CA1175343A - Tower packing elements - Google Patents

Abstract

Abstract of the Disclosure A randomly packed bed in a tower or column to prevent nesting of the packing elements and to improve physical stability and efficiency. Each packing element is a curved strip with reinforcing ribs and with one or more integral tabs or tongues depending downwardly from slots spaced longitudinally of the strips. Multiple rows with slots may be provided along the strip. The strips are perforated throughout their entire area to provide improved drainage and improved interlocking and improved internal liquid distribution in the packed bed.
Point-to-point contact between packing elements, substantially non-varying resistance to fluids flowing and improved mass transfer performance resulting from a more uniform packing density are assured.

Description

3~3 This invention relates to novel details pertaining to tower packing elements of the dumped type. As is well known, these packings are commonly used in distillation, :gas absorp-tion and related operations. Specifically, the dumped packings are usually charged into vertical towers in which they provide a skeleton along which it is endeavored to pass liquid downwardly, while through the interstices between the individual packing elements, gases or vapors are passed upwardly. Thus with the liquid stream finely divided over a major portion of the dumped packings, mass transfer will occur between the liquid and vapor phases.
In order to be effective to bring about such a mass trans-fer exchange between the flowing phases, a dumped packing must exhibit a large number of mechanical as well as physical proper-ties. These properties are described in considerable detail inthe technical as well as patent literature, and to enumerate even a modest number of the many publications and patents which are concerned with this would be laborious. However, in order to provide an introduction, see "Tower Packings and Packed Tower Design" written by me and published in 1953 by "The United States Stoneware Company", Akxon, Ohio. As far as a patent is concerned that describes the required properties of dumped packings in an instructive manner, reference is made to my U. S. Patent No.
4,203,934-Without reciting all the required qualitites which the ultimate packing should comprise, let it be emphasized that one of the most important properties which a dumped packing must have is mechanical strength. This is especially so with packings made of plastics when these are used at elevated temperatures. Since many plastic substances will tend to soften under elevated tem-perature use, plastic packings will frequently become deformed : -2 - ~

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~7~ 3 when used in a high temperature service, which will bring about a deterioration of the geometric shape with the result that the effective packing surface or gas-liquid contact surface will decrease.
Another important attribute which the ultimate packing should have is to provide a maximum available surface area along which the liquid can descend, divide into thin rivulets to create liquid films, and in this hi;ghIy subd~ivided state contact the ascending gases or vapors.
A third very important attribute of the ultimate dumped tower packing is that the resulting packed bed should impart a high state of turbulence on the ascending gas or vapor and there-by bring about enhanced mass-transfer performance.
With these three importa~t aspects and requirements of the ultimate dumped tower packing it has been found entirely un-expectedly and surprisingly that in tower packings of the open curved strip type with curvature essentially in a single direction such as are described in my U. S. Patent No. 4,203,934 dated May 20, 1980, all three key qualities in dumped tower packings may be achieved;by a proper choice and arrangement of baffles and ribs in the parent piece. Whereas the prbvision of baffles and ribs ; may be used wlth whole ring-type packings or other shapes, it was found particularly useful and advantageous to have the novel baf-fling associated with the open ended strip structures which are described ln my U. S. Patent No. 4,203,934.

