PETROLEUM
EXCISEERING LABORATORIES, UNIVERSITY
O F OKLAHOhlA
Factors Affecting Entrainment in Bubble-Cap Columns WILLIAM T. PYOTT,' C. A. JACKSON,
NTRAINMENT in absorbers and fracAND R. L. HUNTINGTON tionating towers has long been recognized University of Oklahoma, Norman, Okla. to be one of the chief limiting factors govlerning the capacity of such columns. I n their-effort to inhave found crease the capacity - - of such equipment,, designers tative data are not available showing the relative magnitude that high vapor velocities prbmote more rapid rates of apof certain factors, such as tray spacing, mass velocities of proach toward equilibrium conditions between countercurvapor, liquid rates, submergence, plate design, and certain rent streams of vapor and liquid. In other words, the inphysical properties of the materials processed, such as surface timacy of contact and less resistant films of vapor and liquid tension, density, viscosity, etc. resulting from these higher vapor velocities offset by far the Souders and Brown (10) have reported results in which element of time, often considered a controlling factor in many the effects of liquid and vapor velocities as well as surface processes. The problem, therefore, resolves itself into one of reducing entrainment. tension were emphasized. Their theoretical attack has At the mesent. entrainment is being minimized in several paved the way for further research in this field. Chillas and ways. Increase bf plate spacing has accomplished the result to a certain degree, but a t the expense A brief description of the column constructed for this work is given. of added i n v e s t m e n t . Larger The effect on entrainment of temperature, linear and mass velocity of downspouts have, perhaps, netted the vapor, plate spacing, and physical characteristics of the product the g r e a t e s t r e t u r n , since the has been investigated. T w o systems have been studied : kerosene-air p i l i n g u p of l i q u i d on a tray amounts to the same thing as reand water-air. ducing the plate spacing. Mist Temperature, in general, produces an increase in the amount of extractors located between trays entrainment. Entrainment may be decreased by such methods as its well as a t the top of towers offer greater tray spacing, slower linear velocity of the gas, and less rate of promising possibilities . The flow of the circulated liquid. Equations of a general nature are proeffects of these improvements in commer ci a1 equipment can be posed. Their application is limited, but they are of value over a noted in a rather rough qualitamoderate range of the variables i n question. tive way, but sufficient quantiThe impossibility of comparing entrainment effects of the two liquids in question is discussed. * Present address, Great Lakes Pipe
@E
Line Company, Ponca City, Okla.
821
Keir (3) hare rep o r t e d quantitative data on a viater-air system . They have also shown the efficacy of using mist ext r a c t o r s o f bhe Yen e t i ai1 b l i n d t y p e . Holbrook a n d R a k e r (4) studied a steamsalt water system. Their results are interesting, especially to those industries employing evaporation a n d drying processes. Ashraf, Cubbage, and Huntington ( I ) have recently reported entrainFIGURE1. SCHEMATIC DIAGRAM OF ment data in EXPERIMENTAL APPARATUS which t h e equations as presented by Souders (IO) and also by Carey (2) were largely substantiated. The work of Ashraf and eo-workers included the effects of the density and mass velocity of the vapor. In this investigation, the influences of temperature and liquid rates have been emphasized. Rhodes (T) has studied the effect of entrainment on plate efficiency in rectification. Sherwood and Jenny (9) have also presented entrainment data, and the effect of gas velocity, plate spacing, and liquid effect has been clearly shown. They have included sample calculations on entrainment effects. Kallam (5, 6) has discussed various factors influencing absorber capacity.
Experimental Work
means of a centrifugal pump. The flow of liquid was metered and adjusted to any desired rate. The circulating liquid was pumped into the tower slightly above the lower tray and allowed to splash doT1-nonto this tray. The downspout of the upper tray was kept TABLE 1. DIMESSJOSS Tower: Inner diam., inches No. of chimneys Chimnev: Inner'diam inches Outer diam.: inches Length Eroni bottom of plate, inches Ratio. cross-sectional area of.ohimnevs t o t h a t of tower Bubble cap (square in shape): No. of caps Bubble caps: Inner dimensions, inches Outer dimensions, inches
12.b
2 2 2310 2'/k 0.05
2
x 35/a 4.0 X 4.0
3'/a
32 1.
