Oil Dehydration Improved by Dual Frequency Electrostatic Process
Authors: Armstrong John , Sams Gary Wayne 
Published: February 2016

Abstract
With the world's production of crude oil becoming heavier and moving offshore into deeper waters, the need for efficient, compact separation and dehydration is essential. Application of improved electrostatic dehydration technologies has the potential to have a major impact in reducing oil production costs. Improved hydraulic efficiency, the use of alternative electrodes and the application of dual frequency modulation to the electrostatic power supply shows significant production benefits. Nearly a 100% improvement in the hydraulic efficiency of electrostatic coalescers has been achieved by utilising an effective flow distribution and collection system. A 30% dehydration improvement is achieved by the use of electrodes constructed of alternative materials. Finally, a 100% dehydration improvement in the capacity and performance of existing oil dehydrators have been demonstrated from an improved, patented electrostatic power supply utilising a dually modulated electrostatic field. This patented power supply allows the operator to adjust the energy supplied to the drop interface as necessary for overcoming interfacial tension while also adjusting the time available for electrostatic field decay as required to minimize the effects of oil conductivity. It has not previously been possible to directly address either of these parameters. It has been shown in both laboratory and field tests that significant improvement in dehydration results from application of these techniques.
These results have been confirmed at a production facility in South America handling 45,000 bopd per dehydrator of a medium gravity crude oil. This oil was processed by five 10 ft. diameter x 45 ft. long electrostatic dehydrators using combined AC/DC electrostatic technology. The vessel capacity increased significantly, while maintaining or exceeding the required oil specification. The field trial demonstrated conclusively that this dual frequency electrostatic system provides producers and refiners with the ability to dehydrate and/or desalt oils more efficiently and to better process more difficult crudes.

Applied Technology
Utilising this South American oil facility, two of the five vessels were retrofitted with an improved distribution and electrode system. A third vessel received an improved oil distributor and enhanced electrostatic dehydration technology. The application of these technologies was intended to quantify at an operating facility the improvements that could be achieved in a commercial oil dehydration process and to demonstrate the robustness of the equipment, and establish confirmation of the laboratory test results.

Commercial Facility
The commercial production facility shown includes five oil dehydration vessels operating in parallel. Each horizontal dehydrator is 10 ft OD x 45 feet long and utilises Dual Polarity® AC/DC electrostatic technology. Three vessels contained open bottom inlet spreaders, steel high voltage electrodes and pipe collectors. The other two vessels contained similar spreaders and collectors but used composite high voltage electrodes, in lieu of steel. All five vessels were equipped with Dual PolarityÒ (AC/DC), 150 kVA transformers operating on 480 volt, single phase power. This facility is shown in Figure 1.