A dry-wet coupling process and a device and method for optimizing energy-saving sulfuric acid production by low-temperature heat recovery

Abstract

The application discloses a dry-wet coupling process and a device and method for optimizing energy-saving sulfuric acid production by low-temperature heat recovery. The technology cancels the traditional drying tower system, adopts an innovative process combining primary conversion (wet method) and secondary conversion (dry method), and realizes process flow shortening and zero consumption of circulating water. The system is provided with a flue gas heater or an air heater and three desalted water heaters, traditional low-temperature heat energy such as dilution heat of the drying system and absorption heat of the secondary absorption system is fully recovered, and the heat energy recovery efficiency of the sulfuric acid device is improved to nearly 100%. Compared with the traditional process, the investment of the new process is slightly reduced, the operation cost is significantly reduced, and the net external supply of low-pressure steam is increased by about 100%. The technology is suitable for various sulfuric acid production processes such as sulfuric acid production, pyrite acid production, SO2-containing flue gas acid production, sulfur-containing waste gas and waste liquid acid production or mixed raw material acid production.

Description

Technical Field

[0001] This invention belongs to the field of sulfuric acid production technology that utilizes all low-temperature thermal energy, specifically relating to a dry-wet coupling process and a device and method for low-temperature heat recovery optimization and energy-saving sulfuric acid production. Background Technology

[0002] Sulfuric acid plants are green energy factories that not only produce sulfuric acid but also generate medium- and low-pressure steam as a byproduct. Traditional sulfuric acid plants, through the installation of medium-pressure waste heat boilers, superheaters, and economizers, only recover 60%–70% of the high- and medium-temperature heat energy. The low-temperature heat energy in the dry absorption section, accounting for approximately 24.5% of the plant's energy, is not only unutilized but also requires energy to remove. The application of low-temperature heat recovery technology has increased the heat recovery efficiency of sulfuric acid plants to over 90%, reducing the overall energy consumption per ton of acid by 50–55%. The research and application of low-temperature heat recovery technology has greatly promoted the progress and development of the sulfuric acid industry. However, low-temperature heat recovery technology is only used in the primary absorption system. The dilution heat from the drying system and the absorption heat from the secondary absorption system remain unutilized and require the consumption of circulating water for cooling. Even when demineralized water is used instead of circulating water, the amount of heat recovered cannot be fully recovered using only the demineralized water required by the sulfuric acid plant. In today's increasingly prominent energy situation, maximizing heat recovery and generating greater economic benefits is an urgent pursuit for the sulfuric acid industry.

[0003] Figure 3 as well as Figure 4 The diagrams show the process flow charts for the conventional flue gas system and acid system. Liquid sulfur from the sulfur melting process is injected into the sulfur incinerator through mechanical nozzles. The air required for sulfur incineration is sent to a drying tower by an air blower to remove moisture. The dry air mixes with sulfur vapor and combusts to generate gas at approximately 1100°C. After heat recovery in a waste heat boiler, the temperature drops to 410-415°C and proceeds to the first stage of the converter for further conversion. The outlet temperature of the first stage converter rises to approximately 610°C and is cooled to 440°C by a high-temperature heat exchanger before entering the second stage of the converter bed for reaction. The outlet gas temperature of the second stage rises to 520-550°C and enters a hot-to-hot heat exchanger for heat exchange, where the temperature drops to approximately 440°C before entering the third stage of the converter for further reaction. The outlet gas temperature of the third stage rises to approximately 460-480°C. The flue gas from the first stage of conversion after three stages enters the low-temperature heat recovery system, where circulating water is used to recover the heat from acid absorption in the low-temperature heat recovery system and the heat absorbed by the secondary absorption system. This process requires the consumption of circulating water. The gas entering the low-temperature heat recovery tower contacts concentrated sulfuric acid to absorb sulfur trioxide and water. The unabsorbed gas passes through a fiber demister at the top of the tower to remove acid mist, and then passes through cold and hot heat exchangers in sequence. It is heated to about 410~415℃ using the waste heat from the second and third stages of the conversion and enters the fourth stage of the converter for conversion. The gas temperature at the outlet of the fourth stage rises to about 440℃. After passing through the heat exchanger and economizer, the temperature drops to 160~180℃ and enters the second absorption tower. After contacting concentrated sulfuric acid to absorb sulfur trioxide, the tail gas goes to the tail absorption tower. Summary of the Invention

[0004] The purpose of this invention is to provide an apparatus and method for energy-saving sulfuric acid production using a dry-wet coupling process and low-temperature heat recovery, which addresses the aforementioned problems. This purpose is achieved through the following technical solutions.

