US3607734A

US3607734A - Light hydrocarbon absorption and fractionation

Info

Publication number: US3607734A
Application number: US874592A
Authority: US
Inventors: Thomas R Stafford Sr
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1969-11-06
Filing date: 1969-11-06
Publication date: 1971-09-21
Anticipated expiration: 1988-09-21

Abstract

A mixture of gaseous and liquid hydrocarbons are processed in an integrated column in which absorbing, demethanizing (or deethanizing or depropanizing) and splitting operations are combined. Gaseous feed is introduced to the absorber section and liquid feed to the absorber section and/or the splitter section. A light naphtha fraction from the splitter section is used as the primary absorbing medium in the absorber section. Heavy naphtha, also from the splitter section is used as lean oil in a sponge section, primarily to remove light lean oil from absorber section overhead. Absorber fat oil, light naphtha, heavy naphtha, bottoms and fuel gas are or can be produced as products.

Description

United States Patent [72] Inventor Thomas R. Stafford, Sr.

Baton Rouge, La. [21] Appl. No. 874,592 [22] Filed Nov. 6, 1969 [45] Patented Sept. 21,197] [73] Assignee Esso Research and Engineering Company [54] LIGHT HYDROCARBON ABSORPTION AND FRACTIONATION 4 Claims, 4 Drawing Figs.

[52] U.S.Cl 208/341, 208/35 1 208/358 [51] lnt.Cl Cl0g5/04 [50] Field oi Search 208/341, 358, 35 1 [56] References Cited UNITED STATES PATENTS 2,281,282 4/1942 Gerhold 208/341 2,472,810 6/1949 Denig 2,710,278 6/1955 Gilmore Primary Examiner-Herbert Levine Attorneys-Pearlman and Stahl and C. D. Stores ABSTRACT: A mixture of gaseous and liquid hydrocarbons are processed in anintegrated column in which absorbing, demethanizing (or deethanizing or depropanizing) and splitting operations are combined. Gaseous feed is introduced to the absorber section and liquid feed to the absorber section and/or the splitter section. A light naphtha fraction from the splitter section is used as the primary absorbing medium in the absorber section. Heavy naphtha, also from the splitter section is used as lean oil in a sponge section, primarily to remove light lean oil from absorber section overhead. Absorber fat oil, light naphtha, heavy naphtha, bottoms and fuel gas are or can be produced as products.

AND

TOTAL [RMOF F HIGH PRESSURE GAS 204 H2,N2,CO.C02 mo ABSORP- HYDROCARBONS c. THRU SPLITTI KE SECTION LOW PRESSURE CONTRG. LED

WIT FEED ZIO UP TO 330' F 209 KAVY NAPHTHA BOT TOMS 430'F 214 ND HEAVIER PATENTEU SEP21 can SHEU 1 [IF 4 PATENTEI] SEP21 I971 SHEET 2 OF 4 PATENTEDSEPZI I97! 3,607,734

sum 3 [IF 4 H2, N2, co, c0 ,c AND AND CONTROLLED AMOUNT OF c 8& FUEL GAS OR 0 RECOVERY UNIT FEED 0o HEAVY H LEAN OIL K SPONGE 2n TOTAL SECTION LIGHT HIGH PRESSURE GAS L20 n H2,N2,CO,CO2 AND f HYDROCARBONS c THRU i, 250F i i I i K u T0 330 F i F l i I i SPLITTING i SECTION 2 Low PRESSURE DISTILLATE L c -45o F f LHEAVY NAPHTHA I E y 330-430 F BOTTOMS AND HEAVIER INVENTOR.

ATTORNEY PATENTED SEP2I 1911 LEAN NON-OLEFINIC GAS CAT. CR ACKER OVERHEAD LIQUID PRODUCT ABSORBER SEQTIQN TOTAL PRODUCT FROM UNSATURATE COMPRESSION FACI LITIES SHEET III 4 I30 PSIA A LEAN GAS T0 TREATING AND FUEL AIR FIN COOLER II6 F 300 I34 PSIA mum STRIPP R-SPLITT R S CTI ELW' HEAVY LEAN OIL LT. LEAN OIL FE ED TO DEBUTANIZER HEAT SOURCE r I NVEN'TOR.

