A process for efficiently recovering hydrogen from waste gas

Abstract

The present invention discloses a process for efficiently recovering hydrogen from waste gas, which belongs to the field of hydrogen recovery technology and includes the following steps: 1. Raw gas pretreatment: including dust removal and dehydration treatment; 2. Primary compression and pressure swing adsorption pretreatment: The primary compressed nitrogen / hydrogen mixed gas enters PSA adsorption cylinder A or PSA adsorption cylinder B, and the PSA adsorption cylinder is filled with adsorbent for preliminary purification, and the hydrogen concentration is increased to more than 99.99%; 3. Secondary compression and cryogenic distillation: The secondary compressed hydrogen first enters the main heat exchanger and then enters the distillation tower, where the nitrogen is preferentially liquefied, and hydrogen with a purity of ≥99.999% is output from the top of the tower. The present invention optimizes the PSA adsorbent so that the hydrogen concentration can be increased to more than 99.99% after preliminary purification, and the hydrogen recovery rate can reach more than 90%, with high adsorption efficiency and high hydrogen recovery rate. Further combined with cryogenic distillation, the purified hydrogen meets the ultra-high purity requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen recovery, and in particular to a process for efficiently recovering hydrogen from waste gas. Background Art

[0002] With the global energy transition and the growing demand for clean energy, hydrogen has garnered widespread attention as an efficient and clean energy carrier. Hydrogen holds broad application prospects in a wide range of fields, including industrial production, energy storage, and transportation. However, hydrogen typically exists in low concentrations in various feed gases, such as natural gas, industrial by-product gases, and electrolyzed water. Therefore, efficient separation and purification of hydrogen has become a critical link in the hydrogen energy industry chain.

[0003] The separation of nitrogen (N2) and hydrogen (H2) plays an important role in the chemical, energy and electronics industries. The current mainstream technologies include:

[0004] Pressure swing adsorption (PSA): Hydrogen is purified by selectively adsorbing impurity gases (N2) with adsorbents. It has the advantages of simple equipment and low energy consumption, but the purity is usually limited to below 99.9%, and the hydrogen recovery rate is limited by the adsorbent regeneration efficiency.

[0005] Cryogenic distillation: It uses boiling point differences (N2: -196°C, H2: -253°C) to achieve high-purity separation and is suitable for large-scale production (such as liquid hydrogen production). However, it has high energy consumption and is sensitive to impurities.

[0006] The existing technology has the following technical problems:

[0007] Limitations of a single technology: PSA is difficult to meet ultra-high purity requirements (such as 99.999%), and energy consumption increases dramatically when cryogenic distillation alone processes high-impurity raw materials.

[0008] Complex gas systems are difficult to treat: Industrial waste gases (such as synthetic ammonia tail gas and refinery gas) often contain impurities such as CH4 and CO2. Traditional PSA adsorbents have low efficiency in multi-component competitive adsorption, resulting in low hydrogen purity and recovery rate. The adsorption performance of the adsorbent still needs to be further improved.

[0009] Based on this, the present invention designs a process for efficiently recovering hydrogen from waste gas to solve the above problems. Summary of the Invention

[0010] In view of the above-mentioned shortcomings of the prior art, the present invention provides a process for efficiently recovering hydrogen from waste gas.

[0011] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0012] A process for efficiently recovering hydrogen from waste gas comprises the following steps:

[0013] 1. Raw gas pretreatment: including dust removal and dehydration;

[0014] Second, primary compression and pressure swing adsorption pretreatment: The primary compressor pressurizes the nitrogen / hydrogen mixture; the nitrogen / hydrogen mixture enters PSA adsorption cylinder A or PSA adsorption cylinder B. PSA adsorption cylinders A and B operate alternately. The PSA adsorption cylinders are filled with adsorbent for preliminary purification, and the hydrogen concentration is increased to above 99.99%. PSA adsorption cylinders A and B then transport the preliminarily purified hydrogen to the secondary compressor;

[0015] 3. Secondary compression and cryogenic distillation: The initially purified hydrogen enters the secondary compressor for further pressurization. The secondary compressed hydrogen first enters the main heat exchanger, where it recovers cold energy with the reflux cryogenic liquefied gas. It then passes through an expander to cool it to -180°C~-200°C. The cooled hydrogen enters the distillation tower, where nitrogen is preferentially liquefied and the liquid nitrogen at the bottom of the tower is discharged from the bottom. After the cold energy is recovered, it becomes gaseous nitrogen for venting. Hydrogen with a purity of ≥99.999% is output from the top of the tower.

