A new approach to insight the pharmaceutical fluidized bed process with microwave tomography


Most recently, fluidized beds have found applications in pharmaceutical industry, mainly for particles coating and granulation. Such applications involve the use of complex gas flow processes. Therefore, it is highly desirable to have a real time monitoring and control system so as to enable a bubbling stable fluidization and reduce the chance of defluidization due to agglomeration with high moisture contents particles. Recent technological advances have led to the development of the microwave tomography (MWT) technology which has been explicitly employed in medical sectors. This novel technology has a wide range of frequency and can be utilized in measuring materials with high permittivity and conductivity. This makes it a suitable candidate for monitoring fluidized bed coating and granulation processes. Unfortunately, little has been done about microwave tomography applicability in fluidized bed coating and granulation processes despite such promising attributes.

Recently, a team of researchers from the Institute of Engineering Thermophysics at Chinese Academy of Sciences leading by Professor Haigang Wang in collaboration with Professor Wuqiang Yang Prof. Zhipeng Wu at University of Manchester in the UK investigated the wet gas-solids flow characteristics in a fluidized bed with top-spray and bottom-spray systems based on the microwave tomography technology. They successfully employed the microwave tomography technology for the first time in a real dynamics gas-solids fluidized bed. Their work is currently published in the research journal, Chemical Engineering Science.

The research method employed entailed the design and application of a MWT system with 16 antennas in monitoring the wetting and coating processes in a lab-scale fluidized bed with top-spray and bottom-spray system. Next, the gas-solids flow characteristics of different types of fluidized bed, pellet and spraying liquid were analyzed and compared. Lastly, the standard deviation of normalized permittivity and the dominating frequency and the standard deviation of pressure signal were used and compared for the detection of defluidization of the bed.

The research team observed that for the top spray fluidized bed process, the changes in the flow regimes due to the variation in solids moisture and air velocity could be recorded and recognized by the MWT measurements. In addition, they noted that for cellulose pellets, the MWT measurement was applicable with the solids moisture even increased to 35%, and the measured normalized permittivity value followed the same trend with the solids moisture. Eventually, when the technology was employed in monitoring of wetting and coating experiments with bottom spray fluidized bed, it was revealed that both the types of pellets and spraying solutions could affect the flow regimes in fluidized bed.

In summary, the study presented for the first time, the successful application of MWT sensor to monitor the dynamic processes of two types of fluidized bed, and utilization of the dynamic calibration strategy for image reconstruction. Collectively, the result obtained show that MWT is available for online monitoring of gas solids flow with different moisture content. Altogether, their work is an excellent example that microwave tomography has clear advantages over single point based measurement technology for process fault diagnose.

Pharmaceutical fluidized bed process with microwave tomography - Advances Engineering

About the author

Dr Hanqiao Che received his PhD degree from the Institute of Engineering Thermophysics, Chinese Academy of Sciences in 2018. His specialty is focused on the development and application of novel process tomography techniques to investigate the gas-solids flow behaviors in different fluidised beds, i.e. bubbling fluidised bed and Wurster type fluidised bed. Both Electrical Capacitance Tomography and Microwave Tomography were applied in multi-scale and complex structure gas-solids fluidized beds. He compared the measurement results of the two techniques and evaluated the possibility of fusion measurement.

He has published four peer reviewed papers in prestigious journals including Chem. Eng. Sci., Chem. Eng. Res. Des., Flow Meas. Instrum. and Meas. Sci. Technol. His researches were also delivered at four world-leading conferences. On Nov.12th, 2016, he received the Best Student Paper Award at the Engineering Thermophysics Annual Conference in China.

About the author

Professor Haigang Wang received his PhD from the Institute of Engineering Thermophysics, Chinese Academy of Sciences in 2003 and he is member of AIChE and the IEEE. His specialty is in the areas of multiphase flow CFD simulation and process tomogrpahy measurment, espceially in the gas/solids fluidised beds. In the past few years he led several key research projects, e.g. “Fluidised bed coating process control in pharmaceutical industry”, and “Investigation of gas-solids flows in circulating fluidized bed by ECT”. During these projects, he developed a novel approach to multiphase flow measurement based on ECT and numerical models, to investigate the complicated gas-solids behaviour and to measure the solids concentration and mass flow rate in gas-solids systems. He proposed a conical ECT sensor to measure gas-solids flows in cyclone separators, and reconstructed 3D images. He also measured the solids flow rate in diplegs of CFBs, based on ECT imaging and cross correlation, to achieve product quality control by combining modelling, imaging and distributed control.

