US 3466151 A
Description (OCR text may contain errors)
SCpLQ, 1969 $|ARD ETAL FLUID EXCHANGE COLUMN 4' Sheets-Sheet 1 Filed Sept. 22, 1964 IN VE N TOPS L was S/cARD BY CLAUDE D4 114mm) arrow/v5 Y5 p 1969 1.. SICARD A- FLUID EXCHANGE COLUMN 4 Sheets-Sheet 2 Filed Sept. 22, 1964 nvvs/vro s Laws SIC/JED Gun 05 DAUMHRD A TTORNEYS Sept. 9, 1969 L, ICAR ETAL 3,466,151
FLUID EXCHANGE COLUMN Filed Sept. 22, 1964 4 Sheets-Sheet 5 if w 1 I I I I INVENTORS Lou/5 S/c/JRD CAM/05 DAL/MAPD e4 TTOPNE Y5 Sept. 9, 1969 L slCARD ETAL 3,466,151
' FLUID EXCHANGE COLUMN Filed Sept. 22, 1964 4 Sheets-Sheet 4 INVEN TOPS Lou/5 516A RD CL UDE flAUM/IRD A T TOIQNE Y5 United States Patent Int. Cl. lion 9/02 US. Cl. 23-288 11 Claims ABSTRACT OF THE DISCLOSURE A column for the exchange of fluid flowing through packing elements contained in the column and for the uniform repartition of the fluids over each packing element. Each of the packing elements includes a body of packing material having a porous intricate structure and at least one partition wall dividing the material into a plurality of thin longitudinal strips to suppress the radial components of the flowing fluids. The packing elements are supported by at least one redistribution platform sealing held in the column, which platform has means for spacing the packing elements from the platform so as to define a reservoir for fluid therebetween.
The present invention relates to fluid exchangers and particularly to exchangers of the column type.
In a vertical exchange chamber, or column, when it is desired to effect a transfer of material between two phases under the best possible conditions, it is necessary to increase the contact area between the two phases while maintaining the surface levels of the concentrations flat and perpendicular to the axis of the columns.
Furthermore, it is necessary to obtain an increased temperature gradient for these concentrations along this axis, while permitting only a small pressure drop.
In a distillation column, the surface levels of the concentrations should be the horizontal surfaces along which the liquid and the vapor are in equilibrium. In order that the column operates effectively, it is necessary that any two equilibrium surfaces (corresponding to the separation of the mixture by a theoretical plate) be as close as possible.
In present devices, it is common that preferential paths for the two phases will be established along the column. This arrangement prevents a large portion of the potential exchange region from participating in the exchange process because it experiences an excessively rapid vapor current or, on the other hand, because it is flooded by large masses of liquid. In either case, the two phases are not in contact in these regions and the portions of the heat exchange region in which these flow conditions are established, are not fully utilized. In general, such a condition is uncorrectable and if it appears at a given point, it will continue to exist from that point onward.
Experience has shown that certain specific conditions must exist for the eflicient operation of a jacketed exchanger column. Firstly, the structure of the exchange region must be such as to present a large surface area per ice they should be easy to install in the column and should be resistant to chemical changes during the operation of the exchanger.
In so far as concerns the conditions under which an exchanger should be put into operation, the device can only achieve maximal effective operation if certain conditions are fulfilled. A uniform distribution of the liquid phase must be assured at the top of the column, below the level of the input to the device. A uniform distribution of the velocities of the gaseous phase must be had below the packing structure. There must be a means to restore the uniform distribution of both phases at any point where it might be upset by an external cause such as: change in cross-section, addition of secondary piping, insertion of measuring devices etc. Finally, all possibility of the creation of a preferential path must be eliminated by the provision of means adapted to effect a redistribution of both phases after the traversal of a certain length of the exchange structure.
The present invention provides structure which eliminates the shortcomings of the prior exchange units by conforming with the conditions set forth in the two preceding paragraphs and by eliminating the possibility of the initiation of two phenomena which have been discovered during the course of tests and which contribute in a large measure to a reduction in the efliciency of prior art exchange packings.
These phenomena are:
The existence of radial components of phase flow velocity; and
The progressive concentration of the liquid phase, along its flow path, into a region having a small cross-sectional area perpendicular to the length of the column, after the liquid has traversed a certain portion of the packing. These phenomena substantially contribute to the creation of preferential paths for the two phases.
