Kim Ann Shollenberger

Gamma-densitometry tomography of gas holdup spatial distribution in industrial-scale bubble columns

Gamma-densitometry tomography (GDT) experiments have been performed to measure gas holdup spatial variations in two bubble columns: a 0.19 m inside diameter Lucite column and a 0.48 m inside diameter stainless steel vessel. Two-phase air/water flows were examined. Horizontal scans at one vertical position in each column were made for several air flow rates. An axisymmetric tomographic reconstruction algorithm based on the Abel transform has been used to calculate the time-averaged gas holdup radial variation. Integration of these profiles over the column cross section has yielded area-averaged holdup results, which have been compared with volume-averaged gas holdups determined from differential pressure measurements and from the rise in the air/water interface during gas flow. The results agree reasonably well.

Validation of Electrical-Impedance Tomography for Measurements of Material Distribution in Two-Phase Flows

A series of studies is presented in which an electrical-impedance tomography (EXT) system is validated for two-phase flow measurements. The EIT system, developed at Sandia National Laboratories, is described along with the computer algorithm used for reconstructing phase volume fraction profiles. The algorithm is first tested using numerical data and experimental phantom measurements, with good results. The EIT system is then applied to solid-liquid and gas-liquid flows, and results are compared to an established gamma-densitometry tomography (GDT) system. In the solid-liquid flows, the average solid volume fractions measured by EIT are in good agreement with nominal values; in the gas-liquid flows, average gas volume fractions and radial gas volume fraction profiles from GDT and EIT are also in good agreement.

Electrical-Impedance Tomography for Opaque Multiphase Flows in Metallic (Electrically-Conducting) Vessels

A novel electrical-impedance tomography (EIT) diagnostic system, including hardware and software, has been developed and used to quantitatively measure material distributions in multiphase flows within electrically-conducting (i.e., industrially relevant or metal) vessels. The EIT system consists of energizing and measuring electronics and seven ring electrodes, which are equally spaced on a thin nonconducting rod that is inserted into the vessel. The vessel wall is grounded and serves as the ground electrode. Voltage-distribution measurements are used to numerically reconstruct the time-averaged impedance distribution within the vessel, from which the material distributions are inferred. Initial proof-of-concept and calibration was completed using a stationary solid-liquid mixture in a steel bench-top standpipe. The EIT system was then deployed in Sandias pilot-scale slurry bubble-column reactor (SBCR) to measure material distributions of gas-liquid two-phase flows over a range of column pressures and superficial gas flow rates. These two-phase quantitative measurements were validated against an established gamma-densitometry tomography (GDT) diagnostic system, demonstrating agreement to within 0.05 volume fraction for most cases, with a maximum difference of 0.15 volume fraction. Next, the EIT system was combined with the GDT system to measure material distributions of gas-liquid-solid three-phase flows in Sandias SBCR for two different solids loadings. Accuracy for the three-phase flow measurements is estimated to be within 0.15 volume fraction. The stability of the energizing electronics, the effect of the rod on the surrounding flow field, and the unsteadiness of the liquid temperature all degrade measurement accuracy and need to be explored further. This work demonstrates that EIT may be used to perform quantitative measurements of material distributions in multiphase flows in metal vessels.

Quantitative tomographic measurements of opaque multiphase flows

An electrical-impedance tomography (EIT) system has been developed for quantitative measurements of radial phase distribution profiles in two-phase and three-phase vertical column flows. The EIT system is described along with the computer algorithm used for reconstructing phase volume fraction profiles. EIT measurements were validated by comparison with a gamma-densitometry tomography (GDT) system. The EIT system was used to accurately measure average solid volume fractions up to 0.05 in solid-liquid flows, and radial gas volume fraction profiles in gas-liquid flows with gas volume fractions up to 0.15. In both flows, average phase volume fractions and radial volume fraction profiles from GDT and EIT were in good agreement. A minor modification to the formula used to relate conductivity data to phase volume fractions was found to improve agreement between the methods. GDT and EIT were then applied together to simultaneously measure the solid, liquid, and gas radial distributions within several vertical three-phase flows. For average solid volume fractions up to 0.30, the gas distribution for each gas flow rate was approximately independent of the amount of solids in the column. Measurements made with this EIT system demonstrate that EIT may be used successfully for noninvasive, quantitative measurements of dispersed multiphase flows.

Measuring Material Distributions of Multiphase Flows in Electrically Conducting Vessels Using Electrical-Impedance Tomography

An implementation of resistive electrical-impedance tomography (EIT) for measuring material distributions of multiphase flows in vessels with electrically conducting walls is presented. Seven ring electrodes are equally spaced on a thin nonconducting rod that is inserted into the vessel. The vessel wall is grounded and serves as the ground electrode. Voltage distribution measurements are used to numerically reconstruct the time-averaged impedance distribution within the vessel, from which the material distributions are inferred. Experimental results for the case in which the rod is inserted coaxially into a liquid-filled vertical standpipe containing beds of different heights of nonconducting solid particles are presented. Agreement between the direct measurement and the numerical reconstruction of the particle-bed height is good. Application of this technique to a pilot-scale slurry bubble-column reactor is discussed.© 2002 ASME

Gas Distribution in Air/Water and Air/Oil Bubble-Column Flows

The effect of liquid properties on axial development of gas-volume-fraction profiles in bubble-column flows is investigated. Experiments are conducted in a cylindrical vessel with an inner diameter of 0.48 m and a height of 3 m. The liquids examined include water and two lightweight mineral oils. A cross sparger with 96 holes is used to inject air into the column with all the holes facing either upwards or downwards. The superficial gas velocity ranges from 5 to 30 cm/s, and the absolute column pressure ranges from 0.1 to 0.5 MPa. Gamma-densitometry tomography (GDT) is used to measure radial distributions of gas volume fraction at eight axial locations. The development length of the gas-volume-fraction profile is shown to increase with gas velocity and column pressure for all three liquids. The development of the cross-sectionally averaged gas-volume fraction for the air/water flow is remarkably different from that for the air/oil flows.© 2002 ASME