Carbon dioxide pretreatment system applied to natural gas

Abstract

The invention relates to a carbon dioxide pretreatment system applied to natural gas. The carbon dioxide pretreatment system comprises a primary dehydration and dealkylation unit and a separation and decarbonization unit, the feed gas entering the first molecular sieve enters the separator after water is separated out, enters the membrane separation device to complete preliminary decarbonization and then enters the absorption tower, and the absorption tower is used for further removing carbon dioxide in the feed gas. After being treated by the primary dehydration and dealkylation unit, the raw material gas is subjected to primary dehydration and heavy hydrocarbon removal procedures and enters the separation and decarbonization unit, the membrane separation device starts to perform decarbonization treatment on the raw material, the concentration of carbon dioxide in the gas is reduced, then the gas enters the absorption tower for further decarbonization treatment, and after further decarbonization by the absorption tower, the gas enters the separation and decarbonization unit; the carbon dioxide content in the gas can be further reduced, the whole system has high carbon dioxide separation efficiency, the application of the technology not only can significantly improve the energy utilization efficiency, but also can reduce the pollution to the environment, and meets the requirements of sustainable development.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas pretreatment, and in particular to a carbon dioxide pretreatment system applied to natural gas. Background Art

[0002] With the growth of global energy demand and the enhancement of environmental protection awareness, efficient and low-energy natural gas processing technology has become a research hotspot. The pretreatment of high-carbon dioxide natural gas in offshore oil fields is a key link in the development and utilization of natural gas. According to convention, the natural gas with high carbon dioxide content needs to be removed to meet the national natural gas pipeline transportation standards. Therefore, the main goal of the early membrane natural gas carbon dioxide separation and capture device is to achieve the standard transportation of natural gas and recover as much hydrocarbons as possible, but there is no special requirement for the captured carbon dioxide content.

[0003] In order to further achieve the goal, the raw gas treatment standards cannot simply meet the national natural gas pipeline transportation standards, so there is an urgent need for a pretreatment device that can further improve the carbon dioxide separation efficiency. Summary of the invention

[0004] In response to the above technical problems, the present invention provides a carbon dioxide pretreatment system for natural gas, which has a high carbon dioxide separation efficiency. The application of this technology can not only significantly improve energy utilization efficiency, but also reduce environmental pollution, which meets the requirements of sustainable development.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A carbon dioxide pretreatment system for natural gas, comprising a primary dehydration and dehydrocarbonization unit and a separation and decarbonization unit; The primary dehydration and dehydrogenation unit comprises a first molecular sieve and a separator, and the feed gas input pipeline is connected to the first molecular sieve and the separator in sequence; the feed gas entering the first molecular sieve enters the separator after water is separated, and the separator is used to separate hydrocarbons in the feed gas; The separation and decarbonization unit includes a membrane separation device and an absorption tower. The raw gas treated by the separator is connected to the membrane separation device and the absorption tower in sequence; after entering the membrane separation device to complete preliminary decarbonization, it enters the absorption tower, and the absorption tower is used to further remove carbon dioxide in the raw gas.

[0006] In one possible implementation manner, a first pressure reducing valve is connected between the first molecular sieve and the separator.

[0007] In one possible implementation, a second molecular sieve is further included, and the raw gas treated by the absorption tower enters the second molecular sieve.

[0008] In one possible implementation manner, a valve is connected between the second molecular sieve and the membrane separation device.

[0009] In one possible implementation, it further includes a heat exchanger, wherein the heat exchanger has a cooling channel, and the cooling channel is connected to an input pipeline of the raw gas. The raw gas enters the first molecular sieve after being cooled by the heat exchanger.

[0010] In one possible implementation manner, the heat exchanger further comprises a temperature-increasing flow channel, and the temperature-increasing flow channel is connected between the membrane separation device and the separator.

[0011] In one possible embodiment, the absorption tower has a gas input port, an absorbent input port, a gas output port, and a liquid output port; The system also includes a desorption circulation unit, which is connected to the liquid output port and the absorbent input port; the desorption circulation unit is used to replace the lean and rich liquids and circulate the supply to the absorption tower.

[0012] The present invention adopts the above technical solution, which has the following advantages: Membrane separation technology has gradually become a new choice for pretreatment of high-carbon dioxide-containing natural gas in offshore oil fields due to its advantages of high efficiency, low energy consumption, simple operation, and compact equipment. This technology separates carbon dioxide from other components by utilizing the different permeation rates of gas components in membrane materials. Compared with traditional processes, membrane separation technology has significant advantages: First, the membrane separation process does not involve phase change, has low energy consumption, and is easy to operate, making it suitable for offshore platforms with limited space and harsh environments. Second, the membrane separation device has a compact structure and a small footprint, which can effectively save space resources on offshore platforms. In addition, membrane separation technology is highly flexible and scalable, and can be modularly designed and expanded according to actual needs to adapt to offshore oil fields of different sizes and processing requirements.

