Vol. 39, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
718
3. McMahon packing gives less pressure drop than Ytedinari, which is of special advantage in vacuum fractionation. The maximum capacity and the liquid holdup are essentially the same for the two packings. 4. MclClahon packing has a number of mechanical advantage, over Stedman packing. It does not require accurately machined column walls, is not limited to a partirular column diameter, anti is more readily installed and removed. NOMENCLATURE
G = mass velocity, pounds,/hour,/square foot H.E.T.P. = height equivalent to a theoretical plate p = vapor density, pounds/cubic foot L I T E R A T U R E CITED
(1) Bragg, L. B., IXD.ESG.CHEX.,33, 279 (1941); E'ostei, C17hieler Bull. ID-44-2. (2) Biagg, L. B., and Richards, -4.l t . , ISD.Esc:. ('HEM., 34, 1088
(1942).
on, H. C., and Colburn, A. P.. I h i d . . 34, 1533 (194"). ke, 11. K., Lawroski, S.,and Tongberg. C . O., I M . , 30, 299
(1935). ( 5 ) Lettieri, V. J., master's thesis, Pa. State College, Jan. 194%. (6) McMahon, H. O., ISD. ESG. CHEM., ( 7 ) Podbielniak, W. J., ISD. ESG.CHEM.. ( 8 ) Robinson, C. S.,and Gilliland, E . T
pcrtsidrntical with that cle;c.rihcd i n Figure 3. TWENTY-NINE TRAY BEBBLE-PLATE COLL-MA.This toivcr wa.5 12 inches in inside diameter arid was composed of three t y e C-1 trays above and twenty-six type ( ’ - 2 trays bcloiv the vapor fcrd inlet. (Table 1 gives specifications of these tlay5.j -111 t1,ays: were on 2-inch tray spacing. The t,wo types diffcr only in t h a t five cap sides were blanked in each of the 2-C tray-: to en>urc’uniform 6ubbling a t low vapor velocities
STEDJIAN PACKED COLUMX.This column, whose fractionating height was limited to only 32ljz inches because of space specification, consisted of a 6.08inch-diameter round Stedman section 3 inches high above t8hevapor fecd point, and a 6-inch triangular packed sect,ion26 inches h i d l below. For liauid distribution and- liquid disengaging space a t the top, 21;r inches were allowed, and a space or 3 , inch was left bet,ween the packing and the reboiler. 1-apor feed n-as introduced into the shell around the top section, and entered thr packing from the side around the bottom of the circular packing. h space of ’ ’h inch wa$ left between the sec-
Figure 4.
Type C Tray and Baffle
June 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY ~
722
~ _ _ ~
TABLE 11. LIQGID -4IR FR4CTIONATION
IN PACKED
TOWERS
(Packing, I/cinch Berl saddles: diameter, t o p section 10 inches, bottom section 8 inches. packed height, top section 12 inches, bortom section 47 inches; vapor feed introduced between sections: liquid feed ihtroduced above t o p section)
Run
So. 5 5 -4 8A 8B 8C 9.4 9B 9c 10 11 12 13 14 15 16 17 18 19 20 21 22 23.4 23B 25 26 27 28.4 29 30 31 32 33 34.4 34B 35B 36 37 38 39 40 41.4 41B 42 43 44.4 44B 454 458 45c 45D 45E 45F 45G 45H 451 468 47 48 49 50
Length of Run,
Hr.
...
... ...
...
...
2 3.5 2 6 6 6 4 4 6 6 6 6 3 7 4 6 8 8 3 6 6 6 6 4 6 6 6 3 2 5 6 6 6 4 6 1.5 5.5 6 5
... ... ...
... ... ...
... ... ... ... , . .
6 3 3 3 3.5
Feed Rates,
~
Liquid feed 5050 5610 4700 3340 3180
4980 4690 5000 5040 5120 4970 4990 5100 6260 6480 6410 6450 6320 6260 7270 6660 6720 6960 6820 6880 7010 7290 5050 4960 5210 5300 5100 5040 5020 5010 5080 4970 5090 5000 4970 4320 5040 5430 5240 6300 6460 5400 5840 6580 7150 7435 7970 8320 8670 8080 8060 7730 7800 8000 8040
~
Vapor feed 0 0 0 0 0 0 1500 2880 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2200 2360 2130 2160 4660 4350 4330 4340 4220 4450 4560 4630 6650 6510 6860 6390 6630 0 4540 0 0 0 0 0 0 0 0 0
0 0 0
2160 4080
Oxygen Product Yield Yield. from 0 2 s:c.f./lOO s.c.f./lOO in liquidI s.c.f. liauid s.c.f. total feed feed feed 0 0 0 0 0 0 45 9.5 9.5 0 0 0 33 6.9 6.9 42.65 9.0 9.0 49.1 10.4 7.9 47.6 6.5 10.2 23.7 5.0 5.0 40.9 8.6 8.6 58.8 12.3 12.3 64.5 13.5 13.5 44.2 9.3 9.3 29.9 6.3 6.3 45.6 9.6 9.6 11.3 53.9 11.3 12.9 61.7 12.9 10.2 10.2 48.5 11.8 56.3 11.8 30.4 6.4 6.4 31.0 6.5 6.5 46.1 9.7 9.7 46.5 9.8 9.8 46.0 9.7 9.7 45.4 9.6 9.6 51.0 10.7 10.7 58.5 12.2 12.2 50.6 7.4 10.6 16.2 11.0 77.5 3.5 24.0 5.0 62.0 13.0 9.2 63.5 14.3 7.5 8.5 75.5 15.8 56.5 6.4 11.8 3.5 31.0 6.5 46.5 9.8 5.4 59.0 12.4 6.5 9.0 81.0 17.0 10.1 93.0 19.5 6.3 40.4 8.5
70 Recovered
s.c F n
Rate, s.c.f.h.
