Method and system for using sodium sulfate to assist sulfuric acid decomposition in hydrogen production by sulfur-iodine cycle

Abstract

The application discloses a method and system for decomposing sulfuric acid with the aid of sodium sulfate in a sulfur-iodine cycle hydrogen production process. The method does not change the existing main body of the sulfur-iodine cycle, and decomposes sulfuric acid with the aid of sodium sulfate. The system comprises a concentrated sulfuric acid absorption tower, a sulfur trioxide decomposition tower, a sulfur trioxide decomposition gas-liquid separator, a sulfur trioxide storage tank and a sulfur trioxide feeding pump. The concentrated sulfuric acid absorption tower is provided with anhydrous sodium sulfate in excess of the input concentrated sulfuric acid. The application divides the process of decomposing sulfuric acid into sulfur dioxide into multiple small steps, avoiding the strong corrosion caused by heating sulfuric acid to high temperature. The application directly separates water and sulfur trioxide generated by decomposition by controlling the temperature gradient. Compared with the existing process, the generated water does not need to be heated to high temperature, the energy input of the decomposition tower is reduced, and the total energy efficiency is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sulfur-iodine cycle hydrogen production, and particularly relates to a method and system for decomposing sulfuric acid with the aid of sodium sulfate in sulfur-iodine cycle hydrogen production. BACKGROUND

[0002] Hydrogen is an important chemical raw material and energy storage form with high value. Hydrogen energy is a new green energy and is widely concerned. Green and low-cost hydrogen production methods are also the focus of current research. The thermochemical sulfur-iodine cycle hydrogen production is the most ideal and mature method in the thermochemical cycle hydrogen production process. The main reactions are as follows:

[0003]

[0004]

[0005]

[0006] The three reactions are Bunsen reaction, sulfuric acid decomposition and hydrogen iodide decomposition. Through the circulation of materials, the sulfur-containing material and the iodine-containing material are not consumed in the process, and only water is consumed as the source of hydrogen and oxygen. The total reaction is that water is decomposed into hydrogen and oxygen. The whole process only needs to add water and does not need to add other chemicals, which is green and environmentally friendly. Compared with other hydrogen production methods, the thermochemical sulfur-iodine cycle hydrogen production has the advantages of relatively mild operating conditions, scalability, and high overall energy efficiency. For the sulfur-iodine cycle hydrogen production process, the biggest challenge is the corrosion of the equipment, especially the corrosion of the sulfuric acid decomposition unit. Since the complete decomposition of sulfuric acid into sulfur dioxide requires a temperature above 700℃, the corrosion of high-temperature concentrated sulfuric acid is much stronger than that of low-temperature concentrated sulfuric acid. Even if the sulfuric acid decomposition is divided into two steps, i.e., the decomposition of sulfuric acid into sulfur trioxide and the decomposition of sulfur trioxide into sulfur dioxide, the temperature of the first step reaction needs to be 400-500℃, and it is difficult to find suitable materials to make the container for the reaction.

[0007] The patent CN 116715191 A discloses a sulfuric acid phase decomposition process and system for sulfur-iodine cycle hydrogen production, which proposes a method that can complete the decomposition of sulfuric acid without high temperature. The relevant operation is as follows: concentrated sulfuric acid is slowly added and mixed with solid phosphorus pentoxide, and phosphoric acid and sulfur trioxide are generated. After the sulfur trioxide gas is cooled into liquid, it is fully stirred with sulfur dichloride liquid, and the generated sulfur dioxide gas is returned to the Bunsen tower to continue participating in the Bunsen reaction. Although this method avoids the corrosion of high-temperature sulfuric acid on the equipment, external substances such as phosphorus pentoxide and sulfur dichloride are introduced in the process, which will be continuously consumed with the sulfur-iodine cycle and generate phosphoric acid and thionyl chloride as by-products, and the entire process cannot be completely closed.

[0008] For example, the invention patent publication number: CN 119660675 A, name: A process and system for hydrogen production by thermochemical iodine-sulfur-barium cycle, adopts the method of barium salt precipitation to avoid the corrosion problem of sulfuric acid, and strengthens the stratification of the two phases after the bunsen reaction, avoiding the possible side reactions in the separation process. The specific operation is as follows: excess Ba 2+ reacts with sulfuric acid in the bunsen reaction product to form barium sulfate, and then a first reaction mixture containing HI, BaSO4, H2O, BaI2 and a small amount of unreacted I2 is obtained. The first reaction mixture is separated by cyclone separation, liquid removal and pressure filtration to obtain barium sulfate filter cake and a second mixed solution containing HI, H2O and BaI2; the barium sulfate filter cake is crushed and decomposed at high temperature, the gas generated by decomposition is returned to participate in the bunsen reaction, and the BaO generated by decomposition returns to the bunsen tower to be dissolved into Ba 2+ The process is recycled. The disadvantage of this process is that the decomposition temperature of barium sulfate is above 1100℃, which requires materials that can withstand this temperature for a long time as containers.

[0009] The invention patent publication number: CN 117587434 A, name: An integrated sulfuric acid decomposer and its application, discloses an integrated sulfuric acid decomposer which can be applied to the sulfur-iodine cycle hydrogen production, comprising a sulfuric acid decomposition tube, a high-temperature gas heating tube and a heat preservation device. The sulfuric acid decomposition tube is sleeved on the outer wall of the high-temperature gas heating tube and forms a reaction chamber with the high-temperature gas heating tube. The reaction chamber is provided with a heat-conducting filling layer and a catalytic filling layer. The device uses silicon carbide as the tube material, which can solve the corrosion problem of sulfuric acid. However, the device is a single tube structure, and the heat exchange efficiency is low, which has limitations in industrialization and application. SUMMARY

[0010] For the corrosion problem of sulfuric acid decomposition process in the sulfur-iodine cycle hydrogen production process, there is no perfect solution in the process or device. To this end, the present invention proposes a method and system for assisting sulfuric acid decomposition with sodium sulfate to solve the corrosion problem of sulfuric acid decomposition process. In addition, the energy efficiency of the sulfur-iodine cycle hydrogen production process is also a bottleneck and difficulty, and the present invention also helps to improve the energy efficiency of the process.

[0011] The present invention provides a method for assisting sulfuric acid decomposition with sodium sulfate in the sulfur-iodine cycle hydrogen production process, comprising the following steps:

[0012] The sulfuric acid generated by the bunsen reaction in the sulfur-iodine cycle hydrogen production process is purified and concentrated to obtain concentrated sulfuric acid, and the concentrated sulfuric acid is input into a concentrated sulfuric acid absorption tower for absorption;

[0013] Excess anhydrous sodium sulfate is provided in the concentrated sulfuric acid absorption tower, and the anhydrous sodium sulfate reacts with the concentrated sulfuric acid to generate sodium bisulfate; the remaining anhydrous sodium sulfate and the sodium bisulfate generated by the reaction absorb the water in the concentrated sulfuric acid in the form of crystal water;

[0014] After absorption is completed, the concentrated sulfuric acid absorption tower is sequentially heated in the following heating modes:

[0015] 1) First heated to 100-200℃, so that sodium bisulfate and sodium sulfate undergo dehydration reaction to remove the carried crystal water;

[0016] 2) After the crystal water is completely removed, the heating temperature is increased to 300-400℃, so that sodium bisulfate undergoes dehydration reaction to generate sodium pyrosulfate;

[0017] 3) After sodium bisulfate is completely dehydrated, the heating temperature is further increased to 400-500℃, so that sodium pyrosulfate further undergoes decomposition reaction to generate anhydrous sodium sulfate and sulfur trioxide; the anhydrous sodium sulfate remains in the concentrated sulfuric acid absorption tower for recycling, and the sulfur trioxide is input into the sulfur trioxide decomposition tower for decomposition to obtain gaseous SO2 and O2;

[0018] The undecomposed sulfur trioxide is separated from the SO2 and O2 by cooling and liquefaction, the liquefied sulfur trioxide is mixed with the sulfur trioxide generated by the decomposition of sodium pyrosulfate, and then re-enters the sulfur trioxide decomposition tower for decomposition; the separated SO2 and O2 are separated by using an oxygen separation membrane, and the separated SO2 is used as a raw material for the Bunsen reaction.

[0019] Preferably, the absorption reaction occurring in the concentrated sulfuric acid absorption tower is: ;

[0020] The excess of anhydrous sodium sulfate refers to the excess of anhydrous sodium sulfate relative to the concentrated sulfuric acid to be reacted which is input into the concentrated sulfuric acid absorption tower.

[0021] Preferably, the reaction formula of the dehydration reaction of sodium bisulfate to generate sodium pyrosulfate is: ;

[0022] The water generated by the reaction is discharged from the concentrated sulfuric acid absorption tower in the form of steam; when the steam discharge amount is lower than a set value or no steam is discharged, it is considered that the sodium bisulfate has been completely dehydrated.

[0023] The application also provides a sodium sulfate-assisted sulfuric acid decomposition system for realizing the above-mentioned method, which comprises a concentrated sulfuric acid absorption tower, a sulfur trioxide decomposition tower, a sulfur trioxide decomposition gas-liquid separator, a sulfur trioxide storage tank and a sulfur trioxide feeding pump.

[0024] The concentrated sulfuric acid absorption tower is provided with an excess of anhydrous sodium sulfate relative to the input concentrated sulfuric acid; the concentrated sulfuric acid absorption tower is provided with a gas outlet, which is connected with the input port of the sulfur trioxide decomposition tower, for transporting the generated sulfur trioxide gas in the concentrated sulfuric acid absorption tower to the sulfur trioxide decomposition tower;

[0025] The sulfur trioxide decomposition gas gas-liquid separator is used for separating the undecomposed sulfur trioxide from the SO2 and O2 by liquefaction;

[0026] The sulfur trioxide decomposition gas gas-liquid separator is connected with the sulfur trioxide storage tank and the sulfur trioxide feeding pump in sequence, and is used for conveying the sulfur trioxide gas generated in the sulfur trioxide decomposition gas gas-liquid separator to the sulfur trioxide decomposition tower for a decomposition reaction.

[0027] Preferably, the sodium sulfate auxiliary sulfuric acid decomposition system further comprises an oxygen separation membrane; and the sulfur trioxide decomposition gas gas-liquid separator is connected with the oxygen separation membrane, and is used for separating the SO2 and O2 obtained by gas-liquid separation in the sulfur trioxide decomposition gas gas-liquid separator.

[0028] Compared with the prior art, the present application has the following advantages:

[0029] 1) The method for decomposing sulfuric acid by using sodium sulfate auxiliary sulfuric acid decomposition provided by the present application does not need to change the main process of the sulfur-iodine cycle hydrogen production system, and only needs to directly replace the sulfuric acid decomposition method and the sulfuric acid decomposition tower in the existing sulfur-iodine cycle hydrogen production process by using the method and the system provided by the present application. The present application adds the cycle of Na2SO4→NaHSO4→Na2S2O7→Na2SO4 without changing the main body of the sulfur-iodine cycle, and the cycle does not cause additional material in and out of the whole system. Therefore, the present application can be widely popularized and used in the existing sulfur-iodine cycle hydrogen production system, and has no influence on other unit operations (such as the Bunsen reaction unit, the sulfuric acid phase purification, the HI phase purification and the decomposition unit) in the sulfur-iodine cycle hydrogen production system.

[0030] 2) The cycle of Na2SO4→NaHSO4→Na2S2O7→Na2SO4 provided by the present application divides the process of decomposing sulfuric acid into sulfur dioxide into multiple small steps, avoids the strong corrosion caused by heating sulfuric acid to high temperature, and can use multiple materials to resist the corrosion of low-temperature sulfuric acid. In addition, the cycle process of Na2SO4→NaHSO4→Na2S2O7→Na2SO4 can directly separate the water and sulfur trioxide generated by decomposition by controlling the temperature gradient, compared with the process of directly decomposing H2SO4 into SO2 or first decomposing H2SO4 into SO3 and then decomposing SO3 into SO2, the generated water does not need to be heated to high temperature, the energy input of the decomposition tower is reduced, and the total energy efficiency is improved.

[0031] 3) In the present application, since SO3 does not contain water after decomposition, SO3 can be directly recovered by liquefaction through cooling. In the traditional process, H2SO4, which is the reaction product of SO3 and H2O, is generally recovered, and the energy required for the recycled H2SO4 to continue decomposition is much higher than the energy required for SO3 to be gasified by heating. Therefore, the process adopted by the present application can greatly reduce the energy input of the system and improve the energy efficiency. Attached Figure Description

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Some specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings indicate the same or similar parts or components. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0033] Figure 1 This is a simplified flowchart of the sulfur-iodine cycle hydrogen production method including the sodium sulfate-assisted sulfuric acid decomposition method of the present invention.

[0034] Figure 2 This is a schematic diagram of the process for sodium sulfate-assisted sulfuric acid decomposition according to the present invention;

[0035] Figure 3 This is a schematic diagram illustrating the process principle of sodium sulfate-assisted sulfuric acid decomposition in the sulfur-iodine cycle hydrogen production of the present invention.

[0036] Figure 4 This is a schematic diagram of a process system connection for sodium sulfate-assisted sulfuric acid decomposition in the sulfur-iodine cycle hydrogen production of this invention.

[0037] In the diagram, 1 is a Bunsen tower; 2 is a layered tower; 3 is a hydrogen iodide phase buffer tank; 4 is a sulfuric acid phase buffer tank; 5 is a distillation tower; 6 is a distillation tower condenser; 7 is a hydrogen iodide gas buffer tank; 8 is a hydrogen iodide decomposition tower; 9 is a hydrogen iodide decomposition gas cooling heat exchanger; 10 is a hydrogen iodide phase gas-liquid separator; 11 is a hydrogen separation membrane; 12 is an iodine-containing material buffer tank; 13 is a sulfuric acid phase purification tower; 14 is a vacuum pump; 15 is a sulfuric acid concentration heat exchanger; 16 is a sulfuric acid concentration gas-liquid separator; 17 is a concentrated sulfuric acid absorption tower; 18 is a steam condenser; 19 is a water storage tank; 20 is a sulfur trioxide decomposition tower; 21 is a cooling heat exchanger; 22 is a sulfur trioxide decomposition gas-liquid separator; 23 is a sulfur trioxide storage tank; 24 is a sulfur trioxide feed pump; 25 is an oxygen separation membrane; 26 is a sulfur dioxide buffer tank; 27 is a sulfur dioxide storage tank; 28 is a sulfur dioxide compressor; and 29 is an iodine-containing material delivery pump. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0039] Before introducing this invention, a description of the thermochemical sulfur-iodine cycle hydrogen production process will be provided, such as... Figure 1As shown, the thermo-chemical sulfur-iodine cycle hydrogen production mainly includes three reactions: Bunsen reaction, sulfuric acid decomposition and hydrogen iodide decomposition, in addition, it also involves several separation processes, such as phase separation and separation of Bunsen reaction products, purification and concentration of sulfuric acid phase, purification and concentration of HIx phase; it should be noted that the present application mainly relates to the improvement of sulfuric acid decomposition process in the sulfur-iodine cycle hydrogen production, and the existing technology can still be used for other reaction units and separation units.

[0040] In an illustrative thermo-chemical sulfur-iodine cycle hydrogen production process, the Bunsen reaction can be carried out as follows: using I2, SO2 and water as raw materials to generate the Bunsen reaction , the reaction temperature is 80-130℃, and the reaction pressure is 1-10atm; in the Bunsen reaction, I2 and water as raw materials are excessive, and I2 and I - are combined to make the HIx phase and the sulfuric acid phase completely separated; the mixture enters the demixing column for two-phase separation; wherein, the HIx phase is in the lower layer due to its larger density, and the sulfuric acid phase is in the upper layer.

[0041] In an illustrative thermo-chemical sulfur-iodine cycle hydrogen production process, the purification and decomposition of the HIx phase can be carried out as follows:

[0042] The HIx phase is first purified by rectification in a rectification column, and gaseous HI and a small amount of azeotropic water are separated from the top of the rectification column; the remaining I2, HI, H2O and H2SO4 flow out from the bottom of the rectification column and are finally recycled back to the Bunsen column for the next round of Bunsen reaction; the top temperature of the rectification column is maintained at 80-150℃, the bottom temperature is controlled at 100-200℃, and the operating pressure is 0.5-5atm.

[0043] The purified HI enters the hydrogen iodide decomposition column for decomposition, and the decomposition reaction formula is .

[0044] The hydrogen iodide decomposition column is provided with a catalyst bed, and the catalyst bed is a carrier itself or a carrier loaded with active metals; the carrier includes any one of Al2O3, zeolite and activated carbon;

[0045] The active metals include any one of Pt, Pd and Ru;

[0046] The temperature is controlled at 400-600℃, and the operating pressure is 1-10atm;

[0047] After the decomposition reaction in the hydrogen iodide decomposition tower is completed, the mixture contains I2, HI, H2O and H2; cooling and heat exchange are performed through the hydrogen iodide decomposition gas cooler, I2, H2O and part of HI in the mixture are condensed to realize gas-liquid separation through the hydrogen iodide phase gas-liquid separator, the condensed liquid is sent back to the Bunsen tower reaction, and H2 and HI are separated through membrane separation; H2 is obtained after separation, and HI is sent back to the hydrogen iodide decomposition tower and mixed with the HI gas purified through the rectification tower and then returned to the HI decomposition tower for decomposition.

[0048] In an exemplary thermochemical sulfur-iodine cycle hydrogen production process, the purification and concentration of the sulfuric acid phase can be performed according to the following flow:

[0049] After two-phase separation, the sulfuric acid phase is first input into the sulfuric acid phase purification tower for purification, the pressure is reduced through a vacuum pump, and the reverse reaction of the Bunsen reaction is utilized HI contained in the sulfuric acid phase is removed and separated;

[0050] The separated substances are reactants of the Bunsen reaction and are input back into the Bunsen tower for continuous reaction;

[0051] The purified sulfuric acid is then input into the sulfuric acid concentration heat exchanger and the sulfuric acid concentration gas-liquid separator for concentration to 75-90 wt.%, and the water generated during the concentration process is sent back to the Bunsen tower after condensation for use as raw material.

[0052] The method for decomposing sulfuric acid with the aid of sodium sulfate proposed in the present application uses concentrated sulfuric acid obtained through purification and concentration of the sulfuric acid phase in the thermochemical sulfur-iodine cycle hydrogen production process as raw material. As shown in Figure 2 , a flow diagram and the heating step temperature are given, and the main steps of the method for decomposing sulfuric acid with the aid of sodium sulfate are as follows:

[0053] Concentrated sulfuric acid obtained after purification and concentration of the sulfuric acid phase generated by the Bunsen reaction of the sulfur-iodine cycle hydrogen production is input into a concentrated sulfuric acid absorption tower for absorption;

[0054] Excessive anhydrous sodium sulfate is arranged in the concentrated sulfuric acid absorption tower, the anhydrous sodium sulfate reacts with the concentrated sulfuric acid to generate sodium bisulfate, and the remaining anhydrous sodium sulfate and the generated sodium bisulfate absorb water in the concentrated sulfuric acid in the form of crystal water; the absorption reaction is: ; the excessive anhydrous sodium sulfate refers to the excessive anhydrous sodium sulfate relative to the concentrated sulfuric acid to be decomposed input into the concentrated sulfuric acid absorption tower.

[0055] As shown in Figure 2 , after absorption is completed, the concentrated sulfuric acid absorption tower is sequentially heated in the following heating modes:

[0056] 1) first heated to 100-200℃, sodium bisulfate and sodium sulfate dehydration reaction to remove the carrying water; this step to remove the water in the form of steam from the concentrated sulfuric acid absorption tower;

[0057] 2) after the complete removal of the crystallization water, the heating temperature is increased to 300-400℃, sodium bisulfate dehydration reaction to generate pyrosulfate; reaction formula is: ; the water produced in this step also leaves the concentrated sulfuric acid absorption tower in the form of steam; when the steam discharge is less than the set value or no steam is discharged, it is considered that the sodium bisulfate has been completely dehydrated; the water removed by two steps is cooled and condensed by the water vapor condenser 18, mixed with the make-up water necessary for the system and the water produced by the condensation of concentrated sulfuric acid, and then sent back to the Bunsen tower;

[0058] 3) after the complete dehydration of sodium bisulfate, the heating temperature is further increased to 400-500℃, the pyrosulfate is further decomposed to generate anhydrous sodium sulfate and sulfur trioxide; the anhydrous sodium sulfate is left in the concentrated sulfuric acid absorption tower 17 for recycling; the sulfur trioxide is input into the sulfur trioxide decomposition tower 20 for decomposition to obtain gaseous SO2 and O2.

[0059] In one embodiment of the present application, the product after decomposition in the sulfur trioxide decomposition tower 20 in step 3 is liquefied by cooling to separate the undecomposed sulfur trioxide from SO2 and O2, and the liquefied sulfur trioxide is mixed with the sulfur trioxide generated by the decomposition of pyrosulfate and then enters the sulfur trioxide decomposition tower 20 for decomposition. The separation of the undecomposed sulfur trioxide from SO2 and O2 by liquefaction by cooling specifically includes: the product after decomposition in the sulfur trioxide decomposition tower 20 is cooled by the sulfur trioxide decomposition gas cooler 21, and the undecomposed sulfur trioxide is separated from SO2 and O2 by liquefaction in the sulfur trioxide decomposition gas liquid separator 22; the separated SO2 and O2 are separated by the oxygen separation membrane 25, the separated SO2 is used as the raw material for the Bunsen reaction of the sulfur-iodine cycle hydrogen production, and the O2 is the byproduct of the process.

[0060] The mixing of the liquefied sulfur trioxide with the sulfur trioxide generated by the decomposition of pyrosulfate specifically includes: the liquefied sulfur trioxide is stored in the sulfur trioxide storage tank 23 and mixed with the sulfur trioxide generated by the decomposition of pyrosulfate by the sulfur trioxide feeding pump 24.

[0061] In one embodiment of the present application, a catalyst is provided in the sulfur trioxide decomposition tower to improve the decomposition rate of sulfur trioxide, and the catalyst is a carrier itself or a carrier loaded with active metal, and the content of the loaded metal is generally 0-10wt.%.

[0062] The carrier is any one or a combination of the following: SiO2, Fe2O3, SiC, Ta2O5;

[0063] The active metal is any one or more combinations of the following: Pt, Pd, Ru.

[0064] In the sulfur trioxide decomposition tower, the sulfur trioxide decomposition temperature is set to 700-1000℃, and the pressure inside the sulfur trioxide decomposition tower is 0.1-1 atm.

[0065] like Figure 3 and Figure 4 As shown in the embodiment of the present invention, a sulfur-iodine cycle hydrogen production system using sodium sulfate-assisted sulfuric acid decomposition of the present invention is specifically proposed. The system includes the following units: Bunsen tower 1; layered tower 2; hydrogen iodide phase buffer tank 3; sulfuric acid phase buffer tank 4; distillation tower 5; distillation tower condenser 6; hydrogen iodide gas buffer tank 7; hydrogen iodide decomposition tower 8; hydrogen iodide decomposition gas cooling heat exchanger 9; hydrogen iodide phase gas-liquid separator 10; hydrogen separation membrane 11; iodine-containing material buffer tank 12; and sulfuric acid phase purification tower 13. ; Vacuum pump 14; Sulfuric acid concentration heat exchanger 15; Sulfuric acid concentration gas-liquid separator 16; Concentrated sulfuric acid absorption tower 17; Steam condenser 18; Water storage tank 19; Sulfur trioxide decomposition tower 20; Sulfur trioxide decomposition gas cooling heat exchanger 21; Sulfur trioxide decomposition gas gas-liquid separator 22; Sulfur trioxide storage tank 23; Sulfur trioxide feed pump 24; Oxygen separation membrane 25; Sulfur dioxide buffer tank 26; Sulfur dioxide storage tank 27; Sulfur dioxide compressor 28; Iodine-containing material delivery pump 29.

[0066] The units mentioned above, which are used to realize the sodium sulfate-assisted sulfuric acid decomposition, mainly include concentrated sulfuric acid absorption tower 17, sulfur trioxide decomposition tower 20, sulfur trioxide decomposition gas-liquid separator 22, sulfur trioxide storage tank 23 and sulfur trioxide feed pump 24.

[0067] The concentrated sulfuric acid absorption tower 17 contains an excess of anhydrous sodium sulfate relative to the input concentrated sulfuric acid; the concentrated sulfuric acid absorption tower 17 is provided with a gas outlet, which is connected to the inlet of the sulfur trioxide decomposition tower 20 for transporting the sulfur trioxide gas generated in the concentrated sulfuric acid absorption tower 17 to the sulfur trioxide decomposition tower 20.

[0068] The sulfur trioxide decomposition gas-liquid separator 22 is used to separate undecomposed sulfur trioxide from SO2 and O2 through liquefaction.

[0069] The sulfur trioxide decomposition gas-liquid separator 22 is connected in sequence to the sulfur trioxide storage tank 23 and the sulfur trioxide feed pump 24, and is used to transport the sulfur trioxide gas generated in the sulfur trioxide decomposition gas-liquid separator 22 to the sulfur trioxide decomposition tower 20 for decomposition reaction.

[0070] The sodium sulfate assisted sulfuric acid decomposition system further comprises an oxygen separation membrane 25; the sulfur trioxide decomposition gas-liquid separator 22 is connected to the oxygen separation membrane 25, and is used for separating SO2 and O2 obtained by gas-liquid separation in the sulfur trioxide decomposition gas-liquid separator 22.

[0071] The following will be described in combination with Figure 3 and Figure 4 The whole process of the hydrogen production by the sulfur-iodine cycle using the sodium sulfate assisted sulfuric acid decomposition method of the present application will be introduced as follows:

[0072] The initial materials of the system are iodine, sulfur dioxide and water. After the materials are added in a set proportion according to the process, the three materials will undergo the Bunsen reaction under suitable conditions The reaction temperature is generally selected to be 80-130℃, and the reaction pressure is 1-10 atm. When the initial materials are added, the iodine and water are generally added in excess, which is beneficial to the two-phase separation after the reaction is completed. After the reaction is completed, the mixture is introduced into the demixing column for two-phase separation. Due to the presence of excess iodine, the I2 will combine with I - to make the HIx phase and the sulfuric acid phase completely separated. Since the HIx phase has a large density, it will be in the lower layer of the demixing column, and the sulfuric acid phase will be in the upper layer of the demixing column.

