WO1999003554A1

WO1999003554A1 - Venturi swirl tube for vapor liquid contact tray

Info

Publication number: WO1999003554A1
Application number: PCT/US1998/014866
Authority: WO
Inventors: Adam T. Lee; Zhongliang L. Fan
Original assignee: Koch-Glitsch, Inc.
Priority date: 1997-07-18
Filing date: 1998-07-17
Publication date: 1999-01-28
Also published as: AU8411598A; WO1999003554A9

Abstract

A swirl tube (152) for positioning on a contact device, such as a tray (130), within a vapor liquid process column is disclosed. The swirl tube (152) includes a riser tube (156) having a venturi-shaped geometry, an inlet, and an outlet. The swirl tube further includes a separator (158) and means for movably coupling the separator to the riser tube proximate the outlet. Positioning such a swirl tube on a contact device improves the mass and/or energy transfer between vapor and liquid in the column, reduces or eliminates the flooding problem created by liquid entrained in descending vapor within the column, and reduces or eliminates the flooding problem created by vapor entrained in descending liquid within the column.

Description

VENTURI SWIRL TUBE FOR VAPOR LIQUID CONTACT TRAY

Field of the Invention

The present invention pertains to chemical process columns or towers and, more particularly, but not by way of limitation, to the use of a venturi swirl tube to maximize the mass and/or energy transfer in a vapor liquid process column.

History of the Related Art

Distillation columns are utilized to separate selected components from a multi component stream. Successful fractionation in the column is dependent upon intimate contact between liquid and vapor phases. Some columns use vapor and liquid contact devices such as trays.

Such trays are generally installed on support rings within the tower and have a solid tray or deck with a plurality of apertures in an "active" area. Liquid is directed onto the tray by means of a vertical channel from the tray above. This channel is referred to as the downcomer. The liquid moves across the active area and exits through a similar downcomer. The location of the downcomers determine the flow pattern of the liquid. Vapor ascends through the apertures in the trays and contacts the liquid moving across the tray. The liquid and vapor mix in the active area and fractionation occurs.

Maximum utilization of the active area of a tray is an important consideration to chemical process tower design. Regions of the tray which are not effectively used for vapor liquid contact can reduce the fractionation capacity and efficiency of the tray. Therefore, there is a need for devices and methods that optimize the active area design of a fractionation tray in a chemical process tower. It is well known that the concentration-difference between the vapor and the liquid is the driving force to effect mass and/or energy transfer. This concentration-difference can be effected in many ways; some reducing fractionation efficiency. When operating pressure is such as to produce a vapor density above about 1.0 lbs/cu. ft., there is the possibility that some amount of vapor bubbles are commingled or entrained with the downcomer incoming liquid. For example, as operating pressure increases due to an increase in the vapor concentration, descending liquid begins to absorb vapor as it moves across a tray. This is above that normally associated as dissolved gas as governed by Henry's Law and represents much larger amounts of vapor bubbles that are commingled or "entrained" with the liquid. This vapor is not firmly held and is released within the downcomer, and, in fact, the majority of said vapor must be released, otherwise the downcomer can not accommodate the liquid/vapor mixture and will flood, thus preventing successful tower operation.

Similarly, an exothermic reaction in the downcomer will generate vapors from the equilibrium mixture, which also will be released. For conventional trays, the released vapor will oppose the descending frothy vapor/liquid mixture flowing into the downcomer. In many cases, such opposition leads to poor tower operation and premature flooding. Therefore, there is a need for devices and methods that reduce or eliminate such "liquid" flooding within a downcomer of a chemical process tower.

Another serious problem which manifests itself in such operational applications is entrainment of liquid droplets in the ascending vapor. This phenomenon, which is virtually the opposite of the above-described vapor entrainment, can prevent effective vapor liquid contact. Liquid entrainment is, in one sense, a dynamic flow condition. High velocity vapor flow can suspend descending liquid droplets and prevent their effective passage through the underlying froth mixture zone. It is particularly difficult to prevent this problem when the tower applications require high volume vapor flow in a direction virtually opposite to that of high volume, descending liquid flow. In addition, as the vapor flow rate increases, the entrained liquid droplets may prevent vapor from effectively flowing through the apertures in the active area of a tray-. This in turn increases the pressure drop across the tray, increases the loading on the tray, and reduces the mass and/or energy transfer efficiency of the tower. Therefore, there is a need for devices and methods that reduce or eliminate such "vapor" flooding beneath a tray within a chemical process tower.

