A method for pre-liquefaction and decarbonization of methanated natural gas

Abstract

This invention relates to the field of natural gas liquefaction technology, specifically to a method and apparatus for pre-liquefaction decarbonization of methanated synthetic natural gas (SNG). The method includes the following steps: (1) using synthetic natural gas as feedstock, sequentially undergoing a first heat exchange and a second heat exchange to obtain a mixed gas by mixing the heat-exchanged feedstock gas with hydrogen; (2) contacting the mixed gas with a methanation catalyst and reacting it to obtain a decarbonized gas, which is then sequentially subjected to a first heat exchange and a third heat exchange, followed by gas-liquid separation to obtain refined natural gas and condensate. This method effectively removes CO2 from SNG while meeting decarbonization requirements, thereby increasing LNG production.

Description

Technical Field

[0001] This invention relates to the field of natural gas liquefaction technology, specifically to a method for pre-liquefaction decarbonization of methanated synthetic natural gas and a device for pre-liquefaction decarbonization of methanated synthetic natural gas. Background Technology

[0002] Conventional coal-to-natural-gas plants, both domestically and internationally, use coal as raw material, sequentially undergoing coal gasification, CO conversion, acid gas removal, and methanation to produce synthetic natural gas (SNG). When this SNG is used as feedstock for liquefaction to produce liquefied natural gas (LNG), the CO2 in it can cause freezing and blockage of the heat exchange tubes or pipelines in the cryogenic liquefaction tank. To address this, existing natural gas liquefaction plants generally employ solid adsorption or solvent absorption methods to remove CO2 from the SNG.

[0003] Solid-state adsorption methods commonly employ molecular sieve adsorbents and utilize molecular sieve adsorption towers. The feed gas (SNG) is cooled and separated before being sent to the molecular sieve adsorption tower, where CO2 is adsorbed and removed. The CO2-free SNG is then sent to a cold box for cryogenic liquefaction and separation to produce LNG. The CO2-rich molecular sieve can be regenerated using high-temperature nitrogen, and the high-temperature regeneration waste gas needs to be cooled before being vented at a high point. However, existing solid-state adsorption methods typically require three molecular sieve adsorption towers, 13-21 programmable valves and a programmable control system, heaters and coolers for the regeneration gas, and other equipment. This results in a large molecular sieve loading, numerous pieces of equipment, a large footprint, and a high initial investment. Furthermore, the nitrogen consumption for regeneration is significant, and the regeneration waste gas contains small amounts of CH4, but its calorific value is extremely low, necessitating high-point venting, which not only pollutes the environment but also incurs high operating costs.

[0004] The solvent absorption method utilizes MDEA (N-methyldiethanolamine) as the solvent and requires a CO2 absorption tower and an MDEA regeneration tower. The feed gas (SNG) enters from the bottom of the CO2 absorption tower, where it reacts counter-currently with MDEA to decarbonize. The CO2-free SNG is sent to a cold box for cryogenic liquefaction and separation to produce LNG. The CO2-rich MDEA solution is sent to the MDEA regeneration tower, where it is regenerated by steam heating at the bottom. The regenerated lean MDEA solution is cooled and returned to the CO2 absorption tower, thus completing the cycle. However, the MDEA solvent absorption method requires a complex process setup, including a CO2 absorption tower and an MDEA regeneration tower. It also involves MDEA solvent circulation, high energy consumption, and the need for timely solvent replenishment, resulting in high operating costs. Furthermore, during CO2 removal, MDEA carries a small amount of methane gas, causing a certain degree of loss of usable gas.

[0005] Therefore, there is an urgent need for a simple, fast, and effective method for removing synthetic natural gas. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned technical problems and provide a method for pre-liquefaction decarbonization of methanated synthetic natural gas (SNG) and a device for pre-liquefaction decarbonization of SNG. This method effectively removes CO2 content from SNG and increases LNG production while meeting the decarbonization index requirements. At the same time, this method also simplifies the process flow and facilitates industrial production.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for pre-liquefaction and decarbonization of methanated natural gas, the method comprising the following steps:

[0008] (1) Synthetic natural gas is used as raw material gas and subjected to first heat exchange and second heat exchange in sequence to obtain the raw material gas after heat exchange and hydrogen gas to obtain mixed gas.

[0009] (2) The mixed gas and methanation catalyst are contacted and reacted to obtain a refined decarbonized gas. After the first heat exchange and the third heat exchange are performed, gas-liquid separation is performed to obtain refined natural gas and condensate.

