WO1999003553A1

WO1999003553A1 - Tray-to-tray transfer device for chemical process tower

Info

Publication number: WO1999003553A1
Application number: PCT/US1998/014594
Authority: WO
Inventors: Adam T. Lee; Kuang Wu; Larry Burton
Original assignee: Koch-Glitsch, Inc.
Priority date: 1997-07-18
Filing date: 1998-07-17
Publication date: 1999-01-28
Also published as: AU8404298A

Abstract

An assembly for transferring fluid between trays in a liquid-liquid chemical process or contact tower (12) is disclosed. The contact tower (12) contains a continuous phase (126) and a dispersed phase (128). The assembly includes first (102) and second trays (103), each having a plurality of apertures providing a flow path for the dispersed phase. The assembly further includes a tray-to-tray transfer device providing a flow path for the continuous (126) phase between the first (102) and second (103) trays. The transfer device includes an angled section (107) having a plurality of apertures (144) providing a flow path for the continuous phase near the inner surface of the angled section (107) to interact with the dispersed phase (128) near the outer section of the angled section. A contacting device for liquid-liquid contact tower is also disclosed. The contacting device includes a tray having an active area. The active area has an array of undimpled apertures and arrays of dimpled apertures on either side of the array of undimpled apertures.

Description

TRAY-TO-TRAY TRANSFER DEVICE FOR CHEMICAL PROCESS TOWER

Field of the Invention

The present invention pertains to chemical process towers and, more particularly, but not by way of limitation, to a tray-to-tray transfer device for maximizing efficiency in a liquid-liquid chemical process tower.

History of the Prior Art

Distillation columns are utilized to separate selected components from a multicomponent stream. Generally, such contact columns utilize either trays, packing, or combinations of each. In the liquid-liquid contact art, it is highly desirable to utilize methods and apparatus that efficiently improve the quantity of the mass and/or energy transfer occurring in the process tower. The technology of such process towers is replete with various tray, downcomer, and packing designs. The types of trays, downcomers, and packing employed are functions of the particular process to be effected within the tower. The design of downcomer-tray assemblies, or the shape of the random (dumped) or structured packing elements, determines the flow patterns in the tower, the density of the contact array, and the resultant resistance to flow caused thereby. Close fractionation and/or separation of the feed stock constituents introduced into the tower and the elimination of harmful or undesirable residual elements impart criticality to the particular liquid-liquid contact apparatus chosen for a given application. It has been found particularly desirable in the prior art to the provide apparatus and methods affording efficient mass and/or energy transfer, whereby liquid- liquid contact is accomplished with a minimum pressure drop through a given zone of minimum dimensions. High efficiency, low pressure drop, and reduced temperatures are important design criteria in the chemical engineering art, such as liquid-liquid extraction operations. Liquid-liquid chemical process towers for effecting such operations are generally of the character providing descending heavy liquid flow from an upper portion of the tower and ascending, light liquid flow from the bottom portion of the tower. Sufficient surface area for liquid-liquid contact is necessary for the primary function of mass and/or energy transfer and the reduction or elimination of heavy liquid entrainment present in the ascending lighter liquid. Most often it is necessary for the trays and/or packing arrays to have sufficient surface area in both horizontal and vertical planes so that fractions of the heavy constituents are conducted downwardly and the lighter liquid is permitted to rise through the trays or packing with minimum resistance. With such apparatus, heavy or light constituents of the feed are recovered at the bottom and top of the tower, respectively.

A plurality of tower internals, including trays, downcomers, and/or packing layers, are designed to afford compatible and complemental design configurations for assembly within a single process column. These tower internals utilize the velocity and kinetic energy of the ascending lighter liquid to perform the dual functions of eliminating heavy liquid entrainment in the ascending liquid phase and the thorough contacting of the light and heavy liquids to accomplish sufficient separation or extraction of the fluids into desired components.

Oppositely inclined, corrugated lamellae, or plates, have been utilized in the prior art for affording multiple light phase passages through the horizontal and vertical planes of packing layers to insure the flow of lighter liquid and distribution thereof within the lamellae and to prevent maldistribution, or channeling, of the lighter liquid through certain portions of the layers and not others. An improvement in this technique is set forth and show in U.S. Patent No. 5,188,773 assigned to the assignee of the present invention.

It should be noted that the structural configuration of inclined, corrugated contact plates of the prior art variety often incorporates holes for vapor or light liquid passage. Light phase turbulence is created by such holes to insure intimate light and heavy phase contact. It is also necessary to insure that the ascending light phase performs a dual function of phase contact and liquid di entrainment within close proximity to the vertical location at which the ascending phase approaches or leaves the holes. In this manner maldistribution of the ascending or descending phases is reduced. It is, moreover, a paramount concern of the prior art to provide such methods and apparatus for liquid- liquid contact in a configuration of economical manufacture. Such considerations are necessary for cost-effective operation and should be considered for all aspects of process tower operation.

Oppositely inclined corrugated plates do, however, provide but one method and apparatus for countercurrent liquid-liquid interaction. Another approach is the use of trays. With trays and downcomers, the heavy phase introduced at or near the top of the column and withdrawn at the bottom is effectively engaged by light phase being introduced at or near the bottom of the column and withdrawn at the top. The critical feature in such methods and apparatus is to insure that the two phases achieve the desired degree of contact with each other so that the planned mass and/or energy transfer occurs at the designed rate. The internal structure is, of course, passive in the sense that it is generally not power driven externally and has few, if any, moving parts. The prior art is replete with passive vapor-liquid and liquid-liquid contact devices which are designed to encourage the liquid passing through the tower to form itself into films having, in the aggregate, a large area over which the light phase may pass. However, the design problem is not merely a matter of providing a large surface area, such as a tray with a multitude of perforations. A number of other interrelated design considerations must be taken into account, particularly when considering the flow of liquid through and around downcomers.

