Cross flow tray and support system for use in a mass transfer column

Cross flow trays are provided with a support system. The support system interconnects the upper cross flow tray to a downcomer of the lower cross flow tray to provide support for the upper tray. In some aspects, the support system may also interconnect the downcomer of the lower cross flow tray to an upper tray of an underlying pair, providing additional support for the assembly. Such tray assemblies may facilitate easier installation without impeding the performance of the column.

BACKGROUND OF THE INVENTION

The present invention relates generally to cross flow trays used in mass transfer columns in which mass transfer and/or heat exchange processes occur and, more particularly, to apparatus and methods for supporting such cross flow trays.

Cross flow trays are used within mass transfer columns to facilitate interaction between fluid streams flowing in countercurrent relationship within the column. The term mass transfer column as used herein is not intended to be limited to columns in which mass transfer is the primary objective of the processing of the fluid streams within the column, but is also intended to encompass columns in which heat transfer rather than mass transfer is the primary objective of the processing. The fluid streams are typically an ascending vapor stream and a descending liquid stream, in which case the cross flow trays are commonly referred to as vapor-liquid cross flow trays. In some applications, both fluid streams are liquid streams and the cross flow trays are commonly referred to as liquid-liquid cross flow trays. In still other applications, the ascending fluid stream is a gas stream and the descending fluid steam is a liquid stream, in which case the cross flow trays are referred to as gas-liquid cross flow trays.

The cross flow trays are positioned within the column in vertically spaced-apart relationship with each of the tray decks extending horizontally to fill the entire internal cross-section of the column. Each of the cross flow trays has a planar tray deck on and above which interaction between the ascending fluid stream and the descending fluid stream occurs, a plurality of apertures to allow upward passage of the ascending fluid stream through the tray deck and into the descending fluid stream to create a froth or mixture in which the desired mass transfer and/or heat exchange occurs, and at least one downcomer that directs the descending fluid stream from the associated tray deck to a tray deck on an underlying cross flow tray. The portion of the tray deck that receives the descending fluid stream from the downcomer of an overlying cross flow tray typically comprises an inlet panel that is either imperforate or contains bubble promoters or other structures that allow upward passage of the ascending fluid stream but impede the descending fluid stream from weeping through the inlet panel.

Cross flow trays having a single side downcomer located at one end of the tray deck are known as single-pass trays. In other applications, typically those involving higher descending liquid flow rates, multiple downcomers may be used on some or all of the cross flow trays. For example, in two-pass configurations, two side downcomers are positioned at opposite ends of one cross flow tray and a single center downcomer is positioned in the center of the adjacent cross flow trays. In four-pass configurations, one cross flow tray has two side downcomers and a center downcomer and the adjacent contact trays have two off-center downcomers.

The tray decks of cross flow trays are typically secured by clamps to support rings welded to the interior surface of the column shell. The downcomer walls are also normally bolted at their opposite ends to bolting bars that are welded to the interior surface of the column shell. In some applications, such as in larger diameter columns and in columns in which vibratory forces are a concern, it is known to add further support to portions of the tray deck by using a strut that extends upwardly from major beams, lattice trusses or a system of hangers to connect the tray deck of a cross-flow tray to the downcomer walls of a similar tray located directly above, or below. When hangers are utilized, the downcomer walls act as beams to carry a portion of the load of the coupled tray, thereby reducing sagging and bracing against uplift of the tray deck. These hangers and other structures, however, add complexity to the design and increase the cost of fabrication and installation of the cross flow tray.

