Separation and purification process and process system for hydrogen-nitrogen mixed gas

Abstract

The invention provides a separation and purification process and process system for hydrogen-nitrogen mixed gas. The separation and purification process comprises the following steps that hydrogen-nitrogen mixed gas is subjected to pressure swing adsorption treatment, product gas and desorption gas are obtained, and an adsorbent for pressure swing adsorption treatment is a 5A type molecular sieve and / or a 10X type molecular sieve; and performing membrane separation on the desorbed gas to obtain retentate gas and permeate gas, and combining the permeate gas with the hydrogen-nitrogen mixed gas to perform pressure swing adsorption treatment. The invention also provides a process system for the separation and purification process of the hydrogen-nitrogen mixed gas. The separation and purification process of the hydrogen-nitrogen mixed gas provided by the invention is specially used for hydrogen purification of ammonia decomposition product gas, adopts a combined process of hydrogen membrane separation and pressure swing adsorption, and greatly improves the total recovery rate of hydrogen from 78% to more than 95% compared with a conventional pressure swing adsorption purification process.

Description

Technical Field

[0001] The present invention relates to a separation and purification process and process system for a hydrogen-nitrogen mixed gas, belonging to the field of hydrogen energy technology. Background Art

[0002] CN109970029A discloses a pressure swing adsorption hydrogen purification process for high hydrogen-containing refinery gas with membrane separation enhancement. In this process, an organic vapor membrane separation unit is introduced into the pretreatment system of the pressure swing adsorption device to efficiently and deeply remove hydrocarbon heavy components with five or more carbon atoms, improve the regeneration conditions of the adsorbent, extend the service life of the adsorbent, and improve the long-term operation stability of the adsorption device; a hydrogen membrane separation unit is introduced into the post-treatment system to further recover low-concentration hydrogen in the organic vapor permeate gas and the pressure swing adsorption tail gas. By extending the service life of the adsorbent and increasing the hydrogen recovery rate, the pressure swing adsorption purification process for high hydrogen-containing refinery gas with membrane separation enhancement has a lower hydrogen separation and purification cost. This process is aimed at the separation and purification of refinery gas with a hydrogen content greater than 75v%, and adopts a combination of two-stage membrane separation and pressure swing adsorption. The raw material gas entering the pressure swing adsorption unit has undergone three-stage pressurization, and multiple cooling and gas-liquid separation are involved in the removal of hydrocarbons in the refinery gas. Although the total hydrogen recovery rate exceeds 95%, the process flow is complex and the energy consumption is high at the same time. Summary of the Invention

[0003] To solve the above technical problems, the object of the present invention is to provide a separation and purification process for a hydrogen-nitrogen mixed gas, which can obtain a high-purity hydrogen product and a high total recovery rate through the combination of pressure swing adsorption and membrane separation.

[0004] To achieve the above object, the present invention provides a separation and purification process for a hydrogen-nitrogen mixed gas, which includes the following steps:

[0005] Perform pressure swing adsorption on the hydrogen-nitrogen mixed gas to obtain a product gas and a desorbed gas, wherein the adsorbent for the pressure swing adsorption is 5A molecular sieve and / or 10X molecular sieve;

[0006] Perform membrane separation on the desorbed gas to obtain a retentate gas and a permeate gas, and the permeate gas is combined with the hydrogen-nitrogen mixed gas and then subjected to pressure swing adsorption treatment.

[0007] In the above separation and purification process, preferably, the main components of the hydrogen-nitrogen mixed gas are hydrogen and nitrogen, wherein the nitrogen content is 25v%, and the hydrogen content is 75v%. The volume ratio of hydrogen to nitrogen in the product gas decomposed from ammonia is fixed at 3:1.

[0008] In the above separation and purification process, preferably, the volume ratio of the 5A molecular sieve to the 10X molecular sieve is 1:1.

[0009] In the above separation and purification process, preferably, the pressure of the pressure swing adsorption is not greater than 2.5 MPa, more preferably 1.5 MPa - 2.0 MPa.

[0010] In the above separation and purification process, preferably, the temperature of the pressure swing adsorption is not higher than 40 °C, more preferably 25 °C - 35 °C.

[0011] In the above separation and purification process, preferably, the separation and purification process further includes: before the membrane separation of the desorbed gas, a step of pressurizing the desorbed gas. More preferably, the pressurization treatment is to pressurize to the operating pressure of the membrane separation.

[0012] In the above separation and purification process, preferably, the separation and purification process further includes: before the permeate gas is combined with the hydrogen-nitrogen mixed gas, a step of pressurizing the permeate gas. More preferably, the pressurization treatment is to pressurize to the adsorption pressure of the pressure swing adsorption treatment.

