US 2600710 A
Description (OCR text may contain errors)
June 17, 1952 y' y||. N. WADE 2,600,710 BUBPLL cAP FOR WASHING GASES AND vAPoRs Filed Nov. 15, 1947 HENRY N WADE /NVE/vron A TTORNEV Patented `une 17, 1952 UNITED STATES TENT OFFiiE BUBBLE CAP FOR WASHING GASES AND VAPORS Henry N. Wade, Los Angeles, Calif.
Application November 15, 1947, Serial No. 'l86,l75
(Cl. Ztl-114) 2 Claims. 1
This invention relates generally to a method of and devices for intimately contacting liquids with gases or vapors, and specically to improved forms of bubble caps for use in vapor fractionating columns.
A purpose of the invention is to ensure that the liquid collecting on the fractionating plate is contacted once only with vapor before passing to the plate next below.
A purpose of the invention is to provide means for ensuring that the quantitative relation between liquid and vapor passing through each of the bubble caps on any one plate is substantially uniform.
A purpose of the invention is to avoid the bypassing and short-circuiting of vapor and/or of liquid which may occur in the use of other forms of bubble cap when the plates on which they are mounted are imperfectly levelled.
A purpose of the invention is to avoid the inequality in degree of treatment on different parts of a plate which follows from extended horizontal flow of liquid over the plate.
These and other advantages will be evident on inspection of the attached drawings and the following description thereof, in which Fig. 1 illustrates in internal elevation a form of the bubble cap in which the contacted liquid is collected in a centrally disposed basin provided with a central downcomer;
Fig. 2 illustrates, in the same manner, a slightly modified form of the bubble cap in which the liquid-collecting receptacle and associated downcomers are disposed around the periphery of the cap proper;
Fig. 3 is a diagram, on a much reduced scale, suggesting a suitable arrangement on the plate of the form of cap shown in Fig. 1, and
Fig. 4 is a similar diagram suggesting an arrangement on the plate of the form of cap shown in Fig. 2.
Referring first to Fig. 1. lil is a fragment of a plate extending from wall to wall of a fractionating column, scrubber or absorber. A vapor uptake Il extends above the plate for a sufcient distance to maintain a pool of liquid of a desired depth on the plate when the apparatus is out of operation and preferably, but not necessarily, extends also to a slight distance below the plate. i
The vapor uptake is surrounded by a sleeve l2 which is slotted or perforated along its lower edge in any conventional manner, as at I3. At a level somewhat below the upper edge of this sleeve a ring I4 is inserted, this ring carrying a dependent downcomer i5, the ring and downcomer preventing upward flow of vapor and directing it through perforations i3. The downcomer seals in liquid on the plate next below, as is illustrated by the fragmental tubes Iii-I6 which represents the downcomers from. two caps on the plate next above and which extend below the surface of liquid pool Il. The extension of sleeve l2 above ring I4 forms a relatively shallow catchment basin for contacted liquid. this liquid draining through downcomer l5.
Around sleeve I2 and preferably concentric therewith is placed an eduction shield I8 so supported above the upper face of plate It (by any means not shown) as to allow a free flow of liquid beneath its lower edge. The upper end of this ring-shaped shield may be open but I prefer to close it partially, as by I neans of a hat ring i9 having a central opening 20.
The functioning of this device is illustrated by the solid lines 2|-2l showing, in a generalized manner, the directions of gas flow, and by the broken lines 22-22 showing the general directions of liquid flow.
Gas or vapor, as the case may be, flows upwardly through uptake Il, encounters ring I4 and is directed downwardly through the annular space between sleeves ll and l2 and outwardly through slots or perforations I3. Assuming a sufficient depth of liquid on the plate to submerge the upper ends of the slots, the upward flow of vapor through the annulus between sleeves i2 and I8 entrains a iiow of liquid which is ejected from the upper end of the annulus. At low vapor velocities the liquid will merely well up and overflow; at higher velocities it will be ejected in the form of a spray. In either case the mixture of vapor and liquid is retarded in the enlarged space above the annulus, the liquid falls into catchment basin 23 and is delivered through downcomer l5 onto the plate next below, and the vapor passes through opening 2i into the vapor space below the plate next above.
