Ammonium Iodide Crystallization-Based Hydrogen Production Process and System for Sulfur-Iodine Cycle

Abstract

The present disclosure relates to the technical field of hydrogen production, in particular to a sulfur-iodine cycle hydrogen production process and system based on ammonium iodide crystallization. The process includes S1, Bunsen reaction and two-phase separation; S2, sulfuric acid decomposition and gas circulation; S3, ammonium iodide crystallization and circulation; S4, ammonium iodide drying and decomposition; S5, gas circulation and hydrogen purification. The present disclosure adopts a process of circulating ammonia-ammonium iodide, successfully extracts anhydrous and iodine-free hydrogen iodide gas, and at the same time adopts a pressurization and cooling process to realize the condensation and reuse of excess ammonia, making the economy of the sulfur-iodine cycle hydrogen production reach the industrialization threshold.

Description

Technical Field

[0001] The present disclosure relates to the technical field of hydrogen production, in particular to a sulfur-iodine cycle hydrogen production process and system based on ammonium iodide crystallization. Background Art

[0002] In the field of thermochemical hydrogen production technology, the sulfur-iodine cycle is regarded as one of the most promising hydrogen production routes for industrialization due to its good compatibility with medium and low temperature heat sources (400 - 500 °C), the spatial isolation characteristics of hydrogen and oxygen products, and the feasibility verified by pilot-scale systems. Through a three-step closed cycle of the Bunsen reaction - sulfuric acid decomposition - hydrogen iodide decomposition, it can achieve hydrogen-oxygen co-production with a theoretical thermal efficiency of 60%. The 10NL / h system of JAEA in Japan and the 5m³ / h pilot-scale device of Zhejiang University have confirmed the engineering feasibility of this process. However, the technical bottlenecks in the purification and decomposition of hydrogen iodide (HI) severely restrict its large-scale application.

[0003] The current technical difficulties mainly focus on the impurity separation and efficient decomposition in the hydroiodic acid phase: The hydroiodic acid phase generated by the Bunsen reaction contains key impurities such as H2SO4 and I2, and their residues will cause catalyst poisoning and lead to a sharp drop in the HI decomposition rate from the theoretical value of 33% to less than 20%. Existing purification technologies all have various systematic defects. For example, the extraction method: Lanchi et al. used H3PO4 to extract HI (DOI: 10.1016 / j.ijhydene.2009.06.010). Although two-phase separation can be achieved, new impurity phases are introduced, resulting in an energy consumption as high as 237 kJ / mol for subsequent phosphoric acid recovery, and the multi-component system increases the process complexity. The membrane separation method: The electrodialysis - rectification coupling process proposed in CN105018960A reduces the energy consumption to 180 kJ / mol, but there are technical obstacles such as pore swelling and rupture of the proton exchange membrane and difficulty in forming a large-area membrane, making it difficult to meet the long-term operation requirements of industrial equipment. The gas purge method: The purge process developed in CN101830443A has problems such as low impurity removal rate (<85%), the energy consumption of purge gas circulation accounting for more than 12% of the total system energy consumption, and insufficient separation efficiency for the H2O - I2 - HI azeotropic system. The precipitation method: Although the use of barium salt precipitation in CN116143079A can improve the purity, the purification cost per kilogram of H2 reaches 5 yuan, which already accounts for 71% of the target hydrogen production cost of 7 yuan / (kg H2), and the economy is seriously insufficient.

[0004] Common technical defects: The water content of the HI solution obtained by the existing method is as high as 45 - 60 wt%, resulting in a large amount of H2O-I2-HI azeotrope during evaporation and concentration. Experiments show that (JAEA data), the equilibrium decomposition rate of water-containing HI vapor at 500 °C is only 23%, far lower than the theoretical value of 33% for anhydrous HI gas. More seriously, to achieve the cyclic evaporation of the HI-H2O mixture, the system needs to consume an additional 28% of thermal energy for the phase change of water, directly reducing the actual thermal efficiency to below 43%. The above technical and economic defects make it difficult for the current sulfur-iodine cycle hydrogen production cost to break through the threshold of 7 yuan / (kg H2). Therefore, developing a new process that can simultaneously achieve the efficient extraction and direct decomposition of anhydrous and iodine-free HI gas has become the core proposition for breaking through the industrialization bottleneck of thermochemical hydrogen production. Summary of the Invention

[0005] In order to solve the problems of high purification difficulty, low decomposition efficiency, and high energy consumption of hydrogen iodide, and improve the industrial application feasibility and economy of the thermochemical sulfur-iodine cycle hydrogen production technology, the present disclosure proposes a process method and device for extracting high-purity hydrogen iodide gas by using cyclic ammonia gas and continuously producing hydrogen at low cost through a combined photothermal catalytic reaction.