Cylindrical swirl tubes have been used to combat the entrainment of liquid droplets in the ascending vapor of a chemical process tower, and an example of such a conventional cylindrical swirl tube is shown in FIG. 1. A cylindrical swirl tube assembly 200 is disposed in a tray 202 of a chemical process tower (not shown). Cylindrical swirl tube assembly 200 generally comprises a hollow tube 204, an axial swirler 206 fixedly coupled within the interior of tube 204, and a separator 208 disposed over an upper end of tube 204. Tube 204 has an inlet 210 below tray 202 which allows the entry of an ascending vapor 212. Tube 204 has annular holes 214 which allow the entry of a liquid 216 flowing across tray 202. Tube 204 has an outlet 205 on its upper end, and tube 204 may also comprise annular ribs 218 and 220 proximate holes 214. Axial swirler 206 includes a center sleeve 222 having a plurality of inclined vanes 224 on its upper end. Inclined vanes 224 are fixed to the interior of tube 204 by conventional means, such as tack welds 226. Separator 208 is coupled to tube 204 by conventional means, such as rod 228, to define an annular passage 230. A diaphragm member 232 is located on the upper end of separator 208. A separation zone 234 is defined within separator 208 between outlet 205 of tube 204 and diaphragm member 232.

During operation of the chemical process tower in which swirl tube assembly 200 is disposed, ascending vapor 212 sprays liquid 216 entering through holes 214. Liquid droplets that are entrained within vapor 212 move upward with vapor 212 through the tube 204. Inclined vanes 224 impart a vortex motion to the vapor/liquid mixture, causing the entrained droplets to form a rotating, upwardly moving film on the inner surface of tube 204. In separation zone 234, the separated vapor 212 swirls out separator 208 via a hole 236 in diaphragm member 232, as indicated by the arrow in separation zone 234. The separated out liquid droplets run down annular passage 230 into liquid 216 flowing across tray 202. Diaphragm member 232 prevents any liquid on the inner wall of separator 208 from passing through hole 236.

FIGS. 2 and 3 show a second example of a conventional cylindrical swirl tube assembly 300 disposed below a tray 302 in a chemical process tower (not shown). Cylindrical swirl tube assembly 300 generally comprises tube 304 coupled to a separator 306 below a valve 308. Tube 304 has an inlet 310 allowing the entry of an ascending vapor 312 containing droplets of entrained liquid from below tray 302. Tube 304 also has a plurality of inclined vanes 314 fixedly coupled within its interior and an outlet 316 on its upper end. Separator 306 is coupled to tube 304 to form an annular passage 318. A cone-shaped diaphragm member 320 having a hole 322 is located in the top of separator 306 below valve 308.

During operation of the chemical process tower in which cylindrical swirl tube assembly 300 is disposed, ascending vapor 312 having entrained liquid droplets enters inlet 310. The inclined vanes 314 impart a vortex motion to the vapor/liquid mixture, causing the entrained droplets to form a rotating, upwardly moving film on the inner surface of tube 304. Upon reaching outlet 316, the separated vapor swirls out of separator 306 via hole 322 and valve 308. The separated liquid droplets flow over tube 304, into annular passage 318, and down into the region of the tower below tray 302. Diaphragm member 320 prevents any liquid from passing from the inner walls of separator 306 through valve 308. While conventional cylindrical swirl tubes, such as cylindrical swirl tube assemblies 200 and 300, are effective in removing entrained liquid from ascending vapor in a chemical process tower, such assemblies may not be commercially practical in some applications. For example, in applications where each tray of a chemical process tower requires numerous cylindrical swirl tube assemblies, such conventional assemblies may prohibitively increase the manufacturing cost of the tower due to their relatively large number of component parts. In addition, such conventional assemblies may not adequately address the problems of liquid and vapor flooding in a chemical process tower. Therefore, a need exists in the chemical process tower industry for simple, inexpensive devices which effectively combat flooding in a process tower caused by liquid entrained in ascending vapor and vapor entrained within a descending liquid, as well as the corresponding drop in mass and/or energy transfer efficiency caused by such flooding. The apparatus and methods of the present invention provide such an improvement over the prior art by utilizing venturi swirl tubes in the trays of such towers.

