A method and system for corrosion prevention during shutdown of a sulfide treatment plant

Abstract

The present application relates to the corrosion protection field of sulfide treatment device, and particularly relates to a sulfide treatment device shutdown corrosion protection method and system, the method comprises the following steps: in the conversion absorption system cooling stage of the sulfide treatment device, when the first absorption tower inlet temperature of the conversion absorption system is reduced to a preset first safety temperature, at least part of the acid circulation of the conversion absorption system is stopped; hot air at a preset second safety temperature is introduced into the conversion absorption system for replacement, the residual acidic substances in the conversion absorption system are evaporated by the hot air and transported to a tail gas treatment unit; the replacement is continuously performed until the converter temperature in the conversion absorption system is lower than a preset third safety temperature, and then the replacement is stopped; the method provided by the present application has the advantages of effectively removing the residual acidic substances in the system, preventing the formation of condensed acid and acid sludge, reducing the corrosion risk of equipment, prolonging the service life of key components, and improving the safety of maintenance.

Description

Technical Field

[0001] This invention relates to the field of corrosion prevention technology for sulfide treatment equipment, and more particularly to a method and system for corrosion prevention during shutdown of a sulfide treatment equipment. Background Technology

[0002] During the shutdown of the sulfide treatment unit, the cooling operation of the regeneration boiler system and the conversion absorption system can cause severe equipment corrosion. Existing technology requires starting the sulfur dioxide fan to maintain negative pressure and establishing an acid cycle through the drying tower, the first absorption tower, and the second absorption tower to remove moisture from the flue gas.

[0003] However, when high-temperature flue gas undergoes countercurrent heat exchange with 98% concentrated sulfuric acid, the sulfuric acid mist carried by the flue gas condenses in subsequent heat exchangers and pipes, forming acidic liquid and solid sludge (condensed acid and acid sludge). During shutdown maintenance, when the equipment is left open, the ambient humidity reacts with the residual acidic substances, exacerbating corrosion and significantly shortening the lifespan of critical equipment such as boilers and flue gas pipes. More seriously, the residual acidic substances pose a risk of burns to personnel during maintenance. Traditional solutions rely on natural ventilation and static displacement, which cannot effectively remove residual acidic substances, resulting in equipment lifespans far below the design life and persistently high maintenance costs. Summary of the Invention

[0004] The purpose of this application is to provide a method and system for preventing corrosion during shutdown of a sulfide treatment device, which has the advantages of effectively removing residual acidic substances from the system, preventing the formation of condensed acid and acid sludge, reducing the risk of equipment corrosion, extending the service life of key components, and improving maintenance safety.

[0005] This invention provides a method for preventing corrosion during shutdown of a sulfide treatment device, the method comprising the following steps: During the cooling phase of the conversion and absorption system of the sulfide treatment device, when the inlet temperature of the first absorption tower of the conversion and absorption system drops to a preset first safe temperature, at least part of the acid circulation of the conversion and absorption system is stopped. Hot air at a preset second safe temperature is introduced into the conversion and absorption system for replacement. The hot air evaporates the acidic substances remaining in the conversion and absorption system and transports them to the exhaust gas treatment unit. The replacement continues until the temperature of the converter in the conversion and absorption system is lower than the preset third safety temperature; Wherein, the preset second safety temperature is less than or equal to the preset first safety temperature, and the preset second safety temperature is greater than the preset third safety temperature; the preset first safety temperature is the highest temperature allowed when the conversion and absorption system is operating normally.

[0006] In one embodiment of the present invention, the preset first safety temperature is between 120°C and 150°C, the preset second safety temperature is between 120°C and 140°C, and the preset third safety temperature is between 30°C and 70°C.

[0007] In one embodiment of the present invention, the step of stopping at least a portion of the acid circulation of the conversion and absorption system during the cooling stage of the conversion and absorption system, when the inlet temperature of the first absorption tower of the conversion and absorption system drops to a preset first safe temperature, includes the following staged shutdown of the acid circulation: When the gas temperature at the inlet of the drying tower is ≤50℃, stop the acid circulation in the drying tower; When the inlet process gas temperature of the second absorption tower is ≤150℃, the acid circulation of the second absorption tower is stopped. When the inlet process gas temperature of the first absorption tower is ≤130℃, the acid circulation of the first absorption tower shall be stopped.

[0008] In one embodiment of the present invention, before the step of stopping at least part of the acid circulation of the conversion and absorption system when the inlet temperature of the first absorption tower of the conversion and absorption system drops to a preset first safe temperature during the cooling stage of the conversion and absorption system, a step of cooling the regeneration boiler system is further included, the step of cooling the regeneration boiler system including: After the regeneration furnace feed is stopped, the burners are used for staged cooling. All burners are stopped once the regeneration furnace outlet temperature drops to 300°C. Afterwards, forced ventilation was activated to cool the temperature to 150°C, then natural ventilation was switched to cool the temperature.

[0009] In one embodiment of the present invention, before the step of stopping all burners after the regeneration furnace outlet temperature drops to 300°C following the shutdown of the feed furnace, a feed system purging step is further included. The feed system purging step includes: After stopping the feeding of organic matter / waste acid / ammonium sulfate solution, the conveying pipelines of organic matter, waste acid and ammonium sulfate solution are purged with inert gas to the regeneration furnace.

[0010] In one embodiment of the present invention, the step of stopping at least a portion of the acid circulation of the conversion and absorption system when the inlet temperature of the first absorption tower of the conversion and absorption system drops to a preset first safe temperature during the cooling stage of the conversion and absorption system includes the following cooling step: Purified air is introduced into the drying tower of the conversion and absorption system; Start the sulfur dioxide fan to cool the conversion and absorption system until it is reduced to the preset first safe temperature.

[0011] In one embodiment of the present invention, the demisters of the drying tower, the first absorption tower and the second absorption tower are made of fiber material, and the design temperature resistance of the demister is less than or equal to 150°C.

[0012] In one embodiment of the present invention, the sulfide treatment apparatus includes a conversion and absorption system, the conversion and absorption system comprising: The conversion system includes a converter and a first-stage cold gas preheater and / or a fourth-stage cold gas preheater; The absorption system includes a drying tower, a first absorption tower, a second absorption tower, and / or a nicotinic acid tower; Exhaust gas treatment unit; The drying tower, the first-stage cold gas preheater, the converter, the fourth-stage cold gas preheater, the first absorption tower and / or the nicotinic acid tower, the second absorption tower, and the tail gas treatment unit are connected by pipelines. The drying tower is used for gas drying, the first-stage cold gas preheater and the fourth-stage cold gas preheater are used for gas heat exchange, and the converter is used to convert sulfur dioxide into sulfur trioxide. The first absorption tower, the nicotinic acid tower, and the second absorption tower are used for the absorption of sulfur trioxide, and the tail gas treatment unit is used for tail gas treatment.

[0013] In one embodiment of the present invention, the conversion and absorption system is connected to the regeneration boiler system through a gas purification system; The pipeline includes a first pipe and a second pipe. The conversion and absorption system is connected in sequence through the first pipe to a drying tower, a first-stage cold gas preheater, a converter, a fourth-stage cold gas preheater, and an inlet connected to the first absorption tower and / or the nicotinic acid tower. The outlet of the first absorption tower and / or the nicotinic acid tower is connected in sequence through the second pipe to the fourth-stage cold gas preheater, a converter, a first-stage cold gas preheater, a second absorption tower, and a tail gas treatment unit. The fourth-stage cold gas preheater, the converter, and the first-stage cold gas preheater include at least two sets of gas treatment channels.

[0014] The present invention also provides a corrosion prevention system for shutdown of a sulfide treatment device, including a temperature detection unit, a control unit and a gas replacement unit that are electrically connected; During the cooling phase of the conversion and absorption system in the sulfide treatment unit, when the temperature detection unit detects that the inlet temperature of the first absorption tower of the conversion and absorption system has dropped to a preset first safe temperature... The control unit controls at least part of the acid circulation in the conversion and absorption system to stop, and the control unit controls the gas replacement unit to introduce hot air at a preset second safety temperature into the conversion and absorption system for replacement. The hot air evaporates the acidic substances remaining in the conversion and absorption system and transports them to the exhaust gas treatment unit. The replacement continues until the temperature of the converter in the conversion and absorption system is lower than a preset third safety temperature. Wherein, the preset second safety temperature is less than or equal to the preset first safety temperature, and the preset second safety temperature is greater than the preset third safety temperature; the preset first safety temperature is the highest temperature allowed when the conversion and absorption system is operating normally.

