Circulation of Geldart D type particles: Part I – High solids fluxes. Measurements and computation under solids slugging conditions Mayank Kashyap a,n , Dimitri Gidaspow a , William J. Koves b a Department of Chemical and Biological Engineering, Illinois Institute of Technology, Chicago, IL 60616, USA b UOP LLC, A Honeywell Company, Des Plaines, IL 60017, USA article info Article history: Received 2 June 2010 Received in revised form 17 September 2010 Accepted 6 October 2010 Available online 14 October 2010 Keywords: Solids slugging Gamma ray densitometer Kinetic theory Computational fluid dynamics Anti core-annular Dispersion coefficient abstract Solids slugging phenomena were studied in a symmetric IIT riser using gamma ray densitometers. No core-annular regime was observed at high solids fluxes. Computations using the kinetic theory based IIT CFD code confirmed the elimination of the undesirable core-annular regime. The computer code was also used to calculate dispersion coefficients. The computed radially averaged total granular temperatures, axial and radial solids dispersion coefficients and axial gas dispersion coefficients agreed well with the literature. The 5/3 Kolmogorov energy spectrum law was followed at high frequencies. The dimensionless form of the spectral distribution showed good agreement with the Hinze correlation for single phase flow turbulence. The IIT CFD code computed high slip and anisotropy in the fluidized bed system. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction Large industrial scale fluidized beds, such as gasifiers for the FutureGen project, are widely used in the chemical, petroleum, metallurgical, process and power industries because of their excellent heat and mass transfer properties, effective use of active catalytic surface due to fine particle sizes, isothermal conditions throughout the bed, ease of solids circulation, gas phase polymer- ization, and the possibility of continuous operation. Circulating fluidized beds (CFB) have been used extensively for catalytic cracking of oil, coal combustion and gasification, manufacturing of fine powders and ceramic, alumina calcinations, and so on (Reh, 1971, 1986; Pandey et al., 2004; Radmanesh et al., 2006; Wang et al., 2006; Gel et al., 2009; Syamlal et al., 2009). CFBs have the capability to operate in different flow regimes, such as turbulent, fast fluidization and dilute transport (Grace, 2000). In bubbling fluidization, the bubbles coalesce as they move up the bed, thus, increasing their size. Slugging takes place as the bubble size becomes close to the diameter of the fluidized bed. Hetsroni (1982) and Grace et al. (1997) described that in slugging fluidized beds, the voids fill most of the column cross section. Fluidized beds have been operated in slugging fluidization regimes (Baeyens and Geldart, 1974; Chen et al., 1997; Lettieri et al., 2004; Wang et al., 2006; Constantineau et al., 2007). The slugging fluidization gives larger fluctuations in the solids concentration than the bubbling regime. Lettieri et al. (2004) and Constantineau et al. (2007) summarized the necessary conditions for slugging as: (1) initial height of the bed should be greater than the critical height (Baeyens and Geldart, 1974); (2) superficial gas velocity should be sufficiently high; (3) the minimum slugging velocities are obtained for deep and shallow beds from the correlations given by Stewart and Davidson (1967) and Baeyens and Geldart (1974), respectively; (4) maximum stable bubble size must be of the order of the diameter of the fluidized bed. Despite the fact that slugging behavior is generally considered to be detrimental to fluidized reactor performance, the use of slugging fluidized beds as reactors is not uncommon in practice, as they possess some advantages, such as avoiding of particles from sticking towards the walls. Computational fluid dynamics (CFD) has recently become a significant and fundamental part of industrial research to endorse engineering designs in single and multiphase systems (Jiradilok et al., 2006, 2007, 2008; Pugsley et al., 2010). Descriptions of the kinetic theory based CFD models are given in Gidaspow (1994), Fluent Inc. (2005a, b), Gidaspow and Jiradilok (2009) and Pannala et al. (2010). Besides many advantages that the CFBs possess, one major disadvantage is the coexistence of high concentration of downward flowing particles in the wall region and a dilute core region through which most of the gas passes (Yerushalmi and Avidan, 1985; Sinclair and Jackson, 1989; Miller and Gidaspow, 1992; Benyahia et al., 2000; Tartan and Gidaspow, 2004; Jiradilok et al., 2006, 2007; Zhu and Zhu, 2008a, b; Chalermsinsuwan et al., 2009). Sinclair and Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science 0009-2509/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2010.10.012 n Corresponding author. Tel.: + 1 312 730 5955. E-mail address: kashmay@iit.edu (M. Kashyap). Chemical Engineering Science 66 (2011) 183–206