Low-energy-consumption natural gas low-temperature rectification decarburization process and system

Abstract

The invention discloses a low-energy-consumption natural gas low-temperature rectification decarburization process. The process comprises the following steps: S1, firstly removing water and sulfur-containing compounds in raw material gas; s2, cooling the raw material gas without water and sulfur-containing compounds to-30 DEG C to-27 DEG C, and introducing a separated gas-phase material without C4 and above light hydrocarbon substances into a tower kettle reboiler of a low-temperature rectifying tower as a heat source of the tower kettle reboiler to form a gas-liquid mixed material at-37 DEG C; and S3, controlling the pressure of the gas-liquid mixture at-37 DEG C to be 2.5-3.5 MpaA, introducing the gas-liquid mixture into a low-temperature rectifying tower, and finally harvesting methane-rich natural gas at the top of the tower and liquid-phase carbon dioxide at the bottom of the tower. The method has the advantages that the energy consumption is low, and the natural gas with complex components and ultrahigh carbon dioxide content can be decarbonized.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas decarbonization, and in particular to a natural gas low-temperature distillation decarbonization process and system which is particularly suitable for decarbonizing natural gas with complex components and ultra-high carbon dioxide content. Background Art

[0002] The traditional natural gas decarbonization process uses MDEA solution for absorption-regeneration. Although this process is relatively mature, it is only applicable to conditions with low carbon dioxide content. When the carbon dioxide in natural gas is high, the amine liquid circulation volume increases dramatically, the load of the amine regeneration tower kettle reboiler is huge, and the investment cost of pumps and heat exchange equipment increases greatly; at the same time, due to the need for large amounts of amine liquid circulation, the operating cost is also huge. In addition, the carbon dioxide desorbed from the rich amine liquid by this process cannot be effectively enriched and can only be discharged into the atmosphere.

[0003] The application of cryogenic distillation technology in the field of natural gas purification has not yet been popularized in my country. When the natural gas contains a large amount of light hydrocarbons and the components are more complex, the separation task of the distillation tower is heavy, and the traditional process often cannot effectively separate the light and heavy components in the natural gas. In addition, the load of the tower bottom reboiler and the tower top condenser is often large.

[0004] A few companies abroad have developed low-temperature decarbonization technology for natural gas, the more typical representatives of which are the Ryan-Holmes process and the CryCell process.

[0005] Among them, the feed pressure of the Ryan-Holmes process is about 4.5MpaA, and four-tower operation is required. In order to avoid carbon dioxide solidification, this process must add C3~C5 hydrocarbons in the top condenser so that the theoretical boundary line of carbon dioxide separation leaves the solidification zone.

[0006] The CryCell process requires the material to be cooled to -65℃~-50℃ and the pressure to be 5.5~6.5MpaA. The material enters the tower as a three-phase mixture, and the final carbon dioxide product needs to be heated to become a liquid phase. In the process of cooling-solidification-entering the tower-heating, a large amount of unnecessary losses will be generated, which makes the equipment investment of the process huge. In addition, high-pressure materials are required to enter the tower, and the energy consumption level of the compressor is also relatively high. Summary of the invention

[0007] The first object of the present invention is to provide a process which has low energy consumption and can decarbonize natural gas with complex components and extremely high carbon dioxide content.

[0008] To achieve the above object, the present invention adopts the following technical solution: a low-energy consumption natural gas low-temperature distillation decarbonization process, comprising the following steps: S1: Control the inlet pressure of the raw gas at 2.5-3.5MpaA, and then remove water and sulfur compounds from the raw gas; S2: The raw gas from which water and sulfur compounds have been removed is cooled to -30°C to -27°C via a heat exchange cold box, so that C4 and above light hydrocarbons in the natural gas are condensed into a liquid phase, and then the natural gas is separated into a gas-liquid phase, and the separated gas-phase material that does not contain C4 and above light hydrocarbons is passed into the bottom reboiler of the low-temperature distillation tower as a heat source for the bottom reboiler. After the gas-phase material is heat-exchanged in the bottom reboiler, a gas-liquid mixed material at -37°C is formed; S3: The pressure of the gas-liquid mixture at -37℃ is controlled at 2.5~3.5MpaA, and then introduced into a cryogenic distillation tower. When the gas and liquid phases contact step by step on the surface of the tower plate, volatile components such as methane will absorb heat and partially evaporate, and easily condensable carbon dioxide will release heat and partially condense. After multiple partial evaporations, methane-rich natural gas is finally harvested at the top of the tower and liquid carbon dioxide is harvested at the bottom of the tower.

