US2880980A

US2880980A - Low pressure drop fractionating tray

Info

Publication number: US2880980A
Application number: US519839A
Authority: US
Inventors: Vernon O Bowles
Original assignee: Socony Mobil Oil Co Inc
Current assignee: ExxonMobil Oil Corp
Priority date: 1955-07-05
Filing date: 1955-07-05
Publication date: 1959-04-07
Anticipated expiration: 1976-04-07

Description

April 7, 1959 v. o. BowLEs 2,880,980

LOW PRESSUREDROP FRACTIONATING TRAY Filed Julys, 1955 s sheets-shea 1 4 4 INVENTOR 7eme w//zs v ATTORNEY April 7, 1959 -vfo.. BowLr-:s'

2,880,980 Low PRESSUR DROP FRACTIONATING TRAY'I Filed July 5, -1955 v 5 Sheets-Sheet 3 INVENTOR /mau d 13am/es' 8 y BY cleaning, of bubble cap type trays is cumbersome.

United States Patent A Low PRESSURE DROP FRACTIONATING TRAY Vernon 0. Bowles, Rye, N.Y., assignor to Socony Mobil Oil Company, Inc., a corporation of New York Application July 5, 1955, Serial No. 519,839

8 Claims. (Cl. 261-114) The present invention relates to an improvement in fractionating towers and particularly to the trays used therein in which a gas passes through a liquid. This application is a continuation-impart of my co-pending application Serial No. 326,481, led December 17, 1952, and issued as U.S. 2,714,504 on August 2, 1955, which, in turn, is a continuation-in-part of my application Serial No. 186,860, led September 26, 1950, and issued as U.S. 2,692,128 on October 19, 1954.

Fractionating towers of the type widely employed in the refining industries for fractionating hydrocarbon liquids and the like have heretofore generally been constructed by mounting a plurality of rigid horizontal plates at various elevations within a cylindrical tank. These horizontal plates are ordinarily pierced by a plurality of orifices over which are placed bubble caps so that vapors rising in the tower pass up through the orifices and bubble down into the liquid on the plate. The downwardly flowing liquid passes from plate to plate by means of downcomers to afford contact between vapor and liquid at a number of various levels as determined by the relative position of the horizontal plates or bubble trays.

The trays of the bubble cap type of tower are usually constructed of metal and supported by annular anges spaced along the outer edge of the trays and secured to the inside wall of the tank. To aord the necessary rigidity and strength, the trays must be constructed of relatively thick metal plate and must frequently have supporting beams to avoid deection of the plate. As generally recognized, the maintenance, and particularly the It is, for example, well known that, during fractionation of petroleum hydrocarbons, a gummy or carbonaceous deposition frequently takes place on the plates due to polymerization, coking, and the action of sulfur compounds and other agents. The cleaning of bubble cap plates made up of numerous bubble caps, risers, and associated fastenings in such instances is a tedious operation, accomplished only at the expenditure of considerable time and labor. Furthermore, while the trays are preferably constructed of a corrosion-resistant metal such as stainless steel, the cost of fabricating a tray of such material having suflicient thickness, together with supporting beams to provide the necessary rigidity and strength, has heretofore been an expensive proposition. Common practice has been to construct trays of less expensive material such as cast iron and, more recently, steel. A tray fabricated from such metals affords the necessary thickness in construction at a comparatively reasonable cost but such trays are heavy and are unsatisfactory when liquid and vapors coming in contact therewith are of a corrosive nature. Corrosion of the trays necessitates frequent replacement or repair thereof which, as pointed out hereinabove, is not only an expensive proposition but a laborious and time-consuming operation due to the complexity of design and to the weight of the heavy metal parts used in fabrication. Thus, economics often dictate that the fractionating tray be con- 2,880,980 Patented Apr.. 7, .1959

rice

structed of corrosion-resistant alloy regardless of initial cost.

In my aforementioned co-pending application Serial No. 326,481, issued as U.S. 2,714,504 on August 2, 1955, there is described a lightweight fractionating tray designed to overcome the above disadvantages in fractionating tray construction and to provide a fractionating tower wherein a corrosion-resistant metal can be employed in relatively thin sections for fabrication of the tray. The functional members making up such tray serve as lightweight structural beams extending transversely across the tankA and afford construction of a comparatively light tray which is easy to fabricate, assemble, and maintain in operation.

