A fischer-tropsch synthesis tail gas rectification energy-saving device and a treatment method

Abstract

The application provides a Fischer-Tropsch synthesis tail gas rectification energy-saving device and a treatment method. The device comprises a first rectification tower, a second rectification tower, a third rectification tower and a first heat exchanger, and is used for treating Fischer-Tropsch synthesis tail gas. Compared with a rectification device without a heat exchanger, the device in the application realizes the joint optimization of a process and a heat exchange network, reduces the investment and energy consumption of the process while ensuring the diversification of the structure of Fischer-Tropsch synthesis oil products, and improves the comprehensive utilization efficiency of the whole Fischer-Tropsch synthesis tail gas rectification device.

Description

Technical Field

[0001] This invention relates to the field of waste gas recovery and utilization, and more specifically, to an energy-saving device and treatment method for the distillation of Fischer-Tropsch synthesis tail gas. Background Technology

[0002] Natural gas, as a clean and efficient energy source, is receiving increasing attention. The production of liquefied natural gas (LNG) from chemical waste gas is an emerging technology that fully utilizes the effective hydrocarbon components in the waste gas, producing high-value-added hydrocarbon products through low-temperature distillation and liquefaction. However, because the composition of waste gas varies, the requirements for waste gas treatment processes also differ, necessitating careful selection based on specific circumstances.

[0003] The tail gas components of Fischer-Tropsch synthesis mainly include unreacted hydrogen, carbon monoxide, nitrogen, and byproducts such as carbon dioxide and low-carbon hydrocarbons. Generally, when there are three or more components to be separated in the tail gas, a separation process with three or more towers is required to achieve the separation of the target product.

[0004] For example, CN105838465B discloses a process for producing liquefied natural gas from Fischer-Tropsch synthesis tail gas. This process involves cooling and separating water and heavy hydrocarbons, then sending the mixture to a heavy hydrocarbon washing process to reduce the content of C5 and C5+ components to below 1 ppm. A water washing process removes organic acids and alcohols. The washed tail gas undergoes decarbonization treatment to reduce the carbon dioxide content to below 50 ppm. It then undergoes drying, mercury removal, and liquefaction separation processes to separate mixed hydrocarbons, hydrogen-rich gas, liquefied natural gas, and carbon monoxide-rich gas. This patented Fischer-Tropsch synthesis tail gas distillation process involves three towers: a liquefied petroleum gas (LPG) distillation tower, a dehydrogenation tower, and a methane tower. The LPG distillation tower separates mixed hydrocarbons from the tail gas; the dehydrogenation tower separates hydrogen-rich gas; and the methane tower produces liquefied natural gas. This technology does not involve the separation between C2 and C3+ components, and directly recovers the C2+ components as mixed hydrocarbons. As a result, the economic value of effective hydrocarbon components such as C2 and C3 in the Fischer-Tropsch synthesis tail gas is not fully realized, leading to low energy utilization and poor economic benefits.

[0005] CN110631326B discloses a process for recovering and utilizing Fischer-Tropsch synthesis tail gas. The Fischer-Tropsch synthesis tail gas first undergoes a purification section to remove impurities such as oxides, acidic gases, and water. Then, a cryogenic separation method is used to cool and liquefy the purified Fischer-Tropsch synthesis tail gas, recovering ethane, polymer-grade ethylene, propane, propylene, C4, C5, and LNG products. The components are cooled to -170 to -160°C in a cryogenic heat exchanger (No. 4) before entering a dehydrogenation tower. The bottom liquid phase of the dehydrogenation tower enters a denitrification tower for further separation to obtain LNG and the top tail gas. This patented Fischer-Tropsch synthesis tail gas distillation process involves four towers: an ethane removal tower, a methanation removal tower, a dehydrogenation tower, and a denitrification tower. The ethane removal tower recovers qualified C3 products; the methanation removal tower recovers qualified C2 products; the dehydrogenation tower extracts hydrogen; and the denitrification tower achieves the liquefaction and distillation of methane. Four-tower distillation technology can effectively utilize Fischer-Tropsch synthesis tail gas, with good treatment effect, high utilization rate, and stable and safe operation. However, the cryogenic liquefaction unit involves many heat exchange devices and the cryogenic temperature is relatively low, resulting in large investment in process equipment and high energy consumption during system operation.

[0006] As can be seen, existing tail gas distillation technology can effectively utilize Fischer-Tropsch synthesis tail gas, with good treatment effect, high utilization rate, and superior economy. However, the entire process involves cryogenic recovery, which inevitably leads to problems such as large equipment investment and high operating energy consumption. Therefore, it is necessary to propose an energy-saving Fischer-Tropsch synthesis tail gas distillation process. Summary of the Invention

[0007] The main objective of this invention is to provide an energy-saving device and treatment method for the distillation of Fischer-Tropsch synthesis tail gas, so as to solve the problems of large equipment investment and high operating energy consumption in the prior art.

