RECTIFICATION of LIQUID AIR a PACKED COLUMN John
in
A. W e e d m a n
CONTINENTAL AVIATION A N D ENGINEERING CORPORATION, DETROIT, MICH.
Barnett
F.
Dodge
YALE UNIVERSITY, NEW HAVEN, CONN.
A
study was made of the rectification of air in a 2-inchdiameter exhausting column with liquid air feed at the top, gaseous oxygen withdrawal at the bottom, gaseous nitrogen withdrawal at the top, and with electrical energy input to the boiler, Special care was taken to develop a test setup with low heat leak to the column, since this is important in the interpretation of results. The best method of achieving low heat leak was b y the use of a vacuum chamber. Seventeen packings were tested in a search for the most efficient packing. The operating variables studied included reflux
rate, reflux ratio, packing height, column inclination, packing size, packing density, heat leak, and flooding. The method of interpreting the observed data in terms of H.E.T.P. is discussed in some detail, and the point is stressed that the absolute values are, in certain cases, quite sensitive to operating conditions and to assumptions made; hence they should b e used with due caution. O n the other hand the reproducibility of values was good-on the order hence i t is believed that reliance can b e of 0.1 to 0.2 inch-and placed on the comparative results.
HIS study of t h e rectificalion of liquid air in packed colums mas undertaken in connection with the general oxygen program of Division 11 of t h e Sational Defense Research Committee. T h e general objectives of this program have been reported elsewhere (8); this laboratory was assigned the task of testing and developing certain items of equipment such as rectifying columns, heat exchangers, regenerators, expanders, and air purification equipment, for use in small mobile oxygen plants or plants t o be located on a ship. The present paper reports the results of tests on small packed rectifying columns. T h e air separation industry had always used bubble-cap tray columns for this purpose, but packed columns appeared t o offer certain potential advantages; chief among them are (a) lighter n-eight, ( b ) loxer columri height, (c) cheaper and simpler construction, jd) lower heat, capacity a n d hence less time for cooling don-n t o operating temperature, and ( e ) less effect by the rocking t o which a shipboard unit n-ould be subjected. T h e investigation was undertaken with three major object3 in mind: t o determine if packed columns ~ o u l dhe sa air rectification, t o determine the most efficient packing and the best operating conditions, and t o obtain general performance data for the design of rectifying columns t o be used in small oxygen-producing units. Although packed rectifying columns have been quite extensively studied for t h e separation of liquids boiling above room temperature, t h e literature contained no information on their use for the rectification of liquid air a t the time this investigation was started. Those who were experienced in the oxygen industry could offer no data, and opinions on t h e desirability of packed columns for this application were conflicting and of little value. T h e only tests on air rectification with packed columns t h a t had come to our attention n-ere the few made a t t h e Stamford Laboratory of t h e S i r Reduction Company, Inc., and reported by S. 9. Prentiss ( 7 ) . These tests were made for t h e primary purpose of determining the effect of rocking on t h e efficiency of a column, because this effect would be present when a column m-as located on a ship. Six tests were made on packed columns, two on Stedman packing (type not stat’ed but presumably the triangular pyramid) and four on 1/4-inch Berl saddles. The tests were made on a 6-inchdiameter exhausting column with 48 inches of packing depth under conditions of total boil-up (zero oxygen recovery). The con-
clusions reached are quoted as follou-s: “Preliminary tests with columns packed n-ith Berl saddles, or with Stedman packing, gave an unsatisfactory low efficiency, presumably bpcause the packings tested ryere not n e t by the liquid air. Further exploration of the que-tion of wetting will be necelsary before definite conclusions upon packed columns can be reached. Packed columns appeared to be little affected by rocking.” Table I summarizes the data reported for these six tests. The results on the packings 15-eredisappointing from the standpoint of efficiency (as measured by number of theoretical plates per foot), since they 7Tei-e quite inferior to those obtained with bubble-cap plates, hut it x a s demonstrated t h a t rocking had little effect. Stedman packing was inferior t o the saddle$, and this was attributed to a nonvietting of the packing by liquid air. (Teits made subsequently a t this laboratory indicated t h a t the s wetted by liquid air as would be expected packing ~ m thoroughly from its l o n surface tewion, and hence the poor results are prohably due to some other factor.)