Summary of the Invention

The present invention relates to the use of a venturi swirl tube to maximize the mass and/or energy transfer in a vapor liquid process column. More particularly, one aspect of the present invention may be incorporated into a contact tray for a vapor liquid process column. The contact tray includes a generally planar member having an active area with a plurality of apertures therethrough. In addition, at least one venturi swirl tube is disposed in the active area of the tray.

In another aspect, the present invention comprises a swirl tube for positioning on a contact device within a vapor liquid process column. The swirl tube includes a riser tube having a venturi-shaped geometry, an inlet, and an outlet. The swirl tube further includes a separator, and a means for movably coupling the separator to the riser tube near the outlet.

In a further aspect, the present invention comprises a method of interacting an ascending vapor and a descending liquid within a chemical process tower. A tray is supported within the process tower. A tray has an active area with a plurality of apertures therethrough, a top side, and a bottom side. A swirl tube is formed on the top side of the tray in the active area. The swirl tube has a venturi-shaped geometry, an inlet in fluid communication with the bottom side of the tray, and an outlet. Vapor and froth from below the bottom side of the tray are drawn through the inlet of the swirl tube for interaction therein.

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 side-elevational, sectional view of an exemplary, conventional cylindrical swirl tube assembly;

FIG. 2 is a side-elevational, sectional view of a second exemplary, conventional cylindrical swirl tube assembly; FIG. 3 is a top, sectional view of the conventional cylindrical swirl tube assembly of FIG. 2 along line 3-3;

FIG. 4 is a perspective view of a packed column with various sections cut away for illustrating a variety of tower internals including a downcomer-tray assembly according to a preferred embodiment of the present invention; FIG. 5 is an enlarged, fragmentary, perspective view of the downcomer-tray assembly of FIG. 4 taken from the exterior of the tower;

FIG. 6 is an enlarged, fragmentary, perspective view of the downcomer-tray assembly of FIG. 4 taken from the interior of the tower and illustrating a tray including venturi swirl tubes according to a preferred embodiment of the present invention;

FIG. 7 is an enlarged, side-elevational, sectional view of one of the venturi swirl tubes of FIG. 6;

FIG. 8 is a top, sectional view of the venturi swirl tube of FIG. 7 along line 8-8; and FIG. 9 is a schematic, side-elevational, sectional view of the downcomer-tray assembly of FIGS. 5 and 6 illustrating the principles of operation of the present invention.

Detailed Description of the Preferred Embodiment

The preferred embodiment of the present invention and its advantages are best understood by referring to FIGS. 4-9 of the drawings, like numerals being used for like and corresponding parts of the various drawings.

Referring first to FIG. 4, there is shown a fragmentary, perspective view of an illustrative packed exchange tower or column with various sections cut away for showing a variety of tower internals and including a downcomer-tray assembly according to a preferred embodiment of the present invention. An exchange column 10 comprises a cylindrical tower 12 having packing beds 38 and 39, and a downcomer-tray assembly 100 incorporating the principles of the present invention. The tower 12 of the column 10 includes a skirt 28 for the support of the tower 12. A plurality of manways 16 are constructed for facilitating access to the internal region of the tower 12. A stream vapor feed line or reboiler return line 32 is provided in a lower portion of the tower 12 and a vapor outlet or overhead line 26 is provided in an upper portion of the tower 12. A reflux return line 34 is provided in an upper portion of the tower 12 and a bottom stream draw off line 30 is provided at the bottom of the tower 12. Also provided are a side stream draw offline 20 and a liquid side feed line 18 in the tower 12. Referring still to FIG. 4, in operation, vapor 15 is fed into the tower 12 through the return line 32, and liquid 13 is fed into the tower 12 through the reflux return line 34 and the liquid side feed line 18. The vapor 15 flows upwardly through the column 10 and ultimately leaves the tower 12 through the vapor outlet 26. The liquid 13 flows downwardly through the column 10 and ultimately leaves the tower 12 either at the side stream draw off line 20, or at the bottom stream draw off line 30. In its downward flow, the liquid 13 is depleted of some material which is gained by the vapor 15 as they pass through the tray assembly 100 and the packing beds 38 and 39 of the column 10, and the vapor 15 is depleted of some material which is gained by the liquid 13.

