A low-energy natural gas cryogenic rectification decarbonization system

Abstract

The application relates to a low-energy-consumption natural gas cryogenic rectification decarburization system, which comprises a raw material gas feeding pipeline, a shell-and-tube heat exchanger, a refrigerant distribution tank, a main heat exchanger, and a plurality of refrigerant channels. The raw material gas feeding pipeline is connected to the shell inlet of the shell-and-tube heat exchanger; the refrigerant feeding pipeline is connected to the inlet of the refrigerant distribution tank; the main heat exchanger has a raw material gas channel, a first natural gas reheat channel, a second natural gas reheat channel, and a plurality of refrigerant channels. Through the above structure, the gas-phase refrigerant of the refrigerant distribution tank is sequentially connected to the bottom reboiler of the cryogenic rectification tower, the first refrigerant channel of the main heat exchanger, the overhead condenser, and the second refrigerant channel, so that the gas-phase refrigerant simultaneously undertakes the functions of heat supply and cold supply in the system, the refrigerant cold and heat is utilized in stages, and the liquid-phase refrigerant is expanded through throttling and used as the main cold source to provide the main cold quantity for the main heat exchanger. The cold and hot fluids are fully heat-exchanged in the multi-channel structure of the main heat exchanger.

Description

Technical Field

[0001] This invention relates to a natural gas decarbonization system, particularly a low-energy-consumption natural gas cryogenic distillation decarbonization system. The system connects the gaseous refrigerant from the refrigerant separator to the second refrigerant channel in sequence through the bottom reboiler of the cryogenic distillation column, the first refrigerant channel of the main heat exchanger, and the top condenser. This allows the gaseous refrigerant to simultaneously perform both heating and cooling functions within the system, achieving cascaded utilization of the refrigerant's heat and cold properties. Background Technology

[0002] Natural gas, as a clean energy source with high calorific value, requires the removal of its acidic carbon dioxide gas before pipeline transportation and liquefaction to avoid problems such as reduced calorific value, pipeline corrosion, and carbon dioxide freezing at low temperatures. Natural gas decarbonization technologies mainly include solvent absorption, adsorption, membrane separation, and cryogenic separation. Among these, cryogenic distillation technology utilizes the differences in volatility of various components in natural gas to separate carbon dioxide from light hydrocarbon components such as methane through distillation. It offers advantages such as not using chemical solvents, a relatively simple process, and the simultaneous production of liquid carbon dioxide, making it highly economical for applications requiring carbon dioxide collection.

[0003] However, existing cryogenic distillation decarbonization processes still have many shortcomings in engineering applications. Cryogenic distillation decarbonization typically involves pre-cooling or throttling the multiphase stream before directly feeding it into the distillation column, leading to excessive column load and complex control systems. Furthermore, conventional processes lack systematic integrated design for cold energy supply and recovery, resulting in low energy utilization and significant unrecovered cold energy, leading to high energy consumption. For applications with less stringent carbon dioxide yield requirements, existing processes remain complex, with high equipment investment and operating costs, hindering the widespread application of cryogenic distillation decarbonization technology. Summary of the Invention

[0004] To address the aforementioned deficiencies in existing technologies, this invention provides a low-energy-consumption natural gas cryogenic distillation and decarbonization system. By sequentially passing the gaseous refrigerant from the refrigerant separator through the bottom reboiler of the cryogenic distillation column, the first refrigerant channel of the main heat exchanger, and the top condenser of the column, the gaseous refrigerant is connected to the second refrigerant channel. This allows the gaseous refrigerant to simultaneously perform both heating and cooling functions within the system, achieving cascaded utilization of the refrigerant's heat and cold properties.