While many prior art downcomers and upcomers for liquid-liquid contact have been shown to be relatively effective, certain disadvantages still remain. In particular, contact towers incorporating descending heavy liquid flow and ascending light liquid flow generally manifest poor distribution of constituents on active areas. For example, retrograde flow on opposite lateral sides of trays is a typical flow problem resulting in decreased tower efficiency. Problems also exist with surfaces that face downward because such surfaces are generally not effectively covered by the heavy liquid. One such surface is that of a downcomer side wall, which often slopes from the tray above. Few, if any, prior art designs effectively address proper coverage of such a downwardly faced surface by the heavy phase or light phase passage. It should also be noted that light phase flow is ultimately sensitive to pressure differentials, and is easily diverted by the myriad of exposed areas of tower internals.

It would be an advantage, therefore, to overcome the problems of the prior art by providing a tray-to-tray transfer device that improves and/or energy transfer between the descending heavy liquid and the ascending light liquid in a chemical process tower exhibiting counter-current flow. The apparatus and methods of the present invention provide such an improvement over the prior art by utilizing a tray-to-tray transfer device with a perforated wall. In this mariner, the continuous phase is caused to flow upon and through a wall of the tray-to-tray transfer device, substantially increasing the liquid-liquid contact between the continuous phase and dispersed phase normally passing on opposite sides of the tray-to-tray transfer device. In addition, the present invention also utilizes a specific array of apertures in the active area of its trays to improve the efficiency of the tower at lower flow rates. The present invention thus maximizes mass and/or energy transfer efficiency and may be provided with a minimal increase in production cost over that of conventional downcomer and upcomer tray assemblies.

Summary of the Invention

One aspect of the present invention includes a downcomer-tray assembly for a liquid-liquid contact tower having a downcomer and a tray disposed below the downcomer. The downcomer has an angled section defining a discharge region for a descending liquid, an inner surface, an outer surface, and a first plurality of apertures from the inner surface to the outer surface. The tray has an active area with a second plurality of apertures. The first plurality of apertures allow a descending liquid proximate the inner surface of the angled section to flow through the angled section for interaction with an ascending liquid proximate the outer surface of the angled section.

In another aspect, the present invention comprises a method of interacting a descending liquid and an ascending liquid in a liquid-liquid contact tower. The contact tower has a downcomer positioned above a tray for discharge of the descending liquid thereon, and the tray has a perforated active area for the dispersion of the ascending liquid. The downcomer is formed with an angled section defining a discharge region for the descending liquid, an inner surface, an outer surface, and a plurality of apertures from the inner surface to the outer surface. An inlet region is formed in the active area of the tray generally below the outer surface of the angled section. The method further includes dispersing the ascending liquid through the inlet region and toward the outer surface of the angled section, and flowing the descending liquid proximate the inner surface of the angled section and through the plurality of apertures for interaction with the ascending liquid proximate the outer surface of the angled section.

In a further aspect, the invention includes an upcomer-tray assembly for a liquid-liquid contact tower having an upcomer and tray disposed above the upcomer. The upcomer has an angled section defining a discharge region for an ascending liquid, an inner surface, and outer surface, and a first plurality of apertures from the inner surface to the outer surface. The tray has an active area with a second plurality of apertures. The first plurality of apertures allow an ascending liquid proximate the inner surface of the angled section to flow through the angled section for interaction with a descending liquid proximate the outer surface of the angled section.

In a further aspect, the invention comprises a method of interacting a descending liquid and an ascending liquid in a liquid-liquid contract tower. The contact tower has an upcomer positioned below a tray for discharge of the ascending liquid thereon, and the tray has a perforated active area for the dispersion of the descending liquid. The upcomer is formed with an angled section defining a discharge region for the ascending liquid, an inner surface, and outer surface, and a plurality of apertures from the inner surface to the outer surface. An inlet region is formed in the active area of the tray generally above the outer surface of the angled section. The method further includes dispersing the descending liquid through the inlet region and proximate the outer surface of the angled section, and flowing the ascending liquid proximate the inner surface of the angled section and through the plurality of apertures for interaction with the descending liquid. In a further aspect, the invention includes an assembly for transferring fluid between trays in a liquid-liquid contract tower. The contact tower has a continuous phase and a dispersed phase. The assembly includes a first tray having a plurality of apertures providing a flow path for the dispersed phase, a second tray disposed below the first tray and having a second plurality of apertures providing a flow path for the dispersed phase, and a tray-to-tray transfer device providing a flow path for a continuous phase between the first tray and the second tray. The tray-to-tray transfer device has an angled section with an inner surface, an outer surface, and a third plurality of apertures. The third plurality of apertures provide a flow path for the continuous phase proximate the inner surface of the angled section to interact with the dispersed phase proximate the outer surface of the angled section.

In a further respect, the present invention includes a contacting device for a liquid-liquid contact tower having a dispersed phase. The device comprises a tray having an active area. The active area includes a first array of undimpled apertures, a second array of dimpled apertures on a first side of the first array, and a third array of dimpled apertures on a second side of the first array.

In yet another aspect, the present invention comprises a method of forming droplets of a dispersed phase from an active area of a tray in a liquid-liquid contact tower. A tray is disposed in the contact tower. The tray has an active area with alternating arrays of dimpled apertures and undimpled apertures. A dispersed phase is flowed through the active area.

