Device system and method for capturing, purifying and reinjecting carbon dioxide on offshore platform

Abstract

The invention discloses a device system and method for capturing, purifying and reinjecting carbon dioxide on an offshore platform. The device system comprises a molecular sieve dehydration system, a precooler, a liquefier, a low-temperature separator and a low-temperature rectifying tower, wherein a reboiler is arranged at the tower bottom of the low-temperature rectifying tower; the device comprises a fractional condenser, a return tank, a subcooler, a carbon dioxide reinjection pump, a refrigeration system and a membrane separation system. According to the device and the method, a low-temperature rectification technology and a membrane separation technology are combined, self-produced natural gas obtained after molecular sieve deep dehydration is subjected to low-temperature liquefaction and then enters a low-temperature rectification tower for carbon dioxide purification, and the purified carbon dioxide is in a liquid state and can be reinjected through pump equipment; the mode that a single membrane separation technology and other decarburization technologies use a compressor to conduct carbon dioxide reinjection is replaced, the membrane separation device can improve the concentration of carbon dioxide in raw material gas entering the low-temperature rectifying tower, and therefore the cold and heat load requirement of the low-temperature rectifying tower is lowered.

Description

Technical Field

[0001] The present invention belongs to the technical field of offshore oil and gas production, and relates to a device system and method for capturing, purifying and reinjecting carbon dioxide on an offshore platform. Background Art

[0002] With the development of offshore oil and gas fields high in CO2, technologies for capturing, purifying, and reinjecting CO2 are gradually being applied to offshore platforms. Currently, offshore decarbonization processes primarily rely on amine and membrane separation methods. The separated CO2 is in a gaseous / supercritical state, and subsequent reinjection requires the addition of high-power compressors, increasing the construction and operating costs of offshore platform CO2 recovery systems.

[0003] Onshore cryogenic distillation decarbonization processes are primarily used to purify chemical exhaust gases to produce food-grade carbon dioxide, or for small-scale decarbonization of produced gas from gas wells and stations. Large-scale carbon capture of produced gas from oil and gas fields has yet to be applied. Currently, cryogenic distillation decarbonization and process improvements are not available for offshore platforms. Summary of the Invention

[0004] The purpose of the present invention is to provide a device system and method for capturing, purifying, and reinjecting carbon dioxide on offshore platforms. The device and method combine cryogenic distillation technology with membrane separation technology. The self-produced natural gas after deep dehydration of molecular sieves is liquefied at low temperature and then enters a cryogenic distillation tower for carbon dioxide purification. The purified carbon dioxide is in liquid form and can be reinjected through pump equipment, replacing the single membrane separation process and other decarbonization processes that use compressors for carbon dioxide reinjection. The membrane separation device can increase the carbon dioxide concentration in the feed gas entering the cryogenic distillation tower, thereby reducing the cooling and heating load requirements of the cryogenic distillation tower. In the present invention, the offshore platform cryogenic distillation and membrane separation coupling decarbonization device and method significantly reduces the energy consumption and equipment investment for offshore natural gas decarbonization and carbon dioxide reinjection.

[0005] The present invention provides a device system for capturing, purifying and reinjecting carbon dioxide on an offshore platform, the device system comprising:

[0006] Molecular sieve dehydration system, used for natural gas dehydration;

[0007] Precooler, used to pre-cool the dehydrated natural gas before liquefaction;

[0008] Liquefier, used to cool down and partially liquefy the pre-cooled natural gas;

[0009] a low-temperature separator for separating the natural gas partially liquefied by the liquefier into gas and liquid;

[0010] A cryogenic distillation tower is used to separate the natural gas containing carbon dioxide to obtain liquid carbon dioxide and a gaseous stream containing natural gas, wherein a reboiler is provided at the bottom of the cryogenic distillation tower;

[0011] A partial condenser, used for condensing and liquefying part of the vapor from the top of the cryogenic distillation tower;

[0012] A reflux tank is used to separate the gas-liquid flow of the partially condensed and liquefied vapor from the top of the cryogenic distillation tower, with the liquid phase flow refluxed to the top of the tower and the gas phase flow sent to the membrane separation device;