[0005] To achieve the above objectives, the present invention provides a low-energy-consumption natural gas cryogenic distillation and decarbonization system, comprising: Raw material gas feed pipeline; A wound-tube heat exchanger, wherein the feed gas inlet line is connected to the shell-side inlet of the wound-tube heat exchanger; Refrigerant feed line; A refrigerant separator, wherein the refrigerant inlet line is connected to the inlet of the refrigerant separator; The main heat exchanger has a raw material gas channel, a first natural gas reheating channel, a second natural gas reheating channel, and multiple refrigerant channels; A raw material gas separator, wherein the inlet of the raw material gas separator is connected to the outlet of the raw material gas channel; Low-temperature distillation column; Subcooler; Reinjection pump; The gas phase outlet of the raw gas separator is connected to the natural gas export pipeline via the first natural gas reheating channel, and the liquid phase outlet of the raw gas separator is connected to the feed inlet of the cryogenic distillation column. The gas phase outlet of the cryogenic distillation column is connected to the natural gas export pipeline via the second natural gas reheating channel, and the liquid phase outlet of the cryogenic distillation column is connected to the second medium channel of the coiled tube heat exchanger via the subcooler and the reinjection pump in sequence. The vapor outlet of the refrigerant separator passes sequentially through the bottom reboiler, the refrigerant channel, and the top cooler of the cryogenic distillation column before connecting to the inlet of the second refrigerant channel. The liquid phase outlet of the refrigerant separator is connected to the inlet of the first refrigerant channel via a throttling element.

[0006] Traditional cryogenic distillation decarbonization units directly feed multiphase streams into the distillation column after pre-cooling or throttling the stream, leading to excessive column load and complex control systems. To improve this, this invention connects the vaporized refrigerant from the refrigerant separator sequentially through the bottom reboiler, the first refrigerant channel of the main heat exchanger, and the top condenser of the cryogenic distillation column before connecting it to the second refrigerant channel. This allows the vaporized refrigerant to simultaneously perform both heating and cooling functions within the system, achieving cascaded utilization of refrigerant heat and cold.

[0007] The main heat exchanger has a six-channel structure, consisting of a raw material gas channel, a first natural gas reheating channel, a second natural gas reheating channel, and multiple refrigerant channels, namely a first refrigerant channel, a second refrigerant channel, and a third refrigerant channel.

[0008] The gas phase outlet of the raw gas separator is connected to a second pipeline, which is connected to the first natural gas reheating channel. The first natural gas reheating channel is connected to a third pipeline, which is connected to a natural gas export pipeline. The gas phase outlet of the cryogenic distillation column is connected to a fifth pipeline, which is connected to the second natural gas reheating channel. The second natural gas reheating channel is connected to a sixth pipeline, which is connected to a natural gas export pipeline. The third pipeline merges with the sixth pipeline.

[0009] The liquid phase outlet of the raw material gas separator is connected to a fourth pipeline, which is connected to the feed inlet of a cryogenic distillation column. A first liquid level control valve is installed on the fourth pipeline, which is used to adjust the opening degree according to the liquid level of the raw material gas separator.

[0010] The vapor outlet of the refrigerant separator is connected to a first refrigerant circulation pipeline, which is connected to the shell-side inlet of the reboiler at the bottom of the cryogenic distillation column. The shell-side outlet of the reboiler is connected to a second refrigerant circulation pipeline, which is connected to the inlet of a third refrigerant channel. The outlet of the third refrigerant channel is connected to a third refrigerant circulation pipeline, which is connected to the shell-side inlet of the overhead cooler at the cryogenic distillation column. The shell-side outlet of the overhead cooler is connected to a fourth refrigerant circulation pipeline, which is connected to the inlet of the second refrigerant channel.

[0011] The liquid phase outlet of the refrigerant separator is connected to a fifth refrigerant circulation pipeline, which is sequentially connected to the main heat exchanger and the throttling element. The outlet of the throttling element is connected to the inlet of the first refrigerant channel, and the outlet of the first refrigerant channel is connected to a refrigerant circulation pipeline, which is connected to an external compressor system.

[0012] The liquid outlet of the cryogenic distillation column is connected to a seventh pipeline, which is connected to the subcooler. A second liquid level control valve is installed on the seventh pipeline, which is used to adjust the opening degree according to the liquid level at the bottom of the cryogenic distillation column.

[0013] The outlet of the reinjection pump is connected to a ninth pipeline, which is connected to the tube-side inlet of the wound-tube heat exchanger, and the tube-side outlet of the wound-tube heat exchanger is connected to the carbon dioxide export pipeline.

[0014] The throttling element is a refrigerant throttling valve.

