Process for efficiently recovering hydrogen from waste gas

Abstract

The invention discloses a process for efficiently recovering hydrogen from waste gas, which belongs to the technical field of hydrogen recovery, and comprises the following steps: 1, pretreatment of raw material gas, including dust removal and dehydration treatment; 2, primary compression and pressure swing adsorption pretreatment: nitrogen / hydrogen mixed gas subjected to primary compression enters a PSA adsorption barrel A or a PSA adsorption barrel B, the PSA adsorption barrels are filled with an adsorbent for primary purification, and the hydrogen concentration is increased to 99.99% or above; and 3, secondary compression and cryogenic distillation: hydrogen subjected to secondary compression firstly enters a main heat exchanger and then enters a rectifying tower, nitrogen is liquefied preferentially in the rectifying tower, and hydrogen with the purity being greater than or equal to 99.999% is output from the tower top. By optimizing the PSA adsorbent, the hydrogen concentration after preliminary purification can be increased to 99.99% or above, the hydrogen recovery rate can reach 90% or above, the adsorption efficiency is high, the hydrogen recovery rate is high, and the purified hydrogen meets the ultra-high purity requirement by further combining with deep cooling.

Description

Technical Field

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

[0002] With the transformation of the global energy structure and the growing demand for clean energy, hydrogen, as an efficient and clean energy carrier, has received extensive attention. Hydrogen has broad application prospects in many fields such as industrial production, energy storage, and transportation. However, hydrogen usually exists in various raw gas in a low concentration form, such as natural gas, industrial by-product gas, electrolyzed water, etc. Therefore, the efficient separation and purification of hydrogen have become a key link in the hydrogen energy industry chain.

[0003] The separation of nitrogen (N2) and hydrogen (H2) is of great importance in the chemical, energy, and electronics industries. Existing mainstream technologies include: Pressure Swing Adsorption (PSA): Hydrogen purification is achieved by the selective adsorption of impurity gas (N2) by an adsorbent. 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 regeneration efficiency of the adsorbent.

[0004] Cryogenic distillation: High-purity separation is achieved by utilizing the boiling point difference (N2: -196 °C, H2: -253 °C), which is suitable for large-scale production (such as liquid hydrogen preparation), but it has high energy consumption and is sensitive to impurities.

[0005] The existing technologies have the following technical problems: Limitations of single technology: PSA is difficult to meet the demand for ultra-high purity (such as 99.999%), and the energy consumption increases sharply when cryogenic distillation is used to separately treat raw materials with high impurities.

[0006] High difficulty in treating complex gas systems: Industrial waste gas (such as synthetic ammonia tail gas, refinery gas) often contains impurities such as CH4 and CO2. The traditional PSA adsorbent has low efficiency in competitive adsorption of multi-components, resulting in low hydrogen purity and recovery rate. The adsorption performance of the adsorbent still needs to be further improved.

[0007] 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

[0008] In view of the above-mentioned drawbacks of the existing technology, the present invention provides a process for efficiently recovering hydrogen from waste gas.

[0009] To achieve the above object, the present invention is realized through the following technical solutions: A process for efficiently recovering hydrogen from waste gas, comprising the following steps: I. Pretreatment of raw gas: including dust removal and dehydration treatment; II. Primary compression and pressure swing adsorption pretreatment: The primary compressor pressurizes the nitrogen / hydrogen mixture gas; the nitrogen / hydrogen mixture gas enters PSA adsorption cylinder A or PSA adsorption cylinder B. PSA adsorption cylinder A and PSA adsorption cylinder B operate alternately. The PSA adsorption cylinder is filled with adsorbent for preliminary purification, and the hydrogen concentration is increased to over 99.99%. PSA adsorption cylinder A and PSA adsorption cylinder B transport the preliminarily purified hydrogen to the secondary compressor. III. Secondary compression and cryogenic rectification: The preliminarily purified hydrogen enters the secondary compressor for further pressurization. The hydrogen after secondary compression first enters the main heat exchanger to recover cold energy with the refluxing low-temperature liquefied gas inside, and then passes through the expander to be cooled to -180°C to -200°C. The hydrogen cooled again enters the rectification tower. In the rectification tower, nitrogen is preferentially liquefied, and the bottom liquid nitrogen is discharged from the bottom. After recovering cold energy, it becomes gaseous nitrogen and is vented; hydrogen with a purity ≥99.999% is produced from the top of the tower.

