A storage and injection system and method based on offshore platform carbon dioxide capture

Abstract

The present invention discloses a storage and injection system and method based on offshore platform carbon dioxide capture. The injection system includes a connectable multi-stage boosting system, a movable filtration system, and an injection pipeline phase change suppression system. The connectable multi-stage boosting system is used to implement boosting operations at different injection stages. The movable filtration system is used to perform secondary solid and liquid phase capture and filtration on the pressurized medium during the initial injection stage. The injection pipeline phase change suppression system is used to control the inlet temperature of the seabed injection pipeline. Based on the boundary conditions and reinjection process characteristics of marine carbon dioxide storage, and targeting the characteristics of marine geological storage such as long injection time, high medium inventory, large boundary pressure variation range, and relatively stable injection flow, the present invention provides a guarantee for the efficient and safe storage and injection of carbon dioxide in marine geology from the perspectives of rationally configuring boosting facilities, overcoming the high medium flow rate in the initial injection stage, and compensating for the large temperature drop of the marine pipeline flow during mid-term injection.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dioxide sequestration, and in particular relates to a sequestration and injection system and method based on offshore platform carbon dioxide capture. Background Art

[0002] Against the backdrop of growing demands for energy conservation, emission reduction, and environmental protection in the energy and chemical industries, large-scale capture and utilization of carbon dioxide (CO2) is a preferred approach for effectively reducing carbon emissions. Carbon sequestration is a recognized effective means of controlling CO2 emissions. Geological storage of CO2 using depleted oil and gas reservoirs or saline formations can achieve long-term, large-scale storage. CO2 has a critical temperature of approximately 31.1°C and a critical pressure of approximately 7.38 MPa. Geological storage generally maintains a storage pressure above 15 MPa.g.

[0003] Compared with onshore geological storage, the use of marine geological storage for carbon dioxide is also a more recognized storage model with future potential. It has good implementation scenarios near large coastal refineries and offshore processing platforms. Furthermore, it is advisable to directly reinject carbon dioxide into the storage area after processing and capture by offshore natural gas platforms. Compared with carbon dioxide flooding, the storage process has the process characteristics of gradually increasing pressure in the storage area and continuous filling of the medium. Furthermore, the storage area will experience phase changes such as gas phase and supercritical phase. In addition, based on the aforementioned storage characteristics, it also faces the problem of deepwater injection pipeline transportation.

[0004] Unlike conventional natural gas storage, geological CO2 storage has significantly longer reinjection times (the injection-production cycle for natural gas storage is typically one year), relatively small reinjection flows, relatively lower initial formation pressures, and no other means of absorbing the reinjected medium. Injection facilities must maintain stable injection rates over long periods of time, adapt to ultra-low-pressure to high-pressure pressures over a long timeframe, and face phase changes in injection channels. These challenges pose significant challenges to effective equipment configuration and safe injection processes. For marine storage in particular, injection pipelines are also subject to the impact of low-temperature ocean temperatures.

[0005] Currently, CO2 ocean storage is still in its infancy. While promising, available technical information is extremely limited, and reports on the aforementioned issues are even rarer. Therefore, it is necessary to conduct research on safe CO2 injection systems and methods for ocean storage, build sufficient technical expertise, and provide reference and lessons for subsequent large-scale CO2 pipeline transportation projects. Summary of the Invention

[0006] The purpose of the present invention is to provide a system and method for the efficient and economical implementation of CO2 marine geological storage and reinjection operations based on CO2 capture on offshore platforms in order to address the above-mentioned problems.

[0007] The present invention is based on the boundary conditions and reinjection process characteristics of marine carbon dioxide storage, and targets the characteristics of marine storage such as long injection time, high medium inventory, large range of boundary pressure variation, and relatively stable injection flow. From the perspectives of rationally configuring the carbon dioxide boosting facilities after recovery on the offshore platform, overcoming the high medium flow rate in the initial injection stage, and controlling the large temperature drop of the ocean pipeline flow during mid-term injection, corresponding boosting systems are set according to different periods of carbon dioxide injection to form a connectable multi-stage boosting system. By setting up a movable filtration system and an injection pipeline phase change suppression system, the safe and efficient injection of carbon dioxide for marine geological storage is achieved.

[0008] Among them, the connectable multi-stage boosting system mainly includes a first-stage boosting device, a multi-stage reserved boosting device, a pipeline residual pressure bypass, etc., which are used to implement boosting operations in different injection stages; the movable filtration system mainly includes a filter separator, etc., which is used to deal with the erosion problem of high flow rate under low-pressure injection in the initial stage of reinjection; the injection pipeline phase change suppression system mainly includes an air cooler, an air cooler bypass, etc., by reasonably controlling the inlet temperature of the submarine injection pipeline, avoiding the liquefaction of the medium in the submarine pipeline during the medium-pressure injection process, affecting the flow stability and safety of the injected medium.

[0009] The technical solution adopted by the present invention is: a storage and injection system based on offshore platform carbon dioxide capture, characterized by: comprising a connectable multi-stage boosting system, a movable filtration system and an injection pipeline phase change suppression system;

[0010] The connectable multi-stage boosting system includes a first-stage boosting unit provided at the initial stage of carbon dioxide injection, a second-stage boosting unit provided at the middle stage of carbon dioxide injection, and a third-stage boosting unit provided at the late stage of carbon dioxide injection, for implementing boosting operations at different injection stages;

[0011] The movable filtration system is connected to the primary pressurizing unit and is used to perform secondary solid and liquid phase capture and filtration on the pressurized medium during the initial injection stage;

[0012] The injection pipeline phase change suppression system is respectively connected to the secondary boosting unit or the tertiary boosting unit to control the inlet temperature of the submarine injection pipeline;

[0013] At the initial stage of CO2 injection, a first-stage booster unit is connected to the CO2 injection port of the offshore platform. The outlet of the first-stage booster unit is connected to a mobile filtration system. The CO2 treated by the mobile filtration system is injected into the deepwater storage area through a submarine pipeline.

