Electrical Resistance Tomography for Control Applications: Quantitative Study of the Gas-Liquid Distribution inside A Cyclone

Abstract

Phase separation based centrifugal forces is effective, and thus widely explored by the process industry. In an inline swirl separator, a core of the light phase is formed in the center of the device and captured further downstream. Given the inlet conditions, this gas core created varies in shape and size. To predict the separation behavior and control the process in an optimal way, the gas core diameter should be measured with the minimum possible intrusiveness. Process tomography techniques such as electrical resistance tomography (ERT) allows us to measure the gas core diameter in a fast and non-intrusive way. Due to the soft-field nature and ill-posed problem in solving the inverse problem, especially in the area of low spatial resolution, the reconstructed images often overestimate the diameter of the object under consideration leading to unreliable measurements. To use ERT measurements as an input for the controller, the estimated diameters should be corrected based on secondary measurements, e.g., optical techniques such as high-speed cameras. In this context, image processing and image analysis techniques were adapted to compare the diameter calculated by an ERT system and a fast camera. In this paper, a correction method is introduced to correct the diameter obtained by ERT based on static measurements. The proposed method reduced the ERT error of dynamic measurements of the gas core size from over 300% to below 20%, making it a reliable sensing technique for controlled separation processes.

A Fast Electrical Resistivity-Based Algorithm to Measure and Visualize Two-Phase Swirling Flows

“…Indeed, a considerable difference in the diameter estimation by the algorithm and the ERT image reconstruction is present, as shown in Figure 13. In past studies [30], the image reconstruction overestimated the diameter of the phantoms by 98% for small sizes and gradually improved with the increase in the phantom size. This discrepancy is mainly due to the illposed nature of image reconstruction algorithms.…”

“…The flow taking place in the facility was recorded by a high-speed camera, Basler acA 1920 150uc, at 60fps. The same method described in [30] is used to recover the core size from the images and correct the observed values based on refraction theory due to the curved pipe walls. The images are processed in a window of 0.5D starting 6cm above the electrodes, inside the shield in the bottom of Figure 6b.…”

“…To numerically validate the comparison the tomograms were processed using a graph-cut image segmentation method as described in [30]. The graph-cut method combines energy minimization and graph theory to detect sharp transition or object edges locally.…”

“…Both speed and spatial resolution are important to capture the relevant dynamics of the separation inside ISS in real-time. Previous works based on the correction of the lightphase core size measured by the sensor via calibration against a camera were successful in increasing the accuracy of the ERT system for non-iterative schemes [30] [31], and approaches relying on artificial intelligence and machine learning are also present in literature [32]. However, there is still a mismatch between the flow time-scales and the temporal resolution of the ERT with the correction.…”

A Fast Electrical Resistivity-Based Algorithm to Measure and Visualize Two-Phase Swirling Flows

“…Both speed and spatial resolution are important to capture the relevant dynamics of the separation inside ISS in real time. Previous works based on the correction of the lightphase core size measured by the sensor via calibration against a camera were successful in increasing the accuracy of the ERT system for non-iterative schemes [30,31], and approaches relying on artificial intelligence and machine learning are also present in literature [32]. However, there is still a mismatch between the flow time scales and the temporal resolution of the ERT with the correction.…”