US1947817A - Method for fractionating vapors - Google Patents

Description

lFeb. 20, 1934.

`J. S. WALLIS METHOD FOR FRACTIONATING VAPORS Filed Feb. 4, 1932 2 Sheets-Sheet 1 lill;

Feb. 20, 1934. J. s. wALLls METHOD FOR FRACTIONATING VAPORS Filed Feb. 4, 1932 2 Sheets-Sheet 2 N INVENTOR Joh/7 S. M///lls Jdmi ATToRN Y.

Patented Feb. 20, 1934 PATENT OFFICE METHOD Fon rnAoTIoNA'rnvG vArons John s. Wallis, New rink, N. Y., assigns: to Alco Products, Incorporated, .New York, N. Y.. a corporation o! Delaware Application February 4, 1932. serial No. 590,813 1 claims'. (ci. 19o-94) My invention relates to a method for fractionating hydrocarbon vapors or vapors of a similar character, and refers more particularly to a method of stripping;t side streams.

In order to remove the lighter constituents from the fractions which are segregated in the various. stages of a fractionating tower, it has been the practice to treat a side stream with open steam in order to strip it of its lighter and more volatile constituents. This practice is illustrated by United States patent to J. W. Lewis, 1,680,421 of August 14, 1928.

In the Lewis disclosure, two modications are shown, namely one in which the side streams are stripped by steam in separate stripping towers, and another modification showing the interior of a fractionating tower so constructed as to provide an auxiliary stripping section built within the tower.

When the stripping is performed in a separate stripping tower apart from the main fractionating tower, the stripped vapors are returned to the same fractionating zone from which the side stream being stripped is Withdrawn.

When the side streams are stripped within the mainfractionating tower, the number of trays which are served by the stripping section within the tower is xed. Usually, a tower having an internal stripping section is designedV for fractionating certain oils. If subsequently, it is desirable to run a new oil through the tower diiering from the` ones for which the tower was designed, or if it is desired to change the viscosity ilash or boiling range of the stream to be Withdrawn, the tower built with inside strippers will not permit the number of trays to be varied betweendrawos of side streams. It will readily be appreciated that a fractionating tower having a steam stripping section built into it is a very inflexible arrangement.

The position of the lowest drawoff for overhead stock must necessarily be fixed with relation to the vapor inlet to the tower and, consequently, no advantage will be gained from changing its location.

One object of my invention is to provide a method of fractionating in which a steam stripping of side streams is employed, which is more exible than a system wherein all'the side streams are steam stripped within the main fractionating tower.

Another object of my invention is to provide a fractionating method in which the bottommost side stream is stripped within the tower.

Another object of my invention is to provide tion is provided. The vapors rise upwardly through the tower, while the condensate I0 collects inY the trays provided therefor at various stages depending upon the boiling point a range of the respective fractions. Side streams are withdrawn from various trays to give oils of various Viscosities, or boiling point ranges. 26 These side streams are introduced into a stripping tower provided with a plurality of independent stripping sections wherein open live steam strips the various side streams of the lighter constituents. The stripped side streams are withdrawn from the respective stripping sections and passed to storage through suitable heat exchangers. The stripped vapors are reintroduced into the fractionatingv tower. The bottommost reux which collects in the lowest tray is stripped within the tower in a stripping section built therein. The object of maintaining one stripping section within the tower is to per.-

Amit the steam and light vapors to be introduced into the tower to effect a saving of steam and to reduce the partial pressure existing within the tower to enable a more complete fractionating to take place.

According to another modification of my process, I contemplate the collection of the stripped vapors from the stripping sections without the tower and their introduction into the stripping section within the tower, and the provision of means for introducing a portion of the vapors and light constituents from the stripping section within the tower to a point within the tower at or below the point of the main vapor introduction. A

According to another modification of my invention, I introduce the light constituents fromy the irst external stripping section into the next external stripping section, and from said stripping section into the internal stripping section.

Referring now to the drawings:

Figure 1 illustrates a schematic drawing of im one embodiment of my invention in which the side streams are stripped in an external stripping tower and the bottommost side stream is stripped within the fractionating tower.

