Mixing Characteristics of a Novel Annular Spouted Bed with Several

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Ind. Eng. Chem. Res. 2007, 46, 8248-8254

Mixing Characteristics of a Novel Annular Spouted Bed with Several Angled Air Nozzles Hao Huang and Guoxin Hu* School of Mechanical Engineering, Shanghai Jiaotong UniVersity, Shanghai 200030, China

A novel spouted bed, namely, an annular spouted bed with several angled angled air nozzles, has been proposed for dryness, catalytic pyrolysis, and gasification of biomass. It consists of two concentric upright cylinders with eight annularly located angled air nozzles between inner and outer cylinders. A rotating cone is adopted as an accessorial feeder. Experiments have been performed to study mixing characteristics of the annular spouted bed. The test materials studied are soybean and black bean. The effect of feeding mode and air velocity as well as static bed height on particle mixing of the spouted bed under various operating conditions was investigated. In addition, the lateral particle motion was studied experimentally and theoretically. 1. Introduction

2. Experimental Setup, Materials, and Methods

Spouted bed reactors are a kind of gas-solid granular contactor appropriated for a variety of chemical engineering and mining operations that deal with the handling, through cyclic flow patterns, of heavy, coarse, sticky, and/or irregularly shaped solids inventories.1-4 Besides conventional fields of physical transformations in coating, drying, and granulation,2,3 spouted beds are also expected to operate in chemical transformations such as in coal gasification and in catalytic polymerization.5-7 However, several shortcomings such as low annulus aeration, slow solids turnover, and bad mixing effect greatly limit the application of the conventional spouted bed (CSB). Since the conventional spouted bed suffers from these shortcomings, many modified spouted beds have been proposed and studied during the past decades, for example, jet-spouted bed,7 pulsed spouted bed,8 rotating spouted bed,9-11 multiple spouted beds,12-14 spouted fluidized beds,15,16 conical spouted beds,17-19 and a draft tube spouted bed.20-24 Recently, on the basis of the conventional cylindrical (or square) multiple air nozzle spouted bed, a novel annular spouted bed with several angled air nozzles was developed by Shanghai Jiaotong University.25 The spouted bed, which combines spouting and biomass dryness, catalytic pyrolysis, and gasification, is extremely innovative. It is expected to offer good conditions for biomass catalytic gasification. The annular spouted bed consists of two concentric upright cylinders. Eight angled nozzles and V-shaped deflectors are mounted symmetrically along the annular bottom between the inner and outer cylinders. The spouting phenomenon takes place in the annular space between the inner and outer cylinder. A particular design of the annular spouted bed is adopting a rotating cone as an accessorial feeder, which is hung above the inner cylinder. The hydrodynamic characteristics of the annular spouted bed have been studied in a previous paper.26 In the present paper, the mixing characteristics of the annular spouted bed were studied. The mixing experiments were performed to investigate the effects of feeding mode and air velocity as well as static bed height on particle mixing under various operating conditions. In addition, the lateral particle motion and the formation of the dead zone in the annular spouted bed were also analyzed experimentally and theoretically.

2.1. Experimental Setup. Figure 1 shows a schematic diagram of the experimental setup and the associated instrumentation. The novel annular spouted bed consists of two concentric upright pellucid plexiglass cylinders. The inner cylinder is 300 mm in diameter and 1000 mm in height, and the outer cylinder is 400 mm in diameter and 1740 mm in height. The spouting air supplied by the air line is regulated by a gate valve. It is a well-documented fact that the multiple-orifices spouted beds are not easy to operate properly because certain orifices may collapse, and consequently, dead zones are formed in the bed. To avoid this problem, an independent inlet for each orifice has been proposed in the literatures.12,14 The inlet, 100 mm in diameter, is located at the center of the room base, through which the gas is supplied to the gas room. Then, the air is divided equivalently into the nozzles, which is helpful to develop uniform spouting without partial choking of the nozzle. Eight nozzles are mounted uniformly along the circumference on the bottom of the annular space between the inner and outer cylinders. On the nozzle, a V-shaped deflector is arranged to prevent formation of the dead zone. Its height is 130 mm. The oscillating feeder machine and rotating cone work together to feed materials into the novel annular spouted bed. To compare the effects of different feeding modes on particle mixing in the spouted bed, two different feeding modes are adopted: (1) the conventional feeding mode, where the feed is sent into the spouted bed from a fixed point on the outer cylinder, namely, the feeding at a fixed point, and (2) the novel feeding mode of the annular spouted bed, namely, feeding by a rotating cone, where the feed is first sent into the rotating cone by an oscillating feeder machine and, then, these materials are homogeneously projected into the annular space with the help of the centrifugal force produced by the rotating cone driven by an electromotor. The air velocity (uv) in this paper defines the outlet velocity of the air blower. A pressure sensor, a serial port, and a personal computer are used to determine the dynamic pressure of the outlet of the air blower. The air velocity is calculated by

