US2578925A - Fractionating tower - Google Patents

Description

'Dt-2C. 18, 1951 I H; R DAVIS 2,578,925

FRACTIONATING TOWER Filed Jan. l5, 1948 2 SHEETS-SHEET l IN VEN TOR.

Dec. 18, 1951 H. R. DAVIS 2,578,925

FRACTIONATING TOWER Filed Jan. 15, 1948 2 SHEETS-SHEET 2 INVENTOR.

159mm mayas T RNEY Patented Dec. 18, 1951 UNITED STATES PATENT fol-FICE FRACTIONATING TGWEB Hyman R. Davis, Jackson Heights, N. Y. Application January 15, 1948, Serial No. 2,412

2 Claims. (Cl. 202-158) This invention relates to improvements in vaporizing chambers, fractionating columns and the like and more particularly to an arrangement of heat exchangers or condensers for the condensation of overhead vapors therefrom.

In ythe continuous fractional distillation of chemical mixtures, as an example, it is common to establish a temperature difference in the fractionating column with a relatively high temperature at the bottom and with a lower temperature at the top so that the lighter boiling vapors will continuously rise through the downcoming liquidy for the desired fractionation. With vacuum distillation, columns become of substantially larger dimensions than with pressure columns and it is frequently necessary to construct columns which are ten feet or more in diameter at their upper part.

With a column of this type the vapors are removed from the uppermost part through one or more vapor lines which are carried over to suitable heat exchangers or condensers which are generally mounted independently at some suitable elevated position. It has been found, however, that the mechanical connection of the heat exchangers or condensers with the upper part of the column is a substantial problem due to the fact that vapor lines may be of the order of 36.

inches or more in diameter and large radius bends are required for the connection. These bends made the entire vapor lines oversize Bourdon tubes so that with dilerences in temperature or pressure, extraordinary stresses are set up in the lines, or on the column or on the heat exchangers or on the supporting equipment. Furthermore, external vapor lines must withstand pressure differences that are substantial and with corrosive vapors, suitable alloy overhead lines become extremely costly.

The principal feature of my invention is the provision of a novel construction of vaporizing chamber and vapor condenser therefor in which the vapors which pass to an upper zone of the chamber may be drawn downwardly within the chamber and removed at a lower point to the condenser for economy of construction and simplification of maintenance.

A more specific object of my invention is to provide a fractionating column having internal vapor downcomers so that the heat exchange equipment for overhead vapor condensation can be mounted substantially at grade level and overhead vapor lines may be eliminated.

, placed in a vaporizing chamber in such a manner as to make it possible to directly connect the condenser equipment at the lower part of the column. A still further object of the invention is to simplify the construction of vapor ducts in vacuum distillation equipment by placing the duets within the vacuum space so that there is a minor pressure diiference across the ducts.

Further objects and advantages will appear from the following description of a preferred form of embodiment of my invention taken in l connection with the attached drawings which are illustrative thereof and in which;

Figure 1 is a substantially central vertical section through a fractionating column adapted for\ vacuum operation;

Figure 2 is a horizontal cross section taken substantially on the line 2-2 of Figure l;

Figure 3 is a horizontal cross section taken substantially along the line 3-3 of Figure l;

Figure 4 is a substantially central vertical section of a modified form of vacuum distillation column;

Figure 5 is a horizontal cross section taken substantially along the line 5 5 of Figure 4;

Figure 6 is a partial vertical cross section taken substantially along the line 6-6 of Figure 5;

Figure 7 is a vertical cross section of a detail of a further form oi embodiment.

In accordance with the preferred form of embodiment of my invention, the column generally indicated at I0 in Figure 1 is a vacuum distillation column supported by skirt Il. The feed is' introduced to the column through the dual inlets I2 shown in Figures 2 and 3 which enter behind baiiles I4 to introduce the charge largely in vapor phase into the bottom of the chamber I6.

