Methods for liquefying gases

Abstract

The present invention relates to a method for liquefying a gas. The method comprises compressing a main body of gas. The method further comprises cooling the compressed main body. Cooling the main body comprises first dividing the compressed main body. The first division provides a first cooling flow. Cooling the main body further comprises dividing the compressed main body at least one subsequent time. At least one subsequent division of the compressed main body provides at least one subsequent cooling flow. Cooling the main body further comprises cooling the first cooling flow by at least one subsequent cooling flow. Cooling the main body further comprises cooling the compressed main body by the first cooling flow and cooling the main body by at least one subsequent cooling flow.

Description

Technical Field

[0001] The present disclosure relates to the technical field of processes and apparatuses for the liquefaction of gases such as natural gas or biomethane.

Background Art

[0002] In gas liquefaction facilities such as natural gas or biomethane, by liquefying and storing the gas, the liquefied gas can be transported at a pressure slightly higher than atmospheric pressure. Currently, there are several technologies and processes for gas liquefaction, including liquefaction processes based on the Linde cycle. The principle of the Linde cycle is to split the gas stream to obtain a secondary stream that cools the main stream, whereby the gas stream is divided and self-cooling is achieved.

[0003] In this context, improved technical means for gas liquefaction are still needed.

Summary of the Invention

[0004] The present disclosure proposes a method for liquefying a gas. The method includes compressing a main stream of the gas. The method further includes cooling the compressed main stream. Cooling the main stream first includes splitting the compressed main stream. A first cooling stream is provided by the first split. Cooling the main stream further includes subsequently splitting the compressed main stream at least once. At least one subsequent cooling stream is provided by at least one subsequent split of the compressed main stream. Cooling the main stream further includes cooling the first cooling stream by at least one subsequent cooling stream. Cooling the main stream further includes cooling the compressed main stream by the first cooling stream and cooling the main stream by at least one subsequent cooling stream.

[0005] As will be described later, in this method, the gas is provided in liquid form at the output (i.e., after performing the steps of the method including the cooling step), that is, the gas is in a liquefied state.

[0006] Cooling of the first cooling flow may include pre-cooling of the first cooling flow by at least one subsequent cooling flow. Cooling of the first cooling flow may further include expanding the pre-cooled first cooling flow.

[0007] Compressed mainstream cooling may include using an expanded first cooling flow in a heat exchanger.

[0008] The method may further include expanding at least one subsequent cooling flow after at least one subsequent split and before precooling the first cooling flow.

[0009] Pre-cooling of the first cooling flow with at least one subsequent cooling flow may include using a subsequent cooling flow that has expanded in the heat exchanger.

[0010] The method may further include recycling the expanded cooling flow.

[0011] The method may further include, before splitting, a first cooling of the main stream using aqueous glycol, and a pre-cooling of the main stream using a cooling unit or cooling source (e.g., -45°C).

[0012] The method may further include expanding the cooled main flow after cooling the compressed main flow with a first cooling flow.

[0013] The method may further include storing the cooled and expanded mainstream in a bulk unit after the expansion of the cooled mainstream.

[0014] This method can be automated, that is, it can be carried out using any technology suitable for automating the gas liquefaction process.

[0015] Equipment for liquefying gas according to this method has also been proposed. This equipment is adapted for carrying out this method and is an apparatus or system for carrying out this method, including the equipment necessary to perform this method. This equipment is, Mainstream lines intended for compression, splitting, and cooling, A first dividing line intended for cooling the first cooling flow and the main flow, It includes a first cooling flow and at least one second split line intended for cooling the main flow.

[0016] The mainstream line is, A four-stage high-pressure compressor compresses the main flow, A cooling device using water glycol for mainstream primary cooling, and A cooling unit that pre-cools the main stream using a cooling unit, A control valve for the first division, At least one other control valve for at least one subsequent split, A heat exchanger that cools the main flow with a first cooling flow, An expander that expands the cooled main stream, It may also include a bulk unit for storing the cooled and expanded mainstream.