Brief Description of the Drawings

For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic, fragmentary, cross-sectional view of an improved downcomer-tray assembly according to a first preferred embodiment of the present invention secured within a process tower and illustrating the counter-current flow of first and second liquids therein;

FIG. 2 is a first perspective view of the downcomer-tray assembly of FIG. 1, with portions thereof cut away for purposes of clarity;

FIG.3 is a second, perspective view of the downcomer-tray assembly of FIG. 1, with portions thereof cut away for purposes of clarity; FIG. 4 is a schematic, fragmentary, cross-sectional view of an improved upcomer-tray assembly according to a second preferred embodiment of the present invention secured within a process tower and illustrating the counter-current flow of first and second liquids therein;

FIG. 5 is a detailed view of a portion of the active area of the tray assembly of FIG. 1;

FIG. 6 is a first perspective view of the upcomer-tray assembly of FIG. 4, with portions thereof cut away for clarity;

FIG. 7 is a second perspective view of the upcomer-tray assembly of FIG. 4, with portions thereof cut away for clarity; and FIG. 8 is a detailed view of a portion of the active area of the tray assembly of FIG. 4.

Detailed Description of the Preferred Embodiments

The preferred embodiments of the present invention and their advantages are best understood by referring to FIGS. 1-8 of the drawings, like numerals being used for like and corresponding parts of the various drawings. Referring first to FIG. 1, a schematic, fragmentary, cross-sectional view of an improved downcomer-tray assembly 100 according to a first preferred embodiment of the present invention is illustrated in a conventional liquid-liquid chemical process tower 10. Chemical process tower 10 has a cylindrical contact tower 12. Contact tower 12 has a plurality of trays formed therein, three of which, trays 102, 104, and 105, are shown in FIG. 1. Tower 12 also has a plurality of downcomers associated with its trays, two of which, downcomers 106 and 116, are shown in FIG. 1. Although not shown in FIG. 1, contact tower 12 may have a variety of other structures, such as a bottom inlet, a top outlet, side stream draw off lines, sides steam feed lines, manways for facilitating access to the internal region of tower 12, or other conventional liquid- liquid contact tower structures.

Downcomer 106 provides a path for liquid to flow between tray 102 and tray 104. Downcomer 106 preferably includes a chordal member 130 coupled to tray 102 and an angled section 107 depending from chordal member 130 into the interior of downcomer 106. Alternately, downcomer 106 may be formed with an angled section coupled to tray 102 and no chordal member, or with a chordal member and no angled section. A weir 108 is preferably located on the upper end of chordal member 130 proximate tray 102, and a weir 110 is preferably located on tray 104 proximate the lower end of downcomer 106. At the lower end of downcomer 106, tray 104 has an unperforated tray inlet region 112 generally defined by the inner wall of contact tower 12 and weir 110. Downcomer 106 also has a liquid tunnel 114 that directs liquid flow from a tunnel inlet region 115 located on tray 104 radially inwardly from weir 110.

Downcomer 116 provides a path for liquid to flow between tray 104 and tray 105. Downcomer 116 preferably includes a chordal member 158 coupled to tray 104 and an angled section 117 depending from chordal member 158 into the interior of downcomer 116. Alternatively, downcomer 116 may be formed with an angled section coupled to tray 104 and no chordal member, or with a chordal member and no angled section. A weir 118 is preferably located on the upper end of chordal member 158 proximate tray 104, and a weir 120 is preferably located on tray 105 proximate the lower end of downcomer 116. Tray 105 has an unperforated tray inlet region 122 near the lower end of downcomer 116 defined by the inner wall of contact tower 12 and weir 120. Downcomer 116 has a liquid tunnel 124 that directs liquid flow from a tunnel inlet region 125 located on tray 105 radially inward of weir 120. Downcomer 116 is preferably located on the opposite side of contact tower 12 from downcomer 106.

In conventional counter-current flow operation, downcomer-tray assembly 100 directs the flow of a heavy, descending liquid 126 through contact tower 12, as indicated by arrows generally labeled 126 in FIG. 1. More specifically, heavy liquid 126 generally flows across tray 102, down downcomer 106, across tray 104, down downcomer 116, and across tray 105. Downcomer-tray assembly 100 also directs the flow of a light, ascending liquid 128 within contact tower 12, as indicated by arrows, dispersed droplets, and regions generally labeled 128 in FIG. 1. More specifically, light liquid 128 flows upward through perforations (not shown) in an active area of each of trays 105, 104, and 102, forming dispersed droplets 128a within flowing heavy liquid 126. Below each of trays 105, 104, and 102, dispersed droplets 128a accumulate to form coalesced light liquid regions 128b. Dispersed light liquid droplets also flow from a tunnel inlet region 125 in the active area of tray 105 into liquid tunnel 124, as indicated by arrow 128c. As is described in greater detail hereinbelow, liquid tunnel 124 facilitates mass and/or energy transfer between light liquid 128 and heavy liquid 126 and directs the flow of liquid 128 toward tray 104. Furthermore, dispersed light liquid droplets flow from a tunnel inlet region 115 in the active area of tray 104 into liquid tunnel 114, as indicated by arrow 128d. As is described in greater detail hereinbelow, liquid tunnel 114 facilitates mass and/or energy transfer between light liquid 128 and heavy liquid 126 and directs the flow of liquid 128 toward tray 102.

