A device and method for co-producing LNG and liquid CO2 from biogas using mixed refrigeration

Abstract

The present invention discloses a device and method for co-producing LNG and liquid CO2 from biogas using mixed refrigeration. This device belongs to the field of natural gas processing technology and aims to address the technical problem of the failure to maximize the utilization of biogas resources in the prior art. It comprises a biogas input module, comprising a biogas input pipeline, a biogas compressor, and an MDEA amine process system interconnected in sequence; a refrigeration module, comprising a mixed refrigerant compressor and a refrigerant separator; the output end of the mixed refrigerant compressor is connected to the input end of the refrigerant separator; an LNG production module, and a CO2 production module. The present invention can be used to better separate and utilize biogas, achieving high resource utilization and excellent economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas processing, and in particular to a device and method for co-producing LNG and liquid CO2 from biogas using mixed refrigeration. Background Art

[0002] Biogas is mainly composed of 50% to 80% methane, 20% to 40% carbon dioxide, 0% to 5% nitrogen, 0.1% to 3% H2S, etc. In the field of biogas utilization, existing technologies mainly include direct combustion for power generation, heat supply, and purification to produce biogas.

[0003] Existing technologies for biogas utilization primarily rely on direct combustion for power generation and heating, failing to fully maximize biogas utilization. Furthermore, existing technologies struggle to efficiently separate LNG (liquefied natural gas) and liquid carbon dioxide simultaneously. This results in the failure to maximize biogas resource utilization and relatively low added value products.

[0004] Therefore, in order to improve the utilization of biogas resources and reduce carbon emissions while converting biogas into LNG, and at the same time converting CO2 into liquid CO2 products, it is urgent to provide a device and method for co-producing LNG and liquid CO2 using mixed refrigeration. Summary of the Invention

[0005] The object of the present invention is to provide a device and method for co-producing LNG and liquid CO2 from biogas using mixed refrigeration, so as to solve the technical problem in the prior art that biogas resources cannot be maximized.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] The present invention provides a device for co-producing LNG and liquid CO2 from biogas using mixed refrigeration, comprising:

[0008] A biogas input module, the biogas input module comprising a biogas input pipeline, a biogas compressor and an MDEA amine process system connected in sequence; an output end of the MDEA amine process system is connected to an output pipeline 1 and an output pipeline 2 respectively;

[0009] A refrigeration module, comprising a mixed refrigerant compressor and a refrigerant separator; an output end of the mixed refrigerant compressor is connected to an input end of the refrigerant separator; and an output end of the refrigerant separator is connected to an output pipe 3 and an output pipe 4, respectively;

[0010] LNG production module, the output pipeline 1 and the output pipeline 3 are respectively connected to the LNG production module;

[0011] The CO2 production module, the output pipeline 2 and the output pipeline 4 are respectively connected to the CO2 production module.

[0012] Optionally or preferably, the LNG production module includes a molecular sieve, a denitrification tower and a main heat exchanger;

[0013] The input end of the molecular sieve 1 is connected to the output pipe 1, and the output end of the molecular sieve 1 is connected to the denitrification tower for denitrification after heat exchange in the main heat exchanger; the denitrified natural gas enters the main heat exchanger through the secondary heat exchange pipe for supercooling and forming an LNG product; the secondary heat exchange pipe is connected to the LNG product output pipe, and the LNG product is output through the LNG product output pipe;

[0014] The top of the denitrification tower is connected to the dirty nitrogen venting pipeline.

[0015] Optionally or preferably, the output pipeline three passes through the main heat exchanger and the top of the denitrification tower respectively, and then returns to the input end of the mixed refrigerant compressor.

[0016] Optionally or preferably, the CO2 production module includes a CO2 compressor, a dry desulfurization device, a molecular sieve II, a gas-to-gas heat exchanger, a CO2 precooler and a CO2 distillation tower;

[0017] The output pipeline 2 is connected to the input end of the CO2 compressor, and the CO2 compressor is connected to the input end of the dry desulfurization device; the output end of the dry desulfurization device is connected to the molecular sieve 2; the output end of the molecular sieve 2 is connected to the input end of the CO2 precooler after heat exchange through the gas-to-gas heat exchanger and the bottom of the CO2 distillation tower; the output end of the CO2 precooler is connected to the CO2 distillation tower.

