Isotope separation system and isotope separation method

Abstract

The invention provides an isotope separation system and an isotope separation method.The isotope separation system comprises a cryogenic temperature and pressure swing adsorption device, the cryogenic temperature and pressure swing adsorption device comprises at least two adsorber units, each adsorber unit comprises a liquid nitrogen container and an adsorber, and in each adsorber unit, the liquid nitrogen container is communicated with the adsorber; the adsorber is soaked in the liquid nitrogen in the liquid nitrogen container; the adsorber comprises a pipe wall, the material of the pipe wall comprises a first material, the constant volume heat capacity Qvh of the unit length of the pipe wall is larger than a first preset value, and the wall thickness D of the pipe wall is 0.5-8 cm; a modified Nusselt criterion # imgabs0 # related to the material and thickness of the tube wall is controlled to be within a predetermined range. The problems of low isotope separation efficiency, poor regeneration effect, high liquid nitrogen consumption and high energy consumption in the prior art are solved, and the cyclic utilization rate of the adsorbent and the heavy component isotope recovery rate are remarkably increased.

Description

Technical Field

[0001] The present invention relates to the field of gas separation, and relates to an isotope separation system and an isotope separation method, and particularly relates to an isotope separation system with a cryogenic temperature and pressure swing device and a method for isotope separation using the cryogenic temperature and pressure swing device. Background Art

[0002] Gas separation is an important link in many industrial fields. As an efficient and energy-saving gas separation technology, the temperature and pressure swing adsorption technology has been widely used in this field. This technology utilizes the difference in the adsorption capacity of adsorbents for different gases under different temperature and pressure conditions to achieve the separation of gas components by adjusting the temperature and pressure.

[0003] However, for some special gas components, it is difficult to achieve efficient separation with the existing temperature and pressure swing adsorption technology. Taking isotope separation as an example, such as the separation of deuterium gas in hydrogen gas, due to the extremely similar physical and chemical properties of isotopes, the difference in the adsorption capacity of traditional adsorbents for them is small, resulting in low separation efficiency. Therefore, it is urgent to develop new adsorbents and process routes to improve the efficiency of the temperature and pressure swing adsorption technology in the field of isotope gas separation.

[0004] To solve the above problems, a large amount of research work has adopted the cryogenic adsorption process, but the low vacuum regeneration efficiency is a problem that needs to be solved urgently, and using thermal regeneration is contradictory to the cryogenic adsorption system, resulting in a large amount of cold loss. Therefore, it is necessary to develop a new separation system and an isotope separation method based on this separation system. Summary of the Invention

[0005] In the prior art, there are problems such as small difference in the adsorption capacity of the adsorbent for isotope light components and heavy components, low regeneration effect of the adsorbent, and the need to optimize the structure of the adsorber and the composition of the adsorbent bed.

[0006] To solve the above problems, in the first aspect of the present invention, an isotope separation system is provided. The isotope separation system includes a cryogenic temperature and pressure swing adsorption device. The cryogenic temperature and pressure swing adsorption device includes at least two adsorber units. Each adsorber unit includes a liquid nitrogen container and an adsorber. In each adsorber unit, the adsorber is immersed in the liquid nitrogen in the liquid nitrogen container; the adsorber includes a tube wall, and the material of the tube wall includes a first material. The fixed-volume heat capacity Q per unit length of the tube wall vh is greater than a first predetermined value, and the wall thickness D of the tube wall is 0.5 - 8 cm; controlling the modified Nusselt number related to the material and the thickness of the tube wall within a predetermined range, the expression of the modified Nusselt number is:

[0007] Among them, h is the convective heat transfer rate of the gas in the adsorber, k is the thermal conductivity of the pipe wall, and D is the wall thickness of the pipe wall; The constant volume heat capacity Q vh The expression of is: Q vh = mC v T Among them, m is the mass of the pipe wall of the effective length of the adsorber, C v is the specific heat of the material of the pipe wall, and T is the absolute temperature of the pipe wall.

[0008] In one embodiment, the modified Nusselt number The predetermined range is 0.07 ≤ ≤ 1.

[0009] In one embodiment, the first material is any one of stainless steel, nickel alloy or metal composite material, and the first predetermined value is 2000 kJ / m.

[0010] In the second aspect of the present invention, an isotope separation method is provided. The above cryogenic temperature and pressure swing adsorption device is used for isotope separation, and has the following steps: Step 1, adsorption The raw material gas is pre-cooled and then introduced into the lower channel of the adsorber filled with adsorbent from the inside. At a predetermined working temperature, the adsorber adsorbs the heavy components in the raw material gas, and the light components in the raw material gas are output from the upper channel of the adsorber; Step 2, co-current release When the heavy components in the light components at the outlet of the adsorber reach the breakthrough point concentration, switch to the regeneration process: close the lower channel, and the gas in the adsorber is discharged from the upper part of the adsorber to discharge the light components in the voids of the adsorbent; Step 3, vacuum desorption and thermal purge Open the lower channel and close the upper channel. The gas in the adsorber is discharged from the lower channel. When the air pressure in the adsorber approaches atmospheric pressure, vacuum desorption is carried out; open the upper channel, and the high-temperature regeneration gas enters the adsorber from the upper channel and thermally purges the adsorbent to desorb, and the desorbed gas containing the heavy components is discharged from the lower channel; Step 4, cold purge After the thermal purge is completed, cold air enters from the upper channel to cold purge and cool down the adsorbent, and the desorbed gas containing the heavy components is discharged from the lower channel; Step 5, recompression After the cold purge is completed, the adsorbent is regenerated and the adsorber is repressurized. Step 6, Circulation Prepare for the next cycle.