In accordance with this invention, the packing elements, which consist of solid elements having intricate structures through which the fluids flow, are divided into thin vertical slices by at least one partition which serves to eliminate the radial components of the flow velocities of the fluids and which urges these fluids into vertical paths. The exchange or packing elements thus formed are combined with a plurality of platforms, each of which has a plurality of passages passing therethrough, each passage being reserved for one or the other of the fluids, and all of the passages being distributed in the most regular fashion possible across the surface of each platform. These platforms can be disposed not only in the upper portion of the column, but also between two groups of exchange elements in such a way as to support the elements disposed ple interwoven corrugated wires or threads. In the deunit volume and this surface area must be uniformly disscription to follow, reference will be specifically made to an exchange device, but this is intended to be illustrative and not limitative.
Various other characteristics of the present invention will become readily apparent from the following detailed description of various embodiments of the present invention.
These various embodiments are shown in the accompanying drawings in which:
' FIG. 1 is a longitudinal cross-sectional view of a distillation column employing the exchange packing structure of the present invention;
FIG. 2 is an axial crosssectional view, taken along the plane 11-11 of FIG. 1, to an enlarged scale, showing one form of exchange packing element of the present invention;
FIG. 3 is a perspective view showing the exchange packing element of FIG. 2 at an intermediate point in its fabrication;
FIG. 4 is an axial cross-sectional view, similar to that of FIG. 2, showing a second embodiment of applicants novel exchange packing element;
FIG. 5 is a perspective, partially cut-away view of the element of FIG. 4 at an intermediate point in its fabricatlon;
FIG. 6 is an axial cross-sectional view of the column of FIG. 1, taken along plane VI-VI of FIG. 1 and to an enlarged scale, illustrating one form of flow redistributing platform for use between exchange elements:
FIG. 7 is a longitudinal cross-sectional view, taken along the plane VIIVII of FIG. 6, showing a portion of the exchange column;
FIG. 8 is a cut-away cross-sectional view, showing a portion of a second type of flow-distributing platform,
FIG. 9 is a cut-away perspective view showing an exchange element of the column, performing as a mist eliminator.
Referring first to FIG. 1, there is shown a distillation column representing one type of device readily adapted to be equipped with the exchange means of the present invention. This column is constituted by a series of aligned tubular envelope segments 1, fastened together by mating flanges, a dome-shaped upper cover element 2, and a cup-shaped base 3.
Within these segments are stacked a series of packing elements 4, each being separated into groups of several elements by flow-redistributing platforms, several of which, designated by the reference numeral 5 and shown in detail in FIGS. 6 and 7, are simply interspersed between successive groups of elements, and others of which, designated by the reference numeral 6 and shown in FIG. 8, are attached between the connecting flanges of two adjacent envelope segments 1. Between the uppermost cylindrical envelope segment and upper cover element 2 is attached a distribution platform 7 which is structurally analogous to redistribution platforms 6. Finally a packing element 8, specially adapted to the requirements created by its location, is housed in the upper end of base 3, below the lowest redistributor platform 6, so as to constitute a means for suppressing the formation of or for removing drops of liquid suspended in the gaseous phase.
The packing elements 4 and 8, as well as the platforms 5, 6 and 7, form the basic structure embodying the present invention. But, for the sake of clarity all of the operations of which a distillation column is capable will be described below without going into the details of how to perform these operations.
The above-mentioned operations comprise: absorption; cleaning; liquid-to-liquid extraction; division between two liquid phases; humidifying of gas, drying of vapor; placing two vapor phases in contact; reheating of a gas (in which case the packing elements are disposed in a heating jacket); placing of the various phases in contact in the presence of catalysts, and drying of a vapor containing drops of liquid.
It has been found that better results are obtained by dividing the solid bodies of intricate configuration into thin vertical slices, each slice forming one heat exchange element 4. These bodies are preferably formed by a sheet having a plurality of wires or threads which are interwoven and either corrugated or crimped.
According to a first embodiment of the invention shown in FIGS. 2 and 3, the partition is constituted by a continuous strip 9 which is more or less rigid and impermeable. This partition strip and at least one woven strip (two woven strips 10 appear in these figures) are rolled together into a spiral having a uniformly increasing radius. There is thus formed a passage having a spiral crosssection occupied by the woven strips and through which the two phases flow.
According to one variation of this embodiment which is not shown in the drawings, the partition is made up of a plurality of cylindrical sleeves arranged concentrically and between which are interposed cylindrical sleeves of woven, corrugated strips.
According to a second embodiment of the packing element as shown in FIGS. 4 and 5, the partition is constituted by a plurality of semi-rigid, impermeable or semiimpermeable sheets 11, interposed between successive layers 12 of woven corrugated sheets. Each layer 12 may comprise one or several sheets and in the case of several sheets, the sense of the corrugations of one sheet may differ from that of the adjacent sheet.
