Chapter 9 - Electrical capacitance imaging of fluidized beds

Abstract

This chapter emphasizes capacitance type systems that are better developed for process applications than either resistance or inductance systems. Capacitance imaging is a valuable tool for examining the detailed voidage distributions within fluidized beds. The high speed of the technique allows the dynamic behavior of fluidized beds to be studied in detail. The technique confirms many early observations in a much more direct way and reveals previously unobserved behaviors. Electrical Impedance Tomography (EIT) uses the measurement of electrical property to construct maps of that property through several dimensions. Properties, which have been or may be used, include capacitance, resistance, eddy current, and inductance. The selection of the electrical property for measurement in a specific application depends on the process stream and how sensitive the electrical property is to the stream variation that is being measured. Resistance sensing devices are suitable for electrically conducting systems while capacitance sensing is suitable for electrically insulating systems. Inductance sensing devices are useful for detecting components that generate eddy currents or affect magnetic permeability. All three types of systems may be used for multiphase systems if the phases meet the appropriate electrical conditions. Capacitance imaging shows promise for real time evaluation of gas-solid, liquid-liquid, and liquid-solid process streams. Besides dynamic systems, it may also find use in the non-destructive evaluation of ceramic, plastic and composite materials and in the inspection of non-conducting containers.