A T TORNE Y LIGHT HYDROCARBON ABSORPTION AND FRACTIONATION BACKGROUND OF THE INVENTION This invention relates to an improved method for processing liquid and gaseous hydrocarbons such as the fractionator overhead from a catalytic cracking unit.

The invention combines and expands the advantages inherent in various absorbing, splitting and demethanizing flow sequences in one simple and compact absorbing and fractionating tower.

At the normal catalytic cracking unit, motor gasoline and lighter materials are produced as fractionator overhead vapor and liquid products. The vapor product contains most of the butane and lighter material and a small portion of the motor gasoline boiling range material (pentane and heavier). The liquid product consists primarily of material in the motor gasoline boiling range.

Various processing schemes are employed to recover the desired material from the vapor product and to separate the recovered material and liquid product into the desired fractions. Each of the various processing sequences has its own advantages. Common to essentially all processing schemes are absorbing, splitting and debutanizing operations. Most of the absorbers contain a heated stripping section to remove unwanted material from the fat oil product.

The conventional method for handling the overhead from a catalytic cracking fractionator introduces the gaseous and liquid products (either at the same point or at different points) to an absorption unit where absorption oil (lean oil) and heat are used to recover (absorb) the desirable material as a fat oil and purge out the undesirable material as absorber overhead tail or residue gas). The overhead from the absorber is passed to a second absorber where it is contacted with a heavier absorbent such as a heating oil fraction or heavy naphtha fraction. The overhead from this absorber is used as fuel gas (or further processed if desired) while the fat oil may be fractionated as desired. The fat oil from the first absorber is generally fed to a second tower, often called a splitter, which separates a heavy naphtha bottoms and a light overhead which can be debutanized to separate butane and lighter overhead, a light naphtha as a sidestream and an intermediate naphtha fraction as bottoms. If desired, the heavy naphtha fraction may be separated in a rerun tower into a heavy naphtha overhead and a heating oil fraction, suitable as such or as feed to catalytic cracking.

It is also known in the prior art to first debutanize the fat oil from the first absorber and then pass the bottoms from that tower to a splitter from which light naphtha is taken off overhead and heavy naphtha as bottoms. Other side streams may be removed from the splitter as desired.

Each of the towers described above requires its own heat input, usually reboiler sections, overhead product pumps and condensers, accumulator drums, heat exchangers and various pressure, temperature, flow and level control and recording systems.

SUMMARY OF THE INVENTION The present invention provides large improvements over prior art methods by combining in one tower the functions of the several towers of the prior art. By combining absorbing, stripping and splitting operations in one tower, the following advantages result:

I. Hot vapors from the splitter section will supply heat to the stripper section (normally bottom section ofa reboiled absorber tower). This eliminates the need for splitter reflux and overhead product pumps, splitter overhead condensers, splitter accumulator drum, absorber reboiler exchangers and various pressure, temperature, flow and level control and recording systems. Complete recovery of the heat contained in the splitter section overhead vapors is accomplished. ln present processing schemes, splitter overhead vapor temperature levels permit recovery of only a small portion, if any, of

the heat contained in this stream. The one tower will be more economical to build, operate and maintain.

2. Complete advantage is taken of the separation afforded by the partial condensation occurring in the catalytic cracking units fractionator overhead accumulator. The light motor gasoline fraction contained in the vapor product is recombined with the liquid product in such a way that this material does not have to be reseparated from the heavier motor gasoline fractions. This reduces equipment size and utility consumption.

3. Tower loadings, and therefore tower size, are reduced by the unique manner in which the vapor and liquid feed streams are introduced into the absorber splitter tower and the manner in which the product streams are withdrawn. Although the required amount of lean oil (absorbing medium) and all of the catalytic cracking unit fractionator overhead product are contained in the absorber splitter tower, these materials are distributed so that tower loadings are not excessive in any section. Controlled absorption of all components is possible at minimum tower size.