[0016] Furthermore, in step one, the nitrogen-hydrogen mixed raw gas passes through a particulate filter for dust removal, and the raw gas with particulate impurities removed continues to enter the dehydration adsorption cylinder for dehydration. After filtering out water and trace CO2, the outlet dew point drops to ≤-70°C, and impurities such as particulate matter and water are discharged, and the nitrogen / hydrogen mixed gas continues to enter the first-stage compressor.

[0017] Furthermore, in step 2, the first-stage compressor pressurizes the nitrogen / hydrogen mixed gas to 0.2-0.6 MPa.

[0018] Furthermore, in step 2, the initially pressurized nitrogen / hydrogen mixture is divided into two paths through the PSA adsorption tube A inlet valve and the PSA adsorption tube B inlet valve. The nitrogen / hydrogen mixture entering PSA adsorption tube A enters PSA adsorption tube A, or the nitrogen / hydrogen mixture entering PSA adsorption tube B enters PSA adsorption tube B.

[0019] Furthermore, PSA adsorption cylinder A and PSA adsorption cylinder B respectively transport the hydrogen preliminarily purified by PSA to the secondary compressor through the PSA adsorption cylinder A outlet valve and PSA adsorption cylinder B outlet valve installed on the top.

[0020] Furthermore, a PSA adsorption tube regeneration gas inlet valve is installed between the top of PSA adsorption tube A and PSA adsorption tube B; a PSA adsorption tube B regeneration gas outlet valve and a PSA adsorption tube A regeneration gas outlet valve are installed between the bottom of PSA adsorption tube A and PSA adsorption tube B, and the PSA adsorption tube regeneration gas exhaust gas is discharged through the PSA adsorption tube B regeneration gas outlet valve and the PSA adsorption tube A regeneration gas outlet valve.

[0021] Furthermore, when PSA adsorption cartridge A is adsorbing and PSA adsorption cartridge B is regenerating, the nitrogen / hydrogen mixture gas that has been initially pressurized by the first-stage compressor is passed through the PSA adsorption cartridge A through the open inlet valve and the closed inlet valve of the PSA adsorption cartridge B. The nitrogen / hydrogen mixture gas that has entered PSA adsorption cartridge A enters PSA adsorption cartridge A, and after the nitrogen is adsorbed by the internal adsorbent, 99.99% hydrogen gas is output from the top of PSA adsorption cartridge A. After the outlet valve of PSA adsorption cartridge A is opened and the outlet valve of PSA adsorption cartridge B is closed, the hydrogen gas that has been initially purified by PSA is finally output. At this time, PSA adsorption tube B is in the regeneration stage. The regeneration gas inlet valve of PSA adsorption tube is opened, leading a small flow of hydrogen out of PSA adsorption tube A. The regeneration gas inlet of PSA adsorption tube enters PSA adsorption tube B from the top, reducing the pressure in the tube and releasing nitrogen through analysis. The nitrogen / hydrogen mixed gas entering PSA adsorption tube B passes through the regeneration gas outlet valve of PSA adsorption tube B, the regeneration gas outlet valve of PSA adsorption tube B is opened, the regeneration gas outlet valve of PSA adsorption tube B is closed, and the regeneration gas exhaust gas of PSA adsorption tube A is closed, and the hydrogen-rich and nitrogen-rich PSA adsorption tube regeneration gas exhaust gas is discharged to the combustion system for venting.

[0022] Furthermore, the initially purified hydrogen enters a secondary compressor and is further pressurized to 1.5-2.0 MPa.

[0023] Furthermore, the secondary compressed hydrogen first enters the main heat exchanger, where it recovers cold energy with the reflux cryogenic liquefied gas. After initial cooling, preliminarily cooled hydrogen is obtained, which is then cooled to -180°C~-200°C by the expander. The re-cooled hydrogen enters the distillation tower through the hydrogen inlet valve. The temperature at different heights in the distillation tower is different. The distillation tower uses the boiling point difference between hydrogen and nitrogen to liquefy nitrogen first and flow to the bottom of the tower. The liquid nitrogen outlet valve at the bottom of the tower is opened to discharge the liquid nitrogen from the bottom. After recovering cold energy, it becomes gaseous nitrogen for venting. The hydrogen component is more difficult to liquefy than the nitrogen component and gathers at the top of the distillation tower. The hydrogen is separated in gaseous form and outputs high-purity hydrogen with a purity of ≥99.999% through the high-purity hydrogen outlet valve at the top of the tower. After heat exchange with the main heat exchanger, high-purity hydrogen at room temperature is produced.