[0011] In one embodiment, in Step 2, the adsorbent is a single-layer or composite-layer adsorbent, and the single-layer or composite-layer adsorbent is at least one of 3A type, 5A type, 13X type molecular sieves, activated carbon, and MOFs (metal-organic frameworks).

[0012] In one embodiment, in Step 3, the vacuum pressure is 0.1 - 500 mbara.

[0013] In one embodiment, in Step 3, the high-temperature regeneration gas is one or more of nitrogen, helium, and neon. The temperature of the high-temperature regeneration gas is 50 - 150 °C, and the pressure inside the adsorber is 1 bara to 3 bara. When performing hot gas purge desorption, countercurrent vacuum can be carried out simultaneously.

[0014] In one embodiment, in Step 4, the cold gas is any one of low-temperature nitrogen, helium, or neon. The cold gas temperature is -50 °C to -180 °C, and the time of the cold purge is 1 - 4 times the time of the hot purge.

[0015] In one embodiment, in Step 5, the raw material gas is used for forward-flow repressurization, or the light components discharged from the upper channel in Step 1 are used for countercurrent repressurization.

[0016] In one embodiment, in Step 3 and Step 4, the desorbed gas containing heavy components obtained is concentrated or repeatedly concentrated and purified again through membrane separation, adsorption, or distillation to obtain concentrated and purified isotope heavy components.

[0017] In one embodiment, at the breakthrough point concentration at the outlet of the adsorber, the content of heavy components in the light components is 0.1 - 0.001 wt%; preferably 0.01 - 0.05 wt%.

[0018] In one embodiment, in Step 2, the forward release time is 0.2 - 2 s. Forward release is different from the equalization process. It only discharges the light components between the adsorbents in the adsorber to increase the content of heavy components in the regeneration gas obtained during the subsequent regeneration process.

[0019] In one embodiment, in Step 3, the countercurrent vacuum pressure is 0.1 - 500 mbara; preferably 1 - 100 mbara.

[0020] In one embodiment, the two adsorbers are in fluid communication. The regenerated adsorber receives the pressure relief pressure of the other adsorber and then is repressurized.

[0021] In one embodiment, the adsorption system includes at least two adsorber units, a multi-stream heat exchanger, a liquid nitrogen container, a vacuum system, and a storage unit. The adsorber is immersed in the liquid nitrogen container, and the wall thickness of the adsorber is 0.5 - 8 cm; preferably 2 - 5 cm.

[0022] In one embodiment, the storage unit includes a light component gas storage tank, a co-current vacuum discharge light component storage tank. In steps 3 and 4, the obtained regenerated concentrated gas components are stored in a heavy component storage tank.

[0023] In one embodiment, the purge gas is nitrogen, helium, neon, or a mixture thereof.

[0024] In one embodiment, the obtained regenerated concentrated gas components can be concentrated again to obtain heavy components with the required purity. The obtained regenerated concentrated gas components can be concentrated again or multiple times, and the concentration is carried out by a membrane separation, adsorption, or distillation process.

[0025] In one embodiment, at least two of the adsorbers operate alternately, with the same adsorption and regeneration time, to achieve continuous separation.

[0026] A novel temperature-swing and pressure-swing adsorber and its method for separating isotope gases provided by the present invention have the following beneficial effects: 1. By using a thick-walled cryogenic adsorber immersed in liquid nitrogen, the adsorption capacity of the adsorbent for heavy components is enhanced under cryogenic temperature conditions, thereby improving the separation efficiency of heavy components.

[0027] 2. Through steps such as vacuum purging, high-temperature hot gas regeneration, and low-temperature cold blowing, the recovery of the target product and the efficient regeneration of the adsorbent are achieved, improving the recycling efficiency of the adsorbent and reducing the loss rate of heavy components.

[0028] 3. The structural design of the adsorber and the composition of the adsorbent bed are optimized to further improve the adsorption effect and adsorption capacity; 4. A thick-walled adsorber is used to buffer the heat pulse generated during hot gas purging, improving the cryogenic adsorption regeneration efficiency and reducing the liquid nitrogen consumption; Energy consumption reduction: The liquid nitrogen immersion design reduces the external cooling energy consumption, and the thick-walled design buffers the heat pulse generated during hot gas purging, reducing the comprehensive energy consumption by more than 70% compared with the traditional method.

[0029] 5. It provides a new technical route for isotope gas separation and expands the application range of the temperature-swing and pressure-swing adsorption technology. Description of the Drawings

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, obtaining other drawings based on these drawings still falls within the scope of the present invention.

[0031] Figure 1 It is a schematic diagram of a cryogenic temperature-variable and pressure-swing adsorption device; Figure 2 It is a process flow diagram of the adsorption-regeneration cycle steps for separating isotopes; Figure 3 It is a schematic diagram of the cross-section and parameters of an adsorber. Detailed implementation manners

[0032] The following will elaborate on the preferred embodiments of the present invention in conjunction with the drawings to more clearly understand the purpose, features, and advantages of the present invention. It should be understood that the embodiments shown in the drawings are not limitations on the scope of the present invention, but only to illustrate the essential spirit of the technical solution of the present invention.

[0033] In the following description, for the purpose of illustrating various disclosed embodiments, certain specific details are set forth to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the relevant art will recognize that the embodiments can be practiced without one or more of these specific details. In other instances, well-known devices, structures, and technologies associated with the present application may not be shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0034] References to "one embodiment" or "an embodiment" throughout the specification mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of "in one embodiment" or "in an embodiment" throughout the specification are not necessarily all referring to the same embodiment. Additionally, the particular features, structures, or characteristics may be combined in any manner in one or more embodiments.

[0035] In the following description, in order to clearly show the structure and working mode of the present invention, many directional terms will be used for description. However, words such as "front", "rear", "left", "right", "outside", "inside", "outward", "inward", "up", "down", etc. should be understood as convenient terms and should not be construed as limiting terms.

