Method of carrying out absorption/distillation in a single column design

Abstract

Embodiments of the invention are directed to a process wherein two different unit operations (absorption and distillation) take place on either side of a top dividing wall column. One side of the dividing wall column uses absorption to separate non-condensable components from the feed; the other side of the dividing wall uses distillation to separate heavier liquid components.

Claims

1. A separation system comprising: a top divided column comprising: a vertical dividing wall disposed in the top divided column, the vertical dividing wall extending from a top of the top divided column and terminating above a bottom of the top divided column, the vertical dividing wall dividing the top divided column into a first side and a second side disposed on opposites sides of the vertical dividing wall; wherein the vertical dividing wall extends downward from a peripheral wall of the top divided column and terminates at a length that is less than the entire vertical length of the top divided column; a first top section disposed in the top of the top divided column and on the first side of the vertical dividing wall and a second top section disposed in the top of the top divided column and on the second side of the vertical dividing wall; a first section positioned beneath the first top section and on the first side of the vertical dividing wall, the first section extending from beneath the first top section; a second section positioned beneath the second top section and on the second side of the vertical dividing wall, the second section extending from beneath the second top section; and a first inlet fluidly coupled to the first section; a first condenser fluidly coupled to the first top section; an exchanger fluidly coupled to the second top section; a second condenser fluidly coupled between the exchanger and the second top section; and a pump fluidly coupled to a second inlet of the first section and an outlet of a third section of the top divided column, the third section disposed in the bottom of the top divided column and beneath the first and second sections; wherein the first top section comprises a third inlet fluidly coupled to the first condenser; wherein the first section comprises a fourth inlet fluidly coupled to the pump; and wherein the second top section comprises a fifth inlet fluidly coupled to the second condenser.

2. The separation system of claim 1, wherein the condenser further comprises a second outlet fluidly coupled to the condenser.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents a conventional C.sub.5 stabilizer in accordance with the prior art;

(2) FIG. 2 represents a conventional dehepatnizer column in accordance with the prior art;

(3) FIG. 3 represents a process scheme in accordance with an embodiment of the invention for a stabilizer design; and

(4) FIG. 4 represents a process scheme in accordance with an embodiment of the invention for a deheptanizer design.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(5) An embodiment of the invention is directed to a process wherein two different unit operations (absorption and distillation) take place on either side of a top dividing wall of a column.

(6) In an embodiment of the invention shown in FIG. 3, a process scheme of the claimed invention is designed to separate light components (non-condensable) 124, C.sub.5 (Top liquid product) 126, and C.sub.6+ (Heavies) 128 in a top divided column 100. A feed stream 102 is first sent to the pre-fractionation side of the top divided column 100 via a feed inlet 103. A vertical dividing wall 104 splits the top portion of the column into two halves. A feed side of the vertical dividing wall 104 is called a pre-fractionation section 106. An opposite side of the vertical dividing wall 104 is called a main section 107. Non-condensables (used as offgass) are removed as overhead vapor product 122 from a vent condenser 108. In certain embodiments of the invention, a column overhead pressure is set at 2.7 kg/cm.sup.2 g via a pressure controller on an overhead vapor product line 110. A top section 105 is located above the pre-fractionation section 106 and the main section 107 and a bottom section 111 is located below the pre-fractionation section 106 and the main section 107. The top section 105 is comprised of a first top section 1 and a second top section 2. The first top section 1 above the feed acts as an absorption section that is primarily used to minimize a loss of heavier components. The pre-fractionation section 106 side has reflux coming from two sources: 1) a liquid stream 109 condensed from the vent condenser 108; and 2) a heavy stream or reflux 121 from a bottoms feed line 120 that is pumped by a bottoms pump 112.

(7) In an embodiment of the invention, the light components (a vapor) 124 from the second top section 2 (the overhead of the main section 107) is condensed and cooled to 40 C. in air-cooled exchanger 114, and then fed to a water-cooled condenser 116. An outlet of the water-cooled condenser 116 is collected in an overhead receiver. The C.sub.5 liquid 126 is pumped out of the drum via reflux pumps. A portion of the light components 124 is sent back to the top divided column 100 as reflux 130 and the remainder is withdrawn as C.sub.5 product 126.

(8) In an embodiment of the invention, the temperature in the second top section 2 of the main section 107 is controlled in cascade with a reflux flow control loop that comprises a flow of fluid from top section 2 to the air-cooled exchanger 114, followed by the water-cooled condenser 116. This allows control over the quality of the C.sub.5 product 126 by suppressing a tendency of heavier components from going to the top of the top divided column 100.

(9) In an embodiment of the invention, a reboiler 118 is connected to the main section 107. The reboiler 118 may be a thermosyphon steam reboiler that uses steam as heating medium. Heat that is input to the reboiler 118 is regulated by controlling a flow of steam cascaded to the single top divided column 100 bottom tray temperature controller.

(10) The C.sub.5 bottom product is controlled by a level control loop in cascade with the bottom product flow rate.

(11) Table 1 presents a comparison of operational parameters between the conventional stabilizer design and the TDWC stabilizer design of the claimed invention.

(12) TABLE-US-00001 TABLE 1 Stabilizer Conventional design of the Operational Parameters Units Design invention C.sub.5 in product Kg/hr 367 659 Operating Pressure Kg/cm.sup.2g 8.3 2.7 RVP Psia 107 27 Overhead temperature C. 40 40 Duty MMkcal/hr 4.7 4.7 (integrated with HAC Overhead) C.sub.5 recovery Wt % 52.3% 96.8% C.sub.5 purity Wt % 59.1% 90.4% Benzene in C5 product Wt % 0.1% 0.1% Bottoms temperature C. 229 183

(13) FIG. 4 represents a process scheme in accordance with an embodiment of the invention for a deheptanizer design 200. FIG. 4 illustrates a top divided column 200 that is similar to the top divided column 100. Parts in FIG. 4 that are similar to the parts of FIG. 3 include similar part numbers. A pressure of the top divided column 200 is reduced to 1.8 kg/cm.sup.2 g. GT-Low pressure deheptanizer reduces consumption of energy by 19%. Similar to FIG. 3, top divided column 200 includes a feed stream 202, a feed inlet 203, a vertical dividing wall 204, a top section 205, a pre-fractionation section 206, a main section 207, a vent condenser 208, a liquid stream 209, an overhead vapor product line 210, a bottom section 211, a bottoms pump 212, an air-cooled exchanger 214, a water-cooled condenser 216, a reboiler 218, a bottoms feed line 220, a heavy stream or reflux 221, and overhead vapor product 222.

(14) Table 2 presents a comparison between the conventional deheptanizer design and the TDWC stabilizer design of the claimed invention.

(15) TABLE-US-00002 TABLE 2 Stabilizer Conventional design of the Operational Parameters Units Design invention Operating Pressure Kg/cm.sup.2g 5 1.8 Overhead temperature C. 40 40 Duty Mmkcal/hr 23.3 18.9 Bottoms temperature C. 227 193

(16) Overall aspects of the invention relate to methods for increasing the energy efficiency or better product purities in a distillation process using a top divided column. Those having skill in the art, with the knowledge gained from the present disclosure, will recognize that various changes could be made to the methods disclosed herein without departing from the scope of the present invention. Mechanisms used to explain theoretical or observed phenomena or results, shall be interpreted as illustrative only and not limiting in any way the scope of the appended claims.