In other applications, the inlet panel on the tray deck is formed as a structural beam to provide added support to the tray deck. The inlet panel must then be interconnected to the adjacent portions of the tray deck using fasteners of various types, thereby adding to the complexity in the design and the installation of the tray deck. A need has thus arisen for a method of supporting and bracing the tray deck while reducing the disadvantages resulting from the conventional methods of providing additional support in larger diameter columns and in columns in which vibratory forces are present.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to a tray assembly for use in a mass transfer column. The tray assembly comprises a first upper cross flow tray comprising a first generally planar upper tray deck and at least one downcomer for removing liquid from the first upper deck and a first lower cross flow tray vertically spaced from the first upper tray. The first lower tray comprises a first generally planar lower tray deck and an inlet area positioned proximate the downcomer of the first upper tray for receiving liquid from the first upper tray. The first lower tray further comprises at least one centrally located downcomer positioned at or near the center of the lower deck for removing liquid therefrom and the centrally located downcomer comprises a pair of spaced-apart parallel walls extending in a direction generally perpendicular to the direction of liquid flow across the first lower deck. The tray assembly also comprise a support system at least partially disposed between the first upper and lower trays. The support system comprises a plurality of horizontally-spaced braces coupled to and extending between the walls of the centrally located downcomer, a support beam coupled to a lower surface of the upper deck, and a plurality of elongated strut members coupled to and extending between the support beam and each of the braces.

In another aspect, the invention is directed to a mass transfer column comprising an outer column shell defining an open internal volume and at least one cross-flow tray assembly as described above positioned in the open internal volume of the shell.

DETAILED DESCRIPTION

Turning now to the drawings in greater detail and initially toFIG. 1, a mass transfer column suitable for use in processes in which mass transfer and/or heat exchange is intended to occur between countercurrent-flowing fluid streams is represented generally by the numeral10. Mass transfer column10includes an upright, external shell12that is generally cylindrical in configuration, although other orientations, such as horizontal, and configurations, including polygonal, are possible and are within the scope of the present invention. Shell12is of any suitable diameter and height and is constructed from one or more rigid materials that are desirably inert to, or are otherwise compatible with the fluids and conditions present during operation of the mass transfer column10.

Mass transfer column10is of a type used for processing fluid streams, typically liquid and vapor streams, to obtain fractionation products and/or to otherwise cause mass transfer and/or heat exchange between the fluid streams. For example, mass transfer column10can be one in which crude atmospheric, lube vacuum, crude vacuum, fluid or thermal cracking fractionating, coker or visbreaker fractionating, coke scrubbing, reactor off-gas scrubbing, gas quenching, edible oil deodorization, pollution control scrubbing, and other processes occur.

The shell12of the mass transfer column10defines an open internal region14in which the desired mass transfer and/or heat exchange between the fluid streams occurs. Normally, the fluid streams comprise one or more ascending vapor streams and one or more descending liquid streams. Alternatively, the fluid streams may comprise both ascending and descending liquid streams or an ascending gas stream and a descending liquid stream.

The fluid streams are directed to the mass transfer column10through any number of feed lines16positioned at appropriate locations along the height of the mass transfer column10. One or more vapor streams can also be generated within the mass transfer column10rather than being introduced into the mass transfer column10through the feed lines16. The mass transfer column10will also typically include an overhead line18for removing a vapor product or byproduct and a bottom stream takeoff line20for removing a liquid product or byproduct from the mass transfer column10. Other column components that are typically present, such as reflux stream lines, reboilers, condensers, vapor horns, and the like, are not illustrated in the drawings because they are conventional in nature and an illustration of these components is not believed to be necessary for an understanding of the present invention.

Turning additionally toFIGS. 2 and 3, any desired number of pairs of an upper cross flow tray22and a lower cross flow tray24constructed according to the present invention are positioned within the open internal region14of the mass transfer column10in vertically-spaced apart relationship with respect to each other. Each of the upper cross flow trays22comprises a generally planar tray deck26and two side downcomers28and30that are positioned at opposite ends of the tray deck26. The tray deck26is formed from individual panels32that are joined together using any of various conventional methods. The panels32extend longitudinally in the direction from one end to the other end of the tray deck26. In one embodiment, most or all of the panels32extend continuously between the ends of the tray deck26. In another embodiment, most or all of the panels32extend from the ends of the tray deck26to the centerline of the tray deck26where they are joined together in a conventional fashion. Some or all of panels32include stiffening flanges34that extend perpendicularly downward from the panels32, typically along one of the longitudinal edges of each of the panels32.

