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Thermodynamics, Transport, and Fluid Mechanics
Parameters Affecting Efficient Solid Circulation Rate in Draft Tube Spouted Bed Palash Kumar Mollick, Aniruddha Bhalchandra Pandit, and Pallippattu Krishnan Vijayan Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b01691 • Publication Date (Web): 05 Jun 2018 Downloaded from http://pubs.acs.org on June 5, 2018
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Parameters Affecting Efficient Solid Circulation Rate in Draft Tube Spouted Bed Palash Kumar Mollick1,2, Aniruddha Bhalchandra Pandit2, *, Pallippattu Krishnan Vijayan3 1
Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai-400085, India
2
Dept. of Chemical Engineering, Institute of Chemical Technology, Mumbai-400019, India 3
Reactor Engineering Division, Bhabha Atomic Research Centre, Mumbai-400085, India
Abstract: Solid circulation rate in a draft tube spouted bed is an important parameter for its industrial use. It can be manipulated adjusting the dimensions of the draft tube and entrainment height above the gas inlet nozzle and is studied here for a wide range of spouting gas velocities. A maximum entrainment height is identified and seen to show strong correspondence with the ratio between the projected volumes of annulus and spout zones below the draft tube. Overall energy loss at the spout-annulus interface has been reported for the first time as a function of particle size. Solid circulation rate is seen to be highly affected by flow resistance due to the passage of solid flow between conical apparatus wall and the draft tube and solid pressure in the annulus and can be well varied by changing the spouting gas velocity and fixing at a critical value.
Keywords: Spouted bed, draft tube, solid circulation, entrainment height, draft tube diameter, spout-annulus interface.
*Corresponding author: Prof. A. B. Pandit, Email:
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1. Introduction: Spouted bed is an alternative to fixed and fluidized beds and finds application in coal gasification, catalytic particle oxidation, catalytic polymerization, pyrolysis, coating by chemical vapor deposition and catalytic oxidative coupling reactions apart from its conventional uses as a grain dryer and mixer 1-31. Various non-fidelities in conventional gassolid spouted beds such as spout gas bypassing, spout instability at high temperature, limited flexibility to adjust the maximum spoutable bed height and solid circulation rate can be eliminated by using an axially positioned draft tube above the gas inlet nozzle of a conventional spouted bed 8, 9, 11, 32-49. For particles that are too small to attain spouting; Gerald A and B particles as per Gerald’s powder classification, the insertion of a draft tube aids in a better control over solid circulation, narrowing the particle residence time distribution, precise control of gas flow rate and pressure drop at its minimum spouting velocity 8-11. On studying the flow behaviour of a particle in a spouted bed, it has been found that the insertion of a porous draft tube provides a way of controlling the particle history by enhancing mass exchange of a gas phase between the spout and the annulus
33, 36, 39
. It was
also seen that the spouted bed with a non-porous draft tube could reduce the net gas solid contacting efficiency which may rely on particle gas contact and heat transfer coefficient in both the spout and the annulus 10, 34, 37. However, a porous draft tube suffers from a drawback in the sense that the particles can also enter the spout, from the annulus, at all levels manifesting random gas-solid contacting behaviour 33. Particle recycle times and solid circulation rates are highly dependent on the type of draft tube, solid density and contact angle and the draft tube spouted beds can be used for scaling up of spouted beds with a hydrodynamic performance, similar to those without tubes. The desired recycle times of the particles, as per the investigations, can be obtained for the conical spouted bed by choosing a suitable configuration of both the bed material and the 2 ACS Paragon Plus Environment
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draft tube
11, 44
. It was found that magnetic particle tracing was useful for understanding the
dynamics of spouted beds
50
. The bulk solid circulation rate was found to depend on gas
superficial velocity, minimum spouting velocity, density and bed height 9, 35, 40. The particle velocity profiles in the spout of the Draft Tube Spouted Bed (DTSB) are flatter and their variations along the radial position are linear. In the spout of the DTSB, the particle velocity was found to increase with an increase in the superficial gas velocity, entrainment height decreases as the draft tube diameter decreases. The tube diameter and entrainment height (He) serves as a basis for optimizing solid circulation rate in the DTSB9, 35. Here, an attempt has been made to find out the key parameters that influence the solid circulation rate inside a spouted bed with a non-porous draft tube. Minimum spouting velocity (Ums) and solid circulation rate (Rs) have been estimated by varying the diameter of the draft tube (Dt) and at various heights of the entrainment zone (He). A maximum He (max.) is found for various Dt for the first time and reported here correlating with the size of the particles (dp) used. Further, solid circulation rates are studied for various superficial gas velocities with different Dt at different He. Objective of this study was to identify optimum operating zones for a given DT configured SB at various superficial gas velocity. The variation in trends of solid circulation rates are compared with the similar phenomena happens in gas-liquid stirrer tank. The geometrical dimensions of all the symbols & nomenclature are defined in Figure1(a) and are discussed in the next section.