Referring next to FIG. 2, the structure of downcomer-tray assembly 100 from a radially inward perspective is described in greater detail. Angled section 107 preferably has a generally semi-conical geometry, and angled section 107 is preferably formed from a plurality of plates 132, 134, 136, and 138. This preferred geometry of angled section 107, with its center closer to the inner wall of contact tower 12 than each of its outer sides, partially chokes the flow of heavy liquid 126 through the center of downcomer 106 and results in a highly uniform, efficient flow of liquid 126 across tray 104. In addition, as shown best in FIG. 1, angled section 107 preferably defines a discharge region 109 at a lower end of downcomer 106 that is narrower than an upper end of downcomer 106. Discharge region 109 establishes a dynamic liquid seal in downcomer 106 that prevents the upward flow of light liquid 128 into downcomer 106. Although four plates are shown coupled together in FIG. 2 to form angled section 107, angled section 107 can be formed from fewer or greater numbers of plates.

In addition, alternate geometries may be used for angled section 107 for specific applications of contact tower 12. For example, angled section 107 may have semi- conical geometry formed by a single surface.

Angled section 107 is preferably formed with an array of apertures 144, which allow the flow of heavy liquid 126 through angled section 107 and into liquid tunnel 114. As shown in FIG. 2, each plate 132, 134, 136, and 138 contains a similarly spaced array of apertures 144 having identical diameters. The number, diameter, and spacing of apertures 144 depends on a variety of factors, including the specific process being performed in chemical process tower 10 and the relative densities of liquids 126 and 128.

Chordal member 130 is generally vertical and preferably has an unperforated region 140 proximate its upper end. Unperforated region 140 allows the formation of coalesced light liquid region 128b below tray 102. In a contact tower 12 with a typical tray-to-tray spacing of approximately ten inches, region 140 preferably has a height of approximately two to three inches. With the exception of unperforated region 140, the remainder of chordal member 130 is preferably formed with an array of apertures 145, which allow the flow of heavy liquid 126 through chordal member 130 into the area between trays 104 and 102. The number, diameter, and spacing of apertures 145 depends on a variety of factors, including the specific process being performed in chemical process tower 10 and the relative densities of liquids 126 and 128.

Continuing to FIG. 3, the structure of downcomer-tray assembly 100 from a radially outward perspective is described in greater detail. As shown best in FIG. 3, liquid tunnel 114 is preferably defined by the intersection of the outer surface of angled section 107 and the outer surface of chordal member 130. Tunnel inlet region 115 is located on tray 104 radially inward of weir 110 and below liquid tunnel 114.

Tray 104 has an active area 152. Active area 152 has an array of apertures that preferably extends over the entire surface of tray 104 between weir 110 and weir 118. The apertures allow the flow of light liquid 128 through tray 104, and these apertures may comprise holes, valve structures, or other conventional fractionation tray apertures. The apertures in active area 152 preferably comprise alternating arrays of dimpled apertures 148 and undimpled apertures 150, the preferred structure of which is best illustrated in FIG. 5. By forming active area 152 with alternating arrays of dimpled apertures 148 and undimpled apertures 150, dispersed light liquid droplets 128a are more evenly formed across substantially the entire surface of active area 152 at low flow rates of chemical process tower 10. Of course, active area 152 may also be formed using only dimpled apertures 148 or only undimpled apertures 150. The number, diameter, and spacing of apertures 148 and 150 depends on a variety of factors, including the specific process being performed in chemical process tower 10 and the relative densities of liquids 126 and 128.

Trays 102 and 104 are preferably supported within contact tower 12 by support rings 142. Support rings 142 comprise a plurality of internal truss members 156. As shown in FIG. 3, internal truss members 156 preferably have an array of apertures 157 formed therethrough. Apertures 157 allow a more uniform formation of coalesced light liquid regions 128b below trays 102 and 104. The number, diameter, and spacing of apertures 157 depends on a variety of factors, including the specific process being performed in chemical process tower 10 and the relative densities of liquids 126 and 128.

The structure of tray 102, downcomer 1 16, chordal member 158, angled section 117, and liquid tunnel 124 of downcomer-tray assembly 100 are preferably similar to the structure of tray 104, downcomer 106, angled section 107, chordal member

130, and liquid tunnel 114, respectively. In addition, as chemical process tower 10 typically employs many more than three trays and two downcomers as shown in FIG. 1 , such additional trays and downcomers preferably have a structure similar to that of downcomer-tray assembly 100.

Having described the structure of downcomer-tray assembly 100, the operation and advantages of downcomer-tray assembly 100 are now described in greater detail. Referring first to FIGS. 1-3, as descending heavy liquid 126 flows across tray 102, light ascending liquid 128 flows from coalesced liquid region 128b below tray 102 through apertures 148 and 150 in active area 152 of tray 102 (not shown). As is conventional, apertures 148 and 150 disperse light liquid droplets 128a within flowing liquid 126 above plate 102, improving the mass and/or energy transfer between heavy liquid 126 and light liquid 128.

As is also conventional, heavy liquid 126 flows over weir 108, into downcomer 106, into inlet region 112, over weir 110, and across tray 104. However, apertures 144 of angled section 107 and apertures 145 of chordal member 130 effect improved mass and/or energy transfer between heavy liquid 126 and light liquid 128 as compared to conventional downcomers. More specifically, as heavy liquid 126a flows across the inner surface of plates 132 through 138, some of liquid 126a flows through apertures 144, interacting with light liquid 128d in liquid tunnel 114. Liquid 126a also flows through apertures 145 of chordal member 130 to interact with light liquid 128 in the area between trays 104 and 102 proximate the outer surface of chordal member 130. In this way, direct contact between liquids 126 and 128, and the corresponding mass and/or energy transfer between liquids 126 and 128, is accomplished in a region typically devoid of such interaction in conventional liquid-liquid contact towers. As shown best in FIGS. 1 and 3, liquid tunnel 114, and more specifically the outer surface of plates 132 through 138, also impart a horizontal vector to the mixture of heavy liquid 126 and light liquid droplets 128d in liquid tunnel 114. This horizontal flow vector directs heavy liquid 126 into the area between trays 104 and 102, further increasing the interaction between liquids 126 and 128 in this area. As heavy liquid 126 exits downcomer 106 and flows across tray 104, dispersed light liquid droplets 128a flow into heavy liquid 126 from apertures 148 and 150 in active area 152 of tray 104. As is conventional, such interaction improves the mass and/or energy transfer between heavy liquid 126 and light liquid 128. When heavy liquid 126 flows over weir 118 into downcomer 116, liquid tunnel 124 and the apertures of downcomer 116 effect improved mass and/or energy transfer between liquids 126 and 128, in a manner similar to that described above in connection with liquid tunnel 114 and downcomer 106.

