US2531030A - Tunnel-type bubble cap and means for controlling vapor distribution therethrough - Google Patents

Description

Nov. 21, 1950 2,531,030

W. S. CRAFT TUNNEL-TYPE BUBBLE CAP AND MEANS FOR CONTROLLING VAPOR DISTRIBUTION THERETHROUGH Filed Oct. 21, 1947 CO'i'LLzlahQ 5. Craft Gnvenbor' bg l/ 'D. 7 Obbor'na used for a considerable period or time.

Patented Nov. 21, 1950 TUNNEL-TYPE BUBBLE CAP AND MEANS FOR CONTROLLING VAPOR DISTBIB TION THEBETHROUGH William 8. Craft, CranIord, N. 1., assignor to Standard Oil Development Company, a corporation of Delaware Application October 21, 1947, Serial No. 781,102

6 Claims. (Cl. 261-114) L the plates.-

Channel or tunnel-type bubble caps have been Ordinarily they are designed to extend'over substantially the full width of the plates, arranged in spaced relation parallel with the direction of liquid flow across the plates. The caps themselves, like the more conventional circular bubble caps, are provided with a slotted or notched skirt portion to facilitate distribution or vapors thereover. Various types of baiiie members internally of the caps and plate chimneys have also been proposed to aid such distribution and equalize now.

In practice, however, it has been observed that.

the efliciency of fractionating towers equipped with channel-type caps is not satisfactory, and in some cases there has been a marked tendency toward surging in the rates of flow of vapors and liquid with resultant erratic operating characteristic's. Further, it has been observed in studies of the hydraulics of bubble tray operation, and by visual inspection of all types of operating equipment, that an appreciable gradient normally exists in the depth of liquid from one side of a tray to the other. In many cases the depth at the inlet side of the tray may be several inches higher than the depth at the outlet side. When operating with tunnel-type bubble eapa this difference in the head of liquid from one end or a cap to the other has the efiect of inducing the major portion of the vapor flow to pass through or over the notches at the outi let end of the cap. The excessive discharge of vapors at the outlet side of the plates produces excessive turbulence at that point, impeding liquid flow, and further aggravating the gradient condition. Excessive cross-flow of vapors between plates also results.

It is an object of this invention to provide a channel or tunnel-type bubble cap which will produce the same vapor flow at the inlet end as at the outlet end, thereby improving over-all flow distribution over the full area of the bubble cap trays. By such improvement, higher plate emciency may be obtained, with more stable opcrating characteristics. and higher permissible vapor velocities in a tower of given size. The benefit of such improvements may be realized by the attainment ofhigher capacities, and better efliciency in existing apparatus, or by reduction in the size of apparatus required for a given capacity in new units.

The invention and its objects may be fully understood "from the followingdescription when read in conjunction with the accompanying drawings, inwhich:

Fig. 1 is'a vertical section through a portion of a fractionation tower showing one form of the bubble cap according to the invention.

Fig. 2 is a similar view showing another form of the invention.

Fig. 3 is a similar view showing a third form of the invention, and

Fig. 4 is a horizontal section through a tower of the type shown in Figs. 1 to 3 inclusive.

With particular reference to the drawings, the numeral I designates the shell of a fractionating tower in which is disposed a vertical series of trays or plates 2, equipped with channel or tunnel-type bubble caps 3 disposed over the conventional elongated chimney elements indicated at 2c which provide for upward flow of fluids through the plates 2. In a cylindrical tower as shown, each tray is circular in shape, fitting the tower walls in fluid-tight relation, except that a segment of each tray is removed or omitted, as at X to provide an opening which permits liquid flow downward from tray to tray. In locating the trays in' the tower, the segmental openings in the several trays are oppositely positioned to pro vide cross-flow over the trays in succession. A weir-ballle member, including a weir portion 2a, and a baffle portion 2b, is provided along the tray edge at each segmental opening in order to maintain a desired liquid level on each tray, and to prevent passage of vapors from tray to tray, except through the bubble cap elements 3.

The normal liquid gradient on the trays or plates 2 is indicated at Y, and as shown, runs from the deepest point at the inlet side of the plate, at the bailie 2b, to the shallowest point at the outlet side, at the weir 2a. The gradient as indicated has been exaggerated for the purpose gf illustration. The line H indicates the center line of the tower and plates.