[0005] A device for optimizing energy-saving sulfuric acid production using a dry-wet coupling process and low-temperature heat recovery is disclosed. The device includes a sulfur incinerator and a converter. The flue gas from the sulfur incinerator is connected to a first stage of the converter via a first waste heat boiler. The flue gas from the first stage is connected to a second stage of the converter via a high-temperature superheater. The flue gas from the second stage is connected to a third stage of the converter via a heat exchanger. The flue gas from the third stage is connected to a fourth stage of the converter via a second waste heat boiler, a second economizer, a low-temperature heat recovery tower, a cold heat exchanger, and a heat exchanger. The output of the fourth stage of the converter is connected to a cold heat exchanger, a first economizer, and a second suction tower. The flue gas from the second suction tower is sent to the tail suction tower.

[0006] The sulfuric acid at the bottom of the low-temperature heat recovery tower is connected to the steam generator. One sulfuric acid output end of the steam generator is connected to the upper part of the low-temperature heat recovery tower through a diluent, and the other sulfuric acid output end of the steam generator is connected to the deoxygenated water preheater. One sulfuric acid output end of the deoxygenated water preheater is connected to the circulation tank of the second absorption tower through a flue gas heater, and the other sulfuric acid output end also enters the circulation tank of the second absorption tower through a third demineralized water heater.

[0007] In the above-mentioned device, the sulfuric acid at the bottom of the second absorption tower is connected to the first demineralized water heater through a circulation tank. One sulfuric acid output end of the first demineralized water heater is connected to the second demineralized water heater, and the other sulfuric acid output end is connected to the top of the second absorption tower.

[0008] In the above-mentioned apparatus, the demineralized water required by the sulfuric acid unit is connected to the first demineralized water heater and the second demineralized water heater respectively. The output ends of the first demineralized water heater and the second demineralized water heater are both connected to the third demineralized water heater. The water output end of the third demineralized water heater is connected in sequence through a deaerator, a deoxygenated water preheater and a steam generator.

[0009] A method for optimizing and saving energy in sulfuric acid production using the above-mentioned apparatus to achieve a dry-wet coupling process and low-temperature heat recovery includes the following steps:

[0010] Liquid sulfur from the sulfur melting process is injected into the sulfur incinerator through mechanical nozzles. The air required for sulfur incineration is sent into the sulfur incinerator after passing through a filter and a main blower. The air and sulfur vapor are mixed and burned to generate gas. After recovering heat in the first waste heat boiler, the gas goes to the first stage of the converter for conversion. The flue gas from the first stage converter is cooled by a high-temperature superheater and then enters the second stage of the converter bed for reaction. The gas from the second stage first enters the heat exchanger for heat exchange, and then enters the third stage of the converter for reaction. The gas from the third stage enters the fourth stage of the converter after passing through the second waste heat boiler, the second economizer, the low-temperature heat recovery tower, the cold heat exchanger, and the heat exchanger. The gas from the fourth stage enters the second absorption tower after passing through the cold heat exchanger and the low-temperature heat recovery tower.

[0011] The primary conversion process involves one stage, two stages, or one, two, and three stages of conversion within the converter. The remaining stage is secondary conversion. Moisture in the air or moisture generated from the combustion of raw materials enters the primary conversion process along with the SO2-containing flue gas without being dried. Therefore, the primary conversion process uses wet conversion. After the primary conversion, the flue gas enters a low-temperature heat recovery tower for primary absorption. The absorbed flue gas becomes dry flue gas and enters the secondary conversion process. Therefore, the secondary conversion process uses dry conversion. After the secondary conversion, the flue gas enters a secondary absorption process and is then treated to meet emission standards before being discharged.

