Fischer-Tropsch synthesis tail gas purification system

Abstract

The invention provides a Fischer-Tropsch synthesis tail gas purification system which comprises a decarburization unit, a drying tower, a mercury removal tower, a gas-liquid separator, a heavy hydrocarbon washing tower, a methane rectifying tower and a PSA unit, the decarburization unit is used for removing carbon dioxide in Fischer-Tropsch synthesis tail gas, the drying tower is used for drying and dehydrating the decarburized Fischer-Tropsch synthesis tail gas, and the mercury removal tower is used for removing mercury in the Fischer-Tropsch synthesis tail gas. The mercury removal tower is used for carrying out mercury removal treatment on the dried Fischer-Tropsch synthesis tail gas, the mercury removal tower is connected to the gas-liquid separator, the gas-liquid separator is used for carrying out gas-liquid separation treatment on the Fischer-Tropsch synthesis tail gas, the gas-liquid separator is connected to the heavy hydrocarbon washing tower, and the heavy hydrocarbon washing tower is used for carrying out heavy hydrocarbon washing on the Fischer-Tropsch synthesis tail gas; the heavy hydrocarbon washing tower is connected to the methane rectifying tower, the methane rectifying tower is used for rectifying the Fischer-Tropsch synthesis tail gas, the PSA unit is connected with the top of the methane rectifying tower through a pipeline, and the PSA unit is used for purifying the rectified Fischer-Tropsch synthesis tail gas. According to the scheme, the recycling effect of the Fischer-Tropsch synthesis tail gas is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of Fischer-Tropsch synthesis tail gas recovery, and in particular to a Fischer-Tropsch synthesis tail gas purification system. Background Art

[0002] Fischer-Tropsch synthesis is the process of converting synthesis gas into high-carbon hydrocarbons. It is an important way to efficiently convert and utilize non-petroleum carbon-containing resources. Its products mainly include heavy oil, light oil, wax, synthetic water, methane, low-carbon hydrocarbons, unreacted synthesis gas (H2+CO) and nitrogen. Through a series of process treatment and separation, liquid hydrocarbons, solid wax and a large amount of Fischer-Tropsch synthesis tail gas are finally formed. The tail gas is mainly composed of methane, hydrogen and carbon monoxide, and the methane content is usually 30-60% (mol / mol).

[0003] If the tail gas of Fischer-Tropsch synthesis can be recycled, the efficiency of indirect coal liquefaction will be greatly improved. There are four common methods for treating tail gas of Fischer-Tropsch synthesis. The first is to convert the tail gas into hydrogen-rich gas with a higher calorific value; the second is to recover the hydrocarbons in the tail gas and send them to the boiler device to burn the by-product steam; the third is to separate the low-carbon hydrocarbons in the tail gas by low-temperature fractionation for the synthesis of LNG, etc.; the fourth is to convert the hydrocarbons in the tail gas into synthesis gas by conversion and transformation and return it to the Fischer-Tropsch synthesis reactor. However, the tail gas of Fischer-Tropsch synthesis contains impurities such as carbon dioxide, hydrocarbons, and mercury. The impurities must be removed and purified when recycled. However, the existing technology has poor effect on the recycling of tail gas of Fischer-Tropsch synthesis. Summary of the invention