[0013] A subcooler is used to further cool the high-purity carbon dioxide at the bottom of the cryogenic distillation tower to prevent cavitation in the subsequent carbon dioxide reinjection pump;

[0014] a carbon dioxide reinjection pump, used to reinject the liquid carbon dioxide obtained from the cryogenic distillation tower into the formation;

[0015] A refrigeration system, used to provide a low-temperature cooling source to the precooler, liquefier, and decondenser;

[0016] The membrane separation system is used to separate and concentrate the carbon dioxide content of the flow entering the cryogenic distillation tower or to separate the flow in the outlet pipeline at the top of the cryogenic distillation tower to concentrate the carbon dioxide.

[0017] In the above-mentioned device system for capturing, purifying and reinjecting carbon dioxide on offshore platforms, the natural gas containing carbon dioxide dehydrated by the molecular sieve dehydration system is used as the heat source of the reboiler at the bottom of the cryogenic distillation tower to exchange heat with the bottom product of the cryogenic distillation tower.

[0018] In the above-mentioned device system for capturing, purifying and reinjecting carbon dioxide on an offshore platform, the membrane separation system is arranged on the logistics inlet pipeline or the logistics outlet pipeline of the precooler+liquefier.

[0019] In the above-mentioned device system for capturing, purifying and reinjecting carbon dioxide on offshore platforms, when the membrane separation system is arranged on the precooler and the liquefier logistics inlet pipeline, a cold dryer is arranged on the logistics inlet pipeline of the membrane separation system to increase low-temperature water and hydrocarbon control.

[0020] The present invention also provides a method for capturing, purifying, and reinjecting carbon dioxide from an offshore platform using the device system for capturing, purifying, and reinjecting carbon dioxide from an offshore platform of the present invention, comprising the following steps:

[0021] When the membrane separation system is arranged on the precooler + the liquefier logistics outlet pipeline: the carbon dioxide-containing natural gas is deeply dehydrated by the molecular sieve dehydration system and used as the heat source of the reboiler at the bottom of the cryogenic distillation tower. After heat exchange with the bottom logistics in the reboiler, heat exchange with the gas phase of the cryogenic separator in the precooler, and partial liquefaction is achieved by cooling in the liquefier by the cold source from the precooler, and then sent to the cryogenic separator for gas-liquid separation; the liquid phase separated by the cryogenic separator enters the cryogenic distillation tower for carbon dioxide purification, and the gas phase is successively heated by the precooler and the heater and enters the first membrane separation device for rough carbon dioxide removal; the permeate gas with high carbon dioxide content separated by the first membrane separation device is pressurized. After being pressurized by the compressor, it is heat exchanged with the gas phase in the reflux tank at the top of the cryogenic distillation tower and then sent back to the cryogenic distillation tower; the raffinate gas after decarbonization is sent to the subsequent natural gas processing process of the offshore platform; the gas phase at the top of the cryogenic distillation tower is partially condensed and liquefied by the decondenser, and then subjected to gas-liquid separation in the reflux tank. After the gas phase is heat exchanged with the pressurized permeate gas of the first membrane separation device, it enters the second membrane separation device for rough carbon dioxide removal; the permeate gas with high carbon dioxide content separated by the second membrane separation device is pressurized together with the permeate gas of the first membrane separation device and sent back to the cryogenic distillation tower, and the raffinate gas is sent to the subsequent natural gas processing process of the offshore platform; the high-purity liquid carbon dioxide at the bottom of the cryogenic distillation tower is supercooled by the supercooler and pressurized and reinjected by the carbon dioxide reinjection pump.