[0012] (2) The sulfuric acid at the bottom of the low-temperature heat recovery tower first enters the steam generator. The sulfuric acid exiting the steam generator is divided into two streams. One stream of sulfuric acid enters the low-temperature heat recovery tower through the diluent for circulation absorption, and the other stream of sulfuric acid enters the deoxygenated water preheater for preheating the deoxygenated water. After that, it enters the flue gas heater and the third demineralized water heater respectively. The sulfuric acid at the outlet of the third demineralized water heater and the flue gas heater both enter the circulation tank of the second absorption tower.

[0013] In the above method, the sulfuric acid at the bottom of the second absorption tower enters the first demineralized water heater through the circulation tank. A portion of the sulfuric acid in the first demineralized water heater enters the second absorption tower for circulation absorption, while the other portion enters the second demineralized water heater to heat the demineralized water. The sulfuric acid coming out of the second demineralized water heater is the produced acid.

[0014] In the above method, the temperature of the gas generated by the combustion of air and sulfur vapor is 1000~1200℃; the temperature of the gas entering the first stage converter is 410~415℃; the temperature of the gas exiting the first stage converter is 600~620℃; the temperature of the gas entering the second stage converter is 430~450℃; the temperature of the gas exiting the second stage converter is 520~550℃; the temperature of the gas entering the third stage converter is 430~450℃; the temperature of the gas exiting the third stage converter is 460~480℃; the temperature of the gas entering the fourth stage converter is 410~415℃; and the temperature of the gas exiting the fourth stage converter is 430~450℃.

[0015] Depending on whether water is present during SO2 catalytic oxidation, sulfuric acid production processes are divided into two types: dry acid production and wet acid production. The acid formation mechanism of dry acid production is "absorption acid formation," while the acid formation mechanism of wet acid production is "condensation acid formation." Therefore, this application involves a primary conversion to condensation acid formation and a secondary conversion to absorption acid formation.

[0016] In the technical solution of this invention, the process flow is shortened by using a dry-wet coupling process, which saves the power consumption and circulating water of the drying system. In the absorption system, the heat of acid recovery from the low-temperature heat recovery system and the absorption heat of the secondary absorption system are recovered by setting up a flue gas heater or air heater and three demineralized water heaters, thereby saving the circulating water of the secondary absorption tower circulating acid system and the product acid system, and realizing zero circulating water consumption of the sulfuric acid plant.

[0017] In the technical solution of this invention, a waste heat boiler, economizer and other thermal equipment are set in front of the low temperature heat recovery tower to recover heat, while avoiding dew point corrosion.

[0018] In some preferred technical solutions, when the atmospheric humidity is too high, a refrigerated dryer or other facilities can be used to control the moisture in the air entering the system to ensure that the device is not subject to dew point corrosion.

[0019] In the technical solution of this invention, the sulfuric acid production process includes, but is not limited to, sulfuric acid production from sulfur, sulfuric acid production from pyrite, sulfuric acid production from SO2-containing flue gas, sulfuric acid production from sulfur-containing waste gas and waste liquid, or sulfuric acid production from mixed raw materials, and other sulfuric acid production processes.

[0020] In some specific technical solutions: the first, second and third stages of the converter are wet conversion processes, while the fourth stage of the converted gas is a dry conversion process. The acid production process is shortened by coupling dry and wet processes, and zero consumption of circulating water is achieved.

[0021] Wet conversion mechanism: SO2 is oxidized in the presence of moisture, converting SO2 into SO3;

[0022] Dry conversion mechanism: SO2 is oxidized in the absence of moisture, converting SO2 into SO3.

[0023] The mechanism of this invention: Conventional processes are dry conversion processes where the flue gas contains no water. SO3 in the flue gas is absorbed by concentrated sulfuric acid in an absorption tower, and the absorbed sulfuric acid becomes a more concentrated sulfuric acid. This acid formation mechanism is called "absorption-to-acidification". The present invention uses humid air or moisture generated from the combustion of raw materials that has not been dried in a drying tower, which is then introduced into the primary conversion process along with the SO2-containing flue gas. In the presence of moisture, SO2 is catalytically converted to SO3. The reaction SO3 + H2O = H2SO4 in the flue gas is an equilibrium reaction. When the flue gas temperature is above the dew point temperature of sulfuric acid (100℃~300℃), the generated H2SO4 is gaseous. When the flue gas temperature drops below the dew point temperature of sulfuric acid, the gaseous H2SO4 becomes liquid H2SO4. This acid formation mechanism is called "condensation-to-acidification". Furthermore, excess SO3 in the flue gas continues to be absorbed by concentrated sulfuric acid in the absorption tower, and the absorbed sulfuric acid becomes a more concentrated sulfuric acid. The "absorption-to-acidification" mechanism still exists.