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2. Experimental Section
2.1 Experimental set up Figure 1(a) shows a schematic of the experimental set up used in this study along with all the defined dimensions as above. A transparent body made of poly-carbonate is used as a spouted bed apparatus and the draft tube along with its holder is made of SS340. Photograph of various parts of assemble is shown in Figure 1(b). Draft tube holder assembly is an arrangement to hold the draft tube at the centre inside a ring which is fixed with three metal rods with the cross sectional piece of cylindrical section having similar diameter to that of the cylinder. Draft tube is inserted inside the ring and is tightened by a screw. Entire holder assembly bridges the conical bottom and the cylindrical section of the spouted bed apparatus. Below the top of the DT an opening for particles collection was made, covering 1/6th of the peripheral length with a marginal height required for inserting the collection plate as shown in schematic Figure 1(a). Diameter of the cone (DC) at the top is 90 mm having its conical height (HC) of 90 mm with an inlet orifice size (Di) of 6 mm. Three types of DT having diameter (Dt) 10, 12 and 13 mm of similar height (Dl) 120 mm were used in this study. 2.2 Materials and method Minimum spouting velocity (Ums) was experimentally determined for Zirconia (ZrO2) as solid particles of three different sizes using Argon as a spouting gas. Average density of the zirconia microsphere is 6200 kg/ m3 where as the average size of three particles set are 573, 730 and 890 µm. Size distribution was measured by particle analyzer (Zephyr, Occhio, dry method) and is shown in Figure 2.
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Ums for all the types of particles were determined for DT and conventional spouted beds keeping a constant bed height (H0) at 90 mm (up to conical part of the apparatus). Method of determining Ums for conventional spouted bed is described elsewhere 46. Ums was calculated based on the total flow rate of the Argon gas at the inlet orifice having diameter (Di) of 6 mm. Table 1 presents experimental design along with the aims and experimental conditions. In order to determine Ums for DTSB, tubes were assembled maintaining the intended He and the screw was tightened to fix the intended draft tube. For the DTSB, spouting gas velocity was kept in the higher range (>Ums) and the particles were charged from the top of the apparatus so as to avoid unwanted chocking of the DT with particles. Gas flow was then slowly reduced to attain Qms and hence Ums was estimated for a particular H0, as per the methodology reported elsewhere
46
. Pressure data were collected using both the
pressure sensors via data acquisition card (positions of the sensors are shown in Figure1 (a)). Solid circulation rates (Rs) were also determined using the set up shown in Figure1. For any fixed dp, H0, Dt and He combination, solids were collected using ‘particle collecting tray’ at U= 1.2 to 2.0 Ums over a specified period of time. Area of the particle collecting plate is exactly 1/6th of the cross sectional area of the annulus region, hence total collection of the solid was evaluated as six times of the collected volume of solid for the specified period of time. An optimum time period of 15 seconds were chosen for all the cases to achieve reproducibility and consistent reading to avoid errors due to the reduction in particles volume in the annulus region with time.