[0004] The invention provides a Fischer-Tropsch synthesis tail gas purification system to improve the recycling effect of the Fischer-Tropsch synthesis tail gas.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a Fischer-Tropsch synthesis tail gas purification system, comprising a decarbonization unit, a drying tower, a demercuration tower, a gas-liquid separator, a heavy hydrocarbon washing tower, a methane distillation tower, and a PSA unit. The decarbonization unit is used to remove carbon dioxide in the Fischer-Tropsch synthesis tail gas. The drying tower is connected to the decarbonization unit through a pipeline. The drying tower is used to dry and dehydrate the decarbonized Fischer-Tropsch synthesis tail gas. The demercuration tower is connected to the top of the drying tower through a pipeline. The demercuration tower is used to demercurate the dried Fischer-Tropsch synthesis tail gas. The outlet of the demercuration tower is connected to the gas-liquid separator. The gas-liquid separator is used to perform gas-liquid separation on the Fischer-Tropsch synthesis tail gas. The gas-liquid separator is connected to the heavy hydrocarbon washing tower. The heavy hydrocarbon washing tower is used to wash the Fischer-Tropsch synthesis tail gas with heavy hydrocarbons. The heavy hydrocarbon washing tower is connected to the methane distillation tower. The methane distillation tower is used to distill the Fischer-Tropsch synthesis tail gas. The PSA unit is connected to the top of the methane distillation tower through a pipeline. The PSA unit is used to purify the distilled Fischer-Tropsch synthesis tail gas.

[0006] Furthermore, the Fischer-Tropsch synthesis tail gas purification system further comprises a first precooler and a second precooler, wherein:

[0007] A first precooler is connected to the bottom of the demercuration tower through a pipeline, and the first precooler is used for first cooling and lowering the temperature of the Fischer-Tropsch synthesis tail gas after the demercuration. A gas-liquid separator is connected to the first precooler through a pipeline, and the gas-liquid separator is used for gas-liquid separation of the Fischer-Tropsch synthesis tail gas after the first cooling and lowering.

[0008] The second precooler is connected to the top of the gas-liquid separator by a pipeline, and the second precooler is used to perform a second cooling and temperature reduction treatment on the Fischer-Tropsch synthesis tail gas after the gas-liquid separation treatment. The heavy hydrocarbon washing tower is connected to the second precooler by a pipeline, and the heavy hydrocarbon washing tower is used to wash the heavy hydrocarbons on the Fischer-Tropsch synthesis tail gas after the second cooling and temperature reduction treatment.

[0009] Furthermore, the Fischer-Tropsch synthesis tail gas purification system also includes a third precooler, which is connected to the top of the heavy hydrocarbon washing tower through a pipeline, and the third precooler is used to perform a third cooling and temperature reduction treatment on the Fischer-Tropsch synthesis tail gas after the removal of heavy hydrocarbons. The methane distillation tower is connected to the third precooler through a pipeline, and the methane distillation tower is used to distill the Fischer-Tropsch synthesis tail gas after the third cooling and temperature reduction treatment.

[0010] Furthermore, in the decarbonization unit, carbon dioxide is removed from the raw gas from the upstream system to reduce the carbon dioxide content in the raw gas to below 20 ppm.

[0011] Furthermore, the decarbonization unit uses an amine method or temperature swing adsorption for decarbonization.

[0012] Furthermore, the decarbonized raw gas is sent to a drying tower, and the moisture in the tail gas is removed by molecular sieve adsorption in the drying tower to obtain dry and qualified purified gas, wherein the dew point of water is less than -65°C.

[0013] Furthermore, in the demercuration tower, chemical adsorption is used to remove mercury. When the raw gas continuously passes through the demercuration tower, it chemically reacts with the demercuration adsorbent loaded in the demercuration tower, thereby removing mercury in the raw gas to control the mercury content below 0.01μg / m3.

[0014] Furthermore, the dried and qualified purified gas is sent to the first precooler for cooling, and after being cooled to 10-15°C, it enters the gas-liquid separator, and an aqueous solution is obtained at the bottom of the gas-liquid separator. The gas phase component at the top of the gas-liquid separator enters the second precooler for further cooling, and after being cooled to -40--50°C, it enters the heavy hydrocarbon washing tower to remove heavy hydrocarbons. The precooling medium in the first precooler is propylene, and the precooling medium in the second precooler is ethane or ethylene.