[0024] The beneficial effects of this invention are:

[0025] Compared to traditional sulfuric acid plants, this process eliminates the need for a drying system, shortening the process flow, reducing investment costs, and saving on power consumption and circulating water for the drying system, thus saving on drying system investment. The low-temperature heat recovery system of this invention saves circulating water for both the secondary absorption tower circulating acid system and the product acid system, achieving zero circulating water consumption for the entire plant. Compared to traditional sulfuric acid plants, electricity consumption, circulating water consumption, and operating costs are reduced. With this invention, while maintaining the same high-pressure steam production rate, the low-pressure steam production rate is increased by approximately 36%, and the net external supply of low-pressure steam is increased by approximately 100%. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the flue gas system in the sulfuric acid production process of this invention.

[0027] Figure 2 This is a process flow diagram of the acid system in the sulfuric acid production process of this invention.

[0028] Among them, 1 is a filter, 2 is a main fan, 3 is a sulfur incinerator, 4 is a first waste heat boiler, 5 is a high-temperature superheater, 6 is a converter, 7 is a heat exchanger, 8 is a cold heat exchanger, 9 is a second waste heat boiler, 10 is a second economizer, 11 is a low-temperature heat recovery tower, 12 is a first economizer, 13 is a second suction tower, 14 is a circulation tank, 15 is a deaerator, 16 is a steam generator, 17 is a deoxygenated water preheater, 18 is a diluent, 1-1 is a flue gas heater, 2-1 is a first demineralized water heater, 2-2 is a second demineralized water heater, and 2-3 is a third demineralized water heater.

[0029] Figure 3 This is a process flow diagram of the flue gas system in a conventional sulfuric acid production process.

[0030] Figure 4 This is a process flow diagram of the acid system in a conventional sulfuric acid production process. Detailed Implementation

[0031] The technical solution and implementation of the present invention will be described below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0032] like Figures 1-2 A device for optimizing energy-saving sulfuric acid production using a dry-wet coupling process and low-temperature heat recovery is disclosed. The device includes a sulfur incinerator 3 and a converter 6. The flue gas from the sulfur incinerator 3 is connected to the first stage of the converter 6 via a first waste heat boiler 4. The flue gas from the first stage is connected to the second stage of the converter 6 via a high-temperature superheater 5. The flue gas from the second stage is connected to the third stage of the converter 6 via a heat exchanger 7. The flue gas from the third stage is connected to the fourth stage of the converter 6 via a second waste heat boiler 9, a second economizer 10, a low-temperature heat recovery tower 11, a cold heat exchanger 8, and a heat exchanger 7. The output of the fourth stage of the converter is connected to the fourth stage of the converter via a cold heat exchanger 8, a first economizer 12, and a second suction tower 13. The flue gas from the second suction tower 13 is sent to the tail suction tower.

[0033] The sulfuric acid at the bottom of the low-temperature heat recovery tower 11 is connected to the steam generator 16. One sulfuric acid output end of the steam generator 16 is connected to the upper part of the low-temperature heat recovery tower 11 through the diluent 18, and the other sulfuric acid output end of the steam generator 16 is connected to the deoxygenated water preheater 17. One sulfuric acid output end of the deoxygenated water preheater 17 is connected to the circulation tank 14 of the second absorption tower 13 through the flue gas heater 1-1, and the other sulfuric acid output end also enters the circulation tank 14 of the second absorption tower 13 through the third demineralized water heater 2-3.

[0034] The sulfuric acid at the bottom of the second absorption tower 13 is connected to the first demineralized water heater 2-1 through the circulation tank 14. One sulfuric acid output end of the first demineralized water heater 2-1 is connected to the second demineralized water heater 2-2, and the other sulfuric acid output end is connected to the top of the second absorption tower 13.

[0035] The demineralized water required by the sulfuric acid plant is connected to the first demineralized water heater 2-1 and the second demineralized water heater 2-2 respectively. The output ends of the first demineralized water heater 2-1 and the second demineralized water heater 2-2 are both connected to the third demineralized water heater 2-3. The water output end of the third demineralized water heater 2-3 is connected in sequence through the deaerator 15, the deoxygenated water preheater 17 and the steam generator 16.