3. Results and Discussion 5 ACS Paragon Plus Environment
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3.1. Effect of Draft Tube Diameter (Dt) and Entrainment Height (He) on Minimum Spouting Velocity (Ums) Ums is seen to be always higher for a conventional spouted bed for a constant H0= 90 mm as shown in Figure3, when Argon is used as a spouting gas and Zirconia particles as solids. Ums for Dt = 10, 12 and 13 mm is seen to increase with He nearly linearly. Ums is also seen to increase with Dt at any particular He. It is interesting to note that there is always a maximum He for all the DT used, beyond which solids were not found to be in the circulating mode through the DT and it is linearly proportional to Dt as shown in Figure3 (inset). Ums increases with an increase in He due to an increase in solid flux from the annulus to DT which is a result of increase in the clearance between DT wall and the wall of the conical apparatus. Evidence of an increase in the solid flux is shown and discussed later in detail. Ums is further seen to increase with an increase in Dt. As the diameter of the DT increases, it can accommodate more volume of solids for circulation, necessitating higher velocity of spouting gas hence the Ums. On the other hand, a proportional change in He (max.) is observed with Dt which indicates that there exists a correlation between both the parameters. Hence an attempt has been made to find the volume ratio of two important zones confined within the inlet orifice and the bottom of the DT. Figure4 shows a schematic of two zones namely VA (may be called volume of bed in annulus) and VB (may be called volume of bed above nozzle), ratio of which is calculated and plotted against He, for different Dt in Figure5. Calculated volume ratio of VA and VB for various He and Dt and the corresponding VA by VB ratio at He (max.) are shown in Figure5. It is found that the corresponding VA/VB for He (max.) is slightly above 1.25 and is almost identical for all the Dt used in this work. Therefore, it can be concluded that the VA/VB appears to be the key parameter for any gassolid system to determine He (max.) required for maximum solid circulation in DTSB. However, the ratio is expected to be different for various gas-solid systems and cone angle of 6 ACS Paragon Plus Environment
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the spouted bed apparatus owing to the fact that the properties of gas and solid will be different for different system and the cone angle of SB which dictate the angle of exerted solid pressure force in the latter case. The said volume ratio thus be different as the ratio of pressure within both the zones will be affected by the solid-gas properties as well as the angle of cone of the SB apparatus.
3.2. Effect of Particle size (dp) on Maximum Entrainment Height (He-Max.) Ums was experimentally found out for the conventional spouted beds using various dp and is shown in Figure6. Ums is also found out at an arbitrary and maximum He which is also shown in Figure6 for comparison. Arbitrary He was chosen to be 26 mm which is the maximum He for the biggest size particle (dp = 893 µm of ZrO2) used here. Figure6 therefore proves that the use of DT for the present gas-solid systems is favourable, as Ums for DTSB was always found to be lower than that of conventional spouted bed below He (max.). Ums for both the conventional SB as well as DTSB was found to increase with increasing dp, whereas, He (max.) is found to reduce linearly with an increase in dp (Figure6, inset). Reduction in He (max.) with an increase in dp could be due to an increase in the gas voidage in the annulus region favouring gas escape from the annulus, limiting its contribution to the spouting action at higher He. A constant He was chosen (He = 26 mm) which is He (max.) for dp = 893 µm (ZrO2) and corresponding Ums was experimentally found and is plotted in order to compare Ums for conventional SB for various dp. Difference in Ums for the fixed He (=26 mm) is thus attributed to the energy loss as by the gas due to friction among the moving particles in a counter current manner at the spout-annulus interface. Under similar conditions, calculated kinetic energy loss by the gas stream, is a measure of difference in the Ums for various dp, which is 7 ACS Paragon Plus Environment
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plotted in a logarithmic scale and is shown in Figure7. It is found that the loss of kinetic energy head is linearly increasing with increasing dp. Hence, it can be concluded that the energy loss is not only due to the number of collisions but also due to the particle size & its inertia contributing as well (for a fixed bed height, number of particles at the spout-annulus interface is higher for lower dp and vice versa). Calculated energy loss is seen to be proportional to the dp3 as is expected.