[0010] In this invention, unless otherwise specified, synthetic natural gas is abbreviated as SNG; liquefied natural gas is abbreviated as LNG.

[0011] Preferably, the CO2 content in the synthetic natural gas is ≤2.5 mol%, and more preferably 0.089-2.5 mol%.

[0012] Preferably, the refined natural gas has a CH4 content of ≥93.5 mol%, preferably 93.5-98 mol%, more preferably 94-98 mol%; and a CO2 content of ≤50 ppm, preferably 0.1-15 ppm, more preferably 0.1-5 ppm.

[0013] A second aspect of the present invention provides a fine decarbonization device for pre-liquefaction of methanated synthetic natural gas, the device comprising a first heat exchanger, a second heat exchanger, a fine decarbonization tower, a third heat exchanger, and a gas-liquid separator connected in sequence;

[0014] The first heat exchanger and the second heat exchanger are used to sequentially perform the first heat exchange and the second heat exchange on synthetic natural gas as raw material gas to obtain the raw material gas after heat exchange.

[0015] The decarbonization tower is filled with a methanation catalyst, which is used to mix the heat-exchanged raw gas with hydrogen. The resulting mixed gas contacts and reacts with the methanation catalyst to obtain decarbonized gas, which is then sent to a gas-liquid separator after passing through the first heat exchanger and the third heat exchanger to obtain refined natural gas and condensate.

[0016] Through the above technical solution, the method provided by the present invention uses a unique low-temperature methanation catalyst to remove CO2 from synthetic natural gas, which not only effectively reduces the CO2 content but also increases the CH4 content. In particular, by controlling the H2 / CO2 molar ratio in the mixed gas, the CO2 content in the refined natural gas is ≤50ppm. At the same time, the method also reduces the energy consumption of the system by coupling and utilizing the heat of the decarbonized gas.

[0017] The method provided by this invention, while meeting the decarbonization index, also has the advantages of simple process, low initial investment, low operating cost, flexible operation, and low energy consumption, making it easy for industrial production.

[0018] The device provided by this invention achieves effective CO2 removal and increases CH4 content to a certain extent by using a decarbonization tower filled with a special low-temperature methane catalyst. In particular, the device is equipped with an online CO2 analyzer, which flexibly adjusts the hydrogen replenishment amount in real time according to the CO2 analysis index in the refined natural gas, which helps to reduce operating costs. Attached Figure Description

[0019] Figure 1 This invention provides a schematic diagram of a pre-decarbonization device for methanation-to-natural gas liquefaction.

[0020] Explanation of reference numerals in the attached figures

[0021] 1. First heat exchanger; 2. Second heat exchanger; 3. Thermometer; 4. Temperature regulating valve; 5. Fine decarbonization tower; 6. Third heat exchanger; 7. Gas-liquid separator; 8. Online CO2 analyzer; 9. Flow control valve; 01. Raw material gas; 02. Raw material gas after heat exchange; 03. Saturated steam; 04. Steam condensate; 05. Hydrogen; 06. Mixed gas; 07. Fine decarbonization gas; 08. Fine decarbonization gas after the first heat exchange; 09. Fine decarbonization gas after the third heat exchange; 010. Refined natural gas; 011. Condensate. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] In this invention, unless otherwise specified, "first," "second," and "third" do not indicate a sequence or limit the specific materials or steps; they are merely used to distinguish or indicate that these are not the same material or step. For example, in "first heat exchange," "second heat exchange," and "third heat exchange," "first," "second," and "third" are only used to indicate that these are not the same heat exchange.

[0024] The first aspect of this invention provides a method for pre-liquefaction and decarbonization of methanated natural gas, the method comprising the following steps:

[0025] (1) Synthetic natural gas is used as raw material gas and subjected to first heat exchange and second heat exchange in sequence to obtain the raw material gas after heat exchange and hydrogen gas to obtain mixed gas.

[0026] (2) The mixed gas and methanation catalyst are contacted and reacted to obtain a refined decarbonized gas. After the first heat exchange and the third heat exchange are performed, gas-liquid separation is performed to obtain refined natural gas and condensate.

