CA2117975A1 - Tower packing - Google Patents

Abstract

An improved tower saddle packing having a general shape that is a segment of a hollow torus. The circumferential outer edges of the saddle define a plurality of radially, outwardly extending convex lobes. The lobes and wing portions preferably have weep holes to effectual wetting of all surfaces of the saddle. The hub of the saddle has in one aspect a plurality of apertures extending substantially across the hub. The saddle provides improved gas-liquid interaction, permits enhanced gas throughput in an absorption tower and allows for reduced tower packing sections.

Description

TOWER PACKING

Field of the Invention This invention relates to tower packing for use in exposing a liquid to a gas in co-current or counterc~ t flow and, particularly, to tower packing of thesaddle type of use in the manufacture of sulphuric acid.

Back~round to the Invention Toroidal ceramic saddles of the type described in United States Patent No.
2639909, issued May 26, 1953 to Leva, have been used extensively as tower packing for dec~es with little physical shape change. The ceramic saddle described in U.S.P. No. 2639909 has a general shape that is a segment of an inner-peripheral portion of a hollow torus, with respect to the axis of generation of the torus, the packing having at each of its ends an arcuate end-edge face that lies substantially in a plane that is radial in relation to the axis of the torus, with the axis also lying substantially in the plane of the respective arcuate end-edge face, the margins of the packing that are farthest from the axis being substantially circular arcs with their centres at the axis. This saddle, thus, consists of a half section of the inner half of a toroid having a concave surface to the outside, i.e.
to the gas/liquid phase, and has proven to be commercially successful.
With the continuing pressure to reduce cost, saddle sizes have grown as larger saddles have lower flow resistance to gas. Absorption towers containing the ~117g7S
-packing can be built with smaller diameters with lower cost. On the other hand, large saddle sizes have less interfacial area for mass transfer in a given volume of packing and higher p~c~ing depths are needed for the same mass transfer duty.At this time with ceramic ~ s, it appears that a 75 mm diameter ceramic saddle is about as large as is practical. A larger size of packing, i.e. 150 mm is available, but at ~ignifi~nt extra cost and so far has not been found cost-effective.
One alternative type of packing which has been used to a lesser degree is a ring-type p~king in which a cross is inserted to form what is called a "mini-ring". This shape is available in siæs up to 150 mm and have a modestly greater capacity than the standard saddle. The ring is not, however, as good at spreading liquid across the tower cross-section and extra care is thus needed in design.
Although an improved saddle, described in United States Patent No.

3,232,589, issued February 1, 1966 to Eckert J.S. has been available for some time, it has not been widely accepted for in~ tri~l use.
Notwith~t~n~ing the continued commercial success of the basic toroidal shaped saddle p~ck-ing element, there remains a demand for more cost-effective p~cl~in~.

Summary of the Invention It is an object of the present invention to provide an improved cost-effective saddle p~ ing.
It is a further object of the invention to provide saddles for tower packing which permit significantly enhanced gas throughput in the tower.
It is a further object of the invention to provide improved saddles which allows use of larger sizes of p~cl~in~ with greater gas handling capacity without requiring the ~ignifi~ntly increased height of the packing section of a gas absorption tower.
These and other objects will become apparent from a reading of the disclosure as a whole.

