- Email: [email protected]
Phase holdup characteristics in three phase fluidized beds
The Chemwal
Engrneermg
Phase Holdup
JOOH
43 (1990)
Characteristics
67
- 73
67
in Three Phase Fluidized
Beds
HAN
Department (Korea) GABRIEL Laboratowe SANG
Journal,
of Chemwal
Engmeerrng,
Korea
Advanced
Institute
of Science
and Technology,
Seoul.
130-650
WILD des Sciences
du Geme
Chlmrque
CNRS-ENSIC,
I rue Crandudle,
54042
Nancy
Cedex
(France)
D KIM*
Department (Korea) (Received
of Chemical
June
8, 1989,
Engmeermg,
Korea
Advanced
In final form September
Institute
of Scwnce
and Technology,
Seoul.
130-650
9. 1989)
ABSTRACT
1 INTRODUCTION
The bed porosity and the mdrvzdual phase holdup characterlstlcs m three phase flurdlzed beds with a wide range of hquld properties have been examined The effects of liquid and gas velocltles, particle size, column diameter and liquid properties such as vlscoslty and surface tension on the mdwtdual phase holdup and bed porosrty m three phase fluldlzed beds have been determined The liquid phase holdup increases with llquld velocity and vlscoslty, column dlameter and lrqutd surface tension, it decreases with gas velocity, particle size and the density difference between sohd and liquid phases The bed porosity increases with hquld velocltres and vlscosl ty, whereas it decreases wl th mcreasmg particle size, liquid surface tension and the density difference between sohd and liquid phases Bed porosity increases with gas velocity m the mltlal bed expansion regime, but it shows a mmimum value wrth respect to gas velocity m the m&al bed contraction regime The liquid phase holdup and the bed porosrty data have been combined with over 5000 pomts from the literature to yield dimensionless correlations
A three phase fluldlzed bed, as defmed m this study, 1s a batch of solid particles which are fluldlzed by concurrent upflow of liquid as the contmuous phase, and gas as the dlspersed bubble phase Recently, the apphcatlons of three phase fluldlzed bed reactors have been Increasing in the chemical and blochemlcal processing fields Therefore, the hydrodynamic properties such as the phase holdups, bubble properties and mixing characteristics have to be studied m order to provide the basic mformatlon required for designing these fluldlzed bed reactors Among the hydrodynamic properties, the most Important for analyzmg the performance of a three phase fluldlzed bed reactor are the bed porosity and the mdlvldual phase holdups Various aspects of these fluldlzed bed reactors have been reviewed by several mvestlgators [ 1 - 91 The bed porosity and the mdlvldual phase holdups have been determined by means of pressure gradient, electroreslstlvlty probe and optical fiber probe methods, and by sunultaneous closure of the gas and liquid feeds From the probe methods, it has been found that the solid phase holdup near the top of the bed slowly decreases along the expanded bed height m a transltlon region from the mam three phase fluldlzed bed to a two-phase gas-liquid region above the bed However, m the mam fluldlzed bed region, the phase holdups are very uniformly dlstnbuted across the bed [lo - 111 Therefore,
*Author addressed
to
0300-9467/90/$3
whom
50
correspondence
should
be
@ Elsevler
Sequora/Prmted
In The Netherlands
68
we shall consider the mean values of the holdups and bed porosity m the bed. In addltlon, the gas holdup values obtamed from the probe methods are somewhat lower than those from the pressure gradient method [12] However, m general, the difference 1s found to be mslgnlflcant On the other hand, comparmg the pressure gradient method with the simultaneous closure method showed that the former provides a systematic underevaluation of gas holdup, when the column diameter 1s below 0 08 m [13] There 1s plenty of data ‘available m the literature’ on phase holdups and bed porosity m three phase fluldlzed beds However, this data has not been compiled since the Begovlch and Watson [lo] compllatlon about 10 years ago Therefore, m this study, the phase holdup and bed porosity data of the present and previous studies have been summarized, dlmenaonless correlations on liquid phase holdup and bed porosity m three phase fluldlzed beds are presented These correlations take mto account the effects of liquid and gas velocltles, surface tension of hquld phase, particle size, column diameter and density of liquid phase
2
EXPERIMENTAL
Experunents were carried out m a bench scale(lBmh~hX152mmID)andapllot plant scale (2 1 m high X 376 mm I D ) Plexlglas column as shown m Fig 1 Pressure taps were mounted flush with the wall of the
