Isotope separation system and isotope separation method

Abstract

The present invention provides an isotope separation system and an isotope separation method. The isotope separation system includes a cryogenic temperature-swing pressure-swing adsorption device, the cryogenic temperature-swing pressure-swing adsorption device includes at least two adsorber units, each of the adsorber units includes a liquid nitrogen container and an adsorber, and in each adsorber unit, the adsorber is immersed in liquid nitrogen in the liquid nitrogen container; the adsorber includes a tube wall, the material of the tube wall includes a first material, and the constant volume heat capacity per unit length of the tube wall is Q vh The wall thickness D of the tube wall is greater than a first predetermined value, and the wall thickness D is 0.5-8 cm; and the modified Nusselt number #imgabs0# associated with the material and thickness of the tube wall is controlled within a predetermined range. The present invention solves the problems of low isotope separation efficiency, poor regeneration effect, and high liquid nitrogen consumption in the prior art, significantly improving the adsorbent recycling rate and the recovery rate of heavy fraction isotopes.

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 in particular to an isotope separation system with a cryogenic temperature-variable pressure device and a method for isotope separation using the cryogenic temperature-variable pressure device. Background Art

[0002] Gas separation is a critical component of many industrial sectors. Temperature and pressure swing adsorption (TPS) technology, as a highly efficient and energy-efficient gas separation technique, has been widely used in this field. This technology utilizes the differences in the adsorption capacity of adsorbents for different gases under varying temperature and pressure conditions to separate gas components by adjusting temperature and pressure.

[0003] However, existing temperature and pressure swing adsorption (TPSA) technology struggles to achieve efficient separation of certain specialized gas components. For example, in isotope separation, such as the separation of deuterium from hydrogen, traditional adsorbents have minimal differences in their adsorption capacity due to the extremely similar physical and chemical properties of the isotopes, resulting in low separation efficiency. Therefore, there is an urgent need to develop new adsorbents and process routes to improve the efficiency of temperature and pressure swing adsorption (TPSA) technology for isotope gas separation.

[0004] To address these issues, extensive research has employed cryogenic adsorption processes. However, low vacuum regeneration efficiency is a pressing issue, while thermal regeneration is incompatible with cryogenic adsorption systems, resulting in significant cooling losses. Therefore, a new separation system and isotope separation method based on this separation system are needed. Summary of the Invention

[0005] The existing technology has problems such as the small difference in adsorbent adsorption capacity for isotope light components and heavy components, low adsorbent regeneration effect, and the need to optimize the adsorber structure and adsorbent bed composition.

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

[0007]

[0008] Wherein, h is the convective heat transfer rate of the gas in the adsorber, k is the thermal conductivity coefficient of the tube wall, and D is the wall thickness of the tube wall;

[0009] The constant volume heat capacity Q vh The expression is:

[0010] Q vh =mC v T

[0011] Wherein, 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.

[0012] In one embodiment, the modified Nusselt number The predetermined range is 0.07≦ ≦1.

[0013] 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.

[0014] A second aspect of the present invention provides an isotope separation method, which uses the above-mentioned cryogenic temperature and pressure swing adsorption device to perform isotope separation, comprising the following steps:

[0015] Step 1: Adsorption

[0016] The feed gas is pre-cooled and introduced into the lower channel of an adsorber filled with an adsorbent. At a predetermined operating temperature, the adsorber adsorbs the heavy components in the feed gas, and the light components in the feed gas are discharged from the upper channel of the adsorber.

[0017] Step 2: Place in order

[0018] When the heavy component in the light component at the outlet of the adsorber reaches a breakthrough point concentration, the regeneration process is switched to: the lower channel is closed, and the gas in the adsorber is discharged from the upper portion of the adsorber to discharge the light component in the adsorbent voids;

[0019] Step 3: Vacuum desorption and thermal purge

[0020] The lower channel is opened, and the upper channel is closed, so that the gas in the adsorber is discharged from the lower channel. When the gas pressure in the adsorber approaches normal pressure, vacuum desorption is performed. The upper channel is opened, and high-temperature regeneration gas enters the adsorber from the upper channel and performs thermal purge on the adsorbent to desorb, and the desorbed gas containing the heavy component is discharged from the lower channel.

[0021] Step 4: Cold Purge

[0022] After the hot purge is completed, cold air enters from the upper channel to perform cold purge and cool the adsorbent, and the desorbed gas containing the heavy components is discharged from the lower channel;

[0023] Step 5: Re-press

[0024] After the cold purge is completed, the adsorbent is regenerated and the adsorber is re-pressurized;

[0025] Step 6: Loop

[0026] Prepare for the next cycle.

[0027] 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, 5A, 13X molecular sieves, activated carbon, and MOFs (metal organic frameworks).

[0028] In one embodiment, in step 3, the vacuum pressure is 0.1-500 mbara.

[0029] 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 in the adsorber is 1 bara to 3 bara. When hot gas purge desorption is performed, countercurrent vacuuming can be performed simultaneously.

[0030] 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 cold purge time is 1-4 times the hot purge time.