[0014] In the middle stage of carbon dioxide injection, a secondary boosting unit is connected to the primary boosting unit, the injection pipeline phase change suppression system is connected to the boosting outlet end of the secondary boosting unit, and the carbon dioxide pressurized by the primary and secondary boosting units is injected into the deepwater storage area through a submarine pipeline;

[0015] In the later stage of carbon dioxide injection, a three-stage boosting unit is set up to be connected to the two-stage boosting unit, and the injection pipeline phase change suppression system is connected to the boosting outlet end of the three-stage boosting unit. The carbon dioxide pressurized by the one-stage boosting unit, the two-stage boosting unit and the three-stage boosting unit is injected into the deepwater storage area through the submarine pipeline.

[0016] The storage and injection system based on offshore platform carbon dioxide capture described in the present invention has the first-stage boosting unit composed of at least one group of boosting air-cooling combinations, each group of boosting air-cooling combinations including a first-stage compressor and a first-stage air cooler connected in sequence. At the initial stage of carbon dioxide injection, the outlet end of the last group of boosting air-cooling combinations in the first-stage boosting unit is connected to a movable filtration system.

[0017] The storage and injection system based on offshore platform carbon dioxide capture described in the present invention, wherein the movable filtration system includes a filter separator, and the filter separator is provided with a filter separator inlet shut-off valve and a filter separator outlet shut-off valve. The filter separator inlet shut-off valve is connected to the first-stage boosting unit via a pipeline provided with a first-stage boosting bypass shut-off valve, and the filter separator outlet shut-off valve is connected to the deepwater storage area via a pipeline.

[0018] The storage and injection system based on offshore platform carbon dioxide capture described in the present invention is characterized in that the filter separator is provided with a filter separator bypass, a filter separator bypass shut-off valve is provided on the filter separator bypass, and a pressure transmitter and a sampling shut-off valve are provided on the pipeline at the outlet end of the filter separator.

[0019] The storage and injection system based on offshore platform carbon dioxide capture described in the present invention has a secondary boosting unit composed of a secondary compressor and a secondary air cooler. The inlet end of the secondary compressor is connected to the primary boosting unit, and the outlet end is connected to the secondary air cooler. The outlet end of the secondary air cooler is connected to the deepwater storage area via a pipeline provided with a secondary boosting bypass shut-off valve.

[0020] The storage and injection system based on offshore platform carbon dioxide capture described in the present invention, wherein the injection pipeline phase change suppression system is connected to the two ports of the secondary air cooler to form its bypass, and the injection pipeline phase change suppression system includes a first shut-off valve of the air cooler bypass branch line, an air cooler bypass shut-off valve, a bypass regulating valve, a second shut-off valve of the air cooler bypass branch line and an air cooler downstream temperature transmitter connected in sequence, the first shut-off valve of the air cooler bypass branch line and the second shut-off valve of the air cooler bypass branch line are respectively arranged upstream and downstream of the secondary air cooler, and are used to connect the air cooler bypass shut-off valve and the bypass regulating valve.

[0021] The storage and injection system based on offshore platform carbon dioxide capture described in the present invention has a three-stage boosting unit composed of at least one group of boosting air-cooling combinations, each group of boosting air-cooling combinations includes a three-stage compressor and a three-stage air cooler connected in sequence, the inlet end of the first group of boosting air-cooling combinations in the three-stage boosting unit is connected to the second-stage boosting unit, and the outlet end of the last group of boosting air-cooling combinations is connected to the deep-water storage area via a pipeline provided with a three-stage boosting bypass shut-off valve.

[0022] The storage and injection system based on offshore platform carbon dioxide capture described in the present invention, wherein the injection pipeline phase change suppression system is connected to the two ports of the three-stage air cooler of the last group of boosted air cooling combination in the three-stage boosting unit to form its bypass, and the injection pipeline phase change suppression system includes a first shut-off valve of the air cooler bypass branch line, an air cooler bypass shut-off valve, a bypass regulating valve, a second shut-off valve of the air cooler bypass branch line and an air cooler downstream temperature transmitter connected in sequence, the first shut-off valve of the air cooler bypass branch line and the second shut-off valve of the air cooler bypass branch line are respectively arranged upstream and downstream of the secondary air cooler, and are used to connect the air cooler bypass shut-off valve and the bypass regulating valve.

[0023] An injection method using a storage injection system based on offshore platform carbon dioxide capture, characterized by specifically comprising the following methods:

[0024] Step 1: At the initial stage of CO2 injection, a first-stage compressor and a first-stage air cooler are deployed to perform a first-stage pressurization on the CO2 captured from the offshore platform, so that the pressurized gaseous CO2 meets the pressure requirements for reinjection. The pressurized medium enters the bypass pipeline or is introduced into the mobile filtration system through the first-stage boosting bypass shut-off valve. The CO2 pressurized by the first-stage boosting unit is injected into the deepwater storage area through the submarine pipeline.

[0025] Step 2: During the mid-stage of CO2 injection, a secondary compressor and a secondary air cooler are added, the primary boost bypass shutoff valve and the movable filtration system are closed, the secondary boost bypass shutoff valve is opened, and the injection pipeline phase change suppression system is activated to increase the discharge temperature of the pressurized medium and ensure that the medium remains in the gas phase before flowing to the injection wellhead. The CO2 pressurized by the primary and secondary boosting units is injected into the deepwater storage area through a submarine pipeline.

