Absorption of Gases in Spray Towers A. W. HIXSONAND C. E. SCOTT,Columbia University, New York, N. Y.
T
HE absorption of gases in liquids h a s i 11 t e r e s t e d
many investigators . C o n s i d e r a b l e work has been done on the resistance to gas flow (27), the distribution of the liquid over the packed surface (S), the form of the packing material, and the mechanism of transfer ( 2 , 7 , 9, 10, 13, 15, 16, 21, 25, $4, 25, 27). S o study has been reported in the literature on the earliest type of absorption apparatus, the spray tower (12, 17). It has been the purpose of this investigation to obtain data on the absorption of typical gases in Ypray towers and to discover, if possible, a correlation for the more important variables.
COKCEPTS O F hfATERIAL TRAKSFER The following mathematical equation for expressing the mechanism of material transfer from a gas to a liquid has been developed by Lewis (24): PHYBIC.4L
where P = gas concn. C = liquid concn. S = interfacial surface dW/de = weight of material transferred per unit of time Subscripts g, i, L refer, respectively, to conditions at the outside of the gas film, a t the interface, and at the inside of the liquid film. Equation 1 in the integrated form is: 0 := K g a V(AP)*". (2) weight of material absorbed, lb./min. a = interfacial area, sq. ft./cu. ft. of tower vol. (an indeterminate quantity and usually expressed with K g as Koa) Koa = material absorbed, 1b.l min./cu. ft. of tower vol. /mm. of partial pressure driving force V = vol. of the tower, cu. ft. ( AP)av. = logarithmic mean p a r tial pressure (driving force) difference in the s o l u t e gas and the l i q u i d between the top and bottom of the tower
where W / e
=
The evaluation of these over-all coefficients under various
conditions has been determined hy a number of investigators. Seedless to state, the data are far from complete even with the most common gases. Hasl a m , H e r s h e y , and Keen (9) give data for the absorption of sulfur dioxide in a wetted wall tower. These authors have analyzed the data and found that the over-all gas film resistance, 1/K, is proportional to 1/G0.8, where G is the mass velocity of the gas. The correlated data of several workers (24) i n this field indicate that for a packed column the o v e r - a l l t r a n s f e r resistance is p r o p o r t i o n a l to where L / A represents pounds of effluent per
Over-all transfer coefficients f o r the absorption of ammonici and sulfur dioxide into a water spray, and the absorption of benzene vapor from air into art, oil spray, were determined for a n inner "wall-free" section of a spray type absorption tower. The effects of variable jluid jlows at three tower heights were investigated. Empirical equations indicating the correlation of these variables are developed and the results compared, when possible, with previous accepted data. The use of these equations for practical spray tower design is pointed out with special consideration of their limitations. I
~V'WGO.~
square foot per minute. Kowalke and others ( I S ) , working on the absorption of ammonia in various types of towers, took the over-all coefficient and set it equal to the sums of the conductances of the liquid and gas films, and various equations were developed by these authors to show the difference between the true absorption coefficient and the distribution factor of the liquid. Hanks and McAdams (8) have investigated the effect of various carrier gases on the absorption coefficient and have made use of the Reynolds modulus to demonstrate their results. They show that the coefficient is a function of the modulus. Colburn ( d ) , from consideration of heat transmission coefficients of Colburn and Hougen (6), has developed a theoretical equation for mass transmission coefficients. Agreement of this equation with experimental data for both dehumidification and absorption in a packed tower is given to prove the theory. Hennel ( I I ) , in a n attempt to contribute to the mathematical analysis of the packed absorption tower, has proposed a method of obtaining the height of the tower by using a method other than the saturation curve method of other investigators (24). However, no illustrations or experimental data are given to substantiate this analysis or its adaptation to design practice.