[0036] It should be noted that the features shown in the drawings of this application may belong to one embodiment or different embodiments, as long as there is no conflict between these features. To save space, this application can use the same drawing to illustrate different embodiments, that is, the same drawing of this application can be used to embody the features in different embodiments.

[0037] The purpose of this embodiment is to overcome the shortcomings existing in the prior art, and to provide a cryogenic temperature and pressure swing system for separating isotopes and a method for separating isotopes using this system. Specifically, a novel temperature and pressure swing adsorber and a method for separating deuterium from a hydrogen and deuterium mixture are provided.

[0038] This embodiment provides a system for separating isotopes, which has a cryogenic temperature and pressure swing adsorption device. The cryogenic temperature and pressure swing adsorption device includes a first adsorber unit, a second adsorber unit, a vacuum pumping unit 40, a purge gas unit, a light component storage tank 60, a desorbed gas storage tank 50 and a control unit.

[0039] As Figure 1 shown, the first adsorber unit includes a first liquid nitrogen tank 11, a first adsorber 12, a first heat exchanger 13, a first liquid nitrogen metering component 14, a first liquid nitrogen inlet pipe 111, a first nitrogen discharge pipe 112, a first inlet pipe 101, and a first outlet pipe 102.

[0040] The first adsorber 12 is arranged in the first liquid nitrogen tank 11; liquid nitrogen LN2 enters the first liquid nitrogen tank 11 through the first liquid nitrogen inlet pipe 111. One end of the first nitrogen discharge pipe 112 communicates with the upper part of the first liquid nitrogen tank 11, and the other end communicates with the nitrogen discharge pipe 113; one end of the first inlet pipe 101 communicates with the raw material inlet, and the other end communicates with the lower part of the first adsorber 12. One end of the first outlet pipe 102 communicates with the upper part of the first adsorber 12, and the other end communicates with the light component pipe 601. Among them, a valve L1 is provided on the first liquid nitrogen inlet pipe 111, a valve 1A is provided on the first inlet pipe 101, and valves 1B and 1C are provided on the first outlet pipe 102; the first inlet pipe 101, the first outlet pipe 102, and the first nitrogen discharge pipe 112 pass through the first heat exchanger 13; the first liquid nitrogen metering component 14 is arranged on the first liquid nitrogen tank 11 for measuring the liquid nitrogen amount in the first liquid nitrogen tank 11. The first inlet pipe 101 can be a lower channel, the first outlet pipe 102 can be an upper channel, and the upper channel and the lower channel can also be other air-permeable pipes.

[0041] The second adsorber unit includes a second liquid nitrogen tank 21, a second adsorber 22, a second heat exchanger 23, a second liquid nitrogen metering component 24, a second liquid nitrogen inlet pipe 211, a second nitrogen discharge pipe 212, a second inlet pipe 201, and a second outlet pipe 202.

[0042] The second adsorber 22 is arranged in the second liquid nitrogen tank 21; liquid nitrogen LN2 enters the second liquid nitrogen tank 21 through the second liquid nitrogen inlet pipe 211. One end of the second nitrogen discharge pipe 212 communicates with the upper part of the second liquid nitrogen tank 21, and the other end communicates with the nitrogen discharge pipe 113. One end of the second inlet pipe 201 communicates with the raw material inlet, and the other end communicates with the lower part of the second adsorber 22. One end of the second outlet pipe 202 communicates with the upper part of the second adsorber 22, and the other end communicates with the light component pipe 601. Among them, a valve L2 is provided on the second liquid nitrogen inlet pipe 211, a valve 2A is provided on the second inlet pipe 201, and valves 2B and 2C are provided on the second outlet pipe 202; the second inlet pipe 201, the second outlet pipe 202 and the second nitrogen discharge pipe 212 pass through the second heat exchanger 23; the second liquid nitrogen metering component 24 is arranged on the second liquid nitrogen tank 21 for measuring the liquid nitrogen amount in the second liquid nitrogen tank 21. The second inlet pipe 201 can be a lower channel, the second outlet pipe 202 can be an upper channel, and the upper channel and the lower channel can also be other ventilated pipes.

[0043] Both the first heat exchanger 13 and the second heat exchanger 23 are three-stream heat exchangers, which are used to pre-cool the raw material gas to the target temperature in stages and simultaneously recover the cold energy of the tail gas. In the embodiment, the raw material hydrogen H2 / D2 is pre-cooled to -150 °C to -175 °C through heat exchange and then introduced into the adsorber. Among them, the pressure of the co-current isotope mixture gas is about 10 bar (controlled by the back pressure valve 6A), and the flow rate is 10 Nm 3 / h, the inlet is 293 K, and the outlet temperature is 83 K.

[0044] The design criteria for the adsorber (the first adsorber 12 and the second adsorber 22, and the adsorber mentioned later can be understood as the first adsorber 12 and / or the second adsorber 22) are as follows: For a system using a cryogenic temperature swing and pressure swing adsorption device for isotope separation, a material with a thick wall and a relatively low thermal conductivity (for example: 12 - 24 W / m·K) is selected as the tube wall of the adsorber. The design of the thick-walled adsorber is based on the system-corrected Nusselt number in the range of 0.07 ≦ ≦ 1, that is, to ensure that the convective heat transfer amount (h) of the gas on the inner wall is lower than the heat conduction amount (k / D) of the adsorber tube wall. The specific heat capacity Q per unit volume of the tube wall per meter of the adsorber vh is greater than 2000 kJ, that is, each meter of the adsorber tube wall should have sufficient heat storage capacity.

