Electrical Tomography Sensors - Interface Level Measurements Inside Desalters and Dehydrators

Abstract In crude oil process vessels, precise control of oil and water levels is vital. In oil refining, high-voltage electrostatic coalescers create strong electric fields for desalting and dehydration, which may disrupt electrical level measurements. Stilling wells improve measurement conditions and shield devices from external electrical interference. This paper proposes enclosing electric tomography- based level measurement technology within a perforated stilling well to counteract high-voltage grid effects. Electrical Tomography (ET) enables comprehensive real-time monitoring of material distributions in various environments, such as pipes, tanks, and vessels. The ET probe sensor provides information on liquid levels within separators, identifying water-emulsion, emulsion-oil and oil-gas interfaces. The probe sensor is confined by a rather narrow stilling well to investigate its effects on measurement accuracy. The stilling well, with an inner diameter of 91.3 mm, accommodated a probe with a diameter of 59.0 mm. The system was tested with 11 different configurations of stratified liquids so that its level measurement capabilities were assessed with water, emulsion, oil and gas. In general, ET measurements within stilling wells are very localized since the proximity of the metal wall of the stilling well affects the electric interactions between the electrodes. The test results showed that the measured information still contains a sufficient amount of information so that the conductivity profile and subsequent interface levels can be estimated with good accuracy. The Root Mean Square Error (RMSE) across all interface levels in the entire series of test cases was 20.6 mm. This equates to approximately 1% of the length of the measurement area. This is of the same order of magnitude as in standard test measurements in identical conditions but without the stilling well. Electrical Tomography is well-suited for real-time measurement of various interface levels in challenging operating conditions where good repeatability and time-resolution are needed. This study demonstrated that Electrical Tomography based level measurements are successful even when installed in narrow stilling wells, without significant impact on measurement accuracy.