Liquid-state recovery system for offshore oilfield associated gas with high carbon dioxide content and operation method of liquid-state recovery system

Abstract

The invention relates to a liquid recovery system for offshore oilfield associated gas with high carbon dioxide content. The liquid recovery system comprises a desulfurization tank, a converter, a synthesis gas compressor, a methanol synthesis unit, a methanol rectification unit, a synthesis gas recovery unit, a purge gas recovery unit and a CO2 compressor, the offshore associated gas is treated by the desulfurization tank, converged with an outlet of the CO2 compressor and introduced into the reformer; the converter is connected with the methanol synthesis unit through a synthesis gas compressor; a liquid phase outlet of the methanol synthesis unit is connected with the methanol rectification unit, a first purge gas outlet is connected with the purge gas recovery unit, and a second purge gas outlet is connected with a fuel gas inlet of the converter; a first purge gas outlet of the methanol rectification unit is connected with the methanol synthesis unit, and a second purge gas outlet of the methanol rectification unit is connected with the purge gas recovery unit; the outlet of the converter is connected with the outlet of the purge gas recovery unit and is connected with the inlet of the CO2 compressor. According to the invention, liquid in the offshore oilfield associated gas can be effectively recovered, and the resource utilization rate is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of offshore oilfield development, and in particular relates to a liquid recovery system for associated gas in offshore oilfields with a high carbon dioxide content and an operating method thereof. Background Art

[0002] In recent years, my country's offshore oilfield development has accelerated, with significant increases in oil and gas production. However, the associated gas produced during offshore oilfield production presents numerous challenges.

[0003] Associated gas from offshore oilfields typically contains methane, light hydrocarbons, and high concentrations of carbon dioxide (CO2), with CO2 levels exceeding 15%. Emissions are also dispersed and numerous. Because both hydrocarbons and CO2 are significant greenhouse gases contributing to global warming, reducing CO2-rich associated gas emissions and recovering the hydrocarbons within have become critical challenges in offshore oilfield development.

[0004] Oilfield associated gas, high in CO2, has low calorific value, low pressure, and poor quality. This makes traditional associated gas recovery methods difficult to achieve optimal results when applied to this type of associated gas. Furthermore, the unique offshore environment poses significant challenges to its storage and transportation.

[0005] At present, the conventional offshore associated gas production of CNG (compressed natural gas) and LNG (liquefied natural gas) solutions have obvious drawbacks. In order to meet product standards, a large amount of carbon dioxide in the associated gas needs to be removed and discharged, which not only increases the complexity of the processing flow, but also leads to large amounts of carbon dioxide emissions. In addition, CNG requires high-pressure storage, while LNG requires ultra-low temperature storage. These two storage conditions are extremely unfriendly to the effective operating space utilization of offshore platforms, severely limiting other uses of platform space. In addition, the product is difficult to unload and transport at sea, which can easily lead to a series of chain problems such as large amounts of carbon dioxide emissions in the associated gas recovery process, large land area, and difficulty in product storage and transportation. These problems greatly affect the efficient recovery and utilization of associated gas resources in offshore oil fields and also have potential impacts on the environment. Summary of the Invention

[0006] The present invention aims to address at least one of the technical problems existing in the prior art. To this end, the present invention provides a system and operating method for recovering liquid associated gas from offshore oilfields containing high levels of carbon dioxide. The system is intended to be applicable to the recovery and utilization of associated gas from offshore platforms, the recovery of high levels of carbon dioxide from associated gas, and environmentally friendly emission reduction.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a liquid recovery system for associated gas from offshore oil fields with a high carbon dioxide content, comprising a desulfurization tank, a reformer, a synthesis gas compressor, a methanol synthesis unit, a methanol distillation unit, a synthesis gas CO2 recovery unit, a purge gas CO2 recovery unit, a CO2 compressor, and a methanol storage tank;