3.3. Effect of Draft Tube Diameter (Dt), Entrainment Height (He) and Spouting Gas Velocity (U) on Solid Circulation Rate (Rs) Solid circulation rate (or volumetric flow rate of solid denoted as Rs, ml/ min.) was experimentally found out using the apparatus described in the experimental section with procedures as described earlier, using 572 µm size particles of ZrO2. Figure8(a) shows the variation of Rs with an increasing He for Dt = 10 mm. Rs is found to increase with He for Dt = 10 mm at lower He. However, it becomes constant after a certain He for U/Ums= 1.2 & 1.5. It is also interesting to note that the Rs continues to increase with He if U/Ums is kept constant at 2.0. As can be seen in the inset of Figure 8 (a), with an increase in the gas velocity (U/Ums), Rs increases owing to the fact that the gas hold up is also increasing along with the solid hold up at a relatively lower He. At a lower, He, developed suction head is higher for a constant spouting gas velocity, as the majority of the gas stream would pass through the DT without bypassing through the annular region. Higher in suction head inside DT, at lower He, results in faster rate of solid loading as compared to gas loading. Higher in the solid loading compared to the gas loading increases the average density of gas-solid mixture inside the DT which constantly reduces the suction head (pressure) inside the DT and thus reduces the 8 ACS Paragon Plus Environment
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inward solid flux from the annulus to DT similar to the phenomena described in gas-liquid stirred tank
51-53
. When the average density of the gas-solid mixture has already reached a
maxima, does not further allow the creation of suction head (pressure) at the centre and at the entrance of the DT and hence does not promote further solids movement from the annulus to the DT for circulation. A numerical result reported by researchers has shown the similar trend showing the saturation in Rs.54 At a relatively higher He, situation is such that the Rs continues to increase if the gas velocity increases from U/Ums = 1.5 to 2.0. This is so happen due to the fact that, at a higher gas velocity, average density of the gas-solid mixture continues to reduce maintaining lesser density than the solid alone and hence promotes developing more suction head inside DT, as a result, Rs increases. Figure 8(b) shows the variation of Rs with He for Dt = 13 mm. Comparing both the Figs. 8 (a) and (b) it is well understood that the Rs, in general is higher for larger Dt. Rs is seen to increase nearly at the same rate with He when corresponding ∆P also shows similar trends for U/Ums= 1.2. However, it shows higher slope for Rs and corresponding ∆P as well, in the case of U/Ums= 1.5 than U/Ums= 1.2. Higher the slope for Rs and corresponding ∆P is so found due to the development of a larger suction head inside the DT at a higher U/Ums and thus solids move at a faster rate from the annulus to DT resulting in a relative increase in Rs. Here again, similar phenomena is happening as was seen for the case in Dt = 10 mm at higher He and U. As we have seen that the requirement of U is higher at a higher Dt (=13 mm) and further the requirement is higher if we increase U up to 1.5 Ums which constantly increases suction head resulting higher in Rs. Figure 9 shows the comparative changes of Rs, ∆P and corresponding U for a constant He = 15 mm and U/Ums = 1.5 for different Dt (here, Ums is changing as the Dt is changing, however, U by corresponding Ums is maintained at 1.5). It is found that the required U 9 ACS Paragon Plus Environment
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increases with an increase in Dt whereas, Rs and the corresponding ∆P is also higher. However, the value of the slope for Rs is higher than the slop for corresponding ∆P at the same time slope for U is further lower, inferring that higher in Dt is favourable to achieve higher Rs. A typical ratio of solid to fluid circulation is estimated to be nearly 66 x 10-3 by v/v (volumetric flow rate of solid to volumetric flow rate of the spouting gas) and the value is about 2.3 if it is presented in w/w (mass flow rate of solid to mass flow rate of fluid), for Dt = 10 mm, He = 15 mm with U/Ums = 1.5. The estimation shows that, more than a double of the mass of the solid is flowing compared to the fluid when the energy resource for such a movement is only associated with the fluid pumping energy only.
