Ind. Eng. Chem. Res. 1994, 33, 950-956
950
GENERALRESEARCH Determination of &a Values Using C02 Mass Balance Technique in a Coal Desulfurization Bioreactor C. Guell a n d J. Giralt’ Departament Enginyeria Qulmica, Escola T8cnica Superior d’Enginyeria, Universitat Rovira i Virgili, Carretera de Salou sin 43007 Tarragona, Spain
Techniques based on 0 2 measurements such as gassing out or oxygen balance techniques which are generally used in determining KLUvalues are hardly applicable when a solid phase is present in the medium or during a fermentation process. In this study a new technique was used in achieving KLa values. This technique is based on the continuous response measurement of the outlet gas phase to a C 0 2 step change in the inlet. This method was applied t o determine KLa values in a bubble column where a microbiological coal desulfurization process takes place using Thiobacillus ferrooxidans. T o check the results obtained by using the COZmass balance technique, a series of runs were carried out to find the KLUvalue in an aidwater system. The results were compared with previous ones already reported by other authors, and they were seen to be in good agreement. Other KLUvalues were achieved by using an inorganic salt solution as a growth medium for the bacterium and also as a liquid medium in the desulfurization experiments. It was found that KLa increased as the salt concentration increased. When a solid phase was introduced into the reactor KLa decreased as the amount of the solid present increased; however, KLU increased when the superficial gas velocity increased. Finally, other KLUvalues were obtained during various coal desulfurization runs. I t was found that KLa remained constant throughout the reaction time, because T.ferro0xidan.s does not produce any substances that can alter the medium viscosity. It was also found that this method of determining KLUcan be used during bacterial treatment without interfering with the microorganism action. Introduction Bubble columns are widely used in chemical processes due to their versatility and low cost. These advantages are also valid for their application in biotechnology. One of the problems related with this kind of reactor arises with scale-up, due to the lack of data necessary for their design and operationlg mainly when three-phase and biological systems5J2J7 are involved. Out of all of the parameters required for correct scale-up in aerobic bubble columns, the overall volumetric mass-transfer coefficient (KLu)is essential. The evaluation of this parameter is important in order to establish the efficiencyand the effect of the operation variables on the 0 2 provjsion. The methods generally used in order to determine KLa values are sulfite oxidation and gassing-out techniques, such as static and dynamic evaluations and the oxygen balance technique.25 There are three main problems in using these types of techniques. One of them is finding appropriate electrodes, which have an adequate response time necessary to measure the 02 concentration, and the presence of a solid even makes this process more difficult. Another problem related with dynamic evaluations is that if the 0 2 level stays below the critical value it is possible that the fermentation process will stop. Finally, gassingout techniques are difficult to apply in equipment bigger than a pilot scale, mainly due to the fact that the amount of gas (usually Nz) required to replace the air makes the process uneconomical. In this study a technique using the continuous response measurement of the outlet gas-phase composition to a step change in the inlet has been applied in order to determine KLUin a bioreactor where microbial coal desulfurization
takes place. This method, apart from being applicable to two- and three-phase systems, has the advantage of being applicable to full-size equipment. Also,KLa measurements can be carried out during the fermentation run, thus providing even more accurate values than if they were taken in absence of live microorganisms. However, it has to be noted that in order to obtain accurate KLa values using this technique, the pH of the liquid phase has to be preferably below 4, and above this pH a correction has to be made to take into account the effect of reaction kinetics of CO2 with water on the absorption rates.2 Theory As mentioned above, the techniques most commonly used in determining KLU values are based on oxygen concentration measurements in the liquid phase. The method employed in this study, previously described by Andre et al.,3is based on the study of the dynamics of the gas phase of a fermenter and consists of a continuous response measurement of the gas outlet composition to a step change in the gas inlet. First of all, it is necessary to come up with a mixing model for both liquid and gas phases in the fermenter, which will provide us with a set of equations that will describe the behavior of the system. Following Andre’s work, the mixing pattern applied in the bubble column used to carry out the desulfurization runs is as follows: the gas phase is considered as plug flow, whereas the liquid phase is considered as well mixed; the accumulation term in the gas phase is not considered negligible. Under these circumstances the linear differential equation system obtained is
0888-588519412633-0950$04.50/0 0 1994 American Chemical Society
Ind. Eng. Chem. Res., Vol. 33, No. 4, 1994 951 depends on the gas holdup (eg), the dimensionless solubility (A), the residence time of the gas ( r g )and , the parameter
gas phase:
81.