[0015] Furthermore, the cooled gaseous components enter the heavy hydrocarbon washing tower from the lower part, and part of the LNG on the product line is used as the top reflux, so that the Fischer-Tropsch synthesis tail gas containing heavy hydrocarbons and the LNG are countercurrently transferred in the heavy hydrocarbon washing tower, so that the heavy hydrocarbon content is reduced to below 70ppm, and the qualified purified gas after removing the heavy hydrocarbons is transported from the top of the heavy hydrocarbon washing tower to the methane distillation tower, and the heavy hydrocarbons are obtained at the bottom of the heavy hydrocarbon washing tower and sent to the low-temperature oil washing unit to recover the low-carbon hydrocarbons.

[0016] Furthermore, the gaseous material at the top of the heavy hydrocarbon washing tower is cooled and sent to the methane distillation tower. The top pressure of the methane distillation tower is controlled at 0.5-0.8 MPa, the top temperature is -190--180°C, and the bottom temperature is -180--170°C. The gaseous material at the top of the tower is sent to the PSA unit to purify hydrogen. After heat exchange and supercooling, part of the liquid-phase material at the bottom of the tower is used as LNG product, and part of it is used as washing liquid for the heavy hydrocarbon washing tower.

[0017] The present invention aims to solve the problem of energy utilization rate of Fischer-Tropsch synthesis tail gas, takes the oil-washed dry gas after low-temperature oil washing of Fischer-Tropsch synthesis tail gas as the research object, and proposes a Fischer-Tropsch synthesis tail gas purification process consisting of multiple steps such as decarbonization, dehydration, demercurization, precooling, heavy hydrocarbon washing, and low-temperature separation, so as to achieve the recovery and utilization of effective components with high added value such as hydrogen, methane and low-carbon hydrocarbons in the tail gas, reduce the operating cost of the device, and improve the comprehensive utilization efficiency of indirect coal liquefaction.

[0018] Compared with the prior art, the Fischer-Tropsch synthesis tail gas purification system proposed in the present invention has the following advantages:

[0019] 1. The present invention separates the tail gas of Fischer-Tropsch synthesis into high-value-added high-purity hydrogen, heavy hydrocarbons and liquefied natural gas by a relatively optimal process route. The method not only obtains qualified purified gas from the tail gas rich in heavy hydrocarbons, recovers qualified products, solves the problem of waste of tail gas resources of Fischer-Tropsch synthesis, but also can realize the purpose of comprehensive resource utilization of effective components of tail gas while saving resources, and has strong process applicability;

[0020] 2. According to the component characteristics of the raw gas itself, the present invention proposes a process flow for removing heavy hydrocarbons from oil-washed dry gas. Compared with the existing technology, this technology can flexibly adapt to the fluctuation of the raw gas component content by adjusting the reflux rate of LNG. At the same time, the investment in the process flow for removing heavy hydrocarbons is relatively low. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0022] Figure 1 A schematic structural diagram of a Fischer-Tropsch synthesis tail gas purification system provided by an embodiment of the present invention is shown.

[0023] The above drawings include the following reference numerals:

[0024] 10. Decarbonization unit;

[0025] 20. Drying tower;

[0026] 30. Mercury removal tower;

[0027] 40. Gas-liquid separator;

[0028] 50. Heavy hydrocarbon washing tower;

[0029] 60. Methane distillation tower;

[0030] 70. PSA unit;

[0031] 81. The first precooler;

[0032] 82. Second precooler;