[0008] To achieve the above objectives, according to one aspect of the present invention, an energy-saving device for distilling Fischer-Tropsch synthesis tail gas is provided. The device comprises: a first distillation column having a Fischer-Tropsch synthesis tail gas inlet, a first gaseous light component outlet at the top of the column, and a C3 and heavier component outlet at the bottom of the column; the first distillation column is used to perform a first distillation on the Fischer-Tropsch synthesis tail gas to separate the first gaseous light component and C3 and heavier components; and a second distillation column having a first light component inlet, a second gaseous light component outlet at the top of the column, and a C2 component outlet at the bottom of the column, wherein the first light component inlet is connected to the first gaseous light component outlet at the top of the column, and the second distillation column is used to perform a second distillation on the first gaseous light component. The system comprises: a third distillation column, having a second light component inlet, a third light component outlet at the top of the column, and an LNG outlet at the bottom of the column, wherein the second light component inlet is connected to the second light component outlet at the top of the column, and the third distillation column is used to perform third distillation on the second light component to separate LNG and the third light component; and a first heat exchanger, having a first heat exchange channel and a second heat exchange channel, wherein the first heat exchange channel is connected to the C3 and above heavy component outlet at the bottom of the column, and the second heat exchange channel is connected to the C2 component outlet at the bottom of the column, and the first heat exchanger is used to exchange heat between the C3 and above heavy component and the C2 component.

[0009] Furthermore, the second heat exchange channel of the first heat exchanger also has a C2 component outlet after heat exchange; the Fischer-Tropsch synthesis tail gas distillation energy-saving device also includes: a second heat exchanger, which has a C2 component inlet after heat exchange and a C2 product outlet, wherein the C2 product outlet is connected to the fuel gas pipeline network, and the second heat exchanger is used to reheat the C2 after heat exchange to obtain the C2 product.

[0010] Furthermore, the energy-saving device for Fischer-Tropsch synthesis tail gas distillation also includes a pressure swing adsorption (PSA) unit. The PSA unit has a third light component inlet and carbon monoxide and hydrogen outlets. The third light component inlet is connected to the third gas phase light component outlet at the top of the column. The PSA unit is used to perform pressure swing adsorption on the third gas phase light component to produce carbon monoxide and hydrogen.

[0011] Furthermore, the first distillation column is a bubble cap column with a tray height of 20–21 m; the second distillation column is a bubble cap column with a tray height of 10–12 m; and the third distillation column is a sieve tray column with a tray height of 3–4 m.

[0012] Furthermore, the Fischer-Tropsch synthesis tail gas distillation energy-saving device also includes: a first reboiler, wherein the lower part of the first distillation column is provided with a first bottom liquid reflux port and a first bottom liquid outlet, the inlet of the first reboiler is connected to the first bottom liquid outlet, and the outlet of the first reboiler is connected to the first bottom liquid reflux port; and / or, a second reboiler, wherein the lower part of the second distillation column is provided with a second bottom liquid reflux port and a second bottom liquid outlet, the inlet of the second reboiler is connected to the second bottom liquid outlet, and the outlet of the second reboiler is connected to the second bottom liquid reflux port; and / or, a third reboiler, wherein the lower part of the third distillation column is provided with a third bottom liquid reflux port and a third bottom liquid outlet, the inlet of the third reboiler is connected to the third bottom liquid outlet, and the outlet of the third reboiler is connected to the third bottom liquid reflux port.

[0013] Furthermore, the Fischer-Tropsch synthesis tail gas distillation energy-saving device also includes: a first reflux tank having a first gaseous light component inlet, a first reflux outlet, and a first light component outlet; a first reflux liquid inlet being provided at the top of the first distillation column, the first gaseous light component inlet being connected to the first gaseous light component outlet at the top of the column, the first reflux outlet being connected to the first reflux liquid inlet, and the first light component outlet being connected to the first gaseous light component inlet; and / or, a second reflux tank having a second gaseous light component inlet, a second reflux outlet, and a second light component outlet; a second reflux liquid inlet being provided at the top of the second distillation column. The reflux inlet, the second gas phase light component inlet, and the second gas phase light component outlet at the top of the column are connected; the second reflux outlet is connected to the second reflux inlet; and the second light component outlet is connected to the second gas phase light component inlet. And / or, a third reflux tank has a third gas phase light component inlet, a third reflux outlet, and a third light component outlet. The upper part of the third distillation column is provided with a third reflux inlet, the third gas phase light component inlet is connected to the third gas phase light component outlet at the top of the column, the third reflux outlet is connected to the third reflux inlet, and the third light component outlet is connected to the third gas phase light component inlet.