Referring still to FIG. 4, it may be seen that the upper packing bed 38 is of the structured packing variety. The regions of the exchange column 10 beneath the upper packing bed 38 are shown for the purpose of illustration only and include a liquid collector 40 disposed beneath a support grid 41 in support of the upper structured packing 38. A liquid distributor 42, adapted for redistributing liquid 13, is likewise disposed there-beneath. A second type of distributor 42a is shown below the cut-line and disposed above the lower packing bed 39. The internal arrangement of the column 10 is diagrammatical only and is provided for referencing various component arrays therein.

Referring now to FIGS. 5 and 6, there are shown two fragmentary perspective views of the downcomer-tray assembly 100 in FIG. 4 taken from opposite angles relative to the tower 12. In this preferred embodiment, the downcomer-tray assembly 100 includes a first tray 110 connected to a first downcomer 120, and a second tray 130 connected to a second downcomer 140. The trays 110 and 130 are generally planar panels that have central active areas 111 and 131, respectively. The trays 110 and 130 are supported by support rings 98 and 99, respectively, of the tower 12. Outlet weirs 112 and 132 are disposed on the first and second trays 110 and 130, respectively, adjacent to the downcomers 120 and 140, respectively. The outlet weirs 112 and 132 are preferably an upright plate or strip welded to the planar panels of the trays 110 and 130.

Still referring to FIGS. 5 and 6, the downcomers 120 and 140 have semi-conical walls 121 and 141, respectively, that taper from the outlet weirs 112 and 132 of the trays 110 and 130, downwardly towards the inner surface of the tower 12. The walls 121 and 141 of the downcomers 120 and 140 are preferably formed from flat plates 121a-d and 141 a-d, respectively, that are welded together in a configuration shown herein. The actual construction of the downcomer may vary in accordance with the principles of the present invention. For example, the segmented-angled construction of the downcomer side walls may be modified with more downcomer sections or with fewer downcomer sections, or alternatively, an arcuate or curved construction may be used for the downcomer side walls. Downcomer outlets 122 and 142 are formed between the bottom of the walls 121 and 141 and the inner surface of the tower 12.

Referring still to FIGS. 5 and 6, the tray 130 has an inlet weir 133 positioned around the area directly below the downcomer outlet 122. The inlet weir 133 is preferably an upright plate or strip welded to the planar panel of the tray 130. The lower portion of the downcomer 120 is preferably supported by clips 134 that are welded to the inlet weir 133 and bolted to the lower portion of the downcomer 120.

Still referring to FIGS. 5 and 6, the tray 130 includes a plurality of venting chambers 135 that are disposed in the area of the tray 130 located on the opposite side of the inlet weir 133 from the downcomer outlet 122. The venting chambers 135 each have a plurality of apertures 135a for using the vapor 15 to impart a horizontal flow to the liquid 13 spilling over the inlet weir 133.

Referring to FIG. 6, tray 130 has a plurality of valves 150 arranged in an array throughout active area 131. Valves 150 are preferably a floating type valve sold under the trademark MINI VALVE by the assignee of the present invention and are more fully disclosed in U.S. Patent No. 5,120,474, which is owned by the assignee of the present invention and is incorporated herein by reference. Although not shown in FIG. 6, other conventional fractionation tray valves may be utilized for valves 150, or, alternatively, active area 131 may be formed with an array of perforations or holes instead of valves. The number, diameter, and spacing of valves 150 depends on a variety of factors, including the specific process being performed in column 10 and the properties of liquid 13 and vapor 15.

