US2787453A - Fractionating tower utilizing directional upflow means in conjunction with slanted trays - Google Patents

Description

i 1957 H. J. HIBSHMAN ETAL 87,

FRACTIONATING TOWER UTILIZING DIRECTIONAL UPFLOW MEANS IN CONJUNCTION WITH SLANTED TRAYS Filed Nov. 30, 1953 2 Sheets-Sheet 1 HENRYJHIBSHMAN sTEPHE HDOLE av monnsy Apnl 2, 957 H. J. HIBSHMAN ETAL 2,737,453

FRACTIONATING TOWER UTILIZING DIRECTIONAL UPFLQW MEANS IN CONJUNCTION WITH SLANTED TRAYS Filed Nov. 30, 1953 2 Sheets-Sheet 2 Fl ca.- 2

3 2 6| E 26 FIC5.2A

HENRYJ.HIBSHMAN I STEPHEN H. DOLE '"VENTORS Inf L0 momm' FRACTIONATING TOWER UTILIZING DIREC- TIONAL UPFLOW MEANS 1N CONJUNCTION WITH SLANTEE TRAYS Henry J. Hibshrnan, Plainiicld, and Stephen H. Date,

Westtield, N. 5., assignors to Esso Research and Engineering Company, a corporation of Delaware The present invention relates to improved apparatus for operating a countercurrent-vapor-liquid treating zone. The invention is more particularly concerned with an improved fractionation zone and is especially directed toapparatus for contacting upflowing vapor and downflowing liquid utilizing improved contacting trays. In accordance with the present invention, the capacity of particular contacting trays and the entire treating zone is markedly increased by providing a means for efliciently and effectively contacting the countercurrently flowing phases. In accordance with the present invention, selected directional vapor and liquid streams are produced on the respective trays which facilitates the passage of the downfiowing liquid across the tray, thus reducing liquid holdup on the tray. The directional stream is secured by a contacting tray which i characterized by containing directional openings, such as tab openings. A specific adaptation of the present invention is to utilize a slanted tray in conjunction with the directional upfiow means. 'A

particular adaptation of the present invention is to arrange the upflow means, such as the tabs in an elliptical pattern on the tray. When employing this latter modifi cation, especially excellent uniform liquid distribution is secured by employing vertical vanes in conjunction with broad crested or sharp edged weirs at the inlet side of the tray.

It is well known in the art to carry out many chemical reactions and separations wherein vapor and liquid'are contacted in a countercurrent zone, such as in a vapor' liquid fractionation zone. Normally the liquid passes from one zone to a lower zone by means of downcomers or their equivalent while the vapors pass upwardly from zone to zone through chimneys in the tray, around various types of hell caps or their equivalent into the liquid phase disposed on top of the tray. The liquid phase flows across the tray and over weirs on the respective trays into downcomers and onto the tray in the zone below. The height of the liquid phase on the tray is determined by the height of the weir. The downcomer from the zone above must of necessity extend below the top of the liquid phase on the lower tray in order that vapor will not pass up through the downcomer instead of through the bubble caps. In liquid-gas, contacting operations of this character, the capacity of the tray and consequently the tower is determined to a large extent by the degree of efiiciency with which the downfiowing liquid flows across the tray and into the downcomer. Thus, aside from limitations of auxiliary equipment, such as furnaces, feed pumps, and condensers, the capacity of a fractionation tower is determined by several factors. Basically, these arelimitations to passage of liquid down'and vapor up the tower in such a manner that efiicient contacting is achieved.

The requirement of efiicient contacting means that the limitation may be one of too rapid or free passage of one or more of the phases through the tower, as well as restrictions to flow of the phases. Tray dumping, liquid running down throughbub'ole cap chimneys, is an example ats atent of too free flow of liquid. Downcomer filling with backup of liquid on the tray is the opposite type of limitation, resulting in poor efiiciency because of excessive entrainmerit and ultimately in tower flooding. A similar high entrainment result is produced by excessive vapor rates. In a typical bubble cap tower, each of these limitations predominates over a diiierent vapor rate range.

One operating disadvantage comprises excessive liquid holdup which, in the absence of a downcomer limitation and obstructions on the tray, is determined by the linear velocity at which liquid is able to pass across the tray. For a given liquid velocity across the tray the liquid holdup is directly proportional to the volume of liquid flowing across the tray in a unit of time. Since the liquid on the tray is aerated by the vapor, the volume occupied by the liquid is a function of the velocity of the vapor in the tower and the amount of liquid holdup on the tray. At normal tray spacings a tower will ultimately be limited in capacity by the liquid flow approaching the tray above, resulting in excessive entrainment. Accord ingly, higher capacities can be reached if the liquid holdup is reduced. Reduced holdup is accomplished by the present invention which directs the upflowing vapor stream through the trays in such a manner as to push liquid across the tray at a faster rate.

