R.A. Williams

Process tomography : a European innovation and its applications

Recent developments in the design and application of tomographic sensors for measurements in industrial processes are reviewed. The principal sensing methods and their relative performance are summarized. Industrial scale applications, future prospects and limitations of the technology are discussed.

Application of capacitance tomography to gas-solid flows

The fundamental principles of electrical capacitance tomography (ECT) are presented. In particular, the recent developments in the use of a back-projection algorithm applied to solve an inverse problem are discussed. Experimental results obtained for monitoring a pneumatic conveying system and bubbling fluidization are reviewed and revised data are presented. The performance of the ECT is assessed in quantitative and qualitative terms. The use of ECT to provide novel on-line measurement information suitable for modelling or control purposes is illustrated.

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.

Real time capacitance imaging of bubble formation at the distributor of a fluidized bed

Abstract This paper describes the use of a transputer-based 8-electrode capacitance tomography system for imaging gas bubbles in a fluidized bed in the vicinity of an air distributor plate. The quantitative results show how the solid concentration distribution varies as a function of time for three different flow regimes: bubbling, slugging and the transition to turbulent. Bubble shape, length and coalescence can be observed.

Industrial Monitoring of Hydrocyclone Operation using Electrical Resistance Tomography

Abstract The development and application of electrical resistance tomography for on-line auditing of an industrial hydrocyclone separation is reported. The work demonstrates the retrofitting of electrodes into a commercially available separator and their use in laboratory, pilot plant scale investigations of clay refining. A number of new and significant applications are described including: the development of methodologies to allow observation of the occurrence of faults in underflow discharge (spraying, roping, blockage); accurate measurement of the air core size for different operational conditions; direct calculation of solid concentration profiles based on parametric reconstruction of conductivity data in three dimensions.

Controlled Production of Emulsions Using a Crossflow Membrane

A method for manufacturing emulsions - crossflow membrane emulsification has been studied. This involves the formation of emulsions by breaking up the discontinuous phase into droplets in a controlled manner without the use of turbulent eddies. This is achieved by passing the discontinuous phase through a suitable microporous medium and injecting the droplets so formed directly into a moving continuous phase. This paper presents two examples of experimental data for droplet formation using a single pore (capillary tube) and a membrane tube. A high-speed video camera (up to 1000 frames per second) was used to record the formation of droplet from a single pore and thus measure droplet growth and the detachment processes as a function of process parameters such as transmembrane pressure drop, membrane pore size, continuous phase crossflow velocity etc. Real emulsions were prepared using a membrane tube.

Electrical tomography techniques for process engineering applications

Abstract This paper summarizes the characteristics of electrical tomography techniques, highlights their current applications and gives an indication of their future applications in the chemical process engineering environment.

On-line monitoring of dense phase flow using real time dielectric imaging

Abstract Two significant advances in the development of on-line tomographic imaging methods for visualization and quantification of powder flow are illustrated based on pilot-plant studies of pneumatic conveying and fluidization. The dynamic behaviour of a circulating fluidized bed is described, in which the thickness of the downflowing solids along the wall is measured. The data enables a more realistic (non axi-symmetric) model or heat transfer to the wall to be formulated. The application of electrical capacitance images to derive, in real time, visualization of moving stratified powder beds and slugs and subsequent analysis of image data for identification of the prevailing flow structure for control purposes is described.

Real time visualisation and analysis of dense phase powder conveying

Investigation and control of flow phenomena in the pneumatic conveying of solids requires a detailed knowledge on the flow regimes and a number of phase flow properties. Electrical capacitance tomography (ECT) is shown here to be a robust tool for this purpose, particularly when dense phase plug flow is to be monitored. The application of ECT to dense phase powder conveying in an experimental vacuum system is demonstrated and described, including the visualisation of slug size, shape and velocity. Measured gas and solid flow rates were also analysed in an attempt to ultimately provide a basis for comprehensive on-line analysis. A number of statistical estimators were selected and used in data processing, in order to distinguish between particular types of dense flow. The results show the potential for use of the method for the on-line control of dense phase pneumatic conveyors.

The origin of the fish-hook effect in hydrocyclone separators

Abstract Experimental evidence suggests that under certain circumstances the selectivity (or classification) function for hydrocyclones does not always conform