* Corresponding author. Tel./fax: +86 21 62812034. E-mail: [email protected].

uv )

x

2P Fair

(1)

where P is the dynamic pressure of the outlet of the air blower. Fair is the density of air at room temperature and atmospheric pressure.

10.1021/ie070643o CCC: $37.00 © 2007 American Chemical Society Published on Web 10/12/2007

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Figure 2. Division of sampling cells.

Figure 1. Schematic diagram of the overall experimental apparatus: (1) air blower; (2) gate valve 1; (3) pressure transducer; (4) surge tank; (5) gate valve 2; (6) nozzle; (7) V-shaped deflectors; (8) inner cylinder; (9) outer cylinder; (10) rotating cone; (11) tundish; (1)2 exhaust tube; (13) electromotor; (14) oscillating feeder; (15) A/D converter; (16) port; (17) PC. Table 1. Dimensions of Particles Used in the Experiments for given material

for given material L (mm) W (mm) Z (mm) Dpe a (mm)

soybean

black bean

6.968 6.604 6.092 8.121

9.148 7.808 5.592 9.331

Dpgm b (mm) Dp c (mm) φd

soybean

black bean

6.545 7.626 0.939

7.519 7.670 0.822

a Equivalent spherical diameter. b Geometric particle diameter ) (L × W × Z)1/3. c Effective particle diameter ) Dpeφ. d Sphericity ) Dpgm/L.

2.2. Materials. Soybean and black bean were used as the test materials. According to Geldart’s classification,27 these particles belong to group D (spoutable, large, and dense particles). Dimensions and physical properties (average values) of the particles calculated by means of the correlation proposed in previous papers9,21 were given in Table 1. For each test material 100 particles were measured. 2.3. Methods. The spouting air was blown into the air room first, and then, it was spouted into the annular space of the spouted bed through eight nozzles. Subsequently, the oscillating feeder machine began to offer the rotating cone with bed material (soybean). With the help of the centrifugal action produced by the rotating cone driven by the electromotor, the bed material (soybean) moved upward along the wall of the cone, escaped the cone, and then fell into the annular space between the inner and outer cylinders. The rotational speed of the cone was Z ) 6 Hz. The bed materials were lifted and suspended by the air flow in the annular space. The air flow was discharged from the exhaust tube on the top of the annular spouted bed. When the annular spouted bed reached stable spouting conditions, the tracer particles (black bean) were also sent into the annular spouted bed. For feeding the tracer particles, the rotational speed of the cone was adjusted to Z ) 1 Hz first, and then the tracer particles (black bean) were fed into the cone as in the above method. Because of the small rotational speed of the cone, the tracer particles only fill into the cone and cannot be spread into the annular space. Finally, the tracer particles were fed into the annular space by readjusting the rotational speed of the cone to Z ) 6 Hz. After a preconcerted mixing time, the mixing operation was stopped by closing gate valve 1 and opening gate valve 2 simultaneously. The whole annular

Figure 3. Mixing curves for feeding at a fixed point (feeding mode, feeding at a fixed point; air velocity, 20 m/s).

space was divided into several cells with the same volume according to the divisions drawn on the surface of the outer cylinder, as shown in Figure 2.28,29 The concentration of tracer particles of each cell was measured. To assess the mixing characteristic of the annular spouted bed, the degree of mixing was introduced in this study.28 The degree of mixing, DM, is defined by

DM ) σ/σ0

(2)

The standard deviation σ for the concentration of tracer particles in each cell is given by

[ ] i

σL or A )

(xi - xj)2 ∑ i)1 N-1

1/2

(3)

where xi is the concentration of tracer particles of the cell i. xj is the mean concentration of tracer particles of the annular spouted bed, and the suffix letters L and A denote lateral and axial, respectively. N is the number of cells laterally or axially. The suffix 0 denotes the completely unmixed state; σ0 is given by29

σ0 ) [xj(1 - xj)]1/2

(4)

The measurement uncertainty values due to random errors are the ones supplied by the manufacturers or are estimated from a “single-sample” experiment.30-32 The rule of thumb in the

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Figure 4. Initial distribution of tracer particles after feeding: (a) Feeding at a fixed point for CSB; (b) feeding at a fixed point for the annular spouted bed; (c) feeding by rotating cone for the annular spouted bed.

