US1945600A - Contact apparatus - Google Patents

Description

Feb. 6, 1934. G B, COUBRQUGH I1,945,600

CONTACT APPARATUS Original Filed NOV. 15. 1929 2 Sheets-Sheet l 54N v JilNl (da 64, re Z6 56 D I f90 /62 76 G/ Wnwu A Fig/ador auf M7/gi,

Feb; 6, 1934. G. B. COUBROUGH M CONTACT APPARATUS Original Filed Nov. 16, 1929 2 Sheets-Sheet 2 /neJJ Ewenior Patented Feb. 6, 1934 UNITED STATES PATENT OFFICE CONTACT APPARATUS Application November 16, 1929, Serial No. 407,670 Renewed July 12, 1933 Claims. (Cl. BB1-111) The present invention relates to contact apparatus and more particularly to contact apparatus for fractionating petroleum vapors.

One object of the present invention is to pro vide an apparatus for affording intimate repeated contact between a liquid and a gas or vapor. l

Another object of the invention is to fractionate petroleum vaporsto obtain a plurality of sharplyr defined separate products. l

With these and other objects in view, as will hereinafter appear, the principal invention contemplates forming one or `more contact zones in each of which the vapors are passed transversely through a vertical curtain or shower of liquid in streams of small dimensions. rThe liquids in the several zones are continuously and independently circulated for repeated contacts wtih the vapors. In the rectification of petroleum vapors, for which the present' invention is especially well adapted, provision is made for progressive flow of a portion of the liquid from one zone to another, whereby continuous counter-current reflux action is obtained.

The present invention, although applicable to any-process where intimate contact is desired, is particularly useful for rectification under vacuum because it provides a free passage for a large volume of vapors without interfering with the apparatus. Moreover, by virtue of the recirculation of the refiux liquid, a sufficient contact is assured to effect the desired degree of rectification, even though the volume of vapors may be excessively large and the'total quantity of refiux comparatively small.

As in any process of rectification, the' volume of reflux employed in any single zone is necessarily regulated to obtain the desired composition'of the products. One difficulty in usual vacuum distillation processes has been that with the excessively large volume of vapors, the regulated quantity of reflux is not sufficient to produce the desired intimacy of contact. With the present lnvention, however, this disadvantage is entirely avoided because by the continuous recirculation of the reflux in the separate zones, a high degree of contact may be maintained even with a relatively small total volume of reflux liquid.

A still further feature of the invention consists of a fractionating apparatus, whereby the recirculated refiux in some or all of the zones is cooled. The effect of cooling the liquid is to cause condensation of some of the vapors with which they contact. This condensation takes themaintenance of high vacuum in all parts of I place in addition to the liquefaction of vapors obtained by normal rectification; in fact, it tends actually to enhance the rectification by the establishment of well-defined gradient throughout the column, which makes for more complete frac- 6a tionation as the vapors proceed through the reflux zones.

Other features of the invention consist of certain novel features of construction hereinafter described and particularly defined in the claims. In the accompanying drawings, Fig. 1 is a diagrammatic sectional elevation of the preferred form of tower for practising the present invention; Fig. 2 is a section on line 2--2 of Fig. 1; Fig. 3 is a section online 3-3 of Fig. 1; and Fig. 70 4 is a section on line 4-4 of Fig. 1.

The illustrated embodiment of the invention is employed for the rectification ofhigh boiling petroleum oils to divide them into a plurality of sharply defined fractions of different physical characteristics. The method is particularly directed to operation on petroleum bottoms which comprise a mixture of gas oil and lubricating stocks. The oils are vaporized in any suitable still and are admitted to a counter-current column 6 through the inlet 8. The vapors pass through a plurality of rectifying zones indicated by the characters A to I inclusive. Each rectifying zone comprises a shower or spray in the form of a curtain of nely divided liquid. The vapors pass in a zigzag course horizontally through the curtains and in a general upward course through the column, as indicated by the arrows. Any number of rectifying zones may be employed, nine of such zones being indicated in the drawings.

Each zone is formed between an upper perforated spray or shower plate 10 and a lower collecting plate 12 both of which extend across the` column and are4 secured tothe wall thereof. As shown in Fig. 3, the shower plate 10 is provided with a large number of small perforations through which the oil passes in a fine vertical spray or shower to the collecting plate below. The perforations are sufficiently small to form streams of considerable aggregate surface area, 100

