272
Ind. Eng. Chem. Res. 1990,29, 272-277
Spray- and Bubble-Type Absorption of Acetone from Air into Water in a Two-Impinging-Jets Absorber A b r a h a m Tamir* Department of Chemical Engineering, Ben Gurion University, Beer Sheva, Israel
Dov Herskowits and V a r d a Herskowits 16 Shapira Street, Petach-Tikva, Israel
Karl S t e p h a n Institut fur Technische Thermodynamik und Thermische Verfahrenstechnik, Universitaet Stuttgart, Stuttgart, Federal Republic of Germany
Spray- and bubble-type absorption of acetone from air into water was conducted by applying the method of impinging streams, which has proven to be very efficient. Two two-phase critical nozzles (Caldyn CSL 2) were used. The nozzles were positioned on the same axis and sprayed the gas-liquid mixture against each other. It was found that for identical gas and liquid flow rates the mass-transfer for the spray absorber and 0.5-21 s-l for the bubble coefficients, KGu,vary in the range 0.3-15.4 absorber. The KGU’Swere correlated in dimensionless groups. The typical two-maxima behavior of the absorption rate (or KGu) against the internozzle distance was found in this case as in a previous investigation. This phenomenon is attributed to two distinct enhancing effects inherent to the impinging of liquid-gas mixtures. The first maximum is due to secondary droplets splitting in the impingement zone, and the second maximum is the result of an increase in the residence time due to the oscillatory motion of individual droplets in the impingement zone. The major aim of the present study was to further investigate absorption processes in impinging streams with a particular emphasis on spray and bubble absorption of acetone from air into water. The special design of the employed nozzles, in which contact between the two phases takes place already in the nozzles, causes an appreciable portion of the whole absorption process to occur inside the nozzle. Thus, the rest of the process, usually the most problematic one, is carried out outside the nozzle where the enhancing effects of impinging streams are significant. The essence of impinging streams, which provide a simple tool for intensifying transfer processes in heterogeneous systems, lies in utilizing a flow configuration of two streams of gas-solid or gas-liquid suspensions (as in absorption) flowing countercurrently on the same axis and colliding with each other. The following effects enhance the mass transfer: increase of the relative velocity between the droplets and the opposite gas stream; increase of the mean residence time of the droplets due to their oscillatory motion; secondary splitting of the droplets or bubbles under certain circumstances in gas-liquid mixtures, hence, increasing the mass-transfer area, as well as inducing an effect of surface renewal inside the droplets, thus increasing the effective mass-transfer gradient. The method of impinging streams was applied successfully to many technological processes such as solid mixing (Tamir and Luzzatto, 1985a,b; Kitron et al., 19871, drying of solids (Tamir et al., 1984; Kitron et al., 1987; Kitron and Tamir, 1988; Tamir and Kitron, 1989), combustion (Ziv et al., 1988; Luzzatto and Tamir, 1989), and heat treatment of solids like roasting of phosphates, dissolution of solids (Tamir and Grinholtz, 1987; Tamir and Falk, 1988), preparation of emulsions (Tamir and Sobhi, 1985),and liquid-liquid and solid-liquid extraction, as well as absorption and desorption processes. As a matter of fact, almost any process in chemical engineering can be carried out with impinging streams, most likely with a higher efficiency than found in conventional systems. The
* To whom correspondence should be addressed. 0888-5~85/90/2629-0272$02.50/0
monograph by Elperin (1972) and the reviews by Tamir and Kitron (1987) and by Tamir (1989) summarize the state of the art in this field through 1987. The subject of absorption in impinging jets has recently gained much interest. Publications by Tamir and Herskowits (1985), Tamir (1986), and Herskowits et d. (1987, 1988) summarize a wide spectrum of investigations on physical absorption of COz and acetone in water, as well as desorption of acetone from water solutions. All the investigations have been carried out in an apparatus with single-phase nozzles, where the phases come in contact only after leaving the nozzles. Herskowits (1990) investigated the absorption of COz in water and NaOH solutions in an absorber equipped with two-phase critical nozzles (Caldyn CSL 2), and the results were published by Herskowits et al. (1988, 1989). In the latter nozzles, both phases come already into intensive contact inside the nozzles and are ejected as a two-phase jet. The