[0014] Furthermore, the Fischer-Tropsch synthesis tail gas distillation energy-saving device also includes: a first pretreatment device, having an inlet for the Fischer-Tropsch synthesis tail gas to be treated and a non-permeable gas outlet, the first pretreatment device being used to perform oil washing separation and membrane separation on the Fischer-Tropsch synthesis tail gas to be treated; and a second pretreatment device, having a non-permeable gas inlet and a pretreated tail gas outlet, the non-permeable gas inlet being connected to the non-permeable gas outlet, and the pretreated tail gas outlet being connected to the Fischer-Tropsch synthesis tail gas inlet, the second pretreatment device being used to perform decarbonization and dehydration pretreatment on the non-permeable gas.

[0015] According to another aspect of the present invention, an energy-saving treatment method for Fischer-Tropsch synthesis tail gas distillation is provided. This method employs the aforementioned energy-saving device for Fischer-Tropsch synthesis tail gas distillation and includes the following steps: Step S1, performing a first distillation treatment on the Fischer-Tropsch synthesis tail gas using a first distillation column, obtaining a first gaseous light component at the top of the first distillation column and a C3 or higher heavy component at the bottom of the first distillation column; Step S2, performing a second distillation treatment on the first gaseous light component using a second distillation column, obtaining a second gaseous light component at the top of the second distillation column and a C2 component at the bottom of the second distillation column; Step S3, performing a third distillation treatment on the second gaseous light component using a third distillation column, obtaining a third gaseous light component at the top of the third distillation column and LNG at the bottom of the third distillation column; wherein the C3 or higher heavy component obtained in Step S1 and the C2 component obtained in Step S2 are heat-exchanged through a first heat exchanger.

[0016] Furthermore, the top pressure of the first distillation column is 2.2–2.4 MPa, and the bottom temperature is 70–80 °C; the top pressure of the second distillation column is 2.0–2.2 MPa, and the bottom temperature is -4–-9 °C; the top pressure of the third distillation column is 1.8–2.0 MPa, and the bottom temperature is -152–-154 °C.

[0017] Furthermore, after heat exchange, C3 and higher heavy components are formed into LPG and sent to the boundary area; C2 components are reheated to obtain C2 product, which is then sent to the fuel gas pipeline network; the reheating process pressure is 1.4 MPa.

[0018] Further, before step S1, the Fischer-Tropsch synthesis tail gas is subjected to oil washing separation and membrane separation in sequence to obtain non-permeable gas. Then, the non-permeable gas is subjected to decarbonization and dehydration pretreatment in sequence to obtain pretreated tail gas.

[0019] Furthermore, the third gas phase light component was subjected to pressure swing adsorption treatment to obtain carbon monoxide and hydrogen.

[0020] Furthermore, prior to pressure swing adsorption treatment, the third gas phase light component is pressurized to 3.2–3.4 MPa.

[0021] The technical solution of this invention achieves efficient utilization of Fischer-Tropsch synthesis tail gas. The main components of the aforementioned Fischer-Tropsch synthesis tail gas include hydrogen, carbon monoxide, nitrogen, carbon dioxide, and low-carbon hydrocarbons. In this invention, the first distillation column separates the C3 and higher heavy components from the first gaseous light component, which includes hydrogen, carbon monoxide, methane, and C2 components. The second distillation column separates the second gaseous light component from the C2 component, which includes hydrogen, carbon monoxide, and methane. The third distillation column separates the third gaseous light component from LNG, which includes carbon monoxide and hydrogen, and the main component of the LNG is methane. Furthermore, while achieving the separation of the aforementioned multiple oil products, this invention also fully utilizes the process conditions of the external feed streams of each distillation column. In the existing separation process, it leverages the refrigerant characteristics of the C2 component to cool the higher-temperature C3 and higher-grade heavy components to the receiving conditions of the boundary LPG (liquefied petroleum gas), thereby achieving heat exchange coupling between the C3 and higher-grade heavy components at the bottom of the first distillation column and the C2 component at the bottom of the second distillation column, which have different temperature potentials. Therefore, this invention achieves joint optimization of the process and the heat exchange network, ensuring the diversification of the Fischer-Tropsch synthesis oil product structure while reducing process investment and energy consumption, and improving the overall utilization efficiency of the entire Fischer-Tropsch synthesis unit. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0023] Figure 1 A schematic diagram of an energy-saving device for Fischer-Tropsch synthesis tail gas distillation according to an embodiment of the present invention is shown.

