Flow, in fluidized beds

Gas-particle flows in fluidized beds and riser reactors are inherently unstable and they manifest inhomogeneous structures over a wide range of length and time scales. There is a substantial body of literature where researchers have sought to capture these fluctuations through numerical simulation of microscopic TFM equations, and it is now clear that TFMs for such flows do reveal unstable modes whose length scale is as small as ten particle diameters (e.g., see Agrawal et al., 2001 Andrews et al., 2005). 

Littman H. An overview of flow in fluidized beds. Pharm Technol 1985 9(3) 48. 

Littman, H. An overview of flow in fluidized Beds. Pharm. Technol. 9(3) 48, 1985. Whitehead, A. B. Behavior of fluidized bed systems. Pharm. Technol. 2(13) 1981. Story, M. J. Granulation and film coating in the fluidized bed. Pharm. Technol. 2(19) 1981. 

Stewart, P. S. B. and Davidson, J. F. (1967). Slug Flow in Fluidized Beds. Powder Tech., 1,61. Thonglimp, V. (1981). Contribution a L itude Hydrodynamique des Couches Fluidiseis pour un Gaz Vitesse Minimale de Fluidisation et Expansion. Docteur-Ingenieur thesis. Institut National Polytechnique, Toulouse. 

Although general treatments of the flow in fluidized beds of coarse particles, in view of the difficulty of the problem, will only evolve slowly, there have been some promising developments. These include the success achieved in correlating heat transfer data (7, 113., 114) and the development of scaling parameters that permit the use of cold flow models to study many of the characteristics of AFBC s (114%115). 

There are two principal approaches to formulate particle-fluid two-phase flow in fluidized beds the pseudo-fluid model and the two-phase model. 

Ding and Gidaspow [16], for example, prosed an empirical relation being a function of the particulate phase volume fraction to be used for granular flows in fluidized beds given by ... 

Moreover, very few parameterizations are reported on the wall- and fluid-granular material convective thermal heat transfer coefficients. For introductory studies, the work of Natarajan and Hunt [55], Gunn [25], Kuibe and Broughton [40], Kuipers et al [41] and Patil et al [59] might be consulted. To enable validation and reliable predictions of non-isothermal non-adiabatic reactive granular flows the thermal conductivity and the convective heat transfer coefficients have to be determined with sufficient accuracy. For certain processes this may be an important task for future research in the field of granular flows in fluidized beds. 

The first attempts at describing the gas-particle flows in fluidized beds were performed using rather simple models neglecting both the Reynolds stresses, jRe,Xk (10.86), and the kinetic pressure-gradient term, ap pp kin) , in (10.91). No turbulence models are thus used for any of the phases. 

Lindborg H, Lysberg M and Jakobsen HA (2007) Practical validation of the two-fluid model applied to dense gas-solid flows in fluidized beds. Chem Eng... 

Lindborg H, Lysberg M, Jakobsen HA (2007) Practical Validation of the Two-Fluid Model Applied to Dense Gas-Solid Flows in Fluidized Beds. Submitted to Chem Eng Sci 2007... 

Chapter 4 contains a summary of the basic theory of granular flow. These concepts have been adopted describing particulate flows in fluidized bed reactors. The theory was primarily used for dense bed reactors, but modified closures of this type have been employed for more dilute flows as well. Compared to the continuum theory presented in the third chapter, the granular theory is considered more complex. The main purpose of introducing this theory, in the context of reactor modeling, is to improve the description of the particle (e.g., catalyst) transport and distribution in the reactor system. 

As mentioned above, even and stable distribution of the fluidizing gas is a prerequisite for sustained operation. Distribution plates ensure optimal fluidization and powder movement. The original distribution plate design, the perforated plate (top of Fig. 7.70), has a number of disadvantages (see Tab. 7.2). It was also discovered that it could be advantageous if the direction of particle flow in fluidized beds can be influenced. This, and the desire to overcome some of the other disadvantages... 

Littman H. An overview of flow in fluidized beds. Pharm Technol 1985 9(3) 48. Whitehead AB. Behavior of fluidized bed systems. Pharm Technol 1981 2(13). 

Stewart PSB, Davidson JF. Slug flow in fluidized beds. Powder Tech 1 61-80, 1967. 

Stewart, P.S.B. and J.F. Davidson. Slug Flow in Fluidized Beds. Powder Technol. 1 (1967) 61-80. 

Governing Equations for Reactive Flows in Fluidized Beds... 

Chao Z, Wang Y, Jakobsen JP, Femandino M, Jakobsen HA (2011) Derivation and validation of a binary multi-fluid Eulerian model for fluidized beds. Chem Eng Sci 66 3605-3616 Chao Z (2012) Modeling and simulation of reactive three-phase flows in fluidized bed reactors appUcation to the SE-SMR process. Doctoral thesis. The Norwegian Univerity of Science and Technology, Trondheim... 

Lindborg H (2008) ModeUng and simulation of reactive two phase flows in fluidized beds. Dr ing Thesis, The Norwegian University of Science and Technology, Trondheim... 

Step algorithm was employed for the solution of an unsteady two-fluid granular flow model [136], The latter semi-implicit procedure has also been extended in order to simulate reactive flows in fluidized beds [138],... 

Chao Z (2012) Modeling and simulation of reactive three-phase flows in fluidized bed reactors application to the SE-SMR process. Doctoral thesis, the Norwegian Univerity of Science and... 

Lindborg H (2(X)8) Modeling and simulation of reactive two phase flows in fluidized beds. Doctering thesis, the Norwegitm University of Science and Technology, Trondheim, Norway Lun CKK, Savage SB (1986) The effect of an impact velocity dependent coefficient of restitution on stresses developed by sheared granular materials. Acta Mechanica 63 15-44... 

Xie, N., Battaglia, F., Fox, R.O. Simulations of multiphase reactive flows in fluidized beds using in situ adaptive tabulation. Combust. Theory Model. 8, 195-209 (2004)... 

While attempts have been made to assign axial dispersion coefficients to the gas flow in fluidized beds or to represent the flow field in terms of a series of well-mixed vessels, none of these methods is really satisfactory. Perhaps the most promising approach to the problem of gas flow patterns is provided by a bubbling model [47]. 

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