Application of electrical capacitance tomography in pharmaceutical manufacturing processes

It is difficult to know the details of material distribution in a fluidised bed. Electrical capacitance tomography (ECT) technology has been developed for imaging industrial processes containing dielectric materials. This paper discusses the principles of ECT and presents the first experimental results of using ECT to measure gas/solids distribution in square circulating fluidised beds (CFB). A wide range of fluidisation conditions was tested, from bubbling to circulating fluidisation. It has been shown that over the range, ECT can provide solids concentration and voids distribution instantaneously. Different fluidisation regimes could also be identified from the reconstructed images.

This article presents capabilities of the application of electrical capacitance tomography (ECT) to hopper flow dynamics analysis. The two main goals are to demonstrate a number of tomographic data analysis methods in the application to core flow and to propose some simple parameters depicting this flow via funnel description. Experiments have been conducted for various diameters of hopper orifice using two types of materials with different physicochemical properties, rice and polyamide pellets. ECT allows noninvasive in situ measurement, visualization, and study to be carried out on nonconducting media such as particulate systems or powders. Tomographic images give valuable information about solids concentration distribution inside the measurement space delimited by electrodes. Proper interpretation of concentration changes during the hopper discharging allows the investigation of phenomenon dynamics to be performed. Data analysis consists of raw signal (the measured capacitances) interpretation and tomographic image post-processing manipulation. The present study focuses on the tracking of particulate concentration changes and the hopper discharge rate parameter proposition. Preliminary attempts at funnel propagation velocity measurements are presented here. On the other hand, funnel propagation velocity rate in the initial stage of hopper unloading is based on the calculation of transition time between characteristic points indicated on unloading dynamics diagram. Transition time is calculated using stochastic processes theory-based methods. The novel approach proposed by the authors is based on the estimation of velocity using just one plane of sensing electrodes in contrast to standard applied inter-plane correlation techniques. However, basic parameter estimators such as autocorrelation and variance are used in order to examine the gravitational flow as well.

The results of the measurements of the solids concentration region in a circulating fluidized bed are described. An electrical capacitance tomography system has been used to measure both instantaneous and average solid distributions as a function of a superficial air velocity and a solid mass flux. The fractional wall coverage by clusters and the solids concentration within the annulus layer was measured. The data is compared with the results available from the literature.

Based on the electrical capacitance tomography technique, a new method for the void fraction measurement of two-phase flow is proposed. A 12-electrode void fraction measurement system is established. A mathematical model of image reconstruction of electrical capacitance tomography is developed. To obtain the quantitative information of two-phase flow, combining the Tikhonov regularization principle and the algebraic reconstruction technique algorithm, a new image reconstruction algorithm is presented. The experimental results show that the accuracy of void fraction measurement is satisfactory. The proposed method is suitable for the void fraction measurement of many kinds of two-phase flow.

Acoustic fluidized bed hydrodynamics characterization using X-ray computed tomography

The moisture content of granules in fluidised bed drying, granulation and coating processes can typically be between 1%~25%, resulting in the change of permittivity and conductivity during the processes. Electrical capacitance tomography (ECT) has been used for this purpose, but has a limit because too much water can cause a problem in capacitance measurement. Considering that microwave tomography (MWT) has a wide range of frequency (1~2.5 GHz) and can be used to measure materials with high permittivity and conductivity, the objective of this research is to combine ECT and MWT together to investigate the solids concentration with different moisture content and different flow patterns. The measurement results show that both ECT and MWT are functions of moisture content as well as flow patterns, and their measurements are complementary to each other. This is the first time that these two tomography modalities have been combined together and applied to image the complex solids distribution. The obtained information may be used for the process control of fluidised bed drying, granulation and coating to improve operation efficiency.