[0033] 83. The third precooler. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] like Figure 1As shown, an embodiment of the present invention provides a Fischer-Tropsch synthesis tail gas purification system, including a decarbonization unit 10, a drying tower 20, a mercury removal tower 30, a gas-liquid separator 40, a heavy hydrocarbon washing tower 50, a methane distillation tower 60, and a PSA unit 70 (i.e., a pressure swing adsorption unit). The decarbonization unit 10 is used to remove carbon dioxide from the Fischer-Tropsch synthesis tail gas. The drying tower 20 is connected to the decarbonization unit 10 through a pipeline, and is used to dry and dehydrate the decarbonized Fischer-Tropsch synthesis tail gas. The demercuration tower 30 is connected to the top of the drying tower 20 through a pipeline, and is used to demercurate the dried Fischer-Tropsch synthesis tail gas. The outlet of the demercuration tower 30 is connected to the gas-liquid separator 40, and the gas-liquid separator 40 is used to perform gas-liquid separation on the Fischer-Tropsch synthesis tail gas. The gas-liquid separator 40 is connected to the heavy hydrocarbon washing tower 50, and the heavy hydrocarbon washing tower 50 is used to wash the heavy hydrocarbons of the Fischer-Tropsch synthesis tail gas. The heavy hydrocarbon washing tower 50 is connected to the methane distillation tower 60, and is used to distill the Fischer-Tropsch synthesis tail gas. The PSA unit 70 is connected to the top of the methane distillation tower 60 through a pipeline, and is used to purify the Fischer-Tropsch synthesis tail gas after distillation.

[0036] Through the above series of purification treatments, this solution effectively removes harmful components in the tail gas of Fischer-Tropsch synthesis, improves the utilization value of the tail gas, and is suitable for the chemical industry, energy and other industries, especially for the treatment of tail gas generated by the Fischer-Tropsch synthesis process, which has important application value. Through this solution, the recycling effect of the tail gas of Fischer-Tropsch synthesis is improved.

[0037] like Figure 1 As shown, the Fischer-Tropsch synthesis tail gas purification system also includes a first precooler 81 and a second precooler 82. The first precooler 81 is connected to the bottom of the mercury removal tower 30 through a pipeline, and is used for the first cooling and cooling treatment of the Fischer-Tropsch synthesis tail gas after the mercury removal. The gas-liquid separator 40 is connected to the first precooler 81 through a pipeline, and is used for gas-liquid separation treatment of the Fischer-Tropsch synthesis tail gas after the first cooling and cooling treatment; the second precooler 82 is connected to the top of the gas-liquid separator 40 through a pipeline, and is used for the second cooling and cooling treatment of the Fischer-Tropsch synthesis tail gas after the gas-liquid separation treatment. The heavy hydrocarbon washing tower 50 is connected to the second precooler 82 through a pipeline, and is used for heavy hydrocarbon washing of the Fischer-Tropsch synthesis tail gas after the second cooling and cooling treatment.

[0038] The setting of the above-mentioned precooler not only improves the efficiency of subsequent processing units, but also effectively reduces energy consumption. It is suitable for industrial scenarios that process large amounts of exhaust gas, such as large-scale Fischer-Tropsch synthesis plants, ensuring stable operation and efficient processing of the system.

[0039] Furthermore, the Fischer-Tropsch synthesis tail gas purification system also includes a third precooler 83, which is connected to the top of the heavy hydrocarbon washing tower 50 through a pipeline, and is used to perform a third cooling and cooling treatment on the Fischer-Tropsch synthesis tail gas after the heavy hydrocarbon removal, and the methane distillation tower 60 is connected to the third precooler 83 through a pipeline, and is used to distill the Fischer-Tropsch synthesis tail gas after the third cooling and cooling treatment. The three cooling and cooling treatments ensure that the various components in the tail gas are fully separated, providing a purer feed for the distillation tower, which is suitable for industrial applications with high requirements for tail gas purity, such as the production of high-purity hydrogen and liquefied natural gas (LNG), and improves the quality and market competitiveness of the products.

[0040] In the decarbonization unit 10, carbon dioxide is removed from the raw gas from the upstream system to reduce the carbon dioxide content in the raw gas to below 20 ppm. This treatment step effectively avoids the impact of carbon dioxide on subsequent processes, such as contamination of the adsorbent in the PSA unit 70, and is suitable for industrial gas processing scenarios that require carbon dioxide purification, such as the production process of chemical products such as synthetic ammonia and methanol, thereby improving the operating efficiency and product quality of the entire system.