[0010] Furthermore, in step I, the nitrogen-hydrogen mixed raw material gas passes through a particulate filter for dust removal. The raw material gas removing particulate impurities continues to enter the water removal adsorption cylinder for dehydration. After filtering out moisture and trace CO2, the outlet dew point drops to ≤ -70°C. Particulates, water and other impurities are discharged, and the nitrogen / hydrogen mixture gas continues to enter the primary compressor.

[0011] Furthermore, in step II, the primary compressor pressurizes the nitrogen / hydrogen mixture gas to 0.2 - 0.6 MPa.

[0012] Furthermore, in step II, the preliminarily pressurized nitrogen / hydrogen mixture gas is divided into two paths through the PSA adsorption cylinder A inlet valve and the PSA adsorption cylinder B inlet valve. The nitrogen / hydrogen mixture gas entering PSA adsorption cylinder A enters PSA adsorption cylinder A, or the nitrogen / hydrogen mixture gas entering PSA adsorption cylinder B enters PSA adsorption cylinder B.

[0013] 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 the PSA adsorption cylinder B outlet valve installed at the top.

[0014] Furthermore, a PSA adsorption cylinder regenerated gas inlet valve is also installed between the tops of PSA adsorption cylinder A and PSA adsorption cylinder B; a PSA adsorption cylinder B regenerated gas outlet valve and a PSA adsorption cylinder A regenerated gas outlet valve are also installed between the bottoms of PSA adsorption cylinder A and PSA adsorption cylinder B. The PSA adsorption cylinder regenerated gas waste gas is discharged through the PSA adsorption cylinder B regenerated gas outlet valve and the PSA adsorption cylinder A regenerated gas outlet valve.

[0015] Furthermore, when PSA adsorption cylinder A is in adsorption and PSA adsorption cylinder B is in regeneration, the preliminarily pressurized nitrogen / hydrogen mixture after being pressurized by the first-stage compressor enters PSA adsorption cylinder A through the opening of the inlet valve of PSA adsorption cylinder A and the closing of the inlet valve of PSA adsorption cylinder B. After the nitrogen in the mixture is adsorbed by the internal adsorbent, hydrogen with a purity of 99.99% is produced at the top of PSA adsorption cylinder A. Then, through the opening of the outlet valve of PSA adsorption cylinder A and the closing of the outlet valve of PSA adsorption cylinder B, hydrogen preliminarily purified by PSA is finally produced. At this time, PSA adsorption cylinder B is in the regeneration stage. The inlet valve of the PSA adsorbent regeneration gas is opened to introduce a small flow of hydrogen out of PSA adsorption cylinder A. The regeneration gas of PSA adsorption cylinder enters PSA adsorption cylinder B from the top, reducing the pressure inside the cylinder to release the adsorbed nitrogen. The nitrogen / hydrogen mixture entering PSA adsorption cylinder B passes through the opening of the outlet valve of the regeneration gas of PSA adsorption cylinder B, the closing of the inlet valve of PSA adsorption cylinder B, and the closing of the outlet valve of the regeneration gas of PSA adsorption cylinder A, and the waste gas of the regeneration gas of PSA adsorption cylinder containing hydrogen-rich nitrogen is discharged to the combustion system for venting.

[0016] Furthermore, the preliminarily purified hydrogen enters the second-stage compressor for further pressurization to 1.5 - 2.0 MPa.

[0017] Furthermore, the hydrogen after secondary compression first enters the main heat exchanger to recover cold energy with the refluxing low-temperature liquefied gas inside, and the hydrogen is preliminarily cooled after the initial temperature reduction. Then it passes through an expander to be cooled to -180°C to -200°C. The hydrogen cooled again enters the distillation column through the hydrogen inlet valve of the distillation column. At different heights inside the distillation column, the temperatures are different. The distillation column utilizes the boiling point difference between hydrogen and nitrogen to preferentially liquefy nitrogen, which flows to the bottom of the column. The outlet valve of the liquid nitrogen at the bottom of the column is opened, and the liquid nitrogen at the bottom of the column is discharged from the bottom. After recovering the cold energy, it becomes gaseous nitrogen for venting. The hydrogen component is less likely to liquefy than the nitrogen component and accumulates at the top of the distillation column. Hydrogen is separated in gaseous form, and high-purity hydrogen with a purity of ≥99.999% is produced through the outlet valve of the high-purity hydrogen at the top of the column. After heat exchange with the main heat exchanger, normal-temperature high-purity hydrogen is produced.

