A method for producing sulfuric acid based on liquid sulfur dioxide

Abstract

This invention relates to the field of sulfuric acid production technology using waste gas recycling, and discloses a method for producing sulfuric acid based on liquid sulfur dioxide. The method includes an SO2 reactor with an inlet and an outlet, and a multi-stage heat exchanger for gas cooling. After the raw gas temperature is reduced, sulfuric acid is used to absorb water, followed by secondary cooling of the gas. Finally, liquid sulfur dioxide is obtained through cryogenic separation in a separation tower. Liquid SO2 is mixed with pure O2 and then exchanged with the raw gas from the previous step to increase its temperature. This mixture then enters the SO3 reactor for reaction, yielding SO3 product gas. After absorption, unreacted SO2 and O2 are recycled back to the initial stage, mixed with air, and then fed into the SO2 reactor for further reaction. Compared to traditional sulfuric acid production processes, this invention eliminates the flow of nitrogen in pipelines, significantly reducing equipment volume. Furthermore, because the exhaust gas is recycled, the discharged gas consists of nitrogen and a small amount of oxygen, resulting in less environmental pollution.

Description

Technical Field

[0001] This invention relates to the field of waste gas recycling for sulfuric acid production technology, specifically to a method for producing sulfuric acid based on liquid sulfur dioxide. Background Technology

[0002] Sulfuric acid, a strong dibasic inorganic acid, is a core raw material of modern chemical industry, hailed as the "mother of chemical industry." It is widely used in fertilizer production, mineral processing, petroleum refining, battery material synthesis, wastewater treatment, and explosives manufacturing, among many other fields. Its production volume is a crucial indicator of a country's industrial strength. In 2024, my country's sulfuric acid production reached 103.699 million tons, a year-on-year increase of 6.9%, with continued strong market demand. The stable, efficient, and low-cost production of sulfuric acid directly supports the healthy development of multiple industries, including chemical, metallurgical, and agricultural sectors. It plays an irreplaceable role in ensuring the stability of the industrial chain, reducing the production costs of downstream products, and improving the overall economic benefits of the industry. Furthermore, the environmental friendliness and energy efficiency of its production process are also crucial for the green and sustainable development of the chemical industry.

[0003] In existing technologies, the contact process is the mainstream technology for industrial sulfuric acid production. To reduce total production costs and improve economic efficiency, the industry mainly optimizes cost control through various technical approaches. The core of these approaches includes: First, optimizing raw material selection by using different sulfur-containing raw materials such as sulfur, pyrite, and smelting flue gas. Sulfur-based sulfuric acid production is preferred for cost reduction in mid-to-high-end sulfuric acid due to its low product impurities and simple process. Pyrite-based sulfuric acid production relies on low-cost raw materials to control initial input, while smelting flue gas-based sulfuric acid production utilizes metallurgical byproducts to achieve resource recycling and reduce raw material costs. Second, improving process parameters by optimizing catalytic oxidation and sulfur trioxide absorption. The key aspects include: 1) Improving the operating conditions of core processes, such as adjusting reaction temperature and spray density, to increase raw material conversion rate and reduce waste; 2) Enhancing energy recovery by optimizing heat exchange systems and converting waste heat into steam for power generation or heating, thereby reducing energy costs; 3) Optimizing tail gas treatment processes by adopting efficient desulfurization technologies such as ammonia and sodium alkali methods to reduce reagent consumption and recover by-products for resource utilization, thus reducing environmental protection costs; and 4) Promoting intelligent control by using automated systems to regulate production parameters in real time, thereby improving product qualification rate and reducing cost losses caused by parameter fluctuations.