[0009] The offshore associated gas is connected to the inlet of the desulfurization tank, the outlet of the desulfurization tank is merged with the outlet of the CO2 compressor, the merged offshore associated gas pipeline is connected to the raw gas inlet of the reformer, and the synthesis gas outlet of the reformer is connected to the inlet of the synthesis gas compressor;

[0010] The outlet of the synthesis gas compressor is connected to the synthesis gas inlet of the methanol synthesis unit, the liquid phase outlet of the methanol synthesis unit is connected to the inlet of the methanol distillation unit, the first purge gas outlet of the methanol synthesis unit is connected to the first purge gas inlet of the purge gas CO2 recovery unit, and the second purge gas outlet of the methanol synthesis unit is connected to the fuel gas inlet of the reformer;

[0011] The liquid phase outlet of the methanol distillation unit is connected to the inlet of the methanol storage tank, the first purge gas outlet of the methanol distillation unit is connected to the purge gas inlet of the methanol synthesis unit, and the second purge gas outlet of the methanol distillation unit is connected to the second purge gas inlet of the purge gas CO2 recovery unit;

[0012] The exhaust port of the reformer is connected to the inlet of the synthesis gas CO2 recovery unit, the outlet of the synthesis gas CO2 recovery unit merges with the outlet of the relaxation gas CO2 recovery unit, and the merged CO2 pipeline is connected to the inlet of the CO2 compressor.

[0013] In a second aspect, the present invention provides a method for operating the high-CO2-containing offshore associated gas liquid recovery system as described in the first aspect of the present invention, comprising the following steps:

[0014] High-CO2 offshore associated gas enters the desulfurization tank, where it is mixed with the recovered pressurized CO2 after impurities are removed and then enters the reformer. In the high-temperature and pressurized environment of the reformer, it undergoes catalytic reforming to produce synthesis gas.

[0015] The synthesis gas enters the synthesis gas compressor for pressurization and then enters the methanol synthesis unit to be produced into crude methanol product under the action of catalyst;

[0016] The crude methanol product enters the methanol distillation unit, where it is separated and purified into refined methanol products. The refined methanol products enter the methanol storage tank, and the unsynthesized synthesis gas enters the methanol synthesis unit for further synthesis.

[0017] The unconverted gas discharged from the reformer enters the synthesis gas CO2 recovery unit, where CO2 is separated by pressure swing adsorption;

[0018] A portion of the purge gas produced by the methanol synthesis unit and the purge gas produced by the methanol distillation unit enter the purge gas CO2 recovery unit, and H2, N2 and CO2 are separated by pressure swing adsorption in the purge gas CO2 recovery unit. H2 and N2 are burned and discharged, while CO2 enters the CO2 compressor together with the CO2 recovered by the synthesis gas CO2 recovery unit for pressurization, and is mixed with the desulfurized raw gas before entering the converter, thereby achieving the carbon replenishment goal of the synthesis gas preparation process; another portion of the purge gas produced by the methanol synthesis unit enters the converter as fuel gas, serving as part of the energy source for the converter.

[0019] Preferably, another part of the energy of the converter comes from offshore wind power / low-carbon shore power.

[0020] Preferably, the operating temperature of the converter is 850° C. and the operating pressure is 2.4 MPa.

[0021] Preferably, the reaction temperature of the methanol synthesis unit is 240°C.

[0022] Preferably, the storage pressure of the methanol storage tank is 0.5 MPa, and the temperature is controlled not higher than 30°C.

[0023] The present invention has the following advantages due to the adoption of the above technical solution:

[0024] 1. The present invention can realize the function of liquid recovery, storage and external transmission of offshore associated gas with high CO2 content. By recovering CO2 from the unsynthesized gas in the converter and the CO2 from the methanol synthesis unit purge gas, high-temperature reforming in the converter can be used to replenish carbon and produce synthesis gas, and liquid refined methanol products can be produced, thereby reducing high-concentration CO2 emissions.