[0036] A method for optimizing and saving energy in sulfuric acid production using the above-mentioned device to achieve a dry-wet coupling process and low-temperature heat recovery, taking a sulfuric acid production unit as an example, is as follows:

[0037] (1) Liquid sulfur from the sulfur melting process is injected into the sulfur combustion furnace through mechanical nozzles. The air required for sulfur combustion is directly supplied by an air blower. The air and sulfur vapor are mixed and burned to generate gas at 1050°C. After the heat is recovered by the waste heat boiler, the temperature drops to 410~415°C and goes to the first stage of the converter for conversion. The outlet temperature of the first stage converter rises to about 610°C and is cooled to 440°C by a high-temperature heat exchanger before entering the second stage of the converter bed for reaction. The outlet gas temperature of the second stage rises to 520~550°C and enters the hot-hot heat exchanger for heat exchange. The temperature drops to 440°C and enters the third stage of the converter for reaction. The outlet gas temperature of the third stage rises to 460~480°C.

[0038] (2) The primary conversion flue gas (which is converted sequentially by the first, second and third stages of the converter, and the primary conversion flue gas here refers to the flue gas at the outlet of the third stage converter) enters the low-temperature heat recovery system. By setting up a flue gas heater and three demineralized water heaters, the acid heat of the low-temperature heat recovery system and the absorption heat of the secondary absorption system are recovered, thereby saving the circulating water of the secondary absorption tower circulating acid system and the product acid system.

[0039] (3) The gas entering the low-temperature heat recovery tower comes into contact with concentrated sulfuric acid to absorb sulfur trioxide and water. The unabsorbed gas passes through the fiber demister at the top of the tower to remove acid mist, and then passes through the cold and hot heat exchangers in sequence. The residual heat from the second and third stages of the conversion is used to raise the temperature to 410~415℃ and enter the fourth stage of the converter for conversion. The outlet gas temperature of the fourth stage rises to 440℃~445℃. After passing through the heat exchanger and economizer, the temperature drops to 160~180℃ and enters the second absorption tower. After coming into contact with concentrated sulfuric acid to absorb sulfur trioxide, the tail gas goes to the tail absorption tower.

[0040] (4) Part of the demineralized water required by the sulfuric acid plant enters the first demineralized water heater to cool the circulating acid in the second absorption tower, and the other part enters the second demineralized water heater to cool the product acid. The demineralized water after the two are heated is combined and enters the third demineralized water heater to cool the acid in the low temperature heat recovery system. The demineralized water after the temperature is raised enters the deaerator.

[0041] (5) After the acid in the low-temperature heat recovery system is cooled by the deoxygenated water preheater, part of it enters the third demineralized water heater to heat the demineralized water, and the other part enters the flue gas heater to heat the flue gas at the outlet of the low-temperature heat recovery tower or the air heater to heat the air at the inlet of the incinerator, thus transferring the low-temperature heat to the high-temperature heat and producing more high-pressure steam. The concentrated sulfuric acid after the above two parts are cooled is combined and then fed into the circulation tank of the second absorption tower.

[0042] In the sulfuric acid production process described in the technical solution of this invention: the first, second and third stages of the converter are wet conversion, and the fourth stage of the conversion gas is dry conversion. The sulfuric acid production process is shortened by the coupling of dry and wet processes, and zero consumption of circulating water is achieved.

[0043] In the sulfuric acid production process described in this invention, a waste heat boiler, economizer, and other thermal equipment are installed before the low-temperature heat recovery tower to recover heat, while avoiding dew point corrosion.

[0044] Implementation Case:

[0045] Taking an 800,000-ton / year sulfuric acid plant as an example, in conventional processes: the main blower is electrically driven, and all the produced steam is sent out. Even with low-temperature heat recovery, conventional processes still have ~47,247,903.6 kJ / h of low-temperature heat (~60℃) that cannot be recovered. This heat can only be removed by cooling with circulating water, consuming ~1410 t / h of circulating water. The dry-wet coupling process of this application can save circulating water in the drying system; by setting up a flue gas heater or air heater and three demineralized water heaters in the absorption system, the heat from the low-temperature heat recovery system and the absorption heat from the secondary absorption system can be recovered, thus saving circulating water in the secondary absorption tower's circulating acid system and the product acid system, achieving zero circulating water consumption for the sulfuric acid plant. A comparison of circulating water consumption in the examples is shown in Table 1.