[0027] The inventors of this invention have discovered that, compared to solid adsorption and liquid absorption methods, this invention employs a unique low-temperature methanation catalyst. This catalyst operates at temperatures between 250-400°C, and under a high CH4 concentration atmosphere, CO2 and H2 undergo a methanation reaction, increasing the methane content in the synthesized natural gas (SNG). In particular, by controlling the H2 / CO2 molar ratio in the mixed gas, the CO2 content is reduced to ≤50ppm, preventing CO2 freezing and blockage in heat exchangers or pipelines within the liquefaction cold box. Furthermore, the method provided by this invention allows for flexible adjustment of hydrogen replenishment based on CO2 analysis indicators in the refined natural gas, reducing operating costs.

[0028] In some embodiments of the present invention, preferably, in step (1), the CO2 content in the synthetic natural gas is ≤2.5 mol%, preferably 0.089-2.5 mol%, for example, 0.089 mol%, 0.09 mol%, 0.1 mol%, 0.11 mol%, 0.12 mol%, 0.2 mol%, 0.5 mol%, 0.8 mol%, 1 mol%, 1.2 mol%, 1.5 mol%, 1.8 mol%, 2 mol%, 2.2 mol%, 2.5 mol%, and any value within the range of any two values.

[0029] In some embodiments of the present invention, preferably, the synthetic natural gas contains 90-96 mol% CH4, 1.5-3 mol% H2, 0-0.1 mol% CO, and 0.1-0.2 mol% H2O.

[0030] In this invention, the content parameters of each component in the synthetic natural gas are measured using the test methods described in GB / T 33445-2023 "Coal-to-Synthetic Natural Gas".

[0031] In some embodiments of the present invention, preferably, the pressure of the synthetic natural gas is 2.2-5.5 MPa(G), for example, 2.2 MPa(G), 2.5 MPa(G), 3 MPa(G), 3.5 MPa(G), 4 MPa(G), 4.2 MPa(G), 4.5 MPa(G), 4.8 MPa(G), 5 MPa(G), 5.5 MPa(G), and any value within any range of any two values, preferably 4-5 MPa(G); the temperature is 20-50°C, for example, 20°C, 25°C, 30°C, 32°C, 35°C, 38°C, 40°C, 50°C, and any value within any range of any two values, preferably 30-40°C.

[0032] In this invention, the type of synthetic natural gas can be selected from a wide range, as long as it meets the above-mentioned parameter limitations. Preferably, the synthetic natural gas includes, but is not limited to, methanated synthetic natural gas.

[0033] In one specific embodiment of the present invention, methanated synthetic natural gas is used as raw material, with CO2 content of 0.221 mol%, CH4 content of 93.06 mol%, H2 content of 1.925 mol%, CO content of 0 mol%, and H2O content of 0.185 mol%; the pressure is 4.53 MPa (G), and the temperature is 40°C.

[0034] In some embodiments of the present invention, preferably, in step (1), the first heat exchange process includes: performing the first heat exchange between the raw material gas and the decarbonized gas to obtain the raw material gas after the first heat exchange and the decarbonized gas after the first heat exchange.

[0035] In this invention, unless otherwise specified, the raw material gas is transformed into raw material gas after the first heat exchange, and the fine decarbonization gas is transformed into fine decarbonization gas after the first heat exchange.

[0036] In this invention, unless otherwise specified, the first heat exchange, the second heat exchange, and the third heat exchange only involve the temperature change of the substance before and after the heat exchange, and do not involve the change of the content of each component in the substance.

[0037] In some embodiments of the present invention, preferably, the temperature of the first heat-exchange raw material gas is 150-160°C, for example, 150°C, 152°C, 155°C, 158°C, 160°C, or any value within a range of any two values; the temperature of the first heat-exchange fine decarbonization gas is 160-170°C, for example, 160°C, 162°C, 165°C, 168°C, 170°C, or any value within a range of any two values.

[0038] In some embodiments of the present invention, preferably, the second heat exchange process includes: performing the second heat exchange between the first heat-exchanged raw material gas and saturated steam to obtain the heat-exchanged raw material gas and steam condensate.

[0039] In this invention, more preferably, the temperature of the saturated steam is 315-340°C, for example, 315°C, 320°C, 325°C, 330°C, 335°C, 340°C, or any value within a range of any two values.

[0040] In this invention, more preferably, the temperature of the raw material gas after heat exchange is 250-260℃, such as 250℃, 252℃, 258℃, 260℃, or any value within a range of any two values. That is, this invention employs a first heat exchange and a second heat exchange to raise the temperature of the raw material gas to 250-260℃.