Most of the tray deck26includes apertures36to allow an ascending vapor, gas or liquid stream to pass through the tray deck26for interaction with a liquid stream traveling along an upper surface of the tray deck26. The apertures36can be in the form of simple sieve holes or directional louvers or they may include structures such as fixed or movable valves. The portion of the tray deck26containing the apertures36is known as the active area of the cross flow tray24. A center portion of the tray deck26is imperforate and functions as an inlet region38for receiving liquid flowing downwardly from an overlying liquid distributor (not shown) or a center downcomer40of an overlying one of the lower cross flow trays24. The inlet region38may include bubble promoters or other structures to allow the ascending fluid stream to pass upwardly through the center portion of the tray deck26.

The lower cross flow tray24likewise comprises a tray deck42formed from interconnected individual deck panels44and containing apertures36of the type described above. The deck panels44contain downwardly extending stiffening flanges46along their longitudinal edges. Both end portions of the tray deck26of the lower cross flow tray24are normally imperforate and function as inlet regions48and50to receive the liquid flowing downwardly through the side downcomers28and30from the upper cross flow tray22. The inlet regions48and50may include bubble promoters or other structures to allow the ascending fluid stream to pass upwardly through the end portions of the tray deck42.

The lower cross flow tray24includes the center downcomer40that receives the liquid flowing towards the center of the tray deck42from the end portions and delivers it to the inlet panel38of the upper cross flow tray22in the next underlying pair of upper and lower cross flow trays22and24.

The center downcomer40in each cross flow tray24comprises a pair of spaced apart, parallel walls52that extend in a chordal fashion across the open internal region14within the mass transfer column10. Each wall52comprises an upper wall segment54and a lower wall segment56that may be vertically adjusted in relation to each other during installation of the upper and lower cross flow trays22and24. Opposite ends of each wall52are bolted to bolting bars (not shown) that are welded to the internal surface of the shell12.

A plurality of horizontally-spaced-apart upper braces58extend perpendicularly between and are bolted to the upper wall segments54of the center downcomer40to stiffen and maintain the desired spacing between the walls52of the center downcomer40. A plurality of similar, horizontally-spaced-apart, lower braces60extend perpendicularly between and are bolted to the lower wall segments56. The lower braces60also serve to stiffen and maintain the desired spacing between the walls52. The lower braces60extend below a lower edge of the lower wall segments56and rest on and are bolted to the tray deck26of an underlying upper cross flow tray22. In this manner, the lower braces60interconnect the walls52of the center downcomer40to the tray deck26of the underlying upper cross flow tray22to provide support to the center downcomer40and to maintain the desired vertical clearance57between the lower edge of the lower wall segments56and the tray deck26of the underlying upper cross flow tray22.

Turning additionally toFIGS. 4-6, in accordance with the present invention, a support system62is provided to interconnect and support the center portion of the tray deck26of one or more of the upper cross flow trays22with the center downcomer40of the paired lower cross flow tray24. The support system62comprises the upper braces58, elongated struts64that are bolted or otherwise secured to the upper braces58and extend upwardly therefrom, and a horizontally-extending beam66that is bolted or otherwise secured to an upper end of each of the struts64. The struts64are formed from angled metal stock or other suitable materials having the necessary strength, rigidity, and compatibility with the conditions within the mass transfer column10. The number of struts64and the horizontal spacing between adjacent struts64can be varied and are selected based on the loads and vibratory forces expected in the intended application.

The beam66is likewise formed from metal or other suitable materials and, in one embodiment, comprises a vertical segment68, an upper flange70that extends perpendicularly from an upper edge of the vertical segment68in one direction, and a lower flange72that extends perpendicularly from a lower edge of the vertical segment68in an opposite direction. Cutouts74(FIG. 6) are provided at spaced apart locations in the upper flange70and in part of the vertical segment68to accommodate the stiffening flanges34of the individual panels32in the tray deck26of the upper cross flow tray22. Alternatively, the cutouts74may be omitted by removing the stiffening flanges34in the portions of the tray deck26that overlap the beam66. The panels32of the tray deck26rest on the beam66and are bolted or otherwise secured the upper flange70of the beam66. Shims may be placed between the lower end of one or more of the struts64and a flange on the upper brace58to which the strut64is mounted to level the tray deck26during installation.