investigations have already proven unequivocally the effectiveness of the technique of impinging jets. As mentioned before, absorption of acetone is investigated in the present study for characterizing the process of absorption when the resistance to the mass transfer lies mainly on the gas side. Experimental Section Spray Nozzles. The core of the experimental system is two nozzles mounted on the same axis that spray two jets one against the other. The two nozzles are located in an absorption chamber made of glass. The major characteristics of the nozzle are as follows. (a) It consists of an efficient mixing cell, an acceleration path, and an orifice. Thus, the absorbed gas and the liquid are initially contacted inside the nozzle, and part of the absorption (up to 80% in the absorption of COz in water (Herskowits, 1990)) takes place already inside the nozzle. (b) The two-phase gas-liquid mixture is always leaving the nozzle at a critical velocity (sound velocity, provided a minimum pressure drop is applied across the nozzle), which is lower than that of each component (Chawla and 0 1990 American Chemical Society
Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 273
ACETO
@f-
E x i t and Sompling Point
4 Spray Collector
8 A i r Salurator 9 Healer
6 Large Absorption VosseI
Figure 1. Experimental setup for acetone absorption.
von Bockh, 1971); consequently, the energy consumption is reduced. Moreover, the mixing process inside the nozzle is included in the same energy investment. (c) The nozzles produce very small droplets with a narrow size distribution, thus creating a large mass-transfer area and a homogeneous drop size distribution, which is a major factor in the efficiency of the impinging effect (Herskowits et al., 1988). The critical velocity of the gas-liquid mixture may be computed from the following formula (Chawla and von Bockh, 1971): 1/~,2 = ( a / ~ , 2 ) [+1 (1 - a ) ( R- l)]+ ((1- . ) / a m + a ( l / R - 1)1 (1) where R = PdPg For the system under consideration, al = 1500 m/s for water, and for air (neglecting the content of the acetone), a = 330 m/s, whereas R = 1000. The volume fraction of t i e gas in the gas-liquid mixture, a,was computed from their individual flow rates. Setup. The experimental setup shown schematically in Figure 1 consisted of the following elements. (1) The absorption cell (1)was made of glass tubes (3) of different lengths (0.06,0.08,0.1,0.12,0.15, and 0.2 m) and a diameter of 0.06 m with a liquid outlet and two carefully centered Teflon supports for the two nozzles (2) on both ends. The small absorption cell was introduced into a large vessel (5). (2) The gas and liquid rotameters (6) were mounted on the gas and the liquid inlet pipes. (3) The water feed vessel (7) was made from stainless steel with a total volume of about 0.07 m3. The water was injected through the nozzles by an air pressure of about 4 atm. (4)An air saturator (8)was used. Acetone was absorbed from air into water. In order to obtain the acetone-air solutions, air was bubbled at the bottom of a vessel of 0.75-m height filled with acetone. The vessel was heated by means of electrical tape (9) to obtain the desired acetone concentration in the air and to provide the heat needed for vaporizing the acetone into the air. Modes of Operation. The absorber was operated separately in one of two modes: either as a spray absorber with the gas being the continuous phase or as a bubble absorber with the water forming the continuous phase. The latter mode was simply obtained by rotating the glass tube upside down so that the exit of the fluid is located on top of the glass tube. Experimental Procedure and Measurements. A typical run consisted of the following steps: (1)filling the feed vessel with water as well as the air saturator with
Table I. Range of Operatinu Conditions. Data. and Results nozzle diameter, m 0.002 absorber length, m 0.06-0.2 absorber diameter, m 0.06 (1.7-5.7) X lo4 absorber volume, m3 critical velocity, a,, m/s 35-135 water flow rate, kg f h 20-100 1.5-17 gas flow rate, kg/h (7-25) x 104 Red (+I" (2-25) x 109 Re, (+) C,, kmol/m3 solution 0.24-0.86 ~ 0 . 1 4 3corresponding to 25% acetone Yi on a weight basis and ~ 0 . 0 5 2 6 corresponding to 10% YO
Y* N , kg/h KGa,s-l spray absorption bubble absorption P, atm AI', atm
I (+I
0.003-0.12 0.0094.01404 0.2-1.75 0.3-15.4 0.5-21.0 0.93-0.97 0.55-7.0 (5.65-406) X
Y
spray absorption bubble absorption Ca (+) Sc (25 "C) VI, m2/s 01,k f / m P I , (N s)/m2 (Y
temp in absorber, "C
(2.34-3100) X 10" (5.44-4100) X 10'' 4.8-25 721 (1.013-1.116) X 10" -1.62 x 104wA 7.33 x io-'; WA (% by wt of acetone in the range 0.2-6%) (24.1WA 1003) X 10" 0.82-0.99 15-30
+
+
(+) = for both bubble and spray absorption.