[0004] However, existing sulfuric acid production processes based on the contact process still have many significant shortcomings in cost control, making it difficult to achieve the production goals of high efficiency, low cost, and environmental protection. Firstly, the raw material conversion process is costly. Traditional contact processes require the combustion or roasting of raw materials to generate sulfur dioxide, a cumbersome process. Furthermore, sulfur-to-acid production uses air as the oxygen source, and the 78% inert nitrogen in the air significantly increases the equipment's processing load, necessitating larger equipment, increased investment, floor space, and maintenance costs. Simultaneously, nitrogen dilutes the reactant concentration, reducing the reaction rate, limiting conversion, and increasing raw material loss. Secondly, energy consumption and environmental costs remain high. Traditional heat exchange systems are mostly single-stage or simple multi-stage heat exchangers, resulting in low heat recovery efficiency and significant waste of reaction heat. The existing sulfuric acid production process suffers from several drawbacks. First, the catalytic oxidation reaction temperature is difficult to control precisely, further impacting the conversion rate. Second, tail gas treatment requires complex additional steps, resulting in high reagent consumption and limited sulfur dioxide recovery, increasing treatment costs and posing environmental emission risks, making it difficult to meet stringent environmental standards. Third, different raw material processes have inherent cost limitations. Pyrite-based sulfuric acid production is complex, energy-intensive, and has high environmental treatment costs. Smelting flue gas-based sulfuric acid production requires complex acid washing and purification processes, leading to significant catalyst loss and unstable product purity due to impurities, thus limiting its applicability. Fourth, the existing process does not break through the traditional path of "raw material generating sulfur dioxide - catalytic oxidation - absorption," failing to utilize the high concentration of liquid sulfur dioxide to simplify the process, making it difficult to further reduce overall process costs. In summary, the existing sulfuric acid production process faces numerous bottlenecks in cost control, urgently requiring a new production method to overcome the limitations of traditional processes and achieve low-cost, efficient, and clean sulfuric acid production. Summary of the Invention

[0005] The present invention aims to provide a method for producing sulfuric acid based on liquid sulfur dioxide, in order to solve the existing technical problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a system for producing sulfuric acid based on liquid sulfur dioxide, comprising a first mixer, a sulfur dioxide reactor, a first heat exchanger, a second heat exchanger, a third heat exchanger, a dehydration tower, a compressed air fan, a fourth heat exchanger, a fifth heat exchanger, a separation tower, a second mixer, a sixth heat exchanger, a sulfur trioxide reactor, and an absorption tower, all connected in a mixing sequence. The first mixer is provided with a circulating raw material gas inlet, and the gas phase outlet at the top of the separation tower is connected to the heat exchange medium inlet of the fifth heat exchanger; the second mixer is also provided with an oxygen inlet, and the outlet of the second mixer is connected to the heat exchange medium inlet of the fourth heat exchanger; the heat exchange medium outlet of the fourth heat exchanger is connected to the heat exchange medium inlet of the third heat exchanger, the heat exchange medium outlet of the third heat exchanger is connected to the heat exchange medium inlet of the sixth heat exchanger, and the heat exchange medium outlet of the sixth heat exchanger is connected to the sulfur trioxide reactor; the inlet and outlet of the heat exchanged channel of the sixth heat exchanger are connected to the sulfur trioxide reactor and the absorption tower, respectively, and the outlet of the absorption tower is connected to the circulating raw material gas inlet.

[0007] Preferably, as an improvement, the first mixer is also provided with an air inlet.

[0008] Preferably, as an improvement, the heat exchange medium channels of the second heat exchanger and the first heat exchanger are connected sequentially according to the flow direction of the heat exchange medium.