[0031] In one embodiment, in step 5, the feed gas is used for co-current re-pressurization, or the light component discharged from the upper channel in step 1 is used for counter-current re-pressurization.

[0032] In one embodiment, in steps 3 and 4, the desorbed gas containing heavy components is concentrated again or concentrated and purified multiple times by membrane separation, adsorption or distillation to obtain concentrated and purified isotope heavy components.

[0033] In one embodiment, the heavy component reaches a breakthrough concentration at the adsorber outlet, and the heavy component content in the light component is 0.1-0.001 wt %, preferably 0.01-0.05 wt %.

[0034] In one embodiment, in step 2, the discharge time is 0.2-2 s. Different from the pressure equalization process, the discharge only discharges the light components between the adsorber adsorbents to increase the heavy component content in the regeneration gas obtained in the subsequent regeneration process.

[0035] In one embodiment, in step 3, the countercurrent vacuum pressure is 0.1-500 mbara; preferably 1-100 mbara.

[0036] In one embodiment, the two adsorbers are fluidically connected, and the regenerated adsorber receives the depressurized pressure of the other adsorber and then is re-pressurized.

[0037] In one embodiment, the adsorption system comprises 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 adsorber wall thickness is 0.5-8 cm, preferably 2-5 cm.

[0038] In one embodiment, the storage unit includes a light component gas storage tank, a downstream vacuum discharge light component storage tank, and in steps 3 and 4, the regenerated concentrated gas component obtained is stored in a heavy component storage tank.

[0039] In one embodiment, the purge gas is nitrogen, helium, neon or a mixture thereof.

[0040] In one embodiment, the obtained regenerated concentrated gas component can be concentrated again to obtain a heavy component of desired purity. The obtained regenerated concentrated gas component can be concentrated again or multiple times, and the concentration is carried out by membrane separation, adsorption or distillation process.

[0041] In one embodiment, at least two of the adsorbers are operated alternately, with the adsorption and regeneration times being the same, to achieve continuous separation.

[0042] The present invention provides a novel temperature and pressure swing adsorber and a method for separating isotopic gases thereof, which have the following beneficial effects:

[0043] 1. A thick-walled cryogenic adsorber immersed in liquid nitrogen is used to enhance the adsorption capacity of the adsorbent on heavy components under cryogenic temperature conditions, thereby improving the separation efficiency of heavy components.

[0044] 2. Through vacuum purge, high-temperature hot gas regeneration and low-temperature cold purge, the target product recovery and efficient regeneration of the adsorbent are achieved, the recycling efficiency of the adsorbent is improved, and the loss rate of heavy components is reduced.

[0045] 3. The structural design of the adsorber and the composition of the adsorbent bed have been optimized to further improve the adsorption effect and adsorption capacity;

[0046] 4. Thick-walled adsorbers are used to buffer the thermal pulses generated during hot gas purge, improve cryogenic adsorption regeneration efficiency, and reduce liquid nitrogen consumption. Energy consumption is reduced: the liquid nitrogen immersion design reduces external cooling energy consumption, and the thick-walled design buffers the thermal pulses generated during hot gas purge, reducing overall energy consumption by more than 70% compared to traditional methods.

[0047] 5. It provides a new technical route for isotope gas separation and expands the application scope of temperature and pressure swing adsorption technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0049] Figure 1 This is a schematic diagram of a cryogenic temperature and pressure swing adsorption device;

[0050] Figure 2 The process flow chart for the separation of isotopes adsorption-regeneration cycle steps is shown;

[0051] Figure 3 Schematic diagram of the cross section and parameters of the adsorber. DETAILED DESCRIPTION

[0052] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the objects, features and advantages of the present invention can be more clearly understood. It should be understood that the embodiments shown in the accompanying drawings are not intended to limit the scope of the present invention, but are only intended to illustrate the essential spirit of the technical solution of the present invention.

[0053] In the following description, for the purpose of illustrating the various disclosed embodiments, certain specific details are set forth in order to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the relevant art will recognize that the embodiments may be practiced without one or more of these specific details. In other cases, well-known devices, structures, and techniques associated with this application may not be shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0054] Reference throughout this specification to "one embodiment" or "an embodiment" means 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" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any manner in one or more embodiments.

[0055] In the following description, in order to clearly show the structure and working mode of the present invention, many directional words will be used for description, but words such as "front", "back", "left", "right", "outside", "inside", "outward", "inward", "up", and "down" should be understood as convenient terms and should not be understood as restrictive terms.

[0056] It should be noted that the features shown in the drawings of this application may belong to one embodiment or to different embodiments, as long as there is no conflict between these features. To save space, this application may use the same drawing to illustrate different embodiments. In other words, the same drawing of this application can be used to illustrate features of different embodiments.

[0057] The purpose of this embodiment is to overcome the shortcomings of the prior art and provide a cryogenic temperature-pressure swing system for separating isotopes and a method for separating isotopes using the system. Specifically, a new temperature-pressure swing adsorber and a method for separating deuterium from a mixture of hydrogen and deuterium are provided.

