A sulfuric acid gasifier and modes of use, applications thereof

Abstract

The application provides a sulfuric acid gasifier and a use mode and application thereof, comprising a molten salt flow resistance layer, a molten salt flow area, and a plurality of silicon carbide heat exchange pipes penetrating through the molten salt flow resistance layer and the molten salt flow area, wherein the molten salt flow resistance layer is provided with a porous solid heat-resistant and corrosion-resistant material, and the molten salt flow area and a liquid sulfuric acid cavity are isolated from each other by the salt distributed in the porous solid heat-resistant and corrosion-resistant material; a molten salt inlet is located above a molten salt outlet; and the molten salt is in direct contact with the silicon carbide heat exchange pipes. The molten salt liquid seal solves the problems of poor processing and connection of the silicon carbide pipes. When applied to the thermochemical sulfur-iodine cycle hydrogen production, the recycling of part of the energy on the sulfuric acid heating is realized through a circulating molten salt system.

Description

Technical Field

[0001] This invention relates to the field of thermochemical sulfur-iodine cycle hydrogen production technology, and in particular to a sulfuric acid vaporizer and its usage and application. Background Technology

[0002] Thermochemical hydrogen production technology uses high-temperature heat as an energy source to decompose water into hydrogen and oxygen, which are then delivered from the system through separate devices. Among these, the thermochemical sulfur-iodine cycle hydrogen production technology is considered the most industrially promising, boasting the lowest cost for large-scale hydrogen production. The thermochemical sulfur-iodine cycle employs a three-step closed-loop system—Bunsen reaction, sulfuric acid decomposition, and hydrogen iodide decomposition—theoretically achieving a thermal efficiency of up to 60% for hydrogen and oxygen co-production. Examples include Japan's JAEA's 10NL / h system and Zhejiang University's 5m... 3 The results of the / h-level pilot plant have fully demonstrated the engineering feasibility of this process.

[0003] Currently, there are no dedicated reaction devices or equipment on the market for the gasification and decomposition of high-concentration sulfuric acid (H2SO4). During the sulfur-iodine cycle, the sulfuric acid phase can be purified and concentrated to produce sulfuric acid with a mass concentration of not less than 80%. However, to effectively improve the system's hydrogen production efficiency, the sulfuric acid concentration needs to be further increased to over 96%.

[0004] The process of decomposing sulfuric acid into SO2 involves several key steps: sulfuric acid must first vaporize, then decompose into water and SO3, and further decompose into SO2 and O2. Specifically, sulfuric acid needs to vaporize after reaching its boiling point (336.6℃ at normal pressure), then be heated to 450-550℃ to decompose into SO3, and further decompose into SO2 under the action of a catalyst when the temperature is raised above 700℃.

[0005] While sulfuric acid can be heated and vaporized at atmospheric pressure using a quartz reactor in a laboratory environment, quartz materials pose significant safety risks during industrial scale-up due to their fragility and limited reactor size, making it difficult to meet the demands of large-scale industrial production. Tsinghua University (CN111167382A) disclosed a sleeve-shaped bayonet-shaped sulfuric acid heat exchange gasification and decomposition reactor, which uses a silicon carbide sleeve to achieve the entire process of sulfuric acid heating, vaporization, decomposition, and heat recovery. This reactor integrates the heating, vaporization, and decomposition of low-temperature sulfuric acid within the sleeve. Except for the silicon carbide tube at the 120°C sulfuric acid inlet, which requires sealing, there are no other sealing surfaces in contact with sulfuric acid. Due to the low temperature at this point, fluororubber can be used for sealing. However, this device cannot be scaled up industrially. Furthermore, to ensure the sealing components operate at low temperatures, the sulfuric acid needs to be cooled by external circulating water, resulting in heat loss. Furthermore, the sulfuric acid decomposition reactor disclosed in CN119425535A is essentially structurally identical to that in CN111167382A, both being bayonet-type sleeves. This device does not specify the type of metal material used and similarly fails to address the corrosion problem of boiling sulfuric acid. The thermochemical sulfur-iodine cycle hydrogen production process only achieves low hydrogen production costs on a large scale, and the bayonet-type reactor is clearly unsuitable for large-scale industrial hydrogen production. CN113274755A discloses a process and apparatus for sulfuric acid decomposition to produce oxygen, proposing the use of a composite tower made of corrosion-resistant and high-temperature-resistant stainless steel to process sulfuric acid. The "Corrosion Data and Material Selection Handbook" (Chemical Industry Press) indicates that all chromium-nickel steels exhibit significant corrosion and are unsuitable for medium-concentration sulfuric acid and fuming acid.

[0006] Silicon carbide is brittle and, as a ceramic material, lacks the ductility of metals. It is prone to microcracks under high-temperature thermal stress concentration, especially in geometrically discontinuous areas of tube-to-sheet connections (such as welds and expansion joints). The coefficient of thermal expansion of silicon carbide is ~4.5 × 10⁻⁶. -6 The temperature (°C) is significantly lower than that of metal tube sheets (such as stainless steel, approximately 12 × 10⁻⁶). -6 / ℃). At high temperatures, the difference in expansion between the two materials causes shear stress at the joint, leading to cracking or leakage. This limits the use of silicon carbide as a coating on the surface of metal pipes for corrosion protection (such as the inner tube structure disclosed in CN111167382A). Silicon carbide has an extremely high melting point (~2800℃), making it impossible to achieve a reliable connection between the pipe and the tube sheet using traditional fusion welding (such as arc welding). High-temperature brazing or diffusion welding processes are complex and costly, and it is difficult to guarantee the joint strength. The commonly used expansion joint method for metal tube sheets relies on the plastic deformation of the material, but the brittleness of silicon carbide makes it impossible to form a seal through mechanical expansion. If trace amounts of oxygen or water vapor are present in the system, a silicon dioxide oxide layer may form on the surface of the silicon carbide, leading to material loss or weakening at the joint.