[0041] In this scheme, the decarbonization unit 10 uses the alcohol amine method or temperature swing adsorption for decarbonization. Both the alcohol amine method and temperature swing adsorption are mature decarbonization technologies, which can be flexibly selected according to the characteristics and processing volume of the raw gas, and are suitable for the treatment of Fischer-Tropsch synthesis tail gas of different scales, such as small-scale pilot plants to large-scale industrial production, ensuring the adaptability and economy of the system.

[0042] Among them, the alcohol amine method is to use amine-based solvents to react chemically with CO2 in the raw gas to remove it. The main process flow of this method is: under normal temperature and pressure conditions, alkaline amine liquid reacts with acidic gas, and then changes the process conditions to regenerate under low pressure and temperature conditions. It has a large acid gas load on the treated gas and a strong selectivity for acidic gas, and the solvent has a very low solubility in hydrocarbons. The amine-based solvent uses monoethanolamine (MEA) or diethanolamine (DEA) or methyldiethanolamine (MDEA).

[0043] Temperature swing adsorption is to separate carbon dioxide by utilizing the difference in adsorption performance of gas components on solid materials and the change in adsorption capacity at different temperatures. Through the cycle of temperature rise and fall, the carbon dioxide components adsorbed in low temperature environment are desorbed at high temperature, so that the adsorbent is regenerated. The adsorbent is molecular sieve or activated carbon.

[0044] like Figure 1As shown, the decarbonized raw gas is sent to the drying tower 20, and the moisture in the tail gas is removed by molecular sieve adsorption in the drying tower 20 to obtain dry and qualified purified gas, wherein the dew point of water is less than -65°C. This treatment ensures that the moisture in the tail gas is completely removed, avoiding the influence of moisture on subsequent processing units such as PSA units, and is suitable for industrial gas processing scenarios that require deep drying, thereby improving the purity and performance of the product. In the dehydration process, molecular sieve dehydration technology is used, and the molecular sieve is 3A, 4A or 5A.

[0045] In the demercuration tower 30, a chemical adsorption method is used to remove mercury. When the raw gas continuously passes through the demercuration tower 30, a chemical reaction occurs with the demercuration adsorbent filled in the demercuration tower 30, thereby removing mercury from the raw gas to control the mercury content to 0.01 μg / m 3 the following.

[0046] Mercury removal treatment ensures that mercury in the exhaust gas is effectively removed, avoiding mercury pollution to the environment and subsequent process equipment. It is suitable for all industrial gas treatment scenarios that require mercury purification, such as coal gasification, petroleum refining, etc., improving the environmental performance of the system and the service life of the equipment.

[0047] In this scheme, the dried and qualified purified gas is sent to the first precooler 81 for cooling, and enters the gas-liquid separator 40 after being cooled to 10-15°C. The aqueous solution is obtained at the bottom of the gas-liquid separator 40, and the gas phase components at the top of the gas-liquid separator 40 enter the second precooler 82 for further cooling. After being cooled to -40--50°C, it enters the heavy hydrocarbon washing tower 50 to remove heavy hydrocarbons. The precooling medium in the first precooler 81 is propylene, and the precooling medium in the second precooler 82 is ethane or ethylene. The cooling of the precooler not only realizes the effective separation of gas and liquid, but also provides suitable temperature conditions for the subsequent heavy hydrocarbon washing. It is suitable for treating industrial gases containing a large amount of heavy hydrocarbons, such as Fischer-Tropsch synthesis, cracking gas, etc., and improves the recovery rate of heavy hydrocarbons and the overall economic benefits of the system.

[0048] In this solution, the gas-liquid separator adopts a vertical wire mesh gas-liquid separator. Based on the different particle sizes of gas and liquid, the liquid and gas are mixed and filtered through the wire mesh. The gas flows out from the top of the separator, and the liquid is intercepted on the wire mesh and flows to the bottom of the separator under the action of gravity and is discharged.

