CT-Scan Sinogram Measurements to Study Dynamic Fluidized Bed Properties
Bennett, M., Wu, B., Kryuchkov, S., Zhang, Q., Li, Y., Hodgson, D. and Kantzas, A.
5th World Congress on Industrial Process Tomography, Bergen, Norway, September 3-6, 2007.
Motion artifacts are typical in Computed Tomography (CT) images of fast moving objects. The imaging of bubbling gas-solid fluidized beds, where many bubbles may pass through the sensing cross-section in a tomographic measurement, gives such a problem. Removing artifacts from the reconstructed image is problematic due to lost information from the images, but when the concentration of bubbles is low, they are prominent and their shape is close to cylindrically symmetric, analysis of the sinogram can give valuable information about the individual bubbles size, shape and position as well as their frequency.
In this work, the emulsion and bubble portions are identified in individual attenuation projections, which occur every 2ms in the sinogram. Simple trigonometric calculations based on the sinogram are then used to give the position, diameter and frequency of the bubbles in the slice. Then, applying the Inverse Abel transform for the emulsion and bubble separately, density within the emulsion and the bubble itself can be reconstructed. Although the technique is currently limited to larger bubbles due to the resolution of the sinogram and difficulty distinguishing smaller bubbles from fluctuations in bed voidage, collecting this information over time could also give good estimations of time averaged parameters, such as an artifact free voidage distribution, bubble phase area fraction, spatial bubble number distribution and average bubble diameter for larger bubbles.
Pressure meters are commonly used in fluidized bed research to study bed dynamics. Since the pressure fluctuations typically observed can detect the presence of smaller bubbles, this non-invasive technique is ideal to compare with the results produced from analysis of the sinogram in order to assess current limitations in detecting smaller bubbles. In this work, two pressure transducers connected to pressure taps located at the column wall, are also then used to sample the pressure oscillations in the bed at the same flow rate and conditions as the sinogram measurement.