US2545691A - Fractionating apparatus - Google Patents

Description

March 20,1951 c. G. GE RHOLD FRACTIONATING APPARATUS Filed Jan. 51, 1947 Patented Mar. 20, 1951 UNITED STATES F F ICE FRACTIONATKNG APPARATUS Application January 31, 1947, Serial No. 725,517

1 Claim. 1

This invention relates to an improved contacting column of the fractionating type, or more specifically to means for effecting a relatively uniform liquid flow and liquid pressure over each bubble tray within a column and providing thereby a more uniform vapor distribution upwardly through each bubble tray or deck.

Bubble decks for fractionating and rectifying types of apparatus have been made in a variety of forms and have been made to operate in various manners. Normally, the downwardly flowing liquid within the chamber is received at one side of the deck by means of a down spout communicating with the top of the deck just below, thus the liquid flow is across the deck in a slight gradient to a downspout or downspouts, at the other side of the deck and in turn is discharged to the side of the deck next below. Vapors rising upwardly through the column are brought into contact with the cross flowing liquid stream on the deck plate by means of a number of vapor riser openings and vapor caps spaced throughout the main body of the deck.

In fractionating columns having bubble decks or trays of the usual conventional designs there are two tendencies which provide weaknesses fundamentally undesirable. One weakness is the flow pattern of the upwardly rising vapor stream whereby the passage of the vapors upwardly through the vapor riser and bubble caps is not uniform, or in other words, there is a' tendency for channelling through a part of the deck. This vapor channelling action is also one which tends to increase when once it has started to occur, for when vapor rises through a small section of liquid on a tray it reduces the apparent density of the liquid in that area and liquid is pumped outwardly therefrom along the top surface of the liquid flowing across the deck to further increase pressure head at the zones where less bubbling and mixing is taking place, The increased pressure head at the other portions of the deck thus still further increases the intensity of the channelling to the point where the vapors are concentrating in their upward flow through the deck. The second weakness of the conventional deck, is that coincidental with a channelling action there is a recirculation or a more stagnant region and returns along the deck floor to the zone in which the vapor rate is high. This recirculation eddy seriously interforce with the normal flow of net liquid across the deck and tends to increase the hydraulic pressure gradient across the deck with a resulting unequality of pressure differential conditions and a further increasing tendency to cause {an unequal vapor flow upwardly through the ,eck.

It is a principal object of this invention to provide bailiing or partitioning means between decks which provides for the maintenance of a substantially constant liquid head over the entire tray and to deter the recirculation of fluid and vapor bubbles along the top of the liquid flow and to thus attain an equalization of vapor flow upwardly through the deck.

Broadly, the improvement comprising this invention resides in the positioning of a plurality of partitioning members within the fractionating column between each of the bubble decks, with said partitioning members being placed vertically and made to intersect in a manner to form a plurality of open ended cells or standpipes above each of the decks. The lower extremities of each of the partitioning members forming the cells should extend into the liquid stream flowing the liquid within the cells directly above and the liquid head or back pressure is increased to provide resistance to a further increase in vapor channelling.

In the normally operating fractionating column, the depth of the liquid flow across each of the decks is controlled by the height of the overflow weirs, with the top surface of theliquid stream overflowing the outlet Weirs into the downspouts provided and thus passing to the deck next below. Thus, in the present invention, the lower edges of the partitioning members are spaced above the deck plate at a distance equal to approximately that of the weir height such that their lower ends extend just slightly into the flowing liquid stream. If the lower ends of the members are brought too close to the deck plate, the liquid flow and the normal hydraulic gradient is seriously interfered with.

In a preferable embodiment of the fractionating column, the baflie or partitioning members should intersect one another in a manner to provide a plurality of relatively small cells, contiguous with one another, such that a standpipe action may be provided for a relatively small area of the deck. With small cells or standpipes, vapor channelling through a small area, such as at one small type bubble cap or at a portion of the slots of a large cap, will produce a rather immediate build-up of pressure head inthe cell or standpipe above and thereby be in turn counteracted by this increased pressure head above. It may thus be seen, that the advantage of the present invention, is that where there is a tendency for one section of the deck to get a substantially larger percentage of the vapor flow than average, a pumping action of the increased vapor flow would result in forcing liquid into the cells above that section and the cells would in turn increase the back pressure on that section to provide a reduction in vapor flow. Also, the tendency of a channelling action to cause recirculation or back-flow and to thereby choke-off the normal liquid flow is substantially eliminated since the surface component of the eddy is blocked by the baflie members.

