WO2016123586A1

WO2016123586A1 - Methods for enhancing product recovery from light hydrocarbons in a distillation system

Info

Publication number: WO2016123586A1
Application number: PCT/US2016/015851
Authority: WO
Inventors: Weihua Jin; Mircea Cretoiu
Original assignee: Gtc Technology Us Llc
Priority date: 2015-01-30
Filing date: 2016-01-30
Publication date: 2016-08-04

Abstract

Systems and methods for improved recovery of LPG from a hydrocarbon feed include a distillation column, a receiver coupled to an overhead section of the distillation column, and an absorber comprising a first inlet coupled to the receiver and a second inlet coupled to a heavy hydrocarbons stream. A vapor stream is separated from the hydrocarbon feed and sent to a receiver. The receiver separates a non-condensables stream comprising LPG components from the vapor stream, and the non-condensables feed is combined with a heavy hydrocarbon stream in an absorber. In the absorber, the heavy hydrocarbon stream absorbs the LPG components. A stream that includes the heavy hydrocarbons and the absorbed LPG components is fed back to the distillation column to recover additional LPG.

Description

METHODS FOR ENHANCING PRODUCT RECOVERY FROM LIGHT HYDROCARBONS IN A DISTILLATION SYSTEM

CROSS REFERENCES TO RELATED APPLICATIONS [0001] This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/110,313, filed January 30, 2015, which is incorporated herein by reference in its entirety as if fully set forth herein.

TECHNICAL FIELD

[0002] The present disclosure relates to systems and methods of product recovery from a hydrocarbon feed. In particular, the disclosure relates to systems and methods to increase recovery of LPG from a hydrocarbon feed using a system that includes a partial condenser and an absorber.

BACKGROUND

[0003] Partial condensers are used in distillation columns when a distillate product is removed as a vapor stream. This approach is commonly employed when there are very light components in the feed to the column that would require a high column pressure or a low condenser temperature to completely condense these volatile components. The use of a partial condenser can avoid the use of costly refrigeration in the condenser. Many partial distillation schemes have both liquid and vapor products. In such cases there is considerable loss of heavier components in the vapor product and vice versa. It is not possible to maintain a sharp split between liquid and vapor products in conventional partial condensation schemes.

[0004] There are several distillation schemes in refinery and petrochemical complexes which use partial condensers for separation of lighter components. Figure 1 represents a prior art system for conventional recovery of liquid petroleum gas (LPG) from a feed hydrocarbon stream. The prior art system includes a distillation column 1, an air-cooled exchanger 2, a water-cooled condenser 3, and a partial condenser 4. The distillation column 1 operates at a pressure of 17 kg/cm² gauge with an overhead temperature of 40°C. In certain embodiments the operational temperature ranges from 30°C to 50°C. The prior art system of FIG. 1 recovers approximately 60 % of the LPG from the feed hydrocarbon stream. [0005] However, the prior art possesses several disadvantages. It is not possible to condense the lighter components in the overhead product at 17 kg/cm² gauge while using cooling water as the overhead cooling media. The overhead system includes the partial condenser 4. Lighter components (used as off gas or fuel gas) are drawn as the vapor product from the partial condenser 4. LPG product is the liquid stream from the partial condenser 4. A considerable amount of LPG (C3) components are lost to the off gas vapor stream. The loss of LPG components can be prevented by decreasing the overhead temperature (e.g., by using refrigeration) or increasing the column pressure. However, this increases the capital and operating cost of the column. The prior art systems provide a loose split between C1-C2 in vapor and C3 in liquid product, the recoveries of these components is also low as they are lost in the off gas vapor stream.

[0006] In present invention, an improved process is disclosed which uses an absorber to absorb liquid product components from off gas stream to increase the liquid product yield in a partial condensing distillation system, including, in embodiments, the combination of various streams and processes which provides significant advantages over prior systems.

SUMMARY

[0007] In various embodiments, systems and processes for enhanced product recovery with an absorber in a partial condensing distillation system are disclosed. The methods comprise: 1) an absorption column (absorber) to absorb liquid product components with a heavy hydrocarbons stream; and 2) a distillation column with partial condenser to separate light components from heavy components.