Investigation of wetting and drying process in a gas-solid fluidized bed by electrical capacitance tomography and pressure measurement

Simulation and experimental studies on fluidization properties in a pressurized jetting fluidized bed

Electrical capacitance tomography as a monitoring tool for high-shear mixing and granulation

The wet granulation route of tablet manufacturing in a pharmaceutical manufacturing process is very common due to its numerous processing advantages such as enhanced powder flow and decreased segregation. However, this route is still operated in batch mode with little (if any) usage of an automatic control system. Tablet manufacturing via wet granulation, integrated with online/inline real time sensors and coupled with an automatic feedback control system, is highly desired for the transition of the pharmaceutical industry toward quality by design as opposed to quality by testing. In this manuscript, an efficient, plant-wide control strategy for an integrated continuous pharmaceutical tablet manufacturing process via wet granulation has been designed in silico. An effective controller parameter tuning strategy involving an integral of time absolute error method coupled with an optimization strategy has been used. The designed control system has been implemented in a flowsheet model that was simulated in gPROMS (Process System Enterprise) to evaluate its performance. The ability of the control system to reject the unknown disturbances and track the set point has been analyzed. Advanced techniques such as anti-windup and scale-up factor have been used to improve controller performance. Results demonstrate enhanced achievement of critical quality attributes under closed-loop operation, thus illustrating the potential of closed-loop feedback control in improving pharmaceutical tablet manufacturing operations.

Electrical capacitance tomography (ECT) has been developed to provide 2D images, representing the cross-sectional permittivity distribution of industrial processes, such as oil pipelines and pharmaceutical fluidised beds. In some cases, 3D visualisation is more attractive than 2D. While some researchers worked on 3D ECT, the imaging speed was very slow, far away from real time. This paper introduces an approach to real-time 3D visualization in ECT, which can generate 3D images at almost the same speed as the traditional 2D images.

Gas and solids mixing characteristics in the bubbling and turbulent regimes of a gas‐solid fluidized bed are examined using helium and phosphor tracer techniques to obtain the gas and solids dispersion coefficients, respectively. The real time, quasi‐3‐D flow behavior is qualified and quantified by the electrical capacitance tomography (ECT) technique. The mixing behavior varies significantly with the flow regimes. As the gas velocity increases, axial and radial gas dispersion coefficients increase in the bubbling regime, reach a peak at Uc, the transition velocity from the bubbling to turbulent regimes, and then decrease. In contrast, as the gas velocity increases, axial and radial solids dispersion coefficients increase in the bubbling regime and continuously increase through Uc to the turbulent regime. Temperature and pressure have little effect on the gas and solids mixing behavior. A small quantity of fine particles is noted to drastically affect the gas and solids mixing behavior in the turbulent fluidized bed. The axial and radial dispersion coefficients of gas and solids reach their maximum when the fines content is about 15%. The ECT measurements illustrate the effect of adding fines on the flow behavior in the bed. A small quantity of fine particles disintegrate the bubble/void phase, significantly modifying bubble/void‐ and emulsion‐phase mixing behavior.

Characterisation of fluidised bed granulation processes using in-situ Raman spectroscopy

The tomographic imaging of process parameters in industrial applications can be based on different sensing modalities, e.g. ultrasonic waves and electrical capacitance, all of which are sensitive to specific properties of the materials to be imaged. They have shown to be useful tools for process monitoring in different industries. However, the achievable image quality and resolution are generally limited in practice due to the ill-posedness of the inverse problem and limited available data. To further improve the results, the fusion of ultrasound transmission tomography (UTT) and electrical capacitance tomography (ECT) for monitoring two-phase flows is proposed in this paper. The two methods offer complementary properties, making them well suited for data fusion. The ultrasound image is used as a priori information for the finite element method-based capacitance reconstruction algorithm. A tentative dual-mode sensor and static measurements of gas-solid two-phase material distributions are presented. The results indicate that a significant improvement in image quality can be achieved with the proposed sequential tomography sensor fusion

Application of capacitance electrical tomography for on-line and off-line analysis of flow pattern in horizontal pipeline of pneumatic conveyer