[0009] Furthermore, the aforementioned low-energy consumption natural gas low-temperature distillation decarbonization process, wherein: in S1, the raw gas is sequentially passed through a molecular sieve inlet separator, a molecular sieve adsorption tower, a desulfurization bed and a desulfurization filter to remove water and sulfur-containing compounds in the raw gas.

[0010] Furthermore, in the aforementioned low-energy consumption natural gas low-temperature distillation decarbonization process, wherein: in S2, the heat exchange cold box has four channels, which are: a feed gas channel, an ethylene channel, a natural gas reheating channel, and a propane channel; Propane is used as the primary cooling medium of the heat exchange cold box and passed into the propane channel; the low-temperature natural gas harvested from the low-temperature distillation tower is used as the secondary cooling medium of the heat exchange cold box and passed into the natural gas reheating channel, and the low-temperature natural gas is reheated to 25°C after heat exchange with the hot fluid flowing through the heat exchange cold box to become the final product gas output; the raw gas from which water and sulfur-containing compounds have been removed obtained by S1 is passed into the raw gas channel of the heat exchange cold box, and propane and low-temperature natural gas are used to cool the raw gas from which water and sulfur-containing compounds have been removed before gas-liquid separation; ethylene is used as the condensing agent of the top condenser of the low-temperature distillation tower, and the ethylene heated after passing through the top condenser is passed into the ethylene channel of the heat exchange cold box, and propane and low-temperature natural gas are used to pre-cool the ethylene before it refluxes into the top condenser.

[0011] The second object of the present invention is to provide a system with low energy consumption and capable of decarbonizing natural gas with complex components and extremely high carbon dioxide content.

[0012] To achieve the above object, the present invention adopts the following technical scheme: a low-energy consumption natural gas low-temperature distillation decarbonization system, including a raw gas feed pipeline, a molecular sieve inlet separator, a molecular sieve adsorption tower, a desulfurization bed, a desulfurization filter, a heat exchange cold box, a low-temperature distillation tower, a light hydrocarbon separation tank, a propane compressor and an ethylene compressor; The heat exchange cold box has four channels, which are: a raw gas channel, an ethylene channel, a natural gas reheating channel, and a propane channel; The raw gas feed pipeline is connected to the inlet of the molecular sieve separator through the raw gas compressor, the outlet of the molecular sieve separator is connected to the inlet of the molecular sieve adsorption tower, the outlet of the molecular sieve adsorption tower is connected to the inlet of the desulfurization bed, the outlet of the desulfurization bed is connected to the inlet of the desulfurization filter, the outlet of the desulfurization filter is connected to the inlet of the raw gas channel in the heat exchange cold box, the outlet of the raw gas channel is connected to the inlet of the light hydrocarbon separation tank, the gas phase outlet of the light hydrocarbon separation tank is connected to the tube side inlet of the tower bottom reboiler of the low-temperature distillation tower, the tube side outlet of the tower bottom reboiler is connected to the feed port of the low-temperature distillation tower, the shell side inlet of the tower bottom reboiler is connected to the liquid outlet of the lower part of the low-temperature distillation tower, and the shell side outlet of the tower bottom reboiler is connected to the gas inlet of the lower part of the low-temperature distillation tower; The top gas phase outlet of the cryogenic distillation tower is connected to the heat medium inlet of the top condenser of the cryogenic distillation tower, the heat medium outlet of the top condenser is connected to the inlet of the top reflux tank of the distillation tower, the bottom outlet of the top reflux tank of the distillation tower is connected to the upper reflux port of the cryogenic distillation tower, the top outlet of the top reflux tank of the distillation tower is connected to the inlet of the natural gas reheating channel of the heat exchange cold box through a low-temperature natural gas throttle valve, and the outlet of the natural gas reheating channel is connected to the product gas discharge pipeline; The outlet of the propane channel of the heat exchange cold box is connected to the inlet of the propane channel of the heat exchange cold box through a propane circulation pipeline, and a propane compressor, a propane cooler and a propane throttle valve are sequentially arranged on the propane circulation pipeline along the propane flow direction; The outlet of the ethylene channel of the heat exchange cold box is connected to the cold medium inlet of the top condenser of the low-temperature distillation tower through an ethylene throttle valve, and the cold medium outlet of the top condenser is connected to the inlet of the ethylene channel of the heat exchange cold box through an ethylene liquid outlet pipeline. An ethylene compressor and an ethylene cooler are sequentially arranged on the ethylene liquid outlet pipeline along the ethylene flow direction.