[0045] (1) (2) Among them, m is the mass of the tube wall of the effective length of the adsorber (unit: kg), C vis the specific heat of the tube wall material (in J / (kg·K)), T is the absolute temperature of the tube wall (in K), h is the convective heat transfer rate of the gas (in W / (m 2 ·K)), k is the thermal conductivity of the adsorber tube wall (in W / (m·K)), and D is the wall thickness (in m).

[0046] As Figure 3 shown, the adsorber is a cylinder, and its cross-section (transverse section) is an annulus. Calculate the absolute temperature T of the tube wall.

[0047] Figure 3 Among them, T0 represents the temperature of liquid nitrogen in the liquid nitrogen storage tank, and q i (t) represents the convective heat transfer integral of the inner wall of the adsorption tank, and q o (t) represents the convective heat transfer integral of the outer wall of the adsorption tank, and T g (t) represents the temperature of the gas in the adsorber, and t is the time.

[0048] In particular, the tube wall material is one of stainless steel, nickel alloy or metal composite material.

[0049] Isotope separation is carried out by a cryogenic temperature and pressure swing adsorption device. The raw material is gas, and the adsorption is carried out at the temperature of liquid nitrogen or liquid helium; preferably, the predetermined working temperature of the adsorber is the liquid nitrogen temperature, which can be -180°C to -196°C, and the precooling temperature is -165°C to -185°C. The adsorber is immersed in liquid nitrogen, and the liquid nitrogen quantity is measured by a liquid level gauge and the liquid nitrogen level is controlled; the volatilized nitrogen is used as a purge gas after recovering the cold energy through a multi-stream heat exchanger and is stored in the purge gas source 30.

[0050] The thick-walled adsorber is different from the adiabatic adsorber. The adsorption heat of the adiabatic adsorber cannot be removed, while the thick-walled adsorber can remove the adsorption heat in time to increase the equilibrium adsorption capacity. During the adsorption process, the physical adsorption heat is usually several hundred to several thousand J / mol, and the maximum does not exceed 40 kJ / mol. It should be noted that the adsorption heat in the embodiment is transferred outward through the convective heat transfer between the inner and outer walls and the heat conduction of the tube wall, and finally reflected in the consumption of liquid nitrogen. That is, liquid nitrogen removes the heat of the system by gasification. If the liquid nitrogen consumption is large, the system generates a large amount of heat, and vice versa.

[0051] The adsorption system including the adsorber is provided with different temperature detection points, such as at the inlet of the adsorber, the outlet of the adsorber, and the lower and upper ends of the adsorbent filled in the adsorber, to assist the concentration detector in judging the adsorption and regeneration processes.

[0052] The adsorber is immersed in liquid nitrogen, and the immersion depth of the liquid nitrogen is adjusted by a liquid level gauge. The saturation temperature of the liquid nitrogen is determined by the saturated vapor pressure of the liquid nitrogen in the closed container. For example, at atmospheric pressure, the saturation temperature of the liquid nitrogen is about -196 °C. As the pressure increases, the temperature of the liquid nitrogen increases. For example, at 1.5 atmospheres, the saturation temperature of the liquid nitrogen is about -192 °C. The adsorber is filled with adsorbents, which can be a single adsorbent or a composite adsorbent bed composed of multiple adsorbents. The adsorbents include molecular sieves, activated carbon, and metal-organic framework compounds (MOFs).

[0053] Pipe 205 is connected to the raw material inlet, the first inlet pipe 101, and the second inlet pipe 201. Valves 5B and 5A are provided on pipe 205. Among them, valve 5A is located between the raw material inlet and the first inlet pipe 101, and valve 5B is located between the raw material inlet and the second inlet pipe 201. Pipe 206 is connected to the first outlet pipe 102 and the second outlet pipe 202. Valves 3B and 3A are provided on pipe 206.

[0054] Pipe 301 is connected to the purge gas source 30 and the first outlet pipe 102. Pipe 304 is connected to the second outlet pipe 202 and pipe 301. Pipe 302 is connected to the purge gas source 30 and pipe 206. Pipe 305 is connected to the first inlet pipe 101 and the second inlet pipe 201. Valves 4C, 4A, and heater 31 are provided on pipe 301. Valve 4B is provided on pipe 304. Valve 4D is provided on pipe 302. Among them, valve 4A is located between the first outlet pipe 102 and pipe 304, and valve 4C and heater 31 are located between pipe 304 and the purge gas source 30.

[0055] The vacuum pumping unit 40 includes a dry vacuum pump, and the working ultimate vacuum degree of the dry vacuum pump is ≤0.1 kPa. Pipe 401 is connected to the vacuum pumping unit 40 and pipe 305. The vacuum pumping unit 40 is connected to the desorbed gas storage tank 50. The desorbed gas is stored in the desorbed gas storage tank 50 by relying on the exhaust pressure of the vacuum system, or a booster pump is placed between the vacuum system and the desorbed gas storage tank 50.

[0056] Pipe 601 is connected to the light component storage tank 60, the first outlet pipe 102, and the second outlet pipe 202. A back pressure valve 6A is provided on pipe 601, and valve 6B is connected in parallel with the back pressure valve 6A.

[0057] The control unit realizes the switching between the adsorption and regeneration of the adsorber by controlling the opening and closing of different flow control valves.

[0058] In one embodiment, a cryogenic temperature and pressure swing system for separating isotopes includes at least two adsorber units. Each adsorber unit includes a liquid nitrogen container and an adsorber. When the adsorber in one adsorber unit adsorbs, the adsorber in the other adsorber unit regenerates. The adsorption time is equal to the regeneration time to achieve continuous production. In the same adsorber unit, the adsorber is immersed in the liquid nitrogen in the liquid nitrogen container, and the wall thickness of the adsorber is 2 - 5 cm.