[0026] Step 3: In the later stage of carbon dioxide injection, a three-stage compressor and a three-stage air cooler are added, the second-stage boost bypass shut-off valve is closed, the third-stage boost bypass shut-off valve is opened, the injection pipeline phase change suppression system of the second-stage boost unit is transferred to the third-stage boost unit, and the injection pipeline phase change suppression system is opened; the carbon dioxide pressurized by the first-stage boost unit, the second-stage boost unit and the third-stage boost unit is injected into the deepwater storage area through the submarine pipeline.

[0027] The storage and injection method based on offshore platform carbon dioxide capture described in the present invention comprises the following steps: in the first step, at the initial injection stage, the medium pressure is low and the flow rate in the reinjection pipeline is high; the filter separator bypass shut-off valve is closed, and the medium after the primary pressurization is introduced into the movable filter system to remove impurities carried in the pressurized medium and reduce erosion of the downstream reinjection pipeline; the sampling shut-off valve is periodically opened to perform impurity detection on the medium after the secondary filtration; when the reinjection volume is small, the filter separator bypass shut-off valve can be opened and the movable filter system can be closed to reduce the additional compression caused by the medium passing through the filter separator; at the end of the primary air cooler, a pressure regulating valve is provided to stabilize the compressor outlet pressure; the valve inlet pressure of the pressure regulating valve is automatically set and adjusted according to the amplitude of 0.1 MPag, and the pressure difference between the valve inlet and outlet does not exceed 0.1 MPag;

[0028] In the steps 2 and 3, the specific method for opening the injection pipeline phase change suppression system is as follows: opening the first shut-off valve of the air cooler bypass branch line, the air cooler bypass shut-off valve, the bypass regulating valve and the second shut-off valve of the air cooler bypass branch line, and appropriately increasing the medium flow across the secondary or tertiary air cooler after the secondary or tertiary pressurization by adjusting the opening of the bypass regulating valve, increasing the discharge temperature of the pressurized medium, and ensuring that the medium flowing to the injection wellhead remains in the gas phase; at the end of the secondary air cooler, a pressure regulating valve is provided to stabilize the compressor outlet pressure in stages, and the valve inlet pressure of the pressure regulating valve is automatically set and adjusted in an amplitude of 0.1 MPag, and the pressure difference between the valve inlet and outlet does not exceed 0.1 MPag; at the same time, the outlet medium of the first-stage compressor bypasses the regulating valve at the outlet of the first-stage compressor;

[0029] In step three, a pressure regulating valve is provided at the end of the three-stage air cooler to stabilize the compressor outlet pressure. The inlet pressure of the pressure regulating valve is automatically set and adjusted in increments of 0.1 MPag, and the pressure difference between the inlet and outlet of the valve does not exceed 0.1 MPag. At the same time, the outlet medium of the first-stage compressor and the second-stage compressor bypasses the corresponding regulating valve.

[0030] Compared with the existing technology, the positive effects of the present invention are: based on the boundary conditions and reinjection process characteristics of marine carbon dioxide storage, the present invention targets the characteristics of marine geological storage such as long injection time, high medium inventory, large range of boundary pressure variation, and relatively stable injection flow. From the perspectives of rationally configuring boosting facilities, overcoming the high medium flow rate in the initial injection stage, and compensating for the large temperature drop of marine pipeline flow during mid-term injection, it provides a guarantee for the efficient and safe storage and injection of carbon dioxide in marine geology, and provides a reference and reference for the subsequent large-scale marine storage of carbon dioxide.

[0031] Specifically:

[0032] (1) Scientific setting

[0033] The present invention focuses on the capture and injection rules of supercritical carbon dioxide marine geological storage, compares the operating mode of conventional natural gas geological storage, and proposes an injection mode with a long period, stable flow, and step-by-step increase in reinjection pressure using a multi-stage boosting system, thereby achieving efficient configuration and utilization of reinjection equipment; in view of the relatively stable characteristics of capture and reinjection volumes, the early injection stage has a low medium pressure, resulting in an extremely fast flow rate in the reinjection submarine pipeline, and thus proposes the provision of a movable filtration system for secondary filtration of the reinjection medium after pressure regulation, thereby further reducing the impurity content in the medium and slowing down the impact of the submarine pipeline system. Corrosion; In view of the problems of relatively high reinjection pressure, relatively low ocean pipeline temperature, and increasing pressure of deepwater reinjection riser with increasing depth in the mid-injection stage, in order to avoid flow phase change in the ocean pipeline during this stage, it is proposed to set up an injection pipeline phase change suppression system to adjust and control the temperature of the injection medium in this stage. By appropriately increasing the pressure of the medium entering the reinjection pipeline or riser, the liquefaction of the gas phase medium caused by excessive temperature drop during flow in the reinjection pipeline or riser can be avoided. The hydraulic curve can also be kept away from the critical temperature, so that the gas phase can transition smoothly to the supercritical phase, ensuring the phase stability of the flow process.

[0034] (2) Good economic efficiency

[0035] This system utilizes a connectable multi-stage boosting system, effectively optimizing the one-time investment in boosting equipment and increasing equipment utilization. A removable filtration system effectively reduces the risk of erosion in submarine pipelines at high flow rates, replacing the previous solution of installing a secondary pipeline (i.e., a second parallel submarine pipeline) to reduce pipeline transmission loads. By fully utilizing the thermal energy from boosting, the temperature of the medium injected into the pipeline is properly controlled, avoiding phase changes in the marine pipeline system. Therefore, this system offers excellent economic benefits.