[0009] Preferably, as an improvement, this solution also provides a method for producing sulfuric acid based on liquid sulfur dioxide, relying on the above-mentioned system, including the following steps: Step 1, Mixing and Reaction Stage: The recycled raw material gas is mixed with air and then reacted with sulfur to obtain raw material gas containing sulfur dioxide; Step 2, Heat Exchange Stage: The raw gas is subjected to two-stage heat exchange and mixed stream preheating in sequence to obtain cooled raw gas; Step 3, Dehydration and Pressurization Stage: Concentrated sulfuric acid is used to remove free moisture from the cooled feed gas, and pressurization is applied to dehydrate and obtain pressurized feed gas; Step 4, Secondary Cooling Stage: Heat exchange is carried out sequentially using a mixed stream, exhaust gas, and pressurized raw material gas; Step 5, cryogenic separation stage: The raw gas after deep cooling is cryogenically separated to obtain liquid sulfur dioxide and exhaust gas; Step 6, Pre-reaction preparation stage: Liquid sulfur dioxide is mixed with fresh pure oxygen from the outside to form a mixed stream. After multi-stage heat exchange, a preheated mixed stream is obtained. Step 7, Sulfur Trioxide Reaction Stage: The preheated mixed stream is reacted under the action of a catalyst to obtain sulfur trioxide product gas. The product gas is cooled and the sulfur trioxide is absorbed to obtain recycled raw material gas, which is then reintroduced into Step 1 to continue the next cycle.

[0010] Preferably, as an improvement, in step one, the oxygen concentration in the mixed gas when in contact with liquid sulfur is 20-25%.

[0011] Preferably, as an improvement, in step two, the temperature of the raw gas after the two-stage heat exchange is 240~260℃; after the mixed stream is preheated, the temperature of the raw gas is 180~200℃, and the temperature of the mixed stream is 210~220℃.

[0012] Preferably, as an improvement, in step three, the concentration of concentrated sulfuric acid is 98.3%~98.5%; the temperature of the dehydrated raw material gas is 70~80℃; and the pressure of the pressurized raw material gas is 40~50 kPaG.

[0013] Preferably, as an improvement, in step five, the temperature of the pressurized raw gas before entering the cryogenic separation stage is -60 to -40°C; and the oxygen concentration in the raw gas is 23% to 25%.

[0014] Preferably, as an improvement, in step six, the liquefied sulfur dioxide and pure oxygen are mixed in a ratio of 60~65:35~40.

[0015] Preferably, as an improvement, in step seven, after the product gas and the mixed stream exchange heat and cool down, the temperature of the product gas is 240~250℃ and the temperature of the mixed stream is 440~450℃.

[0016] Preferably, as an improvement, in step seven, the reaction process includes a heat exchange medium that carries away the heat generated by the reaction. The heat exchange medium is a molten salt, which is a eutectic salt of alkali metal and alkaline earth metal chlorides.

[0017] The principles and advantages of this scheme are: This invention recycles the sulfur dioxide-containing feed gas obtained by reacting the recycled feed gas after sulfuric acid absorption with sulfur. This feed gas is then cooled and cryogenically separated to obtain pure liquid sulfur dioxide, which is then mixed with oxygen to produce sulfuric acid. The process works synergistically, recovering heat and cold energy in a cyclical manner, reducing energy waste. Furthermore, by recycling the recycled feed gas after sulfuric acid absorption, the production of sulfuric acid effectively reduces waste gas emissions and treatment steps. Compared to existing sulfur-to-sulfuric acid processes, it has the following technical advantages: 1. This solution completely removes inert gases such as nitrogen through cryogenic separation, which greatly reduces the equipment's processing load, reduces the equipment's size, and lowers equipment investment, floor space, and operation and maintenance costs.

[0018] 2. This scheme adopts a multi-stage heat exchange design, combined with molten salt heat storage and heat exchange, to achieve full recovery of reaction heat, process gas waste heat and exhaust gas waste heat, which greatly improves energy utilization and reduces production energy consumption.

[0019] 3. The third option is to construct a closed-loop circulation system of unreacted sulfur dioxide and oxygen, and to combine it with the synergistic reaction of high-purity liquid sulfur dioxide and pure oxygen to increase the concentration of reactants and further improve the conversion rate of sulfur dioxide and the purity of the product.

[0020] 4. This solution emits only nitrogen and a small amount of oxygen in its exhaust gas, with no sulfur dioxide or other pollutants escaping. It has superior environmental performance and can meet stringent environmental emission standards. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the system for producing sulfuric acid based on liquid sulfur dioxide in an embodiment of the present invention.