[0024] Furthermore, the preparation method of the adsorbent is as follows:

[0025] Step 1, 2.2-3.8 parts of aluminum nitrate, 1.1-1.6 parts of calcium nitrate, 0.5-1 part of molybdenum nitrate, and 0.6-0.8 parts of zinc nitrate are added to 48-55 mL of deionized water, mixed evenly, and then 12.4-13.6 parts of L-malic acid are added to the mixed solution, stirred at 78-83 ° C for 1.5-2.5 hours, and then the pH is adjusted to 4.8-6. 100-110 parts of a magnesium acetate solution with a concentration of 0.2-0.3 mol / L is added to the mixed solution, and stirring is continued for 20-30 minutes to obtain a mixed gel;

[0026] Step 2: Grind and sieve the Chlorella biomass carbon through 100-200 mesh, then add it to the mixed gel at an addition amount of 1-1.5%, stir it at 38-43°C and 300-400 r / min for 20-30 minutes, then dry it at 120-140°C under nitrogen protection to constant weight, grind and sieve it through 100-150 mesh, and obtain intermediate A;

[0027] Step 3: Place intermediate A in a container, introduce water vapor at 100-105°C, treat intermediate A for 1-1.2 hours, then calcine intermediate A at 400-450°C, re-grind and sieve to 100-150 mesh to obtain intermediate B;

[0028] Step 4: Place intermediate B in a fixed bed, control the fixed bed temperature to 400-420°C, and introduce a mixture of carbon dioxide and nitrogen at a flow rate greater than 165 mL / min. Keep warm for 8-10 hours to obtain intermediate C;

[0029] Step 5: Disperse the intermediate C in water, add polyvinyl alcohol and lithium nitrate under high-speed stirring conditions of 1200-1500 r / min, and then dry and calcine at 550-575°C for 4-5 hours to obtain an adsorbent.

[0030] The present invention adopts PSA+cryogenic combined process, which has the following technical effects:

[0031] 1) Efficient coupling: PSA pretreatment reduces cryogenic load, while cryogenic distillation compensates for the upper limit of PSA purity, with an overall recovery rate of >85%.

[0032] 2) Flexibility: Applicable to mixed gases with nitrogen content of 10% to 50% (such as synthetic ammonia tail gas and coke oven gas).

[0033] 3) Low energy consumption: PSA reduces cryogenic processing capacity, and cryogenic high-pressure operation reduces refrigeration requirements.

[0034] 4) High purity: Double separation (adsorption + phase change) ensures hydrogen purity ≥5N.

[0035] The present invention optimizes the PSA adsorbent so that the hydrogen concentration can be increased to above 99.99% after preliminary purification, and the hydrogen recovery rate can reach above 90%. The adsorption efficiency is high and the hydrogen recovery rate is high. Further combined with deep cooling, the purified hydrogen can meet the ultra-high purity requirements (such as 99.999%). BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0037] Figure 1 The present invention is a flow chart of a process for efficiently recovering hydrogen from waste gas.

[0038] The numbers in the figure represent:

[0039] 1-particulate filter, 2-water removal adsorption cylinder, 3-first stage compressor, 4-PSA adsorption cylinder A, 5-PSA adsorption cylinder B, 6-second stage compressor, 7-main heat exchanger, 8-expander, 9-distillation tower;

[0040] a-nitrogen-hydrogen mixed feed gas, b-feed gas from which particulate impurities have been removed, c-nitrogen / hydrogen mixed gas, d-impurities such as particulate matter and water, e-initial pressurized nitrogen / hydrogen mixed gas, f-nitrogen / hydrogen mixed gas entering PSA adsorption tube A, g-nitrogen / hydrogen mixed gas entering PSA adsorption tube B, h-hydrogen exiting PSA adsorption tube A, i-hydrogen exiting PSA adsorption tube B, j-PSA adsorption tube regeneration gas inlet (99.99% hydrogen), k-PSA adsorption tube regeneration gas exhaust, l-PSA initially purified hydrogen, m-secondary compressed hydrogen, n-initial cooled hydrogen, o-recooled hydrogen, p-liquid nitrogen at the bottom of the tower, q-gas nitrogen, r-high-purity hydrogen at the top of the tower, s-high-purity hydrogen at room temperature;