Referring now to FIG. 4, a schematic, fragmentary, cross-sectional view of an improved upcomer-tray assembly 200 according to a second preferred embodiment of the invention is illustrated in a conventional chemical process tower 10. Chemical process tower 10 has a cylindrical contact tower 12. Tower 12 has a plurality of trays formed therein, three of which, trays 202, 204, and 205 are shown in FIG. 4. Tower 12 also has a plurality of upcomers associated with its trays, two of which, upcomers 206 and 216, are shown in FIG. 4. As may be appreciated by one skilled in the art referring to FIGS. 1 and

4, the structure of upcomer-tray assembly 200 is substantially identical to downcomer- tray assembly 100, except that contact tower 12 must be inverted, or turned "upside down", to form upcomer-tray assembly 200. Upcomer 206 provides a path for liquid to flow between tray 202 and tray 204. Upcomer 206 preferably includes a chordal member 230 coupled to tray 202 and an angled section 207 depending from chordal member 230 into the interior of upcomer 206. Alternatively, upcomer 206 may be formed with an angled section coupled to tray 202 and no chordal member, or with a chordal member and no angled section. A weir 206 is preferably located on the lower end of chordal member 230 proximate tray 202, and a weir 210 is preferably located on tray 204 proximate the upper end of upcomer 206. At the upper end of upcomer 206, tray 204 has an unperforated tray inlet region 212 generally defined by the inner wall of contact tower 12 and weir 210. Upcomer 206 also has a liquid tunnel 214 that directs liquid flow from a tunnel inlet region 215 located on tray 204 radially inwardly from weir 110.

Upcomer 216 provides a path for liquid to flow between tray 204 and tray 205. Upcomer 216 preferably includes a chordal member 258 coupled to tray 204 and an angled section 216 depending from chordal member 258 into the interior of upcomer 216. Alternatively, upcomer 216 may be formed with an angled section coupled to tray 204 and no chordal member, or with a chordal member and no angled section. A weir 218 is preferably located on the lower end of chordal member 258 proximate tray 204, and a weir 220 is preferably located on tray 205 proximate the upper end of upcomer 216. Tray 205 has an unperforated tray inlet region 222 near the upper end of upcomer 216 defined by the inner wall of contact tower 12 and weir 220. Upcomer 216 has a liquid tunnel 224 that directs liquid flow from a tunnel inlet region 225 located on tray 205 radially inward of weir 220. Upcomer 216 is preferably located on the opposite side of contact tower 12 from upcomer 206.

In conventional counter-current flow operation, upcomer-tray assembly 200 directs the flow of a light, ascending liquid 228 through contact tower 12, as indicated by arrows generally labeled 228 in FIG. 4. More specifically, light liquid 228 flows across tray 202, up upcomer 206, across tray 204, up upcomer 216, and across tray 205. Upcomer-tray assembly 200 also directs the flow of a heavy, descending liquid 226 within contact tower 12, as indicated by arrows, droplets, and regions generally labeled 226 in FIG. 4. More specifically, heavy liquid 226 flows downward through aperture (not shown) in an active area of each of trays 205, 204, and 202, forming droplets 226a within flowing light liquid 228. Above each of trays 205, 204, and 202, droplets 228a accumulate to form coalesced heavy liquid regions 226b. Dispersed heavy liquid droplets also flow from a tunnel inlet region 225 in the active area of tray 205 into liquid tunnel 224, as indicated by arrow 226c. As is described in greater detail hereinbelow, liquid tunnel 224 facilitates mass and/or energy transfer between light liquid 228 and heavy liquid 226 and directs the flow of heavy liquid 226 toward tray 204. Furthermore, dispersed heavy liquid droplets flow from a tunnel inlet region 215 in the active area of tray 204 into liquid tunnel 214, as indicated by arrow 226d. As is described in greater detail hereinbelow, liquid tunnel 214 facilitates mass and/or energy transfer between light liquid 228 and heavy liquid 226 and directs the flow of liquid 226 toward tray 202.

Referring next to FIG. 6, the structure of upcomer-tray assembly 200 from a radially inward perspective is described in greater detail. Angled section 207 preferably has a generally semi -conical geometry, and angled section 207 is preferably formed from a plurality of plates 232, 234, 236, and 238. This preferred geometry of angled section 207, with its center closer to the inner wall of contact tower 12 than each of its outer sides, chokes the flow of light liquid 228 through the center of upcomer 206 and results in a highly uniform, efficient flow of liquid 228 across tray 204. In addition, as shown best in FIG. 4, angled section 207 preferably defines a discharge region 209 at an upper end of upcomer 206 that is narrower than a lower end of upcomer 206. Discharge region 209 establishes a dynamic liquid seal in upcomer 206 that prevents the downward flow of heavy liquid 226 into upcomer 206.