[0022] Explanation of reference numerals in the attached drawings: First mixer 11, sulfur dioxide reactor 12, first heat exchanger 21, second heat exchanger 22, third heat exchanger 23, dehydration tower 31, compressed air fan 32, fourth heat exchanger 41, fifth heat exchanger 42, separation tower 51, second mixer 61, sixth heat exchanger 62, sulfur trioxide reactor 71, absorption tower 72. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the technical means used in the following embodiments and experimental examples are conventional means well known to those skilled in the art, and the materials and reagents used can all be obtained commercially.

[0024] Example This solution provides a system for producing sulfuric acid based on liquid sulfur dioxide, such as... Figure 1 As shown, it includes a reaction unit, a heat exchange unit, a dehydration and pressurization unit, a secondary cooling unit, a cryogenic separation unit, a pre-reaction preparation unit, and a sulfur trioxide reaction unit that are connected in a mixing sequence.

[0025] The mixing reaction unit includes a first mixer 11 and a sulfur dioxide reactor 12 connected in sequence. Specifically, the first mixer 11 is provided with an air inlet and a circulating raw material gas inlet, and the sulfur dioxide reactor is provided with a liquid sulfur inlet and a raw material gas outlet. The raw material gas outlet is connected to the inlet of the heat exchange unit. The heat exchange unit includes a first heat exchanger 21, a second heat exchanger 22, and a third heat exchanger 23 connected in sequence. The heat exchange medium channels of the second heat exchanger 22 and the first heat exchanger 21 are connected in sequence according to the flow direction of the heat exchange medium. The outlet of the third heat exchanger 23 is connected to the dehydration and pressurization unit.

[0026] The dehydration and pressurization unit includes a dehydration tower 31 and a compressed air fan 32 connected in sequence; The secondary cooling unit includes a fourth heat exchanger 41 and a fifth heat exchanger 42 connected in sequence; The cryogenic separation unit includes a separation tower, and the gas phase outlet at the top of the separation tower is connected to the heat exchange medium inlet of the fifth heat exchanger 42; The pre-reaction preparation unit includes a second mixer 61 and a sixth heat exchanger 62. The second mixer 61 is also provided with an oxygen inlet. The outlet of the second mixer 61 is connected to the heat exchange medium inlet of the fourth heat exchanger 41. The heat exchange medium outlet of the fourth heat exchanger 41 is connected to the heat exchange medium inlet of the third heat exchanger 23. The heat exchange medium outlet of the third heat exchanger 23 is connected to the heat exchange medium inlet of the sixth heat exchanger 62. The sulfur trioxide reaction unit includes a sulfur trioxide reactor 71 and an absorption tower 72 connected in sequence. A sixth heat exchanger 62 is connected between the sulfur trioxide reactor 71 and the absorption tower 72 to facilitate heat exchange between the product gas and the raw material gas. The outlet of the absorption tower 72 is connected to the inlet 112 of the circulating raw material gas.

[0027] This solution also provides a method for producing sulfuric acid based on liquid sulfur dioxide, including: Step 1, Mixed Reaction Stage: The recycled raw material gas is mixed with air in the first mixer and then fed into the sulfur dioxide reactor to react with sulfur to generate raw material gas containing sulfur dioxide. The circulating feed gas consists of unreacted sulfur dioxide and oxygen remaining after sulfur trioxide is absorbed in subsequent processes. The sulfur dioxide reactor is a furnace-type combustion reactor equipped with a high-efficiency sulfur gun for sulfur injection combustion. By increasing the oxygen content of the mixed gas, the sulfur dioxide gas concentration in the final converted feed gas can reach 18%.