[0073] After sufficient demixing, the HIx phase and the sulfuric acid phase are discharged from the demixing column in sequence. The HIx phase is first introduced into the rectifying column 5 for rectification and purification, and the gaseous HI is separated from the top of the rectifying column. Due to the azeotropic effect, the HI separated from the top generally contains a certain amount of water. The remaining I2, HI, H2O and H2SO4 are discharged from the bottom of the rectifying column, and are finally recycled back to the Bunsen column for the next round of reaction. The temperature at the top of the rectifying column is maintained at 80-150℃, the temperature at the bottom of the rectifying column is controlled at 100-200℃, and the operating pressure is 0.5-5 atm. The purified HI is then introduced into the hydrogen iodide decomposition column 8 for decomposition, and the decomposition reaction formula is Limited by reaction equilibrium and reaction rate, the decomposition rate of HI is very low even at high temperatures. Without a catalyst, the decomposition rate generally does not exceed 1%, and even with a catalyst, it is less than 30%. The hydrogen iodide decomposition tower 8 typically contains a catalyst bed. Catalysts can generally be Al2O3, zeolite, activated carbon, and corresponding supported Pt, Pd, and Ru catalysts. The temperature is controlled at 400-600℃, and the operating pressure is 1-10 atm. After the decomposition reaction, the mixture contains I2, HI, H2O, and H2. Through cooling (9-hydrogen iodide decomposition gas cooling heat exchanger), the I2, H2O, and part of the HI in the mixture are condensed to achieve gas-liquid separation (10-hydrogen iodide phase gas-liquid separator). The condensed liquid is returned to the Bunsen tower for further reaction, while the gas is separated into H2 and HI using membrane separation technology. The separated H2 is collected, and the HI is returned to the decomposition tower, mixed with HI gas purified by the distillation column, and then returned to the HI decomposition tower for further decomposition.

[0074] The sulfuric acid phase, after being separated into layers, first enters the purification unit (13-sulfuric acid phase purification tower) for purification. Purification is achieved by reducing pressure (14-vacuum pump), utilizing the reverse reaction of the Bunsen reaction. The trace amounts of HI contained in the sulfuric acid phase are removed and separated. The separated substance is the reactant of the Bunsen reaction and can be returned to the Bunsen tower to continue the reaction. The purified sulfuric acid then enters the next unit for concentration (15-sulfuric acid concentrator heat exchanger; 16-sulfuric acid concentrator gas-liquid separator). The concentration of sulfuric acid before concentration is generally 40-70 wt.%, and after concentration, the concentration can reach 75-90 wt.%. The concentrated sulfuric acid then enters the absorption tower (17-concentrated sulfuric acid absorption tower) for absorption. The absorption tower contains excess anhydrous sodium sulfate, which reacts with concentrated sulfuric acid. Excess water in concentrated sulfuric acid will combine with NaHSO4 or Na2SO4 as water of crystallization, and eventually all the concentrated sulfuric acid will be absorbed by Na2SO4. After sufficient absorption, the concentrated sulfuric acid absorption tower is heated to 100-200℃ to allow sodium bisulfate and sodium sulfate to undergo a dehydration reaction, removing the carried water of crystallization. Further increasing the temperature to 300-400℃ will cause sodium bisulfate to undergo a further dehydration reaction to form sodium pyrosulfate. The water removed in the two steps is cooled and condensed (using an 18-water vapor condenser). This mixture is then sent back to the Bunsen absorber after being combined with the necessary makeup water and water produced during the sulfuric acid concentration process. After the two-step dehydration, the temperature of the absorber is further increased to 400-500℃, causing further decomposition of the sodium pyrosulfate. The sodium sulfate produced after decomposition will remain in the absorption tower for recycling, while the generated SO3 will enter the decomposition tower (20-sulfur trioxide decomposition tower) for further decomposition. The decomposition tower is provided with a catalyst to improve the decomposition rate. The catalyst can be SiO2, Fe2O3, SiC, Ta2O5 and corresponding supported Pt, Pd, Ru catalysts. The decomposition temperature is generally 700-1000°C, the decomposition rate is generally 40-70%, and the pressure in the tower is 0.1-1 atm. After the decomposition product is cooled (21-sulfur trioxide decomposition gas cooler), the unreacted SO3 is separated from SO2 and O2 by liquefaction (22-sulfur trioxide decomposition gas gas-liquid separator), and the liquefied SO3 is stored in the liquid storage tank (23-sulfur trioxide storage tank). The SO3 is mixed with the SO3 produced by sodium pyrosulfate decomposition by the liquid feeding pump (24-sulfur trioxide feeding pump) and then enters the decomposition tower for decomposition. The separated SO2 and O2 are separated by a gas separation membrane (25-oxygen separation membrane), and the separated O2 is collected as a byproduct or directly discharged. The separated SO2 is recycled and then enters the Bunsen tower for reaction.

[0075] When starting, the SO2 required for the Bunsen reaction is stored in the sulfur dioxide storage tank 27, and then enters the Bunsen tower 1 through the sulfur dioxide buffer tank 26 and the sulfur dioxide compressor 28. The I2 and H2O required for the Bunsen reaction are stored in the iodine-containing material buffer tank 12, and then enter the Bunsen tower 1 through the iodine-containing material liquid feeding pump 29. After the Bunsen reaction, the reaction product enters the separation tower 2 from the Bunsen tower 1, and after a period of separation, the upper layer of the separation tower 2 is sulfuric acid, and the lower layer is HIx. After separation, the two-phase materials flow out from the bottom of the separation tower 2, and then flow into the hydrogen iodide phase buffer tank 3 and the sulfuric acid phase buffer tank 4, respectively. Because the density difference between the sulfuric acid phase and the hydrogen iodide phase is large, the flow direction of the two-phase materials is controlled by monitoring the density of the outflow material and controlling the opening and closing of the valve. The separation tower 2 is provided with two tank bodies, which are switched back and forth by a valve to ensure that the material in the Bunsen tower is not disturbed during the separation process.

[0076] HIx phase from hydrogen iodide phase buffer tank 3 enters into rectification column 5 through a pressure reducing valve, HI and I2 are separated by rectification, and the column top is provided with rectification column condenser 6. The bottom material after rectification contains I2, HI, H2O and H2SO4, which is sent back to iodine-containing material buffer tank 12. The top material is HI and H2O, part of which is condensed and enters into hydrogen iodide gas buffer tank 7, and after mixing with the recycled HI gas, it is sent into hydrogen iodide decomposition column 8. The hydrogen iodide gas is partially converted into I2 and H2 in the decomposition column, and the gas discharged from hydrogen iodide decomposition column 8 enters into hydrogen iodide decomposition gas cooling heat exchanger 9 for cooling. After the I2, H2O and part of the HI produced by the reaction are condensed and liquefied, the gas-liquid mixture enters into hydrogen iodide phase gas-liquid separator 10 for separation of gas and liquid. The liquid phase after separation is transported to iodine-containing material buffer tank 12, and the gas phase enters into hydrogen separation membrane 11 to separate H2 and the remaining HI in the gas phase. The hydrogen is stored or directly used, and the HI is recycled back to hydrogen iodide gas buffer tank 7 and mixed with the HI gas purified by the rectification column.

