Electrical Capacitance Volume Tomography: Design and Applications

This article reports recent advances and progress in the field of electrical capacitance volume tomography (ECVT). ECVT, developed from the two-dimensional electrical capacitance tomography (ECT), is a promising non-intrusive imaging technology that can provide real-time three-dimensional images of the sensing domain. Images are reconstructed from capacitance measurements acquired by electrodes placed on the outside boundary of the testing vessel. In this article, a review of progress on capacitance sensor design and applications to multi-phase flows is presented. The sensor shape, electrode configuration, and the number of electrodes that comprise three key elements of three-dimensional capacitance sensors are illustrated. The article also highlights applications of ECVT sensors on vessels of various sizes from 1 to 60 inches with complex geometries. Case studies are used to show the capability and validity of ECVT. The studies provide qualitative and quantitative real-time three-dimensional information of the measuring domain under study. Advantages of ECVT render it a favorable tool to be utilized for industrial applications and fundamental multi-phase flow research

Non-invasive and non-intrusive diagnostic techniques for gas-solid fluidized beds – A review

Gas-solid fluidized-bed systems offer great advantages in terms of chemical reaction efficiency and temperature control where other chemical reactor designs fall short. For this reason, they have been widely employed in a range of industrial application where these properties are essential. Nonetheless, the knowledge of such systems and the corresponding design choices, in most cases, rely on a heuristic expertise gained over the years rather than on a deep physical understanding of the phenomena taking place in fluidized beds. This is a huge limiting factor when it comes to the design, the scale-up and the optimization of such complex units. Fortunately, a wide array of diagnostic techniques has enabled researchers to strive in this direction, and, among these, non-invasive and non-intrusive diagnostic techniques stand out thanks to their innate feature of not affecting the flow field, while also avoiding direct contact with the medium under study. This work offers an overview of the non-invasive and non-intrusive diagnostic techniques most commonly applied to fluidized-bed systems, highlighting their capabilities in terms of the quantities they can measure, as well as advantages and limitations of each of them. The latest developments and the likely future trends are also presented. Neither of these methodologies represents a best option on all fronts. The goal of this work is rather to highlight what each technique has to offer and what application are they better suited for

Computer Tomograph Measurements in Shear and Gravity Particle Flows

The paper reports the recent results obtained on the applicability of cross-sectional digital imaging method to study particle flow characteristics in 3D particle beds forced to move by gravity or shear. X-ray CT imaging technique is widely used in medical diagnostics and, during the last decades, its spatial and temporal resolution has been improved significantly. In this study, an attempt was made to use this technique for engineering purposes. Two experimental set-ups with different types of particle flows were investigated using Siemens Somatom Plus type CT equipment. A series of trials were carried out in a small model hopper with flat bottom and almost cylindrical side wall slightly deviating from verticality. Non steady-state flow was studied during the outflow of particulate material from this vessel, through a central hole at the bottom. Further investigation was fulfilled in a modified Cuette-type shearing device to study steady-state shear flow. This equipment consisted of an almost cylindrical vessel identical to that used for gravity flow measurements, and a smaller inner cylinder rotating within this vessel concentrically, around its vertical axis. The surface of the inner cylinder was notched vertically, i.e. perpendicularly to the direction of rotation to increase wall friction between the particles and the cylinder. Almost spherical sucrose granules, also used for gravity flow measurements, were filled into the gap between the rotating cylinder and the outer wall of the equipment. Movement of particles took place due to shear, generated within the particle bed. By using X-ray CT technique, cross-sectional digital images were obtained in every two seconds for both types of particle flows. For this, the cross-sectional variation of the local Hounsfield density values were measured in a matrix of 0.1x0.1x2.0 mm space elements. It was proved that the applied non-invasive crosssectional imaging technique was suitable to distinguish the stationary and moving particle regions, and by this, to estimate the location of the boundary zone between them

Measuring the Gas-Solids Distribution in Fluidized Beds - A Review

This paper reviews techniques for measuring the voidage distribution in gas-solid fluidized beds, with a focus on the developments during the last ten years. Most attention is given to recent progress in tomography and pressure measurements, but visual observations, capacitance probes and optical probes are also covered

Electrical Capacitance Volume Tomography (ECVT) for industrial and medical applications-An Overview

Tomography is a non-invasive, non-intrusive imaging technique allowing the visualization of phase dynamics in industrial and biological processes. This article reviews progress in Electrical Capacitance Volume Tomography (ECVT). ECVT is a direct 3D visualizing technique, unlike three-dimensional imaging, which is based on stacking 2D images to obtain an interpolated 3D image. ECVT has recently matured for real time, non-invasive 3-D monitoring of processes involving materials with strong contrast in dielectric permittivity. In this article, ECVT sensor design, optimization and performance of various sensors seen in literature are summarized. Qualitative Analysis of ECVT image reconstruction techniques has also been presented