T
SCOPE
TYPEOF ~ I ~ I ~ . L R . ~ T L -.4S11. teats were conducted in a 2-inch diameter cxliausting column with liquid air feed at the top, gaseou? oxygen n.ithdran-a1 at the bottom, gaseous oxygen-nitrogen
Run Xo.
9 9
10
Packing Stedman Same
l/a-in. Berl saddles 10 S a m e 11 S a m e 12 S a m e
Colu&in, ent a t C u . F t 1 t o p of \Iin. column 135 20.0 135 21.0
130 127 128 128
21.0 21.0 21.0 21.0
bdttorii of column 98.8 97.0
99.07 99.0 98.2 99.2
Perfect Plates Column per F t . Position 1 . 1 7 Vertical 0 . 9 3 Rocked through total angle of IS,’, 2 cycles/ min. 1.26 1.22
Yertical Rockedasinrung
1.07 Vertical 1.28
Vertical
a S o indication given of t h e condition under which this volume was measured.
732
June 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
Steam
733
* Sample Line
N2 P r o d u c f Heater :ompressed
Air
NZ
Column
S a m p / e Line
"
Sfeorn
I, f
Packed
*u
/ . F
'
h I nel e, t
AP
?
SontoCe I
Column
......
-. .
I
Feed Tank
nsuiation
- ...
...-.
Heater
I '
I10 L! Figure 1 .
Apparatus for Distillation of L i q u i d A i r
withdraiwl a t the top, and with electrical energy input t o the boiler. T h e column assembly ivas insulated in the first 182 tests by burying it in a tank of Saritocel ( a silica aerogel produced by the Monsanto Chemical Company). ; i vacuum insulation system Tvas used in the last forty-nine t e x-ith the coluiiin placet1 inside a vacuum chamber and tlie pressure reduced to 1 x 10-5 mm. of mercury. VARIABLES STUDIED.Seventeen packings \\-ere tested under a variety of conditions. T h e reflux rate was varied from a very low figure t o the flooding point. T h e per cent oxygen yield (related t o reflux ratio) was varied for most packings from zero to the maximum possible in an exhausting column- namely, about 73'%, depending on feed composition. T h e height of packing was varied from 10 to 48 inches. By surrounding the column with a liquid air jacket, glass rings were tested with heat leak into and out' of the column. T h e effect of flooding the packing before making a test was studied with the glasj rings. Theeffect of column inclination on the performance of glass rings and Stedman packing was measured n-ith an angle of inclination ranging from 0' to 6". T h e packing density of glass wool was varied from 0.7 t o 21.0 pounds per cubic foot. T o determine the effect of packing size upon performance, '/,-inch and '/,-inch glass rings were tested. An exhaustive study of these variables was not attempted. T h e main objectives were better met by a large number of ',high spot" tests rather than a systematic study of the variables, which would have taken much longer and would not have been justified. APPARATUS
Since it n-as desired to test a considerable number of packings under a >-ariety of conditions, it ]\-as essential to develop an apparatus that was simple and flexible. These conditions v,-ere best met by a small exhausting columii ivith liquid air feed and electrical energy input to the boiler. T h e first apparatus was assembled in a hurry, and insufficient attention was given to niinimizing heat leak; as a result heat leak was such a large fraction of t h e total heat input that interpretation of the data was difficult. These preliminary runs, the results of lyhich are not reported, served ai: the basis for development of tn.0 better assemhlies, the
first of n-hich is illustrated diagrammatically in Figure 1. With the exception of the method of insulating the column, the main features of the tn-o assemblies are identical and may be outlined as follows: COLIXS. Two interchangeable columns were used, one 24 inches and the other 54 inches long. Each was constructed from a 1.94-inch inside diameter by 2-inch outside diameter copper inch tube, to the ends of which were silver-soldered 4 X 2 x brass flanges. T h e first packing support was a 16-mesh copper screen silver-soldered in the column 3 inches above the bottom. T o carry off the liquid, a '/?