CA1098028A

CA1098028A - Packing element for mass transfer devices

Info

Publication number: CA1098028A
Application number: CA284,742A
Authority: CA
Inventors: Ralph F. Strigle, Jr.
Original assignee: Norton Co
Current assignee: Saint Gobain Abrasives Inc
Priority date: 1976-09-02
Filing date: 1977-08-15
Publication date: 1981-03-24
Also published as: AU509577B2; JPS5335144U; JPS5736249Y2; GB1573745A; AU2809577A; DE7726885U1

Abstract

ABSTRACT OF THE DISCLOSURE
The packing is in the form of a surface defining a space which is at least partially enclosed thereby. A finger is formed from the surface and extends into the space, the surface of the finger making an angle of between 4° and 45° with the axis of flow of gas passing through the space. In a preferred form the surface is cylindrical and portions of the cylindrical surface are cut therefrom to form fingers which are bent inwardly towards the axis of the cylinder to provide liquid vapor contact surfaces in the interior of the cylinder. At least some of these surfaces are bent at an angle which is between 4° and 45° to the axis of the cylinder to provide turbulence in the gas flowing parallel to the axis of the cylinder so as to increase the in-teraction between the flowing gas and the wetted surface of the finger.

Description

This invention relates to packing elements for use in mass transfer towers.
Contact elements partially enclosing a space for fluid ~l~w have found wide uses in mass tr~nsfer devices such as scrubber tdwers, absorption columns, distillation columns and the like. One example of a popular form of packing element is based on the cylindrical type described in U.S. Patent 3,266,~87 to Eckert where contact fin~ers are punched out of the cylin-drical wall and bent inwardly into the space de:Eined by the cylinder. The type of packing descrihed in the Eckert patent works w~ll in the smaller sizes of packings. ~owever for the larger size packings, which are becoming increasingly important for ~crubber towers adapted to hand].e tremendous volumes of gas, ..
uah as encountered in the scrubbing of p~wer plant ~tack gases, the effic~enay ~alls o~f as the diame~er of the packing element ~: is increased. I~ is believed that this fall-off in efficiency result~ ~rom the fa~t that, with ~he larger diameter of packing ; ~lement, the g~s ha~ a tendency to flow axially o~ the pa~king ~lement a~d parallel to the elem~nt sur~aces. In this circum-~anb~ th~ contact betweon the gas and ~he wetted surfaae~ of the flnger~ extending in~o the fluid ~low spao~ is not ~3 com-ple~e as desired. In:the pr~ ent lnvention the effici~ncy of the packing element is substantially increased by twi~sting some o~ the inwardly projecting fingers so that their surfaces .
~, 25 each form an angle at between 4 and 45 to the axis of the B : ? ,, ~

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enclosed fluld flow space This imparts a turbulence ~o the gas flowing along the axis of the space so as to provide more intimate contact between the flowing gas and the wetted surfaces projecting into this-enclosed space as well as increasing contact with the wetted surface of the wall defln-ing the space.
In accordance with the present invention the fingers extending towards the axis of the fluid flow space are twisted sufficiently to obtain some turbulence, but not enough to provide aerodynamic shielding of the back surfaces of the fingers~ In .ccordance with the pres~nt invention the~e is provided a generally cylindrical packing element, portions of the surface bèing cut from the cylinder to form fingers which are directed inwar~ly towar~s the cylinder axis, the surface ~f some of said fingers being bent at an angle of between 4 and 45 to the axis of the cylinder/ each such inwardly directed finger having a transverse dimension extending along less than 35% of the axis of the packing ~lem~.nt, whereby the inwardly : directed fingers create turbulent flow wi`thin the element of gases flowing past the finge~s and generally parallel to the axis. The exact amount of angle will depend on a number of faators including the spacing of the fingers, ~he amoun~ of penetration of the fingers into the empty ~pace, the width of the fingers parallel to the axis, the flow rate of the gas In one packing alement, having a diameter of about 3-1j2", it was found that a 10 angle seemed to give the highest ~ficiency. The efficiency started to fall off as the.angle was increased to about 16 until it was about equal to the efficiency with the surfaces parallel to the axisO As far as is known, prior packing elements of the type described : - ' .