[0013] Furthermore, the aforementioned low-energy consumption natural gas low-temperature distillation decarbonization system, wherein: a plurality of molecular sieve adsorption towers are connected in parallel between the outlet of the molecular sieve inlet separator and the inlet of the desulfurization bed, and the inlet of each molecular sieve adsorption tower is connected to the outlet of the molecular sieve separator; and the outlet of each molecular sieve adsorption tower is connected to the inlet of the desulfurization bed.

[0014] Through the implementation of the above technical scheme, the beneficial effects of the present invention are: avoiding the solidification area of ​​carbon dioxide, increasing the universality of the process, being able to process natural gas with poor gas quality conditions, complex components and ultra-high carbon dioxide content, being able to reduce the separation load of the tower, while reducing the load of the top condenser and the reboiling load of the tower bottom, effectively reducing energy consumption, and improving the economy and feasibility of the process; being able to more thoroughly remove carbon dioxide and mixed light hydrocarbon compounds therein, and the purity of the exported natural gas and carbon dioxide is relatively high. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the principle of a low-energy consumption natural gas low-temperature distillation decarbonization system described in the present invention.

[0016] Figure 2 for Figure 1 A partial schematic diagram of . DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0018] like Figure 1 , Figure 2 As shown, the low-energy consumption natural gas low-temperature distillation decarbonization system comprises a raw gas feed pipeline 1, a molecular sieve inlet separator 2, a molecular sieve adsorption tower 3, a desulfurization bed 4, a desulfurization filter 5, a heat exchange cold box 6, a low-temperature distillation tower 7, a light hydrocarbon separation tank 8, a propane compressor 25 and an ethylene compressor 31; The heat exchange cold box 6 has four channels, which are: a raw gas channel 61, which is used as a hot fluid channel, an ethylene channel 62, which is also used as a hot fluid channel, a natural gas reheating channel 63, which is used as a cold fluid channel, and a propane channel 64, which is used as a low-pressure cold fluid channel. The raw gas feed pipeline 1 is connected to the inlet of the raw gas compressor 9, and the outlet of the raw gas compressor 9 is connected to the inlet of the molecular sieve separator 2. A plurality of molecular sieve adsorption towers 3 are connected in parallel between the outlet of the molecular sieve inlet separator 2 and the inlet of the desulfurization bed 4. In this embodiment, the number of molecular sieve adsorption towers 3 is three, and the inlet of each molecular sieve adsorption tower 3 is connected to the outlet of the molecular sieve separator 2; the outlet of each molecular sieve adsorption tower 3 is connected to the inlet of the desulfurization bed 4; the outlet of the desulfurization bed 4 is connected to the inlet of the desulfurization filter 5, and the outlet of the desulfurization filter 5 is connected to the inlet of the raw gas channel 61 in the heat exchange cold box 6; The outlet of the raw gas channel 61 is connected to the inlet of the light hydrocarbon separation tank 8 through the first pipeline 10, the gas phase outlet of the light hydrocarbon separation tank 8 is connected to the tube side inlet of the tower bottom reboiler 71 of the cryogenic distillation tower 7 through the second pipeline 11, the tube side outlet of the tower bottom reboiler 71 is connected to the feed port of the cryogenic distillation tower 7 through the third pipeline 13, the shell side inlet of the tower bottom reboiler 71 is connected to the liquid outlet of the lower part of the cryogenic distillation tower 7 through the fourth pipeline 15, and the shell side outlet of the tower bottom reboiler 71 is connected to the gas inlet of the lower part of the cryogenic distillation tower 7 through the fifth pipeline 16; The top gas phase outlet of the cryogenic distillation tower 7 is connected to the heat medium inlet of the top condenser 72 of the cryogenic distillation tower 7 through the sixth pipeline 17, the heat medium outlet of the top condenser 72 is connected to the inlet of the top reflux tank 19 of the distillation tower through the seventh pipeline 18, the bottom outlet of the top reflux tank 19 of the distillation tower is connected to the upper reflux port of the cryogenic distillation tower 7 through the eighth pipeline 20, the top outlet of the top reflux tank 19 of the distillation tower is connected to the inlet of the natural gas reheating channel 63 of the heat exchange cold box 6 through the ninth pipeline 21, a low-temperature natural gas throttle valve 22 is provided on the ninth pipeline 21, and the outlet of the natural gas reheating channel 63 is connected to the product gas discharge pipeline 23; The outlet of the propane channel 64 of the heat exchange cold box 6 is connected to the inlet of the propane channel 64 of the heat exchange cold box 6 through the propane circulation pipeline 24, and a propane compressor 25, a propane cooler 26 and a propane throttle valve 27 are sequentially arranged on the propane circulation pipeline 64 along the propane flow direction; The outlet of the ethylene channel 62 of the heat exchange cold box 6 is connected to the cold medium inlet of the tower top condenser 72 of the low-temperature distillation tower 7 through the tenth pipeline 28, and an ethylene throttle valve 29 is arranged on the tenth pipeline 28; the cold medium outlet of the tower top condenser 72 is connected to the inlet of the ethylene channel 62 of the heat exchange cold box 6 through the ethylene liquid outlet pipeline 30, and an ethylene compressor 31 and an ethylene cooler 32 are arranged in sequence on the ethylene liquid outlet pipeline 30 along the ethylene flow direction.