acetone; (2) adjusting the water and air flow rates, as well as the temperature in the air saturator, to the desired operating conditions; (3) measuring the concentration of acetone, the temperatures, and the pressures at points shown in Figure 1. The outlet concentration of acetone in water was determined by means of a gas chromatograph. The water inlet and outlet temperatures were determined by means of a thermocouple. Pressures were measured in the water feed line and in the gas line before the nozzles. The liquid and gas flow rates were measured by rotameters. It should be noted that each data point represents the mean value of three to five measurements of acetone concentration with a standard deviation of f2-5%.
Results The range of the operating conditions in the absorption experiments is detailed in Table I, which gives the reader an idea about the absorption capability of the two-impinging-streams absorber. Definition of the Mass-TransferCoefficient. The experimental results were reported in terms of the mean overall mass-transfer coefficient (&a) defined by the following equation: NM = L(C, - Ci) = KGaVAYh(P,/RT) (3) where M is the molecular weight of the solute, which is equal to 58 for acetone, and (Yj - Yi*) - (Yo - Yo*) AYh = (4) In
[ I
z]
In the present study, Ci = 0; thus, Yi* = 0. The mole fraction of acetone in the gas phase at the inlet to the absorber, Yi, was determined as follows: it was possible to obtain the vapor pressure, PA, of acetone from the
274 Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 Table 11. Parameters for Equation 8 absorber length, m loa K a b Spray Absorption 0.06 3.1245 0.7673 0.1387 0.08 4.4880 0.6317 0.4586 0.10 3.9309 0.6825 0.2947 0.12 2.2858 0.7966 0.1935 0.15 0.8024 0.9032 0.3576 0.8851 0.3545 0.20 0.9171 all data 4.4025 0.6363 0.4461
no
98 116 172 115 98 99 627
D%b
14t
/
18.5 19.2 20.7 25.2 15.0 14.2 21.9 05
0.06 0.08 0.12 0.15 0.20 all data
Bubble Absorption 0.8110 0.9293 0.3446 1.6460 0.8207 0.8119 -0.2995 0.9891 0.3246 0.9206 0.4238 0.4922 0.8080 0.3434 1.9837 4.1372 0.6501 0.5900
82 55 77 96 105 347
0 1 5
14.2
16.7 19.2 12.6 18.2 24.9
a n = number of data points. bD% = (l/n)z$lDi where D is the mean deviation and Di is the deviation of the calculated value from the experimental value corresponding to a certain data point. Data points with D, > 50% were eliminated.
temperature in the air saturator by log PA (mmHg) = 7.02447 - 116l/(t 224) where t is in O C . Hence, from the total pressure that was measured, Yiwas determined. Yois calculated from the mass balance on the acetone in both phases, namely, N = G(Yi - Yo),whereas Yo* is computed from Yo* = PAYAXo/Pton the basis of measurements of C, (namely,XJ. The activity coefficient (yA) was computed from = 6.6 - 140X0,which is applicable for the experimental range of X, (Tamir, 1986). Representation of the Data. The absorption process in the impinging streams is very complex because of the complicated hydrodynamics and the interrelations between the various parameters. Therefore, a dimensional analysis based on Pawlowski's (1971) method was employed in order to obtain a relationship between the measured quantitites. It was assumed that the following parameters play a significant role in the absorption process:
02
80
60
100
120
140
I
160
~
I
I
180
200
Internozzle Distance ( m m )
Figure 2. Absorption rate of acetone vs internozzle distance for water flow rate L.= 90 kg/h in the spray absorber.