[0049] like Figure 1As shown, the gaseous components after cooling enter the heavy hydrocarbon washing tower 50 from the lower part of the heavy hydrocarbon washing tower 50, and part of the LNG in the product line is used as the top reflux, so that the Fischer-Tropsch synthesis tail gas containing heavy hydrocarbons and LNG are countercurrently transferred in the heavy hydrocarbon washing tower 50, so that the heavy hydrocarbon content is reduced to below 70ppm, and the qualified purified gas after removing the heavy hydrocarbons is transported from the top of the heavy hydrocarbon washing tower 50 to the methane distillation tower 60, and the heavy hydrocarbons are obtained from the bottom of the heavy hydrocarbon washing tower 50 and sent to the low-temperature oil washing unit to recover the low-carbon hydrocarbons. In addition, during the start-up stage of the device, the washing liquid can use the LPG produced by the device.

[0050] This processing step not only effectively removes heavy hydrocarbons, but also realizes the recycling of heavy hydrocarbons. It is suitable for industrial gas processing scenarios that require the recovery of heavy hydrocarbons, such as refineries, chemical plants, etc. It not only reduces resource waste, but also increases economic benefits, reflecting the concept of circular economy.

[0051] like Figure 1 As shown, the gaseous material at the top of the heavy hydrocarbon washing tower 50 is cooled and sent to the methane distillation tower 60. The top pressure of the methane distillation tower 60 is controlled at 0.5-0.8 MPa, the top temperature is -190--180°C, and the bottom temperature is -180--170°C. The gaseous material at the top of the tower is sent to the PSA unit 70 for purifying hydrogen. After heat exchange and supercooling, part of the liquid-phase material at the bottom of the tower is used as LNG product, and part of it is used as washing liquid for the heavy hydrocarbon washing tower 50.

[0052] The design parameters of the methane distillation tower 60 (such as pressure and temperature control) are optimized based on the physical properties of methane and hydrogen, ensuring efficient separation of the two gases and providing high-purity raw gas for downstream processes. It is suitable for industrial scenarios that require the production of high-purity hydrogen and LNG, such as fuel cells, LNG energy supply, etc., which not only increases the added value of the product, but also provides technical support for the development and utilization of clean energy.

[0053] The Fischer-Tropsch synthesis tail gas purification system of the present application effectively removes carbon dioxide, moisture, mercury and heavy hydrocarbons in the Fischer-Tropsch synthesis tail gas through multi-stage treatment, and finally distills and purifies high-purity hydrogen and LNG products. The system runs stably and is easy to operate. It not only improves the utilization efficiency of tail gas and reduces environmental pollution, but also provides high-quality raw gas for downstream processes, with significant economic and environmental benefits. In addition, the system can also be modularly designed according to actual needs, which is easy to maintain and upgrade. It is suitable for Fischer-Tropsch synthesis plants of various sizes. Whether it is a new project or the transformation of an existing plant, it can provide flexible and efficient solutions, opening up new ways for industrial gas purification and resource recycling, and has good application prospects and market potential.

[0054] The present invention aims to solve the problem of energy utilization rate of Fischer-Tropsch synthesis tail gas, takes the oil-washed dry gas after low-temperature oil washing of Fischer-Tropsch synthesis tail gas as the research object, and proposes a Fischer-Tropsch synthesis tail gas purification process consisting of multiple steps such as decarbonization, dehydration, demercurization, precooling, heavy hydrocarbon washing, and low-temperature separation, so as to achieve the recovery and utilization of effective components with high added value such as hydrogen, methane and low-carbon hydrocarbons in the tail gas, reduce the operating cost of the device, and improve the comprehensive utilization efficiency of indirect coal liquefaction.