In each of the three forms or the invention illustrated by Figs. 1, 2 and 3, the desired regulation of vapor flow is obtained by somewhat difierent means, but the main object of the inven- 3 tion is retained. This object involves a distribution of vapor flow over the total periphery of each cap in such fashion that the pressure cheat or resistance to such flowat the inlet end of the cap, by reason of the greater depth of liquid at that end, is substantially overcome. This result is obtained by providing a progressively greater area for-vapor flow per unit of length of the bubble cap from the outlet end to the inlet end of each cap. with up to about 70 percent of the total vapor flow area, and preferably from 55% to 70% of such area being disposed in that half of the cap extending from the center line H toward the plate inlet end at the baiile 2b.

In the construction illustrated by Fig. 1, the cap I is provided with notched or slotted portions to which are of similar shape. and of equal dimensions but are more closely spaced, center to center, at the inlet end than at the outlet end, the spacing being increased in a generally progressive fashion toward the outlet.

In the construction illustrated by Fig. 2, the 4 cap 3 is provided with notched or slotted portions to which are of equal width, and are equally spaced, from center to center, about the cap skirt, but are deeper, extending into the skirt in greater depth, as the inlet end of the cap is approached. The inner or upper ends of the notched portions thus lie along a sloped line, which line normally will have substantially the same gradient as that anticipated for the level of the liquid flowing across the plate.

In the construction illustrated by Fig. 3, the cap 3 is provided, with notched or slotted portions 3a which are of equal height, and are equally spaced from center to center about the periphery of the cap, but the width of each slot is increased regularly from the outlet end toward the inlet end of the cap. In this form, and also in the forms illustrated by Figs. 1 and 2, in the end portions of the caps 3, the notches or slots is generally will be of the same dimensions. and be spaced to the same degree as those in the adjacent side wall portions of the cap skirt.

Although described in relation to its use in connection with fractionation apparatus, for the purpose of illustration, it is not intended that the invention be limited thereto. but only by the appended claims.

I claim:

1. In a fluid contacting tower, vertically spaced transverse plates in said tower, each 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 across an intermediate portion 55 Number or said plate from inlet to outlet, elongated chimney elements opening upwardly through each plate in the intermediate portion thereof, extending substantially from a plate inlet at one end to a plate outlet at the other end in the direction of .0 23741950 liquid flow across said plate, said chimney elements providing for the flow of a second fluid upwardly through said plate and the tower, a tunnel-type bubble cap for each chimney element and substantially co-extensive therewith, each bubble cap having a peripheral dependent skirt normally submerged in the liquid ilowing across the plate, and a plate inlet and a plate outlet end, and means for equalizing the distribution of said second fluid normally flowing upwardly through said chimney elements over the lower peripheral edge of each bubble cap shirt in service, comprising a plurality of notch portions disposed in peripherally spaced relation along the lower edge of said skirt and extending upwardly therein, the total area of said notch portions per unit of length of the bubble cap increasing progressively from the plate outlet end to the plate inlet end of said bubble cap with the total area of said notch portions from the lateral center line of the cap to the plate inlet end thereof being greater than the total area of said notch portions from the center line of the cap to the plate outlet end thereof.

2. A means according to claim 1, in which the area of the individual notch portions increases progressively from the outlet end to the inlet end of said cap.

3. A means according to claim 1. in which the total area of said notch portions from the lateral center line to the inlet end is from about to percent of the area of all such portions in the skirt of said cap.

4. A means according to claim 2, in which the width of said notch portions progressively incgases while the depth and spacing remain cons nt.

5. A means according to claim 2 in which the depth of said notch portions progressively increases while the width and spacing remain constan 6. A means according to claim 1, in which the individual notch portions are of equal area, said portions being spaced along the lower edges of said skirt at progressively increasing center to center distances from the outlet end to the inlet end of said cap.

WILLIAM S. CRAFT.

REFERENCES CITED The followlng references are of record in the flle of this patent:

' 111mm) s'ra'ms PA'I'ENIS Name Date 1,620,751 Bartlett Mar.'15, 1927 1,824,836 Plggot Sept. 29, 1931 1,893,906 Primrose et a1 Jan. 10, 1933 1,935,709 Hall Nov. 21, 1933 Packie et al. May 1, 1945

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