Application of microwave tomography to investigation the wet gas-solids flow hydrodynamic characteristics in a fluidized bed

Fluidized beds are widely used in pharmaceutical industry for particles coating and granulation. Due to the complex gas solids flow process, it is extremely desirable that a real time monitoring and control system is used in the process in order to enable a bubbling stable fluidization and reduce the chance of defluidization due to agglomeration with high moisture contents particles. The microwave tomography (MWT) technology has been developed for more than twenty years and was mainly applied in medical sectors. MWT has a wide range of frequency (1–2.5 GHz) and can be used to measure materials with high permittivity and conductivity. Therefore, it is a good choice for the monitoring of fluidized bed coating and granulation processes. In this paper, a MWT system with 16 antennas was designed and applied for the monitoring of wetting and coating processes in a lab-scale fluidized bed with top-spray and bottom-spray system. The hydrodynamics characteristics of wet gas-solids flow with different moisture content were investigated by MWT technology. This is the first time that MWT was applied in a real dynamics gas-solids fluidized bed. Experiment result shows that the MWT is available for the online monitoring of the gas solids flow with different moisture content. Different flow regimes were revealed based on the MWT images combined with pressure signals. The results indicate that the MWT provides valuable information to identify the defluidization in the fluidized bed process with high moisture contents materials. It is evident that microwave tomography has clear advantages over single point based measurement technology for process fault diagnose.