It has been established by commercial use of the latter tray construction that the same is more economical to install and maintain in operation than other types of commercially available fractionating trays. In addition, it has been found that such tray is highly effective in accomplishing the desired fractionation. It has been observed, however, with utilization of these trays under conditions of extremely low pressure drop, such as desired in a vacuum fractionation system,` that back-flow of liquid through the inlet vapor sections of the trays is sometimes encountered. Such liquid back-ow has kbeen particularly prevalent under conditions of low` or partial submergence of the slots or serrations, i.e., where the top of the same is actually at an elevation higher than the top of the riser. Under such conditions, maintained to secure the desired low pressure drop, if vapor does not flow through the slots or serrations, liquidi's bound to back-iiow. As will be evident, back-iiow of liquid in the inlet tray section is undesirable since the eiciency ofthe Kfractionating tower is thereby greatly diminished because only a portion of the liquid is being contacted.

It is accordingly the major object of the present invention to eliminate back-flow of liquid throughthe inlet vapor sections of trays using the above type of design, while retaining the advantages of economy and inherent structural strength of such tray construction.

A further object is the provision of means for activating the inlet upstream vapor section of a tray ofthe type described in co-pending application Serial No. 326,481, issued as U.S. 2,714,504 on August 2, 1955, when the same is used under conditions of low pressure drop.

A fractionating tray construction designed to fulll the aforesaid objects is hereinafter described, together with other features of the invention.

The invention will be more readily understood by reference to the accompanying drawings wherein:

Figure l is an elevational view partly in section of a portion of a fractionating tower showing trays constructed in accordance with one embodiment of the invention.

Figure 2 is a plan view of a fractionatiug tray embodying one form of the invention.

Figure 3 is an isometric view of a fractionating tray fabricated in accordance with the invention.

Figure 4 is a detailed side isometric viewv showing one means of interlocking of the inlet vapor section of the tray with an adjacent section. l

Figure 5 isa detailed side isometric view showing an alternate means of interlocking of the inlet vapor section of the tray with an adjacent section.

Figure 6 is an enlarged isometric view ofthe inlet vapor section of the fractionating tray showing one embodiment of the invention.

Figure 7 is an enlarged isometric View similar to Figure 6 but illustrating an alternate means for activation of the inlet vapor section.

Figure 8 is an enlarged isometric view similar to Figure 6 but illustrating another alternate means for activation of the inlet vapor section. v

l lFigure 9 is an enlarged isometric-view similar to Fig# assenso nre 6 but illustrating still another means for activation of the inlet vapor section.

Figure 10 is an enlargegzlr isometric view similar to Figure o but showing another alternate ernbodinrent for activating the inlet vapor section.

Referring there particularly to the drawings, in which like .reference characters. denote lilce parts, 1 designates an elo. ated cylindrical tanlt which forrns the shell of the .fractionating towert Since the tanls rnay be of any desired height and diameter., only a Portion thereof is shown.- A, plurality of trays vare .rnounted at various elevatious throughout the tanlr, the number .of said trays depending upon the requirements .of the fractionation to be pertornied- While only two trays .have been shown in Figure l, .it ill be understood that additional trays rnay bepositioned ab e and below the particular set of trays illustrated A plu .y oi support rings 2. are welded or otherwiseA secured the inside wall of tank 1, Resting upon and ailhtcd to each, .port ring are the rnernbers Which-thaise up the. fractionating tray Adjacent to .each group of horizontal trays are downcorners 3 through `vhich liquid passes- Each .downcorner is .sealed by the level of liquid the tray below, thus preventing the upward passage of vapors therethrough,