[0058] This embodiment provides a system for separating isotopes, which has a cryogenic temperature-swing pressure-swing adsorption device, which includes a first adsorber unit, a second adsorber unit, a vacuum unit 40, a purge gas unit, a light component storage tank 60, a desorption gas storage tank 50 and a control unit.

[0059] like Figure 1 As 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 outlet pipe 112 , a first air inlet pipe 101 , and a first air outlet pipe 102 .

[0060] The first adsorber 12 is disposed within the first liquid nitrogen tank 11. Liquid nitrogen (LN2) enters the first liquid nitrogen tank 11 through a first liquid nitrogen inlet pipe 111. One end of a first nitrogen outlet pipe 112 is connected to the upper portion of the first liquid nitrogen tank 11, and the other end is connected to a nitrogen outlet pipe 113. The first inlet pipe 101 is connected to the raw material inlet at one end and to the lower portion of the first adsorber 12 at the other end. The first outlet pipe 102 is connected to the upper portion of the first adsorber 12 at one end and to the light fraction branch 601 at the other end. 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 outlet pipe 112 pass through the first heat exchanger 13. A first liquid nitrogen metering component 14 is disposed on the first liquid nitrogen tank 11 for measuring the amount of liquid nitrogen within the first liquid nitrogen tank 11. The first air inlet pipe 101 may be a lower channel, the first air outlet pipe 102 may be an upper channel, and the upper channel and the lower channel may also be other ventilation pipes.

[0061] 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 outlet pipe 212 , a second air inlet pipe 201 , and a second air outlet pipe 202 .

[0062] The second adsorber 22 is disposed within the second liquid nitrogen tank 21. Liquid nitrogen LN2 enters the second liquid nitrogen tank 21 through a second liquid nitrogen inlet pipe 211. One end of the second nitrogen outlet pipe 212 is connected to the upper portion of the second liquid nitrogen tank 21, and the other end is connected to the nitrogen outlet pipe 113. The second inlet pipe 201 is connected to the raw material inlet at one end and to the lower portion of the second adsorber 22 at the other end. The second outlet pipe 202 is connected to the upper portion of the second adsorber 22 at one end and to the light fraction branch 601 at the other end. 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 outlet pipe 212 pass through the second heat exchanger 23. A second liquid nitrogen metering component 24 is disposed on the second liquid nitrogen tank 21 for measuring the amount of liquid nitrogen within the second liquid nitrogen tank 21. The second air inlet pipe 201 may be a lower channel, the second air outlet pipe 202 may be an upper channel, and the upper channel and the lower channel may also be other ventilation pipes.

[0063] The first heat exchanger 13 and the second heat exchanger 23 are both three-stream heat exchangers, which are used to pre-cool the raw gas to the target temperature in stages and recover the tail gas cooling capacity at the same time. In the embodiment, they are used to pre-cool the raw hydrogen H2 / D2 to -150 ℃ to -175 ℃ after heat exchange and then pass it into the adsorber. The pressure of the positive flow isotope mixture is about 10 bar (controlled by the back pressure valve 6A), and the flow rate is 10Nm 3 / h, inlet 293 K, outlet temperature 83 K.

[0064] The design criteria of the adsorber (the first adsorber 12 and the second adsorber 22; the adsorber mentioned hereinafter may be understood as the first adsorber 12 and / or the second adsorber 22) are as follows:

[0065] In a system using a cryogenic temperature and pressure swing adsorption device for isotope separation, thick-walled, low thermal conductivity (e.g., 12-24 W / m·K) materials are used for the adsorber tube wall. The design of the thick-walled adsorber is based on the system's modified Nusselt number. The range is 0.07≦ ≦1, that is, to ensure that the convection heat transfer of the gas on the inner wall (h) is lower than the heat conduction rate of the adsorber tube wall (k / D). The constant volume heat capacity Q per meter of adsorber tube wall vh Greater than 2000 kJ, that is, each meter of adsorber tube wall must have sufficient heat storage capacity.

[0066] (1)

[0067] (2)

[0068] Where m is the mass of the tube wall of the effective length of the adsorber (in kg), C v is the specific heat of the pipe wall material (unit: J / (kg·K)), T is the absolute temperature of the pipe wall (unit: K), h is the gas convection heat transfer rate (unit: W / (m 2 ·K)), k is the heat conductivity coefficient of the adsorber tube wall (unit: W / (m·K)), and D is the wall thickness (unit: m).

[0069] like Figure 3 As shown, the adsorber is a cylinder with a circular cross section. Calculate the absolute temperature T of the tube wall.

[0070] Figure 3 In the figure, T0 represents the temperature of liquid nitrogen in the liquid nitrogen storage tank, q i (t) represents the integral of the convective heat transfer on the inner wall of the adsorption tank, q o (t) represents the integral of convective heat transfer on the outer wall of the adsorption tank, T g (t) represents the temperature of the gas in the adsorber, and t is the time.

[0071] Particularly, the pipe wall material is one of stainless steel, nickel alloy or metal composite material.

