroleum Environmental Conference, Houston, TX, November 8-11. Available at [PDF - external site].

Saad, M., M.J. Plebon, and S. Fraser, 2006, "Fundamental Approach to Produced Water Treatment: Validation of An Innovative Technology," presented at the 16th Produced Water Seminar, Houston, TX, January.

Sinker, A., 2007, "Less Oil In, Less Oil Out: A Holistic Approach to Enhanced Produced Water Treatment," 17th Produced Water Seminar, Houston, TX, January 17-19.

Tulloch, S.J., 2003, "Development & Field Use of the Mare's Tail® Pre-Coalescer," presented at the Produced Water Workshop, Aberdeen, Scotland, March 26-27.

Veil, J.A., M.G. Puder, D. Elcock, and R.J. Redweik, Jr., 2004, "A White Paper Describing Produced Water from Production of Crude Oil, Natural Gas, and Coal Bed Methane," prepared by Argonne National Laboratory for the U.S. Department of Energy, National Energy Technology Laboratory, January. Available at