The-tractionating trays, .as will be seen, are composed of a series of troughs 4 spaced at uniform intervals transversely across the .tanlt and positioned in co-planar rela.- ticnship one with the oth... Each of the troughs is se-A cured yto the support .rig 2 by suitable fastening means such .as bolts 5 held in position by nuts 6 The vertical walls ot each yof .the-troughs are positioned at substantially right angles tothe respective trough bottoms, However, said walls rnay vary Ifrorn .the vertical as rnuch .as .30Vo without atlecting tu tional property thereof, it being understood .that the individual troughs in a given tray are preferably ot the sarne design! To each trough is attached an .ls-shaped `section co'rnposed of a horizontal les .7 attached to the downstream edge of the trough and avertical 'leg .8, the lower edge .of which is serrated. The aforementioned 4Lsliape1 section overhangs into the next succeeding troughz thereby providinga passage 9 between each pair of adjacent troughs, The'L-,shaped ysection overhanging the. upstream trough of each tray is. attached to a vertical plate 1.0 which, in turn, is aixed by suitable fastening Ineens, such as bolts .11, .to .angle support plate 12, the horizontal extension o f the latter being contiguous with and aliirred to .support ring 2 by bolts 13. The downstrearn wall .of .the trough terminating each tray section is atlirred by bolts ld to plate 1,5, which extends vertically below the horizontallevel o f said trough to ja point suillcient .to eiiect adequate vapor seal-` This may be accornplished by extending plate .1.5 downwardly to a point sufficiently above plate f1.2.- of the next lower tray so that liquid can easily lilow ythererulder but .sutliciently below the top .of vertical plate .19 oi said lower tray to provide a vapor seal.-

the liquid ow is very large, plate 10 is'desirably vertically extended to provide an adequate vapor seal: Alternately, a weir .19 ,may be vertically extended to provide .the vapor seal.. Access between trays for maintenance or repaircan be obtained by sirnply r'emoving a-tcw .tray sections, For such purpose, it is desirable to facilitate vertical entry through the tray secby Providing alternate trays with a removable L- sllaped section 116 which is fastened by bolt 17 or other suitable means to plate .1.15, Access into the tray .section when .desired can .be-gained byeiiecting removal .of section .lo and the rernaining .downstrear.Il troughs .making up the tray. An appropriate number of lthe upstream troughs ofthe next lower tray-can then easily be .renuoued and .likewise .alternate groups of .downstream and upstream troughs of succeeding levels of trays may be rfe.- moved until .the desired point of entry .is attaineddotvnconiers arelstaggercd on alternate trays in such manner as to cause a bach-andfforth travel .of liquid ingo horizontal direction lacross each successive .tray in addition to the vertical flow from tray to tray. The hori-v zontal flow of liquid across each tray isy caused by vapor impact compensating for the hydraulic gradient between the point Where liquid enters the tray and the point where 5 it leaves the tray.

Thus, the vapors being contacted issue in the same direction as liquid flow across the tray and the impinging action of the vapors serves to rnove the liquid across each tray and thereby compensates for the hydraulic gradient. The design is such2 however, that the liquid is not too rapidly accelerated across the tray with undesirable reduction in contacting eilciency.l The Vertical plate 10 of each tray is aflixed through plate 12 to suport ring 2 in such manner that it is substantially perpendicular to the flow of liquid proceeding across each tray after the same has entered the tray through downcomer 3. Likewise, since the vertical walls of each of the L-shaped sections are parallel to the vertical plate 1ll,thes.e .inembers are also located perpendicularly to the horizontal dow of liquid across the tray The result ci this perpendicular arrangerncnt ot troughs and overhanging. L-shaped sections to the line ci liouid liow .is a rippling. effect as the linuid travels across each. .tray and passes downwardly through the tank.- The combination ofthe rippling eiicct. of the liquid .and .the bubbling action ofthe vapors passing therethrough thus affords an intimate degree of contact between vapor and liquid and so compensates. tor .the hydraulic gradient required .to .etiect horizontal liquid .how that a high degree ofV contacting efficiency is attained Referring to the plan view oi the .iractionating ,tray shown in Figure l; it will be seen that the troughs d and overhanging hsshaped sections rnade up

ot legs

7 and 8 extend transversely i across .tanls l and are suitably stitieued by one or ruote webs .21,.- These plateflilsc .tal strips entend across the trough section of the tray .1n a right .angle direction to .the troughs and serve to stiiien. the vertical walls oi the trough section against deliect'on, particularly in the central portion of the tray. Any clesired number of stiiicning webs may be employed they are, however, generally positioned on approximately l2 to SKO-.inch centers. 'lhe'webs are slotted so that .the serrated edge of overhanging vertical .leg .8 interiits into the slot provided .and thereby serves to irnpart structural strength to the .fractionating tray- The slot .in web .21 is shown particularly in Figure 4 and is denoted as .29 While the aforementioned .stilienlng webs are not generally .necessary in trays .of srnall diameter, they .have been found to greatly Iimprove the overall structural strength of the trays and their use .is ther-etere preferred.

