Production method of liquid sulfur trioxide

Abstract

The invention relates to the technical field of preparation of sulfur trioxide, and discloses a production method of liquid sulfur trioxide, which comprises the following steps: conveying fuming sulfuric acid in a fuming sulfuric acid storage tank to a first-stage preheater, exchanging heat with acid from a film evaporator, heating by flowing through a second-stage preheater, entering the film evaporator, and evaporating and separating to obtain the liquid sulfur trioxide. Gas-phase sulfur trioxide obtained through evaporation and separation enters a condenser to be condensed, a fuming sulfuric acid solution obtained through evaporation and separation flows back to the fuming sulfuric acid storage tank after flowing to the first-stage preheater and exchanging heat with the fuming sulfuric acid in the fuming sulfuric acid storage tank to be cooled, and then the fuming sulfuric acid solution flows back to the fuming sulfuric acid storage tank and is circulated again. In addition, the evaporation efficiency of sulfur trioxide is improved, and the evaporation rate reaches up to 37.2%. According to the invention, the energy consumption of the nicotinic acid circulation amount is reduced, the treatment efficiency of fuming sulfuric acid is improved, the heat exchange coefficient is high, and the risk of short operation period caused by corrosion due to excessive evaporation caused by long working condition retention time and local overheating of an original circulation evaporation system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of sulfur trioxide preparation, and specifically relates to a method for producing liquid sulfur trioxide. Background Art

[0002] In the prior art, for the method of producing liquid sulfur trioxide, concentrated oleum is mainly directly fed into a preheater, preheated by the dilute oleum acid after evaporation, and then sent to a sulfur trioxide evaporator to heat the concentrated oleum, evaporating the free sulfur trioxide. The evaporated sulfur trioxide then enters a condenser for condensation. Among them, the sulfur trioxide evaporator is the core device of this process, and the evaporator forms are mainly vertical and horizontal evaporation.

[0003] In the patent with the publication number CN2863760Y and the name of the device for preparing liquid sulfur trioxide from oleum, the sulfur trioxide evaporation and separation are integrated into one device, so the device is very large and inconvenient for installation and maintenance. Adopting a vertical structure, the evaporation tubes adopt a serpentine tube structure, and a sulfur trioxide separator is separately set to solve the problem of the large volume of the integrated device being inconvenient for maintenance, but it does not fundamentally solve the problem of the large volume of the device, only solves the problem of the large volume of a single device by splitting the device functions.

[0004] In the patent with the publication number CN217472721U and the name of a novel sulfur trioxide evaporator, an inner tube stirrer with a driving device and steam inlet is adopted to make the sulfur trioxide solution fully and evenly contact inside the evaporator, so as to improve the evaporation effect. This method is prone to generate a large amount of acid mist during the evaporation process. When certain reaction conditions are met, reactions will also occur to generate sulfur dioxide and sulfuric acid. Most importantly, in this device, the heating medium and the heated medium need to be in full contact, and the oleum acid will be diluted after contacting water vapor, resulting in a violent exothermic reaction. Therefore, it is completely not applicable to the evaporation working condition of sulfur trioxide with oleum acid.

[0005] The horizontal evaporator occupies a large area (such as the anodic protection sulfur trioxide evaporator disclosed in patent CN201110304706.3), which belongs to large-volume pool evaporation. The evaporation process uses steam heating. The oleum acid is basically static between the heat exchange tubes. Sulfur trioxide gas is gradually generated at the heating tube wall. The gas overcomes the hydrostatic pressure of the liquid column and rises to the evaporation space at the top of the shell, and then enters the condenser through a wire mesh demister to obtain condensate. The evaporation capacity of this device is more stable than that of the flue gas evaporation device, but the horizontal evaporator has a large equipment volume and a large floor area.

[0006] The vertical structure, as disclosed in Publication No. CN116692779A, provides a fuming sulfuric acid evaporator that uses the flue gas of a conversion furnace as a heat source. The calorific value of the flue gas is low, and the heat transfer efficiency is even lower. The diameter of the equipment cylinder is large, and the heat exchange area is much larger than that of a horizontal evaporator. Even two or more devices need to be used in parallel, increasing the upfront investment cost of the equipment.

[0007] The above technology does not solve the problem of the large equipment volume by improving the heat transfer efficiency and evaporation effect. At the same time, there is also a problem that if the nicotine acid is unevenly distributed, it will cause local over-evaporation of the evaporator, resulting in a low acid concentration and local corrosion, affecting the service life of the equipment and causing nicotine acid leakage. Summary of the Invention

[0008] 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 method for producing liquid sulfur trioxide.

