Tom Dyakowski

Application of electrical resistance tomography to interrogate mixing processes at plant scale

This paper presents an application of electrical resistance tomography to the investigation of mixing processes at plant scale. An 8-plane 16-electrode ring sensor installed within a stirred tank with a 1.5 m inner diameter is described. Three-dimensional and non-stationary behaviour of mixing processes are illustrated by the images obtained simultaneously from eight axial levels along the tank height. The results illustrate air-core vortex detection, miscible fluid mixing and gas-liquid mixing processes.

Development of mixing models using electrical resistance tomography

Abstract The network-of-zones concept provides a simplified basis for constructing mixing models appropriate to tomography. For miscible single-phase mixing in three-dimensions, of the order of 10 4 volume elements (voxels) are needed to interpret mixing results from 16 element electrical resistance tomographic (ERT) sensing rings stacked axially. Experimental mixing and dispersion in passive scalar pulse tests can be acquired at video frame rates by ERT and simulated by integration of sets of first-order ordinary differential equations. Non-uniformities in gas hold-up and solids suspension can also be detected and quantified in three-dimensions by resistance tomography. Modelling the approximately axisymmetric mixing of these two-phase examples can be achieved by a much smaller number of algebraic equations. Tomographic modelling provides new insights into the fundamentals of mixing in a stirred vessel. The reduced computational requirements of networks-of-zones make real-time model-based control more feasible.

Imaging nylon polymerisation processes by applying electrical tomography

The paper presents an application of electrical tomography for imaging a nylon polymerisation process at elevated temperatures (up to 275°C) and pressures (up to 22 bar). The process was realised within a metal walled tank using a sensor constructed in the form of a ceramic sleeve with electrodes coated on the inner surface. The images obtained show the dynamic behaviour of the process and how the electrical properties of the material varied with time.

GAS-LIQUID AND MISCIBLE LIQUID MIXING IN A PLANT-SCALE VESSEL MONITORED USING ELECTRICAL RESISTANCE TOMOGRAPHY

Abstract A large-scale electrical tomography system has been designed and set-up at UMIST to study imperfect mixing and improve the design of stirred vessels and their impeller configuration at plant-scale. The sensing system was constructed with 8-planes of sensing rings, each containing 16-electrodes and installed into a 2.7 m3 polypropylene vessel fitted with a standard Rushton turbine. Images were reconstructed using the sensitivity theorem algorithms. Some illustrative results for pseudo-stationary gas-liquid mixing and unsteady semi-batch mixing of miscible fluids are reported. Issues related to qualitative and quantitative reconstruction in 2-D and 3-D are discussed.

Dual-modality probe for characterization of heterogeneous mixtures

This paper presents a laboratory feasibility study aiming at the development of a dual modality sensor for development within an oil and gas extraction plant to measure the composition of heterogeneous mixtures. The technology of manufacturing the sensor is briefly described and the preliminary measurements, conducted for mixtures of vegetable oil and saline water, using two modalities: ultrasound and electrical, are presented. The experimental results obtained from ultrasonic measurements are compared with theoretical predictions. Finally, conclusions and recommendations for future work are presented.

Analysis of Gas-Solids Feeding and Slug Formation in Low-Velocity Pneumatic Conveying

Gas and solids feeding is a key operation in pneumatic conveying of particulate materials. This article presents an analysis of the interfacing effects between a nozzle gas supplier, a rotary valve solids feeder with dropout box, and the pipeline of a pneumatic conveying test rig for low-velocity dense-phase flow. Experiments were carried out to examine the flow pattern of slugs in different combinations of gas flow conditions and solids loading ratios. The effect of gas and solids feeding on the formation of slugs is analyzed by using both experimental data and computer-modeled results. Solids accumulation and sliding motion at the bottom of the dropout box and near the entrance of the downstream pipe, which happen prior to the bulk motion in the form of a slug, are found important in determining the size of a slug. Gas retention and pressure buildup characteristics in the feed section are also found crucial in influencing the flow patterns of slugs.

Performance of Some Finite Elements in Numerical Simulation of Complex Incompressible Three Dimensional Flow

A numerical approach is applied to study the flow in some three-dimensional flow configurations. A physical problem has been discretizied using a finite element method based on mixed approximation of the velocity and pressure space. The effectiveness of the method is confirmed by the computational examples representing the class of internal flows having one inlet and more than one outlet. The selected outflow boundary conditions enable the avoidance of mass split-ratio. The computational examples showed that the choice of function spaces for approximation of velocity and pressure has a critical effect on physically meaningful solutions. It was illustrated that the lack of element mass balance limits the application of the well known Taylor-Hood elements for particular types of flow.

Application of Electrical Capacitance Tomography to Flow Modelling within a Circulating Fluidized Bed

The results of the measurements of the solids concentration region in a circulating fluidized bed are described. An electrical capacitance tomography system has been used to measure both instantaneous and average solid distributions as a function of a superficial air velocity and a solid mass flux. The fractional wall coverage by clusters and the solids concentration within the annulus layer was measured. The data is compared with the results available from the literature.