Particle Velocity, Solids Hold-Up, and Solids Flux ... - ACS Publications

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Particle Velocity, Solids Hold-Up, and Solids Flux Distributions in Conical Spouted Beds Operating with Heavy Particles Gorkem Kulah,*,†,∥ Salih Sari,‡ and Murat Koksal*,§,∥ †

Department of Chemical Engineering, Middle East Technical University, 06800 Ankara, Turkey Department of Nuclear Engineering, Hacettepe University, Beytepe, 06800 Ankara, Turkey § Department of Mechanical Engineering, Hacettepe University, Beytepe, 06800 Ankara, Turkey ‡

ABSTRACT: Conical spouted beds operating with highdensity particles have recently gained attention because of their potential use as nuclear fuel coaters for next-generation nuclear reactors. To design, scale-up, and manufacture these coaters, detailed investigation of local flow structure is of paramount importance. Therefore, in this study, local instantaneous particle velocity and solids hold-up and flux measurements were carried out in spouted beds having a wide range of cone angles (30°, 45°, 60°) using zirconia particles (dp = 0.5, 1 mm; ρp = 6050 kg/m3). Effects of axial height, particle diameter, conical angle, and static bed height on local flow behavior were investigated. Comparisons were also made with the results of low-density particle studies. It is shown that particle velocity decreases and solids hold-up and flux increase along the bed height in the spout. The solids circulation is augmented as particle diameter and conical angle are decreased and static bed height is increased.

1. INTRODUCTION Conical spouted beds have been commonly used for various applications such as pyrolysis, drying, coating, gasification, etc. because of their superior gas−solid contact characteristics.1 One of the emerging applications of conical spouted beds is chemical vapor deposition (CVD) coating of uranium dioxide kernels with pyrolytic carbon and silicon carbide to produce spherical tristructural-isotropic (TRISO) type fuel elements for very high-temperature gas-cooled reactors (VHTR). During this coating process, the density of the uranium dioxide kernels decreases from 10 000 kg/m3 to 2 500 kg/m3 where the average density of the particles is around 6 000 kg/m3. Currently, TRISO particles are produced in laboratory scale, small spouted bed coaters for prototype reactors. Once the full-scale reactors are in operation, there will be a huge need for large-scale CVD spouted bed coaters. To design and scale up these coaters, it is of fundamental importance to have a detailed understanding of their hydrodynamics. However, limited number of studies have been conducted in spouted beds operating with the heavy particles (ρp > 2500 kg/m3) typically encountered in CVD coating of nuclear fuels.2−10 These studies focused mainly on the determination of the minimum spouting velocity, bed pressure drop, and spectral characterization based on bed pressure drop fluctuations. Although they have shed some light on the fundamental hydrodynamic characteristics of these systems, for complete characterization of high-density conical spouted beds, determination of the local flow structure based on particle velocity and solids hold-up and flux distributions is of paramount importance. © XXXX American Chemical Society

Mainly two research groups, those at University of British Columbia, Canada11 and University of the Basque Country, Spain12−19 have conducted experiments using optical fiber probes to delineate and understand the local flow structure in conical spouted beds. These studies show that local particle flow in conical spouted beds is similar to that observed in conventional cylindrical spouted beds marked by an upward flowing spout and a denser annulus region where the particles move slowly downward. Wang and co-workers11 investigated the factors that affect the calibration of the optical probe and concentrated on the differences between the particle velocity and solids hold-up profiles in full and half columns. They obtained similar particle velocity profiles, spout, and fountain shapes in both types of columns. The study carried out by Olazar and co-workers13 in a 36 cm ID conical spouted bed (diameter of the cylindrical section) with glass sphere particles (dp = 3−5 mm, ρp = 2420 kg/m3) indicate that regardless of the operating conditions (superficial gas velocity and static bed height) and geometrical design parameters (cone angle and inlet gas diameter), in the spout region, the particles accelerate to a maximum velocity, which is reached close the bottom of the bed, and then decelerate as they move toward the bed surface. In the annulus region, the downward particle velocity increases toward the bottom of the Received: November 26, 2015 Revised: February 29, 2016 Accepted: March 2, 2016

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DOI: 10.1021/acs.iecr.5b04496 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