liquid phase: dCL = K L a t ( C * , - CL)d[ dt which can be solved by using Laplace transforms. Finally, an equation that relates the gas output concentration with time is
During fermentation experiments, CO2 is a more suitable gas than 0 2 or Nz to produce astep change in the However, the KLa values obtained are based on C02 measurements, so it is necessary to convert the (KLa)coz values into (KLa)ozusing the correlation for K Lproposed by Dan~kwerts:~
(DCO,
KLao, = KLUCO,
YIZ
(14)
Materials and Methods where a,01, and 82 are defined as follows:
(5)
and (7)
Equation 3 can be applied to every nonreactive gas simply by adjusting the solubility parameter (A) included in a and 8. As a result of plotting ln(1- YO))versus time and taking into account that the second exponential term of eq 3 can be neglected under present ~onditions,~ a straight line with 81 as the slope is obtained. Then, with the equation derived from the linear differential equation system, it is possible to find the values of KLa:
where
Pz =
&(
Tg +
PStg
KLU)
(12)
As can be seen from these equations the final KLa value
Equipment. The main experimental apparatus used in finding KLa values during a microbial coal desulfurization process is presented in Figure 1, and can be divided into three sections. The first section consists of a bubble column, used as a bioreactor in coal desulfurization processes, and whose KLa is evaluated under different experimental conditions. The second section consists of aset of devices used to regulate and measure the gas phase. The third section is composed of devices used in measuring, collecting data, and calculating the response curve of the system to a step change in the inlet gas. As mentioned before, the fermenter used in this study consists of a glass bubble column. The bubble column was 0.75 m high and 0.15 m in inside diameter, and its bottom part was equipped with a porous plate (0.12 mm porous diameter) in order to sparge the gas into the liquid phase. The top part of the bubble column was designed with a device to take samples, another to introduce liquids or solids in the fermenter, and a third to allow gas outlet. Air was supplied by the building air network, and the step change was controlled by using a solenoid valve, also shown in Figure 1, which allowed C02 from a gas cylinder to flow into the bubble column. A thermal conductivity detector (TCD) placed in the gas outlet was used to measure the response to the step change produced in the inlet. The TCD temperature as well as the gas flow rate which went through the detector were maintained at 150 "C and 3.12 lo4 L/s, respectively, in all the runs. The response from the TCD was conveniently converted by using an interface Beckman 406 and then stored in a PC computer. Microorganism. Thiobacillus ferrooxidans was used to carry out all of the experiments in this study. The strain was obtained from the National Collection of Industrial Bacteria (Aberdeen, U.K.) and its reference number is NCB 9490 (ATCC 19859). The microorganisms used to inoculate the desulfuriza~~ tion runs were grown in the Silverman & L ~ n d g r e n9K medium during 4-5 days in a Gellenkamp orbital incubator at 28 OC and 180 rprn. The 9K medium was made by mixing the two different inorganic salt solutions presented in Table 1. After the growth period the culture was left to settle for 24 h a t 4 "C. The precipitate, which contained mainly iron compounds, was discharged, and the liquid phase was centrifuged at 15280 X g for 10 min and resuspended in acidified water (pH = 2.5 with H2SO4 10 M) in order to attain a final inoculum of loe cell/mL. Cell concentrations in solution were obtained by direct reading using a counting chamber. From this point on, the salt solution, without iron sulfate, used as the liquid medium for the desulfurization runs, will be referred to as 9K salts. Coal. The coal used in this study was a lignite supplied by "Carbones de Berga S.A.", Catalonia, Spain. Table 2 shows the proximate and ultimate analysis of the lignite. Prior to its utilization, the coal was ground, sieved, and
952 Ind. Eng. Chem. Res.,Vol. 33, No. 4,1994
A
I
I
ATMOSPHERE
