Electrical capacitance tomography for conventional fluidized bed measurements-remarks on the measuring technique

Electrical capacitance tomography (ECT) is a unique measuring technique with great potential in multiphase flow measurements. ECT has received a considerable attention amongst the process engineering community, and particularly in fluidization research. However, a precise measuring scenario, in particular the experimental span, and its reliability in a wide range of operating conditions has not been carefully investigated in the past. For this purpose, an experimental study, conducted in a cold conventional fluidized bed using a twin-plane ECT system has been carried out using different particle groups and at different gas velocities. Different experiment scenarios in the range of 10-80 s has revealed that, in measuring a dynamic parameter such as the standard deviation or the average bubble velocity or frequency, it is highly recommended to consider a minimum measuring span of 60 s. Local measurement accuracy for the dynamic parameters appears to be strongly dependent on the measuring location, with the wall region being the most sensitive. In measuring the solid fraction, a measurement span of 20 s appears to be quite sufficient in order to achieve a good representation, either for the cross-sectional average, or the local measurement at a selected point inside the bed. The study also reveals that the recommended spans are applicable to a wide range of particle sizes covering Geldart groups A/B, B and D. A brief discussion about the ECT software and the image/data improvement procedure is also given. (C) 2004 Elsevier B.V. All rights reserved.