[0018] Furthermore, the preparation method of the adsorbent is as follows: Step 1: Add 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 into 48 - 55 mL of deionized water. After mixing evenly, add 12.4 - 13.6 parts of L-malic acid to the mixed solution, stir at 78 - 83°C for 1.5 - 2.5 h, then adjust the pH to 4.8 - 6. Add 100 - 110 parts of magnesium acetate solution with a concentration of 0.2 - 0.3 mol / L to the mixed solution and continue to stir for 20 - 30 min to obtain a mixed gel. Step 2: Grind the Chlorella biomass carbon and sieve it through 100 - 200 meshes, then add it to the mixed gel at an addition amount of 1 - 1.5%, stir at 38 - 43°C and 300 - 400 r / min for 20 - 30 min, then dry it to constant weight under nitrogen protection at 120 - 140°C, grind and sieve it through 100 - 150 meshes to obtain Intermediate A; Step 3: Put Intermediate A into a container, introduce steam at 100 - 105°C, treat Intermediate A for 1 - 1.2 h, then calcine Intermediate A at 400 - 450°C, re - grind and sieve it to 100 - 150 meshes to obtain Intermediate B; Step 4: Put Intermediate B into a fixed bed, control the temperature of the fixed bed to rise to 400 - 420°C, and introduce a mixed gas of carbon dioxide and nitrogen with a flow rate greater than 165 mL / min, keep the temperature for 8 - 10 h to obtain Intermediate C; Step 5: Disperse Intermediate C in water, add polyvinyl alcohol and lithium nitrate under the condition of high - speed stirring at 1200 - 1500 r / min, then dry and calcine at 550 - 575°C for 4 - 5 h to obtain the adsorbent.

[0019] The present invention adopts the PSA + cryogenic combination process, and has the following technical effects: 1) High - efficiency coupling: PSA pretreatment reduces the cryogenic load, and cryogenic rectification makes up for the upper limit of PSA purity. The comprehensive recovery rate > 85%.

[0020] 2) Flexibility: Applicable to mixed gases with a nitrogen content of 10% - 50% (such as synthetic ammonia tail gas, coke oven gas).

[0021] 3) Low energy consumption: PSA reduces the cryogenic treatment volume, and cryogenic high - pressure operation reduces the refrigeration demand.

[0022] 4) High purity: Double separation (adsorption + phase change) ensures that the hydrogen purity ≥ 5N.

[0023] By optimizing the PSA adsorbent, the present invention can increase the hydrogen concentration to more than 99.99% after preliminary purification, and the hydrogen recovery rate can reach more than 90%. The adsorption efficiency is high and the hydrogen recovery rate is high. Further combined with cryogenic treatment, the purified hydrogen can meet the demand of ultra - high purity (such as 99.999%). Brief Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following - described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 This is a flow chart of a process for efficiently recovering hydrogen from waste gas according to the present invention.

[0026] The labels in the figure respectively represent: 1 - particulate filter, 2 - water removal adsorption cylinder, 3 - primary compressor, 4 - PSA adsorption cylinder A, 5 - PSA adsorption cylinder B, 6 - secondary compressor, 7 - main heat exchanger, 8 - expander, 9 - distillation column; a - nitrogen-hydrogen mixed feed gas, b - feed gas with particulate impurities removed, c - nitrogen / hydrogen mixed gas, d - impurities such as particulate matter and water, e - preliminarily pressurized nitrogen / hydrogen mixed gas, f - nitrogen / hydrogen mixed gas entering PSA adsorption cylinder A, g - nitrogen / hydrogen mixed gas entering PSA adsorption cylinder B, h - hydrogen gas exiting PSA adsorption cylinder A, i - hydrogen gas exiting PSA adsorption cylinder B, j - PSA adsorption cylinder regeneration gas inlet (99.99% hydrogen), k - PSA adsorption cylinder regeneration gas exhaust, l - PSA preliminarily purified hydrogen, m - secondary compressed hydrogen, n - preliminarily cooled hydrogen, o - re-cooled hydrogen, p - bottom liquid nitrogen of the tower, q - gaseous nitrogen, r - top high-purity hydrogen, s - room-temperature high-purity hydrogen; V1 - PSA adsorption cylinder A inlet valve, V2 - PSA adsorption cylinder B inlet valve, V3 - PSA adsorption cylinder A outlet valve, V4 - PSA adsorption cylinder B outlet valve, V5 - PSA adsorption cylinder regeneration gas inlet valve, V6 - PSA adsorption cylinder A regeneration gas outlet valve, V7 - PSA adsorption cylinder B regeneration gas outlet valve, V8 - hydrogen gas inlet valve to the distillation column, V9 - bottom liquid nitrogen outlet valve of the tower, V10 - top high-purity hydrogen outlet valve. Specific embodiments

