SYSTEM AND METHOD FOR GAS LIQUEFICATION

Abstract

A method and a system are provided for liquefying an industrial gas. Industrial gas is compressed, at a three-stage feed recycle compressor, to produce a first compressed gas portion and a second compressed gas portion. The second compressed gas portion is further compressed and divided into a first part and a second part. The first compressed gas portion is turbo-expanded to form a first turbo-expanded gas portion. The first turbo-expanded gas portion is warmed, at a heat exchanger, to form a first return stream. The first return stream is fed back to the three-stage feed recycle compressor, between a first compression stage and a second compression stage. A cooled first part is turbo-expanded to form a turbo-expanded first part. The turbo-expanded first part is warmed at the heat exchanger to form a second return stream. The cooled and liquefied second part is recovered as liquefied industrial gas.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. provisional patent application Ser. No. 63/389,974 filed on Jul. 18, 2022 the disclosure of which is incorporated by reference.

TECHNICAL FIELD

The present system and method relates generally to liquefication systems that include a compressors and turbo-expanders, and more particularly, to a method and system for liquefication of industrial gases.

BACKGROUND

In improving the performance of liquefaction of low boiling point gases, such as, for example, oxygen and nitrogen, multiple turbines and liquid expanders have been used in a gas liquefication system. A low-medium pressure liquefier (LMPL) typically underutilizes a warm turbine as compared to high pressure liquefier (HPL) and medium pressure liquefier (MPL) cycles. LMPL cycle turbines are easier to construct.

An example of a low-medium pressure liquefier (LMPL) is described in U.S. Pat. No. 6,220,053 while an example of a medium pressure liquefier (MPL) is disclosed in U.S. Pat. No. 4,778,497 and an example of a high pressure liquefier (HPL) is described in U.S. Pat. No. 5,231,835.

SUMMARY

According to an embodiment, a method is provided for liquefying an industrial gas. Industrial gas is compressed at a three-stage feed recycle compressor to produce a first compressed gas portion and a second compressed gas portion. The second compressed gas portion is further compressed and divided into a first part and a second part. The first compressed gas portion is turbo-expanded, at a warm turbine, to form a first turbo-expanded gas portion. The first turbo-expanded gas portion is warmed, forming a first return stream, at a heat exchanger, by countercurrent flow indirect heat exchange with the first part and the second part. The first return stream is fed back from the heat exchanger, to the three-stage feed recycle compressor, between a first compression stage and a second compression stage. The first part and the second part are cooled in the heat exchanger. The cooled first part is turbo-expanded, at a cold turbine, to form a turbo-expanded first part. The turbo-expanded first part is warmed, at the heat exchanger, to form a second return stream, by indirect heat exchange with the second part, assisting in liquefying the second part. The liquefied second part is recovered as liquefied industrial gas.

According to an embodiment, a system for liquefying industrial gas is provided. The system includes a three-stage recycle compressor for compressing industrial gas to produce a first compressed gas portion and a second compressed gas portion. The system also includes a warm booster and a cold booster for further compressing the second compressed gas portion. The second compressed gas portion is split into a first part and a second part. The system also includes a warm turbine for turbo-expanding the first compressed gas portion to form a first turbo-expanded gas portion. The system additionally includes a heat exchanger for warming the first turbo-expanded gas portion by countercurrent flow indirect heat exchange with the first part and the second part, forming a first return stream that is fed back between a first compression stage and a second compression stage of the three-stage recycle compressor, and cooling the first part and the second part. The system further includes a cold turbine for turbo-expanding the cooled first part to form a turbo-expanded first part. The turbo-expanded first part is warmed at the heat exchanger, to form a second return stream, by indirect heat exchange with the second part to assist in liquefying the second part. The liquefied second part is recovered as liquefied industrial gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certain embodiments of the present disclosure will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a low pressure gas liquefication system, according to an embodiment;

FIG. 2 is a flowchart illustrating a method for liquefying a gas, according to an embodiment; and

FIG. 3 is a block diagram illustrating a controller for controlling a gas liquefication system, according to an embodiment.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure are described in detail with reference to the accompanying drawings. It should be noted that the same elements will be designated by the same reference numerals although they are shown in different drawings. In the following description, specific details such as detailed configurations and components are merely provided to assist with the overall understanding of the embodiments of the present disclosure. Therefore, it should be apparent to those skilled in the art that various changes and modifications of the embodiments described herein may be made without departing from the scope of the present disclosure. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness. The terms described below are terms defined in consideration of the functions in the present disclosure, and may be different according to users, intentions of the users, or customs. Therefore, the definitions of the terms should be determined based on the contents throughout this specification.