The limit of capacity of the cap is reached at the point at which the vapor-liquid spray is ejected so forcibly that the liquid is unable to separate from the vapor within the confines of the cap, it being essential to the best functioning of the device that only an immaterial proportion of the liquid be carried over into the vapor space and thus returned to the pool on the plate from which it was withdrawn. The ring IB in the upper end or the cap acts as a baffle and assists in separating and returning liquid to the collecting basin and is highly desirable where the vapor 3 velocity is high, though it may be omitted if the caps are to operate at low vapor velocities.
In the form shown in Fig. 2 a sleeve 24 is concentrically arranged around sleeve I3 and the annulus thus formed is closed at the bottom by a ring 25, forming an annular catchment well 26. This well is drained by one or more downcovers 21 which seal in liquid on the plate next below. The central downcomer I5 may be omitted, substituting a disc I4' for the ring I4 of Fig. 1, or, if desired, it may be retained to afford additional drainage. It is preferable to omit it from the form of Fig. 2 to fperrnit the caps to be placed closer together.
The form of Fig. 2 functions inaexactly the manner above described, the only difference between the two forms being in the location of the collecting receptacle and downcomers. `The second form allows somewhat more room above the electing annulus for the separation of liquid from vapor and will tolerate a higher vapor velocity through the perforations. On -theother hand, this separating space is "gained 'at the expense of a greaterv cap diameter, allowing a smaller number or caps on a plate of given diameter.
As the contact between liquid and vapor isproduced solely within the 'connes' of "the cap, no exterior space 'for the bubbling of vap'or 'through liquid is required. vIn consequence, vthe 'caps may be very closely spaced on the plate, even lface to face as illustrated in Figs. 3 and 4. l
In these figures, the solid 'circles i8 and 24`indicate the positions of the caps n'o'ne' plate and the dotted circles I8 and 24 the relative positions of the caps on the plates'immediately above 'and below. 1n Fig. 3 the downcomer l5 (of Fig. 1) is centered in the free space bounded by four adjacent caps. In Fig. 4 this space receives the downcomers 21 of two adjacent "caps" of 'the'type shown in Fig. 2. These figures suggest 'merely a minimum spacing and the caps may in 'practice be distributed over the plate'in any preferred pattern. Y y Y Columns equipped with these bubble caps have several advantages over columns ofthe conventional form in which the vapor is bubbled through a pool of liquid and in which Vthe liquid flows from one sideof the plate tothe other before passing to the plate next below. n
For example, in the conventional column vthe resistance to vapor flow through any 'one cap 'is a function of the depth to which the slots or perforations are submerged. It follows that'if any plate departs from level by tilting, sagging or buckling, the higher lying caps will'pass a vgreater amount of vapor through a shallower layer of liquid than those lying at a lowerlevel,
and the vapor will be unequally treated'over different areas of the plate. In extreme cases the caps on the higher part of the plate may lose submergence and permit vapor to blow through, or those lying at lower levels may drown out and permit no vapor to pass, or permit liquid to "now down through the vapor uptake.
Even though the plates be maintained level,
-the flow of liquid across the plate requires a material hydraulic head and in columns of' relatively great diameter, which are now coming-into common use, the difference in depth of liquid between the two sides of a plate may be enough'to cause a material difference in effectiveness between caps in different plate areas.
In the use of the form of bubble cap above described, the resistance to vapor nowls xedby the pressure drop through the perforations or slots and by the height of the contacting annulus 3| and is largely independent of the depth of liquid surrounding the cap. As these factors are uniform for all the caps on a given plate, and as the quantity of liquid entering the contacting annulus is determined by the quantity which the vgas now is able to eject (assuming sufficient free space below shield I8) the liquid flowthrough the annulus is atleast substantially independent Vof the depth of liquid surrounding the cap. Thus vit is impossible for a cap to unload or blow vdoing the liquid lissuccessiv'ely 4contactedwith several streams of vapor from a common'source and of identical composition. The *maximum difference in'composition between the liq'uid and the Vapor exists only at the pointfatwhich `the rst contact is effected and decreasesas the'contacts are repeated, only the lrstcap in the line of flow functioningatthemaximum efciency.