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0028] Embodiment 1: Please refer to Figure 1 in the accompanying drawings of the specification, a process for efficiently recovering hydrogen from waste gas includes the following steps: I. Pretreatment of the feed gas; The nitrogen-hydrogen mixed feed gas a passes through the particulate filter 1 for dust removal, and the feed gas b with particulate impurities removed continues to enter the water removal adsorption cylinder 2 for dehydration. After filtering out moisture and trace CO2, the outlet dew point drops to ≤ -70 °C, and the impurities d such as particulate matter and water are discharged. The nitrogen / hydrogen mixed gas c continues to enter the primary compressor 3; II. Primary compression and pressure swing adsorption (PSA) pretreatment; The primary compressor 3 pressurizes the nitrogen / hydrogen mixture gas c to the pressure required for PSA (0.2 - 0.6 MPa); the preliminarily pressurized nitrogen / hydrogen mixture gas e is divided into two paths through the PSA adsorption cylinder A inlet valve V1 and the PSA adsorption cylinder B inlet valve V2. The nitrogen / hydrogen mixture gas f entering the PSA adsorption cylinder A enters the PSA adsorption cylinder A4, or the nitrogen / hydrogen mixture gas g entering the PSA adsorption cylinder B enters the PSA adsorption cylinder B5. The two towers operate alternately. In the PSA adsorption cylinder, using the selective adsorption characteristics of the adsorbent for gas components, impurities are adsorbed under high pressure, and hydrogen penetrates the adsorption bed layer to achieve preliminary purification, and the hydrogen concentration is increased to more than 99.99%. The PSA adsorption cylinder A4 and the PSA adsorption cylinder B5 respectively send the PSA preliminarily purified hydrogen l to the secondary compressor 6 through the PSA adsorption cylinder A outlet valve V3 and the PSA adsorption cylinder B outlet valve V4 installed at the top; a PSA adsorption cylinder regenerated 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 regenerated gas outlet valve V7 and a PSA adsorption cylinder A regenerated 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 regenerated gas waste gas k is discharged through the PSA adsorption cylinder B regenerated gas outlet valve V7 and the PSA adsorption cylinder A regenerated gas outlet valve V6; Among them, the two-tower adsorption valve position process is as follows: Taking the PSA adsorption cylinder A4 for adsorption and the PSA adsorption cylinder B5 for regeneration as an example. The preliminarily pressurized nitrogen / hydrogen mixture gas e after being pressurized by the primary compressor 3 passes through the opening of the PSA adsorption cylinder A inlet valve V1 (the PSA adsorption cylinder B inlet valve V2 is closed), and the nitrogen / hydrogen mixture gas f entering the PSA adsorption cylinder A enters the PSA adsorption cylinder A4. After the internal adsorbent adsorbs nitrogen, the hydrogen h with a purity of 99.99% is produced at the top of the PSA adsorption cylinder A. After the PSA adsorption cylinder A outlet valve V3 is opened (the PSA adsorption cylinder B outlet valve V4 is closed), the PSA preliminarily purified hydrogen l is finally produced; at this time, the PSA adsorption cylinder B5 is in the regeneration stage, the PSA adsorption cylinder regenerated gas inlet valve V5 is opened, and a small flow of hydrogen h from the PSA adsorption cylinder A is introduced. The PSA adsorption cylinder regenerated gas inlet j enters the PSA adsorption cylinder B5 from the top to reduce the pressure in the cylinder, so that nitrogen is desorbed and released. The nitrogen / hydrogen mixture gas g entering the PSA adsorption cylinder B is discharged through the opening of the PSA adsorption cylinder B regenerated gas outlet valve V7 (the PSA adsorption cylinder B inlet valve V2 is closed and the PSA adsorption cylinder A regenerated gas outlet valve V6 is closed) to discharge the hydrogen-rich nitrogen PSA adsorption cylinder regenerated gas waste gas k, which goes to the combustion system for venting.

