Ammonium iodide crystal-based sulfur-iodine circulating hydrogen production process and system

Abstract

The invention relates to the technical field of hydrogen preparation, in particular to a sulfur-iodine circulating hydrogen production process and system based on ammonium iodide crystallization, and the process comprises the following steps: S1, Bunsen reaction and two-phase separation; s2, sulfuric acid decomposition and gas circulation; s3, ammonium iodide crystallization and circulation; s4, drying and decomposing ammonium iodide; and S5, gas circulation and hydrogen purification. According to the present invention, the anhydrous iodine-free hydrogen iodide gas is successfully extracted by using the circulating ammonia gas-ammonium iodide process, and the condensation recycling of the excessive ammonia gas is achieved by using the pressurization cooling process so as to make the economy of the sulfur-iodine circulating hydrogen production achieve the industrialization threshold.

Description

Technical Field

[0001] The present disclosure relates to the technical field of hydrogen preparation, and 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 industrially promising water decomposition hydrogen production routes due to its good compatibility with medium and low temperature heat sources (400-500℃), the spatial isolation characteristics of hydrogen and oxygen products, and the feasibility of pilot system verification. It can achieve hydrogen and oxygen co-production with a theoretical thermal efficiency of 60% through a three-step closed cycle of Bunsen reaction-sulfuric acid decomposition-hydrogen iodide decomposition. The 10NL / h system of Japan JAEA and the 5m³ / h pilot plant of Zhejiang University have confirmed the engineering feasibility of the process. However, the technical bottlenecks in the purification and decomposition of hydrogen iodide (HI) have seriously restricted its large-scale application.

[0003] The current technical difficulties focus on the impurity separation and efficient decomposition of the hydroiodic acid phase: the hydroiodic acid phase produced by the Bunsen reaction contains key impurities such as H2SO4 and I2, the residues of which will cause catalyst poisoning and cause the HI decomposition rate to drop sharply from the theoretical value of 33% to below 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 the two-phase separation can be achieved, the introduction of a new impurity phase causes the subsequent phosphoric acid recovery energy consumption to be as high as 237 kJ / mol, and the multi-component system increases the complexity of the process. Membrane separation method: Although the electrodialysis-distillation coupling process proposed in CN105018960A reduces the energy consumption to 180 kJ / mol, the proton exchange membrane has technical obstacles such as pore swelling and rupture and difficulty in forming a large-area membrane, which makes it difficult to meet the long-term operation requirements of industrial equipment. Gas purge method: The purge process developed by CN101830443A has problems such as low impurity removal rate (<85%), purge gas circulation energy consumption accounting for more than 12% of the total system energy consumption, and insufficient separation efficiency for H2O-I2-HI azeotropic system. Precipitation method: Although CN116143079A uses barium salt precipitation to improve purity, the purification cost of each kilogram of H2 is 5 yuan, which accounts for 71% of the target hydrogen production cost of 7 yuan / (kg H2), and the economic efficiency is seriously insufficient.

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

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

[0006] On the one hand, the present disclosure proposes a sulfur-iodine cycle hydrogen production process 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 circulating iodine, H2O comes from sulfuric acid decomposition, circulating solvent water and / or supplementary raw material water, the reaction product is separated into sulfuric acid phase and hydroiodic acid phase after standing and stratification, and the two phases are separated; S2, sulfuric acid decomposition and gas circulation, the gas obtained by sulfuric acid decomposition is returned to participate in the reaction of S1; S3, ammonium iodide crystallization and circulation, under the conditions of 1.2-1.5MPa and 100-130°C, excess ammonia is introduced into the hydroiodic acid phase, the gas-liquid ratio is (3-5):1, the reaction produces ammonium iodide precipitation, liquid-solid Ammonium iodide crystals are obtained by separation, and the mother liquor obtained by separation is returned to S1; S4, ammonium iodide drying and decomposition, the ammonium iodide crystals are dried to reduce the attached H2O and I2 contents to <500ppm, and the temperature is controlled at 120-160°C by cooling, and then the dried ammonium iodide is decomposed into gas under the conditions of pressure of -0.05-0.02MPa and temperature of 560-580°C, and then the gas is decomposed into H2 and I2 under the catalysis of photothermal catalyst, and the mixed gas after the reaction contains NH3, HI, H2, I2, and the molar ratio thereof 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 pressurized and returned and successively passed through S4 and S3, and 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 to 25 atm, the temperature is 90 to 140° C., and the total feed molar ratio is SO 2 : I 2 : H 2 O = 1: (4 to 6): (12 to 20).

[0008] Preferably, the molar amount of the supplementary raw water is twice the molar amount of the circulating SO2.

[0009] Preferably, the sulfuric acid phase is purified, concentrated, gasified and decomposed, and the decomposition conditions are normal pressure and 400-1000°C.

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

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

[0012] Preferably, the mixed gas is pressurized to 1.2-1.5 MPa and sent to S4 as a 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 an ammonia source. After part of the ammonia is removed by reaction, the remaining gas is cooled, and the remaining mixed gas is filtered through a reverse osmosis membrane to obtain hydrogen, and the hydrogen content is not less than 95%.

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

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

[0015] Preferably, the photothermal catalyst coating is at 400-500°C and 100-1000W / m 2 Catalyzes the decomposition of hydrogen iodide under 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 comprising a sulfuric acid phase storage tank and a hydroiodic acid phase storage tank connected to a 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, wherein the sulfuric acid phase pretreatment and decomposition unit comprises an impurity separator, a sulfuric acid concentrator, and a sulfuric acid dehydration decomposition tank; the hydroiodic acid phase storage tank is sequentially connected to an ammonium iodide crystallizer, an ammonium iodide dryer, an ammonium iodide decomposer, and a hydrogen iodide decomposer, and the ammonium iodide crystallizer branch 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 loop with the ammonium iodide crystallizer, the ammonium iodide crystallizer is also connected in sequence with a liquid ammonia condensation separator and a hydrogen membrane separation component, the liquid ammonia condensation separator and the hydrogen membrane separation component are also provided with a connection loop with the ammonium iodide crystallizer, and the liquid ammonia condensation separator is also connected to a refrigerator.

[0018] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present disclosure.

[0019] The above technical solution has the following advantages or beneficial effects: The present disclosure adopts the process of circulating ammonia-ammonium iodide to successfully extract anhydrous and iodine-free hydrogen iodide gas, and at the same time adopts the process of pressurizing and cooling to realize the condensation and reuse of excess ammonia. The present disclosure achieves a simultaneous breakthrough in HI purification cost and decomposition efficiency for the first time through innovation in three aspects: materials, processes, and equipment, so that the economic efficiency of sulfur-iodine cycle hydrogen production reaches the industrialization threshold (<6 yuan / kg H2). Of course, any technical solution of the present disclosure does not necessarily achieve all the advantages described above at the same time. 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 drawings required for use in the embodiments or the prior art description are briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on the provided drawings without creative work.

[0021] Figure 1 Shown is a schematic diagram of the process flow of the present disclosure.

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

[0023] Figure 3 yes Figure 2 Schematic top view 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 membrane separation component, 13. hydrogen outlet, 14. oxygen outlet, 15. raw water inlet, 17. photothermal catalytic bed, 18. catalytic light column, 19. catalyst coating. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present disclosure are clearly and completely described below in conjunction with the drawings of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure and are intended to be used 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 work are within the scope of protection of the present disclosure.

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

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

[0028] For the Bunsen reaction unit, in the steel-lined tetrafluoroethylene Bunsen tower 1, the absolute pressure is 5 to 25 atm and the temperature is 90 to 140°C, and the following Bunsen reaction occurs: 2H2O+SO2+I2→H2SO4+2HI, and the total feed molar ratio is SO2:I2:H2O=1:(4 to 6):(12 to 20). Among them, SO2 comes from the decomposition product of sulfuric acid, iodine mainly comes from the decomposition product of hydroiodic acid and the circulating iodine in the system, and water comes from the decomposition product of sulfuric acid, the circulating solvent water of sulfuric acid and hydroiodic acid and / or the supplementary raw water. The molar amount of the supplementary water is twice the molar amount of the circulating SO2, that is, the water inlet 15 of the raw water inlet is twice 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% to 16.7% SO2, 6.7% to 8.3% O2, and 75% to 80% water. Since SO2:O2=2:1 in the sulfuric acid decomposition product, there is also 33% O2 ​​mixed with SO2 flowing into Bunsen tower 1. O2 neither participates in the reaction nor dissolves in the liquid, and is discharged from the system from the oxygen outlet 14 of Bunsen tower 1. The liquid from the ammonium iodide crystallizer 5 has 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 Bunsen tower 1 is allowed to stand for stratification for 10 to 60 minutes to form 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 composition of the sulfuric acid phase is H2SO4 45±5wt.%, HI≤5wt.%, I2≤3wt.%, and the balance is H2O; the composition of the hydroiodic acid phase is HI 25±5wt.%, I2 55±5wt.%, H2SO45wt.%, and the balance is H2O.

