Device and process for producing liquid sulfur trioxide by utilizing film evaporator

Abstract

The invention relates to the technical field of separation and evaporation of sulfur trioxide, and discloses a device and a process for producing liquid sulfur trioxide by utilizing a film evaporator, the separation of gas-phase sulfur trioxide and low-concentration fuming acid is realized by utilizing the film evaporator, and the liquid sulfur trioxide is separated from the low-concentration fuming acid under the action of gravity and a rotary movable scraper of the film evaporator. Nicotinic acid forms an underspin film on the inner wall of the cylinder wall, and liquid is distributed into a uniform film, so that sulfur trioxide is quickly evaporated, and the evaporation capacity per unit area can be about 6-9 times that of a traditional evaporator; and meanwhile, under the action of high-speed rotating film scraping of the circumference, the heating time is short, the retention time of low-concentration nicotinic acid on the wall surface is shortened, and corrosion of the low-concentration nicotinic acid to the inner wall of the cylinder body at high temperature is avoided. According to the invention, the cyclone is arranged in the film evaporator, so that the material is prevented from being carried by gas, the removal efficiency of fog drops with the particle size of more than 1 micron reaches more than 99.9%, and the evaporation rate can be effectively improved by 1.0-2.6%.

Description

Technical Field

[0001] The present invention belongs to the technical field of sulfur trioxide separation and evaporation, and particularly relates to a device and process for producing liquid sulfur trioxide by using a thin-film evaporator. Background Art

[0002] In the prior art, the production method of liquid sulfur trioxide has many years of operation experience in China, and the prior art is described in the "Practical Handbook of Sulfuric Acid Production, Processing and Equipment". There are mainly two types of evaporators in the production of oleum, namely falling-film evaporators and horizontal evaporators, both of which are shell-and-tube heat exchangers, and the heat transfer efficiency is far lower than 500 w / m2·K. The falling-film evaporator requires the oleum to be evenly distributed to each heat exchange tube, and the outside of the tube is heated by the countercurrent of conversion gas. This equipment has extremely high requirements for the distribution and installation of oleum. Otherwise, there will be a small amount of acid entering some heat exchange tubes, excessive evaporation of oleum, and the local concentration of free sulfur trioxide will be lower than 15%, resulting in corrosion and leakage; the horizontal evaporator shell is provided with an evaporation space, and the cylinder diameter is large, occupying a large area. The wall thickness of the heat exchange tubes of both types of heat exchangers is generally ≥2.0 mm, the tube wall is relatively thin, which is the corrosion-weak link of the whole equipment. Due to the large number and density of the tube bundles, it is not easy to carry out anti-corrosion design.

[0003] In the prior art, the concentration of oleum is mostly evaporated from 25% - 30% to 15%, and even the outlet concentration is evaporated to 12%. At this time, the corrosion rate of the equipment is high and it needs to be replaced frequently. Some manufacturers evaporate the oleum concentration from 40% to 30%. The evaporation rate of sulfur trioxide with the same circulation volume is lower than 20%. To increase the output, the circulation volume needs to be increased accordingly; the evaporation efficiency of the prior art equipment is low. When the evaporation amount increases, the tube bundle area needs to be increased, resulting in an increase in the weight and floor area of the equipment.

[0004] Regarding the evaporation method of conventional sulfur trioxide gas, how to achieve rapid evaporation, improve the evaporation rate, how to improve the heat transfer efficiency during the evaporation process, and how to prevent the accelerated corrosion of low-concentration oleum are technical problems that need to be solved for the sulfur trioxide gas production device of oleum to reduce the floor area and improve the unit production capacity. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problems existing in the evaporation of sulfur trioxide in the prior art, and provide a device and process for producing liquid sulfur trioxide by using a thin-film evaporator.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: A device for producing liquid sulfur trioxide using a thin-film evaporator, comprising a fuming sulfuric acid storage tank and a thin-film evaporator. The fuming sulfuric acid storage tank is connected to the acid outlet of the thin-film evaporator. A heat medium pipeline and a fuming sulfuric acid pipeline are also connected to the thin-film evaporator. The top of the thin-film evaporator is connected to a gaseous sulfur trioxide pipeline, which is connected to a condenser. The condenser is connected to a liquid sulfur trioxide tank. Two sets of cyclones are installed in the thin-film evaporator, and the two sets of cyclones are respectively installed in the upper and lower parts inside the thin-film evaporator. A variable-speed transmission mechanism is provided between the cyclone and the scraper shaft of the thin-film evaporator.