[0006] On the one hand, the present disclosure proposes a hydrogen production process by the sulfur-iodine cycle based on ammonium iodide crystallization, including S1, Bunsen reaction and two-phase separation; S2, sulfuric acid decomposition and gas circulation; S3, ammonium iodide crystallization and circulation; S4, ammonium iodide drying and decomposition; S5, gas circulation and hydrogen purification; characterized in that: S1, Bunsen reaction and two-phase separation, the reactant SO2 comes from sulfuric acid decomposition, I2 comes from hydroiodic acid decomposition and recycled iodine, H2O comes from sulfuric acid decomposition, recycled solvent water and / or supplemented raw material water, and the reaction product is statically layered into a sulfuric acid phase and a hydroiodic acid phase, and the two phases are separated; S2, sulfuric acid decomposition and gas circulation, the gas obtained by sulfuric acid decomposition is sent back to participate in the reaction of S1; S3, ammonium iodide crystallization and circulation, under the conditions of 1.2-1.5 MPa and 100-130 °C, excessive ammonia gas is introduced into the hydroiodic acid phase, and the gas-liquid ratio is (3-5):1, and ammonium iodide precipitate is generated by reaction, and the ammonium iodide crystal is obtained by liquid-solid separation, and the separated mother liquor is sent back to S1; S4, ammonium iodide drying and decomposition, the ammonium iodide crystal is dried to reduce the content of attached H2O and I2 to <500 ppm, and at the same time its temperature is controlled at 120-160 °C by cooling, and then the dried ammonium iodide is decomposed into gas under the conditions of a pressure of -0.05 to -0.02 MPa and a temperature of 560-580 °C, and then under the catalysis of a photothermal catalyst, HI in it is decomposed into H2 and I2, and the reaction mixture gas contains NH3, HI, H2, I2, and their molar ratio is NH3:HI:H2:I2 = 1:(0.78-0.8):(0.10-0.11):(0.10-0.11); S5, gas circulation and hydrogen purification, the mixed gas is sent back by pressurization and sequentially passes through S4 and S3, and is cooled to 20-25 °C, and the uncondensed gas is purified to obtain hydrogen.

[0007] Preferably, the absolute pressure of the Bunsen reaction is 5-25 atm, the temperature is 90-140 °C, and the total feed molar ratio is SO2:I2:H2O = 1:(4-6):(12-20).

[0008] Preferably, the molar amount of the supplemented raw material water is twice the molar amount of the recycled SO2.

[0009] Preferably, the sulfuric acid phase undergoes purification, concentration, gasification, and decomposition processes, and the decomposition conditions are normal pressure and 400-1000 °C.

[0010] Preferably, when the ammonium iodide is crystallized, the solution supersaturation is controlled at 1.5-2.0, and the crystal particle size is controlled at 100-200 μm.

[0011] Preferably, the ammonium iodide crystal is contacted with a countercurrent high-temperature gas at a temperature of 400-450 °C in a fluidized bed dryer under the conditions of a pressure of 1.0-1.2 MPa and a temperature of 140-150 °C.

[0012] Preferably, the mixed gas is pressurized to 1.2 - 1.5 MPa and then sent to S4 as the drying gas for ammonium iodide crystals. After heat exchange, the mixed gas is cooled to 120 - 160 °C, and the cooled mixed gas is sent to S3 as the ammonia source. The remaining gas is cooled after reacting to remove part of the ammonia, and the remaining mixed gas is filtered through a reverse osmosis membrane to obtain hydrogen with a hydrogen content of not less than 95%.

[0013] Preferably, the liquid ammonia separated after cooling is recycled to S3 as the ammonia source, and the hydrogen-ammonia mixed gas obtained by reverse osmosis membrane filtration is also recycled to S3 as the ammonia source.

