Numerical Study of Bubbling Fluidized Beds Operating at Sub-atmospheric Conditions

Authors: Lanka Dinushke Weerasiri, Subrat Das, Daniel Fabijanic, William Yang

Abstract:

Fluidization at vacuum pressure has been a topic that is of growing research interest. Several industrial applications (such as drying, extractive metallurgy, and chemical vapor deposition (CVD)) can potentially take advantage of vacuum pressure fluidization. Particularly, the fine chemical industry requires processing under safe conditions for thermolabile substances, and reduced pressure fluidized beds offer an alternative. Fluidized beds under vacuum conditions provide optimal conditions for treatment of granular materials where the reduced gas pressure maintains an operational environment outside of flammability conditions. The fluidization at low-pressure is markedly different from the usual gas flow patterns of atmospheric fluidization. The different flow regimes can be characterized by the dimensionless Knudsen number. Nevertheless, hydrodynamics of bubbling vacuum fluidized beds has not been investigated to author’s best knowledge. In this work, the two-fluid numerical method was used to determine the impact of reduced pressure on the fundamental properties of a fluidized bed. The slip flow model implemented by Ansys Fluent User Defined Functions (UDF) was used to determine the interphase momentum exchange coefficient. A wide range of operating pressures was investigated (1.01, 0.5, 0.25, 0.1 and 0.03 Bar). The gas was supplied by a uniform inlet at 1.5U_mf and 2U_mf. The predicted minimum fluidization velocity (U_mf) shows excellent agreement with the experimental data. The results show that the operating pressure has a notable impact on the bed properties and its hydrodynamics. Furthermore, it also shows that the existing Gorosko correlation that predicts bed expansion is not applicable under reduced pressure conditions.

Keywords: Computational fluid dynamics, fluidized bed, gas-solid flow, vacuum pressure, slip flow, minimum fluidization velocity.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.3566303

References:

[1] A. Kumar, P. Hodgson, D. Fabijanic, and W. Gao, "Numerical solution of gas–solid flow in fluidised bed at sub-atmospheric pressures," Advanced Powder Technology, vol. 23, no. 4, pp. 485-492, 2012/07/01/ 2012.
[2] M. F. Llop, F. Madrid, J. Arnaldos, and J. Casal, "Fluidization at vacuum conditions. A generalized equation for the prediction of minimum fluidization velocity," Chemical Engineering Science, vol. 51, no. 23, pp. 5149-5157, 1996/12/01/ 1996.
[3] A. Kumar, P. Hodgson, W. Gao, S. Das, and D. Fabijanic, "Investigating the effect of segregation of particles and pressure gradient on the quality of fluidisation at sub-atmospheric pressures," Powder Technology, vol. 254, pp. 137-149, 2014/03/01/ 2014.
[4] S. Zarekar, A. Bück, M. Jacob, and E. Tsotsas, "Numerical study of the hydrodynamics of fluidized beds operated under sub-atmospheric pressure," Chemical Engineering Journal, vol. 372, pp. 1134-1153, 2019/09/15/ 2019.
[5] S. Kawamura and Y. Suezawa, "Mechanism of gas flow in a fluidized bed at low pressure," 化学工学, vol. 25, no. 7, pp. 524-530, 1961.
[6] S. Ergun, "Fluid flow through packed columns," Chem. Eng. Prog., vol. 48, pp. 89-94, 1952 1952.
[7] K. Kusakabe, T. Kuriyama, and S. Morooka, "Fluidization of fine particles at reduced pressure," Powder Technology, vol. 58, no. 2, pp. 125-130, 1989/06/01/ 1989.
[8] S. Dushman, J. M. Lafferty, and R. Pasternak, "Scientific foundations of vacuum technique," Physics Today, vol. 15, p. 53, 1962.
[9] S. Dushman, Scientific Foundations of Vacuum Technique. John Wiley and Sons, Inc., New York, 1949.
[10] S. Zarekar, A. Bück, M. Jacob, and E. Tsotsas, "Reconsideration of the hydrodynamic behavior of fluidized beds operated under reduced pressure," Powder Technology, vol. 287, pp. 169-176, 2016/01/01/ 2016.
[11] A. Kumar, P. Hodgson, W. Gao, D. Fabijanic, and S. Das, "Drag models comparison by single injection in vacuum fluidised beds," in ICMF 2013: Proceedings of the International Conference on Multiphase Flow, 2013, pp. 1-6: ICMF.
[12] J. A. M. Kuipers, W. Prins, and W. P. M. Van Swaaij, "Numerical calculation of wall-to-bed heat-transfer coefficients in gas-fluidized beds," AIChE Journal, vol. 38, no. 7, pp. 1079-1091, 1992.
[13] A. Kumar, S. Das, D. Fabijanic, W. Gao, and P. Hodgson, "Bubble–wall interaction for asymmetric injection of jets in solid–gas fluidized bed," Chemical Engineering Science, vol. 101, pp. 56-68, 2013/09/20/ 2013.
[14] A. Kumari, P. Hodgson, W. Gao, D. Fabijanic, and S. Das, "Drag models comparison by single injection in vacuum fluidised beds," in ICMF 2013: Proceedings of the International Conference on Multiphase Flow, 2013, pp. 1-6: ICMF.
[15] A. Kumar, "Investigations into hydrodynamics and heat transfer in vacuum fluidised beds," Deakin University, 2014.
[16] Y. Wang, Z. Zou, H. Li, and Q. Zhu, "A new drag model for TFM simulation of gas–solid bubbling fluidized beds with Geldart-B particles," Particuology, vol. 15, pp. 151-159, 2014/08/01/ 2014.
[17] B. G. M. van Wachem, J. C. Schouten, R. Krishna, and C. M. van den Bleek, "Eulerian simulations of bubbling behaviour in gas-solid fluidised beds," Computers & Chemical Engineering, vol. 22, pp. S299-S306, 1998/03/15/ 1998.
[18] B. G. M. van Wachem, J. C. Schouten, R. Krishna, and C. M. van den Bleek, "Validation of the Eulerian simulated dynamic behaviour of gas–solid fluidised beds," Chemical Engineering Science, vol. 54, no. 13, pp. 2141-2149, 1999/07/01/ 1999.
[19] H. Enwald, E. Peirano, A. E. Almstedt, and B. Leckner, "Simulation of the fluid dynamics of a bubbling fluidized bed. Experimental validation of the two-fluid model and evaluation of a parallel multiblock solver," Chemical Engineering Science, vol. 54, no. 3, pp. 311-328, 1999/02/01/ 1999.
[20] V. Verma, J. T. Padding, N. G. Deen, and J. A. M. Kuipers, "Numerical Investigation on the Effect of Pressure on Fluidization in a 3D Fluidized Bed," Industrial & Engineering Chemistry Research, vol. 53, no. 44, pp. 17487-17498, 2014/11/05 2014.
[21] W. Zhong, M. Zhang, B. Jin, and Z. Yuan, "Flow behaviors of a large spout-fluid bed at high pressure and temperature by 3D simulation with kinetic theory of granular flow," Powder Technology, vol. 175, no. 2, pp. 90-103, 2007/06/06/ 2007.
[22] A. Acosta-Iborra, C. Sobrino, F. Hernández-Jiménez, and M. de Vega, "Experimental and computational study on the bubble behavior in a 3-D fluidized bed," Chemical Engineering Science, vol. 66, no. 15, pp. 3499-3512, 2011/08/01/ 2011.
[23] N. Xie, F. Battaglia, and S. Pannala, "Effects of using two- versus three-dimensional computational modeling of fluidized beds: Part I, hydrodynamics," Powder Technology, vol. 182, no. 1, pp. 1-13, 2008/02/15/ 2008.
[24] T. W. Asegehegn, M. Schreiber, and H. J. Krautz, "Influence of two- and three-dimensional simulations on bubble behavior in gas–solid fluidized beds with and without immersed horizontal tubes," Powder Technology, vol. 219, pp. 9-19, 2012/03/01/ 2012.
[25] S. Cloete, S. T. Johansen, A. Zaabout, M. van Sint Annaland, F. Gallucci, and S. Amini, "The effect of frictional pressure, geometry and wall friction on the modelling of a pseudo-2D bubbling fluidised bed reactor," Powder Technology, vol. 283, pp. 85-102, 2015/10/01/ 2015.
[26] A. Srivastava and S. Sundaresan, "Analysis of a frictional–kinetic model for gas–particle flow," Powder Technology, vol. 129, no. 1, pp. 72-85, 2003/01/08/ 2003.
[27] D. Gidaspow, R. Bezburuah, and J. Ding, "Hydrodynamics of circulating fluidized beds: kinetic theory approach," Illinois Inst. of Tech., Chicago, IL (United States). Dept. of Chemical Engineering1991.
[28]
[C. Y. Wen and Y. H. Yu, "Mechanics of fluidization," in Chemical Engineering Progress Symposium Series, 1966, vol. 62, pp. 100-111, 1966.
[29] M. Syamlal and T. J. O’Brien, "Computer simulation of bubbles in a fluidized bed," in AIChE Symp. Ser, 1989, vol. 85, no. 1, pp. 22-31: Publ by AIChE.
[30] L. Weerasiri, V. Kumar Panangipalli, S. Das, and D. Fabijanic, "Predicting Minimum Fluidization Velocity For Vacuum Fluidized Beds," presented at the 3th International Conference on CFD in the Minerals and Process Industries, Melbourne, Australia, 2018.
[31] S. C. Saxena, "Heat Transfer between Immersed Surfaces and Gas-Fluidized Beds," in Advances in Heat Transfer, vol. 19, J. P. Hartnett and T. F. Irvine, Eds.: Elsevier, 1989, pp. 97-190.
[32] M. F. Llop and N. Jand, "The influence of low pressure operation on fluidization quality," Chemical Engineering Journal, vol. 95, no. 1, pp. 25-31, 2003/09/15/ 2003.
[33] L. Mörl, S. Heinrich, and M. Peglow, "Chapter 2 Fluidized bed spray granulation," in Handbook of Powder Technology, vol. 11, A. D. Salman, M. J. Hounslow, and J. P. K. Seville, Eds.: Elsevier Science B.V., 2007, pp. 21-188.