[0007] Further, the cyclone includes a mounting disc and a plurality of swirling vanes. The mounting disc is rotatably arranged on the scraper shaft, and the plurality of swirling vanes are circumferentially distributed on the outer peripheral surface of the mounting disc. The swirling vanes are vanes with a higher middle and a lower edge. A plurality of flow guiding grooves are provided on the swirling vanes, and a foam breaker is also provided on the swirling vanes located in the lower part inside the thin-film evaporator.

[0008] Further, the flow guiding grooves are multi-mesh grooves arranged horizontally and vertically through the swirling vanes, and the foam breaker is a plurality of conical tips arranged on the swirling vanes.

[0009] Further, the swirling vanes are inclined with respect to the horizontal plane, and a retaining plate is installed on the downwardly inclined side of the swirling vanes.

[0010] Further, the variable-speed transmission mechanism includes a mounting frame fixed on the shell of the thin-film evaporator. An inclined gear one is rotatably arranged on the mounting frame. An inclined gear two meshed with the inclined gear one is fixedly installed on the scraper shaft. A slide rod with a hexagonal cross-section is coaxially arranged through the inclined gear one. A connecting column is provided at the end of the slide rod away from the inclined gear one. A friction wheel is fixedly arranged on the connecting column. A friction disc is installed on the upper surface of the mounting disc, and the outer peripheral surface of the friction wheel is in close contact with the surface of the friction disc. A hydraulic driving structure for controlling the position of the connecting column is provided on the mounting frame.

[0011] Further, the hydraulic driving structure includes a push rod fixedly installed on the mounting frame and a support rod rotatably connected to the connecting column. An oil cylinder is fixedly installed at the top of the support rod. A sealing plug in sealing cooperation with the oil cylinder is provided at the end of the push rod. The oil cylinder is connected to an oil pipe extending outside the thin-film evaporator.

[0012] Further, the outlet of the liquid sulfur trioxide tank is connected to a liquid sulfur trioxide metering pump, and a flow regulating valve is provided on the liquid phase inlet pipeline of the thin-film evaporator.

[0013] Further, the condenser is connected to a vacuum pump through a pipeline, and a pressure regulating valve is provided on the pipeline between the vacuum pump and the condenser.

[0014] A process for producing sulfur trioxide includes the following steps: Step 1: Introduce 109%-109.6% fuming sulfuric acid into the thin-film evaporator. The heating medium pressure of the thin-film evaporator is 0.8 MPa, and the saturated steam or heat-conducting oil has a temperature of 175°C. The temperature of the thin-film evaporator is controlled at 100-120°C. Step 2: Under the action of gravity and the rotating movable scraper of the thin-film evaporator, the fuming sulfuric acid in the thin-film evaporator forms a downward-rotating thin film on the inner wall of the cylinder. The liquid is distributed into a uniform thin film, and the evaporated sulfur trioxide gas and entrained liquid flow towards the cyclone. Step 3: When passing through the swirling blades of the lower cyclone, the entrained fuming sulfuric acid is broken into small droplets by the foam breaker, converges in the diversion trough, and flows towards one side of the cofferdam plate. The droplets not captured are secondarily captured after contacting the upper cyclone and finally contact the heating wall surface of the thin-film evaporator for evaporation. The ultimate evaporation rate according to the change of working conditions can be adjusted by the variable-speed drive mechanism of the cyclone. Step 4: The pressure of the pressure regulating valve is controlled at 5 kPa-25 kPa, and the evaporation rate of sulfur trioxide is controlled at 31-36%. Step 5: The 102.5%-103% liquid sulfur trioxide at the bottom is discharged from the condenser into the closed liquid sulfur trioxide tank by gravity. Step 6: The vacuum degree is stabilized within the system pressure range of the thin-film evaporator to complete continuous evaporation.

[0015] Furthermore, the thin-film evaporator is a scraping-type thin-film evaporator, and the scraper of the scraping-type thin-film evaporator is a movable scraper, and the inner wall is polished.

[0016] Furthermore, the inner surface of the shell of the thin-film evaporator is set as a heat transfer and evaporation surface, and the wall thickness of the shell of the thin-film evaporator is ≥6 mm.

[0017] The present invention has the following beneficial effects compared with the prior art: The present invention can achieve the rapid evaporation of sulfur trioxide, improve the evaporation efficiency, and increase the evaporation amount per unit circulation flow. By using the thin-film evaporator, the separation of gaseous sulfur trioxide and low-concentration fuming sulfuric acid is realized. Under the action of gravity and the rotating movable scraper of the thin-film evaporator, the fuming sulfuric acid forms a downward-rotating thin film on the inner wall of the cylinder, and the liquid is distributed into a uniform thin film, enabling the rapid evaporation of sulfur trioxide. The evaporation amount per unit area can reach about 6-9 times that of the traditional evaporator. At the same time, under the high-speed rotating film scraping action on the circumference, the heating time is short, reducing the residence time of low-concentration fuming sulfuric acid on the wall surface and avoiding the corrosion of the inner wall of the cylinder caused by low-concentration fuming sulfuric acid at high temperature. By changing the process conditions, the evaporation pressure is controlled at a vacuum degree of 5-25 kPa, which can improve the evaporation efficiency of the equipment, increase the heat transfer temperature difference, and reduce the heat transfer area by about 26.7% or more compared with the prior art under the same production capacity. The optimization of this process condition is more conducive to reducing the corrosion rate of fuming sulfuric acid.

[0018] By arranging a cyclone in the thin-film evaporator, the entrainment of materials by gas is avoided. The removal efficiency of droplets above 1 micron reaches over 99.9%, which can effectively increase the evaporation rate by 1.0 - 2.6%. Moreover, the cyclone is arranged in two levels, upper and lower, which can effectively increase the evaporation rate of sulfur trioxide. The present invention also reduces the external dimension of the equipment, decreases the consumption of steel, and can effectively avoid the equipment corrosion problem caused by excessive evaporation.

[0019] The scraper shaft usually cannot rotate quickly due to speed limitations, which may cause the cyclone to not fully exert its efficacy in some cases. The use of a variable-speed transmission mechanism allows the cyclone to operate at a more appropriate speed, reducing mechanical wear and vibration caused by speed mismatch, thereby extending the service life of the equipment. By precisely controlling the rotation speed of the cyclone, the energy consumption during the evaporation process can be optimized. Increase the speed when necessary to improve evaporation efficiency, and decrease the speed when not needed to reduce energy consumption. This dynamic adjustment helps to minimize energy consumption and maximize economic benefits. Description of the Drawings

[0020] Figure 1 It is a schematic structural flow diagram of the present invention.

[0021] Figure 2 It is a schematic diagram of the installation position of the cyclone of the present invention in the thin-film evaporator.

[0022] Figure 3 It is a schematic structural diagram of the cyclone of the present invention.

[0023] Figure 4 It is a schematic structural diagram of the cyclone vane of the present invention.

[0024] Figure 5 is Figure 3 an enlarged structural schematic diagram of part A in

[0025] Figure 6 It is a schematic structural diagram of the variable-speed transmission mechanism of the present invention.

[0026] Figure 7 It is a schematic structural diagram of the friction wheel of the present invention.

[0027] The meanings of the reference numerals are as follows: 1. Oleum storage tank; 2. Thin-film evaporator; 21. Scraping knife shaft; 3. Heat medium pipeline; 4. Oleum pipeline; 5. Gaseous sulfur trioxide pipeline; 6. Pressure regulating valve; 7. Condenser; 8. Liquid sulfur trioxide tank; 9. Cyclone; 10. Cyclone vane; 11. Mounting plate; 111. Friction plate; 12. Cofferdam plate; 13. Diversion trough; 14. Demister; 15. Liquid sulfur trioxide metering pump; 16. Flow regulating valve; 17. Vacuum pump; 18. Variable speed drive mechanism; 181. Mounting frame; 182. Helical gear 1; 183. Helical gear 2; 184. Slide bar; 185. Friction wheel; 186. Connecting column; 187. Push rod; 188. Sealing plug; 189. Oil cylinder. Detailed implementation manners

[0028] The present invention will be further described below in conjunction with the accompanying drawings and the detailed implementation manners.