INTERFACE
-----
H'
Figure I. Main experimental apparatw. Table 1. 9K Medium of 9K salts (NH~ZSOI KCI K~HPOI MgSOi.7HzO Ca(N0s)z HzSO, 10 N distilled Hz0 energy source FeS04.7Hz0
Silverman and Llmdsren" 3.0 g 0.1 g 0.5 g 0.5 g 0.01 g 1 mL
VD was obtained through HD; VL and Vs were already known; and then V, was calculated using the following equation:
I00 mL
In all the experiments, the initial liquid height was maintainedat0.45m, whichmeansthatthecolumnheight/ diameterratiowas3. Thegasflowraterangedfrom0.183 L/sto 0.518 L/s, which in turn resulted in a superficialgas velocity, uag,between 0.0104 and 0.0293 m/s. The slurry concentrations studied were 5,10, and 15%. KLaDetermination. The method used indetermining KLQvalues consisted of introducing a step change in the inlet gas by means of COz. The COz concentration used was always 4% of the main gas flow rate. A t this point it must be mentioned that while COZwas not supplied to the column, it was replaced by a secondary air stream, a t the same flow rate, in order to keep constant the total gas flow rate. Every run lasted 20 min, and during this period the response of the system to the COS step change was measured by a TCD, transformed by an interface, and recorded and stored in a PC computer. The plot obtained by using these procedures allowed us to calculate 81 for CO2 absorption and desorption processes by plotting ln(1 - Y ( 0 )versus time. Equations 10 and 14 allowed us to obtain KLQvalues for all the systems studied, that includes when 7 '. jerrooxidans were present in the medium. As each KLQdetermination lasted just 20 min it was considered that the amount of COz uptake by the microorganism during this period could be neglected,thus having no effed on the COz mass balance. It has to be mentioned that in order to take into account the time delay caused by piping, control, measurement, and detection systems, a series of runs were carried out using the experimental apparatus, presented in Figure 1, without any reaction medium. That way it was possible
v,= v, - v,- v,
300 mL of a solution 14.74% (wlv)
Table 2. Proximate Analysis and Sulfur Content of the Catalan Lignite proximate analpis ash moisture volatile matter carhon
ultimate snalvsis carbon hydrogen nitrogen oxygen' total sulfur sulfate sulfur pyritic sulfur organic s u l f e 0
(16)
weight (%) 47.41
6.99 34.16 11-44
weight 1%) 46.53 2.64 1.18 43.05 6.60 0.87 1.83
3.90
By difference.
stored under inert atmosphere. The coal particle size fractions used were 20-60 mesh (0.50-0.246 mm), 60-100 mesh (0.246-0.147 mm), 100-200 mesh (0.147-0.074 mm), and sub-200 mesh (less than 0.074 mm). e, Determination. In the two-phase systems, e, was determined by reading the height of the liquid with and without aeration (HDand HL.respectively) and by using the following equation: t, = (HD- HL)/HD (15) In the three-phase systems, a more general equation using the volumes of the phases was used to obtain fp:
(17)
0.30
0.12
OZ5
0.10
1
Ind. Eng. Chem. Res., Vol. 33, No. 4, 1994 953 I
I
I
+ 9K Salts
9KMedium
d
0 20
A
0.08 a 2
e
u)
$
0.06
0.04
0.05
0.00
0.02 0.01
0015
0 02
0 025
0.01
0 03
Figure 2. Dependence of gas holdup on uyrfor the aidwater system. Experimental results are compared with those obtained through different correlations.
to find out the time delay of the system, and then calculate 01 for the bubble column. The experimental conditions (initial liquid volume, gas flow rates, and slurry concentrations) used for KLU determination were the same as those used for tg. When T.ferrooxidans was present in the medium, the slurry concentration was maintained at 5 % and the superficial gasvelocity was kept at 0.0125 m/s. Obviously,with higher gas velocities the aeration efficiencywould have been much better; however, it was found that this gas velocity provided enough aeration and stirring to the medium, and prevented excessive medium evaporation during the reaction time (10-12 days for the desulfurization runs). The initial T. ferrooxidans concentration was maintained in all the experiments at 2.106 cell/mL by adding the appropriate amount of the concentrate inoculum to the reaction volume.
