A process for extracting crude helium gas by cryogenic distillation

Abstract

The present invention provides a process for extracting crude helium gas by cryogenic distillation, which relates to the field of purifying helium. The process is that the purified NG enters the denitrification tower after absorbing heat through the second heat exchanger, the LNG at the bottom of the denitrification tower is transported through the second heat exchanger to release heat and enter the storage tank, the gas evaporated in the storage tank enters the second heat exchanger after passing through the first compressor to release heat and then enters the denitrification tower; the gas evaporated in the denitrification tower is compressed and enters the helium stripping tower after passing through the first heat exchanger to release heat, the gas evaporated in the helium stripping tower is compressed and enters the PSA dehydrogenation treatment after passing through the first heat exchanger to release heat, and the organic matter separated by the PSA returns to the helium stripping tower through the first heat exchanger; the helium separated by the PSA enters the catalytic dehydrogenation tank for dehydrogenation treatment, and then is sent to the dehydration tower for drying to obtain high-purity helium; the liquid substance at the bottom of the helium stripping tower enters the distillation tower to separate nitrogen for the first heat exchanger to absorb heat or to be pressurized into liquid nitrogen. The present invention reduces the energy consumption of the entire process by optimizing and integrating heat exchange.

Description

Technical Field

[0001] The invention relates to the technical field of helium purification, in particular to a process for extracting crude helium gas by cryogenic distillation. Background Art

[0002] The main components of natural gas are alkanes, of which methane accounts for the vast majority, with small amounts of ethane, propane and butane. In addition, there are generally hydrogen sulfide, carbon dioxide, nitrogen and water vapor, a small amount of carbon monoxide and trace amounts of rare gases such as helium and argon. The current way to obtain helium is basically to separate and purify it from natural gas. Nitrogen and other substances are also separated from helium during the separation process of natural gas. The boiling point of helium is -268.93℃, the boiling point of nitrogen is -196℃, and the boiling point of natural gas is around -162℃. Helium is extracted by distillation.

[0003] The existing helium separation and purification process is basically modular. First, the liquid natural gas is gasified, and then the gaseous natural gas is sent to the BOG crude helium extraction cold box to separate the crude helium. The crude helium is then dehydrogenated and dehydrated before being pressurized and stored. In this process, the material is pressurized or depressurized several times, that is, liquefied or gasified, that is, the temperature of the material changes, and the material is dissipated or heated as needed. Due to the modular setting, the heat exchange in the process is lost, or there is no relevant heat exchange structure set between them, which makes the energy consumption of helium separation and purification high. Summary of the invention

[0004] 1. Technical issues to be solved

[0005] In view of the deficiencies of the prior art, the present invention provides a process for extracting crude helium gas by cryogenic distillation, which solves the problem of high energy consumption in the prior helium extraction process.

[0006] (II) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] A process for extracting crude helium gas by cryogenic distillation includes a storage tank, a first compressor, a denitrification tower, a helium extraction tower, a distillation tower, a first heat exchanger, a PSA, a dehydration tower, a second compressor, a catalytic dehydrogenation tank and a second heat exchanger. The process is specifically as follows:

[0009] The purified NG enters the denitrification tower after absorbing heat through the second heat exchanger, and the LNG at the bottom of the denitrification tower is transported through the second heat exchanger to release heat and enter the storage tank. The evaporated gas in the storage tank enters the second heat exchanger through the first compressor to release heat and then enters the denitrification tower;

[0010] The gas evaporated in the above-mentioned denitrification tower is compressed and released through the first heat exchanger before entering the helium extraction tower. The gas evaporated in the helium extraction tower is compressed and released through the first heat exchanger before entering the PSA dehydrogenation treatment, that is, by controlling the pressure and using a suitable adsorbent, the hydrogen-containing substance is adsorbed to obtain relatively pure helium. The organic matter separated by the PSA passes through the first heat exchanger and returns to the helium extraction tower, that is, it is cooled and liquefied and returns to the helium extraction tower.

[0011] The helium separated by the PSA is sent to a catalytic dehydrogenation tank for dehydrogenation treatment. At the same time, oxygen is added to the catalytic dehydrogenation tank. The hydrogen-containing impurities and oxygen are combined to form water, which is then sent to a dehydration tower for drying to obtain high-purity helium.