[0018] Optionally or preferably, the top of the CO2 distillation tower is connected to a top condenser, and the output end of the top condenser is connected to a top separator;

[0019] The output ends of the tower top separator are respectively connected to the output pipe 5 and the output pipe 6; the tower top separator is used to separate the gas from the top of the CO2 distillation tower into a gas phase and a liquid phase; wherein the gas phase is connected to the residual gas venting pipe after passing through the tower top condenser and the gas-to-gas heat exchanger through the output pipe 5; wherein the liquid phase is refluxed to the CO2 distillation tower through the output pipe 6;

[0020] The bottom of the CO2 distillation tower is connected to a CO2 supercooler, and the output end of the CO2 supercooler is connected to a CO2 product output pipeline.

[0021] Optionally or preferably, the output pipeline 4 includes multiple branches, and the multiple branches respectively pass through the CO2 precooler, the CO2 subcooler and the top condenser and return to the input end of the mixed refrigerant compressor.

[0022] Optionally or preferably, the refrigerant used by the refrigeration module is MRC refrigerant.

[0023] A method for co-producing LNG and liquid CO2 using biogas using mixed refrigeration, comprising an LNG production process, a liquid CO2 production process, and a refrigerant circulation process;

[0024] The LNG production process is as follows: biogas enters the MDEA amine process system through a biogas compressor; the biogas from which CO2 and H2S have been removed by the MDEA amine process enters molecular sieve one through output pipe one for drying, mercury removal, and dust filtration; the biogas passing through molecular sieve one enters the main heat exchanger for cooling and then enters the denitrification tower for denitrification; the denitrified biogas enters the main heat exchanger through a secondary heat exchange pipe for supercooling to form LNG product, which is finally output through the LNG product output pipe; the contaminated nitrogen at the top of the denitrification tower is reheated by the main heat exchanger and then enters the contaminated nitrogen vent pipe for discharge.

[0025] Optionally or preferably, the liquid CO2 production process is as follows: after CO2 and H2S are removed by the MDEA amine system, the gas enters the CO2 compressor for pressurization and is then passed into a dry desulfurization device for desulfurization. The desulfurized gas enters molecular sieve 2 for drying, dehydration and dust filtration. The gas phase after molecular sieve 2 is heat exchanged with the residual gas through a gas-to-gas heat exchanger and the cold energy is recovered, and then enters the bottom of the CO2 distillation tower as the reboiler heat source of the CO2 distillation tower. After exiting the bottom of the CO2 distillation tower, it enters the CO2 precooler for cooling, and after cooling, it enters the CO2 distillation tower; the gas at the top of the CO2 distillation tower is cooled by the top condenser and passed into the top separator for separation; the gas phase and the liquid phase are separated by the top separator, wherein the gas phase passes through the output pipe five, is reheated through the top condenser and the gas-to-gas heat exchanger, and is discharged through the residual gas vent pipe; the liquid phase is refluxed to the CO2 distillation tower through the output pipe six; the liquid at the bottom of the CO2 distillation tower is output through the CO2 product output pipe after passing through the CO2 supercooler.

[0026] Optionally or preferably, the refrigerant circulation process is as follows: the high-pressure refrigerant from the mixed refrigerant compressor is separated by a refrigerant separator; a portion of the refrigerant enters the main heat exchanger through the output pipe 3 and provides cooling for the main heat exchanger; the low-pressure refrigerant passing through the main heat exchanger returns to the mixed refrigerant compressor for compression after heat exchange at the top of the denitrification tower;

[0027] The other part of the high-pressure refrigerant enters the CO2 precooler, CO2 subcooler and tower top condenser through multiple branches of the output pipeline 4 and provides cooling capacity, and then returns to the mixed refrigerant compressor for compression.