[0077] The sulfuric acid phase flows out from the sulfuric acid phase buffer tank 4, enters a pressure reducing valve, and then enters the sulfuric acid phase purification tower 13. The purification tower is connected to a vacuum pump 14, which reduces the pressure in the purification tower. The removal of a small amount of HI in the sulfuric acid phase is achieved by utilizing the inverse reaction of the Bunsen reaction, which is more likely to occur at low pressure. The separation of I2 is achieved by utilizing the low pressure and the reduction of boiling point. The I2, SO2, and a small amount of water extracted by the vacuum pump 14 enter the iodine-containing material buffer tank 12 and mix with other materials entering the tank. The purified liquid in the sulfuric acid phase purification tower 13 then enters the sulfuric acid concentration heat exchanger 15 for heating and concentration. The heated gas-liquid mixture enters the sulfuric acid concentration gas-liquid separator 16 for gas and liquid separation. The gas phase is water vapor, and the liquid phase is concentrated sulfuric acid. The gas phase exits the sulfuric acid concentration gas-liquid separator 16 and enters the water vapor condenser 18 for condensation. The separated concentrated sulfuric acid enters the concentrated sulfuric acid absorption tower 17 for absorption. The concentrated sulfuric acid absorption tower 17 is filled with sufficient anhydrous sodium sulfate solid. The concentrated sulfuric acid reacts with anhydrous sodium sulfate to form sodium bisulfate, and the water in the concentrated sulfuric acid is absorbed by the solid to form crystalline water. After a period of absorption, the valve is switched, and the second concentrated sulfuric acid absorption tower continues the absorption. The first absorption tower is heated for dehydration reaction to remove the crystalline water carried by Na2SO4 and NaHSO4. After the crystalline water is removed, the heating temperature is further increased to convert NaHSO4 to Na2S2O7. The water generated in the first and second dehydration reactions is mixed with the water separated from the sulfuric acid concentration gas-liquid separator 16 and enters the water vapor condenser 18 for condensation. The condensed liquid enters the water storage tank 19. The water storage tank 19 has another pipeline that can be used to supplement water to maintain the balance of the total water in the system. The water in the water storage tank 19 then exits the tank and mixes with the materials in the iodine-containing material buffer tank 12. After the reaction of NaHSO4 dehydration to Na2S2O7 is completed in the concentrated sulfuric acid absorption tower 17, the valve is switched, and the temperature is further increased to decompose Na2S2O7 into Na2SO4 and SO3, thereby regenerating Na2SO4. The generated SO3 enters the sulfur trioxide decomposition tower 20 for decomposition. The concentrated sulfuric acid absorption tower 17 requires three towers, one for concentrated sulfuric acid absorption, one for heating and dehydration, and one for cooling standby. The three towers operate in rotation. The sulfur trioxide decomposition tower contains a catalyst, and the decomposed gas enters the sulfur trioxide decomposition gas cooling heat exchanger 21 for cooling. The undecomposed SO3 is condensed into liquid. The cooled gas-liquid mixture enters the sulfur trioxide decomposition gas-liquid separator 22 for separation. The liquid SO3 enters the sulfur trioxide storage tank 23 for buffering. The liquid SO3 is then transported back to the sulfur trioxide decomposition tower 20 by a liquid pump and mixed with the SO3 generated by the decomposition of Na2S2O7.The gaseous components separated by the sulfur trioxide decomposition gas-liquid separator 22 enter the oxygen separation membrane 25 for SO2 and O2 separation. The separated O2 leaves the system, while the SO2 enters the sulfur dioxide buffer tank 26, mixes with the sulfur dioxide storage tank 27, and is then pressurized by the sulfur dioxide compressor 28 before being sent to the Bunsen tower 1 for reaction. When the system is operating stably, the sulfur dioxide storage tank 27 does not need to supply SO2; SO2 can be self-sufficient through recycling.

[0078] Example 1

[0079] like Figure 4 As shown, after a period of operation following the previously described procedures, the system reached a stable state. The temperature in Bunsen tower 1 remained at 100℃, and the pressure at 10 atm. The gaseous SO2 input flow rate was 100 mol / h, the liquid feed I2 flow rate was 1229 mol / h, the HI flow rate was 81 mol / h, the H2O flow rate was 2067 mol / h, and the H2SO4 flow rate was 5 mol / h. Approximately 3 mol / h of SO2 dissolved in the liquid phase was also present. After the reaction in the Bunsen tower, the SO2 was completely converted, and the material then entered the separator for separation. The temperature and pressure in the separator were maintained consistent with those in the Bunsen tower. After one hour of separation, the HIx phase and the sulfuric acid phase flowed out of the separator successively and entered their respective buffer tanks.

[0080] The HIx phase, after being depressurized to 1 atm by a pressure reducing valve, enters a distillation column for rectification. The column has a bottom temperature of 150°C, a top temperature of 120°C, and 15 trays. The top feed consists of 151 mol / h H2O and 228 mol / h HI. The bottom feed consists of 1353 mol / h H2O, 1126 mol / h I2, 53 mol / h HI, and 5 mol / h H2SO4. The bottom product is returned to the iodine-containing buffer tank. The top product is mixed with 772 mol / h HI gas from the recirculation and then enters the HI decomposition column for decomposition. The decomposition column operates at 400°C and 1 atm. The decomposition tower contains a catalyst with a catalytic decomposition rate of 20%. The decomposed gas is cooled and then separated into gas and liquid phases. The liquid phase contains 100 mol / h of I2, 151 mol / h of H2O, and 28 mol / h of HI. This liquid phase is returned to the iodine-containing buffer tank. The gas phase passes through a gas separation membrane to produce 100 mol / h of hydrogen. The remaining HI gas continues to decompose in the decomposition tower.

[0081] The layered sulfuric acid phase is depressurized to 1 atm by a pressure reducing valve and then enters a sulfuric acid phase purification column, wherein the input flow rates of sulfuric acid, water, and HI are 103 mol / h, 563 mol / h, and 6 mol / h, respectively. The pressure in the purification column is 0.1 atm, and the small amount of HI in the sulfuric acid phase is removed by a reverse reaction at low pressure. The generated I2, SO2, and small amount of water are pumped out by a vacuum pump and enter the iodine-containing material buffer tank 12. The purified sulfuric acid phase enters a concentration heat exchanger for evaporation and concentration. Before concentration, the flow rates of sulfuric acid and water are 100 mol / h and 544 mol / h, respectively. The concentration temperature is controlled at 220°C, and the pressure is 1 atm. The concentrated water vapor is separated from the concentrated sulfuric acid by a gas-liquid separator. The water vapor is cooled to 40°C and then enters the water storage tank at a flow rate of 484 mol / h. The concentrated sulfuric acid has a concentration of 90% after concentration, and the flow rates of sulfuric acid and water are 100 mol / h and 60 mol / h, respectively.

