Dual-plane Electrical Resistance Tomography Research Articles

Column flotation hydrodynamics operating in the heterogeneous regime estimated by electrical resistance tomography and multi-phase CFD model

ABSTRACT This paper investigates the two-phase flow hydrodynamics of a column flotation operated from a homogeneous to a heterogeneous flow regimes using experimental and computational fluid dynamics (CFD) techniques. Experiments were conducted in a lab scale column flotation of 0.1 m internal diameter and 2.5 m length at various superficial gas velocities using a dual plane electrical resistance tomography (ERT). The mean gas holdup increased from 2 to 18% with the increase in superficial gas velocity from 0.6 to 7.2 cm/s. The gas holdup-based bubble swarm velocity method identified four distinct flow regimes, i.e. homogeneous bubbling regime, narrow discrete bubbling regime, a sustained helical flow regime and churn turbulent flow regime in the column. Further, transient simulations were conducted using a two-fluid model coupled with a population balance model to assess the flow behavior inside the column. Virtual mass, lift and drag forces were incorporated into the model to account for the interphase forces. Numerical simulations predicted mean gas holdup was matching with the experimental data at low gas velocities (<2.4 cm/s), and a marginal deviation was noted at higher gas velocities (>2.4 cm/s). The predicted radial gas holdup profiles were found to change from flatter to parabolic with the increase in gas velocities, i.e. similar to the experiments. The effect of particle size on the rate constant and recovery was estimated with Luttrell and Yoon’s performance model using the particle floatability input data and the two-phase experimental data. The developed CFD model can be useful to optimize the operating and design parameters for efficient operation of the column flotation process.

Electrical resistance tomography-based multi-modality sensor and drift flux model for measurement of oil–gas–water flow

This paper proposes a novel method to measure each constituent of an oil–gas–water mixture in a water continuous flow, typically encountered in many processes. It deploys a dual-plane electrical resistance tomography sensor for measuring dispersed phase volume fraction and velocity; a gradiomanometer flow density meter and a drift flux model to estimate slip velocities; with absolute pressure and temperature measurements. These data are fused to estimate constituent volume flow rates. Other commonly used operational parameters can be further derived: water cut or water liquid ratio (WLR) and gas volume fraction (GVF). Trials are described for flow rates of water 5–10 m3 h−1; oil 2–10 m3 h−1 and gas 1–15 m3 h−1. The comparative results are included with published data from the Schlumberger Gould Research flow facility. The paper proposes the use of the described configuration for measurement of volume flow rates in oil–gas–water flows with an absolute error of ±10% within GVF 9%–85% and WLR > 45%.

Liquid–Solid Two-Phase Flow Rate Measurement by Electrical and Ultrasound Doppler Sensors

Flow rate measurement in multiphase flow is essential for process control and safety production. As the drawbacks of conventional flowmeter measurement error produced by the heterogeneous phase or velocity distribution, a measurement technique combining an electrical resistance tomography (ERT) and an ultrasound Doppler (UD) sensor is proposed. The UD sensor obtains the dispersed particle velocity distribution, and the ERT acquires the solid phase distribution. An experimental platform is constructed for the liquid-solid two-phase horizontal flow experiments. The dual-plane ERT with the cross-correlation signal analysis compensates for the inaccurate particle velocity measurement at the bottom of the pipe by using UD independently due to the locally high concentration. The liquid-solid two-phase mixed flow rate under different flow regimes is measured with the two sensors. The proposed method has a 6.3% maximum uncertainty for the liquid-solid two-phase flow rate measurement.

Characterization of oil-water two-phase flow in a horizontal pipe with multi-electrode conductance sensor

Measurement of oil-water flow parameters is of great importance in petroleum industry. Due to its complicated flow structure, it is still a challenging problem. This paper presents the use of a multi-electrode conductance sensor and a dual-plane electrical resistance tomography (ERT) sensor to measure phase fraction and velocity in a horizontal oil-water flow. A series of experiments is carried out on a two-phase flow loop using mineral white oil and tap water. Taking advantage of different conductivity values of two fluids, the estimation of phase fraction is obtained by conductance measurements. By correlating voltage fluctuation signals measured from upstream and downstream sensor, the velocity of oil-water flow is evaluated. The phase fraction and velocity measured from two techniques are compared. Experimental results show that the multi-electrode conductance sensor is more suitable to estimate phase fraction of oil-water mixture. For the velocity measurement, cross correlation velocity obtained with multi-electrode conductance sensor is more closer to the mixture velocity of oil-water mixture.

