South China Sea carbon-rich natural gas decarburization process and device for methanation

Abstract

The invention discloses a South China Sea carbon-rich natural gas decarburization process and device for methanation, and belongs to the technical field of new energy consumption and natural gas chemical industry. The decarburization device comprises an absorption system, a condensation liquefaction system, a flash evaporation system, a thermal regeneration system and a water washing system. By means of high integration of natural gas condensation and liquefaction, decarburization load distribution, throttling refrigeration and the like and process parameter optimization, the good energy-saving purpose can be achieved, good economical efficiency and reliability are achieved, the process is environmentally friendly, and the method is suitable for treating natural gas resources with high CO2 content in the South China Sea.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy consumption and natural gas chemical industry, and particularly relates to a decarburization process and device for the methaneization of South China carbon-rich natural gas. BACKGROUND

[0002] South China is rich in natural gas resources and is an important basis for ensuring the stable development of the national natural gas industry. However, the carbon dioxide content in the natural gas produced by some typical gas fields in this region is generally between 20% and 80%, which belongs to high-carbon natural gas resources. The efficient development and resource utilization of such carbon-rich natural gas is of great significance to promoting the green transformation of the marine oil and gas industry and supporting the supply of carbon sources in the field of new energy chemical industry.

[0003] At present, the chemical absorption method (such as solvent decarburization process using monoethanolamine (MEA), diethanolamine (DEA), N-methyldiethanolamine (MDEA), etc.) is a commonly used technology for natural gas decarburization. Its process flow is relatively simple and the technology is mature. However, this method still has the following obvious problems when dealing with high-concentration carbon dioxide natural gas: the overall energy consumption is relatively high, resulting in high decarburization cost and the need for economic improvement; it cannot fully face the new energy chemical consumption scenario and achieve efficient separation and recycling of carbon dioxide under low energy consumption conditions; in addition, the corrosion of amine liquid system to equipment also restricts the long-term stable operation of the decarburization equipment and process.

[0004] Chinese patent CN117887496A discloses a low-temperature methanol washing one-step dehydration decarburization coupling carbon capture system and method. By connecting a dehydration unit, a decarburization unit, a methanol regeneration unit and a carbon dioxide liquefaction unit in series, combining a multi-stage flash evaporation section and a inter-stage cooler, and utilizing system waste heat to realize methanol regeneration, the process flow is simplified and the energy consumption is reduced, thereby improving the adaptability and stability of the process. However, when this patent technology is applied to the decarburization treatment process of high-carbon South China natural gas, there is still a problem of limited reduction of process energy consumption.

[0005] Therefore, in view of the composition characteristics of South China carbon-rich natural gas with high carbon dioxide content and the urgent need for low-cost carbon sources coupled with new energy consumption, it is urgent to develop a decarburization process and device with low energy consumption, low corrosion and economic carbon recovery, to help achieve high-quality development of China's marine oil and gas industry. SUMMARY

[0006] To solve the above technical problems, the application provides a decarburization process and device for the methaneization of South China carbon-rich natural gas, which effectively reduces the decarburization cost and the compression energy consumption of carbon dioxide recovery by designing the material flow conversion mode, thereby helping the chemical consumption of new energy.

[0007] The application achieves the technical effects through the following technical scheme: A decarburization device for South China carbon-rich natural gas for methanation, comprising an absorption system, a condensation and liquefaction system, a flash system, a thermal regeneration system and a water washing system.

[0008] The absorption system comprises an absorption tower, a first heat exchanger, a second heat exchanger and a first propylene cooler.

[0009] The condensation and liquefaction system comprises a second propylene cooler, a throttling heat exchanger and a flash tank.

[0010] The flash system comprises a flash tower, a circulating gas compressor, a carbon dioxide multi-stage compressor and a circulating gas cooler.

[0011] The thermal regeneration system comprises a third heat exchanger, a thermal regeneration tower, a third propylene cooler, a thermal regeneration tower cooler and a thermal regeneration tower reboiler.

[0012] The water washing system comprises a water washing tower, a methanol water tower, a methanol water tower cooler, a methanol water tower reboiler and a water washing water cooler.

[0013] Further, along the direction of the raw material gas flow, the first outlet of the first heat exchanger is connected with the first inlet of the second heat exchanger, the first inlet of the second heat exchanger is connected with the first outlet of the second heat exchanger, the first outlet of the second heat exchanger is connected with the inlet of the second propylene cooler, the outlet of the second propylene cooler is connected with the first inlet of the throttling heat exchanger, the first inlet of the throttling heat exchanger is connected with the first outlet of the throttling heat exchanger, and the first outlet of the throttling heat exchanger is connected with the inlet of the flash tank.

[0014] The bottom outlet of the flash tank is connected with the second inlet of the throttling heat exchanger, the second inlet of the throttling heat exchanger is connected with the second outlet of the throttling heat exchanger, the second outlet of the throttling heat exchanger is connected with any one or more of the first flash tower section, the second flash tower section, the third flash tower section or the fourth flash tower section of the flash tower, the top outlet of the flash tank is connected with the second inlet of the second heat exchanger, the second inlet of the second heat exchanger is connected with the second outlet of the second heat exchanger, and the second outlet of the second heat exchanger is connected with the raw material gas inlet at the bottom of the absorption tower.

[0015] Further, the absorption tower is composed of a main washing section and a fine washing section, and the first propylene cooler is arranged in the middle of the main washing section of the absorption tower.