[0017] The first dividing line is, A heat exchanger that pre-cools the first cooling flow with at least one subsequent cooling flow, The system may also include an expander for expanding a pre-cooled first cooling flow.

[0018] At least one second dividing line is, An expander that expands at least one subsequent cooling flow, The system may also include a heat exchanger that pre-cools the first cooling flow with at least one subsequent cooling flow, The equipment can be automated, that is, it may include any automation technology suitable for automatically carrying out the method.

[0019] A non-limiting embodiment will be described below with reference to the drawings. [Brief explanation of the drawing]

[0020] [Figure 1] A schematic diagram of an example of the method and equipment is shown. [Figure 2] Shows a schematic diagram of an example of a method and equipment. [Figure 3] Shows a schematic diagram of an example of a method and equipment. [Figure 4] Shows a schematic diagram of an example of a method and equipment.

Embodiments for Carrying Out the Invention

[0021] A method for liquefying a gas has been proposed. The method includes compressing the main stream of the gas. The method further includes cooling the compressed main stream. Cooling the main stream first includes dividing the compressed main stream. The first division provides a first cooling stream. Cooling the main stream further includes subsequently dividing the compressed main stream at least once, and at least one subsequent division of the compressed main stream provides at least one subsequent cooling stream. Cooling the main stream further includes cooling the first cooling stream with at least one subsequent cooling stream. Cooling the main stream further includes cooling the compressed main stream with the first cooling stream and cooling the main stream with at least one subsequent cooling stream.

[0022] This is an improved method for gas liquefaction.

[0023] In fact, different from the conventional cooling process based on the Linde cycle, this method is based on a modified Linde cycle in which the main stream is first divided to generate the main stream and the first cooling stream, then the (at least) second division is performed, the first cooling stream is cooled using at least one subsequent cooling stream generated from at least one subsequent division, and the first cooling stream itself cools the main stream. The at least one subsequent cooling stream also cools the main stream. Compared with the normal Linde cycle where this division is the only one and only the cooling stream is used for cooling the main stream, this multiple division can reduce the flow required for the cooling stream during the first division. By reducing the flow of the first cooling stream, the flow of the main stream can be increased, thereby improving the efficiency of the liquefaction process and the efficiency of the equipment.

[0024] At least one subsequent partition consists of a single subsequent partition called the "second partition." In this case, at least one subsequent cooling flow consists of a single subsequent cooling flow called the "second cooling flow" that cools the first cooling flow. Alternatively, at least one subsequent partition may consist of N subsequent partitions, each of which the main stream is divided into the main stream and each subsequent cooling flow, where N is a natural number strictly greater than 1. In this case, the subsequent cooling flow n-1 (i.e., corresponding to the subsequent partition n, where n is a natural number in [2, N]) is cooled by the subsequent cooling flow n, which in turn cools the subsequent cooling flow n-2, and the subsequent cooling flow 1 is the first cooling flow, which cools the main stream.

[0025] Equipment for liquefying gas according to this method has also been proposed. Therefore, such equipment is a device or system adapted to carry out this method. This equipment is, Mainstream lines intended for compression, splitting, and cooling, A first dividing line intended for cooling the first cooling flow and the main flow, It includes at least one second dividing line intended for cooling the first cooling flow.

[0026] If there is only one second division, that is, only a second division, then at least one second division line consists of a single second division line called the "second division line".

[0027] The method and equipment will be described in more detail below with reference to the drawings. Hereinafter, at least one subsequent division may consist of a single subsequent division referred to as the “second division,” but please understand that the following description applies equally to cases where there are multiple subsequent divisions. Figures 1-4 are merely schematic diagrams of the equipment and its lines, and the steps of the method performed herein. These figures are intended to illustrate the sequence of steps of the method and the technology used in each step. These figures are not intended to limit the arrangement of technology in the equipment or the technology that constitutes the equipment.

[0028] Unless otherwise specified, all temperatures shown below are in degrees Celsius, and all pressures are in bar, representing absolute pressure. Therefore, the notation "bar" in this disclosure is equivalent to "bar a" or "bara" (indicating absolute pressure). The numerical values ​​shown in the following diagrams are specific to cases where the gas is methane or biomethane. For other gases, the values ​​must be appropriately adjusted. In particular, all values ​​shown below can be adjusted according to the knowledge of those skilled in the art so that the gas is 100% liquefied, depending on the gas's saturation pressure.