[0029] As Figures 1-7 shown, a device for producing liquid sulfur trioxide by using a thin-film evaporator includes an oleum storage tank 1. The oleum storage tank 1 is connected to the acid outlet of the thin-film evaporator 2. A flow regulating valve 16 is provided on the oleum pipeline 4 of the thin-film evaporator 2. The thin-film evaporator 2 is also connected with a saturated steam or heat-conducting oil pipeline 3. The top of the thin-film evaporator 2 is connected with a gaseous sulfur trioxide pipeline 5. The gaseous sulfur trioxide pipeline 5 is connected with a condenser 7. The condenser 7 is connected with a liquid sulfur trioxide tank 8. The condenser 7 is connected to the vacuum pump 17 through a pipeline. A pressure regulating valve 6 is provided on the pipeline between the vacuum pump 17 and the condenser 7. The outlet of the liquid sulfur trioxide tank 8 is connected with a liquid sulfur trioxide metering pump 15.

[0030] The thin-film evaporator 2 is equipped with two sets of cyclones 9. The two sets of cyclones 9 are respectively installed in the upper and lower inner parts of the thin-film evaporator 2, and a variable-speed transmission mechanism 18 is arranged between the cyclone 9 and the scraper shaft 21 of the thin-film evaporator 2. The cyclone 9 includes a mounting disc 11 and a plurality of swirl vanes 10. The mounting disc 11 is rotatably arranged on the scraper shaft 21. The plurality of swirl vanes 10 are circumferentially distributed on the outer peripheral surface of the mounting disc 11. The swirl vanes 10 are blades with a higher middle part and a lower edge. A plurality of flow guiding grooves 13 are provided on the swirl vanes 10, and a foam breaker 14 is further provided on the swirl vanes 10 located in the lower inner part of the thin-film evaporator 2. The flow guiding grooves 13 are multi-mesh grooves arranged horizontally and vertically through the swirl vanes 10. The foam breaker 14 is a plurality of conical tips arranged on the swirl vanes 10. The swirl vanes 10 are inclined to the horizontal plane, and a cofferdam plate 12 is installed on the side where the swirl vanes 10 incline downward. The fuming sulfuric acid intercepted by the swirl vanes 10 is collected and guided through the flow guiding grooves 13. The fuming sulfuric acid is broken into small droplets by the foam breaker 14 and collected in the flow guiding grooves 13. The liquefied fuming sulfuric acid collected in the flow guiding grooves 13 flows to the side of the cofferdam plate 12 and finally contacts the heating wall surface of the thin-film evaporator 2 for evaporation.