Design and implementation of a multi-sensor system for gas–water flow measurement

Gas–water two-phase flow is commonly encountered in industrial processes. It is still a challenging problem to accurately measure the flow parameters due to complex flow mechanics of the two-phase flow. This paper presents the design and implementation of a multi-sensor system for accurate measurement of gas–water flow in a horizontal pipe. Information detected from spatially distributed sensors can be analysed and integrated to extract effective information and obtain complete description of the gas–water flow, which is more reliable than that is estimated with a single sensor. The multi-sensor system included a dual-plane electrical resistance tomography sensor, a six-electrode conductance sensor, a dual-cone flowmeter, a pressure gauge and a temperature sensor. The position and distribution of the multiple sensors was investigated according to their measurement properties and the multi-sensor system was designed based on the combination of PXI modular instrument and FPGA technique. Experiments were conducted to study the performance of the multi-sensor system. Experimental results indicated that the proposed multi-sensor system could be used to investigate characteristics of the gas–water two-phase flow. This study underpins further study for the multi-sensor data fusion of two-phase flow measurement.

Characterisation of a high concentration ionic bubble column using electrical resistance tomography

Attentions has been given to ionic liquids as an alternative physical solvent for carbon dioxide (CO2) absorption because of their potential for gas selectivity, absorption capacity and low desorption energy by tailoring the molecules. Ionic liquid normally have a high viscosity, which influences the performance of absorption processes, and therefore, efficiency. This study investigates the hydrodynamics of ionic liquids in a two-phase gas–liquid flow by determination of the bubble formation, distribution of gas and bubble velocity profiles. A dual plane electrical resistance tomography (ERT) system and an optical imaging device were applied to a bubble column reactor of 50mm internal diameter for the study. The model ionic liquids were aqueous solutions of sodium chloride (NaCl) with conductivity adjusted by altering the concentration of NaCl. Gas holdup has been estimated by analyses of conductivity data obtained from ERT by application of Maxwell's relationship which reveals significant increase in gas holdup as ionic concentration increases and is in good agreement with other studies.

ERT Investigation on Horizontal and Vertical Counter-gravity Slurry Flow in Pipelines

Abstract The occurrence of separation and slippage of the two phases in settling solid-liquid flow in pipelines make the flow unpredictable and time dependent. Therefore it is paramount for the operator of slurry pipelines to monitor and measure the flow continuously, particularly from the local point of view. This paper reports the laboratory experiments carried out on an open flow loop and the use of Electrical Resistance Tomography (ERT) to interrogate the internal structure of horizontal and vertical counter-gravity slurry flow. The use of high performance dual-plane ERT system, which is called Fast Impedance Camera System (FICA), is attempted for fast impedance measurement of the media with a temporal resolution up to 1000 dual-frames per second (dfps). The internal images of the pipeline are captured along with the measurement of solids volumetric concentration for both orientations, while the dualplane ERT is combined with cross-correlation technique to estimate axial solids velocity distribution. A set of experiments was carried out on coarse and medium sand-water slurry flow with 2% and 10% throughput volumetric concentration and the transport velocity range of 1.5-5 m/s. A flow diversion technique was used for validation of mean local solids concentration and solids axial velocity obtained from the ERT.

Characterization of Air-Water Two-Phase Vertical Flow by Using Electrical Resistance Imaging

The characterization of air-water two-phase vertical flow in a 12 m flow loop with 1.5 m of vertical section is studied by using electrical resistance tomography (ERT). By applying a fast data collection to a dual-plane ERT sensor and an iterative image reconstruction algorithm, relevant information is gathered for implementation of flow characteristics, particularly for flow regime recognition. A cross-correlation method is also used to interpret the velocity distribution of the gas phase on the cross section. The paper demonstrates that ERT can now be deployed routinely for velocity measurements and this capability will increase as faster measurement systems evolve.