-inch outside diameter copper tube n-as placed in the center of the support and extended t o the bottom of the boiler. T o determine if this packing support were limiting column capacity, another support consisting of a crimped 16-mesh screen Ti-ithout a liquid don-n-pipe was later tried and used in subsequent tests. BOILER. T h e boiler was constructed from a 6-inch-diameter brass tube 12 inches long and was fastened to the bottoni flange of the column with soft solder. T h e heating element lvas a 2500watt General Electric Calrod unit; this was coiled in the bottoni of the boiler, and the ends were brought out through the hottom plate, the joints being made tight w-ith d y e r solder. Figure 2 rhons the column and boiler assembly as used in the Santorel insulation unit. FEEDSYSTEM.Liquid air (produced a t Eloane Physics Laboratory) vias stored in a 100-liter vacuum flask (made by Superior hir Products Company) and forced into the top of the column through a capillary line by controlled air pressure on tlie Aark. T h e liquid air issued directly from the feed line onto the to]) layer of the packing, the end of the feed line being 1 inch above the top of the packing. S o special provision lvah made for liquid di+ tribution except for one packing (referred to as regenerator packing) when a special distributor was used; tlie latter consisted of a cross made of '/,-inch tubing in Tvhich were drilled 9 holes ot about 0.04-inch diameter. Rate of liquid air flow to the column was varied by changing the pressure on tlie storage flask rather than by use of a valve in the feed line. T o prevent clogging of the capillary feed line with solid particles always present i n liquid air, a glass wool filter was placed in the line. T h e feed
734
INDUSTRIAL AND ENGINEERING CHEMISTRY
line n a b insulated by placing I t in a sheet-metal cylinder 16 inches in diameter and 42 inches long which was filled with Santocel. The cylinder was airtight except for a breather line throughnhich dry air was drawn in when t h e insulation was cooling. Heat conduction from t h e metal shell t o the feed line was minimized by passing t h e latter through large rubhei stoppers. T h e feed rate could be varied f r o m 0 t o 50 pounds per hour by increasing the pressure on the vacuum flask t o a maximum of 15 pounds per square inch. T o prevent Figure 2. Boiler and Column Assembly any higher presfor Use in Santocel Insulation Unit sure from being inadvertently placed on this tank, an ordinary pop safety valve Iyas installed. T h e pressure in the feed tank was closely controlled by a reducing and regulating valve attached to a high pressure air cylinder, and was indicated on a mercury manometer. Liquid air level in the feed tank Tvas initially indicated by a mercury differential manometer, one leg of which was connected t o the top of the flask and the other extended through t'he neck t o the bottom. To cause the manometer t o indicate the true level, it was found necessary t o place a small Sichronie n-ire heating element in the latter line. Current $\-aspassed through the heater which vaporized the liquid in the line; the line n-as thus cleared of liquid and a pressure differential thereby produced equal to the hydrostatic head in the tank. This liquid level device was later abandoned and the level determined by the simple expedient of placing platform scales under the feed tank t o folloxv the change in w i g h t . The feed tank \vas filled from 15-liter metal vacuum flasks by applying air pressure to t,he latter and forcing the liquid through a 3/s-inch copper tuheline \\-hiell extended from the bottom of the small flasks t o the top of the feed tank. The capacity of the feed tank \vas large enough so that several tests could be made Tyithout refilling. IKSTLATIOS w r H SASTOCEL L-SIT. The column and boiler assembly (Figure 2) was buried in Rantocel, which \?-as contained in a sheet-steel shell 26 inches in diameter and 60 inches high. The top of the container had a removable head through which all connect,ing lines t o the column were soldered. It was made gahtight by means of an oil seal and was provided with a breather containing activated alumina, by means of xvhich dry air wa.s introduced into t h e Santocel when the unit was being cooled. The entire column a s e m b l y was fastened to this floating head and thus could readily be removed for change of packing. The Santore1 was sufficiently fluid t o permit reinsertion of the column into