[0031] Such as Figures 5-6The speed change transmission mechanism 18 includes a mounting frame 181 fixed on the shell of the thin film evaporator 2. The mounting frame 181 is arranged according to the specific situation and can be a rigid structure of any shape. A bevel gear 182 is rotatably arranged on the mounting frame 181 (one side of the mounting frame 181 is movably sleeved and clamped in the groove on one side of the bevel gear 182, and the bevel gear 182 can rotate but cannot move). A bevel gear 2 183 meshing with the bevel gear 182 is fixedly installed on the scraper shaft 21. When the scraper shaft 21 rotates, the bevel gear 2 183 is driven to rotate, and then the bevel gear 182 is driven to rotate. The bevel gear 182 is coaxially penetrated by a The slide bar 184 has a hexagonal cross section and can slide along the axis of the bevel gear 182. Since the slide bar 184 has a hexagonal cross section, the slide bar 184 can maintain effective transmission with the bevel gear 182 while sliding. A connecting column 186 is fixedly provided at one end of the slide bar 184 away from the bevel gear 182. A friction wheel 185 is fixedly provided on the connecting column 186. A friction disk 111 is installed on the upper surface of the mounting plate 11. The outer peripheral surface of the friction wheel 185 is in close contact with the surface of the friction disk 111. The friction wheel 185 is driven to rotate by the connecting column 186. The friction wheel 185 drives the friction disk 111 to rotate by the friction force. In the example, two groups of friction wheels 185 are provided to jointly drive a friction disk 111, and a hydraulic drive structure for controlling the position of a connecting column 186 is provided on the mounting frame 181. The transmission speeds of the bevel gear 182 and the bevel gear 2 183 remain unchanged, and the bevel gear 2 183 has more effective teeth, so the bevel gear 182 will rotate at a faster speed and drive the friction wheel 185 to rotate at the same speed. When the friction wheel 185 drives the friction disk 111 to rotate with friction force, the peripheral linear speed of the friction wheel 185 is consistent with the linear speed of the contact point of the friction disk 111. After the connecting column 186 is controlled to move by the hydraulic drive structure, the friction wheel 185 and the friction disk 111 are connected. The contact position of the wiping plate 111 changes, and the circumference of the circular range of the contact points of the friction plate 111 and the friction wheel 185 is different. Therefore, when the friction wheel 185 is driven at the same linear speed, the angular velocity corresponding to the rotation of the friction plate 111 will change, thereby realizing stepless adjustment of the rotation speed of the friction plate 111. The outer surface of the friction wheel 185 has axial texture, and the surface of the friction plate 111 is a rough surface. When the friction wheel 185 moves, the friction wheel 185 moves along the direction of the texture, and the friction resistance is small. However, when the friction wheel 185 rotates, the rotation direction is perpendicular to the texture direction, which can provide a large friction force to drive the friction plate 111.

[0032] The hydraulic drive structure includes a push rod 187 fixedly installed on the mounting frame 181 and a support rod rotatably connected to the connecting column 186 (one end of the support rod is movably sleeved and clamped with the connecting column 186). The support rod can control the axial displacement of the connecting column 186 while not affecting the rotation of the connecting column 186. An oil cylinder 189 is fixedly installed at the top of the support rod. The oil cylinder 189 is a high-temperature resistant oil cylinder. A sealing plug 188 that is hermetically matched with the oil cylinder 189 is arranged at the end of the push rod 187. The oil cylinder 189 is connected with an oil pipe extending to the outside of the thin-film evaporator 2. By means of an external hydraulic device, the oil pressure in the oil cylinder 189 is controlled, and then the elongation of the push rod 187 and the oil cylinder 189 is controlled to realize the control of the position of the oil cylinder 189, and further realize the adjustment of the contact position between the friction wheel 185 and the friction disc 111.

[0033] Fuming sulfuric acid enters from the liquid inlet of the thin-film evaporator 2. An acid pickling replacement pipeline is arranged at this liquid inlet. The jacket of the thin-film evaporator is filled with heat-conducting oil or steam for heating, and the inner wall is polished. The scraper is installed on a rotatable scraper shaft. In the thin-film evaporator 2, high-concentration sulfuric acid after heating realizes the separation of gaseous sulfur trioxide and low-concentration sulfuric acid. The gaseous sulfur trioxide enters the condenser 7 through a pipeline. A liquid discharge port is arranged at the bottom of the condenser 7, and this liquid discharge port is connected with a liquid sulfur trioxide tank 8 through a pipeline. The condensed liquid sulfur trioxide flows into the liquid sulfur trioxide tank 8 by gravity through the pipeline. The liquid sulfur trioxide tank 8 has one in use and one in reserve.

[0034] A liquid discharge port is arranged at the bottom of the thin-film evaporator, and this liquid discharge port is communicated with a liquid storage tank through a pipeline. The liquid storage tank is arranged below the thin-film evaporator. The vacuum pump is connected with the condenser through a pipeline, and a pressure regulating valve is arranged on the pipeline connecting the vacuum pump and the condenser. A liquid level gauge is arranged at the liquid discharge port at the bottom of the thin-film evaporator to ensure that there is always a certain liquid level height at the liquid discharge port.