column at 75 mm height intervals from the dlstnbutor The static pressure at each of these pomts was measured with a hquld manometer The solid particles were supported on a grid, under that grid, a perforated stamless steel plate with evenly spaced holes of 3 mm I D (156 holes for smaller column, 786 holes for larger column) was used as a liquid dlstrlbutor The distributor was situated between the mam column sectlon and the distributor box The hquld flow rate was measured with two calibrated flowmeters and regulated by means of globe valves on the feed and bypass lmes Oil-free compressor au- was fed to the column through a pressure regulator, a filter and two calibrated flowmeters It was admltted to the bed through 4 and 19 evenly spaced 6 4 mm I D perforated feed pipes m the smaller and larger dlstnbutors, respectively With this arrangement, a triangular pitch can be placed on the surface of the dlstrlbutor plate with 26 and 232 holes of 1 0 mm I D , respectively Seven different sizes of glass beads (1 0, 1 7, 2 3, 3 0, 3 7,6 0, 8 0 mm) with a density of 2500 kg m -3 were used as the sohd phase, air as the gas phase, and tap water and aqueous solutions of glycerol as the llquld phase Details of the experlmental variables and their ranges are summarized m Table 1 The bed porosity was determmed by measurmg the dry mass of the sohd and the bed height, which was taken as the pomt at which a change m slope of the pressure profile was observed The gas and hquld holdups were obtained by measurmg the slope of the pressure prohle m the three-phase bed The descrlptlon of these classical techmques may be found m Wild et al [4]
3 RESULTS
Fig 1 SchematIc diagram of experlmental apparatus (0, = 152 mm I D ) 1 Mam column, 2 pressure taps, 3 dlstrlbutor box, 4 dram, 5 flowmeters, 6 centrlfugal pump, 7 hquld reservoir, 8 pressure regulator
AND DISCUSSION
3 1 Effect of gas velocrty The bed porosity c is an mcreasmg function of liquid velocity and hquld vlscoslty It 1s a decreasmg function of particle diameter and density difference between the sohd and the hquld Smce the paper by Masslmllla et al [14] was published the influence of gas velocity has been a well debated SUbJeCt for almost 30 years In some cases, bed porosity decreases as a function of the gas velocity 1 e the bed contracts at the mtroduc-
69 TABLE Ranges
1 of experlmental
Weight of glycerol
variables
c11 Pa
s)
CJ, (mN m-l)
d, (mm)
UI (m s-l)
Us (m s-l)
72 66 64 62
10 80 23-80 30-80 30-80
0 01 0 01 0 01 001
O-012 o-o 12 O-012 0 012
(S) 00 75 0 83 0 86 0
0 0 0 0
001 020 040 060
8 5 1 8
tion of the gas m a liquid solid fluldlzed bed This behavior 1s usually observed with highly expanded beds conslstmg of small particles (d,, < 2 5 mm) [15] As can be seen m Fig 2(a), the bed porosltles of smaller particles (dp 5 2 3 mm) reach a mmunum with mcreasing gas velocity The commonly accepted explanation 1s that the bubble wakes of large bubbles entram hquld which 1s no longer avtiable to fluldlze the solid particles However, as can be seen, the bed porosity mcreases with mcreasmg gas velocity in the beds of larger particles due to the bubble breakage by the larger mertla of particles (Fig 2(a)) On the other hand, the expanded bed height with a further mcrease m liquid vlscoslty contracts as gas velocity IS Increased, as can be seen m Fig 2(b)
- 0 14 - 0 12 - 0 10 010
The mertlal force of the particles decreases and the boundary layer thickness on the bubble surface mcreases with an increase m liquid vlscoslty Consequently, the larger particles cannot easily penetrate through the bubbles [16] Therefore, it can be claimed that bubbles m the highly viscous solutions (p, 2 40 mPa s) are coalescmg regardless of particle sizes 3 2 Effect of llquld phase mcoslty In the present study the liquid vlscoslty has been vmed from 1 to 60 mPa s with aqueous glycerol solutions. The bed porosity or expanded bed height and liquid holdup dlrectly mcrease with liquid vlscoslty due to the mcrease of drag force on the particles As can be seen m Fig 3, a sumlar trend [17] has been observed m the beds of 6 mm glass beads
06
06
0
2
4
6
8
10
12
UgxlOO m/s
Fig 2 Effect of gas velocity on bed porosity m two and three phase fluldlzed beds of different hquld VlSCOSl t>
1
5
10
50
100
J+ or k. mPas ormPusm Fig 3 Effect of hquld vlscoslty on (a) bed porosity and (b) hquld holdup m two and three phase fluldlzed beds of 8 mm glass beads (UJ = 0 1 m s-‘)
70
with carboxymethyl cellulose (CMC) solutions However, the shape of the bed porosity and liquid holdup curves is different since the CMC solution has a non-Newtonian fluid behavior with a lower apparent vlscoslty m the beds Therefore, the bed porosity and liquid holdup mcrease non-linearly m the beds with CMC solutions 3 3 Effect of column drameter
scale-up
effect
The effect of column size on gas and liquid phase holdups and bed porosity 1s shown m Fig 4 with the data of the present and prevlous studies [l&19] As can be seen, the gas holdup decreases slightly with mcreasmg column diameter up to 0.254 m, since the bubbles may rise more freely than those m the smaller column [lo], thereafter, it does not change appreciably The liquid holdup, however, shows a reverse trend, (Fig 4(b)), while the bed porosity IS nearly independent of column diameter from D, = 0 1 to D, = 0 376 m