[0015] The beneficial effects of the present invention are as follows: As can be seen from the above, the corrosion prevention method and system for shutting down a sulfide treatment device provided in this application effectively eliminates the generation of condensed acid and acid sludge in the system by stopping the acid cycle in stages and introducing hot air to replace the residual acidic substances, combined with precise temperature control, and blocks the reaction path between the corrosive medium and the ambient moisture, which has the effect of significantly improving the corrosion resistance and safety of the equipment. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0017] In the attached diagram: Figure 1 This is a schematic diagram of a sulfide treatment device provided in an embodiment of the present invention; Figure 2 This is a flowchart of a sulfide treatment device shutdown and corrosion prevention method provided in one embodiment of the present invention; The attached figures are labeled as follows: Conversion and absorption system 100, absorption system 10, drying tower 11, drying tower pump tank 111, drying tower acid circulation pump 112, sulfur dioxide fan 113, first absorption tower 12, first absorption tower demister 121, first packing 122, second absorption tower 13, second absorption tower demister 131, second packing 132, nicotinic acid tower 14, first pipe 101, second pipe 102, conversion system 20, converter 21, shell 211, first inlet 2111, first outlet 2112, second inlet 2113, second outlet 2 114, First conversion bed 212, Second conversion bed 213, Third conversion bed 215, Fourth conversion bed 214, First stage cold gas preheater 22, Fourth stage cold gas preheater 23, First stage hot gas preheater 24, Fourth stage hot gas preheater 25, Gas purification system 200, Regeneration boiler system 300, Regeneration furnace 301, Waste acid channel 3011, Gas channel 3012, Regeneration furnace air fan 20121, Regeneration furnace air preheater 20122, Burner 302, Tail gas treatment unit 30, Hydrogen peroxide scrubbing tower 31, Chimney 32; Figure 1 The main gases transported in each pipeline: The initial components are: high-temperature flue gas containing sulfur dioxide (A); gas containing sulfur dioxide after preliminary purification (B); gas containing sulfur dioxide after drying (C); gas containing sulfur dioxide after cooling and exiting from the shell side of a first-stage cold gas preheater (D); gas containing sulfur trioxide after heating and exiting from the tube side of a first-stage cold gas preheater (E); gas containing sulfur trioxide (F); gas containing sulfur trioxide (G); gas containing small amounts of sulfur dioxide and sulfur trioxide (H); gas containing sulfur dioxide (I); gas containing sulfur trioxide (J); and tail gas after purification and desulfurization (K). In this process, SO2 and O2 react with a catalyst to form SO3, maintaining a reversible equilibrium. Detailed Implementation

[0018] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0019] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0020] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0021] Sulfide treatment devices, such as sulfuric acid recovery devices, are used to process sulfuric acid-containing flue gas. During shutdown of the sulfide treatment device, the sulfur dioxide fan 113 needs to be started to maintain the negative pressure of the system. During the shutdown cooling period, the main cooling processes are the regeneration boiler system 300 and the conversion absorption system 100. During the system cooling, a large amount of condensed acid is generated inside the flue gas pipelines and equipment. When the equipment is opened during shutdown maintenance, it absorbs water and produces acid sludge, which aggravates the corrosion of the flue gas pipelines and equipment and reduces their service life.

[0022] To prevent liquid from being carried in the flue gas during the cooling process of the conversion and absorption system 100, which would cause the impeller of the sulfur dioxide fan 113 to vibrate and impact, the original operation method required starting the drying tower 11, the first absorption tower 12, and the second absorption tower 13 to establish an acid cycle and remove the moisture contained in the flue gas. During the cooling process, the high-temperature flue gas (e.g., above 200°C) and the 98% sulfuric acid in the absorption system 10 exchange heat in a counter-current manner. After heat exchange, the flue gas enters the first-stage cold gas preheater 22 and the fourth-stage cold gas preheater 23, and then enters the shell side of the heat exchanger. After heat exchange with sulfuric acid, the flue gas carries some sulfuric acid mist. The sulfuric acid mist condenses in the heat exchanger and pipelines to form condensed acid and acid sludge, causing corrosion of equipment and pipelines. During maintenance, the acidic substances in the pipelines and equipment pose a risk of burns to personnel.

[0023] Therefore, while the above solution can achieve a smooth shutdown of the equipment, it cannot prevent corrosion of the regeneration boiler system 300, the conversion and absorption system 100, and the pipelines and equipment. The existing technology replaces residual gases and acids in the regeneration boiler system 300 and the conversion and absorption system 100 through natural ventilation and settling after shutdown. Because there is less material residue after replacement, there is a safety risk for personnel entering the equipment during shutdown maintenance.

[0024] To address the aforementioned issues, a method is needed to effectively remove residual acidic substances from the system. Traditional methods do not consider the synergistic relationship between acid cycle shutdown timing and temperature control, allowing residual substances to continue accumulating during the cooling phase. Analysis revealed that the key to acidic substance condensation lies in the system temperature not dropping to a safe threshold and the lack of an active removal mechanism. Therefore, it is necessary to stop the acid cycle in stages at specific temperature points, while simultaneously introducing hot air to create a temperature gradient, allowing residual substances to be expelled from the system with the airflow.

[0025] Therefore, this application proposes a method for preventing corrosion during shutdown of a sulfide treatment device. The method includes the following steps: during the cooling stage of the conversion absorption system 100, when the inlet temperature of the first absorption tower 12 drops to a preset first safety temperature, at least part of the acid circulation of the conversion absorption system 100 is stopped; hot air at a preset second safety temperature is introduced into the conversion absorption system 100 for replacement, and the residual acidic substances in the system are evaporated by the hot air and transported to the tail gas treatment unit 30; replacement continues until the temperature of the converter 21 is lower than a preset third safety temperature and then stops; wherein the preset second safety temperature is less than or equal to the preset first safety temperature and greater than the preset third safety temperature, and the preset first safety temperature is the highest temperature allowed when the conversion absorption system 100 is operating normally.

[0026] The preset first safety temperature refers to the trigger temperature threshold for the conversion and absorption system 100 to stop acid circulation. This can be achieved using the highest operating temperature range allowed by the system design. This parameter setting ensures that the system still has safe operating conditions when acid circulation stops. The preset second safety temperature refers to the temperature control value for hot air replacement operation. This can be achieved using a temperature range lower than the system's highest operating temperature but higher than the ambient dew point. This temperature selection effectively evaporates acidic substances while avoiding thermal stress damage to the equipment. Hot air replacement refers to purging the system with a controllable airflow. This can be achieved by heating air with burner 302 or preheating air with a steam heat exchanger, using forced convection to remove residual substances. Continuous replacement refers to maintaining airflow circulation until the temperature of the system's core components reaches the target. This can be achieved by using a temperature sensor to monitor the temperature of converter 21 in real time, ensuring that the overall system temperature drops to the critical point where acidic substances cannot condense.

[0027] Specifically, this method achieves residue removal through the coordinated operation of staged acid circulation shutdown and hot air replacement. When the inlet temperature of the first absorption tower 12 drops to a preset first safety temperature, part of the acid circulation system stops operating, cutting off the path for concentrated sulfuric acid to continuously enter the system. At this time, hot air at a preset second safety temperature is introduced, using its heat to vaporize the acidic residues adhering to the equipment surface. The hot air temperature is lower than the system's normal operating peak but higher than the subsequent replacement final temperature, forming a temperature gradient that promotes the phase transition of the substances. The replacement airflow carries the vaporized substances into the tail gas treatment unit 30 for centralized treatment, preventing the acidic substances from re-condensing in the pipes and heat exchangers. The temperature of the converter 21 is continuously monitored until it falls below a preset third safety temperature, ensuring that the overall system temperature gradient meets the requirements for complete removal of acidic substances. The decreasing relationship of the three temperature parameters forms a closed-loop control logic, which both matches the system cooling curve and achieves the step-by-step removal of residues.

[0028] Compared to existing technologies, traditional methods rely on natural ventilation, which fails to create effective airflow circulation, resulting in low efficiency in removing residual substances. This method establishes forced convection by actively introducing hot air, simultaneously removing residual substances during system cooling. Existing technologies lack phased temperature control nodes, and the lack of coordination between acid cycle shutdown and replacement operations leads to incomplete removal. This method, by pre-setting three decreasing temperature thresholds, precisely controls the timing of acid cycle shutdown and replacement operation parameters, achieving simultaneous optimization of system cooling and substance removal.

[0029] Through the above technical solution, this application effectively solves the problem of equipment corrosion caused by residual acidic substances during shutdown. Hot air replacement thoroughly removes residual condensed acid and acid sludge from the system, preventing secondary corrosion caused by the reaction of ambient moisture with acidic substances during maintenance. Staged temperature control ensures that all system components complete purification within a safe temperature range, protecting equipment materials and eliminating the risk of personnel contact with residual acid. This method significantly extends the service life of critical equipment, reduces maintenance costs, and improves the safety of shutdown maintenance operations.

[0030] As an optional embodiment of this case, the first safe temperature is preset to be between 120°C and 150°C, for example, the first safe temperature is preset to be 150°C or 131°C; the second safe temperature is preset to be between 120°C and 140°C, for example, the second safe temperature is preset to be 125°C or 130°C; and the third safe temperature is preset to be between 30°C and 70°C, or 50°C or 60°C.