Results and Discussion Gas Holdup. In Figure 2 a plot shows the tg values in the air/water system. The experimental values obtained using eq 15 were compared to the eg values calculated by using correlations presented by other authors.7l8J4 As can be observed the experimental and calculated values are in good agreement, except for the tg values calculated by using Hughmark's correlation. The differences between the experimental and calculated tg values might be explained by the effect that certain distinctive features in the reactor used (height, diameter, geometry, and type of sparger) have on the gas holdup. Even still, the column diameter used in the present study was in the range of the ones used to find all the correlations presented. Figure 3 represents a plot of tgfor the two-phase systems examined in this study. The linear dependence of tg on usgwas observed in all of the systems for the range of usg covered, as also reported by other authors.15 As can be seen, an increase in the salt concentration in the medium results in an increase of the cg. The presence of electrolytes decreases the bubble coalescence, so the amount of gas retained increases as the inorganic salt concentration increases. Table 3 presents tg,obtained using eq 16, for the threephase system air/SK salts/coal, with slurry concentrations of 5, 10, and 15%, and the coal particle size fractions of 20-60,60-100, and 100-200 mesh. It can be seen that the presence of coal in the reaction medium results in a have shown that decrease of the eg. Other author~~0*23927*~8
0.015
0.025
0.02
0.03
usg ( W
Usg (mis)
Figure 3. Dependence of gas holdup values on uq for the aidwater, air/9K salts, and air/9K medium systems. Table 3. Gas Holdup Values Obtained for the Three Coal Particle Fractions Studied at Three Slurry Concentrations (5,10, and 15%) gas holdup u, (m/s) 0% solids 5% solids 10% solids 15% solids 0.013 0.078 0.056O 0.0500 0.0400 0.071b O.05lb 0.0E~8~ 0.047c 0.064' 0.058' 0.021 0.135 0.1200 0.119 0.107" 0.119b 0.110b 0.103b 0.116' 0.117c 0.116' 0.025 0.162 0.155a 0.144c 0.14P 0.144C 0.029 0.192 0.187O 0.1700 0.154" 0.173b 0.1706 0.151b 0.17Oe 0.17Oe 0.165' a
20-60 mesh. 60-100 mesh. 100-200 mesh.
there is an increase in bubble coalescence when a solid is present in the medium, which in turn decreases the amount of gas retained. A decrease in tg has also been reported with solid particles 1mm in size or smaller present in the r e a ~ t o r .In ~ Table 3 a slight decrease in the gas holdup is observed when the amount of solids is increased, which also has been shown by other authors.llt= In general, when there is an increase in the solid concentration there is a decrease in tg values, but this becomes irrelevant at high gas velocities (10-20 m/s). It has to be noted that the experimental error associated with all the tg values presented was always within 6 % &a Values. As mentioned previously, the first step to obtainKLa values using the C02 mass balance technique is to calculate 81values. In Figure 4 is presented a typical plot of ln(1- Y ( t ) )versus time obtained with data of the present study. Using the simplified form of eq 3 it is possible to obtain 01, as the slope of the straight line plotted in that figure. A. Two-Phase Systems. Figure 5 shows the KLa values obtained by using the COZmass balance technique for an air/water system in the bubble column. The experimental results are compared in this figure with KLU values calculated from correlations presented by other authors1~13~18~19,22,26 for the same type of system and the same usgrange used in this study. The KLUvalues represented in Figure 5 attained by using the COZmass balance technique appear to be in good agreement with the calculated results obtained by the correlations. It must be taken into account that all the experimental results presented come from C02 absorption curves. Even though
.