and are preferably so staggered as to present to the vapors the appearance of a complete curtain of liquid, whereby the vapors are assured of intimate contact with all of the liquid. The collecting plate 12 has a small upstanding overflow 105 lip 14. The collecting plate 12 of one zone is attached directly to the shower plate 10 of the zone immediately below, a small space 16 being provided between the two plates. Each shower plate is provided with a large upstandinglip 20 which 110 rises to a suiiicient height to prevent the flow of liquid over it. Each collecting plate 12 is formed with an extension 22 which blocks a portion of the column and forces the vapors to take the zigzag path as indicated. Each plate 22 connects with a trough 24 from which the liquid is witndrawn through a pipe 26. The pipe 26 connects with a pump 28 which forces the liquid through a cooler 30 and a pipe 32 into the space 16 immediately above the shower plate for that zone. It will be seen that there are provided eight trays, each comprising a collecting plate 10, a shower plate 12, and an extension 22. A11 of the assembled trays are of identical construction, except that the extensions 22 are connected alternately to opposite sides of the tower. There are also provided eight of the pumps 28 with suitably connectedcirculating pipes for maintaining a continuous independent liquid reflux circulation in each of the zones A to H. A circulating system for the uppermost zone I is not usually required, as will hereinafter be explained. The coolers 30 may be provided for several or all of the zones, as desired. As shown in the drawings, coolers are provided for all of the zones.. The coolers may comprise any suitable tubular heat exchangers, which may be cooled by water.

Above the uppermost rectifying zone I is a condensing or liquefying zone J which operates to effect a partial condensation of the vapors in accordance with the invention disclosed in my application Serial No. 355,870, filed April 17, 1929. This condensing zone comprises an upper shower plate 40 and a lower collecting plate 42. The plate 42 forms a part of a tray assembly 44 which is identical in construction with the trays above described. The tray 44 has a plate 48 connected with a trough 50 from which liquid is drawn off by a pump 52 to be circulated through the cooler 54 and returned to the shower plate 40. In the zone J, the liquid circulated by the pump 52 is employed for the purpose of condensing the vapors. Thus, the liquid collecting on the plate 42 is withdrawn rapidly, cooled inthe cooler 54, and returned to the shower plate 40 for repeated contact with the vapors. The liquid circulated 1n the zone J is of the same composition as the vapors passing through the zone, except as affected by the mixture therewith of a part of the light end product as a. refiux. The contact of the cooled descending liquid in the zone J with the hot vapors acts to condense a large part of the vapors, and thereby to permit the use of a final condenser of relatively small size. Overflow of liquid from the plate 42 is employed as reiiux in the rectifying zone I.

The vapors effluent from the tower pass through a vapor pipe 56 to be condensed in a condenser 68 leading to any suitable vacuum means. A portion of condensate from the condenser 68 is drawn off as a product through a pipe '70 and a portion is returned as reflux by a pipe 72 to the shower plate 40 of the upper zone J. The yproduct withdrawn through the pipe '70 is cooled in a cooler '76. The amount of product withdrawn, and hence the amount of reflux returned, is controlled by a valve '78. This product, which maybe a gas oil product, is the lightest condensate obtained by the process.

By the return of final condensate as reflux to the plate 40, the zone J is employed not only for the purpose of effecting condensation, but also to rectify the vapors to some extent.

The reux for the uppermost vrectifying zone I comprises the overfiow from the condensing zone J. From the bottom of the rectifying zone I, a product which may be designated the first intermediate product is drawn off through a pipe which is controlled by a valve 82. The product is cooled by passage through a cooler 84. In view 80 of the fact that a considerable amount of vapor is condensed in the liquefying zone J, there is a considerable overflow into the rectifying zone I so that a continuous independent circulation of reflux in the zone I is not required.

From the zone I, such liquid as is not drawn olf through the pipe 80 overflows onto the shower plate of zone H next below. In this zone, a con- `tnuous circulation of refiux is maintained by a lpump 28. The circulation is suiiiciently rapid sol that the shower plate is maintained completely covered, thus permitting the formation of a substantially complete wall of descending liquid across the path of the vapors. The circulation is maintained at such a rate that the liquid backs up on the collecting plate to the level of the lip 14, as indicated by the line 81. As vapors are liquefied in zone I, the excess liquid overfiows the lip and falls on the shower plate of the zone G next below. 'Ihis process is carried out for all the other 100 rectifying zones. A second intermediate product is withdrawn from the collecting trough of zone E through the pipe 86 which, in common with the other draw-off pipes, is provided with a cooler 88 and a control valve 90. Similarly, a third inter- 1;,5

mediate product is drawn ofi through the pipe 92 which has a cooler 94 anda control valve 96, and a heavy end product is drawn off from the lowest trough 38 through the pipe 98 which includes a cooler and a control valve 102.

It will be seen that the invention affords an accurate control of the constitutions of the several products. The heaviest product comprises the material obtained by the contact of the vapors constitution of this product is controlled by the valve 102. As the valve ,is opened, a greater proportion of the liquid is withdrawn and'a 'correspondingly less proportion is returned as reflux to the shower plate. products which are withdrawn through the pipes 92, 86 and 80 are controlled in composition by adjustment of their valves 96, 90 and 82. The amount of refiux returned to the uppermost rectilil-J with the liquid in the lowermost zone A. The no Similarly, the intermediate 1 o fying zone I is controlled by the overflow from the 12 condensing zone J, which in turn is controlled by the flow of refiux from the final condenser.