[0072] A cryogenic temperature-swing pressure-swing adsorption device is used for isotope separation. The raw material is gas, and the adsorption is carried out at the temperature of liquid nitrogen or liquid helium. Preferably, the predetermined operating temperature of the adsorber is the temperature of liquid nitrogen, which can be between -180°C and -196°C, and the pre-cooling temperature is between -165°C and -185°C. The adsorber is immersed in liquid nitrogen, and the amount of liquid nitrogen is measured and the liquid level is controlled by a liquid level gauge. The volatilized nitrogen is used as a purge gas after the cooling capacity is recovered by a multi-stream heat exchanger and stored in a purge gas source 30.

[0073] Thick-walled adsorbers are different from adiabatic adsorbers. The adsorption heat of adiabatic adsorbers cannot be removed, while thick-walled adsorbers can remove the adsorption heat in a timely manner, thereby increasing the equilibrium adsorption capacity. During the adsorption process, the physical adsorption heat is usually several hundred to several thousand J / mol, with a maximum of no more than 40 kJ / mol. It should be noted that the adsorption heat in the embodiment is transferred outward through convection heat transfer between the inner and outer walls and heat conduction of the tube wall, and is ultimately reflected in the consumption of liquid nitrogen. That is, liquid nitrogen removes heat from the system through vaporization. If the liquid nitrogen consumption is large, the system generates large amounts of heat, and vice versa.

[0074] The adsorption system including the adsorber is provided with different temperature detection points, such as at the adsorber inlet, adsorber outlet and the lower and upper ends of the adsorbent filled in the adsorber, to assist the concentration detector in judging the adsorption and regeneration process.

[0075] 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 normal pressure, the saturation temperature of 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 liquid nitrogen is about -192°C. The adsorber is filled with adsorbent, which is 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).

[0076] Pipe 205 connects the raw material inlet, the first air inlet pipe 101 and the second air inlet pipe 201, and is provided with valve 5B and valve 5A, wherein valve 5A is located between the raw material inlet and the first air inlet pipe 101, and valve 5B is located between the raw material inlet and the second air inlet pipe 201; pipe 206 connects the first air outlet pipe 102 and the second air outlet pipe 202, and is provided with valve 3B and valve 3A.

[0077] Tube 301 connects the purge gas source 30 with the first gas outlet pipe 102, tube 304 connects the second gas outlet pipe 202 with tube 301, tube 302 connects the purge gas source 30 with tube 206, and tube 305 connects the first gas inlet pipe 101 with the second gas inlet pipe 201; valve 4C, valve 4A and heater 31 are provided on tube 301, valve 4B is provided on tube 304, and valve 4D is provided on tube 302; wherein, valve 4A is located between the first gas outlet pipe 102 and tube 304, and valve 4C and heater 31 are located between tube 304 and the purge gas source 30.

[0078] Vacuum unit 40 includes a dry vacuum pump with an operating limit vacuum of ≤0.1 kPa. Pipe 401 connects vacuum unit 40 to pipe 305, which in turn connects to desorbed gas storage tank 50. Desorbed gas is stored in 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 desorbed gas storage tank 50.

[0079] The pipe 601 is connected to the light component storage tank 60, the first gas outlet pipe 102 and the second gas outlet pipe 202. A back pressure valve 6A is provided on the pipe 601, and a valve 6B is connected in parallel with the back pressure valve 6A.

[0080] The control unit switches the adsorber between adsorption and regeneration by controlling the opening and closing of different flow control valves.

[0081] In one embodiment, a cryogenic temperature and pressure variable system for separating isotopes includes at least two adsorber units, each of which includes a liquid nitrogen container and an adsorber. When the adsorber in one adsorber unit is adsorbing, the adsorber in another adsorber unit is regenerating, and the adsorption time is equal to the regeneration time to achieve continuous production; within the same adsorber unit, the adsorber is immersed in liquid nitrogen in the liquid nitrogen container, and the wall thickness of the adsorber is 2-5 cm.

[0082] In one embodiment, the adsorber is a thick-walled adsorber having a wall thickness of 3-4 cm, and is used to buffer the heat pulse generated by the hot gas purge to reduce refrigerant consumption.

[0083] The embodiment also provides a method for separating isotopes, using a cryogenic temperature and pressure swing adsorption device to perform isotope separation, including an adsorption process and a regeneration process, including: Figure 2 Steps shown:

[0084] Step 1: Pre-cool the raw gas and pass it into an adsorber filled with adsorbent to adsorb the heavy components in the raw gas at a cryogenic temperature and discharge the light components. Figure 2 The middle rectangle is a schematic diagram of the adsorber, I represents the adsorption unsaturated zone in the adsorber, II represents the adsorption saturated zone in the adsorber, and the adsorption front is the interface between the adsorption unsaturated zone and the adsorption saturated zone in the adsorber. In the embodiment, the raw gas is hydrogen (a mixture of H2 and D2).