+
(5) KGa = f ( d , P1, V l , 61, D,1, a,, v,@ ) where a, is computed according to eq 1. AP,the pressure across the nozzle, is calculated from the pressure inside the nozzle, which is obtained from diagrams based on the gas and the liquid mam flow rates (Chawla and von Bockh, 1971), as well as the pressure measured in the absorber. Equation 5 may be transformed into the following dimensionless equation:
Y = f&edalRepIaaCabScc
(6)
It was found that the fitted parameters al, a2,and a3 are almost identical, and hence, it has been decided to fit the data by
Y = R(RedRelI)"CabScc
(7)
In the present case, Sc is a constant value, and hence,
Y = K(RedRell)"Cab
(8)
The constants a, b, and K are given in Table I1 for the spray and bubble absorbers. It should be noted that the last row in this table gives a correlation of all data points so that the constants are independent of the reactors length. Discussion. Figures 2 and 3 demonstrate the variation of the absorption rate of acetone, N, and the mass-transfer coefficient, KGu, respectively, vs the internozzle distance for a liquid flow rate of 90 kg/h and different gas flow rates. The data in the figures correspond to a spray-type
1
15c
\\
0L60
I
80
100
, 120
1
,
1
,
140
160
180
200
1
lnternozzle Distance ( m m ) Figure 3. Mass-transfer coefficient va internozzle distance for water flow rate L = 90 kg/h in spray-type absorption of acetone.
absorber; namely, the mixture of acetone in air is the continuous phase. It should also be noted that for comparison purposes the absorption data were normalized (as detailed in the Appendix) to 1 atm, 25 O C , and an inlet concentration of acetone in air of 10% by weight acetone for gas flow rates of 12-17 kg/h and 25% by weight for 1.5-7 kg/h. The following trends were observed from the experimental results. (1)The liquid flow rate has practically no influence on N (not shown here). (2) Increasing the gas flow rate increases N. This trend may be expected especially in the present chemical system of acetone-air where the major resistance to mass transfer lies in the gas phase. ( 3 ) N a n d KGu vs the internozzle distance shows the typical behavior characterized by the two maxima first observed by Herskowits (1990) in the absorption of C 0 2 into water and NaOH solutions. Typical graphical representations of the phenomena were published by Herskowits et al. (1988, 1989). While the location of both maxima with respect to the internozzle distance remains practically constant by changing the gas flow rates, their absolute values and the relationship between them are strongly affected by the gas flow rates. The absolute values of both maxima increase with increasing gas flow rate. For low gas flow rates, the first maximum, corresponding to the lower internozzle distance, is dominant. For moderate gas flow rates, both maxima have equal values, while for high gas flow rates the second maximum corresponding to the lower internozzle distance is highest. This type of behavior fully complies with the mechanism proposed by Herskowits et al. (1988). According to the proposed mechanism, the two-maxima shape of N vs the internozzle distance is attributed to two
Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 275
0.3 60
-
n T
80
100
120
1
140
, -.
