US2862698A

US2862698A - Contact device

Info

Publication number: US2862698A
Application number: US558982A
Authority: US
Inventors: Arthur E Howerton; Kenneth R Dale
Original assignee: Columbia Southern Chemical Corp
Current assignee: Columbia Southern Chemical Corp
Priority date: 1956-01-13
Filing date: 1956-01-13
Publication date: 1958-12-02
Anticipated expiration: 1975-12-02

Description

VDec- 1958 A. E. HOWERTON ETAL 2,362,693

' CONTACT DEVICE Filed Jan. 13, 1956 2 Sh'ets-Sheet 2 z I Q; M llllllzfl/ lllllIi 23 (1%.9

IIIIIIIHIIIHIHIII! I Illllllll INVENTORS Ari/z ur'E Hower tan W Kenneth 3.9a Ze ATTORNEY United States Patent() CONTACT DEVICE Arthur E. Howerton and Kenneth R. Dale, Corpus Christi,

Tex., assignors to Columbia-Southern Chemical Cor- The present invention relates to an improved device for obtaining intimate contact between liquids and gases. This invention is particularly concerned with an improved design for bell caps used in connection with the plates or trays in a gas-liquid contact tower. More specifically, the invention is directed to an improvement in the construction of a channel-type bell cap which improves the efficiency of the contact tower, increases the flexibility of the tower, and allows the use of extremely high gas velocity through the tower, while eliminating wave motion in the liquid.

Channel caps, tunnel caps, rectangular caps, square caps, and round caps are all common cap forms well known in the fluid contact art. Such bubble or hell caps have been used for a considerable period of time in the petroleum industry. Ordinarily, channel bell caps are designed to extend over substantially the full available width of each plate in the contact tower and are arranged in spaced relation parallel with the direction of liquid flow across the plate. The channel bell caps themselves, like the more common circular bell caps, are each provided with a slotted or notched skirt portion which facilitates the distribution of gases and vapors therethrough.

Liquid may be introduced at the top ofthe tower, to

flow downwardly over the plates in succession. The gas or vapor is introduced at a lower point in the tower, to flow upwardly usually through the chimney-type openings in the plate. The bell caps are frequently disposed telescopically over chimney elements in such a manner that the gases rising in the tower are forced to escape around the lower edges of each bell cap under its slotted skirt portion through the liquid medium which is flowing over the plates.

The present invention was developed as an improvement over a conventional circular bubble cap tower, and is useful in a variety of gas-liquid contact situations. It is particularly useful in the purification of chlorine gas.

At high tower throughputs of chlorine gas, in which chlorine gas was scrubbed with liquid chlorine, it was observed that the efiiciency of the purifying operation was not satisfactory. This appeared to be attributable to a surging of the liquid, or a wave motion of the liquid, with resultant erratic operation characteristics of the tower. 1

An object of the present invention is to provide an improved bell cap which will provide intimate, efficientfrom the primary bell cap, so as to cause a reformation of the bubbles and provide a more intimate and eflicient contact.

A more specific object of the invention is to provide an improved contact device for the scrubbing of chlorine gas with liquid chlorine,'which will allow for the purification of larger amounts of chlorine gas in tower equipment of the same size, than has heretofore been possible, by improving the contact between the purifying liquid chlorine and uprising chlorine gas in a bell cap tower.

A still further object of the invention is to provide a liquid-gas contact device of high efficiency over a wide range of flow rates, so that a single contact apparatus may be characterized by superior efiiciency over a wide operating range.