[0029] III. Secondary compression and cryogenic rectification; The hydrogen gas l preliminarily purified by PSA enters the secondary compressor 6 and is further pressurized to the pressure required for cryogenic cooling (1.5 - 2.0 MPa). The hydrogen gas m after secondary compression first enters the main heat exchanger 7, where it recovers cold energy with the refluxing cryogenic liquefied gas inside, and the hydrogen gas n is preliminarily cooled after the initial temperature reduction. Then, it passes through the expander 8 to be cooled to -180°C to -200°C. The hydrogen gas o after further cooling enters the distillation column 9 through the hydrogen inlet valve V8 of the distillation column. The temperature at different heights inside the distillation column 9 is different. The distillation column 9 utilizes the boiling point difference between hydrogen (boiling point -253°C) and nitrogen (boiling point -196°C) to preferentially liquefy nitrogen, which flows to the bottom of the column. The bottom liquid nitrogen outlet valve V9 at the bottom of the column is opened, and the bottom liquid nitrogen p is discharged from the bottom. After recovering the cold energy, it becomes gaseous nitrogen q and is vented; the hydrogen component is less likely to liquefy than the nitrogen component and accumulates at the top of the distillation column. The hydrogen gas is separated in gaseous form and high-purity hydrogen gas r (purity ≥ 99.999%) is produced through the high-purity hydrogen gas outlet valve V10 at the top of the column. After heat exchange with the main heat exchanger 7, normal-temperature high-purity hydrogen gas s is produced.

[0030] Table 1 Comparison of hydrogen purity, nitrogen removal rate, and energy consumption of different recovery processes

[0031] The present invention adopts the PSA + cryogenic combined process and has the following technical effects: 1) High-efficiency coupling: PSA pretreatment reduces the cryogenic load, and cryogenic rectification makes up for the upper limit of PSA purity. The comprehensive recovery rate > 85%.

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

[0033] 3) Low energy consumption: PSA reduces the cryogenic treatment volume, and cryogenic high-pressure operation reduces the refrigeration demand.

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

[0035] Example 2: This example discloses an adsorbent, which is used to be filled inside the PSA adsorption cylinder A4 and the PSA adsorption cylinder B5 to adsorb gases such as nitrogen; The preparation method of the adsorbent is as follows: 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. After mixing evenly, 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 0.2 mol / L) to the mixed solution, and continue stirring for 20 min to obtain a mixed gel; Step 2: Grind the Chlorella biomass carbon through a 100-mesh sieve, then add it to the mixed gel at an addition amount of 1%, stir at 38 °C and 300 r / min for 20 min, then dry to constant weight at 120 °C under nitrogen protection, and grind through a 100-mesh sieve to obtain Intermediate A; Step 3: Place Intermediate A in a container, introduce steam at 100 °C, treat Intermediate A for 1.2 h, then calcine Intermediate A at 400 °C, re-grind and sieve to 100 mesh to obtain Intermediate B; Step 4: Place Intermediate B in a fixed bed, control the temperature of the fixed bed to rise to 400 °C, and introduce a mixed gas of carbon dioxide and nitrogen (carbon dioxide: nitrogen = 3:2) at a flow rate of 168 mL / min, and keep warm for 8 h to obtain Intermediate C; Step 5: Disperse Intermediate C in water, add polyvinyl alcohol and lithium nitrate under high-speed stirring at 1200 r / min, then dry and calcine at 550 °C for 5 h to obtain the adsorbent.