0
0
450 0 220 450 490 505 250 445 625 695 475 395 620 740 855 635 750 465 435 665 690 670 660 760 920 540 820 265 700 735 805 600 325 495 620 870 1000 420 630 655 805 1020 745 530 300 310 315 325 380 420 450 485 400 845 985 0 975 980
Purity,
%
99 99 97 99 99 99 99 98 99 99 98 97 99 99 99 98 97 99 98 99 99 98 98 98 99 99 98 99 98 99 99 99 98 99 99 99 99 98 98 99 99 99 96 98 98 99 99 99 99 99 99 99 99 99 99 99 98 99 98 99
0 2
70 59 9 41 34 21 13 80 41 13 30 12 13 44 14 66 53 17 89 20 16 33 32 78 25 04 36 38 32 6 11 17 86 25 5 24 23 58 08 37 05 10 98 46 31 59 51 43 48 56 51 66 71 42 74 32 36 90 96 28
68 0 61 5 70.0 91.5 55.5 39 26.4 25.4 22.8 21.6 24.4 25.1 25.8 26.6 23.4 50.0 59,5 0 57.5 57.5
14.3 12.9 14.7 19.2 11.6 8.2 p.6 0.3 4.8 4.5 5.1 5.3 5.4 5.6 4.9 10.5 12.5 0 12.1 12.1
tions. I n this gap liquid dropping from the portion of the circle overlapping the triangle was brought back to the triangle by three copper circular segments slightly tilted towards the center. A baffled type of differential reboiler (4)was used t o give all possible help to the oxygen recovery system. I n a sense, therefore, the M-3 Stedman column was not designed, but rather represented the best effort to accomplish a difficult task. TRAY COLUMN.This tower was ~ I / sinches in inside diameter and consisted of three trays of the E type (Figure 5 ) having 3-inch spacing above the vapor feed and thirteen trays of the F type (Figure 6) on 11/2-inch spacing below. The E tray was thus more or less similar in design to the C-2 type, whereas the F tray utilized the coordinated reflux principle previously described. (Other details are given in Table I and Figures 5 and 6.) TRAYS FOR M-5 UNIT
’
The fractionating tower for this unit was to be designed specifically for use in a large shipboard installation. For this reason it was necessary to be able to test proposed trays under conditions simulating the motion encountered a t sea, as well as under static conditions,
9.5 9.5 12.5 15.3 11.6 4.8 5.6 5.3 4.8 4.5 5 1 5 3 5.4 5.6 4.9 10.5 12.5 0 9.5 8.0
Ratio, F’apor Feed: Liauid Feed .
I
.
0 0 0 0
0
0.32 0.575 0
0
0 0 0 0 0
0 0 0 0 0 0 0 0 0
0 0 0 0.435 0.475 0.41 0.42 0.91 0.86 0.86 0.86 0.83 0.90 0.90 0.93 1.34 1.51 1.36 1.17 1.26
0
0.7
0 0
0 0 0 0 0 0 0
0 0
0 0.27 0.51
H.E.T.P., In.
8.0 8.8 8.7 9.8 7.0 6.1
.. .. ..
7.6 6.5 4.6
...
6.0 6.7 5.8 5.3 4.8 5.2 4.3 7.8 7.8 7.6 7.6 6.7 5.5 5.0 4.8
...
... ...
Column Pressure Lb./Sq.’ I n . Abs.
17.5 17.5 16.5 15.5 15.5 16 16 16.5 17 17 17 17 17 17 17 17 18 17 17 18 17.5 17.5 17.5 17 17.5 17.5 17.5 17 17.5 17.5
... ...
17.5 17 25 24 20
... ... ...
20 21 20 20 22
... ... ... ...
... ... ... , . .
...
5.5
...
7.0 7.4 7.2 6.8 7.0 6.2 5.7 7.4 5.5
4.7 4.5 5.8
...
...
22 22 22 23 21 19.5 19 19 21 19 20 20 20 20 19.5 21 19 20 21 20
Column Pressure
Droi), I n . HzO Upper section
Lower section
0.4 1.0 0.4 0.4 0.4 0.4 0.9 1.3 1.3 0.5
3.4 4.0 3.0 1.3 1.0 2.7 2.7 2.3 3 2.5 2.5 2.5 3.0 4.3 1.3
1.5 1 0.5 1.6 1 2 1 0.5 0.6 1 0.8 0.5 2.0 0.5 1.5 0.5 1.3 1 2 1.5 1.8 1.5 1.8 2.5 1 2 1 0.8 1.7 1
1 0.6 1 0.5 1.5 1.1 0.4 0.4 0.4 0.5 0.5
0.7 1.4 8.3 1.0
1.1 1.1
i’:
0.0
0%at
vapor Feed
Point,
%
.-
..
.. ._
.. .. ..