[0016] Further, the flash tower is composed of a first flash tower section, a second flash tower section, a third flash tower section and a fourth flash tower section, the bottom outlet of the first flash tower section is connected with the inlet of the second flash tower section, the bottom outlet of the second flash tower section is connected with the inlet of the third flash tower section, and the bottom outlet of the third flash tower section is connected with the inlet of the fourth flash tower section.

[0017] Further, the top outlet of the first flash tower section is connected with the inlet of the recycle gas compressor, the outlet of the recycle gas compressor is connected with the inlet of the recycle gas cooler, and the outlet of the recycle gas cooler is connected with the first inlet of the first heat exchanger. The top outlets of the second flash tower section, the third flash tower section and the fourth flash tower section are all connected with the carbon dioxide multi-stage compressor.

[0018] Further, the outlet pipeline of the fourth flash tower section is divided into four routes, the first route is connected with the top semi-lean methanol inlet of the absorption tower, the second route is connected with the inlet of the second propylene cooler, the third route is connected with the first inlet of the third heat exchanger, the first outlet of the third heat exchanger is connected with the bottom inlet of the thermal regeneration tower, and the fourth route is connected with the top inlet of the first flash tower section.

[0019] Further, the top of the thermal regeneration tower is provided with a thermal regeneration tower cooler, the outlet of the thermal regeneration tower cooler is connected with the bottom inlet of the water washing tower, and the bottom of the thermal regeneration tower is provided with a thermal regeneration tower reboiler. The bottom outlet of the thermal regeneration tower is connected with the second inlet of the third heat exchanger, the second outlet of the third heat exchanger is connected with the inlet of the third propylene cooler, and the outlet of the third propylene cooler is connected with the top lean methanol inlet of the absorption tower.

[0020] Further, the bottom outlet of the water washing tower is connected with the inlet of the methanol water tower, and the top outlet of the water washing tower is connected with the carbon dioxide multi-stage compressor.

[0021] Further, the bottom outlet of the methanol water tower is connected with the inlet of the water washing water cooler, the outlet of the water washing water cooler is connected with the top inlet of the water washing tower, the top outlet of the methanol water tower is provided with a methanol water tower cooler, the outlet of the methanol water tower cooler is connected with the inlet of the thermal regeneration tower, and the bottom of the methanol water tower is provided with a methanol water tower reboiler.

[0022] Secondly, the application also provides a decarbonization process using the above device, which comprises the following steps: The raw gas is sequentially heat-exchanged by the first heat exchanger and the second heat exchanger, and then flows into the condensation liquefaction system. The raw gas is sequentially heat-exchanged by the second propylene cooler and the throttling heat exchanger, and then flows into the flash tank.

[0023] Further, the molar composition of the raw gas comprises 20% to 80% CO2, 40% to 60% CH4 and 4% to 15% N2.

[0024] Further, the condensing liquefaction system is used for preliminary separation of carbon dioxide, the condensing liquefaction temperature of the second propylene cooler is -40℃~ -52℃, and the throttling pressure of the throttling heat exchanger is 0.2~0.8 MPaG.

[0025] Further, the flash condensate flowing out of the bottom of the flash tank is sent to the first flash column section, the second flash column section, the third flash column section or the fourth flash column section after heat exchange with the raw material gas in the throttling heat exchanger; the condensed liquefied flash gas flowing out of the flash tank is sent into the absorption tower after heat exchange with the raw material gas in the second heat exchanger, and is contacted with the lean / half-lean methanol absorbent flowing from top to bottom in the absorption tower to absorb carbon dioxide, and then forms carbon-rich methanol flowing out of the absorption tower into the flash system; the purified gas flowing out of the top of the absorption tower is heat-exchanged with the raw material gas in the first heat exchanger to reduce the temperature of the raw material gas.

[0026] Further, the absorption tower is used for final decarburization of the raw material gas, and the absorbent comprises lean methanol and half-lean methanol; the molar ratio of the raw material gas, the lean methanol and the half-lean methanol in the absorption tower is 1.0:0.5~1.2:0.4~0.6.

[0027] Further, the operating pressure of the absorption tower is 3.3~3.5 MPaG, and the CO2 content in the purified gas flowing out of the absorption tower is less than 2.5%.

[0028] The carbon-rich methanol enters the first flash column section of the flash tower in the flash system, and the flash liquid of the first flash column section flows into the second flash column section, the third flash column section and the fourth flash column section in turn; the gas flowing out of the top of the first flash column section is pressurized by a circulating gas compressor and cooled by a circulating gas cooler, and then flows into the raw material gas; the carbon dioxide flowing out of the top of the second flash column section, the third flash column section and the fourth flash column section is compressed by a multi-stage carbon dioxide compressor; the half-lean methanol flowing out of the bottom of the fourth flash column section is divided into four parts, the first part flows into the absorption tower as a carbon dioxide absorbent, the second part flows into the second propylene cooler as an anti-freezing liquid mixed with the raw material gas, the third part flows into the third heat exchanger of the thermal regeneration system for heat exchange and then flows into the thermal regeneration tower, and the last part flows into the first flash column section as a circulating gas absorbent.

[0029] Further, the flash in the first flash column section is used for recovering CH4 components in the raw material gas, and the flashed CH4 components are pressurized by a circulating gas compressor and then sent back to the raw material system; the flashes in the second, third and fourth flash column sections are used for recovering CO2, and the multi-stage design is used to reduce the pressure loss; preferably, the flash pressure of the first flash column section is 0.2~1.4 MPaG, the flash pressure of the second flash column section is 0.6~1.4 MPaG, the flash pressure of the third flash column section is 0.3~1.0 MPaG, and the flash pressure of the fourth flash column section is 0.02~0.3 MPaG.