He has published more than 100 peer reviewed international journal and conference papers and has an international patent granted. Recent results on multiphase flow measurement, fundamentals of fluidised bed coating, mathematical modelling and online process control using tomographic imaging have been published in high impact journals, e.g. AIChE J., Chem. Eng. Sci. and Meas. Sci. Technol., which have received strong interest from industry, e.g. GEA Pharma System, AstraZeneca and DuPont.

About the author

Dr. Jiamin Ye received her BEng, MSc and PhD degrees in control science and engineering from Tianjin University, Tianjin, China, in 2004, 2006 and 2009, respectively. She was a Postdoctoral Research Associate at Tsinghua University, Beijing, China from 2009 to 2011 and at University of Leeds, Leeds, UK from 2011 to 2012. She is currently a Professor at the Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing, China. She is a senior member of IEEE since 2013. Her current research interests include industrial process tomography, image reconstruction, instrumentation and multiphase flow measurement.

She has been developing electrical capacitance tomography for the on-line measurement of concentration and velocity of gas-solid two-phase flows and processes, including the gas-biomass and gas-coal powder. She has also been working on characterisation of biomass and fossil fuels in circulating fluidised beds based on the coupling simulation of fluid field and electrostatic field. Furthermore, the modern signal processing technique and the multi-sensor fusion method were integrated to estimate the process parameters. This method has been successfully applied in several areas, e.g. biomass combustion process monitoring and space furnace design.

Since 2010 the Applicant has 2 patents granted, has filed 4 patents, and published 30 peer reviewed papers in SCI index journals, including one hot paper and 2 cover papers. Among the 30 papers, 12 of them are published in series of IEEE Transactions and journals.

About the author

Professor Wuqiang Yang has 30 year experience in instrumentation and measurement. He is a Fellow of the IET (formerly the IEE), Fellow of the Institute of Measurement and Control, and Fellow of the IEEE. Since 1991, he has been working with University of Manchester (formerly University of Manchester Institute of Science and Technology (UMIST)) in the UK. He became the Professor of Electronic Instrumentation in the School of Electrical and Electronic Engineering in 2005. He is also a founder and director of ECT Instruments Ltd, who is specialised in developing and supplying AC-based ECT systems.

His main research interests include industrial tomography, especially ECT, sensing and data acquisition systems, electronic circuit design, image reconstruction algorithms, instrumentation and multiphase flow measurement, including powder property and powder flow measurement. He works with many companies, involving powder, such as AstraZeneca and GEA (pharmaceutical fluidised beds), Dalian Institute of Chemical Physics (MTO), Institute of Engineering Thermophysics (CFB for improved coal combustion), Shanxi Institute of Coal Chemistry (coal-gasifying), PSRI and UOP (FCC).

He has published over 400 papers, is a referee for over 50 journals (including 6 IEEE journals), Associate Editor of IEEE Trans. Instrumentation and Measurement, editorial board member of 6 other journals (including Meas. Sci. and Technol.), guest editor of many journal special issues and visiting professor at several other universities. His biography has been included in Who’s Who in the World since 2002.

About the author

Prof. Zhipeng Wu obtained his BSc degree in Radio Technology from the Northeast University, China in 1983, and PhD degree in Antennas and Propagation from the University of Birmingham in 1988. He was also awarded a DEng degree by the University of Birmingham in 2003. During 1988-1991, he was appointed as a Research Fellow at the University of Birmingham. In 1992, he joined UMIST as a lecturer.

Currently he is a Professor in the School of Electrical and Electronic Engineering, and the Head of the Microwave and Communication Systems Group. He is Principal Investigator for more than ten projects supporting by EPSCR/TSB/UMIP. Until now, he has published 150 peer reviewed journal and international conference papers.

His research interests includes: Antennas and Propagation, Microwave Sensors, and Microwave Imaging Systems. In 2010, he made the first set of real-time microwave tomography system. Microwave Doppler Flowmeter will be tested/used for flow velocity measurement since the instrument is used in the TSB project for “Gas-oil-water multiphase flow production to improve productivity and reservoir management”. He is Fellow of IET and Senior Member of IEEE.


H.Q. Che, H.G. Wang*, J.M. Ye, W.Q. Yang, Z.P. Wu. Application of microwave tomography to investigation the wet gas solids flow hydrodynamic characteristics in a fluidized bed. Chemical Engineering Science 180 (2018) 20–32.

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