4. Conclusions A comparative solid circulation rate has been successfully studied here for different Dt at various He in a DTSB. Three different sizes of zirconia particles were used for this study and the following major findings are reported. •
There exists He (max) for a given Dt and both varies proportionally above which DTSB has no advantage.
•
Volumetric ratio of two zones within the length of He is found to be a constant value and has a strong correspondence with He (max.).
•
Estimated energy loss at the spout-annulus interface is found to be proportional to dp3 inferring that dominant energy loss is due to the particle volume rather than the number of particles present at the interface.
•
In general, solid circulation rate increases with He and Dt, however, fixing up a required U/Ums would be decided carefully in order to operate the DTSB away from 10 ACS Paragon Plus Environment
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critical solid hold up condition, where the average density of gas-solid mixture saturates.
Acknowledgement: Authors sincerely acknowledge financial support received from Bhabha Atomic Reseach Centre, Mumbai, India for this work. Dr. Madangopal Krishnan and Prof. D. Sathiyamoorthy are acknowledged for their valuable suggestions and technical discussion.
Abbreviations: DT
draft tube
DT-SB
draft tube spouted bed
SB
spouted bed
Nomenclature Dt
diameter of draft tube, (mm)
Dc
diameter of the conical section, (mm)
dp
diameter of solid particle, (µm)
Hc
height of the conical part, (mm)
Hdt
height of the draft tube, (mm)
He
height of the entrainment zone below draft tube, (mm) 11 ACS Paragon Plus Environment
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H0
height of particulate bed, (mm)
∆P
pressure drop across bed, (Pa)
∆PHe
pressure drop by gas phase till entrainment height (till bottom of the DT), (Pa)
p
pressure, (Pa)
Q
volumetric flow rate of fluid, (ml/min)
Rs
volumetric flow rate of solid, (ml/min)
u
gas velocity, in general term, (m/s)
U
superficial gas velocity of spouting gas, (m/s)
Ums
minimum spouting velocity, (m/s)
Greek letters
ρ
density of gas, (kg/m3)
ρp
density of solid, (kg/m3)
Ƞ
solid loading coefficient, (-)
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(24) Lopez, G.; Alvarez, J.; Amutio, M.; Arregi, A.; Bilbao, J.; Olazar, M. Assessment of steam gasification kinetics of the char from lignocellulosic biomass in a conical spouted bed reactor. Energy 2016, 107, 493-501. (25) Arregi, A.; Lopez, G.; Amutio, M.; Barbarias, I.; Bilbao, J.; Olazar, M. Hydrogen production from biomass by continuous fast pyrolysis and in-line steam reforming. RSC Adv. 2016, 6 (31), 25975-25985. (26) Erkiaga, A.; Lopez, G.; Barbarias, I.; Artetxe, M.; Amutio, M.; Bilbao, J.; Olazar, M. HDPE pyrolysis-steam reforming in a tandem spouted bed-fixed bed reactor for H2 production. J. Anal. Appl. Pyrolysis 2015, 116, 