[0028] Based on the above technical solution, the present invention can produce at least the following technical effects:

[0029] The present invention provides a device for co-producing LNG and liquid CO2 from biogas using mixed refrigeration. Through independent LNG production modules, CO2 production modules and mixed refrigeration modules, LNG and liquid CO2 can be effectively separated from biogas, thereby improving the utilization rate of biogas and increasing economic benefits. Moreover, each module in the device is relatively independent, and operators can flexibly adjust and control it according to actual needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the arrangement structure of the device for co-producing LNG and liquid CO2 by biogas using mixed refrigeration according to the present invention.

[0031] In the figure: 10, biogas input module; 11, biogas input pipeline; 12, biogas compressor; 13, MDEA amine process system; 131, output pipeline 1; 132, output pipeline 2;

[0032] 20. Refrigeration module; 21. Mixed refrigerant compressor; 22. Refrigerant separator; 221. Output pipeline three; 222. Output pipeline four;

[0033] 30. LNG production module; 31. Molecular sieve 1; 32. Denitrification tower; 321. Secondary heat exchange pipeline; 33. Main heat exchanger; 34. LNG product output pipeline; 35. Dirty nitrogen venting pipeline;

[0034] 40. CO2 production module; 41. CO2 subcooler; 42. CO2 compressor; 43. Dry desulfurization unit; 44. Molecular sieve II; 45. Gas-to-gas heat exchanger; 46. Residual gas venting pipeline; 47. Top condenser; 48. Top separator; 481. Output pipeline five; 482. Output pipeline six; 49. CO2 product output pipeline; 410. CO2 precooler; 411. CO2 distillation tower. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work shall fall within the scope of protection of the present invention.

[0036] Example 1

[0037] See also Figure 1A device for co-producing LNG and liquid CO2 using biogas with mixed refrigeration includes a biogas input module 10, a refrigeration module 20, an LNG production module 30 and a CO2 production module 40.

[0038] It should be noted that, for the sake of ease of description, the description of some valve bodies and control devices is omitted in this embodiment, and technicians can choose the settings based on actual work needs.

[0039] In this embodiment, the biogas input module 10 includes a biogas input pipeline 11, a biogas compressor 12 and an MDEA amine process system 13 connected in sequence; the MDEA amine process system 13 is used to remove CO2 and H2S from the biogas; the output ends of the MDEA amine process system 13 are respectively connected to an output pipeline 1 131 and an output pipeline 2 132, wherein the content of the output pipeline 1 131 is biogas, and the content of the output pipeline 2 132 is CO2 and H2S.

[0040] In this embodiment, the refrigeration module 20 includes a mixed refrigerant compressor 21 and a refrigerant separator 22; the output end of the mixed refrigerant compressor 21 is connected to the input end of the refrigerant separator 22; the output end of the refrigerant separator 22 is respectively connected to the output pipe three 221 and the output pipe four 222, the output pipe three 221 is connected to the LNG production module 30, and the output pipe four 222 is connected to the CO2 production module 40, and the refrigerant is MRC refrigerant.

[0041] Specifically, the LNG production module 30 includes a molecular sieve 31, a denitrification tower 32 and a main heat exchanger 33; the input end of the molecular sieve 31 is connected to the output pipe 131, and the output end of the molecular sieve 31 is connected to the denitrification tower 32 for denitrification after heat exchange through the main heat exchanger 33; the denitrified natural gas enters the main heat exchanger 33 through the secondary heat exchange pipe 321 for supercooling and forming an LNG product; the secondary heat exchange pipe 321 is connected to the LNG product output pipe 34, and the LNG product is output through the LNG product output pipe 34; the top of the denitrification tower 32 is connected to the dirty nitrogen venting pipe 35.

[0042] In the LNG production module 30, the refrigerant from the mixed refrigerant compressor 21 is mainly used to provide cooling to the main heat exchanger 33. Therefore, the output pipe three 221 passes through the main heat exchanger 33 and the top of the denitrification tower 32, and then returns to the input end of the mixed refrigerant compressor 21 for circulation.

[0043] The CO 2 production module 40 includes a CO 2 compressor 42 , a dry desulfurization device 43 , a molecular sieve 44 , a gas-to-gas heat exchanger 45 , a CO 2 precooler 410 and a CO 2 distillation tower 411 .