[0030] Furthermore, the outlet pressures of the multi-stage carbon dioxide compressor are 0.2~0.4 MPaG, 0.3~0.8 MPaG, 1.0~2.0 MPaG, and 3.0~3.6 MPaG, respectively. The CH4 content in the recovered carbon dioxide is 4~20%, which can be adjusted by regulating the flow rate and operating pressure of the flash condensate to the first flash tower section, as well as the position of the flash condensate entering the flash tower section.

[0031] Furthermore, the molar ratio of semi-lean methanol flowing into the first flash tower section, the absorption tower, the second propylene cooler, and the third heat exchanger is 3-5:30-40:1-10:45-70.

[0032] Furthermore, the molar composition of the semi-lean methanol is: 2%~5% CO2 and 95%~98% CH3OH; the temperature of the semi-lean methanol is -20℃~-50℃.

[0033] Furthermore, the regenerated lean methanol flowing from the bottom of the thermal regeneration tower first exchanges heat with the semi-lean methanol in the third heat exchanger, and then flows into the absorption tower as a carbon dioxide absorbent after being cooled by the third propylene cooler. The methanol-containing gas generated at the top of the thermal regeneration tower is condensed by the thermal regeneration tower cooler and then flows into the water washing tower.

[0034] Furthermore, the operating pressure of the thermal regeneration tower is 0.1~0.5 MPaG.

[0035] Furthermore, the de-alcoholized carbon dioxide gas at the top of the water washing tower flows into a carbon dioxide multi-stage compressor for recovery and treatment, the alcohol-water mixture flowing out from the bottom of the water washing tower flows into a methanol water tower, the methanol flowing out from the top of the methanol water tower is condensed by the methanol water tower cooler and then flows into a thermal regeneration tower, and the regenerated wash water flowing out from the bottom of the methanol water tower is cooled by the wash water cooler and then flows into the water washing tower for use.

[0036] Furthermore, the operating pressure of the water washing tower is 0.1~0.5 MPaG; the operating pressure of the methanol water tower is 0.02~0.4 MPaG.

[0037] The beneficial effects of this invention are: (1) This application specifically designs a pre-condensation liquefaction system for the high CO2 (20-80%) characteristics of natural gas in the South China Sea. In the condensation liquefaction system, part of the CO2 in the feed gas is separated to reduce the load on the subsequent absorption tower. In addition, this application designs a semi-lean methanol diversion and utilization system. The semi-lean methanol obtained from the bottom of the flash tower is distributed to the heat-regenerating tower, absorption tower, flash tower and condensation liquefaction system as an antifreeze to prevent the feed gas from freezing. This reduces the total amount of methanol that needs to enter the high-energy-consuming heat regeneration tower, realizes energy recovery and utilization, and reduces energy consumption.

[0038] (2) This application designs a four-stage flash tower and optimizes the pressure levels of different flash tower sections to achieve staged desorption of gas. The first stage flash tower is dedicated to CH4 recovery. By controlling the flow rate, operating pressure and feed position of the condensation and liquefaction system to the first stage, the CH4 content entrained in the final CO2 product can be flexibly adjusted, which has excellent operational flexibility.

[0039] (3) This application achieves good energy saving through high integration and process parameter optimization of natural gas condensation and liquefaction, decarbonization load distribution and throttling refrigeration. It has good economic efficiency and reliability, and the process is environmentally friendly. It is suitable for processing natural gas resources with high CO2 content such as those in the South China Sea. Attached Figure Description Figure 1 : A diagram of the apparatus for the carbon-rich natural gas decarbonization process of this application.

[0040] T1 - Absorber, T2 - Flash evaporator (4 stages from I to IV), T3 - Thermal regeneration tower, T4 - Water washing tower, T5 - Methanol water tower, E1 - First heat exchanger, E2 - Second heat exchanger, E3 - Second propylene cooler, E4 - Throttling heat exchanger, E5 - First propylene cooler, E6 - Circulating gas cooler, E7 - Third propylene cooler, E8 - Thermal regeneration tower cooler, E9 - Thermal regeneration tower reboiler, E10 - Third heat exchanger, E11 - Methanol water tower cooler, E12 - Methanol water tower reboiler, E13 - Water washing water cooler, C1 - Circulating gas compressor, C2 - Carbon dioxide multi-stage compressor, F1 - Flash evaporator. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] All raw materials involved in this invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be used as a reference.

[0043] The working principle of each system in this application: (1) Condensation and liquefaction system: This system gradually cools CO2 gas to below its dew point temperature through a series of heat exchangers, thereby condensing and liquefying it, and initially separating CO2 from the raw material. Its key components include a propylene cooler and a heat exchanger with a throttling device. In the propylene cooler, propylene refrigerant exchanges heat with the process fluid (such as carbon-rich natural gas containing methanol antifreeze) to provide cooling capacity; the heat exchanger with a throttling device reduces the pressure of the fluid, further lowering its temperature.

[0044] (2) Absorption System: The raw material natural gas is brought into countercurrent contact with low-temperature methanol (or lean / semi-lean methanol) in the absorption tower at a certain temperature (usually provided by refrigerants such as propylene) and pressure. The methanol selectively absorbs acidic gases such as CO2, and the purified gas (purified gas) is discharged from the top of the tower. The methanol that has absorbed acidic gases is called rich methanol and is sent to the flash evaporation system for regeneration. This system can deeply remove CO2 gas, meeting the decarbonization requirements of commercial natural gas.