2. EXPERIMENTAL SETUP The experimental study was carried out in three different conical spouted beds having conical angles γ = 30°, 45°, 60°. A schematic diagram of the units is given in Figure 1, and their

bed, and its maximum value is obtained close to the interface between the spout and the annulus. Among the design and operating parameters tested, the static bed height and particle diameter were found to have the most significant effect on particle velocity along the spout axis, showing an increase as the static bed height was increased and particle diameter was decreased at the minimum spouting velocity. Furthermore, it was shown by the same group that as the particle diameter and static bed height were increased, the solids hold-up along the spout axis also decreased.14 The spout shape determined by the solids hold-up measurements showed an expansion near the bed inlet, followed by a neck and another expansion toward the fountain. The spout diameter at the upper part of the bed was found to reach approximately three times the gas inlet diameter.12 The effects of particle density on the local flow dynamics in conical spouted beds were also investigated by Olazar and coworkers.17,18 Experiments carried out using different types of relatively light particles (65 kg/m3 < ρp < 2420 kg/m3) show that the vertical (axial) component of the particle velocity in the spout and horizontal component of particle velocity in both the spout and annulus increase as the particle density increases. The radial distribution of the vertical (axial) velocity in the annulus was found to be independent of the particle density.18 The effects of cone angle on particle velocity, solids hold-up, and area-averaged solids circulation in the spout region for glass bead particles were also reported at minimum spouting velocity.13,14,19 Interestingly, the particle velocity in the spout increases as the cone angle increases from 30° to 45° followed by a decrease as the angle is further increased to 60°. The solids hold-up in the spout increases slightly as the cone angle is increased from 33° to 45°. The solids mass flow rate in the spout also increases with the cone angle (between 33° and 45°). All the aforementioned studies are exclusively limited to relatively light particles (ρp < 2500 kg/m3). Because the particle density significantly dictates the hydrodynamic behavior as shown in previous studies, further detailed investigations are required to characterize the systems operating with heavy particles. In this respect, a comprehensive research project supported by the Scientific and Technological Research Council of Turkey (Project No: MAG 108M435) was conducted, and particle velocity and solids hold-up measurements were carried out in 15 cm ID conical spouted beds at different static bed heights and cone angles (30°, 45°, 60°) with zirconia particles (dp = 0.5, 1 mm; ρp = 6050 kg/m3). Since the optical probe was capable of simultaneously measuring of the particle velocity and solids hold-up, local instantaneous solids flux could also be determined and is reported for the first time in this study. Using a small part of this data, the predictive ability of the Eulerian−Eulerian (two fluid) model to simulate the gas−solid flow in conical spouted beds was recently investigated, and the quantitative variations of the particle velocity and solids hold-up and flux with axial height were successfully captured.20 In this paper, the objective is to report and discuss the characteristic features of the gas−solid flow dynamics in conical spouted beds operated with high-density particles based on the results of the optical probe measurements. Comparisons are made, where possible, with the results of the previous low particle density studies.

Figure 1. Geometric sketch of conical spouted beds.

geometric parameters are summarized in Table 1. In the figure, Hb denotes the static bed height, Hc the height of the conical section, and Hp the axial distance of the optical probe from the bed bottom. Table 1. Geometric Parameters of the Spouted Beds γ (deg)

Do (mm)

Di (mm)

Dc (mm)

Hc (mm)

30 45 60

15 15 15

25 25 25

150 150 150

233 151 108

The spouted beds are made of polyoxymethylene (also known as Delrin) that is an excellent thermoplastic that can withstand the continuous impact of hard zirconia particles without significant erosion. Compressed air at ambient conditions was used as the spouting gas. The compressed air was supplied from a screw type compressor operating with a supply pressure of 8 bar at a maximum flow rate of 0.05 m3/s. The air flow rate was measured by two rotameters (Dwyer RMC-103-BV and RMC-123-BV). Two air tanks of 30 L in volume were placed in series between the supply line and the spouted bed to eliminate the possible fluctuations of the air flow rate. Spherical yttria-stabilized zirconia (YSZ) particles (dp = 0.5 and 1 mm; ρp = 6050 kg/m3) were used to simulate the particle properties in hot bed conditions.