Vol. 39, No. 6
the container without removal of the insulation. This operatioir 15-asfacilitated by a Tvooden cone fastened to the base of the hoilw and by the use of compressed air t o expand the Santocel. The chief objection to this procedure \\-as the dust storm created and the subsequent covering of everything in the neighborhood x\-ith fine Santocel dust. T o ensure that the column was perfectly vertical after heing placed in the tank, four lja-inch rods of equal l e n d h were extended horizontally through small holes in the side of the tank until they touched the columfi. Two rods at right angles t o each other touched the side of the column a t the top, and two touched the column a t the bottom. The bottom of the column was t'hen moved until plumb lines extending from the ends of the upper rods coincided with the ends of the lower rods. This method was also used to measure the angle of inclination in some tests. Figure 3 is a photograph of the entire apparatus and the Santocel tank. INSUL.~TIOS WITH T-ACCUU UNT. The most satisfartory method of insulating the column proved t o be the vacuum unit. The same column and boiler assembly used in the Santocel unit n-as attached t o a different, removable head and suspended in a vacuum chamber consisting of a 10-foot length of 2-foot diameter iron pipe. A plate was welded in the bottom of the chamber and the entire unit painted with Glyptal paint. .4t the top was welded a heavy 24 X 28 X 2 inch flange. T h e removable head consisted of a 26 x 2 inch circular piece of steel which merely rested on the upper flange without any fastening, the seal being made with apiezon sealing compound (James Biddle Company). Connecting lines to the column passing through the head were made airtight by silver solder. Vacuum \vas produced by use of a Cenco Hy-vac pump as the forepump and an oil diffusion pump (Distillation Products, Inc.). .4 pressure of 10-6 mm. of mercury, satisfactory for column operation, could he obtained in about 2 hours. T o prevent heat leak by radiation, the column and boiler were wrapped x i t h aluminum foil (Figure 3 ) . The entire testing apparatus and t h e vacuum chamher and pumps are shown in Figure 5 .
Figure 3.
Entire Testing Apparatus with Cantocel Insulation
June 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
ISSTRCMESTS FOR MEASI-REMEST . n u COSTROL.The feed rate \vas determined by neighing the feed tank periodically during a test. This value was checked by measurenient of the nitrogen andoxygen products. The nitrogen product rate was controlled by a n orifice and manometer, and total How measured by a rotary wet displacement meter. The osygen product rate \vas also controlled by a n orifice meter, and total flow measured t)y a bellow type of displacement meter. T-alve$ Jr-ere used as variable orifices in both lines so that wide variations in flow rate could be conveniently indicated. Liquid level i n the boiler \vas indicated on a vertical water-filled manonieter \r.ith an inclined {r-ater-filled manometer in series t o incre3.e the sensitivity. This level indicator operated automaticall?- and >atisfactorilyon the differential gas pressure developed by the hydrostatic head of liquid in the boiler. Pressure in the feed storage vessel way indicated on a mercury manometer. Energy input t o the boiler \\-as controlled by a variable autotransformer and meaiured by a v-attmeter. Static pressure in t h e boiler n-as measured by a niercury manometer, and pressure drop across the column, hy a differential water manometer. Pressure in the vacuum insulation unit \\-asmeasured by a standard McLeod gage. Temperatures of both product streams n-ere measured at the meters by thermocouplestoal low conversion of volume flow t o mass flon-. Temperatures in the coluriiii and boiler x e r e initially measured but later abandoned as they seemed t o have little value. Sitrogen product and feed were analyzed for osygen with an ordinary portabIe Orsat apparatus such as is conrnionly used for Hue gae analyses. I t could lie read t o about 0.1%. T h e oxygen product was analyzed on a similar apparatus provided with a buret with special scales from 95 t o 98% and from 98 to 100% oxygen, so t h a t t h e sensitivity in this region \vas greatly increased. In the first range it ivas graduated t o 0.1 cc. and in the second t o 0.01 cc. ~ I I S C E L L . A N E O U B E Q C I P M E S T . T h e osygen product \vas drawn off through a 1,'2-inchoutpide diameter copper tube soldei,ed to the boiler near the top and well above the liquid level, .