For this work, electrical capacitance volume tomography (ECVT) is used in a BFB for bubble detection, to evaluate bubble diameter, frequency, and rise velocity. The ECVT sensor consists of 24 electrodes which generate a three-dimensional image of the solids concentration from the capacitance data. This results in a 20x20x20 grid in a 10 cm wide bubbling bed, with a sensor height of 20 cm. A picture of the sensor mounted on the bubbling bed is seen in Fig 1. Based on the sensors data, a new phase detection method was developed which more fully utilizes the three-dimensional potential of the sensor. With this method, the bubble boundaries and velocities could be accurately detected. The obtained data was validated by comparisons with capacitance probes and by feeding virtual bubbles into the algorithm (Fig. 2). Due to the three-dimensional nature of the novel bubble detection technique, insight into the directional tendencies of detected bubbles can be gained. For example, bubble migration toward the radial center of the bed, as well as radial and axial bubble coalescence, and splitting, are more evident from the trends that are producible with this method. In a CFB system ECVT is compared to capacitance probes and borescopic high-speed camera particle tracking velocimetry (PTV) (Fig. 3). The experiments focus on turbulent and fast fluidization regime in the fully developed region of an 8 m high and 0.1 m diameter riser with Geldart group A particles. The ECVT and capacitance probe measurements had comparable radial and axial solids volume fraction trends. Variations in gas velocity, solid circulation rate, and total particle holdup result in different axial and radial concentrations in the riser. With borescopic PTV, particle trajectories were evaluated at different radial positions. In the radial center, mostly upward particle movement was detected, while particle movement was more chaotic in the wall zone. Furthermore, single particles and particle clusters were detected individually (Fig. 4). With all measurement systems a 2 cm wide core flow was observed in the fully developed region.

Poster: Dynamic Bubble Tracking in Fluidized Beds via Electrical Capacitance Volume Tomography

As a next step, a comparison of the ECVT method for bubble detection with magnetic resonance imaging (MRI) will be conducted. The data generated with the borescopic high-speed camera system will be used as validation for CFD-DEM simulations.

Publication

Watson, B., Lindmüller, L., Heinrich, S. Theuerkauf, J., Yao, Y., Fan, Yi.:
Dynamic Bubble Tracking in Fluidized Beds via Electrical Capacitance Volume Tomography
Chemical Engineering Journal, (2024), DOI: doi.org/10.1016/j.cej.2024.150461