3. MEASUREMENT METHOD AND CALIBRATION OF THE OPTICAL PROBE A multifiber optical probe system, PV-6, developed by the Institute of Process Engineering, Chinese Academy of Sciences, was used to measure simultaneously local instantaneous solids hold-up (solids volume concentrations), velocities, and fluxes. A B


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agreement with the ones obtained by optical fiber probes and concluded that distortion of flow by the probe was not significant. Light was projected into multiphase suspension through the emitting fibers. The backscattered light from the particles was transmitted by the receiving fibers to two photomultipliers, one for each bundle, and was converted to a voltage signal. The signals were digitized by the high-speed data acquisition board and processed using LabVIEW software, as shown in Figure 3. If the flow structure does not change between these two bundles and the particles move in the same direction, the two signals would be identical but separated by a time delay, τ. This time delay, which was obtained by cross-correlating the two signals, was used to calculate the axial particle velocity in eq 1:

photograph of the measurement system inserted in the conical spouted bed with a conical angle of 30° is given in Figure 2.

Up =

Le τ

(1)

where Le is the effective distance between the two bundles. In this study, Le was determined to be 2.11 mm through the calibration studies performed with rotating disks with different designs and rotating disks with particles glued to it. Because the particle velocity changed significantly in different radial locations of the spouted bed, the sampling frequency and time had to be varied accordingly. For each measurement, a total of 180 000−500 000 data points were collected through each bundle with a sampling frequency of 1−100 kHz. During the particle velocity measurements, particles may reverse directions, or a flow structure traveling nonvertically passing one bundle may not be detected by the second one, causing the cross-correlation coefficients to be low or indeterminate. Such uncorrelatable or poorly correlated data need to be eliminated. In this study, the approach proposed by Kirbas23,24 was followed for the elimination of poorly correlated data. The optical fiber probe was capable of simultaneously measuring solids hold-up together with particle velocity. The same data used in the calculation of particle velocity was integrated over time, and by utilizing a calibration equation, solid hold-ups were calculated. Before experiments, the probe

Figure 2. Photograph of the measurement system placed on the conical spouted bed with a conical angle of 30°.

Two optical probes, specially designed for this study to withstand heavy 0.5 and 1 mm zirconia particles, were used. The outer diameters of the probes are 4 and 5 mm, respectively. Each probe consists of two bundles of optical fibers. The dimensions of the bundles are 0.4 × 0.4 mm and 1.1 × 1.1 mm, respectively. Inside each bundle, there are alternating arrays of light-emitting and -receiving fibers. The fibers have a uniform diameter of 15 μm. Because the diameters of the fibers are smaller than the mean size of the particles used in this work, single-particle movements can be detected. Use of glass window in front of the probe tip to eliminate the blind regions was not necessary in this special design.21−24 Pugsley et al.25 and Maurer et al.26 verified optical fiber measurements with noninvasive electrical capacitance tomography and X-ray measurements, respectively. Both studies showed that the results obtained by the noninvasive methods were in good

Figure 3. Optical fiber probe particle velocity and solids hold-up measurement system. C


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them with the corresponding bed pressure drop values and its spectral characteristics. The minimum spouting velocities were also determined in full circular conical spouted beds via bed pressure drop measurements. In light of the results of this previous work, in this study, spouting gas velocity was set to 1.25 times higher than the minimum spouting velocity (based on the diameter of the gas inlet nozzle, Do) to ensure that experiments were performed during stable spouting operation. In this study, local instantaneous particle velocities and solids hold-up and fluxes were measured at several radial positions and three different heights in the same conical spouted beds. Information on the measurement locations and operating conditions are presented in Table 2. In this table, R indicates the radial distance from the spout axis to the wall corresponding to each probe location, Hp. In this study, each measurement was repeated three times, and the corresponding averages are reported in this paper. Effect of axial location on the local time−mean particle velocities and solids hold-up and fluxes measured in the spouted bed with a cone angle of 45° for 1 mm particles is illustrated in Figure 5. An example on the change of particle velocity is separately shown in Figure 6 in order to accentuate the change of particle velocity in the annulus region. As depicted in Figures 5 and 6, the spouted bed is made up of two distinct regions: spout and annulus. A high-velocity gas (57 m/ s) enters the bed, and the particles are carried up in the spout. It is interesting to note that the vertical component of the local particle velocity at the axis is around 2.0 m/s, indicating a large slip between gas and particles. This slip is much more significant with the high-density particles used in this study compared to the one with lower-density particles. The particle velocity at any axial location decreases from its maximum value at the axis to zero at the spout−annulus interface. At the center of the spout, the particles accelerate from the bottom of the bed (Hp < 42 mm) to a maximum velocity, after which their velocities decrease with axial distance. This trend is consistent with that observed in low-density conical spouted beds.13 In the annulus, the particles falling down from the fountain move slowly downward with particle velocities of approximately −0.003 m/s. As seen in Figure 6, the particle velocity in the annulus is maximum (−0.006 m/s) at a location close to spout−annulus interface. This was also reported by Wang et al.11 and Olazar et al.13 for low-density glass bead particles.