[0036] Example 3: This example discloses an adsorbent for filling inside PSA adsorption cylinders A4 and B5 to adsorb gases such as nitrogen; The preparation method of the adsorbent is as follows: Step 1: Add 3.8 g of aluminum nitrate, 1.6 g of calcium nitrate, 1 g of molybdenum nitrate, and 0.8 g of zinc nitrate to 55 mL of deionized water. After mixing evenly, add 13.6 g of L-malic acid to the mixed solution, stir at 83 °C for 1.5 h, then adjust the pH to 4.8, add 110 g of magnesium acetate solution (concentration 0.3 mol / L) to the mixed solution, and continue stirring for 30 min to obtain a mixed gel; Step 2: Grind the Chlorella biomass carbon through a 200-mesh sieve, then add it to the mixed gel at an addition amount of 1.5%, stir at 43 °C and 400 r / min for 30 min, then dry to constant weight at 140 °C under nitrogen protection, and grind through a 150-mesh sieve to obtain Intermediate A; Step 3: Place Intermediate A in a container, introduce steam at 105 °C, treat Intermediate A for 1 h, then calcine Intermediate A at 450 °C, re-grind and sieve to 150 mesh to obtain Intermediate B; Step 4: Place Intermediate B in a fixed bed, control the temperature of the fixed bed to rise to 420 °C, and introduce a mixed gas of carbon dioxide and nitrogen (carbon dioxide: nitrogen = 3:2) at a flow rate of 170 mL / min, and keep warm for 10 h to obtain Intermediate C; Step 5: Disperse Intermediate C in water, add polyvinyl alcohol and lithium nitrate under high-speed stirring at 1500 r / min, then dry and calcine at 575 °C for 4 h to obtain the adsorbent.

[0037] Example 4: This example discloses an adsorbent for filling inside PSA adsorption cylinders A4 and B5 to adsorb gases such as nitrogen. The preparation method of the adsorbent is as follows: Step 1: Add 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 into 52 mL of deionized water. After mixing evenly, add 13.1 g of L-malic acid to the mixed solution, stir at 80 °C for 2 h, then adjust the pH to 5.8, add 108 g of magnesium acetate solution (concentration 0.25 mol / L) to the mixed solution, and continue to stir for 27 min to obtain a mixed gel. Step 2: Grind and sieve the Chlorella biomass carbon through a 150-mesh sieve, then add it to the mixed gel at an addition amount of 1.4%, stir at 41 °C and 350 r / min for 23 min, then dry to constant weight at 130 °C under nitrogen protection, grind and sieve through a 120-mesh sieve to obtain intermediate A. Step 3: Place intermediate A in a container, introduce steam at 103 °C, treat intermediate A for 1.1 h, then calcine intermediate A at 430 °C, and re-grind and sieve to 130 mesh to obtain intermediate B. Step 4: Place intermediate B in a fixed bed, control the temperature of the fixed bed to rise to 410 °C, and introduce a mixed gas of carbon dioxide and nitrogen (carbon dioxide: nitrogen = 3:2) at a flow rate of 166 mL / min, keep warm for 9 h to obtain intermediate C. Step 5: Disperse intermediate C in water, add polyvinyl alcohol and lithium nitrate under the condition of high-speed stirring at 1400 r / min, then after drying and calcining at 565 °C for 4.2 h, obtain the adsorbent.

[0038] Comparative Example 1: Different from Example 3, step 3 is missing.

[0039] Comparative Example 2: Different from Example 3, step 4 is carried out first, and then step 3.

[0040] Comparative Example 3: Different from Example 3, in step 1, add 2 g of aluminum nitrate, 2 g of calcium nitrate, 0.7 g of molybdenum nitrate, and 1 g of zinc nitrate into 52 mL of deionized water. After mixing evenly, add 20 g of L-malic acid to the mixed solution, stir at 80 °C for 2 h, then adjust the pH to 5.8, add 108 g of magnesium acetate solution (concentration 0.25 mol / L) to the mixed solution, and continue to stir for 27 min to obtain a mixed gel.

[0041] Experimental Example: The adsorbents prepared in Examples 2 to 4 and Comparative Examples 1 to 3 were used to perform performance tests on the synthetic ammonia tail gas (containing 40% hydrogen, 28% nitrogen, 7% ammonia, and 25% methane). The results are shown in Table 1.