The. area encompassed by the overhanging hnliaped sections .and the vertical trough walls .to which .said .sections are attached .is iitted with end closure plates 2.2, as particularly shown in figure 4 theends oi the troughs in such .enibodirnent rernaiuing .opeu- .

End closure plates

2,2. .are perpendicularly attire-d by welding or other suitable nieans to th aped .sections and the vertical trough walls to which .sections .are attached to pro vide a satisfactory end closure oi such arce- These end plates .are slotted .and their lowerrnost edges are .flush with support ring .2- The srnall clearance between the shell of tank 1 and the end closure plates may, if desired.. be filled with packing, although the use of packing is not considered essential and is not generally practiced cornrnerciallytroughs and .overhangiug l--shaped the v-ays nia-y he titted with lend Aelo sure plate. -..n.applicatiou Serial No, .32.6 4.311, issued as 1li-. S- .Nfl/4,504 on .August .2, ,19.5.5,orendclosure rnay be eliected by a plurality .of angular plates as described in .detail in Patent No., 2,629,929- Such ineans of end closure .is shown .Figure :5- Referring .te this figure, end closure .o f the area encompassed by the loverhanging .l--shapcd sections aud the vet-.tical trough walls to which .said .sections `are attached `is eiiected .by plates 30 and 3.1.- These plates are angular in torni outrwa-l-l thereof serving to effect end closure of a designated portion of the aforesaid area and the other wall thereof being contiguous with and affixed to the upstream wall of the adjacent downstream trough. The angle between walls comprising said plates may be substantially a right angle or may, depending upon the contour of the members making up the tray of which it is desired to effect end closure, vary from a right angle by as much as 45.

Plates

30 and 31 are attached by spot welding or by suitable fastening means, such as bolts 32 and nuts 33, to the adjacent upstream trough wall with which these plates are contiguous. The walls of the plates which are contiguous with the adjacent upstream trough wall, as well as said wall, are pierced by openings through which said bolts pass and are allixed, serving to impart structural strength to the arranged members. Plate 31, which serves to effect closure of the space between overhanging leg 8 of the L-shaped section and the upstream wall of the adjacent and interlocking downstream trough, is preferably provided with a tab 34 which is substantially perpendicular to the end closure wall of these plates and contiguous with leg 7 of the aforesaid overhanging L- shaped section. Tabs 34 are aliixed to legs 7 by suitable means, for example, bolts 35 and nuts 36. It is to be realized that end closure plates 31 will function without top tabs 34. Generally, however, it is desirable to employ tabs on end closure plates 31 since the same further serve to impart structural strength to the overall arrangement of interlocking troughs.

The invention as setV forth hereinabove is particularly directed to activation of the inlet vapor sections of the trays to eliminate back-flow of liquid therethrough. Backflow has been found tobe the result of insuicient gasification of the liquid phase in the initial trough with the result that density of the liquid therein is greater than that contained in subsequent trough and gases are' thus prevented from ilowing through the serrations or slots entering this section. It accordingly becomes necessary to gasify liquid in the initial trough sufficiently so that the density thereof will be no greater than the density of liquid in subsequent downstream troughs and therefore the tendency toward back-flowing will be eliminated.-

Such is accomplished in accordance with the present invention by providing means for effecting the drawing of liquid away from the vertical leg of the initial upstream L-shaped section above the serrations therein to an extent suflcient to prevent submergence of said serrations by liquid owing `over the horizontal leg of the initial upstream L-shaped section, down the vertical leg thereof and into the adjacent trough. Referring to Figures 1--6 of the drawing, activation of the inlet vapor section is brought about by axing to the horizontal leg 7 of the initial upstream L-shaped section overhanging the adjacenttrough of each tray a weir 19. This weir may be affixed by suitable means such as by welding, bolting, or the like. Weir 19 should suitably be of such height that liquid, instead of flowing over the horizontal leg of the initial upstream L-shaped section and down the vertical leg of such section above the serrations therein is forced to ow over the weir edge under conditions such that a vapor space exists between the downstream faceof the weir and the stream of liquid flowing thereover as is usually observed with sharp edged weirs. The upper part of the serrations thus becomes free to act and once the action is initiated, the typical turbulence is set up land the entire vapor section and trough become activated.