[0019] A low-energy consumption natural gas low-temperature distillation decarbonization process, using the above-mentioned low-energy consumption natural gas low-temperature distillation decarbonization system, comprises the following steps: S1: The raw gas is passed through the raw gas compressor 9, the molecular sieve inlet separator 2, each molecular sieve adsorption tower 3, the desulfurization bed 4 and the desulfurization filter 5 in sequence along the raw gas feed pipeline 1, the raw gas inlet pressure is controlled at 2.5-3.5MpaA by the raw gas compressor 9, the water in the raw gas is removed by the molecular sieve inlet separator 2 and each molecular sieve adsorption tower 3, and the sulfur-containing compounds in the raw gas are removed by the desulfurization bed 4 and the desulfurization filter 5; S2: The raw gas from which water and sulfur compounds have been removed is introduced into the raw gas channel 61 of the heat exchange cold box 6. In the process of the raw gas passing through the raw gas channel 61, the raw gas in the raw gas channel 61 is cooled to -30°C to -27°C by the cooling medium such as propane and low-temperature natural gas in the heat exchange cold box 6 and then output. After the raw gas is cooled to -30°C to -27°C, C4 and above light hydrocarbon substances in the natural gas will be condensed into liquid phase, and then the cooled natural gas is introduced into the light hydrocarbon separation tank 8 through the first pipeline 10, and the light hydrocarbon separation tank 8 is used to separate the natural gas from gas and liquid, and then the gas phase material that does not contain C4 and above light hydrocarbon substances in the natural gas is used as the heat source of the tower bottom reboiler through the second pipeline. 11 is passed into the tube side of the tower bottom reboiler 71 of the low-temperature distillation tower 7. After the gas-phase material exchanges heat with the cold medium in its shell side in the tube side of the tower bottom reboiler 71, the gas-phase material will be partially condensed and liquefied to form a gas-liquid mixed material at -37°C for output; using the gas-phase material as the heat source of the tower bottom reboiler not only saves the heat that should have been supplied to the tower bottom reboiler, reduces the operating burden of the low-temperature distillation tower, and reduces the load of the top condenser, but also because part of the latent heat and sensible heat in the gas-phase material is utilized by the tower bottom reboiler, the pure gaseous gas-phase material is partially condensed, which meets the gas-liquid two-phase feeding state required by the low-temperature distillation tower, and optimizes the process and saves energy consumption. S3: The gas-liquid mixture at -37°C is introduced into the cryogenic distillation tower 7 through the third pipeline 13. At this time, the pressure of the gas-liquid mixture before entering the cryogenic distillation tower 7 will still be maintained at 2.5-3.5MpaA; in the material, the boiling points of carbon dioxide and methane are different. When the gas-liquid two phases contact step by step on the surface of the tower plate, the volatile methane and other components will absorb heat and partially evaporate, and the easily condensed carbon dioxide will release heat and partially condense. The saturated steam ascending in the tower contacts the saturated liquid flowing downward, and the gas phase and the liquid phase exchange substances and heat. In the process of step-by-step contact between the gas-liquid two phases, light components such as methane evaporate more and condense less, and gradually enrich in the ascending gas phase; carbon dioxide evaporates less and condenses more, and gradually enriches in the liquid phase flowing to the bottom of the tower; after multiple partial evaporations, methane-rich natural gas is finally harvested at the top of the