[0029] Step 2: Sulfuric acid decomposition and gas circulation.

[0030] The sulfuric acid decomposition unit purifies, concentrates, gasifies and decomposes the sulfuric acid phase obtained by static stratification, and decomposes the sulfuric acid at normal pressure and 400-1000°C through a decomposition reaction: H2SO4→H2O+SO2+0.5O2. The decomposed SO2, O2 and H2O are sent back to Bunsen tower 1, wherein the molar ratio of the gas components is SO2:O2:H2O=2:1:(9-12).

[0031] Step 3: ammonium iodide crystallization and circulation.

[0032] The liquid in the hydroiodic acid phase storage tank 4 is pumped into the ammonium iodide crystallizer 5. Under the conditions of 1.2-1.5MPa and 100-130°C, excess ammonia gas is introduced, with a gas-liquid ratio of (3-5):1, and the following reaction HI+NH3→NH4I occurs, and the ammonium iodide produced is a precipitate. The solution supersaturation is controlled to be 1.5-2.0, and the crystal particle size is 100-200μm. The liquid-solid mixture is separated by centrifugation at a speed of 3000-4000rpm to produce ammonium iodide crystals, and the mother liquor is sent back to the Bunsen tower 1.

[0033] Step 4: drying and decomposing ammonium iodide.

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

[0035] The decomposition rate of hydrogen iodide in conventional hydrogen iodide decomposers is low and the decomposition rate is slow. In order to increase the decomposition reaction rate of hydrogen iodide, the present disclosure adopts a photothermal combined catalytic reaction unit to decompose hydrogen iodide. The mixed gas enters the hydrogen iodide decomposer 8, and the hydrogen iodide is decomposed in the photothermal catalytic bed 17 therein. The photothermal catalytic bed 17 includes a plurality of cavities, and the wall surface of the cavity is coated with a photothermal catalyst coating 19, and a catalytic light column 18 is inserted in the cavity. The photothermal 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. Figure 2 and Figure 3 A specific photothermal catalytic bed 17 is shown. The photothermal catalytic bed 17 includes a honeycomb cavity arranged along its length. The cavity cross-section is hexagonal. Each cavity wall is coated with a photothermal catalyst coating 19. A catalytic light column 18 is inserted inside each cavity. The photothermal catalyst coating 19 can catalyze the decomposition of hydrogen iodide at 400-500°C and at 100-1000W / 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% to 30%. HI decomposition reaction: HI→0.5H2+0.5I2. The decomposition gas after the reaction contains NH3, HI, H2, and I2. The 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 from the hydrogen iodide decomposer 8 is pressurized to 1.2-1.5 MPa by the four-stage gas compressor 9 and then sent to the ammonium iodide dryer 6 as the drying gas for the wet ammonium iodide crystals, and is cooled to 120-160°C in the ammonium iodide dryer 6. The decomposed gas and the evaporated water vapor and iodine vapor are blown into the ammonium iodide crystallizer 5 as the ammonia gas source, and the ammonia reacts with the hydrogen iodide in the solution to produce ammonium iodide crystals, and the hydrogen and the excess ammonia and the hydrogen that cannot be absorbed 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 is condensed into liquid ammonia and discharged from the bottom of the liquid ammonia condensation separator 10. It is mixed with the mixed decomposition gas in the ammonium iodide dryer 6 and gasified before being circulated and blown into the ammonium iodide crystallizer 5. The uncondensed gas contains 97%-99% hydrogen and 1%-3% ammonia. The gas is sent to the hydrogen membrane separation component 12. After being filtered through the reverse osmosis membrane, the hydrogen content is increased to 99.97%. The remaining hydrogen-ammonia mixed gas contains 10%-15% hydrogen and 85%-90% ammonia, which is returned to the ammonium iodide crystallizer 5.