[0013] In the above separation and purification process, preferably, the adsorbent is a combination of 5A molecular sieve and 10X molecular sieve, and the volume ratio of the two is (0 - 1):(0 - 1), and neither of them is 0.

[0014] In the above separation and purification process, preferably, the separation membrane used in the membrane separation treatment is a polysulfone hollow fiber membrane.

[0015] In the above separation and purification process, preferably, the process conditions of the membrane separation treatment are as follows: the operating pressure is 2.0 - 2.5 MPa, and the operating temperature is 20 - 25 °C.

[0016] The present invention also provides a process system for the separation and purification process of the above hydrogen-nitrogen mixed gas, which includes: a pressure swing adsorption unit, a hydrogen membrane separation unit, a first compressor, and a second compressor;

[0017] Among them, the pressure swing adsorption unit is provided with a hydrogen-nitrogen mixed gas inlet, a product gas outlet, and a desorbed gas outlet;

[0018] The hydrogen membrane separation unit is provided with a desorbed gas inlet, a permeate gas outlet, and a retentate gas outlet;

[0019] The desorbed gas outlet is connected to the inlet of the first compressor, the outlet of the first compressor is connected to the desorbed gas inlet of the hydrogen membrane separation unit, the permeate gas outlet of the hydrogen membrane separation unit is connected to the inlet of the second compressor, and the outlet of the second compressor is connected to the hydrogen-nitrogen mixed gas inlet of the pressure swing adsorption unit.

[0020] According to the specific implementation of the present invention, the separation and purification process of the hydrogen-nitrogen mixed gas provided by the present invention may include the following specific steps:

[0021] The hydrogen-nitrogen mixed gas (hydrogen content of 75v%, nitrogen content of 25v%) directly enters the pressure swing adsorption unit as the raw gas (the adsorption pressure is not more than 2.5MPa, the adsorption temperature is not more than 40°C; the adsorption tower is filled with 5A and 10X molecular sieve adsorbents, and the volume ratio of the two is 1:1), and the product hydrogen and analytical gas that meet the requirements of GB / T 37244-2018 "Hydrogen Fuel for Proton Exchange Membrane Fuel Cell Vehicles" are obtained through separation and purification;

[0022] The analyzed gas obtained by pressure swing adsorption is pressurized by the first compressor (pressurized to the adsorption pressure of pressure swing adsorption) and then enters the hydrogen membrane separation unit; the retentate gas with a hydrogen content of less than 13v% is obtained on the high-pressure side of the membrane separation unit; the permeate gas with a hydrogen content of more than 90v% is obtained on the low-pressure side of the membrane separation unit; the permeate gas is pressurized by the second compressor (pressurized to the adsorption pressure of pressure swing adsorption) and then combined with the hydrogen-nitrogen mixed gas to serve as the feed gas of the pressure swing adsorption unit.

[0023] The calcium ion content in the framework of the 5A and 10X molecular sieves used in the present invention is greater than 75%; since the adsorbate nitrogen molecule contains a lone pair of electrons and has a relatively large quadrupole moment, the adsorption force between it and the calcium ion in the molecular sieve framework is relatively strong, and since the hydrogen molecule is an adsorbed inert molecule without a lone pair of electrons, the above two types of molecular sieves show good performance in adsorbing nitrogen molecules. At the same time, the pore sizes of the 5A molecular sieve and the 10X molecular sieve are about 0.4nm and about 0.9nm, respectively, which are both greater than the kinetic diameter of the nitrogen molecule, and the adsorption capacity of the 10X molecular sieve for nitrogen molecules is almost twice that of the 5A molecular sieve. Therefore, the 10X molecular sieve is set as the initial adsorption bed of the adsorption tower, which can greatly adsorb nitrogen in the high nitrogen content mixed gas, avoid penetration of the adsorption bed in a short time, and then assist with the 5A molecular sieve as the second adsorption bed to further adsorb to obtain high-purity hydrogen, while increasing the hydrogen yield as much as possible and reducing the overall cost of the adsorbent. The present invention obtains hydrogen with a purity of 99.97% by simultaneously loading 5A and 10X molecular sieve adsorbents in an adsorption tower of a pressure swing adsorption unit, thereby improving the hydrogen yield of the pressure swing adsorption unit; at the same time, since the separated gas is repeatedly circulated in a membrane separation unit and a pressure swing adsorption unit, a total hydrogen recovery rate of more than 95% is obtained.