[0012] The liquid substance at the bottom of the helium extraction tower enters the distillation tower to separate nitrogen for heat absorption in the first heat exchanger or is pressurized into liquid nitrogen. The nitrogen expands and absorbs heat after entering the first heat exchanger.

[0013] Preferably, the medium compressed by the second compressor passes through the second heat exchanger twice to achieve heat release and heat absorption. At least five groups of heat exchange structures are provided in the second heat exchanger, and the second compressor occupies two of them, one of which is used for evaporation heat absorption, the other is used for condensation heat release, and the other ones are used for heat absorption and heat release. Further, to avoid heat exchange between the two heat exchange structures connected to the second compressor, the two heat exchange structures can be placed at both ends of the second heat exchanger, and the heat exchange structure used for heat absorption can exchange heat with the heat release structure connected to the second compressor, and the heat exchange structure used for heat release can exchange heat with the heat absorption structure connected to the second compressor.

[0014] Preferably, the storage tank and the distillation tower separate out LNG, that is, LNG that can be used directly.

[0015] Preferably, the catalytic dehydrogenation tank and the dehydration tower are provided with drainage pipes to drain the generated water.

[0016] Preferably, the storage tank can directly exchange heat with the environment, that is, the storage tank is heated by the environment so that the easily vaporized helium and nitrogen in the storage tank boil, thereby facilitating separation from LNG. The environmental heating method mentioned here refers to the waste heat generated during the process operation or the heat in the environment heating the storage tank by heat transfer, that is, there is no need to add a heating device, which reduces energy consumption. The size of the heat leakage window set in the storage tank affects the vaporization rate of helium and nitrogen, so it needs to be reasonably set according to the processing volume.

[0017] Preferably, the above-mentioned denitrogenation tower, helium extraction tower and distillation tower all include a tank body, and a third compressor is provided at the upper end of the tank body, and the input end of the third compressor is connected to the tank body. Regardless of the material sent out from the upper end of the tank body or the material sent out from the lower end of the tank body, if it is in a gaseous state, it can be pressurized and liquefied by the third compressor.

[0018] Preferably, both upper and lower ends of the tank body are provided with direct-connected pipe openings, and if the material sent out of the tank body does not need to be pressurized, it can be sent out through the direct-connected pipe openings.

[0019] Preferably, a reheater is provided in the connecting pipeline of the process to prevent the material from solidifying at low temperature. During the processing, if a large amount of material in the pipeline evaporates, the temperature of the pipeline will decrease, which may cause the material in the local pipeline to solidify and cause the pipeline to be blocked. Therefore, a reheater is used to heat the pipeline.

[0020] (III) Beneficial effects

[0021] The present invention provides a process for extracting crude helium gas by cryogenic distillation, which has the following beneficial effects:

[0022] 1. The process of the present invention is provided with a first heat exchanger and a second heat exchanger, and multiple heat exchange structures are arranged inside, which can handle the heat exchange requirements of multiple streams of materials at the same time. At the same time, the heat exchange between the materials can reduce the energy consumption of the entire process.

[0023] 2. The process of the present invention is provided with a storage tank and a heat leakage window. By heating the environment stably and slowly, low-boiling-point nitrogen and helium can be effectively separated from natural gas. This operation does not require energy consumption and further reuses the heat dissipated into the environment during the process.

[0024] 3. In the process of the present invention, a distillation tower for nitrogen / liquid nitrogen separation is provided, which can further produce effective by-products. At the same time, nitrogen / liquid nitrogen can be used for cooling the first heat exchanger, which further reduces the energy consumption of the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0026] Figure 2 It is a schematic diagram of a tank body of the present invention.

