Experimental study on gas–solids flows in a circulating fluidised bed using electrical capacitance tomography

It is difficult to measure the gas–solids flow in a circulating fluidised bed (CFB) because of the complicated and rapid transient process. Electrical capacitance tomography (ECT), a cross-sectional imaging technique, has been used to measure the dilute flow in a large square CFB. A sensor has been specifically designed for the measurement and a new algorithm has been developed for image reconstruction. Flow conditioning parts (internals) are designed and placed inside the CFB, aiming to enhance the contact between gas and particles in the dilute gas–solids flow. The dynamic characteristics and detailed information were obtained on two sections in the bed at different height. The performance of the internals is related to their size, combination, height in the bed and the superficial gas velocity. It has been confirmed that a particular combination of internals can increase the solids concentration in the central area of a cross-section, and can improve the probability density distribution (PDD) with a moderate gas velocity. Using a combination of a large internal at an upper location and a small one at a lower location can optimise the flow in the CFB.

Using a suitable sensor and the Semi-Landweber image reconstruction algorithm for ECT, the transient states of a complicated gas–solids flow in a CFB riser can be measured under different conditions of geometric structure and operation of the riser. PDF analysis based on the ECT experiments is a useful method for finding optimal flow conditions. Stagger-arranged internal structures are better than opposite-arranged ones.Figure optionsDownload as PowerPoint slide