The present disclosure may have various modifications and various embodiments, among which embodiments are described below in detail with reference to the accompanying drawings. However, it should be understood that the present disclosure is not limited to the embodiments, but includes all modifications, equivalents, and alternatives within the scope of the present disclosure.

Although the terms including an ordinal number such as first, second, etc. may be used for describing various elements, the structural elements are not restricted by the terms. The terms are only used to distinguish one element from another element. For example, without departing from the scope of the present disclosure, a first structural element may be referred to as a second structural element. Similarly, the second structural element may also be referred to as the first structural element. As used herein, the term “and/or” includes any and all combinations of one or more associated items.

The terms used herein are merely used to describe various embodiments of the present disclosure but are not intended to limit the present disclosure. Singular forms are intended to include plural forms unless the context clearly indicates otherwise. In the present disclosure, it should be understood that the terms “include” or “have” indicate the existence of a feature, a number, a step, an operation, a structural element, parts, or a combination thereof, and do not exclude the existence or probability of the addition of one or more other features, numerals, steps, operations, structural elements, parts, or combinations thereof.

Unless defined differently, all terms used herein have the same meanings as those understood by a person skilled in the art to which the present disclosure belongs. Terms such as those defined in a generally used dictionary are to be interpreted to have the same meanings as the contextual meanings in the relevant field of art and are not to be interpreted to have ideal or excessively formal meanings unless clearly defined in the present disclosure.

Embodiments provide an industrial gas liquefication system having an improved design and lower costs than conventional industrial gas liquefication systems.

FIG. 1 is a diagram illustrating a low pressure gas liquefication system, according to an embodiment. Industrial gas 1 (e.g. nitrogen), generally having a pressure up to approximately 15 pounds per square inch absolute (psia), from an air separation plant, is passed to a gas liquefication system having a compression system with a plurality of compressors or compression stages and a plurality of turbo-expanders.

The industrial gas 1 is fed to a three-stage feed recycle compressor 100, which includes a first stage compressor 102, a second stage compressor 104, and third stage compressors 106 and 108. The three-stage feed recycle compressor 100 may be embodied as a single machine. Within the first stage compressor 102, the industrial gas 1 is compressed to a pressure of approximately 30 psia, and a first resulting gas stream 2 is combined with a first return stream 3 to form a first combined gas stream 4, which is fed to the second stage compressor 104. Within the second stage compressor 104, the first combined gas stream 4 is compressed to a pressure of approximately 70 psia.

A second resulting gas stream 5 from the second stage compressor 104 is combined with a second return stream 6 and an additional stream 7, which is from the air separation plant, to form a second combined gas stream 8, which is fed to the third stage compressors 106 and 108. A third resulting gas stream 9 from the third stage compressors 106 and 108 has a pressure of approximately 320 psia, which is lower than a resulting pressure from a feed recycle compressor having four or more stages.

The third resulting gas stream 9 is split with a first portion passed to a warm turbine (turboexpander) 110 and a second portion directed to a warm booster (compressor) 114. The warm turbine 110 and the warm booster 114 may be embodied as a single machine. After turbo-expansion at the warm turbine 110, a fourth resulting gas stream 10 is fed to a heat exchanger 112 at a pressure of approximately 33 psia, which is lower than resulting pressures from warm turbines used in combination with feed recycle compressors having four or more stages. The heat exchanger 112 may include three zones, identified in the drawings as zones 1, 2, and 3.

The fourth resulting gas stream 10, which represents the exhaust stream from the warm turbo-expander, enters the heat exchanger in zone 3, combines with resulting gas 15, is warmed by flow through that passage, and exits the warm end of the heat exchanger 112 in zone 3 as the first return stream 3. The first return stream has a pressure of approximately 30 psia. The expansion to this lower pressure allows the first return stream 3 to be fed back between the first stage compressor 102 and the second stage compressor 104 of the three-stage feed recycle compressor 100, as opposed to between the second stage compressor 104 and the third stage compressors 106 and 108.