[0085] like Figure 1 As shown, the deuterium-containing hydrogen feedstock passes through valves 5A and 1A, is pre-cooled in a multi-stream heat exchanger, and then enters adsorber A, which is filled with adsorbent, from the bottom along pipeline 101. The entire adsorber 12 is immersed in liquid nitrogen, the liquid nitrogen level of which is controlled by a first liquid nitrogen metering component 14. At the liquid nitrogen temperature, the adsorbent absorbs the deuterium, a heavy component of the hydrogen. The light component, primarily hydrogen, is output from the upper end and passes through pipeline 102 and pipeline 601 to enter light component storage tank 60. The light component contains less than 0.01 wt% deuterium, and the pressure of the adsorption system is controlled by a backpressure valve at the outlet.

[0086] The remaining steps will not be repeated.

[0087] Tables 1 and 2 show valve behavior during the adsorption and regeneration processes. The values ​​in the tables represent valve behavior during the adsorption and regeneration phases, where a value of 0 indicates a closed valve and a value of 1 indicates an open valve. The hot gas in the tables refers to the high-temperature regeneration gas.

[0088] In the embodiment, tower A represents the first adsorber 12 , and tower B represents the second adsorber 22 .

[0089] Table 1 Adsorption process of tower A and regeneration process of tower B

[0090]

[0091] Table 2 Adsorption process of tower B and regeneration process of tower A

[0092]

[0093] In the embodiment, the pre-cooling 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 with a control accuracy of ±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 compounds MOFs.

[0094] In the first step, the mixed gas enters the adsorber from the bottom for adsorption. During the adsorption process, the heavy components are adsorbed and the light components are discharged from the top of the adsorber. It should be noted that the discharged light components contain a very small amount of heavy components.

[0095] Step 2: As the adsorption progresses, the adsorption front gradually moves upward, and the concentration of the heavy component in the light component discharged from the upper part of the adsorber gradually increases. When the concentration of the heavy component at the adsorber outlet reaches the set value, such as 0.01%, the concentration of the heavy component at the outlet reaches the breakthrough point, the air intake is stopped, and the regeneration stage begins.

[0096] When the heavy component reaches the breakthrough point concentration, the regeneration process is switched: the lower channel of the adsorber is closed, and the gas in the adsorber is discharged from the top for 0.2-2 s. The downstream discharge is different from the pressure equalization process. It only discharges the light components in the adsorbent gap to increase the heavy component content in the regenerated gas. At this time, the adsorption front moves upward.

[0097] Step 3: Open the lower channel of the adsorber and close the upper channel of the adsorber. The gas in the adsorber is discharged from the lower part to atmospheric pressure, and then vacuum desorption is carried out. 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. 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 a mixture thereof as the purge gas. The purge gas temperature is 50-150 ° C and the pressure is 1 bara to 3 bara. At this time, the adsorption front moves downward.

[0098] The regeneration time of high-temperature regeneration gas is generally determined by the temperature of the adsorbent bed at the adsorber outlet. For example, when the inlet temperature of the high-temperature regeneration gas is 120°C, heat exchange with the adsorbent simultaneously heats the adsorber wall, and the heat front gradually moves downward, causing the temperature of the adsorbent bed at the lower adsorber outlet to gradually increase. It is generally believed that the hot-blowing process ends when the temperature of the adsorbent bed at the adsorber outlet reaches 30°C. The hot-blowing process produces desorbed gas containing heavy components at the outlet.

[0099] There are two issues that require attention: first, a large amount of heat is introduced into the low-temperature adsorption system, and how to reduce the cooling 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 recombination and decomposition air.

[0100] Step 4: After the hot gas (high-temperature regeneration gas) purge is completed, low-temperature cold blowing and reheating are started. Cold gas enters from the upper part of the adsorber to purge and cool the adsorber, and the desorbed gas containing heavy components is discharged from the lower part of the adsorber. In one embodiment, the low-temperature cold blowing uses low-temperature nitrogen gas vaporized from liquid nitrogen, with a temperature of -50°C to -180°C. The cold blowing time is 1-4 times the hot gas (high-temperature regeneration gas) purge time. After the cold blowing is completed, the adsorption front peak basically reaches the adsorber inlet, and the regeneration is completed.

[0101] The cold blow time is determined by the temperature of the adsorbent bed at the adsorber outlet. During the cold blow process, the outlet temperature gradually increases, 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 complete when the outlet temperature reaches -30°C.

[0102] It should be noted that during the regeneration process, all desorbed gases containing heavy components obtained in steps 3 and 4 must be collected and stored for further concentration processing.

[0103] Step 5: After cold blowing, re-pressurize with light component gas or raw gas. Re-pressurize with raw gas downstream or with stored light component gas countercurrent (e.g. Figure 2 In step 5 of the process), the pressure reaches the same or similar pressure as during adsorption.

[0104] The desorbed gas containing heavy components obtained in steps 3 and 4 is stored in the desorbed gas storage tank 50.

[0105] Step 6: After regeneration is completed, prepare for the next cycle.

