Measurement And Control Fluidized Bed Coating And Granulation Processes By Process Tomography

Fluidised beds are widely used in pharmaceutical industry for particle drying,granulation and coating.The process is a typical multi-phases process which includes gas,solids and droplets three phase.The process efficiency as well as the end-point product quality are strongly depended on the property operating parameters setting and flow regimes control.However,most of the fluidized bed processes in pharmaceutical industry are operated without on-line measurement and the process is still in 'black' box.Therefore,it is extremely desirable that a reliable process analysis tool(PAT)is used in the fluidized bed processes to improve the product quality.Process tomography can reconstruct the solids distribution in the measuring region and it is one of the good options for fluidised bed monitoring than conventional single-point based measurement due to its non-intrusive and non-invasive nature.The main contribution of this thesis is to apply electrical capacitance tomography(ECT)and microwave tomography(MWT)techniques to investigate the gas-solids flow behaviors inside a fluidised bed for particles granulation.A closed loop control strategy is proposed based on ECT and MWT tomography images to optimize the fluidized bed granulation and coating process.Firstly,a new ECT sensor with combined 12-4-8 electrodes were proposed and constructed in a Wurster type fluidized bed.The gas-solids flow in different flow regimes were measured synchronously.In addition,a twin-planes eight electrodes ECT sensor was designed and used to measure the different regions inside the Wurster tube.It was revealed that mainly seven types of flow regimes,i.e.bubbling-core,intermittent-core,intermittent-dispersed,plug-bubbling,bubbling-dispersed,plug-core and defluidization,existed in the coating process.The effects of the operation parameters on flow regimes were investigated.By comparing the agglomeration rates in the end products with different batches,it is observed that the intermittent flow and plug flow could result in heavy particle agglomeration.Considering that ECT has a limitation in high moisture granules measurement,a MWT sensor was applied to monitor the wetting and coating processes in a lab-scale fluidized bed with top-spray and bottom-spray system.MWT has a wide range of operational frequency and can be used to measure materials with high permittivity and conductivity.The hydrodynamics characteristics of wet gas-solids flow with high moisture content were investigated by MWT.The results indicate that MWT provides valuable information to identify the defluidization in the fluidized bed process with wet materials.A closed-loop control strategy was proposed and a PID controller was applied to keep a low void fraction in the annulus zone by manipulating the frequency of blower,the peristaltic pump was also manipulated by a bangbang controller to avoid the occurrence of intermittent and plug flow in the annulus zone.The tests showed that the stability of flow regime improved and the particle agglomeration rate decreased obviously by applying the proposed control strategy.This thesis presents several key issues including flow regime monitoring,process parameters measurement,fault diagnose and feed back control related with fluidized bed dying,granulation and coating.The proposed measurement methods and research results provide valuable information for pharmaceutical industry.