Figure 5. Typical particle mixing images for various feeding modes: (a) feeding at a fixed point; (b) feeding by a rotating cone.

latter case is that the maximum possible error is equal to plus or minus half of the smallest scale division (the least count) of

the instrument. The precision of the electronic balance is (0.001 g for weight determined. A staff gauge accurate to (0.001 m


Figure 6. Effect of feeding modes on particle mixing (air velocity, 20 m/s).

is used for drawing the divisions and static bed height determination. To investigate the reproducibility of the results in the experiment, replicates are made of randomly selected experiments. From these tests the reproducibility values for the degree of particle mixing laterally and axially were within 5.3 and 3.2% of their respective reported values. 3. Results and Discussion DM represents the uniformity of mixture at a certain mixing time, and the lower DM is, the better the uniformity of the mixture is. To discuss the mixing characteristics of the annular spouted bed and the effects of several factors on particle mixing, mixing curves are examined under various operating conditions. The mixing curve displays the relationship between DM and the mixing time. Usually, a mixing curve presents two different trends as mixing time increases. At the outset of mixing, the mixing curve decreases with the increasing mixing time, and the slope of the mixing curve represents the mixing speed. After this stage, the mixing curve takes a constant value with slight fluctuation even if there is an endless prolonged mixing time. The constant value represents the uniformity of the final mixture (FDM, the mixing degree of the final mixture), which indicates the final mixing results corresponding to a certain operating condition. 3.1. Effects of Feeding Mode. 3.1.1. Particle Mixing Behavior for Feeding at a Fixed Point. For the conventional

spouted bed (CSB), the feed was usually sent into CSB from a fixed point by various machines, for example, feed pump and oscillator feeder. In the present paper, the conventional feeding mode was predigested by inserting a tundish (50 mm in diameter) at the upper end of the out cylinder, as shown in Figure 2. The test results for feeding at a fixed point are presented in Figure 3. From Figure 3, it can be observed that there is significant difference between the lateral and axial mixing curves. The decreasing of lateral DM is much faster than that of axial DM, and lateral FDM is higher than that in axial FDM. The results indicate that not only the lateral mixing speed is slower than the axial mixing speed but also the lateral uniformity of the final mixture is worse than that axially, which suggests a poor lateral mixing. This is because the axial particle motion is more intensive than the lateral particle motion. Usually, the axial particle motion depends on the axial component air flow and the gravity of the particles. However, the lateral particle motion is mainly attributed to the collisions of particles with the wall and others particles as well as the horizontal component of air flow. Compared with the axial forces, the lateral forces are weaker and irregular. As a result, the axial mixing is better than the lateral mixing. The similar hydrodynamic characteristic also can be found in other types of gas-solid granular contactor. So, the poor lateral particle motion is an important reason for the poor lateral particle mixing, which has to be a widespread problem for most of the gas-solid reactor, and an effective improvement on the poor lateral mixing is urgent. 3.1.2. Particle Mixing Behavior for Feeding by a Rotating Cone. Figure 4 presents the initial distribution of the tracer particles after feeding with different modes. In Figure 4a, the tracer particles usually cannot cover the whole round section. Due to the poor lateral motion of particles in CSB, the particle mixing laterally is slow. However, if feeding at a fixed point is used as the feeding mode in the annular spouted bed, the tracer particle only drops onto a small region under the effect of the internal cylinder, as is shown in Figure 4b. At that time, the tracer particles require traveling a long distance along the circumferential direction to mix with bed materials, resulting in a long mixing time for lateral particle mixing. So, feeding at a fixed point is unsuitable for the annular spouted bed. To improve on the lateral particle mixing, a novel feeding mode was adopted in the annular spouted bed, in which a rotating cone driven by an electromotor was used as an accessorial feeder. By this way, the tracer particles would be uniformly

Figure 7. Effect of static bed height on the uniformity of the final mixture (feeding mode, feeding by a rotating cone; air velocity, 20 m/s).