These and other objects of the invention, which will become obvious from a consideration of the detailed description of the invention which follows hereinafter, are accomplished in a preferred embodiment of the invention by an improved channel-type bell structurev having a double bell of rectangular cross-section. This double bell may, in its simplest form, comprise a modification of a conventional channel cap in which vertical walls defining the double bells depend downwardly from a flat platecap, The two inner vertical walls which define the first bell are disposed telescopically in spaced relation with respect to the chimney, while the two outer vertical walls, defining the secondary bell, are telescopically disposed with respect to the walls of the first bell, and are spaced therefrom. Each bell is provided with the conventional slotted edges which promote bubble formation and intimate gas-liquid contact. In order to eliminate wave formation in the liquid, it has been found that the lowermost edges of-the slots in the secondary (outer) bell should substantially coincide with the vertical elevation of the uppermost extremity of the slots in the primary (inner) bell.

While .the preceding brief description relates to a preferred embodiment of the invention, it will be understood that the invention. may take a variety .of forms. Thus, for example, in some instances it may be desirable to admit the gas to the contact area by some means other than a chimney protruding through a horizontal plate in a tower. In a specific instance, on the bottom plate of a scrubber for gaseous chlorine, it may be desirable to pass the gaseous chlorine into the contact tower directly from a horizontally-directed pipe. In this case, the extension of the pipe within the contact tower may become an'integral part of the contact device by providing direct connections between the extension of the pipe and channeltype bell caps which may be arranged in a direction perpendicular: to the axis of the gas inlet pipe extension. In still'another embodiment of the invention, the gas may be piped directly into the side or top ofthe bell caps, rather than through a chimney.

These and other features of the invention may be best understood by detailed reference to the drawings, in

which:

Fig-1 is a vertical elevation in section of'a contact tower embodying improvements according to the present invention; 7 I p Fig. 2 is a vertical section of a portion of the contact tower along the line 22 in Fig. 1;

Fig. 3 is a partial side elevation in section taken line 33 of Fig. 2; V Y I Fig. 4 is an enlarged side elevation of an improved channel-type bell cap; a I

Fig. 5 is a side elevation in section taken on line 5-5 of Fig. 4;

.. 'Fig. 6 is a' vertical elevation in section of a modified form of contact tower according to the present invention;

Fig. 8 is a side elevational view in partial section taken on line 8-8 of Fig. 7;

Fig. 9 is a sectional elevational view taken on line 99 of Fig. 8.

Referring now in detail to the drawings, the improved fluid contact accomplished by this invention may be obtained through the use of improved bell caps mounted in a contact tower 10 having a vertical series of trays, plates, or partitions 12, provided with bell caps 13. In a preferred form of the invention, the bell caps 13 are of the Channel type, and are disposed on each partition 12 so as to be in the direction of liquid flow across that partition. In a generally cylindrical tower of the type illustrated in the drawings, each horizontal partition 12 may be approximately circular in shape, and secured to the tower walls in fluid-tight relation.

A downward movement of the liquid through the tower may be provided by an arrangement of suitable weirs and pipes. Thus, in a chlorine scrubber of the type illustrated in Fig. 1, of very simple design, liquid chlorine may be conducted into the tower through an input line 15 disposed to discharge directly on the partition 12 behind the input weir 16. Since the liquid chlorine discharges from behind the input weir 16 by overflowing the weir, a substantially uniform flow of liquid chlorine is obtained across the entire width of the input weir and the partition 12. To facilitate cleaning of the portion of the partition 12 behind the input weir 16, a discharge 17 may be provided. A uniform depth of liquid chlorine across the partition 12 may be maintained by an output weir 18, over which the liquid chlorine may overflow, discharging into a downpipe 19 through which the liquid chlorine is conducted directly to the bottom of the scrubber. Eventual discharge of the liquid chlorine from the tower is through a large drain 20 disposed at the low point in the. curved bottom of the cylindrical tower. Alternatively, the liquid chlorine may be discharged from the tower through a liquid overflow drain 21, disposed at the liquid input level at the bottom of the scrubber. For use in starting up, and for emergency conditions, a liquid chlorine feed line 33 may be disposed at the bottom of the contact tower 10.