80 65 47 27 71 80 69
4.3 4 3.5 3.7 3.5 2.5 2.0 3.7 2.7 3.5 6.0 3.9 2 4.0 4.0 4 3 2 2 3 4 6 3.5 4 4.5
65 31 51 41 54 60 39 39 43
4.5 1.7 1 1 2.5 3.9 3.5 4.3 6.1 7.2 8.0 10.4 15.2 27 3 11.8 8 7.1 10 5 6.4
58 58 53 54 34 22 71 76
sz
75 44 40’ 28 50
37 47 37 4 5,
6a 68 8D 58 54 62
68
77 77 76 73 94 77 4%
..
85
50’ 61’
For such a study the entire test unit a t The Pennspivanis State College was mounted on a platform on n hich the motion of a ship could be simulated by an arrangement of cams, rocker arms, and gimbals. The unit was so designed that a 5 tilt from the vertical was obtainable in one direction and a 15’ tilt in a direction a t right angles to the first. The directions n-ere designated by the terms “pitch” and “roll,” respectively. I n the pitch direction the axis of motion was below the tower and about 2 feet away, while the axis of rocking motion passed through the tower slightly below the midpoint. The form Q€ the pitching and rolling motion was described by stating the n u m k of cycles per minute and the maximum angle. An exact descrip tion of the tower motion in terms of the three spacial coordinates and time is a difficult and probably unnecessary task The towers tested in this rocking platform under both static, and moving conditions were the following.
PACKED COLUMN.This column was the same as-tliat STEDMAN described for the M-7 unit.
722
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
TABLE 111. LIQUID-&Ill
FRhCTIONATIOZ IN PACKED
Vol. 39, ,No. 6
TOWERS
(Packing. N o . 115 Stedman, diameter, top section 6.08 inches, bottom section 6.08 inches: packed height, top section 9 inches, bottom section 36 inches; vapor feed intrdduced between sections; liquid feed introduced above t o p section: packing flooded with liquid before runs 93-103)
Run
No.
Feed Rates, Length - S.C.F.H. of R u n , Liquid Vapor Hr. feed feed
Oxygen Product __ r/o RecovYield, Yield. ered from s.c.f./100 ' s . c . f . l l 0 0 Purity, 02 inliq- 6.c.f. liquid s . c . f . total 02 uid feed feed feed
Rate, s.c.f.11.
Ratio, ~~l~~~ Column Pressure o1 at Vapor Feed: Pressure, Drop. In. H20 T-apor Liquid H.E.T.P., Lb./Sq. Upper Loner Feedn Feed In In. h b s . section bection Point, ,o
2 2.5 2.5 2.5 2
3020 5030 6380 7030 7940
0 0 0 0 0
190 275 310 355 405
99.14 99.46 99.40 99.30 99.44
30.0 26 0 24 0 24 0 24.0
6 . .3 5.4 4.9 5.0 5.1
0 ,3 5 4 4 9 5.0 5.1
0 0 0 0 0
6.3 5.4 5 9 6.3 5 8
16 17.5 19.5 21 18.5
0.6 2.1 1.4 2.9 1.7
2 7 7 2 10 0 10.0 8.9
88.6 91.7 96.5 97.7 94.1
2
2 1.5
2920 3570 3400 3970 4000
0 0 0 0 0
170 360 390 400 450
99.85 99.48 99.18 99.48 99,27
28.0 43.0 45 0 48.0 53.0
5.8 10.0 11.4 10.1 11.2
5.8 10.0 11 4 10.1 11.2
0 0 0 0 0
3.6 4 0 3.3 3 4 3 3
17.5 19 18.5 18.5 18.5
0.5 0.9 0.7 1.0 a1.2
2.1 2.5 2.5 4.0 4.0
94.1 75.5 70 8 73 1 81 0
98 99 100 101 102
2.5 1.5 2 2 5 1.5
4680 4580 5100 5100 6060
0 0 0 0 0
455 520 510 558 600
99.4' 99 17 99 60 99.74 99.38
47.0 54 0 58 0 52 0 47.0
9.9 11.3 10.0 10 8 9 9
9.9 11 :i 10 0 10 8 9 9
0 0 0 0 0
3.7 3.3 3.2 2.5 3 8
20 19 19 185
..
1.4 1.4 1.8 1 8
...
5 0 5,0 6.5 1.5 8 0
79.7 63 5 89 4 93 8 845
103
2
5600
2350
600
98 86
jl
10.7
7 3
047
..,
18 5
..,
7.5
23 2
86
87
88 89 90 93 94 9c 96 97
6
2
*
TABLE IT. 1 , l Q ~ ~ I.\IR l) FRACTIOXLTIOS IS PACKEI) TOWERS Packing, 4--6 mesh Haydite; diameter, top section 10 inches. bottom section 8 inches: packed heiphr, t o p section 12 inches, bottom section 46 inrhes: feed introduced above t o p section) O x y g_ e n_ Product ___.~.~
Yield _ _ _ _ _ ~ _ . Run
SO.
422 423 424 425 426 427 428
Length of R u n , Hr.
hir Feed, S.C.F.H.
S.C.F.H.