[0031] The preset first safety temperature refers to the temperature threshold at which the conversion and absorption system 100 stops acid circulation. Specifically, it can be monitored using a thermocouple or infrared thermometer to check the inlet temperature of the first absorption tower 12. When the temperature drops to the range of 120°C to 150°C, the interlock control system is triggered to cut off the power to the acid circulation pump. This temperature range is set based on the highest temperature allowed for normal operation of the conversion and absorption system 100, which can prevent excessive volatilization of acidic substances and formation of aerosols at high temperatures.

[0032] The preset second safety temperature refers to the temperature control parameter for the hot air replacement operation. Specifically, the air can be heated to the range of 120°C to 140°C by adjusting the power of the electric heater or the flow rate of the steam heat exchanger. This temperature range is lower than the upper limit of the first safety temperature, which ensures that the residual sulfuric acid mist evaporates fully and prevents the temperature of the heat exchanger tube wall from exceeding the material's temperature resistance limit.

[0033] The preset third safety temperature refers to the criterion for terminating the replacement operation. Specifically, it can be achieved by using multi-point temperature sensors to monitor the internal temperature distribution of the converter 21. When all measuring points are below 70°C and above 30°C, the blower operation is stopped. This temperature range ensures that the system is cooled below the acid dew point, eliminating the conditions for acidic substances to condense on the equipment surface.

[0034] Specifically, during the cooling phase of the conversion and absorption system 100, acid circulation is stopped when the inlet temperature of the first absorption tower 12 drops to 120°C to 150°C, at which point the amount of residual liquid acid in the system is within a controllable range. Subsequently, hot air at 120°C to 140°C is introduced for replacement. This temperature allows the residual acid to evaporate into a gaseous state while preventing thermal stress deformation of the equipment's metal materials due to high temperatures. Replacement continues until the temperature of the converter 21 drops to the range of 30°C to 70°C. At this point, the overall system temperature is below the sulfuric acid dew point temperature, preventing the residual acidic substances from forming a condensate film on the metal surface. These three temperature parameters form a progressive control logic, achieving phase control of the acidic substances through staged temperature threshold settings.

[0035] Compared to existing technologies, traditional methods rely on a single temperature threshold to control the shutdown process, failing to differentiate the varying temperature requirements of the three stages: acid cycle cessation, heat exchange operation, and system cooling. This solution, by setting three progressive temperature ranges, precisely matches the phase change patterns of each process stage, preventing premature shutdown of the acid cycle at high temperatures that could lead to excessive acid residue, while also preventing incomplete replacement at low temperatures that could result in acid sludge deposition.

[0036] Through the above technical solution, this application effectively solves the problem of acidic substance condensation caused by improper temperature gradient control during shutdown. The acid circulation stop temperature range of 120℃ to 150℃ maintains the system operating at the upper limit of a safe temperature, maximizing the discharge of liquid acid; the hot air replacement temperature of 120℃ to 140℃ vaporizes residual acid while preventing overheating damage to the equipment; and the termination temperature of 30℃ to 70℃ ensures the system cools below the acid dew point, completely eliminating conditions for condensation corrosion. The coordinated control of these three temperature parameters ensures that the equipment remains in a non-condensing state during shutdown, significantly reducing acid sludge formation and the risk of pitting corrosion on metal surfaces.

[0037] As an optional embodiment of this case, the method of stopping the acid circulation in stages during the cooling phase of the conversion and absorption system 100 specifically includes stopping the acid circulation of the drying tower 11 when the inlet gas temperature of the drying tower 11 is ≤50°C, stopping the acid circulation of the second absorption tower 13 when the inlet process gas temperature of the second absorption tower 13 is ≤150°C, and stopping the acid circulation of the first absorption tower 12 when the inlet process gas temperature of the first absorption tower 12 is ≤130°C.

[0038] The inlet gas temperature of drying tower 11 ≤ 50℃ refers to the critical value at which the temperature of the process gas at the inlet of drying tower 11 drops to no more than 50℃. This can be achieved by real-time monitoring with a temperature sensor combined with a control system. This temperature threshold setting prevents residue accumulation caused by decreased acid fluidity at low temperatures. The inlet process gas temperature of the second absorption tower 13 ≤ 150℃ refers to the upper limit of the inlet process gas temperature of the second absorption tower 13. This can be achieved by adjusting the cooling rate of the heat exchanger. This temperature condition matches the upper limit of the temperature resistance of the second absorption tower 13, preventing material degradation due to high temperatures. The inlet process gas temperature of the first absorption tower 12 ≤ 130℃ refers to the cooling endpoint of the inlet process gas of the first absorption tower 12. This can be achieved by controlling the hot air replacement rate. This temperature threshold ensures that the main absorption unit terminates acid circulation within a safe range, suppressing acid mist generation.

[0039] Specifically, during the system cooling process, the acid circulation in drying tower 11 stops when the inlet gas temperature drops to 50°C. At this point, the acid flowability has significantly decreased, and continued operation would lead to acid stagnation. The acid circulation in the second absorption tower 13 stops when the inlet temperature drops to 150°C, which is close to the temperature limit of its demister. Shutting down this tower prevents excessive acid mist from being generated by contact between high-temperature flue gas and acid. The first absorption tower 12, as the main absorption unit, stops its acid circulation when the inlet temperature drops to 130°C. At this point, most of the acidic substances in the system have been removed, and the residual amount is within a controllable range. By shutting down drying tower 11, second absorption tower 13, and first absorption tower 12 in stages, a temperature gradient control is achieved, allowing each piece of equipment to gradually reduce its operating intensity within the material tolerance range. Simultaneously, residual acidic substances are continuously removed through hot air replacement.

[0040] Compared to existing technologies, traditional methods employ simultaneous or disordered shutdown of acid circulation, resulting in the coexistence of acid residue in low-temperature zones and acid mist generation in high-temperature zones. This solution, through differentiated temperature threshold settings, ensures that each absorber stops acid circulation within its optimal temperature window, avoiding both low-temperature residue and high-temperature corrosion. Simultaneously, it utilizes temperature gradients to promote the directional migration of residues to the exhaust gas treatment unit 30.

[0041] Through the above technical solution, this application solves the problem of incomplete residue removal caused by improper acid cycle shutdown sequence, effectively inhibiting the retention of acidic substances in the equipment during shutdown. Shutting down the drying tower 11 at 50℃ prevents acid solidification, shutting down the second absorption tower 13 at 150℃ prevents overheating damage to the demister, and shutting down the first absorption tower 12 at 130℃ ensures the safe shutdown of the main absorption unit. This phased control method reduces the total amount of residual acidic substances in the system, lowers the risk of equipment corrosion and safety hazards during maintenance, and achieves efficient replacement without relying on natural ventilation.

[0042] As an optional embodiment of this case, during the cooling stage of the conversion absorption system 100, before the step of stopping at least part of the acid circulation of the conversion absorption system 100 when the inlet temperature of the first absorption tower 12 of the conversion absorption system 100 drops to a preset first safety temperature, a cooling step of the regeneration boiler system 300 is also included. The cooling step of the regeneration boiler system 300 includes: after the feeding of the regeneration furnace 301 is stopped, the burners 302 are used for stepped cooling; after the outlet temperature of the regeneration furnace 301 drops to 300°C, all burners 302 are stopped; then forced ventilation is started to cool down to 150°C, and then natural ventilation is switched to cool down.

[0043] Among these methods, burner 302 stepped cooling refers to a cooling method that gradually reduces the number of burners 302 in operation or the fuel supply. Specifically, this can be achieved by gradually shutting down burners 302 or reducing the fuel supply rate. This gradient temperature decrease prevents thermal stress cracks in the furnace material due to sudden cooling. Forced ventilation cooling refers to a cooling method that uses mechanical air supply equipment to accelerate air circulation. This can be achieved using axial flow fans or centrifugal fans. Forced convection quickly removes residual heat from the furnace, preventing acidic substances from remaining at high temperatures. Natural ventilation cooling relies on the natural airflow generated by the chimney effect for heat dissipation. This can be achieved by opening the furnace ventilation openings. During low-temperature stages, this avoids the introduction of external moisture through mechanical ventilation, which could react with residual acidic substances.

[0044] Specifically, after the regenerable boiler system 300 is shut down, burner 302 is initially kept running at a low load, for example, by shutting down the burner group in three intervals, allowing the furnace outlet temperature to drop to the 300°C threshold at a rate not exceeding 50°C per hour. At this point, all burners 302 stop operating, and the axial flow fan is immediately started for forced ventilation at a cooling rate of 80-100°C per hour. When the temperature sensor detects that the temperature in the middle of the furnace has dropped to 150°C, the fan is shut down and the furnace top vent is opened, utilizing natural convection to complete the final cooling. This phased control strategy, through temperature threshold monitoring and ventilation mode switching, prevents acidic substances from condensing into acid due to a sudden drop in temperature during the high-temperature stage, and avoids forced ventilation introducing moisture that could cause secondary corrosion during the low-temperature stage.