The gas inlet to the tower is preferably through a relatively large, horizontally directed gas inlet pipe 23. Depending downwardly from the gas inlet pipe 23. may be a series of hoods 24, as best illustrated in Fig. 7. In this form of improved contact device, the chlorine (or other) gas escapes from the gas inlet pipe 23 under the hoods or caps 24 and bubbles up through the liquid chlorine. A sufficient pressure difierential is applied to the tower to cause the gas to pass upwardly toward the next horizontally-disposed partition 12, through a chimney 25, through the channel-type bell caps 13 disposed over the chimney on the partition 12, and thence upwardly in the tower. In order to prevent the escape of liquid chlorine along with the gas leaving the tower, a metal mesh mist eliminator 26 is preferably disposed across the upper outlet ,of the tower 10, through which the gas must pass before it passes through the gas outlet 27.

For most economical design and best operating results, the outlet weir 18 on the upper partition 12 is desirably at approximately the same level as the horizontal plane of the flat top plate cap 31 of the channel-type bell cap 13. At the lower level, the liquid level is desirably maintained somewhat about the uppermost extremity of the slots or apertures 41 of the secondary bell cap 35.

Referring now specifically to Fig. 5, in a conventional bell cap, vapor entering the chimney would be down wardly deflected upon contact with the inner surface of the fiat plate cap 31, and would pass outwardly into the liquid through the slots in the bell cap. With bell caps made according to the prior art, the gas would then escape directly upwardly through the liquid, and at ordinary gas throughput, and particularly at high velocities, severe surging and wave action frequently take place.

This type of physical reaction between the gas bubbles and the liquid is highly undesirable, since there is very little intimate contact between the gas and the liquid under these conditions. The present invention completely eliminates surging and wave formation even at high gaseous velocities. Bubbles escaping through the slots 40 in the inner bell cap 44 pass upwardly through the liquid and are trapped within the walls 43 of the secondary bell cap. In the area 36 enclosed between the walls 43 of the secondary bell cap and the walls 44 of the inner bell cap, and beneath the inner surface of the flat plate cap 31 a volume of gas is trapped in an enclosed area 36. The gas is continuously changing, although its volume is substantially uniform. This trapped gas continuously escapes through the slots 41 in the side walls 43 of the secondary or outer bell cap. The relationship between the secondary or outer bell cap-walls 43 and the inner bell cap walls 44 is desirably such that the bubbles break up and lose their identity within the enclosed area 36, and new bubbles are continuously reformed by the gas escaping from secondary bell cap through the slots 41.

This same sort of phenomenon is also caused to occur at the bottom of the contact tower 10 by the hoods 24 and secondary bell caps 35 disposed thereon, and is illustrated in Figs. 7, 8 and 9. The use of the horizontally extended pipe 23 as the gas conduit directly into the contact tower 10 has the advantage of simplifying piping arrangements and minimizing the resistance to gaseous flow at the input point of the tower.

In the modified form of the invention illustrated in Figure 6, a contact tower It) is illustrated in which there may be provided a plurality of horizontal partitions, 12 in order to increase the amount of liquid-gas, contact within the tower. As in the simple form of the tower illustrated in Figure, 1, liquid flow through the tower is in a downward direction through a plurality of downpipes 61, which are arranged to discharge from the area of the horizontal partition 12 behind the discharge weir 18 into the corresponding enclosed area on the next lower horizontal partition 12 behind the inlet weir 16 on that lower partition. In all forms of the invention, it is desirable to provide each plate or horizontal partition 12 with a plate discharge drain line 63 for use in cleaning the apparatus periodically.