[0025] 2. The present invention adopts offshore wind power, green shore power and other power supply forms and methanol synthesis unit relaxation gas fuel supplement to meet the energy consumption of the offshore associated gas liquid methanol preparation process, effectively solving the problem of offshore associated gas liquid recovery and utilization with high CO2 content and solving the problem of carbon emission reduction in offshore oil fields. It has the characteristics of reasonable design, high integration, energy saving and environmental protection.

[0026] 3. The methanol produced by the present invention is stored in a storage facility at normal temperature and pressure. The physical properties of the product can give full play to the advantages of offshore methanol liquid storage and transportation, realize the integrated functions of production, storage and transportation on offshore movable offshore platforms, greatly reduce the difficulty of offshore storage and external transportation of methanol, and help reduce the flare emissions of associated gas during the development and production of offshore oil and gas fields, solve the carbon emission problem of high-CO2 associated gas, realize the recycling and utilization of hydrocarbon resources, and protect the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. Throughout the drawings, the same reference numerals are used to denote the same components. In the drawings:

[0028] Figure 1 A schematic structural diagram of a liquid recovery system for offshore associated gas containing high levels of carbon dioxide, provided in accordance with one embodiment of the present invention.

[0029] The reference numerals in the figures are as follows:

[0030] 1-Desulfurization tank; 2-Converter; 3-Synthesis gas compressor; 4-Methanol synthesis unit; 5-Methanol distillation unit; 6-Synthesis gas CO2 recovery unit; 7-Purge gas CO2 recovery unit; 8-CO2 compressor; 9-Methanol storage tank. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the present invention more apparent, specific embodiments of the present invention are further described below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means more than two, unless otherwise specifically defined.

[0034] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0035] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0036] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0037] The present invention provides a system for recovering liquid associated gas from offshore oilfields with high carbon dioxide content, comprising a desulfurization tank, a reformer, a synthesis gas compressor, a methanol synthesis unit, a methanol distillation unit, a synthesis gas recovery unit, a purge gas recovery unit, and a CO2 compressor; after the offshore associated gas is processed by the desulfurization tank, it is merged with the CO2 compressor outlet and passed into the reformer; the reformer is connected to the methanol synthesis unit through the synthesis gas compressor; the liquid phase outlet of the methanol synthesis unit is connected to the methanol distillation unit, the first purge gas outlet is connected to the purge gas recovery unit, and the second purge gas outlet is connected to the reformer fuel gas inlet; the first purge gas outlet of the methanol distillation unit is connected to the methanol synthesis unit, and the second purge gas outlet is connected to the purge gas recovery unit; the reformer exhaust port is connected to the synthesis gas recovery unit, and its outlet is merged with the purge gas recovery unit outlet and connected to the CO2 compressor inlet. The present invention can achieve effective recovery of liquid in offshore oilfield associated gas and improve resource utilization.

[0038] Hereinafter, a system for recovering liquid associated gas containing high carbon dioxide content at sea and an operating method thereof provided by an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0039] Example 1

[0040] See also Figure 1 The liquid recovery system for offshore associated gas with a high carbon dioxide content provided in this embodiment includes a desulfurization tank 1, a converter 2, a synthesis gas compressor 3, a methanol synthesis unit 4, a methanol distillation unit 5, a synthesis gas CO2 recovery unit 6, a purge gas CO2 recovery unit 7, a CO2 compressor 8 and a methanol storage tank 9.