[0014] Preferably, the photothermal catalyst coating can be selected from iodine-doped porous carbon nitride (CNI); Pt / KTaO3; TiO2 / SiO2 composite; CeO2-Ni; Pt / C; Ir / C; Pt-Ir / C.

[0015] Preferably, the photothermal catalyst coating catalyzes the decomposition of hydrogen iodide at 400 - 500 °C under illumination of 100 - 1000 W / m 2 light.

[0016] On the other hand, the present disclosure also proposes a sulfur-iodine cycle hydrogen production system based on ammonium iodide crystallization. The system includes a sulfuric acid phase storage tank and a hydroiodic acid phase storage tank connected to the Bunsen tower. The sulfuric acid phase storage tank forms a circulation loop with the Bunsen tower through a sulfuric acid phase pretreatment and decomposition unit, where the sulfuric acid phase pretreatment and decomposition unit includes an impurity separator, a sulfuric acid concentrator, and a sulfuric acid dehydration and decomposition tank; after the hydroiodic acid phase storage tank, an ammonium iodide crystallizer, an ammonium iodide dryer, an ammonium iodide decomposer, and a hydrogen iodide decomposer are connected in sequence, and a branch circuit of the ammonium iodide crystallizer forms a circulation loop with the Bunsen tower.

[0017] Preferably, the hydrogen iodide decomposer is connected to the ammonium iodide dryer through a gas compressor. The ammonium iodide dryer is also provided with a connection circuit to the ammonium iodide crystallizer. The ammonium iodide crystallizer is also sequentially connected with a liquid ammonia condensation separator and a hydrogen gas membrane separation module. The liquid ammonia condensation separator and the hydrogen gas membrane separation module are also provided with connection circuits to the ammonium iodide crystallizer, and the liquid ammonia condensation separator is also connected to a refrigerator.

[0018] Based on common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present disclosure.

[0019] The above technical solutions have the following advantages or beneficial effects: The present disclosure adopts a process of circulating ammonia gas - ammonium iodide, and successfully extracts anhydrous and iodine - free hydrogen iodide gas. At the same time, a pressurization and cooling process is adopted to realize the condensation and recycling of excessive ammonia gas. Through innovations in three aspects of materials, processes, and equipment, the present disclosure has achieved a simultaneous breakthrough in the purification cost and decomposition efficiency of HI for the first time, making the economy of the sulfur - iodine cycle for hydrogen production reach the industrialization threshold (<6 yuan / kg H2). Of course, not necessarily all of the above - mentioned advantages can be achieved simultaneously by any technical solution of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, for those skilled in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0021] Figure 1 The schematic process flow diagram of the present disclosure is shown.

[0022] Figure 2 It is a three - dimensional structure schematic diagram of the photo - thermal combined catalytic fixed - bed module in the hydrogen iodide decomposer.

[0023] Figure 3 is Figure 2 top - view schematic diagram of

[0024] Among them, 1. Bunsen tower, 2. sulfuric acid phase storage tank, 3. sulfuric acid phase pretreatment and decomposition unit, 4. hydroiodic acid phase storage tank, 5. ammonium iodide crystallizer, 6. ammonium iodide dryer, 7. ammonium iodide decomposer, 8. hydrogen iodide decomposer, 9. gas compressor, 10. liquid ammonia condensation separator, 11. refrigerator, 12. hydrogen gas membrane separation module, 13. hydrogen gas outlet, 14. oxygen outlet, 15. raw water inlet, 17. photo - thermal catalytic bed, 18. catalytic light column, 19. catalyst coating. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present disclosure in conjunction with the drawings of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, aiming to explain the inventive concept. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present disclosure.

[0026] As Figure 1 shown, the thermochemical sulfur - iodine cycle for hydrogen production process involved in the present disclosure includes 5 steps: Bunsen reaction and two - phase separation, sulfuric acid decomposition and gas circulation, ammonium iodide crystallization and circulation, ammonium iodide drying and decomposition, and gas circulation and hydrogen purification.

[0027] Step 1, Bunsen reaction and two-phase separation.