tlon [3] The mam drawback of these models 1s that one needs reliable correlations of the volume of the bubble wakes and of their solid content However Wild et al [20] were able to correlate their results by combmmg a bubble wake model with a correlation of the slip velocity, Nacef et al [21] showed that this approach can be generalized when a slip velocity correlation adapted to the dlstrlhutor used IS known One of the ObJectives of this study 1s to develop a general correlation by using a data base as large as possible Therefore, a large amount of expenmental data - more than 5000 data points - were considered, covermg a wide range of experunental condltlons [l&19,22 - 461 The new dlmenslonless correlations of the liquid holdup and bed porosity m three phase fluldlzed beds which have been proposed in this study are based on the Richardson and Zakl equation [47] They take the following general form (E, or E) = (U, Ut-‘)““f(U,,
1 CORRELATIONS
where
There are two mam techniques by which we can try to represent the phase holdups m gas-hquld-solid fluldlzed beds We can use the bubble wake models which have been summarized m a previous pubhca-
f(U,,
100
150
200
250 300 350 Ul0 DC mm Fig 5 Effect of column diameter on hquld holdup and bed porosity m three phase fluldlzed beds of 6 mm glass beads (/.I, = 1 0 mPa s)
019 Wug=
ol, DC)
(1)
o= 1
The best way to determme the terminal velocity U, and the index n of the hquldsolid fluldlzed bed IS by experiment, since they are strongly dependent on the particle diameter and shape. On the other hand, the experimental determmatlon may be done m a small scale column, smce both coefflclents are independent of the distributor If that 1s not possible, however, we may calculate Ut and n from equations m the literature [48] Recently two new correlations of the index n have been proposed, by Carey [49] and by Rowe [ 501. In previous studies [32, 511, the correlations of liquid and solid phase holdups m three phase fluldlzed beds have been proposed based on the Rlchardson and Zakl equation [ 471 However, the correlation of Kato et al [32] can predict only liquid phase holdup, whereas the correlation of Jean and Fan [ 511 predicts bed porosity only in the u-utlal expansion beds with lower vscous solutions in three phase fluldlzed beds with a margmal accuracy as can be seen m Fig 5 The hquld holdup and bed porosrty have been correlated m the followmg form
71
Lrquld holdup (1 - 0 374Fr,’
176We,-o
‘73)
(2)
m which the range of variables covers 0 054 G (U,/U,) < 0.899, 0 395 X 10m4 < Fr, Q 2 551, 0 918 X 10m3 < We,,, < 5 013 with a correlation coefflclent of 0.921 and a relative standard deviation of 8 7% for 2875 data polnts Bed porosl ty The data points were separated into two categories, according to the expansion or contraction of the bed upon uyectlon of gas into a liquid fluldlzed bed a) Inrtlal expansion (1 + 0 123Fr,O 0
2
4
6 8 10 UgxlOO m/s
12
14
Fr, < 3 788,O 895 X 10m2 < We, < 5 479 with a correlation coefflclent of 0 912 and a relative standard deviation of 6 4% for 1946 data pomts
2
Comparison Authors number
(3)
m which the range of variables covers 0 029 < (U,/U,) < 0 481, 0.173 X 1O-4 <
Fig 5 Comparisons of (a) hquld holdup, (b) bed porosity m the mltlal expansion resme and (c)bed porosity In the lmtlal contractlon regime In two and three phase fluldlzed beds between the present and previous studies
TABLE
347We,,,o 03’)
of empIrIca
or equation
Dakshlnamurty et al 127,281 Klmetal [15] Begovlch and Watson
correlations
of hquld holdup
cl (2875)a RC
and bed porosity
In three phase fluldlzed
beds
e SD(W)
IER ( 1946)a
ICR (1121)a
RC
SD (%)
RC
SD (%)
0 892
14 4
0 858
33 8
-
-
0 802 -
18 2 -
0 791 0 817
10 7 95
0 693 0 732
12 9 11 2
0 202 0 866
1418 11 3
0 751 -
25 -I -
0 562 -
l-1 4 -
0 812
18 2
0 827
18 8
0 779
32 6
-
-
0 912 -
-
-
-
1101 Razumov et al [46] Kato at al [ 321 SaberIan-Brodlenni eta1 [13] Eqn Eqn Eqn
(2) (3) (4)
0 921
-
aNumber of data pomts IER. Inltlal expansion regime ICR, Inltlal contractlon regime RC, RegressIon coefflclent SD, relative standard devlatron
87 -
64
0 860
70
72 b)
Per S&oft,
Inltlal contractron
Teknlsk
Forlag,
Copenhague,
1977,
p 165
0 359Fr,O ‘52We,0 121
Fr go 5 where the range of vanables covers 0 024 < (UJU,) < 0 899, 0.928 X 10h4 < Fr, < 2 551, 0 659 X 1O-4 < We, < 1 529 with a correlation coefficient of 0 860 and a relative standard deviation of 7 0% for 1121 data pomts The goodnesses-of-fit between eqns (2) (4), the emplrlcal correlations of previous studies [lo, 13, 15, 27, 28, 32, 46, 511 and the present experimental data are shown m Fig 5 The advantages of the correlations presented here are the followmg they have a large experimental basis and the correlation coefficients are much better than those of the other correlations m the literature, as shown m Table 2 In summary, the liquid phase holdup mcreases with liquid velocity, hquld vficoslty, column diameter and liquid surface tension, it decreases with increasing gas velocity, particle size and the density difference between sohd and liquid phases The bed porosity increases with liquid velocltles and liquid vlscoslty, whereas it decreases with mcreasmg particle size, liquid surface tension and the density difference between solid and liquid phase It increases with gas velocity m the mltlal bed expansion regime, but it shows a mmunum value m the mltlal bed contraction regime The liquid phase hold up and the bed porosity data have been combmed with over 5000 pomts from the literature to yield the dlmenslonless correlations