2 4 6 6 3.5 6 6
6090 6020 6050 6020 4640 4666 4640
0 810 665 560 600 445 350
CCOz 99 97 99 94 97 98 99
91 05 06 54
44 99 28
Cii. it ,100 cuft,air
'.;
0 13 5 11 0 9 30 12.9 9 55 7.55
TYPE J TRAY. The complete tray for the proposed installation was envisioned as composed of several rectangular compartments, each a-it'h its own liquid downflow, leading to a similar section on the tray below. Each compartment was t o be 3 X 9 inche-, the length so placed as to be parallel to the greater motion of the vessel. The trays in this case were t o be of the perforated typca on 6-inch tray spacing. (Table I gives details.) I n order to test the performance of such a tray, a small four-tray t,ox-er was built. Each tray consisted of one of the small compartments with a vertical partition baffle or weir across its center. DISCUSSION OF RESULTS
The results of the test on towers for the ?VI-7 unit are shown iir Figures 7-11. Tables 11-TI contain the pertinent data and calculated results.
Figure 5.
Type
E Tray and Baffle
Recovered S,i, of froni O? 'l'hroretii,al infeed Plates 0 64 52 44 61 45 36
4 5 3 5
5 0
10 13 12 12 10 9 8
+ 4 3 5 8
H.E.T.P., In.
'Tower pressure, Lb.,'Sq. I n . Gage
5.1 4 8 5.0 5.1 3.1 3 2 4 2
5 8-
:;
4 7 5 8 6 1 6.6
__
Pressure Ilroii, I n . HrO Tqp Bot t o in sectioii section ~~
11.2 11 11 11 ' 1.0 1 0 1.0
33.8 29 5 3._ 3
33 11 5 13 0 13 7
Results of the tests on the tower for the hl-3 unit are shown in Figures 11, 12, and 13, and the data are given in Tables TI1 and T T I . The tests on the J-tray for the ?VI-5 unit were completed at the Thermodynamics Research Laboratory of the Cniversity of Pennsylvania. The results of these tests are listed in Tahle I S and are briefly discussed in the following paragraphs. PACKED TOWERS FOR AI-7 USIT. Early in the program, judging froni the results obtained by Weedman and Dodge (14) on the small columns, it appeared that a packed column usirrg '/;-inch Her1 saddles would meet the required performance. The indicated capacity and H.E.T.P. were good, and it \vas felt that the low liquid holdup would keep the starting-up time of tlie plant down t o a minimum. The performance of the saddle-packed tower was disappointing 7 ) . The 8-inch column gave an H.E.T.P. between 7 and (Figure 8 inches, as compared to slightly under 3 inches in the 2-inch inside diameter column. Data on this type of packing obtained
Figure 6.
Type
F Tray and BaHle
June 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
t7
3
- 3
z
723
INDUSTRIAL AND ENGINEERING CHEMISTRY
724
TABLE VI.
IJQLII)
Vol. 39, No. 6
.kIR F R ~ C Ti TI IO O S~I S 29-TR.kY TOWER
(Feed rates corrected for x a p o r feed superheat)
Run so.
Measured ValuesLiquid, Vapor, s c.f h . s c f h.
Vapor Feed
~~
Liquid Feed Lost b y Recor+d Super- Superheat, temp., F. h e a t , ' F . S . C . F . H .
Corrected Values Ratio, vapor I,iquid, \-apor, feed.liquid s.c.f.h. s.c.f.h. feed
VAPORFEEDISIROUC-CE.D B L T U - E E S TK.AIS 2 ASU 3 170 5130 2410 0 47
154 158 159 l6OA 160B 161 162 163 164B 165 166 167 168 169 170A 170B 17 1
5300 5230 5230 5200 5100 5250 5200 5250 6900 5200 5200 5300 5200 6500 6800 6800 6700
2240 2270 2300 4300 4400 4300 4350 4400 5300 6550 6500 6400 6500 5550 5100 5200 5200
-279 -285 - 280 -285 - 283 -284 - 285 -281 - 284 -285 -285 -280 - 280 - 287 -279 - 280 - 283
26 20 25 20 22 21 20 24 21 20 20 25 25 18 26 25 22
130 170 250 270 260 250 310 340 380 380 470 470 320 390 3 80 330
5100 3060 4950 4830 5000 4950 4940 6560 4820 4820 4830 4730 6120 6410 6420 6270
2400 2470 4550 4670 4560 4600 4710 5640 6930 6880 6870 6970 5870 5490 5580 5530
172 173 174 176
8200 6750 6700 6650 6400 6600 6600 4100 4000 5400 6100 6200 7250 7200 6950
5500 5450 5500 6000 6150 5400 5500 5860 6000 4700 4000 4000 2750 2850 5150
- 295 - 280 -261 -278 - 278 - 273 -276 - 280 -276 -276 - 280 - 301 - 283 - 284 -279
10 25 44 27 27 32 29 25 29 29 25 4 22 21 26
160 400 700 470 490 500 460 430 510 400 290 50 180 180 390
8040 6350 6000 6180 5910 6100 6140 3670 3490
5660 5850 6200 64i0 6640 5900 5960 6290 6510 5100 4290 4050 29930 3030 5540