FIGURE1. DIAGRAM OF APPARATUS 307
L4.BSORPTION BY
SPRAYSAND DROPS W h itm a n , Lo n g , and Wang (26) have studied the absorption coefficient of a single falling drop of water in carbon dioxide, in ammonia, and in the humidification of dry air. The size of the drop was made to vary over a small range and al-
INDUSTRIAL AND ENGINEERING CHEMISTRY
308
16 14
I2
10
-8
I"
.3 e
6
0 x
g 4
'r:
I
2 0
10 20 30 40 50 L = L B S . W A T E R / 5 Q F T J MIN.
0
60
70
2
3
4
5
H : H E I G H T OF T O W E R IN FT. FIGURE 4. Koa vs. H; MEANSLOPE= -0.5; K,a a HQ.6
FIGURE2. VALUESOF Koa AT SEVERAL GAS LIQUIDFLOWRATESFOR SPRAYSECTION
AND
lowed t o f a l l a given d i s t a n c e . From the results of this investigation it is evident that the over-all c o e f f i c i e n t s obtained in this manner are very much greater than those obtained over flat surfaces. Morgan (18) in discussing the results of these workers (26) points out that the values o b t a i n e d by the 20 30 40 50 60 falling drop L = LB.5. WATER/SQ.FS;/ MI N. method are about five hundred times FIGURE 3. K,avs. L; MEANSLOPE= 1; K,a L greater than those obtained over a flat surface. He indicates that the falling drop, by the velocity of its fall and any rotary motion during the fall, would tend to give a comparatively thin film of stagnant gas. For this reason it is believed that, while the packed tower offers a greater absorption surface owing to the liquid flowing over the packing, the thickness of the stagnant film of gas is enormously increased. One of the chief difficulties in the design of a spray tower is the problem of distributing the liquid in fine drops. Unless the drops are small, the surface of the liquid is small in comparison to its volume. If the drops are very small, similar to atomized spray, the gas stream will carry them out of the tower. Lenard ( I C ) , in observing the action of rain drops, believes that a drop cannot fall with a terminal velocity greater than 8 meters per second. Drops large enough to fall with a greater velocity are broken up and considerably deformed before disruption. A drop initially spherical is found to take the shape of an inverted cup before it bursts into fragments. The velocity of uprushing air required to keep drops in suspension varies from 6.4 to 8 meters per second when the drop varies from 2.5 to 6 mm. in diameter. The velocity of disruption varies from 10 to 20 meters per second.
Vol. 27, No. 3
KO data are reported in the literature on a correlation of the effect of tower height and fluid flow on the over-all coefficient. One investigator has reported data on the spray absorption of ammonia a t a constant tower height (9), with varying liquid and gas flows. Another (IS) has reported data for sulfur dioxide a t a fixed liquid flow at a cons t a n t tower height. In order to contribute to this gap in the literature the following investigation, using different tower heights as well as varying gas and l i q u i d flows, was u n d e r taken.