Although four plates are shown coupled together in FIG. 6 to form angled section 207, angled section 207 can be formed from fewer or greater numbers of plates. In addition, alternate geometries may be used for angled section 207 for specific applications of contact tower 12. For example angled section 207 may have sem-conical geometry formed by a single surface.

Angled section 207 is preferably formed with an array of apertures 244, which allow the flow of light liquid 228 through angled section 207 and into liquid tunnel 214. As shown in FIG. 6, each plate 232, 234, 236, and 238 contains a similarly spaced array of apertures 244 having identical diameters. The number, diameter, and spacing of apertures 244 depends on a variety of factors, including the specific process being performed in chemical process tower 10 and the relative densities of liquids 226 and 228. Chordal member 230 is generally vertical and preferably has an unperforated region 240 proximate its lower end. Unperforated region 240 allows the formation of coalesced heavy liquid region 226b above tray 202. In a contact tower 12 with a typical tray-to-tray spacing of approximately ten inches, region 240 preferably has a height of approximately two to three inches. With the exception of unperforated region 240, the remainder of chordal member 230 is preferably formed with an array of apertures 245, which allow the flow of light liquid 228 through chordal member 230 into the area between trays 204 and 202. The number, diameter, and spacing of apertures 245 depends on a variety of factors, including the specific process being performed in chemical process tower 10 and the relative densities of liquids 226 and 228.

Continuing the FIG. 7, the structure of upcomer-tray assembly 200 from a radially outward perspective is described in greater detail. As shown best in FIG. 7, liquid tunnel 214 is preferably defined by the intersection of the outer surface of angled section 207 and the outer surface of chordal member 230. Tunnel inlet region 215 is located on tray 204 radially inward of weir 210 and above liquid tunnel 214.

Tray 204 has an active area 252. Active area 252 has an array of apertures that preferably extends over the entire surface of tray 204 between weir 210 and weir 218. The apertures allow the flow of heavy liquid 226 through tray 204, and these apertures may comprise holes, valve structures, or other conventional fractionation tray apertures. However, the apertures in active area 252 preferably comprise alternating arrays of dimpled apertures 248 and undimpled apertures 260, the preferred structure of which is best illustrated in FIG. 8. By forming active area 252 with alternating arrays of dimpled apertures 248 and undimpled apertures 250, heavy liquid droplets 226a are more evenly formed across substantially the entire surface of active area 252 at low flow rates of chemical process tower 10. Of course, active area 252 may also be formed using only dimpled apertures 248 or only undimpled apertures 250. The number, diameter, and spacing of apertures 248 and 250 depends on a variety of factors, including the specific process being performed in chemical process tower 10 and the relative densities of liquids 226 and 228.

Trays 202 and 204 are preferably supported within contact tower 12 by support rings 242. Support rings 242 comprise a plurality of internal truss members 256. As shown in FIG. 7, internal truss members 256 preferably have an array of apertures 257 formed therethrough. Apertures 257 allow a more uniform formation of coalesced heavy liquid regions 226b above trays 202 and 204. The number, diameter, and spacing of apertures 257 depends on a variety of factors, including the specific process being performed in chemical process tower 10 and the relative densities of liquids 226 and 228. The structure of tray 205, upcomer 216, chordal member 258, angled section 217, and liquid tunnel 224 of upcomer-tray assembly 200 are preferably similar to the structure of tray 204, upcomer 206, angled section 207, chordal member 230, and liquid tunnel 214, respectively. In addition, as chemical process tower 10 typically employs many more than three trays and two upcomers as shown in FIG. 4, such additional trays and upcomers preferably have a structure similar to that of upcomer-tray assembly 200.

Having described the structure of upcomer-tray assembly 200, the operation and advantages of upcomer-tray assembly 200 are now described in greater detail. As is conventional, light, ascending liquid 228 flows over weir 208, into upcomer 206, into inlet region 212, over weir 210, and across tray 204. However, apertures 244 of angled section 207 and apertures 245 of chordal member 230 effect improved mass and/or energy transfer between light liquid 228 and heavy liquid 226 as compared to conventional upcomers. More specifically, as light liquid 228a flows across the inner surface of plates 232 through 238, some of liquid 228a flows through apertures 244, interacting with heavy liquid 226d in liquid tunnel 214. Liquid 228 also flows through apertures 245 of chordal member 230 to interact with heavy liquid 226 in the area between trays 204 and 202 proximate the outer surface of chordal member 230. In this way, direct contact between liquids 226 and 228, and the corresponding mass and/or energy transfer between liquids 226 and 228, is accomplished in a region typically devoid of such interaction in conventional liquid-liquid contact towers.

As shown best in FIGS. 4 and 7, liquid tunnel 214, and more specifically the outer surface of plates 232 through 238, also impart a horizontal factor to the mixture of light liquid 228 and heavy liquid droplets 226d in liquid tunnel 114. This horizontal flow vector directs light liquid 228 into the area between trays 204 and 202, further increasing the interaction between liquids 226 and 228 in this area.

As light liquid 228 exits upcomer 206 and flows across tray 204, dispersed heavy liquid droplets 226a flow into light liquid 228 from apertures 248 and 250 in active area 252 of tray 204. As is conventional, such interaction improves the mass and/or energy transfer between heavy liquid 226 and light liquid 228. When light liquid 228 flows over weir 218 into upcomer 216, liquid tunnel 224 and the apertures of upcomer 216 effect improved mass and/or energy transfer between liquids 226 and 228, in a manner similar to that described above in connection with liquid tunnel 214 and upcomer 206.