was calibrated by using original and black zirconium particle mixtures. For this purpose, different concentration mixtures were prepared by combining known masses of original zirconium particles and black painted zirconium particles. Because the painted zirconium particles were black and therefore absorbed most visible light, it was assumed that they behaved as voids, while only original particles reflected light. The calibration was performed in a system similar to the one described by Kirbas.23 Using different concentration mixtures, solids hold-ups were simulated. As can be seen in Figure 4, a linear relationship was observed between the voltage and solids hold-up for both channels.

Figure 4. Correlation between the voltage signal and solids hold-up.

Since the optical fiber probe was capable of simultaneously measuring solids hold-up together with particle velocity, it was also possible to calculate instantaneous local solids flux by Gs(t ) = ρp Up(t ) εs(t )

(2)

4. RESULTS AND DISCUSSION Prior to this study, a comprehensive work was conducted to determine the minimum spouting velocities (Ums) and the stable spouting regimes at different operating conditions in the same units operating with the same zirconia particles.9 In that study, for the determination of minimum spouting velocities and complete characterization of the hydrodynamic regimes, simultaneous high-speed camera and bed pressure drop measurements were carried out in a half circular conical spouted bed to visualize the gas−solid flow patterns and match

Table 2. Information on the Measurement Locations and Operating Conditions

D


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calculation of local instantaneous solids fluxes. Solids flux, defined as mass of solids passing per unit time and per unit area normal to the flow, provides exceptional information on solids flow dynamics. Because of its importance, solids flux distributions have been measured, especially in circulating fluidized beds, by many researchers. However, to the authors’ knowledge, there is no study in the literature reporting radial solids flux distributions both in the spout and annulus regions in spouted beds. Olazar and co-workers determined only the area-averaged solids flow rate in the spout region by counting the number and frequency of the ascending particles using the probe signals.17 As can be seen in Figure 5, higher upward fluxes are observed at higher axial locations, indicating the extent of solids cross-flow (radial flow) into the spout from the annulus. In the annulus region, on the other hand, axial fluxes do not change significantly with the axial location. Olazar and co-workers17 reported an increase in the area-averaged axial solids flow rate in the spout for different types of low-density particles. As far as the absolute values of the solids flux is concerned, for glass bead particles (ρp = 2420 kg/m3), near the top of the bed in the spout region, an area-averaged value of approximately 400 kg/m2s can be calculated from the reported solids mass flow rate if the spout diameter is assumed to be three times the inlet gas diameter, as suggested by the authors.17,18 Furthermore, the solids flow rate in the spout was found to decrease with the increasing solids density. Therefore, the values obtained in this study are significantly greater than the values reported for low-density conical spouted beds. Figure 7 shows the effect of particle diameter on local time− mean particle velocities and solids hold-up and fluxes measured in the spouted bed with a cone angle of 60° at the same static bed height and probe measurement location. It was monitored and reported earlier that the minimum spouting velocity increases with particle diameter.9 Therefore, with the increase of particle diameter from 0.5 to 1 mm, almost twice as much of spouting air is required to keep inlet gas velocity equal to 1.25Ums during the experiments (Uo = 25.3 and 45.3 m/s for 0.5 and 1 mm particles, respectively, as indicated in Table 2). Gas velocity is the dominant factor affecting the particle velocity. To take into account the differences in gas velocities during comparison of particle velocity distributions, time− mean particle velocity was normalized by dividing it to the inlet gas velocity in Figure 7. This approach was also used in a recent scale-up study of spouted beds.27 The absolute value of the particle velocity was measured as 2.68 and 2.26 m/s for 1 and 0.5 mm particles at the spout axis, respectively. As illustrated in the figure, the normalized particle velocity, contrary to absolute value of the particle velocity, decreases as particle diameter increases. Solids hold-up profiles show that particle concentration decreases with particle diameter in the core of the spout region. This is consistent with the results of the low particle density studies.14 However, in the spout−annulus interface, higher particle concentration values were measured for 1 mm particles compared to 0.5 mm particles. No significant effect of particle diameter was monitored in the annulus region. As particle diameter increases, there is a noticeable decrease in solids flux in the spout region, indicating lower circulation of the solids and particle−gas interaction. Toward the walls of the bed, however, this effect vanishes. Effect of conical angle on the local time−mean particle velocities and solids hold-up and fluxes is illustrated in Figure 8. Since already available measurement holes on the systems were