Many advantages flow from the use of the improved form of contact device. With conventional types of bell caps, throughput capacity is severely limited because of the tendency to wave action with the consequent diminution or complete elimination of all beneficial contact between the gas and the liquid. Particularly at high velocities of the gas, the liquid adjacent the discharge slots of each bell cap may be blown aside, so that substantially all of the gas may blow across the surface of the liquid without entering into direct contact with the liquid, merely exerting sufiicient pressure on the surface of the liquid to maintain the liquid in the form of a wave. This wave action can be clearly observed through the formation of crests between adjacent channel bell caps. Although occassionally small droplets of liquid may be torn from the peak of each crest by the force of the gas passing by, in such cases there is little or no bubbling of gas through, the liquid, and hence there is substantially no gas-liquid contact. This undesirable type of action is eliminated completely by the improvements and innovations of the present invention. The addition of the secondary bell cap, and the breaking up of the gas stream issuing from the primary bell cap, disrupts movement of the liquid and of the stream of bubbles in such a way as to prevent wave motion with the formation of crests between adjacent channels or bell caps. In addition, intimate con tact between the gas and liquid is assured through the double formation of bubbles which actually increase the contact between gas and liquid which is obtained by a single passage of gas through a bell cap.

Many other advantages accrue from the improved apparatus illustrated. Thus, the depth of liquid on each horizontal partition may be regulated so that a sufiicient depth is provided to produce a settling effect on each tray. Material which is settled out in this manner, whether derived from the gas or the liquid in the tower, accumulates on each horizontal partition and is readily removed. The use of external downpiping, as suggested in Figure l, simplifies the cleaning of the contact tower a great deal. In addition, because of the improved gasliquid contact obtained through the use of the multiple bubble cap, a much wider variation in gas and liquid throughputs can be handled in a single contact tower than is possible otherwise. Thus, the multiple bubble cap will operate satisfactorily at liquid and vapor flows which would cause coning and pulsations, blowing, high entrainment, and dumping, with ordinary bubble caps.

While the invention is primarily directed to channeltype bell caps of rectangular cross-section in all three dimensions, some improvement in the action of conventional circular bell caps can be obtained by the provision of a superimposed secondary bell cap over the conventional single primary bell cap. However, it has been found that the rectangular channel-type bell caps provide the best performance, providing complete elimination of wave action at practically all throughputs.

In a specific application of the teachings of this invention, the improved channel-type bell caps were installed in a chlorine-purification tower. Liquid chlorine was introduced at the top of the tower, and gaseous chlorine was introduced through the horizontally extended pipe at the bottom of the tower. The contacttower had a sixfoot outer diameter shell, with each'inlet weir being secured two feet four inches from the center line of the shell, and each outlet weir being secured to its partition two feet six inches from the center line of the shell. Each inlet weir had a total height of fifteen and three-quarter inches, with one-half inch V-notches at three-inch centers along the upper edge of the weir. Each outlet weir was twelve inches high, with a notched upper edge having onehalf inch V-notches spaced on three-inch centers. The outlet weir was thus approximately three and three-quarter inches lower in height than the upper edge of the inlet weir, in each case. Each top plate cap was seven inches across, with the length varying, depending upon the position of each channel-type hell on the horizontal partition. Each chimney had an internal diameter of one and onehalf inches. Primary bells having an internal width of four inches were mounted around each chimney, with a free space above the top of the chimney of approximately one inch. The walls forming the secondary bell were spaced away from the'walls forming the primary bell along the marginal edge of the top plate cap. While the walls of the primary bell cap extended downwardly approximately six and five-sixteenths inches, the walls of the secondary cap extended downwardly only five inches, thus vertically spacing the lower extremity of the walls of the secondary bell cap at a level considerably higher than the lowermost extremity of the walls of the primary bell cap.

Each bell cap was provided with slots which were one and one-'halfinches deep, one-eighth inch wide, on three-eighthsinch centers, As may be seen from the description and drawings, the fiat plate cap is imperforate, the

gas distribution slots

40, 41 are the sole perforate portions of the primary and. secondary bell walls, and the space therebetween is unobstructed. In addition it may be seen that in the preferred embodiment the gas distribution means take the form of substantially rectangular, vertically elongated slots extending upwardly from the lower margins of each of the primary and secondary bell walls. The slots in the respective bell caps were disposed in opposition to each other, in the fashion illustrated in Figure 4 of the drawings. The spacing between adjacent channel bell caps was about four inches of free area, based upon a spacing of eleven and one-half inches between the center lines of the chimneys of adjacent bell cap assemblies. A minimum spacing of one and one-half inches of free area between adjacent bell caps has been found essential for efficient operation.