177
179.4 179B 180 181 182 183 184 185 186 187
5000 5810 6150 7070 7200 6550
by two other investigators (4, I O ) on other sizes of towers are included in this figure, and these also indicated decreasing efficiency with increasing tower diameter. The effect is undoubtedly caused by t'he varying distribution of liquid and vapor. That this i? not easily overcome n-as shown by t,he identical perforniance of the column with three different distributing devices which introduced the liquid a t one, three, and seventeen points. The lowest curve on Figure 8 shows the product purity as a function of yield-that is, cubic feet of oxygen per hundred cubic feet of air feed. It may be seen that Tvith this toxer a yield of only slightly over 8 cubic feet of oxygen per hundred cubic feet of
0 0 0 0 0 0 0 0 1 1
47 49 92 99 91 91 96 85 44 43 41 47 96 86 87 88
1
1 0 0 0 0
0 70 0 92 1 03 1 05 1 12 0.97 0.97 l.il 1.86 1.02 0 74 0 66 o 42
0.42 0.85
Rate , c f.11
Oyxgen P _________ roduct Yield, % Recovered -.c.f./lOO from 0 2 Purity, s.c.f. liquid in total 502 feed feed
495 910 80 0 310 510 800 890 810 510 805 985 1010 1010 1100 1095 0
99 86 98 55 99 62 99 84 99 i o 99 76 99 76 99 12 99 48 99 71 99 45 98 99 98 12 99 71 99 24 99 45 99.84
9 65 17 8 15 8 0 6 4 10 2 16.2 18 0 12 4 10 6 16 7 20 4 21 4 16 5 17 1 li 1 0
46 85 75 0 30 4 48 5 77 86 59 50 79 97 102 79 81 81 0
830 820 825 990 903 1000 1100 820 640 830 900 1110 1240 970 800
99 99 99 98 99 99 98 99 99 99 99 99 99 99 99
10.3
44 61 65 76 73 78 86 107 88 i9 74 86 83 64 58
3
44 43 69 88 45 52 93 10 62 65 73 14 15 75 57
;;,;
16 15 16 18 22 18 16 15 18 17 13 12
0 3 4 0 4 4
6 5 1 5 4 2
air could be obtained xvhen withdraiTing a product purity of 99.5 yo. Figure 9 also s1io.i~the performance of the towers; the H.E.T.P. is shoxn to be a function of oxygen production as vie11 as of the type of fractionating medium used. This dependence is a fallacy of the H.E.T.P. concept as a fundamental unit when applied t o varying reflux ratios and composition ranges. The performance of the toner packed n-it11 Haydite instead of 1/4-iiicliBerl saddles is also shown on Figure 8. The results !?ere somei\-hat improved in that a yield of about 9.5 cubic feet of oxygen per 100 cubic feet of air could be obtained when xith-
UE A I R F R A C T I O N A T I O N IN u 1/4" B E R L S A D D L E P A C K I N G E F F E C T OF TOWER DIAMETER ON PACKING EFFICIENCY ___ TRAFFIC IN PACKING I300 LBS./HR./SO.FT.
7
58'PACKED HEIGHT AT 3"H.E.T.P.(AVG.STEDMANI 5 9 ' P A C K E D HEIGHT OF I / 4 " B E R L SADDLES 5 8 " P A C K E D HEIGHT O F 4 - 6 MESH HAYDITE
988-
98 6 c
2
3
4
6 TOWER DIAMETER, INCHES
Figure 7
7
9
L I Q U I D AIR FRACTIONATION SINGLE L I Q U I D F E E D OPERATION
I
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1947
TABLE YII.
PERFOR\I 4SCE O F
Product ~
Run S O .
207.1 207R 208 209 210 210 "12 213 214.1 214B 216 21i.1 2liB 218 219.1 220.4 221 223 225 226 226E 227.1 228 230 231 "1R 232 23.3 234 (1
Length of R u n , Hr. 2 7
1.5 3.5 1 5 1.5 I
5.5 1 1 5 3 5 1 5 6 6 6 6 5.5 6 6 1.5 6 6.5 6
,
5.5 6 6 5
Feed Rates, S.C.F.H. Liquid Vapor 0 0 500 830 1500 2100 2000 2000 2000 2000 0 2100 1750 2350 2400 1750 1700 0 0 0 0 2500 2050 0 2100 0 2100 0 2150 0 1850 0 1800 0 1500 0 1500 0 ~
S.C.F.H.
Oa,
L.'c
0 2 from liquid feed, L.'c
0 195 195 175 200 195 285 320 315 315
170 135 125 160 185 100 125 80 100
11-3 STEDhfAZr Column Pressure, Lb.,Sq. I n . .1bs.
0 33 32 28 33 33 50 55 55 54 0 38 43 49 59 42 38 32 28 30 32 31 28 36 41 26 33 25 32
98.49 98.9 99.12 98 41 98.36 99.42 98.58 98.92 97.0
72s
cOLUMXa
Column Pressure
In. H2°
Top
19 19 19 19 20 19 19 17.5 17.5 17
2.7 2.5 2.5 2.3 2.5 2.3 2.2 2 3
17 17 17 17 17 5 17 17 18 18 16.5 16.5 16.5 1 6 ,8 16.2 16.t 16.8 18 15.5 16.0
2.7 2.9 2.5 2.7 2.8 2.5 2.3 2.6 2.4 2.5 2.5 0.3 2.6 2.2 2.4
2.5
2.5
...
0 0 0
Bottom 14.2 12.5 13.5 13.6 13 5 13 0 13 3 13.3 12 9 13.0 14.5 13.3 13.7 13.8 13.5 12.9 13.3 12.1 13.0 13.1 12.4 5.; 13.1 13.0 12.7 14 1 8 0.7 0.7
y o . of Theoretical Plates 6 2 6 1
H.E.T.P., In. 4 7 4 75
Entrainment S.C.F.H.