[0055] Compared with the prior art, the Fischer-Tropsch synthesis tail gas purification system proposed in the present invention has the following advantages:

[0056] 1. The present invention separates the tail gas of Fischer-Tropsch synthesis into high-value-added high-purity hydrogen, heavy hydrocarbons and liquefied natural gas by a relatively optimal process route. The method not only obtains qualified purified gas from the tail gas rich in heavy hydrocarbons, recovers qualified products, solves the problem of waste of tail gas resources of Fischer-Tropsch synthesis, but also can realize the purpose of comprehensive resource utilization of effective components of tail gas while saving resources, and has strong process applicability;

[0057] 2. According to the component characteristics of the raw gas itself, the present invention proposes a process flow for removing heavy hydrocarbons from oil-washed dry gas. Compared with the existing technology, this technology can flexibly adapt to the fluctuation of the raw gas component content by adjusting the reflux rate of LNG. At the same time, the investment in the process flow for removing heavy hydrocarbons is relatively low.

[0058] The above are only optional embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may be modified and varied in various ways. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0059] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0060] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of this solution. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being only exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so that once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0061] In the description of this scheme, it needs to be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing this scheme and simplifying the description. Unless otherwise stated, these directional words do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they cannot be understood as limiting the scope of protection of this scheme; the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0062] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0063] In addition, it should be noted that the use of words such as "first" and "second" to limit components is only to facilitate the distinction between corresponding components. Unless otherwise stated, the above words have no special meaning and therefore cannot be understood as limiting the scope of protection of this scheme.

Claims

1. A Fischer-Tropsch synthesis tail gas purification system, characterized in that: The invention comprises a decarbonization unit (10), a drying tower (20), a demercuration tower (30), a gas-liquid separator (40), a heavy hydrocarbon washing tower (50), a methane rectification tower (60), and a PSA unit (70). The decarbonization unit (10) is used to remove carbon dioxide from Fischer-Tropsch synthesis tail gas. The drying tower (20) is connected to the decarbonization unit (10) through a pipeline. The drying tower (20) is used to dry and dehydrate the decarbonized Fischer-Tropsch synthesis tail gas. The demercuration tower (30) is connected to the top of the drying tower (20) through a pipeline. The demercuration tower (30) is used to remove mercury from the dried Fischer-Tropsch synthesis tail gas. The outlet of the tower (30) is connected to the gas-liquid separator (40), and the gas-liquid separator (40) is used to perform gas-liquid separation on the Fischer-Tropsch synthesis tail gas. The gas-liquid separator (40) is connected to the heavy hydrocarbon washing tower (50), and the heavy hydrocarbon washing tower (50) is used to wash the heavy hydrocarbons on the Fischer-Tropsch synthesis tail gas. The heavy hydrocarbon washing tower (50) is connected to the methane distillation tower (60), and the methane distillation tower (60) is used to distill the Fischer-Tropsch synthesis tail gas. The PSA unit (70) is connected to the top of the methane distillation tower (60) through a pipeline, and the PSA unit (70) is used to purify the Fischer-Tropsch synthesis tail gas after distillation.

2. The Fischer-Tropsch synthesis tail gas purification system according to claim 1, characterized in that: The Fischer-Tropsch synthesis tail gas purification system further comprises a first precooler (81) and a second precooler (82), wherein: The first precooler (81) is connected to the bottom of the mercury removal tower (30) through a pipeline, and the first precooler (81) is used to perform a first cooling and temperature reduction treatment on the Fischer-Tropsch synthesis tail gas after the mercury removal. The gas-liquid separator (40) is connected to the first precooler (81) through a pipeline, and the gas-liquid separator (40) is used to perform a gas-liquid separation treatment on the Fischer-Tropsch synthesis tail gas after the first cooling and temperature reduction treatment. The second precooler (82) and the top of the gas-liquid separator (40) are connected by a pipeline, and the second precooler (82) is used to perform a second cooling and temperature reduction treatment on the Fischer-Tropsch synthesis tail gas after the gas-liquid separation treatment. The heavy hydrocarbon washing tower (50) is connected to the second precooler (82) by a pipeline, and the heavy hydrocarbon washing tower (50) is used to wash the heavy hydrocarbons on the Fischer-Tropsch synthesis tail gas after the second cooling and temperature reduction treatment.