[0044] The output pipeline 2 132 is connected to the input end of the CO2 compressor 42, and the CO2 compressor 42 is connected to the input end of the dry desulfurization device 43; the output end of the dry desulfurization device 43 is connected to the molecular sieve 2 44; the output end of the molecular sieve 2 44 is connected to the input end of the CO2 precooler 410 after heat exchange through the gas-to-gas heat exchanger 45 and the bottom of the CO2 distillation tower 411; the output end of the CO2 precooler 410 is connected to the CO2 distillation tower 411.

[0045] In addition, the top of the CO2 distillation tower 411 is connected to a tower top condenser 47, and the output end of the tower top condenser 47 is connected to a tower top separator 48;

[0046] The output ends of the top separator 48 are connected to an output pipe 5 481 and an output pipe 6 482 respectively. The top separator 48 is used to separate the gas from the top of the CO2 distillation tower 411 into a gas phase and a liquid phase. The gas phase passes through the output pipe 5 481, sequentially passes through the top condenser 47 and the gas-to-gas heat exchanger 45, and is connected to the residual gas vent pipe 46. The liquid phase flows back to the CO2 distillation tower 411 through the output pipe 6 482.

[0047] The bottom of the CO2 distillation tower 411 is connected to a CO2 subcooler 41, and the output end of the CO2 subcooler 41 is connected to a CO2 product output pipeline 49. After the liquid phase is cooled by the CO2 subcooler 41, a liquid CO2 product is formed and output through the CO2 product output pipeline 49.

[0048] In the CO2 production module, the refrigerant from the mixed refrigerant compressor 21 is mainly used to provide cooling to the CO2 precooler 410, the CO2 subcooler 41 and the top condenser 47; specifically, the output pipeline 222 includes multiple branches, and the multiple branches pass through the CO2 precooler 410, the CO2 subcooler 41 and the top condenser 47 respectively, and then return to the input end of the mixed refrigerant compressor 21.

[0049] Example 2

[0050] Based on the first embodiment, this embodiment provides a method for co-producing LNG and liquid CO2 from biogas using mixed refrigeration, which includes an LNG production process, a liquid CO2 production process and a refrigerant circulation process.

[0051] Specifically, the LNG production process is as follows: biogas enters the MDEA amine process system 13 through the biogas compressor 12, and the biogas from which CO2 and H2S are removed by the MDEA amine process system 13 enters the molecular sieve 31 through the output pipe 131 for drying, mercury removal and dust filtration; the biogas passing through the molecular sieve 31 enters the main heat exchanger 33 for cooling to -140°C and then enters the denitrification tower 32 for denitrification. The denitrified biogas enters the main heat exchanger 33 through the secondary heat exchange pipe 321 for supercooling and forming LNG products, and is finally output through the LNG product output pipe 34; the dirty nitrogen at the top of the denitrification tower 32 is reheated by the main heat exchanger 33 and then enters the dirty nitrogen vent pipe 35 for discharge.

[0052] The CO2 production process is as follows: after CO2 and H2S are removed by the MDEA amine system 13, the gas enters the CO2 compressor 42 for pressurization, and then enters the dry desulfurization device 43 for desulfurization. The desulfurized gas enters the molecular sieve 2 44 for drying, dehydration and dust filtration. The gas phase after the molecular sieve 2 44 is heat-exchanged with the residual gas through the gas-to-gas heat exchanger 45 and the cooling capacity is recovered. The gas then enters the bottom of the CO2 distillation tower 411 as the reboiler heat source of the CO2 distillation tower 411. After exiting the bottom of the CO2 distillation tower 411, the gas enters the CO2 precooler 410 and is cooled to -25°C. After cooling, it enters the CO2 distillation tower 411; the gas at the top of the CO2 distillation tower 411 is cooled by the top condenser 47 and then passed into the top separator 48 for separation; the gas phase and the liquid phase are separated by the top separator 48, wherein the gas phase passes through the output pipe five 481, passes through the top condenser 47 and the gas-to-gas heat exchanger 45 for reheating, and is then discharged through the residual gas venting pipe 46; the liquid phase refluxes to the CO2 distillation tower 411 through the output pipe six 482; the liquid at the bottom of the CO2 distillation tower 411 passes through the CO2 supercooler 41 and is output through the CO2 product output pipe 49.