[0008] A method of recovering LPG includes providing a hydrocarbon feed to a distillation column and separating, with the distillation column, a first stream comprising a vapor portion of the hydrocarbon feed. The first stream is fed to a partial condenser and separated into two or more streams that comprise a non-condensables stream comprising LPG components. The non-condensables stream and a heavy hydrocarbons stream are fed into an absorber. In the absorber, the heavy hydrocarbons stream absorbs LPG components from the non- condensables stream. A stream comprising the heavy hydrocarbons stream and absorbed LPG components is fed to the distillation column to recover additional LPG. [0009] A method of recovering LPG includes providing a heavy hydrocarbons feed that includes LPG components to a distillation column. A first stream comprising a vapor portion of the heavy hydrocarbons feed is separated from the heavy hydrocarbons feed in the distillation column. The first stream is then fed to a partial condenser and separated into two or more streams that comprise a non-condensables stream comprising LPG components. The non-condensables stream is then fed into an absorber. A heavy hydrocarbons stream is also fed into the absorber where the heavy hydrocarbons stream absorbs LPG components from the non-condensables stream. A stream comprising the heavy hydrocarbons stream and absorbed LPG components is then fed to the distillation column to recover additional LPG.

[0010] A system for recovery of liquid petroleum gas from a hydrocarbon feed includes a distillation column, a partial condenser coupled to an overhead section of the distillation column, and an absorber comprising a first inlet coupled to the partial condenser and a second inlet coupled to a heavy hydrocarbons stream.

[0011] The foregoing has outlined rather broadly the features of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter, which form the subject of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions to be taken in conjunction with the accompanying drawings describing specific embodiments of the disclosure, wherein: [0013] FIG. 1 is an exemplary prior art system for LPG recovery from a feed hydrocarbon stream.

[0014] FIG. 2 is an illustrative enhanced product recovery system with an absorber placed downstream of a distillation column; and

[0015] FIG. 3 is an illustrative enhanced product recovery system with an absorber placed upstream of a distillation column.

[0016] It is also known to those skilled in the art that other than LPG recovery, this system can also be applied to other product separation from hydrocarbon stream containing non- condensable light components. Therefore, the current disclosure is not limited to LPG recovery. DETAILED DESCRIPTION

[0017] In the following description, certain details are set forth such as specific feedstock, quantities, temperature, etc. so as to provide a thorough understanding of the present embodiments disclosed herein. However, it will be obvious to those skilled in the art that the present disclosure may be practiced without such specific details. In many cases, details concerning such considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present disclosure and are within the skills of persons of ordinary skill in the relevant art.

[0018] FIG. 2 shows an illustrative enhanced product recovery system 100 with an absorber placed downstream of a distillation column. The system 100 of FIG. 2 comprises a distillation column 102, a receiver 104, an absorber 106, a downstream process 108, an air-cooled condenser 110, and a water-cooled condenser 112. The system 100 of FIG. 2 is designed to separate light components (non-condensable), LPG (top liquid product), and C₄₊ (heavies).