From the above, one skilled in the art will appreciate that the present invention may be incorporated into any tray-to-tray transfer device. Such a tray-to-tray transfer device may comprise a perforated downcomer with an angled section as shown in FIGS. 1-3; a perforated upcomer with an angled section as shown in FIGS. 4, 6, and 7; or a perforated, vertical downcomer or upcomer. In addition, such a tray-to-tray transfer device may be formed using a contact tower wall, as shown in FIGS. 1-3 and 4, 6, and 7, or with the device being disposed on the interior of a tray away from a contact tower wall. With such a tray-to-tray transfer device, the "continuous phase" is the liquid that generally flows through the tray-to-tray transfer device. The "dispersed phase" is the liquid that generally flows through, and is dispersed by, the perforated active areas of the trays. The continuous phase may be descending and the dispersed phase may be ascending, or, alternatively, the continuous phase may be ascending and the dispersed phase may be descending. In either flow configuration, liquid-liquid contact between the continuous and dispersed phases in increased, and improved mass and/or energy transfer is obtained, by flowing the continuous phase through apertures in a wall of the tray-to- tray transfer device into the dispersed phase on the other side of the wall.

From the above, it may be appreciated that present invention provides improved mass and/or energy transfer between heavy and light liquids in a liquid- liquid contact tower by utilizing a tray-to-tray transfer device with a perforated wall. In addition, more uniform, efficient dispersion of the dispersed phase is accomplished at lower flow rates of a chemical process tower by using alternating arrays of dimpled and undimpled apertures in the active areas of the trays. These advantages are provided with only a minimal increase in production costs over that of conventional downcomer-tray and upcomer-tray assemblies.

The present invention is illustrated herein by example, and various modifications may be made by a person of ordinary skill in the art. For example, numerous geometries and/or relative dimensions could be altered to accommodate a given application of a tray-to-tray transfer device.

It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description. While the method and apparatus shown or described has been characterized as being preferred it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the following claims.

Claims

What is claimed is:

1. A downcomer-tray assembly for a liquid-liquid contact tower, comprising: a downcomer having an angled section defining a discharge region for a descending liquid, an inner surface, an outer surface, and a first plurality of apertures from inner surface to said outer surface; and a tray disposed below said downcomer, said tray having an active area with a second plurality of apertures therethrough; said first plurality of apertures allowing said descending liquid proximate said inner surface of said angled section to flow through said angled section for interaction with an ascending liquid proximate said outer surface of said angled section.

2. The downcomer-tray assembly of claim 1 further comprising a chordal member coupled to said angled section, and wherein said first plurality of apertures allows said descending liquid proximate said inner surface of said chordal member to flow through said chordal member for interaction with said ascending liquid proximate said outer surface of said chordal member.

3. The downcomer-tray assembly of claim 1 wherein said angled section has a generally semi-conical geometry.

4. The downcomer-tray assembly of claim 3 wherein said angled section comprises a plurality of generally planar walls.

5. The downcomer-tray assembly of claim 1, wherein said active area comprises an inlet region generally below said outer surface of said angled section.

6. The downcomer-tray assembly of claim 5, wherein said inlet region is for allowing a flow of ascending liquid along said outer surface of said angled section for interaction with said descending liquid flowing through said first plurality of apertures.

7. The downcomer-tray assembly of claim 6 wherein said inlet region comprises a first array of undimpled apertures and a second array of dimpled apertures.

8. The downcomer-tray assembly of claim 1 wherein said active area comprises alternating arrays of undimpled apertures and dimpled apertures.

9. The downcomer-tray assembly of claim 4 wherein said angled section is for at least partially choking a flow of said descending liquid through a center of said downcomer so that said descending liquid exhibits a uniform flow across said tray.

10. A method of interacting a descending liquid and an ascending liquid in a liquid-liquid contact tower, said contact tower having a downcomer positioned above a tray for discharge of said descending liquid thereon, said tray having a perforated active area for dispersion of said ascending liquid, comprising the steps of: forming said downcomer with an angled section defining a discharge region for said descending liquid, an inner surface, an outer surface, and a plurality of apertures from said inner surface to said outer surface; forming said active area of said tray with an inlet region generally below said outer surface of said angled section; dispersing said ascending liquid through said inlet region and toward said outer surface of said angled section; and flowing said descending liquid proximate said inner surface of said angled section and through said plurality of apertures for interaction with said ascending liquid proximate said outer surface of said angled section.

11. The method of claim 10, wherein said downcomer comprises a chordal member coupled to said angled section, and further comprising the step of flowing said descending liquid proximate said inner surface of said chordal member and through said plurality of apertures for interaction with said ascending liquid proximate said outer surface of said chordal member.

12. The method of claim 10 further comprising the step of flowing said descending liquid through said discharge region, and wherein said angled section has a generally semi-conical geometry that at least partially chokes said flow of said descending liquid through a center of said downcomer and creates a uniform flow of said descending liquid across said tray.

13. An upcomer-tray assembly for a liquid- liquid contact tower, comprising: an upcomer having an angled section defining a discharge region for an ascending liquid, an inner surface, an outer surface, and a first plurality of apertures from said inner surface to said outer surface; and a tray disposed above said upcomer, said tray having an active area with a second plurality of apertures therethrough; said first plurality of apertures allowing said ascending liquid proximate said inner surface of said angled section to flow through said angled section for interaction with a descending liquid proximate said outer surface of said angled section.

14. The upcomer-tray assembly of claim 13 further comprising a chordal member coupled to said angled section, and wherein said first plurality of apertures allows said ascending liquid proximate said inner surface of said chordal member to flow through said chordal member for interaction with said descending liquid proximate said outer surface of said chordal member.