[0027] Among them, 1. storage tank; 2. first compressor; 3. denitrification tower; 4. helium extraction tower; 5. distillation tower; 6. first heat exchanger; 7. PSA; 8. dehydration tower; 9. second compressor; 10. catalytic dehydrogenation tank; 11. second heat exchanger; 12. tank body; 13. third compressor. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0029] Embodiment 1:

[0030] like Figure 1-2 As shown, the embodiment of the present invention provides a process for extracting crude helium gas by cryogenic distillation, comprising a storage tank 1, a first compressor 2, a denitrification tower 3, a helium extraction tower 4, a distillation tower 5, a first heat exchanger 6, a PSA 7, a dehydration tower 8, a second compressor 9, a catalytic dehydrogenation tank 10 and a second heat exchanger 11. The process is specifically as follows:

[0031] The purified NG enters the denitrification tower 3 after absorbing heat through the second heat exchanger 11, that is, the purified NG avoids a sudden drop in pressure when being sent to the denitrification tower 3, causing a drop in temperature and causing the material in the pipeline to solidify. Therefore, it is preheated so that the material can be put into the denitrification tower 3 to avoid pipeline blockage. The LNG at the bottom of the denitrification tower 3 is transported through the second heat exchanger 11 to release heat and enter the storage tank 1. The material is affected by the temperature in the denitrification tower 3 and pipeline transportation. As mentioned above, pipeline blockage is avoided; the gas evaporated in the storage tank 1 passes through the first compressor 2 and enters the second heat exchanger 11 to release heat and then enters the denitrification tower 3. The gas evaporated in the storage tank 1 contains helium, nitrogen, etc. Pressurizing it here is a way to facilitate transportation in the pipeline. At the same time, its temperature is high after being pressurized, so the second heat exchanger 11 is used to achieve its cooling effect;

[0032] The gas evaporated in the denitrification tower 3 is compressed and released through the first heat exchanger 6 before entering the helium stripping tower 4. The gas evaporated in the denitrification tower 3 contains a large amount of helium and nitrogen. Here, the temperature of the denitrification tower 3 is controlled below -162°C, but not lower than -196°C. The gas evaporated in the helium stripping tower 4 is compressed and released through the first heat exchanger 6 before entering the PSA 7 for dehydrogenation treatment. The gas evaporated in the helium stripping tower 4 is mainly helium. Here, the temperature of the helium stripping tower 4 is controlled below -196°C and above the boiling point of helium. The organic matter separated by the PSA 7 passes through the first heat exchanger 6 and returns to the helium stripping tower 4. The PSA 7 is a new gas separation technology called pressure swing adsorption. By using an adsorbent, the hydrogen-containing substance is adsorbed to achieve further purification of the helium, and the separated hydrogen-containing substance returns to the helium stripping tower 4 again.

[0033] The helium separated by PSA 7 enters the catalytic dehydrogenation tank 10 for dehydrogenation treatment, that is, the hydrogen-containing substances are oxidized into water by oxidation-reduction. If there is carbon dioxide, it can be removed by removing carbon dioxide, which is conducive to washing with alkaline water, etc., and then sent to the dehydration tower 8 for drying to obtain high-purity helium;

[0034] The liquid material at the bottom of the helium extraction tower 4 enters the distillation tower 5 to separate the nitrogen for the first heat exchanger 6 to absorb heat or is pressurized into liquid nitrogen, that is, the compressed nitrogen or liquid nitrogen is introduced into the first heat exchanger 6 to evaporate it, providing refrigeration for the first heat exchanger 6, which can reduce the energy consumption during the process movement.

[0035] In the process that the medium compressed by the second compressor 9 passes through the second heat exchanger 11 twice to release and absorb heat, the temperature gradient in the second heat exchanger 11 is enlarged by the second compressor 9, which is more conducive to heating or cooling the material in the line pipe.

[0036] The second heat exchanger 11 adopts a multi-stage type, that is, it adopts multiple heat exchange structures, each heat exchange structure has an inlet and an outlet, and the second compressor 9 is connected to two heat exchange structures, which can be called the first heat exchange structure and the second heat exchange structure. If the first heat exchange structure is used for heat release and the second heat exchange structure is used for heat absorption, and the other heat exchange structures can be divided into heat absorption and heat release, the heat absorbing heat exchange structure exchanges heat with the first heat exchange structure, and the heat releasing heat exchange structure exchanges heat with the second heat exchange structure.

[0037] Furthermore, to avoid the second compressor 9 from doing useless work, the first heat exchange structure and the second heat exchange structure need to be separated so that no heat exchange occurs between them. The purpose of setting the second compressor 9 here is to increase the gradient of heat exchange. At the same time, the multi-stage second heat exchanger 11 can reduce heat loss, and the equipment integrity during operation is higher.