[0007] Therefore, there is an urgent need to develop a sulfuric acid gasification decomposition system that does not rely on high-cost sealing structures and can adapt to industrial-scale production capacity, so as to break through the industrialization bottleneck of thermochemical sulfur-iodine cycle hydrogen production technology. Summary of the Invention

[0008] The purpose of this invention is to provide a solution to the problems of material corrosion and insufficient heat exchange capacity in large-scale sulfuric acid decomposition systems, and to realize the industrial application of thermochemical sulfur-iodine cycle hydrogen production technology and the sulfuric acid vaporizer and its usage and application for large-scale hydrogen production.

[0009] To solve the above-mentioned technical problems, the present invention provides a sulfuric acid vaporizer, comprising a shell, sulfuric acid inlets respectively opened at both ends of the shell, and a sulfuric acid vaporization gas outlet, wherein the medium flows from the sulfuric acid inlet to the sulfuric acid vaporization gas outlet.

[0010] The interior of the shell is provided with, in sequence along the direction of medium flow, a liquid sulfuric acid chamber for supplying liquid sulfuric acid, a molten salt flow barrier layer, a molten salt flow zone, and a sulfuric acid vaporization gas discharge chamber for outputting sulfuric acid vaporization gas.

[0011] The shell contains several silicon carbide heat exchange tubes arranged along the direction of medium flow. The silicon carbide heat exchange tubes penetrate the molten salt flow barrier layer and the molten salt flow zone so that the liquid sulfuric acid chamber and the sulfuric acid vaporization gas discharge chamber are interconnected through the silicon carbide heat exchange tubes.

[0012] The molten salt flow barrier layer is provided with a porous solid heat-resistant and corrosion-resistant material to isolate the molten salt flow zone from the liquid sulfuric acid cavity;

[0013] The molten salt flow zone includes molten salt and a salt heating assembly, with the molten salt covering the outer periphery of the silicon carbide heat exchange tube.

[0014] Furthermore, several baffles are staggered inside the molten salt flow zone so that the molten salt flow zone is divided by several baffles to form a main molten salt channel for molten salt flow, and the salt heating components are arranged along the main molten salt channel.

[0015] Furthermore, a top-layer isolation plate is provided at the junction of the molten salt flow zone and the sulfuric acid vaporization gas discharge chamber, a bottom-layer isolation plate is provided at the junction of the molten salt flow zone and the molten salt flow barrier layer, and a tube sheet is provided at the junction of the molten salt flow barrier layer and the liquid sulfuric acid chamber. At least one of the top-layer isolation plate, the bottom-layer isolation plate, and the tube sheet is provided with a limiting hole that matches the silicon carbide heat exchange tube. The limiting hole is used to limit the silicon carbide heat exchange tube.

[0016] Furthermore, the tube sheet is provided with tube holes adapted to the diameter of the silicon carbide heat exchange tube as limiting holes. The limiting holes include a stepped support structure with a recessed arrangement, and the port of the silicon carbide heat exchange tube is placed on the support structure.

[0017] Furthermore, a molten salt inlet and a molten salt outlet are respectively provided on both sides of the molten salt flow zone. The molten salt inlet is located on the side of the molten salt flow zone near the molten salt flow barrier layer, and the molten salt outlet is located on the side of the molten salt flow zone near the sulfuric acid vaporization gas discharge chamber.

[0018] The inner surface of the housing is provided with several protrusions at intervals along the direction of medium flow, and the top isolation plate, bottom isolation plate and tube sheet are all placed on the protrusions.

[0019] Furthermore, the silicon carbide heat exchange tube is a pressureless sintered silicon carbide tube with an outer diameter of 8-38mm, an inner diameter of 6-28mm, and a length of not less than 2m. The portion of the silicon carbide heat exchange tube located in the molten salt flow zone serves as a heat exchange section with a length of not less than 1.5m, and the portion of the silicon carbide heat exchange tube located in the molten salt flow barrier layer has a length of not less than 0.3m.

[0020] The salt heating component is an electric heating rod, and the salt heating component is arranged in the molten salt flow path;

[0021] The porous solid heat-resistant and corrosion-resistant material is quartz wool.

[0022] The inner wall of the housing is coated with a corrosion-resistant coating.

[0023] This invention also discloses a method of using a sulfuric acid vaporizer, comprising the following steps:

[0024] Maintain the temperature of the liquid sulfuric acid chamber below the melting point of the molten salt; introduce the molten salt into the molten salt flow zone, exchange heat with the silicon carbide heat exchange tube to cool it down, and then flow out of the molten salt flow zone.

[0025] Molten salt enters the molten salt flow barrier layer through the molten salt flow zone. The flow resistance of the molten salt is increased by using porous solid heat-resistant and corrosion-resistant materials, thereby reducing the flow rate of the molten salt. This causes the molten salt that penetrates close to the liquid sulfuric acid chamber to solidify, forming solid molten salt, which then seals the molten salt flow zone and the liquid sulfuric acid chamber, forcing the medium input into the liquid sulfuric acid chamber to enter the silicon carbide heat exchange tube.

[0026] Liquid sulfuric acid at a temperature below 350°C is introduced into the liquid sulfuric acid chamber and then into the silicon carbide heat exchange tube;

[0027] By controlling the flow rate of liquid sulfuric acid and the temperature of molten salt, the gas-liquid interface in the silicon carbide heat exchange tube is controlled to be located in the molten salt flow zone, so that gaseous sulfuric acid and water vapor continue to rise and heat up in the silicon carbide heat exchange tube and carry out sulfuric acid decomposition reaction to produce a mixed gas including SO3 and H2O. The mixed gas rises and flows out of the silicon carbide heat exchange tube and enters the sulfuric acid vaporization gas discharge chamber.

[0028] Maintain the temperature of the molten salt in the upper part of the molten salt flow zone above the boiling point of the mixed gas;

[0029] The pressure in the sulfuric acid vaporization gas discharge chamber is controlled to balance the pressure of the molten salt in the molten salt flow zone, so that a gas-liquid interface is formed between the pressure in the sulfuric acid vaporization gas discharge chamber and the molten salt flow zone, which is no higher than the upper end of the silicon carbide heat exchange tube.