[0053] The refrigerant circulation process is as follows: the high-pressure refrigerant from the mixed refrigerant compressor 21 is separated by the refrigerant separator 22; a portion of the refrigerant enters the main heat exchanger 33 through the output pipe 3 221 and provides cooling for the main heat exchanger 33; the low-pressure refrigerant passing through the main heat exchanger 33 returns to the mixed refrigerant compressor 21 for compression after heat exchange at the top of the denitrification tower 32;

[0054] Another part of the high-pressure refrigerant enters the CO2 precooler 410, the CO2 subcooler 41 and the top condenser 47 through multiple branches of the output pipeline 4 222 and provides cooling capacity, and then returns to the mixed refrigerant compressor 21 for compression.

[0055] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "provided with," "mounted / connected," and "connected" should be understood in a broad sense. For example, "connected" can mean a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be internal communication between two components. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention in specific circumstances.

[0056] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A device for co-producing LNG and liquid CO2 by using mixed refrigeration, characterized in that: include: A biogas input module (10), the biogas input module (10) comprising a biogas input pipeline (11), a biogas compressor (12), and an MDEA amine process system (13) connected in sequence; an output end of the MDEA amine process system (13) is connected to an output pipeline 1 (131) and an output pipeline 2 (132), respectively; A refrigeration module (20), the refrigeration module (20) comprising a mixed refrigerant compressor (21) and a refrigerant separator (22); the output end of the mixed refrigerant compressor (21) is connected to the input end of the refrigerant separator (22); the output end of the refrigerant separator (22) is respectively connected to an output pipe three (221) and an output pipe four (222); LNG production module (30), the output pipeline 1 (131) and the output pipeline 3 (221) are respectively connected to the LNG production module (30); A CO2 production module (40), wherein the second output pipeline (132) and the fourth output pipeline (222) are respectively connected to the CO2 production module (40); The LNG production module (30) includes a molecular sieve (31), a denitrification tower (32), a main heat exchanger (33), an LNG product output pipeline (34), and a waste nitrogen venting pipeline (35); The input end of the molecular sieve 1 (31) is connected to the output pipe 1 (131), and the output end of the molecular sieve 1 (31) is connected to the denitrification tower (32) for denitrification after heat exchange in the main heat exchanger (33); the natural gas after denitrification enters the main heat exchanger (33) through the secondary heat exchange pipe (321) to be supercooled and form an LNG product; the secondary heat exchange pipe (321) is connected to the LNG product output pipe (34), and the LNG product is output through the LNG product output pipe (34); The top of the denitrification tower (32) is connected to the dirty nitrogen venting pipe (35); The output pipe 3 (221) passes through the main heat exchanger (33) and the top of the denitrification tower (32) and then returns to the input end of the mixed refrigerant compressor (21); The CO2 production module (40) includes a CO2 compressor (42), a dry desulfurization device (43), a molecular sieve II (44), a gas-to-gas heat exchanger (45), a CO2 precooler (410) and a CO2 distillation tower (411); The output pipe 2 (132) is connected to the input end of the CO2 compressor (42), and the CO2 compressor (42) is connected to the input end of the dry desulfurization device (43); the output end of the dry desulfurization device (43) is connected to the molecular sieve 2 (44); the output end of the molecular sieve 2 (44) is connected to the input end of the CO2 precooler (410) after heat exchange through the gas-to-gas heat exchanger (45) and the bottom of the CO2 distillation tower (411); the output end of the CO2 precooler (410) is connected to the CO2 distillation tower (411). The top of the CO2 distillation tower (411) is connected to a tower top condenser (47), and the output end of the tower top condenser (47) is connected to a tower top separator (48); The output end of the tower top separator (48) is connected to the output pipe five (481) and the output pipe six (482); the tower top separator (48) is used to separate the gas from the top of the CO2 distillation tower (411) into a gas phase and a liquid phase; wherein the gas phase passes through the output pipe five (481) and the tower top condenser (47) and the gas-to-gas heat exchanger (45) in sequence and is connected to the residual gas venting pipe (46); wherein the liquid phase flows back to the CO2 distillation tower (411) through the output pipe six (482); The bottom of the CO2 distillation tower (411) is connected to a CO2 supercooler (41), and the output end of the CO2 supercooler (41) is connected to a CO2 product output pipeline (49); The output pipeline 4 (222) includes a plurality of branch pipes, and the plurality of branch pipes respectively pass through the CO2 precooler (410), the CO2 subcooler (41) and the tower top condenser (47) and then return to the input end of the mixed refrigerant compressor (21).

