In a circulating fluidized bed (CFB) the cross-sectional solids distribution in the top zone may differ from that in the lower zones. Particularly, the solids concentration distribution around the exit could be noticeably higher than that in other places. As an important factor affecting heat transfer in CFBs, cross-sectional solids concentration has rarely been investigated by means of online process tomographic (PT) visualization. This work uses electrical capacitance tomography (ECT) to visualize the solids distributions in the top zone of a CFB. In addition, wavelet methods are used for de-noising and image enhancement, and the effects are found in three aspects: (1) the influence of noise in the raw data can be reduced, which improves the quality of the reconstructed images; (2) the noise in the reconstructed ECT images can be reduced, providing a means for further image enhancement; (3) the rough patches of the images can be visibly smoothed, which is valuable for image refinement under coarse image pixel divisions. Experimental data revealed important features of the solids distribution, including (1) the core-annulus flow pattern, (2) the high solids concentration in the corners of the riser, (3) the moderate effect of the cap of the riser, and (4) the high solids concentration near the exit.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.