[0029] Figure 1 is a schematic diagram of the equipment and method. The equipment includes a main flow line P, a first splitting line Sub2, and a second splitting line Sub3. As shown in the figure, the method includes compressing the main flow and then cooling the compressed main flow. Cooling the compressed main flow includes a first splitting S40 which divides the main flow into a main flow and a first cooling flow, a second splitting S50 which divides the main flow into a main flow and a second cooling flow (subsequent cooling flow), cooling of the first cooling flow by the second cooling flow S55-S555, cooling of the main flow by the first cooling flow S60, and cooling of the main flow by at least one subsequent cooling flow S60'.

[0030] Figure 2 is a schematic diagram of the main line P of the equipment and the steps of the method performed on the main line P. The main flow product (FP) of the gas (e.g., natural gas such as biomethane) is supplied at a constant pressure of 2 bar to 8 bar (step S0). Next, the method includes compressing the main flow product to 250 bar using a four-stage HP (high pressure) compressor 10 S10. Next, the method may include cooling the main flow product to 0°C using water glycol by any suitable apparatus or system 20 for cooling using water glycol S20. Next, the method may include pre-cooling the main flow product to -40°C using a cooling unit 30 S30. Next, the method includes a first splitting S40 of the main flow product into the main flow product and a first cooling flow FSub2 using a valve 50. The method includes cooling the main flow FP with a first cooling flow FSub2 S60, cooling with a second cooling flow FSub3 S60', cooling FSub2 with FSub3 (S55 in Figure 3), and a second splitting S50 of the main flow FP into the main flow FP and the second cooling flow FSub3 using another valve 50. The main flow FP is cooled to a maximum of -157°C in the exchanger using the first cooling flow FSub2 by the cooling S60, and the first cooling flow FSub2 itself is cooled using the second cooling flow FSub3. Next, the method may include expanding the main flow FP in the expander 70 to a saturation temperature of -150°C (corresponding to a pressure of 2.3 bar) S70. The cooling flow FSub2 is not mixed with the main flow FP before expansion, but is exchanged with glycol water after suction cooling by the compressor to restore cold air. Next, the method may include storing the main flow FP in a bulk unit 80 S80. A small amount of BOG may be generated during the final expansion S70 and / or due to thermal penetration in the bulk unit 80.

[0031] In order to perform the steps S0 to S80 described above, the main line P of the equipment is Heat exchanger, HP (high pressure) compressor with cooling function, An LP (low-pressure) compressor recompresses the gas from FSub3 to a pressure of 1 bar to 2-8 bar, Oil separator, Buffer volume and Expander, All-or-nothing (AON) valve and Bulk unit and, It may also include a shut-off valve.

[0032] Figure 3 is a schematic diagram of the first split line Sub2 and its use in the implementation of the method. As shown in the figure, the method includes cooling S55-S555 of the first cooling flow FSub2 by the second cooling flow FSub3. S55-S555 may include pre-cooling S55 of the first cooling flow FSub2 by the second cooling flow FSub3 in the heat exchanger 55 and expansion S555 of the pre-cooled first cooling flow FSub2 in the expander 555. Alternatively, the heat exchanger 55 may be part of at least one second split line. Expansion may be performed at MP pressure, which is the suction pressure of the HP compressor, ranging from 2 bar to 8 bar, depending on the application. This reduces compression costs. The temperature of FSub2 is in the range of -128°C to -152°C. Next, cooling S60 of the compressed main flow (FP) may include the use of the first cooling flow FSub2 in the heat exchanger. In other words, the cold energy of the cooled FSub2 cools the main flow in the exchanger, taking into account a 3°C pinch. The temperature of the cooling flow discharged from the exchanger is approximately -40°C. Therefore, in S65, the method may also include recovering the remaining cold energy in the heat exchanger to partially cool the chilled water, and then recycling the cooling flow FSub2, which is then combined with FSub3 and recycled within the system.