0 1.5 I
160
I
180
200
Internozzle Distance ( m m ) Figure 4. Absorption rate of acetone vs internozzle distance for water flow rate of L = 90 kg/h in the bubble absorber.
different enhancement effects. The first maximum, designating the “short-range impingement effect” (SRIE), is attributed mainly to the increase in the surface area of the droplets and to an effective increase of the mass-transfer gradient due to surface rejuvenation resulting from secondary atomization or fragmentation of droplets in the impinging zone. The second maximum, designating the “long-range impingement effect” (LRIE), is attributed mainly to the increase in the residence time of individual droplets caused by their oscillatory motion in the impinging zone, which is superimposed on the “conventional” increase in the residence time with increasing reactor length (in the present case, the internozzle distance). The latter effect is probably the major reason that the second maximum (for long internozzle distances) is higher than that for short distances. It is evident that the behavior observed in Figure 2 is very complex and that there is no single parameter determining the favored mode but rather there is a collection of parameters, the following being the most significant: the initial kinetic energy of droplets, the relative size of the colliding droplets, the angle of collision, the hydrodynamics of the continuous surroundings, the physical properties of the liquid and gas phases, and, possibily, the volumetric density of the droplets. For additional details, the attention of the reader is addressed to Herskowits et al. (1988). An important insight into the mechanism governing the behavior of droplets in impinging streams was provided by Kitron (1990). He performed a Monte Carlo simulation of droplet behavior in reactors with different internozzle distances and could predict qualitatively the observed behavior. As expected, a continuous increase was found in the droplets surface area vs the internozzle distance due to the increase in the reactor volume (by increasing its length). However, when interparticle collision was taken into account, the simulation gave a maximum in the droplets surface area vs the internozzle distance. An explanation for the maximum takes into account at least two mechanisms for reducing the surface area of the droplets. One mechanism is the decrease in fragmentation when decreasing the collision rate, possibly under conditions of reduced density of droplets in the reactor. The second mechanism is attributed to a transition from the fragmentation mode to the coalescence mode where the collision energy is not sufficient for droplet breakup. Figures 4 and 5 demonstrate the behavior of the absorption rate-internozzle distance relation for the bubble-type absorber. This configuration is characterized by the liquid being the continuous phase which is absorbing acetone from air-acetone bubbles. The general trend of
Internozzle @istonce( m m ) Figure 5. Mass-transfercoefficient vs internozzle distance for water flow rate L = 90 kg/h in bubble-type absorption of acetone.
-‘I
Y
,BUBBLE ABSORBER
Ow
5
2
60
I
80
I
100
I
120
I
140
160
180
200
Internozzle Distance ( m m ) Figure 6. Comparison between spray- and bubble-type absorption of acetone in water for L = 90 kg/h and G = 17 kg/h.
the two maxima in the values of N and KGa is repeated here, and, as before, it depends on the operating conditions. However, the first maximum value moves toward shorter internozzle distances because the effect of the exit velocity from the nozzle is decayed by viscosity effects which here are more appreciable than in the spray configuration where the liquid was the noncontinuous phase. This accounts also for the increase in N toward decreasing values of the internozzle distance as observed in Figure 4. It is surprising to observe that the highest value of N in Figure 4 corresponds to G = 7 kg/h rather than to G = 17 kg/h. However, this occurs because the inlet concentation of acetone in the gas is higher for G = 7 kg/h, namely, 25% by weight as compared to 10% by weight for G = 17 kg/h. In Figure 6, a comparison is made between the masstransfer coefficients vs the internozzle distance for the spray- and bubble-types absorbers. It should be noted that the liquid and gas flow rates are identical in both configurations and that the inlet concentrations of acetone in the air are also identical, so the comparison demonstrates indeed the effect of the internozzle distance on the rate of absorption of acetone. The procedure for normalizing the data to identical conditions is detailed in the Appendix. The prominent fact in the figure is that the bubble configuration is superior to the spray-type absorber for absorption of acetone from air into water. It should be noted that a similar behavior was observed also for absorption of COPinto water (Herskowits et al., 1988). An explanation for this behavior lies in the intensive turbulence that is created in both phases, thus enhancing the mass-transfer rates. For high liquid flow rates, the degree of turbulence observed in the reactor was so high that the gas bubbles