[0038] The storage tank 1 and the distillation tower 5 separate LNG. In this process, the storage tank 1 is the main LNG discharge container, and the distillation tower 5 separates a small amount of LNG, and the LNG is sent out from the bottom of the container.

[0039] The catalytic dehydrogenation tank 10 and the dehydration tower 8 are provided with drainage pipes to discharge the water generated by oxidation.

[0040] The storage tank 1 can directly exchange heat with the environment, that is, the storage tank 1 is provided with a heat leakage window, and the storage tank 1 is heated by the heat in the environment. The storage tank 1 is heated by the heat in the environment without consuming additional energy. By controlling the size of the heat leakage window, the storage tank 1 can be gently heated, so that the helium, nitrogen and other gases therein are gasified and separated, which is achieved by distillation.

[0041] The denitrification tower 3, the helium extraction tower 4 and the distillation tower 5 all include a tank body 12, and a third compressor 13 is provided at the upper end of the tank body 12, and the input end of the third compressor 13 is connected to the tank body 12. If the material sent out from the tank body 12 needs to be pressurized, it can be compressed by the third compressor 13. For example, when the LNG sent out from the bottom of the denitrification tower 3 first passes through the second heat exchanger 11 and then is sent to the storage tank 1, in order to ensure that the LNG is transported at a suitable pressure and temperature, a pressurization operation can be performed.

[0042] Both upper and lower ends of the tank body 12 are provided with direct-connected pipe ports. If pressurization treatment is not required, the material can be directly discharged from the direct-connected pipe ports. For example, the material evaporated in the denitrification tower 3 can be directly discharged from the direct-connected pipe ports.

[0043] The connecting pipeline of this process is equipped with a reheater to prevent the material from solidifying at low temperature. That is, during the pipeline transportation process, there is local material vaporization, which causes a sudden drop in the temperature inside the pipeline, causing part of the material to solidify, thereby causing the pipeline to be blocked. In addition, related equipment such as temperature and pressure measurement, and filtration are also installed on the pipeline.

[0044] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for extracting crude helium gas by cryogenic distillation, characterized in that: The process comprises a storage tank (1), a first compressor (2), a denitrification tower (3), a helium extraction tower (4), a distillation tower (5), a first heat exchanger (6), a PSA (7), a dehydration tower (8), a second compressor (9), a catalytic dehydrogenation tank (10) and a second heat exchanger (11). The process is specifically as follows: The purified NG passes through the second heat exchanger (11) to absorb heat and then enters the denitrification tower (3); the LNG at the bottom of the denitrification tower (3) is transported through the second heat exchanger (11) to release heat and then enters the storage tank (1); the evaporated gas in the storage tank (1) passes through the first compressor (2) to enter the second heat exchanger (11) to release heat and then enters the denitrification tower (3); The medium compressed by the second compressor (9) passes through the second heat exchanger (11) twice to release and absorb heat; the storage tank (1) and the distillation tower (5) separate LNG; the storage tank (1) can directly exchange heat with the environment; The gas evaporated in the denitrification tower (3) is compressed and released through the first heat exchanger (6) before entering the helium extraction tower (4); the gas evaporated in the helium extraction tower (4) is compressed and released through the first heat exchanger (6) before entering the PSA (7) for dehydrogenation treatment; and the organic matter separated by the PSA (7) passes through the first heat exchanger (6) and returns to the helium extraction tower (4); The denitrification tower (3), the helium extraction tower (4) and the distillation tower (5) all include a tank body (12), the upper end of each of the tank bodies (12) is provided with a third compressor (13), and the input end of the third compressor (13) is connected to the tank body (12), and the upper and lower ends of the tank body (12) are provided with direct-connection pipe ports; The helium separated by the PSA (7) enters a catalytic dehydrogenation tank (10) for dehydrogenation treatment, and then is sent to a dehydration tower (8) for drying to obtain high-purity helium; the catalytic dehydrogenation tank (10) and the dehydration tower (8) are provided with drainage pipes; the liquid material at the bottom of the helium extraction tower (4) enters a distillation tower (5) to separate nitrogen for heat absorption in a first heat exchanger (6) or is pressurized into liquid nitrogen.

2. The process for extracting crude helium gas by cryogenic distillation according to claim 1, characterized in that: A reheater is provided in the connecting pipeline of the process to prevent the material from solidifying at low temperature.

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