954 Ind. Eng. Chem. Res., Vol. 33, No. 4, 1994 0 -0.2 -0.4 -0.6 -0.8 -1 -1.2 -1.4 +
h
-1.6 7
y -
-1.8 -2 -2.2 -2.4 -2.6 -2.8 -3 -3.2 -3.4
0
20
40
60
80
100
120
140
160
180
time (s) Figure 4. Typical plot of ln(1 - Y ( t ) )versus time obtained with data of COz step change. 0.15
0 OB
I
I
I
A
0 07 0.10
-m
-
v)
2!? 006
Y
e
0.05 0 05
9KSalts
t 0.00 0 01
1
0 04
0 015
0 02
0 025
0 03
Usg ( m h )
Figure 6. Dependence of KLa on ulg for the aidwater system. Experimental results are compared with reported values for the same system.
the model used to describe the system is considered to be applicable to either absorption or desorption experiments, KLa desorption values found in the present study were always slightly lower than the absorption ones. This fact was also found by Andre2 who reported KLa desorption values 5-15% lower than absorption ones. Andre considered some mechanisms and factors which could explain this fact, such as surface aeration, bubble shrinkage or expansion and counterdiffusion of nitrogen and oxygen, concluding that when a low C02 concentration (4 5% ) is used there is no simple explanation for this phenomenon. In Figure 6 the KLa values attained from all of the twophase systems used in this study are shown. As can be observed KLa increases when the inorganic salt content of the medium increases, so the highest KLa values were obtained with the 9K medium. Koide et al.13also noticed this kind of behavior and reported KLa values for electrolytic solutions higher than water, under the same experimental conditions.
0 01
0 015
, 0 02
, 0 025
I 0 03
Usg ( m i s )
Figure 6. Dependence of K L on~ u,for the two-phase systems air/ water, air/SK salts, and air/SK medium.
B. Three-phase Systems. To understand the differences caused by the presence of a solid phase in the volumetric mass-transfer coefficient, the systems studied were airl9K saltslcoal and airl9K saltslcoal-T. ferrooxidans. Table 4 presents the KLa values attained in the three-phase system without microorganisms, at 5,10, and 15% of slurry concentrations and using coal particle size fractions of 20-60,100-200, and sub-200mesh. The results show that KLa increases when usgincreases, but when coal particles were present, the KLa values were lower. Even using the smallest coal particle size fractions led to small KLa values as the amount of solids introduced increased. As the coal particle size fraction decreased, the KLa values were practically constant for all the slurry concentrations. Some authors have pointed out that KLa values decrease when solids are present in the medi~m.'3J6Jg*~~ Sun26 agrees with this when the particle size is smaller than 1 mm, but he suggested that when particle size is bigger than 6 mm it helps the bubble breakdown, increasing the surface area and KLa.
Ind. Eng. Chem. Res., Vol. 33, No. 4,1994 955 Table 4. &a Values Obtained for Three Different Coal Particle Size Fractions at Three Slurry Concentrations (5, 10, and 15%) KLa (8-1) at slurry concentrations of u.. (m/s) 0% 5% 10% 15% 0.021" 0.018" 0.0125 0.049 0.032" 0.033b 0.030b 0.041b 0.033' 0.03' 0.041' 0.0167 0.053 0.035' 0.021" 0.043' 0.029c 0.0209 0.061 0.041" 0.034" 0.026" 0.0446 0.027b 0.033b 0.044' 0.027' 0.033' 0.042" 0.033" 0.0251 0.068 0.0293 0.073 0.067" 0.055' 0.047" 0.0266 0.044b 0.033b 0.044' 0.026' 0.033' 20-60 mesh. 6 100-200 mesh. Sub-200 mesh.
0.06
I
1
Nomenclature
U
-
0.05
cr 0
0
B
0
1
0
11
0
0
I
003
002
Acknowledgment The authors wish to mention that a part of the experimental work was supported by a scholarship given by the Catalan Government (CIRIT, Comissi6 Interdepartamental de Recerca i Inovaci6 Tecnolbgica).
f
0'07
results with the ones obtained by using oxygen measurements in the liquid phase. This method was proven to be applicable when solid phases, like coal or T. ferrooxidam, were present in the medium. With the presence of a microorganism in the medium (T.ferrooxidam)KLUcan be determined during the desulfurization runs without causing any disturbances in the bacterial action. As a result, the growth curves and desulfurization yields achieved were very similar to those obtained when the KLUdetermination runs were not performed. KLUvalues tend to decrease when a solid phase is present in the medium, as was clearly pointed out from the results attained in this study. Finally, the KLUvalues attained when T. ferrooxidans was also present in the medium were very similar to those achieved when coal was present.