[0042] Table 1 Hydrogen Recovery Performance Test Results

[0043] By optimizing the PSA adsorbent of the present invention, the hydrogen concentration can be increased to more than 99.99% after preliminary purification, the hydrogen recovery rate can reach more than 90%, the adsorption efficiency is high, and the hydrogen recovery rate is high. Further combined with cryogenic cooling, the purified hydrogen can meet the requirements of ultra-high purity (such as 99.999%).

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and 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 embodiments of the present invention.

Claims

1. A process for efficiently recovering hydrogen from waste gas, characterized in that, It includes the following steps: I. Pretreatment of raw material gas: including dust removal and dehydration treatment; II. Primary compression and pressure swing adsorption pretreatment: The primary compressor (3) pressurizes the nitrogen / hydrogen mixture gas (c); the nitrogen / hydrogen mixture gas (c) enters the PSA adsorption cylinder A (4) or enters the PSA adsorption cylinder B (5). The PSA adsorption cylinder A (4) and the PSA adsorption cylinder B (5) operate alternately. The adsorption agent is filled in the PSA adsorption cylinder 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); III. Secondary compression and cryogenic rectification: The preliminarily purified hydrogen enters the secondary compressor (6) for further pressurization. The hydrogen (m) after secondary compression first enters the main heat exchanger (7) to recover cold energy with the refluxing low-temperature liquefied gas inside, and then passes through the expander (8) to cool it down to -180°C to -200°C. The hydrogen (o) cooled again enters the rectification tower (9). In the rectification tower (9), nitrogen is preferentially liquefied and the bottom liquid nitrogen (p) is discharged from the bottom. After recovering cold energy, it becomes gaseous nitrogen (q) and is vented; hydrogen with a purity ≥ 99.999% is produced from the top of the tower.

2. The process for highly efficient hydrogen recovery from waste gas according to claim 1, characterized in that, In step I, the nitrogen-hydrogen mixed raw material gas (a) passes through the particulate filter (1) for dust removal. The raw material gas (b) removing particulate impurities continues to enter the water removal adsorption cylinder (2) for dehydration. After filtering out moisture and trace CO2, the outlet dew point drops to ≤ -70°C. The particulate matter and water impurities (d) are discharged, and the nitrogen / hydrogen mixture gas (c) continues to enter the primary compressor (3).

3. The process for highly efficient hydrogen recovery from waste gas according to claim 2, characterized in that, In step II, the primary compressor (3) pressurizes the nitrogen / hydrogen mixture 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 II, the preliminarily pressurized nitrogen / hydrogen mixture gas (e) is divided into two paths through the PSA adsorption cylinder A inlet valve (V1) and the PSA adsorption cylinder B inlet valve (V2). The nitrogen / hydrogen mixture gas (f) entering the PSA adsorption cylinder A enters the PSA adsorption cylinder A (4), or the nitrogen / hydrogen mixture gas (g) entering the PSA adsorption cylinder B enters the PSA adsorption cylinder B (5).

5. The process for highly efficient hydrogen recovery from waste gas according to claim 4, characterized in that, The PSA adsorption cylinder A (4) and the PSA adsorption cylinder B (5) respectively transport the PSA preliminarily purified hydrogen (l) to the secondary compressor (6) through the PSA adsorption cylinder A outlet valve (V3) and the PSA adsorption cylinder B outlet valve (V4) installed at the top.

6. The process for highly efficient hydrogen recovery from waste gas according to claim 5, characterized in that, A PSA adsorption cylinder regeneration gas inlet valve (V5) is also installed between the tops of the PSA adsorption cylinder A (4) and the PSA adsorption cylinder B (5); 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 A (4) and the PSA adsorption cylinder B (5). 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).

