Monitoring and control of coating and granulation processes in fluidized beds – A review

This review presents a compilation of works of the main techniques for monitoring and control fluidization regimes, particle size and moisture content during coating and granulation processes in the fluidized bed. The development of monitoring and control systems for coating and granulation of particles is highly desirable, not only to allow the operation in a stable bubbling fluidization regime, which intensifies heat and mass transfer, but also to ensure strict quality specifications for products, such as, uniform particle size distribution, low moisture content and good flowability. This paper focuses on the discussion of methods used and results obtained in studies on monitoring and control of granulation and coating process in the fluidized bed reported in the literature in the last decades. Pressure fluctuation signal analysis is widely discussed as a tool of regime monitoring. To monitor particle size, techniques such as, Near Infrared spectroscopy (NIR), Focused Beam Reflectance Measurements (FBRMs), among others are presented in detail. As for moisture content tracking, the methods are reviewed like acoustic signals, capacitance, microwave resonance and spectroscopy. It is evident that although these processes are highly complex, the techniques presented here have evolved mainly due to the efforts of several research groups, showing great potential for applications in industry, emphasizing the importance of this research field.