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in the above mentioned Eckert patent ha~e been made with surfaces either parallel to the axis of the cylindrical packing element or normal to the axis as shown in French patent 542,902. ~See Figs. 5,7 and 8). The only packing elements described in the prior art known to applicant having an inclined internal surface are the old spiral type rings, However these spiral rings were entirely different since their interior surfaces were not formed by fingers which were punched from the cylinder itself and bent inwardly, rather their spiral surfaces were completely enclosed by imperforate cylinders.-- A structure similar in performance -3a-'.. , ' ' ' " '' - ',,'' ''' ' ' ' ~ ' ~ ' . :
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to ~he old "~piral rings" is shown in Fig. 3 of British patent 1,385,672. Another type of prior art packing is illustrated in ~rman DA5 1~029,346 published May 8,1958. This shows a saddle ale~ent having fingers punched from the surface and bent inwardly to the ~pace partially defined by the curved saddle surface. In ~hi~ D~S, however, the angle between the finger surfaces a~d the axis o~ ga~ flow approximateq 90. While the recently issued U.S.
~at~n~ 3,957d931 contains ~he cryptic sta~emen~ (col. 5 lines 13-14) that ~Ithese tabs may be angled to the longitudinal axis of ~ha cylindric~l mem~er" there i~ no discussion of specific angle~
or how they are mea~ured or the effect of the angulation.
~he invention will now be described, by way of example, ~th re~erenc:e to the accompanying drawings, in which:
. Fig. 1 i~ a side view of one embodiment of the packing aleme~t having three rows o~ finger~ punched from its surface an~ b~n~ inwardly.
Fig. 2 is a ~ ard sectional view along line 2-2 o~ ~g. 1 looking parallel to the axis of the cylinder~
Fig. 3 i~ a diagr~mmatia perspec~ive view of another o~bodiment of thQ invention.
Referr~.ng now to Fig. 1 the packing element, which is gen~r~lly lndiaat~ at 10, i~ ~ormed of a ~ylindrical surfa~e 12 ~xo~ ~hi~h a number of ~lnger~ 14 and 14a are cut and bent in~
w~rdly o ~xtend into th~ interior spa~e 13 de~lned by the oylindri~al surf~ae 12~ A~ ind~a~ed on Fig. 1 ~he finger 14 r~d by a roughly rectangular cut. ~ha surface ~ finger 14 will have a 10 angl~ "a" with respect to the axis. The hinge llno 167 along which the ~.inger 14 is bent inwardly, also con ~ ntly ha~ ~h~ ~ame 10 angle "b" wi~h the axis A. Thus the ~ao ~l~wing do~n th~ cylinder parallel to the axis A is deflected . ~_ ' ' somewhat by the surfaees 14 to create turbulence which increases the amount of interaction between the flowing gas and the liquid on the wetted surfaces on the fingers 14 and the interior surface of the cylinder 12.
As viewed from the top (~ig. 2) the projected area of the bent fingers 14 intercepts an appreciable amount of the cross-sectional area of the empty space 13, thus substantially in-creasing the chance of interaction of the gas with the liquid on a wetted surface during travel of the gas down the inside of the packing element. In Fig. 2 it is seen that fingers 14a are not twisted with respect to the axis.
Tests of packings made in accordance with the present invention by using humidification of air as a performance test showed considerable improvement over standard commercially available packing elements made in accordance with the prior art techniques where the finger surfaces were essentially parallel to the axis of the cylinder. It was found that a 3-l/2" diameter ring packing element (90 millimeters) had a heat transfer effi-ciency equal to the 2" prior art packing element even though the pressure drop across a bed of the 3-l/2" packing elements of the present invention was considerably less than the pressure drop across a bed of similar height of the 2" packing elements. In a ~referred embodiment of the invention, the packing element made in accordance with Fig. l is formed of cylindrical elements approximately 3.54" high (90 millimeters) by 3.54" (90 milli-meters) in diameter. Each element has ~hree rows of fingers with eight fingers in each row of the approximate relative dimension shown in Figs. l and 2. The center row of fingers 14a is parallel to the cylinder axis and the finger of the top and bottom rows are twisted so that the surface of these fingers forms an angle of . ' ,, :' ' ~ ~ ' " ~
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approximately 10 with respect to the axis of the cylinder. In Fig. 2 the bottom row of bent fingers is not visible since they would be shielded by the top row.
With the dimensions of the approximate size shown in Fig. 1 when the angle is somewhat greater than 15 (e.g. about 16) the performance falls off somewhat.
While actual tests have not b~en run with a narrower flnger it is believed, on the basis of theoretical considerations, that when the width of the finger in the axial direction is about 5~ of the total axial length of the packing element the angle "a" can be up to 45 and still provide improved performance. In this lattPr case there will not be so much "shadowing" of the back side of the finger, i.e. the side which is down stream of the flowing gas. However, when the width of the finger extends between about 25% and 50% of the axial length of the packing element, then the angle is preferably between 4 and 8~ with respect to the axis of the element. In the preferred embodiment illustrated in Figs. 1 and 2, the transverse dimension of the finger extends along about 17% to 20~ of the axial length of the packing element and the angle of the finger is ~referably around 10 for improved performance.
While a preferred embodiment of the inv~ntion has been described above wherein the finger is more or less rectangular and is bent at a constant angle to the axis, considerable departure from this simple structure can be achieved without departing from the spirit of the inventionO For example the angle of the surface can change along the length, being rel-atively shallow near the cylinder wall and increasing towards the free end. Similarly the shape of the finger can be triangular, ellip~ical, or any other shape that furnishes an inwardly ~r~
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extending surface having an angle oE 4 to 45 to the axis of the cylinder.
Another embodiment of the invention is based on a saddle of the type shown in the above mentioned DAS 1,029,346 and is formed from a single saddle shaped piece of metal (or plastic) as illustxated in Fig. 3. Each finger 20, cut from the saddle 22, and bent inwardly towards the flow axes 24 and 24a (ther will be two axes) is bent so that the finger surface forms an angle of between 4 and 45 with respect to the flow lQ axis adjacent the finger. In general the narrower the finger the higher can be the angle, as discussed above.

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Claims

1. A substantially cylindrical packing element, adapted for contact with gas flow, portions of the surface being cut from the cylinder to form fingers which are directed inwardly towards the cylinder axis, some of said fingers each having an elongate cross-section normal to its length extending at an angle between 4° and 45° to the axis of the cylinder, and extending along less than 35% of the axis of the packing element, whereby the inwardly directed fingers create turbulent flow within the element of gases flowing past the fingers and generally parallel to the axis.

2. The element of claim 1, wherein each bent finger is formed by a generally rectangular cut, the sides of which are at an angle of 4° to 15° with respect to a plane normal to the axis of the cylinder.

3. The element of claim 1, wherein the majority of the fingers are inwardly directed at an angle to the axis.

4. The element of claim 1, wherein there are several rows of fingers spaced along the axis of the element and in at least one row the fingers are inwardly directed at an angle to the axis.

5. The element of claim 4, wherein the outer rows of fingers along the axis are inwardly directed at an angle to the axis.

6. The element of claim 1, wherein each inwardly directed finger has a dimension transverse to its length of between 17% to 20% of the axial length of the packing element and the finger has an angle of 10° to the axis.