[0082] The concentrated sulfuric acid then enters a concentrated sulfuric acid absorption tower and reacts with the sodium sulfate contained therein. Each absorption tower contains 170 kg of anhydrous sodium sulfate. After 6 hours of absorption, the absorption tower is switched to continue absorption. The absorption tower that has absorbed sulfuric acid is first heated to 200°C to remove crystal water for 2 h, then heated to 300°C for further dehydration for 2 h, and then heated to 500°C to decompose sodium pyrosulfate to remove sulfur trioxide for 2 h. After the end, the absorption tower is switched again to cool to room temperature, and the process lasts for 6 h. The water vapor generated by dehydration is cooled to 40°C and then enters the water storage tank. After adding 100 mol / h of supplementary water to the water storage tank, the water is transported to the iodine-containing material buffer tank. The 100 mol / h of high-temperature sulfur trioxide generated by decomposition is mixed with 100 mol / h of liquid sulfur trioxide from the sulfur trioxide storage tank and then gasified and enters the sulfur trioxide decomposition tower for decomposition. The decomposition tower is filled with 1 kg of ferrous sulfate catalyst, the decomposition temperature is 900°C, the pressure is 1 atm, and the decomposition rate is 50%. The mixed gas after decomposition is cooled to 30°C. The 100 mol / h of undecomposed SO3 in the gas is liquefied and then subjected to gas-liquid separation. The SO3 enters the storage tank and is transported back to the decomposition tower by a liquid delivery pump. The remaining SO2 and O2 are separated by a gas separation membrane, and the separation efficiency is 99%. The oxygen production is 50 mol / h, the flow rate of recovered SO2 is 100 mol / h, and the SO2 is pressurized to 10 atm by a compressor and then sent back to the Bunsen tower for reaction. The energy consumption of the concentration heat exchanger is about 10 KW, the total energy consumption of the sulfuric acid absorption tower is about 26 KW, and the total energy consumption of the sulfur trioxide decomposition tower is about 4 KW. The equipment is continuously operated for 168 hours, and the absorption tower made of zirconium operates normally.

[0083] Example 2,

[0084] The same operating procedure and operating conditions as in Example 1 were used in this example, except that each absorption tower was filled with 120 kg of anhydrous sodium sulfate. After 4 hours of absorption, the absorption towers were switched for continued absorption. The absorption tower that had already absorbed sulfuric acid was first heated to 200°C to remove crystallization water for 1 h, then heated to 300°C for further dehydration for 2 h, and then heated to 500°C for decomposition of pyrosulfate to remove sulfur trioxide for 1 h. After the end of the process, the absorption tower was switched again to cool to room temperature, and the process lasted for 4 h. The energy consumption of the concentration heat exchanger in this example was about 10 KW, the total energy consumption of the sulfuric acid absorption tower was about 19 KW, and the total energy consumption of the sulfur trioxide decomposition tower was about 4 KW.

[0085] Example 3

[0086] The same operating procedure and operating conditions as in Example 1 were used in this example, except that the concentrated sulfuric acid had a concentration of 80% after concentration, and the flow rate of the sulfuric acid was 100 mol / h, and the water content was 135 mol / h. Then the concentrated sulfuric acid entered the concentrated sulfuric acid absorption tower to react with the sodium sulfate filled in the tower. Each absorption tower was filled with 170 kg of anhydrous sodium sulfate. After 6 hours of absorption, the absorption towers were switched for continued absorption. The absorption tower that had already absorbed sulfuric acid was first heated to 200°C to remove crystallization water for 2 h, then heated to 300°C for further dehydration for 2 h, and then heated to 500°C for decomposition of pyrosulfate to remove sulfur trioxide for 2 h. After the end of the process, the absorption tower was switched again to cool to room temperature, and the process lasted for 4 h. The energy consumption of the concentration heat exchanger in this example was about 9 KW, the total energy consumption of the sulfuric acid absorption tower was about 27 KW, and the total energy consumption of the sulfur trioxide decomposition tower was about 4 KW.

[0087] Comparative Example 1

[0088] The same operating procedure and operating conditions as in Example 1 were used in this example, except that the concentrated sulfuric acid was directly decomposed. The flow rate of the sulfuric acid entering the sulfuric acid decomposer was 200 mol / h, and the water content was 120 mol / h. In the decomposer, the sulfuric acid was heated to 500°C to decompose to produce sulfur trioxide and water vapor, with flow rates of 200 mol / h and 320 mol / h, respectively, and then entered the sulfur trioxide decomposition tower for decomposition. After decomposition, the decomposition gas was cooled to 40°C. The water and sulfur trioxide cooled to generate 63% sulfuric acid, with a flow rate of 100 mol / h and a water content of 320 mol / h. The generated sulfuric acid was input into the concentration heat exchanger to be concentrated to 90% with the purified sulfuric acid, and then re-entered the decomposer for decomposition. The energy consumption of the concentration heat exchanger in this example was about 18 KW, the energy consumption of the sulfuric acid decomposer was about 18 KW, and the total energy consumption of the sulfur trioxide decomposition tower was 6 KW.

[0089] The energy consumption of the examples and the comparative examples is shown in Table 1. From the above examples and the comparative examples, it can be seen that, because the ordinary sulfuric acid decomposition process cannot achieve complete separation of water and sulfuric acid, the energy consumption of the sulfur trioxide decomposition tower is increased by about 50%. The unreacted sulfur trioxide after the decomposition tower will generate dilute sulfuric acid with water, and this part of sulfuric acid needs to be re-concentrated before it can enter the sulfuric acid decomposer again, resulting in an increase of about 40% in the energy consumption of the sulfuric acid concentration device. Although the energy consumption of the present application in the sulfuric acid absorption tower is greater than that of direct decomposition of sulfuric acid due to the presence of sodium sulfate, the total energy consumption of the system is lower than that of direct decomposition of sulfuric acid. And the present application can further optimize the total energy consumption by optimizing the loading amount of sodium sulfate and the switching time of the absorption tower. More importantly, the use of sodium sulfate assisted sulfuric acid decomposition can avoid the corrosion of high-temperature sulfuric acid and reduce the risk of equipment corrosion.