[0036] (3) Promoting technological development

[0037] The solution proposed by this system plays an important role in engineering guidance and reference. The proposed key process system configurations such as the connectable multi-stage boosting system, movable filtration system and injection pipeline phase change suppression system meet key technical requirements and promote the development of technical concepts and technological progress in this field. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be described by way of specific embodiments with reference to the accompanying drawings, in which

[0039] Figure 1 It is a structural schematic diagram of the present invention.

[0040] Markings in the figure: 1 is the first-stage compressor, 2 is the first-stage air cooler, 3 is the second-stage compressor, 4 is the second-stage air cooler, 5 is the third-stage compressor, 6 is the third-stage air cooler, 7 is the first-stage boost bypass shut-off valve, 8 is the bypass temperature transmitter, 9 is the bypass pressure transmitter, 10 is the filter separator bypass shut-off valve, 11 is the second-stage boost bypass shut-off valve, 12 is the third-stage boost bypass shut-off valve, 21 is the first shut-off valve of the air cooler bypass branch line, 22 is the air cooler bypass shut-off valve, 23 is the bypass regulating valve, 24 is the second shut-off valve of the air cooler bypass branch line, 25 is the air cooler downstream temperature transmitter, 31 is the filter separator inlet shut-off valve, 32 is the filter separator, 33 is the filter separator outlet shut-off valve, 34 is the pressure transmitter, and 35 is the sampling shut-off valve. DETAILED DESCRIPTION

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0042] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0043] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0044] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0045] In the description of the embodiments of the present invention, it should be noted that the indicated orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the inventive product is typically placed when in use, or the orientations or positional relationships commonly understood by those skilled in the art, or the orientations or positional relationships in which the inventive product is typically placed when in use. These are merely for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as limiting the present invention. In addition, the terms "first" and "second" are used only to distinguish descriptions and should not be understood as indicating or implying relative importance.

[0046] In describing the embodiments of the present invention, it should be noted that, unless otherwise specified or limited, the terms "disposed" and "connected" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to direct connections or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0047] like Figure 1 As shown, a storage and injection system based on offshore platform carbon dioxide capture includes a connectable multi-stage boosting system, a movable filtration system and an injection pipeline phase change suppression system. The connectable multi-stage boosting system includes a first-stage boosting unit set at the initial stage of carbon dioxide injection, a second-stage boosting unit set at the middle stage of carbon dioxide injection, and a third-stage boosting unit set at the late stage of carbon dioxide injection, which are used to implement boosting operations at different injection stages.

[0048] Among them, the first-stage boosting unit is composed of at least one group of boosting air cooling combination, each group of boosting air cooling combination includes a first-stage compressor 1 and a first-stage air cooler 2 connected in sequence, the second-stage boosting unit is composed of a second-stage compressor 3 and a second-stage air cooler 4 connected in sequence, and the third-stage boosting unit is composed of at least one group of boosting air cooling combination, each group of boosting air cooling combination includes a third-stage compressor 5 and a third-stage air cooler 6 connected in sequence.

[0049] Specifically, the first-stage compressor 1, the second-stage compressor 3, and the third-stage compressor 5 are preferably reciprocating compressors, which provide the reinjection pressure required for the initial, mid-term, and late injection, respectively. A pressure regulating valve is provided downstream of the compressor and is automatically controlled to periodically stabilize the compressor outlet pressure. The pressure upstream of the pressure regulating valve is adjusted in increments of 0.1 MPa, and the pressure difference between the upstream and downstream pressures does not exceed 0.1 MPa. The pressure regulating valve is provided downstream of the corresponding air cooler. The first-stage air cooler 2, the second-stage air cooler 4, and the third-stage air cooler 6 are preferably water-cooled air coolers that can directly utilize seawater for heat exchange to fully improve the compression efficiency of each stage. The compressors and air coolers at each stage are installed in a modular splicing mode and are deployed in stages according to the pressure of the sealing target. Preferably, the discharge pressure of the first-stage compressor 1 is less than 4 MPa.g, the discharge pressure of the second-stage compressor 3 is less than 8 MPa.g, and the discharge pressure of the third-stage compressor 5 is less than 12 MPa.g. In this example, only the three-stage boosting mode is proposed for illustration, and the number of stages can be adjusted according to the actual conditions of reinjection and sealing.

[0050] The removable filtration system is connected to a primary boosting unit, which is used to perform secondary solid and liquid phase capture and filtration on the pressurized medium during the initial injection phase. During the initial CO2 injection phase, a primary boosting unit is connected to the CO2 injection port on the offshore platform. The outlet of the primary boosting unit is connected to the removable filtration system. The treated CO2 is then injected into the deepwater storage area via a submarine pipeline, ensuring the purity of the medium entering the downstream area and addressing erosion issues caused by high medium flow rates during the initial low-pressure injection phase of the pipeline.