[0019] In a typical embodiment, a feed stream 10 comprising hydrocarbons is fed into the distillation column 102. The distillation column 102 separates the feed stream 10 into at least a vapor stream 11 and a bottoms stream 20. The vapor stream 11 is fed from the overhead of the distillation column 102 to the air-cooled condenser 110, which condenses and cools the vapor stream 11. In some embodiments, the vapor stream 11 may be cooled and/or condensed by a different type of exchanger. In some embodiments, the vapor stream 11 is cooled to desired temperature in the air-cooled condenser 110. The condensed vapor stream 12 is further cooled by the water-cooled condenser 112 and outputted as a stream 13 into the receiver 104. In some embodiments, the vapor stream 11 may be cooled and/or condensed by a different type of condenser. The receiver 104 allows the stream 13 to be separated into vapor and liquid streams. For example, the system 100 shown in FIG. 2 may output a non- condensables stream 14, an LPG product stream 15, and a light liquids stream 16. The non- condensables stream 14 includes LPG components and is removed as overhead vapor product from the top of the partial condenser 104 and fed to the absorber 106. The absorber 106 may be an absorption column. The LPG product stream 15 is pumped out of the receiver 104 via reflux pumps. The LPG product stream 15 can be captured and stored or sent downstream for use in another process. The light liquids stream 16 is fed to the distillation column 102 as reflux. [0020] A heavy hydrocarbons stream 17 is fed to the top of the absorber 106. The heavy hydrocarbons stream 17 may include either or both of a bottoms stream 17' from the distillation column 102 or a heavy hydrocarbons stream 17" from the downstream process 108 after light components have been removed. In some embodiments, the heavy hydrocarbons stream 17 may be fed from another process. The bottoms stream 17' may include some or all of the bottoms stream 20. In the absorber 106, the LPG components from the non-condensables stream 14 are absorbed by the heavy hydrocarbons stream 17 and removed from the bottom of the absorber 106 via a stream 19. The remainder of the non- condensables stream 14 exits the top of the absorber 106 via a stream 18 and can be used as off gas, collected and stored, or used in a downstream process.

[0021] Although any heavy hydrocarbons can be used as absorption agent in the absorber 106, it is preferred to use a heavy fraction of hydrocarbons from the feed stream 10 that will not cause any product contamination in the downstream separation. The stream 19 that includes the heavy hydrocarbons stream 17 and the absorbed LPG components exits the bottom of the absorber 106 and is sent to the distillation column 102. The absorbed LPG components are then cycled through the system 100 to be processed, thereby recovering additional LPG from non-condensables.

[0022] FIG. 3 shows an illustrative enhanced product recovery system 200 with an absorber placed upstream of a distillation column. The system 200 of FIG. 3 comprises a distillation column 202, a receiver 204, an absorber 206, a downstream process 208, an air-cooled exchanger 210, and a water-cooled condenser 212. The system 200 of FIG. 3 is designed to separate light components (non-condensable), LPG (top liquid product), and C₄₊ (heavies). A feed stream 21 comprising hydrocarbons is sent to the absorber 206. The absorber 206 may be an absorption column. A non-condensables stream 22 that includes LPG components is fed from the receiver 204 to the bottom of the absorber 206 and a heavy hydrocarbons stream 23 is fed to the top of the absorber 206. The heavy hydrocarbons stream 23 can include either or both of a bottoms stream 23' from the distillation column 202 or a heavy hydrocarbons stream 23" from the downstream process 208 after additional light components have been removed. In some embodiments, the heavy hydrocarbons stream 23 may be fed from another process. The bottoms stream 23' may include some or all of a bottoms stream 31 from the distillation column 202.

[0023] In the absorber 206, the LPG components from the non-condensables stream 22 are absorbed by the heavy hydrocarbons stream 23. A stream 24 comprising the heavy hydrocarbons stream 23 and the absorbed LPG components is removed from the bottom of the absorber 206 and fed to the distillation column 202 to recover additional LPG. The absorbed LPG components are then cycled through the system 200 to be processed, thereby recovering additional LPG from non-condensables.

[0024] A non-condensables stream 25 from the absorber 206 exits the top of the absorber 206 and can be used as off gas, collected and stored, or used in a downstream process. Although other heavy hydrocarbons can be used as absorption agent in the absorber 206, it is preferred to use a heavy fraction of hydrocarbons from the feed stream 21 that will not cause any product contamination in downstream separation processes.

[0025] A vapor stream 26 from the overhead of the distillation column 202 is condensed and cooled to desired temperature in the air-cooled condenser 210. A stream 27 feeds the condensed vapor into the water-cooled condenser 212. The water-cooled condenser 212 further cools the stream 27 and outputs a stream 28 into the receiver 204. The receiver 204 allows the stream 28 to be separated into vapor and liquid streams. For example, the system 200 shown in FIG. 3 may output the non-condensables stream 22, an LPG product stream 29, and a light liquids stream 30. The non-condensables stream 22 feeds non-condensables from the partial condenser 204 to the absorber 206. The LPG product stream 29 is pumped out of the partial condenser 204 via reflux pumps. The LPG product stream 15 can be captured and stored or sent downstream for use in another process. The light liquids stream 30 is fed back to the distillation column 202 as reflux.