Thus, in one aspect the invention provides an improved tower packing saddle having a general shape that is, essenti~lly, a segment of an inner-peripheral portion of a hollow torus, with respect to the axis of generation of the torus, said saddle having a hub central of the torus defined by a pair of parallel aligned ribs S remote one from the other extending the inner circumference of the saddle, said hub formed of a first thickness of m~teri7~1 and having hub portion defining a plurality of apertures within said hub, a pair of circumferential outer edges wherein each of said edges and said rib closest to said edge define a wing portion formed of a second thickness of m~tPri~l, the improvement comprising said outer edges clefininP a plurality of radially outwardly extPn~inP convex lobes, wherein each lobe is separated from an adjacent lobe by an interlobal distance and adjacent lobes define therebetween a recess depth.
Preferably, each lobe defines a subst~nti~lly flat outer edge portion of a length greater than the interlobal ~ t~nce and greater than the recess depth. More preferably, the flat outer edge portion length is at least two times, and more preferably three times, greater than each of the interlobal ~ t~nce and recess depth.
In a further aspect the invention provides an improved tower pacl~ing saddle having a general shape that is a sPgmPnt of an inner-peripheral portion of a hollow torus, with respect to the axis of generation of the torus, said saddlehaving a hub central of the torus defined by a pair of parallel aligned ribs remote one from the other exten(linP the inner-circumference of the saddle, said hub formed of a first thickness of material and having hub portions defining, a plurality of apellures within said hub, a pair of circumferential outer edges wherein each of said edges and said rib closest to said edge define a wing portion formed of a second thickness of materi~l; the improvement comprising wherein said wing portion comprises a plurality of body portions defining apertures of sufficient size and number to effect subst~nti~lly full wetting of all surfaces of said saddle.

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In a yet further aspect the invention provides an improved tower packing saddle having a general shape that is a segment of an inner-peripheral portion of a hollow torus, with respect to the axis of generation of the torus, said saddlehaving a hub central of the torus defined by a pair of parallel aligned ribs remote one from the other e~t~Pn~ling the inner-circumference of the sàddle, said hub formed of a first thicknPss of m~t~ri~l and having hub portions defining hub apertures within said hub, a pair of circumferential outer edges wherein each ofsaid edges and said rib closest to said edge define a wing portion formed of a second thickness of m~tPn~l; the improvement comprising said hub aperture e~tPn-ling subst~nti~lly across the distance between said ribs.
The Eckert saddle described in aforesaid USP No. 3,232,589 has scallops cut in its edges to break up the liquid flow by means of portions defining relatively pointed areas where the scalloped sections meet. These edges are thusformed into a series of concave hollows between ~dj~çnt scallops having relatively sharp points. The saddles according to one aspect of the present invention, in contrast have ~ignific~ntly large flat lobe edges in which the lobes have clear, sharp interlobal di~t~nces. The interlobal ~ t~nce must be sufficient to ensure that liquid does not easily bridge from one lobe to the next. A gap ofabout 1 cm is preferred. The slot or separation recess depth between lobes needsto be sufficiçntly deep to ensure that the edge of the wing replesellts a number of discrete se~)alate lobes and that the wings retain adequate mechanical strength.The convex shape creates significant drip points as liquid is much less likely to run back to the root than where the concave hollows of Eckert are used.
The saddles as hereinabove defined, thus, preferably comprise outer circumferential edges comprising a plurality of lobes separated one from the other by interlobal distances, each lobe con~ti~ted as substantially fl~ttened circular arcs having their centres at the axis of generation of the torus. The surface ofeach lobe at its portion remote from the body of the wing alternatively may be gently rounded i.e. for example, oval, semi-circular or elliptical; and/or substantial concentric with the inner surface of the toroid.

In a more prefe~ed embodiment, the interlobal separations on the wings are more in the nature of slots, each having a rounded bottom to avoid cracking during manufacture and having escenti~lly parallel radial side walls. A plefe~red angle between the top of the flattened lobe and a slot side is close to a right angle.
This minimices the possibility of liquid running back around the slot. Liquid testing suggests that the slot width should preferably be at least 10 mm to reduce liquid bridging and sealing of the slot.
S~ os of the present invention are of a shape relative to prior art that the counlel.;u~ie,lt flow of gas and liquid streams are more dispersed, while the gas flow paths are less tortuous than those found in the prior art saddle packed towers. This provides for enhanced tower gas throughput. The contact areas between the liquid and gas is increased by the additional divisions of the streams as well as providing additional ceramic surfaces exposed to both fluids in the apertures and allows of a relatively large base shape to provide agood mass transfer efficiency presently held only by relatively smaller saddles of the prior art.
The saddles may be formed of any suitable m~tPri~l, such as a suitable metal or thermoplastics m~tPri~l or preferably, a ceramics m~t~ri~l Brief Description of the Drawings In order that the invention may be better understood, a prefelled embodiment will now be described by way of example only, with reference to the accol-lpanying drawings wherein:
Fig. 1 represents a perspective view of a prior art saddle;
Fig. 2 represents a plan view of a prior art saddle;
Fig. 3 re~lesents a perspective view of a ceramic saddle according to the invention;
Fig. 4 f~r~sents a diagr~mm~tic plan view of a ceramic saddle according to the invention;