[0033] To perform the above steps, the first division line Sub2 of the equipment is: Heat exchanger, Expander, It may also include a shut-off valve.

[0034] Figure 4 shows a schematic diagram of the second splitting line Sub3 and its use in each step of the method. Following splitting S50, the method may include expanding the second cooling flow FSub3 in the expander 5555 S5555. The expansion pressure is 1.1 bar (saturation temperature = -160°C), and this pressure is selected so that the temperature in cooling the main flow S60 in the heat exchanger 55 is approximately -157°C, taking into account a 3°C pinch. Next, the method includes step S55, cooling the first cooling flow FSub2 using the second cooling flow FSub3 in the heat exchanger 55. In the heat exchanger 55, taking into account a 3°C pinch, the temperature of FSub3 is approximately -43°C. Next, the method may include a recycling step S655 of the cooling flow FSub3. The latter, after joining with BOG (boil-off gas) as it exits the bulk unit 80, undergoes energy recovery using a room-temperature glycol water flow in a heat exchanger (not shown). BOG is at storage tank level. Next, the temperature of the cooling flow FSub3 rises before the cooling flow FSub3 is compressed to MP pressure by a low-pressure (LP) compressor (not shown), thereby allowing it to be recycled within the system. The discharged cooling flow is then cooled to ambient temperature before being recycled within the system along with the cooling flow FSub2.

[0035] The thermodynamic cycle used in the mainstream line P may include technologies such as instrumentation, heat exchangers, a four-stage HP compressor with cooling, oil separators, buffer volumes, electronic expanders, all-or-nothing (AON) valves, bulk storage devices, and shut-off valves.

[0036] The thermodynamic cycle used in the first division line Sub2 may include technologies such as instrumentation, heat exchangers, electronic expanders, and shut-off valves.

[0037] The thermodynamic cycle used in the second division line Sub3 may include technologies such as instrumentation, heat exchangers, electronic expanders, a two-stage LP compressor with cooling function, and shut-off valves.

[0038] The equipment may include some auxiliary devices. These auxiliary devices may consist of automated equipment such as instrumentation, switches, gas detectors for CH4 (e.g., two), an air heater for cooling the refrigerant fluid, a pump for the glycol water network of the air heater, a chilled water group with a pump for cooling the entire process, a cooling unit for pre-cooling the main stream, and a fan for extracting air from the container.

[0039] Therefore, the method relating to the embodiment described above with reference to the drawings consists of liquefying a gas (such as biomethane or any natural gas) and storing it at a saturation temperature of -150°C (2.3 bar). This process is based on a modified Linde cycle, in which the main gas flow is compressed to 250 bar and then pre-cooled to -40°C using a cryogenic refrigerant cycle. In the cryogenic section, the main flow is split into two flows: one is a cooling flow that is expanded using a JT (Joule-Thomson) valve, and the other is a main flow that is cooled in a heat exchanger. The two stages of expansion and cooling make it possible to cool the temperature of the main flow to below -150°C. The main flow is then expanded to a saturation temperature of -150°C and stored. A small amount of BOG may be generated and recycled within the system.

[0040] The examples of equipment and methods described above with reference to the drawings achieve the following objectives.

[0041] The purpose of mainstream HP compression and liquefaction is, The mainstream is compressed using an HP compressor with a maximum capacity of 250 bar. Pre-cool the main stream to -40°C, The liquefaction process involves dividing the main body into two parts, cooling them, and then expanding them for storage at -150°C.

[0042] The purpose of the Sub2 subset is The Sub2 line controls the flow, expanding it to BP1=MP. Perform the mainstream first cooling stage, It is about circulating the flow within the system.

[0043] The purpose of the Sub3 subset is The Sub3 line controls the flow and expands it to BP2 = 1.1 bar. Perform the mainstream second cooling stage, Pre-cool the Sub2 flow, This involves compressing the flow to BP1 using LP (low pressure) compression.