An isometric view of the fractionating tray of the type described herein is illustrated by Figure A3. The vertical Vleg 8 of the overhanging section is serrated with the serrations 20 pointing downward and extending into the adjacent downstream trough to provide an eiective bubbling means for passing vapor through liquid flowing perpendicularly across the trough. It will further be vnoted that slotted stilfening webs 21 interlit into and engage the serrated edges of the overhanging sections. ,-During operation, vapors from the tray below pass up through passage 9 between two adjacent troughs over the upstream edge of the downstream trough and then through the serrated edge of leg 8 where vapor bubbles are released into the liquid on this trough. Downflowing liquid enters the tray through downcomer 3 and flows over the roof of the iletvapor section, coming in contact with Weir 19 and flowing over said Weir into the adjoining trough and thereafter proceeding across the tray section. l The arrangement of end closure plate 22 and weir 19 is shown in detail by the isometric view of Figure 6. The characteristic of the weir 19, even at very low liquid ow, is that a vapor space exists between the downstream face of the weir and the stream of liquid flowing thereover. The upper portion of the serrated edges of leg 8 is accordingly free to act and once the action is initiated the typical turbulence is set up and the entire vapor section and trough become activated. The plate, as shown in the arrangement of Figure 4 for one of the troughs, is provided with a slot 23 which extends vertically from the lower edge of the end plate ata point corresponding to the juncture of the upstream wall of the adjacent downstream trough and the end closure plate. Such slot interits over the vertical edge of the adjacent downstream trough.

An alternate provision of means for activating the inlet vapor section of the tray is shown in Figure 7. Referring more particularly to this figure, it will be seen that the roof of the inlet vapor section, i.e., horizontal leg 7, is provided with a row of perforations or openings' 24. Over these openings is positioned a dellecting bar 25. This embodiment results in a small s-tream of vapor or vapor bubbles flowing along the roof of the inlet vapor section downstream of the point of introduction with the result that at a number of localized points` theliquid is pulled away from the vertical face of the vapor section, i.e. vertical leg 8, above the serrated edge thereof and bubbling is initiated. vOncethe bubbling is initiated, typical turbulent action starts and the density of liquid in the trough is reduced with the result that back-flow is minimized or entirely eliminated even though the top of the riser, i.e., the upstream edge of the adjacent downstream trough, does not extend ashigh as the root of the serrations in vertical leg 8.

In Figure 8, another alternate means for activating the inlet vapor section is shown. In this modification the roof of the inlet vapor section, i.e., horizontal leg V7, is provided with a horizontal extension 26 jutting a small distance beyond the vertical leg 8, overlying and being substantially horizontal to the bottomof .the adjacent trough.

In Figure 9 is shown still another alternate means for activating the inlet vapor section. In this modification, the desired activation is brought about by means of a plurality of elongated openings 27 extending from the roots of the serrations in leg 8 vertically upward to the roof of the inlet vapor section. In thisfembodimengit is contemplated that the desired activation may be attained with elongated openings on every other or perhaps even -on every third one of .the'slots. Utilizing this modification, activation is initiated because of vapor issuance from the top of the elongated openings. This vapor issuance breaks up the action of the liquid tending to cling to the face of vertical leg 8 and allows bubbling action by the main part of the serrated edge thereof to proceed with consequent reduct-ion in. liquid density in the initial trough. v

