EA007771B1 - Ngl recovery plant and method for operating thereof - Google Patents

Abstract

A two-column NGL recovery plant includes an absorber (110) and a distillation column (140) in which the absorber (110) receives two cooled reflux streams, wherein one reflux stream (107) comprises a vapor portion of the NGL and wherein the other reflux stream (146) comprises a lean reflux provided by the overhead (144) of the distillation column (140). Contemplated configurations are especially advantageous in a upgrade of an existing NGL plant and typically exhibit Crecovery of at least 99% and Crecovery of at least 90%.

Description

Many natural and man-made gases contain a number of different hydrocarbons, and numerous gas separation processes and plant configurations are known to produce fractions of commercial interest from such gases. In a typical gas separation process, the pressurized gas feed stream is cooled by a heat exchanger, and liquids condense as the gas cools from the cooled gas. The pressure of these liquids is then reduced and separated in a distillation column (for example, a column for separating ethane or methane) to separate residual components, such as methane, nitrogen and other volatile gases, in the form of an overhead vapor stream from the desired C ₂ , C ₃ and heavier components.

For example, US Pat. No. 5,890,378 (Bato e! A1.) Describes a system in which reflux is supplied to the absorber, where the condenser of the ethane separation unit provides reflux for both the absorber and the ethane separation unit, while cooling requirements are carried out using a turboexpander, and where the absorber and the ethane separation unit operate at practically the same pressure. Although the advantage of the Batto configuration is the reduction in capital costs of equipment associated with providing reflux for the absorption section and the installation of the ethane separation, the propane yield decreases significantly as the operating pressure in the absorber increases, especially at overpressure above 3.45 MPa (500 psi). inch) when the separation of ethane from propane in the installation of the separation of ethane becomes more and more difficult. Therefore, the BATO system is usually limited by the upper limit of the working pressure in the ethane separation unit. In the configuration of the BatO process, increasing the pressure in the absorber while maintaining the desired propane yield becomes difficult, if not impossible. Moreover, the operation of the absorber and the ethane separation unit at an overpressure of about 3.45 MPa (500 psi) or lower usually necessitates a more significant re-compression of the residual gas, which leads to relatively high operating costs.

To avoid at least some of the problems associated with the relatively high cost of re-compressing the residual gas, US Pat. No. 5,953,935 (Zogeikei) describes a plant configuration in which absorber reflux is obtained by compressing, cooling, and expanding according to the Joule-Thomson diverted feed stream gas. Although Zogeikei’s configuration generally provides an improved propane yield with virtually no increase in power needed to compress the residual gas, the propane yield decreases significantly as the operating pressure in the absorber increases, especially at overpressure above 3.45 MPa (500 psi) square inch). In addition, the production of ethane using known systems designed to produce propane is usually limited to a yield of about 20%.

To increase the yield of ethane with a low CO ₂ content in the ethane produced, US Pat. No. 6182469 (Satbе11) describes a column type re-evaporation scheme in which one or more liquid streams obtained by distillation in a column from a point located above in the absorber are used for distillation of light fractions of undesirable components (for example, carbon dioxide in a methane separation unit). The SatpbE11'a scheme usually requires additional distillation of the light fractions from the ethane obtained, and the removal of CO _{2 is} usually limited to about 6%. In addition, the additional removal of CO2 using the CatPe11 method will significantly reduce the yield of ethane and increase the power consumption. In addition, especially if the ethane obtained is used for chemical production, the product of the Satreb11 installation usually requires further processing to remove CO ₂ to the level of 500 ppm (vol.) Or lower, which often requires significant capital investments and operating costs.

In other configurations, a turboexpander is used to provide cooling of the feed gas to achieve a high yield of propane or ethane. Examples of configurations are described, for example, in US Pat. No. 4,278,457 and US Pat. No. 4,854,955 (Satl e11 e! A1.), In US Pat. No. 5953935 (McEgto e! A1.), In US Pat. No. 6244070 (Exo !! e! A1. ) or in US Pat. No. 5,890,377 (Eodya). Although such configurations may provide at least some advantages over other methods, they usually require changes to existing expanders if the installation is being reconstructed to obtain higher performance. In addition, in such configurations, the separated liquid fractions are fed to a methane separation unit operating at cryogenic temperature.

Thus, although various configurations and methods are known for producing various fractions from gas gasoline (liquid components of natural gas), all or almost all of them have one or more disadvantages. Therefore, there is still a need for methods and configurations for improved production of gas gasoline.

An object of the present invention is methods and configurations of an apparatus in which double irrigation in an absorber is provided, where one of the reflux streams is provided with a steam portion of the feed gas and the other reflux stream is provided with a product from the top of the distillation column.

In one aspect of the subject invention, the liquid portion of the feed natural gas and a second vapor portion of the feed natural gas, the pressure of which is reduced by means of a turboexpander, are additionally introduced into the absorber. Preferred absorbers additionally provide a bottoms product that cools at least one of the first and second reflux streams, and at least a portion

- 1 007771 of this bottoms product may enter the distillation column. The intended products from the top of the absorber can be used to cool at least one of the first and second reflux streams and can additionally be used to cool at least one of such streams as natural gas feed and a vapor portion of natural gas feed. Preferred devices other than a turboexpander include a Joule-Thomson valve, and preferred distillation columns include methane or ethane separation units. If C ₂ is particularly preferred, it is contemplated that the first lean (“lean”) reflux stream can be fed to the absorber as a liquid feed stream, and the distillation column includes a methane separation unit. Preferred configurations are particularly useful in combination with an existing gasoline gas production plant in order to increase productivity while increasing the yield of C ₂ and C ₃ .

Therefore, in yet another aspect of the invention, a method of increasing the productivity of a natural gas separation apparatus having an absorber and a distillation column comprises one step in which a first reflux stream to the absorber is provided, and this first reflux stream comprises an overhead from the distillation column. At another stage, a bypass (upstream) line is provided upstream of the turboexpander, and the steam part of the cooled gasoline is sent to this bypass line and the steam part is provided for the absorber, and in another stage, the pressure of this steam part is reduced before this steam part enters the absorber as a second reflux stream. In yet another step, a heat exchanger is provided that cools at least one of the first and second reflux streams using at least one of the products: bottoms of the absorber and product from the top of the absorber.

Thus, the method of operation of the installation may include one stage in which an absorber and a distillation column are provided. In the next step, the cooled depleted product from the top of the distillation column is fed into the absorber as a first reflux stream, and in another step, the pressure of the cooled steam portion of the feed natural gas is reduced using a device other than the turboexpander, while the cooled steam portion, the pressure of which is reduced, is supplied into the absorber as a second reflux stream.

In the drawing of FIG. 1 is a diagram of an example configuration of an apparatus according to the subject of the present invention.

The inventors have found that a high yield of gas gasoline (for example, at least 99% C ₃ and at least 90% C ₂ ) can be obtained in a new and improved installation configuration in which two reflux streams enter the absorber. In addition, the configurations in question can advantageously allow the output of the components to be changed by changing the process temperature and changing the feed location of one of the reflux streams into the absorber.

More specifically, preferred plant configurations may include an absorber which receives a first reflux stream and a second reflux stream, wherein the first reflux stream contains a cooled depleted product from the top of the distillation column, and the second reflux stream contains a cooled vapor portion of the feed natural gas, the pressure of which is reduced using a device other than a turboexpander.

In a particularly preferred configuration depicted in the attached figure, the installation 100 includes an absorber 110, which is connected by flow to the distillation column 140. Natural gas feed 101 with a typical composition in mol.% 85% C1, 6% C2, 3% C3, 3% C4 + and 3% CO ₂ at 32.2 ° C (90 ° B) and an overpressure of 8.28 MPa (1200 psi) is cooled in a heat exchanger 124 to produce natural gas 102 with a temperature of -31.7 ° C ( -25 ° B). A portion of the chilled feed natural gas, which is a condensed liquid, is separated in a separator 170 to form a chilled liquid stream 103, and the chilled steam portion 106 is further cooled in a heat exchanger 122, typically to −37.2 ° C. (−35 ° C.), to obtain another portion 107 of chilled steam. The liquid obtained from the additionally cooled vapor stream 107 is separated from the vapors in the separator 180, whereby an additionally cooled vapor stream 108 and an additionally cooled liquid stream 104 are obtained. The cooled liquid stream 103 and the additionally cooled liquid stream 104 are combined to form a combined cooled liquid stream 105, typically having a temperature of −75 ° C. (−75 ° C.) and a pressure of 2.83 MPa (410 psi), which is then injected as a feed stream into the lower section of the absorber 110.

In particularly preferred configurations in the range of products obtained from propane to ethane, typical temperature ranges are illustrated as follows. The additionally cooled steam stream 108 is divided into a first portion, which is expanded in a turboexpander 150 to form an expanded stream 109, usually with a temperature of from -73.3 to -81.7 ° C (-100 to -115 ° B), which is introduced into the absorber 110, and the second part 130 of the stream, which is additionally cooled in the heat exchanger 120, usually to a temperature of from -67.8 to -92.8 ° C (from -90 to -135 ° B), and reduce the pressure in it through a Joule valve -Tomson 132 before being introduced into absorber 110 as a reflux stream, usually at a temperature of from -87.23 to -95.6 ° C (-125 to -140 ° B).

The absorber 110 forms the product 114 from the top, usually at a temperature of from -73.3 to -92.8 ° C (from -100 to

- 2 007771

-135 ° E), which is used as a cooling agent in the heat exchangers 120, 122 and 124 before the compression of this residual gas is performed in the compressor 160 for recompressing the residual gas. Thus, it should be understood that the product from the top cools the first and second absorber reflux streams, 146 and 130, respectively, and can then be used as a cooling agent for cooling at least one of the parts of the feed natural gas vapor from the first and second separators. Absorber 110 also gives bottoms product 112, usually at a temperature of from -73.3 to -81.7 ° C (-100 to -115 ° E), which also plays the role of a cooling agent in the heat exchanger 120 for further cooling of the first and second flows 146 and 130 phlegms. The heated bottoms product 112, usually at a temperature of from -53.9 to -65.0 ° C (-65 to -85 ° E), is then introduced into the distillation column 140, which separates the desired bottoms product 142 (for example, propane or ethane / propane) from depleted residual gas 144. The depleted residual gas 144 can then be cooled in a cooler before being introduced into a separator 190 that produces reflux 148 for a distillation column and a depleted reflux 146 stream for an absorber, typically at a temperature of from -65 to -81.7 ° C (-85 to -115 ° E).

It should be especially emphasized that the discussed configurations can be used both to obtain a high yield of propane and to obtain a high yield of ethane. For example, if it is desired to obtain a high ethane yield, a cooler is usually not required for the stream 144 from the top of the distillation column and can be bypassed, and the depleted absorber reflux stream 146 is introduced into the lower part of the absorber 110 as a bottom (bottoms) feed stream, as indicated by dashed lines on the figure.

With regard to acceptable feed gas streams, it is contemplated that various feed gas streams are suitable, and particularly suitable feed gas streams may include various hydrocarbons with different molecular weights. With regard to the molecular weight of the intended hydrocarbons, it is usually preferred that the feed gas stream includes substantially C ₁ C 6 hydrocarbons. However, suitable feed gas streams may further comprise acid gases (e.g., carbon dioxide, hydrogen sulfide) and other gaseous components (e.g., hydrogen). Therefore, particularly preferred feed gas streams are natural gas and gas gasoline (a natural gas liquefaction product).

In other preferred aspects of the present invention, the feed gas streams are cooled to condense at least a portion of the heavier components in the feed gas stream, and in particularly preferred configurations, the feed gas stream is cooled, separated into a vapor part and a liquid part, while the steam part is further cooled and divided into a second vapor part and a second liquid part. Without limiting the concept of the invention, it is particularly preferred that these cooling steps can be carried out using the cold storage capacity of the product from the top of the absorber and / or bottoms of the absorber.

In the considered configurations, it is also preferable that the liquids separated from the feed gas stream are (combined and) supplied to the absorber. As for the steam parts, it should be understood that the second steam part is divided into a bypass (bypass) stream and a stream going through a turbo expander, and the stream going through a turbo expander is fed to a turbo expander and then to an absorber, and the bypass stream a) is additionally cooled. preferably using the cold storage capacity of the overhead of the absorber and / or the bottom product of the absorber, and then b) reduce the pressure in it using a device other than a turboexpander before it is fed to the upper section of the absorber as a first flow egma. Particularly suitable devices include Joule-Thomson valves, however, it can also be considered that any other pressure reduction configurations and methods are also suitable in this case. For example, suitable alternative devices could include turbines for generating energy and devices with expansion nozzles.

Products from the top and from the cube of the absorber are preferably used as a cooling agent in the heat exchanger, the heat exchanger cooling the first and second reflux streams. In addition, it is preferable that the overhead of the absorber can serve as a cooling agent in at least one, and preferably at least two additional heat exchangers, where this product from the top of the absorber cools and separates the vapor part of the feed gas and the feed gas stream before repeated compression to residual gas pressure. Similarly, the bottom product of the absorber is used (preferably in the same heat exchanger) as a cooling agent to cool at least one of the first and second reflux streams before being fed to the distillation column as a column feed. Suitable absorbers may vary depending on specific configurations, however, it is usually preferred that the absorber is a plate or packed type absorber.

The bottom product of the absorber is separated in a distillation column to obtain the desired bottom product (for example, C ₂ / C ₃ or C ₃ and C ₄ ⁺ ). Therefore, depending on the desired still product, suitable distillation columns include a methane and ethane separation unit. If the desired bottoms product is C ₃ and C ₄ ⁺ , it is assumed that the overhead of the distillation column is cooled in a cooler (for example, using an external cooling agent) and is divided into a portion representing the reflux of the distillation column and into a steam portion. Thus, it should be particularly appreciated that the vapor product from the top of the distillation column can be used as a first stream

- 3 007771 reflux for an absorber, the first reflux stream being a depleted reflux stream which is fed to the upper plate of the absorber.

Similarly, if the desired bottoms product is C ₂ / C ₃ ⁺ , it is assumed that the overhead of the distillation column bypasses the cooler, and after separation in the separator, the liquid part is used as reflux for the distillation column, while the vaporous part is used as power fed into the cube of the absorber. Again, it should be especially appreciated that in such configurations, upon receipt of ethane, the vaporous product from the top of the distillation column is recycled back to the absorber to reabsorb the C ₂ ⁺ components, which leads to a high yield of ethane.

Thus, it should be particularly understood that in the configurations under consideration, the cooling requirements for the absorber are at least partially provided by reflux flows (by cooling with products from the bottom and from the top of the absorber) and that the production of C ₂ / C _{3 is} significantly improved when using the first and second streams of phlegm. With regard to the production of C ₂ , it is believed that such configurations provide a yield of at least 85%, more typically at least 88% and most typically at least 90%, while it is believed that the yield of C ₃ will be at least 95%, more typically at least 98%, and most typically at least 99%.

In another aspect of the subject matter, it is understood that the proposed configurations have particular advantages when reconstructing an existing natural gas processing plant, where the performance of the reconstructed plant is significantly increased without replacing the expander turbine or replacing the absorber and / or distillation column. Additional equipment for such reconstructions usually includes a heat exchanger and a piping system.

Therefore, a method of increasing the productivity of a natural gas processing plant having an absorber and a distillation column includes a step of providing a first reflux stream to the absorber, where this first reflux stream comprises an overhead from the distillation column. At another stage, a bypass line (bypass) is provided upstream of the turboexpander, where the steam portion of the cooled gas gas is supplied to this bypass line and this vapor portion is provided for the absorber. In another stage, the pressure of this vapor part is reduced before the vapor part is supplied to the absorber as a second reflux stream, and in another stage, a heat exchanger is provided that cools at least one of the first and second reflux streams using at least one of the products cubic product of the absorber and product from the top of the absorber.

Particularly preferred methods also include a step in which a second vaporous portion of the cooled gas gasoline is expanded in a turboexpander and fed to an absorber, to which a liquid portion of the cooled gas gasoline is also fed. In addition, the overhead of the absorber can further cool gas gasoline and / or the vaporous portion of gas gasoline, and the reflux stream can be supplied to the absorber as a liquid or as a vapor / liquid feed stream, the distillation column including an ethane separation unit. Alternatively, the distillation column may also play the role of a methane separation unit, if liquid ethane is the preferred product.

Thus, the method of operation of the installation may include a stage at which an absorber and a distillation column are provided. At another stage, the cooled depleted product from the top of the distillation column is fed into the absorber as a first reflux stream, and the pressure of the cooled vaporous portion of the feed natural gas is reduced by means of a device other than a turboexpander. In yet another step, this cooled vaporous portion, the pressure of which is reduced, is supplied to the absorber as a second reflux stream. Similarly, the discussed methods may also include a stage in which the liquid part of the feed natural gas and the second vaporous part of the feed natural gas are fed to the absorber, and the pressure of the second part is reduced using a turboexpander.

Additionally, a heat exchanger may be provided in which at least one of the products — the bottom product of the absorber and the product from its top — is used to cool at least one of the first and second reflux streams. Moreover, it is usually preferred that in such methods at least a portion of the bottoms product is fed from the absorber to the distillation column and that a device other than the turboexpander includes a Joule-Thomson valve. In addition, if it is desired to obtain C ₂ , it is assumed that the depleted reflux stream is provided with steam from the separator and fed to the absorber as a liquid feed stream, and the vapor stream from the top of the distillation column is fed into the absorber cube, while the distillation column includes a methane separation unit .

Additionally, in another aspect of the subject matter, it should be understood that the discussed configurations with an absorber operating at a higher pressure than the distillation column downstream are particularly advantageous. This proposed configuration requires a compressor to increase the pressure of the vapor stream from the distillation column to the pressure required for the absorber. It should be understood that such a dual-pressure column configuration provides significant overall savings in compression power since the power required for a compressor that compresses the residual gas is significantly reduced.

Thus, specific embodiments and applications of the improved

- 4 007771 receiving gas gasoline. Professionals, however, should understand that it is possible, without departing from the concept of the invention set forth herein, to carry out a significantly larger number of modifications than those already described. Thus, the subject matter of the invention should be limited only by the essence of the attached claims. Moreover, in interpreting both the description and the claims, all terms should be interpreted as broadly as possible within the context. In particular, the terms “includes” and “including” should be interpreted as referring to elements, components or steps in a non-exclusive manner, indicating that the elements, components or steps in question may be presented, or used, or combined with other elements, components or stages that were not specifically indicated.

Claims (19)

1. Installation for producing gas gasoline containing an absorber, a distillation column, means for cooling a depleted overhead product from a distillation column, means for supplying a first reflux stream containing said cooled depleted overhead product from a distillation column and a second reflux stream containing the cooled steam portion of the feed natural gas, and means for reducing the pressure of the specified cooled steam portion of the feed natural gas using a device other than tour odetandera, before it is fed into the absorber. 2. The installation according to claim 1, which further comprises means for supplying to the absorber the liquid part of the feed of natural gas, and also contains a turboexpander to reduce the pressure of the second steam part of the feed of natural gas and means for supplying the specified second steam of the feed of natural gas to the absorber. 3. The installation according to claim 1, which contains cooling means for at least one of the first and second reflux streams with the bottoms product of the absorber. 4. The installation according to claim 1, which contains means for cooling at least one of the first and second reflux streams with the overhead product of the absorber. 5. The installation according to claims 3 to 4, which further comprises a turboexpander to reduce the pressure of the second steam portion of the feed natural gas and means for supplying the specified second steam portion of the feed natural gas to the absorber, and these means for supplying the first reflux stream are made in the form of a bypass located above the turboexpander upstream. 6. The apparatus of claim 5, further comprising means for supplying a liquid portion of the feed natural gas to the absorber. 7. The installation according to claim 3, which further comprises means for supplying at least a portion of the bottoms product to the distillation column. 8. Installation according to any one of claims 1 to 7, further comprising means for cooling the feed natural gas and / or the steam portion of the feed natural gas with said overhead product. 9. Installation according to any one of claims 1 to 8, in which said device, other than a turboexpander, is a Joule-Thomson valve. 10. Installation according to any one of claims 1 to 9, in which the distillation column includes an installation for the separation of methane. 11. Installation according to any one of claims 1 to 10, which further comprises means for supplying the first reflux stream to the absorber in the form of a vapor / liquid mixture or in the form of a liquid, the distillation column comprising an ethane separation unit. 12. Installation according to any one of claims 1 to 11, which contains a compressor for compressing the steam of the overhead of the distillation column, operating at a lower pressure than the pressure of the absorber, to the pressure of the absorber. 13. The installation according to claim 5, in which the distillation column includes a methane separation unit and which comprises a separator and means for irrigating the absorber with chilled gas from the separator, as well as means for supplying vapor from the top of the unit for separating methane into the absorber cube to produce ethane. 14. The method of operation of the installation according to claim 1, comprising supplying the cooled depleted overhead product from the distillation column to the absorber as a first reflux stream, reducing the pressure of the cooled steam portion of the feed natural gas using a device other than the turbine expander, and supplying the cooled steam portion, the pressure of which is reduced to the absorber as a second reflux stream in addition to the first reflux stream. 15. The method according to 14, in which the absorber is additionally supplied with a liquid part of the feed natural gas and a second vapor part of the feed natural gas, and the pressure of this second part before - 5 007771 supply to the absorber is reduced using a turboexpander. 16. The method according to 14, in which at least one of the first and second reflux streams is cooled in a heat exchanger, into which the absorber bottom product and / or overhead absorber are fed as a cooler. 17. The method according to 14, in which at least a portion of the bottoms product from the absorber is fed to the distillation column. 18. The method of claim 14, wherein a Joule-Thomson valve is used as said device other than a turboexpander. 19. The method according to 14, in which the first reflux stream is fed into the absorber in the form of a steam / liquid feed stream and ethane is separated in the distillation column.