[0041] In some embodiments of the present invention, preferably, the molar ratio of H2 / CO2 in the mixed gas is ≥4, for example, 4, 5, 6, 7, 8, 8.7, 10, etc. The present invention effectively removes CO2 by adjusting the above molar ratio range, thereby controlling the CO2 content in refined natural gas.

[0042] In this invention, a mixed gas with a molar ratio within the above-mentioned range, based on the equation 4H₂ + CO₂ = CH₄ + H₂O, ensures the complete methanation reaction of CO₂. The process flow provided by this invention allows for the provision of a hydrogen pipeline; the hydrogen replenishment amount can be set and adjusted according to actual conditions, eliminating the need to pre-set the H / C ratio in the feed gas.

[0043] In this invention, the reaction aims to react a small amount of CO2 and H2 in a mixed gas with a methanation catalyst to obtain CH4 and H2O. Preferably, in step (2), the reaction conditions include: a temperature of 250-350℃, for example, 250℃, 260℃, 265℃, 270℃, 275℃, 280℃, 300℃, 320℃, 350℃, and any value within any range of any two of these values, preferably 260-280℃; and a volume hourly space velocity of 5000-10000 h⁻¹. -1 For example, 5000h -15200h -1 5500h -1 5800h -1 6000h -1 6500h -1 7000h -1 8000h -1 9000h -1 10000h -1 And any value within the range of any two values, preferably 5000-8000h. -1 .

[0044] In some embodiments of the present invention, preferably, in step (2), the methanation catalyst comprises: a support and an active component supported on the support, the active component being selected from nickel and / or rare earth elements.

[0045] In this invention, the carrier includes, but is not limited to, alumina, silicon oxide, etc.; the rare earth elements are selected from lanthanum (La) and cerium (Ce).

[0046] In some embodiments of the present invention, preferably, based on the total mass of the methanation catalyst, the nickel content is 15-25 wt%, for example, 15 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, and any value within the range of any two values, preferably 20-25 wt%; the rare earth element content is 0.1-5 wt%, for example, 0.1 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 2 wt%, 3 wt%, 5 wt%, and any value within the range of any two values, preferably 0.5-2 wt%.

[0047] In some embodiments of the present invention, preferably, in step (2), the third heat exchange process includes: after the decarbonized gas has undergone the first heat exchange, it undergoes a third heat exchange with circulating water to obtain decarbonized gas after the third heat exchange.

[0048] In this invention, the temperature of the circulating water is 30-43℃, for example, 30℃, 32℃, 35℃, 38℃, 40℃, 43℃, or any value within any range of two such values. In this invention, the circulating water originates from the circulating water plant's utilities supply.

[0049] In some embodiments of the present invention, preferably, the temperature of the decarbonized gas after the third heat exchange is 35-45°C, for example, 35°C, 38°C, 40°C, 42°C, 45°C, and any value within a range of any two values.

[0050] In this invention, lowering the temperature of the decarbonized gas after the third heat exchange does not significantly affect the CH4 and CO2 content in the refined natural gas, but it increases the consumption of circulating water and the investment in equipment.

[0051] In some embodiments of the present invention, preferably, in step (2), the refined natural gas contains CH4 content ≥ 93.5 mol%, preferably 93.5-98 mol%, for example, 93.5 mol%, 94 mol%, 95 mol%, 96 mol%, 97 mol%, 98 mol%, and any value within the range of any two values, more preferably 94-98 mol%.

[0052] In some embodiments of the present invention, preferably, in step (2), the CO2 content in the refined natural gas is ≤50ppm, for example, 50ppm, 40ppm, 30ppm, 20ppm, 15ppm, 10ppm, 5ppm, 4ppm, 3ppm, 2ppm, 1ppm, 0.9ppm, 0.8ppm, 0.5ppm, 0.4ppm, 0.2ppm, 0.1ppm, 0ppm, and any value within the range of any two values, preferably 0.1-15ppm, more preferably 0.1-5ppm.

[0053] In this invention, when the CO2 content in the refined natural gas is too high, it will cause the heat exchange tube bundles or pipes in the cryogenic liquefaction cold box to freeze and become blocked.

[0054] In this invention, the synthetic natural gas is sent to the LNG unit after fine decarbonization. After entering the LNG unit, the refined natural gas needs to be sent to a cold box for heat exchange to -162°C. CO2 will freeze into dry ice at low temperatures, clogging pipelines and equipment. Therefore, CO2 needs to be removed to below 50 ppm before entering the cold box.