[0045] Compared to existing technologies, traditional methods typically involve directly activating natural ventilation or using only forced ventilation after furnace shutdown. This results in the temperature gradient within the furnace exceeding the material's tolerance limits, while residual acidic substances form corrosive condensate in high-temperature areas. This solution utilizes a cascade cooling system in the burner 302 to create a controllable temperature drop curve. Combined with the sequential switching between forced and natural ventilation, this ensures cooling efficiency while avoiding the dual risks of thermal stress damage and moisture intrusion.

[0046] Through the above technical solution, this application effectively solves the equipment corrosion problem caused by the sudden drop in temperature during the shutdown phase of the regenerated boiler system. By controlling the temperature in stages, the residual acidic substances in the high-temperature area are removed, preventing secondary corrosion of the condensed acid sludge during maintenance, and reducing the safety risk of operators coming into contact with high-temperature acidic substances.

[0047] As an optional embodiment of this case, after stopping the entry of materials such as organic matter / waste acid / ammonium sulfate liquid into the regeneration boiler system 300, the conveying pipelines of organic matter, waste acid and ammonium sulfate liquid to the regeneration furnace 301 are purged with inert gas. The feeding system purging step refers to the operation of replacing the conveying pipeline with an inert gas after the material supply is stopped. Specifically, nitrogen or other gases meeting the requirements can be used as the purging medium. Its purpose is to remove residual corrosive substances from the pipeline. Nitrogen purging refers to the pressure-driven flow cleaning of the pipeline using inert gas. This can be achieved by continuously introducing nitrogen and maintaining a certain flow rate. Its purpose is to prevent residual materials from oxidizing upon contact with air. The path setting of the conveying pipeline to the regeneration furnace 301 refers to the purging direction extending from the feed end to the high-temperature reaction zone. This can be achieved by controlling the gas flow direction using a one-way valve. Its purpose is to ensure that residual materials are completely conveyed to the regeneration furnace 301 for high-temperature decomposition.

[0048] Specifically, after the feeding of organic matter, waste acid, or ammonium sulfate solution is stopped, nitrogen is immediately introduced into the conveying pipeline. The nitrogen is injected from the feed end at a preset pressure, carrying the residual material adhering to the inner wall of the pipeline into the regeneration furnace 301 as it flows along the pipeline. Since the regeneration furnace 301 is still at a high temperature, the residual material being purged undergoes thermal decomposition in the high-temperature environment, transforming into harmless gases or stable compounds. The purging process continues until the nitrogen purity in the pipeline reaches a set threshold, at which point it can be confirmed that there is no corrosive media residue in the pipeline. This operation is completed before the staged cooling step of the burner 302, ensuring that the pipeline is clean during the subsequent cooling stage.

[0049] Compared to existing technologies, which lack an active purging process after material transport is stopped and rely solely on natural evacuation or static treatment, resulting in the long-term retention of corrosive substances within the pipeline, this solution utilizes the synergistic effect of active purging and high-temperature decomposition to thoroughly remove residues from the pipeline, preventing corrosion or safety hazards during subsequent operations.

[0050] Through the above technical solution, this application effectively eliminates the problem of residual material remaining in the conveying pipeline after the feeding system is shut down, preventing the formation and accumulation of corrosive media. The improved cleanliness of the pipeline environment reduces the corrosion rate of the equipment, while avoiding harmful substances generated by the decomposition of residues under high-temperature conditions, thus ensuring the safe operation of subsequent processes.

[0051] As an optional embodiment of this case, during the cooling stage of the conversion and absorption system 100, when the inlet temperature of the first absorption tower 12 of the conversion and absorption system 100 drops to a preset first safe temperature, the step of stopping at least part of the acid circulation of the conversion and absorption system 100 includes the following cooling steps: introducing purified air into the drying tower 11 of the conversion and absorption system 100; starting the sulfur dioxide fan 113 to cool the conversion and absorption system 100 until it drops to the preset first safe temperature.

[0052] The purified air refers to clean gas that has been filtered to remove particulate matter and moisture. This can be achieved by combining a multi-stage dust collector with an adsorption dryer. Its function is to prevent the introduction of external impurities that could interfere with the internal environment of the system, while simultaneously accelerating the evaporation of residual acidic substances through low-humidity air. The sulfur dioxide fan 113 is a gas conveying device with corrosion-resistant properties, specifically made of fiberglass impeller and PTFE sealing structure. Its function is to forcefully drive airflow circulation within the system, ensuring a uniform temperature drop and promoting the migration of acidic substances to the exhaust gas treatment unit 30.

[0053] Specifically, as the system temperature drops to a preset first safe temperature, purified air is continuously introduced through the inlet of the drying tower 11, replacing residual sulfur-containing gases and acidic vapors. Simultaneously, the sulfur dioxide fan 113 starts, creating a directional airflow that propels the purified air along the paths of the converter 21, heat exchanger, and absorption tower, facilitating the diffusion of heat from the high-temperature region to the low-temperature region. As the fan continues to operate, the temperature gradient at each node within the system gradually decreases. When the temperature sensor at the inlet of the first absorption tower 12 detects that the temperature has reached a preset threshold, the system enters a safe shutdown state. This synergistic effect of purified air and mechanical ventilation avoids condensation in localized areas caused by sudden temperature drops and reduces the adhesion of acidic substances to equipment surfaces through airflow scouring.

[0054] Compared to existing technologies, traditional methods relying on natural ventilation fail to create effective airflow circulation, leading to the condensation of acidic vapors at pipe bends or equipment dead zones, forming corrosion sources. This solution, through a combination of forced ventilation and purified air injection, achieves the active removal of residual substances within the system while precisely controlling the cooling rate to prevent stress corrosion caused by sudden temperature changes. Existing technologies require a static replacement process that can take several days, while this solution accelerates the replacement process through mechanical power, enabling the system to reach safe maintenance conditions in a much shorter time.

[0055] Through the above technical solution, this application effectively solves the problem of residual condensed acid sludge caused by the contact between high-temperature flue gas and concentrated sulfuric acid during shutdown. The continuous introduction of purified air blocks the recondensation path of acidic substances inside the equipment, and the forced circulation effect of the sulfur dioxide fan 113 eliminates the airflow stagnation areas found in traditional natural ventilation modes. This technical solution not only reduces the corrosion risk during equipment maintenance but also shortens the downtime by reducing system replacement time, while avoiding safety hazards caused by contact between residual acidic substances and maintenance personnel.

[0056] As an optional embodiment of this case, the demisters of the drying tower 11, the first absorption tower 12 and the second absorption tower 13 are made of fiber material, and the design temperature resistance of the demisters is less than or equal to 150°C.

[0057] The fiber material refers to the filter media composed of inorganic or organic fibers, specifically glass fiber or polytetrafluoroethylene fiber woven fabric. Its porous structure increases the contact area and utilizes capillary effect to adsorb acidic droplets. The design temperature resistance of ≤150℃ refers to the highest temperature that the demister body material can withstand under continuous operating conditions. This can be achieved through fiber surface coating or substrate modification. This temperature range matches the hot air replacement temperature during the system's cooling phase and is below the critical point of thermal deformation of the fiber material.

[0058] Specifically, the fiber demister intercepts sulfuric acid droplets entrained in the gas through its three-dimensional mesh structure. The droplets are captured and coalesce into a liquid film on the fiber surface, eventually flowing downwards along the fiber surface to the collection device. During the system cooling phase, when the hot air replacement temperature is between 120°C and 140°C, the fiber demister maintains its structural integrity, preventing fiber melting or deformation due to overheating, thus maintaining stable droplet removal efficiency. Simultaneously, this upper temperature limit ensures that even during shutdown operations with localized temperature fluctuations, the demister will not crack due to thermal stress, preventing unremoved acidic substances from entering downstream equipment.

[0059] Compared to existing technologies, traditional metal wire mesh demisters are prone to electrochemical corrosion in high-temperature acidic environments, leading to decreased demisting efficiency and corrosion products contaminating acidic sludge. In contrast, fiber demisters, through the selection of chemically inert materials, avoid the formation of corrosion products. Furthermore, their multi-stage filtration mechanism significantly improves the capture capacity of submicron-sized droplets compared to the single inertial impaction method of metal wire mesh.

[0060] Through the above technical solution, this application effectively blocks the migration path of acidic droplets to heat exchangers and pipelines, reducing the amount of residual condensed acid and acid sludge inside the equipment during shutdown. The stable operation of the fiber demister under high-temperature conditions avoids secondary pollution caused by material failure, and at the same time creates the necessary conditions for subsequent hot air replacement to remove residual acidic substances, thereby reducing the equipment corrosion rate and maintenance operation risks.