tower, and liquid carbon dioxide at the bottom of the tower; In the process of distilling natural gas in the cryogenic distillation tower, part of the liquid phase at the bottom of the tower will continuously enter the shell side of the tower bottom reboiler 71 through the fourth pipeline 15, and after heat exchange with the heat medium in the tube side in the shell side of the tower bottom reboiler 71, form steam and reflux into the cryogenic distillation tower 7; while the gas phase natural gas at the top of the tower continuously enters the tower top condenser 72 through the sixth pipeline 17. In the process of the gas phase natural gas passing through the tower top condenser 72, the carbon dioxide and the heavy components in the gas phase natural gas will be condensed into liquid phase by the cold medium ethylene in the tower top condenser 72, and enter the tower top reflux tank 19 through the seventh pipeline 18. The liquid in the tower top reflux tank 19 The carbon dioxide and heavy components are deposited at the bottom of the tower top reflux tank 19 and refluxed into the cryogenic distillation tower 7 through the eighth pipeline 20, while the gas phase low-temperature natural gas in the tower top reflux tank 19 is exported from the top of the tower top reflux tank and enters the natural gas reheating channel 63 of the heat exchange cold box 6 through the ninth pipeline 21 and the low-temperature natural gas throttle valve 22, serving as the cooling medium of the heat exchange cold box 6, thereby heat-exchanging and cooling the raw gas in the raw gas channel 61 and the ethylene in the ethylene channel 62 and other hot fluids. After heat exchange, the low-temperature natural gas in the natural gas reheating channel 63 will be heated to 25°C to become the final product gas, and will be output through the product gas discharge pipeline 23; The propane in the propane channel 64 of the heat exchange cold box 61 is heated to 40°C after heat exchange with the raw gas and hot fluids such as ethylene in the heat exchange cold box 61, and the propane pressure is 0.13MpaA at this time, and then enters the propane circulation pipeline 24. When the propane passes through the propane compressor 25, the propane cooler 26 and the propane throttle valve 27 along the propane circulation pipeline 24 in sequence, the propane compressor 25 will compress the 0.13MpaA propane to 1.98MpaA, the propane cooler 26 will cool the propane to 40°C, and the propane throttle valve 27 will throttle the propane to 0.15MpaA, so that the temperature of the propane is reduced to -32.83°C, and then enters the propane channel 64 as the cooling medium of the heat exchange cold box 61, thereby cooling the raw gas and hot fluids such as ethylene in the heat exchange cold box 61; The ethylene in the ethylene channel 62 of the heat exchange cold box 61 comes from the condensing agent of the tower top condenser 72 of the low-temperature distillation tower 7. The ethylene heated up after heat exchange with the gas-phase natural gas passing through the tower top condenser 72 enters the ethylene liquid outlet pipeline 30. When flowing in the ethylene liquid outlet pipeline 30, the ethylene will pass through the ethylene compressor 31 and the ethylene cooler 32 in sequence. The ethylene compressor compresses 0.11MpaA to 2.46MpaA. The ethylene cooler 32 cools the ethylene to 45°C and then enters the ethylene channel 62 of the heat exchange cold box 61. The ethylene entering the ethylene channel 62 exchanges heat with the low-temperature natural gas and propane and other cold fluids in the heat exchange cold box 61 and is cooled to -30°C before entering the tenth pipeline 28. It is then throttled to 0.12 MpaA by the ethylene throttle valve 29 on the tenth pipeline 28. At this time, the ethylene temperature is -101.1°C, and then goes to the tower top condenser 72 to serve as the condensing agent of the tower top condenser 72 again.