In accordance with the present invention, directional jet or tab-style fractionating trays are used in conjunction with slanted trays. While directional jet or tab-style fractionating trays have been shown in laboratory and plant scale operations to possess vapor handling capacities, up to and greater than 40% higher than conventional bubble cap plates, one disadvantage of these directional trays has been their tendency to dump or spill liquid through the tray at vapor rates below about 40 to 50% of the tray capacity. Thus, since the jet style tray dumps or spills more liquid than bubble cap tray at low liquid loadings, their usefulness has been somewhat limited.

In accordance with the present invention, it has been found that if these jet or tab trays are slanted from about 5 to 10 degrees from the horizontal toward the downcomer, this spilling of the liquid is substantially eliminated. It has also been found that if the pattern of the direc tional means is arranged in a family of ellipses, unexpected desirable results are secured with respect to the tray phase contacting efiiciency. It is very desirable to use in conjunction with the slanted tray, vertical vanes in conjunction with broad crested or sharp edged weirs at the inlet side of the tray, the weirs being perpendicular to the elliptical flow lines.

The present invention may be readily understood by reference to the drawings illustrating embodiments of the 1 same.

Figure 1 is a vertical cross-sectional view illustrating a plurality of tray elements disposed Within a countercurrent treating zone.

Figure 2 is a top cross-sectional view of tray element 2.

Figure 2A is a detailed vertical cross-sectional view of tray element 2. Referring specifically to Figure l, a plurality of tray elements 1, 2, 3, 4 and 5 are disposed within a countercurrent contacting zone s. Plate ele ment 1 contains openings 7 secured by punching tabs. 8. In a similar manner trays 2, 3, 4 and 5 contain ope-r, lugs 99, 10, 11, and 12., respectively, secured by punch-- ing tabs 13, 14, 15 and 16, respectively. These openings permit communication from the area below the respec tive trays to the area above the respective trays. Downcomers are provided by means of bathe elements 17, 18, 19, 2t), 21, and 22. These baffle elements extend into liquid seal reservoirs 23, 2d, 25, 26 and 27, associated with plates 1, 2, 3, 4 and 5, respectively. It is to be understood that counter-current contacting zone 6 is pr o- Patented Apr. 2, 1957 vided with a means for withdrawing vapor from the top of the zone, a means for withdrawing liquid from the bottom of the zone as well as other input and output means at selected portions of, the zone.

In operation, liquid flows downwardly onto plate 1 through downcomer 17 into liquid seal reservoir 23. The liquid flows across the plate past tabs or equivalent means 8. Upilowing vapor passes through openings 7 inthe direction of the cross flowing liquid and thereby intimately contacts the same. The liquid flows across the plate into downcomer 18 and passes to the liquid seal reservoir 24 associated with plate 2. In a similar manner the downflowing liquid passes over tray .2 into downcomer 19 and into well element 25. As the liquid flows across tray 2, it contacts upfiowing vapor passing through the openings 9. Thus the liquid passes across tray 3 into well 26 across tray 4 into well 27 and across tray 5.

The character and particular dimensions of the plates illustrated in Figure 1 may vary appreciably. For instance, a typical lO-foot diameter tower would have trays having preferably a 7.5 degree slope with respect to the horizontal. The trays themselves would be about 7 feet in length and the average distance between the rehandling capacity of about 10 feet per second, the superficial air velocity at which 5% dumping occurred, was reduced from 3.1 feet per second to 1.97 feet per second by changing the tray slope from to degrees and further reduced to 0.66 feet per second by slanting the tray degrees. Thus, the operability range of the tray was increased from 69%;to 80% and 93% by sloping the tray 5 degrees-and 10 degrees respectively.

Although the specific reduction in dumping obtained by slanting a jet tray depends upon the design of the tray such as'number of openings of unit area, opening size, opening shape, openingangle, and percent open area of the tray, nevertheless the preferred sloped angle remains from about 5 to 10 degrees. In general, with jet trays such as tab trays, dumping is most severe at low liquid loadings.