[0028] For the Bunsen reaction unit, in the steel-lined tetrafluoro Bunsen tower 1, at an absolute pressure of 5 - 25 atm and a temperature of 90 - 140 °C, the following Bunsen reaction occurs: 2H2O + SO2 + I2 → H2SO4 + 2HI, and the total feed molar ratio is SO2:I2:H2O = 1:(4 - 6):(12 - 20). Among them, SO2 comes from the decomposition product of sulfuric acid, iodine mainly comes from the decomposition product of hydroiodic acid and the recycled iodine in the system, water comes from the decomposition product of sulfuric acid, the recycled solvent water of sulfuric acid and hydroiodic acid, and / or the supplemented raw material water. The molar amount of the supplemented water is 2 times the molar amount of the recycled SO2, that is, the water inflow at the raw material water inlet 15 is 2 times the molar amount of SO2 from the sulfuric acid phase pretreatment and decomposition unit 3. The gas from the sulfuric acid phase pretreatment and decomposition unit 3 contains 13.3% - 16.7% SO2, 6.7% - 8.3% O2, and 75% - 80% water. Since SO2:O2 = 2:1 in the decomposition product of sulfuric acid, and there is also 33% O2 in the mixed SO2 flowing into the Bunsen tower 1, and O2 neither participates in the reaction nor dissolves in the liquid, it is discharged from the oxygen outlet 14 of the Bunsen tower 1. The liquid from the ammonium iodide crystallizer 5 has a composition of water:iodine:ammonium iodide = (5.6 wt.% - 13.9 wt.%):(65.3 wt.% - 86.0 wt.%):(8.4 wt.% - 20.8 wt.%). The reaction product of the Bunsen tower 1 is allowed to stand and layer for 10 - 60 minutes, forming two phases. The sulfuric acid phase is sent to the sulfuric acid phase storage tank 2, and the hydroiodic acid phase is sent to the hydroiodic acid phase storage tank 4. The sulfuric acid phase composition is H2SO4 45 ± 5 wt.%, HI ≤ 5 wt.%, I2 ≤ 3 wt.%, and the balance is H2O; the hydroiodic acid phase composition is HI 25 ± 5 wt.%, I2 55 ± 5 wt.%, H2SO4 5 wt.%, and the balance is H2O.

[0029] Step 2, sulfuric acid decomposition and gas recycling.

[0030] The sulfuric acid decomposition unit subjects the sulfuric acid phase obtained by standing and layering to purification, concentration, gasification, and decomposition processes. Sulfuric acid is decomposed at normal pressure and 400 - 1000 °C through the decomposition reaction: H2SO4 → H2O + SO2 + 0.5O2. The decomposed SO2, O2, and H2O are sent back to the Bunsen tower 1, where the gas component molar ratio is SO2:O2:H2O = 2:1:(9 - 12).

[0031] Step 3, ammonium iodide crystallization and recycling.

[0032] Pump the liquid in the hydroiodic acid phase storage tank 4 into the ammonium iodide crystallizer 5. Under the conditions of 1.2 - 1.5 MPa and 100 - 130 °C, introduce excessive ammonia with a gas-liquid ratio of (3 - 5):1. The following reaction occurs: HI + NH3 → NH4I, and the generated ammonium iodide is a precipitate. Control the solution supersaturation at 1.5 - 2.0 and the crystal size at 100 - 200 μm. Centrifuge the liquid-solid mixture at a speed of 3000 - 4000 rpm to separate, generating ammonium iodide crystals, and the mother liquor is sent back to the Bunsen tower 1.

[0033] Step 4, drying and decomposition of ammonium iodide.

[0034] The wet ammonium iodide crystals are in a fluidized bed dryer. Under the conditions of a pressure of 1.0 - 1.2 MPa and a temperature of 140 - 150 °C, they are contacted with a countercurrent high-temperature gas at a temperature of 400 - 450 °C to reduce the content of H2O and I2 attached to <500 ppm. The ammonium iodide dryer 6 uses a water bath jacket to cool down to 120 - 160 °C to prevent the direct decomposition of ammonium iodide after contacting the high-temperature gas and is sent back to the ammonium iodide crystallizer 5. The dried ammonium iodide is sent into the ammonium iodide decomposer 7 through a screw feeder. The ammonium iodide decomposer 7 is a negative pressure reactor, and the dried ammonium iodide decomposes in the negative pressure reactor. The decomposition reaction formula is NH4I → HI + NH3, and the decomposition conditions are a pressure of -0.05 - -0.02 MPa and a temperature of 560 - 580 °C, with a decomposition rate higher than 99%. The water content of HI in the produced gas is less than 0.5%, and the volume concentrations of hydrogen iodide and ammonia are both higher than 49.75%. This mixed gas enters the hydrogen iodide decomposer 8. Since NH3 neither reacts nor occupies the active site, it does not affect the hydrogen iodide decomposition reaction.