276 Ind, Eng. Chem. Res., Vol. 29, No. 2, 1990 Table 111. ComDarison between Nozzles for AbsorDtion of Acetone from Air into Water contact between gas and liquid contact between gas and liquid already inside nozzle (present work) only after leaving nozzle (Tamir, 1986) concn of acetone, 70 by wt spray absorber bubble absorber spray absorber in air at inlet to the absorber 10 10 30-37 in water at exit of the absorber 0.58-4.2 0.69-4.6 0.1-3 in air at inlet to the absorber 25 25 0.34-7.9 0.3-6.9 in water at exit of the absorber Table IV. Comparison of Mass-Transfer Coefficients for Various Absorption Devices and the Present ImpingingStream Absorber (Gianetto and Silverston, 1986, D 40) kLa, s-1 x 100 type of absorber packed columns countercurrent 0.04-7 cocurrent 0.04-102 plate columns 1-20 bubble cap sieve plates 1-40 bubble columns 0.5-12 packed bubble columns 0.6-12 tube reactors horizontal and coiled 0.5-70 vertical 2-100 spray columns 0.07-1.5 mechanically agitated bubble reactors 0.3-80 submerged and plunging jet 0.03-0.6 hydrocyclone 2-15 venturi 8-25 impinging jets 2.5-122
were finely dispersed and the impingement zone was very intense. It is useful to compare the capability of the absorption of acetone into the spray by using two types of nozzles. The present nozzle is where the gas and liquid phases come already into intimate contact inside the nozzles and are ejected as a two-phase jet. The second nozzle has been used in the past (Tamir, 1986), where the two phases come into contact only after leaving the nozzle. The above comparison is given in Table I11 where it is clearly demonstrated that the nozzle in which contact between the phases takes place already inside it is superior. In other words, the concentration of the absorbed acetone in water is higher in this nozzle in spite of the lower concentration of acetone in the gas at the inlet to the absorber. It was also found by Herskowits (1990) that between 40% and 80% of the total absorption takes place already inside the nozzle, depending on the operating conditions, while the remaining percentage is absorbed in the impingement zone. Finally, it is useful to compare the performance of the impinging-stream absorber, which was studied in the present work, with other commonly used devices for absorption of gases in liquids. The comparison of the mass-transfer coefficients, kLa, for absorption of COz in water is made in Table IV (Gianetto and Silverston, 1986, p 40). It may be concluded that the values of the masstransfer coefficients of the impinging-stream absorber are the highest among the conventional absorbers. The energy consumption of transferring the water through the spray nozzles is 6-16 kJ/ kg of H,O. It was also found that this absorber offers a high effectiveness with respect to maintainability, operability, and versatility, which makes it a very attractive device for industrial applications.
Conclusions and Recommendations The absorption process of acetone from air into water indicated the following trends. (1)The liquid flow rate has practically no influence on the rate of absorption, N , while the gas flow rate has a
significant effect on N and KGa. (2) The rate of absorption of acetone, N, vs the internozzle distance showed, under some circumstances, two maxima in N, where the one corresponding to large internozzle distances is higher. Thus, optimal conditions prevail in impinging streams that do not exist in other devices. (3) A comparison between the bubble- and the spraytype absorbers indicated the superiority of the bubble-type device with respect to the mass-transfer coefficient, KGa. ( 4 ) The present spray nozzles, in which part of the absorption already takes place inside the nozzle (due to their simultaneous introduction into the nozzle), were found to be superior to the nozzles in which the contact between the phases takes place only after leaving the nozzle (Tamir, 1986).
Acknowledgment Acknowledgment is made to Drora Shmilovich for help with the experimental work.