APPARATUS AND EXPERIMENTAL METHOD SPRAYTOWER.This was constructed of galvanized-iron tubing of 2'/8 inches (7.3 cm.) inside diameter. The tubing was mounted on a short glass section of the same inside diameter, in order to observe the action of the falling s ray. By connecting additional lengths of tubing, the tower couyd be extended from 19 to 54 inches (48 to 137 cm.). All joints were neatly butted and smoothed so that a minimum of flow disturbance would be encountered. The collector plate a t the bottom of the tower was made of 3-mm. wrought iron. Circular partitions were arranged so that samples of the falling spray could be obtained from an inside wall-free section of l a / 8 inches (3.5 cm.) in diameter. Finally an outer ring was placed to separate and collect the liquid running down the side of the wall. Even distribution of the entering gas was secured by means of an annular copper tube s u p ported above the collector rings, and perforated on the top and sides with l/le-inch (1.6-mm.) holes on 3/*-inch (9.5-mm.) centers. Exit liquor tubes were l/r-inch (6.3-mm.) iron pipe, and a small S-trap in each prevented any gas entrainment in the effluent. It was found that this arrangement would handle flow rates up to 1550 cc. per minute (76 pounds per square foot per minute) without flooding the tower. The top of the tower was constructed as illustrated in Figure 1. Gas was withdrawn into a piezometer ring and from this ring was made to flow over wetand dry-bulb thermometers. SPRAYNOZZLE.Several commercial nozzles of the so-called full cone type were tried. However, on actual test all of these nozzles produced an uneven spray attern. A spray nozzle was developed in this laboratory and kund t o be satisfactory from a viewpoint of even spray distribution. While this nozzle produced a rather large drop 0.059 to 0.078 inch (1.5 to 2.0 mm.) in diameter, it proved ideal for the conditions of experimentation. It was constructed by drilling a 3/ls-inch (4.75-mm.) brass plate with thirty-seven holes, 0.028 inch (0.71 mm.) in diameter spaced on 3/8-inch (9.5-mm.) centers. Even spray distribution could be obtained by this arrangement at any rate of flow in excess of 200 cc. per minute. Below this rate a large trickling stream would be produced at the center of the nozzle. The length of the liquid jet from the nozzle until spray occurred was found t o vary with the liquid flow. The relationship between jet length end liquid flow for the nozzle used in all of the following experiments is as follows: TOTAL FLOW
Cc./min. 450 600 766 920
1100
LENGTEOF LIQUIDJET8
Cm. 0.2 1.7 2.5 3.3 3.9
The minimum height of tower used was 19 inches (48.3 cm.), and at the maximum flow of liquid down the tower the liquid jet was only 8 per cent of the total hei ht. At the extended tower height of 54 inches (137.2 cm.) the% uid jet was only 2.8 per cent of the tot,al height. While these %stances represent a small section of the tower, it is apparent that the absorption taking place in the liquid jet is negligible. The jet is in the zone of lowest solute gas concentration, and the surface area exposed
March. 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
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30 to the gas is small in c o m p a r i s o n to the volume of liquid flow25 ing. Over the range of flow encountered in the following experiments, 20 the exit liquid velocity 3 from the nozzle varied from 0.23 to 1.58 feet d ‘5 (7 to 48 cm.) per sec0 ond. IO GAS PRESSURE u . Y REGULATOR.In all of t h e experiments a i r 5 was used as the carrier gas. The s o u r c e of 0 s u p p l y w a s a large 0 IC 20 30 40 50 60 70 compressed-air t a n k L LBS.WATER/5Q.F%/MIN. which supplied the enFIGURE6 . VALUESOF Koa AT SEVERALGAS ” tire building, and slow IC 20 30 40 50 60 70 AND LIQUIDFLOW RATESFOR SPRAYSECTION fluctuations in pressure L: LB5. WATER /W.FT,/MIN. would result over the time necessary to make FIGURE 5 . CALCULATED us. EXPERIMENTAL a run on the appara25 VALUESFOR K,a tus. A pressure reguI I lator was constructed and is shown diagramrriatically in Figure 1. In actual operation l o g a r i t h m i c cothe bell “hunted” slightly and kept a constant static pressure ordinates. Figure on the line within 2 mm. of the desired value. G4s HUMIDITY.Wet- and dry-bulb thermometers were in- 3 i l l u s t r a t e s the stalled to determine the partial pressure of the water vapor in variation in slope the entering and exit gases. The total pressure was always a t s e v e r a l condicorrected for the amount of water vapor carried by the gas. tions of a b s o r p tion, and while all L4BSORPTION OB AMMONIA of the lines