Anti-jump baffles76extend between and are bolted or otherwise mounted to the struts64. The anti-jump baffles76function to impede liquid and dense froth from jumping over rather than entering the center downcomer40. The anti-jump baffles76are positioned so that their lower edges are roughly at the same horizontal elevation as an upper edge of weirs78positioned on the tray deck42at the inlet to the center downcomer40. The anti-jump baffles76have a height sufficient to block the liquid and dense froth from jumping over the center downcomer40, while at the same time allowing an upper edge of each anti-jump baffle76to be spaced a sufficient distance below the overlying upper cross flow tray22to permit vapor to readily flow above the anti-jump baffles76.

Each anti-jump baffle76comprises a vertically-extending plate80, a strengthening flange82at an upper and/or lower edge of the plate80, and, as best shown inFIG. 5, a dog-legged mounting flange84positioned along each of the side edges of the plate80. The mounting flanges84overlap and are bolted or otherwise secured to the struts64. The dog-legged construction of the mounting flanges84allow the plates80and the struts64to be positioned along the longitudinal centerline of the center downcomer40. Alternatively, the struts64can be offset slightly from the centerline so that the plates80can be positioned along the centerline without requiring the mounting flanges84to have a dog-legged construction.

It can be seen that the support system62interconnects the upper and lower cross flow trays22and24and functions to support the center portion of the upper cross flow tray22using the center downcomer40of the lower cross flow tray24. The support system62eliminates the need for the tray deck26of the upper cross flow tray26to have a separate inlet panel that functions as a support beam and must be interconnected with the panels32. Using the support system62to provide support at the center of the tray deck26allows some or all of the panels32to span from end to end of the tray deck26as a single piece, thereby greatly simplifying the design and installation of the tray deck26. Alternatively, some or all of the panels32may extend from the end to the center of the tray deck26where they may abut or overlap panels32extending to the center from the other end of the tray26. The abutting or overlapping panels32may then be bolted or otherwise secured to the beam66that underlies the panels32.

The upper and lower cross flow trays22and24that are interconnected by the support system62are also interconnected to the underlying pair of upper and lower cross flow trays22and24by the lower braces60that join the center downcomer40to the tray deck26and/or the beam66of the support system62associated with the underlying pair of upper and lower cross flow trays22and24. By interconnecting and supporting the upper and lower cross flow trays22and24in this manner, the upper and lower cross flow trays22and24are better able to resist the loading and vibratory forces exerted during operation of the column10. The tray decks26and42are thus more likely to remain level and stationary during such operation.

The support system62can be used or readily adapted for use with center downcomers of various constructions. For example, inFIGS. 8 and 9, the support system62is used with a lower cross flow tray124that has a center downcomer140with inclined downcomer walls152rather than the vertical downcomer walls52associated with the center downcomer40of the lower cross flow tray24illustrated inFIGS. 1-4 and 6-8. In all other respects, the lower cross flow tray124ofFIGS. 8 and 9may have the same construction as the previously described lower cross flow trays24and the same reference numerals preceded by the numeral “1” are used to reference the like components.

Turning now toFIGS. 10 and 11, upper and lower cross flow trays222and224and a support system262are shown and differ in the following respects from upper and lower cross flow trays22and24and support system62shown inFIGS. 1-4 and 6-8. All of the panels226except for the outer panels226of the upper cross flow tray222extend from the side downcomers228and230to the centerline of the tray deck226where they abut and are bolted to the beam266of the support system262. Because the panels226abut at the centerline, the stiffening flanges234can be removed in the area of the beam266so that the beam266does not need to include cutouts for the stiffening flanges234. The center downcomer240includes additional rectangular-framed braces286are of a sufficient height to be bolted to both the upper and lower wall segments254and256of the downcomer walls252. These additional braces286are spaced apart at predetermined intervals from each other and from the upper braces258and260. In all other respects, the upper and lower cross flow trays222and224and support system262are generally the same as the upper and lower cross flow trays22and24and support system62. For ease of reference, the same reference numerals preceded by the numeral “2” have been used inFIGS. 10 and 11to refer to like components shown inFIGS. 1-4 and 6-8.

