Online monitoring and flow regime identification of fluidised bed drying and granulation processes

Fluidised beds are widely used in the pharmaceutical industry for granulation, drying and coating. The product quality strongly depends on the operation parameters and process conditions, e.g. inlet airflow rate, temperature and spraying flow rate. For granulation and drying processes, the flow conditions can change dramatically due to different moisture level, because of the change in physical characteristics of particles, including viscosity, density and diameter. Also, the flow regime of a fluidised bed would change with the diameter and density of particles. Due to high moisture content, particles could agglomerate and stick up to the wall and distributor plate, resulting in a fault process. Therefore, it is necessary to monitor a drying or granulation process, identify their flow regime and control the processes according to the particle properties. This paper describes an application of electrical capacitance tomography (ECT) to monitor the process conditions and for diagnosis of fault with a semi-industrial scale pharmaceutical fluidised bed. Preliminary test results with granulation and drying processes are given. Future work on fluidised bed control based on the information provided by ECT will be discussed.