[0035] In a conventional hydrogen iodide decomposer, the decomposition rate of hydrogen iodide is low and the decomposition rate is slow. To improve the decomposition reaction rate of hydrogen iodide, the present disclosure uses a photo-thermal combined catalytic reaction unit to decompose hydrogen iodide. The mixed gas enters the hydrogen iodide decomposer 8, and the decomposition of hydrogen iodide occurs in the photo-thermal catalytic bed 17 therein. The photo-thermal catalytic bed 17 includes several cavities, and the wall surfaces of the cavities are coated with a photo-thermal catalyst coating 19, and catalytic light columns 18 are inserted into the cavities. The photo-thermal catalyst coating can be selected from the following materials: iodine-doped porous carbon nitride (CNI); Pt / KTaO3; TiO2 / SiO2 composite material; CeO2-Ni; Pt / C; Ir / C; Pt-Ir / C. As Figure 2 and Figure 3 shows a specific photo-thermal catalytic bed 17. The photo-thermal catalytic bed 17 includes honeycomb-shaped cavities arranged along its length direction. The cross-section of the cavity is hexagonal, and each cavity wall surface is coated with a photo-thermal catalyst coating 19, and each cavity internally inserts a catalytic light column 18. The photo-thermal catalyst coating 19 can catalyze the decomposition of hydrogen iodide at 400 - 500 °C and at 100 - 1000 W / m 2It can also catalyze the decomposition of hydrogen iodide under light. The combined action of heat and light can significantly increase the decomposition rate of hydrogen iodide until it approaches its equilibrium decomposition rate. The decomposition rate of hydrogen iodide is 20% - 30%. The HI decomposition reaction: HI → 0.5H2 + 0.5I2. The decomposed gas after the reaction contains NH3, HI, H2, and I2, and their molar ratio is NH3:HI:H2:I2 = 1:(0.78 - 0.8):(0.10 - 0.11):(0.10 - 0.11).

[0036] Step Five, gas circulation and hydrogen purification.

[0037] The decomposed gas coming out of the hydrogen iodide decomposer 8 is pressurized to 1.2 - 1.5 MPa by a four-stage gas compressor 9 and then sent to the ammonium iodide dryer 6 as the drying gas for wet ammonium iodide crystallization, and is cooled to 120 - 160 °C in the ammonium iodide dryer 6. The decomposed gas, the evaporated water vapor, and the iodine vapor are blown into the ammonium iodide crystallizer 5 as the ammonia gas source. Ammonia reacts with hydrogen iodide in the solution to produce ammonium iodide crystals. Hydrogen, the excessive ammonia, and the unabsorbed hydrogen are sent to the liquid ammonia condensation separator 10. The operating pressure in the liquid ammonia condensation separator 10 is 1.2 - 1.5 MPa. The refrigerator 11 is used to provide cooling water at 0 - 20 °C to the liquid ammonia condensation separator 10 to cool the mixed gas to 20 - 25 °C. The boiling point of ammonia at 1.2 - 1.5 MPa is 31 - 39 °C. At 20 - 25 °C, ammonia condenses into liquid ammonia and is discharged from the bottom of the liquid ammonia condensation separator 10, mixed with the mixed decomposed gas in the ammonium iodide dryer 6, vaporized, and then cyclically blown into the ammonium iodide crystallizer 5. The uncondensed gas contains 97% - 99% hydrogen and 1% - 3% ammonia. This gas is sent to the hydrogen membrane separation module 12. After reverse osmosis membrane filtration, the hydrogen content is increased to 99.97%. The remaining hydrogen-ammonia mixed gas contains 10% - 15% hydrogen and 85% - 90% ammonia, and is sent back to the ammonium iodide crystallizer 5.