The arrangement of channel bell caps of rectangular cross-section, as illustrated in Figure l and described above, was employed with a throughput of chlorine gas which ranged between sixty-five tons per day and two hundred tons per day. With this wide range of throughputs, excellent gas-liquid contact was obtained'at every gas throughput. No wave action, surging, or other undesirable type of liquid movement was observed at any throughput.

When these same chlorine throughputs were employed with conventional channel-type bell caps in equipment of comparable size, a much less efficient operation occurred because of the variety of surging, pulsation, and wave action which could be observed through windows placed in the walls of the tower for that purpose. While it was found that the use of the double bell cap required a slightly higher pressure differential across the tower for comparable gas throughputs, the improved performance was more than ample in order to justify the slightly increased pressure differential.

In the preferred form of the invention, the slots in the primary and secondary bell caps are oppositely disposed as illustrated in Figure 4. However, while this arrangement seems -to give a highly desirable type of contact action, a considerable improvement over the action obtained with a conventional bell cap is obtained when the slots are not in opposition but are spaced along different centers. Such an arrangement does cause a breaking of the bubble formation within the enclosed area between the walls of the secondary bell and the primary bell by trapping the gas and causing the reformation of bubbles asvthey escape through the slots in the secondary bell cap. Similarly, the same slot spacing need not be employed in the secondary bell cap as is employed in the primary bell breaking up of the bubble stream from the primary bell :cap, and its reformation as the trapped gas issues from the secondary bell cap. In achieving this desired result, it is obviously essential that the lowermost extremity of the secondary bell cap be spaced at a vertical elevation which is superior to the corresponding lowermost elevation of the primary bell cap. While this vertical relationship does not appear to be critical, provided that the primary bubble stream is completely broken up, excellent results are obtained .where the bottom or lowermost extremity of the secondary bell cap is at the same vertical elevation as the upper extremity of the slots in the primary bell cap. As these vertical elevations are brought closer to each other, thereis a tendency and a danger of a failure of the bubble stream to break up and of the trapped gas volume to reform as a new stream of bubbles. This vertical elevation must, therefore, be carefully controlled. However, the vertical elevation of the caps above the tray is not of great importance. This is largely governed by conventional considerations of bubble cap design. It is important to provide sufiicient slot area in each bubble cap so that all of the vapors pass through the slots and not under the edge of the caps. This requirement applies to the secondary as well as the primary bell caps.

The above specific description of the invention has been made for purposes of illustration, and should not be employed to limit the invention in any sense. Many changes in the embodiments of the invention specifically described herein will occur to. those skilled in the art, and, of course, will be Well' within the scope of this invention. For example, it is contemplated that many other types of gaseous distribution means may be employed in the double, bell caps other than the rectangular slots which are specifically illustrated in the drawings. For example, round apertures or V-notches may be employed with similar good results in the elimination of wave action and in the improvement of liquid-gas contact. Similarly, while it is preferred that the outlet weir be on a level with the top of the secondary bell cap, any normal liquid level may be maintained in the tower which produces good contact. In the chlorine scrubbing operation specifically referred to, a liquid depth of at least three, and one-half inches, above the top of the slots in the secondary bell cap provided best results. Since the liquid depth above theslot level controls the period of contact between the gas bubbles and the liquid, liquid depth over the slots is, therefore, an important control factor in the operation of the contact apparatus. This control factor is well appreciated in the art where primary bell caps have been employed, and variations in this liquid depth will undoubtedly be found to be. desirable for various types of contact operations. In the actual structure within the contact tower, it will readily be appreciated that passage of the vapor or gas between the horizontal plates need not necessarily be accomplished through the expedient of providing chimneys through the plates or partitions. Gas may be piped directly into the sides or tops. of any contact bell cap, in much the same fashion as. is, illustrated in Figure 1 of the drawings of the present invention, Where the use of a horizontally directed pipe is shown. A similar arrangement could be employed on each partition in the entire tower.