[0041] V1-PSA adsorption tube A inlet valve, V2-PSA adsorption tube B inlet valve, V3-PSA adsorption tube A outlet valve, V4-PSA adsorption tube B outlet valve, V5-PSA adsorption tube regeneration gas inlet valve, V6-PSA adsorption tube A regeneration gas outlet valve, V7-PSA adsorption tube B regeneration gas outlet valve, V8-hydrogen inlet valve for distillation tower, V9-liquid nitrogen outlet valve at the bottom of the tower, V10-high-purity hydrogen outlet valve at the top of the tower. DETAILED DESCRIPTION

[0042] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0043] Example 1: Please refer to the accompanying drawings of the specification Figure 1 , a process for efficiently recovering hydrogen from exhaust gas, comprising the following steps:

[0044] 1. Raw gas pretreatment;

[0045] The nitrogen-hydrogen mixed raw gas a passes through the particulate filter 1 for dust removal. The raw gas b with particulate impurities removed continues to enter the dehydration adsorption cylinder 2 for dehydration. After filtering out water and trace CO2, the outlet dew point drops to ≤-70°C, and impurities such as particulate matter and water d are discharged. The nitrogen / hydrogen mixed gas c continues to enter the first-stage compressor 3;

[0046] 2. Primary compression and pressure swing adsorption (PSA) pretreatment;

[0047] The first-stage compressor 3 pressurizes the nitrogen / hydrogen mixture c to the pressure required by PSA (0.2-0.6MPa); the initially pressurized nitrogen / hydrogen mixture e is divided into two paths through the PSA adsorption tube A inlet valve V1 and the PSA adsorption tube B inlet valve V2. The nitrogen / hydrogen mixture f entering the PSA adsorption tube A enters the PSA adsorption tube A4, or the nitrogen / hydrogen mixture g entering the PSA adsorption tube B enters the PSA adsorption tube B5. The two towers operate alternately. In the PSA adsorption tube, the selective adsorption characteristics of the adsorbent for gas components are utilized to adsorb impurities under high pressure. The hydrogen penetrates the adsorption bed layer to achieve initial purification, and the hydrogen concentration is increased to above 99.99%. PS The A adsorption cylinder A4 and the PSA adsorption cylinder B5 respectively deliver the hydrogen l preliminarily purified by the PSA to the secondary compressor 6 through the PSA adsorption cylinder A outlet valve V3 and the PSA adsorption cylinder B outlet valve V4 installed on the top; a PSA adsorption cylinder regeneration gas inlet valve V5 is also installed between the tops of the PSA adsorption cylinder A4 and the PSA adsorption cylinder B5; a PSA adsorption cylinder B regeneration gas outlet valve V7 and a PSA adsorption cylinder A regeneration gas outlet valve V6 are also installed between the bottoms of the PSA adsorption cylinder A4 and the PSA adsorption cylinder B5, and the PSA adsorption cylinder regeneration gas waste gas k is discharged through the PSA adsorption cylinder B regeneration gas outlet valve V7 and the PSA adsorption cylinder A regeneration gas outlet valve V6;

[0048] The double tower adsorption valve position process is as follows: Take the adsorption of PSA adsorption tube A4 and the regeneration of PSA adsorption tube B5 as an example. The nitrogen / hydrogen mixed gas e that is initially pressurized by the first-stage compressor 3 is opened through the inlet valve V1 of PSA adsorption tube A (the inlet valve V2 of PSA adsorption tube B is closed). The nitrogen / hydrogen mixed gas f entering PSA adsorption tube A enters PSA adsorption tube A4. After the nitrogen is adsorbed by the internal adsorbent, 99.99% of hydrogen h is produced at the top and exits PSA adsorption tube A. After the outlet valve V3 of PSA adsorption tube A is opened (the outlet valve V4 of PSA adsorption tube B is closed), the hydrogen l that is initially purified by PSA is finally produced. At this time, PSA adsorption tube B5 is in During the regeneration stage, the PSA adsorption tube regeneration gas inlet valve V5 is opened, leading a small flow of hydrogen h out of the PSA adsorption tube A. The PSA adsorption tube regeneration gas inlet j enters the PSA adsorption tube B5 from the top, reducing the pressure in the tube and releasing the nitrogen by decomposition. The nitrogen / hydrogen mixed gas g entering the PSA adsorption tube B is discharged through the PSA adsorption tube B regeneration gas outlet valve V7, which is opened (PSA adsorption tube B regeneration gas inlet valve V2 is closed, and PSA adsorption tube A regeneration gas outlet valve V6 is closed) to discharge the hydrogen-rich and nitrogen-rich PSA adsorption tube regeneration gas waste gas k to the combustion system for venting.