539~3 Having ~hus described the essence o my inven~ion, the accompanying drawings will serve the purpose of further exempl~
ification and description without lirniting the scope of the in~
vention or the claims ~hereto, wherein:
Figure 1 is a sectional front elevational view of a packing element embodying the invention;
Figure 2 is a side elevation of the packing elenlent shown in Figure 1:
Figure 3 is a sectional front elevation showing a packing element e~ibodying various special features of the invention;
Figure 4 is a front elevation of another embodiment of the inven~ion;
Figure 5 is still another modification of ~he invention, and ; Figure 6 represents still another form of the invention.
Referring now to Figure l, the arcua~e wall of ~he packing element is denoted by numeral 1. Numeral 2 denotes tongues de-pending inwardly from the ends of slots 3, contained in the open ended curved strip. As will be seen, ~he open ended strip is ,~ .
essentially semi circular and extends through an angle of abou~
180 degrees. Tt is; of course, understood that the open ended strip could comprise any other open-ended shape, such as a hyperbola, parabola or ~he like, and extend through an angle;of from 90 to more or less 180p without influencing the spirit of ~he inven~ion.
It will be seen that numeral 4 denoi:es a baffle depending downwardly from the open ended curved strip surface, pointing toward the center of the curved strip. It will be noted that the depth of the baffle is uniform over its en-~ire course and is denoted by letter "R". On the other hand, the largest expanse of the ba~fle is S;3~3 denoted by letter "D", it has been found that in order for the baffles or ribs to be effective to bring about an important additional measure of mechanical strength, as weIl as add materially to the contact area of the packing element and thirdly provide additional turbulence to the flowing liquid and gas or vapor streams, it was found desirable that the ratio of the quantities D/R should not be greater than six. On the other hand, it has also been found that the ratio of D/R should not be smaller than 2.5, without having adverse effects. Thus for most favorable results, it was found that D/R should var~ between 5.S and 3Ø
A side elevation of Figure 1 is shown in Figure 2. The packing wall of the element is denoted by numeral 5. The slots in the element are indicated by numeral 6. A total of three ribs are shown, identified by numeral 7. The distance between the ribs or baffles is indicated by letter "W". Just as there is a critical relationship between quantities "R" and "D", as outlined in connection with Figure 1, a critical relationship does also exist between "W" and "D" for which results are best. Thus it i5 noted that the ratio of D/W should not be greater than three, nor ; 20 less than one. However, for most favorable results the ratio of ~/W should be between 2.5 and 1.5.
Figure 2 contains drainholes, indicated by numeral 8. Ow-ing to the relative considerable width "R" of the baffles, there would be an appreciable accumulation of liquid hold-up during any typical operation that would interfere unfavorably with the operat-ing efficiency of the packing. Moreover, this liquid hold-up would in many instances of inclination of the packing in relation to the horizontal position prevent the packing from draining completely.

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~ ~5 ~ ~ 3 Thus~without drain holes, ~here would be unavoidable liquid con~amination if the packing was used successively with differen~ liquid systems.
Normally the liquid drain holes would be relatively small perforations, either circular or otherwise, spaced primarily on both sides of the ba~fles.
Figure 3 shows a typical ~rontal elevation of a packing element, the surface of which is denoted by numeral 9. The baffle is identified by numeral 10, and it appears ~hat drain holes 11 may also be provided in the baffles.
There are additional features which may be provided in the baffles. Thus the ends of the baffles may be pointed downward, as shown by numeral 12. This will encourage a coordinate liquid run-off o~ liquid from one packing element to a neighboring packing element, by virtue of the additional point-to-point contact which is achieved 15 between neighboring packing elements. The drainholes 8 of Figure 3 in the strip also assist in interlocking o the packing elements 8uch as wi~h the pointed parts o baf~les 12 or ~he corners of ~he strips.~Also they form ~vulets to create liquid films.
The rims of the baffles may be serrated as shown by numeral 13, 20 to encourage drop formation, or the baffles may carry grooves a~
~: shown by numeral 14, whicb would likewise assist wi~h dropwise liquid :
;~ run-off, C~nsidering the actual increase in surface area that will be obtained by providing a typical packing element of two inches diameter 25 and two inches width with three baffles, each of 0.5 inch of depth, it is noted ~hat the addi~ional surface area contribu~ed by three baffles amounts to about 33 percent of the total surface area of the piece.

~.~ 7 5 3 ~ 3 Figure 3 shows a Lypical s~ctlon~l ~rontal elevation of a packing element9 the surface of which is denoted by numeral 9.
The baf~le is identified by numeral 10, and it appears ~ha~ drain holes 11 may also be provided in ~he baffles.
S There are additional features which may be provided in the baffles. Thus the ends of the baffles may be pointed downwardly, as.show~ by numeral 12. This will encourage a more coordina~ed liquid run-off o~ liquid from one packing element ~o a neighboring packing element, by virtue of the additional point-to-point contact which is achieved between neighboring packing elements. Poin~s 12 will also bring about addi~ional in~erlockin~ and grea~er bed stability, by engaging drain holes 8, reer~ed to in connection with Figure 2.
The rims o~ the ba~fles may be serra~ed as shown by numeral 13, to encourage drop formation, ox ~he ba~fles may carry grooves as shown by numeral 14, which would likewise assist wi~h dropwise liquid run-off.

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It.will be noted that baf~le 10 proceeds in a direction along he path of curvature of the packing element.