[0028] Step 2, Heat Exchange Stage: This includes sequential two-stage heat exchange and mixed stream preheating to obtain cooled feed gas; Two-stage heat exchange involves two heat exchangers connected in series to exchange heat with the feed gas. The generated feed gas is sequentially passed through the first and second heat exchangers for two-stage heat exchange. The heat exchange medium passes through the second and first heat exchangers sequentially, achieving heat exchange with the feed gas. During the heat exchange process, the feed gas releases heat, heating the heat exchange medium. For reference, deoxygenated water with an inlet temperature of 100~110℃ is used as the heat exchange medium. After the two-stage heat exchange, the feed gas is cooled to 240~260℃, and the deoxygenated water is heated to 240~250℃.

[0029] The preheating of the mixed stream involves heat exchange between the mixed stream of liquid sulfur dioxide and pure oxygen and the cooling raw gas. After two-stage heat exchange, the raw gas exchanges heat with the mixed stream of liquid sulfur dioxide and pure oxygen before heating in subsequent steps in the third heat exchanger, further cooling the raw gas and preheating the mixed stream for subsequent processes, thus realizing the cascade utilization of heat.

[0030] Step 3, Dehydration and Pressurization Stage: Use concentrated sulfuric acid to remove free moisture from the cooled raw gas, and pressurize and dehydrate to obtain pressurized raw gas; Specifically, the cooled raw gas is fed into a dehydration tower, where it is treated with 98.3% to 98.5% concentrated sulfuric acid to absorb moisture. The excellent hygroscopic properties of concentrated sulfuric acid remove free water from the raw gas, preventing moisture from affecting the subsequent cryogenic separation effect and reaction purity. At the same time, the raw gas is further cooled to 70 to 80°C. The dehydrated raw gas is then pressurized to 40 to 50 kPaG by a compressed air fan to increase the raw gas pressure, creating suitable conditions for the subsequent cryogenic separation process and promoting the liquefaction and separation of sulfur dioxide.

[0031] Step 4, Secondary Cooling Stage: A mixed stream of liquid sulfur dioxide and pure oxygen is used sequentially to exchange heat with the exhaust gas and pressurized raw material gas. The pressurized feed gas is reintroduced into the fourth heat exchanger to exchange heat with the mixed stream of liquid sulfur dioxide and pure oxygen, reducing the temperature of the feed gas to 30°C, further preparing for cryogenic separation, and simultaneously preheating the mixed stream for subsequent processes.

[0032] The raw gas, after being cooled by the above heat exchange, is then exchanged with the exhaust gas in the fifth heat exchanger to further reduce the temperature of the raw gas, thereby maximizing the reduction of energy consumption in subsequent cryogenic separation. At the same time, the cold energy of the exhaust gas is recovered, improving the overall energy utilization efficiency.

[0033] Step 5, cryogenic separation stage: The deeply cooled raw gas is passed into the separation tower for cryogenic separation to obtain liquid sulfur dioxide; In the cryogenic separation process, the difference in saturated vapor pressure of different substances at different temperatures and pressures is used to liquefy sulfur dioxide in the raw gas, while inert gases such as nitrogen and a small amount of oxygen are discharged from the top of the tower, and liquid sulfur dioxide with a purity greater than 99.9% is obtained at the bottom of the tower, completely eliminating interference from inert gases such as nitrogen.

[0034] Step 6, Pre-reaction preparation stage: The high-purity liquid sulfur dioxide obtained from the separation tower is mixed with fresh pure oxygen in the second mixer to form a mixed stream for subsequent processes. After multi-stage heat exchange, the mixed stream is preheated. In this embodiment, the mixed stream is sequentially fed into the fourth, third, and sixth heat exchangers, where it exchanges heat with the pressurized raw material gas in step four, the cooled raw material gas in step two, and the product gas obtained from the subsequent reaction, respectively, thereby preheating the mixed stream and raising its temperature to 440~450℃, reaching the suitable initial temperature for the catalytic oxidation of sulfur dioxide to sulfur trioxide. This eliminates the need for additional energy consumption for heating, thus reducing energy consumption. Specifically, the three-stage preheating process for the mixed-flow stream is as follows: The mixed stream is preheated in the first stage by mixing the high-purity liquid sulfur dioxide discharged from the bottom of the separation tower with fresh pure oxygen from the outside to form a mixed stream. This mixed stream is then introduced into the fourth heat exchanger to exchange heat with the pressurized raw material gas (corresponding to the secondary cooling of the pressurized raw material gas in step four), raising the temperature of the mixed stream to 25~30℃ and completing the initial preheating.