[0049] 3. Two-stage compression and cryogenic distillation;

[0050] The hydrogen l initially purified by PSA enters the secondary compressor 6 and is further pressurized to the pressure required for deep cooling (1.5-2.0MPa). The secondary compressed hydrogen m first enters the main heat exchanger 7, where it recovers cold energy with the refluxed low-temperature liquefied gas. After initial cooling, the initially cooled hydrogen n is obtained. The hydrogen n is then cooled to -180℃~-200℃ by the expander 8. The cooled hydrogen o enters the distillation tower 9 through the hydrogen inlet valve V8. The temperature at different heights in the distillation tower 9 is different. Taking advantage of the boiling point difference between hydrogen (boiling point -253°C) and nitrogen (boiling point -196°C), nitrogen is preferentially liquefied and flows to the bottom of the tower. The liquid nitrogen outlet valve V9 at the bottom of the tower is opened to discharge the liquid nitrogen p from the bottom of the tower. After recovering the cold energy, it becomes gaseous nitrogen q for venting. The hydrogen component is more difficult to liquefy than the nitrogen component and gathers at the top of the distillation tower. The hydrogen is separated in gaseous form and passes through the high-purity hydrogen outlet valve V10 at the top of the tower to produce high-purity hydrogen r (purity ≥99.999%) at the top of the tower. After heat exchange with the main heat exchanger 7, it produces high-purity hydrogen s at room temperature.

[0051] Table 1 Comparison of hydrogen purity, nitrogen removal rate and energy consumption of different recovery processes

[0052]

[0053] The present invention adopts PSA+cryogenic combined process, which has the following technical effects:

[0054] 1) Efficient coupling: PSA pretreatment reduces cryogenic load, while cryogenic distillation compensates for the upper limit of PSA purity, with an overall recovery rate of >85%.

[0055] 2) Flexibility: Applicable to mixed gases with nitrogen content of 10% to 50% (such as synthetic ammonia tail gas and coke oven gas).

[0056] 3) Low energy consumption: PSA reduces cryogenic processing capacity, and cryogenic high-pressure operation reduces refrigeration requirements.

[0057] 4) High purity: Double separation (adsorption + phase change) ensures hydrogen purity ≥5N.

[0058] Example 2: This example discloses an adsorbent for filling inside PSA adsorption cylinder A4 and PSA adsorption cylinder B5 to adsorb gases such as nitrogen;

[0059] The preparation method of the adsorbent is as follows:

[0060] Step 1: Add 2.2 g of aluminum nitrate, 1.1 g of calcium nitrate, 0.5 g of molybdenum nitrate, and 0.6 g of zinc nitrate to 48 mL of deionized water, mix well, add 12.4 g of L-malic acid to the mixed solution, stir at 78 ° C for 2.5 h, then adjust the pH to 6, add 100 g of magnesium acetate solution (concentration of 0.2 mol / L) to the mixed solution, and continue stirring for 20 min to obtain a mixed gel;

[0061] Step 2: Grind and sieve the Chlorella biomass carbon through 100 mesh, then add it to the mixed gel at a rate of 1%, stir it at 38°C and 300 rpm for 20 minutes, then dry it at 120°C under nitrogen protection to a constant weight, grind and sieve it through 100 mesh, and obtain intermediate A;

[0062] Step 3: Place intermediate A in a container, introduce 100°C steam, treat intermediate A for 1.2 hours, then calcine intermediate A at 400°C, re-grind and sieve to 100 mesh to obtain intermediate B;

[0063] Step 4: Place intermediate B in a fixed bed, control the fixed bed temperature to 400°C, and introduce a mixture of carbon dioxide and nitrogen (carbon dioxide: nitrogen = 3:2) at a flow rate of 168 mL / min. Maintain the temperature for 8 h to obtain intermediate C.

[0064] Step 5: Disperse the intermediate C in water, add polyvinyl alcohol and lithium nitrate under high-speed stirring conditions of 1200 r / min, and then dry and calcine at 550° C. for 5 h to obtain an adsorbent.