2. The device for co-producing LNG and liquid CO2 by using mixed refrigeration of biogas according to claim 1, characterized in that: The refrigerant used by the refrigeration module (20) is MRC refrigerant.

3. A method for co-producing LNG and liquid CO2 from biogas using hybrid refrigeration, characterized in that: A method for producing LNG and liquid CO2 using a device for co-producing LNG and liquid CO2 using mixed refrigeration based on any one of claims 1-2, comprising an LNG production process, a liquid CO2 production process, and a refrigerant circulation process; The LNG production process is as follows: biogas enters the MDEA amine process system (13) through a biogas compressor (12); the biogas from which CO2 and H2S are removed by the MDEA amine process system (13) enters the molecular sieve one (31) through an output pipe one (131) for drying, mercury removal and dust filtration; the biogas from the molecular sieve one (31) enters the main heat exchanger (33) for cooling and then enters the denitrification tower (32) for denitrification; the denitrified biogas enters the main heat exchanger (33) through a secondary heat exchange pipe (321) for supercooling and forming LNG products, and is finally output through an LNG product output pipe (34); the dirty nitrogen at the top of the denitrification tower (32) is reheated by the main heat exchanger (33) and then enters the dirty nitrogen venting pipe (35) for venting.

4. The method for co-producing LNG and liquid CO2 by using mixed refrigeration of biogas according to claim 3, characterized in that: The liquid CO2 production process is as follows: after CO2 and H2S are removed by the MDEA amine system (13), the gas enters the CO2 compressor (42) for pressurization, and then enters the dry desulfurization device (43) for desulfurization. The desulfurized gas enters the molecular sieve II (44) for drying, dehydration and dust filtration. The gas phase after the molecular sieve II (44) exchanges heat with the residual gas through the gas-to-gas heat exchanger (45) and recovers the cold energy. The gas then enters the bottom of the CO2 distillation tower (411) as the reboiler heat of the CO2 distillation tower (411). The gas from the top of the CO2 distillation tower (411) is cooled by the top condenser (47) and then passed into the top separator (48) for separation. The gas phase and the liquid phase are separated by the top separator (48), wherein the gas phase passes through the output pipe five (481), is reheated by the top condenser (47) and the gas-to-gas heat exchanger (45), and then is discharged through the residual gas venting pipe (46); The liquid phase flows back to the CO2 distillation tower (411) through the output pipe six (482); the liquid at the bottom of the CO2 distillation tower (411) passes through the CO2 supercooler (41) and is output through the CO2 product output pipe (49).

5. The method for co-producing LNG and liquid CO2 by using mixed refrigeration of biogas according to claim 4, characterized in that: The refrigerant circulation process is as follows: the high-pressure refrigerant from the mixed refrigerant compressor (21) is separated by the refrigerant separator (22); a portion of the refrigerant enters the main heat exchanger (33) through the output pipe 3 (221) and provides cooling capacity for the main heat exchanger (33); the low-pressure refrigerant passing through the main heat exchanger (33) returns to the mixed refrigerant compressor (21) for compression after heat exchange at the top of the denitrification tower (32); Another portion of the high-pressure refrigerant enters the CO2 precooler (410), the CO2 subcooler (41) and the tower top condenser (47) through multiple branches of the output pipeline four (222) and provides cooling capacity before returning to the mixed refrigerant compressor (21) for compression.

Images