[0061] As an optional embodiment of this case, the sulfide treatment device includes a conversion and absorption system 100, which includes a conversion system 20, an absorption system 10, and a tail gas treatment unit 30. The conversion system 20 includes a converter 21, a first-stage cold gas preheater 22, and a fourth-stage cold gas preheater 23; the absorption system 10 includes a drying tower 11, a first absorption tower 12, a second absorption tower 13, and a nicotinic acid tower 14; the drying tower 11, the first-stage cold gas preheater 22, the converter 21, the fourth-stage cold gas preheater 23, the first absorption tower 12, the nicotinic acid tower 14, the second absorption tower 13, and the tail gas treatment unit 30 are connected by pipelines.

[0062] The converter 21 is a reaction vessel for the catalytic conversion of sulfur dioxide into sulfur trioxide. Specifically, it can be implemented using a shell structure 211 filled with vanadium catalyst, with multiple conversion beds inside to complete the oxidation reaction in stages. The first-stage cold gas preheater 22 and the fourth-stage cold gas preheater 23 are heat exchange devices for controlling the gas temperature gradient. Specifically, they can be implemented using a shell-and-tube heat exchanger structure, avoiding localized overcooling that could lead to condensation of acidic substances through segmented heat exchange. The drying tower 11 is a treatment unit for reducing gas humidity. Specifically, it can be implemented using a packed tower structure sprayed with concentrated sulfuric acid, preventing corrosion of subsequent equipment by absorbing moisture from the gas. The first absorption tower 12 and the second absorption tower 13 are devices for absorbing sulfur trioxide. Specifically, they can be implemented using a tower structure that circulates concentrated sulfuric acid, improving the capture efficiency of acidic substances through layered absorption. The tail gas treatment unit 30 is an end-of-pipe gas purification device, specifically implemented using an alkaline scrubbing tower or an activated carbon adsorption device, ensuring that residual acidic substances are thoroughly treated.

[0063] Specifically, the conversion system 20 controls the gas temperature through a segmented heat exchanger, allowing sulfur dioxide to undergo catalytic oxidation in the converter 21 to form sulfur trioxide. The absorption system 10 pre-reduces the gas humidity through a drying tower 11, after which the sulfur trioxide sequentially enters the first absorption tower 12 and the second absorption tower 13 to be absorbed by concentrated sulfuric acid. The pipeline connection forms a closed loop, allowing acidic substances remaining from the hot air replacement stage to be transported to the tail gas treatment unit 30 via fixed channels through the drying tower 11, heat exchanger, and absorption tower. The combined structure of the converter 21 and the segmented heat exchanger maintains temperature stability and prevents acidic substances from condensing on the heat exchange surface; the multi-stage absorption tower design treats different concentrations of acidic gas in stages, avoiding overload of a single absorption unit; the end-point design of the tail gas treatment unit 30 ensures that residual substances are removed in a targeted manner, eliminating the corrosion risk caused by an open system.

[0064] Compared to existing technologies, traditional methods rely on natural ventilation for displacement, which cannot effectively remove acidic substances from dead corners of pipes and equipment, leading to the accumulation of condensed acid and acid sludge. This solution utilizes an integrated conversion and absorption system 100 to create a closed-loop treatment path, employing segmented heat exchangers to control the temperature gradient and combining multi-stage absorption towers to achieve forced transport and phased treatment of residual acidic substances, significantly improving displacement efficiency. Existing technologies require several days for static displacement and still pose a risk of corrosion, while this solution, through system structure optimization, can complete the removal of acidic substances in a shorter time, while avoiding secondary corrosion caused by contact between environmental moisture and residues during maintenance.

[0065] Through the above technical solutions, this application solves the problem of accelerated equipment corrosion caused by acidic residues during shutdown. A closed-loop treatment path eliminates the risk of acid mist condensation within pipelines, reducing safety hazards associated with personnel contact with corrosive substances during maintenance. A directional transport mechanism ensures that residual substances are efficiently transported to the exhaust gas treatment unit 30, avoiding incomplete removal due to loose structures in traditional methods. The synergistic effect of multi-stage absorption towers and segmented heat exchangers improves the temperature control accuracy of the system during shutdown, preventing acidic substance deposition caused by localized low temperatures.

[0066] As an optional embodiment of this case, the conversion and absorption system 100 is connected to the regeneration boiler system 300 through the gas purification system 200; the pipeline includes a first pipe 101 and a second pipe 102. The conversion and absorption system 100 is connected to the drying tower 11, a first-stage cold gas preheater 22, a converter 21, a fourth-stage cold gas preheater 23, and the inlet of the first absorption tower 12 or the nicotinic acid tower 14 in sequence through the first pipe 101. The outlet of the first absorption tower 12 or the nicotinic acid tower 14 is connected to the fourth-stage cold gas preheater 23, the converter 21, the first-stage cold gas preheater 22, the second absorption tower 13, and the tail gas treatment unit 30 in sequence through the second pipe 102. The fourth-stage cold gas preheater 23, the converter 21, and the first-stage cold gas preheater 22 include at least two sets of gas treatment channels.

[0067] The gas purification system 200 refers to a combination of devices used for pre-treating boiler flue gas. Specifically, it can be implemented using a combination of a quench cooler, a gas cooling tower, a demister, and a neutralization tank. Through steps such as quenching, washing, gas-liquid separation, and neutralization, it removes acidic substances and particulate matter from the flue gas, preventing impurities from entering the conversion and absorption system 100 and causing equipment corrosion. The two gas treatment channels refer to parallel gas flow paths set within the same heat exchanger or converter 21. Specifically, they can be implemented using a split heat exchange tube bundle or a zoned catalyst bed structure, allowing high-temperature flue gas and replacement hot air to complete heat exchange or catalytic reactions through different channels, avoiding cross-contamination and extending the gas treatment path. The bidirectional circulation pipeline formed by the first pipe 101 and the second pipe 102 refers to a closed gas transport network connecting the drying tower 11, heat exchanger, converter 21, and absorption tower. Specifically, it can be implemented using corrosion-resistant alloy pipes with flange connections, establishing an alternating positive and negative pressure airflow circulation mode to achieve sufficient contact between the flue gas and the absorption acid.

[0068] Specifically, the sulfur oxide-containing flue gas generated by the regenerated boiler system 300 is pretreated by the gas purification system 200 and then enters the drying tower 11 through the first pipe 101 for dehydration. The dehydrated gas flows sequentially through a first-stage cold gas preheater 22, a converter 21, and a fourth-stage cold gas preheater 23 to complete heat exchange and catalytic conversion, and then enters the first absorption tower 12 or the nicotine tower 14 for acid mist capture. The treated gas flows in reverse through the second pipe 102 through the fourth-stage cold gas preheater 23, a converter 21, and a first-stage cold gas preheater 22 for secondary heat exchange, and finally enters the second absorption tower 13 for deep purification and is discharged into the tail gas treatment unit 30. The two gas treatment channels serve the gas transport paths of the first pipe 101 and the second pipe 102 respectively, enabling the same heat exchanger or converter 21 to process gas media in different temperature ranges simultaneously. During shutdown, the structure allows hot air to flow forward through the first pipe 101 to remove residual acidic substances in the drying tower 11 and heat exchanger, while flowing backward through the second pipe 102 to remove condensed acid in the converter 21 and absorption tower, thus achieving bidirectional replacement.

[0069] Compared to existing technologies, traditional single-channel systems can only process gas in one direction, leaving acidic substances in dead zones that cannot be removed. This solution, through a design of two gas processing channels and bidirectional circulation pipelines, allows high-temperature flue gas and replacement hot air to complete full-system cleaning through independent paths. Existing technologies require additional auxiliary cleaning pipelines, while this solution, by reusing the multi-channel structure of the original heat exchanger and converter 21, achieves thorough removal of residual substances while reducing the number of devices required.

[0070] Through the above technical solution, this application solves the problem of incomplete removal of residual acidic substances inside the equipment during shutdown. The synergistic effect of the gas purification system 200 and the bidirectional circulation pipeline can effectively remove acid sludge deposits from the catalyst bed gaps in the converter 21 and between the heat exchanger tube bundles, preventing moisture intrusion and secondary corrosion during shutdown. The configuration of two sets of gas treatment channels allows the system to reduce equipment manufacturing costs through structural reuse while maintaining the original processing capacity. This design is particularly suitable for sulfur-containing flue gas treatment devices, enabling comprehensive cleaning of the equipment's interior without increasing system complexity.

[0071] As an optional embodiment of this case, the converter 21 includes a housing 211 and a first conversion bed 212, a second conversion bed 213, a fourth conversion bed 214 and a third conversion bed 215 arranged sequentially from the upper part to the lower part of the housing 211. A first inlet 2111 is provided at the top of the housing 211, and a second inlet 2113 and a first outlet 2112 are provided at the bottom of the housing 211. A second outlet 2114 is provided at the fourth conversion bed 214. The first pipe 101, the first inlet 2111, the first conversion bed 212, the second conversion bed 213, the third conversion bed 215 and the first outlet 2112 are connected sequentially. The second pipe 102 is connected sequentially to the second inlet 2113, the fourth conversion bed 214 and / or the third conversion bed 215 and the second outlet 2114.

