Hydrodynamics of gas–solids flow in a bubbling fluidized bed with immersed vertical U-tube banks

Abstract We apply a two-fluid model (TFM) from the open-source code Multiphase Flow with Interphase eXchanges (MFIX) to investigate hydrodynamics in a gas–solids fluidized bed with immersed vertical tubes. The cut-cell method implemented in MFIX is used to fully resolve the flow around vertical U-tube banks. Simulations are performed in a bed diameter of 0.145 m with square and triangular tube arrangements, for inlet gas velocities of U 0 / U mf  = 2.3, 4.5 and 6.8. Simulation results are compared with experimental results from the literature and show very good agreement for the bubble size. The efficiency of vertical tubes in reducing bubble size depends upon inlet gas velocity and tube arrangement. Reduction in bubble size is due to the vertical tubes preventing bubble coalescence and promoting bubble splitting. In-bed vertical tubes result in uniform distribution of bubbles within the bed with increase in bubble frequency. The bubble frequency is higher within the bed for square tube arrangements. For a bed with vertical tubes, the bubble shape is generally elongated, which results in high bubble rise velocity. Axial solid velocity and solids circulation patterns are significantly affected by the vertical tubes, where triangular tube arrangements rarely show any solids circulating zone.

[1]  Jpk Seville,et al.  Experimental study on the influence of bed material on the scaling of solids circulation patterns in 3D bubbling gas–solid fluidized beds of glass and polyethylene using positron emission particle tracking , 2012 .

[2]  G. Wozny,et al.  CFD study on solids flow pattern and solids mixing characteristics in bubbling fluidized bed: Effect of fluidization velocity and bed aspect ratio , 2015 .

[3]  Ng Niels Deen,et al.  Effect of bed size on hydrodynamics in 3‐D gas–solid fluidized beds , 2015 .

[4]  J. R. Ommen,et al.  Effects of pressure and fines content on bubble diameter in a fluidized bed studied using fast X-ray tomography , 2012 .

[5]  C. Sobrino,et al.  Experimental and computational study on the bubble behavior in a 3-D fluidized bed , 2011 .

[6]  A. Almstedt,et al.  Hydrodynamics, erosion and heat transfer in a pressurized fluidized bed: influence of pressure, fluidization velocity, particle size and tube bank geometry , 1997 .

[7]  Yongzhi Zhao,et al.  Particle‐scale simulation of the flow and heat transfer behaviors in fluidized bed with immersed tube , 2009 .

[8]  P. Olowson.  Influence of pressure and fluidization velocity on the hydrodynamics of a fluidized bed containing horizontal tubes , 1994 .

[9]  J. R. Ommen,et al.  Comparison of bubble growth obtained from pressure fluctuation measurements to optical probing and literature correlations , 2012 .

[10]  Teklay Weldeabzgi Asegehegn,et al.  Influence of two- and three-dimensional simulations on bubble behavior in gas–solid fluidized beds with and without immersed horizontal tubes , 2012 .

[11]  Tingwen Li,et al.  Cartesian grid simulations of bubbling fluidized beds with a horizontal tube bundle , 2011 .

[12]  J. R. Ommen,et al.  Radial Bubble Distribution in a Fluidized Bed with Vertical Tubes , 2012 .

[13]  P. Foscolo,et al.  Cold model characterisation of a fluidised bed catalytic reactor by means of instantaneous pressure measurements , 2002 .

[14]  N. Subramanian,et al.  Axial solids mixing and bubble characteristics in gas-fluidized beds with vertical internals , 1981 .

[15]  J. R. Ommen,et al.  Bubble Characterization in a Fluidized Bed with Vertical Tubes , 2012 .

[16]  D. Gidaspow.  Multiphase Flow and Fluidization: Continuum and Kinetic Theory Descriptions , 1994 .

[17]  Jam Hans Kuipers,et al.  Theoretical and experimental bubble formation at a single orifice in a two-dimensional gas-fluidized bed , 1991 .

[18]  S. Armfield,et al.  A representation of curved boundaries for the solution of the Navier-Stokes equations on a staggered three-dimensional Cartesian grid , 2003 .

[19]  Tingwen Li,et al.  Cartesian grid simulations of gas–solids flow systems with complex geometry , 2013 .

[20]  Morten Christian Melaaen,et al.  A comparative study between electrical capacitance tomography and time-resolved X-ray tomography , 2013 .

[21]  He Yurong,et al.  Hydrodynamics of gas-solid flow around immersed tubes in bubbling fluidized beds , 2004 .

[22]  Ahmed F. Ghoniem,et al.  Towards accurate three-dimensional simulation of dense multi-phase flows using cylindrical coordinates , 2014 .

[23]  J. G. Yates,et al.  INTERACTION BETWEEN HORIZONTAL TUBES AND GAS BUBBLES IN A FLUIDIZED BED , 1987 .

[24]  M. Alonso,et al.  Fluid bed gas RTD: Effect of fines and internals , 2006 .

[25]  Sankaran Sundaresan,et al.  Coarse-Grid Simulation of Gas-Particle Flows in Vertical Risers , 2005 .

[26]  Dong Hyun Lee,et al.  Heat transfer and bubble characteristics in a fluidized bed with immersed horizontal tube bundle , 2003 .

[27]  M. Syamlal,et al.  The effect of numerical diffusion on simulation of isolated bubbles in a gas-solid fluidized bed , 2001 .

[28]  Wen-Ching Yang,et al.  Effect of Internal Tubes and Baffles , 2003 .

[29]  Paola Lettieri,et al.  2D and 3D CFD Simulations of Bubbling Fluidized Beds Using Eulerian-Eulerian Models , 2003 .

[30]  D. Gidaspow,et al.  A bubbling fluidization model using kinetic theory of granular flow , 1990 .

[31]  Ted M. Knowlton,et al.  Scale-up of fluidized-bed hydrodynamics , 2005 .

[32]  H. Jakobsen,et al.  Practical validation of the two-fluid model applied to dense gas-solid flows in fluidized beds , 2007 .

[33]  Masayuki Horio,et al.  Particle and bubble movements around tubes immersed in fluidized beds : a numerical study , 1999 .

[34]  Pradeep K. Agarwal,et al.  Influence of horizontal tube banks on the behavior of bubbling fluidized beds: 1. Bubble hydrodynamics , 1999 .

[35]  A. Almstedt,et al.  Hydrodynamics of a pressurized fluidized bed with horizontal tubes : influence of pressure, fluidization velocity and tube-bank geometry , 1995 .