Gas Backmixing in the Dense Region of a Circulating Fluidized Bed

Won Namkung; Sang Done Kim

Korean Journal of Chemical Engineering, Vol.16, No.4, 456-461, July, 1999

DOI10.1007/BF02698268 Export Citation

Gas Backmixing in the Dense Region of a Circulating Fluidized Bed

Won Namkung, and Sang Done Kim^†

Department of Chemical Engineering and Energy & Environment Research Center, Korea Advanced Institute of Science and Technology, Taejon, Korea

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The gas backmixing characteristics in a circulating fluidized bed (0.1 m-ID×5.3-m high) have been determined. The gas backmixing coefficient(D_ab) from the axial dispersion model in a low velocity fluidzation region increases with increasing gas velocity. The effect of gas velocity on D_ab in the bubbling bed is more pronounced compared to that in the Circulating Fluidized Bed (CFB). In the dense region of a CFB, the two-phase model is proposed to calculate D_ab from the two-phase model and mass transfer coefficient (k) between the crowd phase and dispersed phase. The gas backmixing coefficient and the mass transfer coefficient between the two phases increase with increasing the ratio of average particle to gas velocities(U_p/U _g).

Keywords:Fluidized Bed;Gas Backmixing;Two-phase Model

[References]

Amos G, Rhodes MJ, Mineo H, Chem. Eng. Sci., 48, 943 (1993)
Arena U, "Circulating Fluidized Bed," Editors J.R. Grace, A.A. Avidan and T.M. Knowlton, Blackie A & P, London, chap 3 (1997)
Brereton CMH, Grace JR, Yu J, "Axial Gas Mixing in a CFB," CFB Technol. II, Editors P. Basu and J.F. Large, Pergamon Press, New York, 307 (1988)
CanKurt NT, Yerushalmi J, "Gas Backmixing in High Velocity Fluidized Beds," Fluidization, Editors J.F. Davidson and D.L. Kearins, Cambridge Univ. Press, London, 387 (1978)
Haider A, Levenspiel O, Powder Technol., 58, 63 (1989)
Ishii H, Horio M, Adv. Powder Technol., 2, 25 (1991)
Latham R, Potter OE, Chem. Eng. J., 1, 152 (1970)
Lee JS, Kim SD, HWAHAK KONGHAK, 20(3), 207 (1982)
Lee GS, Kim SD, Chem. Eng. Commun., 86, 91 (1989)
Li Y, Wu P, "A Study on Axial Gas Mixing in a Fast Fluidized Bed," CFB Technol. III, Editors P. Basu, M. Horio, M. Hasatani, Pergamon Press, New York, 581 (1991)
Li J, Weinstein H, Chem. Eng. Sci., 44, 1697 (1989)
Mason EA, Sc. D. Thesis, MIT, Cambridge, U.S.A. (1950)
Mason EA, cited in van Deemter (1961)
Namkung W, Kim SD, "Gas Mixing in the Upper Dilute Region of a Circulating Fluidized Bed," CFB Technol. V, Editors M. Kwauk and J. Li, Science Press, Beijing, 134 (1997)
Namkung W, Kim SD, Powder Technol., 99(1), 70 (1998)
Namkung W, Kim SD, HWAHAK KONGHAK, 36(5), 797 (1998)
Namkung W, Kim SW, Kim SD, Chem. Eng. J., in press (1999)
Nguyen NV, Whitehead AB, Potter OE, AIChE J., 23, 913 (1977)
Nguyen HV, Potter OE, Dent DC, Whitehead AB, AIChE J., 28, 509 (1981)
Overchasier RH, Todd DB, Olney RB, AIChE J., 5, 54 (1957)
van Deemter JJ, Chem. Eng. Sci., 13, 143 (1961)
van Deemter JJ, "Fluidization," J.F. Davidson, D. Harrison and R. Clift, Academic Press, London, Chap. 7 (1985)
Werther J, Hartge EU, Kruse M, Powder Technol., 70, 293 (1992)
Wippen D, Wittemann K, Kuhne J, Helmrich H, Schugerl K, Chem. Eng. Commun., 10, 307 (1981)
Yerushalmi J, "Gas Mixing in High Velocity Fluidized Bed," Gas Fluidization Technology, Eds. D. Geldart, Wiley, Chichester, U.K., Chap. 7 (1986)
Zhang W, Tung Y, Johnsson F, Chem. Eng. Sci., 46, 3045 (1991)