indiAmmonia gas was introduced into the apparatus from a cate a trend with cylinder of the compressed gas. While the concentration a slight variation, could be varied within wide limits, it was decided to keep the t h e solid l i n e is range between 1 and 3 per cent. drawn t o represent The amount of ammonia in the gas was determined by t h e m e a n s l o p e . bubbling a portion of the gas into standard hydrochloric acid, T h i s i s approxiand the residual gas leaving the absorption bottle was me- mately unity. tered, as shown by Figure 1. From the volume of standard Figure 4 illusacid used and the amount of residual gas as registered by the trates the effect of meter, the gas concentration was calculated. I’opoff (20) constant gas and 15 20 30 40 50 00 shows that the electrometric titration curve for ammonia liquid flow condiL: LBS. WATER /SQ.FT/MIN. with hydrochloric acid is such that methyl orange can be t i o n s a t s e v e r a l used as an indicator. The amount of ammonia absorbed by d i f f e r e n t t o w e r FIGURE7 . K,a vs. L; MEANSLOPE = the tower at any given set of conditions was determined by h e i g h t s o n t h e 0.9; Koa a Lo.@ titrating a sample of the effluent to a methyl orange end point o v e r - a l l coeffiwith hydrochloric acid. This method was correct for the cient. This plot was constructed from the data of Figure residual alkalinity of the tap water. 2 in which the absorption coefficient a t a given set of fluid The solubility of ammonia in water a t low concentrations flow conditions may be plotted against the height of the has been determined by Kowalke, Hougen, and Watson (IS). tower. Three slopes, one for each of the conditions of liquid These data are necessary in order to determine the back pres- flow a t 20, 40, and 60 pounds per square foot per minute sure of the ammonia in the effluent. Over-all coefficients (0.162, 0.324, and 0.486 gram per sq. cm. per second) are have been determined a t several tower heights and fluid shown, and the solid line indicates a mean slope of approxiflows. Table I contains not only the coefficients calculated mately -0.5. While the temperature of the system has an for the entire volume of the tower but also for the inner wall- important influence on the rate of absorption, sufficient data free section. These later data have been plotted against have been presented by other investigators (19) to indicate liquid flow, a t two gas velocities and three tower heights as that an increase in temperature of 20” C. produces a negligible shown by Figure 2. Since the falling spray strikes the wall effect on the over-all coefficient. I n the temperature range and runs down slowly, a higher concentration of ammonia covered by these experiments, the over-all coefficient may be should be expected from the total tower effluent than from expressed as the inner wall-free section. I n order to avoid any erroneous conclusions which might result from considerations of the “wall effect,” all data correlation was made on the inner core where C = a constant section. G, L = gas and liquid, respectively, lb./sq. ft./min. The effect of gas flow on the rate of absorption has been inH = height of tower, ft. vestigated by several workers (9), and the results indicate that the coefficient varies directly as the 0.8 power of the mass The value of C in Equation 3 has been found to be approxigas flow. This well-established value has been used for pur- mately 2.5 X poses of data correlation in this work. From the data as While Koa involves an area term, a, it is practically imposplotted in Figure 2, the value of K,a a t constant gas flows sible to evaluate K , alone. However, if it is assumed that the and tower heights was plotted against the liquid flow on full drops are spherical and fall under the action of gravity, the h
3
/r97
INDUSTRIAL AND ENGINEERING CHEMISTRY
310
TABLE I. ABSORPTIONOF RUN NO.
GAS I N
E: Ei: c.
O
c.
Wet bulb C.
%I
-TOTAL C.
Cc./min.
EFFLUENTC.
G./1.
TOWER 18 INCHES (48.8 CM.) I N HEIGHT;
1 2 3 4 5 6
16 16 14 15 15 15
23 22 22 21 23 23
19 16 15 16 18 16
7 8 9 10 12
13 13 13 14 14 14
23 23 23 24 24 24
16 16 16 14 14 14
20 20 20 21 20 20
13 14 15 16 17 18
16 16 16 16 16 16
24 24 24 24 24 24
15 15 15 15 15 15
21 22 23 22 22 22
980 740 902 476 620 866
19 20 21 22 23 24
13 13 11 12 13 13
22 22 21 21 23 23
14 14 12 12 13 13
17 17 17 17 19 19
550 560 948 670 876 954
25 26 27 28 29
13 14 15 15 15
22 25 25 23 23
17 17 18 21 21
23 24 25 23 23
560 716 726 900 1031
30 31 32 33 34 35
17 12 13 14 14 14
22 22 23 24 24 24
14 14 14 15 15 15
19 19 19 19 19 19
730 720 1026 800 410 745
SPRAYSECTION Cc./min. G./L GAS FLOW 1.80 LB./SQ.