[0106] The desorbed gas in the desorbed gas storage tank 50 can be subjected to membrane separation, adsorption or distillation processes to further concentrate the desorbed gas containing heavy components or to concentrate the desorbed gas multiple times, for example, to obtain isotope heavy components with a desired purity (eg, 99.99%).

[0107] The focus of the present invention is to separate isotopes with a smaller separation factor, such as H2 / D2. After the initial separation of H2 and D2, D2 is obtained as a heavy component and forms a mixed gas with nitrogen, helium, and neon with a large separation factor. The subsequent separation and purification process is not a controlling step.

[0108] It should be pointed out that the forward placement or reverse placement mentioned in the present invention refers to the direction compared with the feeding direction during adsorption. When the direction is the same as the feeding direction during adsorption, it is defined as forward placement, otherwise it is reverse placement.

[0109] It should also be noted that, while the embodiment of the present invention emphasizes feeding from the bottom during adsorption, in actual operation, feeding from the top is also possible. In this case, the other operating directions should also be changed accordingly.

[0110] It should also be pointed out that some of the directions emphasized in the present invention can be changed according to actual operating conditions. The purpose is to move the adsorption front as much as possible upward when meeting the emission standards of heavy components in light components during adsorption to improve the utilization rate of the adsorption bed. At the same time, it is hoped that the adsorption front will move downward as much as possible during desorption; to extend the adsorption time, the desorption time must also be extended or the temperature or flow rate of the hot purge gas must be increased, so that the heat accumulated in the adsorption bed increases, resulting in an extension of the cold blow time.

[0111] Example 1

[0112] Design of thick-walled adsorber

[0113] In the embodiment, the wall thicknesses of the two adsorbers are 0.5 and 2.5 cm.

[0114] Table 3 shows the design parameters of the adsorber, and Table 4 shows the design parameters of the thick-walled adsorber and the calculated absolute temperature T of the adsorber tube wall (q i and q o ), Table 5 shows the design parameters of the thin-wall adsorber and the calculated absolute temperature T of the tube wall (q i and q o ).

[0115] Table 3 Adsorber design parameters

[0116]

[0117] In the calculations in Tables 4 and 5, the following formulas are used.

[0118] (3)

[0119] (4)

[0120] Where A i and A oare the inner and outer areas of the adsorber, respectively. The calculation formula for T is given in Eq. 10-13 and Eq. 10-3 of "Heat Transfer Calculations, Kutz Myer, The McGraw-Hill Companies, Inc., McGraw-Hill, 2006."

[0121] in:

[0122] (5)

[0123] (6)

[0124] T f is the hot blowing temperature T fh Or cold blowing temperature T fc , T is the absolute temperature of the adsorber tube wall, Tm represents the average temperature, Represents the mean temperature difference.

[0125] Table 4 Design parameters of thick-wall adsorber

[0126]

[0127] Table 5 Design parameters of thin-wall adsorber

[0128]

[0129] Equation (1) Constant volume heat capacity Q vh The definition of m is

[0130] (7)

[0131] For stainless steel 316, 7650 kg / m 3 .

[0132] The constant volume specific heat C of stainless steel 316 V It is 590 J / (kg·K).

[0133] According to the heat balance, the integral difference of convective heat transfer between the inner and outer walls of the adsorption tank is q i -q O Should be equal to the constant volume heat capacity Q vh However, since the calculation adopts the lumped parameter method, calculation errors are inevitably introduced. The errors in Table (4) and Table (5) are The calculation is as follows:

[0134] (8)

[0135] As shown in Tables (4) and (5), when a thick-walled (2.5 cm) adsorber is used, the liquid nitrogen consumption during the 600 s vacuum-hot blowing period is 6.79 kg, while when a thin-walled (0.5 cm) adsorber is used under the same conditions, the liquid nitrogen consumption during the 600 s vacuum-hot blowing period is 14.91 kg; when a thick-walled (2.5 cm) adsorber is used, the liquid nitrogen consumption during the 1200 s cold blowing period is 9.06 kg, while when a thin-walled (0.5 cm) adsorber is used under the same conditions, the liquid nitrogen consumption during the 1200 s cold blowing period is 16.51 kg. The simulation results show that the thick-walled adsorber can effectively buffer the impact of thermal shock, as shown in the constant volume heat capacity Q of the thick wall. vh It is 4123 (hot blowing) - 3888 (cold blowing) kJ, which is less than the corresponding thin-wall constant volume heat capacity Q vh (770-653 kJ) is much higher.

[0136] Existing technology indicates that vacuum desorption alone, due to the low partial pressure corresponding to the equilibrium adsorption capacity of strongly adsorbed or heavy components, requires high vacuum desorption for 30 minutes to reach a desorption degree of 80%. Effective desorption requires a combination of vacuum and hot-blowing technology, but this comes with the requirement for cold-blowing. Thick-walled adsorbers can effectively reduce cooling consumption during both hot-blowing regeneration and cold-blowing.