4. Because only one tower is involved and this tower feeds the overhead products of another tower, the products of thermal degradation are not present above the bottom tray of the absorber splitter. This permits the withdrawal of the heaviest motor gasoline fraction as a sidestream below the lower feed tray. This reduces tower size and utility consumption.

5. The unique flow sequence, which results when the absorber splitter tower is combined with other towers, permits absorbing, splitting and debutanizing operations to be accomplished with minimum utility consumption and minimum equipment size and number. This occurs because all material is produced as an overhead product only one time during absorbing, splitting and debutanizing operations. The overhead vapor from the splitter section (of the absorber splitter) may be considered as an overhead product. However, all heat is recovered from this material and tower loadings in the stipper section are approximately the same as that which would occur if a separate reboiler absorber was being used.

BRIEF REFERENCES TO THE DRAWINGS FIG. I represents a conventional method for separating a mixture of gaseous and liquid hydrocarbons.

FIG. 2 represents the present invention in functional form to show how the invention operates and differs from the conventional form illustrated in FIG. I.

FIG. 3 represents the actual single tower contemplated by the present invention.

FIG. 4 shows another embodiment of the invention in which the absorber, stripper, and splitter sections are integrated.

DETAILED DESCRIPTION OF THE DRAWINGS Conventional Design Referring now to FIG. 1, a gas and liquid feed stream, for example, the total overhead from the fractionator of a catalytic cracking unit (containing hydrogen, nitrogen, carbon dioxide, hydrogen sulfide and various hydrocarbons, ranging from methane to material boiling as high as 450 F.) is introduced by line 1 to absorber 2. If desired, the liquid feed may be introduced further up the tower, as by line 3. Light lean absorption oil is introduced by line 4 and flows down the tower absorbing both desirable and undesirable components. Unabsorbed components are removed overhead through line 5 and are passed to sponge tower 6, where they contact heavy lean absorption oil introduced by line 7. This lean oil generally boils in the neighborhood of 330430 F. However a heavier lean oil, such as 430-600 fraction may be used if desired. The sponge absorber may or may not be equipped with a reboiler. The fat oil is removed by line 8 while the overhead, consisting of H N CO H S, C and controlled amounts of C saturates and unsaturates, leaves by line 9.

Returning to absorber 2, the fat oil leaves by line and is passed to splitter 11. A portion of bottoms is passed through heater 12 by line 13 and returned to the absorber 2 by line 14 to supply heat thereto. The splitter serves to separate the absorbed portions of the fat oil from the absorption oil itself and to separate the absorbed materials and liquid feed (to absorber) into the desired fractions. The lighter portions are removed by line 15 and passed to debutanizer 16. Splitter bottoms, consisting of both recycle absorption oil and heavy product, are removed from splitter 11 by line 17 and a portion returned to absorber 2 by line 4. A portion is also passed by line 18 through heater 19 and line 20 back to the splitter to supply heat thereto. The remainder of the absorber oil is removed as product heavy naphtha through line 21. However, if desired, it may instead be passed by line 22 to rerun tower 23 and separated into heavy naphtha proper which is removed by line 24 and heating oil through line 25. As usual, a portion is passed by line 26, heater 27, and line 28 back to the rerun tower to supply heat thereto.

The overhead from the splitter 11, passed to the debutanizer 16 by line 15, is stabilized to remove butane and lighter overhead through line 29. A light naphtha fraction may be removed as a sidestream through line 30 while the bottoms are removed through

lines

31 and 32 as an intermediate naphtha fraction. A portion is returned to the debutanizer to supply heat thereto by passage through line 33, heater 34 and line 35.

As can be seen, this conventional system requires at least four and possibly five separate towers with their attendant reboiler and reflux equipment.

TH E INVENTION Turning now to FIG. 2, the simplest embodiment of the present improved system is described.

