ELSEVIER Powder Technology 84 (1995) 221-229 POWDER TECHNOLOGY Dilute fluidized cracking catalyst particles-gas flow behavior the riser of a circulating fluidized bed Yu-Feng Zhang, Hamid Arastoopour Department of Chemical Engineering, Illinois Institute of Technology, Chicago, IL 60616, USA Received 8 August 1994; revised 18 February 1995 in Abstract Laser Doppler anemometry (LDA) was used to measure velocity, fluctuating velocity and size distribution in the riser of a circulating fluidized bed. Fluidized cracking catalyst (FCC) particles with volume average size of 70/xm and density of 1650 kg/m 3, in a dilute gas--solid flow system with solid volume fraction ranging from 0.2% to 2.5% and solid mass flux of 10-120 kg/m 2 s were experimentally studied at the test section which was 1.07 meters away from the entrance zone. More particle collision and less slip velocity between particles of different size were observed at higher solids loadings and superficial gas velocities. At lower superficial gas velocities and lower solids loadings, instantaneous reversal flow of particles and lower particles fluctuating velocities and larger particles/aggiomerates were measured along the wall. The radial distribution of axial particles velocity profile was flatter than a parabolic shape with maximum velocity of particles of different size in most cases away from the center. The particles fluctuating velocities was about 20%--30% of the particle velocity. However, it decreased at the wall region due to less probability of collision with moving particles and significant collision with the wall. In contrast, the turbulence intensity increased at the wall region due to lower particles velocities in this zone. Keywords: Laser Doppler anemometry; Velocity; Fluctuating velocity; Circulating fluidized bed; Fluidized cracking catalyst 1. Introduction The first FCC commercial unit was built and went into operation in 1942 although the hydrodynamics of gas-solid flow were not understood clearly. Since then, FCC has become one of the major processes used in the oil refineries industry. In 1962, Mobil developed a new type of catalyst, high-activity zeolite. Because of the high activity of this catalyst, reactor designers promptly introduced the riser cracker in which feed is introduced into the upflow pneumatic transport line. As a result of this process, 90% of the feed was cracked. It became a worldwide effort to understand the hy- drodynamics of a gas-solid mixture in a riser [1-5]. Various techniques have been used to measure hy- drodynamic flow behaviors such as pressure, velocity, flowrate and concentration. Recently, researchers have become interested in more details of the flow param- eters, for example, vibration, turbulence, fluctuation and slip velocities with the hope of achieving the scale- up of the system for commercial applications. Weinstein et al. [6] measured the radial profile of the particle concentration in a fast fluidized bed using the X-ray 0032-5910/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSD1 0032-5910(95)02991-A technique. Bader et al. [1] used the sample tube to obtain the solid flux radial profile. Miller and Gidaspow [7] studied FCC particle flow behavior in a circulating fluidized bed. Fluxes were measured by means of an extraction probe and the particle concentrations were measured with an X-ray densitometer. Optical instru- ments are among the most promising measurement techniques for dilute gas-solids flow systems. Soo et al. [8] were among the first to use optical fiber in- struments to measure particle concentration. Lesinski et al. [9] and Tsuji et al. [10,11] measured both air and particles velocities simultaneously by setting thresh- old values against the pedestal and Doppler components of the photomultiplier signal. Farmer [12] attempted to obtain information regarding particle size and ve- locities. Yang et al. [13] measured FCC particle slip velocity using LDA in the riser of a dilute circulating fluidized bed. A circulating fluidized bed with a laser Doppler anemometer as the measuring tool has been under development at Illinois Institute of Technology since 1986. A series of gas flow measurements using LDA under line packing conditions have been performed