Figure 5. Radial profiles of local time−mean particle velocity, solids hold-up, and flux at different axial locations (dp = 1 mm, γ = 45°, Hb = 140 mm, Uo = 1.25Ums).

Figure 6. Radial profile of local time−mean particle velocity (dp = 1 mm, γ = 45°, Hb = 140 mm, Hp = 120 mm, Uo = 1.25Ums).

With the increase in axial distance, the particle velocity profile in both spout and annulus regions become flatter. When the solids hold-up profiles are examined, it is observed that in the spout, solids hold-up is much lower compared to the annulus where particles are in close contact with each other and the solids hold-up is uniform and almost equal to the loosely packed solids hold-up at all levels. Solids hold-up increases sharply in the interface region between the spout and the annular zones. The increase in solids hold-up with axial distance along the spout axis monitored in this study is in accordance with the trends observed in low-density particle beds.14 The probe allows the simultaneous measurement of particle velocity and solids hold-up and therefore enables the E


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Figure 8. Effect of conical angle on the radial profiles of local time− mean particle velocity, solids hold-up, and flux (for γ = 30°, Hb = 140 mm, Hp = 100 mm, Hp/Hb = 0.71; for γ = 45°, Hb = 100 mm, Hp = 82 mm, Hp/Hb = 0.82; Uo = 1.25Ums).

Figure 7. Effect of particle diameter on the radial profiles of local time−mean particle velocity, solids hold-up, and flux (γ = 60°, Hb = 100 mm, Hp = 50 mm, Uo = 1.25Ums).

obtained in the spout region compared to 60 mm static bed case, which is also consistent with the literature on low-density particles.13,14 For this case, also, the time−mean particle velocity was normalized by the inlet gas velocity. The normalization does not alter the trend observed for the absolute velocity; the dimensionless particle velocity increases as the bed height is increased from 60 mm to 100 mm, indicating that the particles are moving at velocities closer to the interstitial gas velocity. The solids flux, hence circulation, increases with static bed height. Figure 10 shows the conceptual diagram of the solids motion based on the data obtained from 45° conical angle bed. In this figure, the length of the black arrows scale with the measured solids flux data. The solids flux in the spout region increases because of radial solids cross-flow from the annulus. The radial solids cross-flow tends to decrease with increasing height. The maximum value of the downward solids flux in the annulus is obtained near the spout−annulus interface.