[0009] To achieve the above purpose, the present invention adopts the following technical solutions: A method for producing liquid sulfur trioxide, comprising the following steps: Step 1): First, connect the acid outlet of the fuming sulfuric acid storage tank to the inlet of the primary preheater. One outlet of the primary preheater is connected to the secondary preheater, and the secondary preheater is connected to the inlet pipeline of the thin-film evaporator. The gas-phase outlet at the top of the thin-film evaporator is connected to the condenser pipeline, the outlet of the condenser is connected to the liquid sulfur trioxide storage tank, the liquid-phase outlet of the thin-film evaporator is connected to the other inlet of the primary preheater, and the other outlet of the primary preheater is connected to the fuming sulfuric acid storage tank: Step 2): Pump the 105%-110% fuming sulfuric acid in the fuming sulfuric acid storage tank to the primary preheater through a circulation pump, and exchange heat with the 102%-107% acid from the thin-film evaporator. The 105%-110% fuming sulfuric acid is heated to 93°C - 128°C, and then flows through the secondary preheater and is heated to 98°C - 133°C before entering the thin-film evaporator; Step 3): Then, perform evaporation separation in the thin-film evaporator. The evaporation rate of sulfur trioxide is controlled at 13% - 37.2%. The evaporation temperature of the thin-film evaporator is 120 - 163°C, and the pressure is controlled at 20 - 68 kPa; Step 4): The gaseous sulfur trioxide obtained by evaporation separation enters the condenser from the gas-phase outlet at the top of the thin-film evaporator for condensation; Step 5): The 102%-107% concentration fuming sulfuric acid solution obtained by evaporation separation flows from the liquid-phase outlet at the bottom of the thin-film evaporator to the primary preheater by gravity, exchanges heat with the 105%-110% fuming sulfuric acid in the fuming sulfuric acid storage tank, cools down to 51 - 66°C, and then flows back to the fuming sulfuric acid storage tank by gravity for recycling.

[0010] Further, the heating medium of the thin-film evaporator is saturated steam with a pressure of 0.8 - 1.26 MPa and a temperature of 170 - 190 °C or heat-conducting oil at 170 - 190 °C.

[0011] Further, the cooling medium in the condenser is circulating cooling water at < 33 °C.

[0012] Further, a shutdown pickling and replacement system is provided on the inlet pipeline of the fuming sulfuric acid of the thin-film evaporator.

[0013] Further, a sulfur trioxide metering pump is provided on the liquid outlet pipeline of the liquid sulfur trioxide storage tank, and a circulating pump is installed on the pipeline connecting the acid outlet of the fuming sulfuric acid storage tank and the primary preheater.

[0014] The present invention has the following beneficial effects compared with the prior art: The present invention can stably and efficiently realize the evaporation of sulfur trioxide in fuming sulfuric acid, and improves the evaporation efficiency of sulfur trioxide, with an evaporation rate as high as 37.2%.

[0015] The method of the present invention reduces the energy consumption of the nicotinic acid circulation volume, improves the treatment efficiency of fuming sulfuric acid, has a high heat transfer coefficient, reduces the risk of short operation cycle caused by long residence time in the original circulation evaporation system, local overheating leading to excessive evaporation and corrosion.

[0016] The present invention solves the problem of low energy efficiency caused by large equipment floor area, large heat dissipation area and large heat loss in the existing circulation evaporation process.

[0017] The present invention can ensure the stability of the solvent evaporation ratio after passing through the thin-film evaporator when the feed load changes, and prevent the corrosion problem caused by excessive evaporation of fuming sulfuric acid inside the evaporator.

[0018] The present invention significantly reduces the energy consumption, increases the operation stability of the system, prolongs the operation cycle of the system device, and improves the energy efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of the present invention.

[0020] The meanings of the reference numerals are as follows: 1. fuming sulfuric acid storage tank; 2. primary preheater; 3. secondary preheater; 4. thin-film evaporator; 5. condenser; 6. liquid sulfur trioxide storage tank; 7. sulfur trioxide metering pump; 8. circulating pump; 9. heating medium inlet. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The present invention will be further described below with reference to the drawings and specific embodiments.

[0022] As Figure 1 shown, a production method of liquid sulfur trioxide includes the following steps: Step 1): Connect the acid outlet of the fuming sulfuric acid storage tank 1 to the inlet of the primary preheater 2. (A circulation pump 8 is installed on the pipeline between the acid outlet of the fuming sulfuric acid storage tank 1 and the primary preheater 2). One outlet of the primary preheater 2 is connected to the secondary preheater 3. The secondary preheater 3 is communicated with the inlet pipeline of the thin film evaporator 4. A parking pickling replacement system is arranged on the fuming sulfuric acid inlet pipeline of the thin film evaporator 4. A flow regulating valve is arranged on the pipeline of the heating medium inlet of the thin film evaporator 4.