[0022] The present invention also provides a method for capturing, purifying, and reinjecting carbon dioxide from an offshore platform using the device system of the present invention, comprising the following steps:

[0023] When the membrane separation device is installed on the precooler + liquefier logistics inlet pipeline: after deep dehydration of the carbon dioxide-containing natural gas by the molecular sieve dehydration system, the hydrocarbon dew point and water point are controlled by the cold dryer and heated by the heater, and then sent to the membrane separation system for rough carbon dioxide removal. The permeate gas with low carbon dioxide content is sent to the subsequent natural gas processing process on the offshore platform. The permeate gas with high carbon dioxide content is pressurized by the compressor and used as the heat source for the reboiler at the bottom of the cryogenic distillation tower. After heat exchange with the bottom logistics in the reboiler, heat exchange with the gas phase of the cryogenic separator in the precooler, and partial liquefaction is achieved by cooling the liquefier with the cold source from the refrigeration system, it is sent to the cryogenic distillation tower. The gas phase at the top of the cryogenic distillation tower is partially condensed and liquefied by the partial condenser, and then gas-liquid separation is carried out in the reflux drum. After heat exchange in the precooler, the gas phase is sent back to the heater inlet. The high-purity liquid carbon dioxide at the bottom of the cryogenic distillation tower is supercooled by the subcooler and pressurized and reinjected by the carbon dioxide reinjection pump.

[0024] The present invention has the following beneficial effects:

[0025] 1. The present invention uses cryogenic distillation technology to separate carbon dioxide from natural gas on offshore platforms in liquid form, reducing equipment investment in subsequent reinjection processes.

[0026] 2. The process flow of the present invention combines membrane separation with cryogenic distillation technology. The heat energy of the dehydrated natural gas enters the refrigeration system after being utilized in the reboiler of the cryogenic distillation tower, making full use of the cold energy in the cryogenic distillation process, improving energy utilization, and effectively reducing the energy consumption in the traditional cryogenic distillation method.

[0027] 3. The process flow of the present invention optimizes the design of relevant processing parameters, and carbon-containing natural gas is subjected to a combined process of membrane separation and cryogenic distillation to capture carbon dioxide, effectively reducing the hydrocarbon loss of traditional carbon dioxide purification processes (cryogenic distillation, membrane separation) and improving the purity of carbon dioxide.

[0028] 4. The process flow proposed by the present invention combines cryogenic distillation and membrane separation. The low-temperature gas separated during carbon capture exchanges heat with the feed gas and membrane permeate gas, thereby improving energy utilization and reducing the energy consumption of the traditional cryogenic distillation carbon dioxide purification process system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the process flow of capturing, purifying and reinjecting carbon dioxide in which the offshore platform membrane separation device of the present invention is arranged on the precooler + liquefier logistics outlet pipeline.

[0030] Figure 2 This is a schematic diagram of the process flow of carbon dioxide capture, purification and reinjection, in which the offshore platform membrane separation device is installed on the precooler + liquefier logistics inlet pipeline.

[0031] The symbols in the figure represent the following:

[0032] 1-molecular sieve dehydration system, 2-reboiler, 3-precooler, 4-liquefier, 5-cryogenic distillation tower, 6-partial condenser, 7-reflux tank, 8-refrigeration unit, 9-subcooler, 10-carbon dioxide reinjection pump, 11-heater, 12-membrane separation system (i.e., membrane separation device), 13-compressor, 14-cryogenic separator, 15-cold dryer. DETAILED DESCRIPTION

[0033] The refrigeration system and cold dryer used in the embodiments of the present application are conventional processes and devices.

[0034] The refrigerants used in the refrigeration system in the embodiments of the present application can be obtained from commercial channels.

[0035] The optimization of the hot and cold logistics heat exchange process, process parameter optimization and equipment optimization based on the embodiments of this application should all fall within the scope of protection of this application.

[0036] The present application provides a device system for capturing, purifying, and reinjecting carbon dioxide on an offshore platform, the device system comprising:

[0037] Molecular sieve dehydration system, used for natural gas dehydration;

[0038] Precooler, used to pre-cool the dehydrated natural gas before liquefaction;

[0039] Liquefier, used to cool down and partially liquefy the pre-cooled natural gas;

[0040] Low-temperature separator, used to separate gas and liquid from the natural gas partially liquefied by the liquefier;

[0041] A cryogenic distillation tower is used to separate the natural gas containing carbon dioxide to obtain liquid carbon dioxide and a gaseous stream containing natural gas. A reboiler is provided at the bottom of the cryogenic distillation tower.