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

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

[0040] By developing an ammonia recycling extraction process (reaction formula: NH3(g)+HI(aq)→NH4I(s)↓+H2O), the following breakthroughs were achieved: (1) Improved purity: the H2O content in HI gas is <500ppm, and the I2 content is <50ppm, which is 2 orders of magnitude higher than the traditional extraction method (H2O 45-60wt%, I2 0.2-0.5wt%); (2) Reduced energy consumption: the separation energy consumption is reduced to 85kJ / mol, which is 64% lower than the phosphoric acid extraction method (237kJ / mol) and 53% lower than the electrodialysis coupling process (180kJ / mol); (3) Breakthrough in decomposition efficiency: the measured decomposition rate of anhydrous HI gas at 450°C reaches 30.2%, breaking through the thermodynamic equilibrium limit of 23% for aqueous systems (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 was designed (reaction formula: NH4I(s)→NH3(g)+HI(g)), which produced significant economic benefits: (1) Cost control: The HI purification cost per kg of H2 was reduced to 1.2 yuan, a 76% reduction compared with the barium salt precipitation method (5 yuan / kg H2), pushing the total hydrogen production cost to 5.8 yuan / kg H2; (2) By-product recycling: Ammonia recovery rate >99.5%, system supplementary ammonia consumption <0.03kg / kg H2; (3) Equipment compatibility: The operating pressure of the crystallization reactor is stable at 0.3~0.5MPa, and it can be directly connected to the existing Bunsen reactor output pipeline.

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

[0044] The closed-loop circulation system of anhydrous HI gas is constructed to achieve (1) thermodynamic advantages: the evaporation step of HI-H2O azeotrope is eliminated, and the system thermal efficiency is increased from 43% to 54% (90% of the theoretical value of 60%); (2) energy consumption reduction: compared with the traditional condensation-reevaporation process, the unit hydrogen production steam consumption is reduced by 82% (from 3.8kg / kg H2 to 0.7kg / kg H2); (3) system compactness: the volume power density of the decomposition reactor reaches 12kW / m 3 , which is 3 times higher than that of the water-containing system, laying the foundation for modular device design. Example 1

[0045] The pressure in the steel-lined polytetrafluoroethylene Bunsen reactor is controlled at 1.8MPa, the temperature is 115℃, and the stratification time is 45min. The sulfuric acid decomposition unit continuously produces 168L / min of water vapor, O2 and SO2 gas, with a SO2 concentration of 15.4% and an oxygen concentration of 7.7%. After the gas is pressurized to 1.8MPa, O2 and SO2 gases are directly fed into the reactor at a flow rate of 1.76L / min; the amount of condensed water is 77.3g / min. The mother liquor flow rate of the ammonium iodide crystallizer 5 circulation is 201.8g / min, containing 24.8g / min of water, 131.7g / min of iodine, 37.1g / min of ammonium iodide, and 8.3g / min of sulfuric acid impurities. The atmospheric pressure O2 flow rate discharged from the Bunsen reactor is 6.9L / min. After separation, the sulfuric acid phase is 135g / min, which is composed of 45wt.% sulfuric acid, 4wt.% hydroiodic acid, 2wt.% iodine, and 49wt.% water. It is decomposed under normal pressure and then pressurized and sent back to the Bunsen reactor; the hydroiodic acid phase is 202g / min, which is composed of 21wt.% hydroiodic acid, 45wt.% iodine, 4wt.% sulfuric acid, 12wt.% water, and 18wt.% ammonium iodide. The hydroiodic acid phase is sent to the ammonium iodide crystallizer 5 at a pressure of 1.3MPa and a temperature of 120°C. 7.3L / min of mixed gas (115°C, 1.3MPa) is passed into the ammonium iodide dryer 6, in which the standard volume flow rate of ammonia is 46.4L / 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. The gas is mixed with the gas produced by precooling and membrane separation and then passed into the ammonium iodide crystallizer 5 to produce crystals with a particle size of 150 μm. After centrifugal separation at 3500 rpm, 213.4 g of ammonium iodide crystals with a purity of 99.5 wt.% are obtained. After drying in the ammonium iodide dryer 6, 212.3 g of dry ammonium iodide crystals are obtained. The mother liquor of 201.8 g / min after the reaction in the ammonium iodide crystallizer 5 is sent to the Bunsen tower 1, wherein 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. The 212.3 g of dry ammonium iodide crystals produce 65.6 L of mixed gas of ammonium iodide and hydrogen in the ammonium iodide decomposer 7, and the contents of ammonia and hydrogen iodide gas are both 50%. In the hydrogen iodide decomposition tower, hydrogen iodide decomposes to produce iodine vapor and hydrogen, with a decomposition rate of 22%. The decomposed gas contains ammonia, hydrogen iodide, hydrogen and iodine vapor, with volumes accounting for 50%, 39%, 5.5% and 5.5% respectively. About 10.5g of ammonia water is produced in the liquid ammonia condensation separator 10 and sent back to the ammonium iodide crystallizer 5. The hydrogen produced in the membrane separation system has a purity of 99.97% and a flow rate of 3.6L / 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 cannot be understood as limiting the present disclosure. Without departing from the spirit and scope of the present disclosure, the present disclosure may also have various changes and improvements, which all fall within the scope of the present disclosure claimed for protection.