[0015] It also includes a cold box, in which the main heat exchanger, the raw material gas separator, the low-temperature distillation column and the subcooler are all installed. The cold box is used to provide cold insulation for the equipment installed inside it.

[0016] Through the above structural design, this invention allows the gaseous refrigerant from the refrigerant separator to sequentially pass through the reboiler at the bottom of the cryogenic distillation column, the first refrigerant channel of the main heat exchanger, and the condenser at the top of the column before entering the second refrigerant channel. This enables the gaseous refrigerant to simultaneously perform both heating and cooling functions within the system, achieving cascaded utilization of the refrigerant's heat and cold properties. Simultaneously, the liquid refrigerant, after throttling and expansion, serves as the main cold source, providing the primary cooling capacity to the main heat exchanger. All hot and cold fluids undergo thorough heat exchange within the multi-channel structure of the main heat exchanger, ensuring efficient energy utilization within the system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the low-energy-consumption natural gas cryogenic distillation and decarbonization system of the present invention. Detailed Implementation

[0018] The directions or similar terms used throughout this invention, such as "front," "back," "left," "right," "top," "bottom," "inner," "outer," and "side," are mainly for reference to the directions in the accompanying drawings. These directions or similar terms are only used to assist in explaining and understanding the various embodiments of this invention and are not intended to limit this invention.

[0019] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. However, the embodiments described are only used to illustrate the technical features of the present invention and are not intended to limit the scope of protection of the present invention.

[0020] Please see Figure 1 As shown, the present invention discloses a low-energy-consumption natural gas cryogenic distillation and decarbonization system, which mainly includes a feed gas pipeline 1, a coiled tube heat exchanger 2, a refrigerant feed pipeline 3, a refrigerant separator 4, a main heat exchanger 5, a feed gas separator 6, a cryogenic distillation column 7, a subcooler 8, a reinjection pump 9, and a cold box 10. The main heat exchanger 5, the feed gas separator 6, the cryogenic distillation column 7, and the subcooler 8 are all located inside the cold box 10. The cold box 10 provides insulation for the equipment inside, thereby reducing system cooling loss.

[0021] The main heat exchanger 5 has a six-channel structure, consisting of a raw material gas channel 51, a first natural gas reheating channel 52, a second natural gas reheating channel 53, a first refrigerant channel 54, a second refrigerant channel 55, and a third refrigerant channel 56. The first refrigerant channel 54 is the main cold source channel, responsible for supplying the system's main cooling capacity; the first natural gas reheating channel 52, the second natural gas reheating channel 53, and the second refrigerant channel 55 serve as cold source channels for cooling hot fluids such as the raw material gas; and the raw material gas channel 51 and the third refrigerant channel 56 serve as heat source channels for reheating low-temperature media.

[0022] The feed gas from the drying system has a pressure of 3250~10000 kPa, a temperature of 10~80℃, and a carbon dioxide content of 10%~85%. The feed gas inlet line 1 connects to the shell-side inlet of the coiled-tube heat exchanger 2. The feed gas from the upstream drying system first enters the shell side of the coiled-tube heat exchanger 2, where it undergoes preliminary heat exchange with the low-temperature carbon dioxide product flowing in the tube side. After being cooled to a certain temperature in the coiled-tube heat exchanger 2, the feed gas enters the feed gas channel 51 inlet of the main heat exchanger 5 through the shell-side outlet. In the feed gas channel 51, the feed gas undergoes sufficient heat exchange with the refrigerant and low-temperature natural gas cooling media in the main heat exchanger 5, and is cooled to -30℃~-80℃ before flowing out from the feed gas channel 51 outlet. At this time, some light hydrocarbons and some carbon dioxide in the feed gas condense into a liquid phase, forming a gas-liquid two-phase mixture.