WATERSPRAY WATER IN
In
OC.
%
AMMONIA out
1.7 1.7 1.4 0.9 1.7 1.4 952 500 552 1200 700 630
0.431 0.330 0.261 0.530 0.445 0.498
GAS FLOW 2.73 LB./BQ.
7 7 7 7 7 7
338 120 105 405 164 102
TOWER 27 INCHES (68.6 CM.) I N HEIGHT;
0.160 0.176 0.187 0.105 0.630 0.480
7 7 7 7 7 7
300 205 280 86 162 246
T O W E R 27 INCHES I N HEIGHT:
0.470 0.260 0.390 0.250 0.320 0.250
7 7 7 7 7 7
(0.0221 GRAM/SQ
FT./MIN.
0.165 0.277 0.202 0.257 0.385 0.386
7 7 7 7 7 7
Rga Core
x
10' Total
%
(o.oio GRAM/SQ.
FT./MIN.
23 20 19 21 23 20 TOWER 19 INCHES IN HEIGHT;
11
AMMONIA BY A
GASOUT
Vol. 21, No. 3
GASPREESURE
Mm. Hg
CM./SEC.)
0.14 0.11 0.07 0.03 0.10 0.07
5.7 6.0 5.2 5.9 5.4 5.9
11.0 10.0 10.7 11.7 11.4 11.4
0.07 0.07 0.08 0.16 0.20 0.17
17.9 13.0 11.0 14.5 15.0 9.9
26.5 20.4 23.5 28.0 23.6 24.9
0.10 0.10 0.10 0.10 0.20 0.20
8.30 5.00 6.50 3.12 4.60 7.20
11.30 6.40 7.90 11.00
0.10 0.10 0.10 0.20 0.15 0.10
6.80 5.50 7.82 7.60 8.90 10.90
17.7 16.4 14.2 14.6 14.5 14.6
0.15 0.15 0.20 0.20 0.20
3.40 3.20 2.00 8.00 8.10
4.80 4.50 2.20 1.20 0.92
0.11 0.12 0.09 0.17 0.15 0.18
6.30 5.20 15.00 6.30 6.80 15.00
14.80 14.70 10.40 10.20 15.80 9.00
CM./SEC.)
1.1 0.5 0.4 1.7 1.1 1.0
868 864 869 872 872 870
GAS €LOW 1.80 LB./SQ. FT./MIN
0.051 0.165 0,114 0.095 0.460 0.358
7 7 7 7 7 7
1.0 1.1 0.8 0.5 2.9 2.9
10.00 6.80
GAS FLOW 2.78 LB./SQ. FT./MIN.
85 70 182 176 260 188
0.350 0.232 0.266 0.246 0.210 0.240
7 7 7 7 7 7
0.72 0.46 1.21 0.78 0.96 0.83
TOWER 64 INCHEB (187.2 CM.) I N HEIGHT: GAS F L O W 1.80 LB./BQ. FT./MIN.
0.240 0.180 0.340 0.300 0.260
9 9 9 9 9
151 160 155 338 278
TOWER M INCHES IN HEIQHT;
0.730 0.420 0.380 0.730 0.960 1.040
9 9 9 9 9 9
0.200 0.180 0,200 0.210 0,180
9 9 9 9 9
GAS F L O W 2.13 LB./SQ.
155 145 330 93 85 292
0.470 0.340 0.520 1.230 1.440 0.520
No.
Wet bulb 0
c.
Dry bulb
c.