&&th inches Width 'inches Area, :quare inches Ratio, slot area to tower area Liquid s u b m e r g e n ~ einohes ,~ Prom the top of the slots t o the surface of the liquid.
*/la
12
0.0975 1 .0
TABLE 11. PROPBETIES OF MATEEIALB Liquid
Specifio Gravity
Viscosity (Centipoises) 10Oo 12Q0
80°
Kerosene Water (bluingsoln.)
0.816
1.00
F.
F.
F.
1.8
I,?
1.6
Surface Tension (Dynes/Cm.) %OO" 120O
SOo
P.
F.
F.
31.6
30.3
2Y.4
0.86 0.69 0.58 6 6 . 2
i
j
.~
80.5
plugged. A constant temperature was maintained by the use of a tube bundle in the bottom of the tower through which steam was fed. In the case of both kerosene and water, the clear product was placed on the upper tray, The circulating liquid was highly
colored with a nonvolatile dye. The degree to which the dear liquid, in the upper tray, was colored at the end of the run gave a measure of the amount of entrainment. In the case of kerosene, oil-soluble I-hydroxy-4-p-toluidoanthraquinone IT as used as a. dye, whereas with water, ordinary laundiy bluing \r.a; used.
Effect of Temperature Figure 2 shows the effect of mass velocity and temperature on entrainment. It i s obvioue that entrainment shows il
The authors have attempted to reproduce as nearly as possible actual commercial conditions, Table I gives the dirnens i o n s of the semi-comi n e r c i a l c o l u m n used. The physical properties of the kerosene and water are given in Table I1 and the original data appear in Tables III and 1V. Every other run of the F series is reported in Table IV. Figure 1gives a schematic diagram of the apparatus, a photograph of which appeared in a previous comniunication ( I ) : The 'bottom tray in the tower rested on a flange and was packed in with asbestos wicking soaked in sodium s i l i c a t e (40' Be.). T h e upper tray was removable, and its distance from the lower tray was adjusted by 2-00 4w L ~ N E A RVELOU~Y, FT/JEC, 200 400 varying the legs and downMASS b ' F L C C / T ~ " R J S Q . f ,? MASS MLOC! r < a- /PR"~SQf r spouts. It, too, was packed FIGWRE 3. EKTRAINYENT EKTRAINIIENT cs, into the tower with asbesFIGCRE2. EIYTRAIXMEW us. vs. LINEARVELOCITY OF FIGURE4. MASS VELOCITYOF VAPO~PAB A tos wicking. The gas used VAPOR AB A FUNCTION OF MASSVELOC~TV OF VAPOR AS A FUNCTIOR: OF PmrE SPACING was air, which was led into TEMPER ATURE FUYCTION OF TEWPERATURE the tower through 8 2-inch Pressure, 14.3 %b. per eq. in: abs.: Pressure, 143, Ib. per s q . in. Pressure, 14 3 lb. per SQ. in. abe : pipe. The liquid was circutemperature, SOo F.: kerosene-a,lr H ~ S abs: kerosene-an system; liquid kerosene-air system, liquid rate, 420 tern; liquid rate, 420 gal. per hr. rate,' 420 gal, per hr. lated over the lower tray by gal. per hr.