The invention may be more fully understood by the following example illustrating the same:

EXAMPLE A number of operations were carried out wherein the air rate was varied as well as the tray angle. The percent dumping was also determined. The results of. these tests are illustrated in .the following table:

Table Dumpz'ng data for tab tray hni1ing 80% tab area .(tabsfl' x 1 1") [Percent dumping at various air rates at 900 G. l. IEL/lt. water rate. Tray pressure drop-mm. H1O in parentheses 'Iab Angle 0 Air Rate, Ft./Sec 0 1 2 3 0' l 2 5 0 l 2 3 Tray Angle:

0 0.2(14. 5) 10 10 2s .ss 100(0 100(1) 58(13) 2608) 0 13 70 0 447(7) 0.7(10) 100(0) 85(1) 34 4) 5 0 0(11) 31(0) 2.6(3) 0.6(7) 0.1(s5) 51(0) 11(2. 5 am. 5 1.1(7 0 11.50) 0.7(3) 0.2(5;5) .0.1(8) 18.560) 2.8.(2) 1.5(4 0.8(5) 4:2(0) 0.4,(2) 0.08.01) 0.0 1(15) 7.4(03 2.1(2) 0.56.5) 0.2(5) (8. 6) (3) spective trays about 2% feet. The height of the down- MR RATE FOR DUMPING comer would be about 1.58 feet and the distance between the respective trays at the farthest point about 3.42 feet. Tab Angie Figure .2 illustrates the preferred elliptical jet pattern on the slanted .tray employed in conjunction with. direcfi 1 m tional vertical vanes and broad crested weirs. Figure 2 0:9: i197 is a top view of plate 2 with similar numerals designating 8 8- ti similar elements. 4.5 0 0 0133 In operation, liquid flows downwardly to tray'2 through downcomer inlet 24. The liquid is directed into elliptical ILmay beseenfl'om hi bl th i order to b R y. means of Vertical vanes The Size stantially reduce dumping, it is necessary to slope the dimensions .of these vanes will vary depending uponthe tray;only.,5 o 1 slanting th tray more th hi size of the unit being utilized. In general, these vanes '50 say 15 .or 20, results in atray more dump-free than is have heights ill the range from bout 2 to 6" and are practically, required in. most commercial fractionating about 4" to 18 long. The vanes at the Ce t r of the towers. Slanting; atray 5 to 10 increases its vapor inlet section of the plate are relatively straight, while handling-capacity about 10% but slanting it more than their curvature increases as they approach the shellwall. 10? ed e th available downcomer height excessively Positioned between the respective vertical vanes as dfmi ht rgduc;$ower a it b making th d ShOWu in Figum 2A arebfoad Crested Weirs leflgt comer limiting. No important reduction in pressure drop of Whlch is m the range of 0" to-6"- accrues fromzslantingthe tray more than 10. Hence In operation as illustrated above, the liquid fiowsacross the preferredtrayxangle in this invention is 5 to 10. the tray and across the jets 13, the elliptical pattern-of What is claimed is: which is illustrated by lines 31. The liquid enters down- 1. Apparatus. adapted for contacting upflowing vapor comer 19 and passes to the next succeeding zone. and downfiowingliquidcomprising a vertical tower, a An advantage of the present invention is that reduced plurality ofvertically spaced plates the plane of said tray inlet liquid heads are secured. In a normal bubble plates being inclined at an angle of from 5 to 10 do cap tray operation there is a tendency for liquid, to build greesv with the horizontal, said plates extending substanup to a higher level at the inlet side of the 'tray than 05 daily across said tower and intersecting vertically posianywhere else on the tray. It has been found .that :the tioned conduits extending through each of 'said plates use of tabs in place of bubble caps producestheopposite. and .terminating below. each plate; in spaced-relation to effect. In this case, the inlet head is lower than anysuccessiveplates, an array ofivertically disposed liquid where else on the tray. directing vanes extendingfrom said conduits a short The design of the tabs is not critical. Hemispherical. v distance .onto;.said plates, the end. of said vanes nearer baffies open on one side towards the downcomer, square orrectangular box-type battles open towards the downused.

In one preferred design of tab tray, which has a vapor said conduit being arrayed along a chord subtendi'ng an arc of the circumferenceof lsaid tower,'.the other end of said.array;- describing anarcuate configuration, thesaid' vanes-being adapted to. direct a. liquid stream in an elliptical' pattern, an array ofvapor directing means carried on said plates, each of said vapor directing means forming vapor ejecting orifices adapted to effect flow of vapor across said plate in a predetermined direction, said vapor directing means being disposed on said plates along the circumference of a plurality of concentric ellipses and oriented with said orifices ejecting vapor along said circumferences, whereby liquid flowing across said plate is directed to a pattern corresponding to the circumference of said concentric ellipses.

2. Apparatus according to claim 1 wherein said vanes are separated by individual weirs positioned perpendicular to the elliptical liquid flow lines across the plate.

References Cited in the file of this patent UNITED STATES PATENTS Sneath Apr. 27, Stone Dec. 5, Rudeen Feb. 8, Piron Apr. 3, Bergman Aug. 31, Rocke Nov. 10, Gadwa et al May 17, Kittel Sept. 25, Thrift et a1. June 15,

FOREIGN PATENTS Austria Dec. 27,

France Aug. 5,

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