The unique design of this invention combines absorption, sponge absorption, demethanization (or deethanization, or depropanization) of fat oil, splitting of distillate feed and processing of fat oils into a single tower. Although the unique integration of these functions enables all of these operations to be combined into a single integrated tower, the various stages will perform the same functions as a three-tower system having separate splitter, absorber-demethanizer (or absorberdeethanizer or absorber depropanizer) and sponge absorber towers. For this reason, the absorber-splitter operation is easier to understand if the tower is considered in sections corresponding to these towers. The splitter section is used to prepare light and heavy naphtha (lean oil) for use as the absorbing medium in the absorber sections, process the fat oil from the sponge absorber section and separate the distillate feed into the desired fractions. The required heat removal in the top portion of the splitter section is provided by the liquid overflow from the bottom of the absorber-demethanizer section. The absorber-demethanizer section is used for the selec tive recovery of materials from the fresh feed gas. Heat required for stripping unwanted components from the fat oil is provided by direct contact with hot vapors from the splitter section. The sponge absorber section is used primarily to recover equilibrium light lean oil from the vapor leaving the absorber-demethanizer section. Overall component recovery and separation is equal to that obtained by conventional light ends processes as described in FIG. 1.

In FIG. 2, a gaseous stream, from catalytic cracking compression facilities, for example, and which contains various components boiling up to approximately 250 F. is introduced to absorber-demethanizer 100 by line 101 where it contacts lean absorber oil introduced by line 103. Condensate (light liquid) may also be introduced at the point of gaseous feed introduction or bypassed directly to debutanization. The loan oil absorbs both desirable material (such as propylene and heavier) and undesirable material (such as methane and lighter). The fat oil leaves the absorber through line 104 where it contacts the overhead vapors leaving splitter tower 105 by line 106. The mixture passes by line 107 to condenser-reboiler 108. This absorber-reboiler" representation is shown for functional purposes only and is actually several stages within the tower itself. Vapors leave condenser reboiler" 108 and return to the bottom of the absorber by line 109. Condensate is removed from 108 by line 110 an passes to the top of the splitter tower 105 by line 111 or is removed to debutanizer (not shown).

Overhead from the absorber 100 is removed by line 112 to sponge absorber 113 where it contacts heavy lean oil introduced by line 114. Overhead light gaseous product is removed from the sponge absorber 113 by line 115. Bottoms (fat oil) from the sponge absorber are removed by line 116 and passed to the lower part of splitter tower 105.

A liquid feed from the overhead accumulator of a catalytic cracking fractionator and boiling C to 450 F. (low pressure distillate) is introduced to the middle portion of the splitter tower 105 by line 117. A light naphtha fraction is withdrawn from a plate above the feed plate by line 103 and used as the lean oil in the absorber tower 100.

A heavy naphtha fraction is removed near the bottom of the splitter tower by line 114 and used as the lean oil in the sponge tower 113. A heavy naphtha suitable for use as motor fuel may be withdrawn at a point slightly above the heavy naphtha lean oil point of withdrawal as by line 119. Bottoms from the splitter tower are withdrawn by

lines

120 and 121 as catalytic cracking feed. A portion of the bottoms product is passed by line 122, furnace 123 and line 124 to supply heat to the splitter tower.

It is evident that the above scheme eliminates all but one reboiler unit and all the reflux-condenser units found in the conventional setup as described in FIG. 1. However, as pointed out above, FIG. 2 is only representative of the functional steps integrally combined in the single tower of this invention. The integrated tower utilizing the functions in the manner described in FIG. 2 is shown in FIG. 3.