In order for these elements to function effectively, it is necessary that the distance between two successive partitions, or two successive turns of the spiral partition of FIGS. 2 and 3, be relatively small with respect to the diameter of the column. The partitions will then serve to eliminate the radial components of the instantaneous flow speeds of the fluids at any point and restore the flow to a two dimensional phenomenon (tangential and longitudinal).
These vertical partitions thus channel the flow of the vapor and the liquid and thereby promote their tendency to encounter one another. As a practical matter, they permit a column in industrial use to be treated as a parallel assembly of a large number of small-diameter columns.
The partitioning of the present invention thus permits the assurance of a rigorous uniformity of the packing structure, because one need only, during the construction of elements 4, exercise a precise control over the distance existing between successive layers. Since the layers are uniformly spaced (spirally, concentrically or in a planar manner), they assure a uniform division of the exchange surfaces throughout the entire volume of the packing element and a uniform distribution of the zones wherein the fluids are retained.
It thereby results that each packing element 4 is perfectly homogeneous on a macroscopic scale, which condition is necessary for the avoidance of local deviations in flow-rate, such deviations being capable of rapidly producing preferential fluid paths along which would flow rapidly increasing quantities of fluids.
Moreover, tests have positively shown that, with the structure of the present invention, the variations from one point to another in a plane perpendicular to the direction of fluid flow are reduced to one-fifth of the value which they would have if vertical partitions were not provided in packing units 4. There is thus obtained a considerable reduction in the equivalent height of a theoretical plate (E.H.T.P.), without any accompanying increase in the pressure drop across each packing unit.
The edges of the partition or partitions may be smooth, notched, scalloped, etc. in the latter case such edges can serve to aid the fitting together of two adjacent packing units 4.
These partitions may be constituted by an impermeable porous or semi-permeable material. In the latter case they may be made of a fabric which is woven, molded or expanded, or of a metal sheet which is perforated or cut, etc., so that it will aid the exchanges by permitting a diffusion between one layer of corrugated packing material and another, while at the same time carefully controlling the magnitude of the diffusion.
The surfaces of the partitions could be smooth (of laminated metal sheets, for example), rough (metal sheets of rough texture or which have been chemically pitted, for example) or specially finished (metal which has been waflied, stamped, honeycombed, etc.).
The partitions are preferably rigid, but may be semirigid (metal which has been drawn but not tempered, for example) or flexible (thin, tempered metal sheets).
Furthermore, the partitions may be relatively malleable in order to be able to conform very closely to any irregularity in the packing layers of the exchange units.
The partitions may be of metal or of any other suitable material. Their surfaces could also be subjected to any type of thermal, chemical or physical treatment, appropriate to the nature of the fluids with which they will come in contact and to the conditions of the exchange reaction.
Finally, the partitions could be attached to a more chemically inert material and, in this case, the layer of this material could be deposited by any appropriate means such as those utilized in electroplating (galvanizing, chromium plating vacuum deposition, spraying of a layer of alumina or other ceramic plating by means of a blow-tool, pyrolysis (carbon depositing), etc. The partitions could also be attached to a layer of material which will give them properties of a catalyst for any chemical reactions which it may be desired to produce in the exchange regions. In such a case, one may form on the partitions, a deposit of alumina, powdered nickel, spongy platinum, etc.
The characteristics of theoretical partitions as described above, apply equally well to the lowermost packing element 8 of the column, which element is shown in FIG. 9. In this element, the sheets forming the active exchange layers 13 could have a relatively simple structure. Radially adjacent sections of these layers are separated by a spiral partition sheet 14 which is analogous to the spiral sheet 9 previously discussed. Partition 14 has a lower edge 15 in the form of a drain whose width increases and whose elevation decreases as one moves outwardly along the spiral. In other words, as FIG. 9 clearly shows, the lower edges 16 of layers 13 are situated above the lower edge of partition 14 and the drain 15 which forms this lower edge unwinds in the form of a descending helix following the surface of an imaginary cone 17 which descends towards :the periphery of unit 8. This helical drain, or gutter, thus has a continuous slope and a continuously increasing width as it descends, which arrangement permits it to drain off the liquid phase under the best conditions. Drain 15 empties over an annular collection surface 18, formed in base 3 and communicating with an outlet conduit 19, this arrangement serves to recover all of the drained, condensed liquid.
The packing element 8 thus described can be utilized as a device for removing suspended liquid from a gaseous atmosphere at the base of a column such as that shown in FIG. 1, in the top of a boiler, as a decompressing stage in a petroleum cracking tower, etc.