[0065] Example 3: This example discloses an adsorbent for filling inside PSA adsorption cylinder A4 and PSA adsorption cylinder B5 to adsorb gases such as nitrogen;

[0066] The preparation method of the adsorbent is as follows:

[0067] Step 1: 3.8 g of aluminum nitrate, 1.6 g of calcium nitrate, 1 g of molybdenum nitrate, and 0.8 g of zinc nitrate were added to 55 mL of deionized water and mixed evenly. 13.6 g of L-malic acid was added to the mixed solution, and the mixture was stirred at 83 ° C for 1.5 h. After that, the pH was adjusted to 4.8. 110 g of magnesium acetate solution (concentration of 0.3 mol / L) was added to the mixed solution, and stirring was continued for 30 min to obtain a mixed gel;

[0068] Step 2: Grind and sieve the Chlorella biomass carbon through 200 mesh, then add it to the mixed gel at a rate of 1.5%, stir at 43°C and 400 rpm for 30 minutes, then dry at 140°C under nitrogen protection to constant weight, grind and sieve through 150 mesh, and obtain intermediate A;

[0069] Step 3: Place intermediate A in a container, introduce 105°C steam, treat intermediate A for 1 hour, then calcine intermediate A at 450°C, re-grind and sieve to 150 mesh to obtain intermediate B;

[0070] Step 4: Place intermediate B in a fixed bed, control the fixed bed temperature to 420°C, and introduce a mixture of carbon dioxide and nitrogen (carbon dioxide: nitrogen = 3:2) at a flow rate of 170 mL / min. Keep warm for 10 hours to obtain intermediate C.

[0071] Step 5: Disperse the intermediate C in water, add polyvinyl alcohol and lithium nitrate under high-speed stirring conditions of 1500 r / min, and then dry and calcine at 575° C. for 4 hours to obtain an adsorbent.

[0072] Example 4: This example discloses an adsorbent for filling inside PSA adsorption cylinder A4 and PSA adsorption cylinder B5 to adsorb gases such as nitrogen;

[0073] The preparation method of the adsorbent is as follows:

[0074] Step 1: 2.8 g of aluminum nitrate, 1.5 g of calcium nitrate, 0.7 g of molybdenum nitrate, and 0.7 g of zinc nitrate were added to 52 mL of deionized water and mixed evenly. 13.1 g of L-malic acid was added to the mixed solution, and the mixture was stirred at 80 ° C for 2 h. After that, the pH was adjusted to 5.8. 108 g of magnesium acetate solution (concentration of 0.25 mol / L) was added to the mixed solution, and stirring was continued for 27 min to obtain a mixed gel;

[0075] Step 2: Grind and sieve the Chlorella biomass carbon through a 150-mesh sieve, then add it to the mixed gel at a rate of 1.4%, stir at 41°C and 350 rpm for 23 minutes, then dry at 130°C under nitrogen protection to a constant weight, grind and sieve through a 120-mesh sieve, and obtain intermediate A;

[0076] Step 3: Place intermediate A in a container, introduce 103°C steam, treat intermediate A for 1.1 hours, then calcine intermediate A at 430°C, re-grind and sieve to 130 mesh to obtain intermediate B;

[0077] Step 4: Place intermediate B in a fixed bed, control the fixed bed temperature to 410°C, and introduce a mixture of carbon dioxide and nitrogen (carbon dioxide: nitrogen = 3:2) at a flow rate of 166 mL / min. Maintain the temperature for 9 h to obtain intermediate C.

[0078] Step 5: Disperse the intermediate C in water, add polyvinyl alcohol and lithium nitrate under high-speed stirring conditions of 1400 r / min, and then dry and calcine at 565° C. for 4.2 h to obtain an adsorbent.

[0079] Comparative Example 1: The difference from Example 3 is that step 3 is missing.

[0080] Comparative Example 2: The difference from Example 3 is that step 4 is performed first and then step 3.

[0081] Comparative Example 3: Different from Example 3, in step 1, 2 g of aluminum nitrate, 2 g of calcium nitrate, 0.7 g of molybdenum nitrate, and 1 g of zinc nitrate were added to 52 mL of deionized water and mixed evenly. Then, 20 g of L-malic acid was added to the mixed solution, and the mixture was stirred at 80 ° C. for 2 h. After that, the pH was adjusted to 5.8, and 108 g of magnesium acetate solution (concentration of 0.25 mol / L) was added to the mixed solution. Stirring was continued for 27 min to obtain a mixed gel.