Referring now to FIG. 3, a single tower 200 is provided with three sections, a sponge absorber section 201, an absorber and stripper section 202 and a splitter section 203. A gaseous feed from catalytic cracking compression facilities containing hydrocarbons with a boiling range of C, to 250 F. is introduced by line 204 to the absorber and stripper section 202 of tower 200 where it meets a light absorber oil introduced at 105 F. by line 205. Condensate from the gas compression facilities may also be introduced at this point if desired or bypassed directly to debutanization. The lean oil absorbs both desirable and undesirable components from the feed and the resulting fat oil passes down the absorber, being stripped of unwanted components and accumulating on the bottom plate 206 thereof from which a sidestream containing material boiling up to 330 F. is withdrawn by line 207. Liquid not withdrawn passes down into splitter section 203 into which the liquid phase from the accumulator of a catalytic cracking fractionator is introduced through line 208. A light naphtha frac tion is removed, above the point of accumulator liquid introduction, by line 205 as the lean absorber oil used therein. A heavy naphtha fraction boiling 330430 F. is withdrawn by line 209 as product and a slightly heavier naphtha fraction is withdrawn at a slightly lower point through line 210 which is introduced into the top of sponge absorber section 201. A pierced plate 211 separates the sponge section 201 from the absorber section 202. This allows vapors to pass upward through the plate but prevents the downflow of liquid through the plate. For this reason all the sponge fat oil accumulates on plate 211 and is withdrawn through line 212 and passed to the midpart of the splitter section 203 where it is fractionated along with the feed introduced through line 208. Heavy bottoms boiling 430 F. +are withdrawn at about a temperature of 580 F. and I40 p.s.i.g. by

lines

213 and 214. A portion is passed by line 215, furnace 216 and line 217 back into the bottom of the splitter section 203 to supply heat thereto. The bottoms are suitable as feed to catalytic cracking or as heating oil.

It is evident that the single tower shown in FIG. 3 represents an advance over the conventional system illustrated by FIG. 1 in that only one reboiler section is needed, the vapors from the splitter section supplying heat to the absorber section.

Referring now to FIG. 4, there is presented an embodiment of the invention in which only the absorber, stripper and splitter sections are integrated while the sponge section exists as a completely separate function.

In this embodiment compressor discharge from a catalytic cracking unit (the hydrocarbon components are primarily C to 250 F.) is introduced at 250 F. into a knockout drum 300 by

lines

301 and 302. Vapor from the stripper-splitter section 311 and liquid from the absorber section 320 are also introduced at this point. The knockout drum is maintained at 116 F. and 134 p.s.i.a. Condensed water is removed by line 303, vapor by line 304 and liquid by line 305. The vapor is introduced into the bottom portion of absorber 320. At the same time a heavy lean absorption oil is introduced on the top stage of absorber 320 by line 306 and a light lean oil at a lower point by line 307 together with the liquid overhead from a catalytic cracking fractionator (primarily C,330 F.). Both lean oils are introduced at 85 F. If desired, an additional lean nonolefinic gas may be introduced at 90 F. below the point of entry of the light lean oil. Both lean oils pass down the absorber tower 305 absorbing both desirable and undesirable components. The unabsorbed gaseous constituents are removed overhead by line 321 and are passed to sponge absorber 322 maintained at 130 p.s.i.a. and fed by a heavy absorber oil by line 308. Lean gas is removed overhead from the sponge section by line 309 while the bottoms are removed by line 323 and passed to the catalytic cracking fractionator or otherwise disposed of.

Fat oil is removed from the bottom of absorber tower 320 by line 310 at 125 F. and passed to knockout drum 300, liquid from which is passed to the top stage of stripper-splitter tower 311. From this tower a light side stream is removed by line 312 at l95 F. and used as feed to a debutanizer or otherwise processed. Another sidestream is removed at 256 F. at a slightly lower point by line 313. This stream is heated by heat exchange and returned to the tower at 282 F. by line 314 at a slightly lower point than from which it was removed to supply heat thereto. A heavier fraction is removed at 323 F. by line 315, cooled and returned to the midsection of the tower by line 307 as the light lean absorption oil. A fraction at 424 F. is removed from near the bottom of the tower through line 316, passed through heater 317 and returned to the tower at 449 F. by line 318 to supply heat thereto. A bottoms fraction at 440 F. and I40 p.s.i.a. is removed by line 319, cooled and returned to the top of the tower by line 306 as the heavy lean absorber oil. The use of this heavy lean oil reduces the amount of lean oil contained in the absorber gas product and thereby reduces the work of the sponge absorber.