[0030] Furthermore, when the sulfuric acid vaporizer is stopped and restarted: the solidified salt in the molten salt flow path is heated by the salt heating component to form a flow path for the molten salt;

[0031] The solidified molten salt is melted by the flow of molten salt into the molten salt flow zone in the flow path.

[0032] This invention also discloses an application of a sulfuric acid vaporizer, which is used as part of a thermochemical sulfur-iodine cycle hydrogen production system;

[0033] The thermochemical sulfur-iodine cycle hydrogen production system also includes an SO3 decomposer, a molten salt heat exchanger, a Bunsen reaction tower, and a sulfuric acid phase treatment unit;

[0034] The mixed gas, including SO3 and H2O, generated by the sulfuric acid vaporizer is sent to the SO3 decomposer for further heating and decomposition to obtain decomposition products at a temperature of 700~1200℃; the decomposition products are fed into the molten salt heat exchanger to exchange heat with the molten salt flowing out of the molten salt flow zone, and then the cooled decomposition products are output from the molten salt heat exchanger and fed into the Bunsen reaction tower.

[0035] The sulfuric acid phase generated by the Bunsen reactor is purified and concentrated by the sulfuric acid phase treatment unit to form 70-95 wt.% liquid sulfuric acid, which is then fed into the liquid sulfuric acid chamber of the sulfuric acid vaporizer.

[0036] Furthermore, the type of molten salt is selected based on the preset temperature of the sulfuric acid decomposition reaction:

[0037] When the preset temperature is 400~800℃, the molten salt is a mixture of sodium nitrate and sodium chloride in a mass ratio of 7:3;

[0038] When the preset temperature is 250~800℃, the molten salt is a mixture of potassium nitrate and sodium chloride in a mass ratio of 1:1;

[0039] When the preset temperature is above 450℃, the molten salt is sodium nitrate;

[0040] When the preset temperature is 250~400℃, the molten salt is a mixture of potassium nitrate and sodium nitrate in a mass ratio of 6:4;

[0041] When the preset temperature is above 280~400℃, the molten salt is potassium phosphate;

[0042] The temperature difference between the molten salt in the input and output molten salt flow zones is controlled at 100-200℃.

[0043] The beneficial effects of this invention are as follows:

[0044] 1. Using molten salt as the heat exchange medium overcomes the problem of ineffective sealing between the heat exchange tube and sulfuric acid in the traditional sulfuric acid gasification process; the high thermal capacity of molten salt improves heat transfer efficiency and ensures the safety and stability of the heat exchange process.

[0045] 2. The significant temperature gradient generated by the molten salt flow barrier layer spontaneously forms a sealing boundary, solving the mixing and leakage problems between sulfuric acid and the heat exchange medium. This not only improves the safety of the system and reduces the risks caused by corrosive substances, but also significantly improves the gasification efficiency. It overcomes the problem of the inability to seal between silicon carbide heat exchange tubes and tube sheets in high-temperature sulfuric acid solutions in existing technologies, thus solving process problems and safety risks such as the inability to find sealing materials and the mixing and leakage of sulfuric acid and heat exchange medium during sulfuric acid gasification.

[0046] 3. To cope with high temperature and corrosive environments, this invention designs a silicon carbide heat exchange tube array without a sealing structure. The upper tube end extends into the sulfuric acid vaporization gas discharge chamber, utilizing the stable interface between the gas and molten salt to prevent molten salt from flowing into the heat exchange tube. This effectively avoids sulfuric acid gas leakage, ensuring process safety and high heat exchange efficiency. It solves the problem in existing technologies where it is impossible to effectively seal the silicon carbide material with the tube sheet in corrosive environments above 400℃. Thus, without a seal, the heat exchange medium and sulfuric acid decomposition gas are physically separated, preventing leakage and corrosion problems.

[0047] 4. This invention enables efficient sulfuric acid decomposition and heat exchange without the need for a sealed structure. By optimizing heat exchange and reaction conditions, it solves the problems of high decomposition temperature, strong corrosiveness, and significant safety risks associated with sulfuric acid under normal pressure. This facilitates the large-scale operation of sulfuric acid gasification and helps achieve stable thermochemical sulfur-iodine cycle hydrogen production.

[0048] 5. The heat exchange tubes made of SiC material have a simple structure and are easy to process and form. They do not have the structure of bending or folding tubes. Under high pressure and high temperature working environment, they avoid the failure caused by stress concentration at bending or folding tubes, thus increasing durability.

[0049] 6. The heat exchange tubes made of SiC material do not make direct and tight contact with the traditional tube sheet connection, thus avoiding the weak points at the point of contact between the heat exchange tubes and the tubes. This overcomes the problem of not being able to withstand high pressure and high temperature caused by different coefficients of thermal expansion and sealing issues. Attached Figure Description

[0050] Figure 1This is a simplified process flow diagram of the present invention.

[0051] Figure 2 This is a simplified structural diagram of a sulfuric acid vaporizer.

[0052] Figure 3 This is a simplified diagram of the sulfuric acid vaporizer under operating conditions.

[0053] Figure 4 This is a simplified diagram of the tube sheet support structure.

[0054] Figure 5 This is a simplified diagram of the top-level isolation panel support structure.

[0055] Figure 6 This is a simplified diagram of the cross-sectional structure of the baffle plate.

[0056] Figure 7 This is a simplified diagram of the silicon carbide heat exchange tube layout inside the sulfuric acid vaporizer in Example 1.