[0051] Specifically, the movable filtration system includes a filter separator 32, which is preferably a horizontal filter separator with a filtration accuracy of not more than 10 μm. The filter separator 32 is provided with a filter separator inlet shut-off valve 31 and a filter separator outlet shut-off valve 33. The filter separator inlet shut-off valve 31 is an electric ball valve, which is only used in the initial injection stage and is used to connect the pressurized gas when the first-stage boosting unit is running alone with the filter separator 32. The filter separator outlet shut-off valve 33 is an electric ball valve, which is only used in the initial injection stage. The filter separator inlet shut-off valve 31 is connected to the first-stage boosting unit through a pipeline provided with a first-stage boosting bypass shut-off valve 7. The first-stage boosting bypass shut-off valve 7 is an electric ball valve, which is normally open and is provided in the bypass downstream of the first-stage boosting unit. It is opened when only the first-stage boosting unit is in use. The filter separator outlet shut-off valve 33 is opened through a pipe. The pipeline is connected to the deep-water storage area, and a bypass temperature transmitter 8 and a bypass pressure transmitter 9 are provided on the pipeline for real-time monitoring of the temperature and pressure of the medium entering the downstream injection pipeline. The filter separator 32 is provided with a filter separator bypass, and a filter separator bypass shut-off valve 10 is provided on the filter separator bypass. The filter separator bypass shut-off valve 10 is an electric ball valve, which is normally closed in the initial stage and opened after the subsequent boosting unit is put into use. A pressure transmitter 34 and a sampling shut-off valve 35 are provided on the pipeline at the outlet end of the filter separator 32. The pressure transmitter 34 is used to monitor the downstream pressure of the filter separator 32 in real time, and form a pressure loss monitoring with the pressure transmitter of the first-stage boosting unit to evaluate the operation effect of the filter separator. The sampling shut-off valve 35 is arranged downstream of the pressure transmitter 34 to provide a channel for periodic sampling monitoring to directly evaluate the purity of the medium after the first-stage boosting.

[0052] In the middle stage of carbon dioxide injection, a secondary boosting unit is set up to be connected to the primary boosting unit, and the injection pipeline phase change suppression system is connected to the boosting outlet end of the secondary boosting unit to control the inlet temperature of the submarine injection pipeline. The carbon dioxide pressurized by the primary boosting unit and the secondary boosting unit is injected into the deepwater storage area through the submarine pipeline.

[0053] Among them, the secondary boosting unit is composed of a secondary compressor 3 and a secondary air cooler 4. The inlet end of the secondary compressor 3 is connected to the primary boosting unit, and its outlet end is connected to the secondary air cooler 4. The outlet end of the secondary air cooler 4 is connected to the deepwater storage area through a pipeline provided with a secondary boosting bypass shut-off valve 11. The secondary boosting bypass shut-off valve 11 is set in the bypass downstream of the secondary boosting unit and is opened when only the primary boosting unit and the secondary boosting unit are put into use. By reasonably controlling the inlet temperature of the submarine injection pipeline, the medium liquefaction in the submarine pipeline during the medium-pressure injection process is avoided, which affects the flow stability and safety of the injected medium.

[0054] Specifically, the injection pipeline phase change suppression system is connected to the two ports of the secondary air cooler 4 to form its bypass. The injection pipeline phase change suppression system includes a first shut-off valve 21 of the air cooler bypass branch line, an air cooler bypass shut-off valve 22, a bypass regulating valve 23, a second shut-off valve 24 of the air cooler bypass branch line and an air cooler downstream temperature transmitter 25 connected in sequence. The first shut-off valve 21 of the air cooler bypass branch line and the second shut-off valve 24 of the air cooler bypass branch line are respectively arranged upstream and downstream of the secondary air cooler 4, and are used to connect the air cooler bypass shut-off valve 22 and the bypass regulating valve 23. When it is predicted that a phase change of the medium may occur in the reinjection pipeline, that is, gas phase liquefaction, the opening of the air cooler shutter and the bypass regulating valve 23 are automatically adjusted. Through the air cooler's own heat dissipation control and bypass control, the medium temperature at the air cooler outlet is increased, and the temperature in the reinjection pipeline is maintained above the dew point temperature to avoid carbon dioxide liquefaction in the reinjection pipeline.

[0055] In the later stage of carbon dioxide injection, a three-stage boosting unit is set up to be connected to the two-stage boosting unit, and the injection pipeline phase change suppression system is connected to the boosting outlet end of the three-stage boosting unit to control the inlet temperature of the submarine injection pipeline. The carbon dioxide pressurized by the first-stage boosting unit, the second-stage boosting unit and the third-stage boosting unit is injected into the deep-water storage area through the submarine pipeline.

[0056] Among them, the three-stage boosting unit is composed of at least one group of boosting air-cooling combination, each group of boosting air-cooling combination includes a three-stage compressor 5 and a three-stage air cooler 6 connected in sequence, the inlet end of the first group of boosting air-cooling combination in the three-stage boosting unit is connected to the second-stage boosting unit, and the outlet end of the last group of boosting air-cooling combination is connected to the deep-water storage area through a pipeline provided with a three-stage boosting bypass shut-off valve 12. The three-stage boosting bypass shut-off valve 12 is set in the bypass downstream of the three-stage boosting unit and is opened when the first-stage boosting unit and the second-stage boosting unit are put into use.

[0057] Specifically, in order to avoid large flow parameter conversions during supercritical transportation, an interface for air cooler bypass temperature adjustment is also reserved in the three-stage boosting unit. After the three-stage boosting unit is put into use, the injection pipeline phase change suppression system in the second-stage boosting unit can be dismantled and transferred and installed, and the injection pipeline phase change suppression system is connected to the two ports of the three-stage air cooler 6 of the last group of boosted air cooling combination in the three-stage boosting unit to form its bypass.

[0058] The working principle of the present invention is:

[0059] (1) Offshore oil and gas field production is one of the sources of carbon dioxide. Capturing carbon dioxide in offshore production facilities supports the efficient implementation of carbon dioxide marine storage, which can achieve on-site carbon dioxide emission reduction and storage. The scenario of the present invention is to implement marine storage after the tail gas carbon dioxide is captured by the offshore oil and gas central processing platform. The carbon dioxide captured from the offshore central processing platform has the characteristic of low pressure and needs to be pressurized before continuous injection into the nearby seabed storage area. Furthermore, the pressure of the storage area is affected by the injection volume and gradually increases with the injection time. This is significantly different from the currently widely implemented carbon dioxide flooding.