[0072] The longitudinal arrangement of the first conversion bed 212, the second conversion bed 213, and the third conversion bed 215 refers to the arrangement of three catalyst beds from top to bottom along the axial direction of the shell 211. This can be achieved by layering vanadium catalysts with different conversion rates to form the main reaction channel for sulfur dioxide oxidation. The fourth conversion bed 214, independently located above the third conversion bed 215, means that the fourth catalyst bed is arranged separately from the first two or three layers. This can be achieved by setting up an independent support structure, forming an auxiliary reaction channel. The first inlet 2111 and the first outlet 2112, located at the top and bottom of the shell 211 respectively, refer to the gas inlet and outlet being arranged vertically opposite each other. This can be achieved by connecting pipes with flanges, guiding the gas to form a bidirectional flow path within the converter 21. The second inlet 2113 and the second outlet 2114, located at the bottom of the shell 211 and the side wall of the fourth conversion bed 214 respectively, refer to the addition of auxiliary gas inlets and outlets. This can be achieved by connecting to bottom pipes through side openings, constructing a gas circulation loop.

[0073] Specifically, in the main reaction channel, gas enters through the first inlet 2111 and sequentially passes through the first three conversion beds to complete the stepwise oxidation reaction of sulfur dioxide. The reaction products are discharged from the first outlet 2112. In the auxiliary channel, some gas enters through the second inlet 2113 and flows directly through the fourth conversion bed 214 for supplementary reaction. The reaction products are discharged from the second outlet 2114. During the shutdown phase, when hot air is replaced, the main channel and the auxiliary channel form a parallel airflow path, allowing hot air to simultaneously flush the gaps between the first three conversion beds and the area of ​​the fourth conversion bed 214, carrying away acidic substances remaining in the catalyst pores and dead corners of the equipment to the outlet. The independent layout of the fourth conversion bed 214 avoids the problem of uneven airflow distribution in the lower area in the traditional single-channel structure. The dual-outlet design allows condensed acid mist from different areas to be discharged through the first outlet 2112 and the second outlet 2114 respectively, preventing the accumulation of acidic substances inside the equipment.

[0074] Compared with existing technologies, the traditional converter 21 adopts a four-layer series conversion bed structure with a single gas flow direction. During shutdown and replacement, the hot air only flows in one direction, which cannot effectively remove residual acid mist from the bottom conversion bed and the connecting parts. This solution separates the fourth conversion bed 214 and constructs a dual airflow channel, so that the replacement airflow can cover the entire reaction area within the converter 21, especially solving the problem of residual acid mist caused by airflow stagnation in the bottom catalyst bed.

[0075] Through the above technical solutions, this application achieves an optimized layout of the internal structure of the converter 21, enabling hot air replacement during shutdown to thoroughly remove residual acidic substances from each conversion bed and connecting pipeline, thus avoiding equipment corrosion and personnel safety risks during maintenance. The dual-channel airflow design effectively improves the cleaning efficiency of dead corners inside the converter 21, solving the problem of acid mist condensation and accumulation caused by uneven airflow distribution in traditional single-channel structures.

[0076] As an optional embodiment of this case, the gas delivered from the regeneration furnace 301 absorbs moisture in the drying tower 11 sprayed with concentrated sulfuric acid, and then mixes with the absorbent acid delivered from the first absorption tower 12 for cooling and continued to circulate and dry. After the first absorption tower 12 and the second absorption tower 13 absorb sulfur trioxide from the gas, the gas is cooled to a predetermined temperature by the acid coolers of the first absorption tower 12 and the second absorption tower 13. Then, the gas is sprayed with concentrated sulfuric acid by the first absorption tower 12 and the second absorption tower 13 to remove water and dry it. Subsequently, the gas exchanges heat with the four-stage cold gas preheater 23 and the one-stage cold gas preheater 22.

[0077] As an optional embodiment of this case, the drying tower 11 includes a drying tower pump tank 111, a drying tower acid circulation pump 112, and a drying tower acid cooler; The first absorption tower 12 includes a first absorption tower acid pump tank, a first absorption tower acid pump, a first absorption tower acid cooler, a first absorption tower demister 121, and a first packing block 122; The second absorption tower 13 includes a second absorption tower acid circulation tank, a second absorption tower acid pump, a second absorption tower acid cooler, a second absorption tower demister 131, and a second packing 132; The drying tower 11 is sprayed with concentrated sulfuric acid at 40°C to 60°C and 94% to 99% concentration. After absorbing the moisture in the furnace gas of the regeneration furnace 301, the sulfuric acid is discharged from the bottom of the drying tower 11 to the drying tower pump tank 111. It is mixed with the absorbent acid from the pump tank of the first absorption tower 12 to adjust the acid concentration to 96%. Then, it is sent to the drying acid cooler by the drying tower acid circulation pump 112. After being cooled to 50°C, it is sent to the drying tower 11 for spraying. The SO2 entrained in the 96% drying acid is removed by the demister 121 of the first absorption tower. Both the first absorption tower 12 and the second absorption tower 13 are sprayed with 98% concentrated sulfuric acid. After absorbing SO3 from the gas, they are discharged from the bottom of the tower to the acid pump tank of the first absorption tower and the acid circulation tank of the second absorption tower. Then, the acid pumps of the first and second absorption towers send the gas to the acid cooler of the first and second absorption towers respectively for cooling. After being cooled to 83°C and 80°C respectively, the gas is sent to the first absorption tower 12 and the second absorption tower for spraying. The gas exchanges heat with the high-temperature flue gas from the converter 21 through a first-stage cold gas preheater 22 (tube inlet 397°C) and a fourth-stage cold gas preheater 23 (tube inlet 441°C).

[0078] The drying tower 11 includes a drying tower pump tank 111, a drying tower acid circulation pump 112, and a drying tower acid cooler. The drying tower pump tank 111 serves as an acid storage and concentration adjustment unit, receiving supplementary acid from the first absorption tower 12 via gravity flow or pumping. The drying tower acid circulation pump 112 uses a corrosion-resistant centrifugal pump or magnetic pump for acid delivery. The drying tower acid cooler uses a shell-and-tube heat exchanger or a plate heat exchanger for temperature control. The first absorption tower 12 system includes a first absorption tower acid pump tank, an acid pump, an acid cooler, a demister, and packing blocks. The demister can use a glass fiber laminate structure or a polytetrafluoroethylene woven mesh for gas-liquid separation, and the packing blocks use ceramic rectangular saddle rings or polypropylene stepped rings to enhance mass transfer efficiency. The second absorption tower 13 system has a similar configuration to the first absorption tower 12, and its acid cooler can be an immersion type or a spray type cooling device. During operation, concentrated sulfuric acid with a concentration of 94% to 99% and a temperature of 40°C to 60°C is sprayed into drying tower 11. This concentration range is monitored in real time via online density meter or laboratory titration analysis. The spraying method can be pressure nozzles or overflow weir distributors. The acid solution after absorbing moisture from the furnace gas flows from the bottom of the tower into the drying tower pump tank 111, where it mixes with the 98% concentrated sulfuric acid delivered by the first absorption tower pump tank. The acid concentration is precisely adjusted to 96% by a proportional regulating valve or frequency converter pump. The mixed acid is pressurized by the drying tower acid circulation pump 112 and then enters the drying acid cooler, where it is cooled to below 50°C using circulating water or chilled water. Finally, it returns to the top of drying tower 11 to form a closed loop. SO2 gas entrained in the drying acid is removed by the first absorption tower demister 121. The demister can be equipped with a pulse backflushing system or a mechanical vibration device to prevent clogging. The first absorption tower 12 and the second absorption tower 13 respectively spray 98% concentrated sulfuric acid to absorb SO3. After absorption, the acid solution is collected in their respective pump tanks and transported by acid pumps to the corresponding acid coolers to be cooled to 80-83℃ before being circulated for spraying. The high-temperature flue gas from the converter 21 flows sequentially through the tube-side inlet of the first-stage cold gas preheater 22 at 397℃ and the tube-side inlet of the fourth-stage cold gas preheater 23 at 441℃ for heat exchange. The preheaters can adopt a fixed tube sheet type or a U-tube structure, and the gas temperature gradient is controlled by segmented heat exchange.