It is obvious that the design described in FIG. 4 also combines the advantages inherent in various absorbing, splitting and debutanizing flow sequences in a simple compact operating sequence. It is also obvious that absorber tower 320 and stripper-splitter tower 311 can be integrated into a single tower with or without sponge section 307 as shown in FIG. 3.

The processes described in FIGS. 2, 3 and 4 are not necessarily limited to processing overhead from the catalytic cracking fractionator but may also be applied to similar stream from hydrocracking, reforming, coking, and crude distillation.

As set forth above, the advantages of the invention lie in the lower initial investment because of fewer towers, less auxiliary equipment and less real estate requirements. The operating costs are lower because of good fractionation efficiency, high thermal efficiency, lower maintenance and less operating manpower and because of compact and flexible operation.

The nature of the present invention having thus been fully described and illustrated, what is claimed as new, useful and unobvious and-desired to be secured by Letters Patent is:

1. An improved unitary distillation and absorption process which comprises introducing a gaseous feed stream into the lower part of the absorption section of an integrated tower having sponge, stripping, absorption and splitter sections, and a heavy feed stream into the middle portion of the splitter section of the said tower, removing a light fraction from the splitter section at a point above the point of heavy feed introduction and introducing the said light fraction into the top of the said absorption section as lean absorber oil therein; withdrawing a heavy fraction from the lower part of said splitter section and introducing it into the top of the sponge section as lean absorption oil therein; withdrawing a bottoms fraction and passing a portion of said bottoms fraction through a heater and back to the lower portion of said splitter section as the only source of heat to said distillation tower, and withdrawing as products a gaseous overhead from said sponge section, a light naphtha fraction from the bottom of said stripping section, a heavy naphtha fraction from the lower portion of the splitter section and a bottoms fraction.

2. An improved unitary distillation and absorption process which comprises introducing a light fraction (in gaseous state or a mixture of gas and liquid) to a column at a point a substantial distance from the top thereof, scrubbing said light fraction with light absorber oil introduced at a point above the point of introduction of the light feed, permitting enriched absorber oils and liquid components of said light feed to descent through an intermediate portion of said column while stabilizing the liquid to remove all the lighter undesirable components therefrom, removing a portion of the thus stabilized liquid from said intermediate portion of said column as product, passing the remainder thereof downwardly through the lower portion of the column wherein it is stripped of lighter undesirable components by countercurrent contact with ascending hotter vapors, introducing a heavy liquid fraction into the said lower portion of said column and mixing it with the stabilized liquid, withdrawing a light fraction just above the point of entry of the said heavy feed portion and returning said light fraction to the upper portion of said column as the light absorber oil therein; passing the mixture of heavy feed and remaining stabilized liquid downwardly through the remaining portion of the column, withdrawing a heavy fraction from the lower portion of said column as product and withdrawing a slightly heavier fraction from a slightly lower portion of said column and introducing it to the top thereof as heavy absorber oil; passing said heavy absorber oil countercurrent to vapors to remove lean oil therefrom, and removing all of the enriched heavy absorber oil from the upper portion of said column at a point just above the point of introduction of the light absorber oil and reintroducing it into the lower section of said column at a point intermediate the point of removal of the light lean oil fraction and the said heavy fraction, reboiling the stripped remainder of said stabilized liquid and heavy feed mixture by heat exchange with a heating medium, passing the resultant vaporized portions thereof upwardly through the lower portion of the column as said ascending vapors, and withdrawing a reboiled fraction from the bottom of said column as product.