34-41. (27) Lopez, G.; Erkiaga, A.; Artetxe, M.; Amutio, M.; Bilbao, J.; Olazar, M. Hydrogen Production by High Density Polyethylene Steam Gasification and In-Line Volatile Reforming. Ind. Eng. Chem. Res. 2015, 54 (39), 9536-9544. (28) Moliner, C.; Curti, M.; Bosio, B.; Arato, E.; Rovero, G. Experimental Tests with Rice Straw on a Conical Square-Based Spouted Bed Reactor. Int. J. Chem. React. Eng. 2015, 13 (3), 351-358. (29) Coelho, R.M.D.; Araújo, A.D.A.; Fontes, C.P.M.L.; da Silva, A.R.A.; da Costa, J.M.C.; Rodrigues, S. Powder lemon juice containing oligosaccharides obtained by dextransucrase acceptor reaction synthesis and dehydrated in sprouted bed. Journal of Food Science and Technology 2015, 52 (9), 5961-5967. (30) Artetxe, M.; Lopez, G.; Amutio, M.; Barbarias, I.; Arregi, A.; Aguado, R.; Bilbao, J.; Olazar, M. Styrene recovery from polystyrene by flash pyrolysis in a conical spouted bed reactor. Waste Management 2015, 45, 8
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(31)Borini, G.B.; Andrade, T.C.; Freitas, L.A.P.; Hot melt granulation of coarse pharmaceutical powders in a spouted bed. Powder Technol. 2009, 189 (3), 520-527. (32) Mollick, P. K.; Goawami, P. S.; Krishnan, M; Vijayan, P. K.; Pandit, A. B. A Novel Approach to Correlate Heat Transfer and Pressure Fluctuation in Gas-Solid Spouted Bed. Particuology, 2018, Accepted [DOI-] (33) Shuyan, W.; Yongjian, L.; Yikun, L.; Lixin, W.; Qun, D.; Chunsheng, W. Simulations of flow behavior of gas and particles in spouted bed with a porous draft tube. Powder Technol. 2010, 199, 238–247 (34) Makibar, J.; Fernandez-Akarregi, A. R.; Diaz, L.; Lopez, G.; Olazar, M. Pilot scale conical spouted bed pyrolysis reactor: Draft tube selection and hydrodynamic performance. Powder Technol. 2012, 219, 49–58. (35) Estiati, I.; Altzibar, H.; Tellabide,M.; Olazar, M. A new method to measure fine particle circulation rates in draft tube conical spouted beds. Powder Technol. 2017, 316, 87–91. (36) Nagashima, H.; Suzukawa, K.; Ishikura, T. Hydrodynamic performance of spouted beds with different types of draft tubes. Particuology 2013, 11, 475– 482. (37) Makibar, J.; Fernandez-Akarregi, A.R.; Alava, I.; Cuev, F.; Lopez, G.; Olazar, M. Investigations on heat transfer and hydrodynamics under pyrolysis conditions of a pilot-plant draft tube conical spouted bed reactor, Chem. Eng. Pros. 2011, 50, 790– 798. (38) Azizia, S.; Hosseinib, S. H.; Moravejia, M.; Ahmadic, G. CFD modeling of a spouted bed with a porous draft tube. Particuology 2010, 8, 415–424. (39) Altzibar, H.; Lopez, G.; Bilbao, J.; Olazar, M. Minimum Spouting Velocity of Conical Spouted Beds Equipped with Draft Tubes of Different Configuration. Ind. Eng. Chem. Res. 2013, 52, 2995−3006. 17 ACS Paragon Plus Environment