[0038] Compared with the prior art, the core innovation and corresponding technical effects of the present disclosure are reflected in the following three aspects.

[0039] 1. Efficient extraction of anhydrous and iodine-free HI gas.

[0040] By developing an ammonia circulation extraction process (reaction equation: NH3(g)+HI(aq)→NH4I(s)↓+H2O), the following breakthroughs are achieved: (1) Purity improvement: The H2O content in HI gas is <500 ppm and the I2 content is <50 ppm, which is two orders of magnitude higher than that of the traditional extraction method (H2O 45-60 wt%, I2 0.2-0.5 wt%); (2) Energy consumption reduction: The separation energy consumption is reduced to 85 kJ / mol, which is 64% lower than that of the phosphoric acid extraction method (237 kJ / mol) and 53% lower than that of the electrodialysis coupling process (180 kJ / mol); (3) Decomposition efficiency breakthrough: The measured decomposition rate of anhydrous HI gas at 450 °C reaches 30.2%, breaking through the thermodynamic equilibrium limit of 23% in the aqueous system (JAEA, 2018).

[0041] 2. Economic breakthrough in the ammonium iodide crystallization separation process.

[0042] Based on the phase change characteristics of the NH4I intermediate, a two-stage decomposition reactor is designed (reaction equation: NH4I(s)→NH3(g)+HI(g)), which generates significant economic benefits: (1) Cost control: The HI purification cost per kilogram of H2 is reduced to 1.2 yuan, which is 76% lower than that of the barium salt precipitation method (5 yuan / kg H2), and promotes the total hydrogen production cost to break through to 5.8 yuan / kg H2; (2) By-product recycling: The ammonia recovery rate is >99.5%, and the system's supplementary ammonia consumption is <0.03 kg / kg H2; (3) Equipment compatibility: The operating pressure of the crystallization reactor is stably maintained at 0.3-0.5 MPa, and it can be directly connected to the output pipeline of the existing Bunsen reactor.

[0043] 3. Energy efficiency optimization of continuous flow decomposition.

[0044] A closed-loop circulation system for anhydrous HI gas is constructed to achieve: (1) Thermodynamic advantage: Eliminate the evaporation link of the HI-H2O azeotrope, and the system's thermal efficiency is increased from 43% to 54% (90% of the theoretical value of 60%); (2) Energy consumption reduction: Compared with the traditional condensation-re-evaporation process, the steam consumption per unit of hydrogen production is reduced by 82% (from 3.8 kg / kg H2 to 0.7 kg / kg H2); (3) System compactness: The volume power density of the decomposition reactor reaches 12 kW / m 3 , which is three times higher than that of the aqueous system, laying a foundation for the design of modular devices. Example 1

