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. (C)2000 Elsevier Science S.A. All rights reserved.