[0060] (2) Due to the long injection time and slow growth of the sealing pressure, the reinjection compressor was configured in a phased manner to significantly reduce the one-time investment and operating energy consumption. In the initial injection phase, the medium in the pipeline is in the gas phase, and due to the low pressure, the flow rate is fast. Therefore, a filter separator is installed at the outlet of the first-stage booster unit to minimize the risk of erosion in the injection pipeline.

[0061] (3) In the middle stage of reinjection, due to the increase in compressor outlet pressure and the influence of elevation, the flow pressure of the reinjection pipeline increases with the increase of water depth. In addition, the deep water environment temperature is low. Under the combined influence, the medium is very likely to liquefy in the injection pipeline, resulting in insufficient flow stability. Therefore, the high temperature that can be used after the secondary boosting unit is used to adjust the inlet medium temperature of the reinjection pipeline after the secondary boosting to ensure that the medium in the reinjection pipeline before the reinjection well is in the gas phase or supercritical phase. Furthermore, since the air cooler has a certain amount of natural heat dissipation, an air cooler regulation bypass is set up to allow part of the high-temperature medium to directly cross the air cooler to further improve the utilization rate of the compressor outlet heat energy.

[0062] (4) In the later stage of reinjection, due to the high outlet pressure of the compressor, carbon dioxide is basically in a supercritical state. As mentioned above, due to the influence of the marine environment, a certain temperature drop may occur in the injection pipeline. Although it will not cause a sudden change in phase state, it may still cause the medium density to increase significantly when the terminal temperature is low, affecting the flow stability. Therefore, an injection pipeline phase change suppression system similar to the second-stage boosting unit is set in the third-stage boosting unit. When implementing the later injection, the system can be moved to the third-stage boosting unit to ensure flow stability.

[0063] The present invention also discloses a storage and injection method based on carbon dioxide capture on an offshore platform. Generally speaking, low-pressure carbon dioxide captured from onshore is transported to the injection platform where the system is located via a submarine pipeline. During the injection stage, since the initial pressure of the target storage site is relatively low, the storage pressure tends to increase continuously. Therefore, it is considered to configure a multi-stage boosting system, and the boosting system at each level is configured in a timely manner according to the time when the outlet pressure of the reinjection is reached, which has the effect of reducing one-time investment and avoiding energy waste. Furthermore, each level of the boosting system is equipped with an outlet pressure regulating function to avoid the secondary pressure reduction of the pressurized carbon dioxide at the injection well as much as possible.

[0064] The specific injection method is:

[0065] Step 1: At the initial stage of carbon dioxide injection, a first-stage compressor 1 and a first-stage air cooler 2 are configured, and the pressurized gaseous carbon dioxide can meet the pressure requirements of reinjection; further, the medium after the first stage of pressurization enters the bypass pipeline through the first-stage pressurization bypass shut-off valve 7. The bypass pipeline is used to collect the pressurized medium of each injection period, which is convenient for the connection of the pressurization system added in each stage later; since the downstream pipeline of the reinjection platform is designed according to the full-cycle reinjection working condition, the flow rate in the reinjection pipeline may be high due to the low medium pressure at the initial stage of injection, so the filter separator bypass shut-off valve 10 is closed, and the medium after the first stage of pressurization is introduced into the movable filter system. The filtering function of the system is used to further remove impurities that may be carried in the pressurized medium, greatly reducing the erosion risk of the downstream reinjection pipeline; the sampling shut-off valve 35 is periodically opened to detect impurities in the medium after secondary filtration; when the reinjection volume is small, the filter separator bypass shut-off valve 10 can be opened to close the movable filter system to reduce the additional compression caused by the medium passing through the filter separator 32 and optimize the system energy consumption. Furthermore, a pressure regulating valve is provided at the end of the first-stage air cooler to stabilize the compressor outlet pressure. The inlet pressure of the pressure regulating valve is automatically set and adjusted in increments of 0.1 MPag, and the pressure difference between the inlet and outlet of the valve does not exceed 0.1 MPag, thereby ensuring that the compressor outlet pressure remains stable for a relatively long time.

[0066] Step 2: In the middle stage of carbon dioxide injection, a secondary compressor 3 and a secondary air cooler 4 are added, the primary boost bypass shutoff valve 7 and the movable filter system are closed, and the secondary boost bypass shutoff valve 11 is opened. In the middle stage of injection, due to the high pressure of the medium entering the pipeline, and during the flow of the marine riser, the pressure at the bottom of the riser is higher due to the effect of the high static pressure difference, and because the temperature of the deep-water marine environment is generally low, it is very likely that the medium will liquefy due to the pressure increase and temperature decrease in the middle and rear sections of the riser. Therefore, the injection pipeline phase change suppression system is opened. Specifically, the first shutoff valve 21 of the air cooler bypass branch, the air cooler bypass shutoff valve 22, the bypass regulating valve 23 and the second shutoff valve 24 of the air cooler bypass branch are opened. By adjusting the opening of the bypass regulating valve 23, the medium flow across the secondary air cooler 4 after the secondary boost is appropriately increased, and the discharge temperature of the boosted medium is comprehensively increased to ensure that the medium flowing to the injection wellhead remains in the gas phase. Furthermore, a pressure regulating valve is provided at the end of the secondary air cooler to periodically stabilize the compressor outlet pressure. Preferably, the inlet pressure of the pressure regulating valve is automatically set and adjusted in increments of 0.1 MPag, and the pressure difference between the inlet and outlet of the valve does not exceed 0.1 MPag, thereby ensuring that the compressor outlet pressure is stable for a relatively long time. At the same time, the outlet medium of the first-stage compressor bypasses the regulating valve at the outlet of the first-stage compressor.