[0042] The dephlegmator is used to condense and liquefy the vapor from the top of the cryogenic distillation tower;

[0043] The reflux tank is used to separate the gas-liquid flow after the condensation of the vapor from the top of the cryogenic distillation tower. The liquid phase flow is refluxed to the top of the tower, and the gas phase flow is sent to the membrane separation device.

[0044] The subcooler is used to further cool the high-purity carbon dioxide at the bottom of the cryogenic distillation tower to prevent cavitation in the subsequent carbon dioxide reinjection pump;

[0045] A carbon dioxide reinjection pump is used to reinject the liquid carbon dioxide obtained from the cryogenic distillation tower into the formation;

[0046] Refrigeration system, used to provide low-temperature cooling source to the precooler, liquefier, and condenser;

[0047] The membrane separation system is used to separate and concentrate the carbon dioxide content of the flow entering the cryogenic distillation tower or to separate the flow in the outlet pipeline at the top of the cryogenic distillation tower to concentrate the carbon dioxide.

[0048] Furthermore, the natural gas containing carbon dioxide dehydrated by the molecular sieve dehydration system is used as a heat source for the reboiler at the bottom of the cryogenic distillation tower to exchange heat with the bottom product of the cryogenic distillation tower.

[0049] Furthermore, the membrane separation system is arranged on the logistics inlet pipeline or the logistics outlet pipeline of the precooler+liquefier).

[0050] Furthermore, when the membrane separation system is installed on the precooler and liquefier logistics inlet pipelines, a cold dryer is installed on the logistics inlet pipeline of the membrane separation system to increase low-temperature water and hydrocarbon control.

[0051] Example 1

[0052] like Figure 1 As shown, the configuration of the device system for capturing, purifying and reinjecting carbon dioxide on an offshore platform of the present invention is as follows:

[0053] The membrane separation system 12 (specifically, two groups, membrane separation device-1 and membrane separation device-2) is set on the logistics outlet pipeline of the precooler 3+liquefier 4: the natural gas containing carbon dioxide is deeply dehydrated by the molecular sieve dehydration system 1 and used as the heat source of the reboiler 2 at the bottom of the cryogenic distillation tower 5. After heat exchange with the bottom logistics in the reboiler 2, it is heat exchanged with the gas phase of the cryogenic separator 14 in the precooler 3. After being cooled by the cold source from the precooler 3 in the liquefier 4 to achieve partial liquefaction, it is sent to the cryogenic separator 14 for gas-liquid separation; the liquid phase separated by the cryogenic separator 14 enters the cryogenic distillation tower 5 for carbon dioxide purification, and the gas phase is successively heat exchanged in the precooler 3 and heated by the heater 11, and then enters the membrane separation device-1 12 for rough carbon dioxide removal; the membrane separation device-1 The high-CO2 permeate gas separated by 12 is pressurized by compressor 13, heat exchanged with the reflux tank gas 7 at the top of the cryogenic distillation tower 5, and then returned to the cryogenic distillation tower 5. The decarbonized retentate gas is sent to the offshore platform for subsequent natural gas processing. The overhead gas phase of the cryogenic distillation tower 5 is partially condensed and liquefied by the partial condenser 6. After gas-liquid separation in the reflux tank 7, the gas phase exchanges heat with the pressurized permeate gas from membrane separation unit-1 12 before entering membrane separation unit-2 12 for crude carbon dioxide removal. The high-CO2 permeate gas separated by membrane separation unit-2 12 is pressurized together with the permeate gas from membrane separation unit-1 12 and returned to the cryogenic distillation tower 5. The retentate gas is sent to the offshore platform for subsequent natural gas processing. The high-purity liquid CO2 at the bottom of the cryogenic distillation tower 5 is supercooled by cooler 9 and pressurized and reinjected by the CO2 reinjection pump 10.