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Fig. 5 ~cplcsellts a diagrammatic sectional view of a wing edge of scalloped design of prior art with schematic liquid drops ~tt~ch~i thereto;
Fig. 6 ,~rescnts a diagr~mm~tic sectional view of wing edges according to the invention with attendant drops of liquid attached thereto;
Fig. 7 ,~,csents a diagrammatic side view of a prefe,,cd saddle according to theinvention;
Fig. 8 rep,csell~s a diagr~mm~tic underside view of a prcfe~cd saddle according to the invention;
Fig. 9 ,c~csc,lL~ a perspective end view of a plcfcllcd saddle according to the invention; and wherein the same numerals denotes like parts.

Detailed Description of a Preferred Embodiment Fig. 1 shows generally as 10 a ceramic saddle having a general shape that is a segment of an inner-peripheral portion of a hollow torus, with respect to the axis of generation of the torus. Saddle 10 has ends 12, 14, each having an arcuate end-edge face that lies subst~nti~lly in a plane that is radial with relation to the axis of the torus. The axis also lies substantially in the plane of the respective arcuate end-edge face and with the margins of saddle 10 that are farthest from the axis being subst~nti~lly circular arcs with their centres at the axis.
Saddle 10 has a hub 16 ccntral of the torus defined by a pair of parallel aligned ribs 18, 20, which extend the circumference of saddle 10 either side of hub 16. Hub 16 is of sufficient thickn~ to provide reasonable strength to the saddle, and has a plurality of apc,lurcs 22 disposed throughout a central portion of hub 10. Saddle 10 has a pair of circumferential outer edges shown generally as 24, 26 which with ribs 18 and 20, respcectively, define wing portions 28, 30 respectively. Each edge 24, 26 defines a plurality of scallops 32, 34 respectively, which radially extends from the body of the wings and which are typically, formed as pointed as feasible. The edges of the adjacent indented surfaces which form the scallops meet in substantially line contacts in saddle 10 edges. Fig. 1shows the surfaces of the scallops to define, preferably pointed extreme portions 36, 38 followed by a concave surface 40, 42 respectively which conctit~ltçs the hollow portion S es~nti~lly between each ~ cçnt pair of scallops.
With reference now to Figs. 3 and 4, these show generally as 100, a ceramic saddle of subst~nti~lly the same general shape as that of Figs. 1 and 2.Saddle 100 has a hub 116, central of the torus defined by a pair of parallel ribs 118, 120, which extend the circumference of saddle 100. Hub- 116 has a plurality of apertures 122, which apellules extend the full width of hub 116 between ribs 118 and 120. Apellur~s 122 define a subst~nti~lly right vertical cylinder through the hub thickness, which cylinder has a continuous serrated surface 119 and has an outer perimeter 123 greater than 4 times the hub thickness. In an ~ltern~tive apelLure 122 has a minimum width, irrespective of the size of the aperture 122, of at least twice the hub thickness Circumferential outer edges shown generally as 124, 126 with ribs 118, 120, respectively define wing portions 128, 130, respectively. Each of wing portions 128, 130, has a plurality of weep apellures 150, 152, l~specLi~ely of sufficient size and number, and so disposed onto another, as to readily effect substantially full wetting of all surfaces of the saddle 100 during operation, without causing non-acceptable structural we~kness to wing portions 128, 130.
Further, the apellures have a cross-sectional width similar to the wing thickn~-cc and are spaced apart a 1ict~nce suffi~iPnt to ensure adequate structural strength in the wing. Weep apellu~s 150, 152 have a maximum width of less than the wing thicl~nP.ss and are spaced apart at a distance of at least three times the maximum width of apellule 150, 152, which is sufficient to ensure adequate structural strength in the wing.
Edges 124, 126 define a plurality of radially extending convex lobes 154, 156, respectively, each lobe being separated by an inter-lobal distance "D" which defines a subst~rlti~lly circular arc having its centre at the axis of generation of 211797~