*iJ that it was alnays a vapor product. The osygen was heated t o room temperature in a coil of 5,'a-inchoutside diameter copper tubing immersed in boiling water. T h e nitrogen product Tvas n-ithdrawn through a !l-inch copper line soldered t o the top flange of the column and heated to room temperature by passage throu.;h a double-pipe heat exchanger. The latter consisted of a 6-foot length of I-inch standard pipe surrounded by a 2-inch standard pipe, ivitli steam in the annulus. -4liquid air jacket n-as placed around the column in some tests t o reverse the direction of heat exchange betn-een the column and the surroundings. T h e jacket consi-ted of a 43'9-inch sheet metal cylinder 18 inches long surrounded by a similar cylindei 6 inches in diameter. T h e annulus het\\-een the tn.o was filled with liquid air, and the annulus between column and jacket ivas filled with SantoceI. Two liquid distributors tvere placed in the 48-inch long column in scme te.sts t o study the effect of liquid distribution. The distributor, designed t o return liquid t o the center of the column, c*on&ted of a brass plate 1/8-inch thick, with a ',-inch outside diameter copper tube 1 inch long estending don-iin-ai,dfrom the center, and four '*-inch outside diameter copper' tubes 1 inch loiig extending upward at points inch from the wall of the coluniri. The distributor designed t o return liquid t o the n-all of the rolnmn, consisted of a similar plate n-ith a '?-inch outside diameter copper tube 1 inch long estending upn-ard from the center, and four 1/4-inchoutside diameter copper tubes 1 inch long cstending do\vnn.ard at points inch from the xsr-all of the colunin. Cimnectioii- n-ere made tight with cilver solder. The di5tributors were placed a t 16-inch intervals i n the c-ulted in a varying heat leak. 12. For all teqts matlc in thc Santocel unit, itc,ni 12
=
item 7 - 0.101 lb. mole/lir.
FtJr n m t t w t s mad[, in the vacuum unit,
T:t\jlt TI; thesc are typical of all thc data taken. The significant rewlts of all tests are preaeritcd graphically in a later wction. D a t a on flooding and on direct measurement of heat leak arc presented separately. An explanation and sample cald a t i o n for some of the items in the table folloiv. T h e numbers i,c.ftti. to corresponding itenis in Table I1 : 5 . The column was inclined in iome tests to dt~tcwiiiiicthe effect of inclin:xtion upon porformaiicc. In other teat* the colunm was vertical, and this is designated by an angle of iiicliiiation of 0". In a h i - tests t h r :inglc ~ v not a ~mea urccl, but it may he assumed that rhr iinclinatic n ~ i - nllt a ~ w f f i i ent to afft3ct the results.
i t p m 12
=
jtem 7 - 0.033 Ib. mo1e)hr.
13, 14, nnd 13. The arithmetic average of samples taken every 20 minutc-. 16. Calcu1:itc.d from tlie amounts and analyses of the nitrogen and oxygen products. 17. Pvr rent oxygen halanccl equals:
oxygen in Rum of products oxygen in feed
Thc numb^^:: in parenthesis rct'er t o items as numbertbd in Tuhle
11. 18. Per cent oxygen yield equals: loo
oxygen in oxygen product osygen in both products
19, The average of 20-minute readings on the n-attmeter. 20. Oxygen vaporized by electrical energy = (item 19,'lOOO) (1.161. This is based on latent heat of vaporization of oxygen of 2940 13.t.u. per pound mole. One kilowatt-hour = 1.16 pound moles of oxygen vaporized. 0.02. Total oxygen vaporized in boiler equals 21. Item 20 that vaporized by electrical energy plus heat leak. Average measured heat leak to boiler was 60 B.t.u. per hour for the Santocel unit and 40 B.t.u. per hour for the vacuum unit. 22. ( 0 / J 7 ) 1 is a reflux ratio and equals the ratio of the moles of overfloiv a t the top of the column to the moles of rapor gtiieratcd in the boiler:
+
(O/V)I = item 11,'item 21 23. (0,'V)rr is the ratio of the moles of overfloiv at the top o f the column to the moles of nitrogen product: (OiVjII
=
item ll,!item 12
24. The average vapor velocity in the column is the linear velocity in the open column based on the average nu.nber of moles of vapor flow in the column as given by items 12 and 21, on the assumption that the temperature is 85' I- packing height. :tiid thi- \vi\- corlfir~medhy Fc,nckr :itid co-worker.; ( I O ) , x h o studird the distilliltioii (IF /i-hrpt:iIl? mfxtllyl cyclohexane at total reflux in :I 0,7%inch inside diamrtrr gl:r.r column pecked n i t h -iiigle-tul,Ii .j &rich t1i:rmeter So. 30 wire helices. For 11 packed height of 2 3 . j ilictie., H.E.T.1'. v:irird from 1.07 t o 1.17 iiichcs for reflux rates of 142 to 645 pciut~cls~if'r square foot per hour, respectively. For B pricked height of 1 I 1 inches, H.E.T.P. varied from 1.11 to 1.09 inches for reflux rates iii 133 to 595 pounds per square foot per hour. Values of H.E.T.P. iihtained in this investigation for the same packing in :I 2-inch * iliameter colunin packed to a height, of 18 inches aver;iged 4.5 inches for reflux rates varying from 600 t o 800 pounds per square foot per hour. Values of H.E.T.P. repurted ill the literature in general i n c r r a s ~ with a n increase in the diameter of the packed column: consequently any comparison ivith values obtained in this investigation should he restricted t o data ohtained in a 2-inch diameter column. Fenske and co-wnrkers (11) reported extensive data on the dis-
E;vrii g:i'r:ltrr c#tv.ts 'n v r r t*x:perieiii*edin some test.-, \vliii,li are not reportrd l.wcxuse the angle of inclination is unkiiimii. In sevrrul ~*a,e.-tlie difference in performance of a Stedi i i i i r i packing in oprixting between a n unknown inclination and a vertical position war a d e r i w s e in H.E.T.P. from 6.5 t o 2 . 5 inches. Sirlve the effert of ineliiia,tion probahly increases wit>h packing height, it is neeeswry to erect a long packed cvlumri in an ahroliitely vrrtical position for rriaximurn rfficienvy . P.I('KINCJ SIZE. T\YO,size>t r f glahs rings, irli*h and inch, were tested to determine the rffwt of packing size tipon performance. The r r w l t - (Figure 13) iiidi(*:ite tlr:it, when the 1i:ic'kiny size of gl:i-.~ring* i- i r i c r ~ e a w lfrom I to ! : inch, t h r cnpncity i* tiouhled and t h r cltticirricy, as determiiirti by H.E.T.P., is rediiceti by approximately 20';. Pac.r;rsc,DESSITT. The deiiaity i r t ' tlie curly 0 60x40 MESH STEOMAN wool packing wx. w r i e d over the rarige 0.7 t o .4.% I)cliinds per cuhic foot; tlie results :ire A I/Q-INCH GLASS RINGS e SHOE EYELETS >l!irivii in Figure 14. T h r dotted line cuiiiiects l)oiiit.- obtained iii trsting a t reflux rates j u t l w l o \ v Hooding for e'~c1ip:tckiiig, the lower rates riit.rr>pondingto the deii>er picking. Increas..? 3 4 5 6 7 irig the density niarlirilly I o i v r r d H.E.T.P. COLUMN INCLINATION, DECREES l)ut also decreased tlir ni:ixiniiini t Iwoiighput. Figure 12. Effect of Column Inclination on Packing Performance The solid lines are tirun-ir to coiinrrt two points obtained a t constant density, I ~ I I Pi ~ Rr flox 5 rate just, below flooding a n d the otllrr for N case of partial flooding. T h k srrk-es t o (lemonstrate :igaiii the impr.overnrnt i n perforni:i:irr [~:iii~ed u) w 4 by flooding. U .I few tests were made \\-it11 rhr IltIirr t\vo z widrs of Fiberglas, but. the relatively poor perfor,mnnce did not justify further test.. O 3 < PRESSURE DROP. Figure 15 illustrwtra presw s u r e drop data obtained during the test?; the 0 1/4-INCH G L A S S RINGS r log of A p is plotted against the meiiii vapor I N D I C A T E S FLOODING 2 velocity for the case of total boil-up. Values of reflux rate corresponding t o the vapor velocities may be obtained from Table VI. I The d a t a plotted for the three packinps repre-. 10 20 30 40 50 60 70 80 sent t h e limiting and arerage raliiri for all REFLUX RATE. LB. M O L E S PER HR.PER 5 Q . F T . packings. D a t a for t h e other p a c k i n g fall Figure 13. Effect of Packing Size on Column Performance ~ . l i r l . - rings.