-In Figure 10 is shown still another kalternate means for bringing about the desired activation of the inlet vapor section. In this embodiment, a 4plurality of openings 28 are provided in the vertical serrated leg 8 of the inlet vapor section at a point abovethe level of the roots of the slots or serrations. Activation utilizing this embodiment would take place in a manner similar to that achieved. with the embodiment shown inlFigure/ 9. -That it estinti@ is. sitetsdbtsaaw @i vapor issuance from the openings 28. This vaporis'suance breaks up the action ofthe liquid `tending to cling te the face of yvertical leg s angl aiiows bubbling action by the main part of the serrated edge thereof'I to proceed with yconsequent reduction in liquid density in the initial trough The lwidth of the troughs# is directly related to the Slot area, Le., the area f all of the s'lots in a given tray. Preferred design empioys slot area equal to abut 8 te about 1 5 percent of 'the total towerl cross section. However, the width of 'the troughs making up the instant trays may be so established as to obtain `sxl ot areas ranging fiom about to about 2() percent of the total tower cross section. An advantage "of the present tray construetion is the highpercentagof riserV area attained, i.e., the cross sectional area between the troughs 4 through which the yapors pass upwardly. Existing bubb le cap trays achieve risei areas"v ranging from 6" to l5 percent, whereas the instantly/'described tr'ay may achieve a riser area of n25 to 304 percent. Moreover, the tray construction of the invention has a comparatively high reversal area and vapor downilow area corresponding'to the annular area'in eiiisting bubble ap tray design. These large areas which the `trays of this invention thus afford result in low pressure drop of vapor ow through the tray, which is particularly advantageous in vacuum fractionation. Under conditions of eiitremely low pressure drop, back-flow of liqnid in the inlet vapor section of the`tray is prevented in aecordance with the present invention by `reduction of the density oi liquid in the initial upstream trough section byinduced gasification thereof. Such gasification may `be accompiished by the Yprovision of means for the drawing ef liquid YawayV from` the vertical face of the yapor `section above the 'slots suic'iently so that these slots do not become submerged by the liquid ilowing over the roof of the vapor section down the face of this section above the 'slots' and into the trough. It is contemplated that any suitable means for effecting activation of the inlet vapor section may be employed. Of the various means show-n inthe attached figures, the embodiment illustrated in Figure 6 is preferred. I t will, however, be realized that any of the other various modifications shown may likewisev be elfective in attaining the desired activation. It is also contemplated that a combination of two or moreof the illust-rated means for effecting the desired activation may be employed. Thus, for example, the'means illustrated in Figures 6 and l7 may be employed. Likewise, the activating means shown in Figures 6 and 9 may be employed in combination as well as the means shown in Figures 6 and l0.' It will thus be apparent that the present invention contemplates any suitable means for effecting activation of the inlet vapor section of the tray by reducing the density of liquid contained therein, whereby back-How of liquid therethrough is prevented, resultingin van increased efficiency.

While there has been described various prefer-red embodiments of the present invention, it will be understood that the invention is not limited .in scope to the specific details of construction illustrated and described but that the same issubject to ,considerable .variation without departing from the lunderlying features of the invention as expressed Ain the claims set forth below. i

I claim: l i

l. In a lightweight .tray for use kin a fractionating tower comprising a plurality of'troughs spacedatluniform intervals transversely across Athe tower and arranged in coplanar relationship one with the other, a plurality of lL-shaped sections having the horizontal legs' thereof attached to one edge of each yof the aforementioned troughs,

the yertical legs of suc-h gsections being serrated and pointing ,downward and overhanging into adjacent troughs,

thereby affording passages for the flow of vapor therethrough, a plnra'lity of end closure plates aiiixed to either end of the troughs v and .overhangingsections",` each of said plates being nslotted and the .slots therein engaging the vertiealwail of the next adjoining trough, a plurality of stiffening webs extending across l"the troughs in a right angle direction thereto, 'said stiffening webs being slotted and the slots therein engaging the serrated edges of said overhanging vertical legs, the' improvement wherein the horizontal leg of the initial upstream L-shaped section is provided with a Weir, protruding from the upper surface of said horizontal leg,whereby liquid after passage over said Weir is subjected to gasification with yaccompanying reduction in density thereof and is drawn away from the vertical leg of said initial upstream L-shaped section above the serrations therein to an extent sufficient to prevent submergence of said serrations by ow of said liquid into the adjacent downstream trough.