[0013] In specific applications, the efficient and compact offshore oilfield high-CO2 natural gas pretreatment process and equipment combines advanced membrane separation technology and optimized process flow, which can effectively remove CO2 from natural gas, reduce the load of subsequent treatment processes, and improve the quality of natural gas. The application of this technology can not only significantly improve energy utilization efficiency, but also reduce environmental pollution, which meets the requirements of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the specific principle of a carbon dioxide pretreatment system in one embodiment of the present invention.

[0015] Reference numerals: 1. First molecular sieve; 2. Separator; 3. Membrane separation device; 4. Absorption tower; 5. First pressure reducing valve; 6. Second molecular sieve; 7. Valve; 8. Heat exchanger; 9. Desorption tower; 10. Mixer; 11. Lean-rich liquid heat exchanger. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work are within the scope of protection of the present invention.

[0017] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons with ordinary skills in the field to which the present invention belongs. The words "first", "second", "third", "fourth" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" and the like mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" and the like are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0018] The pretreatment of high-carbon dioxide natural gas from offshore oil fields is a key link in the development and utilization of natural gas. According to convention, natural gas with a high carbon dioxide content needs to be removed by carbon dioxide to meet the national natural gas pipeline transportation standards. Therefore, the main goal of the early membrane natural gas carbon dioxide separation and capture device is to achieve the standard transportation of natural gas and recover as many hydrocarbons as possible, but there is no special requirement for the captured carbon dioxide content. In order to further achieve the goal, under the standard of raw gas treatment, it is not possible to simply meet the national natural gas pipeline transportation standards. In response to the above technical problems, the present invention provides a carbon dioxide pretreatment system for natural gas, which has a high carbon dioxide separation efficiency. The application of this technology can not only significantly improve energy utilization efficiency, but also reduce pollution to the environment, and meet the requirements of sustainable development. The technical solution of the present invention is described in detail below with specific examples.

[0019] Reference Figure 1 As shown, the present invention relates to a carbon dioxide pretreatment system for natural gas, which includes a primary dehydration and dehydrocarbonization unit and a separation and decarbonization unit.

[0020] The primary dehydration and dehydrogenation unit comprises a first molecular sieve 1 and a separator 2. The feed gas input pipeline is connected to the first molecular sieve 1 and the separator 2 in sequence. The feed gas entering the first molecular sieve 1 separates water and then enters the separator 2. The separator 2 is used to separate hydrocarbons in the feed gas.

[0021] The separation and decarbonization unit includes a membrane separation device 3 and an absorption tower 4. The raw gas treated by the separator 2 is connected to the membrane separation device 3 and the absorption tower 4 in sequence; after entering the membrane separation device 3 to complete preliminary decarbonization, it enters the absorption tower 4, and the absorption tower 4 is used to further remove carbon dioxide in the raw gas.

[0022] It should be noted that during the operation of the membrane separation device 3, hydrocarbon compounds may damage or degrade certain membrane materials, affecting the service life and performance of the membrane. Dehydrocarbonization can prevent the membrane from being contaminated or damaged. At the same time, hydrocarbon compounds may damage or degrade certain membrane materials, affecting the service life and performance of the membrane. Dehydrocarbonization can prevent the membrane from being contaminated or damaged. In addition, the presence of hydrocarbon compounds may also affect the selectivity of the membrane, making it impossible for the membrane to effectively separate the target gas. By dehydrocarbonization, the separation efficiency of the membrane can be improved, making it more effective in separating the required gas components. In summary, by dehydrocarbonization treatment, the overall performance of membrane separation can be improved, the service life of the membrane can be extended, and the stability and safety of the process can be ensured. Therefore, in this system, the gas is first dehydrocarbonized by the separator 2 before being treated by the membrane separation device 3.