[0024] The above figures include the following reference numerals:

[0025] 10. First distillation column; 20. Second distillation column; 30. Third distillation column; 40. First heat exchanger; 50. Second heat exchanger; 60. Pressure swing adsorption unit; 70. First pretreatment device; 80. Second pretreatment device; 11. First reboiler; 21. Second reboiler; 31. Third reboiler; 12. First reflux tank; 22. Second reflux tank; 32. Third reflux tank. Detailed Implementation

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] As described in the background section of this invention, existing technologies suffer from problems such as high equipment investment and high operating energy consumption. To address these problems, according to one aspect of this invention, an energy-saving device for Fischer-Tropsch synthesis tail gas distillation is provided, such as... Figure 1 As shown, the apparatus includes: a first distillation column 10, having a Fischer-Tropsch synthesis tail gas inlet, a first gaseous light component outlet at the top of the column, and a C3 and heavier component outlet at the bottom of the column; the first distillation column 10 is used to perform a first distillation on the Fischer-Tropsch synthesis tail gas to separate the first gaseous light component and C3 and heavier components; and a second distillation column 20, having a first light component inlet, a second gaseous light component outlet at the top of the column, and a C2 component outlet at the bottom of the column, wherein the first light component inlet is connected to the first gaseous light component outlet at the top of the column, and the second distillation column 20 is used to perform a second distillation on the first gaseous light component to separate the second gaseous light component and C2 component. The third distillation column 30 has a second light component inlet, a third gaseous light component outlet at the top of the column, and an LNG outlet at the bottom of the column. The second light component inlet is connected to the second gaseous light component outlet at the top of the column. The third distillation column 30 is used to perform third distillation on the second gaseous light component to separate LNG and the third gaseous light component. The first heat exchanger 40 has a first heat exchange channel and a second heat exchange channel. The first heat exchange channel is connected to the C3 and above heavy component outlet at the bottom of the column, and the second heat exchange channel is connected to the C2 component outlet at the bottom of the column. The first heat exchanger 40 is used to exchange heat between the C3 and above heavy component and the C2 component.

[0028] The technical solution of this invention achieves efficient utilization of Fischer-Tropsch synthesis tail gas. The main components of the aforementioned Fischer-Tropsch synthesis tail gas include hydrogen, carbon monoxide, nitrogen, carbon dioxide, and low-carbon hydrocarbons. In this invention, Fischer-Tropsch synthesis tail gas A achieves separation of C3 and higher heavy components from the first gaseous phase light components in the first distillation column 10. The first gaseous phase light components include hydrogen, carbon monoxide, methane, and C2 components. The second distillation column 20 achieves separation of the second gaseous phase light components from the C2 components. The second gaseous phase light components include hydrogen, carbon monoxide, and methane. The third distillation column 30 achieves separation of the third gaseous phase light components from LNG. The third gaseous phase light components include carbon monoxide and hydrogen, and the main component of the LNG is methane. Furthermore, while achieving the separation of the aforementioned multiple oil products, this invention also fully utilizes the process conditions of the external feed streams of each distillation column. In the existing separation process, it leverages the refrigerant characteristics of the C2 component to cool the higher-temperature C3 and above heavy components to the receiving conditions of the boundary LPG (liquefied petroleum gas), thereby achieving heat exchange coupling between the C3 and above heavy components at the bottom of the first distillation column 10 and the C2 component at the bottom of the second distillation column 20, which have different temperature potentials. Therefore, this invention achieves joint optimization of the process and the heat exchange network, ensuring the diversification of the Fischer-Tropsch synthesis oil product structure while reducing process investment and energy consumption, and improving the overall utilization efficiency of the entire Fischer-Tropsch synthesis unit.

[0029] To further commercialize the C2 component and ensure it meets the temperature requirements of the fuel gas pipeline network, it is preferable that the second heat exchange channel of the aforementioned first heat exchanger 40 also has a C2 component outlet after heat exchange; such as Figure 1 As shown, the above-mentioned Fischer-Tropsch synthesis tail gas distillation energy-saving device further includes: a second heat exchanger 50, which has a C2 component inlet after heat exchange and a C2 product outlet, wherein the C2 product outlet is connected to the fuel gas pipeline network, and the second heat exchanger 50 is used to reheat the C2 after heat exchange to obtain C2 product D.

[0030] In actual operation, the second heat exchanger 50 uses water to reheat C2 after heat exchange. Preferably, the water temperature is 45°C.

[0031] To further improve the utilization efficiency of the third light component and obtain products with high added value, the above-mentioned Fischer-Tropsch synthesis tail gas distillation energy-saving device preferably also includes a pressure swing adsorption unit 60. The pressure swing adsorption unit 60 has a third light component inlet and carbon monoxide and hydrogen outlets. The third light component inlet is connected to the third gas phase light component outlet at the top of the column. The pressure swing adsorption unit 60 is used to perform pressure swing adsorption on the third gas phase light component to produce carbon monoxide and hydrogen.

[0032] In practice, the pressure swing adsorption unit 60 can be a type commonly used in the chemical industry, such as a compressor.