[0054] Example 2

[0055] like Figure 2 As shown, the configuration of the device system for capturing, purifying and reinjecting carbon dioxide on an offshore platform of the present invention is as follows:

[0056] The membrane separation system (i.e. membrane separation device) 12 is arranged on the pre-cooler 3 + liquefier 4 stream inlet pipeline: after the carbon dioxide-containing natural gas is deeply dehydrated by the molecular sieve dehydration system 1, the hydrocarbon dew point and water route point are controlled by the cold dryer 15, and the heater 11 is heated, the carbon dioxide is roughly removed by the membrane separation system 12, the low carbon dioxide-containing permeate gas is sent to the subsequent natural gas treatment process of the offshore platform, the high carbon dioxide-containing permeate gas is pressurized by the compressor 13, and is used as the heat source of the bottom reboiler 2 of the low-temperature rectification tower 5, is heat-exchanged with the tower bottom stream in the reboiler 2, is heat-exchanged with the gas phase of the low-temperature separator 14 in the pre-cooler 3, is partially liquefied in the liquefier 4 by the cold source from the refrigeration unit 8, and is sent into the low-temperature rectification tower 5; the gas phase at the top of the low-temperature rectification tower 5 is partially condensed and liquefied by the partial condenser 6, is separated into gas and liquid in the reflux tank 7, is heat-exchanged with the pre-cooler 3, and is sent back to the inlet of the heater 11; the high-purity liquid carbon dioxide at the bottom of the low-temperature rectification tower 5 is supercooled by the cold cooler 9, is pressurized by the carbon dioxide reinjection pump 10, and is reinjected.

[0057] According to the above-mentioned embodiment 1, the method for capturing, purifying and reinjecting carbon dioxide on the offshore platform is carried out according to the arrangement of the device system for capturing, purifying and reinjecting carbon dioxide on the offshore platform, compared with the conventional method in the art-alcohol amine method and membrane method, the obtained data are shown in Table 1:

[0058] Table 1 Comparison of indexes of different carbon dioxide capture methods

[0059]

[0060] As shown in Table 1, compared with the alcohol amine method, the hydrocarbon loss rate of the present application is equivalent, the occupied area is equivalent, the power consumption is greatly reduced, there is no heating requirement, and the energy consumption is greatly saved.

[0061] Compared with the membrane method, the energy consumption of the present application is equivalent, and the main advantage is that the hydrocarbon loss is greatly reduced, and the equipment operation and maintenance cost is low.

Claims

1. A device system for capturing, purifying and reinjecting carbon dioxide on an offshore platform, characterized in that: The device system includes: Molecular sieve dehydration system, used for natural gas dehydration; Precooler, used to pre-cool the dehydrated natural gas before liquefaction; Liquefier, used to cool down and partially liquefy the pre-cooled natural gas; a low-temperature separator for separating the natural gas partially liquefied by the liquefier into gas and liquid; A cryogenic distillation tower is used to separate the natural gas containing carbon dioxide to obtain liquid carbon dioxide and a gaseous stream containing natural gas, wherein a reboiler is provided at the bottom of the cryogenic distillation tower; A partial condenser, used for condensing and liquefying part of the vapor from the top of the cryogenic distillation tower; A reflux tank is used to separate the gas-liquid flow of the partially condensed and liquefied vapor from the top of the cryogenic distillation tower, with the liquid phase flow refluxed to the top of the tower and the gas phase flow sent to the membrane separation device; A subcooler is used to further cool the high-purity carbon dioxide at the bottom of the cryogenic distillation tower to prevent cavitation in the subsequent carbon dioxide reinjection pump; a carbon dioxide reinjection pump, used to reinject the liquid carbon dioxide obtained from the cryogenic distillation tower into the formation; A refrigeration system, used to provide a low-temperature cooling source to the precooler, liquefier, and decondenser; The membrane separation system is used to separate and concentrate the carbon dioxide content of the flow entering the cryogenic distillation tower or to separate the flow in the outlet pipeline at the top of the cryogenic distillation tower to concentrate the carbon dioxide.

2. The device system for capturing, purifying and reinjecting carbon dioxide on an offshore platform according to claim 1, characterized in that: The carbon dioxide-containing natural gas dehydrated by the molecular sieve dehydration system is used as a heat source for the reboiler at the bottom of the cryogenic distillation tower to exchange heat with the bottom product of the cryogenic distillation tower.