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(40) Luo, K.; Yang, S.; Zhang, K.; Fang, M.; Fan, J. Particle Dispersion and Circulation Patterns in a 3D Spouted Bed with or without Draft Tube. Ind. Eng. Chem. Res. 2013, 52 9620−9631. (41) Hosseini, S. H. Influences of geometric factors on CFD results of a Draft tube cylindrical spouted bed. Prog. Comput. Fluid Dyn. 2016, 16, (2), 78-87. (42) Yang, S.; Luo, K.; Fang, M.; Zhang, K.; Fan, J. Numerical Investigation of the GasSolid Flow Characteristics in a Three-Dimensional Spouted Bed with a Draft Tube. Chem. Eng. Technol. 2013, 36 (12), 2035–2043. (43) Altzibar, H.; Lopez, G.; Bilbao, J.; Olazar, M. Effect of Draft Tube Geometry on Pressure Drop in Draft Tube Conical Spouted Beds. Canadian J. Chem. Eng. 2013, 91, (44) Altzibar, H.; Lopez, G.; Estiati, I.; Bilbao, J.; Olazar, M. Particle Cycle Times and Solid Circulation Rates in Conical Spouted Beds with Draft Tubes of Different Configuration. Ind. Eng. Chem. Res. 2013, 52, 15959−15967. (45) Altzibar, H.; Lopez, G.; Bilbao, J.; Olazar, M. Operating and Peak Pressure Drops in Conical Spouted Beds Equipped with Draft Tubes of Different Configuration. Ind. Eng. Chem. Res. 2014, 53, 415−427. (46) Mollick, P.K.;
Sathiyamoorthy, D.; Assessment of stability of spouted bed using
pressure fluctuation analysis. Ind. Eng. Chem. Res. 2012, 51 (37), 12117-12125. (47) Freitas, L.A.P.; Freire, J.T. Heat transfer in a draft tube spouted bed with bottom solids feed, Powder Technol. 2001, 114 (1-3), 152-162. (48) Sathiyamoorthy, D.; Govardhana Rao, V.; Rao, P.T.; Mollick, P. K. Development Of Pyrolytic Carbon Coated Zirconia Pebbles In A High Temperature Spouted Bed. Indian J. of Eng. Mat. Sci. 2010, 17, 349-352. 18 ACS Paragon Plus Environment
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(49) Souza, C. R. F.; Oliveira, W. P. Drying of Herbal Extract in a Draft-Tube Spouted Bed. Canadian J. Chem. Eng. 2009, 87, 279-288. (50) Patterson, E. E.; Halow, Jack Innovative Method Using Magnetic Particle Tracking to Measure Solids Circulation in a Spouted Fluidized Bed. Ind. Eng. Chem. Res. 2010, 49, 5037–5043. (51) Sun, H.; Mao, Zai-Sha; Yu, G. Experimental and numerical study of gas hold-up in surface aerated stirred tanks. Chem. Eng. Sci. 2006, 61, 4098 – 4110. (52) Vesselinov, H. H.; Stephan, B.; Uwe, H.; Holger, K.; Gunther, H.; Wilfried, S. A study on the two-phase flow in a stirred tank reactor agitated by a gas-inducing turbine. Chem. Eng. Res. Des. 2008, 86, 75-81. (53) Abdullah, B.; Dave, C.; Nguyen, Tuan-Huy; Cooper, C. G.; Adesina, A. A. Electrical resistance tomography-assisted analysis of dispersed phase hold-up in a gas-inducing mechanically stirred vessel. Chem. Eng. Sci. 2011, 66, 5648 – 5662. (54) Shuyan, W.; Zhenghua, H.; Dan, S.; Yikun, L.; Lixin, W.; Shuai, W. Hydrodynamic simulations of gas–solid spouted bed with a draft tube. Chem. Eng. Sci. 2010, 65, 1322– 1333.
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Table-1: Experimental design Expts.
Aim
Average size of ZrO2 particle , (µm)
DT configuration at a constant H0 = 90 mm
Operating condition/ remarks
1
Determination of He (max.)