[0055] A second aspect of the present invention provides a schematic diagram of a pre-liquefaction and decarbonization device for methanation-to-natural gas liquefaction, as shown in the figure below. Figure 1 As shown, the device includes a first heat exchanger 1, a second heat exchanger 2, a fine decarbonization tower 5, a third heat exchanger 6, and a gas-liquid separator 7 connected in sequence.

[0056] Wherein, the first heat exchanger 1 and the second heat exchanger 2 are respectively used to perform the first heat exchange and the second heat exchange on the synthetic natural gas as raw material gas 01 in sequence to obtain the heat-exchanged raw material gas 02.

[0057] The decarbonization tower 5 is filled with a methanation catalyst, which is used to mix the heat-exchanged raw material gas 02 with hydrogen 05. The resulting mixed gas 06 contacts and reacts with the methanation catalyst to obtain decarbonized gas 07, which is then sent to the gas-liquid separator 7 after passing through the first heat exchanger 1 and the third heat exchanger 6 to obtain refined natural gas 010 and condensate 011.

[0058] In this invention, such as Figure 1 As shown, the first heat exchanger 1 is used to perform the first heat exchange between the raw material gas 01 and the decarbonized gas 07 to obtain the raw material gas after the first heat exchange and the decarbonized gas after the first heat exchange 08; the second heat exchanger 2 is used to perform the second heat exchange between the raw material gas after the first heat exchange and the saturated steam 03 to obtain the raw material gas after the heat exchange 02 and the steam condensate 04.

[0059] In this invention, preferably, as follows: Figure 1 As shown, the device further includes a thermometer 3 and a temperature regulating valve 4 connected by a pipeline; wherein the thermometer 3 is installed on the pipeline connecting the second heat exchanger 2 and the decarbonization tower 5, and the temperature regulating valve 4 is installed on the saturated steam pipeline connecting the thermometer 3 and the second heat exchanger 2, for real-time monitoring and control of the temperature of the raw material gas 02 after heat exchange by regulating the temperature of the saturated steam 03.

[0060] In this invention, such as Figure 1 As shown, the third heat exchanger 6 is used to exchange the finely decarbonized gas 07 with circulating water after the first heat exchange to obtain finely decarbonized gas 09 after the third heat exchange.

[0061] In this invention, preferably, as follows: Figure 1 As shown, the device further includes: an online CO2 analyzer 8 and a flow control valve 9 connected by pipelines; wherein, the online CO2 analyzer 8 is installed on the refined natural gas pipeline at the top of the gas-liquid separator 7, and the flow control valve 9 is installed on the hydrogen pipeline connecting the online CO2 analyzer 8 and the decarbonization tower 5, for real-time monitoring and control of the CO2 content in the refined natural gas 010 by adjusting the flow rate of hydrogen 05.

[0062] The method provided by this invention removes CO2 from the methane syngas at the inlet of a natural gas liquefaction unit. After decarbonization, the CO2 content is ≤50ppm. The decarbonized syngas then enters a molecular sieve adsorption tower for further dehydration before entering a cold box to produce LNG. This method differs from the commonly used MDEA solvent absorption method, has a simpler process design, and can effectively reduce initial investment and operating costs.

[0063] According to a particularly preferred embodiment of the present invention, a method for pre-liquefaction and decarbonization of methanated synthetic natural gas includes the following steps:

[0064] (1) Synthetic natural gas is used as raw material gas and subjected to first heat exchange and second heat exchange in sequence. After heat exchange, the raw material gas is mixed with hydrogen to obtain a mixed gas with a molar ratio of H2 to CO2 ≥ 4.

[0065] (2) The mixed gas and the methanation catalyst are contacted and reacted to obtain a refined decarbonized gas. After the first heat exchange and the third heat exchange are performed, gas-liquid separation is performed to obtain refined natural gas and condensate.

[0066] The synthetic natural gas contains 0.089-2.5 mol% CO2, 90-96 mol% CH4, 1.5-3 mol% H2, 0-0.1 mol% CO, and 0.1-0.2 mol% H2O.

[0067] The reaction conditions include: a temperature of 260-280℃ and a volume hourly space velocity of 5000-8000 h⁻¹. -1 ;

[0068] Based on the total mass of the methanation catalyst, the nickel content is 20-25 wt% and the rare earth element content is 0.5-2 wt%.

[0069] The refined natural gas contains 94-98 mol% CH4 and 0.1-5 ppm CO2.

[0070] The present invention will be described in detail below through embodiments.