Nomenclature ag,al, a, = critical (sound) velocity of the gas, the liquid, and the gas-liquid mixture, respectively, m/s Ci, C, = concentration of acetone in the inlet and in the outlet of the absorber, respectively, kg of acetone/kg of water Ca = capillary number defined by a,(pv/u), d = diameter of the spray nozzle D = diffusion coefficient of acetone in water, m2/s G = mass flow rate of the acetone and air mixture, kmol/s G , = mass flow rate of air I = impinging number defined by (AP/a,)(v/u)l KGa = mean mass-transfer coefficient defined by eq 3, l / s kLa = mass-transfer coefficient in the liquid phase, l / s 1 = internozzle distance L = liquid flow rate, kg of water/s M = molecular weight of solute N = mass-transfer rate, kmol of acetone absorbed/s P A = vapor pressure of acetone Pt = total pressure in the absorber, atm 1p = pressure drop across a point inside the nozzle and the exit of the nozzle, atm R = universal gas constant, 0.0821(m3atm)/(kmol K) Red = Reynolds number defined on the basis of the orifice diameter of the nozzle, da,/vl Re, = Reynolds number defied on the basis of the internozzle distance, la,/vl S c = Schmidt number defined by (v/D)l Y = absorption number defined by a&GaV/$ Yi, Yo = mole fraction of acetone in the gas phase in the inlet and outlet of the absorber, respectively. Yo* = equilibrium mole fraction of acetone in the gas phase corresponding to the concentration of acetone in water at the outlet of the reactor .iYh = logarithmic mean concentration,kmol of acetone/kmol of mixture V = volume of the absorber, m3 Greek Letters a = volume fraction of the gas in pl = density of the liquid, kg/m3
the gas-liquid mixture
Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 277 pl
= viscosity of the liquid phase, (N s)/m2
vI = kinematic viscosity of the liquid phase, (m2/s) u1 =
surface tension of the liquid phase, kgf/m
Subscripts and Superscripts g = of the gas 1 = of the liquid * = at equilibrium
Appendix: A Common Basis for Comparison of the Data The experimental procedure was such that different values of Yi were obtained for various combinations of water and air flow rates. This gave different rates of absorption of acetone, N = L(C, - Ci) = LC, (because C, varied as a function of Yi).The normalization procedure of the data was based on the fact that a plot of N vs Yi in the range of the experimental measurements gave a straight line. Thus, for each pair of L and G,, the following procedure was adopted. By varying the temperature of acetone in the air saturator, it was possible to obtain the N-Yi line. For all individual pairs of L and G,, an arbitrary constant value of Yi which lies within the range of the experimental values was selected and a value of N was determined from the above N-Yi plot. The N's were then normalized according to N(P2,T2)= N(P1,TJ(P1/P2)0~5 X (T2/T1)0.75 (and also for &a) as suggested by Nijsing et al. (1959) where T2 = 298 K and P2= 1 atm. Thus, it was possible to obtain values of N corresponding to different pairs of L and G, at the same inlet concentration of acetone, Yi, and identical valuss of T and P. The normalized quantity of C, is N I L = C,. The quaptity Y,js obtained from the mass balance G(Pi - Yo)= LC,, and Yo*is calculated from the equilibrium relation. Thus, it is possible to obtain the normalized &a from eq 3. Registry No. Acetone, 67-64-1. Literature Cited Chawala, J. M.; von Bockh, P. Kritische Massenstromdichte von Flussigkeit/Gas-Gemischen. Chem.-Zng.-Tech. 1971, 43,
1106-1108. Elperin, I. T. Transfer Processes in Impinging Jets (in Russian). Nauk. Tekh. Minsk 1972,213. Gianetto, A,; Silverston, P. L. Multiphase Chemical Reactors; Hemisphere Publishing: New York, 1986. Herskowits, D. Absorption with Impinging-Streams. Ph.D. Thesis, Institute fur Thermische Verfarhrenstechnik, Universitaet Stuttgart, Stuttgart, West Germany, 1990. Herskowits, D.; Herskowits, V.; Tamir, A. Desorption of Acetone in A Two-ImpingingStreams Spray Desorber. Chem. Eng. Sci.
