Abstract

Bulk dry powder is commonly involved in industry. While it is necessary to have in-line sensors for real-time measurement and analysis of bulk dry powder, very few such sensors are commercially available for industrial application, or likely to see application in the near future. This article attempts to provide a comprehensive critical review of in-line sensor technologies for real-time measurement and characterisation of bulk dry powder properties, including application of sensors and associated analytical methods for measurement of such properties as particle size and particle size distribution, morphology, density, blend composition, moisture content, spatial moisture distribution, and for flow rate measurement. To measure a powder flow rate, concentration, concentration profile, velocity and velocity profile must be measured because in almost all cases, it involves in gas/powder multiphase flow measurement. The review of existing sensors is organised in terms of sensing principles or sensing technologies, such as optical (including Laser), capacitance, electrostatic inductance, electrodynamic, triboelectric, microwave, electromagnetic (EM), Coriolis, impact plate and acoustic, with analysis of the economics of implementing the technologies. Electrical capacitance tomography (ECT) is an emerging technology, which is particularly suitable for in-line real-time measurement of bulk dry powder flows and analysis of bulk dry powder properties. This article also reviews ECT technology, in particular the AC-based ECT system, and its applications dealing with bulk dry powder. A particular case study is the use of ECT for investigation of circulating fluidised beds for coal combustion and gasification, which demonstrated the advantages of ECT over conventional sensors for this purpose.