JULY. 1935
INDUSTRIAL AND ESGINEERING CHEMISTRY
823
marked increase with rising temp e r a t u r e . The a m o u n t of entrainment d o e s not increase very rapidly with low m a s s velocities up to a certain point; however, after this point is reached, the increase is marked. This means that FIGURE5. ENTRAINMENT vs. MASS m a s s velocities VELOCITY OF VAPORAS A FUNCTION may be increased OF TRAYSPACING without a great Temperature, SOa F.: pressure, 14.3 lb. per sq. in. abs.; kerosene-air system; liquid rate, lowering of effi420 gal. per hr. ciency up to a certain “critical” point, at which point a further increase is undesirable and will prove decidedly FIGURE7 . ENTR4INMENT detrimental. FIGURE 6 . ENTRAINMENT VS. pL.4TEspACING AS A OF VAPORAS A F~~~~~~~ OF L~~~~~ v-EThe curves in Figure 3 show that the effect of linear velocity LINEARVELOCITY FUNCTION OF PLATE SPACING LOCITY on entrainment is different from that of mass velocity, with increasing temperature. Mass velocity remains constant regardless of temperature, whereas linear velocity varies inper hr. versely with the density of the gas. At higher temperatures for linear velocities, the same temperature differential does not produce as great an increase in entrainment as in the case W = ClogE B of mass velocity measurements. Furthermore, in both cases, where W = mass velocity, lb./hr./sq. ft. entrainment tends to become equalized at low velocities, reE = entrainment, lb./hr./sq. ft. gardless of temperature. C , B = constants dependent upon plate spacing
+
Effect of Plate Spacing In Figure 4 entrainment us. mass velocity is shown for plate spacings from 16 to 30 inches. The shape of these curves is similar to those found by previous investigators (I, 5,4, IO). The same data as in Figure 4 are given in Figure 5 in which the logarithm of entrainment is plotted against mass velocity. With the exception of one point on the 24-inch spacing c u r v e , t h e c u r v e s prove to be straight lines. The general equation for these lines would therefore be :
Holbrook and Baker (4) found that their data followed an equation of this form. Figure 6 includes the same data as Figure 4 but shows the effect of linear velocity. Figure 7 gives a cross plot of Figure 6, showing plate spacing effects. It is obvious that entrainment is reduced by increasing plate spacing. The heavy entrainment for the 16inch spacing is undoubtedly due t o the splashing of large slugs and drops of liquid. Also, there is some entrainment which would take place even a t substantially zero gas velocity. This is the result of the splashing and frothing action of the circulated liquid on the lower plate.
Effect of Liquid Rate
T h e r a t e a t which the liquid is pumped over the tray appears to be an important factor (Figure 8). High liquid rates accentuate the frothing action and tend to tax the overflow capacity of the downspouts. This causes the liquid to pile up on the tray until it reaches n e a r l y t o t h e n e x t tray above. Therefore, the jetI L5 ting action of t h e v a p o r Mo 400 LtNEAR VELOCIT): FTJSEC. LIQOID PATE, GALJHR. could be quite small and FIGURE8. ENTRAIN- FIGURE9. STATICHEIGHTOF LIQUID FIGURE10. STATICHEIGHT still produce large entrainOF LIQUID ON TRAY 21s. MENT vs. LIQUIDRATE ON TRAYus. LIQUIDRATEAS A FUNCment effects. LINEARVELOCITY OF VAPOR AS A FUNCTION OF TION OF TE~WERATURE FOR A CONSTANT AS A FUNCTIONOF LIQUID EFFECT ON SUBMERGENCE. TEMPERATURE LINEAR VELOCITYOF VAPOROF 1.2 RATE Figure 9 shows the effect of Air mass velocitv. 238 lb. FEETPER SECOND Temperature, 80’ F.; pressure, t e m p e r a t u r e and vapor per 8 ~ * . ? .lger hi.:; pres14.3 Ib. per s q in. abs.: kerosure, p.er sq. in. Pressure, 14.3 lb. per sq. in. abs.; kerosene-air velocity for different liquid sene-air system system abs.: kerosene-air system
TABLE 111. EXPERIMENTAL DATA
ON
KEROSENE-AIRSYSTEM
(Tower, 12.5 inches i. d.; pressure, 14.3 pounds per square inch absolute) V --a-po,-r Linear Mass Liquid Run Entrainment velocity velocity Rate NO, Lb./hr./sq. ft. FtJsec. Lb./hr./sq. ft. Gal./h?