[0035] The mixed stream undergoes secondary preheating. After initial heating, the mixed stream is introduced into the third heat exchanger to exchange heat with the feed gas that has undergone two-stage heat exchange (corresponding to the mixed stream preheating in step two), raising the temperature of the mixed stream to 210~220℃.

[0036] The mixed stream undergoes three-stage preheating. After two-stage preheating, the mixed stream is fed into the sixth heat exchanger to exchange heat with the product gas generated in the subsequent reaction. This raises the temperature of the mixed stream to 440~450℃, reaching the suitable initial temperature for the catalytic oxidation of sulfur dioxide to sulfur trioxide. This eliminates the need for additional energy consumption for heating, thus reducing energy consumption.

[0037] Step 7, Sulfur Trioxide Reaction Stage: The mixed stream that has reached the reaction temperature is fed into the sulfur trioxide reactor. Under the action of the catalyst, an exothermic reaction occurs in which sulfur dioxide is oxidized to sulfur trioxide. The product gas obtained from the reaction is cooled and the recycled raw material gas obtained from the sulfur trioxide absorption is re-entered into Step 1 to continue the next cycle.

[0038] During the reaction, molten salt is used as a heat exchange medium to remove the reaction heat. The molten salt is a eutectic salt of alkali metal and alkaline earth metal chlorides, which has the advantages of high boiling point, low viscosity and high volumetric heat capacity. It can efficiently remove the reaction heat, accurately control the reaction temperature, inhibit the reversible reaction from proceeding in reverse, and greatly improve the conversion rate of sulfur dioxide. The heat absorbed by the molten salt is then exchanged with the heated deoxygenated water for the production of medium-pressure steam, realizing the full recovery and utilization of the reaction waste heat.

[0039] The sulfur trioxide-containing product gas generated by the reaction first enters the sixth heat exchanger to exchange heat with the mixed stream (corresponding to the three-stage preheating of the mixed stream), releasing heat to preheat the mixed stream, while its own temperature drops to 240~250℃, completing the recovery of the reaction waste heat.

[0040] After cooling, the product gas is fed into an absorption tower where 98.3%~98.5% concentrated sulfuric acid is used to absorb sulfur trioxide, avoiding the generation of acid mist from direct water absorption. The gas phase at the top of the tower after sulfur trioxide absorption is unreacted sulfur dioxide and oxygen. This gas phase is returned to the first step as a circulating feed gas, combined with air, and then fed into the sulfur dioxide reactor with liquid sulfur to participate in the reaction again, forming a complete closed-loop cycle. This maximizes the utilization rate of sulfur dioxide, reduces the amount of sulfur dioxide emitted in the tail gas, and lowers the risk of environmental pollution.

[0041] In practice, this scheme uses a small-scale device (reactor volume approximately 15m³).3 The annual acid production is approximately 20,000 tons. For example, 821 kg / h of liquid sulfur, recycled sulfur dioxide, oxygen, and air are mixed and fed into a furnace-type sulfur dioxide reactor, where the mixed gas has a flow rate of 3235.25 Nm³. 3 The gas is fed in at a rate of / h, resulting in a feed gas with a sulfur dioxide concentration of 15%~18% due to the increased oxygen concentration. The oxygen content in the recycled feed gas should not be too high, otherwise it will generate excessive heat, leading to the formation of sublimated sulfur. At the same time, oxygen will interfere with the subsequent cryogenic separation process. It is best to control the oxygen concentration in the mixed gas at 23%~25%.