[0023] The outlet of the raw gas channel 51 is connected to a first pipeline 11, which in turn connects to the inlet of the raw gas separator 6. The cooled gas-liquid two-phase raw gas enters the raw gas separator 6 for gas-liquid separation. The gas phase outlet of the raw gas separator 6 is connected to the inlet of the first natural gas reheating channel 52 of the main heat exchanger 5 via a second pipeline 12. The natural gas vapor product with a carbon dioxide content of 5-50% discharged from the top of the raw gas separator 6 enters the first natural gas reheating channel 52 and is reheated to 10℃-70℃ by the hot fluid within the main heat exchanger 5. The outlet of the first natural gas reheating channel 52 is connected to the natural gas export pipeline via a third pipeline 13. The reheated, qualified natural gas is exported via the third pipeline 13. The liquid outlet of the raw gas separator 6 is connected to the feed inlet of the cryogenic distillation column 7 through the fourth pipeline 14. A first liquid level control valve 20 is installed on the fourth pipeline 14. The first liquid level control valve 20 adjusts its opening according to the liquid level signal of the raw gas separator 6 to control the liquid level of the raw gas separator 6 to stabilize.

[0024] The cryogenic distillation column 7 is used for the distillation and separation of liquid materials from the feed gas separator 6. The liquid material enters the middle feed inlet of the cryogenic distillation column 7 via the fourth pipeline 14, at which point the material pressure is 2000~4000 kPa and the temperature is -30℃~-80℃. Inside the cryogenic distillation column 7, the gas and liquid phases come into contact stage by stage on the surface of the trays. Due to the different boiling points of carbon dioxide and methane, the volatile light components such as methane absorb heat and partially evaporate, while the easily condensable carbon dioxide releases heat and partially condenses. During the stage-by-stage contact process, the upward-flowing saturated vapor and the downward-flowing saturated liquid exchange matter and heat: more of the light components such as methane evaporate and less condense, gradually enriching the upward-flowing gas phase, ultimately yielding methane-rich natural gas at the top of the column; less carbon dioxide evaporates and more condenses, gradually enriching the liquid phase flowing at the bottom of the column, ultimately yielding high-purity liquid carbon dioxide at the bottom of the column.

[0025] A top condenser is installed at the top of the cryogenic distillation column 7 to partially condense the rising gas phase at the top, further enriching the natural gas containing methane at the top. The condensate is returned to the column as reflux liquid, and the uncondensed gas phase is discharged from the gas phase outlet of the cryogenic distillation column 7. The gas phase outlet of the cryogenic distillation column 7 is connected to the inlet of the second natural gas reheating channel 53 of the main heat exchanger 5 via the fifth pipeline 15. The methane-rich natural gas discharged from the top of the column enters the second natural gas reheating channel 53 and is reheated to 10°C~70°C by the hot fluid in the main heat exchanger 5. The outlet of the second natural gas reheating channel 53 is connected to the natural gas export pipeline via the sixth pipeline 16, and the sixth pipeline 16 merges with the aforementioned third pipeline 13 for export.

[0026] A reboiler is installed at the bottom of the cryogenic distillation column 7 to heat the liquid phase at the bottom, causing a portion of the liquid phase to evaporate into a gas phase and reflux back into the column, thus improving separation efficiency. The liquid carbon dioxide enriched at the bottom of the column is discharged from the liquid phase outlet of the cryogenic distillation column 7 via the seventh pipe 17, which is connected to the inlet of the subcooler 8. After being further subcooled in the subcooler 8, the liquid carbon dioxide enters the inlet of the reinjection pump 9 via the eighth pipe 18. A second liquid level control valve 21 is installed on the eighth pipe 18, which adjusts its opening degree according to the bottom liquid level signal of the cryogenic distillation column 7 to maintain a stable bottom liquid level. The reinjection pump 9 pressurizes the liquid carbon dioxide to 3~40MPa. The outlet of the reinjection pump 9 is connected to the tube-side inlet of the coiled tube heat exchanger 2 through the ninth pipeline 19. The pressurized liquid carbon dioxide enters the tube side of the coiled tube heat exchanger 2 and exchanges heat with the raw material gas in the shell side. Finally, after the temperature rises to 10℃~40℃, it is discharged from the tube-side outlet of the coiled tube heat exchanger 2 and sent to the carbon dioxide export pipeline.

[0027] The refrigerant system uses a mixed refrigerant circulation to provide the required cooling capacity. The mixed refrigerant has a pressure of 0.7~2MPa and a temperature of 20℃~60℃, and enters the inlet of the refrigerant separator 4 through the refrigerant inlet line 3. In the refrigerant separator 4, the refrigerant is separated into gaseous refrigerant and liquid refrigerant, which participate in the circulation along different paths.