[0071] Feed gas P1: Methanated synthetic natural gas, with CO2 content of 0.221 mol%, CH4 content of 93.06 mol%, H2 content of 1.925 mol%, CO content of 0.00 mol%, H2O content of 0.185 mol%, N2 content of 3.695 mol%, and Ar content of 0.914 mol%; pressure of 4.53 MPa (G) and temperature of 40℃.

[0072] In methanation catalyst A1, the alumina support content is 75.5 wt%, the nickel content is 23 wt%, and the rare earth element (lanthanum, cerium) content is 1.5 wt%.

[0073] In methanation catalyst A2, the alumina support content is 78.6 wt%, the nickel content is 21 wt%, and the rare earth element (lanthanum, cerium) content is 0.4 wt%.

[0074] Example 1

[0075] Devices such as Figure 1As shown, it includes a first heat exchanger 1, a second heat exchanger 2, a fine decarbonization tower 5, a third heat exchanger 6 and a gas-liquid separator 7 connected in sequence, a thermometer 3 and a temperature regulating valve 4, as well as an online CO2 analyzer 8 and a flow control valve 9.

[0076] The method is carried out in the above-described apparatus and includes:

[0077] (1) The above-mentioned raw material gas P1 (flow rate of 23195.1 Nm³) 3 The gas is subjected to a first heat exchange with the decarbonized gas to obtain a first heat exchange feed gas at a temperature of 160℃. The gas is then subjected to a second heat exchange with saturated steam at a temperature of 323℃ to obtain a heat exchange feed gas at a temperature of 260℃. This feed gas is then mixed with hydrogen to obtain a mixed gas (H2 / CO2 molar ratio of 8.7).

[0078] (2) The above mixed gas and methanation catalyst A1 were brought into contact and reacted (temperature 260℃, space velocity 6000h). -1 After the decarbonized gas is subjected to the first heat exchange as described above, the decarbonized gas at a temperature of 161°C undergoes a third heat exchange with circulating water, resulting in a decarbonized gas at a temperature of 40°C. This gas is then subjected to gas-liquid separation to obtain refined natural gas S1 and condensate.

[0079] The refined natural gas S1 contained 0.4 ppm CO2 and 94.14 mol CH4.

[0080] Example 2

[0081] According to the apparatus provided in Example 1,

[0082] The method is carried out in the above-described apparatus and includes:

[0083] (1) The above-mentioned raw material gas P1 (flow rate of 23195.1 Nm³) 3 The gas is subjected to a first heat exchange with the decarbonized gas to obtain a first heat exchange feed gas at a temperature of 150℃. The gas is then subjected to a second heat exchange with saturated steam at a temperature of 323℃ to obtain a heat exchange feed gas at a temperature of 270℃. The gas is then mixed with hydrogen to obtain a mixed gas (H2 / CO2 molar ratio of 8.7).

[0084] (2) The above mixed gas and methanation catalyst A1 were brought into contact and reacted (temperature 270℃, space velocity 6500h). -1 After the decarbonized gas is subjected to the first heat exchange as described above, the decarbonized gas at a temperature of 158°C undergoes a third heat exchange with circulating water, resulting in a decarbonized gas at a temperature of 35°C. This gas is then subjected to gas-liquid separation to obtain refined natural gas S2 and condensate.

[0085] The refined natural gas S2 contained 0.87 ppm CO2 and 94.17 mol CH4.

[0086] Example 3

[0087] According to the apparatus provided in Example 1,

[0088] The method is carried out in the above-described apparatus and includes:

[0089] (1) The above-mentioned raw material gas P1 (flow rate of 23195.1 Nm³) 3 The gas is subjected to a first heat exchange with the decarbonized gas to obtain a first heat exchange feed gas at a temperature of 155℃. The gas is then subjected to a second heat exchange with saturated steam at a temperature of 323℃ to obtain a heat exchange feed gas at a temperature of 280℃. The gas is then mixed with hydrogen to obtain a mixed gas (H2 / CO2 molar ratio of 8.7).

[0090] (2) The above mixed gas and methanation catalyst A1 were brought into contact and reacted (temperature 280℃, space velocity 7000h). -1 After the decarbonized gas is subjected to the first heat exchange as described above, the decarbonized gas at a temperature of 159.4℃ undergoes a third heat exchange with circulating water to obtain a decarbonized gas at a temperature of 45℃. This gas is then subjected to gas-liquid separation to obtain refined natural gas S3 and condensate.