[0041] Among them, the offshore associated gas is connected to the inlet of the desulfurization tank 1, the outlet of the desulfurization tank 1 merges with the outlet of the CO2 compressor 8, and the merged offshore associated gas pipeline is connected to the raw gas inlet of the reformer 2; the synthesis gas outlet of the reformer 2 is connected to the inlet of the synthesis gas compressor 3; the outlet of the synthesis gas compressor 3 is connected to the synthesis gas inlet of the methanol synthesis unit 4; the liquid phase outlet of the methanol synthesis unit 4 is connected to the inlet of the methanol distillation unit 5, the first purge gas outlet of the methanol synthesis unit 4 is connected to the first purge gas inlet of the purge gas CO2 recovery unit 7, and the second purge gas outlet of the methanol synthesis unit 4 is connected to the first purge gas inlet of the purge gas CO2 recovery unit 7. The gas outlet is connected to the fuel gas inlet of the reformer 2; the liquid phase outlet of the methanol distillation unit 5 is connected to the inlet of the methanol storage tank 9, the first purge gas outlet of the methanol distillation unit 5 is connected to the purge gas inlet of the methanol synthesis unit 4, and the second purge gas outlet of the methanol distillation unit 5 is connected to the second purge gas inlet of the purge gas CO2 recovery unit 7; the exhaust port of the reformer 2 is connected to the inlet of the synthesis gas CO2 recovery unit 6, the outlet of the synthesis gas CO2 recovery unit 6 is merged with the outlet of the purge gas CO2 recovery unit 7, and the merged CO2 pipeline is connected to the inlet of the CO2 compressor 8.

[0042] Example 2

[0043] Based on the high-CO2-content offshore associated gas liquid recovery system provided in Example 1, this embodiment further provides an operating method of the high-CO2-content offshore associated gas liquid recovery system, comprising the following steps:

[0044] S100. High-CO2-content associated gas from an offshore crude oil production platform enters desulfurization tank 1, where impurities such as hydrogen sulfide are removed. After being mixed with recovered pressurized CO2, the gas enters reformer 2, where it undergoes catalytic reforming in the high-temperature, pressurized environment of reformer 2 to produce synthesis gas. Reformer 2 operates at a temperature of 850°C and a pressure of 2.4 MPa.

[0045] S200. The synthesis gas enters the synthesis gas compressor 3 and is pressurized to 7.0 MPaG. It then enters the methanol synthesis unit 4 at a reaction temperature of 240°C and is converted into a crude methanol product under the action of a catalyst.

[0046] S300. The crude methanol product enters the methanol distillation unit 5, where it is separated and purified into a refined methanol product with a concentration of 99%. The refined methanol product enters the methanol storage tank 9 (the storage pressure of the methanol storage tank 9 is 0.5 MPa, and the temperature is controlled not to be higher than 30°C), and is then transported to the methanol transport ship through a methanol hose. The unsynthesized synthesis gas then enters the methanol synthesis unit 4 for further synthesis.

[0047] S400. The unconverted gas discharged from the reformer 2 enters the synthesis gas CO2 recovery unit 6, and CO2 is separated by pressure swing adsorption in the synthesis gas CO2 recovery unit 6.

[0048] S500. A portion of the purge gas generated by the methanol synthesis unit 4 and the purge gas generated by the methanol distillation unit 5 enter the purge gas CO2 recovery unit 7, and H2, N2 and CO2 are separated by pressure swing adsorption in the purge gas CO2 recovery unit 7. The purge gases such as H2 and N2 are burned and discharged, and CO2 and the CO2 recovered by the synthesis gas CO2 recovery unit 6 enter the CO2 compressor 8 together with the CO2 pressurized to 2.5 MPa, and then mixed with the desulfurized raw gas and enter the converter 2, thereby achieving the carbon replenishment target of the synthesis gas preparation process; another portion of the purge gas generated by the methanol synthesis unit 4 enters the converter 2 as fuel gas, as a part of the energy source of the converter 2.

[0049] In the above embodiment, preferably, another part of the energy source of the reformer 2 comes from green electricity such as offshore wind power / low-carbon shore power.