[0046] Table 1 Comparison of Circulating Water in Examples

[0047]

[0048] This example eliminates the need for a drying tower, drying tower circulating pump, drying tower acid circulating tank, and related piping and valves, saving approximately 8 million yuan in investment in the drying system and 3.5 million yuan in investment in the circulating water system. Catalyst investment increases by approximately 4.37 million yuan, and equipment and piping costs increase by approximately 3 million yuan. The total investment cost is slightly reduced. A comparison of the main equipment and materials in this example is shown in Table 2.

[0049] Table 2 Comparison of Main Equipment and Materials in the Examples

[0050]

[0051] The comparison of operating costs between the two processes in this example mainly focuses on electricity consumption, circulating water consumption, and steam production; other aspects are largely the same. For the main blower, the dry-wet coupling process reduces the resistance drop of the drying system by approximately 4.5 kPa. For an 800,000-ton / year sulfuric acid production unit, this translates to a saving of approximately 500 kW in main blower electricity consumption. Adding the electricity consumption of the acid circulation pump, the total saving is 720 kW, or 576 × 10⁻⁶ kWh per year. 4 Based on a price of 0.5 yuan per kilowatt-hour, this translates to annual electricity savings of 2.88 million yuan. See Table 3.

[0052] Table 3. Power Consumption Comparison of Examples

[0053]

[0054] This example employs a wet-dry coupling process, saving 1410 m³ of circulating water. 3 / h, based on a circulating water price of 0.2 yuan / m 3 ① This saves 282 yuan / hour in operating costs, totaling 2.256 million yuan / year; ② The net external supply of low-pressure steam is 14.1 t / h more, and at a low-pressure steam price of 150 yuan / t, the annual revenue is 16.92 million yuan. See Table 4.

[0055] Table 4 Comparison of Steam Production and Circulating Water Volume in Examples

[0056]

[0057] This invention shortens the process flow by coupling dry and wet processes and by setting up a flue gas heater or air heater and three demineralized water heaters, enabling the cascade utilization of low-temperature thermal energy and achieving zero circulating water consumption and high economic benefits in sulfuric acid production.

[0058] It should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure, and are not intended to limit them; for those skilled in the art, it will be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A device for energy-saving sulfuric acid production using a dry-wet coupling process and low-temperature heat recovery, characterized in that, The device includes a sulfur incinerator (3) and a converter (6). The flue gas from the sulfur incinerator (3) is connected to one section of the converter (6) through a first waste heat boiler (4). The flue gas from the first section is connected to the second section of the converter (6) through a high-temperature superheater (5). The flue gas from the second section is connected to the third section of the converter (6) through a heat exchanger (7). The flue gas from the third section is connected to the fourth section of the converter (6) through a second waste heat boiler (9), a second economizer (10), a low-temperature heat recovery tower (11), a cold heat exchanger (8), and a heat exchanger (7). The output of the fourth section of the converter is connected to the fourth section of the converter (6) through a cold heat exchanger (8), a first economizer (12), and a second suction tower (13). The flue gas from the second suction tower (13) goes to the tail suction tower. The sulfuric acid at the bottom of the low-temperature heat recovery tower (11) is connected to the steam generator (16). One sulfuric acid output end of the steam generator (16) is connected to the upper part of the low-temperature heat recovery tower (11) through the diluent (18). The other sulfuric acid output end of the steam generator (16) is connected to the deoxygenated water preheater (17). One sulfuric acid output end of the deoxygenated water preheater (17) is connected to the circulation tank (14) of the second absorption tower (13) through the flue gas heater (1-1). The other sulfuric acid output end also enters the circulation tank (14) of the second absorption tower (13) through the third demineralized water heater (2-3).

2. The apparatus for optimizing energy-saving sulfuric acid production using a dry-wet coupling process and low-temperature heat recovery as described in claim 1, characterized in that: The sulfuric acid at the bottom of the second suction tower (13) is connected to the first demineralized water heater (2-1) through the circulation tank (14). One sulfuric acid output end of the first demineralized water heater (2-1) is connected to the second demineralized water heater (2-2), and the other sulfuric acid output end is connected to the top of the second suction tower (13).