[0045] (3) Flash Evaporation System: Based on the principle of flash evaporation, the high-pressure methanol-rich solution, rich in acidic gases and a small amount of useful gases, from the absorption tower is throttled and depressurized before entering the flash evaporation tower, where the pressure decreases sequentially. The pressure reduction causes the dissolved CO2 gas to be rapidly released due to supersaturation, and it is subsequently compressed and recovered. Staged recovery helps reduce the power consumption of feedstock compression in the subsequent carbon dioxide methanation reaction, and the presence of some methane in the feedstock can appropriately alleviate the temperature rise problem in the adiabatic reaction.

[0046] (4) Thermal regeneration system: This system is used to ensure the recycling of methanol solvent and generate CO2 gas stream; the methanol solution containing CO2 is indirectly heated in the thermal regeneration tower by steam or other heat medium, the temperature rise significantly reduces the solubility of CO2 gas in methanol, causing it to desorb violently.

[0047] (5) Water washing system: used to recover methanol entrained in the process tail gas. The tail gas generated during the process enters the water washing tower. Inside the tower, the tail gas comes into countercurrent contact with water, and the methanol vapor entrained in the tail gas is absorbed by the water to form a dilute methanol solution. The purified tail gas is then compressed and recovered. The recovered dilute methanol solution is then sent to a methanol-water separation system (usually by distillation) for concentration, and the recovered regenerated methanol is returned to the absorption system for use as an absorbent.

[0048] Example 1 This embodiment provides a decarbonization device for methanation of carbon-rich natural gas from the South China Sea (see attached). Figure 1 It includes: absorption system, condensation and liquefaction system, flash evaporation system, heat regeneration system and water washing system.

[0049] The absorption system includes an absorption tower T1, a first heat exchanger E1, a second heat exchanger E2, and a first propylene cooler E5. The condensation and liquefaction system includes a second propylene cooler E3, a throttling heat exchanger E4, and a flash evaporator F1. The flash evaporation system includes a flash tower T2, a circulating gas compressor C1, a multi-stage carbon dioxide compressor C2, and a circulating gas cooler E6. The thermal regeneration system includes a third heat exchanger E10, a thermal regeneration tower T3, a third propylene cooler E7, a thermal regeneration tower cooler E8, and a thermal regeneration tower reboiler E9. The water washing system includes a water washing tower T4, a methanol water tower T5, a methanol water tower cooler E11, a methanol water tower reboiler E12, and a water washing water cooler E13.

[0050] Along the direction of raw material flow, the first outlet of the first heat exchanger E1 is connected to the first inlet of the second heat exchanger E2, the first inlet of the second heat exchanger E2 is connected to the first outlet of the second heat exchanger E2, the first outlet of the second heat exchanger E2 is connected to the inlet of the second propylene cooler E3, the outlet of the second propylene cooler E3 is connected to the first inlet of the throttling heat exchanger E4, the first inlet of the throttling heat exchanger E4 is connected to the first outlet of the throttling heat exchanger E4, and the first outlet of the throttling heat exchanger E4 is connected to the inlet of the flash tank F1.

[0051] The bottom outlet of the flash tank F1 is connected to the second inlet of the throttling heat exchanger E4. The second inlet and the second outlet of the throttling heat exchanger E4 are connected. The second outlet of the throttling heat exchanger E4 is connected to any one or more of the first flash tower section I, the second flash tower section II, the third flash tower section III, or the fourth flash tower section IV of the flash tower T2. The top outlet of the flash tank F1 is connected to the second inlet of the second heat exchanger E2. The second inlet and the second outlet of the second heat exchanger E2 are connected. The second outlet of the second heat exchanger E2 is connected to the bottom raw material gas inlet of the absorption tower T1.

[0052] The absorption tower T1 consists of a main washing section and a fine washing section, with a total of 14 trays. The first propylene cooler E5 is located in the middle of the main washing section of the absorption tower T1. The bottom of the absorption tower T1 is provided with a raw material gas inlet and a rich methanol outlet, and the top is provided with a lean methanol inlet, a semi-lean methanol inlet, and a purified gas outlet. The purified gas outlet at the top of the absorption tower T1 is connected to the second inlet of the first heat exchanger E1, and the rich methanol outlet of the absorption tower is connected to the inlet of the first flash tower section I of the flash tower T2.

[0053] Flash tower T2 consists of four sections: Flash Tower Section I, Flash Tower Section II, Flash Tower Section III, and Flash Tower Section IV. The bottom outlet of Flash Tower Section I (containing 15 trays) is connected to the inlet of Flash Tower Section II. The bottom outlet of Flash Tower Section II is connected to the inlet of Flash Tower Section III. The bottom outlet of Flash Tower Section III is connected to the inlet of Flash Tower Section IV. The top outlet of Flash Tower Section I is connected to the inlet of circulating gas compressor C1. The outlet of circulating gas compressor C1 is connected to the inlet of circulating gas cooler E6. The outlet of circulating gas cooler E6 is connected to the first inlet of the first heat exchanger E1. The top outlets of Flash Tower Section II, Flash Tower Section III, and Flash Tower Section IV are all connected to the multi-stage carbon dioxide compressor C2.

[0054] The outlet pipeline of the fourth flash tower section IV is divided into four routes. The first route is connected to the semi-lean methanol inlet at the top of the absorption tower T1. The second route is connected to the inlet of the second propylene cooler E3. The third route is connected to the first inlet of the third heat exchanger E10. The first outlet of the third heat exchanger E10 is connected to the bottom inlet of the thermal regeneration tower T3. The fourth route is connected to the top inlet of the first flash tower section I.