3. An improved unitary hydrocarbon distillation and absorption process comprising introducing a light (in gaseous or mixed gas and liquid states) hydrocarbon fraction boiling C to 250 F. to a column at a point a substantial distance from the top thereof, scrubbing vapors with a light absorber oil in troduced at a point above the point of introduction of the light feed, permitting enriched absorber oils and liquid components of said light feed to descend through an intermediate portion of said column while stabilizing the liquid to remove the undesirable material therefrom, removing a portion of the thus stabilized liquid boiling up to 330 F. as product, passing the remainder thereof downwardly through the lower portion of the column wherein it is stripped of lighter components by countercurrent content with ascending vapors, introducing a heavy hydrocarbon fraction feed, boiling primarily C to 450 F., into the said lower portion of said column and mixing it with the stripped liquid, withdrawing a light fraction just above the point of entry of the said heavy portion of the feed and returning said light fraction to the upper portion of said column as the light absorber oil therein; passing the mixture of heavy feed and remaining stripped liquid downwardly through the remaining portion of the column; withdrawing a heavy fraction boiling 330430 F. from the lower portion of said column as product, withdrawing a slightly heavier fraction at a slightly lower point in said column and introducing it to the top thereof as the heavy absorber oil therein; removing all of the enriched heavy absorber oil from the upper portion of said column at a point just above the point of introduction of the light absorber oil and reintroducing it into the lower section of said column at a point intermediate the point of removal of the light lean oil fraction and the fraction boiling 330430 F., reboiling the stripped remainder of said liquid and heavy feed mixture by heat exchange with a heating medium, passing the resulting vaporized portions thereof upwardly through the lower .portion of the column of said ascending vapors and withdrawing a reboiled fraction boiling 430 F. and higher from the bottom of said column as product.

4. An improved distillation and absorption process which comprises introducing the overhead liquid product from a catalytic cracking fractionator to the absorption section of a unitary absorption-stripping-splitting column at a point a distance from the top thereof, introducing a lean absorption oil at or near the same point, introducing a heavier lean absorption oil at a higher point scrubbing ascending vapors with these lean absorption oils, withdrawing enriched absorber oils from the bottom of said absorption section and introducing said bottom fraction into a separator together with the overhead from the stripper-splitter section and the total product of the compressor discharge of a catalytic cracking unit, producing a vapor fraction and a liquid fraction from said separator, introducing said vapor fraction into the lower portion of said absorber section, introducing said liquid fraction into the upper portion of said stripper-splitter section of said unitary column, passing the liquid fraction downward through said column, withdrawing an intermediate fraction from the upper portion of said stripper-splitter -splitter section as product, withdrawing a heavier fraction from the lower portion of said stripper-splitter section and returning it to said absorption section as the light absorber oil therein, rcboiling the remainder of said liquid fraction by heat exchange with a heating medium, passing the resulting vaporized portions thereof upwardly through the low portion of the column and withdrawing a reboiled fraction from the bottom of said column and returning it to the upper portion of said absorption section as the heavy absorption oil therein, withdrawing vapor overhead from said absorption section and introducing it into a sponge absorber tower, and passing it countercurrent to a sponge absorber oil introduced to the upper part of said sponge absorber, withdrawing lean gas as overhead from the sponge-absorber tower and withdrawing fat sponge absorption oil from the bottom thereof.