3. The apparatus for optimizing and saving energy in sulfuric acid production using a dry-wet coupling process and low-temperature heat recovery as described in claim 2, is characterized in that... The demineralized water required by the sulfuric acid plant is connected to the first demineralized water heater (2-1) and the second demineralized water heater (2-2), respectively. The output ends of the first demineralized water heater (2-1) and the second demineralized water heater (2-2) are both connected to the third demineralized water heater (2-3). The water output end of the third demineralized water heater (2-3) is connected in sequence through the deaerator (15), the deoxygenated water preheater (17) and the steam generator (16).

4. A method for optimizing and saving energy in sulfuric acid production using a dry-wet coupling process and low-temperature heat recovery based on the apparatus described in claim 1, characterized in that... The method includes the following steps: (1) Liquid sulfur from the sulfur melting process is injected into the sulfur incinerator (3) through a mechanical nozzle. The air required for sulfur incineration is sent into the sulfur incinerator (3) after passing through a filter (1) and a main blower (2). The air and sulfur vapor are mixed and burned to generate gas. After recovering heat through the first waste heat boiler (4), the gas goes to the first stage of the converter (6) for conversion. The flue gas from the first stage conversion is cooled by the high temperature superheater (5) and then enters the second stage bed of the converter (6) for reaction. The gas from the second stage first enters the heat exchanger (7) for heat exchange, and then enters the third stage of the converter (6) for reaction. The gas from the third stage enters the fourth stage of the converter (6) after passing through the second waste heat boiler (9), the second economizer (10), the low temperature heat recovery tower (11), the cold heat exchanger (8), and the hot heat exchanger (7). The gas from the fourth stage enters the second absorption tower after passing through the cold heat exchanger (8) and the low temperature heat recovery tower (11). The primary conversion process involves one stage, two stages, or one, two, and three stages of conversion within the converter. The remaining stage is secondary conversion. Moisture in the air or moisture generated from the combustion of raw materials enters the primary conversion process along with the SO2-containing flue gas without being dried. Therefore, the primary conversion process uses wet conversion. After the primary conversion, the flue gas enters a low-temperature heat recovery tower for primary absorption. The absorbed flue gas becomes dry flue gas and enters the secondary conversion process. Therefore, the secondary conversion process uses dry conversion. After the secondary conversion, the flue gas enters a secondary absorption process and is then treated to meet emission standards before being discharged. (2) The sulfuric acid at the bottom of the low temperature heat recovery tower (11) first enters the steam generator (16). The sulfuric acid exiting the steam generator (16) is divided into two streams. One stream of sulfuric acid enters the low temperature heat recovery tower (11) through the diluent (18) for circulation absorption, and the other stream of sulfuric acid enters the deoxygenated water preheater (17) for preheating the deoxygenated water. After that, it enters the flue gas heater (1-1) and the third demineralized water heater (2-3) respectively. The sulfuric acid at the outlet of the third demineralized water heater (2-3) and the flue gas heater (1-1) both enter the circulation tank of the second absorption tower (13).

5. The method according to claim 4, characterized in that, Sulfuric acid at the bottom of the second absorption tower (13) enters the first demineralized water heater (2-1) through the circulation tank (14). Part of the sulfuric acid in the first demineralized water heater (2-1) enters the second absorption tower (13) for circulation absorption, and the other part of the sulfuric acid enters the second demineralized water heater (2-2) to heat the demineralized water. The sulfuric acid coming out of the second demineralized water heater (2-2) is the produced acid.

6. The method according to claim 4, characterized in that, The temperature of the gas produced by the combustion of air and sulfur vapor is 1000~1200℃. The temperature of the gas entering the first stage converter is 410~415℃, and the temperature of the gas exiting the first stage converter is 600~620℃. The temperature of the gas entering the second stage converter is 430~450℃, and the temperature of the gas exiting the second stage converter is 520~550℃. The temperature of the gas entering the third stage converter is 430~450℃, and the temperature of the gas exiting the third stage converter is 460~480℃. The temperature of the gas entering the fourth stage converter is 410~415℃, and the temperature of the gas exiting the fourth stage converter is 430~450℃.

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