[0059] In one embodiment, the adsorber is a thick-walled adsorber with a wall thickness of 3 - 4 cm, which is used to buffer the thermal pulse generated by hot gas purging to reduce refrigerant consumption.

[0060] The embodiment also provides a method for separating isotopes. The cryogenic temperature swing and pressure swing adsorption device is used for isotope separation, including an adsorption process and a regeneration process, including the steps as Figure 2 shown: Step 1: Pre-cool the feed gas and then introduce it into the adsorber filled with adsorbent inside. Adsorb the heavy components in the feed gas at cryogenic temperature and discharge the light components. Among them, Figure 2 the rectangle in the figure is a schematic diagram of the adsorber. Ⅰ represents the unsaturated adsorption area inside the adsorber, Ⅱ represents the saturated adsorption area inside the adsorber, and the adsorption front is the interface between the unsaturated adsorption area and the saturated adsorption area inside the adsorber. In the embodiment, the feed gas is hydrogen (a mixed gas of H2 and D2).

[0061] As Figure 1 shown, the hydrogen gas containing deuterium in the feedstock is pre-cooled by the valve 5A and valve 1A and then enters the adsorber A filled with adsorbent from the bottom along the pipeline 101 through the multi-stream heat exchanger. The entire adsorber 12 is immersed in liquid nitrogen, and the liquid nitrogen height is controlled by the first liquid nitrogen metering component 14. At the liquid nitrogen temperature, the adsorbent adsorbs the heavy component deuterium gas in the hydrogen gas, and the light component mainly hydrogen is output from the upper end and enters the light component storage tank 60 through the pipe 102 and the pipe 601. Among them, the content of the heavy component deuterium gas in the light component is less than 0.01 wt%, and the back pressure valve at the outlet controls the pressure of the adsorption system.

[0062] The remaining steps will not be elaborated.

[0063] Table 1 and Table 2 show the valve actions during the adsorption and regeneration processes. The values in the table are the valve actions during the adsorption and regeneration stages. Among them, the assigned value of 0 indicates that the valve is closed, and the assigned value of 1 indicates that the valve is open. The hot gas in the table is the high-temperature regeneration gas.

[0064] In the embodiment, tower A represents the first adsorber 12, and tower B represents the second adsorber 22.

[0065] Table 1 Adsorption Process of Tower A and Regeneration Process of Tower B

[0066] Table 2 Adsorption Process of Tower B and Regeneration Process of Tower A

[0067] In the embodiment, the precooling temperature is -165°C to -185°C. The adsorber is immersed in liquid nitrogen. The temperature inside the adsorber is related to the temperature of the feed gas and can be partially adjusted by the temperature of the feed gas. The control accuracy is ±5°C. The operating temperature of the adsorber is -180°C to -196°C. The adsorbent bed is a single or composite adsorbent bed, including 3A, 5A or 13X molecular sieves, activated carbon and metal-organic framework compound MOFs.

[0068] Step 1: The mixed gas enters from the bottom of the adsorber for adsorption. During the adsorption process, the heavy components are adsorbed, and the light components are discharged from the upper part of the adsorber. It should be noted that: there is a very small amount of heavy components in the discharged light components.

[0069] Step 2: As the adsorption progresses, the adsorption front gradually moves upward, and the concentration of heavy components in the light components discharged from the upper part of the adsorber gradually increases. When the concentration of heavy components at the outlet of the adsorber reaches the set value, such as 0.01%, that is, when the concentration of heavy components at the outlet reaches the breakthrough point, the gas inlet is stopped and the regeneration stage is entered.

[0070] When the heavy components reach the breakthrough point concentration, switch to the regeneration process: close the lower channel of the adsorber, and the gas in the adsorber is discharged from the upper part for 0.2 - 2 s. The co-current discharge is different from the equalization process. Only the light components in the voids of the adsorbent are discharged to increase the content of heavy components in the regeneration gas. At this time, the adsorption front moves upward.

[0071] Step 3: Open the lower channel of the adsorber, close the upper channel of the adsorber, and discharge the gas in the adsorber from the lower part to atmospheric pressure, and then perform vacuum desorption. The vacuum desorption pressure is 1 - 10 mbara; open the upper channel of the adsorber, and hot gas (high-temperature regeneration gas) enters from the upper part of the adsorber to perform thermal purge desorption on the adsorber, and the desorbed gas containing heavy components is discharged from the lower part of the adsorber. The hot gas (high-temperature regeneration gas) uses nitrogen, helium, neon or their mixed gas as the purge gas. The temperature of the purge gas is 50 - 150 °C, and the pressure is 1 bara to 3 bara. At this time, the adsorption front moves downward; The regeneration time of the high-temperature regeneration gas is generally determined by the temperature inside the adsorbent bed at the outlet of the adsorber. For example, when the inlet temperature of the high-temperature regeneration gas is 120 °C, while heating the cylinder wall of the adsorber by heat exchange with the adsorbent, the heat front gradually moves from top to bottom, resulting in the gradual increase of the temperature inside the adsorbent bed at the lower outlet of the adsorber. Generally, it is considered that when the temperature inside the adsorbent bed at the outlet of the adsorber reaches 30 °C, the thermal purge process ends. The thermal purge process obtains desorbed gas containing heavy components at the outlet.

[0072] There are two issues that need attention: First, a large amount of heat is introduced into the low-temperature adsorption system, and how to reduce the cold energy consumption determines the operating cost; Second, after the hot blow is completed, a large amount of heat accumulates in the adsorber, and the following cold blow process is required to remove the heat accumulated in the adsorber while continuing to obtain the recombinant decomposition desorbed gas.