[0042] The sulfur dioxide reactor outlet concentration is 3235.25 Nm³. 3 The feed gas, at 1400℃ and a flow rate of approximately 4950 kg / h, is cooled by deoxygenated water. This feed gas heats 3000 kg / h of deoxygenated water to 257℃. This deoxygenated water is then sprayed in other production processes for cooling, and after heat exchange with the heat exchange medium in the tubular reactor, it can produce 4000 kg / h of medium-pressure steam at 450℃. This steam is then sent to a pure back-pressure generator set to generate 307.7 kWh of electricity.

[0043] After heat exchange and water absorption, the raw gas is pressurized (pressurized to 50 kPaG) before entering the pre-cooling stage of cryogenic separation. The pressurized raw gas is cooled by the separated waste gas and process gas, and can be cooled to -40℃ before entering the cryogenic separation equipment.

[0044] The condensation temperature of sulfur dioxide is a core parameter in the design of cryogenic units, and optimization has shown that this temperature should be minimized. In actual engineering design, sulfur dioxide vapor condenses at -65°C within the heat exchanger tubes, which are immersed in a refrigerant with an evaporation temperature slightly higher than the freezing point of sulfur dioxide (-75.5°C). To achieve the -65°C condensation condition, a two-stage cryogenic system with high pressure and low pressure is required, using two refrigerants: R23 (trifluoromethane) in the low-pressure circuit and ammonia (NH3) in the high-pressure circuit. Such systems are standardized and mature products from multiple suppliers in the refrigeration industry, and will not be elaborated upon here. The separated liquid phase ultimately contains 99.99 wt% sulfur dioxide, while the gas phase consists of 95.8 wt% nitrogen, 4.1 wt% oxygen, and 50 ppm sulfur dioxide, meeting national emission standards and allowing for direct discharge.

[0045] The liquefied sulfur dioxide obtained from cryogenic separation was mixed with pure oxygen in a ratio of 65:35 to obtain 874.5 Nm³. 3 The mixed stream of / h exchanges heat with the feed gas at different stages, and finally the temperature rises to 213℃. It then reacts further with the sulfur trioxide product gas after the reaction, and finally the temperature rises to 440℃.

[0046] The mixed streams react in a fixed-bed tubular sulfur trioxide reactor, and the heat generated is removed by a heat exchange medium (molten salt is used in this scheme). The reaction is most intense in the middle of the reactor, releasing a large amount of heat. The final conversion rate can be controlled to 99.8% or higher (depending on the reactor size and catalyst type).

[0047] The product gas after the reaction is cooled by heat exchange with the imported mixed process gas stream to 240°C before being sent to the absorption tower for absorption. The absorbent is 98.3% concentrated sulfuric acid, with a lower tower acid concentration of 99.16% and the top gas phase consisting of 99.7 wt% oxygen and other components. The upper tower acid flow rate is 54431 kg / h, and the lower tower acid flow rate is 56478 kg / h. After adding water, approximately 2542 kg / h of 98.3% concentrated sulfuric acid product is obtained. Recycling the top gas phase back to the sulfur dioxide reactor increases the oxygen concentration and avoids the need for tail gas emission treatment.

[0048] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A system for producing sulfuric acid based on liquid sulfur dioxide, characterized in that: It includes a first mixer, a sulfur dioxide reactor, a first heat exchanger, a second heat exchanger, a third heat exchanger, a dehydration tower, a compressed air fan, a fourth heat exchanger, a fifth heat exchanger, a separation tower, a second mixer, a sixth heat exchanger, a sulfur trioxide reactor, and an absorption tower, all connected in a mixing sequence. The first mixer is provided with a circulating raw material gas inlet, and the gas phase outlet at the top of the separation tower is connected to the heat exchange medium inlet of the fifth heat exchanger; the second mixer is also provided with an oxygen inlet, and the outlet of the second mixer is connected to the heat exchange medium inlet of the fourth heat exchanger; the heat exchange medium outlet of the fourth heat exchanger is connected to the heat exchange medium inlet of the third heat exchanger, the heat exchange medium outlet of the third heat exchanger is connected to the heat exchange medium inlet of the sixth heat exchanger, and the heat exchange medium outlet of the sixth heat exchanger is connected to the sulfur trioxide reactor; the inlet and outlet of the heat exchanged channel of the sixth heat exchanger are connected to the sulfur trioxide reactor and the absorption tower, respectively, and the outlet of the absorption tower is connected to the circulating raw material gas inlet.