1987,42,2331-2337. Herskowits, D.; Herskowita, V.; Stephan, K.; Tamir, A. Characterization of a Two-Phase Impinging Jets Absorber, Part I: Physical
Absorption of Carbon Dioxide in Water. Chem. Eng. Sci. 1988, 43,2773-2780(in the abstract, the mass-transfer coefficientsvary s-'). within the range (2.5-122)X Herskowits, D.; Herskowits, V.; Stephan, K.; Tamir, A. Characterization of a Two-Phase Impinging Jets Absorber, Part 11: Absorption with Chemical Reaction of Carbon Dioxide in NaOH Solutions. Chem. Eng. Sci. 1989,in press. Kitron, A. Analysis of Stochastic Interaction Phenomena in Heterogeneous Systems. Ph.D. Thesis in Chemical Engineering, Ben Gurion University of the Negev, Beer Sheva, Israel, 1990. Kitron, Y.; Tamir, A. Performance of a Coaxial Gas-Solid TwoImpinging-Streams (TIS) Reactor: Hydrodynamics, Residence Time Distribution, and Drying Heat Transfer. Znd. Eng. Chem. Res. 1988,27,1760-1767. Kitron, A.; Buchmann, R.; Luzzatto, K.; Tamir, A. Drying and Mixing of Solids and Particles RTD in Four-Impinging-Streams and Multistage Two-Impinging-Streams Reactors. Znd. Eng. Chem. Res. 1987,26,2454-2461. Luzzatto, K.; Tamir, A. Combustion of Gas in a Two-Impinging-Wall Jets Combustor, Combust. Sci. Technol. 1989,65, 67-81. Nijsing, R. A. T. 0.; et al. Absorption of C02 in Jets and Falling Films of Electrolyte Solutions With and Without Chemical Reaction. Chem. Eng. Sci. 1959,10,88-104. Pawlowski, J. Die Ahnlichkeitstheorie in der physikalisch-technischen Forschung, Grundlagen und Andwendung; Springer: Berlin,
1971. Tamir, A. Absorption of Acetone in A Two-Impinging-Streams Absorber. Chem. Eng. Sci. 1986,41,3023-3030. Tamir, A. Processes and Phenomena in Impinging-StreamsReactors. Chem. Eng. Prog. 1989,85,53-61. Tamir, A,; Falk, 0. Hydrodynamics and Dissolution of Solids in a Semibatch Cyclone Reactor and a Two-Impinging-StreamsSemibatch Reactor. Znd. Eng. Chem. Res. 1988,27,1930-1936. Tamir, A.; Grinholtz, M. Performance of a Continuous Solid-Liquid Two-Impinging-Streams Reactor: Dissolution of Solids, Hydrodynamics, Mean Residence Time, Hold-up of the Particles. Znd. Eng. Chem. Res. 1987,26,726-731. Tamir, A.; Herskowits, D. Absorption of C02 in A New Two-Impinging-Streams Absorber. Chem. Eng. Sci. 1985,40,2149-2151. Tamir, A.; Kitron, A. Applications of Impinging-Streamsin Chemical Engineering Processes-Review. Chem. Eng. Comm. 1987,50,
241-330. Tamir, A.; Kitron, Y. Vertical Impinging-Streams and Spouted-Bed Dryers: Comparison and Performance Characteristics. Drying Technol. 1989,7,183-204. Tamir, A.; Luzzatto, K. Solid-Solid and Gas-Gas Mixing Properties of A New Two-Impinging-Streams Mixer, AZChE J. 1985a,31,
781-787. Tamir, A,; Luzzatto, K. Mixing of Solids in Impinging-Streams Reactors. J. Powder Bulk Solids Technol. 198513,9, 15-24. Tamir, A.; Sobhi, S. A New Two-Impinging Streams Emulsifier. AZChE J. 1985,31,2089-2092. Tamir, A,; Elperin, I.; Luzzatto, K. Drying in a New Two-Impinging Streams Reactor. Chem. Eng. Sci. 1984,39 (l),139-146. Ziv, A,; Luzzatto, K.; Tamir, A. Applications of Free-ImpingingStreams to the Combustion of Gas and Pulverized Coal. Combust. Sci. Technol. 1988,60, 31-44.
Received f o r review May 8,1989 Revised manuscript received October 10,1989 Accepted October 27, 1989