[0020] The advantages of the present invention are: (1) Avoid the carbon dioxide solidification zone; Different from foreign cryogenic distillation processes, the cold box of the present invention does not need to cool the incoming tower materials to too low a temperature, and -37°C to -27°C is an ideal working condition; C4 and above light hydrocarbons in natural gas can be removed to meet the tower entry standard, and only one tower is required for operation; the raw gas inlet pressure is maintained at 2.5-3.5MpaA, ensuring that the material pressure of the gas-liquid mixture entering the cryogenic distillation tower is also maintained at 2.5-3.5MpaA, which not only fundamentally avoids the solidification problem of carbon dioxide, but also greatly reduces the load of the raw gas compressor; (2) After the cooled raw gas is separated into gas and liquid, the gas phase material is used as the heat source of the tower bottom reboiler to pass into the tower bottom reboiler of the low temperature distillation tower; Aspen hysys V11 is used for simulation, and the tower processing capacity is 620000Nm 3 / day, when the carbon dioxide content is about 60%, the heat load of the tower bottom reboiler is about 930kW. If the gas-liquid separated gas phase material (-30℃, 2.68MpaA) is introduced into the tower bottom reboiler as a heat source, part of the latent heat and sensible heat in the gas phase material can be used by the material in the tower, so that the pure gaseous material is partially condensed (-37℃, 2.66MpaA), which not only meets the gas-liquid two-phase feeding state required by the low-temperature distillation tower, but also further reduces the load of the tower top condenser; This is because: the material entering the cryogenic distillation tower is a gas-liquid mixture, in which carbon dioxide and methane have different boiling points. When the gas and liquid phases contact each other step by step on the surface of the tower plate, the volatile components such as methane will absorb heat and partially evaporate, and the easily condensable carbon dioxide will release heat and partially condense; the saturated steam ascending in the tower contacts the saturated liquid flowing downward, and the gas phase and the liquid phase exchange substances and heat, the steam releases heat and partially condenses, and the saturated liquid absorbs heat and partially evaporates; in the process of the gas and liquid phases contacting each other on each tower plate, light components such as methane evaporate more and condense less, and gradually enrich in the ascending gas phase; carbon dioxide evaporates less and condenses more, and gradually enriches in the liquid phase flowing to the bottom of the tower; The tower bottom reboiler needs to provide heat for the evaporation of the light component methane at the bottom of the tower, and the tower top condenser needs to provide cold for the condensation of a small amount of heavy component carbon dioxide at the top of the tower. Using dry gas as the heat source for the tower bottom reboiler has triple energy-saving significance; The present invention first cools the natural gas to -30°C to -27°C through a heat exchange cold box, and then cools it to -37°C before entering the tower through a tower kettle reboiler. Compared with directly using a cold box to cool the material to -37°C before entering the tower, the energy consumption of the refrigeration compressor and the tower kettle reboiler is reduced by about 56%; compared with using a cold box to cool the material to -30°C before entering the tower, the overall energy consumption level is reduced by about 77%; (3) In this process, the tower top gas product, low-temperature natural gas (-99.93℃, 2.55MpaA), is passed into a cold box for reheating. At the same time, the cold energy in the low-temperature natural gas is used to cool the feed gas hot fluid and the ethylene hot fluid, which greatly reduces the refrigeration load of the propane compressor. Compared with the process that does not use low-temperature natural gas cooling, the overall energy consumption is reduced several times; (4) The condensing agent of the tower top condenser is ethylene. After passing through the heat exchange cold box, the ethylene is cooled to -30°C by low-temperature natural gas and propane. At this time, the 2.46MpaA ethylene is throttled to 0.12MpaA, and the temperature is reduced to -101.1°C, and then used as the cooling medium of the tower top condenser; (5) Compared with the existing low-temperature distillation process for natural gas decarbonization in foreign countries, this process avoids the solidification area of ​​carbon dioxide, increases the universality of the process, and can process natural gas with poor gas quality conditions, complex components and ultra-high carbon dioxide content. It can reduce the separation load of the tower, while reducing the load of the top condenser and the reboiling load of the tower bottom, reducing the energy consumption of the refrigeration compressor, and improving the economy and feasibility of the process; it can more thoroughly remove the carbon dioxide and mixed light hydrocarbon compounds in it, and the purity of the exported natural gas and carbon dioxide is relatively high. The carbon dioxide content can reach more than 90%, which can be backfilled into the formation to achieve the purpose of carbon sequestration.