[0091] The refined natural gas S3 contained 1.7 ppm CO2 and 94.09 mol CH4.

[0092] Example 4

[0093] The apparatus according to Example 1;

[0094] The method provided in Example 1 is different,

[0095] In step (1), the H2 / CO2 molar ratio in the mixed gas is replaced with 3;

[0096] Under the same conditions, refined natural gas S4 was obtained.

[0097] The refined natural gas S4 contained 4990 ppm CO2 and 93.77 mol CH4.

[0098] Example 5

[0099] The apparatus according to Example 1;

[0100] The method provided in Example 1 is different,

[0101] In step (2), the reaction temperature is replaced with 280℃;

[0102] Under the same conditions, refined natural gas S5 was obtained.

[0103] The refined natural gas S5 contained 1.73 ppm CO2 and 94.19 mol CH4.

[0104] Example 6

[0105] The apparatus according to Example 1;

[0106] The method provided in Example 1 is different,

[0107] In step (2), the reaction temperature is replaced with 300℃;

[0108] Under the same conditions, refined natural gas S6 was obtained.

[0109] The refined natural gas S6 contained 6.28 ppm CO2 and 94.14 mol CH4.

[0110] Example 7

[0111] The apparatus according to Example 1;

[0112] The method provided in Example 1 is different,

[0113] In step (2), the methanation catalyst A1 is replaced with the methanation catalyst A2 to obtain refined natural gas S7.

[0114] The refined natural gas S7 contained 0.9 ppm CO2 and 94.14 mol CH4.

[0115] Comparative Example 1

[0116] The above-mentioned raw material gas P1 (flow rate of 23195.1 Nm³) 3 The adsorption process involves adsorption using molecular sieves ( / h), comprising three towers: one adsorption tower, one heating tower, and one cold blowing tower. Molecular sieve I packing capacity: 4.8 tons / tower (1120 mm), molecular sieve II packing capacity: 26.55 tons / tower (6930 mm), Φ6mm ceramic ball packing capacity: 1.2 tons / tower, Φ13mm ceramic ball packing capacity: 1.2 tons / tower, adsorbent bed resistance ≤40 kPa, regeneration gas flow rate (low-pressure nitrogen): 2500 Nm³. 3 / h, refined natural gas DS1 is obtained.

[0117] The refined natural gas DS1 contained 50 ppm CO2 and 93.19 mol CH4.

[0118] Comparative Example 2

[0119] After heat exchange with the decarbonized gas, the feed gas enters a scrubbing tower and contacts MDEA solvent to reduce CO2 to below 50 ppm. The decarbonized gas at the top of the scrubbing tower is heated to 40°C by a heat exchanger with the feed gas to obtain refined natural gas DS2. The MDEA solution after scrubbing is regenerated and pressurized by a lean solution pump before being sprayed into the top of the scrubbing tower. The methane loss rate in the feed gas after MDEA scrubbing is 6%, approximately 1300 Nm³. 3 The MDEA scrubbing tower has 30 trays per hour and a diameter of 0.8m.

[0120] The refined natural gas DS2 contained 18 ppm CO2 and 93.20 mol CH4.

[0121] Compared with Comparative Examples 1-2, Examples 1-7 use the method provided by the present invention, which not only effectively removes CO2 content from the raw gas, but also increases CH4 content in the refined natural gas, that is, makes the CH4 content in the refined natural gas 94-98 mol%, and the CO2 content 0.1-5 ppm.

[0122] Meanwhile, compared to Comparative Example 1 which uses molecular sieve adsorption, the area occupied is 18×8 m. 2 The project cost is 6.6 million yuan, and the operating cost is 7.154 million yuan per year; while Example 1 uses the device provided by this invention, which occupies an area of ​​12×7.5 m. 2 The project cost is 3.6 million yuan, and the operating cost is 1.7028 million yuan per year. That is, under the same scale, this invention is lower than the existing molecular sieve adsorption method in terms of land area, initial investment, and operating costs.

[0123] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for pre-liquefaction and decarbonization of methanated natural gas before liquefaction, characterized in that, The method includes the following steps: (1) Synthetic natural gas is used as raw material gas and subjected to first heat exchange and second heat exchange in sequence to obtain the raw material gas after heat exchange and hydrogen gas to obtain mixed gas. (2) The mixed gas and methanation catalyst are contacted and reacted to obtain a refined decarbonized gas. After the first heat exchange and the third heat exchange are performed, gas-liquid separation is performed to obtain refined natural gas and condensate.