[0137] The purpose of desorption is to reduce the gas phase equilibrium partial pressure P corresponding to the adsorbed phase (heavy component q) q Vacuum desorption is a method that reduces the partial pressure P of the heavy components in the gas phase to increase the pressure difference P q -P; Hot blowing is another way to increase the gas phase equilibrium partial pressure P corresponding to the heavy component of the adsorption phase q To increase the pressure difference P q Obviously, hot blowing while maintaining vacuum can play a dual role, that is, it reduces the partial pressure P of the heavy components in the gas phase while increasing the gas phase equilibrium partial pressure P corresponding to the heavy components in the adsorption phase. q , which can obviously significantly improve the desorption efficiency.

[0138] Under the same process parameters:

[0139] During the hot gas (high-temperature regeneration gas) purge, the adsorber wall temperature fluctuated by ±20°C, causing the adsorbent to locally heat to -150°C and incomplete desorption of deuterium (loss rate of 15%).

[0140] Liquid nitrogen consumption increased by 40% due to insufficient thermal buffering capacity of thin-walled structures;

[0141] The deuterium content in the output hydrogen fluctuates between 0.01% and 0.03%, and its stability is significantly lower than that of the thick-walled adsorber solution of the present invention.

[0142] The thick-walled adsorber (2.5 cm) proposed in this paper can effectively suppress thermal shock and ensure low-temperature adsorption / regeneration stability.

[0143] Example 2

[0144] A 10-bar mixture containing 99% H₂ and 1% D₂ is precooled to -180°C. Using 5A molecular sieve as the adsorbent, the desorption phase begins when the outlet D₂ concentration reaches 10 ppm. A high-temperature purge at 150°C for 30 minutes can achieve a recovery rate of 90%.

[0145] Example 3

[0146] The 10 bar mixed gas containing 99% H2 and 1% D2 was precooled to -180 °C. The adsorbent was 5A molecular sieve. When the outlet concentration of D2 reached 100 ppm, the adsorption lasted for about 50 minutes and then entered the desorption stage.

[0147] Desorption regeneration parameters: vacuum 0.03 MPa / 15 min, during which 120 °C hot nitrogen was purged three times for a total of 10 min, and -180 °C cold nitrogen was purged for 35 min. The recovery rate of D2 can reach 96%.

[0148] A mixed gas of about 2% D2 and nitrogen can be obtained, and the separation factor of D2 and N2 is increased, which simplifies the subsequent separation process.

[0149] Example 4

[0150] Adsorbent innovation: molecular sieve + silicon carbide composite adsorbent, adsorption temperature -196 ℃.

[0151] The mixed gas containing 99% H2 and 1% D2 at 10 bar was precooled to -180 °C. When the outlet concentration of D2 reached 100 ppm, the adsorption lasted for about 70 minutes and then entered the desorption stage.

[0152] Desorption regeneration parameters: vacuum 0.03 MPa / 30 min, during which 120 °C hot nitrogen was purged three times for a total of 20 min, and -180 °C cold nitrogen was purged for 40 min. The recovery rate of D2 can reach 98%.

[0153] A mixed gas of about 2.4% D2 and nitrogen can be obtained, and the separation factor of D2 and N2 is increased, which simplifies the subsequent separation process.

[0154] Example 5

[0155] This embodiment provides a cryogenic temperature and pressure swing adsorption device and a regeneration process, and the specific steps are as follows:

[0156] Step 1: Adsorber and adsorbent configuration

[0157] A 4-cm-thick stainless steel adsorber was immersed in a liquid nitrogen tank. The adsorber was filled with an adsorbent bed composed of a 1:1 mass ratio of 5A molecular sieve and porous silicon carbide. A distributor was installed at the bottom of the adsorber to ensure uniform airflow through the bed.

[0158] Step 2: Raw hydrogen pretreatment and adsorption

[0159] Feed hydrogen (initial deuterium content: 1%) is pre-cooled to -175°C via a three-stage cold heat exchanger before entering the adsorber. The internal temperature of the adsorber is controlled at -196°C (the boiling point of liquid nitrogen at atmospheric pressure) by adjusting the liquid nitrogen immersion depth. Deuterium is selectively adsorbed by the composite adsorbent. Deuterium-depleted hydrogen discharged overhead desorbs when the deuterium content reaches 100 ppm. The adsorption time is 90 minutes.

[0160] Step 3: Adsorbent regeneration process

[0161] When the adsorbent is saturated, it switches to the regeneration stage:

[0162] Vacuuming: Use a dry scroll vacuum pump to reduce the pressure in the adsorber to 0.1 kPa for 20 min.

[0163] Vacuum-high temperature desorption: introduce high temperature helium at 150 °C (pressure 0.05 MPa) at a flow rate of 2 L / min for 20 min, and store the desorbed deuterium-rich gas.

[0164] Low-temperature cold blowing: Liquid nitrogen is vaporized and the nitrogen at -180 °C is passed into the adsorber. The cold blowing time is 70 min (3.5 times the high-temperature regeneration gas purge time) to store the desorbed deuterium-enriched gas.