;~ 20~ : Whereas this is generally the most frequen~ly prac~iced : construction, it has also been observed that ba~fles which ~proceed transversely offer certain important advantage~ as ~a~ as performanc~ is concerned, T~us ba~fle or ~ong~e lS proceeds transversely, poinking away 25 from the center of ~he packing elemen~, and is seen to connect to the rem~inders of the walls ~hat make up the windows or slots 16.
By providing such a secondary baffle, much more mechanical streng~h is imp~rted to the elemen~ and additional points of contac are provideq in the packed bed be~ween adjoining paeking elements, Finally, by placi~g a transverse baf~le or tongue in~o such a.

t7~ 3 position, a natural path for liquid flow inside the bed is provided, resulting in improved mass transfer.
Besides having transverse baffles or tongues in the posi-tion as shown by 15, other transverse baffles or tongues ma~ be provided. Thus baffle or tongue 17 is sidewise displaced and attached over its entire length to the surface area 16 of the packing element, pointing away from the center of the packing element. Similarly, baffle or tongue 18 is likewise in touch over its entire length with the surface area of the packing ele-ment, however baffle or tongue 18 is seen to point toward theinside of the packing element.
It will be noted that in Figure 3, tongues l9 and 20 are shown to depend from slots 16 and 21. It will be noted that tongues 19 and 20 are longer than the slots from which they depend. It has been found important to have a large degree of freedom in respect to the choice of length of the tongues in rela-tion to the slots from which they appear to depend. Thus general-ly with longer tongues a more uniform spacing of the elements in the bed was observed to result, which was noted to have significant favorable effect upon the uniformity of penetration of the bed by ; the irrigating liquid. Thus, generally speaking, enhanced mass transfer was observed to occur with tongues that are longer than the slots from which the tongues depend.
In some instances, however, it has also been useful to provide tongues which are shorter than the slots from which they depend. This, not shown in any of the Figures, would occur in such instances where a packing element embodies a large number of tongues, and where, due to space dictations, only small tongues can be provided here or there. It must be understood that addi-tion of tongues which are smaller than the slots from which theydepend will in no way limit the present invention.

~75~3 As far as manufacture of the pieces is roncerned, they are usually molded when made of plastics. Thus the way is entirely open to provide tongues of any lengths, provided there is no steric hindrance in the packing element. Furthermore, it is noted that wi~h this general me~hod of manufacture, the material which does cons~itute the tongues does not come from the material missing from the slots. Hence, the ma~erial which is missing rom the slots is not related in any way to the material that comprises the tongues. Hence, the slots and depending tongues are formed entirely independently from one another.
Considering the actual increase in surface area that will be obtained by providing a typical packing element of two inches ; diameter and two inches width with ~hree baffles, each of 0.5 inch of depth, it is noted that the additional surface area lS ~contrlbuted by three baffles amounts to abou~ 33 percen-~ of the otal surface area of the piece, which is noted to be quite appreciable. Thus provision of the baffles as described in the invention will not only provide additional strength, but will add much surface area as well, and through their arrangement 20~ provide more fluid turbuIence and thus better mass ~ransfer.
Ano~her arrangement o baffles is shown in Figure 4. Again he ~urface area of ~he packing elemen~ is indicated by numeral 22. ~t will be noted that three separate baffles are shown.
Thus numerals 23 and 24 denote the baffles whieh are pointing ~25 to the inside of the element, whereas number 25 refers to a baffle which is on the outside, pointing away from the element~

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Since the baffles are now shorter, their depth "R" may be smaller in order for the limits of D/R to be observed~