[0057] In the diagram: 1. Sulfuric acid vaporization gas outlet; 2. Tube orifice; 3. Corrosion-resistant coating; 4. Sulfuric acid vaporization gas discharge chamber; 5. Top layer isolation plate; 6. Molten salt main flow channel; 7. Silicon carbide heat exchange tube; 8. Molten salt flow barrier layer; 9. Tube sheet; 10. Sulfuric acid inlet; 11. Molten salt inlet; 12. Molten salt outlet; 13. Electric heating rod; 14. Liquid sulfuric acid chamber; 15. Molten salt flow zone; 16. Baffle plate; 17. Shell; 18. Bottom layer isolation plate; 19. Boss; 20. Sulfuric acid vaporizer; 21. Molten salt heater; 22. SO3 decomposer; 23. Molten salt storage tank; 24. Molten salt heat exchanger; 25. Hydroiodic acid decomposition section; 26. Make-up water inlet; 27. Hydrogen outlet; 28. Oxygen outlet; 29. ​​Bunsen tower; 30. Sulfuric acid phase treatment unit. Detailed Implementation

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0059] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0060] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0061] like Figure 1-7 As described above, this invention provides a sulfuric acid vaporizer and its usage and applications, such as... Figure 1 The diagram shows a simplified process for the thermochemical sulfur-iodine cycle hydrogen production system of this invention. The thermochemical sulfur-iodine cycle hydrogen production system mainly consists of three parts: a Bunsen reaction system, a hydroiodic acid decomposition hydrogen production system, and a sulfuric acid decomposition oxygen production system. In the system, circulating iodine and sulfur dioxide react with makeup water added to the Bunsen tower to produce a hydroiodic acid phase dominated by hydroiodic acid and a sulfuric acid phase dominated by sulfuric acid, as shown in the following reaction:

[0062]

[0063] The hydroiodic acid decomposition process involves steps such as purification, distillation, decomposition, and recovery of hydrogen iodide from hydroiodic acid to decompose it into hydrogen and iodine. The reaction is as follows:

[0064]

[0065] Hydrogen is sent out of the system, while the iodine produced in the reaction, as well as the recovered hydrogen iodide, water, etc., are recycled back to the Bunsen tower.

[0066] After purification and concentration, the sulfuric acid phase forms concentrated sulfuric acid with a concentration of not less than 70%. The concentrated sulfuric acid enters the sulfuric acid vaporizer, where heating decomposes the liquid sulfuric acid into SO3 and H2O, as follows:

[0067]

[0068] At atmospheric pressure, the azeotropic point of sulfuric acid is 98.3 wt.%, and its boiling point is 336.6℃. At atmospheric pressure, when the sulfuric acid concentration is below 80 wt.%, the water content in the steam generated by heating sulfuric acid is above 99.999 wt.%; when the sulfuric acid concentration increases from 80 wt.% to 98.3 wt.%, the sulfuric acid content in the steam generated by heating sulfuric acid increases from 0.001 wt.% to 98.3 wt.%. Therefore, when starting up a sulfuric acid vaporizer, because the sulfuric acid concentration is usually below 98.3 wt.%, the liquid sulfuric acid in the vaporizer is continuously concentrated, and the sulfuric acid concentration in the generated steam is lower than that in the liquid phase. As the liquid sulfuric acid in the vaporizer is concentrated and approaches 98.3 wt.%, while lower-concentration liquid sulfuric acid continuously flows into the vaporizer, the mass and composition of the substances at the inlet and outlet of the vaporizer gradually reach a dynamic equilibrium. Under dynamic equilibrium, the concentration and mass flow rate of sulfuric acid evaporated in the sulfuric acid vaporizer are the same as those entering the vaporizer, while the concentration of mother liquor sulfuric acid in the vaporizer remains at 97-98.3 wt.%. The gaseous sulfuric acid evaporated in the vaporizer continues to absorb heat and decomposes into SO3 and H2O when heated to above 300℃. The SO3 and H2O mixture exiting the vaporizer enters the SO3 decomposer, where it exchanges heat with high-temperature helium gas at 950-1500℃ and is then heated to above 600℃. Upon heating, SO3 decomposes into SO2 and O2, as follows:

[0069]

[0070] The SO2 and O2 mixture, along with water vapor, exits the sulfuric acid vaporizer, is cooled, and then returned to the Bunsen tower. SO2 and H2O become reactants and continue the reaction, while the remaining O2 in the gas phase is discharged from the Bunsen tower. The sulfuric acid vaporizer needs to heat the inlet liquid sulfuric acid from 100-200°C to 300-500°C, while the mixed gas exiting the SO3 decomposer 22 needs to be cooled from above 600°C to near 100°C. Both fluids are partially recycled through a circulating molten salt system. The molten salt exchanges heat with the high-temperature decomposition gas from the SO3 decomposer 22 outlet, raising the temperature of the molten salt to above 500°C. It is then fed into the sulfuric acid vaporizer to vaporize and heat the sulfuric acid. After exiting the vaporizer, the gas is returned to the molten salt storage tank, thus completing the cycle. Due to the high heat exchange temperature and the direct contact and mixing of the heat exchange medium with sulfuric acid and vaporized gas, using water or heat transfer oil as the heat exchange medium makes it difficult to efficiently and cost-effectively separate the mixed gas from the heat exchange medium, which will disrupt the material balance after prolonged system circulation. After the heat transfer oil comes into contact with the mixed gas, deflagration or other problems may occur in the SO3 decomposer 22. Molten salt, due to its flow characteristics and low volatility, poses no potential risk when in contact with sulfuric acid, SO3, and H2O. However, molten salt heat exchange systems face difficulties in starting and stopping due to the solidification and slagging of the molten salt after shutdown; therefore, a heating start-up system is necessary.

[0071] like Figure 2 The diagram shows a simplified structure of a sulfuric acid vaporizer. The sulfuric acid vaporizer is a vertical device, consisting of, from bottom to top, a liquid sulfuric acid chamber 14, a molten salt flow barrier layer 8, a molten salt flow zone 15, a silicon carbide heat exchange tube 7, and a sulfuric acid vaporization gas discharge chamber 4.