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Figure 8. Particle mixing curves at different air velocities (feeding mode, feeding by a rotating cone).

projected onto the whole annular section, as is shown in Figure 4c. As a result, the lateral mixing time would decrease. The particle mixing behaviors with different feeding modes in the annular spouted bed are recorded by using a highresolution digital CCD camera (Canon Digital IXUS 65). The results are presented in Figure 5. Figure 5a illustrates the fixed point feeding. At the onset of feeding, the tracer particles concentrate at a small region on the bed surface, which confirms the above theoretical analysis. After 15 s, several tracer particles appear in the left side of the picture, which indicates that traveling in a circle along the circumferential direction needs almost 15 s. After 30 s, a viewable well-lateral particle mixing is formed. However, for feeding by a rotating cone, as is shown

in Figure 5b, the tracer particles are spread onto the bed surface of the whole annular section at the onset of feeding, and a viewable well-lateral particle mixing only requires 2.5 s. Obviously, the feeding by a rotating cone greatly decreases the required lateral mixing time. This is because, feeding by a rotating cone, the lateral particle mixing is significantly replaced by homogeneous projecting of particles into the annular section. Furthermore, since the tracer particles only cover a small area of the whole annular section for feeding at a fixed point, only a small amount of air flow would impulse these tracer particles to move, which also causes a poor lateral particle mixing. Besides, the lateral mixing curves are also determined and shown in Figure 6. For feeding by a rotating cone, the decreasing of


Figure 9. Lateral concentration distribution of tracer particles at circumferential space (feeding mode, feeding at a fixed point; hold-ups, 6 kg; air velocity, 20 m/s).

the lateral DM is faster than that for feeding at a fixed point. The result indicates that the introduction of the feeding by a rotating cone greatly enhances the lateral mixing speed. 3.2. Effects of Static Bed Height. The mixing time increases as the static bed height increases at a given air velocity. This trend is expected since it is common to obtain slower mixing in a deeper bed of particles than in a shallower one at the same air mass flow rate.8 In this paper, the aim is to study the effect of the static bed height on the uniformity of final mixture (the mixing degree of final mixture). The test results are presented in Figure 7. It can be found that the FDM varies with the increase of the static bed height. As the static bed increase, the axial FDM decreases first and then increases, and the lateral FDM decreases. The change of the axial FDM is attributed to the following reasons: (a) spout intensity and (b) transport disengagement. With the increasing of the static bed height, the spout intensity declines and transport disengagement decreases. The strengthened spout intensity is helpful to accelerate particle mixing and achieve a better uniformity of the final mixture; however, the increased transport disengagement would aggravate particle segregation, resulting a bad uniformity of the final mixture. For a small static bed height, it is the effect of transport disengagement on the axial FDM that controls the change of the axial FDM since the spout intensity is very strong at that time. So, a slight increasing of the static bed height would cause transport disengagement decreases, and thus, the axial FDM decreases. For a large static bed height, the spout intensity is weak and there is almost no transport disengagement. So, the effect of transport disengagement on the axial FDM can be ignored at the time, and the increasing of the static bed height would make the spout intensity become more and more weak, resulting in the axial FDM increase. As a result, the axial FDM decreases first and then increases as the static bed increases.

Through the above theoretical analysis, it can be understood that too small or too large static bed height causes a bad axial FDM. With too small static bed height, the increased transport disengagement would lead to a bad uniformity of the final mixture. With too large static bed height, the decreased spout intensity would bring a high axial FDM. So there exists an optimal value for static bed height, which is different according to different operating parameters. In the present study, the optimal value of the static bed height is found to be 290 mm. The change of the lateral FDM as the static bed increases maybe ascribes to the uneven air flow distribution at the nozzles. For a small static bed height, the amount of air flow passing each nozzle usually is different. The difference causes inequitable lateral particle mixing. However, with increasing static bed height, the difference will decline gradually. Therefore, the lateral FDM decreases as the static bed height increases. 3.3. Effect of Air Velocity. The effects of the air velocity on the particle mixing at various hold-ups are presented in Figure 8. It can be observed that the air velocity has significant effect on mixing speed. With increasing air velocity, the slope of DM increases. The results indicate that the mixing speed increases as the air velocity increase. This is because the increasing of the air velocity would result in a faster particle motion, which is very helpful for particle mixing. From Figure 8, it can be seen that the air velocity has a slight effect on the uniformity of the final mixture. On the basis of the above analysis, however, there must be transport disengagement and spouted intensity to affect the uniformity of the final mixture. Theoretically, the fast air velocity would increase transport disengagement and spouted intensity. 3.4. Lateral Particle Motion. Usually the lateral particle motion in CSB is driven by the horizontal component of the force of the air and the impact of particles and particles within the well, which results in a disorderly, random, and weak lateral