Wet bulb C.
i%% -TOTAL EFFLUENT"C. Cc./min. G./1. O C. 18
11 11 12 12 14 14
18 18 18 19 21 21
17 17 17 17 18 17
18 l8 18 21 21
7
9 10 11 12
16 15 15 15 13 13
28 26 25 25 21 21
22 24 21 21 21 20
25 25 23 24 22 21
13 14 15 16 17 18
12 13 15 17 14 14
20 20 25 25 24 24
18 19 20 20 20 20
19 20 23 23 22 22
610 730 950 1056 1174 875
1.26 1.41 1.07 1.26 0.95 1.24
16 16 16 16 16 16
143 200 380 396 440 293
0.97 1.09 0.75 0.92 0.65 0.95
TOWER 27 INCHES (68.8 OM.) IN HEIGHT;
8
1391 471 640 795 910 1136
0.21 1.67 1.14 0.98 0.97 0.82
TOWER
a INCHES
513 834 1132 964 1386
1.13 1.36 1.17 1.21 0.78 1.92
660
21 20 20 20 20 20
19 20 21 22 23 24
14 14 13 13 14 14
23 23 22 23 22 22
15 15 15 15 15 15
19 18 17 17 17 17
1262 752 800 1110 615 450
25 26 27 28 29 30
11 11 12 13 14 14
20 22 22 23 25 25
17 17 17 18 15 15
l9 14 14 20 19 19
850 720 1086 1044 866 700
0.87 1.26 0.97 1.02 1.10 1.70
20 20 20 20 20 20
146 262 362 303 375 180 437 275 305 398 210 175
TOWER 27 INCHES I N HEIGHT;
1.31 1.82 1.02 0.87 1.00 1.61
TOWER 64 INCHES
12 12
11
12 12 11
23 21 20 21 21 22
17 21 15 16 16 15
22 23 20 21 22 21
840 740 1046 409 1170 634
1.51 2.42 1.78 2.44 2.45 2.71
11 11 11 11 11 11
16
16
20 18 18 18 18 18
0.65 0.95 0.75 0.80 0.63 1.24 FT./MIN.
0.58 0.87 0.77 0.70 0.85 0.97
19 19 19 19 l9 19
214 210 357 169 390 276
K@ x lo$ Core Total
GAS
Out
%
(o.ous GRAM/SQ. 3.19 3.19 2.74 3.19 3.19 3.18
1.28 1.06 0.91 1.28 0.80 0.90
9.0 15.7 22.8 24.0 22.5 19.5
16.1 23.6 26.4 28.0 27.8 24.4
0.13 0.64 0.64 0.53 0.53 0.53
6.04 1.10 3.40 3.80 6.20 5.03
20.6 12.6 15.2 18.8 21.0 21.8
770 772 770 774 772 770
0.32 0.34 0.30 0.29 0.23 0.53
1.54 3.96 4.38 4.25 4.50 2.80
8.93 16.70 19.50 19.10 18.00 15.60
770 774 770 772 768 772
0.80 0.90 0.90 0.90 0.88 0.85
28.4 23.4 24.9 26.1 17.5 11.5
39.5 29.5 26.2 33.5 28.0 20.0
868 872 870 876 874 870
0.93 0.93 0.58 0.46 0.58 0.93
20.2 16.0 22.6 21.1 19.2 22.6
29.8 25.7 31.5 32.8 29.4 25.7
874 872 873 876 870 872
0.46 0.77 0.66 0.51 0.83 0.76
12.6 12.6 12.6 11.0 14.2 13.5
26.1 22.5 23.7 16.0 26.2 22.2
870 876 878 878 876 874
PRE8SURn
Mm. Hg
CM./SEC.)
FT./MIN.
0.98 3.20 2.60 2.60 2.60 2.60
0.97 1.31 0.70 0.68 0.73 1.31
2.14 2.74 2.74 2.74 2.40 3.20
(0.0221 GRAM/SQ. CM./SEC.)