Figure 2 illustrates a diagrammatic view of a modification of my invention in which the stripped vapors are introduced into the internal stripping section.

-Figure 3 illustrates another modification of my invention in which the stripped vapors from the various stripping sections are introduced into the internal stripping section.

More particularly referring now to the drawings which form part of the specification and in which like parts are designated by like reference numerals throughout the Various drawings, the hydrocarbon oil to be charged is introduced through line 1, through pump 2, through heat exchanger 3, through side stream heat exchangers 4, 5, 6, 7, and 8 to the convection bank 9 of tube still 10. From the convection bank the charge flows through the radiant heat bank 11 of the tube still 10 in which the charge is vaporized, through vapor inlet line 12, into the fractionating tower 13. The vapors course upwardly through the fractionating tower 13 which is provided with the bubble trays 14 in which pools of liquid collect. The lightest vapors pass from the fractionating tower 14 through overhead line 15, to the vapor condenser 16 which is maintained under a vacuum by steam jet 17 or Aother appropriate means. Cooling water flows through line 18 and condenses the lighter vapors. The condensate from the vapor condenser may be withdrawn by v pump 19 in the form of light gas oil or reintroduced into the tower by pump 20 through line 21 in the form of reflux. A coil 22 positioned in the tube still provides a steam superheater. A plurality of drawo lines 23, 24, 25, and 26 are provided for withdrawing side streams for steam stripping. The steam stripping tower 27 is provided with a plurality of independent stripping sections into which the side streams are introduced. The superheated steam leaves the tube still through line 28 which is provided with suitable branches 29 and 30 for leading the steam into the stripping sections. The stripping sections of stripping tower 27 will herein be referred to as the external stripping sections. The stripping section 31 within the fractionating tower 13 will be referred to as the internal stripping section. Suitable steam stripping pipes 32, 33, 34, 35, and 36 are provided within the stripping sections for introducing the open steam for stripping. A stripping pipe 37 is provided in' the bottom of the fractionating tower 13 for stripping the bottoms. The internal stripping section 31 in the modification shown in Figure 1 strips the reiiux which col.- lects in the bottom stripping tray 14A. The stripped vapors from the external stripping sections are reintroduced into the tower at points immediately below the trays from which they are withdrawn through suitable lines 38, 39, 40 and 41. The stripped side streams are withdrawn from the external stripping Asections through lines` 42, 43, 44, and which pass through respective heat exchangers 4, 5, 6, 7, and 8, through respective surge tanks 46, 47, 48, 49 and 50. Suitable coolers 51, 52, 53, 54, and are provided for the various side streams which range in viscosity between solar oil and heavy cylinder oil, depending upon the tray from which the side stream is withdrawn and upon the character of the charge. The bottoms from the fractionating tower 13 are withdrawn through line 56.

It is to be understood that the side stream ldrawoi lines may be4 placed at any suitable points. If desired, the tower may be constructed with manifold drawoi lines so that the tray from which the side stream is taken may be varied by a simple manipulation of valves. In operation, the vapors from the internal stripping section 31 are permitted to rise within the fractionating tower and to reduce the partial pressure existing therein in order to give a more complete fractionation.

In the modification shown in Figure 2, the vapor leaves the tube still as before and enters through vapor inlet line 12 into the fractionating tower 13 which is provided with an overhead vapor line 15 maintained under a sub-at.- mospheric pressure as before. The fractionating tower 13 is equipped with bubble trays 14 and side stream drawoffs 23 and 25. While I have shown only two side stream drawoi lines, it is to be understood that as many side streams as may be desired can be drawn of for stripping. A stripping tower 27 having separate stripping sections provided with stripping pipes 33 and 35 is provided to strip the side streams. The stripped vapors from the external stripping sections pass -through lines 57 and 58 and are collected in a single vapor line 59 which leads to the internal stripping section 31. The internal stripping section is provided with a vapor outlet 60 which extends downwardly to a point at or below the entry of the main vapor inlet line 12. The stripped reflux from the external stripping sections is withdrawn through lines 42 and 44 as before. The stripped reflux from the internal stripping section 31 is withdrawn through line 61.

pressure, has an internal stripping section 31 and an external stripping tower 27. 'I'he stripping towers are provided with steam stripping pipes 32, 33, and 35 as in the previous modincatlons..