used for optical probe measurements, the measurement heights (Hp) in two systems were not equal to each other. Therefore, ratio of the measurement height to static bed height (Hp/Hb) was tried to be set close to each other for comparison. As can be seen from Figure 8, the particle velocity at the spout axis is independent of the cone angle, whereas toward the spout− annulus interface higher particle velocities were measured for 30° cone angle. The solids hold-up almost doubles at 30° cone angle, leading to a significant increase in solids flux in the spout region compared to the 45° cone angle. This indicates that the solids circulation in the 30° bed is higher than that in the 45° spouted bed. The solids hold-up and solids circulation trends obtained in this work for the spout region are the opposite of those obtained in beds operated with low-density particles.13,14,19 Although the effect of cone angle is not found to be significant in the annulus region for the high-density zirconia particles used in this work, with a magnified look, it can be seen that solids downward velocity and flux decrease slightly with conical angle. The increase in the particle velocity in the annulus region with a decrease in conical angle is more pronounced in low particle density beds.13,19 Effect of static bed height on local time−mean particle velocities and solids hold-up and fluxes measured in the spouted bed is shown in Figure 9. Because the minimum spouting velocity increases with static bed height,9 when the bed is operated at Uo = 1.25Ums, significantly higher gas velocity is fed through the bottom of the bed for 100 mm static bed height. Therefore, it is expected that higher particle velocities and lower solids hold-up values are

5. CONCLUSIONS In this paper, results of the optical probe measurements (particle velocity, solids hold-up, and solids flux) are presented for conical spouted beds operated with high-density particles. Experiments were carried out in three different conical spouted beds (γ = 30°, 45°, 60°) having a column diameter of 15 cm. High-density (dp = 0.5, 1 mm; ρp = 6050 kg/m3) zirconia particles were used as the bed material. Effects of axial height, particle diameter, conical height, and static bed height on the time−mean particle velocity, solids hold-up, and solids flux F


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The time−mean particle velocity decreases and the solids hold-up and flux increase along the bed height in the spout region. In the annulus region, the values of solids hold-up and flux are not dependent on axial height. The normalized particle velocity (Up/Uo) decreases with increasing particle diameter, indicating that small particles are moving at velocities closer to gas velocity compared to larger particles. As the particle diameter increases, there is a noticeable decrease in solids hold-up and solids flux in the spout region, indicating a decrease in solids circulation. Out of two cone angles tested in this work, the spouted bed with 30° cone angle resulted in higher solids flux in the spout region compared to the bed with 45° cone angle mainly because of increased solids hold-up. The particle velocities at the spout axis were found to be independent of the cone angle. For a particular cone angle, an increase in static bed height increases the particle velocity, decreases the solids hold-up slightly, and increases the solids flux. Comparisons of the experimental trends obtained in this work with previous studies carried out with relatively lower density particles indicate both similarities and discrepancies. For instance, contrary to the trends observed in low particle density beds, the solids flux in the spout region was found to decrease as the cone angle was increased from 30° to 45°. The values of the solids flux in the spout region were substantially higher (about 2−3 fold) than those measured in low particle density beds. Therefore, there is a need for further research for complete understanding and characterization of the effects of particle density on particle dynamics in conical spouted beds.

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Figure 9. Effect of static bed height on the radial profiles of local time−mean particle velocity, solids hold-up, and flux (for γ = 45°, Hp = 42 mm, Uo = 1.25Ums).

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Tel.: +90312 210 4345. Fax: + 90312 210 2600. *E-mail: [email protected]. Tel.: +903122976208. Fax: +90312 297 6206.

were investigated. The main conclusions are summarized below:

Figure 10. Conceptual diagram of the solids motion based on measured solids flux (dp = 1 mm, γ = 45°, Hb = 140 mm, Uo = 1.25Ums). G


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Industrial & Engineering Chemistry Research Author Contributions ∥