[0021] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A low-energy consumption natural gas low-temperature distillation decarbonization process, characterized by: The following steps are involved: S1: Control the inlet pressure of the raw gas at 2.5-3.5MpaA, and then remove water and sulfur compounds from the raw gas; S2: The raw gas from which water and sulfur compounds have been removed is cooled to -30°C to -27°C via a heat exchange cold box, so that C4 and above light hydrocarbons in the natural gas are condensed into a liquid phase, and then the natural gas is separated into a gas-liquid phase, and the separated gas-phase material that does not contain C4 and above light hydrocarbons is passed into the bottom reboiler of the low-temperature distillation tower as a heat source for the bottom reboiler. After the gas-phase material is heat-exchanged in the bottom reboiler, a gas-liquid mixed material at -37°C is formed; S3: The gas-liquid mixture at -37℃ is passed into a cryogenic distillation tower. When the gas and liquid phases contact step by step on the surface of the tower plate, volatile components such as methane will absorb heat and partially evaporate, and easily condensed carbon dioxide will release heat and partially condense. After multiple partial evaporations, methane-rich natural gas is finally harvested at the top of the tower and liquid carbon dioxide is harvested at the bottom of the tower.

2. A low-energy consumption natural gas low-temperature distillation decarbonization process according to claim 1, characterized in that: In S1, the raw gas is sequentially passed through a molecular sieve inlet separator, a molecular sieve adsorption tower, a desulfurization bed and a desulfurization filter to remove water and sulfur-containing compounds in the raw gas.

