Title:
High ethane recovery from a ryan/holmes additive recovery column
Kind Code:
A1


Abstract:
A method for separating a high ethane-content product from a high methane-content feed stream including the steps of introducing a high methane-content feed stream into a first distillation column containing a plurality of vapor-liquid contact devices and generating a first bottoms stream, and introducing the first bottoms stream into a second distillation column containing a plurality of vapor-liquid contact devices and generating a second bottoms stream. Additional steps include recovering an additive stream from the second bottoms stream and injecting the additive stream into the first distillation column, and recovering a high ethane-content product from the second distillation column.



Inventors:
Hopewell, Richard B. (Medfield, MA, US)
Application Number:
10/234884
Publication Date:
03/13/2003
Filing Date:
09/04/2002
Assignee:
HOPEWELL RICHARD B.
Primary Class:
Other Classes:
208/354
International Classes:
C07C7/04; C10G7/02; (IPC1-7): C10G7/02
View Patent Images:



Primary Examiner:
NGUYEN, TAM M
Attorney, Agent or Firm:
DLA PIPER RUDNICK GRAY CARY US LLP (CHICAGO, IL, US)
Claims:
1. A method for separating a high ethane-content product from a high methane-content feed stream comprising: a. introducing said high methane-content feed stream into a first distillation column containing a plurality of vapor-liquid contact devices and generating a first bottoms stream; b. introducing said first bottoms stream into a second distillation column containing a plurality of vapor-liquid contact devices and generating a second bottoms stream; c. recovering an additive stream from said second bottoms stream and injecting said additive stream into said first distillation column; and d. recovering a high ethane-content product from said second distillation column.

2. The method of claim 1 wherein said high ethane-content product is recovered from a position on said second distillation column which is above a point where said second bottoms stream is removed from said second distillation column and below a point where said first bottoms stream is introduced to said second distillation column.

3. The method of claim 1 wherein said additive stream comprises C2, C3 and C4+ hydrocarbons.

4. The method of claim 1 wherein said high ethane-content stream comprises predominantly C2 and C3 hydrocarbons.

5. The method of claim 1 further including the step of removing a methane product stream from said first distillation column.

6. The method of claim 5 wherein said high ethane-content product is blended with said methane product stream.

7. A method for separating a high ethane-content product from a feed stream comprising: a. introducing said feed stream into a first distillation column containing a plurality of vapor-liquid contact devices and generating a first bottoms stream; b. introducing said first bottoms stream into a second distillation column containing a plurality of vapor-liquid contact devices and generating a second bottoms stream; c. recovering additive from said second bottoms stream and injection of said additive into said first distillation column; and d. recovering a high ethane-content product from said second distillation column, said high ethane-content product comprising: about 93 mole % C2 and C3 hydrocarbons with limited quantities of CO2 or H2S or a combination of CO2 and H2S. e. treating said high ethane-content product to remove CO2 and H2S.

8. The method of claim 7 wherein the feedstream comprises C1, C2, C3 and C4+ components.

9. The method of claim 1 further comprising the step of locating a high ethane-content product stream recovery point at a location optimizing ethane recovery and additive separation within said second distillation column.

10. A method for separating a high ethane-content product from a feed stream including C1, C2, C3 and C4+ components, as well as CO2 and/or H2S comprising: a. introducing said feed stream into a first distillation column containing a plurality of vapor-liquid contact devices and generating a first bottoms stream; b. introducing said first bottoms stream into a second distillation column containing a plurality of vapor-liquid contact devices and generating a second bottoms stream; c. recovering an additive stream from said second bottoms stream and injecting said additive stream into said first distillation column; and d. recovering a high ethane-content product from said second distillation column.

11. A high ethane-content product comprising C2, C3 and C4+ hydrocarbons, said high ethane-content product manufactured by a process including the steps of: a. introducing a high methane-content feed stream into a first distillation column containing a plurality of vapor-liquid contact devices and generating a first bottoms stream; b. introducing said first bottoms stream into a second distillation column containing a plurality of vapor-liquid contact devices and generating a second bottoms stream; c. recovering an additive stream from said second bottoms stream and injecting said additive stream into said first distillation column; and d. recovering a high ethane-content product from said second distillation column.

Description:

PRIORITY CLAIM

[0001] This application claims the benefit of U.S. provisional patent application No. 60/317,093 filed on Sep. 4, 2001 the entirety of which is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention is in the field of cryogenic distillation.

BACKGROUND OF THE INVENTION

[0003] In the early eighties, the Ryan/Holmes process was developed for use in distillation processes. The Ryan/Holmes process uses the injection of an additive into a distillation column in order to increase the effectiveness and/or efficiency of the separation of a feed stream. The additive may be a by-product of the feed stream being processed or may be supplied separately. The Ryan/Holmes process is especially effective in cryogenic distillation processes, wherein certain components of the feed stream which would naturally solidify at the low separation temperatures, are maintained in a non-solid state.