[0072] Figure 3 The diagram shows the sulfuric acid vaporizer in operation. Liquid sulfuric acid at 100~336.6℃ flows into the liquid sulfuric acid chamber 14 from the sulfuric acid inlet 10 and is automatically distributed into the silicon carbide heat exchange tubes 7. As the liquid sulfuric acid continues to flow in, the liquid level in the silicon carbide heat exchange tubes 7 rises until the sulfuric acid inflow rate in the silicon carbide heat exchange tubes 7 is balanced with the sulfuric acid vaporization rate. Gaseous sulfuric acid and water vapor continue to rise and heat up in the silicon carbide heat exchange tubes 7, while the sulfuric acid decomposes. The mixed gas flowing out of the silicon carbide heat exchange tubes 7 enters the sulfuric acid vaporization gas discharge chamber 4 and flows out from the top sulfuric acid vaporizer outlet 1. The molten salt system is selected based on the decomposition temperature of the sulfuric acid decomposition tower. Suitable molten salt systems include: NaNO3-NaCl system (operating temperature approximately 400~800℃, sodium nitrate to sodium chloride ratio 7:3), KNO3-NaCl system (operating temperature approximately 250~800℃, potassium nitrate to sodium chloride ratio 1:1), KNO3-NaNO3 system (operating temperature 250~400℃, potassium nitrate to sodium nitrate ratio 6:4), sodium nitrate system (operating temperature above 330~450℃), and potassium phosphate system (operating temperature 280~400℃). The temperature difference between the molten salt inlet and outlet is controlled at 100-200℃ to reduce thermal stress and instability of the molten salt. The NaNO3-NaCl molten salt, heated to 500~700℃, flows into the sulfuric acid vaporizer from the molten salt inlet, flows through the shell side, moves upward through the "S"-shaped flow channel, exchanges heat with the heat exchange tubes to cool down, and finally flows out of the sulfuric acid vaporizer from the molten salt outlet. When using molten salt as a heat exchange medium, equipment start-up and shutdown must be considered. When the equipment stops, the molten salt cools and solidifies into solid salt. When the machine needs to be restarted, the molten salt cannot flow, thus preventing the external heat exchanger from heating and melting the molten salt in the sulfuric acid vaporizer. Common molten salt heat exchange systems require the installation of electric heating grids or metal heating layers within the equipment. This invention uses electric heating rods 13 to melt a small amount of solid salt in the main molten salt channel, achieving flow-based start-up of the molten salt. When the equipment needs to be started, only a small amount of heat is needed to melt the solid salt surrounding the electric heating rods, forming a main molten salt channel at the inlet and outlet. Subsequently, the molten salt flows at a small flow rate. The same heating rod arrangement is implemented in the molten salt storage tank, thereby achieving a small-flow-rate circulation of the molten salt. During the circulation process, heat from the molten salt heater is continuously introduced into the circulation system, thereby continuously melting more molten salt and accelerating the circulation. Ultimately, all the molten salt in the system is maintained within the operating temperature range and kept in a liquid state. At this point, liquid sulfuric acid is introduced to achieve stable sulfuric acid vaporization and decomposition.

[0073] A molten salt flow-blocking layer 8 is provided in the sulfuric acid vaporizer. When the molten salt flows downward through the gap between the bottom isolation plate 18 and the silicon carbide heat exchange tube 7, the quartz wool filling the molten salt flow-blocking layer 8 increases the flow resistance of the molten salt through its fine pores, thereby controlling the flow rate of the molten salt. As the molten salt continuously permeates to the bottom of the sulfuric acid vaporizer, its temperature gradually decreases to below 350°C, causing the molten salt to gradually become viscous and solidify, thus automatically forming a solid molten salt seal. When sulfuric acid from the liquid sulfuric acid chamber flows into the molten salt flow-blocking layer 8 through the gap between the tube sheet 9 and the silicon carbide heat exchange tube 7, the quartz wool filling the molten salt flow-blocking layer 8 also increases the flow resistance of the sulfuric acid through its fine pores, ultimately completely blocking the small amount of sulfuric acid that comes into contact with the molten salt from entering the solid molten salt.

[0074] The molten salt flow barrier layer 8 solves the problem of molten salt flowing downwards into the liquid sulfuric acid chamber 14 and slagging at the sulfuric acid inlet 10, thus preventing blockage of the sulfuric acid inlet.

[0075] In the sulfuric acid vaporizer discharge chamber at the top of the vaporizer, the temperature of the molten salt drops to 400-600℃, yet it still retains good fluidity. When the mixed gas (SO3, H2O, etc.) produced by sulfuric acid decomposition flows downwards through the gap between the top-layer isolation plate 5 and the silicon carbide heat exchange tube 7, the mixed gas does not condense due to the high temperature of the molten salt, and a stable interface can be formed with the molten salt within a certain pressure fluctuation range. When the molten salt permeates through this gap into the sulfuric acid vaporization gas discharge chamber 4, the silicon carbide heat exchange tube 7 extending above the top-layer isolation plate 5 prevents the molten salt from flowing into the heat exchange tube, and the molten salt surface and the vaporization gas also form a stable interface within a certain pressure fluctuation range.

[0076] Figure 4 The diagram shows a simplified representation of the support structure for the tube sheet 9 and the silicon carbide heat exchange tubes 7. The inner wall of the sulfuric acid vaporizer, the tube sheet, the bottom isolation plate, the baffle plate, the top isolation plate, and the inlet and outlet of sulfuric acid and molten salt are all coated with a suitable corrosion-resistant coating 3. The coating is preferably made of ceramic material, specifically silicon carbide ceramic lining. The tube sheet 9 and the tube holes 2 are coated with 1-10 mm thick silicon carbide ceramic. Each silicon carbide heat exchange tube 7 on the tube sheet 9 has stepped tube holes, and all bends are rounded to avoid stress concentration in the ceramic. The heat exchange tubes stand on the stepped tube holes, and the outside of the tubes is filled with quartz wool.

[0077] Figure 5The diagram shows a simplified representation of the support structure between the top-level isolation plate 5 and the silicon carbide heat exchanger tubes 7. Since the silicon carbide heat exchanger tubes 7 cannot be sealed using the expansion joints or welding methods employed in conventional metal heat exchangers, this area cannot be sealed. In this invention, the top-level isolation plate 5 provides only radial support to the silicon carbide heat exchanger tubes 7, ensuring that the tubes 7 are arranged at a specified distance, without any axial support or restriction. The top-level isolation plate 5, bottom-level isolation plate 18, tube sheet 9, baffle plate 16, etc., are supported by multiple circumferentially arranged support bosses between themselves and the shell 17. The number of bosses is a multiple of four and evenly distributed along the circumference. The plate positions and orientations are controlled by the bosses in conjunction with tie rods and spaced tube bundles.