3. The Fischer-Tropsch synthesis tail gas purification system according to claim 2, characterized in that: The Fischer-Tropsch synthesis tail gas purification system also includes a third precooler (83), which is connected to the top of the heavy hydrocarbon washing tower (50) through a pipeline, and the third precooler (83) is used to perform a third cooling and temperature reduction treatment on the Fischer-Tropsch synthesis tail gas after the heavy hydrocarbons are removed. The methane distillation tower (60) is connected to the third precooler (83) through a pipeline, and the methane distillation tower (60) is used to distill the Fischer-Tropsch synthesis tail gas after the third cooling and temperature reduction treatment.

4. The Fischer-Tropsch synthesis tail gas purification system according to claim 1, characterized in that: In the decarbonization unit (10), carbon dioxide is removed from the raw gas from the upstream system to reduce the carbon dioxide content in the raw gas to below 20 ppm.

5. The Fischer-Tropsch synthesis tail gas purification system according to claim 1, characterized in that: The decarbonization unit (10) uses an alcohol amine method or temperature swing adsorption to perform decarbonization.

6. The Fischer-Tropsch synthesis tail gas purification system according to claim 1, characterized in that: The decarbonized raw gas is sent to the drying tower (20), and is adsorbed by the molecular sieve in the drying tower (20) to remove moisture from the tail gas, thereby obtaining dry and qualified purified gas, wherein the dew point of water is less than -65°C.

7. The Fischer-Tropsch synthesis tail gas purification system according to claim 1, characterized in that: In the demercuration tower (30), a chemical adsorption method is used to remove mercury. When the raw gas continuously passes through the demercuration tower (30), a chemical reaction occurs with the demercuration adsorbent filled in the demercuration tower (30), thereby removing mercury from the raw gas, so that the mercury content is controlled to 0.01 μg / m 3 the following.

8. The Fischer-Tropsch synthesis tail gas purification system according to claim 2, characterized in that: The dried and qualified purified gas is sent to the first precooler (81) for cooling. After being cooled to 10-15°C, it enters the gas-liquid separator (40). An aqueous solution is obtained at the bottom of the gas-liquid separator (40). The gas phase component at the top of the gas-liquid separator (40) enters the second precooler (82) for further cooling. After being cooled to -40--50°C, it enters the heavy hydrocarbon washing tower (50) to remove heavy hydrocarbons. The precooling medium in the first precooler (81) is propylene, and the precooling medium in the second precooler (82) is ethane or ethylene.

9. The Fischer-Tropsch synthesis tail gas purification system according to claim 2, characterized in that: The cooled gaseous components enter the heavy hydrocarbon washing tower (50) from the lower part of the heavy hydrocarbon washing tower (50), and part of the LNG on the product line is used as the top reflux, so that the Fischer-Tropsch synthesis tail gas containing heavy hydrocarbons and the LNG are countercurrently transferred in the heavy hydrocarbon washing tower (50) to reduce the heavy hydrocarbon content to below 70 ppm. The qualified purified gas after removing the heavy hydrocarbons is transported from the top of the heavy hydrocarbon washing tower (50) to the methane distillation tower (60), and the heavy hydrocarbons are obtained at the bottom of the heavy hydrocarbon washing tower (50) and sent to the low-temperature oil washing unit to recover the low-carbon hydrocarbons.

10. The Fischer-Tropsch synthesis tail gas purification system according to claim 1, characterized in that: The gaseous material at the top of the heavy hydrocarbon washing tower (50) is cooled and then sent to the methane distillation tower (60). The top pressure of the methane distillation tower (60) is controlled at 0.5-0.8 MPa, the top temperature is -190--180°C, and the bottom temperature is -180--170°C. The gaseous material at the top of the tower is sent to the PSA unit (70) to purify hydrogen. The liquid material at the bottom of the tower is supercooled after heat exchange and part of it is used as LNG product, and part of it is used as washing liquid for the heavy hydrocarbon washing tower (50).

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