Claims

2. An improved unitary distillation and absorption process which comprises introducing a light fraction (in gaseous state or a mixture of gas and liquid) to a column at a point a substantial distance from the top thereof, scrubbing said light fraction with light absorber oil introduced at a point above the point of introduction of the light feed, permitting enriched absorber oils and liquid components of said light feed to descent through an intermediate portion of said column while stabilizing the liquid to remove all the lighter undesirable components therefrom, removing a portion of the thus stabilized liquid from said intermediate portion of said column as product, passing the remainder thereof downwardly through the lower portion of the column wherein it is stripped of lighter undesirable components by countercurrent contact with ascending hotter vApors, introducing a heavy liquid fraction into the said lower portion of said column and mixing it with the stabilized liquid, withdrawing a light fraction just above the point of entry of the said heavy feed portion and returning said light fraction to the upper portion of said column as the light absorber oil therein; passing the mixture of heavy feed and remaining stabilized liquid downwardly through the remaining portion of the column, withdrawing a heavy fraction from the lower portion of said column as product and withdrawing a slightly heavier fraction from a slightly lower portion of said column and introducing it to the top thereof as heavy absorber oil; passing said heavy absorber oil countercurrent to vapors to remove lean oil therefrom, and removing all of the enriched heavy absorber oil from the upper portion of said column at a point just above the point of introduction of the light absorber oil and reintroducing it into the lower section of said column at a point intermediate the point of removal of the light lean oil fraction and the said heavy fraction, reboiling the stripped remainder of said stabilized liquid and heavy feed mixture by heat exchange with a heating medium, passing the resultant vaporized portions thereof upwardly through the lower portion of the column as said ascending vapors, and withdrawing a reboiled fraction from the bottom of said column as product.
3. An improved unitary hydrocarbon distillation and absorption process comprising introducing a light (in gaseous or mixed gas and liquid states) hydrocarbon fraction boiling C1 to 250* F. to a column at a point a substantial distance from the top thereof, scrubbing vapors with a light absorber oil introduced at a point above the point of introduction of the light feed, permitting enriched absorber oils and liquid components of said light feed to descend through an intermediate portion of said column while stabilizing the liquid to remove the undesirable material therefrom, removing a portion of the thus stabilized liquid boiling up to 330* F. as product, passing the remainder thereof downwardly through the lower portion of the column wherein it is stripped of lighter components by countercurrent content with ascending vapors, introducing a heavy hydrocarbon fraction feed, boiling primarily C1 to 450* F., into the said lower portion of said column and mixing it with the stripped liquid, withdrawing a light fraction just above the point of entry of the said heavy portion of the feed and returning said light fraction to the upper portion of said column as the light absorber oil therein; passing the mixture of heavy feed and remaining stripped liquid downwardly through the remaining portion of the column; withdrawing a heavy fraction boiling 330*-430* F. from the lower portion of said column as product, withdrawing a slightly heavier fraction at a slightly lower point in said column and introducing it to the top thereof as the heavy absorber oil therein; removing all of the enriched heavy absorber oil from the upper portion of said column at a point just above the point of introduction of the light absorber oil and reintroducing it into the lower section of said column at a point intermediate the point of removal of the light lean oil fraction and the fraction boiling 330*-430* F., reboiling the stripped remainder of said liquid and heavy feed mixture by heat exchange with a heating medium, passing the resulting vaporized portions thereof upwardly through the lower portion of the column of said ascending vapors and withdrawing a reboiled fraction boiling 430* F. and higher from the bottom of said column as product.
4. An improved distillation and absorption process which comprises introducing the overhead liquid product from a catalytic cracking fractionator to the absorption section of a unitary absorption-stripping-splitting column at a point a distance from the top thereof, intRoducing a lean absorption oil at or near the same point, introducing a heavier lean absorption oil at a higher point scrubbing ascending vapors with these lean absorption oils, withdrawing enriched absorber oils from the bottom of said absorption section and introducing said bottom fraction into a separator together with the overhead from the stripper-splitter section and the total product of the compressor discharge of a catalytic cracking unit, producing a vapor fraction and a liquid fraction from said separator, introducing said vapor fraction into the lower portion of said absorber section, introducing said liquid fraction into the upper portion of said stripper-splitter section of said unitary column, passing the liquid fraction downward through said column, withdrawing an intermediate fraction from the upper portion of said stripper-splitter -splitter section as product, withdrawing a heavier fraction from the lower portion of said stripper-splitter section and returning it to said absorption section as the light absorber oil therein, reboiling the remainder of said liquid fraction by heat exchange with a heating medium, passing the resulting vaporized portions thereof upwardly through the low portion of the column and withdrawing a reboiled fraction from the bottom of said column and returning it to the upper portion of said absorption section as the heavy absorption oil therein, withdrawing vapor overhead from said absorption section and introducing it into a sponge absorber tower, and passing it countercurrent to a sponge absorber oil introduced to the upper part of said sponge absorber, withdrawing lean gas as overhead from the sponge-absorber tower and withdrawing fat sponge absorption oil from the bottom thereof.