.. . . ..
... . . 7 1
5 6 6 5 6 6 6 6 7 6 7 5
3 7
... ... ... ... ..
5 8 8
5 3 4 .'3 4.3
8 6 9 2 4 8 1 0 4
5.0 4.4 4 2 4 7 4.2 3.t 4.7 4.1 5.4
$500
...
These tests were made on t h e 31-3 tower as ready for installation in a nnit.
TABLE T-111. LIQKILI .IIR FR.\CTIOS.XTIOS IS 11-3 T R A Y TOWER (Three type E trays on 3-inch spacing aboi-e vapor feed: thirteen type F tray. o n tl'r-inch spacing below vapor feed)
Iton Su
321 322 323 324 323 326 327 328 329 330 331 331 333 334 335
Feed Rates. Length S.C,F.H. of R u n , Liquid Yapor Hr. feed feed 6 5.5 6 6 6 5 6 6 6 6 6 6 6 6 6
2840 3180 2840 2880 3680 2800 3660 3160 2660 2900 2940 2850 2840 2900 2840
1870 2020 1940 1920 1870 2400 0 0 0 1820 1770 1900 1980 1940 1960
Feed/ Liquid Feed 0.66 0.64 0.68 0 67 0.51 0.50 0 0 0 0.62 0.60 0.64 0.70 0.67 0.69
Osygen Product Tield; 5 Recoi-- Yield, s c.f. ered s.c.f.: ered from 0 2 100 s , c f. from 02 100 s.c.i. inliquid liquid rotal i n rotal feed feed feed feed
5 Recov-
Ti:,? R a t e , Purity, %02 s.c.f.h. 310 390 400 320 420 365 295 285 250 0 100 205 290 380 410
99.05 98.95 97.96 99.39 99.10 99.07 99.10 99.33 99.71 99.88 99 8 5 99.84 99 67 99 03 98 30
51 3 57.5 65.8 52.5 53.8 61.5 37.9 42.6 44 6 0 16.2 33.0 48.5 62.5 68.5
draviing product of 99.5% purity. When n-ithdran-ing higher purity product the resulting yield Tt-aseven more favorable. Long before the tests with saddles lvere completed it became evident that a much more efficient tovier had to be developed if the process specifications for mobile units XTere to be met. Published Stedman packing performance ( 2 ) with benzeneethylene dichloride mixtures shox-ed only a 2,573 decrease in efficiency in a 6-inch as compared t o a 2-inch diameter packing. On the basis of the .mall column tests it seemed that a 6-inch diameter tower ~vouldbe large enough for the specified air flon-. Although in the preliminary small column tests Berl saddles had been shonn to be ahout twice a i efficient as Stedinan packing, it appeared that in a larger ton-er the latter might be better because of the much smaller effect of diameter. After making the first fen runs on the Stedman packing in a single feed toxver it n-as discovered that, if the packing Ti-ere conipletely vetted by filling the entire tower Jvith liquid air, the efficiency was improved-in fact, almost doubled. This peculiarity of Stednian packing n-as the subject of a great deal of conjecture. There as a queHtion as to whether, at any given feed rate, the screen might eventually become entirely wetted, and so give better efficiency! in the Course of normal operation. It vias also sug,gested that, in liquid air operation, heat leak might tend to dry
10 9 12.2 13.9 11.1 11.4 13.0 8.0 9 0 9 4 0 3.4 6 9 10.2 13 1 14.4
31.0 35.4 39.4 31.6 358 41 0 37.9 42 6 44.6 0 10.0 20 0 28.6 27.2 40.5
6.6 7 5 8.3
;:! 8.6 8.0 9 0 9 4 0 2.1 4.2 6.0 7.8 8 5
Colunin Pressure, Lb./Sq. In. Abs. 18.7 19.9 18.9 19.4 202 19.7 20 7 19.7 19.2 176 17 3 17.5 17.2 16.5 17.2
Pressure Drop, In. H20 Top Bottom 7.8 9 4 9.0 9 6 7.8 9.2 8.5 9 8 10.6 9.2 9.8 9.2 ii:5 8 5 11 8 4.3 10 5 9 5 10.1 9.3 10.3 8.7 10.1 9.0 9.9 8.7 9.8 8.5 9 8
Over-all Tray ~ffiriency,
%
, , ,,
., .. .. .. ., 66 91
..
, ,
. . .. ..