15. The upcomer-tray assembly of claim 13 wherein said angled section has a generally semi-conical geometry.

16. The upcomer-tray assembly of claim 15 wherein said angled section comprises a plurality of generally planar walls.

17. The upcomer-tray assembly of claim 13, wherein said active area comprises an inlet region generally above said outer surface of said angled section.

18. The upcomer-tray assembly of claim 17, wherein said inlet region is for allowing a flow of descending liquid along said outer surface of said angled section for interaction with said ascending liquid flowing through said first plurality of apertures.

19. The upcomer-tray assembly of claim 18 wherein said inlet region comprises a first array of undimpled apertures and a second array of dimpled apertures.

20. The upcomer-tray assembly of claim 13 wherein said active area comprises alternating arrays of undimpled apertures and dimpled apertures.

21. The upcomer-tray assembly of claim 16 wherein said angled section is for at least partially choking a flow of said ascending liquid through a center of said upcomer so that said ascending liquid exhibits a uniform flow across said tray.

22. A method of interacting a descending liquid and an ascending liquid in a liquid-liquid contact tower, said contact tower having an upcomer positioned below a tray for discharge of said ascending liquid thereon, said tray having a perforated active area for dispersion of said descending liquid, comprising the steps of: forming said upcomer with an angled section defining a discharge region for said ascending liquid, an inner surface, an outer surface, and a plurality of apertures from said inner surface to said outer surface; forming said active area of said tray with an inlet region generally above said outer surface of said angled section; dispersing said descending liquid through said inlet region and toward said outer surface of said angled section; and flowing said ascending liquid proximate said inner surface of said angled section and through said plurality of apertures for interaction with said descending liquid proximate said outer surface of said angled section.

23. The method of claim 22, wherein said upcomer comprises a chordal member coupled to said angled section, and further comprising the step of flowing said ascending liquid proximate said inner surface of said chordal member and through said plurality of apertures for interaction with said descending liquid proximate said outer surface of said chodal member.

24. The method of claim 22 further comprising the step of flowing said ascending liquid through said discharge region, and wherein said angled section has a generally semi-conical geometry that at least partially chokes said flow of said ascending liquid through a center of said upcomer and creates a uniform flow of said ascending liquid across said tray.

25. An assembly for transferring fluid between trays in a liquid- liquid contact tower, said contact tower having a continuous phase and a dispersed phase, comprising: a first tray having a plurality of apertures providing a flow path for a dispersed phase; a second tray disposed below said first tray, said second tray having a second plurality of apertures providing a flow path for said dispersed phase; and a tray- to-tray transfer device providing a flow path for a continuous phase between said first tray and said second tray, and having an angled section with an inner surface, an outer surface, and a third plurality of apertures, said third plurality of apertures providing a flow path for said continuous phase proximate said inner surface of said angled section to interact with said dispersed phase proximate said outer surface of said angled section.

26. The assembly of claim 25 wherein said continuous phase is descending and said dispersed phase is ascending.

27. The assembly of claim 25 wherein said continuous phase is ascending and said dispersed phase is descending.

28. The assembly of claim 26 wherein said second tray has a perforated inlet region generally below said outer surface of said angled section for allowing a flow of said ascending dispersed phase along said outer surface of said angled section for interaction with said descending continuous phase flowing through said third plurality of apertures.

29. The assembly of claim 27 wherein said first tray has a perforated inlet region generally above said outer surface of said angled section for allowing a flow of said descending dispersed phase along said outer surface of said angled section for interaction with said ascending continuous phase flowing through said third plurality of apertures.

30. A contacting device for a liquid-liquid contact tower, said contact tower having a dispersed phase, comprising: a tray having an active area; said active area comprising a first array of undimpled apertures, a second array of dimpled apertures on a first side of said first array, and a third array of dimpled apertures on a second side of said first array.

31. The device of claim 30 wherein, during operation of said contact tower at a low flow rate with an ascending dispersed phase, said first, second, and third arrays of apertures cooperate to evenly form droplets of said dispersed phase across substantially all of said active area.

32. The device of claim 31 wherein said dimpled apertures in said second and third arrays have a downwardly facing concave surface.

33. The device of claim 30 wherein, during operation of said contact tower at a low flow rate with a descending dispersed phase, said first, second, and third arrays of apertures cooperate to evenly form droplets of said dispersed phase across substantially all of said active area.

34. The device of claim 33 wherein said dimpled apertures in said second and third arrays have an upwardly facing concave surface.

35. The device of claim 30 further comprising a plurality of arrays of undimpled apertures formed in an alternating arrangement in said active area with a plurality of arrays of dimpled apertures.

36. A method of forming droplets of a dispersed phase from an active area of a tray in a liquid-liquid contact tower, comprising the steps of: disposing a fray in said contact tower, said tray having an active area with alternating arrays of dimpled apertures and undimpled apertures; and flowing a dispersed phase through said active area.

37. The method of claim 36 wherein said flowing step comprises flowing an ascending dispersed phase through said active area at a low flow rate, and wherein said alternating arrays of dimpled apertures and undimpled apertures cooperate to evenly form droplets of said dispersed phase across substantially all of said active area.

38. The method of claim 37 wherein said dimpled apertures have a downwardly facing concave surface.

39. The method of claim 36 wherein said flowing step comprises flowing a descending dispersed phase through said active area at a low flow rate, and wherein said alteraating arrays of dimpled apertures and undimpled apertures cooperate to evenly form droplets of said dispersed phase across substantially all of said active area.

40. The method of claim 39 wherein said dimpled apertures have an upwardly facing concave surface.

41. The method of claim 37 further comprising the step of forming a coalesced dispersed phase region below said tray.

42. The method of claim 39 further comprising the step of forming a coalesced dispersed phase region above said tray.