[0026] From the foregoing description, one skilled in the art can ascertain the essential characteristics of this disclosure and, without departing from the spirit and scope thereof, can make various changes and modifications to adapt the disclosure to various usages and conditions. The embodiments described hereinabove are meant to be illustrative only and should not be taken as limiting of the scope of the disclosure, which is defined in the following claims.

Claims

CLAIMS What is claimed is the following:

1. A method of recovering LPG comprising: providing a hydrocarbon feed to a distillation column; separating, with the distillation column, a first stream comprising a vapor portion; feeding the first stream to a partial condenser; separating, with the receiver, from the first stream a non-condensables stream comprising LPG components; feeding the non-condensables stream into an absorber; feeding a heavy hydrocarbons stream into the absorber, wherein the heavy hydrocarbons stream absorbs LPG components from the non-condensables stream; and feeding, from the absorber, a stream comprising the heavy hydrocarbons stream and absorbed LPG components to the distillation column.

2. The method of claim 1, further comprising, prior to feeding the first stream to the receiver, feeding the first stream to an exchanger to cool and condense the first stream.

3. The method of claim 2, wherein the first stream is cooled to approximately 40 °C.

4. The method of claim 2, further comprising, after feeding the first stream to the exchanger, feeding the first stream to a condenser.

5. The method of claim 1, wherein the heavy hydrocarbons stream comprises a bottoms stream from the distillation column.

6. The method of claim 1, wherein the heavy hydrocarbons stream comprises a bottoms stream from a process downstream of the distillation column.

7. The method of claim 1, further comprising feeding a light liquids stream from the receiver to the distillation column.

8. A method of recovering LPG comprising: providing a heavy hydrocarbons feed to a distillation column, wherein the heavy hydrocarbons feed comprises LPG components; separating, with the distillation column, a first stream comprising a vapor portion; feeding the first stream to a receiver; separating, with the receiver, from the first stream a non-condensables stream comprising LPG components; feeding the non-condensables stream into an absorber; feeding a heavy hydrocarbons stream into the absorber, wherein the heavy hydrocarbons stream absorbs LPG components from the non-condensables stream; and feeding, from the absorber, a stream comprising the heavy hydrocarbons stream and absorbed LPG components to the distillation column.

9. The method of claim 8, further comprising, prior to feeding the first stream to the receiver, feeding the first stream to an exchanger to cool and condense the first stream.

10. The method of claim 9, wherein the first stream is cooled to between 30°C to 50°C.

11. The method of claim 9, further comprising, after feeding the first stream to the exchanger, feeding the first stream to a condenser.

12. The method of claim 8, wherein the heavy hydrocarbons stream comprises a bottoms stream from the distillation column.

13. The method of claim 8, wherein the heavy hydrocarbons stream comprises a bottoms stream from a process downstream of the distillation column.

14. The method of claim 8, further comprising feeding a light liquids stream from the partial condenser to the distillation column.

15. A system for recovery of liquid petroleum gas from a hydrocarbon feed, the system comprising: a distillation column; a partial condenser coupled to an overhead section of the distillation column; and an absorber comprising a first inlet coupled to the receiver and a second inlet coupled to a heavy hydrocarbons stream.

16. The system of claim 15, wherein the absorber further comprises an inlet for the hydrocarbon feed.

17. The system of claim 15, wherein the distillation column further comprises an inlet for the hydrocarbon feed.

18. The system of claim 15, further comprising an exchanger disposed downstream from the distillation column and upstream from the receiver.

19. The system of claim 18, further comprising a condenser disposed downstream from the exchanger and upstream from the receiver.

20. The system of claim 15, wherein the heavy hydrocarbons stream is fed to the absorber from a bottoms section of the distillation column.