Tray 130 further includes a plurality of venturi swirl tubes 152 disposed throughout active area 131. As shown best in FIGS. 7 and 8, each venturi swirl tube 152 generally comprises a base tube 154, a riser tube 156, and a separator 158. The base tube 154 rests on the top side 130a of the tray 130. The base tube 154 has an inlet 159 in fluid communication with the area below tray 130, preferably via an aperture 161 in tray 130 below, and coextensive with, inlet 159. Inlet 159 thus allows the entry of vapor 15, or a frothy liquid/vapor mixture, from below the tray 130. The base tube 154 also has a plurality of annular holes 160 proximate the inlet 159 allowing the entry of liquid 13 flowing across top side 130a of tray 130. The base tube 154 further has a plurality of inclined vanes 162 fixedly coupled within its interior and an outlet 164 in fluid communication with the riser tube 156. Inclined vanes 162 may be coupled to the inner wall of the base tube 154 by tack welding or other conventional means. In the alternative to resting on the top side 130a of the tray 130, the base tube 154 may be disposed in the middle of the tray 130, as illustrated by a tray 130' shown in dashed lines in FIG. 7. Further in the alternative, the base tube 154 may be disposed beneath the tray 130, as illustrated by a tray 130" shown in dashed lines in FIG. 7. When the base tube 154 is disposed in the middle of, or beneath, the tray 130, the apertures 160 may be eliminated, and the inlet 159 allows the entry of vapor 15 and the frothy vapor/liquid mixture from below the tray 130.

The riser tube 156 has an inlet 166 in fluid communication with base tube 154, an outlet 168, and a venturi-shaped geometry. As is well known in the fluid dynamics art, the venturi riser tube 156 has a tapering constriction 170 located generally at its midpoint that causes an increase in the velocity of a fluid flowing through the riser tube 156 and a corresponding decrease in the fluid pressure within the riser tube 156. The diameters of the inlet 166 and the outlet 168 are preferably identical, and these diameters are typically in the range of about one inch to about eight inches for most applications of column 10. The diameter of the riser tube 156 at the constriction 170, the throat length L, the entrance cone angle «, below the constriction 170, and the exit cone angle _°<₂ above the constriction 170 depend on a variety of factors, including the specific process being performed in column 10 and the properties of liquid 13 and vapor 15.

The separator 158 preferably comprises a generally planar member movably coupled to the riser tube 156 at the outlet 168. As shown in FIG. 7, such coupling is accomplished via legs 172 that downwardly depend from opposing sides of the separator 158. Each of the legs 172 is received by a corresponding slot 173 in riser tube 156 near the outlet 168. In this manner, the separator 158 is allowed to vertically move from a first position resting on or near the top of the outlet 168 to a second position, indicated by separator 158' shown in dashed lines, offset from the outlet 168. Each of the legs 172 has a lip 174 that abuts against the riser tube 156 to limit the upward, vertical movement of the separator 158. Of course, the above-described movable coupling between separator 158 and riser tube 156 is merely preferred and such coupling may be accomplished via other means.

Although thirteen venturi swirl tubes 152 are shown in the active area 131 of the tray 130 in FIG. 6, this number is for illustration only. The actual number and spacing of the venturi swirl tubes 152 in the active area 131 depends on a variety of factors, including the specific process being performed in column 10 and the properties of liquid 13 and vapor 15. In addition, although not shown in FIGS. 5 and 6, the active area 111 of the tray 110, as well as the active areas of all other trays within tower 12, are preferably formed with valves and venturi swirl tubes in a manner similar to the active area 131 of the tray 130.