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particle motion. However, in the annular spouted bed, the particle motion is of an inherent horizontal component along the circumferential direction. Figure 9 shows the lateral concentration distribution curve of tracer particles. The feeding mode is feeding at a fixed point. It can be seen that most tracer particles centralize a small region after the feeding, and there is a strong peak in the lateral concentration distribution curve of tracer particles, the peak value is 20%. With the increasing of the mixing time, the peak moves along the circumferential direction and its value gradually decreases. The results confirmed that the particle motion has an inherent horizontal component in the annular spouted bed. So, a regular forward particle flow along the circumferential direction comes into being in the annular spouted bed. Compared with the disorderly and random particle lateral motion of CSB, the well-regulated lateral particle motion of the annular spouted bed would ensure a better lateral particle mixing. 4. Conclusions The mixing characteristics of a novel annular spouted bed with multiple air nozzles were studied experimentally and analytically. The effects of several factors such as the feeding mode and the air velocity as well as the static bed height on particle mixing were investigated. The following conclusions can be drawn from the present investigation. (1) The feeding by a rotating cone greatly improves the lateral particle mixing by homogeneously projecting the particles to the annular bed. With the effect of the angled nozzle, the particle motion is of an inherent lateral component in the annular spouted bed, which is helpful in improving the lateral particle mixing. (2) The axial and lateral mixing speeds all increase as the air velocity increases. The static bed height has great effects on the uniformity of the final mixtures (the mixing degree of final mixture). With increasing static bed height, the axial FDM first decreases and then increases, but the lateral FDM is a monotone decrease. (3) The present results examine the mixing characteristics of a novel annular spouted bed and are useful in the conceptual design and scale-up of an annular spouted bed. Further studies on particle mixing in this device will be summarized in our next study. Acknowledgment The authors gratefully acknowledge financial support by the National Science Foundation of China under Grant No. 50376033. Literature Cited (1) Epstein, N.; Mathur, K. B. In Applications of Spouted Beds; Hetsoni, G., Ed.; Hemisphere: Bristol, PA, 1982. (2) Mathur, K. B.; Epstein, N. Spouted Beds; Academic Press: New York, 1974. (3) Olazar, M.; San Jose´, M. J.; Bilbao, J. Hydrodynamics and Applications of Conical Spouted Beds. Trends Chem. Eng. 1996, 3, 219233. (4) Larachia, F.; Grandjean, B. P. A.; Chaouki, J. Mixing and Circulation of Solids in Spouted Beds: Particle Tracking and Monte Carlo Emulation of the Gross Flow Pattern. Chem. Eng. Sci. 2003, 58, 1497-1507. (5) Epstein, N. Third International symposium on spouted beds (Special issue). Canadian Journal of Chemical Engineering 1992, 70, 833-997. (6) Olazar, M.; Arandes, J. M.; Zabala, G.; Aguayo, A. T.; Bilbao, J. Design and Operation of a Catalytic Polymerization Reactor in a Dilute Spouted Bed Regime. Ind. Eng. Chem. Res. 1997, 36, 1637-1643. (7) Olazar, M.; San, Jose´, M. J.; Zabala, G.; Bilbao, J. A New Reactor in Jet Spouted Bed Regime for Catalytic Polymerizations. Chem. Eng. Sci. 1994, 49, 4579-4588.