[0023] For example, when the system is working normally, the raw gas enters the first molecular sieve 1 to separate the water, and then enters the separator 2, which performs gas-liquid separation on the incoming gas, separates the hydrocarbons and continues to transport the treated gas to the rear. After being processed by the primary dehydration and dehydrogenation unit, the raw gas completes the primary dehydration and heavy hydrocarbon removal process, and enters the separation and decarbonization unit, wherein the membrane separation device 3 begins to decarbonize the raw material to reduce the carbon dioxide concentration in the gas, and then enters the absorption tower 4 for further decarbonization. After further decarbonization by the absorption tower 4, the carbon dioxide content in the gas can be further reduced. The system as a whole has a high carbon dioxide separation efficiency. The application of this technology can not only significantly improve energy utilization efficiency, but also reduce pollution to the environment, which meets the requirements of sustainable development.

[0024] In one embodiment, it is more preferred that a first pressure reducing valve 5 is connected between the first molecular sieve 1 and the separator 2 to facilitate overall maintenance and control.

[0025] During the dehydration process of the first molecular sieve 1, a relatively high pressure is required so that the gas has sufficient power to pass through the first molecular sieve 1. However, during the gas-liquid separation process of the separator 2, it is necessary to reduce some of the pressure so that the light group can be separated out, which is beneficial to the gas-liquid separation, and the first pressure reducing valve 5 plays a role in temperature control.

[0026] In one embodiment, it is more preferred that the system further includes a second molecular sieve 6 , and the raw gas treated by the absorption tower 4 enters the second molecular sieve 6 .

[0027] It should be noted that after the natural gas passes through the absorption tower 4, it may be mixed with water vapor. There are several reasons for this: Impact of the absorption process: In the absorption tower 4, changes in temperature and pressure of the liquid phase may cause evaporation of water, thereby increasing the water vapor concentration in the gas phase. In particular, in certain absorption processes, water transfer may occur when the gas comes into contact with the absorbent.

[0028] Temperature changes: Temperature changes may cause the state of the water to change when the gas enters the absorption tower 4. In some cases, if the gas is heated, it may cause more water vapor to be generated.

[0029] Chemical reaction: If the absorbent used in the absorption tower 4 reacts with certain components in the natural gas, water may be released, further increasing the water vapor content in the gas phase.

[0030] By setting up a second molecular sieve 6, moisture in the gas can be further removed, so that the gas can enter the secondary molecular sieve for deep dehydration after completing deacidification and decarbonization. In many applications, removing moisture is a key step to ensure the normal operation of the system and improve product quality, thereby improving the raw gas processing effect of the system.

[0031] In this embodiment, in order to facilitate overall maintenance and control, a valve 7 is connected between the second molecular sieve 6 and the membrane separation device 3 .

[0032] In one embodiment, the system further comprises a heat exchanger 8 having a cooling channel, the cooling channel being connected to an input pipeline of the raw gas, and the raw gas enters the first molecular sieve 1 after being cooled by the heat exchanger 8 .

[0033] It should be noted that the first molecular sieve 1 is mainly used for preliminary separation of water, and heating and temperature raising are helpful to optimize the dehydration process and ensure efficient adsorption of the molecular sieve, thereby achieving a better dehydration effect.

[0034] In one embodiment, specifically, the heat exchanger 8 further has a temperature-increasing flow channel, and the temperature-increasing flow channel is connected between the membrane separation device 3 and the separator 2 .

[0035] The main reasons for heating the gas before it enters the membrane separation device 3 are as follows: Improve separation efficiency: Heating the gas can reduce its viscosity, thereby increasing the fluidity of the gas within the membrane and helping to enhance the separation efficiency of the membrane.

[0036] Improved membrane performance: Certain membrane materials exhibit better selectivity and permeability at higher temperatures. Heating can make the pore structure and morphology of the membrane more ideal, thereby improving its separation performance.

[0037] Prevent condensation: At low temperatures, moisture in the gas may condense, causing clogging or degradation of the membrane. Heating can reduce the risk of moisture condensation in the gas and extend the service life of the membrane.

[0038] Increased reaction rates: In some cases, heating can increase the reaction rates of reactants in the gas, making the chemical reactions in the membrane separation process more efficient.

[0039] By heating the gas, some physical and chemical barriers can be overcome during the membrane separation process, thereby improving the overall performance of the system.

[0040] The present invention provides a specific implementation example: like Figure 1 As shown, the source of the raw gas is natural gas from offshore gas fields after primary gas-liquid separation, which generally exists in the form of gas phase. This case takes the carbon dioxide molar content of about 60% as an example.

[0041] 2) Primary dehydration and dehydrocarbonization process Taking an offshore oil field with a daily output of 75,000 cubic meters as an example, the raw gas is first dehydrated and deheavy hydrocarbons are removed. The raw gas is cooled to 21.5°C by the heat exchanger 8, and the water content of the gas is reduced to 50ppm by the first molecular sieve 1. The gas-liquid separation is carried out by the separator 2, and the water content of the gas is reduced to 20ppm, and the temperature is raised to 34.44°C by the heat exchanger 8.