[0033] In practice, pressure swing adsorption (PSA) for producing carbon monoxide and hydrogen is divided into two steps: a PSA carbon monoxide purification step and a PSA hydrogen purification step. Preferably, the third gas phase light component is first fed into the PSA carbon monoxide purification step to obtain carbon monoxide and tail gas, and then the tail gas is sent into the PSA hydrogen purification step to obtain hydrogen.

[0034] In practice, pressure swing adsorption is preferably physical adsorption, which relies on the molecular forces between the adsorbent and the adsorbate for adsorption.

[0035] To further improve the distillation effect of the above-mentioned device, preferably, the first distillation column 10 is a bubble cap column with a tray height of 20-21m; the second distillation column 20 is a bubble cap column with a tray height of 10-12m; and the third distillation column 30 is a sieve plate column with a tray height of 3-4m.

[0036] To further maintain the gas-liquid phase balance of the material and the heat balance within the column, preferably, the above-mentioned Fischer-Tropsch synthesis tail gas distillation energy-saving device further includes: a first reboiler 11, the lower part of the first distillation column 10 is provided with a first bottom liquid reflux port and a first bottom liquid outlet, the inlet of the first reboiler 11 is connected to the first bottom liquid outlet, and the outlet of the first reboiler 11 is connected to the first bottom liquid reflux port; and / or, a second reboiler 21, the lower part of the second distillation column 20 is provided with a second bottom liquid reflux port and a second bottom liquid outlet, the inlet of the second reboiler 21 is connected to the second bottom liquid outlet, and the outlet of the second reboiler 21 is connected to the second bottom liquid reflux port; and / or, a third reboiler 31, the lower part of the third distillation column 30 is provided with a third bottom liquid reflux port and a third bottom liquid outlet, the inlet of the third reboiler 31 is connected to the third bottom liquid outlet, and the outlet of the third reboiler 31 is connected to the third bottom liquid reflux port.

[0037] To further improve the distillation effect, increase the component concentration at the top of the column, and maintain the pressure at the top of the column, preferably, the Fischer-Tropsch synthesis tail gas distillation energy-saving device further includes: a first reflux tank 12, having a first gaseous light component inlet, a first reflux outlet, and a first light component outlet; a first reflux liquid inlet is provided at the top of the first distillation column 10, the first gaseous light component inlet is connected to the first gaseous light component outlet at the top of the column, the first reflux outlet is connected to the first reflux liquid inlet, and the first light component outlet is connected to the first gaseous light component inlet; and / or, a second reflux tank 22, having a second gaseous light component inlet, a second reflux outlet, and a second light component outlet. The second distillation column 20 is provided with a second reflux liquid inlet at its upper part, a second gas phase light component inlet connected to the second gas phase light component outlet at the top of the column, a second reflux outlet connected to the second reflux liquid inlet, and a second light component outlet connected to the second gas phase light component inlet; and / or, the third reflux tank 32 has a third gas phase light component inlet, a third reflux outlet, and a third light component outlet; the third distillation column 30 is provided with a third reflux liquid inlet at its upper part, a third gas phase light component inlet connected to the third gas phase light component outlet at the top of the column, a third reflux outlet connected to the third reflux liquid inlet, and a third light component outlet connected to the third gas phase light component inlet.

[0038] To further remove impurities from the Fischer-Tropsch synthesis tail gas and enrich the desired oil and gas, in a preferred embodiment, the above-mentioned Fischer-Tropsch synthesis tail gas distillation energy-saving device further includes: a first pretreatment device 70, having an inlet for the Fischer-Tropsch synthesis tail gas to be treated and a non-permeable gas outlet, the first pretreatment device 70 being used to perform oil washing separation and membrane separation on the Fischer-Tropsch synthesis tail gas A to be treated; and a second pretreatment device 80, having a non-permeable gas inlet and a pretreated tail gas outlet, the non-permeable gas inlet being connected to the non-permeable gas outlet, and the pretreated tail gas outlet being connected to the Fischer-Tropsch synthesis tail gas inlet, the second pretreatment device 80 being used to perform decarbonization and dehydration pretreatment on the non-permeable gas B. After the above pretreatment, impurities such as carbon dioxide and water in the Fischer-Tropsch synthesis tail gas can be effectively removed, thereby further improving the quality of the distillation product.