2. In a iightweight tray for use in a fractionating tower comprising a plurality of troughs spaced at uniform intert/als tra'nvesely aeross the tower" and arranged in copianar reiationship one vwith the other, a plurality of L-shaped sectionsV having the horizontal legs thereof attached to one edge of each of the' aforementioned troughs, the vertical legs'of said sections being serrated and pointing downward and overhanging into adjacent troughs, thereby providing passages for the flow of vapor therethrough, a plurality of angular plates, the walls of which respectively effect end yclosure of space between downstream trough walls and adjacent upstream trough walls and afford support to upstream walls by being contiguous `therewithwandaffixed thereto and a second plurality of angular plates, the walls of which respectively effect end closure of space between upstream trough'walls and adjacent ver-tical legs of said overhanging sections and afford support to said upstream walls yby being contiguous therewith and affixed thereto, the improvement wherein the horizontal leg of the initial upstream L-shaped section is provided with a vveir,l protruding v.from `the upper surface of said horizontal leg,'whereby liquid after passage over said Weir s subjected to gasification with accompanying reduction in density thereof and is drawn away from the vertical leg of said initial upstream L-shaped section above the serrations therein to an extent suflicient to prevent submergence of said serrations by ow of said liquid into the adjacent downstream trough. Y

3. vIn afractionating tower comprising an elongated tank, a plurality of support rings afxed at various elevations to the inner periphery of. said tank, a plurality of troughs arranged iii co-planar relationship upon said support rings and extending transversely across the tank, a plurality of end closure plates, one of which is aihxed to either ,end of said troughs, said end plates being slotted and-the slots therein engaging the vertical walls of adjacent troughs vto rigidly hold said troughs in interlocking arrangement on said support rings perpendicular to the line of liquid flow acrosssaid tank, a plurality of L-shaped sections having the horizontal legs-thereof attached to one .edge of each of said troughs, the vertical legs of said sections* pointing downward, being serrated and overhanging lint-o adjacent troughs to thereby afford passages 'for upward vapor -ow thrtmgh said tank, 'the improvement which comprises providing the horizontal leg of the initial upstream L-shaped section with a weir, protruding from-the lupper surface of said horizontal leg, whereby liquid after passage over said Weir is subjected to gasification with accompanying reduction in 'density thereof and-is drawn away from the 4vertical leg of said initial upstream `L-shaped sectionV above the serrations ytherein to an extent sufficient to prevent submergence of said serra-tions by 4flow of said liquid into the adjacent downstream trough. i

4. In a lightweight tray for .use in a Yf-ractionating tower -comprising' a plurality of .troughs spaced at .uniform .intervals transversely across the tower and arranged in co- `planar relationship one with the other, a plurality of L-shaped sections having .the horizontal `legs thereof attached to one edge vof each ofthe aforementioned troughs, the vertical legs of said sections `being serrated and Ipoint,-

ing downward and overhanging into adjacent troughs, thereby affording passages for the ow of vapor therethrough, a plurality of end closure plates atlixed to either end of the overhanging sections and the vertical trough walls to which said sections are attached, each of said plates being slotted and the slots therein engaging the vertical wall of the next adjoining trough, the improvement wherein the horizontal leg of the initial upstream L-shaped section is provided with a weir, extending vertically from said horizontal leg and contiguousv with the vertical leg of said initial upstream L-shaped section, whereby liquid passing over said weir is subjected to gasification with accompanying reduction in density thereof and is drawn away from the vertical leg of said initial upstream L-shaped section above the serrations therein to an extent such that a vapor space exists between the downstream face of the weir and the stream of liquid flowing thereover and suicient to prevent submergence of said serrations by ow of said liquid into the adjacent downstream trough.

5. In a lightweight tray for use in a fractionating tower comprising a plurality of troughs spaced at uniform intervals transversely across the tower and arranged in coplanar relationship one with the other, a plurality of L-shaped sections having the horizontal legs thereof attached to one edge of each of the aforementioned troughs, the vertical legs of said sections being serrated and pointing downward and overhanging into adjacent troughs, thereby affording passages for the ow of vapor therethrough, a plurality of end closure plates afixed to either end of the overhanging sections and the vertical trough walls to which said sections are attached, each of said plates being slotted and the slots therein engaging the vertical wall of the next adjoining trough, the improvement wherein the initial upstream L-shaped section is provided with an extension jutting from the horizontal leg thereof overlying and substantially horizontal to the adjacent trough, whereby liquid after passage over said extension is subjected to gasification with accompanying reduction in density thereof and is drawn away from the vertical leg of said initial upstream L-shaped section above the serrations therein to an extent suicient to prevent submergence of said serrations by flow of said liquid into the adjacent downstream trough.