[0035] Example 1: Introduce 109.6% fuming sulfuric acid into the thin-film evaporator. The heating medium pressure of the thin-film evaporator is 0.8 MPa, saturated steam at 175 °C or heat-conducting oil at 175 °C. Adjust the temperature of the thin-film evaporator 2 to 100 - 105 °C, the pressure of the pressure regulating valve 6 to 9 - 11 kPa, and the sulfur trioxide evaporation rate to be controlled at 35.78%. Open the drain valve on the drain pipe of the condenser 7. A liquid level control is set at the liquid discharge port to ensure that the liquid level is within the control range, and the liquid discharge port is liquid-sealed. 102.5% fuming sulfuric acid at the bottom is discharged into the closed liquid sulfur trioxide tank 8 by gravity. When the vacuum degree is stable within the system pressure range of the thin-film evaporator 2, the continuous evaporation process is completed.

[0036] Example 2: Introduce 109% fuming sulfuric acid into the thin-film evaporator 2. The heating medium pressure of the thin-film evaporator 2 is 0.8 MPa, saturated steam at 175 °C or heat-conducting oil at 175 °C. Adjust the temperature of the thin-film evaporator 2 to 115 - 120 °C, and the pressure of the pressure regulating valve 6 to 17 - 22 kPa. Control the sulfur trioxide evaporation rate at 31%. Open the drain valve on the drain pipe of the condenser 7. A liquid level control is set at the drain outlet to ensure that the liquid level is within the controlled range, and the drain outlet is liquid-sealed. The 103% fuming sulfuric acid at the bottom is discharged into the closed liquid sulfur trioxide tank 8 by gravity. When the vacuum degree is stable within the pressure range of the thin-film evaporator system, the continuous evaporation process is completed.

[0037] Comparative example: The process currently adopted by the sulfur trioxide unit in the sulfuric acid workshop is to use the 260 °C flue gas at the tube-side outlet of the heat exchanger for cold and heat in the sulfur-burning acid-making unit to heat 30% (equivalent to 106.75%) fuming sulfuric acid to the evaporation temperature, so that sulfur trioxide evaporates in gaseous form, enters the sulfur trioxide condenser, and is cooled with water to obtain liquid sulfur trioxide. After evaporation, the concentration of fuming sulfuric acid is 12%.

[0038] Taking 2.5 t / h as an example for the examples and comparative examples, for the evaporation rate of producing 1 ton of liquid SO3 per hour, respectively detect the heat exchange efficiency and operation stability of the thin-film evaporator 2 in the examples and the evaporator in the comparative examples.

Claims

1. A device for producing liquid sulfur trioxide using a thin film evaporator, comprising an oleum storage tank (1) and a thin film evaporator (2), characterized in that: The oleum storage tank (1) is connected to the acid outlet of the thin film evaporator (2), the thin film evaporator (2) is also connected to a heat medium pipeline (3) and a oleum pipeline (4), the top of the thin film evaporator (2) is connected to a gaseous sulfur trioxide pipeline (5), the gaseous sulfur trioxide pipeline (5) is connected to a condenser (7), the condenser (7) is connected to a liquid sulfur trioxide tank (8), the thin film evaporator (2) is equipped with two groups of cyclones (9), the two groups of cyclones (9) are respectively installed in the upper part and the lower part of the thin film evaporator (2), and a speed transmission mechanism (18) is provided between the cyclone (9) and the scraper shaft (21) of the thin film evaporator (2).

2. The device for producing liquid sulfur trioxide using a thin film evaporator according to claim 1, characterized in that: The cyclone (9) comprises a mounting plate (11) and a plurality of cyclone blades (10); the mounting plate (11) is rotatably mounted on a scraper shaft (21); the plurality of cyclone blades (10) are circumferentially distributed on the outer peripheral surface of the mounting plate (11); the cyclone blades (10) are blades with a high middle and low edges; a plurality of guide grooves (13) are provided on the cyclone blades (10); and a foam breaker (14) is also provided on the cyclone blades (10) located at the lower inner portion of the thin film evaporator (2).

3. The device for producing liquid sulfur trioxide using a thin film evaporator according to claim 2, characterized in that: The guide grooves (13) are multiple mesh grooves arranged on the swirl blades (10) in a horizontal and vertical manner, and the foam breakers (14) are multiple vertebral tips arranged on the swirl blades (10).

4. The device for producing liquid sulfur trioxide using a thin film evaporator according to claim 3, characterized in that: The swirl blade (10) is arranged to be inclined relative to a horizontal plane, and a cofferdam plate (12) is provided on a side of the swirl blade (10) that is inclined downward.

5. The device for producing liquid sulfur trioxide by using a thin film evaporator according to claim 1 or 4, characterized in that: The speed change transmission mechanism (18) comprises a mounting frame (181) fixed on the shell of the thin film evaporator (2), a bevel gear 1 (182) being rotatably arranged on the mounting frame (181), a bevel gear 2 (183) being fixedly mounted on the scraper shaft (21) and meshingly connected with the bevel gear 1 (182), a sliding rod (184) having a hexagonal cross section being coaxially penetrated by the bevel gear 1 (182), a connecting column (186) being arranged at one end of the sliding rod (184) away from the bevel gear 1 (182), a friction wheel (185) being fixedly arranged on the connecting column (186), a friction disk (111) being mounted on the upper surface of the mounting disk (11), an outer peripheral surface of the friction wheel (185) being in close contact with the surface of the friction disk (111), and a hydraulic drive structure for controlling the position of the connecting column (186) being arranged on the mounting frame (181).

6. The device for producing liquid sulfur trioxide using a thin film evaporator according to claim 5, characterized in that: The hydraulic drive structure comprises a push rod (187) fixedly mounted on a mounting frame (181) and a support rod rotatably connected to a connecting column (186); an oil cylinder (189) is fixedly mounted on the top of the support rod; a sealing plug (188) sealingly matched with the oil cylinder (189) is provided at the end of the push rod (187); and the oil cylinder (189) is connected to an oil pipe extending to the outside of the thin film evaporator (2).

7. A process for producing sulfur trioxide using the production device according to claim 1, comprising the following steps: Step 1, introducing 109%-109.6% fuming acid into a thin film evaporator (2), wherein the heating medium of the thin film evaporator (2) has a pressure of 0.8 MPa, a temperature of 175° C., and saturated steam or heat transfer oil, and the temperature of the thin film evaporator (2) is controlled at 100-120° C.; Step 2, the nicotinic acid in the thin film evaporator (2) forms a downwardly rotating thin film on the inner wall of the cylinder under the force of gravity and the rotating scraper of the thin film evaporator (2), and the liquid is distributed into a uniform thin film, and the evaporated sulfur trioxide gas and the entrained liquid flow toward the cyclone (9); Step 3, when passing through the swirl blades (10) of the lower cyclone (9), the entrained fuming acid is broken into small droplets by the foam breaker (14), collected in the guide groove (13), and flows to the side of the cofferdam plate (12). The droplets that are not captured are captured again after contacting the upper cyclone (9), and finally contact the heated wall surface of the thin film evaporator (2) for evaporation; Step 4: The pressure of the pressure regulating valve (6) is controlled at 5 kPa-25 kPa, and the evaporation rate of sulfur trioxide is controlled at 31-36%; Step 5, 102.5%-103% of the liquid sulfur trioxide at the bottom is discharged from the condenser (7) into a closed liquid sulfur trioxide tank (8) by gravity; Step 6: The vacuum degree is stabilized within the pressure range of the thin film evaporator system to complete continuous evaporation.

8. The process for producing liquid sulfur trioxide by using a thin film evaporator according to claim 7, characterized in that: The thin film evaporator (2) is a scraper-type thin film evaporator, and the scraper of the scraper-type thin film evaporator is a movable scraper, and the inner wall is polished.

9. The process for producing liquid sulfur trioxide by using a thin film evaporator according to claim 7, characterized in that: The inner surface of the shell of the thin film evaporator (2) is arranged as a heat transfer evaporation surface, and the shell wall thickness of the thin film evaporator (2) is ≥6 mm.

Images