3. A low-energy consumption natural gas low-temperature distillation decarbonization process according to claim 1, characterized in that: In S2, the heat exchange cold box has four channels, which are: a feed gas channel, an ethylene channel, a natural gas reheating channel, and a propane channel; Propane is used as the primary cooling medium of the heat exchange cold box and introduced into the propane channel; the low-temperature natural gas harvested from the cryogenic distillation tower is used as the secondary cooling medium of the heat exchange cold box and introduced into the natural gas reheating channel, and the low-temperature natural gas is reheated to 25°C after heat exchange with the hot fluid flowing through the heat exchange cold box to become the final product gas output; the raw gas from which water and sulfur-containing compounds have been removed obtained in S1 is introduced into the raw gas channel of the heat exchange cold box, and the raw gas from which water and sulfur-containing compounds have been removed is cooled by propane and low-temperature natural gas before gas-liquid separation; Ethylene is used as the condensing agent of the top condenser of the cryogenic distillation tower. The ethylene heated after passing through the top condenser is passed into the ethylene channel of the heat exchange cold box. Propane and low-temperature natural gas are used to pre-cool the ethylene before it refluxes into the top condenser.

4. A low-energy consumption natural gas low-temperature distillation decarbonization system, characterized by: Including raw gas feed pipeline, molecular sieve inlet separator, molecular sieve adsorption tower, desulfurization bed, desulfurization filter, heat exchange cold box, low-temperature distillation tower, light hydrocarbon separation tank, propane compressor and ethylene compressor; The heat exchange cold box has four channels, which are: a raw gas channel, an ethylene channel, a natural gas reheating channel, and a propane channel; The raw gas feed pipeline is connected to the inlet of the molecular sieve separator through the raw gas compressor, the outlet of the molecular sieve separator is connected to the inlet of the molecular sieve adsorption tower, the outlet of the molecular sieve adsorption tower is connected to the inlet of the desulfurization bed, the outlet of the desulfurization bed is connected to the inlet of the desulfurization filter, the outlet of the desulfurization filter is connected to the inlet of the raw gas channel in the heat exchange cold box, the outlet of the raw gas channel is connected to the inlet of the light hydrocarbon separation tank, the gas phase outlet of the light hydrocarbon separation tank is connected to the tube side inlet of the tower bottom reboiler of the low-temperature distillation tower, the tube side outlet of the tower bottom reboiler is connected to the feed port of the low-temperature distillation tower, the shell side inlet of the tower bottom reboiler is connected to the liquid outlet of the lower part of the low-temperature distillation tower, and the shell side outlet of the tower bottom reboiler is connected to the gas inlet of the lower part of the low-temperature distillation tower; The top gas phase outlet of the cryogenic distillation tower is connected to the heat medium inlet of the top condenser of the cryogenic distillation tower, the heat medium outlet of the top condenser is connected to the inlet of the top reflux tank of the distillation tower, the bottom outlet of the top reflux tank of the distillation tower is connected to the upper reflux port of the cryogenic distillation tower, the top outlet of the top reflux tank of the distillation tower is connected to the inlet of the natural gas reheating channel of the heat exchange cold box through a low-temperature natural gas throttle valve, and the outlet of the natural gas reheating channel is connected to the product gas discharge pipeline; The outlet of the propane channel of the heat exchange cold box is connected to the inlet of the propane channel of the heat exchange cold box through a propane circulation pipeline, and a propane compressor, a propane cooler and a propane throttle valve are sequentially arranged on the propane circulation pipeline along the propane flow direction; The outlet of the ethylene channel of the heat exchange cold box is connected to the cold medium inlet of the top condenser of the low-temperature distillation tower through an ethylene throttle valve, and the cold medium outlet of the top condenser is connected to the inlet of the ethylene channel of the heat exchange cold box through an ethylene liquid outlet pipeline. An ethylene compressor and an ethylene cooler are sequentially arranged on the ethylene liquid outlet pipeline along the ethylene flow direction.

5. A low-energy consumption natural gas low-temperature distillation decarbonization system according to claim 4, characterized in that: Several molecular sieve adsorption towers are connected in parallel between the outlet of the molecular sieve air inlet separator and the inlet of the desulfurization bed. The inlet of each molecular sieve adsorption tower is connected to the outlet of the molecular sieve separator; and the outlet of each molecular sieve adsorption tower is connected to the inlet of the desulfurization bed.

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