2 N Epstem, Can J Chenz Eng, 59 (1981) 649 3 C G J Baker In A E Rodrlgues, J M Calo and N H Sweed (eds ), Multiphase Chemxol Reactors Vol II Design, Sljthoft & Noordhoff, Alphen aan den Rljn, 1981, p 343 4 G Wild, M SaberIan-BrodJenm J L Schwartz and J C Charpentler, Int Chem Eng, 24 (1984) 639 5 K Muroyama and L S Fan, AfChE J, 31 (1985) 1 6 W D Tech,
7
8 9 10
11 12 13
14 15
16 17 18 19 20
21 22
ACKNOWLEDGMENT
We acknowledge a Grant-m-Ad of research from the Korea Science and Engmeermg Foundation
23
24
REFERENCES
25
1 K Bstergaard, In K sstergaard and Aa Fredenslund (eds ), Chemwal Engrneermg with
26
Deckwer and A Schumpe, Chem Ing 55 (1983) 591 H I de Lasa and S L P Lee, NATO ASI Chem~a1 Reactor Design and Technol, London, Canada, 2 12 June 1985 Y H Yu and S D Ktm, Chem Ind Technol, 4 (1986) 11 (In Korean) L S Fan, Gas-Llqwd-Sohd Fluldlzatron Engmeermg, Butterworths, Boston, 1989 J M Begovlch and J S Watson, In J F Davldson and D L Kealrns (eds ), Flutd~zatron, CambrIdge Umverslty Press, UK, 1978, p 190 S L P Lee and H I de Lasa, AfChE J, 33 (1987) 1359 Y H Yu and S D Kim, 4IChE J, 34 (1988) 2069 M Saberian-Broudjennl, G Wild, J C Charpentler, Y Fortm, J P Euzen and R Patoux, Int Chem Eng, 27 (1987) 423 L Masslmllla, N Majurl and P Signormi, La Rlcerca ScrentIfica, 29 (1959) 1934 S D Kim, C G J Baker and M A Bergougnou, Can J Chem Eng, 53 (1975) 131 Y M Chen and L S Fan, Chem Eng SCI, 44 (1989) 117 S D Kim, Ph D Thesis, Unlverslty of Western Ontario, 1974 G T Jm, Ph D Thesis, Korea Advanced Institute of Science and Technology, Seoul, 1985 Y H Yu, Ph D Theses. Korea Advanced Institute of Science and Technology, Seoul, 1989 G Wild, M Saberlan Broudjenni and J C Charpentler, In B D Kulkarnl, R A Mashelkar and M M Sharma (eds ), Recent Trends rn Chemwal Reactlon Engrneermg, Vol 2, Wiley Eastern Ltd , New Delhi, Tndla, 1987, p 531 S Nacef, G Wild, A Laurent and S D Kim, Entropre, 143/144 (1988) 83 J M Begovlch, MS Thesis, Oak Ridge National Laboratory, Massachusetts Institute of Technology, Oak Ridge, 1978 V K Bhatla and N Epstem, Proc Int Symp Fluzdrratlon and Its apphcatlons, H Angehno et al (eds ), Editions Cepadues, Toulouse, France, 1971, p 380 V R Bloxom, J M Costa, J Herranz, G L MacWllham and S R Roth, Oak Ridge National Laboratory, Massachusetts Institute of Technology, Oak Ridge. 219 1975 T M Chlu, Ph D Theses, Polytechmc Instrtute, New York, 1982 T M Chlu and E N Ziegler, AlChE J, 31 (1985) 1504
73
V Subrahmanyam and J N 27 P Dakshmamurty, Rao, Ind Eng Chem Process Des Dew, 10 (1971) 322 28 P Dakshmamurty, K Rao, K V SubbaraJu and V Subrahmanyam, Ind Eng Chem Process Des Deu, I1 (1972)318 29 V R Dhanuka and J B Stepanek, In J F Davldson and D L Kealrns (eds ), Flulduatlon, CambrIdge Unlverslty Press, UK, 1978, p 179 30 G I Efremov and I A Vakhrushev, Int Chem Eng. 10 (1970) 37 31 H S Jang, hlS Theas, Umverslty Soong Jeon, Seoul, 1978 32 Y Kato, K Uchlda, T Kago and S Morooka, Powder Technol, 28 (1981) 173 33 S D Kim, C G J Baker and M A Bergougnou, Can J Chem Eng , 50 (1972) 695 34 H K Kwon, his Thesls, Korea Advanced Instatute of Science and Technology, Seoul, 1985 35 D H Lee, 61 S Thests, Korea Advanced Institute of Science and Technology, Seoul, 1986 36 H K Lee, 111S Thesw, Korea Advanced Institute of Science and Technology, Seoul, 1985 37 M L Mlchelsen and K P)stergaard, Chem Eng J, 1 (1970) 37 38 R N Mukherjee, P Bhattacharya and D K Taraphdar, Proc Int Symp on Flulduatron and its Apphcotlons, 197-1, p 372 39 K &tergaard, Chem Eng Scr , 20 (1965) 165 40 G R Rlgby and C E Capes, Can J Chem Eng , 48 (1970) 343 41 M Saberian-BroudJenm, These de Docteurmgemeur, IPNL, Nancy, 1984 12 M Saberian-Broudjenni, These de Docteur es Sciences Phqslques, INPL Nancy, 1985 -%3 W Y Soung, Ind Eng Chem Process Des Dw , 17 (1978) 33 4-L I S Suh, hlS Theses, Korea Advanced Institute of Science and Technology, Seoul, 1982 45 S Khosrowshahl, S R Bloxom, C Guzman and R hl Schlapfer. Oak Ridge National Laboratory,
46 47 48
49 50 51
Massachusetts Institute of Technology, Oak Ridge, 216 1975 I M Razumov, V V Manshlhn, and L L Nemets, Int Chem Eng , 13 (1973) 57 J F Richardson and W N Zakl, Trans Instn Chem Engrs, 32 (1952) 35 D Kunn and 0 Levensplel, Fluldrzatlon Engrneermg, John Wiley and Sons, Inc , New York (1969) 76 V P Carey, Int J Multlphase Flow. 13 (1987) 429 P N Rowe, Chem Eng Scl , 42 (1987) 2795 R H Jean and L S Fan, Chem Eng Scr, 41 (1986)
2823
NOMENCLATURE
DC
4 Frs k 171 n
Re u!z u, K We,
column diameter, m particle diameter, m gas Froude number, U,* (d,g)-’ fluid consistency index, Pa s’” power law index Richardson and Zakl’s index Reynolds number, (U,d,p,) p,-’ superficial gas phase velocity, m SC’ superficial liquid phase velocity, m SC’ termmal velocity of particle, m SC’ modified Weber number, (U,‘p,D,) -1 01
Greek symbols E bed porosity
f, El
IJl PI
021
gas phase holdup liquid phase holdup vlscoslty of hquld phase, Pa s density of hquld phase, kg m-j surface tension of liquid phase, N m-’
Engrneermg
Phase Holdup
JOOH
43 (1990)
Characteristics
67
- 73
67
in Three Phase Fluidized
Beds
HAN
Department (Korea) GABRIEL Laboratowe SANG
Journal,
of Chemwal
Engmeerrng,
Korea
Advanced
Institute
of Science
and Technology,
Seoul.