(11) Wang, Z.; Bi, H. T.; Lim, C. J. Measurements of local flow structures of conical spouted beds by optical fibre probes. Can. J. Chem. Eng. 2009, 87, 264−273. (12) Olazar, M.; San Jose, M. J.; LLamosas, R.; Alvarez, S.; Bilbao, J. Study of local properties in conical spouted beds using an optical fiber probe. Ind. Eng. Chem. Res. 1995, 34, 4033−4039. (13) Olazar, M.; San Jose, M. J.; Morales, S. A.; Bilbao, J. Measurement of particle velocities in conical spouted beds using an optical fiber probe. Ind. Eng. Chem. Res. 1998, 37, 4520−4527. (14) San Jose, M. J.; Olazar, M.; Alvarez, S.; Bilbao, J. Local bed voidage in conical spouted beds. Ind. Eng. Chem. Res. 1998, 37, 2553− 2558. (15) San Jose, M. J.; Olazar, M.; Alvarez, S.; Izquierdo, M. A.; Bilbao, J. Solid cross-flow into the spout and particle trajectories in conical spouted beds. Chem. Eng. Sci. 1998, 53, 3561−3570. (16) San Jose, M. J.; Olazar, M.; Alvarez, S.; Morales, A.; Bilbao, J. Local porosity in conical spouted beds consisting of solids of varying density. Chem. Eng. Sci. 2005, 60, 2017−2025. (17) San Jose, M. J.; Olazar, M.; Alvarez, S.; Morales, A.; Bilbao, J. Spout and Fountain Geometry in Conical Spouted Beds Consisting of Solids of Varying Density. Ind. Eng. Chem. Res. 2005, 44, 193−200. (18) San Jose, M. J.; Alvarez, S.; Morales, A.; Olazar, M.; Bilbao, J. Solid cross-flow into the spout and particle trajectories in conical spouted beds consisting of solids of different density and shape. Chem. Eng. Res. Des. 2006, 84, 487−494. (19) Olazar, M.; San Jose, M. J.; Izquierdo, M. A.; de Salazar, A.; Bilbao, J. Effect of operating conditions on solid velocity in the spout, annulus and fountain of spouted beds. Chem. Eng. Sci. 2001, 56, 3585− 3594. (20) Lule, S. S.; Colak, U.; Koksal, M.; Kulah, G. CFD Simulations of hydrodynamics of conical spouted bed nuclear fuel coaters. Chem. Vap. Deposition 2015, 21, 122−132. (21) Kirbas G.; Ellis, N. Multiscale analysis of solids flux signals measured in a high density circulating fluidized bed using wavelet transformation. Proceedings of the 8th International Conference on Circulating Fluidized Beds, Hangzhou, China, May 10−13, 2005; Chen, K., Ed.; pp 75−82. (22) Liu, J.; Grace, J. R.; Bi, H. T. Novel multifunctional optical-fiber probe: I. Development and validation. AIChE J. 2003, 49, 1405−1420. (23) Kirbas, G. Solids Motion and Mixing in High-Density Circulating Fluidized Beds. Ph.D. Dissertation, University of British Columbia, Vancouver, BC, 2004. (24) Kirbas, G.; Kim, S. W.; Bi, H. T.; Lim, C. J.; Grace, J. R. Radial distribution of local concentration-weighted particle velocities in highdensity circulating fluidized beds. Proceedings of the 12th Fluidization Conference, Canada, May 13−17, 2007; Bi, X., Berruti, F., Pugsley, T., Eds.; ECI: New York, 2007. (25) Pugsley, T.; Tanfara, H.; Malcus, S.; Cui, H.; Chaouki, J.; Winters, C. Verification of fluidized bed electrical capacitance tomography measurements with a fibre optic probe. Chem. Eng. Sci. 2003, 58, 3923−3934. (26) Maurer, S.; Wagner, E. C.; Schildhauer, T. J.; van Ommen, J. R.; Biollaz, S. M. A.; Mudde, R. F. X-ray measurements on the influence of optical probes on gas−solid fluidized beds. Int. J. Multiphase Flow 2015, 74, 143−147. (27) Du, W.; Xu, J.; Wei, W.; Bao, X. Computational fluid dynamics validation and comparison analysis of scale-up relationships of spouted beds. Can. J. Chem. Eng. 2013, 91, 1746−1754.

G.K. and M.K. contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was carried out with the financial support of the Scientific and Technological Research Council of Turkey (Project No: MAG 108M435).

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NOMENCLATURE

Symbols

dp = Particle diameter, mm Do = Gas inlet diameter, m Di = Cone bottom diameter, m Dc = column diameter, m Gs(t) = Instantaneous local solids flux, kg/m2s Hc = Height of the conical section, m Hb = Height of the static bed, m Hp = Height of the probe location, m Le = Effective distance between the two fiber bundles, mm Ums = Minimum (external) spouting velocity, m/s Uo = Superficial gas velocity based on Do, m/s Up(t) = Instantaneous local particle velocity, m/s Greek Letters

γ = Angle of the conical section, degree εs(t) = Instantaneous local solids hold-up ρp = Particle density, kg/m3

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REFERENCES

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