Radial Gas Mixing Characteristics in a Downer Reactor

Jin Hwan Bang; Yong Jeon Kim; Won Namkung; Sang Done Kim

Korean Journal of Chemical Engineering, Vol.16, No.5, 624-629, September, 1999

DOI10.1007/BF02708142 Export Citation

Radial Gas Mixing Characteristics in a Downer Reactor

Jin Hwan Bang, Yong Jeon Kim, 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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In a downer reactor (0.1 m-I.D.×3.5 m-high), the effects of gas velocity (1.6-4.5 m/s), solids circulation rate (0-40 kg/m²s) and particle size (84,164 ㎛) on the gas mixing coefficient have been determined. The radial dispersion coefficient (D_γ) decreases and the radial Peclet number (Pe_γ) increases as gas velocity increases. At lower gas velocities, D_r in the bed of particles is lower than that of gas flow only, but the reverse trend is observed at higher gas velocities. Gas mixing in the reactor of smaller particle size varies significantly with gas velocity, whereas gas mixing varies smoothly in the reactor of larger particle size. At lower gas velocities, D_γ increases with increasing solids circulation rate (G_s), however, D_γ decreases with increasing G_s at higher gas velocities. Based on the obtained D_γ values, the downer reactor is found to be a good gas-solids contacting reactor having good radial gas mixing.

Keywords:Fluidization;Downer;Circulating Fluidized Bed;Radial Gas Mixing;Dispersion Model

[References]

Adams CK, "Gas Mixing in Fast Fluidized Beds," Circulating Fluidized Bed Technology II, Basu, P. and Large, J.F., eds., 299 (1988)
Amos G, Rhodes MJ, Mineo H, Chem. Eng. Sci., 48, 943 (1993)
Aubert E, Barreteau D, Gsuthier T, Pontier R, "Pressure Profiles and Slip Velocities in a Co-Current Downflow Fluidized Bed Reactor," Circulating Fluidized Bed Technology IV, Adidan, A.A., eds., 403 (1994)
Bader R, Findlay J, Knowlton TM, "Gas/Solid Flow Patterns in a 30.5 cm-Diameter CFB," Circulating Fluidized Bed Technology II, Basu, P. and Large, J.F., eds., 123 (1988)
Bai DR, Jin Y, Yu ZQ, Zhu ZX, Powder Technol., 71, 51 (1992)
Cho YJ, Kim SD, Han GY, Korean J. Chem. Eng., 13(6), 627 (1996)
Gayan P, Dediego LF, Adanez J, Powder Technol., 94(2), 163 (1997)
Han GY, Lee GS, Kim SD, Korean J. Chem. Eng., 2(2), 141 (1985)
Hirschfelder JO, Curtis CF, Bird RB, "Molecular Theory of Gases and Liquids," John Wiley & Sons, New York (1964)
Klinkenberg A, Krajenbrink HJ, Lauwerier HA, Ind. Eng. Chem., 45, 1202 (1953)
Lee GS, Kim SD, Chem. Eng. Commun., 86, 91 (1989)
Namkung W, Kim SD, HWAHAK KONGHAK, 36(5), 797 (1998)
Sherwood TK, Pigford RL, Wilke CR, "Mass Transfer," McGraw-Hill, New York, 112 (1975)
Tsuji Y, Morikawa Y, Shiomi M, J. Fluid Mech., 139, 417 (1984)
Wang Z, Bai DR, Jin Y, Powder Technol., 70, 271 (1992)
Wei F, Jin Y, Yu ZQ, Liu JZ, Chem. Eng. Technol., 18(1), 59 (1995)
Werther J, Hartge EU, Kruse M, Powder Technol., 70, 293 (1992)
Yang G, Zhe H, Zhao L, "Radial Gas Mixing in a Fast Fluidized Bed," Fluidization IV, Kunii, D. and Toei, R., eds., Engineering Foundation, 145 (1984)
Zheng Q, Wei X, Fei L, "Experimental Study on Radial Gas Dispersion and its Enhancement in Circulating Fluidized Beds," Fluidization VII, Potter, O.E. and Nicklin, D.J., eds., Engineering Foundation, 285 (1992)
Zhu JX, Yu ZQ, Jin Y, Grace JR, Issangya A, Can. J. Chem. Eng., 73(5), 662 (1995)

[Referenced By]

[1] Adams CK, "Gas Mixing in Fast Fluidized Beds," Circulating Fluidized Bed Technology II, Basu, P. and Large, J.F., eds., 299 (1988)

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

[3] Aubert E, Barreteau D, Gsuthier T, Pontier R, "Pressure Profiles and Slip Velocities in a Co-Current Downflow Fluidized Bed Reactor," Circulating Fluidized Bed Technology IV, Adidan, A.A., eds., 403 (1994)

[4] Bader R, Findlay J, Knowlton TM, "Gas/Solid Flow Patterns in a 30.5 cm-Diameter CFB," Circulating Fluidized Bed Technology II, Basu, P. and Large, J.F., eds., 123 (1988)

[5] Bai DR, Jin Y, Yu ZQ, Zhu ZX, Powder Technol., 71, 51 (1992)

[6] Cho YJ, Kim SD, Han GY, Korean J. Chem. Eng., 13(6), 627 (1996)

[7] Gayan P, Dediego LF, Adanez J, Powder Technol., 94(2), 163 (1997)

[8] Han GY, Lee GS, Kim SD, Korean J. Chem. Eng., 2(2), 141 (1985)

[9] Hirschfelder JO, Curtis CF, Bird RB, "Molecular Theory of Gases and Liquids," John Wiley & Sons, New York (1964)

[10] Klinkenberg A, Krajenbrink HJ, Lauwerier HA, Ind. Eng. Chem., 45, 1202 (1953)

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

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

[13] Sherwood TK, Pigford RL, Wilke CR, "Mass Transfer," McGraw-Hill, New York, 112 (1975)

[14] Tsuji Y, Morikawa Y, Shiomi M, J. Fluid Mech., 139, 417 (1984)

[15] Wang Z, Bai DR, Jin Y, Powder Technol., 70, 271 (1992)

[16] Wei F, Jin Y, Yu ZQ, Liu JZ, Chem. Eng. Technol., 18(1), 59 (1995)

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

[18] Yang G, Zhe H, Zhao L, "Radial Gas Mixing in a Fast Fluidized Bed," Fluidization IV, Kunii, D. and Toei, R., eds., Engineering Foundation, 145 (1984)

[19] Zheng Q, Wei X, Fei L, "Experimental Study on Radial Gas Dispersion and its Enhancement in Circulating Fluidized Beds," Fluidization VII, Potter, O.E. and Nicklin, D.J., eds., Engineering Foundation, 285 (1992)

[20] Zhu JX, Yu ZQ, Jin Y, Grace JR, Issangya A, Can. J. Chem. Eng., 73(5), 662 (1995)