[Referenced By]

[1] Amos G, Rhodes MJ, Mineo H, Chem. Eng. Sci., 48, 943 (1993)

[2] Arena U, "Circulating Fluidized Bed," Editors J.R. Grace, A.A. Avidan and T.M. Knowlton, Blackie A & P, London, chap 3 (1997)

[3] Brereton CMH, Grace JR, Yu J, "Axial Gas Mixing in a CFB," CFB Technol. II, Editors P. Basu and J.F. Large, Pergamon Press, New York, 307 (1988)

[4] CanKurt NT, Yerushalmi J, "Gas Backmixing in High Velocity Fluidized Beds," Fluidization, Editors J.F. Davidson and D.L. Kearins, Cambridge Univ. Press, London, 387 (1978)

[5] Haider A, Levenspiel O, Powder Technol., 58, 63 (1989)

[6] Ishii H, Horio M, Adv. Powder Technol., 2, 25 (1991)

[7] Latham R, Potter OE, Chem. Eng. J., 1, 152 (1970)

[8] Lee JS, Kim SD, HWAHAK KONGHAK, 20(3), 207 (1982)

[9] Lee GS, Kim SD, Chem. Eng. Commun., 86, 91 (1989)

[10] Li Y, Wu P, "A Study on Axial Gas Mixing in a Fast Fluidized Bed," CFB Technol. III, Editors P. Basu, M. Horio, M. Hasatani, Pergamon Press, New York, 581 (1991)

[11] Li J, Weinstein H, Chem. Eng. Sci., 44, 1697 (1989)

[12] Mason EA, Sc. D. Thesis, MIT, Cambridge, U.S.A. (1950)

[13] Mason EA, cited in van Deemter (1961)

[14] Namkung W, Kim SD, "Gas Mixing in the Upper Dilute Region of a Circulating Fluidized Bed," CFB Technol. V, Editors M. Kwauk and J. Li, Science Press, Beijing, 134 (1997)

[15] Namkung W, Kim SD, Powder Technol., 99(1), 70 (1998)

[16] Namkung W, Kim SD, HWAHAK KONGHAK, 36(5), 797 (1998)

[17] Namkung W, Kim SW, Kim SD, Chem. Eng. J., in press (1999)

[18] Nguyen NV, Whitehead AB, Potter OE, AIChE J., 23, 913 (1977)

[19] Nguyen HV, Potter OE, Dent DC, Whitehead AB, AIChE J., 28, 509 (1981)

[20] Overchasier RH, Todd DB, Olney RB, AIChE J., 5, 54 (1957)

[21] van Deemter JJ, Chem. Eng. Sci., 13, 143 (1961)

[22] van Deemter JJ, "Fluidization," J.F. Davidson, D. Harrison and R. Clift, Academic Press, London, Chap. 7 (1985)

[23] Werther J, Hartge EU, Kruse M, Powder Technol., 70, 293 (1992)

[24] Wippen D, Wittemann K, Kuhne J, Helmrich H, Schugerl K, Chem. Eng. Commun., 10, 307 (1981)

[25] Yerushalmi J, "Gas Mixing in High Velocity Fluidized Bed," Gas Fluidization Technology, Eds. D. Geldart, Wiley, Chichester, U.K., Chap. 7 (1986)

[26] Zhang W, Tung Y, Johnsson F, Chem. Eng. Sci., 46, 3045 (1991)