Turning now toFIGS. 12 and 13, another embodiment of a center downcomer with which the support system62may be used is designated by the numeral340. Center downcomer340has inclined downcomer walls352that terminate at a floor plate388containing louvers390(FIG. 12) or simple apertures392(FIG. 13). The lower braces360, rather than extending between the downcomer walls352, underlie the floor plate388and support the downcomer walls352on the inlet region238of the tray deck226of the underlying lower cross flow tray224. In all other respects, the upper cross flow tray322may be of the same construction as the upper cross flow tray222. The same reference numerals preceded by the numeral “3” rather than “2” have been used to refer to like components shown inFIGS. 10 and 11.

Turning now toFIG. 14, adjacent pairs of upper and lower cross flow trays422and424are shown, along with corresponding first and second support systems462and562. The upper and lower trays422and424and the support systems462and562differ in the following respects from the upper and lower cross flow trays22and24and the support system62shown inFIGS. 1-4 and 6-8. The horizontally-extending beams466and566of the support systems462and562are also vertically elongated. The beam566of the support system562extends to the same vertical elevation as, or to a vertical elevation just below, the upper edges of the walls452of the central downcomer440of the lower tray424of the second pair of trays. As also shown inFIG. 14, the elongated beam566further includes a plurality of laterally-spaced cut-outs567, positioned at a desired interval along the length of the beam566. Although shown as being polygonal in cross-section, the cut-outs567may be of any size and/or shape, and the number and spacing of such cut-outs can be determined based on the specific application.

Additionally, the beams466and566each include a knife edge469located at or near the terminal edge of the support beam466or566for helping to control foam and/or heavy froth within each of the central downcomers440. Neither of the support systems462or562includes a set of lower braces60coupled to an underlying upper tray. Accordingly, in the embodiment shown inFIG. 14, the lower tray424of each pair is not physically coupled to the upper tray422of the underlying pair of trays. In all other respects, both sets of the upper and lower cross flow trays422and424and the support systems462and562shown inFIG. 14are generally the same as the upper and lower cross flow trays22and24and the support system62. For ease of reference, the same reference numerals preceded by the numeral “4” have been used inFIG. 14to refer to like components shown inFIGS. 1-4 and 6-8.

Turning now toFIG. 15, adjacent pairs of upper and lower cross flow trays622and624and first and second support systems662and762are shown and differ in the following respects from the adjacent pairs of upper and lower cross flow trays422and424and the support systems462and562as shown inFIG. 14. As shown inFIG. 15, the first support system652is at least partially disposed between the upper set of upper and lower cross flow trays622and624and includes one or more pairs of anchor tabs positioned along the direction of extension of the downcomer640. Each pair of anchor tabs includes an upper anchor tab651and a lower anchor tab653arranged in a staggered configuration with respect to each other and the direction of extension of the central downcomer640. The upper anchor tab651of each pair is coupled to a lower surface of the upper tray deck626, while the lower anchor tab653is coupled to the upper surface of the upper tray deck626of the underlying upper tray622of the adjacent pair.

A transverse support beam677extends generally diagonally between the upper651and lower653anchor tabs of each pair. Because of the staggered configuration of the anchor tabs651and653, the adjacent transverse beams677extend in generally opposite diagonal directions. The elongated strut members654of the support system652are also coupled to the upper anchor tabs653of each pair and are generally disposed between pairs of oppositely-extending transverse support beams677. The second support system762shown inFIG. 14is nearly the same as the support system62shown inFIGS. 2 and 3, except that the support system762does not include anti-jump baffles. In all other respects, the upper and the lower cross flow trays622and624, as well as the first and second support systems652and762, may be of the same construction as the similar components described with respect toFIGS. 1-4 and 6-8. The same reference numerals preceded by the numeral “6” have been used to refer to like components shown inFigs. 1-14.

While the invention has been described with respect to a support system that connects to a center downcomer of a lower cross flow tray, it is to be understood that the invention also may include using such a support system with an intermediate, rather than a center, downcomer in a multi-pass cross flow tray.

From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objectives hereinabove set forth together with other advantages that are inherent to the structure.