It should be evident that the edges of the vertical partitions could have differing configurations. These edges are situated, generally, in horizontal planes and their vertical lengths are made to be slightly less than that of their associated packing materials or 12) in order that the packing material of one unit extends slightly beyond their partitions in order to effect a good contact with the similar materials of any adjacent, contiguous units.
In accordance with another feature of the present invention, the vertical partitions of units 4 are combined with horizontal partitions constituted by distributing platforms 5 and 6. In effect, despite the homogeneity of element 4, a uniform distribution of the fluid phases cannot be preserved indefinitely, i.e., over a substantial height, by these elements alone; it is equally impossible to maintain the flatness and horizontal orientation of the surfaces of equilibrium existing between the phases over an indefinite height.
In order to re-establish these desired conditions, distributing platforms 5 and 6 are disposed in the column so as to divide the units 4 into groups of several units each, the height of each unit corresponding to the maximum deterioration in uniform fluid distribution which can be tolerated. These platforms permit, in addition to that which will be described below, the complete mixing of the two phases in order to permit each of them to be redistributed uniformly in the vertical regions situated above and below the platform. Such platforms can be used, not only with packing units, such as those described herein, but equally as well with columns containing other types of packing devices.
FIGS. 6 and 7 show that each of the distribution platforms 5, 6 or 7 is comprised of a plate 20 extending perpendicularly to the axis of the column and entirely across the region defined thereby. This plate is rigidly fastened to a rim element 21, extending above it so as to form a basin 22 in which liquid will accumulate until reaching a certain depth, which depth depends on the flow rate existing within the column. The rim element 21 only exists for the platform 5 while the same function is carried out by the tubular element In, situated above the platform, for the interspersed platforms 6 and the upper platform 7 (FIG. 8). The liquid accumulated in basin 22 intermixes so as to become uniform throughout its entire volume and is uniformly distributed to heat exchange unit 4n-I-1, situated directly below the plate, by a plurality of holes 23 pierced in plate 20. The number, form, diameter and arrangement of holes 23 are determined experimentally as a function of the operating conditions of the column. They must be arranged so that all of the holes support a flow when the column is operating at a minimum flow rate and so that at maximum flow rates, the level of liquid in basin 22 will become stabilized at the level of the upper edges of funnels 24 rigidly and sealingly connected in plate 20 in order to permit the upward passage of vapor. There is thus created a large reserve of liquid which will serve to eliminate many of the difficulties which might otherwise result if plate 20 were not perfectly horizontal. This reservoir eliminates variations in the supply of liquid from one point to another along the plane of the plate, thus eliminating the major problem encountered from such an improper orientation of the plate.
Each of the holes 23 arranged for the uniform redistribution of liquid comprises a downwardly projecting nozzle which serves to correctly guide the liquid streams in a vertical direction and to prevent the liquid from adhering to the lower surface of plate 20. These nozzles thus produce liquid streams which are both stable and accurately controllable.
The funnels 24 each present a large horizontal crosssection for the passage of rising vapor and are uniformly distributed over the surface of plate 20, which arrangement permits the plates to produce only a small pressure drop compared with that normally produced across the packing elements. These funnels are covered by cap means 25, which function to divert the liquid flowing from the packing element 4n, situated thereabove, into basin 22 and to prevent this liquid from flowing directly onto the packing element 4n+1. Thus, all of the liquid coming from element 411 is mixed with the liquid contained in basin 22. The cap means 25 are maintained a fixed distance above the upper ends of funnels 24 by two supports 26 and 27 which are sufficiently sturdy to insure that the cap means can easily support the packing elements 411, 411-1, 4n2, etc., situated thereabove. In this way, the plurality of cap means 25 associated with each plate, form a well perforated ceiling for supporting the packing elements resting thereon.
In the case of platforms 6 and 7 the plate 20 is interposed between flanges 2811 and 29n+1 (for platforms 6-) or between the flanges of upper envelope 1.1 and headpiece 2 (for platform 7). Impermeable seals 30 are disposed between each plate and its associated flanges and the assembly thus formed is fixed by means of collars 31, 32 and associated bolts (not shown; their location can be easily discerned from FIG. 8) or by any other suitable means.
In the case of platforms 5, as is shown in FIGS. 6 and 7, a toroidal washer 33, made of flexible material, is disposed around rim 21 and against plate 20. This joint is pressed down by a tubular sleeve 34 which is in turn urged downward by clamp means which tend to firmly force washer 33 against both plate 20 and the inner surface of envelope 1, so as to cause it to form an impermeable seal with these latter elements. These clamp means could be constituted, as is shown in these figures, by bolts 35 traversing plate 20 and the two arms of a U-shaped force transmitting element 36, the ends of these arms resting respectively against the upper edge of sleeve 34 and the shank of bolts 35, the latter passing through a suitably shaped notch 37. The bolts 35 also permit bracing feet 38 to be attached to the lower surface of plate 20. These feet in turn rest on the packing element 4n+1 situated therebelow.