2. The method according to claim 1, wherein, In step (1), The synthetic natural gas has a CO2 content of ≤2.5 mol%, preferably 0.089-2.5 mol%. Preferably, the synthetic natural gas contains 90-96 mol% CH4, 1.5-3 mol% H2, 0-0.1 mol% CO, and 0.1-0.2 mol% H2O. Preferably, the pressure of the synthetic natural gas is 2.2-5.5 MPa(G), more preferably 4-5 MPa(G); and the temperature is 20-50℃, more preferably 30-40℃.

3. The method according to claim 1 or 2, wherein, In step (1), The first heat exchange process includes: exchanging the raw material gas with the decarbonized gas to obtain the raw material gas after the first heat exchange and the decarbonized gas after the first heat exchange. Preferably, the temperature of the raw material gas after the first heat exchange is 150-160℃; the temperature of the finely decarbonized gas after the first heat exchange is 160-170℃. Preferably, the second heat exchange process includes: performing a second heat exchange between the first heat-exchanged raw material gas and saturated steam to obtain the heat-exchanged raw material gas and steam condensate; More preferably, the temperature of the saturated steam is 315-340°C; More preferably, the temperature of the raw material gas after heat exchange is 250-260℃; Preferably, the molar ratio of H2 to CO2 in the mixed gas is ≥4.

4. The method according to any one of claims 1-3, wherein, In step (2), The reaction conditions include: a temperature of 250-350℃; and a volume hourly space velocity of 5000-10000 h⁻¹. -1 ; Preferably, the reaction conditions include: a temperature of 260-280°C and a volume hourly space velocity of 5000-8000 h⁻¹. -1 .

5. The method described according to any one of requirements 1-4, wherein, In step (2), The methanation catalyst comprises: a support and an active component supported on the support, wherein the active component is selected from nickel and / or rare earth elements; Preferably, based on the total mass of the methanation catalyst, the nickel content is 15-25 wt%, more preferably 20-25 wt%; the rare earth element content is 0.1-5 wt%, more preferably 0.5-2 wt%.

6. The method described according to any one of requirements 1-5, wherein, In step (2), The third heat exchange process includes: after the decarbonized gas has passed through the first heat exchange, it undergoes a third heat exchange with circulating water to obtain decarbonized gas after the third heat exchange. Preferably, the temperature of the decarbonized gas after the third heat exchange is 35-45°C.

7. The method described according to any one of requirements 1-6, wherein, In step (2), The refined natural gas has a CH4 content of ≥93.5 mol%, preferably 93.5-98 mol%, more preferably 94-98 mol%; and a CO2 content of ≤50 ppm, preferably 0.1-15 ppm, more preferably 0.1-5 ppm.

8. A pre-liquefaction and decarbonization unit for methanation-synthetic natural gas, characterized in that, The device includes a first heat exchanger, a second heat exchanger, a fine decarbonization tower, a third heat exchanger, and a gas-liquid separator connected in sequence. The first heat exchanger and the second heat exchanger are used to sequentially perform the first heat exchange and the second heat exchange on synthetic natural gas as the feed gas to obtain the feed gas after heat exchange. The decarbonization tower is filled with a methanation catalyst, which is used to mix the heat-exchanged raw gas with hydrogen. The resulting mixed gas contacts and reacts with the methanation catalyst to obtain decarbonized gas, which is then sent to a gas-liquid separator after passing through the first heat exchanger and the third heat exchanger to obtain refined natural gas and condensate.

9. The apparatus according to claim 8, wherein, The device also includes: a thermometer and a temperature regulating valve connected by a pipe; The thermometer is installed on the pipeline connecting the second heat exchanger and the decarbonization tower, and the temperature regulating valve is installed on the saturated steam pipeline connecting the thermometer and the second heat exchanger. The valve is used to monitor and control the temperature of the raw gas after heat exchange in real time by adjusting the temperature of the saturated steam.

10. The apparatus according to claim 8 or 9, wherein, The device also includes: an online CO2 analyzer and a flow control valve connected by a pipeline; The CO2 online analyzer is installed on the refined natural gas pipeline at the top of the gas-liquid separator tower, and the flow control valve is installed on the hydrogen pipeline connecting the CO2 online analyzer and the decarbonization tower. The flow control valve is used to monitor and control the CO2 content in the refined natural gas in real time by adjusting the flow rate of hydrogen.

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