[0055] A thermal regeneration tower cooler E8 is installed at the top of the thermal regeneration tower T3, and the outlet of the thermal regeneration tower cooler E8 is connected to the bottom inlet of the water washing tower T4. A thermal regeneration tower reboiler E9 is installed at the bottom of the thermal regeneration tower T3, and the bottom outlet of the thermal regeneration tower T3 is connected to the second inlet of the third heat exchanger E10. The second outlet of the third heat exchanger E10 is connected to the inlet of the third propylene cooler E7, and the outlet of the third propylene cooler E7 is connected to the lean methanol inlet at the top of the absorption tower T1.

[0056] The bottom outlet of the water washing tower T4 is connected to the inlet of the methanol water tower T5, and the top outlet of the water washing tower T4 is connected to the carbon dioxide multi-stage compressor C2.

[0057] The bottom outlet of the methanol water tower T5 is connected to the inlet of the washing water cooler E13, and the outlet of the washing water cooler E13 is connected to the top inlet of the washing tower T4; the top outlet of the methanol water tower T5 is equipped with a methanol water tower cooler E11, and the outlet of the methanol water tower cooler E11 is connected to the inlet of the thermal regeneration tower T3; the bottom of the methanol water tower T5 is equipped with a methanol water tower reboiler E12.

[0058] Example 2 This embodiment provides a decarbonization process for methanated carbon-rich natural gas from the South China Sea, including the following steps: The feed gas (molar composition: 30% CO2, 60% CH4, and 10% N2) is initially cooled after exchanging heat with the purified gas from the top of the absorption tower T1 in the first heat exchanger E1. It then flows into the second heat exchanger E2, where it is further cooled by exchanging heat with the condensed liquefied flash vapor from flash tank F1. Subsequently, it flows into the condensation and liquefaction system, passing through the second propylene cooler E3 and the throttling heat exchanger E4 before flowing into flash tank F1 for flash evaporation. The flash condensate flowing from the bottom of flash tank F1 is then sent to the first flash tower section I after exchanging heat with the feed gas in the throttling heat exchanger E4. The second flash tower section II, the third flash tower section III, or the fourth flash tower section IV are used to adjust the methane recovery rate. The condensed and liquefied flash vapor from flash tank F1 flows into the second heat exchanger E2 and exchanges heat with the feed gas before being sent to the absorption tower T1. In the absorption tower T1, it contacts the lean / semi-lean methanol flowing from top to bottom. After absorbing carbon dioxide, the carbon-rich methanol formed flows out of the absorption tower T1 and enters the flash system. The purified gas flow from the top of the absorption tower T1 exchanges heat with the feed gas through the first heat exchanger E1.

[0059] The condensation temperature of the second propylene cooler E3 is -48℃, the throttling pressure of the throttling heat exchanger E4 is 0.35 MPaG, and the molar ratio of raw material gas, lean methanol, and semi-lean methanol in the absorption tower T1 is 1.00:1.05:0.55; the temperature of the lean methanol is -41℃, the temperature of the semi-lean methanol is -38℃, and the molar composition is 4% CO2 and 96% CH3OH (the semi-lean methanol comes from the fourth flash tower section IV); the operating pressure of the absorption tower T1 is 3.4 MPaG, and the CO2 content in the purified gas flowing out from the top of the absorption tower T1 is less than 2.5%; the temperature of the carbon-rich methanol is -17℃.

[0060] The carbon-rich methanol enters the first flash tower section I of flash tower T2 in the flash evaporation system. The gas collected from the top of the first flash tower section I is pressurized by the circulating gas compressor C1 and cooled by the circulating gas cooler E6 before flowing into the raw material gas to cool it down. The flash liquid from the first flash tower section I flows into the second flash tower section II, the third flash tower section III, and the fourth flash tower section IV in sequence. The carbon dioxide collected from the top of the second flash tower section II, the third flash tower section III, and the fourth flash tower section IV is compressed by the carbon dioxide multi-stage compressor C2 before flowing out. The semi-lean methanol collected from the bottom of the fourth flash tower section IV is divided into four parts. The first part flows into the absorber T1 as a carbon dioxide absorbent. The second part flows into the second propylene cooler E3 as antifreeze to mix with the raw material gas, avoiding extreme freezing scenarios when the material flows into the throttling heat exchanger. The third part flows into the third heat exchanger E10 of the thermal regeneration system for heat exchange before flowing into the thermal regeneration tower T3. The last part flows into the first flash tower section I as a circulating gas absorbent.

[0061] The flash pressures of the first flash tower section I, the second flash tower section II, the third flash tower section III, and the fourth flash tower section IV are 0.1 MPaG. The outlet pressures of the multi-stage carbon dioxide compressor C2 are 0.2 MPaG, 0.5 MPaG, 1.8 MPaG, and 3.5 MPaG, respectively. The molar ratio of semi-lean methanol flowing into the first flash tower section I, the absorption tower T1, the second propylene cooler E3, and the third heat exchanger E10 is 4.1:31.4:1.8:62.6.