[0024] Aiming at the problem of low recovery rate in the purification of hydrogen in ammonia decomposition product gas by the conventional pressure swing adsorption process, the present invention provides a combined process of membrane separation and pressure swing adsorption. The pressure swing adsorption unit filled with 5A and 10X type molecular sieve adsorbents is used to directly remove the high-content nitrogen in the hydrogen-nitrogen mixed gas, and the product hydrogen meeting the requirements of the standard of GB / T37244-2018 "Fuel Hydrogen for Proton Exchange Membrane Fuel Cell Vehicles" can be directly obtained. At the same time, the desorbed gas generated by pressure swing adsorption is subjected to membrane separation to further recover the hydrogen therein. The hydrogen content in the process tail gas is less than 13v%, and the total hydrogen recovery rate is greater than 95%.

[0025] The separation and purification process of hydrogen-nitrogen mixed gas provided by the present invention adopts the combination of primary membrane separation and pressure swing adsorption, does not involve the cooling and gas-liquid separation operations of hydrocarbons, and the existing process involves three pressurizations, multiple coolings and gas-liquid separations, while the combined process of the present invention only involves two pressurizations, the process flow is simple, and the energy consumption is relatively low.

[0026] The separation and purification process of hydrogen-nitrogen mixed gas provided by the present invention is specifically aimed at the purification of hydrogen in ammonia decomposition product gas, and adopts the combined process of hydrogen membrane separation and pressure swing adsorption. Compared with only using the conventional pressure swing adsorption purification process, the total hydrogen recovery rate is greatly increased from 78% to more than 95%. Brief Description of the Drawings

[0027] Figure 1 It is a process flow diagram of the separation and purification process of hydrogen-nitrogen mixed gas.

[0028] Main reference numeral description:

[0029] 1. Pressure swing adsorption unit; 2. Hydrogen membrane separation unit; 3. First compressor; 4. Second compressor; F0. Hydrogen-nitrogen mixed gas; F11. Product hydrogen; F12. Pressure swing adsorption desorbed gas; F21. Permeate gas; F22. Retentate gas. Detailed Embodiments

[0030] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the implementable scope of the present invention.

[0031] Embodiment

[0032] This embodiment provides a separation and purification process for hydrogen-nitrogen mixed gas in ammonia decomposition product gas with a hydrogen production scale of 400 Nm 3 / h, and its process flow diagram is as Figure 1 shown.

[0033] Table 1 shows the material composition and operating parameters in the embodiment.

[0034] Table 1 Material composition and operating parameters

[0035] Material Name F0 F11 F12 F21 F22 <![CDATA[Flow rate, Nm 3 / h]]> 558.8 400 257.3 98.5 158.7 Pressure, MPa 2.00 1.90 0.01 0.11 2.00 Temperature, °C 25.0 25.0 25.0 25.0 25.0 Composition, v% <![CDATA[H 2 > 75.0 99.97 43.8 95.0 12.1 <![CDATA[N 2 > 25.0 0 56.2 5.0 87.9

[0036] As Figure 1 shown, the hydrogen-nitrogen mixed gas F0 from the ammonia decomposition product gas, with a hydrogen content of 75 v%, and a nitrogen content of 25 v%, enters the pressure swing adsorption unit 1 as the feed gas. The pressure swing adsorption unit is provided with 6 identical adsorption towers arranged in parallel. Each adsorption tower is filled with an equal amount of 5A molecular sieve and 10X molecular sieve. The heights of the 5A molecular sieve and 10X molecular sieve adsorbent beds are both 3 m, and the bed diameter is 0.6 m. The product hydrogen F11 that meets the requirements of the GB / T 37244-2018 "Fuel Hydrogen for Proton Exchange Membrane Fuel Cell Vehicles" standard and the desorbed gas F12 are separated and purified. The hydrogen content of the desorbed gas F12 is 43.8 v%, and the purity of the product hydrogen F11 is above 99.97%;

[0037] The desorbed gas F12 obtained by pressure swing adsorption enters the hydrogen membrane separation unit 2 after being pressurized by the first compressor 3; the retentate gas F22 with a hydrogen content of 12.1 v% is obtained on the high-pressure side of the membrane separation unit 2; the permeate gas F21 with a hydrogen content of 95 v% is obtained on the low-pressure side of the membrane separation unit 2;

[0038] After the permeate gas F21 is pressurized by the second compressor 4, it is combined with the hydrogen-nitrogen mixed gas F0 and used as the feed gas of the pressure swing adsorption unit 1.

[0039] In this embodiment, after the desorbed gas of the pressure swing adsorption unit is concentrated by hydrogen membrane separation, the permeate gas is recycled into the pressure swing adsorption unit again. This combined process does not involve the cooling and gas-liquid separation of hydrocarbons, has a simple process flow, relatively low energy consumption, and the total hydrogen recovery rate of the process reaches 95.4%.

[0040] Comparative example

[0041] This comparative example provides a separation and purification process for the hydrogen-nitrogen mixed gas of the ammonia decomposition product gas with a hydrogen production scale of 400 Nm 3 / h, and the pressure swing adsorption is used to separate and purify the hydrogen-nitrogen mixed gas. Table 2 shows the material composition and operating parameters of the comparative example.

[0042] Table 2 Material composition and operating parameters

[0043] Material Name F0’ F11’ F12’ <![CDATA[Flow rate, Nm 3 / h]]> 683.8 400 283.8 Pressure, MPa 2.00 1.90 0.01 Temperature, °C 25.0 25.0 25.0 Composition, v% <![CDATA[H 2 > 75.0 99.97 39.8 <![CDATA[N 2 > 25.0 0 60.2

[0044] As shown in Table 2, the hydrogen-nitrogen mixed gas F0' from the ammonia decomposition product gas, with a hydrogen content of 75 v% and a nitrogen content of 25 v%, enters the pressure swing adsorption unit as the feed gas. The pressure swing adsorption unit is filled with 5A molecular sieve, and the height and diameter of the adsorbent bed are 6 m and 0.6 m respectively. The product hydrogen F11' meeting the requirements of the standard of "Hydrogen Fuel for Proton Exchange Membrane Fuel Cell Vehicles - GB / T 37244-2018" and the desorbed gas F12' are directly separated and purified. The yield of the product hydrogen is 78%, and the hydrogen content of the desorbed gas is 39.8 v%.

Claims

1. A process for separating and purifying a hydrogen-nitrogen mixed gas, which comprises the following steps: Performing pressure swing adsorption on the hydrogen-nitrogen mixed gas to obtain a product gas and a desorbed gas. Among them, the adsorbent for the pressure swing adsorption is 5A molecular sieve and / or 10X molecular sieve; Performing membrane separation on the desorbed gas to obtain a retentate gas and a permeate gas, and the permeate gas is combined with the hydrogen-nitrogen mixed gas and then subjected to pressure swing adsorption.

2. The separation and purification process according to claim 1, wherein, The main components of the hydrogen-nitrogen mixed gas are hydrogen and nitrogen, among which the nitrogen content is 25 v%, and the hydrogen content is 75 v%.

3. The separation and purification process according to claim 1, wherein, The pressure of the pressure swing adsorption is not greater than 2.5 MPa, preferably 1.5 MPa - 2.0 MPa.

4. The separation and purification process according to claim 1, wherein, The temperature of the pressure swing adsorption is not higher than 40 °C, preferably 25 °C - 35 °C.

5. The separation and purification process according to claim 1, wherein, This separation and purification process further includes: before performing membrane separation on the desorbed gas, a step of pressurizing the desorbed gas, preferably, the pressurization treatment is to pressurize to the operating pressure of the membrane separation.

6. The separation and purification process according to claim 1, wherein, This separation and purification process further includes: before combining the permeate gas with the hydrogen-nitrogen mixed gas, a step of pressurizing the permeate gas; preferably, the pressurization treatment is to pressurize to the adsorption pressure of the pressure swing adsorption treatment.

7. The separation and purification process according to claim 1, wherein, The adsorbent is a combination of 5A molecular sieve and 10X molecular sieve, and the volume ratio of the two is (0 - 1):(0 - 1), and neither of them is 0.

8. The separation and purification process according to claim 1, wherein, The separation membrane used for the membrane separation treatment is a polysulfone hollow fiber membrane.

9. The separation and purification process according to claim 1 or 8, wherein, The process conditions for the membrane separation treatment are as follows: the operating pressure is 2.0 - 2.5 MPa, and the operating temperature is 20 - 25 °C.

10. A process system for the separation and purification process of the hydrogen-nitrogen mixed gas according to any one of claims 1 - 9, which comprises: A pressure swing adsorption unit (1), a hydrogen membrane separation unit (2), a first compressor (3), a second compressor (4); Among them, the pressure swing adsorption unit (1) is provided with a hydrogen-nitrogen mixed gas inlet, a product gas outlet, and a desorbed gas outlet; The hydrogen membrane separation unit (1) is provided with a desorbed gas inlet, a permeate gas outlet, and a retentate gas outlet; The desorbed gas outlet is connected to the inlet of the first compressor (3), the outlet of the first compressor (3) is connected to the desorbed gas inlet of the hydrogen membrane separation unit (2), the permeate gas outlet of the hydrogen membrane separation unit (2) is connected to the inlet of the second compressor (4), and the outlet of the second compressor (4) is connected to the hydrogen-nitrogen mixed gas inlet of the pressure swing adsorption unit (1).

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