[0067] Step 3: In the later stages of CO2 injection, a third-stage compressor 5 and a third-stage air cooler 6 are added, the second-stage boost bypass shutoff valve 11 is closed, and the third-stage boost bypass shutoff valve 12 is opened. In the later stages of injection, because the pressure of the medium entering the pipeline approaches or has already exceeded the critical pressure, the medium pressure at the depth of the middle and rear sections of the riser is higher than the critical pressure of CO2. Because the density change of the medium from the gas phase to the supercritical phase is relatively gradual when the temperature is above the critical temperature, the flow temperature of the medium at the system outlet is appropriately considered, that is, to ensure that the medium flowing to the injection wellhead remains in the high-temperature supercritical phase. To this end, the injection pipeline phase change suppression system of the second-stage boosting unit is transferred to the third-stage boosting unit, and the operation process is the same as in Step 3. Furthermore, a pressure regulating valve is provided at the end of the three-stage air cooler to stabilize the compressor outlet pressure. The inlet pressure of the pressure regulating valve is automatically set and adjusted in increments of 0.1 MPag, and the pressure difference between the inlet and outlet of the valve does not exceed 0.1 MPag, thereby ensuring that the compressor outlet pressure remains stable for a relatively long time. At the same time, the outlet medium of the first-stage compressor and the second-stage compressor bypasses the corresponding regulating valve.

[0068] It should be noted that this embodiment only uses three-stage pressurization as a typical system and method. The actual reinjection pressure is affected by specific underlying conditions and can be appropriately expanded based on this system.

[0069] The present invention is not limited to the foregoing specific embodiments, and the present invention extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A storage and injection system based on offshore platform carbon dioxide capture, characterized by: Includes connectable multi-stage boosting system, movable filtration system and injection pipeline phase change suppression system; The connectable multi-stage boosting system includes a first-stage boosting unit provided at the initial stage of carbon dioxide injection, a second-stage boosting unit provided at the middle stage of carbon dioxide injection, and a third-stage boosting unit provided at the late stage of carbon dioxide injection, for implementing boosting operations at different injection stages; The movable filtration system is connected to the primary pressurizing unit and is used to perform secondary solid and liquid phase capture and filtration on the pressurized medium during the initial injection stage; The injection pipeline phase change suppression system is respectively connected to the secondary boosting unit or the tertiary boosting unit to control the inlet temperature of the submarine injection pipeline; At the initial stage of CO2 injection, a first-stage booster unit is connected to the CO2 injection port of the offshore platform. The outlet of the first-stage booster unit is connected to a mobile filtration system. The CO2 treated by the mobile filtration system is injected into the deepwater storage area through a submarine pipeline. In the middle stage of carbon dioxide injection, a secondary boosting unit is connected to the primary boosting unit, the injection pipeline phase change suppression system is connected to the boosting outlet end of the secondary boosting unit, and the carbon dioxide pressurized by the primary and secondary boosting units is injected into the deepwater storage area through a submarine pipeline; In the later stage of carbon dioxide injection, a three-stage boosting unit is set up to be connected to the two-stage boosting unit, and the injection pipeline phase change suppression system is connected to the boosting outlet end of the three-stage boosting unit. The carbon dioxide pressurized by the one-stage boosting unit, the two-stage boosting unit and the three-stage boosting unit is injected into the deepwater storage area through the submarine pipeline.

2. The offshore platform carbon dioxide capture and storage injection system according to claim 1, characterized in that: The first-stage boosting unit is composed of at least one group of boosting air cooling combinations, each group of boosting air cooling combinations includes a first-stage compressor (1) and a first-stage air cooler (2) connected in sequence, and at the initial stage of carbon dioxide injection, the outlet end of the last group of boosting air cooling combinations in the first-stage boosting unit is connected to the movable filter system.

3. The offshore platform carbon dioxide capture and storage injection system according to claim 2, characterized in that: The movable filtration system comprises a filter separator (32), the filter separator (32) being provided with a filter separator inlet shut-off valve (31) and a filter separator outlet shut-off valve (33), the filter separator inlet shut-off valve (31) being connected to a first-stage boosting unit via a pipeline provided with a first-stage boosting bypass shut-off valve (7), and the filter separator outlet shut-off valve (33) being connected to a deepwater storage area via a pipeline.

4. The offshore platform carbon dioxide capture and storage injection system according to claim 3, characterized in that: The filter separator (32) is provided with a filter separator bypass, a filter separator bypass cutoff valve (10) is provided on the filter separator bypass, and a pressure transmitter (34) and a sampling cutoff valve (35) are provided on the pipeline at the outlet end of the filter separator (32).

5. The offshore platform carbon dioxide capture and storage injection system according to claim 1, characterized in that: The secondary boosting unit is composed of a secondary compressor (3) and a secondary air cooler (4); the inlet end of the secondary compressor (3) is connected to the primary boosting unit, and the outlet end thereof is connected to the secondary air cooler (4); the outlet end of the secondary air cooler (4) is connected to the deep water storage area via a pipeline provided with a secondary boosting bypass shut-off valve (11).

6. The offshore platform carbon dioxide capture and storage injection system according to claim 5, characterized in that: The injection pipeline phase change suppression system is connected to the two ports of the secondary air cooler (4) to form a bypass thereof. The injection pipeline phase change suppression system comprises a first shut-off valve (21) of the air cooler bypass branch line, an air cooler bypass shut-off valve (22), a bypass regulating valve (23), a second shut-off valve (24) of the air cooler bypass branch line, and an air cooler downstream temperature transmitter (25) connected in sequence. The first shut-off valve (21) of the air cooler bypass branch line and the second shut-off valve (24) of the air cooler bypass branch line are respectively arranged upstream and downstream of the secondary air cooler (4), and are used to connect the air cooler bypass shut-off valve (22) and the bypass regulating valve (23).