[0062] The semi-lean methanol, heated by the third heat exchanger E10, is further heated in the thermal regeneration tower T3 for thermal regeneration. The regenerated lean methanol flowing from the bottom of the thermal regeneration tower T3 first exchanges heat with the semi-lean methanol in the third heat exchanger E10, and then flows into the absorption tower T1 as a carbon dioxide absorbent after being cooled by the third propylene cooler E7. The methanol-containing gas generated at the top of the thermal regeneration tower T3 is condensed by the thermal regeneration tower cooler E8 and then flows into the water washing tower T4 for methanol washing and recovery. The de-alcoholized carbon dioxide gas at the top of the water washing tower T4 flows into the carbon dioxide multi-stage compressor C2 for recovery and treatment. The alcohol-water mixture flowing from the bottom of the water washing tower T4 flows into the methanol water tower T5 for heating and alcohol-water separation. The methanol flowing from the top of the methanol water tower T5 is condensed by the methanol water tower cooler E11 and then flows into the thermal regeneration tower T3. The regenerated wash water flowing from the bottom of the methanol water tower T5 is cooled by the wash water cooler E13 and then flows into the water washing tower T4 for use.

[0063] The operating pressure of the thermal regeneration tower T3 is 0.3 MPaG; the operating pressure of the water washing tower is 0.2 MPaG; and the operating pressure of the methanol water tower is 0.1 MPaG. The CO2 recovery rate is 95%, with a CH4 content of 7.5%.

[0064] In this embodiment, the energy consumption for obtaining one ton of carbon dioxide is: 0.58 GJ for circulating water, 0.57 GJ for low-pressure steam, 0.03 GJ for electricity, and 0.41 GJ for propylene cooling; the total standard energy consumption is 1.99 GJ.

[0065] Based on the following costs: circulating water 0.5 yuan / ton, low-pressure steam 60 yuan / ton, electricity 0.5 yuan / kWh, and propylene cooling capacity 600 yuan / MWh; the utility cost for obtaining one ton of carbon dioxide is calculated to be 97 yuan.

[0066] Example 3 This embodiment provides a decarbonization process for methanated carbon-rich natural gas from the South China Sea, including the following steps: The feed gas (molar composition: 60% CO2, 30% CH4, and 10% N2) is initially cooled after exchanging heat with the purified gas from the top of the absorption tower T1 in the first heat exchanger E1. It then flows into the second heat exchanger E2, where it is further cooled by exchanging heat with the condensed liquefied flash vapor from the flash tank F1. Subsequently, it flows into the condensation and liquefaction system, passing through the second propylene cooler E3 and the throttling heat exchanger E4 before flowing into the flash tank F1 for flash evaporation. The flash condensate flowing from the bottom of the flash tank F1 is then sent to the first flash tower section I after exchanging heat with the feed gas in the throttling heat exchanger E4. The second flash tower section II, the third flash tower section III, or the fourth flash tower section IV are used to adjust the methane recovery rate. The condensed and liquefied flash vapor from flash tank F1 flows into the second heat exchanger E2 and exchanges heat with the feed gas before being sent to the absorption tower T1. In the absorption tower T1, it contacts the lean / semi-lean methanol flowing from top to bottom. After absorbing carbon dioxide, the carbon-rich methanol formed flows out of the absorption tower T1 and enters the flash system. The purified gas flow from the top of the absorption tower T1 exchanges heat with the feed gas through the first heat exchanger E1.

[0067] The condensation temperature of the second propylene cooler E3 is -46℃, the throttling pressure of the throttling heat exchanger E4 is 0.6 MPaG, and the molar ratio of raw material gas, lean methanol, and semi-lean methanol in the absorption tower T1 is 1.00:0.65:0.49; the temperature of the lean methanol is -41℃, the temperature of the semi-lean methanol is -21℃, and the molar composition is 4% CO2 and 96% CH3OH (the semi-lean methanol comes from the fourth flash distillation section IV); the operating pressure of the absorption tower T1 is 3.4 MPaG, and the CO2 content in the purified gas flowing out from the top of the absorption tower T1 is less than 2%; the temperature of the carbon-rich methanol is -1℃.

[0068] The carbon-rich methanol enters the first flash tower section I of flash tower T2 in the flash evaporation system. The gas collected from the top of the first flash tower section I is pressurized by the circulating gas compressor C1 and cooled by the circulating gas cooler E6 before flowing into the raw material gas to cool it down. The flash liquid from the first flash tower section I flows into the second flash tower section II, the third flash tower section III, and the fourth flash tower section IV in sequence. The carbon dioxide collected from the top of the second flash tower section II, the third flash tower section III, and the fourth flash tower section IV is compressed by the carbon dioxide multi-stage compressor C2 before flowing out. The semi-lean methanol collected from the bottom of the fourth flash tower section IV is divided into four parts. The first part flows into the absorber T1 as a carbon dioxide absorbent. The second part flows into the second propylene cooler E3 as antifreeze to mix with the raw material gas, avoiding extreme freezing scenarios when the material flows into the throttling heat exchanger. The third part flows into the third heat exchanger E10 of the thermal regeneration system for heat exchange before flowing into the thermal regeneration tower T3. The last part flows into the first flash tower section I as a circulating gas absorbent.

[0069] The flash pressures of the first flash tower section I, the second flash tower section II, the third flash tower section III, and the fourth flash tower section IV are 0.1 MPaG. The outlet pressures of the multi-stage carbon dioxide compressor C2 are 0.2 MPaG, 0.5 MPaG, 1.8 MPaG, and 3.5 MPaG, respectively. The molar ratio of semi-lean methanol flowing into the first flash tower section I, the absorption tower T1, the second propylene cooler E3, and the third heat exchanger E10 is 3.4:38.5:6.6:51.5.