6. In a light weight tray for use in a fractionating tower comprising a plurality of troughs spaced at uniform intervals transversely across the tower and arranged in co-planar relationship one with the other, a plurality of L-shaped sections having the horizontal legs thereof attached to one edge of each of the aforementioned troughs, the vertical legs of said sections being serrated and pointing downward and overhanging into adjacent troughs, thereby affording passages for the flow of vapor therethrough, and a plurality of elements alixed to either end of the overhanging sections and the vertical trough walls to which said sections are attached adapted to interlock adjacent troughs with attached sections one into the other, the improvement wherein the horizontal leg of the initial upstream L-shaped section is provided with a weir, protruding from the upper surface of said horizontal leg, whereby liquid after passage over said weir is subjected to gasification with accompanying reduction in density thereof and is drawn away from the vertical leg of said initial upstream L-shaped section above the serrations therein to an extent sutcient to prevent submergence of said serrations by llow of said liquid into the adjacent downstream trough.

7. In a light Weight tray for use in a fractionating tower comprising a plurality of troughs spaced at uniform intervals transversely across the tower and arranged in co-planar relationship one with the other, a plurality of L-shaped sections having the horizontal legs thereof attached to one edge of cach of the aforementioned troughs, the vertical legs of said sections being serrated and pointing downward and overhanging into adjacent troughs, thereby affording passages for the ow of vapor therethrough, and a plurality of elements aixed to either end of the overhanging sections and the vertical trough walls to which said sections are attached adapted to interlock adjacent troughs with attached sections one into the other, the improvement wherein the horizontal leg of the initial upstream L-shaped section is provided with a weir, extending vertically from said horizontal leg and contiguous with the vertical leg of said initial upstream L-shaped section, whereby liquid passing over said Weir is subjected to gasification with accompanying reduction in density thereof and is drawn away from the vertical leg of said initial upstream L-shaped section above the serrations therein to an extent such that a vapor space exists Vbetween the downstream face of the Weir and the stream of liquid flowing thereover and suflicient to prevent submergence of said serrations by flow of said liquid into the adjacent downstream trough.

8. In a light weight tray for use in a fractionating tower comprising a plurality of troughs spaced at uniform intervals transversely across the tower and arranged in co-planar relationship one with the other, a plurality of L-shaped sections having the horizontal legs thereof attached to one edge of each of the aforementioned troughs, the vertical legs of said sections being serrated and pointing downward and overhanging into adjacent troughs, thereby affording passages for the ilow of vapor therethrough, and a plurality of elements aixed to either end of the overhanging sections and the vertical trough walls to which said sections are attached adapted to interlock adjacent troughs with attached sections one into the other, the improvement wherein the initial upstream L-shaped sections is provided with an extension jutting from the horizontal leg thereof overlying and substantially horizontal to the adjacent trough, whereby liquid after passage over said extension is subjected to gasification with accompanying reduction in density thereof and is drawn away from the vertical leg of said initial upstream L-shaped section above the serrations therein to an extent suicient to prevent submergence of said serrations by llow of said liquidv into the adjacent downstream trough.

References Cited in the ile of this patent UNITED STATES PATENTS 829,700 Drees Aug. 28, 1906 2,428,889 ANutter Oct. 14, 1947 2,693,949 Huggins Nov. 9, 1954 2,702,696 Pappas et al. Feb. 22, 1955 2,714,504 Bowles Aug. 2, 1955 2,752,139 -Huggins June 26, 1956 2,775,915 Huggins Aug. 7, 1956 FOREIGN PATENTS 6,000 Great Britain Mar. 28, 1892 1,048,712 France Aug. 5, 1953 1,071,403 France Mar. 3, 1954