[0073] Step 4: When the hot gas (high-temperature regeneration gas) purge is completed, start the low-temperature cold blow for rewarming. The cold gas enters from the upper part of the adsorber, and the adsorber is cold purged and cooled, and the desorbed gas containing the heavy components is discharged from the lower part of the adsorber; In one embodiment, the low-temperature cold blow uses the low-temperature nitrogen gas after the vaporization of liquid nitrogen, the temperature is -50 °C to -180 °C, and the cold blow time is 1-4 times the hot gas (high-temperature regeneration gas) purge time. After the cold blow is completed, the adsorption front peak basically reaches the inlet of the adsorber, and the regeneration is completed.

[0074] The cold blow time is determined by the temperature inside the adsorbent bed layer at the outlet of the adsorber. During the cold blow process, the outlet temperature gradually rises, reaches a peak and then gradually decreases. If the temperature of the cold blow gas is -120 °C, the cold blow process can be considered completed when the outlet temperature reaches -30 °C.

[0075] It should be noted that during the regeneration process, all the desorbed gas containing the heavy components obtained in Steps 3 and 4 should be collected and stored for further concentration treatment.

[0076] Step 5: After the cold blow, repressurize with the light component gas or the feed gas. The repressurization is carried out by the co-current pressurization of the feed gas or the counter-current pressurization of the stored light component gas (such as Figure 2 in Step 5), and the pressure reaches the same or similar to the pressure during adsorption.

[0077] The desorbed gas containing the heavy components obtained in Steps 3 and 4 is stored in the desorbed gas storage tank 50.

[0078] Step 6: After the regeneration is completed, prepare for the next cycle.

[0079] The desorbed gas in the desorbed gas storage tank 50 can be concentrated again or multiple times through membrane separation, adsorption or distillation processes for the obtained desorbed gas containing the heavy components, for example, obtaining the isotope heavy components with the required purity (such as 99.99%).

[0080] The focus of the present invention is to separate isotopes with a small separation factor, such as H2 / D2. When H2 and D2 are preliminarily separated, D2 is obtained as the heavy component, and a mixed gas is formed with nitrogen, helium, and neon with a very large separation factor. The subsequent separation and purification processes are not the control steps.

[0081] It should be noted that the so-called co-current release or counter-current release in the present invention refers to the comparison with the feeding direction during adsorption. When it is the same as the feeding direction during adsorption, it is defined as co-current release, otherwise it is counter-current release.

[0082] It should also be noted that in the embodiments of the present invention, it is emphasized that the feed is from the bottom during adsorption. In actual operation, the feed can also be from the top. In this case, other operating directions should be changed accordingly; It should also be noted that some directions emphasized in the present invention can be changed according to the actual operating conditions. The purpose is to make the adsorption front move upward as much as possible when meeting the emission standards of heavy components in light components during adsorption, so as to improve the utilization rate of the adsorption bed. At the same time, it is hoped that the adsorption front moves downward as much as possible during desorption; to extend the adsorption time, the desorption time also needs to be extended or the temperature or flow rate of the hot purge gas needs to be increased. In this way, the heat accumulated in the adsorption bed increases, resulting in the need to extend the cold blow time.

[0083] Example 1 Design of thick-walled adsorber In the example, the wall thicknesses of the two adsorbers are 0.5 and 2.5 cm.

[0084] Table 3 shows the design parameters of the adsorber, Table 4 shows the design parameters of the thick-walled adsorber and the calculated values of the absolute temperature T of the adsorber tube wall (where q i and q o ), and Table 5 shows the design parameters of the thin-walled adsorber and the calculated values of the absolute temperature T of the tube wall (where q i and q o ).

[0085] Table 3 Design parameters of the adsorber

[0086] In the calculations of Table 4 and Table 5, the following formulas are used.

[0087] (3) (4) In the formula, A i and A o are the inner and outer areas of the adsorber respectively. The calculation formula for T in the formula can be found in "Heat Transfer Calculations, Kutz Myer, The McGraw-Hill Companies, Inc., McGraw-Hill, 2006" Eq.10-13 and Eq.10-3.

[0088] Among them: (5) (6) T f is the hot blow temperature T fh or the cold blow temperature T fc ; T is the absolute temperature of the adsorber tube wall, Tm represents the average temperature, represents the average temperature difference.

[0089] Table 4 Design Parameters of Thick-Wall Adsorber

[0090] Table 5 Design Parameters of Thin-Wall Adsorber

[0091] The isochoric heat capacity Q in Equation (1) vh The definition of m in (7) For stainless steel 316, 7650 kg / m 3 .

[0092] The isochoric specific heat C of stainless steel 316 V is 590 J / (kg·K).

[0093] According to the heat balance, the integral difference in convective heat transfer q between the inner and outer walls of the adsorption tank i -q O should be equal to the isochoric heat capacity Q vh , but due to the use of the lumped parameter method in the calculation, calculation errors are inevitably introduced. The errors in Table (4) and Table (5) are calculated as follows: (8) As can be seen from Table (4) and Table (5), when using a thick-wall (2.5 cm) adsorber, the liquid nitrogen consumption within 600 s of vacuum-thermal blow is 6.79 kg, while under the same conditions, when using a thin-wall (0.5 cm) adsorber, the liquid nitrogen consumption within 600 s of vacuum-thermal blow is 14.91 kg; when using a thick-wall (2.5 cm) adsorber, the liquid nitrogen consumption within 1200 s of cold blow is 9.06 kg, while under the same conditions, when using a thin-wall (0.5 cm) adsorber, the liquid nitrogen consumption within 1200 s of cold blow is 16.51 kg. The simulation results show that the thick-wall adsorber can effectively buffer the impact of thermal shock, as manifested by the isochoric heat capacity Q of the thick wall vh being 4123 (thermal blow) - 3888 (cold blow) kJ, which is much higher than the corresponding isochoric heat capacity Q of the thin wall vh (770 - 653 kJ).