[0090] Table 1 - Energy consumption comparison of examples and comparative examples

[0091]

[0092] The above is only part of the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for using sodium sulfate to assist in the decomposition of sulfuric acid in a sulfur-iodine cycle hydrogen production process, characterized in that, Includes the following steps: The sulfuric acid phase generated by the Bunsen reaction in the sulfur-iodine cycle hydrogen production process is purified and concentrated to obtain concentrated sulfuric acid, which is then fed into the concentrated sulfuric acid absorption tower (17) for absorption. The concentrated sulfuric acid absorption tower (17) contains an excess of anhydrous sodium sulfate, which reacts with the concentrated sulfuric acid to produce sodium bisulfate; the remaining anhydrous sodium sulfate and the reacted sodium bisulfate absorb the water in the concentrated sulfuric acid as water of crystallization. After absorption is complete, the concentrated sulfuric acid absorption tower (17) is heated sequentially according to the following heating methods: 1) First heat to 100-200℃ to cause sodium bisulfate and sodium sulfate to undergo a dehydration reaction and remove the carried water of crystallization; 2) After the water of crystallization has been completely removed, increase the heating temperature to 300-400℃ to cause sodium bisulfate to undergo a dehydration reaction to produce sodium pyrosulfate; 3) After sodium bisulfate is completely dehydrated, the heating temperature is further increased to 400-500℃, so that sodium pyrosulfate undergoes further decomposition reaction to generate anhydrous sodium sulfate and sulfur trioxide; the anhydrous sodium sulfate is kept in the concentrated sulfuric acid absorption tower (17) for recycling, and the sulfur trioxide is input into the sulfur trioxide decomposition tower (20) for decomposition to obtain gaseous SO2 and O2. Undecomposed sulfur trioxide is separated from SO2 and O2 by cooling and liquefaction. The liquefied sulfur trioxide is mixed with the sulfur trioxide produced by the decomposition of sodium pyrosulfate and then enters the sulfur trioxide decomposition tower (20) for decomposition again. The SO2 and O2 obtained after separation are separated by oxygen separation membrane (25) and the separated SO2 is used as the raw material for the Bunsen reaction of sulfur-iodine cycle hydrogen production.

2. The method as described in claim 1, characterized in that, The reaction that occurs in the concentrated sulfuric acid absorption tower (17) is as follows: ; Anhydrous sodium sulfate excess refers to an excess of anhydrous sodium sulfate relative to the concentrated sulfuric acid to be reacted in the concentrated sulfuric acid absorption tower (17).

3. The method as described in claim 1, characterized in that, The water removed in steps 1) and 2) is cooled and condensed, then mixed with the water required for the Bunsen reaction, and used together as the raw material for the Bunsen reaction. In step 2), the reaction formula for the dehydration of sodium bisulfate to form sodium pyrosulfate is: ; The water generated by the reaction is discharged from the concentrated sulfuric acid absorption tower (17) in the form of steam; when the steam discharge is lower than the set value or no steam is discharged, it is considered that sodium bisulfate and sodium sulfate have been completely dehydrated.

4. The method as described in claim 1, characterized in that, The sulfur trioxide decomposition tower (20) is equipped with a catalyst to improve the sulfur trioxide decomposition rate. The catalyst is either the carrier itself or a carrier loaded with active metals, and the content of the loaded metals is generally 0~10 wt.%. The carrier is any one or more combinations of the following: SiO2, Fe2O3, SiC, Ta2O5; The active metal is any one or more combinations of the following: Pt, Pd, Ru. In the sulfur trioxide decomposition tower (20), the sulfur trioxide decomposition temperature is set to 700-1000℃, and the pressure inside the sulfur trioxide decomposition tower (20) is 0.1-1atm.

5. The method as described in claim 1, characterized in that, In step 3), The undecomposed sulfur trioxide is separated from SO2 and O2 through cooling and liquefaction. Specifically, this includes: After the products decomposed in the sulfur trioxide decomposition tower (20) are cooled by the sulfur trioxide decomposition gas cooling heat exchanger (21), the undecomposed sulfur trioxide is separated from SO2 and O2 by liquefaction in the sulfur trioxide decomposition gas gas-liquid separator (22); SO2 and O2 are separated by oxygen separation membrane (25), with O2 as a by-product.

6. The method as described in claim 5, characterized in that, The liquefied sulfur trioxide is mixed with the sulfur trioxide produced by the decomposition of sodium pyrosulfate, specifically including: The liquefied sulfur trioxide is stored in a sulfur trioxide storage tank (23) and mixed with the sulfur trioxide produced by the decomposition of sodium pyrosulfate through a sulfur trioxide feed pump (24).

7. The method as described in claim 1, characterized in that, The reaction equation for the Bunsen reaction is: ; The reaction temperature is 80-130℃, and the reaction pressure is 1-10 atm; In the Bunsen reaction, iodine and water are in excess as raw materials. The excess iodine is used to react I₂ and I₂. - The combination allows the HIx phase and the sulfuric acid phase to be completely separated; the mixture enters the layered tower (2) for two-phase separation; the HIx phase has a higher density and is located in the lower layer, while the sulfuric acid phase is in the upper layer.

8. The method as described in claim 7, characterized in that, It also includes the following steps: After the two-phase separation, the sulfuric acid phase is first fed into the sulfuric acid phase purification tower (13) for purification. The pressure is reduced by the vacuum pump (14), and the HI contained in the sulfuric acid phase is removed and separated by the reverse reaction of the Bunsen reaction. After purification, the sulfuric acid enters the sulfuric acid concentrator heat exchanger (15) and the sulfuric acid concentrator gas-liquid separator (16) for concentration to obtain 75-90 wt.% concentrated sulfuric acid, which is then absorbed in the concentrated sulfuric acid absorption tower (17). The water generated during the concentration process is condensed and sent back to the Bunsen tower as raw material.

9. A sodium sulfate-assisted sulfuric acid decomposition system, used to implement the method as described in any one of claims 1 to 8, characterized in that, It includes a concentrated sulfuric acid absorption tower (17), a sulfur trioxide decomposition tower (20), a sulfur trioxide decomposition gas-liquid separator (22), a sulfur trioxide storage tank (23), and a sulfur trioxide feed pump (24). The concentrated sulfuric acid absorption tower (17) contains an excess of anhydrous sodium sulfate relative to the input concentrated sulfuric acid; the concentrated sulfuric acid absorption tower (17) is provided with a sulfur trioxide outlet, which is connected to the inlet of the sulfur trioxide decomposition tower (20) for transporting the sulfur trioxide gas generated in the concentrated sulfuric acid absorption tower (17) to the sulfur trioxide decomposition tower (20). The sulfur trioxide decomposition gas-liquid separator (22) is used to separate undecomposed sulfur trioxide from SO2 and O2 by liquefaction; The sulfur trioxide decomposition gas-liquid separator (22) is connected in sequence to the sulfur trioxide storage tank (23) and the sulfur trioxide feed pump (24) to transport the sulfur trioxide gas generated in the sulfur trioxide decomposition gas-liquid separator (22) to the sulfur trioxide decomposition tower (20) for decomposition reaction.

10. The sodium sulfate-assisted sulfuric acid decomposition system as described in claim 9, characterized in that, It also includes an oxygen separation membrane (25); the sulfur trioxide decomposition gas gas-liquid separator (22) is connected to the oxygen separation membrane (25) and is used to further separate SO2 and O2 obtained in the sulfur trioxide decomposition gas gas-liquid separator (22).

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