[0028] The vapor outlet of the refrigerant separator 4 is connected to a first refrigerant circulation line 31. The vapor refrigerant enters the shell-side inlet of the reboiler at the bottom of the cryogenic distillation column 7 via this line. In the shell side of the reboiler, the vapor refrigerant acts as a heating medium, heating the liquid stream at the bottom of the column while being cooled to -5°C to 30°C. The shell-side outlet of the reboiler is connected to a second refrigerant circulation line 32, which connects to the inlet of the third refrigerant channel 56 of the main heat exchanger 5. After entering the third refrigerant channel 56, the vapor refrigerant acts as a hot fluid in the heat source channel and is further cooled by the cold medium within the main heat exchanger 5. The outlet of the third refrigerant channel 56 is connected to a third refrigerant circulation line 33, which connects to the shell-side inlet of the condenser at the top of the cryogenic distillation column 7. In the shell side of the condenser, the vapor refrigerant acts as a cooling medium, cooling and condensing the rising vapor at the top of the column while absorbing heat and increasing its temperature. The shell-side outlet of the top condenser is connected to a fourth refrigerant circulation line 34, which is connected to the inlet of the second refrigerant passage 55 of the main heat exchanger 5. After the gaseous refrigerant enters the second refrigerant passage 55, it acts as a cooling medium in the cold source passage, exchanging heat with hot fluids such as the raw material gas, raising its own temperature to 5℃~30℃, and reducing its pressure to 2~300kPa. Then, it is discharged from the outlet of the second refrigerant passage 55 through the refrigerant circulation line 35 and sent to the compressor system for compression circulation.

[0029] The liquid phase outlet of the refrigerant separator 4 is connected to a fifth refrigerant circulation pipeline 36. The liquid refrigerant first enters the main heat exchanger 5 for pre-cooling via the fifth refrigerant circulation pipeline 36. After pre-cooling, the liquid refrigerant enters the refrigerant throttling valve 22 for throttling and expansion, and its temperature drops to -10℃ to -90℃ after throttling. The low-pressure, low-temperature refrigerant after throttling enters the inlet of the first refrigerant channel 54 of the main heat exchanger 5, serving as the main cold source channel and providing the main cooling capacity for the entire main heat exchanger 5, exchanging heat with hot fluids such as raw material gas. After heat exchange, the refrigerant is heated to 5℃ to 30℃ and its pressure is 2 to 300 kPa. It is then discharged from the outlet of the first refrigerant channel 54 via the refrigerant circulation pipeline 37, where it merges with the gaseous refrigerant from the refrigerant circulation pipeline 35 and is sent to the compressor system. After compression, it re-enters the refrigerant circulation.

Claims

1. A low-energy-consumption natural gas cryogenic distillation and decarbonization system, characterized in that, Include: Raw material gas feed line (1); A coiled tube heat exchanger (2), wherein the raw material gas feed line (1) is connected to the shell-side inlet of the coiled tube heat exchanger (2); Refrigerant feed line (3); A refrigerant separator (4), wherein the refrigerant feed line (3) is connected to the inlet of the refrigerant separator (4); The main heat exchanger (5) has a raw material gas channel (51), a first natural gas reheating channel (52), a second natural gas reheating channel (53) and multiple refrigerant channels; Raw material gas separator (6), the inlet of which is connected to the outlet of the raw material gas channel (51); Low-temperature distillation column (7); Subcooler (8); Reinjection pump (9); The gas phase outlet of the raw gas separator (6) is connected to the natural gas export pipeline via the first natural gas reheating channel (52), and the liquid phase outlet of the raw gas separator (6) is connected to the feed inlet of the low-temperature distillation column (7). The gas phase outlet of the low-temperature distillation column (7) is connected to the natural gas export pipeline via the second natural gas reheating channel (53), and the liquid phase outlet of the low-temperature distillation column (7) is connected to the second medium channel of the coiled tube heat exchanger (2) via the subcooler (8) and the reinjection pump (9). The gas phase outlet of the refrigerant separator (4) is connected to the inlet of the second refrigerant channel (55) after passing through the bottom reboiler, the refrigerant channel and the top cooler of the low temperature distillation column (7) in sequence. The liquid phase outlet of the refrigerant separator (4) is connected to the inlet of the first refrigerant channel (54) via a throttling element.

