Fluid Flow Processes Within Gas-solids Fluidized Beds

Fluidized beds have been widely utilized in many industrial applications, such as chemical reactions, power generation, pharmaceuticals and food processing. Nevertheless, further applications are still hindered due to inadequate comprehension of the complex internal hydrodynamic characteristics. Conventional measurement techniques are not able to avoid the introduction of interference within the internal flow structure and so distorted and inaccurate result are obtained. Electrical capacitance tomography (ECT) has been developed as a non-intrusive measurement technique and applied into the application of gas-solids fluidized beds. However, understanding of the bubble behaviour in gas-solids fluidized beds is still limited.
A customized ECT twin-plane sensor has been designed and constructed to further study the fluid flow structure and processes within a bench-scale gas-solids fluidized bed. A detailed calibration process has been conducted with plastic balls of different diameter to derive the reference cut-off values in estimating bubble diameter in the bubbling regime. The bubble diameter has been estimated by means of the individual cut-off values, linear fitted curves and second-order fitted curves with the derived reference cut-off values. A statistic average approach was proposed and evaluated in estimating the averaged axial bubble rising velocity compared with other approaches, including a three-dimensional utilization of the cross-correlation technique on a pixel-by-pixel basis.
Non-intrusive pressure fluctuation measurements have been carried out in order to compare with the ECT measurements in terms of the capability in investigating the bubble and bed behaviour within the gas-solids fluidized bed. The performance of estimating the minimum fluidization velocity and minimum slugging velocity from both methods have been compared and evaluated. Qualitative analysis of the signal amplitude and quantitative analysis of the dominant frequency results, solids concentration results and bubble rising velocity results derived from both methods have been conducted.