Combined Physical and Chemical Processes

Fact Sheet - Combined Physical and Chemical Processes

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

Other fact sheets describe several physical and chemical separation methods that remove oil and other organics from water. This fact sheet examines several recent technologies that combine physical processes with chemical extraction and adsorption to provide excellent oil and grease removal. These devices are able to removed most of the dispersed oil and some of the dissolved oil and organics.

The discharge standards in the North-East Atlantic and North Sea have grown much stricter over the years. For example, a new discharge standard for oil and grease in produced water of 30 mg/L (previously 40 mg/L) became effective on January 1, 2007. Moreover, reductions in total mass loading of oil and grease are required. In this light, companies operating in the region have looked to new technologies. Three advanced technologies that can achieve compliance with the new standards are described below. As of late 2006, these technologies are not being used in the Gulf of Mexico because operators can meet the discharge standards using more conventional equipment.

Epcon 
The Epcon compact flotation unit (CFU) consists of a vertical vessel acting as a three-phase water/oil/gas separator (Epcon Brochure 2006). Centrifugal forces and gas-flotation contribute to the separation process. The oil drops and droplets are made to agglomerate and coalesce to produce larger oil drops. This eventually creates a continuous oil or emulsion layer at the upper liquid level of the flotation chamber. Internal devices in the chamber and simultaneous gas flotation effects triggered by the release of residual gas from the water facilitate the separation process. In some cases, process optimization can be achieved by introducing external gas and/or specific flocculating chemicals. The resultant oil and gas deposits are removed in a continual process through separate outlet pipes.

     
Schematic drawing of Epcon CFU.click to view larger image
Schematic drawing of Epcon CFU; Source: M-I Epcon AS.
  Photo of Epcon CFU.Epcon CFU; Source: M-I Epcon AS.
Epcon CFU; Source: M-I Epcon AS.





Overall fluid retention time is short (up to one minute) and is determined primarily by the distribution and fineness of the dispersed oil droplets. A chamber with an effective separation volume of 2 m3 will be able to treat a produced water flow volume between 70 and 180 m3/hour. Outer dimensions of the separation units with this capacity typically feature an outer diameter of 1.2 m and an overall height of 2.4 m.

Treatment through a single CFU separation step has proven to reduce the oil-in-water content to 15 to 25 mg/L, while simultaneously degassing the water (Jahnsen and Vik 2003). When more than one CFU is used in series, oil and grease removal performance further improves to levels often below 10 mg/L (Epcon Brochure 2006).

CTour

  Schematic of the CTour process.
Schematic of the CTour process; Source: ProSep Technologies.

The CTour Process System enhances the traditional hydrocyclone technology. It uses gas condensate to extract hydrocarbons from water. The condensate is injected into the produced water stream before being routed through existing hydrocyclone systems. The condensate functions as a solvent, which draws dissolved hydrocarbons out of the water phase and over into the condensate. In addition, the condensate helps to coalesce the small dispersed oil droplets, which then form larger oil droplets before being removed in the hydrocyclones. The CTour Process system is capable of removing many of the dissolved organics from the produced water (CTour Brochure undated).

The CTour Process System includes the following steps:

  • Collect a suitable gas condensate stream;
  • Inject liquid condensate into the produced water stream at a concentration of 0.5-1.5% (volume to volume);
  • Ensure adequate dispersion and mixing (allow at least 3-5 seconds of mixing);
  • Treat the resulting stream in a conventional hydrocyclone; and
  • Send the reject stream (the hydrocarbon-laden concentrate) from the hydrocyclone back to production.

The CTour Process System is capable of achieving:

  • More than 90% improvement of the deoiling efficiency of the existing hydrocyclone processes (<3 mg/l TPH);
  • More than 95% removal of dissolved PAH-and BTX-components;
  • An oil-in-water content of 1.5-3 ppm at Statoil's Ekofisk platform, where it treats a volume of around 300,000 bbl per day of produced water (CTour Brochure undated, Offshore 2006).

Pilot studies at Statoil's Statfjord C platform initially demonstrated 99% removal of dispersed oil, 2-3 ring PAHs, 4-6 ring PAHs, and phenols of C6 or greater (Grini et al. 2003). A subsequent study showed that the performance of the hydrocyclone had improved from 70% removal (pre-CTour) to 85 to 90% removal (post-CTour). Dispersed oil was measured as low as 1 to 5 mg/L (Torvik et al. 2005).

By early 2007, when several new systems are commissioned, the CTour technology will be used to treat 1.7 MMb/d of produced water - the equivalent of two-thirds of all projected produced water discharges in the Norwegian sector at that time (Offshore 2006).

References

CTour Product Description Brochure, undated. Available at http://www.prosep.com/pdfs/ctour_insert.pdf [PDF-external site].

Epcon CFU Technology Brochure, 2006. Available at http://www.epconoffshore.com/upload/epcon/presentations/web%20brochure%20august%202006.pdf [PDF-external site].

Grini, P.G., C. Clausen, and H. Torvik, 2003, "Field Trials with Extraction Based Produced Water Purification Technologies," presented at the 1st NEL Produced Water Workshop, Aberdeen, Scotland, March 26-27.

ahnsen, L., and E.A. Vik, 2003, "Field Trials with EPCON Technology for Produced Water Treatment," presented at the Produced Water Workshop, Aberdeen, Scotland, March 26-27.

Offshore Magazine, 2006, "CTour Technique on Course to Manage Two-thirds of Norway's Produced Water," April 1.

Torvik, H., L. Bergersen, and C. Paulsen, 2005, "One Year of Operational Experience with CTour at Statfjord C," presented at the 3rd NEL Produced Water Workshop, Aberdeen, Scotland, April 20-21.

StayConnected Facebook Twitter LinkedIn RssFeed YouTube