-
:
90
744
INDUSTRIAL AND ENGINEERING CHEMISTRY 9 -
PACKING
DENSITY LBS./CU.FT. 0 CURLY WOOL 0.7 0 ,. I .75
\ I / \
,
I v)
w
r
a
U
/
FLOODING OTHER TESTS HADE JUST BELOW FLOODING RATE
i
DOTTED LINE INDICATES CHANGE IN PERFORMANCE AND CAPACITY WITH [XNSITY OFCURLY WOOL
# /
6 .
'
nenux Figure 14.
I
I
RATE, LB.MOLES PER HR.PER SO.FT.
Effect of Packing Density on Performance oflfiberglas
IO
I
I
2
0 I .o
/
/
I
I
t
0.5
I .o
2
3
VAPOR VELOCITY, FEET PER SECOND
Figure 15.
Pressur e Drop at Total Boil-up
tillntioii oi r~-liel)ttiiieand metliyl cyclolirx:i~ic~ \ritli :I \-:iric'ty or packings in a 2-inch inside diameter gh-h colunm 1):icLccl t ri :I lieiglit of 102 inches. The value-. of I1.K.T.P. i ~ r p o r t d:iw i t r su1istanti:il agreement n-ith tlie vnlues oht:~iiiedd u i , i i i K thi- iiivr-tigatioii for the mme packing lrut \ \ - h ~ t i teqteti I\ i t l i :I p:irlwtl height of 18 inches:. Fenrl.re'- v ~ l n c .of I3 .E.T.P.inc~i~cmc~ sliglit .!I n-ith an increa:e i i i reflux rate in some ea+- a i d i1t.c in others. I t ic therefore difficult to coriclude n I i P t l i r r II.II.T.1'. is iiidepeiitletit of reflus rate a. ~ v a "found in this iiivrstigaticrti. Brtigg'+ values of H.E.T.P. for a 3-foot hriplit of Strdinnli p:icl;ing i i i :I 2-inch column (Table T'II) nre *omen-h:it 11nvi.r thait t h e obtained in tlii. investigation with 18 iiicliei of thc S:IIIIR packing,
Reflux R a t e , Lb.1 (Hr.)(Sq. Fr.)
Pressure Drop, I n . H ? O j F t . of Packing 2.59 0 92
1.li 1.31 1.43 1.61
..
Initial flood goint.
!I =
I.' u !rr. - x
!/D - -
I
=
1.2.50~ - 24.20
From the usual stepivise procetiiii I m e d nii this equation arid tlie osygc~tinitrogen equililirium data, four pl:itc:ire required to reach T = 0.8937, :illti the fifth step would carry the coniy)o>ition t o s = 0.9655: n fr;iction:il pl:itcs itherefore estimated as follow:
Fraction of a plntc
0 lZOXl20 MESH STEDMAN 0 I/41NCH GLASS RINGS A 1/21NCH G L A S S R I N G S 5 - I - INDICATES PARTIAL FLOODING
I
10.5
From Table 11, F = 1.107, U = 0.933, 11- = 0.234, SI' = 0.292, !/ti = 0,123, : i ~ i d)/ir = O.!J70. From matei,inl Ixiluiice tlic eilu:itioti oi tlie operating h i e is:
WOOL
7 '
,v
4.2
SAMPLE CALCULATION BASED O N RUN 18
-I_ INDICATES
/
6
,I
FILTER WOOL
X COARSE FILTER 21,0
/
d
w
Y\
/
X
E
t,
+ FINE
J-
I
.
Vol. 39, No. 6
12
=
0.0600 - 0.8037 - o,!,3 0.9653 - 0.8037 -