[0094] The prior art shows that if there is only vacuum desorption, due to the low partial pressure corresponding to the strong adsorption or the equilibrium adsorption amount of the heavy components, the desorption degree can only reach 80% after 30 minutes of high-vacuum desorption. It is necessary to combine the vacuum-thermal blowing technology to effectively desorb, but the problem is that cold blowing must be carried out, and the thick-walled adsorber can effectively reduce the cold consumption during thermal blowing regeneration and cold blowing.

[0095] The purpose of desorption is to reduce the partial pressure P of the gas phase corresponding to the adsorbed phase (heavy component q). q . Vacuum desorption is a method to increase the pressure difference P by reducing the partial pressure P of the heavy components in the gas phase. q -P; Thermal blowing is another method to increase the partial pressure P of the gas phase corresponding to the heavy components in the adsorbed phase. q to increase the pressure difference P. q -P; Obviously, blowing hot gas while maintaining vacuum can play a dual role, that is, while reducing the partial pressure P of the heavy components in the gas phase, increasing the partial pressure P of the gas phase corresponding to the heavy components in the adsorbed phase. q , obviously, the desorption efficiency can be significantly improved.

[0096] Under the same process parameters: When purging with hot gas (high-temperature regeneration gas), the wall temperature of the adsorber fluctuates by ±20 °C, resulting in local heating of the adsorbent to -150 °C and incomplete desorption of deuterium gas (loss rate of 15%); The liquid nitrogen consumption increases by 40% due to the insufficient heat buffering capacity of the thin-walled structure; The deuterium content in the output hydrogen fluctuates between 0.01% and 0.03%, and the stability is significantly lower than that of the thick-walled adsorber scheme of the present invention.

[0097] The thick-walled adsorber (2.5 cm) proposed by the present invention can effectively suppress thermal shock and ensure the stability of low-temperature adsorption / regeneration.

[0098] Example 2 A mixed gas containing 99% H2 and 1% D2 at 10 bar is precooled to -180 °C. The adsorbent is 5A molecular sieve. When the outlet concentration of D2 reaches 10 ppm, it enters the desorption stage. When desorbing, if purging with high temperature, purging at 150 °C for 30 minutes, the recovery rate can reach 90%.

[0099] Example 3 A mixed gas containing 99% H2 and 1% D2 at 10 bar is precooled to -180 °C. The adsorbent is 5A molecular sieve. When the outlet concentration of D2 reaches 100 ppm, it is adsorbed for about 50 minutes and then enters the desorption stage.

[0100] Desorption and regeneration parameters: Vacuum pumping at 0.03 MPa for 15 min, during which hot nitrogen at 120 °C is purged 3 times for a total of 10 min, and cold nitrogen at -180 °C is purged for 35 min. The recovery rate of D2 can reach 96%.

[0101] A mixture of about 2% D2 and nitrogen can be obtained, and the separation factor of D2 and N2 increases, simplifying the subsequent separation process.

[0102] Example 4 Adsorbent innovation: Molecular sieve + silicon carbide composite adsorbent, adsorption temperature -196 °C.

[0103] A mixture of 99% H2 and 1% D2 at 10 bar is precooled to -180 °C. When the outlet concentration of D2 reaches 100 ppm, adsorption occurs for about 70 min, and then enters the desorption stage.

[0104] Desorption and regeneration parameters: Vacuum pumping at 0.03 MPa for 30 min, during which hot nitrogen at 120 °C is purged 3 times for a total of 20 min, and cold nitrogen at -180 °C is purged for 40 min. The recovery rate of D2 can reach 98%.

[0105] A mixture of about 2.4% D2 and nitrogen can be obtained, and the separation factor of D2 and N2 increases, simplifying the subsequent separation process.

[0106] Example 5 This example provides a cryogenic temperature and pressure swing adsorption device and regeneration process, and the specific steps are as follows: Step 1: Configuration of adsorber and adsorbent A stainless steel adsorber with a wall thickness of 4 cm is immersed in a liquid nitrogen storage tank. The adsorber is filled with an adsorbent bed layer composed of 5A molecular sieve and porous silicon carbide (mass ratio 1:1). A distributor is set at the bottom of the adsorber to ensure uniform gas flow through the bed layer.

[0107] Step 2: Pretreatment and adsorption of raw material hydrogen The raw material hydrogen (initial deuterium content is 1%) is precooled to -175 °C through a three-stage cold exchanger and then introduced into the adsorber. The internal temperature of the adsorber is controlled at -196 °C (boiling point of normal pressure liquid nitrogen) by adjusting the immersion depth of liquid nitrogen. Deuterium gas is selectively adsorbed by the composite adsorbent and desorbed when the deuterium content in the low-deuterium hydrogen output at the top reaches 100 ppm. The adsorption time is 90 min.

[0108] Step 3: Adsorbent regeneration process When the adsorbent is saturated, switch to the regeneration stage: Vacuum pumping: Use a dry scroll vacuum pump to reduce the pressure in the adsorber to 0.1 kPa and continue for 20 min.

[0109] Vacuum-high temperature desorption: Introduce high-temperature helium gas at 150 °C (pressure 0.05 MPa) with a flow rate of 2 L / min for 20 min, and store the desorbed deuterium-rich gas.

[0110] Low-temperature cold blowing: Introduce nitrogen gas at -180 °C vaporized from liquid nitrogen into the adsorber, and the cold blowing time is 70 min (3.5 times the high-temperature regeneration gas purging time), and store the desorbed deuterium-rich gas.