[0082] Experimental Example: The adsorbents prepared in Examples 2-4 and Comparative Examples 1-3 were tested for their performance on synthetic ammonia tail gas (containing 40% hydrogen, 28% nitrogen, 7% ammonia, and 25% methane). The results are shown in Table 1.

[0083] Table 1 Hydrogen recovery performance test results

[0084]

[0085] The present invention optimizes the PSA adsorbent so that the hydrogen concentration can be increased to above 99.99% after preliminary purification, and the hydrogen recovery rate can reach above 90%. The adsorption efficiency is high and the hydrogen recovery rate is high. Further combined with deep cooling, the purified hydrogen can meet the ultra-high purity requirements (such as 99.999%).

[0086] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A process for efficiently recovering hydrogen from waste gas, characterized in that: The following steps are involved:

1. Raw gas pretreatment: including dust removal and dehydration; 2. Primary compression and pressure swing adsorption pretreatment: The primary compressor (3) pressurizes the nitrogen / hydrogen mixed gas (c); the nitrogen / hydrogen mixed gas (c) enters the PSA adsorption cylinder A (4) or enters the PSA adsorption cylinder B (5), and the PSA adsorption cylinder A (4) and the PSA adsorption cylinder B (5) operate alternately. The PSA adsorption cylinder is filled with adsorbent for preliminary purification, and the hydrogen concentration is increased to more than 99.99%. The PSA adsorption cylinder A (4) and the PSA adsorption cylinder B (5) transport the preliminarily purified hydrogen to the secondary compressor (6); 3. Secondary compression and cryogenic distillation: The initially purified hydrogen enters the secondary compressor (6) and is further pressurized to 1.5-2.0 MPa. The secondary compressed hydrogen (m) first enters the main heat exchanger (7) and recovers cold energy with the refluxed low-temperature liquefied gas. After the initial cooling, the initially cooled hydrogen (n) is obtained. The hydrogen is then cooled to -180℃~-200℃ by the expander (8). The cooled hydrogen (o) enters the distillation tower (9) through the hydrogen inlet valve (V8). Different temperatures are set in the distillation tower (9). The height and temperature are different. The distillation tower (9) uses the boiling point difference between hydrogen and nitrogen to liquefy nitrogen first and flow to the bottom of the tower. The bottom liquid nitrogen outlet valve (V9) is opened to discharge the bottom liquid nitrogen (p) from the bottom. After the cooling capacity is recovered, it becomes gaseous nitrogen (q) for venting. The hydrogen component is more difficult to liquefy than the nitrogen component and gathers at the top of the distillation tower. The hydrogen is separated in gaseous form and is output through the top high-purity hydrogen outlet valve (V10) of the tower to produce the top high-purity hydrogen (r) with a purity of ≥99.999%. After heat exchange with the main heat exchanger (7), it produces high-purity hydrogen (s) at room temperature. A PSA adsorption tube regeneration gas inlet valve (V5) is also installed between the tops of the PSA adsorption tube A (4) and the PSA adsorption tube B (5); a PSA adsorption tube B regeneration gas outlet valve (V7) and a PSA adsorption tube A regeneration gas outlet valve (V6) are also installed between the bottoms of the PSA adsorption tube A (4) and the PSA adsorption tube B (5), and the PSA adsorption tube regeneration gas waste gas (k) is discharged through the PSA adsorption tube B regeneration gas outlet valve (V7) and the PSA adsorption tube A regeneration gas outlet valve (V6).

2. The process for efficiently recovering hydrogen from waste gas according to claim 1, characterized in that: In step 1, the nitrogen-hydrogen mixed raw gas (a) passes through the particulate filter (1) for dust removal, and the raw gas (b) with particulate impurities removed continues to enter the dehydration adsorption cylinder (2) for dehydration. After filtering out water and trace CO2, the outlet dew point drops to ≤-70°C, and the particulate matter and water impurities (d) are discharged. The nitrogen / hydrogen mixed gas (c) continues to enter the first-stage compressor (3).

3. The process for efficiently recovering hydrogen from waste gas according to claim 2, characterized in that: In step 2, the first-stage compressor (3) pressurizes the nitrogen / hydrogen mixed gas (c) to 0.2-0.6 MPa.