130-650
WILD des Sciences
du Geme
Chlmrque
CNRS-ENSIC,
I rue Crandudle,
54042
Nancy
Cedex
(France)
D KIM*
Department (Korea) (Received
of Chemical
June
8, 1989,
Engmeermg,
Korea
Advanced
In final form September
Institute
of Scwnce
and Technology,
Seoul.
130-650
9. 1989)
ABSTRACT
1 INTRODUCTION
The bed porosity and the mdrvzdual phase holdup characterlstlcs m three phase flurdlzed beds with a wide range of hquld properties have been examined The effects of liquid and gas velocltles, particle size, column diameter and liquid properties such as vlscoslty and surface tension on the mdwtdual phase holdup and bed porosrty m three phase fluldlzed beds have been determined The liquid phase holdup increases with llquld velocity and vlscoslty, column dlameter and lrqutd surface tension, it decreases with gas velocity, particle size and the density difference between sohd and liquid phases The bed porosity increases with hquld velocltres and vlscosl ty, whereas it decreases wl th mcreasmg particle size, liquid surface tension and the density difference between sohd and liquid phases Bed porosity increases with gas velocity m the mltlal bed expansion regime, but it shows a mmimum value wrth respect to gas velocity m the m&al bed contraction regime The liquid phase holdup and the bed porosrty data have been combined with over 5000 pomts from the literature to yield dimensionless correlations
A three phase fluldlzed bed, as defmed m this study, 1s a batch of solid particles which are fluldlzed by concurrent upflow of liquid as the contmuous phase, and gas as the dlspersed bubble phase Recently, the apphcatlons of three phase fluldlzed bed reactors have been Increasing in the chemical and blochemlcal processing fields Therefore, the hydrodynamic properties such as the phase holdups, bubble properties and mixing characteristics have to be studied m order to provide the basic mformatlon required for designing these fluldlzed bed reactors Among the hydrodynamic properties, the most Important for analyzmg the performance of a three phase fluldlzed bed reactor are the bed porosity and the mdlvldual phase holdups Various aspects of these fluldlzed bed reactors have been reviewed by several mvestlgators [ 1 - 91 The bed porosity and the mdlvldual phase holdups have been determined by means of pressure gradient, electroreslstlvlty probe and optical fiber probe methods, and by sunultaneous closure of the gas and liquid feeds From the probe methods, it has been found that the solid phase holdup near the top of the bed slowly decreases along the expanded bed height m a transltlon region from the mam three phase fluldlzed bed to a two-phase gas-liquid region above the bed However, m the mam fluldlzed bed region, the phase holdups are very uniformly dlstnbuted across the bed [lo - 111 Therefore,
*Author addressed
to
0300-9467/90/$3
whom
50
correspondence
should
be
@ Elsevler
Sequora/Prmted
In The Netherlands
68
we shall consider the mean values of the holdups and bed porosity m the bed. In addltlon, the gas holdup values obtamed from the probe methods are somewhat lower than those from the pressure gradient method [12] However, m general, the difference 1s found to be mslgnlflcant On the other hand, comparmg the pressure gradient method with the simultaneous closure method showed that the former provides a systematic underevaluation of gas holdup, when the column diameter 1s below 0 08 m [13] There 1s plenty of data ‘available m the literature’ on phase holdups and bed porosity m three phase fluldlzed beds However, this data has not been compiled since the Begovlch and Watson [lo] compllatlon about 10 years ago Therefore, m this study, the phase holdup and bed porosity data of the present and previous studies have been summarized, dlmenaonless correlations on liquid phase holdup and bed porosity m three phase fluldlzed beds are presented These correlations take mto account the effects of liquid and gas velocltles, surface tension of hquld phase, particle size, column diameter and density of liquid phase
2
EXPERIMENTAL
Experunents were carried out m a bench scale(lBmh~hX152mmID)andapllot plant scale (2 1 m high X 376 mm I D ) Plexlglas column as shown m Fig 1 Pressure taps were mounted flush with the wall of the
column at 75 mm height intervals from the dlstnbutor The static pressure at each of these pomts was measured with a hquld manometer The solid particles were supported on a grid, under that grid, a perforated stamless steel plate with evenly spaced holes of 3 mm I D (156 holes for smaller column, 786 holes for larger column) was used as a liquid dlstrlbutor The distributor was situated between the mam column sectlon and the distributor box The hquld flow rate was measured with two calibrated flowmeters and regulated by means of globe valves on the feed and bypass lmes Oil-free compressor au- was fed to the column through a pressure regulator, a filter and two calibrated flowmeters It was admltted to the bed through 4 and 19 evenly spaced 6 4 mm I D perforated