[0070] The semi-lean methanol, heated by the third heat exchanger E10, is further heated in the thermal regeneration tower T3 for thermal regeneration. The regenerated lean methanol flowing from the bottom of the thermal regeneration tower T3 first exchanges heat with the semi-lean methanol in the third heat exchanger E10, and then flows into the absorption tower T1 as a carbon dioxide absorbent after being cooled by the third propylene cooler E7. The methanol-containing gas generated at the top of the thermal regeneration tower T3 is condensed by the thermal regeneration tower cooler E8 and then flows into the water washing tower T4 for methanol washing and recovery. The de-alcoholized carbon dioxide gas at the top of the water washing tower T4 flows into the carbon dioxide multi-stage compressor C2 for recovery and treatment. The alcohol-water mixture flowing from the bottom of the water washing tower T4 flows into the methanol water tower T5 for heating and alcohol-water separation. The methanol flowing from the top of the methanol water tower T5 is condensed by the methanol water tower cooler E11 and then flows into the thermal regeneration tower T3. The regenerated wash water flowing from the bottom of the methanol water tower T5 is cooled by the wash water cooler E13 and then flows into the water washing tower T4 for use.

[0071] The operating pressure of the thermal regeneration tower T3 is 0.5 MPaG; the operating pressure of the water washing tower is 0.2 MPaG; and the operating pressure of the methanol water tower is 0.1 MPaG. The CO2 recovery rate is 97%, with a CH4 content of 8.3%.

[0072] In this embodiment, the energy consumption for obtaining one ton of carbon dioxide is: 0.18 GJ for circulating water, 0.20 GJ for low-pressure steam, 0.01 GJ for electricity, and 0.18 GJ for propylene cooling; the total standard energy consumption is 0.78 GJ.

[0073] Based on the following costs: circulating water 0.5 yuan / ton, low-pressure steam 60 yuan / ton, electricity 0.5 yuan / kWh, and propylene cooling capacity 600 yuan / MWh; the utility cost for obtaining one ton of carbon dioxide is calculated to be 40 yuan.

[0074] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A decarbonization device for South China Sea carbon-rich natural gas used in methanation, characterized in that, include: The system comprises an absorption system, a condensation and liquefaction system, a flash evaporation system, a thermal regeneration system, and a water washing system. The absorption system includes an absorption tower, a first heat exchanger, a second heat exchanger, and a first propylene cooler. The condensation and liquefaction system includes a second propylene cooler, a throttling heat exchanger, and a flash evaporator. The flash evaporation system includes a flash tower, a circulating gas compressor, a multi-stage carbon dioxide compressor, and a circulating gas cooler. The flash tower consists of a first flash tower section, a second flash tower section, a third flash tower section, and a fourth flash tower section. Along the direction of raw material gas flow, the first outlet of the first heat exchanger is connected to the first inlet of the second heat exchanger, the first inlet of the second heat exchanger is connected to the first outlet of the second heat exchanger, and the first outlet of the second heat exchanger is connected to the inlet of the second propylene cooler; the outlet of the second propylene cooler is connected to the first inlet of the throttling heat exchanger, the first inlet of the throttling heat exchanger and the first outlet of the throttling heat exchanger are connected, and the first outlet of the throttling heat exchanger is connected to the inlet of the flash tank; the bottom outlet of the flash tank is connected to the second inlet of the throttling heat exchanger, the second inlet of the throttling heat exchanger and the second outlet of the throttling heat exchanger are connected, and the second outlet of the throttling heat exchanger is connected to any one or more of the first, second, third, or fourth flash tower sections of the flash tower; the top outlet of the flash tank is connected to the second inlet of the second heat exchanger, the second inlet of the second heat exchanger and the second outlet of the second heat exchanger are connected, and the second outlet of the second heat exchanger is connected to the raw material gas inlet at the bottom of the absorption tower; The first propylene cooler is located in the middle of the main washing section of the absorption tower; the purified gas outlet at the top of the absorption tower is connected to the second inlet of the first heat exchanger, the methanol-rich outlet of the absorption tower is connected to the inlet of the first flash tower section of the flash tower; the top outlet of the first flash tower section is connected to the inlet of the circulating gas compressor, the outlet of the circulating gas compressor is connected to the inlet of the circulating gas cooler, and the outlet of the circulating gas cooler is connected to the first inlet of the first heat exchanger; the top outlets of the second, third, and fourth flash tower sections are all connected to a multi-stage carbon dioxide compressor.

2. The carbon-rich natural gas decarbonization device according to claim 1, characterized in that, The thermal regeneration system includes a third heat exchanger, a thermal regeneration tower, a third propylene cooler, a thermal regeneration tower cooler, and a thermal regeneration tower reboiler; the water washing system includes a water washing tower, a methanol water tower, a methanol water tower cooler, a methanol water tower reboiler, and a water washing water cooler. The outlet pipeline of the fourth flash tower section is divided into four routes. The first route is connected to the semi-lean methanol inlet at the top of the absorption tower, the second route is connected to the inlet of the second propylene cooler, the third route is connected to the first inlet of the third heat exchanger, the first outlet of the third heat exchanger is connected to the bottom inlet of the thermal regeneration tower, and the fourth route is connected to the top inlet of the first flash tower section.

3. The carbon-rich natural gas decarbonization device according to claim 2, characterized in that, A heat regeneration tower cooler is installed at the top of the heat regeneration tower, and the outlet of the heat regeneration tower cooler is connected to the bottom inlet of the water washing tower; a heat regeneration tower reboiler is installed at the bottom of the heat regeneration tower, and the bottom outlet of the heat regeneration tower is connected to the second inlet of the third heat exchanger, the second outlet of the third heat exchanger is connected to the inlet of the third propylene cooler, and the outlet of the third propylene cooler is connected to the lean methanol inlet at the top of the absorption tower.