Iv. EXPERIMENTAL D A T A OiV f ~ . ~ - h i C1. E D. T O W E B PRESBURE OF 14 Ponms PER SQCARE INCH ABSOLUTE
TABLE AT
Run
No,
A.
16-Inch Tray Spacing; Temperature, 80' F. 0.793 0 62 175 420 258 420 0.946 0.916 1.11 1.12 316 420 1.30 1.31 368 420 1,58 1.342 378 420 1.72 484 420 2.91 B. 20-Knch T r a y Spacing; Temperature, 80' F, 426 420 0.665 1.51 E 9 1 725 486 420 E 10 0.95 538 420 9.07 1.91 E 11 0.89 1,538 433 420 E 12 0.718 202 420 0.232 E 13 0.904 254 420 0.264 E 14 0.433 1.12 316 420 E 15 14.60 0.915 258 615 E 16 2.25 0.915 258 487.5 E 17 0.519 0.915 258 427 5 E 18 258 360 0.127 0.915 E 20 B-1. 20-Inch T r a y Spacing; Temperature, 100' F. 420 0.349 0.708 200 E 21 420 0.444 0.986 277 E 22 420 0.570 1.255 353 E 23 420 1.38 1.57 390 E 24 420 1.41 1.69 398 E 25 420 0.296 0.764 215 E 26 420 0.391 0.987 278 E 27 0.611 1.22 344 420 E 28 420 0.739 1.25 352 E 29 1.21 1.52 420 426 E 30 0.915 258 0.887 442 5 E 31 0.915 258 360 0.211 E 32 0.915 258 300 0. 148 E 33 0.915 480 258 1.90 E 34 405 258 0.915 0 509 E 35 0.391 420 0.238 110 E 36 B-2. 20-Inch T r a y Spacing; Temperature, 120' F, 0.537 0.718 202 420 E 37 420 0.665 0.915 258 E 38 0.664 1.16 325 420 E 39 1.16 1.27 359 420 E 40 420 0.302 0.708 200 E 41 0.915 258 420 0.401 E 42 1.16 325 420 0.792 E 43 2.37 0,915 268 480 E 44 0.211 0.915 258 330 E 45 0.915 258 375 0.402 E 46 1.27 0.915 258 450 E: 47 0.915 258 292.5 0.159 E 48 420 0.412 116 0.158 E 49 0.391 110 420 0.243 E 50 C. Same as A except Plate Spacing Was 24 Inches 1.25 352 420 0.287 E 54 1.41 397 420 0.402 E 55 420 0.411 0.021 115 E 56 420 0,699 0.058 197 E 57 420 1.72 485 0.624 E 58 420 1.10 2.04 574 E 59 D. Same as A except Plate Spacing Was 30 Inches 349 420 0.159 1.24 E 61 249 420 0.073 0,889 E 62 1.49 418 420 0.239 E 63 1.86 523 420 0.570 E 64 1.69 476 420 0.336 E 65 E. Same as A except System Was Water-Air, Plate Spacing, 20 Inches; Temperature, 80' 300 200 4.2 0.0065 0.708 E 85 343 1.22 300 0.130 4.6 E 86 413 1.47 4.8 300 0.195 l? a i 300 0.389 1.67 468 5.0 E 88 1.86 524 5.1 300 0.971 E 89 250 4 .2 420 0.887 0.517 E 90 420 4.4 0.337 196 0.695 E 91 420 312 0.713 4 .8 1.10 E 92 420 1.22 0.906 343 4.9 E 93 413 5 ~ 0 420 1.17 1.47 E 94 F. Same as E except Temperature Was 120' F. 0.695 196 420 3.9 E 95 0.517 0.411 115 420 3.8 E 96 0.389 312 420 4.9 1.04 1.10 E 97 250 420 4.8 0.680 0,887 E 98 1.36 1.22 343 420 5.0 E 99 E E E E E E
VQL. 21, NO. 7
INDUSTRIAL AND ENGINEERING CHEiMISTRY
824
1 2 3 4 5 6
~
E?..
rates upon the height of liquid on the tray. It appears that temperature has little or no effect upon the depth to which the circulating liquid is piled up on the plate. High liquid rates cause ag reat depth of liquid on the tray, but the depth falls off rapidly as the liquid rate is decreased.