Two Methods for Measurement of Gas-Liquid Flows in Vertical Upward Pipe Using Dual-Plane ERT System

In modern industrial processes, the accurate measurement of two-phase flow is an important task. Process tomography can provide a distribution information of a two-phase pipe flow. In order to carry out instantaneous flowrate measurements of the gas-liquid two-phase flow in a vertical upward pipe, a dual-plane electrical-resistance-tomography (ERT) system is combined with a cross-correlation technique to measure the gas-liquid two-phase flow, in which the continuous phase is a conductive liquid. A pixel correlation method and a feature-value-correlation method are applied to estimate the disperse-phase velocity. Two methods are used to estimate the local void fraction and the disperse velocity distribution by reconstructing the image pixel gray value distribution. Estimates of the mean void fraction and the disperse-phase mean velocity are obtained by extracting the feature value of the measured data at the dual-plane ERT boundary. The variation in the disperse-phase distribution with changes in time is considered, and the estimated values for both the disperse-phase void fraction and velocity have been experimentally obtained, which are used in the calculation of the instantaneous flowrate. The air-water two-phase flow experiments are designed to evaluate the validity of the two methods used in estimation. The experimental results agree with the theoretical methods for obtaining the disperse-phase velocity and instantaneous-flowrate measurement in the vertical upward pipe

Measurement of oil volume fraction and velocity distributions in vertical oil-in-water flows using ERT and a local probe

This paper presents the use of a high performance dual-plane electrical resistance tomography (ERT) system and a local dual-sensor conductance probe to measure the vertical upward oil-in-water pipe flows in which the mean oil volume fraction is up to 23.1%. A sensitivity coefficient back-projection (SBP) algorithm was adopted to reconstruct the flow distributions and a cross correlation method was applied to obtain the oil velocity distributions. The oil volume fraction and velocity distributions obtained from both measurement techniques were compared and good agreement was found, which indicates that the ERT technique can be used to measure the low fraction oil-water flows. Finally, the factors affecting measurement precision were discussed.

Plug flow of yoghurt in piping as determined by cross-correlated dual-plane electrical resistance tomography

Cross-correlation of electrical resistance tomography (ERT) was used to determine the velocity profile of yoghurt in a pipe of industrial dimensions. In viscometry, at shear rates higher than 10 s −1, the yoghurt followed the power law model with a K-value of 3.7 Pa s n and an n-value of 0.37. In pipe flow, however, within the tested mean velocity range of 0.05–0.25 m s −1, the yoghurt appeared to flow as a plug. The local velocity was constant from the centreline to within 3 mm of the tube wall, which corresponds to the resolution of the ERT method.

Application of dual-plane ERT system and cross-correlation technique to measure gas–liquid flows in vertical upward pipe

The progress of process tomography provides a new method for two-phase flow measurement. The dual-plane electrical resistance tomography (ERT) is combined with the correlation measurement technique to carry out the two-phase flow measurement in which the continuous phase is conductive liquid. The method of the estimation of void fraction and the disperse phase velocity by extracting the eigenvalue of the dual-plane ERT boundary measured data is presented. This method is applied to the transient flow-rate measurement of the air–water two-phase flow in vertical pipe. The information of disperse phase void fraction and distribution variation with time change can be considered adequately, and the estimated value of disperse phase void fraction and velocity can be gained fairly accurately in this method, which provides the data for the calculation of the transient flow-rate. The experiment results indicate that this kind of measurement method is valid when the distance between the upstream and downstream measured cross section is short enough.

The design of a dual-plane ERT system for crosscorrelation measurement of bubbly gas/liquid pipe flow

Combining electrical resistance tomography (ERT) with thecross-correlation flow measurement technique can provide more information onthe flow than usual. A dual-plane ERT system for use on laboratory- andplant-scale process equipment has been developed on the basis of this idea.This paper focuses on the design of it. The principle of measurement of thelocal gas velocity distribution in a bubbly gas/liquid pipe flow based onpixel-pixel cross correlation of two plane images is described. Methods toimprove the real-time performance of the system are also discussed in detail.Initial experimental results illustrate the feasibility of the methodpresented here.

Measurement of the solids volume fraction and velocity distributions in solids–liquid flows using dual-plane electrical resistance tomography

This paper describes a dual-plane Electrical Resistance Tomography (ERT) system for measuring the local solids volume fraction distribution and the local solids axial velocity distribution in solids–liquid flows. The paper also describes a local, intrusive conductivity probe system for providing reference measurements of the distributions obtained using the dual-plane ERT system. Experiments were performed using both the ERT system and the local probe system in vertically upward and inclined solids–water flows. Good agreement between the two techniques was observed. The local solids volume fraction distribution and the local solids axial velocity distribution obtained using the ERT system enable good estimates to be made of the mean solids volume fraction, the mean solids velocity and the solids volumetric flow rate.