[0078] Figure 6 The diagram shown is a simplified top view of a cross-section of the baffle 16. Eight bosses are evenly distributed along the edge of the shell 17 to support the baffle 16. The edges, top and bottom surfaces, pipe holes, and inner wall of the shell 17 are all coated with a corrosion-resistant coating 3.

[0079] Example 1:

[0080] The sulfuric acid with a concentration of 80 wt.% and an atmospheric pressure of 175 °C obtained by pretreatment of the sulfuric acid phase was evaporated and decomposed into sulfur trioxide and water vapor using a sulfuric acid vaporizer.

[0081] The arrangement of silicon carbide heat exchange tubes 7 in the sulfuric acid vaporizer is as follows: Figure 7 As shown. The silicon carbide heat exchange tube 7 is a pressureless sintered silicon carbide tube with a length of 4m, including a heat exchange section of 3.65m, an extension of 0.05m beyond the top isolation plate, and a molten salt flow-blocking zone 8 with a height of 0.3m. There are 38 silicon carbide heat exchange tubes 7, with an outer diameter of 25mm and an inner diameter of 20mm. The sulfuric acid vaporizer shell 17 has an inner diameter of 294mm and an outer diameter of 338mm. The outer side of the shell 17 is insulated with 30cm thick thermal insulation cotton. The shell 17 is made of 19mm thick carbon steel, with a 3mm silicon carbide coating on the inner wall.

[0082] A NaNO3-NaCl mixed salt (7:3 ratio) was used as the molten salt heat medium. The inlet temperature of the molten salt was 690~710℃, the flow rate was 1050~1060 L / h, and the outlet temperature was 590~610℃. The sulfuric acid temperature in the liquid sulfuric acid chamber was 175℃, the inlet flow rate was 99~100 kg / h, and the outlet temperature of the sulfuric acid vaporization gas was 448~453℃ with a flow rate of 160~162 m³ / h. 3 / h, the concentrations of sulfur trioxide and water vapor were measured to be 29.8% and 70.2%, respectively.

[0083] like Figure 1As shown. Iodine and water recycled from the hydroiodic acid decomposition section 25 back to the Bunsen tower 29, SO2 and water cooled by the molten salt heat exchanger 24 from the SO3 decomposer 22, and water supplemented from the makeup water inlet 26 undergo the Bunsen reaction to produce a hydroiodic acid phase dominated by hydroiodic acid and a sulfuric acid phase dominated by sulfuric acid. The molar ratio of makeup water, recycled SO2, and recycled iodine is 2:1:(2~10). The hydroiodic acid phase is purified, concentrated, purified with hydrogen iodide, and decomposed in the hydroiodic acid decomposition section 25 to produce hydrogen gas and elemental iodine. The hydrogen gas is discharged from the hydrogen outlet 27, and the elemental iodine is cooled and recycled back to the Bunsen tower 29. The sulfuric acid phase is purified and concentrated in the sulfuric acid phase treatment unit 30 to form 70-95 wt.% concentrated sulfuric acid, which is sent to the sulfuric acid vaporizer 20 and heated to 350-600℃ to vaporize and decompose into SO3 and H2O. A mixture of SO3 and H2O is fed into an SO3 decomposer and further heated to 700-1200℃ to decompose into SO2 and O2. A mixture of water vapor, SO2, and O2 at 700-1200℃ is fed into a molten salt heat exchanger 24 to heat the molten salt and recover the heat from the mixture. It is then returned to the Bunsen tower 29, where water vapor and SO2 continue to participate in the thermochemical cycle, while O2 is discharged from the oxygen outlet 28 of the Bunsen tower 29. Molten salt at 400-650℃ is fed from a molten salt storage tank 23 into a molten salt heat exchanger 24 and heated to 500-800℃. It is then fed into a sulfuric acid vaporizer 20 to heat the sulfuric acid and cool it to 400-650℃. The cooled salt then flows out of the sulfuric acid vaporizer 20 and back into the molten salt storage tank, completing the molten salt heat exchange cycle.

[0084] like Figure 2 As shown, all surfaces in the sulfuric acid vaporizer 20 that come into contact with sulfuric acid and molten salt are coated with a corrosion-resistant coating 3. Figure 3 As shown, liquid concentrated sulfuric acid at a temperature of 80~300℃ enters the liquid sulfuric acid chamber 14 of the sulfuric acid vaporizer 20 from the sulfuric acid inlet 10. The inner side of the shell 17 of the sulfuric acid vaporizer 20 is coated with a corrosion-resistant coating 3. The baffle 16, tube sheet 9, bottom isolation plate 18, top isolation plate 5, and pipe holes are all coated with the corrosion-resistant coating 3. The corrosion-resistant coating 3 can be made of various ceramic coatings, preferably silicon carbide coatings. Figure 4 As shown, the top of the liquid sulfuric acid chamber 14 is a tube sheet 9, and each silicon carbide heat exchange tube 7 has a tube hole 2 on the tube sheet 9. The silicon carbide heat exchange tube 7 is supported by the steps of the tube hole 2, and there is no seal between the two. The inside of the silicon carbide heat exchange tube 7 is liquid sulfuric acid, and the outside is a molten salt flow-blocking layer 8. The molten salt flow-blocking layer 8 is filled with quartz wool to increase the flow resistance of the fluid.

[0085] The sulfuric acid level in the silicon carbide heat exchange tube 7 rises continuously. When the level passes through the horizontal plane of the bottom isolation plate 18, the sulfuric acid and molten salt undergo indirect heat transfer through the silicon carbide heat exchange tube 7. The sulfuric acid heats up and gradually vaporizes until it is completely converted into gas. It continues to heat up in the upper part of the silicon carbide heat exchange tube 7 and then enters the sulfuric acid vaporization gas discharge chamber 4, and is then discharged from the sulfuric acid vaporizer 20 through the sulfuric acid vaporization gas outlet 1.