Whatever form the platforms 5 and 7 may take, their combination with the vertical partitioning of packing elements 4 assures the existence of the following conditions:
The uniform distribution of the liquid phase, passing into the packing element situated directly below each platform;
The uniform distribution of the vapor phase ascending into the packing element situated directly above each platform;
The homogenization of the liquid phase in the basin of each platform; and
The homogenization of the vapor phase in the free space below each platform due to the fact that this space permits the creation of convection currents and pressure equalization in the gaseous phase which may aid in the transfer of material between the phases and in the distribution of these phases.
This arrangement also facilitates the sampling of liquid from predetermined levels in the column by the drawingoff of such liquid from the basins in the various platforms.
Moreover, these horizontal partitions form support surfaces for groups of packing elements and thus help to prevent the possible crushing of these elements under the weight of the uppermost elements.
The present invention is, of course, not limited to the specific exemplary forms shown and described herein, since many variations and modifications would occur to one skilled in the art without departing from the spirit thereof. In addition, the use of the novel packing structure of the present invention is not limited to distillation columns, but may be incorporated in any type of column in which it is desired to produce a transfer of material between two phases or in any type of chemical reactor designed to place two or more phases of diverse types in contact in order to produce a chemical reaction. It should therefore be understood that the coverage of the present invention should be limited only by the scope of the appended claims.
1. A column for producing an exchange between a plurality of fluids comprising in combination: a tubular shell open at both ends; a plurality of packing elements through which said fluids must pass disposed within said shell; each of said packing elements including a body of packing material in sheet form having a porous intricate structure, and at least one fluid impermeable or semipermeable, longitudinal, vertically extending partition wall in contact with said material dividing it into a plurality of vertically disposed thin longitudinal slices so as to suppress the radial components of the fluids flowing therethrough; at least one redistribution platform for redistributing said fluids sealingly held in said shell below said packing elements and having means for supporting said packing elements a fixed distance above said platform to thereby form a fluid reservoir for fluid between said platform and said packing elements.
2. A device as recited in claim 1 wherein the surfaces of said partition wall are treated in accordance with the nature of said fluids.
3. A device as recited in claim 1 wherein said one partition wall is made from a malleable material so as to permit it to conform closely to the configuration of said packing material.
4. A device as recited in claim 1 wherein said one partition wall is made of porous material for permitting the diffusion of fluids between adjacent ones of said slices of packing material.
5. A device as recited in claim 1 wherein said one partition wall is treated so as to act as a catalyst for a chemical reaction between said fluids.
6. A device as recited in claim 1 further comprising a body of catalytic material supported on said partition.
7. A device as recited in claim 1 wherein at least one edge of said partition wall is cut in an irregular manner in order to aid the fitting together of adjacent packing elements.
8. A device as recited in claim 1 wherein said partition wall is longitudinally shorter than its associated packing material for improving the contact between the packing materials of adjacent packing elements.
9. A device as recited in claim 1 further comprising a plurality of sealed joints connected to a plurality of platforms disposed between said packing elements for attaching these platforms directly to said tubular shell.
10. A device as recited in claim 9 wherein said platforms disposed between packing elements comprise: at least one funnel having a large cross section for the passage of ascending fluids; and cap means disposed at a distance above each said funnel for supporting said packing elements placed above said cap means and for diverting descending fluid from said funnel.
11. A column for producing an exchange between two fluids comprising: a tubular shell open at both ends; a plurality of packing elements through which the fluids must pass disposed within said shell; each of said packing elements including a body of packing material having a porous intricate structure, and at least one vertical partition wall in contact with said material dividing it into a plurality of thin longitudinal slices so as to suppress the radial components of the fluids flowing therethrough and at least one of said packing elements having a vertical partition which is longitudinally longer at one of its ends than its associated packing material and comprises at said end a helical gutter for recovering fluid which has passed therethrough.
References Cited UNITED STATES PATENTS 1,621,728 3/1927 Jordan 261-l13 2,526,657 10/1950 Guyer 23288 2,809,818 lO/l957 Munters.
2,841,421 7/ 1958 Heere 26l1 14 2,887,456 5/ 1959 Halford et al. 23288 3,094,575 6/1963 Peterson 261-114 2,546,479 3/1951 Sodano.
JAMES H. TAYMAN, 111., Primary Examiner US. Cl. X.R.