[0039] According to another aspect of the present invention, an energy-saving treatment method for Fischer-Tropsch synthesis tail gas distillation is also provided, which employs the above-mentioned energy-saving device for Fischer-Tropsch synthesis tail gas distillation. The treatment method includes the following steps: Step S1, performing a first distillation treatment on the Fischer-Tropsch synthesis tail gas using a first distillation column 10, obtaining a first gaseous light component at the top of the first distillation column 10 and obtaining a C3 or higher heavy component at the bottom of the first distillation column 10; Step S2, performing a second distillation treatment on the first gaseous light component using a second distillation column 20, obtaining a second gaseous light component at the top of the second distillation column 20 and obtaining a C2 component at the bottom of the second distillation column 20; Step S3, performing a third distillation treatment on the second gaseous light component using a third distillation column 30, obtaining a third gaseous light component at the top of the third distillation column 30 and obtaining LNG at the bottom of the third distillation column 30; wherein the C3 or higher heavy component obtained in step S1 and the C2 component obtained in step S2 are heat exchanged through a first heat exchanger 40. The technical solution of this invention achieves efficient utilization of Fischer-Tropsch synthesis tail gas. The main components of the aforementioned Fischer-Tropsch synthesis tail gas include hydrogen, carbon monoxide, nitrogen, carbon dioxide, and low-carbon hydrocarbons. In this invention, the first distillation column 10 separates the C3 and higher heavy components from the first gaseous light component, which includes hydrogen, carbon monoxide, methane, and C2 components. The second distillation column 20 separates the second gaseous light component from the C2 component, which includes hydrogen, carbon monoxide, and methane. The third distillation column 30 separates the third gaseous light component from LNG, which includes carbon monoxide and hydrogen, and the main component of the LNG is methane. Furthermore, while achieving the separation of the aforementioned multiple oil products, this invention also fully utilizes the process conditions of the external feed streams of each distillation column. In the existing separation process, it leverages the refrigerant characteristics of the C2 component to cool the higher-temperature C3 and above heavy components to the receiving conditions of the boundary LPG (liquefied petroleum gas), thereby achieving heat exchange coupling between the C3 and above heavy components at the bottom of the first distillation column 10 and the C2 component at the bottom of the second distillation column 20, which have different temperature potentials. Therefore, this invention achieves joint optimization of the process and the heat exchange network, ensuring the diversification of the Fischer-Tropsch synthesis oil product structure while reducing process investment and energy consumption, and improving the overall utilization efficiency of the entire Fischer-Tropsch synthesis unit.

[0040] To further improve the quality of the distillation products, in a preferred embodiment, the top pressure of the first distillation column is 2.2–2.4 MPa and the bottom temperature is 70–80 °C; the top pressure of the second distillation column is 2.0–2.2 MPa and the bottom temperature is -4–-9 °C; and the top pressure of the third distillation column is 1.8–2.0 MPa and the bottom temperature is -152–-154 °C.

[0041] To better conserve energy, in a preferred embodiment, after heat exchange, the C3 and higher weight components are sent to the boundary area; the C2 component is reheated to obtain C2 product D, which is then sent to the fuel gas pipeline; the reheating process pressure is 1.4 MPa. Reheating the C2 component under these process conditions facilitates more efficient utilization of the heat generated during the distillation process. Preferably, the reheating process is completed within an ethylene heat exchanger. More preferably, the receiving conditions at the boundary area are 1.4–1.6 MPa and 20–40°C, and the receiving conditions at the fuel gas pipeline are 0.5–0.7 MPa and 20–40°C.

[0042] Matching the aforementioned preferred boundary areas and fuel gas pipeline process conditions with the preferred distillation column component outlet process conditions of this invention facilitates more efficient utilization of the heat from C3 and higher heavy components and C2 components. This allows for the design of a rational heat exchange process and minimizes energy consumption.

[0043] To further improve the efficiency of the distillation tail gas in this method, preferably, before step S1, the Fischer-Tropsch synthesis tail gas A is subjected to oil washing separation and membrane separation in sequence to obtain non-permeable gas B, and then the non-permeable gas is subjected to decarbonization and dehydration pretreatment in sequence to obtain pretreated tail gas C.

[0044] To further improve the utilization efficiency of the third light component and obtain products with high added value, preferably, the third gas-phase light component is subjected to pressure swing adsorption treatment to obtain carbon monoxide and hydrogen.

[0045] Preferably, before pressure swing adsorption, the third gas phase light component can be pressurized using conventional methods in the art, for example, by pressurizing it to 3.2–3.4 MPa.

[0046] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0047] Example 1:

[0048] Step S1: The Fischer-Tropsch synthesis tail gas is subjected to oil washing and membrane separation to obtain non-permeable gas. Then, the non-permeable gas is subjected to decarbonization and dehydration pretreatment to obtain pretreated tail gas.

[0049] Step S2: The pretreated tail gas is subjected to a first distillation process using a first distillation column 10. The top pressure of the first distillation column 10 is 2.2 MPa and the bottom temperature is 70°C. A first gaseous light component is obtained at the top of the first distillation column 10, and a heavy component of C3 and above is obtained at the bottom of the first distillation column 10.