2. The system for producing sulfuric acid based on liquid sulfur dioxide according to claim 1, characterized in that: The first mixer also has an air inlet.

3. The system for producing sulfuric acid based on liquid sulfur dioxide according to claim 2, characterized in that: The heat exchange medium channels of the second heat exchanger and the first heat exchanger are connected sequentially according to the flow direction of the heat exchange medium.

4. A method for producing sulfuric acid based on liquid sulfur dioxide, characterized in that: The process, relying on the system described in claim 3, includes the following steps: Step 1, Mixing and Reaction Stage: The recycled raw material gas is mixed with air and then reacted with sulfur to obtain raw material gas containing sulfur dioxide; Step 2, Heat Exchange Stage: The raw gas is subjected to two-stage heat exchange and mixed stream preheating in sequence to obtain cooled raw gas; Step 3, Dehydration and Pressurization Stage: Concentrated sulfuric acid is used to remove free moisture from the cooled feed gas, and pressurization is applied to dehydrate and obtain pressurized feed gas; Step 4, Secondary Cooling Stage: Heat exchange is carried out sequentially using a mixed stream, exhaust gas, and pressurized raw material gas; Step 5, cryogenic separation stage: The raw gas after deep cooling is cryogenically separated to obtain liquid sulfur dioxide and exhaust gas; Step 6, Pre-reaction preparation stage: Liquid sulfur dioxide is mixed with fresh pure oxygen from the outside to form a mixed stream. After multi-stage heat exchange, a preheated mixed stream is obtained. Step 7, Sulfur Trioxide Reaction Stage: The preheated mixed stream is reacted under the action of a catalyst to obtain sulfur trioxide product gas. The product gas is cooled and the sulfur trioxide is absorbed to obtain recycled raw material gas, which is then reintroduced into Step 1 to continue the next cycle.

5. A method for producing sulfuric acid based on liquid sulfur dioxide according to claim 4, characterized in that: In step one, the oxygen concentration in the mixture when in contact with liquid sulfur is 20-25%.

6. A method for producing sulfuric acid based on liquid sulfur dioxide according to claim 5, characterized in that: In step two, the temperature of the raw gas after the two-stage heat exchange is 240~260℃; after the mixed stream is preheated, the temperature of the raw gas is 180~200℃, and the temperature of the mixed stream is 210~220℃.

7. The method for producing sulfuric acid based on liquid sulfur dioxide according to claim 6, characterized in that: In step three, the concentration of concentrated sulfuric acid is 98.3%~98.5%; the temperature of the dehydrated raw material gas is 70~80℃; and the pressure of the pressurized raw material gas is 40~50 kPaG.

8. The method for producing sulfuric acid based on liquid sulfur dioxide according to claim 7, characterized in that: In step five, the temperature of the pressurized feed gas before entering the cryogenic separation stage is -60 to -40°C; the oxygen concentration in the feed gas is 23% to 25%.

9. A method for producing sulfuric acid based on liquid sulfur dioxide according to claim 8, characterized in that: In step six, the liquefied sulfur dioxide and pure oxygen are mixed in a ratio of 60~65:35~40.

10. A method for producing sulfuric acid based on liquid sulfur dioxide according to claim 9, characterized in that: In step seven, after the product gas and the mixed stream exchange heat and cool down, the temperature of the product gas is 240~250℃ and the temperature of the mixed stream is 440~450℃. During the reaction process, the heat generated by the reaction is carried away by the heat exchange medium, which is a molten salt, and the molten salt is a eutectic salt of alkali metal and alkaline earth metal chlorides.

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