_g _ 3~3 The arrangement of baffles or partial baffles as shown in Figure 4 may be implemented in a number of ways. Thus a typical packing element may comprise three separate baffle courses, such as i5 shown in Figure 2~ with the two baffles on each end consisting of baffles 23 and 241 whereas the central baffle being represented by 25. Another implementation in accord with Figure 4 may be the reverse, such that the end baffles may be represented by numeral 25~ with the central baffle split and in accord with numeral 23 and 24n Finally all three partial baffles 23~ 24 and 25 may be in one plane or any combination thereof.
It will be noted that with the arrangements of baffles just outlined, one does not only accomplish the formation of a s-trong element, but by having shortened the baffles and reduced them to partial baffles, the number of partial baffles has been increased over what would be obtained with whole baffles. This provision of partial baffles leads to a packing element that will provide more ready contact points with adjoining packing elements.
Hence, by subdividing the baffles, the internal liquid distribu-tion ln the bed will be further improved over that obtained byprovision of whole ribs. Further improved contacting efficiency will result. Of course, although not specifically shown in a view of the surface area of the packing element, the surface area shall have to be provided with~small perforations, as is already indi-cated in Figure 2 to allow ready drainage of the irriyating liquidaway from otherwise stagnant pockets.
Another implementation of ribs is shown in Figure 5. Again numeral 26 denotes the surface area of the packing element which is provided with slots and tongues as is shown in Figures 1, 2 and 3.
It will be noted that the implementation and arrangement of ri~s in Figure 5 is similar to that already shown in Figure 4 r 3~3 except that in Figure 5, the single partial rib 27 is on the inside of the element and the partial ribs 28 are on the out-side. Generally speaking, the advantages to be derived from the construction of Figure 5 are in principle equivalent to those offered by the construction of Figure 4.
Essentially the same implementation as in Figure 5 is also shown in Figure 5. The wall of the packing element is rep-resented by numeral 29, and two partial baEfl~s 30 are shown on th~ outside. The baffle extending into the interior of the ele-ment denoted by numeral 3I is of a somewhat different shape.With a construction as shbwn in Figure 6, one would, in general, expect similar results as with the construction as shown in Figure 5. However, owi.ng to the varying depth of baffle 31, additional dumped bed irregularit~ would result over that obtained with the element of Figure 5 and added liquid and yas turbulence will result, leading to additional performance improvement.
Although not shown in a separate view of Figures 4 to Figure 6, the surface areas of the packing elements are intended to be with:slots and tongues as is indicated in Fi~ures 1 and 3.
Furthermore, in all instances, perforations through the.surface areas to facilitate better liquid drainage, better internal liquid distribution and added bed stability as shown in Figure 2, are provided, although these perforations are not shown in Figures 3 ; to 6.
~hereas there is no basic limitation as to the material of CQnStrUCtiOn making up the packing indicated in Figures 1 to 6, and the implementation of ribs, it is suggested that the use of plastic substances and the vaxious methods of forming plastic : bodies will be most suitable for implementing the shapes presented in Figures 1 ~o 6.

~ ~753~3 By having provided ribs or bafEles of certain depths and arrangements in combination with generally open ended curved strips, constructions have resulted that exhibit not only maxi-mum mechanical strength, but which have also been ~ound to con~
tribute materially to improved mass transfer between liquid and gases or vapors, when used as contacting media.
While I have illustrated and described several embodiments of my invention, it will be understood that these are by way of illustration only and that various changes and modifications may be contemplated in my invention and within the scope of the follow-ing claims.

Claims (13)

HE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a packing for a gas-liquid contacting tower and the like, a plurality of randomly packed mutually inter-locking packing elements providing a bed, each packing element comprising an intermediate portion curved concavely, and end portions curved convexly, slot means formed in said packing element in both said inter-mediate and end portions, first tongue means depending from said slot means in said concavely-curved inter-mediate portion and extending away only inwardly from said intermediate portion and second tongue means depending from said slot means in said convexly-curved end portions and extending away from said end portions in only the same general direction from said packing element as said first tongue means.

2. In a tower packing as recited in claim 1 wherein lines perpendicular to the tangents at the ends of said packing element define an angle of between zero and about 88 degrees.

3. In a tower packing as recited in claim 1 wherein the curvatures of said intermediate and end portions are non-circular.

4. In a packing element as recited in claim 1 wherein said end portions are of different lengths.

5. In a tower as recited in claim 1 wherein said inter-mediate portion is perforated.

6. In a tower packing as recited in claim 1 wherein at least some of said tongues are arcuate and extend beyond a line joining the extremities of said end portions and wherein at least one of said tongues is perforated.

7. In a tower packing as recited in claim 1 wherein reinforcing ribs are formed on said intermediate and end portions.

8. In a tower packing as recited in claim 1 wherein said tongues of said intermediate portion are arcuate and tapered downwardly and inwardly in a direction away from the concave surface of said intermediate portion and extend approximately to a line joining the extremities of said end portions.

9. In a tower packing, as in claim 1 wherein said tongue means in the intermediate portion extend all centrally inwardly and all of the same length.

10. In a tower packing as recited in claim 1 wherein said intermediate and end portions are circular and exhibit all the same radii of curvature.

11. In a tower packing as in claim 1 wherein the ratio of the length of the packing element to the diameter of the intermediate portion varies from 3 to 1.2.

12. In a tower packing as in claim 1 wherein the inter-mediate portion extends essentially through an arc of 180°.

13. In a tower packing as in claim 1 wherein said tongue means extend beyond a line interconnecting the extremities of said end portions.