Linear Velocity
Statie Height Liquid on Tray
Inches Temperature = 80° F. 0.806 3.6 600 0.806 2.4 390 0,806 2.2 330 0.806 2.2 248 0.806 2.1 210 0.806 2.0 150 0.806 1.9 60 1.21 4.2 615 1.21 3.5 465 1.21 3.0 375 1.21 2.5 300 1.21 2.5 240 1.21 2.2 100 1.46 10.2 615 1.46 7.2 435 1.46 4.0 315 1.46 2.2 210 1.46 2.0 120 1.46 1.8 45 1.63 9.2 540 1.63 7.5 420 1.63 2.5 300 1.36 10.0 600 1.36 8.0 450 1.36 2.2 270 1,36 2.0 106 Temperature = P O O O F. 0.853 3.8 495 0.853 2.6 330 0.853 2.4 210 1.19 10.5 585 1.19 6.0 450 1.19 2.4 300 1.19 2.0 135 1.36 10.8 585 1.36 3.2 450 1.36 2.5 330 1.36 2. I 180 1,46 10.5 570 1.46 7.8 435 1.46 2.4 262 1.46 2.0 100 1.63 9.0 510 1.63 3.0 375 2.0 11.63 180 Ternuerature = 120° F. 0.846 3.8 525 0.846 2.5 375 2.5 0 846 285 2.2 0.846 250 10.2 1.19 585 1.19 8.0 470 1.19 2.5 330 1.19 2.2 210 2.0 1.19 82.5 7.6 1.46 480 1.46 8.5 495 1.46 4.8 330
s"t./MC.
I F 3 F
5F
7 F 9 F 11 F 13 F 15 F 17 F 19 P 21 F 23 F 25 F 27 F 29 F 31 F 33 F 35 F 37 F 39 F 41 F 43 F 45 F 47 F 49 F 51 F 53 F 55 F 57 F 59 F 61 F 63 F 65 F 67 F 69 F 71 F 73 F 75 F 77 F 79 F 81 F 83 F 85 F 87 F 89 F 91 F 93 F 95 F 97 F 99 F 101 F 103 F 105 F 107 F 109 F 111 F 113 F 115 F 117 F 119 F 121 F 123 F
Liquid Rate Gal./ hr.
Pressure Drop through Tray %.A. of HzO 2.5 1.6 1 4 1.4 1.4 1 3 1.1
7.6 2.4 1.8 1.6 1.5 1.3 8 0
6.8
1,7 1.6 1.4 1.2 7.5 6.2 2.0 7.8 6.3 1.5 1.2 2.6 1.5 1.3 8.4 4.3
1.5 I .8
8.5 2.4 1.6 1.4 8.2 6.0
1.6 1.3 7.5 2.3 1.60
2,4 1.5 1.4 1.2 7.7 6.0 1.6
1.4
P.2 6.0 6.8 3.0 7,6 1.6 1.4 8.5 6.8 1.5
The effect of various liquid rates i s shown in Figure 10 where static height is plotted us. linear velocity. The higher liquid rates cause the submergence on the tray to increase geometrically with increasing vapor velocity, In Figure 11 the pressure differential through the tray in inches of water z's. liquid rate i s shown as a function of the linear velocity of the vapor, Previous investigators (1, 8) report data showing the relationship between pressure drop through trays usa vapor velocities, The disagreement in the shape of the curves presented by these investigators is probably due t o the nature of the design of the equipment used.
Air- Water Figure 12 shows air-water curves which are &milas in all respects to those of the kerosene-air aystem. Water may
JULY, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY I
825
such as different petroleum fractions from similar crude oils.