As described, above, the remaining portion of the third resulting gas stream 9 that is not directed to the warm turbo-expander is passed to the warm booster 114, and subsequently, to a cold booster (compressor) 116, where it is further compressed to approximately 780 psia. A fifth resulting gas stream 11 from the cold booster 116 is split into a first stream 12 and second stream 13, both of which enter the heat exchanger 112 in zone 3.

The first stream 12 is cooled by flow through zones 3 and 2 of the heat exchanger 112 by indirect heat exchange with a countercurrent flowing warming stream of the fourth resulting gas stream 10 and the resulting gas 15. The first stream 12 exits the heat exchanger 112 in zone 2 and is passed to a cold turbine (turboexpander) 118. The cold turbine 118 and the cold booster 116 may be embodied as a single machine. A sixth resulting gas stream 14 from the cold turbine 118 is fed back into the heat exchanger 112 in zone 1. The sixth resulting gas stream 14 is warmed by flow through zones 1, 2, and 3 of the heat exchanger 112 by indirect heat exchange with a countercurrent flowing cooling stream of the second stream 13 and exits the heat exchanger 112 in zone 3 as the second return stream 6. As described above, the second return stream 6 is fed back to the three-stage feed recycle compressor between the second stage compressor 104 and the third stage compressors 106 and 108.

The second stream 13 is cooled by flow through zones 3, 2, and 1 of the heat exchanger 112 by indirect heat exchange with countercurrent flowing warming streams of the fourth resulting gas stream 10, the resulting gas 15, and the sixth resulting gas stream 14. The second stream 13 exits the heat exchanger 112 in zone 1 and is passed to a valve 120. The valve 120 may be a Joule-Thomson (JT) valve or a liquid turbine, which liquefies the second stream 13. Any resulting gas 15 that exits the valve 120 is fed back into the heat exchanger 112 in zone 1, and is warmed by flow through zones 1, 2, and 3 of the heat exchanger 112 by indirect heat exchange with counter-currently flowing cooling streams of the first stream 12 and the second stream 13, before being combined with the fourth resulting gas stream 10 in zone 3 and exiting the heat exchanger 112 at zone 3 as the first return stream 3. As described above, the first return stream is fed back to the three-stage feed recycle compressor between the first stage compressor 102 and the second stage compressor 104. A liquid 17 that exits the valve 120 is provided to a tank.

The reduced number of stages in the three-stage feed recycle compressor 100 reduces installation costs. Full expansion of the warm turbine 110 is provided without the need for a very high speed, as is typical in an MPL arrangement. More heat is rejected in the warm section while the total head pressure is maintained.

FIG. 2 is a flowchart illustrating a method for liquefying an industrial gas, according to an embodiment. Initially, at 202, industrial gas from an air separation plant is compressed, at a three-stage feed recycle compressor, to produce a first compressed gas portion and a second compressed gas portion. The first compressed gas portion and the second compressed gas portion may have pressures of approximately 320 psia. A first return stream is combined with the industrial gas between a first compression stage and a second compression stage. A second return stream and an additional stream, which is from the air separation plant, are combined with the industrial gas between a second compression stage and a third compression stage.

At 204, the second compressed gas portion is further compressed at a warm booster and a cold booster and divided into a first part and a second part. At 206, the first compressed gas portion is turbo-expanded, at a warm turbine, to form a first turbo-expanded gas portion. The first turbo-expanded gas portion may have a pressure of approximately 33 psia. At 208, the first turbo-expanded gas portion is warmed in a heat exchanger by countercurrent flow indirect heat exchange with the first part and the second part, forming the first return stream. This also cools the first part and the second part. The first return stream has a pressure of approximately 30 psia.

At 210, the cooled first part is turbo-expanded, at a cold turbine, to form a turbo-expanded first part. At 212, the turbo-expanded first part is warmed in the heat exchanger, to form the second return stream, by indirect heat exchange with the second part, assisting in liquefying the second part.

At 214, a gaseous portion and a liquid portion of the liquefied second part are separated. At 216, the gaseous portion is warmed in the heat exchanger by countercurrent indirect heat exchange with the first part and the second part to assist in liquefying the second part and combined with the first turbo-expanded gas portion to form the first return stream. At 218, the liquefied second part is recovered as liquefied industrial gas.

FIG. 3 is a block diagram illustrating a controller for controlling a gas liquefication system, according to an embodiment. The processor or controller may include at least one user input device 302 and a memory 304. The memory 304 may include instructions that allow a processor 306 to calibrate and control compressors, turboexpanders, and turbines of the system.

Although certain embodiments of the present disclosure have been described in the detailed description of the present disclosure, the present disclosure may be modified in various forms without departing from the scope of the present disclosure. Thus, the scope of the present disclosure shall not be determined merely based on the described embodiments, but rather determined based on the accompanying claims and equivalents thereto.

Claims

1. A method for liquefying an industrial gas comprising:

compressing industrial gas, at a three-stage feed recycle compressor, to produce a first compressed gas portion and a second compressed gas portion;

further compressing and dividing the second compressed gas portion into a first part and a second part;

turbo-expanding the first compressed gas portion, at a warm turbine, to form a first turbo-expanded gas portion;

warming the first turbo-expanded gas portion and forming a first return stream, at a heat exchanger, by countercurrent flow indirect heat exchange with the first part and the second part,

feeding back the first return stream from the heat exchanger, to the three-stage feed recycle compressor, between a first compression stage and a second compression stage;

cooling the first part and the second part in the heat exchanger;

turbo-expanding the cooled first part, at a cold turbine, to form a turbo-expanded first part;

warming the turbo-expanded first part, at the heat exchanger, to form a second return stream, by indirect heat exchange with the second part, assisting in liquefying the second part; and

recovering the liquefied second part as liquefied industrial gas.

2. The method of claim 1, further comprising:

separating a gaseous portion and a liquid portion of the liquefied second part; and

warming the gaseous portion at the heat exchanger by countercurrent indirect heat exchange with the first part and the second part to assist in liquefying the second part.

3. The method of claim 2, further comprising combining the warmed gaseous portion with the first turbo-expanded gas portion at the heat exchanger to form the first return stream.

4. The method of claim 1, wherein, in compressing the industrial gas, the warmed first part is combined with an additional stream from an air separation plant and the industrial gas in the three-stage feed recycle compressor between the second compression stage and a third compression stage.

5. The method of claim 1, wherein the first compressed gas portion and the second compressed gas portion have pressures of approximately 320 pounds per square inch absolute (psia).

6. The method of claim 1, wherein the first turbo-expanded gas portion has a pressure of approximately 33 psia.

7. The method of claim 1, wherein the first return stream has a pressure of approximately 30 psia.

8. A system for liquefying an industrial gas comprising:

a three-stage feed recycle compressor for compressing industrial gas to produce a first compressed gas portion and a second compressed gas portion,

a warm booster and a cold booster further compressing the second compressed gas portion, wherein the second compressed gas portion is split into a first part and a second part;

a warm turbine for turbo-expanding the first compressed gas portion to form a first turbo-expanded gas portion;

a heat exchanger for warming the first turbo-expanded gas portion by countercurrent flow indirect heat exchange with the first part and the second part, forming a first return stream that is fed back between a first compression stage and a second compression stage of the three-stage feed recycle compressor, and cooling the first part and the second part; and

a cold turbine for turbo-expanding the cooled first part to form a turbo-expanded first part,

wherein the turbo-expanded first part is warmed at the heat exchanger, to form a second return stream, by indirect heat exchange with the second part to assist in liquefying the second part, and

wherein the liquefied second part is recovered as liquefied industrial gas.

9. The system of claim 8, wherein a gaseous portion and a liquid portion of the liquefied second part are separated, and the gaseous portion is warmed at the heat exchanger by countercurrent indirect heat exchange with the first part and the second part to assist in liquefying the second part.

10. The system of claim 9, wherein the heat exchanger combines the warmed gaseous portion with the first turbo-expanded gas portion to form the first return stream.

11. The system of claim 8, wherein the first compression system combines the warmed first part with an additional stream from an air separation plant and the industrial gas in the three-stage feed recycle compressor between the second compression stage and a third compression stage.

12. The system of claim 8, wherein the first compressed gas portion and the second compressed gas portion have pressures of approximately 320 pounds per square inch absolute (psia).

13. The system of claim 8, wherein the first turbo-expanded gas portion has a pressure of approximately 33 psia.

14. The method of claim 8, wherein the first return stream has a pressure of approximately 30 psia.

15. The system of claim 8, wherein the first turbo-expander is operatively coupled to and configured to drive a warm booster compressor in the compression system.

16. The system of claim 1, wherein the second turbo-expander is operatively coupled to and configured to drive a cold booster compressor in the compression system.