(8) Devahastin, S.; Mujumdar, A. S. Some Hydrodynamic and Mixing Characteristics of a Pulsed Spouted Bed Dryer. Powder Technol. 2001, 117, 189-197. (9) Devahastin, S.; Mujumdar, A. S.; Raghavan, G. S. V. Hydrodynamic Characteristics of a Rotating Jet Annular Spouted Bed. Powder Technol. 1999, 103, 169-174. (10) Jumah, R. Y.; Mujumdar, A. S.; Raghavan, G. S. V. Aerodynamics of a Novel Rotating Jet Spouted Bed. Chem. Eng. J. 1998, 70, 209-219. (11) Jumah, R. Y. Flow and Drying Characteristics of a Rotating Jet Spouted Bed. Drying Technol. 1995, 13, 2243-2250. (12) Xu, X. P.; Zhu, J. G.; Yang, B.; Zhang, B. Z.; Pan, J. S. Fuel Particle Coating in a Multiple Gas Inlet Spouted Bed. J. Tsinghua UniV. 2000, 40, 63-66 (in Chinese). (13) Albina, D. O. Combustion of Rice Husk in a Multiple-Spouted Fluidized Bed. Energy Sources 2003, 25, 893-904. (14) Saidutta, M. B.; Murthy, D. V. R. Mixing Behaviour of Solids in Multiple Spouted Beds. Can. J. Chem. Eng. 2000, 78, 382-385. (15) Litt, R. D.; Shirley, F. W. Improving Combustor Performance and Operability Using a Spouted Fluidized, Bed. Int. Conf. Fluid. Bed Combust.: FBC-Technol. Today 1989, 1031-1038. (16) Tang, F. X.; Zhang, J. Y. Multi-factor Effects on and Correlation of Minimum Spout-Fluidizing Velocity in Spout-Fluid Beds. J. Chem. Ind. Eng. (China) 2004, 55, 1083-1091 (in Chinese). (17) Olazar, M.; Aguado, R.; Sanchez, J. L.; Bilbao, R.; Arauzo, J. Thermal Processing of Straw Black Liquor in Fluidized and Spouted Bed. Energy Fuels 2002, 16, 1417-1424. (18) San Jose´, M. J.; Alvarez, S.; De Salazar, A. O.; Olazar, M.; Bilbao, J. Influence of the Particle Diameter and Density in the Gas Velocity in Jet Spouted Beds. Chem. Eng. Process. 2005, 44, 153-157. (19) Olazar, M.; San Jose´, M. J.; Aguayo, R.; Bilbao, J. Solid Flow in Jet Spouted Beds. Ind. Eng. Chem. Res. 1996, 35, 2716-2724. (20) Subramanian, G.; Turton, R.; Sheluker, S.; Flemmer, L. Effect of Tablet Deflectors in the Draft Tube of Fluidized/Spouted Bed Coaters. Ind. Eng. Chem. Res. 2003, 42, 2470-2478. (21) Saadevandi, B. A.; Turon, R. Particle Velocity and Voidage Profiles in a Draft Tube Equipped Spouted-Fluidized Bed Coating Device. Chem. Eng. Commun. 2004, 191, 1379-1400. (22) Ljichi, K.; Tanaka, Y.; Uemura, Y.; Hatate, Y.; Yoshida, K. SolidsCirculation Rate and Holdup in the Draft Tube of a Spouted Bed. Int. Chem. Eng. 1994, 34, 370-376. (23) Eng, J. H.; Svrcek, W. Y.; Behie, L. A. Dynamic Modeling of a Spouted Bed Reactor with a Draft Tube. Eng. Chem. Res. 1989, 28, 17781785. (24) Cecen, E. A. Annulus Leakage and Distribution of the Fluid Flow in a Liquid Spout-Fluid Bed with a Draft Tube. Chem. Eng. Sci. 2003, 58, 4739-4745. (25) Hu, G. X. Annular Spouted Bed with the Multi-air-nozzle and the Annular Air Splitter. China Patent 200510029667.5, 2005. (26) Gong, X. W.; Hu, G. X.; Li, Y. H. Hydrodynamic Characteristics of a Novel Annular Spouted Bed with Multiple Air Nozzles. Ind. Eng. Chem. Res. 2006, 45, 4830-4836. (27) Geldart, D. Types of Gas Fluidization. Powder Technol. 1973, 7, 285-292. (28) Yoshitsugu, M.; Toshitsugu, T.; Satoru, K.; Yutaka, T. Discrete Particle Simulation of a Rotary Vessel Mixer with Baffles, Powder Technol. 1997, 93, 261-266. (29) Lacey, P. M. C. Developments in the Theory of Particle Mixing. J. Appl. Chem. 1954, 4, 257. (30) Kline, S. J.; McClintock, F. A. Describing Uncertainties in Single Sample Experiments. Mech. Eng. 1953, 75, 3-9. (31) Moffat, R. J. Describing Uncertainties in Experimental Results. Exp. Thermal Fluid Sci. 1988, 1, 3-17. (32) Schenck, H. Theories of Engineering Experimentation, 2nd ed.; McGraw-Hill: New York, 1968.

ReceiVed for reView May 7, 2007 ReVised manuscript receiVed July 18, 2007 Accepted August 24, 2007 IE070643O

Mixing Characteristics of a Novel Annular Spouted Bed with Several

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