Analysis of Crude Oil Electrostatic Desalters Performance

Abstract

Abstract New equations covering a wide range of oil types are developed to estimate the treating rate and treating temperature for dual polarity electrostatic desalters and AC conventional electrostatic desalters in Iranian oil fields. Production of wet crude had been a growing problem that affected the quality of produced oil in Iran. Application of the correct technology and the installation of proper desalting facilities were required to solve this problem. Therefore, it was decided to install electrostatic desalting plants progressively in Iranian oil fields. By the end of 2004, more than 20 desalting plants with a total capacity of 207,000 standard cubic metres per day of treated crude have been installed. The performance of the majority of these desalting plants have been tested and found satisfactory. It is expected that the rate of wet crude production will increase to 366,000 standard cubic metres per day in 2007. This study shows that a dual polarity electrostatic desalter may operate at a minimum crude oil inlet temperature, resulting in extra fuel savings and eliminating the need for a heating system in the vessel. In addition, the treating rate for a dual polarity electrostatic desalter is more than for an AC conventional electrostatic desalter. Introduction The production of salty wet crudes had affected the quality of Iranian crudes and a number of wells had to be shut in for lack of treatment facilities(1). The water produced with crude in Iranian oil fields contains salts in concentrations of 150,000 to 220,000 ppm. In almost all cases, the salt is found dissolved in the water that is dispersed in the crude oil. This salt water is present in the crude in the form of emulsion and its separation is not an easy task. The installation of current desalting plants within the existing facilities in Iran called for considerable changes in the facilities and other utility systems. These changes have been successfully carried out and the performance of the majority of the desalting plants have been tested and found satisfactory(1, 2). When the produced formation water is highly saline as in the case of Iranian fields, then straight dehydration is not the solution and the crude has to be desalted as well. Dehydration means removing only that water which is in the crude when crude is produced. The term desalting means the addition of comparatively fresh water to the crude. This addition of fresh water dilutes the original brine so that the salt content of the water that remains after treatment is within acceptable limits. In general, the dehydration system can be divided into three classes: gravity, electrical, and chemical, or a combination thereof(3). Therefore, the process adopted in Iran for treating wet crude is a combination of dehydration and desalting. It employs chemical demulsifies, heat, and an electrostatic field to dehydrate the crude. All treaters utilize gravity to separate the phases; however, this is the basic method used to remove the impurities from the crude oil.