[0086] Molten salt enters the sulfuric acid vaporizer 20 through the molten salt inlet 11. Under the action of the baffle 16, the molten salt flows upward in an "S"-shaped channel within the sulfuric acid vaporizer 20 and exits from the sulfuric acid vaporizer 20 through the molten salt outlet 12. An electric heating rod 13 is installed on the "S"-shaped molten salt main channel 6 to locally melt the mixed salt to form flowing molten salt when the sulfuric acid vaporizer 20 is started. The flowing molten salt melts the solid salt layer by layer, eventually forming a high-temperature flow environment in the molten salt flow zone 15.

[0087] Molten salt seeps downwards through the pores 2 of the bottom insulating plate 18 into the molten salt flow-blocking layer 8. The quartz wool increases the flow resistance of the molten salt, but a small amount still seeps downwards. Due to the high thermal resistance of the quartz wool, the temperature below the horizontal plane of the bottom insulating plate 18 is lower, thus cooling the molten salt, causing it to solidify and form a self-sealing layer. Figure 4 As shown, sulfuric acid permeates into the molten salt flow barrier layer 8 through the gap between the tube hole 2 and the silicon carbide heat exchange tube 7. The asbestos filling the molten salt flow barrier layer 8 increases the resistance to the upward flow of sulfuric acid, but a small amount of sulfuric acid still penetrates upward and is isolated by the self-sealing boundary of the solid salt, and cannot continue to pass through the bottom isolation plate 18 into the molten salt flow zone 15.

[0088] like Figure 5 As shown, each silicon carbide heat exchange tube 7 has a tube hole 2 on the top isolation plate 5. There is no seal between the tube hole 2 and the silicon carbide heat exchange tube 7, and there is a gap of 0.5-5mm. When molten salt flows through this gap, it can permeate upwards into the sulfuric acid vaporization gas discharge chamber 4. The tube opening of the silicon carbide heat exchange tube 7 extends 50-200mm beyond the top isolation plate 5, and the molten salt will not flow into the interior of the silicon carbide heat exchange tube 7 after permeation. Conversely, if sulfuric acid vaporization gas permeates downwards through the gap, it neither dissolves in the molten salt nor reacts with the molten salt, so no additional treatment is required. The molten salt outlet flow rate is controlled by detecting the liquid level height of the molten salt above the top isolation plate 5, so there is no need for a seal between the top isolation plate 5 and the silicon carbide heat exchange tube 7.

[0089] When the equipment needs to be restarted after a shutdown, the molten salt stops flowing, and the heat source stops supplying heat, thus cooling and solidifying. The main molten salt channel 6 in the sulfuric acid vaporizer 20 is equipped with an electric heating rod 13. When using the NaNO3-NaCl system, the electric heating rod 13 heats a small amount of nearby NaNO3-NaCl mixed salt until it melts, then stops supplying heat. This portion of molten salt then circulates, heating to 500-800℃ before flowing into the sulfuric acid vaporizer 20, heating other solid salts to melt, significantly reducing power consumption and enabling rapid startup.

[0090] like Figure 6 The diagram shows a top cross-sectional view of the baffle plate 16. The baffle plate 16 is supported by bosses 19 evenly distributed along its circumference. The baffle plate 16 has pipe holes 2, which are coated with a corrosion-resistant coating 3. The spacing of the baffle plates 16 is controlled to be 250~500mm using tie rods and spacer tubes. The silicon carbide heat exchange tube 7 passes through the baffle plate 16 and the molten salt flow zone 15, without a seal between it and the baffle plate 16. The baffle plate 16 provides radial restraint and support for the silicon carbide heat exchange tube 7.

[0091] This invention is not limited to the preferred embodiments described above. Anyone can derive other products in various forms under the guidance of this invention. However, regardless of any changes in shape or structure, any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A sulfuric acid gasifier, comprising a shell (17), a sulfuric acid inlet (10) and a sulfuric acid gas outlet (1) respectively arranged at two ends of the shell (17), and a medium flowing from the sulfuric acid inlet (10) to the sulfuric acid gas outlet (1), characterized in that: a liquid sulfuric acid cavity (14) for supplying liquid sulfuric acid, a molten salt flow resistance layer (8), a molten salt flowing area (15) and a sulfuric acid gas discharge cavity (4) for outputting sulfuric acid gas are sequentially arranged in the shell (17) along the medium flow direction; a plurality of silicon carbide heat exchange pipes (7) are arranged in the shell (17) along the medium flow direction, the silicon carbide heat exchange pipes (7) penetrating through the molten salt flow resistance layer (8) and the molten salt flowing area (15) so that the liquid sulfuric acid cavity (14) and the sulfuric acid gas discharge cavity (4) are communicated with each other through the silicon carbide heat exchange pipes (7); a porous solid heat-resistant and corrosion-resistant material is arranged in the molten salt flow resistance layer (8) for isolating the molten salt flowing area (15) from the liquid sulfuric acid cavity (14); the molten salt flowing area (15) comprises molten salt and a salt heating assembly, and the molten salt is wrapped around the outer periphery of the silicon carbide heat exchange pipes (7); a top isolation plate (5) is arranged at the junction of the molten salt flowing area (15) and the sulfuric acid gas discharge cavity (4), a bottom isolation plate (18) is arranged at the junction of the molten salt flowing area (15) and the molten salt flow resistance layer (8), a tube plate (9) is arranged at the junction of the molten salt flow resistance layer (8) and the liquid sulfuric acid cavity (14), and at least one of the top isolation plate (5), the bottom isolation plate (18) and the tube plate (9) is provided with a limiting hole matched with the silicon carbide heat exchange pipes (7), and the limiting hole is used for limiting the silicon carbide heat exchange pipes (7); the tube plate (9) is provided with a tube hole (2) matched with the tube diameter of the silicon carbide heat exchange pipes (7) as the limiting hole, the limiting hole comprises a recessed stepped support structure, and the port of the silicon carbide heat exchange pipes (7) is placed on the support structure; the porous solid heat-resistant and corrosion-resistant material is quartz wool. A plurality of baffles (16) are arranged in the molten salt flowing area (15) in a staggered manner so that the molten salt flowing area (15) is divided into a molten salt main flow channel (6) for molten salt flowing by the baffles (16), and the salt heating assembly is arranged along the molten salt main flow channel (6). A molten salt inlet (11) and a molten salt outlet (12) are arranged on both sides of the molten salt flowing area (15) respectively, the molten salt inlet (11) is arranged on the side of the molten salt flowing area (15) close to the molten salt flow resistance layer (8), and the molten salt outlet (12) is arranged on the side of the molten salt flowing area (15) close to the sulfuric acid gas discharge cavity (4); A plurality of bosses (19) are arranged on the inner surface of the shell (17) in a spaced manner along the medium flow direction, and the top isolation plate (5), the bottom isolation plate (18) and the tube plate (9) are all placed on the bosses (19). ​ ​ ​ ​ 2. The sulfuric acid gasifier of claim 1, wherein: ​ 3. The sulfuric acid gasifier of claim 1, wherein: ​ ​ 4. The sulfuric acid gasifier of claim 1, wherein: The silicon carbide heat exchange pipe (7) is a pressureless sintering specification silicon carbide pipe with an outer diameter of 8-38 mm, an inner diameter of 6-28 mm, and a length of not less than 2 m. The silicon carbide heat exchange pipe (7) is located in the part of the molten salt flowing area (15) as a heat exchange section, and the length of the heat exchange section is not less than 1.5 m. The length of the silicon carbide heat exchange pipe (7) located in the molten salt flow resistance layer (8) is not less than 0.3 m. The salt heating assembly is an electric heating rod (13), and the salt heating assembly is arranged on the molten salt flowing path. The inner wall of the shell (17) is coated with a corrosion-resistant coating (3).