We claim:

l. A fluid contact tower having vertically spaced transverse partitions, each having an .inlet for liquid atone side and an outlet for liquid on the opposite side, providing for flow of a stream of liquid at a normal level at approximately the same level as the horizontal plane of the plate cap recited below across an intermediate portion of said partition from inlet to outlet, at least one of said partitions having disposed thereon a plurality of channel-type bell caps extending substantially from the partition inlet at one end to the partition outlet at the other end in the direction of liquid flow across said partition, each bell cap comprising an elongated, substantially rectangular, walled chirrmey member opening upwardly through said partition, having an upper end terminating above said partition in vertically spaced relation thereto, with a double bell cap disposed over said chimney member comprising gas-liquid contact means consisting of a flat, imperforate, rectangular plate cap vertically spaced over said chimney member, and a primary, substantially rectangular bell spaced from the outer periphery of said chimney member and formed by opposed, vertically disposed walls depending downwardly from said plate cap, said primary bell walls having gas distribution means therein below the normal liquid level, a. secondary bell telescopically disposed with respect to saidprimary bell and spaced from the outer periphery thereof with thespace therebetween being unobstructed,

said secondary bell having vertical walls depending downwardly from said plate cap, 'said secondary bell walls being provided with gas distribution means therein also below the normal liquid level and vertically spaced above the gas distribution means of said primary bell, said gas distribution means comprising substantially rectangula-r, vertically elongated slots extending upwardly from the lower margins of their respective bell walls, said slots forming the sole perforate portion of said bell walls, and the lowermost extremity of said secondary bell cap being at the same vertical elevation as the upper extremity of the slots of said primary bell cap, whereby the sec ondary bell is adapted to trap gas escaping from said primary bell and then release it for a second contact with the liquid.

2, A fiuid contacting tower having a plurality of vertically spaced transverse partitions therein, each partition having an inlet for liquid on one side and an outlet for liquid on the opposite side, providing for flow of a stream of liquid at a normal level across an intermediate portion of said partition from inlet to outlet, at least one of said partitions having disposed thereon a plurality of channel-type liquid and gas contacting bell caps extending substantially from the partition inlet at one end to the partition outlet at the other end in the direction of liquid flow across the partition, each bell cap assembly comprising gas-liquid contact means consisting of an elongated, substantially rectangular, walled chimney member opening upwardly through said partition, and having an upper end terminating above said partition in vertically spaced relation thereto, and a double bell cap disposed over said chimney member in vertically and peripherally spaced relation thereto, comprising a fiat imperforate top plate cap vertically spaced above the upper extremity of said chimney member, and opposed, vertical, downwardly depending walls secured to said plate cap forming a primary bell spaced from the outer periphery of said chimney member and of substantially rectangular cross-section, said primary bell walls having gas distribution means below the normal liquid level; and a second bell telescopically disposed with respect to said primary bell and spaced from the outer periphery thereof with the space therebetween being unobstructed, said secondary bell formed of vertical walls depending downwardly from said plate cap; said secondary bell having gas distribution means also below the normal liquid level, disposed in opposed.

and vertically spaced relation above the gas distribution means of said primary bell, said gas distribution means comprising substantially rectangular, vertically elongated slots extending upwardly from the lower margins of their respective bell walls, said slots forming the sole perforate portion of said bell walls, and the lowermost extremity of said secondary bell cap being at the same vertical elevation as the upper extremity of the slots of said primary bell cap.

References Cited in the file of this patent UNITED STATES PATENTS 1,765,087 Mase June 17, 1930 1,776,032- Kobernik Sept. 16, 1930 1,918,005 Urquhart July 11, 1933 FOREIGN PATENTS 13,787 Great Britain June 18, 1906