[0079] This solution addresses equipment corrosion caused by acid concentration imbalance and sudden temperature changes during shutdown by constructing a multi-stage acid circulation and temperature control system. The technical principle is as follows: Drying tower 11 uses medium-temperature, medium-concentration sulfuric acid (40-60℃, 94-99%) for initial dehydration, preventing acid viscosity from increasing and causing equipment stagnation due to low temperatures; 96% drying acid continuously absorbs moisture in a closed-loop cycle, maintaining optimal moisture absorption efficiency through precise concentration adjustment; the first absorption tower demister 121 captures SO2 at the end of the drying acid circulation path, preventing acidic gases from condensing in the low-temperature region; the dual absorption towers use high-concentration sulfuric acid (98%) to absorb SO3 in stages, using an acid cooler to control the circulating acid temperature at 80-83℃, ensuring absorption efficiency while preventing high temperatures from exacerbating corrosion; the segmented preheater manages the flue gas heat distribution through precise temperature nodes (397℃ / 441℃), suppressing localized overcooling and the generation of acidic condensate. This structure enables the system to effectively remove residual moisture and acidic media before shutdown and cooling, thus blocking the acid sludge formation chain at its source: the closed-loop circulation of the drying tower 11 eliminates the accumulation of free water, the high-concentration acid circulation of the dual absorption towers reduces SO3 residue, and segmented preheating inhibits condensation in temperature-sensitive areas. Compared to traditional single-stage acid circulation systems, this solution achieves targeted removal of corrosive media in each unit through concentration gradient control (94-99%→96%→98%) and temperature step management (50℃←→80-83℃←→397-441℃), ensuring that the metal surface of the equipment remains in a non-corrosive critical state during shutdown, significantly reducing the risk of pitting and stress corrosion, while also avoiding secondary damage caused by the reaction of residual acid with ambient moisture during maintenance.

[0080] The above implementation achieves three technical effects: First, the medium-temperature, medium-concentration acid circulation in drying tower 11 effectively controls the dehydration rate, preventing stagnation caused by decreased fluidity when the acid temperature is below 40℃, or concentration fluctuations caused by imbalanced water evaporation when the temperature is above 60℃. Second, the high-concentration acid circulation in the dual absorption towers and precise temperature control stabilize the SO3 absorption rate at the upper limit of the process, while maintaining the acid cooler temperature at 80-83℃ balances mass transfer efficiency and material corrosion resistance. Third, the segmented preheater temperature node management forms an optimal thermodynamic gradient, avoiding sulfuric acid condensation below 397℃ and preventing the aggravation of equipment oxidation and corrosion at temperatures above 441℃. This synergistic mechanism ensures that the total amount of acidic medium in the system is reduced by more than 90% before shutdown, the equipment maintenance cycle is extended by 40%, and the risk of acid contact is completely eliminated. In alternative solutions, acid concentration adjustment can be monitored by replacing the density meter with an online conductivity meter, the demister backflushing system can use compressed air or nitrogen, and the packing blocks can be replaced with structured packing or random packing, all of which can achieve equivalent corrosion prevention goals.

[0081] As an optional embodiment of this case, the gas purification system 200 includes a quench cooler, a gas cooling tower, a demisting device and a neutralization tank connected in series, as well as a circulation pump installed between the quench cooler, the gas cooling tower, the demisting device and the neutralization tank. After the boiler flue gas is treated and purified by the quench cooler, the gas cooling tower, the demisting device and the neutralization tank, it enters the conversion and absorption system 100 for further treatment.

[0082] The gas purification system 200 comprises an integrated unit consisting of a quench cooler, a gas cooling tower, a demister, and a neutralization tank. These units are connected in series via pipelines and equipped with circulating pumps to create a closed-loop processing path. The quench cooler uses spray cooling or a rapid cooling coil structure to quickly cool the flue gas. The gas cooling tower employs a packed tower or plate tower for stepped heat exchange. The demister includes an electrostatic precipitator or a fiber filter layer to remove aerosols. The neutralization tank is equipped with mechanical stirring or aeration devices to complete the acid-base reaction. The circulating pump can be a centrifugal pump or a positive displacement pump to maintain forced liquid circulation within the system. During operation, the sulfur-containing flue gas generated by the regenerated boiler first enters the quench cooler and is rapidly cooled by the cooling medium, inhibiting the condensation of acidic gases. It then enters the gas cooling tower and comes into countercurrent contact with the circulating cooling liquid for further cooling. After the demister captures entrained acid mist particles, the residual acidic substances react with alkaline additives in the neutralization tank to form stable salts. Finally, the purified gas enters the conversion and absorption system 100. This solution addresses equipment corrosion caused by residual acidic components in flue gas during shutdowns through a four-stage purification unit temperature gradient control and reaction synergy mechanism: a quench cooler rapidly crosses the acid dew point temperature range to prevent condensation acid formation; a gas cooling tower provides gradual cooling to avoid stress corrosion caused by sudden temperature changes; a demisting device intercepts submicron-sized acid mist particles to prevent their accumulation in system dead zones; and a neutralization tank thoroughly converts residual acidic media. This structure reduces the acidic load of flue gas entering the conversion and absorption system 100, minimizing residual corrosion sources during shutdowns. Simultaneously, the forced flow maintained by the circulating pump avoids localized concentration accumulation caused by traditional static treatment. Compared to a single scrubbing device, the multi-stage unit combination significantly improves the removal efficiency of acidic components, ensuring the cleanliness of the internal environment of the conversion and absorption system 100 during subsequent shutdown operations, eliminating the risk of secondary corrosion caused by the reaction of moisture and residual acid during maintenance, extending equipment service life, and reducing maintenance costs. In alternative implementations, unit connections can use flange seals or welded structures, and the alkaline additive in the neutralization tank can be lime slurry or sodium carbonate solution, both achieving equivalent purification goals.

[0083] As an optional embodiment of this case, the boiler system includes a regeneration furnace 301, which is provided with a waste acid channel 3011 and a gas channel 3012. The gas channel 3012 is used to introduce oxygen and / or fuel gas required for combustion into the regeneration furnace 301. The regeneration furnace 301 is heated by burning the fuel gas through burners 302, which include multiple burners. The fuel gas includes biogas and natural gas. Ammonium sulfate solution, waste acid, and liquid sulfur can be introduced into the waste acid channel 3011. The gas channel 3012 is provided with a regeneration furnace air fan 20121 and a regeneration furnace air preheater 20122, which facilitates the adjustment of the gas flow rate and temperature of the gas supplied to the regeneration furnace 301, and is conducive to the high-efficiency operation of the regeneration furnace 301.

[0084] As an optional embodiment of this case, in the step of stopping the acid circulation of the conversion and absorption system 100 when the inlet process gas temperature of the first absorption tower 12 drops to 120-150°C during the cooling stage of the conversion and absorption system 100, the temperature at which the acid circulation is stopped is 130-135°C.

[0085] The corrosion prevention method for shutdown of the sulfide treatment unit in this case is applicable to the shutdown and cooling treatment of the regenerated boiler system 300, gas purification system 200, and conversion absorption system 100, in order to reduce the formation of condensed acid and acid sludge and extend the service life of the equipment. This case reduces the residue of acidic substances by optimizing the cooling process, controlling temperature nodes, and air replacement, extending the equipment life to 5-10 years and reducing maintenance costs. In actual production, during the cooling of the regenerated boiler system 300, one burner 302 is started (originally, multiple burners 302 work simultaneously when not cooling) to increase the temperature of the cooling air. During the cooling process, the acidic gas attached to the pipe wall and equipment evaporates and is carried into the absorption system 10. During the cooling of the conversion absorption system 100, the temperature of each bed layer in the conversion system is high (see the conversion bed temperature table below). The high-temperature flue gas enters the absorption system 10. The pipelines and equipment of the absorption system 10 are made of high-silicon steel, and the demister screens of the first absorption tower 12 and the second absorption tower 13 are made of fiber material. The relevant temperature resistance properties are shown in the demister screen parameter table.

[0086]

[0087] Conversion bed temperature gauge

[0088] Defogging screen parameter table The first absorption tower demister 121 and the second absorption tower demister 131 can operate at 260℃ for a short time. The maximum allowable temperature during normal operation is 150℃. This operation method is to stop the acid operation of the absorption system 10 after the inlet temperature of the first absorption tower 12 is lower than 130℃ during the cooling period of the conversion system. The conversion absorption system 100 is replaced with air at 130℃. Acidic substances such as acidic gas, sulfuric acid mist, and acid sludge inside the flue gas pipeline, drying tower 11, first absorption tower 12, second absorption tower 13, nicotine tower 14, first-stage cold gas preheater 22, fourth-stage cold gas preheater 23, and converter 21 are evaporated and carried out to the tail gas treatment unit 30 (such as the tail gas desulfurization tower) for tail gas desulfurization, avoiding secondary corrosion of the flue gas pipeline and equipment during the cooling and shutdown maintenance of the unit.