Referring now to FIG. 9, the operation of downcomer-tray assembly 100 will now be described in greater detail. Liquid 13 crossing the active area 111 of the tray 110 engages vapor 15 ascending through the valves 150 of the active area 111. The outlet weir 112 controls the flow of liquid 13 that passes from the active area 111 of the tray 110 into the downcomer 120. Liquid 13 flowing over the outlet weir 112 of the tray 110 passes downwardly between wall 121 of the downcomer 120 and the inner wall of the tower 12. The liquid 13 exits the downcomer 120 through the outlet 122 and accumulates on the tray 130 in an area between the inlet weir 133 and the inner wall of the tower 12. Still referring to FIG. 9, once the level of liquid 13 accumulating in the area of the tray 130 between inner wall of the tower 12 and the inlet weir 133 reaches the height of the inlet weir 133, additional liquid 13 exiting the downcomer outlet 122 will cause liquid 13 to pass or spill over the inlet weir 133. Some of the vapor 15 passing upward in the column 10 flows through the apertures 135a in the vent chambers 135 and engages the liquid 13 spilling over the inlet weir 133. The vapor 15 from the venting chambers 135 imparts a horizontal flow vector to the liquid 13 spilling over the inlet weir 133 across the active area 131 ofthe tray 130. The liquid 13 passing over the active area 131 of the tray 130 engages vapor 15 ascending through the valves 150 of the active area 131. Referring still to FIG. 9, the engagement of the liquid 13 passing across the active area 131 of the tray 130 with the vapor 15 ascending through the active area 131 creates a froth 61. The froth or "foam" 61 is a region of aeration in which the phase of the liquid 13 is continuous. The froth 61 extends with a relatively uniform height, shown in phantom by line 63, across the active area 131 of the tray 130. The length of the active area 131 of the tray 130 is governed by the distance between the inlet weir 133 and the outlet weir 132. The outlet weir 132 also controls the flow of froth 61 or liquid 13 that passes from the active area 131 of the tray 130 into the downcomer 140, where the fluid exits the tray 130 for the next process in the column 10.

Referring now to FIGS. 5, 6 and 9 in combination, the downcomer outlet 122 is narrower than the upper region of the downcomer 120, causing a build up in the region of the downcomer outlet 122 of liquid 13 flowing through the downcomer 120. The build up of liquid 13 in the region of the downcomer outlet 122 causes a dynamic seal that prevents vapor 15 ascending through the column 1 from passing through the downcomer 120 instead of the tray 110. A seal is also created by relative vertical heights of the outlet 122 for the downcomer 120 and the inlet weir 133 of the tray 130. A pool of liquid 13 from the downcomer 120 is created between the inlet weir 133 and the inner wall of the tower 12. When the vertical height of the outlet 122 for the downcomer 120 is located near or below the vertical height of the inlet weir 133 for the tray 130, outlet 122 will be immersed in the pool of liquid accumulated between the inlet weir 133 and the inner surface of the tower 12. Because the outlet 122 of the downcomer 120 is at or below the level of a pool of liquid accumulated between the inlet weir 133 of the tray 130 and the inner surface of the tower 12, vapor 15 ascending through the column 10 will be inhibited from flowing through the downcomer 120 and by-passing the tray 110.

Referring now to FIGS. 5 through 9 in combination, at low flow rates of vapor 15, the separators 158 rest on or near the outlets 168 of the riser tubes 156 of each venturi swirl tube 152. As such, the venturi swirl tubes 152 are inactive or closed at such low vapor flow rates. As the flow rate of vapor 15 increases, more and more droplets of liquid 13 become entrained in ascending vapor 15 immediately below trays 110 and 130. At some point, the amount of liquid 13 entrained in ascending vapor 15 becomes so great that vapor 15 begins to cease flowing through valves 150 of the active areas 111 and 131 of the trays 110 and 130, "vapor" flooding the trays. At this point, the pressure drop across the trays begins to increase, the loading of trays begins to increase, and the mass and/or energy transfer efficiency of column 10 begins to decrease.

However, just before this vapor flooding condition occurs, the separators 158 are moved upward by the ascending flow of vapor 15 within the venturi swirl tubes 152 to an offset position from the outlets 168, as shown by the position of separator 158' in FIG. 7. As such, the venturi swirl tubes 152 open and enter an active mode.

In the active mode, the venturi swirl tubes 152 provide several distinct advantages. First, the venturi swirl tubes act as a "relief valve", allowing some of the ascending vapor 15 to bypass the valves 150 and to reduce or eliminate the above- described vapor flooding condition of trays 110 and 130.