Acknowledgments The authors wish to express their appreciation for the assistance given by several students in petroleum engineering a t the University of Oklahoma. William A. Pearce, Curtiss W. Cannon, and Joseph E. Johnson were of great aid in the operation of the tower.
Literature Cited
FIGURE11. PRESSURE DROPACROSS TRAYvs. LIQUIDRATEAS A FUNCTION OF LINEAR VELOCITY OF VAPOR Temperature, SOo F.; pressure, 14.3 lb. per sq. in. abs.: kerosene-air system
(1) Ashraf, Cubbage, and Huntington, IKD.ENQ. CHEM.,26, 1068 (1934). (2) Carey, Chemical Engineers’Handbook, p. 1197, /oo 200 SO0 400 500 New York, McGraw-Hill Book Co., 1934. MASS v,%ocrry * / m / m F S (3) Chillas and Weir, IND.EXQ.CHEM.,22, 206 (1930). FIGURE12. ENTRAINMENT vs. (4) Holbrook and Baker, Ibid., 26, 1063 (1934). MASS VELOCITY OF VAPORAS A (5) Kallam, F. L., Petroleum Engr., 5, 33 (Apr., FUNCTION OF TEMPERATURE AND 1934). LIQUIDRATE (6) I b i d . , 5, 29 (June, 1934). Pressure, 14.3 lb. peF sq. in. abs.: 20-in. (7) Rhodes, IND.ENQ.CHEM.,27, 272 (1935). tray spacing; water-air system ( 8 ) Rogers and Thiele, Ibid., 26, 524 (1934). (9) Sherwood and Jenny, Ibid., 27, 265 (1935). (10) Souders and Brown, Ibid., 26, 98 (1934). because of the vast
not be comDared with kerosene directly difference and physicafProperties Of the two liquids* A direct comparison between f3everal liquids can be made only if the liquids are of a similar chemical nature,
R ~ ~ E I Maroh ~ E D 12, 1935, The data, of this paper are t o be presented by W. T. Pyott in partial fulfillment of the requirements for the master of science degree in petroleum engineering, University of Oklahoma.
Treatment of Trade Waste with Activated Carbon
FOSTER DEE SNELL Foster D. Snell, hc., Brooklyn, N. Y.
0
F T H E various possible methods of treatment of dye waste, coagulation has received the main consideration. Bleaching and the use of activated carbon have received only passing mention (1). A process of treatment with activated carbon has been carried through the steps of laboratory development. Since, owing to local conditions, this has not been and will not be put into operation in the near future, it seems worth while to publish the preliminary information available because the data indicate the method to be more suitable than coagulation, a t least for this plant. I n comparison with previous papers (1-5) of this series on the chemical treatment of trade waste, it illustrates the variation possible in the waste disposal problems of individual plants of the same general nature. Although the data presented are laboratory data, they were obtained in all cases on waste from the commercial operations. This plant dyes and prints silk and silk-mixed goods. The waste is chiefly from the dye baths, but in addition there is a small volume of very concentrated waste from the printing department at the end of each day. There is a discharge from the boil-off department and both acid and alkaline baths are used, of which the latter is discharged only a t intervals.
The plant under discussion dyes silk and silk-mixed goods. Laboratory data indicate that treatment of the waste, after diversion of printing waste and boil-off, with 6 pounds of activated carbon per 1000 gallons i s more efficient in removal of color than coagulation. Loss on ignition of the solids is not substantially reduced. The material cost is about 2 cents per 1000 gallons. Considering the cost of equipment and operation the cost is probably about half that of coagulation. Sanitary sewage is disposed of separately and does not enter the problem.
Waste Discharged As is often the case with a dye plant, the volume of discharge varies seasonally. The maximum daily consumption of water is estimated at 150,000 gallons, with seasonal reductions to one-third of that amount. This water is largely discharged as a composite of dye and wash baths. Miscellaneous discharges are as follows:
