Staged purification system and staged purification process for hydrogen

Abstract

The application provides a hydrogen gas grading purification system and process, the grading purification system comprises a pressure swing adsorption unit and an electrochemical purification unit connected in sequence, and is used for sequentially performing pressure swing adsorption treatment and electrochemical purification treatment on hydrogen gas raw gas to remove CO2, CO, CH4 and N2 in the hydrogen gas raw gas, so as to obtain hydrogen gas product gas; wherein, the pressure swing adsorption unit is provided with an adsorbent; a feed line is arranged at the feed end of the pressure swing adsorption unit and is used for hydrogen gas raw gas feeding; a discharge line is arranged at the discharge end of the electrochemical purification unit and is used for outputting hydrogen gas product gas; the pressure swing adsorption unit is further provided with a first waste gas discharge line; and the electrochemical purification unit is further provided with a second waste gas discharge line. The grading purification system and process can couple the pressure swing adsorption technology and the electrochemical purification technology, realize purification of hydrogen gas, have high hydrogen gas recovery rate, low purification treatment energy consumption, and high hydrogen gas purity of the obtained hydrogen gas product gas.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of hydrogen production by ammonia decomposition and methanol to olefins, and particularly relates to a hydrogen gas grading purification system and a hydrogen gas grading purification process. BACKGROUND

[0002] Hydrogen fuel cells are chemical energy conversion devices that convert hydrogen gas chemical energy into electrical energy, and have the advantages of high efficiency and cleanliness, and have wide application prospects. The hydrogen gas used by hydrogen fuel cells has a wide range of sources, including coal gasification hydrogen production, industrial by-product hydrogen, methanol reforming, natural gas reforming, water electrolysis, and biomass hydrogen production, etc. Due to the strict requirements of hydrogen fuel cells, especially vehicle hydrogen fuel cells, on the quality of hydrogen gas, hydrogen gas produced by all methods needs to be purified in different ways to meet the fuel cell use standard, such as less than 100 ppm of nitrogen, less than 0.2 ppm of CO, and less than 2 ppm of CO2.

[0003] Pressure swing adsorption is a commonly used hydrogen purification technology in industry. Sulfides, NH3, CO2, etc. in hydrogen gas can be easily removed by pressure swing adsorption, but CO, N2, Ar, etc. in hydrogen gas are not easy to remove (thus affecting the hydrogen recovery rate of pressure swing adsorption), and He cannot be separated.

[0004] Therefore, the existing purification technology cannot purify hydrogen gas well, and the hydrogen recovery efficiency is low. SUMMARY

[0005] A first object of the present application is to provide a hydrogen gas grading purification system that couples pressure swing adsorption technology and electrochemical purification technology, and can purify hydrogen gas with high hydrogen recovery rate.

[0006] A second object of the present application is to provide a hydrogen gas grading purification process that couples pressure swing adsorption technology and electrochemical purification technology, and can purify hydrogen gas with high hydrogen recovery rate.

[0007] To achieve the first object of the present application, the following technical solution is adopted:

[0008] A hydrogen gas grading purification system, comprising a pressure swing adsorption unit and an electrochemical purification unit connected in sequence, for sequentially performing pressure swing adsorption treatment and electrochemical purification treatment on hydrogen raw gas to remove CO2, CO, CH4 and N2 therein, and obtaining hydrogen product gas; wherein the pressure swing adsorption unit is provided with an adsorbent for adsorbing and removing CO2, CO, part of CH4 and part of N2 in the hydrogen raw gas;

[0009] The feed end of the pressure swing adsorption unit is provided with a feed pipeline for hydrogen raw gas feed;

[0010] The discharge end of the electrochemical purification unit is provided with a discharge pipeline for outputting hydrogen product gas;

[0011] The pressure swing adsorption unit is further provided with a first waste gas discharge pipeline for discharging CO2, CO, CH4 and N2 removed by the pressure swing adsorption unit;

[0012] The electrochemical purification unit is further provided with a second waste gas discharge pipeline for discharging CH4 and N2 removed by the electrochemical purification unit.

[0013] Preferably, the discharge end of the electrochemical purification unit is further provided with a purge pipeline, the discharge end of which is connected to the feed end of the pressure swing adsorption unit for returning part of the hydrogen product gas to the pressure swing adsorption unit as purge gas for purging.

[0014] Preferably, the pressure swing adsorption unit comprises at least two pressure swing adsorption towers, and the at least two pressure swing adsorption towers are connected in series, and the adsorbent is arranged in the pressure swing adsorption towers.

[0015] Preferably, the electrochemical purification unit comprises a purification stack, an external power source is applied to the purification stack, and the discharge end of the purification stack is connected to the feed end of the pressure swing adsorption unit, and the residual CH4 and N2 in the purification stack are removed from the anode side of the purification stack, and the hydrogen product gas is obtained from the cathode side of the purification stack.

[0016] To achieve the second object of the present application, a process for the staged purification of hydrogen is also provided, which utilizes the above-mentioned staged purification system to purify hydrogen raw gas to obtain hydrogen product gas.

[0017] Preferably, the staged purification process comprises the following steps:

[0018] (1) hydrogen raw gas is input into the pressure swing adsorption unit through the feed pipeline for pressure swing adsorption treatment, to remove CO2, CO, part of CH4 and part of N2 therefrom, and the removed gas is discharged as first waste gas through the first waste gas discharge pipeline, to obtain intermediate gas containing CH4, N2 and H2;

[0019] (2) the intermediate gas obtained in step (1) is input into the electrochemical purification unit for electrochemical purification treatment, to remove residual CH4 and N2 therefrom, and the removed gas is discharged as second waste gas through the second waste gas discharge pipeline, and hydrogen product gas is obtained from the discharge pipeline.

[0020] Preferably, the staged purification process further comprises step (3), part of the hydrogen product gas obtained in step (2) is returned to the pressure swing adsorption unit as purge gas for purging through the purge pipeline.

[0021] Preferably, the amount of the sweep gas in step (3) accounts for 1-5 wt% of the hydrogen product gas obtained in step (2).

[0022] Preferably, the treatment conditions of the pressure swing adsorption treatment comprise:

[0023] The treatment temperature is 25-100℃, and the treatment pressure is 0.1-5 MPa;

[0024] Preferably, the treatment conditions of the pressure swing adsorption treatment further comprise that the adsorbent comprises a combination of any one or more of molecular sieve, activated carbon and activated alumina.

[0025] Preferably, the treatment conditions of the electrochemical purification treatment comprise:

[0026] The treatment temperature is 25-100℃, and the treatment pressure is 0.05-1 MPa;

[0027] Preferably, the treatment conditions of the electrochemical purification treatment further comprise humidification of the gas; preferably, the gas is humidified to a humidity of 30-100%.

[0028] The present application has the following beneficial effects:

[0029] The present application has the following beneficial effects: BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a structural schematic diagram of the present application in one embodiment of the hydrogen purification system;

[0031] Figure 2 is a structural schematic diagram of the present application in another embodiment of the hydrogen purification system. DETAILED DESCRIPTION

[0032] The technical solutions of the present application and their effects are further described below in combination with specific embodiments / examples. The following embodiments / examples are only used to illustrate the content of the present application, and the present application is not limited to the following embodiments or examples. Simple changes made by applying the concept of the present application are within the scope of the present application.

[0033] A hydrogen purification system, as shown in Figure 1As shown, comprising a pressure swing adsorption unit 1 and an electrochemical purification unit 2 connected in sequence, for sequentially performing pressure swing adsorption treatment and electrochemical purification treatment on the hydrogen raw gas to remove CO2, CO, CH4 and N2 therein, and obtaining hydrogen product gas; wherein the pressure swing adsorption unit 1 is provided with an adsorbent for adsorbing and removing CO2, CO, part of CH4 and part of N2 in the hydrogen raw gas;

[0034] The feed end of the pressure swing adsorption unit 1 is provided with a feed line 3 for hydrogen raw gas feed;

[0035] The discharge end of the electrochemical purification unit 2 is provided with a discharge line 4 for outputting hydrogen product gas;

[0036] The pressure swing adsorption unit 1 is further provided with a first waste gas discharge line 5 for discharging CO2, CO, CH4 and N2 removed by the pressure swing adsorption unit 1;

[0037] The electrochemical purification unit 2 is further provided with a second waste gas discharge line 6 for discharging CH4 and N2 removed by the electrochemical purification unit 2.

[0038] Those skilled in the art understand that the pressure swing adsorption technology (more suitable for removing polar molecular impurities) is an operating method that utilizes the characteristics of the equilibrium adsorption amount of the adsorbent increasing with the increase of the component partial pressure, and is a physical adsorption-desorption method that utilizes the van der Waals force between the gas and the adsorbent. During operation, the impurities in the raw gas are left in the adsorbent, and the hydrogen flows out. When the hydrogen raw gas is subjected to pressure swing adsorption treatment, although it is easy to remove sulfides, NH3, CO2 and other substances in the hydrogen, it is not easy to remove CO, N2, Ar and other substances therein (thus affecting the hydrogen recovery rate of pressure swing adsorption), and He cannot be separated.

[0039] Using a fuel cell-like structure for hydrogen purification is a new type of purification technology-electrochemical purification technology. The basic principle of electrochemical purification technology (more suitable for removing non-polar molecular impurities) is that an external power source is applied to the purification stack, and hydrogen raw gas (containing hydrogen and impurities) is introduced into the anode side of the purification stack, so that the hydrogen therein undergoes an electrochemical reaction (oxidation-reduction reaction), and is electrolyzed into hydrogen protons and electrons, and the impurities flow out from the anode side of the purification stack; the hydrogen protons are transmitted to the cathode side of the purification stack through the proton exchange membrane in the purification stack, and are reduced to hydrogen by the electrons conducted from the external circuit at the cathode side, thereby obtaining high-purity hydrogen product gas. The purification stack is composed of multiple anodes, cathodes and proton exchange membrane repeating units. The basic electrochemical reaction formula of electrochemical purification technology is as follows: anode: H2→ 2H + + 2e; cathode: 2H ++2e→H2. When purifying hydrogen gas by using this electrochemical purification technology, although it has the advantages of fast purification speed, simple equipment, high hydrogen purity and high hydrogen recovery rate, it also has the following disadvantages: consumes electricity, is particularly sensitive to sulfides, NH3 and other substances, but has little effect on inert gases such as N2, Ar and He.

[0040] However, by coupling the pressure swing adsorption technology and the electrochemical purification technology, the CO2, CO, part of CH4 and part of N2 in the hydrogen raw gas are removed and discharged first, and then the residual CH4 and N2 are removed and discharged, which can realize efficient removal of impurity gases in hydrogen and efficient purification of hydrogen, has high hydrogen recovery rate, high hydrogen purity of the obtained hydrogen product gas, low energy consumption, and thus reduces the cost of hydrogen purification.

[0041] In one embodiment, the discharge end of the electrochemical purification unit 2 is also provided with a purge pipeline 7, the discharge end of the purge pipeline 7 is connected to the pressure swing adsorption unit 1 and located at the feed end of the pressure swing adsorption unit 1, for returning part of the hydrogen product gas to the pressure swing adsorption unit 1 as purge gas for purging, so as to blow out the impurity gases CO2, CO, CH4 and N2 adsorbed in the adsorbent to regenerate the adsorbent, and the blown-out impurity gases CO2, CO, CH4 and N2 are discharged through the first waste gas discharge pipeline 5, thereby avoiding the saturation of the adsorbent during long-time operation and affecting the adsorption effect, so that the adsorbent can continue to function.

[0042] In one embodiment, as shown in Figure 2 The pressure swing adsorption unit 1 includes at least two pressure swing adsorption towers, and the at least two pressure swing adsorption towers are connected in series, and the adsorbent is arranged in the pressure swing adsorption towers.

[0043] In one embodiment, the electrochemical purification unit 2 includes a purification stack, the purification stack is applied with an external power supply, the discharge of the pressure swing adsorption unit 1 is introduced from the anode side of the purification stack, the residual CH4 and N2 in the discharge are removed from the anode side of the purification stack, and the hydrogen product gas is obtained from the cathode side of the purification stack.

[0044] The purification stack is a kind of fuel cell structure or battery tank structure. For example, the electrochemical purification stack (equivalent to the purification stack of the electrochemical purification unit 2 in the present application) described in the patent with the application number 202111223147.3. The specific reference is as follows:

[0045] The electrochemical purification stack includes:

[0046] at least one anode plate;

[0047] at least one cathode plate;

[0048] at least one anode electrode;

[0049] at least one cathode electrode;

[0050] at least one membrane located between the anode electrode and the cathode electrode;

[0051] at least one anode gas diffusion layer located between the anode plate and the anode electrode; and

[0052] at least one cathode gas diffusion layer located between the cathode plate and the cathode electrode;

[0053] wherein, the anode plate is provided with an inlet and an outlet, and the cathode plate is provided with an outlet.

[0054] According to the present application, the material of the anode plate can be graphite, stainless steel and titanium plate.

[0055] According to the present application, the thickness of the anode plate can be 0.1mm-10mm, preferably 0.1mm-2mm.

[0056] According to the present application, the material of the cathode plate can be graphite, stainless steel and titanium plate.

[0057] According to the present application, the thickness of the cathode plate can be 0.1mm-10mm, preferably 0.1mm-2mm.

[0058] In some embodiments of the present application, the anode plate is internally provided with a flow channel, and at least one boss is arranged in the flow channel.

[0059] In some embodiments of the present application, the gap between two adjacent bosses is 1 / 10-1 / 5 of the length of the boss in the direction of the gas flow.

[0060] According to the present application, the term "length" refers to the maximum length. For example, when the boss is configured as a hemisphere, the length refers to the diameter of the hemisphere; when the boss is configured as a trapezoid, the length refers to the length of the lower base.

[0061] In some embodiments of the present application, the height of the boss in the direction perpendicular to the gas flow is 95%-100% of the height of the ridge of the flow channel.

[0062] In some embodiments of the present application, the projection of the boss on the plane where the anode plate is located is circular and / or rectangular in shape.

[0063] According to the present application, the arrangement of the boss is conducive to the discharge of impurity gas.

[0064] According to the present application, the inside of the cathode plate is also provided with a flow channel.

[0065] In some embodiments of the present application, the thickness of the anode gas diffusion layer is 1 μm to 500 μm.

[0066] In some embodiments of the present application, the thickness of the anode gas diffusion layer is 10 μm to 250 μm.

[0067] In some embodiments of the present application, the thickness of the cathode gas diffusion layer is 1 μm to 300 μm.

[0068] In some embodiments of the present application, the thickness of the cathode gas diffusion layer is 10 μm to 100 μm.

[0069] In some embodiments of the present application, the anode gas diffusion layer and the cathode gas diffusion layer are the same or different, and each is independently selected from the group consisting of carbon cloth, carbon paper, and titanium mesh.

[0070] In some embodiments of the present application, the anode gas diffusion layer and the cathode gas diffusion layer are carbon paper.

[0071] According to the present application, any commercially available carbon cloth can be used as the anode gas diffusion layer and the cathode gas diffusion layer of the present application and obtain the same technical effect.

[0072] According to the present application, any commercially available carbon paper can be used as the anode gas diffusion layer and the cathode gas diffusion layer of the present application and obtain the same technical effect.

[0073] According to the present application, any commercially available titanium mesh can be used as the anode gas diffusion layer and the cathode gas diffusion layer of the present application and obtain the same technical effect.

[0074] In some embodiments of the present application, the anode electrode is selected from the group consisting of Pt alloy catalysts.

[0075] In some embodiments of the present application, the anode electrode is selected from the group consisting of Pt-Ru alloy catalysts.

[0076] In some embodiments of the present application, in the anode electrode, the content of Pt is 0.01 mg / cm 2 to 0.1 mg / cm 2 .

[0077] In some embodiments of the present application, the cathode electrode is selected from the group consisting of Pt catalysts and Pt-Pd alloy catalysts.

[0078] In some embodiments of the present application, in the cathode electrode, the content of Pt is 0.01 mg / cm 2 to 0.1 mg / cm 2 .

[0079] In some embodiments of the present application, the Pt content of the cathode electrode is lower than the Pt content of the anode electrode.

[0080] According to the present application, the membrane is a membrane capable of conducting hydrogen ions, and the thickness of the membrane is preferably 5mm to 20mm.

[0081] In some embodiments of the present application, the membrane is selected from the group consisting of polybenzimidazole membranes, perfluorosulfonic acid membranes, and aromatic hydrocarbon membranes.

[0082] According to the present application, any commercially available polybenzimidazole membrane can be used as the anode gas diffusion layer and the cathode gas diffusion layer of the present application and achieve the same technical effect.

[0083] According to the present application, any commercially available perfluorosulfonic acid membrane can be used as the anode gas diffusion layer and the cathode gas diffusion layer of the present application and achieve the same technical effect.

[0084] According to the present application, any commercially available aromatic hydrocarbon membrane can be used as the anode gas diffusion layer and the cathode gas diffusion layer of the present application and achieve the same technical effect.

[0085] In some embodiments of the present application, the membrane is a perfluorosulfonic acid membrane.

[0086] In some embodiments of the present application, the perfluorosulfonic acid membrane has a thickness of 5um to 30um, preferably 10um to 25um, for example 15um.

[0087] According to the present application, the perfluorosulfonic acid membrane needs to meet the condition of being able to operate below 100℃.

[0088] Those skilled in the art understand that in one embodiment, the structure of the electrochemical purification unit 2 refers to the electrochemical purification device (equivalent to the electrochemical purification unit 2 in the present application) described in the patent with application number 202111223147.3. The specific reference is as follows:

[0089] "An electrochemical purification device, comprising:

[0090] at least one anode end plate;

[0091] at least one cathode end plate;

[0092] at least one electrochemical purification stack as described in any one of the above embodiments between the anode end plate and the cathode end plate; and

[0093] a power supply connected to the anode end plate and the cathode end plate in the electrochemical purification stack, respectively.

[0094] According to the present application, the positive electrode of the power supply is connected to the anode end plate, and the negative electrode of the power supply is connected to the cathode end plate.

[0095] In some embodiments of the present application, the power supply is a direct current power supply.

[0096] In some embodiments of the present application, the power supply is a stable direct current power supply which can provide low voltage and large current.

[0097] According to the present application, the specific voltage and current to be adopted are related to the specification of the substance to be treated.

[0098] To achieve the second object, the present application further provides a process for the staged purification of hydrogen, which utilizes the aforementioned staged purification system to perform the staged purification of hydrogen raw gas, and obtain hydrogen product gas.

[0099] In one embodiment, the process for the staged purification of hydrogen comprises the following steps:

[0100] (1) hydrogen raw gas is input into the pressure swing adsorption unit 1 via the feed line 3 to perform pressure swing adsorption treatment, remove CO2, CO, part of CH4 and part of N2 therefrom, and discharge the removed gas as first waste gas via the first waste gas discharge line 5, and obtain intermediate gas containing CH4, N2 and H2;

[0101] (2) the intermediate gas obtained in step (1) is input into the electrochemical purification unit 2 to perform electrochemical purification treatment, remove residual CH4 and N2 therefrom, and discharge the removed gas as second waste gas via the second waste gas discharge line 6, and obtain hydrogen product gas from the discharge line 4.

[0102] In order to enable the pressure swing adsorption unit 1 to continuously operate, in one embodiment, the process for the staged purification of hydrogen further comprises step (3), part of the hydrogen product gas obtained in step (2) is returned to the pressure swing adsorption unit 1 as purge gas to purge the adsorbent, thereby blowing out the impurity gases CO2, CO, CH4 and N2 adsorbed in the adsorbent to regenerate the adsorbent, and the blown-out impurity gases CO2, CO, CH4 and N2 are discharged via the first waste gas discharge line 5, thereby avoiding the saturation of the adsorbent during long-time operation and affecting the adsorption effect, and enabling the adsorbent to continuously function.

[0103] In one embodiment, the amount of the purge gas in step (3) accounts for 1-5 wt% of the hydrogen product gas obtained in step (2), such as 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt% and 4.5 wt%.

[0104] In one embodiment, in step (1), the treatment conditions of the pressure swing adsorption treatment comprise:

[0105] The treatment temperature is 25-100°C, such as 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, and 95°C.

[0106] The treatment pressure is 0.1-5 MPa, such as 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, and 4.5 MPa.

[0107] The type of adsorbent can be selected depending on the type of impurity gas. In one embodiment, in step (1), the treatment conditions of the pressure swing adsorption treatment further comprise that the adsorbent comprises a combination of any one or more of molecular sieves, activated carbon, and activated alumina.

[0108] It is understood by those skilled in the art that the molecular sieves can be any one or more of the commonly used molecular sieves in the art, such as 3A, 4A, 5A, 13X, CaX, and LiX, in one embodiment, the molecular sieves are 5A and / or CaX.

[0109] It is understood by those skilled in the art that the activated carbon can be any one or more of the commonly used activated carbons in the art, such as coal-based activated carbon, pitch-based activated carbon, coconut shell-based activated carbon, and corn cob-based activated carbon, in one embodiment, the activated carbon is coconut shell-based activated carbon and / or pitch-based activated carbon.

[0110] It is understood by those skilled in the art that the activated alumina can be the commonly used activated alumina in the art, in one embodiment, the activated alumina is Y-type activated alumina.

[0111] In one embodiment, in step (2), the treatment conditions of the electrochemical purification treatment comprise:

[0112] The treatment temperature is 25-100°C, such as 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, and 95°C.

[0113] The treatment pressure is 0.05-1 MPa, such as 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, 0.55 MPa, 0.6 MPa, 0.65 MPa, 0.7 MPa, 0.75 MPa, 0.8 MPa, 0.85 MPa, 0.9 MPa, and 0.95 MPa.

[0114] In an embodiment, in step (2), the treatment conditions of the electrochemical purification treatment further comprise: humidifying the gas; preferably, the gas is humidified to a humidity of 30-100%, such as 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95%.

[0115] The skilled in the art understands that the humidity refers to the relative humidity of the gas.

[0116] The staged purification system for hydrogen and the staged purification process for hydrogen of the present application can couple the pressure swing adsorption technology and the electrochemical purification technology, so as to purify the hydrogen, and the hydrogen recovery rate is high, the purification treatment energy consumption is low, and the hydrogen purity of the obtained hydrogen product gas is high.

[0117] The present application is further illustrated by specific examples and comparative examples.

[0118] Example 1 (S1)

[0119] A staged purification system as shown in Figure 2 , comprising a pressure swing adsorption unit 1 and an electrochemical purification unit 2 connected in sequence, for sequentially performing pressure swing adsorption treatment and electrochemical purification treatment on hydrogen raw gas to remove CO2, CO, CH4, and N2 therefrom, and obtaining hydrogen product gas; wherein the pressure swing adsorption unit is provided with an adsorbent for adsorbing and removing CO2, CO, part of CH4, and part of N2 in the hydrogen raw gas;

[0120] The feed end of the pressure swing adsorption unit 1 is provided with a feed pipeline 3 for hydrogen raw gas feed;

[0121] The discharge end of the electrochemical purification unit 2 is provided with a discharge pipeline 4 for outputting hydrogen product gas;

[0122] The pressure swing adsorption unit 1 is further provided with a first waste gas discharge pipeline 5 for discharging CO2, CO, CH4, and N2 removed by the pressure swing adsorption unit;

[0123] The electrochemical purification unit 2 is further provided with a second waste gas discharge pipeline 6 for discharging CH4 and N2 removed by the electrochemical purification unit 2;

[0124] The discharge end of the electrochemical purification unit 2 is further provided with a purge pipeline 7, the discharge end of the purge pipeline 7 is connected to the feed end of the pressure swing adsorption unit 1, and the purge pipeline 7 is used for returning part of the hydrogen product gas to the pressure swing adsorption unit 1 as purge gas for purging;

[0125] The pressure swing adsorption unit 1 comprises 2 pressure swing adsorption towers 11, and at least 2 of the pressure swing adsorption towers 11 are connected in series, and the adsorbent is arranged in the pressure swing adsorption towers 11;

[0126] The electrochemical purification unit 2 comprises a purification stack, the purification stack is applied with an external power supply, and the discharge of the pressure swing adsorption unit 1 is introduced from the anode side of the purification stack, and the residual CH4 and N2 in the discharge are removed, and the hydrogen product gas is obtained from the cathode side of the purification stack.

[0127] A kind of for the hierarchical purification process of hydrogen, the hierarchical purification process of hydrogen raw gas using the hierarchical purification system of preceding is carried out hierarchical purification, comprising the following steps:

[0128] (1) hydrogen raw gas is input into the pressure swing adsorption unit 1 via feed line 3 and is subjected to pressure swing adsorption treatment, removes CO2, CO, part of CH4 and part of N2 therein, and removes the gas as first exhaust gas via first exhaust gas discharge line 5, obtains intermediate gas A1 containing CH4, N2 and H2;

[0129] (2) the intermediate gas obtained in step (1) is input into the electrochemical purification unit 2 and is subjected to electrochemical purification treatment, removes residual CH4 and N2 therein, and removes the gas as second exhaust gas via second exhaust gas discharge line 6, obtains hydrogen product gas B1 from discharge line 4;

[0130] (3) part of the hydrogen product gas obtained in step (2) is returned to the pressure swing adsorption unit 1 as its purge gas via purge line 7 for purging;Wherein,

[0131] The amount of the purge gas in step (3) accounts for 2.5wt% of the hydrogen product gas obtained in step (2);

[0132] The treatment conditions of the pressure swing adsorption treatment include:

[0133] The treatment temperature is 45℃, and the treatment pressure is 2.0MPa;The adsorbent is obtained by mixing activated carbon (Ningxia Guanghua Qisi activated carbon, PSA-2050) and 5A molecular sieve (HYD05C molecular sieve specially supplied by Hengye) in a volume ratio of 1:3;

[0134] The treatment conditions of the electrochemical purification treatment include:

[0135] The treatment temperature is 70℃, and the treatment pressure is 0.05MPa;The gas is humidified, and the gas is humidified to a humidity of 60%.

[0136] Example 2 (S2)

[0137] The difference from example 1 is only that:

[0138] The amount of the sweep gas in step (3) is 2.5wt% of the hydrogen product gas obtained in step (2);

[0139] The treatment conditions of the pressure swing adsorption treatment include:

[0140] The treatment temperature is 25℃, and the treatment pressure is 5MPa; the adsorbent is Y-type activated alumina (WHA-103 activated alumina, purity 95.6wt%);

[0141] The treatment conditions of the electrochemical purification treatment include:

[0142] The treatment temperature is 50℃, and the treatment pressure is 0.1MPa; the gas is humidified, and the humidity of the gas is 30%;

[0143] The intermediate gas A2 and the hydrogen product gas B2 are obtained.

[0144] Comparative Example 1 (D1)

[0145] The difference from Example 1 is only that:

[0146] The hydrogen raw gas is purified only by the pressure swing adsorption technology, and the hydrogen product gas B1’ is obtained.

[0147] Comparative Example 1 (D2)

[0148] The difference from Example 1 is only that:

[0149] The hydrogen raw gas is purified only by the electrochemical purification technology, and the hydrogen product gas B2’ is obtained.

[0150] In Example 1-2 (S1-2) and Comparative Example 1-2 (D1-2), the hydrogen raw gas, the intermediate gas, the hydrogen product gas, the related components in the hydrogen standard for vehicle fuel cell and the content thereof, the hydrogen recovery rate, the total hydrogen recovery rate and the energy consumption are shown in Table 1.

[0151]

[0152]

[0153] According to the comparison of Example 1-2 and Comparative Example 1-2 and the data in Table 1, by using Example 1-2, the impurity gas CO2 in the hydrogen gas source (i.e. the hydrogen raw gas) is reduced to 1.38×10 -11 ppm (equivalent to 1.38×10 -5 ppm), 1.25×10 -11% (equivalent to 1.25 x 10 -5 ppm), all reaching the hydrogen standard requirement for vehicle fuel cells (<2 ppm), and CO2 was effectively removed. Inert gases N2, CH4 and Ar were partially removed, and the contents of N2 and Ar did not reach the standard requirement. Subsequently, the hydrogen source was further purified by electrochemical purification, and the contents of impurity gases in the hydrogen source all reached the standard requirement. In this step, a certain amount of electric energy was consumed, and the equivalent electric energy consumed per kilogram of hydrogen was 0.964 degrees (Example 1) and 0.926 degrees (Example 2), respectively. After two-stage purification, the overall hydrogen recovery rates were 90.98% (Example 1) and 91.75% (Example 2), respectively.

[0154] According to the comparison between Example 1 and Comparative Example 1, compared with the purification of the hydrogen source by only using the pressure swing adsorption technology, the present application can improve the hydrogen recovery rate at a lower energy consumption by coupling the pressure swing adsorption technology and the electrochemical purification technology, and the improvement is more than 10%.

[0155] According to the comparison between Example 1 and Comparative Example 2, compared with the purification of the hydrogen source by only using the electrochemical purification technology in Comparative Example 2, the present application can effectively remove N2 and CO2 to meet the hydrogen standard requirement for vehicle fuel cells by coupling the pressure swing adsorption technology and the electrochemical purification technology, and although the overall hydrogen recovery rate is lower than that of Comparative Example 2, the energy consumption of the electrochemical purification technology can be greatly reduced (the energy consumption is reduced to 37.45% of that of Comparative Example 2). In summary, the present application is more economical.

Claims

1. A staged purification system for hydrogen, characterized in that, The graded purification system includes a pressure swing adsorption unit (1) and an electrochemical purification unit (2) connected in sequence, which are used to sequentially perform pressure swing adsorption treatment and electrochemical purification treatment on the hydrogen raw material gas to remove CO2, CO, CH4 and N2 therein, and obtain hydrogen product gas; wherein, the pressure swing adsorption unit (1) is provided with an adsorbent for adsorbing and removing CO2, CO, part of CH4 and part of N2 from the hydrogen raw material gas; The feed end of the pressure swing adsorption unit (1) is provided with a feed pipeline (3) for feeding hydrogen raw material gas; The electrochemical purification unit (2) is equipped with a discharge pipeline (4) at the discharge end for outputting hydrogen product gas; The pressure swing adsorption unit (1) is also provided with a first exhaust gas pipeline (5) for discharging CO2, CO, CH4 and N2 removed by the pressure swing adsorption unit (1); The electrochemical purification unit (2) is also equipped with a second waste gas emission pipeline (6) for discharging the CH4 and N2 removed by the electrochemical purification unit (2); wherein, The pressure swing adsorption (PSA) treatment conditions in the PSA unit (1) include: The processing temperature is 25~35 ℃ or 55~75 ℃, and the processing pressure is 3.5~5 MPa; The electrochemical purification unit (2) includes a purification stack, which is powered by an external power source and receives the output of the pressure swing adsorption unit (1) from its anode side, removes residual CH4 and N2 from its anode side, and obtains hydrogen product gas from its cathode side.

2. The graded purification system according to claim 1, characterized in that, The discharge end of the electrochemical purification unit (2) is also provided with a purge line (7). The discharge end of the purge line (7) is connected to the pressure swing adsorption unit (1) and is located at the feed end of the pressure swing adsorption unit (1). It is used to return part of the hydrogen product gas to the pressure swing adsorption unit (1) as its purge gas for purging.

3. The graded purification system according to claim 1 or 2, characterized in that, The pressure swing adsorption unit (1) includes at least two pressure swing adsorption towers, and the at least two pressure swing adsorption towers are connected in series, and the adsorbent is disposed in the pressure swing adsorption towers.

4. A staged purification process for hydrogen, characterized in that, Hydrogen feed gas is purified by using the staged purification system as described in any one of claims 1-3 to obtain hydrogen product gas.

5. The fractional purification process according to claim 4, characterized in that, Includes the following steps: Step (1): The hydrogen raw material gas is fed into the pressure swing adsorption unit (1) through the feed pipeline (3) for pressure swing adsorption treatment to remove CO2, CO, part of CH4 and part of N2, and the removed gas is discharged as the first waste gas through the first waste gas discharge pipeline (5) to obtain an intermediate gas containing CH4, N2 and H2. Step (2): The intermediate gas obtained in step (1) is input into the electrochemical purification unit (2) for electrochemical purification treatment to remove the residual CH4 and N2. The removed gas is discharged as the second waste gas through the second waste gas discharge pipeline (6) and hydrogen product gas is obtained from the discharge pipeline (4).

6. The fractional purification process according to claim 5, characterized in that, It also includes step (3), in which a portion of the hydrogen product gas obtained in step (2) is returned to the pressure swing adsorption unit (1) via the purge line (7) as its purge gas for purging.

7. The fractional purification process according to claim 6, characterized in that, The amount of purge gas in step (3) is 1 to 5 wt% of the hydrogen product gas obtained in step (2).

8. The fractional purification process according to any one of claims 5-7, characterized in that, The treatment conditions of the pressure swing adsorption process also include: the adsorbent includes any one or more combinations of molecular sieves, activated carbon and activated alumina.

9. The fractional purification process according to any one of claims 5-7, characterized in that, The processing conditions for the electrochemical purification treatment include: The processing temperature is 25~100 ℃, and the processing pressure is 0.05~1 MPa.

10. The fractional purification process according to claim 9, characterized in that, The electrochemical purification process also includes humidifying the gas.

11. The fractional purification process according to claim 10, characterized in that, The gas is humidified to a humidity of 30-100%.

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