2. The low-energy-consumption natural gas cryogenic distillation and decarbonization system according to claim 1, characterized in that, The main heat exchanger (5) has a six-channel structure. The six channels are: raw gas channel (51), first natural gas reheat channel (52), second natural gas reheat channel (53) and multiple refrigerant channels. The multiple refrigerant channels are the first refrigerant channel (54), the second refrigerant channel (55) and the third refrigerant channel (56).

3. The low-energy-consumption natural gas cryogenic distillation and decarbonization system according to claim 1, characterized in that, The gas phase outlet of the raw material gas separator (6) is connected to a second pipeline (12), which is connected to the first natural gas reheating channel (52). The first natural gas reheating channel (52) is connected to a third pipeline (13), which is connected to a natural gas export pipeline. The gas phase outlet of the low-temperature distillation tower (7) is connected to a fifth pipeline (15), which is connected to the second natural gas reheating channel (53). The second natural gas reheating channel (53) is connected to a sixth pipeline (16), which is connected to a natural gas export pipeline. The third pipeline (13) and the sixth pipeline (16) merge.

4. The low-energy-consumption natural gas cryogenic distillation and decarbonization system according to claim 1, characterized in that, The liquid phase outlet of the raw material gas separator (6) is connected to the fourth pipeline (14), which is connected to the feed inlet of the low-temperature distillation column (7). A first liquid level control valve (20) is provided on the fourth pipeline (14), which is used to adjust the opening degree according to the liquid level of the raw material gas separator (6).

5. The low-energy-consumption natural gas cryogenic distillation and decarbonization system according to claim 1, characterized in that, The vapor outlet of the refrigerant separator (4) is connected to a first refrigerant circulation pipeline (31), which is connected to the shell-side inlet of the reboiler at the bottom of the low-temperature distillation column (7). The shell-side outlet of the reboiler is connected to a second refrigerant circulation pipeline (32), which is connected to the inlet of the third refrigerant channel (56). The outlet of the third refrigerant channel (56) is connected to a third refrigerant circulation pipeline (33), which is connected to the shell-side inlet of the cooler at the top of the low-temperature distillation column (7). The shell-side outlet of the cooler at the top of the column is connected to a fourth refrigerant circulation pipeline (34), which is connected to the inlet of the second refrigerant channel (55).

6. The low-energy-consumption natural gas cryogenic distillation and decarbonization system according to claim 1, characterized in that, The liquid phase outlet of the refrigerant separator (4) is connected to a fifth refrigerant circulation pipeline (36), which is connected in sequence to the main heat exchanger (5) and the throttling element. The outlet of the throttling element is connected to the inlet of the first refrigerant channel (54), and the outlet of the first refrigerant channel (54) is connected to a refrigerant circulation pipeline (37), which is connected to an external compressor system.

7. The low-energy-consumption natural gas cryogenic distillation and decarbonization system according to claim 1, characterized in that, The liquid outlet of the low-temperature distillation column (7) is connected to a seventh pipeline (17), which is connected to the subcooler (8). A second liquid level control valve (21) is installed on the seventh pipeline (17), which is used to adjust the opening degree according to the bottom liquid level of the low-temperature distillation column (7).

8. The low-energy-consumption natural gas cryogenic distillation and decarbonization system according to claim 1, characterized in that, The outlet of the reinjection pump (9) is connected to a ninth pipeline (19), which is connected to the tube-side inlet of the coiled tube heat exchanger (2), and the tube-side outlet of the coiled tube heat exchanger (2) is connected to the carbon dioxide export pipeline.

9. The low-energy-consumption natural gas cryogenic distillation and decarbonization system according to claim 1, characterized in that, The throttling element is a refrigerant throttling valve (22).

10. The low-energy-consumption natural gas cryogenic distillation and decarbonization system according to claim 1, characterized in that, It also includes a cold box (10), in which the main heat exchanger (5), the raw material gas separator (6), the low temperature distillation column (7) and the subcooler (8) are all located. The cold box (10) is used to provide cold insulation for the equipment located inside it.

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