'
0
I
0 100.200 mesh
I
,
I
I
I
2
4
6
6
10
lime (days)
Figure 7. KLUevolution during two desulfurizationruns, using coal particle size fractions of 60-100 and 100-200 mesh.
Figure 7 shows the KLUevolution during two desulfurization runs. The coal particle size fractions used were 60-100 and 100-200 mesh, the solid/liquid concentration was 5 % ,and the uagwas 0.0125 m/s. As can be seen there is no change in KLUduring the reaction time, because T. ferrooxidans does not produce any substances that can modify the apparent viscosity of the medium. From the data presented in Figure 7, it is also possible to see that slightly higher KLUvalues were found when a 100-200mesh coal particle size fraction was used. It is also important to mention that this method, based on a step change in the inlet gas, used to find the KLUvalue, did not produce any disturbances in the T. ferrooxidans action. Both growth and desulfurization yields obtained during KLUdetermination were similar to those found when there were not any disturbances introduced in the reaction system.6 It has to be noted that the experimental error of KLUvalues presented was always within 8%. Conclusions From the results obtained in this present study it is possible to conclude that the method used to evaluate eg, measuring the height of the liquid with and without aeration, provides accurate results for the equipment and the experimental conditions covered. It was shown that the presence of an inorganic salt in the medium helped in gas retention, while a solid phase had the opposite effect, due to an increase in the apparent medium viscosity. The COz mass balance technique used in determining the KLUvalues in an aidwater system provided comparable
81, 8 2 = absolute poles of the transfer function (8-1) C, = gas concentration (mol/m3) DcoP= C02 diffusivity (m2/s) Dol = 0 2 diffusivity (m2/s) tg = gas holdup He = Henry's Law constant (atm L mol-') HD = height of the aerated liquid (m) HL = height of the liquid without aeration (m) KLUCO~ = overall volumetricmass-transfercoefficientfor COZ (9-1)
KLUO,= overall volumetric mass-transfer coefficient for 0
2
(s-1)
X = dimensionless solubility (RT/He)
Qg = gas flow rate (m3 8-l) R = gas-law constant (atm L K-l mol-') T = temperature (K) t = time (s) 7, = gas residence time (Vg/Qg) (s) uBg= superficial gas velocity (m/s) VD = dispersion volume (L) V, = gas volume (L) VL = liquid volume (L) VS = solid volume (L) Y ( t )= dimensionless gas concentration 5 = dimensionless coordinate along reactor axis
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Des. Deu. 1973, 12, 76. (2) Andr6, G. Mixing and Mass Transfer Studies of a Novel GasLiquid-Solid Contractor for Application to Solid Substrate Fermentations. Ph.D. Dissertation, University of Waterloo, Waterloo, Ontario, Canada, 1982. (3) Andr6, G.; Moo-Young, M.; Robinson, C. Improved Method for Dynamic Measurement of Mass Transfer Coefficient for Application to Solid-SubstrateFermentation. Biotechnol.Bioeng. 1981,
23,1611-1622. (4) Danckwerts, P. V. Gas-Liquid Reactions; McGraw-HillBook Company: New York, 1970. (5) Fukuma,M.; Muroyama, K.; Yasunishi,A. Propertiesof Bubble Swarm in a Slurry Bubble Column. J. Chem.Eng.Jpn. 1987,20(l), 28-33. (6) Gtiell, C. Determination of Mass Transfer Coefficients in Biological Systems. Application to Coal Biodesulfurization. Ph.D. Dissertation, University of Barcelona, Barcelona, Spain, 1991.