7. The process for efficiently recovering hydrogen from waste gas according to claim 6, characterized in that, When PSA adsorption cylinder A (4) adsorbs and PSA adsorption cylinder B (5) is regenerated, the preliminarily pressurized nitrogen / hydrogen mixture (e) after being pressurized by the first-stage compressor (3) enters PSA adsorption cylinder A (4) through the opening of the PSA adsorption cylinder A inlet valve (V1) and the closing of the PSA adsorption cylinder B inlet valve (V2). After the nitrogen in the mixture is adsorbed by the internal adsorbent, hydrogen (h) with a purity of 99.99% is produced at the top. Then, through the opening of the PSA adsorption cylinder A outlet valve (V3) and the closing of the PSA adsorption cylinder B outlet valve (V4), the preliminarily purified hydrogen (l) is finally produced. At this time, PSA adsorption cylinder B (5) is in the regeneration stage. The PSA adsorption cylinder regenerated gas inlet valve (V5) is opened, and a small flow of hydrogen (h) from PSA adsorption cylinder A is introduced. The PSA adsorption cylinder regenerated gas inlet (j) enters PSA adsorption cylinder B (5) from the top, reducing the pressure inside the cylinder and causing the nitrogen to be desorbed and released. The nitrogen / hydrogen mixture (g) entering PSA adsorption cylinder B passes through the opening of the PSA adsorption cylinder B regenerated gas outlet valve (V7), the closing of the PSA adsorption cylinder B inlet valve (V2), and the closing of the PSA adsorption cylinder A regenerated gas outlet valve (V6), and the PSA adsorption cylinder regenerated gas waste gas (k) containing hydrogen-rich nitrogen is discharged to the combustion system for venting.

8. The process for efficient hydrogen recovery from waste gas according to claim 7, characterized in that, The preliminarily purified hydrogen enters the second-stage compressor (6) and is further pressurized to 1.5 - 2.0 MPa.

9. The process for highly efficient hydrogen recovery from waste gas according to claim 8, characterized in that, The second-stage compressed hydrogen (m) first enters the main heat exchanger (7), where it recovers cold energy with the refluxing cryogenic liquefied gas inside, and the hydrogen is preliminarily cooled to obtain the preliminarily cooled hydrogen (n). Then, it passes through the expander (8) to be cooled to -180 °C to -200 °C. The hydrogen (o) cooled again enters the distillation column (9) through the hydrogen inlet valve to the distillation column (V8). In the distillation column (9), the temperature is different at different heights. The distillation column (9) utilizes the boiling point difference between hydrogen and nitrogen to preferentially liquefy nitrogen, which flows to the bottom of the column. The bottom liquid nitrogen outlet valve (V9) is opened, and the bottom liquid nitrogen (p) is discharged from the bottom. After recovering the cold energy, it becomes gaseous nitrogen (q) and is vented. The hydrogen component is less likely to liquefy than the nitrogen component and accumulates at the top of the distillation column. Hydrogen is separated in gaseous form, and the top high-purity hydrogen (r) with a purity ≥ 99.999% is produced through the top high-purity hydrogen outlet valve (V10), and the normal-temperature high-purity hydrogen (s) is produced after heat exchange with the main heat exchanger (7).

10. The process for highly efficient hydrogen recovery from waste gas according to claim 9, characterized in that, The preparation method of the adsorbent is as follows: Step 1: Add 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 into 48 - 55 mL of deionized water. After mixing evenly, add 12.4 - 13.6 parts of L-malic acid to the mixed solution, stir at 78 - 83 °C for 1.5 - 2.5 h, then adjust the pH to 4.8 - 6. Add 100 - 110 parts of magnesium acetate solution with a concentration of 0.2 - 0.3 mol / L to the mixed solution and continue to stir for 20 - 30 min to obtain a mixed gel; Step 2: Grind the Chlorella biomass carbon and sieve it through 100 - 200 meshes, then add it to the mixed gel at an addition amount of 1 - 1.5%, stir at 38 - 43°C and 300 - 400 r / min for 20 - 30 min, then dry it to constant weight under nitrogen protection at 120 - 140°C, and grind and sieve it through 100 - 150 meshes to obtain Intermediate A; Step 3: Put Intermediate A into a container, introduce steam at 100 - 105°C, treat Intermediate A for 1 - 1.2 h, then calcine Intermediate A at 400 - 450°C, and re - grind and sieve it to 100 - 150 meshes to obtain Intermediate B; Step 4: Put Intermediate B into a fixed - bed reactor, control the temperature of the fixed - bed reactor to rise to 400 - 420°C, and introduce a mixed gas of carbon dioxide and nitrogen with a flow rate greater than 165 mL / min, keep the temperature for 8 - 10 h to obtain Intermediate C; Step 5: Disperse Intermediate C in water, add polyvinyl alcohol and lithium nitrate under the condition of high - speed stirring at 1200 - 1500 r / min, then dry and calcine at 550 - 575°C for 4 - 5 h to obtain the adsorbent.

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