Fluidized bed hydrodynamics by means of electrical capacitance tomography

Fluidized bed reactors are utilized in a variety of applications from hydrocarbon cracking to drying of mineral ore to coating of pharmaceutical pills. A proper understanding of bed hydrodynamics is essential to properly design, operate and control the process. Intrusive and non-intrusive measurement techniques have been utilized to study various aspects of fluidized bed behaviour. Electrical Capacitance Tomography (ECT) has been utilized to determine the distribution of gas-solid mixture in the bed. The Digital Image Analysis Technique (DIAT) is used to determine the bubble behavior in two-dimensional beds. The bubble behavior has not been studied by ECT. The premise of this research is to test a new technique by combining ECT solid fraction maps with image processing techniques to determine the bubble characteristics in the bed. Electrical Capacitance Tomography (ECT) was used to map the relative fractions of sand-air mixture in a 14 cm ID acrylic vessel at two different static bed heights. The voids were defined as the areas of gas-solid mixture with value of less than 0.25. Afterwards simple image analysis techniques were applied to isolate bubbles from the rest of the bed. The resulting data were converted into binary images to extract hydrodynamic information. The two main parameters of interest were the bubble diameter and its rise velocity. The experimental average velocities and average diameters matched the results obtained from respective correlations in the literature. However, large spreads existed for both these parameters due to the simultaneous presence of bubbles and slugs. The experimental fluidized bed did not transition fully into the turbulent regime but has the character of a hybrid bubbling-slugging regime. This is illustrated by experimental diameters which indicate presence of bubbles and slugs simultaneously. The same information was illustrated by experimental velocity-diameter envelopes (minimum and maximum values) which overlapped for higher flow conditions. The radial solid fraction distribution illustrated the same point with an inverted “M” profile which has been associated previously with regime transition. The path of bubble rise was identified, mainly rising through the midway point between the bed’s center and its inner edge. Five different types of bubbles were identified using the two dimensional binary images of voids. However, this technique can only be used for regimes where voids/bubbles are the main source of gas transfer to the surface of the bed

Development And Study Of Measurement Methods For Jets And Bogging In A Fluidized Bed

In the Fluid Coking process, if the local concentration of liquid is very high, particles may stick together which can eventually result in process upset because of poor fluidization or even defluidization, a condition commonly known in industry as bogging . Using a capacitance sensor, the void distribution in a bed of coke particles can be visualized. The voidage fluctuations caused by gas bubbles have been shown to change dramatically as the bed becomes bogged. Therefore, capacitance sensors should be able to predict the bogging condition in fluid cokers. The first part of the thesis focused on designing noiseless capacitance sensors that can be used to measure the liquid concentration and void distribution in a fluidized bed. The effect of bogging on the distribution of a liquid sprayed into fluidized bed was then investigated by determining the impact of bogging on the breakage rate of the liquid-solid agglomerates. Pressure measurements are easier to perform in industrial units than capacitance measurements. The knowledge acquired with capacitance measurements was then applied to the design of early bogging detection methods from pressure measurements. Detection of bogging with acoustic measurements is discussed in the next section. The speed of sound was measured at different levels of particles cohesiveness and fluidization velocities. The last part of the thesis applies the capacitance sensors to the measurement of jet cavity fluctuations. Two types of jets were investigated: the supersonic gas jets and the jets formed when liquid is atomized with a gas into a fluidized bed

Electrical Capacitance Volume Tomography Validation of Column Flotation Process with Gas Injection Variation

Electrical capacitance volume tomography (ECVT) is proposed as a novel real time monitoring system for column flotation process. This study aims to validate the results of static and dynamic simulations using ECVT and ECVT-Computational Fluids dynamics (ECVT-CFD) and real time column flotation monitoring experiment using ECVT system. Bubble fractions with variation of gas velocity (0.02, 0.03 and 0.04 m/s) which were resulted from the simulation and experiments of column flotation process were compared and measured. The results from ECVT experiments successfully reconstruct the images of bubbles inside the column flotation in real time. The comparison results from both of simulations and experiments showed that bubble fraction increases with increasing in gas velocity.  The validation on bubble fraction measurement based on simulations compared with the experimental results gives accuracy at 86%-98%.  It is indicated that at higher gas velocity (0.04 m/s) the accuracy of the simulations compared with the experimental results, is better than that of lower gas velocity (0.02 and 0.03 m/s).Electrical capacitance volume tomography (ECVT) is proposed as a novel real time monitoring system for column flotation process. This study aims to validate the results of static and dynamic simulations using ECVT and ECVT-Computational Fluids dynamics (ECVT-CFD) and real time column flotation monitoring experiment using ECVT system. Bubble fractions with variation of gas velocity (0.02, 0.03 and 0.04 m/s) which were resulted from the simulation and experiments of column flotation process were compared and measured. The results from ECVT experiments successfully reconstruct the images of bubbles inside the column flotation in real time. The comparison results from both of simulations and experiments showed that bubble fraction increases with increasing in gas velocity.  The validation on bubble fraction measurement based on simulations compared with the experimental results gives accuracy at 86 - 98%.  It is indicated that at higher gas velocity (0.04 m/s) the accuracy of the simulations compared with the experimental results, is better than that of lower gas velocity (0.02 and 0.03 m/s)