The coolers 30 are of importance in fractionating the vapors, and in determining the compositions of the intermediate products. Without the im occurs. The liquefied materials are in part withdrawn as intermediate products. The cooling of the reflux provides for a wide range of sharply fractionated intermediate products. The compositions of the intermediate products are subject to control by the degree of cooling effected by the coolers, which may be adjusted by varying the quantity or temperature of the cooling water.

A feature of importance resides in the construction of the shower plates. As illustrated in Figs. 2 and 3, the plates for the rectifying zones 150 are merely plain plates provided with perforations. In the event that the circulation of liquid is not suiciently rapid to keep the plate covered at all times, the type shown in Fig. 4 is to be preferred. This plate has a plurality of upstanding ribs 104 arranged to form a plurality of labyrinth channels. The pipe 55 flows the liquid over the left hand channel as viewed in Fig. 4. In the event that the tower is operated at low capacity, the quantity of recirculated liquid may be only suiiicient to cover the perforations in the left hand channel and the other1 channels will not be filled. As the rate of circulation of liquid is increased, the liquid flows in a manner to cover the perforations in other of the channels. In this manner, it is assured that a complete row of perforations extending completely across the tower is covered and that a complete curtain of spray is maintained. In Fig. 1, this type. of shower plate is shown only for the liquefying zone J, but it may beemployed with equal advantages for all of the rectifying stages.

In practise, all of the pumps and coolers are preferably maintained at a distance below the tower which is at least equal to the length of a barometric column of the liquid when the apparatus is operating under vacuum. This feature is described in the co-pending application of Collins, Serial No. 311,804, filed October l1, 1928. The pumps and coolers are, for reasons of simplicity, shown in the drawings, as being arranged alongside of their respective zones, a construction which would require-complete sealing of each piece of apparatus against the high vacuum maintained in the tower. By placing the external apparatus well below the tower, however, no precautions need be taken to prevent breakage of a vacuum.

The present invention, although useful for promoting contact between any liquid and a vapor, is particularly useful in the rectification of heavy petroleum oils where the operations are necessarily carried out under vacuum. Because of the' free passage of vapors, unobstructed by boiling caps or other well-known Contact expedients, the vacuum may be maintained through all parts of the column and distilling apparatus. As herein illustrated, the invention is applicable to distillation of heavy or high boiling petroleum oils` which are required to be distilled under a high vacuum to prevent decomposition. The oils in passing through the rectifying and condensing zones are subjected to contact with liquids of progressively decreasing boiling points, whereby a true counter-current reflux action is effected. Thus, the light product drawn off through the pipe 74 may consist of gas oil, the first intermediate product may be a light wax distillate, and the three remaining products drawn off through the pipes 86, 92 and 98 may be cylinder stocks of progressively increasing viscosities. By virtue of the high degree of contact obtainable with the present invention, and the fact that the invention permits distillation and rectification under extremelyhigh vacua, the heavy end products Having described the invention, what is claimed is:

1. A contact apparatus comprising a tower, a

plurality of trays inthe tower, each tray includlng a perforated shower plate and a superposed collecting plate, means for continuously circulating liquid collected on the collecting plate of each tray to the perforated shower plate of the tray next above, means permitting overflow of a portion of the liquid from each collecting plate directly to the shower plate immediately below, and means for passing vapors transversely through the showers.

2. An apparatus for rectifying oils under vacuum comprising a column, a plurality of trays in the column, each tray including a perforated shower plate and a superposed collecting plate, alternate trays extending inwardly from opposite sides of the column, means for passing vapors transversely through the showers beneath the shower plates, means for continuously pumping liquid from each collecting plate to the shower plate of the tray next above, and means permitting overflow of a portion of the liquid from each collecting plate to the shower plate next below.

3. A contact apparatus comprising a column, a shower plate having a plurality of perforations to form a vertical shower in the column, means for passing vapors transversely through the shower, a plurality of dams upstanding from the plate and extending across the plate to form a series of narrow labyrinth channels connected at opposite sides of the plate, and means for introducing liquid into one of the channels whereby the perforations in the separate channels are successively covered to assure the formation of a shower extending completely across the column.

4. An apparatus for rectifying oils comprising a column, a plurality of trays in the column, each tray including ay perforated shower plate and a superposed collecting plate, alternate collecting plates extending in opposite directions to the wall of the column, each collecting plate having an overow lip extending across the column, and means for continuously pumping liquid from each collecting plate to the shower plate of the tray next above.

5. Contact apparatus comprising a column, a plurality of trays in the column, each tray'including a perforated shower plate and a superposed imperforate collecting plate, alternate trays extending inwardly in opposite directions from the wall of the column, the shower plate of each tray being above the collecting plate of the tray next below, each collecting plate having an overflow lip extending across the column, and each shower plate having a lip of greater height than said first lip to prevent passage of liquid from a tray to the tray next below except through the shower plate,

means for introducing liquid to shower downwardl ly from one shower plate to the collecting plate next 'below and to overflow from said collecting plate to the shower plate of the corresponding tray, and-means for passing a gaseous uid upwardlythrough the colunm and in general horizontal paths between the trays.

GEORGE B. COUBROUGH.

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