[0004] The Ryan/Holmes process includes a stage wherein the additive, originally injected into a feed stream processing distillation column, is recovered for reuse. This stage may be a second distillation column. In the treatment of a high methane-content feed stream to generate a methane product stream, an additive of heavier hydrocarbons is used to prevent solidification of feed stream components. This additive may be recovered in a second distillation column. In this column, the process of removing undesirable components (typically CO2 and/or H2S) generates a “light” product stream containing these components as well as light hydrocarbons (typically C2 and C3 hydrocarbons).

[0005] Ethane product (C2/C3 light hydrocarbons), however, is desirable for use as an additive to the final methane product stream (to increase heating value) or as a product stream unto itself and so “loss” of ethane product into this “light” product stream is not desired. This invention provides a low cost method of obtaining a high ethane-content product stream (with few CO2/H2S components) from the additive recovery stage of a demethanization process. The invention also provides a method for purifying this high ethane-content product.

SUMMARY OF THE INVENTION

[0006] The invention involves a method for separating a high ethane-content product from a high methane-content feed stream. The steps in this process include, introducing a high methane-content feed stream into a first distillation column containing a plurality of vapor-liquid contact devices and generating a first bottoms stream, and introducing the first bottoms stream into a second distillation column containing a plurality of vapor-liquid contact devices and generating a second bottoms stream. Additional steps include recovering an additive stream from the second bottoms stream and injecting the additive stream into the first distillation column, and recovering a high ethane-content product from the second distillation column.

[0007] This is a low cost enhancement to a methane recovery system. It can be used to improve the heating value of final methane product from the methane recovery system. The process can also generate and additional revenue product stream. Such a process is advantageous for Alaskan North Slope gas processing where there is a limited market for recovered light hydrocarbons and, therefore, it is desirable to retain these components within the final methane product to enhance its heating value.

BRIEF DESCRIPTION OF THE FIGURES

[0008] FIG. 1 is a schematic flow diagram illustrating apparatus suitable for carrying out the invention described herein.

DETAILED DESCRIPTION OF PREFERRED AND ALTERNATE EMBODIMENTS

[0009] Introduction

[0010] A high methane-content feed stream may be processed to remove impurities and to generate a methane product. This process may take place at very low temperatures and utilize the Ryan/Holmes process. The separation takes place within a distillation column, having a plurality of vapor-liquid contact devices. The specifications of issued U.S. Pat. No. 4,462,814 (Holmes et al.), U.S. Pat. No. 4,318,723 (Holmes et al.), U.S. Pat. No. 4,350,511 (Holmes et al.), U.S. Pat. No 4,293,322 (Ryan et al.), U.S. Pat. No. 32,600 (reissue) (Ryan et al.) are incorporated herein by reference.

[0011] Ryan/Holmes Process

[0012] The Ryan/Holmes process utilizes the injection of an additive into a first distillation column to aid in the separation of components contained within the high methane-content feed gas stream. In a situation where the separation is performed under cryogenic conditions, the additive may prevent certain components contained within the feed gas stream from solidifying and plugging the distillation column. The additive used in the distillation may be externally added or may be one or more recycled components from the bottoms product taken from the first distillation column. When recycled components are used, a second distillation may be used to separate the additive from other products.

[0013] Demethanizer

[0014] In the process of the present invention, a first distillation column (Demethanizer) 100 is used to separate a high methane-content feed into an overhead product (methane product) which is substantially free of acid gas components (typically CO2 and/or H2S) and bottoms substantially free of methane. The high methane-content feed stream 10 generally contains C1, C2, C3, C4+ hydrocarbons, as well as N2 and most often at least CO2 and/or H2S. The overhead product stream (methane product stream) 12 contains methane, N2 and limited impurities: CO2 (typically less than 3% by volume) and/or H2S (typically less than 4 ppm). The bottoms stream 14 from the Demethanizer 100 contains the heavier hydrocarbons and larger concentrations of CO2 and/or H2S. An additive stream 16 recovered from a second distillation column (Additive Recovery Column) 120 is introduced into the Demethanizer 100 to maintain all components in a non-solid state. The additive stream 16 may contain C2, C3 and C4+ hydrocarbons.

[0015] Additive & Ethane Recovery

[0016] The Additive Recovery Column 120 is used to separate the bottoms stream 14 from the Demethanizer into an overhead product stream 20 with high concentrations of CO2, H2S and light hydrocarbons and a heavy hydrocarbon bottoms stream 22. The heavy hydrocarbon bottoms removed from the Additive Recovery Column 120 supply the additive requirements for the Demethanizer 100. The heavy hydrocarbon bottoms stream 22 is split into the additive stream 16 and the net heavy hydrocarbon stream 24. A “high ethane-content” product side stream 18 may also be recovered from the Additive Recovery Column 120.

[0017] To facilitate the CO2 and/or H2S removal in the Demethanizer 100, the Additive Recovery Column 120 heavy hydrocarbon bottoms stream 22 is fractionated (as stated above) to be deficient in CO2 and/or H2S. Typically, this results in a substantial portion of the ethane within the bottoms stream 14 from the Demethanizer, to be “lost” within the CO2 overhead stream 20. In the present invention, an ethane product is removed from the Additive Recovery Column 120, from a position which is not adjacent to the uppermost trays. In a preferred embodiment of the invention, the high ethane-content product stream 18 is taken from a position on the Additive Recovery Column 120 which is above a point “A” where the heavy hydrocarbon bottoms stream 16 is removed from the Additive Recovery Column 120 and below a point “B” where the Demethanizer's bottoms stream 14 is introduced into the Additive Recovery Column 120 second distillation column. The specific location between these points for the removal of the high ethane-content product stream 18 may be determined during operation so as to achieve the “optimum” combination of ethane recovery and additive separation. As a result of such processing, a product stream rich in high ethane is obtained. The high ethane-content product stream 18 will contain limited concentrations of CO2 and/or H2S.

[0018] The high ethane-content product stream 18 may be further treated to remove the limited amounts of CO2 and/or H2S. Removal may be performed in a variety of “standard” processing schemes, including, but not limited to: chemical reaction processes (such as amine treating), physical solvent processes (such as Rectisol—a commercially available physical acid gas removal process using an organic solvent such as methanol at subzero temperatures), hot carbonate processes, or batch processes (such as iron-sponge, caustic wash or solid potassium hydroxide bed).

[0019] Table 1 shows a typical material balance within the high ethane recovery process. (Demethanizer=DEM; Additive Recovery Column=ARC) 1

TABLE 1
STREAM NUMBER<10><12><14><16>
STREAMDEMMETHANEDEMDEM
NAMEFEEDPRODUCTBOTTOMSADDITIVE
H2SLBMOLES/HR1.19990.00581.21600.0220
CO21276.0981128.43231147.66620.0003
N259.103059.10300.00000.0000
C17885.56167865.847719.71390.0000
C2550.48451.5971554.30995.4225
C3192.317129.8115706.0288543.5231
C4+35.23584.6422410.2960379.7024
TOTALLBMOLES/HR10000.00008089.43962839.2308928.6704
TEMPERATURE° F.60−11081−70
PRESSUREPSIA650615630625
H2SMOLE %0.01200.00010.04280.0024
CO212.76101.587740.42170.0000
N20.59100.73060.00000.0000
C178.855697.23600.69430.0000
C25.50480.019719.52320.5839
C31.92320.368524.866958.5270
C4+0.35240.057414.451040.8867
TOTALMOLE %100.0000100.0000100.0000100.0000
H2S% OF FEED0.486
CO210.064
N2100.000
C199.750
C20.290
C315.501
C4+% OF FEED13.175
STREAM NUMBER<18><20><22><24>
STREAMETHANECO2ARCNET HEAVY
NAMESIDE DRAWPRODUCTBOTTOMSHYDROCARBON
H2SLBMOLES/HR0.72780.46570.02260.0006
CO27.47541140.19040.00030.0000
N20.00000.00000.00000.0000
C10.000019.71390.00000.0000
C2240.1650308.58185.56300.1405
C3141.03997.3817557.607214.0840
C4+20.75450.0001389.54149.8390
TOTALLBMOLES/HR410.16281476.3335952.734524.0641
TEMPERATURE° F.1133200100
PRESSUREPSIA373365375350
H2SMOLE %0.17740.03150.00240.0024
CO21.822677.23120.00000.0000
N20.00000.00000.00000.0000
C10.00001.33530.00000.0000
C258.553620.90190.58390.5839
C334.38630.500058.527058.5270
C4+5.06010.000040.886740.8867
TOTALMOLE %100.0000100.0000100.0000100.0000
H2S% OF FEED60.65838.8090.047
CO20.58689.3500.000
N20.0000.0000.000
C10.0000.2500.000
C243.62556.0560.026
C373.3373.8387.323
C4+% OF FEED58.9020.00027.923

[0020] It may be readily appreciated that the present invention can be used in any number of applications without departing from the spirit or intent of the invention. While a preferred form of the invention has been shown in the drawings and the specification, since variations in the preferred form will be apparent to those skilled in the art, the invention should not be construed as limited to the specific form shown and described.





 
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