,
,
Entrninment. \Vt. 7"of Liquid Feed 0 8 0 0 28.7 2 12 28 -.I. 7 0 0 0 0 0 0 0
the packing nearest the wall. ilgain, if the tower were flooded n i t h liquid before operation began, the possibility existed that the packing might become unx-etted and t'he fractionation efficiency impaired. That any one or all of these effects occurred to some degree was shown by the erratic performance of Stedman packing in this application. To call the performance of Stedman paeking erratic is not to imply that the material is unsatisfactory. On the contrary, the average H.E.T.P. of 3 inches obtained for this packing is half that of the Berl saddles. Although the deviation from the average is as much as 50yo,the maximum H.E.T.P. is still less than the best yalue for Rerl saddles. Figure 8 presents the operating results for the Stedman tower, and single liquid feed operation is showi. It may be seen that with this tower a yield of slightly over 11 cubic feet of oxygen per 100 cubic feet of air could be obtained when withdrawing product having a purity of lox-er yields the purity of the product obtained from this column was considerably better than that obtained fioni the bulk-packed towers. This curve was obtained by correcting the actual performance to that of a tower with the Fame height as the others tested. The average H.E.T.P. of 3 inches \vas used. With this to\ver there seemed t o be no noticeable effect of feed rate upon efficiency. This \vas unlike the behavior of bulk park-
726
Vol. 39, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
and downflow, height of liquid over the downflow weir, liquid gradient across the tray, froth height, pressure drop, liquid and vapor quantities, and entrainment. At least two trays were required for the air-water tests. If only one \\-ere used, the entrainment could not be measured, and it \vas found as well that the tray above exerted considerable influence upon the pattern of vapor flowing from the tray beneath. In order to apply the air-water capacity data to other systems, the liquid rate, in gallons per hour, a t flooding was plotted against the vapor velocity. In order to allow for differences in densities of liquid and vapor, the superficial vapor velocity was reduced to a dimensionless factor which is defined by the following relation:
Lo
S
r *L.
L i a u i o AIR FRACTIONATION SINGLE COLUMN O P E R A T I O N EFFECT OF RECOVERY ON H E T P
I
I I
1
I
I 5 TRAYS,
I
z=
2" SPACING
K-3TRAYS
c--+
where DL 6
8
=
density of liquid
DV = density of vapor
OXYGEN Y I E L D , G E P E R 100 C.F.FEED
4
dT
/
4 TRAYS, I1/2" SPACING
2
superficial vapor velocity (ft./sec.) x 100 -, 0.227 DL - Dv
12
10
14
Figure 9
ing. Perhaps the reason for this is that a major effect of increased liquid and vapor loads was to increase the wetted surface of other packings; but since the surface of the Stedman packing was already presumably wetted by preliminary flooding, no further increase in its transfer surface F a s possible. TRAY TOWERS FOR M-7 USIT. When i t was becoming apparent that it would be difficult, if not impossible, to meet, the mobile unit production specifications with packed toivers, the use of trays, which was rejected a t first, became more attractive as the H.E.T.P. values with the latter might be lower than those of packing. In the process of development a few trays were fabricated in accordance with a tentative design. With the aid of some sheet celluloid and metal and some ordinary adhesive tape, a great many trial and error tests were made n-ith air and water before a final design could be established. The air-wat,er investigation was concer ned particularly with entrainment removal, equal distribution of liquid in the bubbling channels, and the uniform activity of all slots. In other words, although the tray efficiency could not be obtained with such tests, design factors which might affect the efficiency could be considered. Angle baffles were devised and used to eliminate intertray entrainment. I n addition to the qualitative Observation of the behavior, the following variables were measured quantitatively: liquid level
The technique of air-water testing proved invaluable in the development of trays for efficient oxygen production. The procedure was merely that of duplicating the normal liquid and vapor flows in a tower, measuring rates of flow and entrainment, and making visual observation of the effects. The materials were used at room temperature and pressure to allow easy operation and almost complete visual observation of the tray behavior. One essential difference between packing and trays as a fractionating device is the extreme complexity of the design of tray towers as compared to packed towers. In the case of trays the efficiency and capacity are sometimes such obscure functions of the mechanical factors that tray design is still to some degree art rather than a science. A4nadded complication is that trays do not necessarily conform to theory of models. A design irhich is satisfactory in one size of tower must often be entirely altered if the diameter of the tower is changed. Some of the factors nhich must be considered in designing a tray are tray area, tray spacing, riser area, downflow area, slot area and dimensions, number, type, and arrangement of bubble caps, slot submergence, liquid gradient, and entrainment. At the low spacings used these elements of design become very iniportant, in the performance of the trays.
LlOUlD AIR FRATIONATION M.W.KELLOGG 29-TRAY TOWER EFFECT OF VAPOR F E E D UPON OXYGEN RECOVERY
-
n110 3
0
TABLE IS. IJQTID AIR FRACTIOSATIOS~ IS FOUR Timz J TRAYS Liquid Air Traffic o n Feed Rate, Top T r a y ,
S.C.F.H.
S.C.F.H.
Tower Pressure Over-all Osygen Concentration, 7 c Pressure, Drop across ..lx.. Tray In Flood point L b 'Sq. I n . Trnys, Efficiency, bottonis analysis Gage In. H?O c;
98.0 2990 2550 3380 2900 97.1 4000 3340 97.0 4570 3720 98.7 5270 4350 S i .0 5300 4370 97 5 5350 4410 96.2 5920 4850 96.9 5390 4870 96.8 5970 4910 97.0 6720 5500 97.4 6940 5690 96.6 7200 5890 96.7 8000 6900 97.2 8600 6500 96.0 9325 7600 96.3 9570 7800 95.6 a All runs made a t total reflux.