12 12 12 12 12 12
QAS FLOW 2.78 LB./SQ.
278 212 340 268 254 292
IN HEIGHT:
10 10 10 10 10 10
7SO2-
%
GAS FLOW I . @ LB./SQ. FT./MIN.
GAS FLOW 2.73 LB./BQ.
12 12 12 12 12 12
16 16 16
WATER SPRAY In
GAS FLOW 1.80 LB./SQ.
0.14 0.47 0.47 0.42 0.29 0.26
483 105 222 218 296 380
( 1 1 . 2 CM.) I N HEIGHT;
TOWER 19 INCHES IN HEIQHT;
31 32 33 34 35 36
A
SPRAY SECTION WATERI N Cc./min. G./1. 'C .
TOWER 19 INCHES (48.3 CM.) I N HEIGHT; GAS FLOW 1.80 LB./SQ. FT./MIN.
1 2 3 4 5 6
1.21 0.79 0.93 1.58 1.13 1.31
Gas OUT
GASIN
774 769 770 769 770
FT./MIN.
9 9 9 9 9 9
TABLE11. ABSORPT~ONOF SULFURDIOXIDEBY RUN
0.78 0.78 1.31 1.30 1.20
10 10 10 10 10 10
1.60 1.92 1.60 1.68 1.61 1.70 FT./MIN.
1.39 2.33 1.39 1.26 1.16 1.74
GAS FLOW 2.18 LB./SQ. FT./MIN.
1.01 1.72 0.97 1.27 0.88 1.25
9 9 9 9 9 9
1.16 2.00 2.00 1.60 2.32 2.15
March, 1935
INDUSTRIAL A V D ENGINEERING 25
CHEMISTRY
311
interfacial surface a t several flow congree of turbulence a t the interface. ditions may be calculated roughly. Figure 5 illustrates the agreement 20 The time required to fall 1.58 feet between the calculated values of K,a (48.4 cm.) is about 0.3 second, and in from Equation 4 and that experimen15 tally obtained. While the correlation this time there would be nearly 95 is not so close a t the high gas flow, it standing drops a t a flow rate of 20 is fairly good a t the lower one. The pounds per square foot per minute (0.162 gram per sq. om. per second). two extreme conditions of tower height and gas flows have been illustrated in When the flow rate if; increased to 50 2 IO pounds per square foot per minute $2 Figure 5. However, the intermediate (0.405 gram per sq. cm. per second), tower heights give a better correlation. -0 8 x there are approximately 240 standing While the two gas velocities used in U drops. The surface exposed, therethis work are in t h e c o n d i t i o n of r " 6 fore, varies from 0.9 to 2.4 square feet straight-line flow, no doubt a great of interfacial area per cubic foot (2.95 deal of the turbulence is produced by X lo4 sq. cm. to 7.83 X lo4 sq. cm. the falling spray and by the relatively per cubic meter) of tower volume. large end effects in such an apparatus. 4 Using a value of a of 2.4 square feet of However, the use of the equation for interfacial area per cubic foot of tower design practice would necessarily be 3 limited to conditions which are comvolume, a t a tower height of 1.58 feet 1.5 2 (48.4 cm.), K , a t 2.73 pounds of gas parable to the experimental limitaH: HEIGHT OF TOWER IN FEET per square foot per minute (0.022 gram tions, such as drop size, same ratio of '. MEAN per sq. cm. per second) is found to be length to diameter, and same relative K,a a H-0.5 7.1 X pound of ammonia per degree of turbulence. square foot per mm. partial pressure of ammonia per minute ABSORPTION OB SULFUR DIOXIDE (5.75 x gram of m m ~ n i aPer sq. cm. Per mm. Partial Sulfur dioxide was supplied to the apparatus from a large pressure of ammonia per second). Previous workers, using a cylinder of the compressed gas. The same general arrangewetted wall column, report a value ment was used as that for the abof K , equal to 5.5 >