Second, the pressure drop within venturi riser tube 156 creates a suction that draws vapor 15 and froth 61 from below the trays 110 and 130 into the inlets 159 of the base tubes 154. When the base tubes 154 rest on the top sides 110a and 130a of the trays

110 and 130, such suction also draws liquid 13 into holes 160 proximate the inlets 159. The drawn-in vapor, froth, and liquid pass through and interact within the venturi swirl tubes 152, increasing the mass and/or energy transfer between the liquid 13 and vapor 15 in the column 10. One should note that such mass and/or energy transfer also occurs if the venturi swirl tubes are formed without base tube 154, so that inlets 166 of the riser tubes 156 are coupled directly to the top sides 110a and 130a of the trays 110 and 130 and are in fluid communication with the area below each of the trays via aperatures 161. Such an alternate embodiment of the venturi swirl tubes 152 also guards against the vapor flooding condition described above and may be attractive for some applications of column 10 due to its simplicity.

Third, the inclined vanes 162 of the base tubes 154 impart a vortex motion to the vapor, froth, and liquid sucked into the venturi swirl tubes 152. This vortex motion increases the contact time between liquid 13 and vapor 15 within the venturi swirl tubes 152, improving the mass and/or energy transfer of column 10. In addition, when several venturi swirl tubes 152 are located proximate an outlet weir of a tray, the vortex motion created by the inclined vanes 162 functions to reduce or eliminate "liquid" flooding within the adjacent downcomer. For example, as the amount of entrained vapor in the froth 61 increases, more of the entrained vapor is released as froth 61 passes through the downcomer 140, opposing the downward path of the froth 61 and the liquid 13 in the downcomer 140. However, as shown in FIG. 6, tray 130 preferably has several venturi swirl tubes 152 located proximate outlet weir 132. As these venturi swirl tubes 152 suck in vapor, froth, and liquid, the vortex motion created by inclined vanes 162 causes the liquid phase to form a rotating, upwardly moving film on the inner surface of riser tube 156. When this film reaches outlet 168, it flows over the walls of riser tube 156 back into the liquid 13 flowing on top of the tray 130. Separated vapor 12 swirls out of outlet 168, as well. In this manner, the froth 61 is "clarified", and liquid flooding in downcomer 140 is reduced or eliminated. From the above, it may be appreciated that incorporating the venturi swirl tubes of the present invention in the trays of a chemical process tower improves the mass and/or energy transfer between vapor and liquid in the tower, reduces or eliminates the flooding problem created by liquid entrained in ascending vapor within the tower, and reduces or eliminates the flooding problem created by vapor entrained in descending liquid within the tower. The present invention provides such advantages without substantially increasing, and in some cases decreasing, manufacturing costs as compared to conventional cylindrical swirl tubes.

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 specific applications of a chemical process tower. In addition, while the venturi swirl tube of the present invention has been described above in connection with a downcomer-tray assembly of a chemical process tower, the present invention is applicable to other contact devices within such towers.

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 contact tray for a vapor liquid process column, comprising: a generally planar member having an active area with a plurality of apertures therethrough; and a venturi swirl tube disposed in said active area.

2. The contact tray of claim 1 further comprising a plurality of said venturi swirl tubes disposed in said active area.

3. The contact tray of claim 1 wherein said planar member comprises a top side and a bottom side, and wherein said venturi swirl tube comprises: a riser tube having a venturi-shaped geometry, an inlet proximate said top side of said planar member and in fluid communication with said bottom side of said planar member, and an outlet; and a separator movably coupled to said riser tube proximate said outlet.

4. The contact tray of claim 3 wherein at low vapor flow rates of said process column, said separator rests in a first, closed position proximate said outlet of said riser tube.

5. The contact tray of claim 4 wherein at a higher vapor flow rate of said process column, said separator moves upwardly to a second, open position offset from said outlet of said riser tube.

6. The contact tray of claim 3 wherein said venturi swirl tube further comprises a base tube having an inlet in fluid communication with said bottom side of said planar member, an outlet in fluid communication with said inlet of said riser tube, and a plurality of inclined vanes fixedly coupled within an interior of said tube.

7. The contact tray of claim 6 wherein said base tube is disposed below said bottom side of said planar member.

8. The contact tray of claim 6 wherein said base tube is disposed above said top side of said planar member.

9. The contact tray of claim 6 wherein said inlet of said base tube is disposed below said bottom side of said planar member, and said outlet of said base tube is disposed above said top side of said planar member.

10. The contact tray of claim 3 wherein, during operation of said process column, said riser tube creates a suction that draws in vapor and froth from below said bottom side of said planar member and through said inlet of said riser tube.

