Original Research Paper Using particle trajectory for determining the fluidization regime in gas–solid fluidized beds M.R. Tamadondar a , H. Azizpour a , R. Zarghami a , N. Mostoufi a,⇑ , J. Chaouki b a Multiphase Systems Research Lab., Oil and Gas Processing Centre of Excellence, School of Chemical Engineering, College of Engineering, University of Tehran, P.O. Box 11155/4563, Tehran, Iran b Department of Chemical Engineering, École Polytechnique de Montréal, P.O. Box 6079, Station Centre-Ville, Montréal, Québec, Canada H3C 3A7 article info Article history: Received 25 December 2010 Received in revised form 14 March 2011 Accepted 18 April 2011 Available online 7 May 2011 Keywords: Fluidization Radioactive particle tracking Regime transition Statistical analysis abstract Transition from bubbling to turbulent in a conventional gas–solid fluidized bed was evaluated from tra- jectory of particles in fluidized bed. A series of experiments were carried out in a lab-scale fluidization bed using radioactive particle tracking (RPT) technique for recording the position of a tracer in the bed. Statistical parameters, such as standard deviation and skewness of the time–position data, were uti- lized to determine the transition velocity from bubbling to turbulent regime. The results showed that the data obtained by the RPT technique can predict transition velocity. It was shown that the standard devi- ation of position fluctuations reach a maximum with increasing superficial gas velocity corresponding to regime transition. It was shown that transition from bubbling to turbulent can be determined using skewness and kurtosis of time–position data. The velocities obtained in this work are in good agreement with the available correlations. Ó 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. 1. Introduction Fluidization is one of the most important processes in chemical engineering industries and also is applied due to advantages such as high heat and mass transfer rates. Among different fluidization regimes, turbulent fluidization is the most applied regime in indus- try. Turbulent fluidization is generally characterized by low-ampli- tude fluctuation of void age and pressure which correspond to the absence of large bubble or voids. To determine the transition from bubbling to turbulent fluidization, several measurement methods have been utilized. These methods include pressure fluctuations, visual observation, optical fiber probe and bed expansion [1–4]. Yerushalmi et al. [5] proposed a quantitative criterion by means of relative fluctuations of pressure drop to define the onset velocity of transition from bubbling to turbulent fluidization. Lee and Kim [3] widely used statistical parameters, such as skewness and flat- ness, to determine the velocity of regime transition from bubbling to turbulent. Makkawi and Wright [6] studied fluidization regimes by means of electrical capacitance tomography (ECT) technique. Radioactive particle tracking (RPT) is a non-intrusive method for monitoring the motion of a radioactive tracer among the solid phase of a fluidized bed. This method was originally proposed by Lin et al. [7] and has been used by many researchers such as Degaleesan et al. [8], Limtrakul et al. [9] and Larachi et al. [10,11]. In the present work, the RPT technique was used for iden- tifying fluidization hydrodynamics and determining regime transi- tion from bubbling to turbulent. For this purpose, simple statistical analysis (standard deviation, skewness, and kurtosis) was used to analyze time–position data taken in a dense fluidized bed. 2. Experimental setup and procedure Experiments were carried out in a gas–solid fluidized bed, made of a Plexiglas pipe of 1.5 m height and 15.2 cm inside diameter. Air at room temperature was introduced into the bed through a coni- cal section, passing through a stainless steel porous plate contain- ing 19 holes with 25 mm triangle pitch and a nozzle-type air distributor. The airflow rate was measured by an orifice plate con- nected to a water manometer. The solids used in the experiments were sand particles with mean size of 385 lm and particle density of 2650 kg/m 3 . The size distribution of solids is given in Table 1. The superficial gas velocity at the onset of turbulent fluidization regime was determined to be 1.5 m/s by standard deviation of absolute pressure fluctuations. Initial height of the bed in all exper- iments was 0.22 m (1.5 times the column diameter). A cyclone was placed at the air outlet of column in order for solid particles to re- turn to the bed. The tracers were made of a mixture of gold powder and epoxy resin with a density of 2600 kg/m 3 . The tracer was activated in 0921-8831/$ - see front matter Ó 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. doi:10.1016/j.apt.2011.04.012 ⇑ Corresponding author. Tel.: +98 21 6696 7797; fax: +98 21 6646 1024. E-mail address: mostoufi@ut.ac.ir (N. Mostoufi). Advanced Powder Technology 23 (2012) 349–351 Contents lists available at ScienceDirect Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt