Wet-process acid-making condensation system with pre-cooling and catalytic oxidation functions

Abstract

The invention discloses a wet-process acid-making condensation system with pre-cooling and catalytic oxidation functions, which belongs to the technical field of wet-process acid-making equipment and comprises a process gas inlet, an acid condenser main body and a tail gas outlet, a special cooling device and a catalytic oxidation module are sequentially arranged between the process gas inlet and the acid condenser main body in the process gas flow direction, and the special cooling device is used for cooling process gas entering the catalytic oxidation module to 260 DEG C or below; the catalytic oxidation module is filled with a sulfur dioxide oxidation catalyst suitable for a low-temperature, high-humidity and acid mist-containing environment; and the acid condenser main body is used for condensing sulfur trioxide in the process gas treated by the catalytic oxidation module and generating sulfuric acid. The catalytic oxidation module is integrated at the front section of the acid condenser and is matched with a special cooling technology, so that the total conversion rate of sulfur dioxide is remarkably increased, the emission of tail gas sulfur dioxide reaches the standard, the sulfur recovery rate is increased, and the tail gas treatment difficulty, the investment cost and the operation cost of a heat exchange acid making system are effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of wet acid production equipment technology, specifically a wet acid production condensation system with pre-cooling and catalytic oxidation functions. Background Technology

[0002] The wet sulfuric acid (WSA) process is an important sulfuric acid production technology. Its core lies in the catalytic conversion of process gas containing sulfur dioxide into sulfur trioxide, which is then directly condensed with water vapor in a condenser to produce concentrated sulfuric acid. This process has a unique advantage due to its ability to handle gases with high water content.

[0003] In existing technologies, the sulfur dioxide conversion rate of process gas after treatment by the conversion system can typically reach approximately 99%. However, this means that about 1% of residual sulfur dioxide remains unconverted and will be emitted with the tail gas. This residual sulfur dioxide not only leads to incomplete sulfur resource recovery and economic losses, but also makes it difficult for tail gas emission concentrations to meet increasingly stringent environmental standards. To meet emission limits, it is usually necessary to add an expensive tail gas desulfurization device, such as an alkaline scrubbing tower, after the acid condenser, which significantly increases the complexity and operating cost of the entire acid production system.

[0004] From the perspective of equipment operation safety and lifespan, existing technology faces a key technical contradiction. To prevent severe low-temperature dew point corrosion in the transition section between the conversion tower and the acid condenser due to the process gas temperature falling below the dew point of the sulfuric acid, and to protect the fluoroplastic coating on the inner wall of the acid condenser from burning due to overheating, the temperature of the process gas entering the acid condenser is strictly limited to a narrow range of 280-295℃. While this temperature limit ensures short-term operational safety, it becomes a constraint on the process. The higher inlet gas temperature is not conducive to shifting the sulfur dioxide oxidation reaction equilibrium towards the formation of sulfur trioxide, limiting the potential for further improving the final conversion rate through operational optimization. On the other hand, it also fails to create favorable low-temperature reaction conditions for the deep conversion of residual sulfur dioxide.

[0005] Furthermore, the existing process suffers from low thermal energy utilization and high operating energy consumption. The finished acid collected from the bottom of the acid condenser reaches temperatures as high as 240-253℃, requiring a large amount of circulating cooling water for subsequent cooling before storage or external delivery. Moreover, the air used to cool the process gas is often directly vented after being heated, and the large amount of low- and medium-grade heat energy it carries is not effectively recovered and utilized, resulting in energy waste.

[0006] Therefore, we propose a wet acid production condensation system with pre-cooling and catalytic oxidation functions to alleviate or solve the above problems.

[0007] The information disclosed above in this background section is only for enhancing the understanding of the background section of this invention, and therefore may include prior art that is not known to those skilled in the art. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a wet acid production condensation system with pre-cooling and catalytic oxidation functions. This system solves several issues in existing technologies, including incomplete conversion of residual sulfur dioxide leading to excessive emissions, limitations imposed by inlet gas temperature restricting conversion efficiency, risks of equipment corrosion and heat loss, and low system thermal energy utilization. This invention integrates a catalytic oxidation module with special cooling technology at the front end of the acid condenser, significantly improving the total conversion rate of sulfur dioxide, achieving compliance with sulfur dioxide emission standards in the exhaust gas, while simultaneously increasing sulfur recovery rate. This effectively reduces the difficulty of exhaust gas treatment, investment costs, and operating costs of the heat exchange acid production system.

[0009] To achieve the above objectives, the present invention provides a wet acid production condensation system with pre-cooling and catalytic oxidation functions, comprising a process gas inlet, an acid condenser body, and a tail gas outlet;

[0010] A special cooling device and a catalytic oxidation module are sequentially arranged between the process gas inlet and the acid condenser body along the process gas flow direction. The special cooling device is used to reduce the temperature of the process gas entering the catalytic oxidation module to below 260°C.

[0011] The catalytic oxidation module is filled with a sulfur dioxide oxidation catalyst suitable for low temperature, high humidity, and acid mist environments;

[0012] The acid condenser body is used to condense sulfur trioxide in the process gas after it has been treated by the catalytic oxidation module and generate sulfuric acid.

[0013] Preferably, the special cooling device is an indirect heat exchanger, which includes a heat exchange module A and a heat exchange module B arranged in series, and the heat exchange elements inside are made of silicon carbide or silicon carbide-polymer composite material.

[0014] Preferably, the cooling medium of the heat exchange module A is hot air drawn out from the main body of the acid condenser after heat exchange, and the temperature of the cooling medium of the heat exchange module A is 190-230℃.

[0015] Preferably, the cooling medium of the heat exchange module B is the process tail gas drawn from the top of the acid condenser body, and the temperature of the cooling medium of the heat exchange module B is 90-120℃.

[0016] Preferably, the shell of the catalytic oxidation module is a carbon steel or carbon-lead / titanium metal composite plate structure lined with fluoroplastics and acid-resistant bricks.

[0017] Preferably, the catalytic oxidation module is internally provided with an airflow distribution plate with an opening ratio of more than 35% and a catalyst support grid.

[0018] Preferably, the sulfur dioxide oxidation catalyst is selected from vanadium-based catalysts, noble metal catalysts, or organic catalytic oxidation groups embedded in high-temperature and corrosion-resistant porous fluoroplastics.

[0019] Preferably, the heat exchange tube bundle of the acid condenser body is composed of quartz glass tubes or high borosilicate glass tubes, and the heat exchange tube bundle is arranged vertically or horizontally.

[0020] Preferably, the acid condenser system is connected to an exhaust gas treatment device upstream of the exhaust gas outlet, and the exhaust gas treatment device is one or more of a water washing demister, a wet electrostatic precipitator, or a fiber demister.

[0021] The wet acid production process of the acid condenser system includes the following steps:

[0022] S1. The process gas from the conversion system is introduced into a special cooling device to reduce its temperature to below 260°C;

[0023] S2. The cooled process gas is introduced into the catalytic oxidation module, where the residual sulfur dioxide in the process gas is oxidized into sulfur trioxide under the action of the catalyst.

[0024] S3. The process gas that has undergone catalytic oxidation treatment is introduced into the main body of the acid condenser, so that sulfur trioxide is condensed to generate sulfuric acid;

[0025] S4. The exhaust gas discharged from the main body of the acid condenser is demisted before being discharged.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention integrates a catalytic oxidation module before the acid condenser to perform deep catalytic oxidation on the residual sulfur dioxide in the cooled process gas, thereby increasing the total sulfur dioxide conversion rate of the acid condenser system from about 99% in the traditional process to over 99.9%, which improves the direct recovery rate of sulfur resources and the theoretical production capacity of sulfuric acid.

[0028] The deep conversion process of this invention results in extremely low sulfur dioxide concentrations in the final exhaust gas, requiring only conventional demisting treatment to meet environmental emission standards. It eliminates the need for expensive and additional exhaust gas desulfurization equipment required in traditional processes, simplifies the acid condenser system, and reduces the difficulty and cost of environmental governance.

[0029] The special cooling device in this invention employs corrosion-resistant materials and real-time wall temperature monitoring technology, enabling the process gas to be safely and controllably cooled to below 260°C. This creates favorable conditions for subsequent low-temperature catalytic oxidation and fundamentally eliminates the risk of equipment corrosion caused by wall temperatures below the acid dew point. Simultaneously, the lower inlet gas temperature reduces the possibility of the internal anti-corrosion layer of the acid condenser burning due to overheating, laying a solid foundation for the long-term, stable operation of the entire system.

[0030] This invention modularly integrates pre-cooling and catalytic oxidation functions at the front end of the acid condenser, resulting in a compact structure that facilitates technical upgrades to existing equipment. Simultaneously, the cooling module utilizes hot air and process exhaust gas from within the acid condenser system as the cooling medium, achieving cascaded recovery and utilization of waste heat from the process gas cooling process and the acid condensation reaction. This significantly improves the overall thermal energy utilization rate of the system and effectively reduces production energy consumption.

[0031] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0032] Figure 1 This is the wet acid production condensation system with pre-cooling and catalytic oxidation functions, which is a horizontally placed condenser tube type in Embodiment 2 of the present invention.

[0033] Figure 2 This is a wet acid production condensation system with pre-cooling and catalytic oxidation functions, with vertically placed condenser tubes, as described in Embodiment 1 of the present invention.

[0034] Figure 3 This is a structural diagram of the catalytic oxidation module in this invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be noted that the drawings are schematic and not illustrated to scale. For clarity and convenience, the relative sizes and proportions of the parts shown in the drawings have been exaggerated or reduced in size. Any size is only illustrative and not limiting.

[0036] Example 1

[0037] like Figure 1 As shown, this embodiment provides a wet acid production condensation system with pre-cooling and catalytic oxidation functions, wherein the condensation tube bundle is placed vertically.

[0038] The system, along the flow direction of the process gas, includes, in sequence: a process gas inlet pipe, a special cooling device, a catalytic oxidation module, an acid condenser body, and a tail gas outlet pipe.

[0039] The special cooling device is a shell-and-tube indirect heat exchanger, comprising heat exchange module A and heat exchange module B connected in series via pipes. The shell-side inlet of heat exchange module A is connected to the process gas inlet pipe, and its tube-side inlet is connected to a hot air pipe from the middle of the shell side of the acid condenser main body, used to introduce hot air at a temperature of 190-230℃ as the cooling medium. The shell-side outlet of heat exchange module B is connected to the inlet of the catalytic oxidation module via a pipe, and its tube-side inlet is connected to a process tail gas pipe from the top of the acid condenser main body, used to introduce process tail gas at a temperature of 90-120℃ as the cooling medium. The heat exchange tubes of the special cooling device are made of silicon carbide. The process gas from the conversion system first enters the shell side of heat exchange module A, with an initial temperature of approximately 280-295℃, and exchanges heat with the hot air from the acid condenser in the tube side, reducing the temperature to 260-280℃. Subsequently, the process gas enters the shell side of heat exchange module B, where it exchanges heat with the low-temperature process tail gas from the top of the acid condenser in the tube side. The temperature is then safely and controllably reduced to 230-250℃. Throughout the cooling process, the wall temperature of the heat exchange tubes is monitored to ensure that it remains 5-10℃ above the sulfuric acid dew point temperature, thereby completely avoiding low-temperature dew point corrosion.

[0040] The cooled process gas enters the catalytic oxidation module. For example... Figure 3 As shown, the module's shell is made of carbon steel plate, lined with a fluoroplastic layer and constructed with acid-resistant bricks. Inside the module, a catalyst support grid is arranged from bottom to top, above which a catalyst bed is filled. The catalyst consists of organic catalytic oxidation groups embedded in high-temperature and corrosion-resistant porous fluoroplastic. Below the catalyst bed, a uniform ceramic perforated plate with an opening ratio greater than 35% is installed to ensure that the process gas passes uniformly through the catalyst bed, with a gas flow distribution deviation ≤5%, and the total pressure drop of the module controlled within 1 kPa. Within this module, residual sulfur dioxide reacts with oxygen under the action of the catalyst, being efficiently oxidized to sulfur trioxide.

[0041] The process gas, after catalytic oxidation, then enters the main body of the acid condenser. This main body is a vertical shell-and-tube structure, containing multiple vertically placed quartz glass tube bundles. The process gas flows downwards through the tubes, while the cooling air flows upwards through the shell. Inside the quartz glass tubes, sulfur trioxide in the process gas reacts with water vapor to generate sulfuric acid vapor, which condenses on the cooler inner surface of the tube wall to form a liquid sulfuric acid film. The acid film flows downwards along the tube wall and continuously converges and concentrates, eventually being collected in the acid tank at the bottom to obtain concentrated sulfuric acid product. The cooling air is heated, and a portion of it is drawn off as the cooling medium for heat exchange module A, achieving heat recovery.

[0042] The process exhaust gas discharged from the top of the acid condenser mainly consists of nitrogen, oxygen, water vapor, and trace amounts of acid mist; the sulfur dioxide concentration has been reduced to 30 mg / m³. 3 The exhaust gas then enters a conventional water-washing demister through the exhaust outlet pipe. After removing any entrained trace amounts of acid mist, emissions will meet standards.

[0043] Example 2

[0044] like Figure 2 As shown, the main difference between this embodiment and Embodiment 1 lies in the internal structure of the acid condenser body.

[0045] In this embodiment, the acid condenser body is a horizontal shell-and-tube structure, with multiple horizontally placed high borosilicate glass tube bundles inside. Process gas flows horizontally through the tubes; cooling air flows through the shell, creating a cross-flow with the tube-side airflow. The sulfuric acid generated from the condensation of sulfuric acid collects at the outlet under gravity and airflow, flowing into the acid tank. The remaining components, including the special cooling device and the catalytic oxidation module, operate in the same manner as in Embodiment 1. This configuration can adapt to different equipment layout space requirements.

[0046] Example 3

[0047] This embodiment provides a wet acid production process applied to the system described in Embodiment 1 or Embodiment 2, including the following steps:

[0048] (1) Cooling: The process gas with a temperature of 280-295℃ from the wet acid conversion system, containing SO2, SO3, H2O, O2, N2, etc., is introduced into a special cooling device, and then undergoes two-stage indirect heat exchange with hot air at 190-230℃ and process tail gas at 90-120℃, so that its temperature is precisely controlled within the range of 230-250℃.

[0049] (2) Catalytic oxidation: The cooled process gas is introduced into the catalytic oxidation module and passed evenly through the catalyst bed composed of organic catalytic oxidation groups embedded in high-temperature and corrosion-resistant porous fluoroplastics, so that the residual sulfur dioxide is deeply oxidized into sulfur trioxide.

[0050] (3) Condensation into acid: The process gas that has undergone catalytic oxidation is introduced into the main body of the acid condenser, so that the sulfur trioxide in it reacts with water vapor in the glass tube bundle and condenses to generate concentrated sulfuric acid, which is collected in the acid tank.

[0051] (4) Tail gas treatment: The tail gas discharged from the main body of the acid condenser is fed into the water washing and demisting tower for washing and demisting, and then discharged.

[0052] For situations requiring stricter emission standards, a wet electrostatic precipitator (WESP) or a fiber precipitator can be used in step (4) instead of a water-washing demister.

[0053] The working principle of this invention is as follows: Process gas from the front-end conversion system first enters this system. This invention lowers the temperature of the process gas to a lower, more suitable range while avoiding low-temperature acid dew point corrosion of the equipment, thus creating favorable conditions for the deep catalytic oxidation of residual SO2; subsequently, all generated SO3 is efficiently condensed and recovered as sulfuric acid; ultimately, the tail gas achieves near-zero sulfur dioxide emissions.

[0054] In this special cooling device, heat exchange tubes are made of materials such as silicon carbide, which are resistant to concentrated sulfuric acid corrosion and have excellent thermal conductivity. By monitoring the heat exchange tube wall temperature in real time and controlling it to always be higher than the dew point temperature of sulfuric acid in the process gas, the possibility of sulfuric acid condensing on the heat exchange wall surface is physically eliminated.

[0055] The cooling process is divided into two steps, and the cooling medium comes from inside the system, realizing closed-loop energy utilization.

[0056] Heat exchange module A, serving as the first-stage cooling system, utilizes 190-230°C hot air drawn from the middle of the acid condenser shell side to exchange heat with high-temperature process gas at 280-295°C. It primarily recovers high-temperature heat energy, initially cooling the process gas to 260-280°C, while simultaneously preheating the cooling air entering the acid condenser, thus improving its quality as a heat transfer medium.

[0057] Heat exchange module B, serving as the second stage of cooling, utilizes the 90-120°C low-temperature process exhaust gas discharged from the top of the acid condenser to exchange heat with the process gas after the first stage of cooling. Using the waste heat of the exhaust gas, the process gas is ultimately and precisely cooled to the target temperature range of 230-250°C. This temperature is significantly lower than the traditional acid condenser inlet temperature, yet, due to strict wall temperature control, it is higher than the corrosion hazard zone.

[0058] After being safely cooled, the process gas enters the catalytic oxidation module, where it is reduced to 230-250°C. This temperature range significantly improves the thermodynamic equilibrium conversion rate of the SO2 oxidation reaction while maintaining the high activity of the catalyst. Water vapor in the process gas is not a poison for this type of catalyst; in fact, it can be beneficial to the reaction in some systems.

[0059] The process gas is uniformly distributed within the module via a specially designed gas distributor, and then flows through the catalyst bed. At the active sites of the catalyst, residual SO2 molecules adsorb, activate, and react with O2 molecules from the process gas to generate SO3. The chemical reaction is: 2SO2 + O2 → 2SO3.

[0060] The catalytic oxidation module housing employs a dual corrosion-resistant structure with an inner lining of fluoroplastics and acid-resistant bricks, ensuring the safety of the equipment itself. Uniform airflow distribution and a low bed pressure drop design guarantee high reaction efficiency and energy-efficient system operation. After passing through the catalytic oxidation module, the vast majority of sulfur oxides in the process gas are converted into SO3.

[0061] Process gas rich in SO3 and water vapor enters the glass tube bundle of the acid condenser. The cooling medium flows outside the tubes, carrying away heat and causing the temperature of the process gas inside the tubes to decrease along the way. When the temperature drops below the sulfuric acid dew point, SO3 gas reacts with H2O vapor in the gas phase to generate sulfuric acid vapor, which then condenses on the cooler inner wall of the glass tube, forming a liquid film.

[0062] The sulfuric acid film generated by condensation flows downwards along the wall of the vertical pipe or towards the outlet of the horizontal pipe under the influence of gravity and airflow. During the flow, new sulfuric acid vapor continuously condenses on the surface of the leading edge of the liquid film, causing the film to thicken and its concentration to increase. Finally, the high-concentration liquid sulfuric acid collects in the acid tank at the bottom and is discharged as a product.

[0063] The heated cooling air, with its high-temperature portion extracted, serves as the heat source for heat exchange module A in the special cooling device, achieving effective recovery and utilization of reaction heat and reducing the overall energy consumption of the system.

[0064] After passing through the acid condenser, the sulfur oxides in the process gas have been largely removed and converted into sulfuric acid products. The discharged gas mainly consists of nitrogen, oxygen, water vapor, and trace amounts of entrained acid mist, with its SO2 concentration reduced to extremely low levels. This exhaust gas only needs to be treated with conventional physical methods such as water washing, wet electrostatic precipitators, or fiber precipitators to remove suspended acid mist droplets, which is sufficient to meet stringent environmental emission standards, eliminating the need for complex chemical desulfurization treatment.

[0065] In summary, the system of the present invention performs well in many aspects, such as reducing the frequency of equipment corrosion maintenance, increasing sulfuric acid production, saving investment and operating costs for tail gas treatment, and reducing overall energy consumption. As a result, it reduces the total life cycle operating cost of the wet sulfuric acid production system, has a short investment payback period, and has significant overall economic benefits.

[0066] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0067] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wet acid production condensation system with pre-cooling and catalytic oxidation functions, characterized in that, This includes the process gas inlet, the acid condenser body, and the exhaust gas outlet; A special cooling device and a catalytic oxidation module are sequentially arranged between the process gas inlet and the acid condenser body along the process gas flow direction. The special cooling device is used to reduce the temperature of the process gas entering the catalytic oxidation module to below 260°C. The catalytic oxidation module is filled with a sulfur dioxide oxidation catalyst suitable for low temperature, high humidity, and acid mist environments; The acid condenser body is used to condense sulfur trioxide in the process gas after it has been treated by the catalytic oxidation module and generate sulfuric acid.

2. The wet acid production condensation system with pre-cooling and catalytic oxidation functions according to claim 1, characterized in that: The special cooling device is an indirect heat exchanger, which includes a heat exchange module A and a heat exchange module B arranged in series. The heat exchange elements inside are made of silicon carbide or silicon carbide-polymer composite material.

3. The wet acid production condensation system with pre-cooling and catalytic oxidation functions according to claim 2, characterized in that: The cooling medium of the heat exchange module A is hot air drawn out from the main body of the acid condenser after heat exchange, and the temperature of the cooling medium of the heat exchange module A is 190-230℃.

4. The wet acid production condensation system with pre-cooling and catalytic oxidation functions according to claim 2, characterized in that: The cooling medium of the heat exchange module B is the process exhaust gas drawn from the top of the acid condenser body, and the temperature of the cooling medium of the heat exchange module B is 90-120℃.

5. The wet acid production condensation system with pre-cooling and catalytic oxidation functions according to claim 1, characterized in that, The shell of the catalytic oxidation module is a carbon steel or carbon-lead / titanium metal composite plate structure lined with fluoroplastics and acid-resistant bricks.

6. The wet acid production condensation system with pre-cooling and catalytic oxidation functions according to claim 1, characterized in that, The catalytic oxidation module is internally equipped with an airflow distribution plate with an opening ratio of more than 35% and a catalyst support grid.

7. The wet acid production condensation system with pre-cooling and catalytic oxidation functions according to claim 1, characterized in that, The sulfur dioxide oxidation catalyst is selected from vanadium-based catalysts, noble metal catalysts, or organic catalytic oxidation groups embedded in high-temperature and corrosion-resistant porous fluoroplastics.

8. The wet acid production condensation system with pre-cooling and catalytic oxidation functions according to claim 1, characterized in that, The heat exchange tube bundle of the acid condenser body is composed of quartz glass tubes or high borosilicate glass tubes, and the heat exchange tube bundle is arranged vertically or horizontally.

9. The wet acid production condensation system with pre-cooling and catalytic oxidation functions according to claim 1, characterized in that, The acid condenser system is connected to an exhaust gas treatment device upstream of the exhaust gas outlet. The exhaust gas treatment device is one or more of a water washing demister, a wet electrostatic precipitator, or a fiber demister.

10. A wet acid production process using the acid condenser system as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. The process gas from the conversion system is introduced into a special cooling device to reduce its temperature to below 260°C; S2. The cooled process gas is introduced into the catalytic oxidation module, where the residual sulfur dioxide in the process gas is oxidized into sulfur trioxide under the action of the catalyst. S3. The process gas that has undergone catalytic oxidation treatment is introduced into the main body of the acid condenser, so that sulfur trioxide is condensed to generate sulfuric acid; S4. The exhaust gas discharged from the main body of the acid condenser is demisted before being discharged.

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