The vapors are deflected by the lower edge of the baliies i4 to make a complete 180 turn to discharge any liquid therein and this liquid may be removed through line I8. The vapors then pass upwardly through centrifugal separating devices 20, the sides of which may be conveniently provided with tangentially disposed plates 22. These tend to develop a centrifugal path and vortex to the vapors which will throw out any liquid entrained in the vapors. Liquid line 24 carries oif any such liquid.

The vapors continuously move upward through the central portion of the column as determined by walls or baffles 26 and the vapors may pass through a bubble deck section or a shower o! liquid passing from the shower tray 28a to tra 28. The shower tray 28a is conveniently supplie with reux liquid of a suitable type through line 30.

The column I is provided with a small dome section 32 having a relief valve connection 34. The walls or bales 26 extend almost to this dome section and form vapor ducts or downcomers generally shown at 36. (See Figs. 2 and 3.)

The entire vapor load is thereby carried immediately downward between the inner wall or bafes 26 and the outer shell I0 through these downcomers 36 into a plenum chamber 38. The vapors then pass through the one or more internal heat exchanger or condenser groups as 40 and 42 with the condensate being trapped out on bafe 44 and the vapors passing around the baille as through the path 46. The condensate is removed through line 49 which is suitably sealed to prevent by-passing of vapors. This condensate overiiows into the bottom 50.

Subcooling of the vapors may be accomplished in condenser 48 with any further condensate also collecting in the bottom of the column at 50. A

condensate removal line is provided at 63.

A vapor path 52 is provided around each side of the heat exchange or condenser group 48 so that the vapors may then be drawn upwardly through a bubble cap section generally designated 54 in which they are subjected to further fractionation or absorption in the presence of a suitable liquid introduced at 56. The absorbed liquid may be removed at 51, cross pipe 62 serving to remove the fiow across the tower.

Batlle structure 58 delineates the downwardly moving vapor path from plenum chamber 38 through the heat exchanger groups 4l) and 42 from the upwardly rising vapors passing through the bubble cap section 54. The vapors are then removed by suitable vacuum producing apparatus through line 60. A vapor equalizing pipe 6| is used between opposite sides of the column I0.

The provision of the internal vapor ducts 36 is a fundamental feature of my invention in that external vapor lines can be completely eliminated with but a slight increase in the tower diameter. As more particularly shown in Figure 2, the vapor ducts 36 are established by the chordal plates 26 although it will be understood that other appropriate shapes of section could be provided or a central duct could be used within the shell I0. The inner walls 26 of ducts 36 may be of relatively thin material inasmuch as there is no substantial pressure difference between the respective sides of the ducts.

In this form of embodiment, the column I0 is particularly suitable for the treatment of cracking stock for the removal of objectionable end materials prior to further cracking. In such case, the feed at I2 is from a pipe still, not shown.

A modied form of construction is shown in Figures 4, and 6, In this case, the column 10 is provided with a series of internal vapor downpipesl 12 each of which is formed partially integral with the shell wall. The feed is introduced at 14 and the rising vapors pass through downcoming liquid streams on bubble decks or passing between the shower trays generally designated 16. Initially reflux is introduced to these trays through line 18 but as the heavy portions of the feed are condensed, added reux is formed.

The vapors pass to the dome section 19 of the column `as in the prior construction and then pass downwardly through the vapor ducts 12 to the vapor collection sections 80 from which the vapors pass outwardly through lines 8| and 4 through the condensers 82. Vacuum is applied through lines 84 and the condensate is removed through lines 86 by pump 88.

If desired, a stripping section generally indicated at 90 may be provided below the point of feed with the heavy liquid removed through the pipe 92 which discharges into the seal 93 and thence discharges into the base 94 of the tower. Stripping steam may be introduced through the line 95.