11. The contact tray of claim 6 wherein, during operation of said process column, said riser tube creates a suction that draws in vapor and froth from below said bottom side of said planar member and through said inlet of said base tube.

12. The contact tray of claim 8 wherein said base tube further comprises a plurality of holes proximate said inlet of said base tube and above said top side of said planar member, and wherein, during operation of said process column, said riser tube creates a suction that draws in vapor and froth from below said bottom side of said planar member and through said inlet of said base tube, and that draws in liquid from a top side of said planar member and through said plurality of holes.

13. The contact tray of claim 2 further comprising a plurality of valves disposed in each of said plurality of apertures.

14. The contact tray of claim 13 wherein said active area further comprises a plurality of venting chambers.

15. The contact tray of claim 3 further comprising a plurality of valves disposed in each of said plurality of apertures.

16. The contact tray of claim 6 further comprising a plurality of valves disposed in each of said plurality of apertures.

17. A swirl tube for positioning on a contact device within a vapor liquid process column, comprising: a riser tube having a venturi-shaped geometry, an inlet, and an outlet; a separator; and means for movably coupling said separator to said riser tube proximate said outlet.

18. The swirl tube of claim 17 wherein said movably coupling means comprises: first and second legs depending from said separator and toward said outlet of said riser tube; and first and second slots formed in said riser tube proximate said outlet of said riser tube and receiving said first and second legs.

19. The swirl tube of claim 18 wherein each of said first and second legs has a lip for limiting the movement of said separator away from said outlet of said riser tube.

20. The swirl tube of claim 17 further comprising a base tube having an inlet, an outlet coupled to said inlet of said riser tube, and a plurality of inclined vanes fixedly coupled within an interior of said base tube.

21. The swirl tube of claim 20 wherein said base tube further comprises a plurality of annular holes proximate said inlet of said base tube.

22. A method of interacting an ascending vapor and a descending liquid within a chemical process tower, comprising the steps of: supporting a tray within said tower, said tray having an active area with a plurality of apertures therethrough, a top side, and a bottom side; forming a swirl tube on said top side of said tray in said active area, said swirl tube having a venturi-shaped geometry, an inlet in fluid communication with said bottom side of said tray, and an outlet; drawing vapor and froth from below said bottom side of said tray through said inlet of said swirl tube for interaction therein.

23. The method of claim 22, wherein: said step of forming said swirl tube comprises forming a separator movably coupled to said swirl tube proximate said outlet; and said step of drawing vapor and froth comprises moving said separator from a closed position proximate said outlet of said swirl tube to an open position offset from said outlet of said swirl tube at high vapor flow rates of said process tower.

24. The method of claim 23 wherein said step of drawing vapor and froth reduces vapor flooding of said tray.

25. The method of claim 23 wherein said step of forming said swirl tube comprises forming a plurality of said swirl tubes in said active area of said tray.

26. The method of claim 23 wherein said step of forming said swirl tube comprises forming a base tube having an inlet in fluid communication with said bottom side of said tray, an outlet in fluid communication with said inlet of said swirl tube, and a plurality of inclined vanes fixedly coupled within an interior of said base tube.

27. The method of claim 26 wherein said step of forming said swirl tube comprises disposing said inlet of said base tube on said top side of said tray, and forming a plurality of holes proximate said inlet of said base tube.

28. The method of claim 27 wherein said step of drawing vapor and froth further comprises drawing liquid from said top side of said tray through said plurality of holes for interaction with said vapor and froth within said swirl tube.

29. The method of claim 26 wherein said step of drawing said vapor and froth comprises drawing said vapor and froth through said inclined vanes to impart a vortex motion thereto.

30. The method of claim 28 wherein said step of drawing said vapor, froth, and liquid comprises drawing said vapor, froth, and liquid through said inclined vanes to impart a vortex motion thereto.

31. The method of claim 29 wherein said tray has an exit downcomer, and wherein said step of forming said swirl tube comprises forming a plurality of said swirl tubes proximate said exit downcomer to reduce liquid flooding in said downcomer.

32. The method of claim 23 wherein said step of drawing vapor and froth comprises utilizing said venturi-shaped geometry of said riser tube to create suction.