4. The process for efficiently recovering hydrogen from waste gas according to claim 3, characterized in that: In step 2, the initially pressurized nitrogen / hydrogen mixture (e) is divided into two paths through the PSA adsorption tube A inlet valve (V1) and the PSA adsorption tube B inlet valve (V2). The nitrogen / hydrogen mixture (f) entering the PSA adsorption tube A enters the PSA adsorption tube A (4), or the nitrogen / hydrogen mixture (g) entering the PSA adsorption tube B enters the PSA adsorption tube B (5).

5. The process for efficiently recovering hydrogen from waste gas according to claim 4, characterized in that: PSA adsorption cylinder A (4) and PSA adsorption cylinder B (5) respectively transport the hydrogen (l) initially purified by PSA to the secondary compressor (6) through the PSA adsorption cylinder A outlet valve (V3) and PSA adsorption cylinder B outlet valve (V4) installed on the top.

6. The process for efficiently recovering hydrogen from waste gas according to claim 5, characterized in that: When the PSA adsorption tube A (4) is adsorbing and the PSA adsorption tube B (5) is regenerating, the nitrogen / hydrogen mixed gas (e) that is initially pressurized after being pressurized by the first-stage compressor (3) passes through the PSA adsorption tube A inlet valve (V1) which is opened and the PSA adsorption tube B inlet valve (V2) which is closed. The nitrogen / hydrogen mixed gas (f) that enters the PSA adsorption tube A enters the PSA adsorption tube A (4). After the nitrogen is adsorbed by the internal adsorbent, 99.99% of hydrogen (h) is produced at the top and exits the PSA adsorption tube A. The gas outlet valve (V3) of the PSA adsorption tube A is opened and the gas outlet valve (V4) of the PSA adsorption tube B is closed, and finally the hydrogen (l) that is initially purified by the PSA is produced. At this time, the PSA adsorption tube B (5) is in the regeneration stage. The PSA adsorption tube regeneration gas inlet valve (V5) is opened, leading a small flow of hydrogen (h) out of the PSA adsorption tube A. The PSA adsorption tube regeneration gas inlet (j) enters the PSA adsorption tube B (5) from the top, reducing the pressure in the tube and releasing the nitrogen. The nitrogen / hydrogen mixed gas (g) entering the PSA adsorption tube B passes through the PSA adsorption tube B regeneration gas outlet valve (V7) opened, the PSA adsorption tube B regeneration gas inlet valve (V2) closed, the PSA adsorption tube A regeneration gas outlet valve (V6) closed, and the hydrogen-rich nitrogen PSA adsorption tube regeneration gas waste gas (k) is discharged to the combustion system for venting.

7. The process for efficiently recovering hydrogen from waste gas according to claim 6, characterized in that: The preparation method of the adsorbent is as follows: Step 1, 2.2-3.8 parts of aluminum nitrate, 1.1-1.6 parts of calcium nitrate, 0.5-1 part of molybdenum nitrate, and 0.6-0.8 parts of zinc nitrate are added to 48-55 mL of deionized water, mixed evenly, and then 12.4-13.6 parts of L-malic acid are added to the mixed solution, stirred at 78-83 ° C for 1.5-2.5 hours, and then the pH is adjusted to 4.8-6. 100-110 parts of a magnesium acetate solution with a concentration of 0.2-0.3 mol / L is added to the mixed solution, and stirring is continued for 20-30 minutes to obtain a mixed gel; Step 2: Grind and sieve the Chlorella biomass carbon through 100-200 mesh, then add it to the mixed gel at an addition amount of 1-1.5%, stir it at 38-43°C and 300-400 r / min for 20-30 minutes, then dry it at 120-140°C under nitrogen protection to constant weight, grind and sieve it through 100-150 mesh, and obtain intermediate A; Step 3: Place intermediate A in a container, introduce water vapor at 100-105°C, treat intermediate A for 1-1.2 hours, then calcine intermediate A at 400-450°C, re-grind and sieve to 100-150 mesh to obtain intermediate B; Step 4: Place intermediate B in a fixed bed, control the fixed bed temperature to 400-420°C, and introduce a mixture of carbon dioxide and nitrogen at a flow rate greater than 165 mL / min. Keep warm for 8-10 hours to obtain intermediate C; Step 5: Disperse the intermediate C in water, add polyvinyl alcohol and lithium nitrate under high-speed stirring conditions of 1200-1500 r / min, and then dry and calcine at 550-575°C for 4-5 hours to obtain an adsorbent.

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