Claims

1. A sulfur-iodine cycle hydrogen production process based on ammonium iodide crystallization, comprising 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 the decomposition of sulfuric acid, I2 comes from the decomposition of hydroiodic acid and circulating iodine, H2O comes from the decomposition of sulfuric acid, circulating solvent water and / or supplementary raw material water, the reaction product is separated into sulfuric acid phase and hydroiodic acid phase after standing and stratification, and the two phases are separated; S2, sulfuric acid decomposition and gas circulation, the gas obtained from sulfuric acid decomposition is returned to participate in the reaction of S1; S3, ammonium iodide crystallization and circulation, under the conditions of 1.2-1.5MPa and 100-130℃, excess ammonia gas is introduced into the hydroiodic acid phase, with a gas-liquid ratio of (3-5):1, the reaction produces ammonium iodide precipitation, and liquid-solid separation is performed to obtain ammonium iodide crystals, and the separated mother liquor is returned to S1; S4, drying and decomposition of ammonium iodide, drying the ammonium iodide crystals to reduce the content of H2O and I2 attached to them to <500ppm, and controlling the temperature at 120-160°C by cooling, and then decomposing the dried ammonium iodide into gas under the conditions of -0.05--0.02MPa and 560-580°C, and then decomposing the HI in the gas into H2 and I2 under the catalysis of a photothermal catalyst, and the mixed gas after the reaction contains NH3, HI, H2, and I2, and the molar ratio of 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 pressurized and sent back and passed through S4 and S3 in sequence, the mixed gas is cooled to 20-25°C, and the uncondensed gas is purified to obtain hydrogen.

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

3. The sulfur-iodine cycle hydrogen production process based on ammonium iodide crystallization according to claim 1, characterized in that: The molar amount of the supplementary raw water is twice the molar amount of the circulating SO2.

4. The sulfur-iodine cycle hydrogen production process based on ammonium iodide crystallization according to claim 1, characterized in that: The sulfuric acid phase is purified, concentrated, gasified and decomposed under normal pressure and 400-1000°C.

5. The sulfur-iodine cycle hydrogen production process based on ammonium iodide crystallization according to claim 1, characterized in that: When the ammonium iodide is crystallized, the solution supersaturation is controlled to be 1.5-2.0, and the crystal particle size is controlled to be 100-200 μm.

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

7. The sulfur-iodine cycle hydrogen production process based on ammonium iodide crystallization according to claim 1, characterized in that: The mixed gas is pressurized to 1.2-1.5 MPa and sent to S4 as 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 an 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 sulfur-iodine cycle hydrogen production process based on ammonium iodide crystallization according to claim 7, characterized in that: The liquid ammonia separated after cooling is returned to S3 as an ammonia source, and the hydrogen-ammonia mixed gas obtained by reverse osmosis membrane filtration is also returned to S3 as an ammonia source.

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

10. The sulfur-iodine cycle hydrogen production system 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 loop with the ammonium iodide crystallizer, the ammonium iodide crystallizer is also connected in sequence with a liquid ammonia condensation separator and a hydrogen membrane separation component, the liquid ammonia condensation separator and the hydrogen membrane separation component are also provided with a connection loop with the ammonium iodide crystallizer, and the liquid ammonia condensation separator is also connected to a refrigerator.

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