EXECUTIVE SUMMARY
This report presents a use of an electrical capacitance tomography (ECT) system to study the dynamic behaviour of various modes of fluidization. The results showed that the system can provide instantaneous information on solids distribution for a wide range of gas-solids flow patterns. An application of the ECT system is illustrated here by measurements of the instantaneous behaviour of a fluidised bed. The experimental programme focused on measuring both discrete and continuous parameters which characterise the interaction between the gas and emulsion phases. The first included bubble sizes, their velocities and time scales characterizing a bubble coalescence growth. Solids cross-sectional distribution at various positions in a riser and in a dip leg were measured for a wide range of superficial gas velocities and circulating solids mass fluxes. Instantaneous images showed a flow morphology which is crucial for modelling the heat transfer process. This included details of wall coverage by solids clusters and thickness of the annular layer.
Part of this project was concerned with the development of both hardware and software for capacitance tomography. During the project the software was extended by including a new iterative algorithm and a computer aided procedure for sensor design was developed. As a result the sensors can be designed in different ways to meet differing industrial needs. The data from the ECT system can provide, for the first time, the continuous and on-line information required by the control loop.
The software developed provides the data to the control loop from each individual electrode or from the whole set of electrodes and can be used in in two ways. The first includes images showing solids distribution within a pipe cross-section and the second is based on the statistical analysis of data gathered by a multiplicity of sensor. This can include averaged values, standard deviation and other parameters based on Fourier analysis like spectra or correlation functions. The choice of one of these parameters depends on the particular aim which can be defined by the industrial user.