The vapor'from the tube still enters the fractionating tower through vapor line 12. The side streams are withdrawn through lines 23 and 25 as in the previous modifications and are led to the respective sections of the stripping tower 27 where they are stripped of their lighter constituents. The stripped vapors and lighterproducts from the upper section of the stripping tower 27 which strips the lightest side stream are led through line 62 into the section of the stripping tower 27 in which the next heavier side stream is being stripped. This operation is continued for as many external stripping sections as may be used. The object of so employing the stripped vapors is to reduce the partial pressures existing in each stripping section by introducing thereinto the lighter vapors from the preceding stripping section. The aggrega vapors which are withdrawn from the last external stripping section are introduced into the internal stripping section 31 through line 63. The internal stripping section 31 is provided with a vapor outlet 60 as in the modification shown in Figure 2 `for introducing the stripped vapors into the fractionatlintg tower at a point at or near the main vapor in e It will be appreciated that my method and apparatus permits fractionating. of vapors and the use of steam stripping under very flexible control. By my method I am enabled to retain all the advantages of both internal -and external stripping and at the same time dispense with the respective disadvantages.` By maintaining the last stripping section within the tower, I am enabled to reintroduce into the point below the lowest drawof the steam and light vapors. By stripping the intermediate side streams externally I am enabled to obtain an assembly which is more flexible than that system wherein the side streams are stripped within the main fractionating tower. By reintroducing the stripped vapors and steam into the ash zone of the fractionating tower, I am enabled to reduce the partial pressure existing within the fractionating tower, which will give a lower outlet still temperature than would otherwise be possible and further eiect a distinct saving of the steam or fuel being used.

It will be understood that certain features, sub-combinations and operations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the 'specic details shown and described.

Having thus described my invention, what I claim is:

1. The method of distilling hydrocarbon oils which includes the steps of heating a hydrocarbon oil, separating vapors from unvaporized oil, passing said vapors countercurrent to and in contact with reflux oil in a fractionating zone, withdrawing an intermediate fraction of the reflux oil from said fractionating zone, stripping the same of its lighter constituents in an external stripping zone, stripping the heaviest reflux oil fraction with steam in an internal stripping zone separate from said unvaporized oil while permitting the steam and evolved vapors from said internal stripping step to enter the fractionating zone. 1

2. The method of distilling hydrocarbon oils which includes the steps of heating a hydrocarbon oil, separating vapors from unvaporized oil, passing said vapors countercurrent to and in contact with reflux condensate in a fractionating zone, withdrawing a plurality of intermediate fractions of the reux condensate from said fractionating zone, stripping the fractions so withdrawn in a plurality of respective external stripping zones, stripping the heaviest reux condensate fraction with steam in an internal stripping zone separate from said unvaporized oil while permitting the steam and evolved vapors from said internal stripping step to enter the fractionating zone.

3. The method according to claim 1 in which the unvaporized oil is stripped with steam in a separate zone, while permitting the evolved vapors to enter the fractionating zone.

4. The method according to claim 2 in which the unvaporized oil is stripped with steam in a 100 separate zone, while permitting the evolved vapors to enter the fractionating zone.

5. A method according to claim 1 wherein the vapors evolved in the external stripping zone are introduced into the internal stripping zone.

6.-A method according to claim 2 wherein the vapors in the external stripping zones are passed through each other in series, those from the lighter zone being introduced into the immediately heavier zone and the vapors from the last 11) external stripping zone being introduced into the internal stripping zone.

'7. The method according to claim 1 wherein the vapors from the internal stripping zone are introduced into the fractionating zone at or be- 115 low the point of the main vapor inlet from the heating zone.

JOHN S. WALLIS.

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