feed pipes m the smaller and larger dlstnbutors, respectively With this arrangement, a triangular pitch can be placed on the surface of the dlstrlbutor plate with 26 and 232 holes of 1 0 mm I D , respectively Seven different sizes of glass beads (1 0, 1 7, 2 3, 3 0, 3 7,6 0, 8 0 mm) with a density of 2500 kg m -3 were used as the sohd phase, air as the gas phase, and tap water and aqueous solutions of glycerol as the llquld phase Details of the experlmental variables and their ranges are summarized m Table 1 The bed porosity was determmed by measurmg the dry mass of the sohd and the bed height, which was taken as the pomt at which a change m slope of the pressure profile was observed The gas and hquld holdups were obtained by measurmg the slope of the pressure prohle m the three-phase bed The descrlptlon of these classical techmques may be found m Wild et al [4]
3 RESULTS
Fig 1 SchematIc diagram of experlmental apparatus (0, = 152 mm I D ) 1 Mam column, 2 pressure taps, 3 dlstrlbutor box, 4 dram, 5 flowmeters, 6 centrlfugal pump, 7 hquld reservoir, 8 pressure regulator
AND DISCUSSION
3 1 Effect of gas velocrty The bed porosity c is an mcreasmg function of liquid velocity and hquld vlscoslty It 1s a decreasmg function of particle diameter and density difference between the sohd and the hquld Smce the paper by Masslmllla et al [14] was published the influence of gas velocity has been a well debated SUbJeCt for almost 30 years In some cases, bed porosity decreases as a function of the gas velocity 1 e the bed contracts at the mtroduc-
69 TABLE Ranges
1 of experlmental
Weight of glycerol
variables
c11 Pa
s)
CJ, (mN m-l)
d, (mm)
UI (m s-l)
Us (m s-l)
72 66 64 62
10 80 23-80 30-80 30-80
0 01 0 01 0 01 001
O-012 o-o 12 O-012 0 012
(S) 00 75 0 83 0 86 0
0 0 0 0
001 020 040 060
8 5 1 8
tion of the gas m a liquid solid fluldlzed bed This behavior 1s usually observed with highly expanded beds conslstmg of small particles (d,, < 2 5 mm) [15] As can be seen m Fig 2(a), the bed porosltles of smaller particles (dp 5 2 3 mm) reach a mmunum with mcreasing gas velocity The commonly accepted explanation 1s that the bubble wakes of large bubbles entram hquld which 1s no longer avtiable to fluldlze the solid particles However, as can be seen, the bed porosity mcreases with mcreasmg gas velocity in the beds of larger particles due to the bubble breakage by the larger mertla of particles (Fig 2(a)) On the other hand, the expanded bed height with a further mcrease m liquid vlscoslty contracts as gas velocity IS Increased, as can be seen m Fig 2(b)
- 0 14 - 0 12 - 0 10 010
The mertlal force of the particles decreases and the boundary layer thickness on the bubble surface mcreases with an increase m liquid vlscoslty Consequently, the larger particles cannot easily penetrate through the bubbles [16] Therefore, it can be claimed that bubbles m the highly viscous solutions (p, 2 40 mPa s) are coalescmg regardless of particle sizes 3 2 Effect of llquld phase mcoslty In the present study the liquid vlscoslty has been vmed from 1 to 60 mPa s with aqueous glycerol solutions. The bed porosity or expanded bed height and liquid holdup dlrectly mcrease with liquid vlscoslty due to the mcrease of drag force on the particles As can be seen m Fig 3, a sumlar trend [17] has been observed m the beds of 6 mm glass beads
06
06
0
2
4
6
8
10
12
UgxlOO m/s
Fig 2 Effect of gas velocity on bed porosity m two and three phase fluldlzed beds of different hquld VlSCOSl t>
1
5
10
50
100
J+ or k. mPas ormPusm Fig 3 Effect of hquld vlscoslty on (a) bed porosity and (b) hquld holdup m two and three phase fluldlzed beds of 8 mm glass beads (UJ = 0 1 m s-‘)
70
with carboxymethyl cellulose (CMC) solutions However, the shape of the bed porosity and liquid holdup curves is different since the CMC solution has a non-Newtonian fluid behavior with a lower apparent vlscoslty m the beds Therefore, the bed porosity and liquid holdup mcrease non-linearly m the beds with CMC solutions 3 3 Effect of column drameter
scale-up
effect
The effect of column size on gas and liquid phase holdups and bed porosity 1s shown m Fig 4 with the data of the present and prevlous studies [l&19] As can be seen, the gas holdup decreases slightly with mcreasmg column diameter up to 0.254 m, since the bubbles may rise more freely than those m the smaller column [lo], thereafter, it does not change appreciably The liquid holdup, however, shows a reverse trend, (Fig 4(b)), while the bed porosity IS nearly independent of column diameter from D, = 0 1 to D, = 0 376 m
tlon [3] The mam drawback of these models 1s that one needs reliable correlations of the volume of the bubble wakes and of their solid content However Wild et al [20] were able to correlate their results by combmmg a bubble wake model with a correlation of the slip velocity, Nacef et al [21] showed that this approach can be generalized when a slip velocity correlation adapted to the dlstrlhutor used IS known One of the ObJectives of this study 1s to develop a general correlation by using a data base as large as possible Therefore, a large amount of expenmental data - more than 5000 data points - were considered, covermg a wide range of experunental condltlons [l&19,22 - 461 The new dlmenslonless correlations of the liquid holdup and bed porosity m three phase fluldlzed beds which have been proposed in this study are based on the Richardson and Zakl equation [47] They take the following general form (E, or E) = (U, Ut-‘)““f(U,,