As in the prior case, it will be apparent that the column 10 as well as the condensers 82 may be mounted directly from the-ground, as by skirt 99, the condensers 82 being at substantially grade level with only such elevation as may be necessary to supply the head for pump 88. It is thus possible to more simply maintain the equipment andit is far less expensive to support it close to the ground and to avoid external vapor lines. Considerable economies can also be effected with corrosive crudes by utilizing light guage alloy plate (12 ga.) for downcomers 12 rather than the customary heavy plate for the external vapor lines.

This form of embodiment is particularly applicable to the treatment of lubricating oil stock and, in such case, a medium side cut such as SAE-30 distillate may be removed from trap tray at 96 and an SAE-10 cut with gas oil may be removed as the overhead product from the discharge 91 of pump 88. The heavy residual product which may be utilized for bright stock may be removed from the tower outlet 98.

A still further modified form of construction is partially shown in Figure '1 in which the column ||0 is provided with the vapor ducts ||2 as in the prior case but they extend to the base of the column, the chamber I|4 serving as a plenum chamber to which the external condensers I6 are attached. In this case, the condensers may be provided with an inlet box ||8 for 'direct connection to the base chamber I I4. The residual conduct outlet is shown at |20 and the light material is removed at |22 from the bottom of the condensers. The column may be drained at |24 and steam may be introduced at |25 to the stripping section.

While I have shown and described a preferred form of embodiment of my invention, I am aware that modifications may be made thereto and I therefore de sire a broad interpretation of my invention within the scope and spirit of the description herein and of the claims appended hereinafter.

I claim:

1. A vacuum distillation column having an intermediate vaporization chamber, means to feed a vaporizable material thereto, a scrubbing section to remove heavy components of the vapors above the vaporization chamber, a vapor dome portion above the scrubbing section, integral vapor removal ducts within the column in open communication with the vapor dome, heat exchange means extending transversely of the column below the inlet to the vaporization chamber. integral baiiles confining the vapors to said heat exchange surface, said baffles being open at their lower end, and internally in communication with the lower ends of the ducts, means to apply a vacuum to the space between the bales and intei-mediate the length of the column whereby vapors will flow from the vaporization chamber through the scrubbing section to the upper part of the column, thence through the internal ducts to and across the heat exchange surface, thence to the lower part of the column and thence along the wall of the column to the point of vvacuum application, a series of bubble decks between the heat exchange enclosure batlles and the column Wall, said bubble decks being in the path of vapors passing from the heat exchange means to the point of vacuum application and means to supply i scrubbing liquid thereto.

2. A vertical vacuum distillation column havlng an intermediate vaporization chamber; means to feeda vaporzable material thereto including gas and liquid separating means within the vaporization chamber; liquid draw off means in the CII bottom portion of the vaporization chamber; Y

vapor separating devices including a mountingV deck disposed above said feed means-and comprising the top portion of the vaporization chamber; a scrubbing section above the separating devices to remove heavy components of the vapors from the vaporization chamber; means for removing discharged liquid from said deck; a vaporv dome portion above the scrubbing section; in-` tegral vapor removal ducts within the column in open communication with the vapor dome; surface heat exchange means extending transversely of the column below the feed means ofthe vaporization chamber; integral bailles confining downowing vapors tosaid heat exchange means and forming with the bottom of the vaporization chamber a plenum chamber in open communin cation with the lower ends of said vapor removal f ducts, the internalv space defined by said con- I'lning bailes being open at its lower end; means to apply a vacuum to the outer space between the confining bailles and the column below said plenum chamber, whereby vapors will flow from the vaporization chamber through the vapor separating devices and the scrubbing section to the upper vapor dome of the column. thence through the integral ducts to said plenum chamber and across the heat exchange means to the to the lower part of the column, and thence out of the conning bailies and along the wall of the column to the point of vacuum application; and a liquid removal conduit communicating with the column below the lower end of the confining bailles.

HYMAN R. DAVIS.

REFERENCES CITED The following references are of record inthe

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