956 Ind.
Eng. Chem. Rea., Vol. 33, No. 4,1994
(7) Hikita, H.; A h ,S.; Tanigawa, K.; Segawa, K.; Kitao, M. Gas hold-up in Bubble Columns. Chem. Eng. J. 1980,20,59-67. (8) Hughmark, G. A. Holdup and Mass Transfer in Bubble Columns. Ind. Eng. Chem. Process Des. Dev. 1967,6,218-220. (9) Kara, S.;Kelkar, G.; Shah, Y. T.; Carr, L. W. Hydrodynamics and Axial Mixing in a Three Phase Bubble Column. Ind. Eng. Chem. Process Des. Dev. 1982,21,584. (10) Kato, Y.; Nishiwaki, A.; Fukuma, T.; Tanaka, S. The Behavior of Suspended Solid Particles and Liquid in Bubble Columns. J . Chem. Eng. Jpn. 1972,5 (2),112-118. (11) Kato, Y.; Nishiwaki, A. Longitudinal Dispersion Coefficient of a Liquid in a Bubble Column. Znt. Chem. Eng. 1972,12,182. (12)Kawase, Y.; Moo-Young, M. Liquid-Phase Mam Transfer Coefficient in Slurry Bubble Column Reactors: Theory and Experimental Data in Simulated Fermentation Media. Chem. Eng. Commun. 1990,96,177-192. (13) Koide, K.; Takazawa, A.; Komura, M.; Matsunaga, H. Gas Holdup and Volumetric Liquid-Side Mass Transfer Coefficient in Solid-Suspended Bubble Columns. J . Chem. Eng. Jpn. 1984,17(5), 459-466. (14) Kumar, A.;Degaleesan, T. E.;Laddha, G. S.;Hoelscher, H. E.Bubble Swarm Characteristics in Bubble Columns. Can.J . Chem. Eng. 1976,54,503. (16) Mashelkar, R.A. Bubble Columns. Br. Chem. Eng. 1970,15 (lo),1297-1304. (16) Nigam, K. D.P.; Schumpe, A. Gas-Liquid Mass Transfer in a Bubble Column with Suspended Solids. AIChE J. 1987,33 (2), 328-330. (17) Ozturk, S.S.;Schumpe,A. The Influence of Suspended Solids on Oxygen Transfer to Organic Liquids in a Bubble Column. Chem. Eng. Sci. 1987,42 (71,1781-1785. (18) Ruchti, G.; Dunn, I. J.; Bourne, J. R.;von Stocker, U. Practical Guidelines for the Determination of Oxygen Transfer Coefficients with the Sulfite Oxidation Method. Chem. Eng. J. 1985,30,29-38. (19) Rustemeyer, U.;Pauli, J.; Menzel, Th.; Bucholz, R.;Onken, U. Liquid-Phase Mixing Model for Hydrodynamics of Bubble Columns. Chem. Eng. Process. 1989,26,165-172.
(20) Schumpe, A.; Saxena, K. A.; Fang, L. K. Gas/Liquid Mass Transfer in a Slurry Bubble Column. Chem. Eng. Sci. 1987,42(7), 1787-1796. (21) Schumpe, A.; Saxena, K. A.; Nigem, K. D. P. Gas/Liquid Mass Transfer in a Bubble Column with Suspended Nonwettable Solids. AIChE J . 1987,33 (ll), 1916-1920. (22) Schkgerl, K.; L a e , J.; Oels, U. Bubble Column Bioreactors. In Advances in Biochemical Engineering; Springer-Verlag: Berlin, 1977;Vol. 7,pp 1-84. (23) Shah,Y. T. Gas-Liquid-Solid Reactor Design; McGrawHilk New York, 1979. (24) Silverman, M. P.; Lundgren, D.G. Studies on the Chemoautotrophic iron bacterium Ferrobacillusferooxidans: I. J. Bacteriol. 1959,77,642-647. (25) Stanbury, P.F.; Whitaker, A. Principles of Fermentation Technology; Pergamon Press: Oxford, 1984. (26) Sun, Y .;Nozawa,T.; Furusaki, S. Gas Holdup and Volumetric Oxygen Transfer Coefficient in a Three-phase Fluidized bed Bioreactor. J . Chem. Eng. Jpn. 1988,21(l), 15-20. (27) Ying, D.H.;Givens, E. N.; Weimer, R. F. Gas Holdup in Gas-Liquid and Gas-Liquid-Solid Flow Reactors. Ind. Eng. Chem. Process Des. Dev. 1980,19,635-638. (28) Ying, D.H.; Sivasubramanian, R.;Givens, E.N. Gas/Slurry Jan Flow in Coal Liquefaction Processes. DOE Report FE-14801-3, 1980.
Received for review April 7,1993 Revised manuscript received October 18, 1993 Accepted November 10,1993.
e Abstract published in Advance ACS Abstracts, January 15, 1994.