1 CORRELATIONS
where
There are two mam techniques by which we can try to represent the phase holdups m gas-hquld-solid fluldlzed beds We can use the bubble wake models which have been summarized m a previous pubhca-
f(U,,
100
150
200
250 300 350 Ul0 DC mm Fig 5 Effect of column diameter on hquld holdup and bed porosity m three phase fluldlzed beds of 6 mm glass beads (/.I, = 1 0 mPa s)
019 Wug=
ol, DC)
(1)
o= 1
The best way to determme the terminal velocity U, and the index n of the hquldsolid fluldlzed bed IS by experiment, since they are strongly dependent on the particle diameter and shape. On the other hand, the experimental determmatlon may be done m a small scale column, smce both coefflclents are independent of the distributor If that 1s not possible, however, we may calculate Ut and n from equations m the literature [48] Recently two new correlations of the index n have been proposed, by Carey [49] and by Rowe [ 501. In previous studies [32, 511, the correlations of liquid and solid phase holdups m three phase fluldlzed beds have been proposed based on the Rlchardson and Zakl equation [ 471 However, the correlation of Kato et al [32] can predict only liquid phase holdup, whereas the correlation of Jean and Fan [ 511 predicts bed porosity only in the u-utlal expansion beds with lower vscous solutions in three phase fluldlzed beds with a margmal accuracy as can be seen m Fig 5 The hquld holdup and bed porosrty have been correlated m the followmg form
71
Lrquld holdup (1 - 0 374Fr,’
176We,-o
‘73)
(2)
m which the range of variables covers 0 054 G (U,/U,) < 0.899, 0 395 X 10m4 < Fr, Q 2 551, 0 918 X 10m3 < We,,, < 5 013 with a correlation coefflclent of 0.921 and a relative standard deviation of 8 7% for 2875 data polnts Bed porosl ty The data points were separated into two categories, according to the expansion or contraction of the bed upon uyectlon of gas into a liquid fluldlzed bed a) Inrtlal expansion (1 + 0 123Fr,O 0
2
4
6 8 10 UgxlOO m/s
12
14
Fr, < 3 788,O 895 X 10m2 < We, < 5 479 with a correlation coefflclent of 0 912 and a relative standard deviation of 6 4% for 1946 data pomts
2
Comparison Authors number
(3)
m which the range of variables covers 0 029 < (U,/U,) < 0 481, 0.173 X 1O-4 <
Fig 5 Comparisons of (a) hquld holdup, (b) bed porosity m the mltlal expansion resme and (c)bed porosity In the lmtlal contractlon regime In two and three phase fluldlzed beds between the present and previous studies
TABLE
347We,,,o 03’)
of empIrIca
or equation
Dakshlnamurty et al 127,281 Klmetal [15] Begovlch and Watson
correlations
of hquld holdup
cl (2875)a RC
and bed porosity
In three phase fluldlzed
beds
e SD(W)
IER ( 1946)a
ICR (1121)a
RC
SD (%)
RC
SD (%)
0 892
14 4
0 858
33 8
-
-
0 802 -
18 2 -
0 791 0 817
10 7 95
0 693 0 732
12 9 11 2
0 202 0 866
1418 11 3
0 751 -
25 -I -
0 562 -
l-1 4 -
0 812
18 2
0 827
18 8
0 779
32 6
-
-
0 912 -
-
-
-
1101 Razumov et al [46] Kato at al [ 321 SaberIan-Brodlenni eta1 [13] Eqn Eqn Eqn
(2) (3) (4)
0 921
-
aNumber of data pomts IER. Inltlal expansion regime ICR, Inltlal contractlon regime RC, RegressIon coefflclent SD, relative standard devlatron
87 -
64
0 860
70
72 b)
Per S&oft,
Inltlal contractron
Teknlsk
Forlag,
Copenhague,
1977,
p 165
0 359Fr,O ‘52We,0 121
Fr go 5 where the range of vanables covers 0 024 < (UJU,) < 0 899, 0.928 X 10h4 < Fr, < 2 551, 0 659 X 1O-4 < We, < 1 529 with a correlation coefficient of 0 860 and a relative standard deviation of 7 0% for 1121 data pomts The goodnesses-of-fit between eqns (2) (4), the emplrlcal correlations of previous studies [lo, 13, 15, 27, 28, 32, 46, 511 and the present experimental data are shown m Fig 5 The advantages of the correlations presented here are the followmg they have a large experimental basis and the correlation coefficients are much better than those of the other correlations m the literature, as shown m Table 2 In summary, the liquid phase holdup mcreases with liquid velocity, hquld vficoslty, column diameter and liquid surface tension, it decreases with increasing gas velocity, particle size and the density difference between sohd and liquid phases The bed porosity increases with liquid velocltles and liquid vlscoslty, whereas it decreases with mcreasmg particle size, liquid surface tension and the density difference between solid and liquid phase It increases with gas velocity m the mltlal bed expansion regime, but it shows a mmunum value m the mltlal bed contraction regime The liquid phase hold up and the bed porosity data have been combmed with over 5000 pomts from the literature to yield the dlmenslonless correlations