Reference to the accompanying drawing, and the following description thereof, will more clearly point out the construction and advantageous feature of the invention whereby the vapor flow and liquid contact is maintained fundamentally stable and is automatically returned to a more uniform flow distribution when channelling does tend to occur.

Figure 1 of the drawing is a sectional plan view through a liquid and vapor contacting chamber having bubble decks therein and one 'form of bafiiing and partitioning members.

Figure 2 of the drawing is a sectional View through a portion of a bubble tray chamber having the baffling members of this invention placed therein, as indicated by line 2-2, of Figure 1.

Figures 3 and 4 indicate diagrammatically other patterns for placing and intersecting the baffling members which may be placed above each deck in an improved contacting chamber.

Referring now to Figures 1 and 2 of the drawing, there is shown a shell l of a contacting chamber, such as a fractionating column, ab-

sorber, scrubber, or other liquid and vapor containing chamber, which has a plurality of horizontally placed bubble decks therein. The deck plates 2 in turn have a plurality of vapor riser openings 3 therethrough and over each of the vapor riser openings 3, is a bubble cap A which has a serrated or slotted lower edge. The bubble caps 4 are spaced and mounted above the vapor openings such that the vapor stream is caused to reverse its direction of flow and bubble into the liquid stream 5 which flows across the surface of the deck plate 2. The liquid flow across each of the decks is provided by means of downspouts 6 which alternate in their positioning .method ofv support. Also, the vapor riser open- .-ings 3. and bubble caps 4 are shown tobe ofthe positioned vertically therein such that a multiplicity of cells are formed in the area between bubble decks. The lower extremity of the par- .titioning members 8 terminate at a point approximately equal to the height of the upper end of the, downspout 6, which in the embodiment illustrated provides the over flow weir for the liquid discharging from each deck. As shown ,in Figure 1,. some of the baiiles 8 are disposed directly above certain of the bubble caps 4. The lower edges of these baflles are cut out to accomodate the caps therebelow and to extend to a point near the upperend of downspout 6. In a preferred construction of the improved chamber and deck, the baffling members may be positioned and supported in a manner to have the space between the lower end of the members and the deck 2 adjustable, however, since it is desirable to have the members 8, or the lower ends of the formed open-ended cells, extend into the flowing liquid stream just to a point approximating that where the vapors form bubbles from the vapor stream, such positioning may be normally predetermined from the bubble cap slotting and fromthe overflow weir height. Observation has shown, that the recirculation or back flow of liquid from an excessive vapor flow occurs at the surface of the liquid. Thus, care must be taken in spacing the lower end of the baffling members 8 such that they do not penetrate downwardly into the liquid to such an extent that they retard the normal liquid flow across the deck. As long as just the upper surface of the liquid enters each of the cells or standpipes formed by the vertical partitioning members 8, backflow and build-up in pressure head can be held to a local area and be made to operate against vapor channelling or unequal distribution throughout each of the decks. The partitioning plates 8 extend to or terminate short of the deck next above, such that they do not interfere with vapor distribution to the lower side of that deck.

In Figures 1 and 2 of the drawing, the baffle members 8 are indicated to be at right angles with one another and to provide square or rectangularly shaped cells or standpipes. In the improved contacting column of this invention,

however, it is not necessary that the cells be of any particular shape or cross sectional pattern, for in general cells of nearly any polygonal shape,

contiguous to one another, and placed above each deck may be equallyeffective. However, in a preferred embodiment, as previously noted, it is desirable that the cells be of relatively small cross sectional area such that a slight increase in vapor flow at any particular zone will cause an immediate buildup in pressure head within the cell above and counteract the tendency towards vapor channelling. Figures 3 and 4 of the drawing indicate is not intended to limit the invention to employing one cell or standpipe for each bubble cap.

I claim as my invention:

In a vapor and liquid contacting column comprising a closed chamber, and means to pass liquid and vapor therethrough, a plurality of bubble decks spaced vertically within said chamend of said members terminating at a point approximately the height of said liquid overflow weir whereby the lower end of said open ended cells project into the upper surface of the liquid flowing across said deck.

CLARENCE G. GERHOLD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 882,767 Moran et a1 Mar. 24, 1908 1,865,172 Cook June 28, 1932 1,983,762 Kotzebue Dec. 11, 1934 2,202,071 Van Dongen et a1. May 28, 1940

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