[0050] Step S3: The first gaseous light component is subjected to a second distillation process using a second distillation column 20. The top pressure of the second distillation column 20 is 2.0 MPa, and the bottom temperature is -4 to -9°C. The second gaseous light component is obtained at the top of the second distillation column 20, and component C2 is obtained at the bottom of the second distillation column 20. Further, by designing a heat exchange process, the C3 and higher heavy components and component C2 are fed into the first heat exchanger 40 to obtain LPG. Then, component C2 is reheated through a 1.4 MPa ethylene heat exchanger and connected to the fuel gas pipeline network.

[0051] Step S4: The second gaseous light component is subjected to third distillation using a third distillation column 30. The top pressure of the third distillation column 30 is 1.8 MPa and the bottom temperature is -154°C. The third gaseous light component is obtained at the top of the third distillation column 30, and LNG is obtained at the bottom of the third distillation column 30.

[0052] In step S5, the third gaseous light component is pressurized to 3.2 MPa by a compressor and then sent to the pressure swing adsorption unit 60 to produce carbon monoxide and hydrogen.

[0053] The process described in this embodiment is used to distill the Fischer-Tropsch synthesis tail gas, requiring a water volume of 12.3 t / h.

[0054] Comparative Example 1:

[0055] The difference from Example 1 is that an internal heat exchange stream (C2 component) is not used. The cooling capacity of C3 and higher heavy components is 6.4 t / h of water at 25°C, and the reheating capacity of C2 component is 18.8 t / h of water at 45°C.

[0056] As can be seen from the above description, after implementing this invention, cooling of C3 and higher heavy components no longer requires a cooling medium, and only 12.3 t / h of 45°C water is needed for reheating after heat exchange between C2 and C3 components. Overall, compared with not using a heat exchange process, this invention can save 51.2% of energy. In summary, the above embodiments of this invention achieve the following technical effects: by using the apparatus and method of this invention to distill the Fischer-Tropsch synthesis tail gas, a reasonable separation of hydrogen, carbon monoxide, methane, C2 components, and C3 and higher heavy components is achieved, while heat exchange coupling is realized between the C3 and higher heavy components separated in the first distillation column 10 and the C2 components separated in the second distillation column 20. While ensuring the diversification of the Fischer-Tropsch synthesis oil product structure, energy utilization efficiency is maximized, investment costs are reduced, and the goal of energy saving and consumption reduction is achieved.

[0057] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for energy-saving treatment of Fischer-Tropsch synthesis tail gas by distillation, characterized in that, The processing method includes the following steps: Step S1: The Fischer-Tropsch synthesis tail gas is subjected to a first distillation treatment using a first distillation column (10). A first gaseous light component is obtained at the top of the first distillation column (10), and a heavy component of C3 and above is obtained at the bottom of the first distillation column (10). The pressure at the top of the first distillation column is 2.2~2.4 MPa, and the temperature at the bottom of the column is 70~80℃. Step S2: The first gaseous light component is subjected to a second distillation process using a second distillation column (20). A second gaseous light component is obtained at the top of the second distillation column (20), and a C2 component is obtained at the bottom of the second distillation column (20). The pressure at the top of the second distillation column is 2.0~2.2MPa, and the temperature at the bottom of the column is -4~-9℃. Step S3: The second gaseous light component is subjected to a third distillation process using a third distillation column (30). A third gaseous light component is obtained at the top of the third distillation column (30), and LNG is obtained at the bottom of the third distillation column (30). The pressure at the top of the third distillation column is 1.8~2.0MPa, and the temperature at the bottom of the column is -152~-154℃. In this process, the C3 and above heavy components obtained in step S1 and the C2 component obtained in step S2 are heat exchanged through a first heat exchanger (40); after the heat exchange, the C3 and above heavy components are formed into LPG and sent to the boundary area; the C2 component is reheated to obtain C2 product, and the C2 product is sent to the fuel gas pipeline network; the pressure during the reheating process is 1.4 MPa. The treatment method is carried out in an energy-saving distillation unit for Fischer-Tropsch synthesis tail gas, the unit comprising: The first distillation column (10) has a Fischer-Tropsch synthesis tail gas inlet, a first gas phase light component outlet at the top of the column, and a C3 and heavier component outlet at the bottom of the column. The first distillation column (10) is used to perform a first distillation on the Fischer-Tropsch synthesis tail gas to separate the first gas phase light component and C3 and heavier components. The second distillation column (20) has a first light component inlet, a second gaseous light component outlet at the top of the column and a C2 component outlet at the bottom of the column, wherein the first light component inlet is connected to the first gaseous light component outlet at the top of the column, and the second distillation column (20) is used to perform a second distillation on the first gaseous light component to separate the second gaseous light component and the C2 component. A third distillation column (30) has a second light component inlet, a third gaseous light component outlet at the top of the column, and an LNG outlet at the bottom of the column, wherein the second light component inlet is connected to the second gaseous light component outlet at the top of the column, and the third distillation column (30) is used to perform a third distillation on the second gaseous light component to separate LNG and the third gaseous light component; and The first heat exchanger (40) has a first heat exchange channel and a second heat exchange channel, wherein the first heat exchange channel is connected to the outlet of the bottom C3 and above heavy components, and the second heat exchange channel is connected to the outlet of the bottom C2 component. The first heat exchanger (40) is used to exchange heat between the C3 and above heavy components and the C2 component.