[0050] In summary, the present invention can achieve full liquid recovery of high-CO2-content offshore associated gas, eliminating excess associated gas and CO2 emissions. It can also realize the production, storage, and utilization of high-concentration CO2 in offshore associated gas and liquid methanol synthesized from hydrocarbons, achieving resource recycling. It also reduces carbon emissions during offshore oilfield development and production, protects the marine ecological environment, and has significant economic and environmental benefits. It can effectively solve the problem of recycling high-CO2 content in offshore associated gas. Furthermore, the present invention can effectively reduce the footprint of traditional production equipment and leverage the advantages of methanol liquid storage at room temperature. The products all have high economic value and the production process has low carbon emissions.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A liquid recovery system for associated gas from offshore oil fields with high carbon dioxide content, characterized in that: Including desulfurization tank, reformer, synthesis gas compressor, methanol synthesis unit, methanol distillation unit, synthesis gas CO2 recovery unit, purge gas CO2 recovery unit, CO2 compressor and methanol storage tank; The offshore associated gas is connected to the inlet of the desulfurization tank, the outlet of the desulfurization tank is merged with the outlet of the CO2 compressor, the merged offshore associated gas pipeline is connected to the raw gas inlet of the reformer, and the synthesis gas outlet of the reformer is connected to the inlet of the synthesis gas compressor; The outlet of the synthesis gas compressor is connected to the synthesis gas inlet of the methanol synthesis unit, the liquid phase outlet of the methanol synthesis unit is connected to the inlet of the methanol distillation unit, the first purge gas outlet of the methanol synthesis unit is connected to the first purge gas inlet of the purge gas CO2 recovery unit, and the second purge gas outlet of the methanol synthesis unit is connected to the fuel gas inlet of the reformer; The liquid phase outlet of the methanol distillation unit is connected to the inlet of the methanol storage tank, the first purge gas outlet of the methanol distillation unit is connected to the purge gas inlet of the methanol synthesis unit, and the second purge gas outlet of the methanol distillation unit is connected to the second purge gas inlet of the purge gas CO2 recovery unit; The exhaust port of the reformer is connected to the inlet of the synthesis gas CO2 recovery unit, the outlet of the synthesis gas CO2 recovery unit merges with the outlet of the relaxation gas CO2 recovery unit, and the merged CO2 pipeline is connected to the inlet of the CO2 compressor.

2. An operating method of the high-carbon dioxide content offshore associated gas liquid recovery system according to claim 1, characterized in that: The following steps are involved: High-CO2 offshore associated gas enters the desulfurization tank, where it is mixed with the recovered pressurized CO2 after impurities are removed and then enters the reformer. In the high-temperature and pressurized environment of the reformer, it undergoes catalytic reforming to produce synthesis gas. The synthesis gas enters the synthesis gas compressor for pressurization and then enters the methanol synthesis unit to be produced into crude methanol product under the action of catalyst; The crude methanol product enters the methanol distillation unit, where it is separated and purified into refined methanol products. The refined methanol products enter the methanol storage tank, and the unsynthesized synthesis gas enters the methanol synthesis unit for further synthesis. The unconverted gas discharged from the reformer enters the synthesis gas CO2 recovery unit, where CO2 is separated by pressure swing adsorption; A portion of the purge gas produced by the methanol synthesis unit and the purge gas produced by the methanol distillation unit enter the purge gas CO2 recovery unit, and H2, N2 and CO2 are separated by pressure swing adsorption in the purge gas CO2 recovery unit. H2 and N2 are burned and discharged, while CO2 enters the CO2 compressor together with the CO2 recovered by the synthesis gas CO2 recovery unit for pressurization, and is mixed with the desulfurized raw gas before entering the converter, thereby achieving the carbon replenishment goal of the synthesis gas preparation process; another portion of the purge gas produced by the methanol synthesis unit enters the converter as fuel gas, serving as part of the energy source for the converter.

3. The operating method according to claim 2, characterized in that: Another part of the energy source of the reformer comes from offshore wind power / low-carbon shore power.

4. The operating method according to claim 2, characterized in that: The operating temperature of the converter is 850° C. and the operating pressure is 2.4 MPa.

5. The operating method according to claim 2, characterized in that: The reaction temperature of the methanol synthesis unit is 240°C.

6. The operating method according to claim 2, characterized in that: The storage pressure of the methanol storage tank is 0.5 MPa, and the temperature is controlled not to be higher than 30°C.

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