[0045] The pressure inside the steel-lined tetrafluoro Bunsen reactor is controlled at 1.8 MPa, the temperature is 115 °C, and the stratification time is 45 min. The water vapor, O2, and SO2 gases continuously generated by the sulfuric acid decomposition unit are 168 L / min, the SO2 concentration is 15.4%, and the oxygen concentration is 7.7%. After the gas is pressurized to 1.8 MPa, the O2 and SO2 gases are directly fed into the reactor, and the flow rate is 1.76 L / min; the condensate water volume is 77.3 g / min. The flow rate of the mother liquor circulating in the ammonium iodide crystallizer 5 is 201.8 g / min, containing 24.8 g / min of water, 131.7 g / min of iodine, 37.1 g / min of ammonium iodide, and 8.3 g / min of sulfuric acid impurities. The atmospheric pressure O2 flow rate discharged from the Bunsen reactor is 6.9 L / min. After stratification, 135 g / min of sulfuric acid phase is obtained, with a composition of 45 wt.% sulfuric acid, 4 wt.% hydroiodic acid, 2 wt.% iodine, and 49 wt.%, which is sent back to the Bunsen reactor after decomposition and pressurization under atmospheric pressure; the hydroiodic acid phase is 202 g / min, with a composition of 21 wt.% hydroiodic acid, 45 wt.% iodine, 4 wt.% sulfuric acid, 12 wt.% water, and 18 wt.% ammonium iodide. The hydroiodic acid phase is fed into the ammonium iodide crystallizer 5, with a pressure of 1.3 MPa and a temperature of 120 °C. A 7.3 L / min mixed gas (115 °C, 1.3 MPa) is introduced into the ammonium iodide dryer 6, in which the standard state volume flow rate of ammonia is 46.4 L / min, and the volumes of ammonia, hydrogen iodide, hydrogen, and iodine vapor in the mixed gas account for 50%, 39%, 5.5%, and 5.5% respectively. After this gas is mixed with the gas generated by precooling and membrane separation and then introduced into the ammonium iodide crystallizer 5, crystals with a particle size of 150 μm are produced. After centrifugal separation at 3500 rpm by a centrifuge, 213.4 g of ammonium iodide crystals with a purity of 99.5 wt.% are obtained, and 212.3 g of dry ammonium iodide crystals are obtained after drying in the ammonium iodide dryer 6. After the reaction in the ammonium iodide crystallizer 5, 201.8 g / min of the mother liquor is sent to the Bunsen tower 1, in which the contents of iodine, water, ammonium iodide, and sulfuric acid impurities are 65.3 wt.%, 12.3 wt.%, 18.4 wt.%, and 4 wt.% respectively. 212.3 g of dry ammonium iodide crystals generate a 65.6 L mixed gas of ammonium iodide and hydrogen in the ammonium iodide decomposer 7, and the contents of ammonia and hydrogen iodide gases are both 50%. In the hydrogen iodide decomposition tower, hydrogen iodide decomposes to produce iodine vapor and hydrogen, and the decomposition rate is 22%. The decomposition gas contains ammonia, hydrogen iodide, hydrogen, and iodine vapor with volume ratios of 50%, 39%, 5.5%, and 5.5% respectively. Approximately 10.5 g of ammonia water is produced in the liquid ammonia condensation separator 10 and sent back to the ammonium iodide crystallizer 5, and the purity of the hydrogen gas generated in the membrane separation system is 99.97% and the flow rate is 3.6 L / min.

[0046] Although the embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Without departing from the spirit and scope of the present disclosure, various changes and modifications will occur to the present disclosure, and these changes and modifications fall within the scope of the claimed present disclosure.

Claims

1. Hydrogen production process by sulfur-iodine cycle based on ammonium iodide crystallization, including S1, Bunsen reaction and two-phase separation; S2, sulfuric acid decomposition and gas circulation; S3, ammonium iodide crystallization and circulation; S4, ammonium iodide drying and decomposition; S5, gas circulation and hydrogen purification; characterized in that: S1, Bunsen reaction and two-phase separation, the reactant SO2 comes from sulfuric acid decomposition, I2 comes from hydroiodic acid decomposition and recycled iodine, H2O comes from sulfuric acid decomposition, recycled solvent water and / or supplemented raw material water, and the reaction product is statically separated into a sulfuric acid phase and a hydroiodic acid phase, and the two phases are separated; S2, sulfuric acid decomposition and gas circulation, the gas obtained by sulfuric acid decomposition is sent back to participate in the reaction of S1; S3, ammonium iodide crystallization and circulation, under the conditions of 1.2 - 1.5 MPa and 100 - 130 °C, excessive ammonia gas is introduced into the hydroiodic acid phase, and the gas-liquid ratio is (3 - 5):

1. Ammonium iodide precipitation is generated by the reaction, and the ammonium iodide crystal is obtained by liquid-solid separation. The separated mother liquor is sent back to S1; S4, ammonium iodide drying and decomposition, the ammonium iodide crystal is dried to reduce the content of attached H2O and I2 to <500 ppm, and at the same time, its temperature is controlled at 120 - 160 °C by cooling. Subsequently, the dried ammonium iodide is decomposed into gas under the conditions of -0.05 - -0.02 MPa and 560 - 580 °C. Subsequently, under the catalysis of a photothermal catalyst, HI in the gas is decomposed into H2 and I2. The reacted mixed gas contains NH3, HI, H2, I2, and its molar ratio is NH3:HI:H2:I2 = 1:(0.78 - 0.8):(0.10 - 0.11):(0.10 - 0.11); S5, gas circulation and hydrogen purification, the mixed gas is sent back by pressurization and sequentially passes through S4 and S3. The mixed gas is cooled to 20 - 25 °C. The uncondensed gas is purified to obtain hydrogen. The pressurized mixed gas is sent to S4 as the drying gas for ammonium iodide crystals, and the heat-exchanged mixed gas is sent to S3 as the ammonia source.