2. The energy-saving treatment method for Fischer-Tropsch synthesis tail gas distillation according to claim 1, characterized in that, The second heat exchange channel of the first heat exchanger (40) also has a C2 component outlet after heat exchange; the Fischer-Tropsch synthesis tail gas distillation energy-saving device further includes: The second heat exchanger (50) has a C2 component inlet and a C2 product outlet after heat exchange, wherein the C2 product outlet is connected to the fuel gas pipeline network, and the second heat exchanger (50) is used to reheat the C2 after heat exchange to obtain the C2 product.

3. The energy-saving treatment method for Fischer-Tropsch synthesis tail gas distillation according to claim 1, characterized in that, The Fischer-Tropsch synthesis tail gas distillation energy-saving device also includes a pressure swing adsorption unit (60), which has a third light component inlet and carbon monoxide and hydrogen outlets. The third light component inlet is connected to the third gas phase light component outlet at the top of the column. The pressure swing adsorption unit (60) is used to perform pressure swing adsorption on the third gas phase light component to produce carbon monoxide and hydrogen.

4. The energy-saving treatment method for Fischer-Tropsch synthesis tail gas distillation according to any one of claims 1 to 3, characterized in that, The first distillation column (10) is a bubble cap column, and the height of the trays of the first distillation column (10) is 20~21m; The second distillation column (20) is a bubble cap column, and the height of the trays in the second distillation column (20) is 10~12m; The third distillation column (30) is a sieve tray column, and the height of the trays in the third distillation column (30) is 3~4m.

5. The energy-saving treatment method for Fischer-Tropsch synthesis tail gas distillation according to any one of claims 1 to 3, characterized in that, The Fischer-Tropsch synthesis tail gas distillation energy-saving device also includes: The first reboiler (11) is provided with a first reflux port and a first outlet port at the lower part of the first distillation column (10). The inlet of the first reboiler (11) is connected to the first outlet port, and the outlet of the first reboiler (11) is connected to the first reflux port; and / or, The second reboiler (21) is provided with a second reflux port and a second outlet port at the bottom of the second distillation column (20). The inlet of the second reboiler (21) is connected to the second outlet port, and the outlet of the second reboiler (21) is connected to the second reflux port; and / or, The third reboiler (31) is provided with a third reflux port and a third outlet port at the lower part of the third distillation column (30). The inlet of the third reboiler (31) is connected to the third outlet port, and the outlet of the third reboiler (31) is connected to the third reflux port.

6. The energy-saving treatment method for Fischer-Tropsch synthesis tail gas distillation according to any one of claims 1 to 3, characterized in that, The Fischer-Tropsch synthesis tail gas distillation energy-saving device also includes: The first pretreatment device (70) has an inlet for the Fischer-Tropsch synthesis tail gas to be treated and a non-permeable gas outlet. The first pretreatment device (70) is used to perform oil washing separation and membrane separation on the Fischer-Tropsch synthesis tail gas to be treated. The second pretreatment device (80) has a non-permeable gas inlet and a pretreatment tail gas outlet. The non-permeable gas inlet is connected to the non-permeable gas outlet, and the pretreatment tail gas outlet is connected to the Fischer-Tropsch synthesis tail gas inlet. The second pretreatment device (80) is used to perform decarbonization and dehydration pretreatment on the non-permeable gas.

7. The energy-saving treatment method for Fischer-Tropsch synthesis tail gas distillation according to claim 1, characterized in that, Before step S1, the Fischer-Tropsch synthesis tail gas is subjected to oil washing and membrane separation in sequence to obtain non-permeable gas. Then, the non-permeable gas is subjected to decarbonization and dehydration pretreatment in sequence to obtain pretreated tail gas.

8. The energy-saving treatment method for Fischer-Tropsch synthesis tail gas distillation according to claim 1, characterized in that, The third gas-phase light component was subjected to pressure swing adsorption treatment to obtain carbon monoxide and hydrogen.

9. The energy-saving treatment method for Fischer-Tropsch synthesis tail gas distillation according to claim 8, characterized in that, Prior to the pressure swing adsorption treatment, the third gas phase light component is pressurized to 3.2~3.4 MPa.

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