[0089] The method used in this case specifically includes the following steps: S1: Report to the dispatching and general management departments, wastewater treatment unit, air separation unit, and sulfide treatment unit to prepare for shutdown; S2: Organize the evacuation of unrelated personnel and ensure the safety of laborers; S3: Stop feeding organic matter and purge the organic matter pump outlet with nitrogen purging hose to regeneration furnace 301; S4: The waste acid flow rate slowly decreases from 26t / h to 0t / h. The pump outlet of the waste acid is connected to the nitrogen purging hose and purged to the regeneration furnace 301. S5: Notify the ammonium sulfate unit in waste acid channel 3011 to reduce the ammonium sulfate liquid from 12t / h to 0t / h, and connect the pump outlet to the nitrogen purging hose to purge to the regeneration furnace 301. S6: After all feed is stopped and purged, shut down some burners 302 and run one or two small burners 302 to cool down the regeneration furnace 301 and the regeneration boiler system 300. S7: After the outlet temperature of regeneration furnace 301 drops by 300℃, all burners 302 are stopped, and the regeneration furnace air fan 20121 is started to force ventilation and cooling. S8: After the outlet temperature of regeneration furnace 301 drops by 150°C, stop the air fan 20121 of the regeneration furnace for natural ventilation to cool down to room temperature. S9: Open the air dilution valve of the blind cover 201 and the drying tower 11 to supply air to the conversion system 20, wherein the blind cover 201 is a sealing component used to isolate the conversion absorption system 100 from the external environment; S10: Start the sulfur dioxide fan 113 to cool down the conversion and absorption system 100, reducing the temperature by 50°C per hour to 150°C; S11: When the inlet temperature of drying tower 11 is the air temperature, for example, the air temperature is limited to 50°C, the acid circulation of drying tower 11 is stopped when the cooling begins. S12: The acid circulation of the second absorption tower 13 is stopped after the inlet process gas temperature drops below 150℃. S13: The acid circulation of the first absorption tower 12 is stopped after the inlet process gas temperature drops below 130℃. S14: After the temperature of converter 21 drops below 50℃, the conversion and absorption system 100 is replaced.

[0090] Compared to the previous version, this solution offers the following technical advantages: First, it avoids secondary corrosion of the regenerated boiler system 300, boiler outlet pipes, and expansion joints, increasing equipment lifespan. The industry standard boiler lifespan is approximately 2 years, but this optimization extends it to 5 years, saving on equipment procurement costs. Second, evaporation carries away acidic substances such as acidic gases, sulfuric acid mist, and acid sludge from the flue gas pipes, drying tower 11, first absorption tower 12, second absorption tower 13, nicotine tower 14, first-stage cold gas preheater 22, fourth-stage cold gas preheater 23, and converter 21 to the tail gas treatment unit 30. This avoids secondary corrosion of the flue gas pipes and equipment during cooling and maintenance shutdowns, further increasing equipment lifespan and saving on procurement costs. Third, it implements phased shutdown of the acid cycle (drying tower 11, second absorption tower 13, and first absorption tower 12 are shut down at air temperature, 150℃, and 130℃, respectively). A 130℃ air replacement system is used to evaporate residual acidic substances to the tail gas desulfurization tower. Fourth, after the regeneration purification system and conversion absorption system are replaced by 100%, the gas cleanliness is increased by 10-20%, and the residual acid replacement rate in equipment and facilities such as absorption tower pump tanks, packing, and demisting nets is increased by 10-20%, reducing the safety risks for personnel entering for inspection and operation.

[0091] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preventing corrosion during shutdown of a sulfide treatment device, characterized in that, The method includes the following steps: During the cooling phase of the conversion and absorption system of the sulfide treatment device, when the inlet temperature of the first absorption tower of the conversion and absorption system drops to a preset first safe temperature, at least part of the acid circulation of the conversion and absorption system is stopped. Hot air at a preset second safe temperature is introduced into the conversion and absorption system for replacement. The hot air evaporates the acidic substances remaining in the conversion and absorption system and transports them to the exhaust gas treatment unit. The replacement continues until the temperature of the converter in the conversion and absorption system is lower than the preset third safety temperature; Wherein, the preset second safety temperature is less than or equal to the preset first safety temperature, and the preset second safety temperature is greater than the preset third safety temperature; the preset first safety temperature is the highest temperature allowed when the conversion and absorption system is operating normally. The preset first safety temperature is between 120°C and 150°C, the preset second safety temperature is between 120°C and 140°C, and the preset third safety temperature is between 30°C and 70°C. During the cooling phase of the conversion and absorption system, when the inlet temperature of the first absorption tower of the conversion and absorption system drops to a preset first safe temperature, the step of stopping at least a portion of the acid circulation of the conversion and absorption system includes the following phased shutdown of the acid circulation: When the gas temperature at the inlet of the drying tower is ≤50℃, stop the acid circulation in the drying tower; When the inlet gas temperature of the second absorption tower is ≤150℃, the acid circulation of the second absorption tower is stopped. When the inlet gas temperature of the first absorption tower is ≤130℃, the acid circulation of the first absorption tower is stopped; During the cooling phase of the conversion and absorption system, before the step of stopping at least a portion of the acid circulation in the conversion and absorption system when the inlet temperature of the first absorption tower of the conversion and absorption system drops to a preset first safe temperature, a cooling step for the regeneration boiler system is also included. This cooling step for the regeneration boiler system includes: After the regeneration furnace feed is stopped, the burners are used for staged cooling. All burners are stopped once the regeneration furnace outlet temperature drops to 300°C. Afterwards, forced ventilation was activated to cool the temperature to 150°C, then natural ventilation was switched to cool the temperature.

2. The method for preventing corrosion during shutdown of a sulfide treatment device according to claim 1, characterized in that, Before the step of shutting down all burners after the regeneration furnace outlet temperature drops to 300°C following the shutdown of the feed system, a feed system purging step is also included. This feed system purging step includes: After stopping the feeding of organic matter / waste acid / ammonium sulfate solution, the conveying pipelines of organic matter, waste acid and ammonium sulfate solution are purged to the regeneration furnace by inert gas.

3. The method for preventing corrosion during shutdown of a sulfide treatment device according to claim 1, characterized in that, During the cooling phase of the conversion and absorption system, when the inlet temperature of the first absorption tower of the conversion and absorption system drops to a preset first safe temperature, the step of stopping at least a portion of the acid circulation of the conversion and absorption system includes the following cooling step: Purified air is introduced into the drying tower of the conversion and absorption system; Start the sulfur dioxide fan to cool the conversion and absorption system until it is reduced to the preset first safe temperature.

4. The method for preventing corrosion during shutdown of a sulfide treatment device according to claim 1, characterized in that, The demisters of the drying tower, the first absorption tower, and the second absorption tower are made of fiber material, and the design temperature resistance of the demisters is less than or equal to 150℃.

5. The method for preventing corrosion during shutdown of a sulfide treatment device according to claim 1, characterized in that, The sulfide treatment device includes a conversion and absorption system, which comprises: The conversion system includes a converter and a first-stage cold gas preheater and / or a fourth-stage cold gas preheater; The absorption system includes a drying tower, a first absorption tower, a second absorption tower, and / or a nicotinic acid tower; Exhaust gas treatment unit; The drying tower, the first-stage cold gas preheater, the converter, the fourth-stage cold gas preheater, the first absorption tower and / or the nicotinic acid tower, the second absorption tower, and the tail gas treatment unit are connected by pipelines. The drying tower is used for gas drying, the first-stage cold gas preheater and the fourth-stage cold gas preheater are used for gas heat exchange, and the converter is used to convert sulfur dioxide into sulfur trioxide. The first absorption tower, the nicotinic acid tower, and the second absorption tower are used for the absorption of sulfur trioxide, and the tail gas treatment unit is used for tail gas treatment.

6. The method for preventing corrosion during shutdown of a sulfide treatment device according to claim 5, characterized in that, The conversion and absorption system is connected to the regeneration boiler system through a gas purification system; The pipeline includes a first pipe and a second pipe. The conversion and absorption system is connected in sequence through the first pipe to a drying tower, a first-stage cold gas preheater, a converter, a fourth-stage cold gas preheater, and an inlet connected to the first absorption tower and / or the nicotinic acid tower. The outlet of the first absorption tower and / or the nicotinic acid tower is connected in sequence through the second pipe to the fourth-stage cold gas preheater, a converter, a first-stage cold gas preheater, a second absorption tower, and a tail gas treatment unit. The fourth-stage cold gas preheater, the converter, and the first-stage cold gas preheater include at least two sets of gas treatment channels.

7. A corrosion prevention system for shutdown of a sulfide treatment unit, characterized in that, The shutdown corrosion prevention method for the sulfide treatment device according to any one of claims 1-6 is used to achieve shutdown corrosion prevention; the system includes an electrically connected temperature detection unit, a control unit, and a gas replacement unit; During the cooling phase of the conversion and absorption system in the sulfide treatment unit, when the temperature detection unit detects that the inlet temperature of the first absorption tower of the conversion and absorption system has dropped to a preset first safe temperature... The control unit controls at least part of the acid circulation in the conversion and absorption system to stop, and the control unit controls the gas replacement unit to introduce hot air at a preset second safety temperature into the conversion and absorption system for replacement. The hot air evaporates the acidic substances remaining in the conversion and absorption system and transports them to the exhaust gas treatment unit. The replacement continues until the temperature of the converter in the conversion and absorption system is lower than a preset third safety temperature. Wherein, the preset second safety temperature is less than or equal to the preset first safety temperature, and the preset second safety temperature is greater than the preset third safety temperature; the preset first safety temperature is the highest temperature allowed when the conversion and absorption system is operating normally.

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