Keynote Talk: Visualisation of Pharmaceutical Fluidised Beds By Electrical Capacitance Tomography
Gas-solids fluidised beds are commonly used in the pharmaceutical industry and other industries. However, the understanding of the fluidisation processes is still limited because the measurement methods and tools are limited, which can provide both real-time monitoring and online measurement. Therefore, it is difficult to optimise the operation of fluidised beds. The consequence is low efficiency, more energy consumed, more pollution to the environment and more importantly it is difficult to guarantee the product quality. Electrical capacitance tomography (ECT) has been developed as a visualisation and measurement tool for deal with complicated industrial processes, such as fluidised beds. In recent years, ECT has been used to investigate granulation, drying and coating processes in pharmaceutical fluidised beds. For measuring drying and granulation processes, a novel online calibration method was proposed and implemented to deal with continuous change in moisture content and hence the continuous change in equivalent permittivity. This method provides a means of continuous measurement of the solids' moisture level and its distribution, in addition to gas/solids distribution. Experiments were carried out using different scales of fluidised beds, lab-scale, pilot-scale and production-scale, and good results were achieved. For example, the online measurements of moisture level by ECT are in agreement with those measured offline by a moisture meter. For monitoring the coating process in a lab-scale Wurster fluidised bed, a unique ECT sensor is designed with three sets of electrode, one set on internal wall of drying bowl, one set on outside wall of Wurster tube and one set on internal wall of Wurster tube. By this arrangement, all regions of the fluidised bed can be monitored. Because the coating process involves in gas/solids/liquid three phases, it is more difficult to interpret the measured capacitance data and more difficult to implement image reconstruction than a normal fluidised bed containing gas and solids only. Based on the work done so far, it is concluded that ECT is very useful for monitoring and measurement of pharmaceutical fluidised beds. The remaining challenge is how to deal with engineering and pharmaceutical regulation issues.