4. The carbon-rich natural gas decarbonization device according to claim 3, characterized in that, The bottom outlet of the water washing tower is connected to the inlet of the methanol water tower, and the top outlet of the water washing tower is connected to the multi-stage carbon dioxide compressor. The bottom outlet of the methanol water tower is connected to the inlet of the washing water cooler, and the outlet of the washing water cooler is connected to the top inlet of the washing tower; a methanol water tower cooler is installed at the top outlet of the methanol water tower, and the outlet of the methanol water tower cooler is connected to the inlet of the thermal regeneration tower; a methanol water tower reboiler is installed at the bottom of the methanol water tower.

5. A decarbonization process for carbon-rich natural gas using the apparatus described in claims 1-4, characterized in that, Includes the following steps: The raw gas flows into the condensation and liquefaction system after passing through the first and second heat exchangers in sequence, and then flows into the flash tank after passing through the second propylene cooler and the throttling heat exchanger in sequence. The flash condensate flowing out from the bottom of the flash tank is sent to the first flash tower section, the second flash tower section, the third flash tower section, or the fourth flash tower section after exchanging heat with the feed gas through a throttling heat exchanger. The condensed liquefied flash vapor from the flash tank flows into the second heat exchanger and exchanges heat with the feed gas before being sent to the absorption tower. In the absorption tower, it comes into contact with the lean / semi-lean methanol absorbent flowing from top to bottom. After absorbing carbon dioxide, the carbon-rich methanol formed flows out of the absorption tower and enters the flash system. The purified gas stream taken from the top of the absorption tower exchanges heat with the feed gas through the first heat exchanger. Carbon-rich methanol enters the first flash section of the flash evaporation system. The flash liquid from the first flash section flows sequentially into the second, third, and fourth flash sections. The gas collected from the top of the first flash section is pressurized by a circulating gas compressor and cooled by a circulating gas cooler before flowing into the feed gas. The carbon dioxide collected from the top of the second, third, and fourth flash sections is compressed by a multi-stage carbon dioxide compressor before flowing out. The semi-lean methanol collected from the bottom of the fourth flash section is divided into four parts: the first part flows into the absorption tower as a carbon dioxide absorbent; the second part flows into the second propylene cooler as antifreeze to mix with the feed gas; the third part flows into the third heat exchanger of the thermal regeneration system for heat exchange before flowing into the thermal regeneration tower; and the last part flows into the first flash section as a circulating gas absorbent. The regenerated lean methanol flowing out from the bottom of the thermal regeneration tower first flows through the third heat exchanger to exchange heat with the semi-lean methanol, and then flows into the absorption tower as a carbon dioxide absorbent after being cooled by the third propylene cooler. The methanol-containing gas generated at the top of the thermal regeneration tower is condensed by the thermal regeneration tower cooler and then flows into the water washing tower. The de-alcoholized carbon dioxide gas at the top of the water washing tower flows into the carbon dioxide multi-stage compressor for recovery and treatment. The alcohol-water mixture flowing out from the bottom of the water washing tower flows into the methanol water tower. The methanol flowing out from the top of the methanol water tower is condensed by the methanol water tower cooler and then flows into the thermal regeneration tower. The regenerated wash water flowing out from the bottom of the methanol water tower is cooled by the wash water cooler and then flows into the water washing tower for use.

6. The carbon-rich natural gas decarbonization process according to claim 5, characterized in that, The molar composition of the feed gas includes: 20%~80% CO2, 40%~60% CH4 and 4%~15% N2; And / or, the molar ratio of feed gas, lean methanol, and semi-lean methanol in the absorption tower is 1.0:0.5~1.2:0.4~0.6; And / or, the operating pressure of the absorption tower is 3.3~3.5 MPaG.

7. The carbon-rich natural gas decarbonization process according to claim 5, characterized in that, The condensation and liquefaction temperature of the second propylene cooler is -40℃ to -52℃; And / or, the throttling pressure of the throttling heat exchanger is 0.2~0.8 MPaG.

8. The carbon-rich natural gas decarbonization process according to claim 5, characterized in that, The flash pressure of the first flash tower section is 0.2~1.4 MPaG, the flash pressure of the second flash tower section is 0.6~1.4 MPaG, the flash pressure of the third flash tower section is 0.3~1.0 MPaG, and the flash pressure of the fourth flash tower section is 0.02~0.3 MPaG. And / or, the outlet pressures of the carbon dioxide multistage compressor are 0.2~0.4 MPaG, 0.3~0.8 MPaG, 1.0~2.0 MPaG, and 3.0~3.6 MPaG, respectively.

9. The carbon-rich natural gas decarbonization process according to claim 5, characterized in that, The molar ratio of semi-lean methanol flowing into the first flash tower section, absorption tower, second propylene cooler and third heat exchanger is: 3-5:30-40:1-10:45-70; And / or, the molar composition of the semi-lean methanol is: 2%~5% CO2 and 95%~98% CH3OH; And / or, the temperature of the semi-lean methanol is -20℃ to -50℃.

10. The carbon-rich natural gas decarbonization process according to claim 5, characterized in that, The operating pressure of the thermal regeneration tower is 0.1~0.5 MPaG; And / or, the operating pressure of the water washing tower is 0.1~0.5 MPaG; And / or, the operating pressure of the methanol water tower is 0.02~0.4 MPaG.

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