3. The device system for capturing, purifying and reinjecting carbon dioxide on an offshore platform according to claim 1 or 2, characterized in that: The membrane separation system is arranged on the logistics inlet pipeline or the logistics outlet pipeline of the precooler+liquefier.

4. The device system for capturing, purifying and reinjecting carbon dioxide on an offshore platform according to claim 3, characterized in that: When the membrane separation system is provided on the precooler and the liquefier logistics inlet pipeline, a cold dryer is provided on the logistics inlet pipeline of the membrane separation system to increase low-temperature water control and hydrocarbon control.

5. A method for capturing, purifying, and reinjecting carbon dioxide from an offshore platform, comprising the following steps: using the device system for capturing, purifying, and reinjecting carbon dioxide from an offshore platform according to any one of claims 1 to 4 to capture, purify, and reinject carbon dioxide from the offshore platform.

6. The method according to claim 5, characterized in that When the membrane separation system is arranged on the precooler + liquefier logistics outlet pipeline: the carbon dioxide-containing natural gas is deeply dehydrated by the molecular sieve dehydration system and used as the heat source of the reboiler at the bottom of the cryogenic distillation tower. After heat exchange with the bottom logistics in the reboiler, it is heat exchanged with the gas phase of the cryogenic separator in the precooler, and is cooled in the liquefier by the cold source from the precooler to achieve partial liquefaction, and then sent to the cryogenic separator for gas-liquid separation; the liquid phase separated by the cryogenic separator enters the cryogenic distillation tower for carbon dioxide purification, and the gas phase is successively heat exchanged in the precooler and heated by the heater, and then enters the first membrane separation device for rough carbon dioxide removal; the permeate gas with a high carbon dioxide content separated by the first membrane separation device is pressurized by the compressor, and after heat exchange with the gas phase of the reflux tank at the top of the cryogenic distillation tower, it is sent back to the cryogenic distillation tower; the decarbonized retentate gas is sent to the subsequent natural gas processing process on the offshore platform; The gas phase at the top of the cryogenic distillation tower is partially condensed and liquefied by the partial condenser, and then subjected to gas-liquid separation in the reflux tank. After the gas phase exchanges heat with the pressurized permeate gas from the first membrane separation device, it enters the second membrane separation device for rough carbon dioxide removal; the permeate gas with a high carbon dioxide content separated by the second membrane separation device is pressurized together with the permeate gas from the first membrane separation device and sent back to the cryogenic distillation tower, and the raffinate gas is sent to the subsequent natural gas processing process on the offshore platform; the high-purity liquid carbon dioxide at the bottom of the cryogenic distillation tower is supercooled by the supercooler and then pressurized and reinjected by the carbon dioxide reinjection pump.

7. The method according to claim 5, characterized in that When the membrane separation device is installed on the precooler + liquefier logistics inlet pipeline: after deep dehydration of the carbon dioxide-containing natural gas by the molecular sieve dehydration system, the hydrocarbon dew point and water way point are controlled by a cold dryer and heated by a heater, the natural gas is sent to the membrane separation system for rough carbon dioxide removal. The permeate gas with low carbon dioxide content is sent to the subsequent natural gas processing process on the offshore platform. The permeate gas with high carbon dioxide content is pressurized by a compressor and used as a heat source for the reboiler at the bottom of the cryogenic distillation tower. After heat exchange with the bottom logistics in the reboiler, heat exchange with the gas phase of the cryogenic separator in the precooler, and partial liquefaction is achieved by cooling the liquefier with the cold source from the refrigeration system, the natural gas is sent to the cryogenic distillation tower. The gas phase at the top of the cryogenic distillation tower is partially condensed and liquefied by the partial condenser, and then gas-liquid separation is performed in the reflux drum. After heat exchange in the precooler, the gas phase is sent back to the heater inlet. The high-purity liquid carbon dioxide at the bottom of the cryogenic distillation tower is supercooled by the subcooler and pressurized and reinjected by a carbon dioxide reinjection pump.

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