Claims

1. Compressing the main gas (FP) (S10), This includes cooling the compressed main flow, and cooling the main flow (FP) is A first division (S40) of the compressed main flow (FP) provides a first cooling flow (FSub2), At least one subsequent split (S50) of the compressed main flow (FP) provides at least one subsequent cooling flow (FSub3), Cooling of the first cooling flow (FSub2) by at least one subsequent cooling flow (FSub3) (S55-S555), A method for liquefying a gas, comprising cooling the compressed main flow (FP) with the first cooling flow (FSub2) (S60) and cooling the main flow with at least one subsequent cooling flow (FSub3) (S60').

2. The cooling of the first cooling flow (FSub2) is The first cooling flow (FSub2) is pre-cooled by at least one subsequent cooling flow (FSub3) (S55), The method according to claim 1, comprising expanding the pre-cooled first cooling flow (FSub2) (S555).

3. The cooling of the compressed mainstream (FP) (S60) is performed as follows: The method according to claim 2, comprising using the expanded first cooling flow (FSub2) housed in a heat exchanger.

4. After the at least one subsequent split (S50) and before the pre-cooling (S55) of the first cooling flow (FSub2), The method according to claim 2 or 3, further comprising expanding the at least one subsequent cooling flow (FSub3) (S5555).

5. The pre-cooling (S55) of the first cooling flow (FSub2) by the at least one subsequent cooling flow (FSub3) is performed as follows: The method according to claim 4, further comprising using the expanded subsequent cooling flow (FSub3) in the heat exchanger (55).

6. The method according to claim 5, further comprising recycling the expanded cooling flow (S65-S655).

7. Before the above division (S40-S50), The first cooling (S20) of the main stream (FP) using water glycol, The method according to any one of claims 1 to 6, further comprising pre-cooling (S30) the main stream (FP) using a cooling unit or cooling source (30).

8. After the cooling of the compressed main flow (FP) by the first cooling flow (FSub2) (S60), The method according to any one of claims 1 to 7, further comprising expanding the cooled main flow (FP) (S70).

9. After the expansion of the cooled main stream (FP) (S70), The method according to claim 8, further comprising storing the cooled and expanded main body (FP) in a bulk unit (80) (S80).

10. The method according to any one of claims 1 to 9, which is automated.

11. A apparatus for liquefying gas according to the method described in any one of claims 1 to 10, The main stream (FP) has a main stream line (P) for the purpose of compression, splitting, and cooling, A first dividing line (Sub2) for the purpose of cooling the first cooling flow (FSub2) and the main flow (FP), An apparatus comprising the first cooling flow (FSub2) and at least one second splitting line (Sub3) for the purpose of cooling the main flow (FP).

12. The mainstream line (P) is, A four-stage high-pressure compressor (10) compresses the aforementioned main stream (FP) (S10), A cooling device (20) using water glycol for the first cooling (S20) of the main stream (FP) using water glycol, A cooling unit (30) that pre-cools (S30) the main channel (FP) using the aforementioned cooling unit (30), A control valve (40) for the first division (S40), At least one other control valve (50) for the at least one subsequent division (S50), A heat exchanger that cools the main flow (FP) by at least one subsequent cooling flow (FSub3) (S60), and a heat exchanger that cools the main flow (FP) by the first cooling flow (FSub2) (S60), An expander (70) for expanding the cooled main flow (S70), The apparatus according to claim 11, further comprising a bulk unit (80) for storing (S80) the cooled and expanded main body.

13. The first dividing line (Sub2) is, A heat exchanger (55) pre-cools the first cooling flow (FSub2) with at least one subsequent cooling flow (FSub3) (S55), The apparatus according to claim 11 or 12, further comprising an expander (555) for expanding (S555) the pre-cooled first cooling flow (FSub2).

14. The at least one second division line (Sub3) is, An expander (5555) that expands (S5555) the at least one subsequent cooling flow (FSub3), The apparatus according to claim 11, 12, or 13, further comprising a heat exchanger (55) that pre-cools (S55) the first cooling flow (FSub2) with at least one subsequent cooling flow (FSub3).

15. The equipment according to any one of claims 11 to 14, which is automated.

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