[0042] 3) Separation and decarbonization process The gas after primary dehydration and dehydrocarbonization enters the membrane separation device 3 and flows out from the retention side of the membrane separation device 3. At this time, the molar content of carbon dioxide drops to 23%. After passing through the throttle valve, it enters the absorption tower 4 for deacidification. At this time, the molar content of carbon dioxide in the gas drops to 2%. Then the gas enters the secondary molecular sieve dehydration device.

[0043] 4) Secondary molecular sieve dehydration process The gas after deacidification and decarbonization enters the secondary molecular sieve for deep dehydration at a temperature of 35°C and a pressure of 4.8 MPa, with the water content dropping to 1 ppm.

[0044] In one embodiment, the absorption tower 4 is further refined, and the absorption tower 4 has a gas input port, an absorbent input port, a gas output port, and a liquid output port. In addition, the system also includes a desorption circulation unit, which connects the liquid output port and the absorbent input port, and is used to replace the lean and rich liquids and circulate the supply to the absorption tower 4.

[0045] In this embodiment, the desorption cycle unit comprises a desorption tower 9, which has a rich liquid input port, a heating medium input port, a carbon dioxide output port and a lean liquid output port. The rich liquid input port is connected to the liquid output port, and the lean liquid output port is connected to the absorbent input port.

[0046] The lean liquid outlet and the absorbent inlet are connected with a mixer 10 for water replenishment and mixing. In addition, a lean-rich liquid heat exchanger 11 is provided between the rich liquid inlet and the liquid outlet.

[0047] The arrangement of the mixer 10 and the lean-rich liquid heat exchanger 11 can further optimize the working efficiency of the desorption cycle unit, and can improve the overall processing efficiency when the carbon dioxide processing step is subsequently entered again.

[0048] The main purpose of the analysis tower 9 is to analyze the rich amine liquid after absorbing carbon dioxide, changing the rich amine liquid with high carbon dioxide content into the lean amine liquid with low carbon dioxide content. The absorption process is mostly operated at low temperature, while the desorption process is mostly operated at high temperature. The rich-lean heat exchanger 11 heats the rich liquid and cools the lean liquid, effectively reducing energy consumption. In addition, the top cooler and bottom reboiler of the analysis tower 9 are used for forced tower fluid circulation and are conventional components.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention 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 of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A carbon dioxide pretreatment system for natural gas, characterized in that: It includes a primary dehydration and dehydrocarbonization unit and a separation and decarbonization unit; The primary dehydration and dehydrogenation unit comprises a first molecular sieve and a separator, and the feed gas input pipeline is connected to the first molecular sieve and the separator in sequence; the feed gas entering the first molecular sieve enters the separator after water is separated, and the separator is used to separate hydrocarbons in the feed gas; The separation and decarbonization unit includes a membrane separation device and an absorption tower. The raw gas treated by the separator is connected to the membrane separation device and the absorption tower in sequence; after entering the membrane separation device to complete preliminary decarbonization, it enters the absorption tower, and the absorption tower is used to further remove carbon dioxide in the raw gas.

2. The carbon dioxide pretreatment system according to claim 1, characterized in that: A first pressure reducing valve is connected between the first molecular sieve and the separator.

3. The carbon dioxide pretreatment system according to claim 1, characterized in that: It also includes a second molecular sieve, and the raw gas treated by the absorption tower enters the second molecular sieve.

4. The carbon dioxide pretreatment system according to claim 3, characterized in that: A valve is connected between the second molecular sieve and the membrane separation device.

5. The carbon dioxide pretreatment system according to claim 1, characterized in that: It also includes a heat exchanger, which has a cooling channel. The cooling channel is connected to the input pipeline of the raw gas. The raw gas enters the first molecular sieve after being cooled by the heat exchanger.

6. The carbon dioxide pretreatment system according to claim 5, characterized in that: The heat exchanger further comprises a temperature-increasing flow channel, and the temperature-increasing flow channel is connected between the membrane separation device and the separator.

7. The carbon dioxide pretreatment system according to any one of claims 1 to 6, characterized in that: The absorption tower has a gas input port, an absorbent input port, a gas output port and a liquid output port; The system further comprises a desorption circulation unit, wherein the desorption circulation unit is connected to the liquid output port and the absorbent input port; The desorption circulation unit is used to replace the lean and rich liquids and circulate the liquids to supply the absorption tower.

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