the torus. Each lobe 154, 156 at its surface portions 158, 160, respectively, remote from wings 128, 130, respectively, is gently curved to define an arc of acircle. ~ltPrn~tive lobe embodiments have surface portions defining arcs of an ellipse. Each of lobes 154, 156 has a weep-ap~ e 162, 164.
Figure 5 shows part of the outer edge of a prior art saddle 500 having scalloped portions 501 and projecting points between scallops, 503 - 517. Drops of liquid are shown forming on points 505, 507, 509, 511, 513, 515 where the angle of the lower edge of the scallop does not allow liquid to run back to the main surface of the saddle as occurs in points 503 and 517.
Figure 6, in col.,p~ on, shows a number of convex lobes 602, 604, 606, 608, 610, 612, 614, 616 and 618 on the edge of the wing of saddle 600 according to the invention. Lobes 602 - 618 are separated by interlobal distance 620 such that liquid cannot bridge the gap between ~ cent lobes. Liquid on the lobes willtherefore run off the lowest points on the lobes and droplets, 622 are shown on lobes 604 - 616.
In hereinbefore mentioned prior art USP3232589-EcKert, it is taught to have relatively sharp points between the scallops. Where liquid flows down the edge as is likely to be the case at points 517 and 519, little new liquid surface is created. By co---pa-ison, lobes 602 and 618 in instant application are likely toform droplets which then drip onto the next lower lobes 604 - 616. This gives significantly greater liquid mixing and surface generation. The size of the gapsbetween lobes is clearly up to the de~ignPr but should be sufficient to minimi7ethe liquid bridging from lobe to lobe.
Figures 7, 8 and 9 give side, underside and end views, rt;~ ely, of a plefelled embodimpnt of the improved saddle. The saddle shown generally as 700 has a hub section 702 and wings 704 and 706, which join at ribs 708 and 710. Rib 708 appears on all three drawings while rib 710 appears only on Figures 8 and 9. The rib ~ mtoter will typically be at least 50% larger than thethicknP-ss of either the wings or the hub. Three holes in hub 702 denoted as 712, 714 and 716 are best shown in Fig. 7 while Fig. 9 shows only holes 716 and 714.

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Slots 718, 720, 722, 724 and 726 on the edges of wings 704 are shown best in Fig. 7 as is wing 704 with identical slots in wing 706 (not shown). An end view of four slots 724, 726, 728, and 730 is shown in Fig. 9. Weep holes designed to allow liquid to flow from one side of the wing to the other are shown as 732,734, 736 and 738.
It will be readily appreciated that ~ltern~tive embodiments may have more or less numbers of holes, slots and lobes with appropliate and suitable changes in dimPn~ions. For example, the slots may be con~tituted as radially extending rectangular shaped openings defined by linear sides of adjacent lobes and the outer circumference of the wing as the base of the slot.
In more detail, packing 700 is formed of china clay and has the broad overall lim~ncions of about 7 cm inner ~ meter (ID), about 14 cm outer diameter(OD), about 7 cm overall width (W), about 5.5 cm outer hub width (OW) and about 4.5 cm inner hub width (IW). Packing 700 has a somewhat fl~ttened hub portion 702 and a plurality of lobes 740 that take the shape of a fl~ttened convex protrusion having a subst~nti~lly flat or gently curved edge 742 of a length L that is about three times greater than each of the interlobal distance D at its extreme edge and recess depth R. In the embodiment shown L is about 2.5 cm, D is about 1.2 cm and R is about 0.8 cm. 12~s~s 712, 714 and 716 at their widest dimPn~ion are about 3.5 cm and have a depth of about 1 cm. Apellules 732, 734, 736 and 738 have a ~i~met~r of about 0.8 cm.
While the invention has been described in detail and with reference to specific emb~im~nt~ thereof, it will be appa~e,lt to one skilled in the art thatvarious changes and modification can be made therein without departing from the spirit and scope of invention as described and cl~imed.

