ANALYSIS OF FLOW STRUCTURE IN LARGE-SCALE CIRCULATING FLUIDIZED BEDS
Local transient solids fraction and particle velocity sign al s were measured in a 0.418m×18m large-scale circulating fluidized bed(CFB) by a dual-optical fiber density probe and a Laser Doppler Velocimeter(LDV) system . The probability density distribution(PDD) of both transient solids fraction a nd particle velocity was obtained. The bimodal distribution of PDD for both sol ids fraction and particle velocity can be clearly seen in the riser.While in th e downer, the PDD curves only exhibit single peak distribution.The results indi cate that two phases, i.e., the cluster phase with solids fraction near 1- e_mf and the void phase with solids fraction about 0.01-0.02,exists i n the riser. Meanwhile, only single void phase exists in the downer. Although there exist particle clusters in the downer, they cannot form a stable cluster p hase with solids fraction near 1-e_mf.The dissimilarity of solids flow structure reveal the significant difference in gas-solids flow structure and mechanism between the along-gravity gas-solids flow in the downer and the aga inst-gravity flow in the riser.