In the use'of Ythe bubble caps of 4the'present invention this' difficulty isv entirely avoided; rst by providing each bubble 'c'ap with at i leasty one down'comer, thus' bringing Ithe down'c'omers so close that horizontal flow is reduced to' 'an immaterial distance,` second, 'by contacting liquid and vapor Vin a confined 'space"in"'which liquid and'vapor are again' 'separated and from" which the once treated liquid 'is withdrawn onto 'the next lower plate without returning to 'the liquid pool from Which'the 'untreated liquidwas drawn. In the cooperation of these "two provisions, difficulties due to imperfect liquid distribution entirely disappear and ythe liquidiowingfrom one plate to the next 'may be equally contacted over the entire area of 'the plate.
An important 'advantage in "the 'described structure is the possibilityofmaking the contacting annulus'l rslong'as may be "desired, permitting the time of contact to be Iextended and the intimacy of Contact to' beincreased to any 'extent desired. With Yeven a moderate depth of laimulus and a"'moderate 'vapor velocity, the contact produced is "much more intimate and effective than 'that produced 'by 'the free bubbling of streams ofva'por' through a pool of liquid.
While the drawings Ishow the caps as'consisting of cylindricalelements they' maybe formed with straight sides 'in 'any'desired relative "dimensions, Vso V`long as the walls"l2 vand I8 are kept parallel and the contacting annulusil "of uniform width. `No advantage `is'presently seen `the capsin a` column' m'ay'bev 'expected to'p'er- 'fo'rm'in the same manner, a determination of the capacity and the optimum proportions for a single cap permits a column to be designed for the best performance without the elaborate balancing of numerous variables otherwise required.
I claim as my invention:
1. In a gas-liquid contacting column having a plate, a contacting unit comprising: a gas uptake extending above said plate; an inverted cup surmounting said uptake and provided along its lower edge with means for dividing a gas stream into a plurality of minor streams; a ringshaped shield surrounding said inverted cup and spaced therefrom to form a relatively narrow, vertical, annular conduit having parallel walls, the lower edge of said shield being spaced from said plate to allow liquid from said pool to enter said annular conduit; means disposed within said shield for collecting liquid educted through said annular conduit, said collecting f means arranged to prevent return of the educted liquid to the pool from which it was withdrawn, and means for draining said collected liquid onto a lower-lying plate, said last means arranged to prevent overow of liquid from said pool and to receive only said collected liquid.
2. A contacting unit adapted to be mounted on a horizontal partition plate in a gas-liquid contacting column and to maintain a liquid pool thereon, said unit comprising: a gas riser extending above the surface of said plate; a cup inverted over said gas riser and provided along its lower edge with means for dividing a stream of gas into a plurality of minor streams; a tubular shield surrounding said cup and forming therewith a relatively narrow, vertical, annular conduit having substantially parallel walls, the lower end of said shield being spaced from said plate to allow liquid to enter said conduit from said pool and to be ejected therefrom by said gas streams; means disposed within said shield for collecting the liquid so ejected, said means being arranged to prevent said liquid :from returning to the pool from which it was drawn, and a tube passing through said plate and sealed in liquid on a lower-lying plate for draining said collecting means without permitting the overflow of liquid from said pool.
HENRY N. WADE..
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 1,651,354 Alexander Dec. 6, 1927 1,725,052 Braun Aug. 20, 1929 1,744,543 Grace Jan. 21, 1930 1,748,595 Chillas, Jr. et al. Feb. 25, 1930 1,808,088 Urquhart June 2, 1931 1,821,619 Day Sept. 1, 1931 1,899,409 Bottoms Feb. 28, 1933 1,948,500 Bielfeldt Feb. 27, 1934 1,981,346 De Florez Nov. 20, 1934 1,983,762 Kotzebue Dec. 11, 1934 2,042,150 Hagenbuch May 26, 1936 2,150,498 Geddes et al Mar. 14, 1939 2,345,667 Hachmuth Apr. 4, 1944 2,497,136 Patterson Feb. 14, 1950