24 27 25.5 29 28 24.5 27 27 28.5 25 33 40 37 39 37 38 38
1 4 1.5 2.0 2.2 3.4 3.4 4.5 4.5 4.4 4.2 5,5 6.0 6.0 7.0 8 0 9.0 9.0 ~~
5 4 5 9 6.5 6 0 s.5 8 6 b 6 9 5 9.6 9 5 11 5 12.2 11.9 13.0 12 9. 12.7 13 0 ~~
102 9" 92 112
9" 95 88 92 90 92 95 88 90 92 65 88 82
I
I
$100
1
0
I
>
I
99.0% PRODUCT
-
PERCENT OXYGEN
0
1
0
E 90 n E
> I
1 I
I
I
I
1
0
50 100 150 200 VAPOR FEED R A T E - P E R C E N T O F L I Q U I D FEED
Figure 10
350
300
LIQUID RATE
\ \ 250 I
3s- 200
0 \
p 150. 3
0
I I '0AIR-WATER
\
'
',
0
\ 50
1
i I
T E S T S , 2 TRAYS AIR-WATER T E S T S FLOODING P O I N T ESTIMATED B Y EXTRAPOLATING VAPOR RATE TO POINT WHERE LlOUlO L E V E L I N DOWNFLOW IS E V E N W I T H TOP OF WEIR A I R - L I O U I D A I R T E S T S , 4 TRAYS A I R - L I ~ U I D A I R TESTS, FROM OPERATION OF COMPLETE TOWER I I
1
TYPE D TbAYS
IW
I
'
\
w
ii
VAPOR RATE AT FLOODING POINT FORTRAY TYPES USED IN UNITS
\
I TYPE C-2 TRAYS
iD
DL:
-
LiauiD D E N S I T Y , LBWC
D y * V A P O R D E N S I T Y , LES/CU.FT.
I
0
I5
10
20
25
30
35
I
'
I 40
I
1
~
50
45
55
60
After the design of the trays had been determined by the air-water a set of trays was completely cated and tested by liquid air fractionation. Table [ gives the essential characteristics of all trays tested. TWENTY-SIXE TRAYTOWER. Of all the toivers tested in the full scale size, this proved to be the most satisfactory froni the standpoint of ea,se and dependability of operation, efficiency, and capacity. Figure 8 shows the performance of this tower as compared t o the others previously tested. h yield of 12.5 cubic feet of oxygen per 100 cubic feet of air could be obtained from it when withdrawing a product
13 cubic feet per hundred cubic feet of air. When the withdrawal of oxygen was further increased TABLE x. TRAYLIQEIDC O l l P O S I T I O S -4FTER LIQL-IDA I R beyond this point, the purity dropped sharply and an unstable FR.4CTIOS.4TIOS IS 29-TRliY TOWER performance resulted. Llolal cy 0 2 i n Mole 5 0 2 in Liquid Leaving: I sample points. The svelages of thrse T K I 3 VAPOR 0 0 FEED S.C.F.H. were found to be: ~~
I . I"
L
;r
>- 99
\\
I
I
I
'\
PERFORMANCE OF M-3 AIRBORNE TOWERS AT THE DESIGN FEED RATE ( G A S EOUIVALENT)
I
98
I
8 to 15 to 20 t o 25 t o
',
LIQUID FEED -2800 S.C.F.H.
I
Trni section
1
1I I
15 20 25 product
Axerige Ox el-all 1r a l Cfficienij
93 65 53 21
These n idely varying efficiencies eniphasized the need for a toner in which
TDUSTRIAL AND ENGINEERING CHEMISTRY
728
Vol. 39, No. 6
increased oxygen concentration suggested that there might be a real trend in the efficiency caused by changing diffusional rates. SHORT TOWER TESTS
-->
.-
>
The success of the tray to\ver naturally aroused interest in the further development of this sort of fractionation equipment. Such a developinent should involve the accurate measurement of the efficiency and capacity of all trays tested. For this purpose a toiver n-ith but four trays \vas used. When this tower is operated a t total reflux, the uncertaintieh in equilihrium data exert the least influence; arid if the tower is short enough, the product purity is maim tained in the region in vhich there is a relatively large composition change over each theoretical tray. Thus the error caused by inaccurate product anal) Another advantage of u3ing total reflux is that unknown overhead entrainment does not affect the calculateu tray efficiency. In this n-ork a tray v a s considered to he flooded when the doivnflow were just filled x i t h liquid. Under nornial operation a tray sample could lie taken as vapor from the special sample tubes placed in the donnflo\v, hut \vhtln liquid filled the clo~vnflo~~, a sample of liquid n-as \vithdraivn. When a tray flooded there would thus of the fluid from any be a sharp break in the anal simple puint. .4ctually it \vas found to be possible to operate the ton-er a t rates over the flooding point as defined here. In such cases the liquid level rose above the neir and appeared a: additional submergence. The amount of additional tower capacity nm, therefore, R function of the tray spacing. This extra submergence might often increase tray efficiency, hut at the expense of pressure drop. This effect is probably of little practical importance in trays having 1 1 / 2 - to 2inch tray spacing. iinother factor that had to be considered in the tray tests and their application x a s that a tray might have a practical capacity limit which was less than the flooding capacity. This limit would be the point a t which the tray efficiency fell off badly because of serious intertray entrainment. Low tray hpacings allowed little entrainment disengaging space, and thip fact plal-ed a large part in limiting the capacity of some of the towers tested. There is no way t o measure the intertray entrainment in operating liquid air fractionation towers. Overheud entrainment is another matter. This may result from poor head de ign or from flooding of the trays. I n the fourtral- tests the overhead entrainment was actually mea,sured v i t h an electric calorimeter. .4dditional sample points ivere placed in the bottoms of the don-nflon.s of each of the test trays so that the individual tray efficiencies might be checked. iill te& ?