[0165] Step 4: Dual Towers Continuous Operation

[0166] The system is configured with two identical adsorption towers. In this example, Tower A represents the first adsorber, and Tower B represents the second adsorber. The adsorption and regeneration cycles are both 1.5 hours. While Tower A is adsorbing, Tower B is simultaneously regenerating. Automatic valve switching enables continuous production of a deuterium-enriched mixed gas.

[0167] The beneficial effects of this embodiment are:

[0168] 1) Improved separation efficiency: Under cryogenic conditions (-180°C to -196°C), the composite adsorbent’s adsorption capacity for heavy gas components is enhanced.

[0169] 2) Regeneration optimization: Vacuuming + hot and cold alternating regeneration process improves the adsorbent circulation efficiency and the recovery rate of heavy component gas.

[0170] 3. Reduced energy consumption: The liquid nitrogen immersion design reduces external cooling energy consumption, and the thick wall design buffers the heat pulses generated during hot gas (high-temperature regeneration gas) purge, reducing the overall energy consumption by more than 70% compared with traditional methods.

[0171] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0172] The embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims rather than the foregoing description, and all changes that come within the meaning and range of equivalents of the claims are therefore intended to be embraced therein.

[0173] It should be noted that, in this document, relational terms such as "first" and "second" are used only 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 terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, system or module that includes a series of elements includes not only those elements, but also other elements that are not explicitly listed, or elements that are inherent to such process, method, system or module. In the absence of further restrictions, an element defined by the sentence "comprises a..." does not exclude the presence of other identical elements in the process, method, system or module that includes the element.

[0174] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is to be construed in the widest possible manner 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-swing pressure-swing adsorption device, which includes at least two adsorber units, each of which includes a liquid nitrogen container and an adsorber. In each adsorber unit, the adsorber is immersed in liquid nitrogen in the liquid nitrogen container; the adsorber includes a tube wall, the material of the tube wall includes a first material, and the constant volume heat capacity Q per unit length of the tube wall is vh greater than a first predetermined value, 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 The expression is: ; Wherein, h is the convective heat transfer rate of the gas in the adsorber, k is the thermal conductivity coefficient of the tube wall, and D is the wall thickness of the tube wall; The constant volume heat capacity Q vh The expression is: Q vh =mC v T; Wherein, 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: Modified Nusselt number The predetermined range is 0.07≦ ≦1.

3. The isotope separation system according to claim 1, characterized in that: The tube wall satisfies one or both of the following conditions: (1) The first material is stainless steel; (2) The first predetermined value is 2000 kJ / m.

4. The isotope separation system according to claim 1, characterized in that: The first material is a nickel alloy.

5. The isotope separation system according to claim 1, characterized in that: The first material is a metal composite material.

6. An isotope separation method, comprising performing isotope separation using the isotope separation system according to any one of claims 1 to 5, wherein: The isotope separation method comprises the following steps: Step 1: Adsorption The feed gas is pre-cooled and introduced into the lower channel of an adsorber filled with an adsorbent. At a predetermined operating temperature, the adsorber adsorbs the heavy components in the feed gas, and the light components in the feed gas are discharged from the upper channel of the adsorber. Step 2: Place in order When the heavy component in the light component at the outlet of the adsorber reaches a breakthrough point concentration, the regeneration process is switched to: the lower channel is closed, and the gas in the adsorber is discharged from the upper portion of the adsorber to discharge the light component in the adsorbent voids; Step 3: Vacuum desorption and thermal purge The lower channel is opened, and the upper channel is closed, so that the gas in the adsorber is discharged from the lower channel. When the gas pressure in the adsorber approaches normal pressure, vacuum desorption is performed. The upper channel is opened, and high-temperature regeneration gas enters the adsorber from the upper channel and performs thermal purge on the adsorbent to desorb, and the desorbed gas containing the heavy component is discharged from the lower channel. Step 4: Cold Purge After the hot purge is completed, cold air enters from the upper channel to perform cold purge and cool the adsorbent, and the desorbed gas containing the heavy components is discharged from the lower channel; Step 5: Re-press After the cold purge is completed, the adsorbent is regenerated and the adsorber is re-pressurized; Step 6: Loop Prepare for the next cycle.

7. The isotope separation method according to claim 6, characterized in that: In step 1, the raw gas is a hydrogen isotope mixture, the adsorber is immersed in liquid nitrogen, the predetermined operating temperature of the adsorber is -180°C to -196°C, and the pre-cooling temperature of the adsorber is -165°C to -185°C.

8. The isotope separation method according to claim 6, 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.

9. The isotope separation method according to claim 6, 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; when the hot purge is performed, countercurrent vacuuming is performed simultaneously, and the vacuuming pressure is 0.1-500 mbara.

10. The isotope separation method according to claim 6, 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 hot purge.

11. The isotope separation method according to claim 6, characterized in that: In step 5, the feed gas is used for downstream re-pressurization, or the light component discharged from the upper channel in step 1 is used for countercurrent re-pressurization.

12. The isotope separation method according to claim 6, characterized in that: At least two of the adsorbers are operated alternately, and the time required for step 1 is the same as the time required for steps 2 to 5, thereby achieving continuous separation of the feed gas.

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