5. A mode of use of a sulfuric acid gasifier according to any one of claims 1-4, characterized in that, The method comprises the following steps: The temperature of the liquid sulfuric acid cavity (14) is kept below the melting point of the molten salt; the molten salt is input into the molten salt flowing area (15), exchanges heat with the silicon carbide heat exchange pipe (7) to reduce the temperature, and flows out of the molten salt flowing area (15); The molten salt penetrates through the molten salt flowing area (15) into the molten salt flow resistance layer (8), uses the porous solid heat-resistant and corrosion-resistant material to increase the flow resistance of the molten salt, reduces the flow of the molten salt, so that the molten salt close to the liquid sulfuric acid cavity (14) is solidified to form solid molten salt, thereby sealing the molten salt flowing area (15) and the liquid sulfuric acid cavity (14), and forcing the medium input into the liquid sulfuric acid cavity (14) to enter the silicon carbide heat exchange pipe (7); The liquid sulfuric acid below 350℃ is input into the liquid sulfuric acid cavity (14), and then enters the silicon carbide heat exchange pipe (7); By controlling the flow rate of the liquid sulfuric acid and the temperature of the molten salt, the gas-liquid interface in the silicon carbide heat exchange pipe (7) is located in the molten salt flowing area (15), so that the gaseous sulfuric acid and water vapor continue to rise and warm up in the silicon carbide heat exchange pipe (7), and the sulfuric acid decomposition reaction is carried out to generate mixed gas containing SO3 and H2O, which flows out of the silicon carbide heat exchange pipe (7) into the sulfuric acid gasification gas discharge cavity (4); The temperature of the molten salt at the upper part of the molten salt flowing area (15) is kept higher than the boiling point of the mixed gas; The gas pressure in the sulfuric acid gasification gas discharge cavity (4) is controlled to balance with the pressure of the molten salt in the molten salt flowing area (15), so that the gas-liquid interface between the sulfuric acid gasification gas discharge cavity (4) and the molten salt flowing area (15) is not higher than the upper end of the silicon carbide heat exchange pipe (7).

6. The use of the sulfuric acid gasifier according to claim 5, wherein: when the sulfuric acid gasifier is shut down and restarted, the salt heating assembly heats the solidified salt on the molten salt flowing path to form a flowing path of the molten salt; and the flowing of the molten salt input into the molten salt flowing area (15) in the flowing path melts the solidified molten salt.

7. The application of the sulfuric acid gasifier, which is used as part of a thermochemical sulfur-iodine cycle hydrogen production system, and is the sulfuric acid gasifier according to any one of claims 1-4, wherein: the thermochemical sulfur-iodine cycle hydrogen production system further comprises a SO3 decomposer (22), a molten salt heat exchanger (24), a Bunsen reaction tower (29), and a sulfuric acid phase treatment unit (30). ​ ​ ​ The mixed gas including SO3 and H2O generated by the sulfuric acid gasifier is sent to a SO3 decomposer (22) to continue to be heated and further decomposed to obtain a decomposition product with a temperature of 700-1200℃; the decomposition product is input into a molten salt heat exchanger (24) to exchange heat with the molten salt flowing out from the molten salt flowing area (15), and then the decomposed product after being cooled is output from the molten salt heat exchanger (24) and input into the Bunsen reaction tower (29); The sulfuric acid phase generated by the Bunsen reaction tower (29) is purified and concentrated by a sulfuric acid phase processing unit (30) to form 70-95wt.% liquid sulfuric acid, and is input into the liquid sulfuric acid cavity (14) of the sulfuric acid gasifier.

8. Use of a sulphuric acid gasifier according to claim 7, characterised in that: The type of the molten salt is selected according to the preset temperature of the sulfuric acid decomposition reaction: When the preset temperature is 400-800℃, the molten salt is a mixed salt of sodium nitrate and sodium chloride with a mass ratio of 7:3; When the preset temperature is 250-800℃, the molten salt is a mixed salt of potassium nitrate and sodium chloride with a mass ratio of 1:1; When the preset temperature is above 450℃, the molten salt is sodium nitrate; When the preset temperature is 250-400℃, the molten salt is a mixed salt of potassium nitrate and sodium nitrate with a mass ratio of 6:4; When the preset temperature is above 280-400℃, the molten salt is potassium phosphate; The temperature difference of the molten salt input and output from the molten salt flowing area (15) is controlled to be 100-200℃.

Images