903
He =Variable
At Ums
a) Determination of He (max.) for different particle size, dp
572, 733, 903
2
Dt = 10, 12 and 13 mm
b) He = 26 mm (corresponding to He (max.) for dp = 903 µm)
b) Finding the effect of dp on kinetic energy loss at spout-annulus interface 3
Estimation of solid circulation rate, Rs
a) He = He (max.) for different dp
903
He =Variable
At Ums and comparison with Ums for conventional spouted bed
U/Ums = 1.2-2.0
Dt = 10, 12 and 13 mm
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(a)
(b) Fig. 1 (a) Schematic and (b) photograph of the experimental apparatus
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Page 22 of 27
Fig. 2 Particle size distributions (thick line corresponds to cumulative distribution and thin line corresponds to differential distribution by volume %)
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Page 23 of 27
55
Spouting zone without DT Ums for Conventional Spouted Bed (at H0 = 90 mm)
45
Spouting zone with DT
40
Dt = 10 mm
No spouting zone
Dt = 12 mm Dt = 13 mm
35
He (max.)
50
30 25 20
50
Ums
45
Ums , m/s
Ums, m/s
50
45
He (max.)
40
40
35
35
30
30
25
He (max.), mm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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25 10
11
12
13
Dt, mm
15 0
10
20
30
40
50
60
70
80
90
He, mm
Fig. 3 Change in Ums with He for different Dt
Fig. 4 Schematic of two distinct zones (A & B) within He.
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3.0 Calculated VA/VB at He(max.)
2.5
VA/VB, -
2.0
Dt= 10 mm Dt= 12 mm Dt= 13 mm
1.5 1.0 0.5 0.0 10
20
30
40
50
He, mm
Fig. 5 Calculated change in VA/VB with He for different Dt
100 60
Ums
Dt = 12 mm
90 Ums, m/s
80
He (max)
55 50
40
35
45 30
Ums, m/s
70
He (max), mm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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40
Without draft tube Ums at He = 26 mm
25
35 600
700
60
800
900
dp, micron
Ums at He (max.) 50 40
Dt = 12 mm
30 500
600
700
800
900
1000
dp, micron
Fig. 6 Change in Ums with dp
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Page 25 of 27
7.8 7.6
Equation Adj. R-Square
y = a + b*x 0.99456
B
Intercept
B
Slope
7.4 7.2
1.04886
3.05065
0.15934
7.0 6.8
2
2
Standard Error
-13.07736
Slope ~ 3.0
2
3
ln (U /2 *(ρ)), m /s (*kg/m )
Value
6.6 6.4 6.2 6.3
6.4
6.5
6.6
6.7
6.8
ln (dp), micron
Fig. 7 Change in kinetic energy with dp
300
100
600
80
250 60
500
Rs, ml/min.
40
He = 10 mm
20
400
He = 20 mm He = 30 mm
150
0 1.2
1.4
1.6
1.8
2.0
300
U/Ums, (-)
100
∆P, Pa
200 Rs, ml/min.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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200
50 0 5
10
15
20 He, mm
Rs,
∆P, U/Ums= 1.2
Rs,
∆P, U/Ums= 1.5
Rs,
∆P, U/Ums= 2.0
25
30
35
100 0
(a) Dt = 10 mm
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300 250
600
He = 10 mm He = 20 mm
200
He = 30 mm
Rs, ml/min.
250
500
He = 41mm
150 100
400
50 1.2
150
1.4
1.6 U/Ums, (-)
1.8
2.0
300
100
∆P, Pa
Rs, ml/min.
200
200
50
R s,
∆P, U/Ums= 1.2
R s,
∆P, U/Ums= 1.5
100
0 0
5
10
15
20 25 He, mm
30
35
0 45
40
(b) Dt = 13 mm
Fig. 8 Change of Rs and ∆P with He for different U/Ums
300
U, m/s Rs, ml/min.
45
90
∆P, Pa
275
Constant: H e = 15 mm
250
U, m/s
∆P, Pa
40
80
Rs, ml/min.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 26 of 27
U/U ms = 1.5
35
70
225 200
30
60
25
50
175 10
11
12
13
D t, mm
Fig. 9 Comparative changes among Rs, ∆P and corresponding U at a constant He and U/Ums 26 ACS Paragon Plus Environment
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Schematic of draft tube spouted bed for experimental studies of solid circulation rate
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