[0111] Step 4: Continuous operation of the two towers The system is equipped with two identical adsorption towers. In the embodiment, tower A represents the first adsorber and tower B represents the second adsorber. The adsorption and regeneration cycles are both 1.5 h. When tower A adsorbs, tower B is regenerated synchronously, and continuous production of deuterium-rich mixed gas is achieved through the switching of automatic valves.

[0112] The beneficial effects of this embodiment are 1) Improvement in separation efficiency: Under cryogenic conditions (-180 °C to -196 °C), the adsorption capacity of the composite adsorbent for the heavy components in the gas is improved.

[0113] 2) Optimization of regeneration: The vacuum + thermal and cold alternating regeneration process improves the cycle efficiency of the adsorbent and has a high recovery rate of heavy components in the gas.

[0114] 3) Reduction in energy consumption: The design of liquid nitrogen immersion reduces the external cooling energy consumption, and the thick-wall design buffers the heat pulse generated during the purging of hot gas (high-temperature regeneration gas), and the comprehensive energy consumption is reduced by more than 70% compared with the traditional method.

[0115] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms.

[0116] Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to cover all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

[0117] It should be noted that, in this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, system or module comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, system or module. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, system or module comprising the said element.

[0118] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An isotope separation system, characterized in that, The isotope separation system includes a cryogenic temperature- and pressure-swing adsorption device, and the cryogenic temperature- and pressure-swing adsorption device includes at least two adsorber units. Each adsorber unit includes a liquid nitrogen container and an adsorber. In each adsorber unit, the adsorber is immersed in the liquid nitrogen in the liquid nitrogen container; the adsorber includes a tube wall, and the material of the tube wall includes a first material. The volumetric heat capacity Q per unit length of the tube wall vh is greater than a first predetermined value, and the wall thickness D of the tube wall is 0.5 - 8 cm; controlling the modified Nusselt number related to the material and the wall thickness of the tube wall within a predetermined range, the modified Nusselt number has the following expression: ； Wherein, h is the convective heat transfer rate of the gas in the adsorber, k is the thermal conductivity of the tube wall, and D is the wall thickness of the tube wall; The fixed-volume heat capacity Q vh has the following expression: Q vh = mC v T where m is the mass of the tube wall of the effective length of the adsorber, C v is the specific heat of the material of the tube wall, and T is the absolute temperature of the tube wall.

2. The isotope separation system according to claim 1, characterized in that, The modified Nusselt number has a predetermined range of 0.07 ≦ ≦ 1.

3. The isotope separation system according to claim 1, wherein the tube wall satisfies one or both of the following conditions: (1) The first material is any one of stainless steel, nickel alloy, and metal composite material; (2) The first predetermined value is 2000 kJ / m.

4. An isotope separation method, wherein the isotope separation method uses the isotope separation system according to any one of claims 1 to 3 for isotope separation, characterized in that, The isotope separation method comprises the following steps: Step 1, adsorption The raw material gas is precooled and then introduced into the lower channel of the adsorber filled with adsorbent from the inside. At a predetermined working temperature, the adsorber adsorbs the heavy components in the raw material gas, and the light components in the raw material gas are output from the upper channel of the adsorber; Step 2, co-current pressure release When the heavy components in the light components at the outlet of the adsorber reach the breakthrough point concentration, switch to the regeneration process: close the lower channel, and the gas in the adsorber is discharged from the upper part of the adsorber to discharge the light components in the voids of the adsorbent; Step 3, vacuum desorption and thermal purge Open the lower channel and close the upper channel. The gas in the adsorber is discharged from the lower channel. When the pressure in the adsorber approaches atmospheric pressure, vacuum desorption is carried out; open the upper channel, and the high-temperature regeneration gas enters the adsorber from the upper channel and thermally purges the adsorbent to desorb, and the desorbed gas containing the heavy components is discharged from the lower channel; Step 4, cold purge After the thermal purge is completed, cold gas enters from the upper channel to cold purge and cool down the adsorbent, and the desorbed gas containing the heavy components is discharged from the lower channel; Step 5, recompression After the cold purge is completed, the adsorbent is regenerated, and the adsorber is recompressed; Step 6, circulation Prepare for the next cycle.

5. The isotope separation method according to claim 4, characterized in that, In Step 1, the raw material gas is a hydrogen isotope mixture gas. The adsorber is immersed in liquid nitrogen. The predetermined working temperature of the adsorber is -180°C to -196°C, and the precooling temperature of the adsorber is -165°C to -185°C.

6. The isotope separation method according to claim 4, characterized in that, In Step 2, the adsorbent is a single-layer or composite-layer adsorbent, and the material of the single-layer or composite-layer adsorbent is selected from at least one of 3A, 5A, 13X molecular sieves, activated carbon, and MOFs.

7. The isotope separation method according to claim 4, characterized in that In Step 3, the high-temperature regeneration gas includes one or more of nitrogen, helium, and neon, and the temperature of the high-temperature regeneration gas is 50 - 150 °C; the pressure in the adsorber is 1 bara to 3 bara; during the thermal purge, countercurrent vacuum pumping is carried out simultaneously, and the pressure of the vacuum pumping is 0.1 - 500 mbara.

8. The isotope separation method according to claim 4, characterized in that, In Step 4, the cold gas includes one or more of nitrogen, helium, and neon, the temperature of the cold gas is -50°C to -180°C, and the time of the cold purge is 1 - 4 times the time of the thermal purge.

9. The isotope separation method according to claim 4, characterized in that, In Step 5, co-current recompression is carried out using the raw material gas, or countercurrent recompression is carried out using the light components discharged from the upper channel in Step 1.

10. The isotope separation method according to claim 4, characterized in that, At least two of the adsorbers operate alternately, and the time required for step 1 is the same as the time required for steps 2 to 5, so as to achieve continuous separation of the raw material gas.

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