he solids distribution in circulating fluidized beds (CFB) has been extensively studied because of its importance in design of CFB boilers and reactors. In circulating fluidized bed, normally, the upper region consists of a dilute core surrounded by a relatively dense annulus, with solids down flow near the wall. The literature reports that the solids near the wall move down in the form of film with clusters and variable thickness. Therefore, it is very important to predict solids film thickness near the wall to estimate the heat transfer between a solid suspension in the bed and wall.
In the present work, The experiments were conducted on two laboratory scale CFB units consisting of 0.0508m diameter & 3 m height and 0.1016m diameter & 6m height. Sand (182 µm and 2560 kg//m3) and FCC particles (99 µm and 1600 kg/ m3) were used as bed material. The operating gas velocity and solid circulation rates were in the range of 1-6m/s and 5-125kg/m2-s respectively. The local solids film thickness data were estimated from the experimental data of local solids flux obtained by using U-tube probe. Further, Yersushalmi's [1] homogeneous cluster suspension model was modified by including acceleration and friction effects to characterize clusters. Also, an empirical equation to calculate local solids film thickness was developed. The empirical equation fits quite well with experimental data.
[...] From these data, the following correlation was developed by using non-linear regression analysis; δ D = U cl + slip (Fr dcl ) (ε cl ) Figure 9 shows the comparison between predicted and measured values of the thickness of solids down flow film near the wall in the riser of circulating fluidized bed. It can be seen that the correlation fits with good agreement with 15% error. In the range of operating conditions and material used in experimentation. The R2 values for the correlation developed are 0.9577 for literature data for small column ( 0.0508 m ID & 4m Height) and 0.9886 for large column ( 0.1016 m ID & 6m height) Measured 0.1 Literature Present 0.1016 m dia & 6m height 0.05 Present 0.0508 m dia. [...]
[...] Solid mass fluxes in circulating fluidized beds, Powder Technol (1992) 197- Zhou, B., Li, H., Xia, Y. & Ma, X. Cluster structure in a circulating fluidized bed, Powder Technol (1994) 173- Bai, D., Shibuya, E., Masuda, Y., Nishio, K., Nakagawa, N. & Kato, K. Distinction between upward and downward flows in circulating fluidized beds, Powder Technol (1995) 75- Lim K. S., J. Zhou, C. Finlay, J.R. Grace, C.J. Lim & C. M. H. Brereton Cluster descending velocity at the wall of circulating fluidized bed risers, in: M. [...]
[...] Geldart, Measurement of radial and axial solid flux variations in the riser of a circulating fluidized bed, in Circulating Fluidized Bed Technology II, P. Basu and J.F. Large Eds., Pergamon Press, Oxford, (1988), 155- Horio, Morishita, K., Tachibana, O., Murata, M. Solid distribution and movement in circulating fluidized bed, in P. Basu, J.F. Large (Eds.,) Circulating Fluidized Bed Technology II; Pergamon: Oxford, U.K. (1988) pp 147- Bierl, T.W. & Gajdos, L.T., Phenomenological Modeling of Reaction Experiments in Risers, Final report, DOEMC-14249-1149. [...]
[...] By using these data, the wall layer thickness has been calculated Har r ies et al [ 21] 0.25 Wei et al [ 20] Bi et al [ 16] 0.2 Bai et al [ Zhang et al [ 19] Wer t her [ 18] Pat ience & Chaouki [ 17] Diagonal line M easur ed Figure Flow structure of CFB Figure Comparison of published correlations with measured data Harris et al also calculated t maximum relative error for published experimental results by using correlations available and found them to be between 150% -275% and concluded that the solid down flow film thickness does depend on local flow structure. [...]
[...] Modeling of the internal flow structure of circulating fluidized beds, Can. J. Chem. Eng (1989) 1010- Senior, R. C. & C. Brereton, Modelling of Circulating Fluidized Bed Solids Flow and Distribution, Chem. Eng. Sci (1992), 281- Harris, A.T. & Davidson, J.F. A core- annulus deposition model for circulating fluidized beds, in: A. Avidan Circulating fluidized bed technology IV, AIChE New York (1994) pp 32- Bolton L.W. and Davidson J.F., Recirculation of particles in fast fluidized risers, in Circulating Fluidized Bed Technology II, P. [...]
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