7. The offshore platform carbon dioxide capture and storage injection system according to claim 1, characterized in that: The three-stage boosting unit is composed of at least one group of boosting air cooling combination, each group of boosting air cooling combination includes a three-stage compressor (5) and a three-stage air cooler (6) connected in sequence, the inlet end of the first group of boosting air cooling combination in the three-stage boosting unit is connected to the second-stage boosting unit, and the outlet end of the last group of boosting air cooling combination is connected to the deep water storage area through a pipeline provided with a three-stage boosting bypass shut-off valve (12).

8. The offshore platform carbon dioxide capture and storage injection system according to claim 7, characterized in that: The injection pipeline phase change suppression system is connected to the two ports of the third-stage air cooler (6) of the last group of boost air cooling combination in the three-stage boost unit to form its bypass. The injection pipeline phase change suppression system includes a first shut-off valve (21) of the air cooler bypass branch line, an air cooler bypass shut-off valve (22), a bypass regulating valve (23), a second shut-off valve (24) of the air cooler bypass branch line, and an air cooler downstream temperature transmitter (25) connected in sequence. The first shut-off valve (21) of the air cooler bypass branch line and the second shut-off valve (24) of the air cooler bypass branch line are respectively arranged upstream and downstream of the secondary air cooler (4), and are used to connect the air cooler bypass shut-off valve (22) and the bypass regulating valve (23).

9. An injection method using the offshore platform carbon dioxide capture and storage injection system according to any one of claims 1 to 8, characterized in that: Specifically, the following methods are included: Step 1: At the initial stage of CO2 injection, a first-stage compressor and a first-stage air cooler are deployed to perform a first-stage pressurization on the CO2 captured from the offshore platform, so that the pressurized gaseous CO2 meets the pressure requirements for reinjection. The pressurized medium enters the bypass pipeline or is introduced into the mobile filtration system through the first-stage boosting bypass shut-off valve. The CO2 pressurized by the first-stage boosting unit is injected into the deepwater storage area through the submarine pipeline. Step 2: During the mid-stage of CO2 injection, a secondary compressor and a secondary air cooler are added, the primary boost bypass shutoff valve and the movable filtration system are closed, the secondary boost bypass shutoff valve is opened, and the injection pipeline phase change suppression system is activated to increase the discharge temperature of the pressurized medium and ensure that the medium remains in the gas phase before flowing to the injection wellhead. The CO2 pressurized by the primary and secondary boosting units is injected into the deepwater storage area through a submarine pipeline. Step 3: In the later stage of carbon dioxide injection, a three-stage compressor and a three-stage air cooler are added, the second-stage boost bypass shut-off valve is closed, the third-stage boost bypass shut-off valve is opened, the injection pipeline phase change suppression system of the second-stage boost unit is transferred to the third-stage boost unit, and the injection pipeline phase change suppression system is opened; the carbon dioxide pressurized by the first-stage boost unit, the second-stage boost unit and the third-stage boost unit is injected into the deepwater storage area through the submarine pipeline.

10. The method for storage and injection of carbon dioxide captured on an offshore platform according to claim 9, characterized in that: In the step 1, at the initial stage of injection, the medium pressure is low and the flow rate in the reinjection pipeline is high. The filter separator bypass shut-off valve is closed, and the medium after the first stage of pressurization is introduced into the movable filter system to remove impurities carried in the pressurized medium and reduce the erosion of the downstream reinjection pipeline; the sampling shut-off valve is opened periodically to detect impurities in the medium after the secondary filtration; when the reinjection volume is small, the filter separator bypass shut-off valve can be opened and the movable filter system can be closed to reduce the additional compression caused by the medium passing through the filter separator; at the end of the first stage air cooler, a pressure regulating valve is set to stabilize the compressor outlet pressure, and the valve inlet pressure of the pressure regulating valve is automatically set and adjusted according to the range of 0.1 MPag, and the pressure difference between the valve inlet and outlet does not exceed 0.1 MPag; In the steps 2 and 3, the specific method for opening the injection pipeline phase change suppression system is as follows: opening the first shut-off valve of the air cooler bypass branch line, the air cooler bypass shut-off valve, the bypass regulating valve and the second shut-off valve of the air cooler bypass branch line, and appropriately increasing the medium flow across the secondary or tertiary air cooler after the secondary or tertiary pressurization by adjusting the opening of the bypass regulating valve, increasing the discharge temperature of the pressurized medium, and ensuring that the medium flowing to the injection wellhead remains in the gas phase; at the end of the secondary air cooler, a pressure regulating valve is provided to stabilize the compressor outlet pressure in stages, and the valve inlet pressure of the pressure regulating valve is automatically set and adjusted in an amplitude of 0.1 MPag, and the pressure difference between the valve inlet and outlet does not exceed 0.1 MPag; at the same time, the outlet medium of the first-stage compressor bypasses the regulating valve at the outlet of the first-stage compressor; In step three, a pressure regulating valve is provided at the end of the three-stage air cooler to stabilize the compressor outlet pressure. The inlet pressure of the pressure regulating valve is automatically set and adjusted in increments of 0.1 MPag, and the pressure difference between the inlet and outlet of the valve does not exceed 0.1 MPag. At the same time, the outlet medium of the first-stage compressor and the second-stage compressor bypasses the corresponding regulating valve.

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