2 N Epstem, Can J Chenz Eng, 59 (1981) 649 3 C G J Baker In A E Rodrlgues, J M Calo and N H Sweed (eds ), Multiphase Chemxol Reactors Vol II Design, Sljthoft & Noordhoff, Alphen aan den Rljn, 1981, p 343 4 G Wild, M SaberIan-BrodJenm J L Schwartz and J C Charpentler, Int Chem Eng, 24 (1984) 639 5 K Muroyama and L S Fan, AfChE J, 31 (1985) 1 6 W D Tech,
7
8 9 10
11 12 13
14 15
16 17 18 19 20
21 22
ACKNOWLEDGMENT
We acknowledge a Grant-m-Ad of research from the Korea Science and Engmeermg Foundation
23
24
REFERENCES
25
1 K Bstergaard, In K sstergaard and Aa Fredenslund (eds ), Chemwal Engrneermg with
26
Deckwer and A Schumpe, Chem Ing 55 (1983) 591 H I de Lasa and S L P Lee, NATO ASI Chem~a1 Reactor Design and Technol, London, Canada, 2 12 June 1985 Y H Yu and S D Ktm, Chem Ind Technol, 4 (1986) 11 (In Korean) L S Fan, Gas-Llqwd-Sohd Fluldlzatron Engmeermg, Butterworths, Boston, 1989 J M Begovlch and J S Watson, In J F Davldson and D L Kealrns (eds ), Flutd~zatron, CambrIdge Umverslty Press, UK, 1978, p 190 S L P Lee and H I de Lasa, AfChE J, 33 (1987) 1359 Y H Yu and S D Kim, 4IChE J, 34 (1988) 2069 M Saberian-Broudjennl, G Wild, J C Charpentler, Y Fortm, J P Euzen and R Patoux, Int Chem Eng, 27 (1987) 423 L Masslmllla, N Majurl and P Signormi, La Rlcerca ScrentIfica, 29 (1959) 1934 S D Kim, C G J Baker and M A Bergougnou, Can J Chem Eng, 53 (1975) 131 Y M Chen and L S Fan, Chem Eng SCI, 44 (1989) 117 S D Kim, Ph D Thesis, Unlverslty of Western Ontario, 1974 G T Jm, Ph D Thesis, Korea Advanced Institute of Science and Technology, Seoul, 1985 Y H Yu, Ph D Theses. Korea Advanced Institute of Science and Technology, Seoul, 1989 G Wild, M Saberlan Broudjenni and J C Charpentler, In B D Kulkarnl, R A Mashelkar and M M Sharma (eds ), Recent Trends rn Chemwal Reactlon Engrneermg, Vol 2, Wiley Eastern Ltd , New Delhi, Tndla, 1987, p 531 S Nacef, G Wild, A Laurent and S D Kim, Entropre, 143/144 (1988) 83 J M Begovlch, MS Thesis, Oak Ridge National Laboratory, Massachusetts Institute of Technology, Oak Ridge, 1978 V K Bhatla and N Epstem, Proc Int Symp Fluzdrratlon and Its apphcatlons, H Angehno et al (eds ), Editions Cepadues, Toulouse, France, 1971, p 380 V R Bloxom, J M Costa, J Herranz, G L MacWllham and S R Roth, Oak Ridge National Laboratory, Massachusetts Institute of Technology, Oak Ridge. 219 1975 T M Chlu, Ph D Theses, Polytechmc Instrtute, New York, 1982 T M Chlu and E N Ziegler, AlChE J, 31 (1985) 1504
73
V Subrahmanyam and J N 27 P Dakshmamurty, Rao, Ind Eng Chem Process Des Dew, 10 (1971) 322 28 P Dakshmamurty, K Rao, K V SubbaraJu and V Subrahmanyam, Ind Eng Chem Process Des Deu, I1 (1972)318 29 V R Dhanuka and J B Stepanek, In J F Davldson and D L Kealrns (eds ), Flulduatlon, CambrIdge Unlverslty Press, UK, 1978, p 179 30 G I Efremov and I A Vakhrushev, Int Chem Eng. 10 (1970) 37 31 H S Jang, hlS Theas, Umverslty Soong Jeon, Seoul, 1978 32 Y Kato, K Uchlda, T Kago and S Morooka, Powder Technol, 28 (1981) 173 33 S D Kim, C G J Baker and M A Bergougnou, Can J Chem Eng , 50 (1972) 695 34 H K Kwon, his Thesls, Korea Advanced Instatute of Science and Technology, Seoul, 1985 35 D H Lee, 61 S Thests, Korea Advanced Institute of Science and Technology, Seoul, 1986 36 H K Lee, 111S Thesw, Korea Advanced Institute of Science and Technology, Seoul, 1985 37 M L Mlchelsen and K P)stergaard, Chem Eng J, 1 (1970) 37 38 R N Mukherjee, P Bhattacharya and D K Taraphdar, Proc Int Symp on Flulduatron and its Apphcotlons, 197-1, p 372 39 K &tergaard, Chem Eng Scr , 20 (1965) 165 40 G R Rlgby and C E Capes, Can J Chem Eng , 48 (1970) 343 41 M Saberian-BroudJenm, These de Docteurmgemeur, IPNL, Nancy, 1984 12 M Saberian-Broudjenni, These de Docteur es Sciences Phqslques, INPL Nancy, 1985 -%3 W Y Soung, Ind Eng Chem Process Des Dw , 17 (1978) 33 4-L I S Suh, hlS Theses, Korea Advanced Institute of Science and Technology, Seoul, 1982 45 S Khosrowshahl, S R Bloxom, C Guzman and R hl Schlapfer. Oak Ridge National Laboratory,
46 47 48
49 50 51
Massachusetts Institute of Technology, Oak Ridge, 216 1975 I M Razumov, V V Manshlhn, and L L Nemets, Int Chem Eng , 13 (1973) 57 J F Richardson and W N Zakl, Trans Instn Chem Engrs, 32 (1952) 35 D Kunn and 0 Levensplel, Fluldrzatlon Engrneermg, John Wiley and Sons, Inc , New York (1969) 76 V P Carey, Int J Multlphase Flow. 13 (1987) 429 P N Rowe, Chem Eng Scl , 42 (1987) 2795 R H Jean and L S Fan, Chem Eng Scr, 41 (1986)
2823
NOMENCLATURE
DC
4 Frs k 171 n
Re u!z u, K We,
column diameter, m particle diameter, m gas Froude number, U,* (d,g)-’ fluid consistency index, Pa s’” power law index Richardson and Zakl’s index Reynolds number, (U,d,p,) p,-’ superficial gas phase velocity, m SC’ superficial liquid phase velocity, m SC’ termmal velocity of particle, m SC’ modified Weber number, (U,‘p,D,) -1 01
Greek symbols E bed porosity
f, El
IJl PI
021
gas phase holdup liquid phase holdup vlscoslty of hquld phase, Pa s density of hquld phase, kg m-j surface tension of liquid phase, N m-’