2. The hydrogen production process by the sulfur-iodine cycle based on ammonium iodide crystallization according to claim 1, wherein: The absolute pressure of the Bunsen reaction is 5 - 25 atm, the temperature is 90 - 140 °C, and the total feed molar ratio is SO2:I2:H2O = 1:(4 - 6):(12 - 20).

3. The hydrogen production process by sulfur-iodine cycle based on ammonium iodide crystallization according to claim 1, wherein: The molar amount of the supplemented raw material water is 2 times the molar amount of the recycled SO2.

4. The hydrogen production process by the sulfur-iodine cycle based on ammonium iodide crystallization according to claim 1, characterized in that: The sulfuric acid phase undergoes purification, concentration, gasification, and decomposition processes, and the decomposition conditions are normal pressure and 400 - 1000 °C.

5. The hydrogen production process by the sulfur-iodine cycle based on ammonium iodide crystallization according to claim 1, wherein: When ammonium iodide crystallizes, the solution supersaturation is controlled at 1.5 - 2.0, and the crystal size is controlled at 100 - 200 μm.

6. The hydrogen production process by the sulfur-iodine cycle based on ammonium iodide crystallization according to claim 1, characterized in that: The ammonium iodide crystal is in contact with a countercurrent high-temperature gas at a temperature of 400 - 450 °C in a fluidized bed dryer under the conditions of a pressure of 1.0 - 1.2 MPa and a temperature of 140 - 150 °C.

7. The hydrogen production process by sulfur-iodine cycle based on ammonium iodide crystallization according to claim 1, wherein: The mixed gas is pressurized to 1.2 - 1.5 MPa and then sent to S4 as the drying gas for ammonium iodide crystals. After heat exchange, the mixed gas is cooled to 120 - 160 °C. The cooled mixed gas is sent to S3 as the ammonia source. After part of the ammonia is removed by reaction, the remaining gas is cooled. The remaining mixed gas is filtered through a reverse osmosis membrane to obtain hydrogen, and the hydrogen content is not less than 95%.

8. The hydrogen production process by sulfur-iodine cycle based on ammonium iodide crystallization according to claim 7, wherein: The liquid ammonia separated after cooling is recycled to S3 as an ammonia source, and the hydrogen-ammonia mixture gas obtained by reverse osmosis membrane filtration is also recycled to S3 as an ammonia source.

9. A hydrogen production system based on ammonium iodide crystallization for the sulfur-iodine cycle, wherein the system implements the process according to any one of claims 1-8, characterized in that: The system includes a sulfuric acid phase storage tank and a hydroiodic acid phase storage tank connected to the Bunsen tower. The sulfuric acid phase storage tank forms a circulation loop with the Bunsen tower through a sulfuric acid phase pretreatment and decomposition unit, where the sulfuric acid phase pretreatment and decomposition unit includes an impurity separator, a sulfuric acid concentrator, and a sulfuric acid dehydration and decomposition tank; after the hydroiodic acid phase storage tank, an ammonium iodide crystallizer, an ammonium iodide dryer, an ammonium iodide decomposer, and a hydrogen iodide decomposer are connected in sequence, and a branch circuit of the ammonium iodide crystallizer forms a circulation loop with the Bunsen tower.

10. The hydrogen production system by sulfur-iodine cycle based on ammonium iodide crystallization according to claim 9, characterized in that: The hydrogen iodide decomposer is connected to the ammonium iodide dryer through a gas compressor. The ammonium iodide dryer is also provided with a connection circuit to the ammonium iodide crystallizer. The ammonium iodide crystallizer is also sequentially connected with a liquid ammonia condensation separator and a hydrogen gas membrane separation module. The liquid ammonia condensation separator and the hydrogen gas membrane separation module are also provided with connection circuits to the ammonium iodide crystallizer, and the liquid ammonia condensation separator is also connected to a refrigerator.

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