Claims (18)

1. An improved tower saddle packing having a general shape that is a segment of an inner-peripheral portion of a hollow torus, with respect to the axis of generation of the torus, said saddle having a hub central of the torus defined by a pair of parallel aligned ribs remote one from the other extending the inner-circumference of the saddle, said hub formed of a first thickness of material and having hub portions defining a plurality of apertures within said hub, a pair of circumferential outer edges wherein each of said edges and said rib closest to said edge define a wing portion formed of a second thickness of material; the improvement comprising said outer edges defining a plurality of radially outwardly extending convex lobes, wherein each lobe is separated from an adjacent lobe by an interlobal distance and adjacent lobes define therebetween a recess depth.

2. A saddle as defined in Claim 1, wherein said outer edges further comprise a plurality of interlobal circumferential portions, wherein each of said circumferential portions define a substantially circular arc with its centre at said axis.

3. A saddle as defined in Claim 1 wherein each of said lobes has an outer surface which substantially defines an arc of a circle.

4. A saddle as defined in Claim 1 wherein each lobe defines a substantially flat outer edge portion of a length greater than said interlobal distance and greater than said recess depth.

5. A saddle as defined in Claim 4 wherein said flat outer edge has a length greater than two times said interlobal distance and greater than two times said recess depth.

6. A saddle as defined in Claim 4 having an inner diameter of about

7 cm, an outer diameter of about 14 cm; an overall width of about 7 cm; an outer hub width of about 5.5 cm and an inner hub width of about 4.5 cm.

7. A saddle as defined in Claim 5 wherein said flat outer edge has a length greater than three times said interlobal distance and greater than three times said recess depth.

8. A saddle as defined in Claim 1 where said lobe has a lobe portion defining an aperture.

9. An improved tower saddle packing having a general shape that is a segment of an inner-peripheral portion of a hollow torus, with respect to the axis of generation of the torus, said saddle having a hub central of the torus defined by a pair of parallel aligned ribs remote one from the other extending the inner-circumference of the saddle, said hub formed of a first thickness of material and having hub portions defining, a plurality of hub apertures within said hub, a pair of circumferential outer edges wherein each of said edges and said rib closest to said edge define a wing portion formed of a second thickness of material; the improvement comprising wherein said wing portion comprises a plurality of body portions defining wing apertures of sufficient size and number to effect substantially full wetting of all surfaces of said saddle.

10. A saddle as defined in Claim 9 wherein said wing aperture has a width greater than said second thickness.

11. A saddle as defined in Claim 9 wherein said wing apertures are so spaced apart, one from another, at a distance of at least three times the maximum width of said aperture.

12. A saddle as defined in Claim 9 wherein at least one of said body portions defines a wing aperture defining a right vertical cylinder.

13. A saddle as defined in Claim 9 wherein each of said outer edges define a plurality of radially outwardly extending convex lobes and wherein each of said lobes has a lobe portion defining an aperture.

14. An improved tower saddle packing having a general shape that is a segment of an inner-peripheral portion of a hollow torus, with respect to the axis of generation of the torus, said saddle having a hub central of the torus defined by a pair of parallel aligned ribs remote one from the other extending the inner-circumference of the saddle, said hub formed of a first thickness of material and having hub portions defining hub apertures within said hub, a pair of circumferential outer edges wherein each of said edges and said rib closest to said edge define a wing portion formed of a second thickness of material; the improvement comprising said hub apertures extending substantially across the distance between said ribs.

15. A saddle as defined in Claim 14 wherein said hub apertures have an outer perimeter greater than four times said first thickness of material.

16. A saddle as defined in Claim 14 wherein said hub aperture has a minimum width of at least twice said first thickness.

17. A saddle as defined in Claim 14 wherein said hub portions define an aperture defining a substantially right vertical cylinder having a continuous serrated surface.

18. A tower saddle packing as defined in claim 1, formed of a ceramic material.