[0023] The gas-phase outlet at the top of the thin film evaporator 4 is communicated with the condenser 5 through a pipeline. The outlet of the condenser 5 is connected to the liquid sulfur trioxide storage tank 6. A sulfur trioxide metering pump 7 is arranged on the liquid outlet pipeline of the liquid sulfur trioxide storage tank 6. The liquid-phase outlet of the thin film evaporator 4 is communicated with the other inlet of the primary preheater 2. The other outlet of the primary preheater 2 is connected to the fuming sulfuric acid storage tank 1.

[0024] Step 2): Pump the 105%-110% fuming sulfuric acid in the fuming sulfuric acid storage tank 1 to the primary preheater 2 through the circulation pump 8, and exchange heat with the 102%-107% acid from the thin film evaporator 4. The 105%-110% fuming sulfuric acid is heated to 93°C - 128°C, and then flows through the secondary preheater 3. The fuming sulfuric acid heated to 98°C - 133°C enters the thin film evaporator 4.

[0025] Step 3): Then, perform evaporation separation in the thin film evaporator 4. The heating medium 9 of the thin film evaporator 4 is saturated steam with a pressure of 0.8 - 1.26 MPa and a temperature of 170 - 190°C or heat transfer oil at 170 - 190°C. The evaporation temperature of the thin film evaporator 4 is 120 - 163°C, the pressure is controlled at 20 - 68 kPa, and the sulfur trioxide evaporation rate is controlled at 13% - 36%.

[0026] Step 4): The gaseous sulfur trioxide obtained by evaporation separation enters the condenser 5 from the gas-phase outlet at the top of the thin film evaporator 4 for condensation. The cooling medium in the condenser 5 is circulating cooling water at < 33°C.

[0027] Step 5): The 102%-107% concentration fuming sulfuric acid solution obtained by evaporation separation flows by gravity from the liquid-phase outlet at the bottom of the thin film evaporator 4 to the primary preheater 2, exchanges heat with the 105%-110% fuming sulfuric acid in the fuming sulfuric acid storage tank 1, cools down to 51 - 66°C, and then enters the fuming sulfuric acid storage tank 1 for recycling.

[0028] Example 1: Step 1): Feed the 109% oleum with a stable flow rate in the oleum storage tank 1 to the primary preheater 2 through the circulation pump 8, and exchange heat with the 103% acid from the thin-film evaporator 4 to heat the 109% oleum from 40°C to 118°C, then send it to the secondary preheater 3. The secondary preheater 3 uses the 189°C steam condensate from the shell side of the evaporator to heat the 109% acid at 118°C to around 127°C, and then enters the thin-film evaporator 4 for evaporation. A feedforward control flow regulating valve based on the solution inlet flow rate is set on the inlet pipeline, which is connected to the gas-phase flow outlet of the thin-film evaporator.

[0029] Step 2): Then, perform evaporation separation in the thin-film evaporator 4. The heating medium of the thin-film evaporator 4 is saturated steam with a pressure of 1.26 MPa and a temperature of 190°C. The evaporation temperature of the thin-film evaporator 4 is 150°C - 155°C, the pressure is controlled at 22 - 30 kPa, and the sulfur trioxide evaporation rate is controlled at 31%.

[0030] Step 3): The gaseous sulfur trioxide obtained from evaporation separation enters the condenser 5 through the gas-phase outlet at the top of the thin-film evaporator 4 for condensation. The cooling medium in the condenser 5 is circulating cooling water at <33°C.

[0031] Step 4): The 103% oleum solution obtained from evaporation separation flows by gravity from the liquid-phase outlet at the bottom of the thin-film evaporator 4 to the primary preheater 2, exchanges heat with the 109% oleum in the oleum storage tank 1, cools down to 51°C and then enters the oleum storage tank 1 for recycling.

[0032] Example 2: Step 1): Feed the 107% oleum with a stable flow rate in the oleum storage tank 1 to the primary preheater 2 through the circulation pump 8, and exchange heat with the 103% acid from the thin-film evaporator 4 to heat the 107% oleum from 40°C to 124°C, then send it to the secondary preheater 3. The secondary preheater 3 uses the 189°C steam condensate from the shell side of the evaporator to heat the 107% acid at 124°C to around 130°C, and then enters the thin-film evaporator 4 for evaporation. A feedforward control flow regulating valve based on the solution inlet flow rate is set on the inlet pipeline, which is connected to the gas-phase flow outlet of the thin-film evaporator.

[0033] Step 2): Then, perform evaporation separation in the thin-film evaporator 4. The heating medium of the thin-film evaporator 4 is saturated steam with a pressure of 1.126 MPa and a temperature of 190°C. The evaporation temperature of the thin-film evaporator 4 is 150°C - 155°C, the pressure is controlled at 22 KPa - 30 KPa, and the sulfur trioxide evaporation rate is controlled at 23%.

[0034] Step 3): The gaseous sulfur trioxide obtained from evaporation separation enters the condenser 5 through the gas-phase outlet at the top of the thin-film evaporator 4 for condensation. The cooling medium in the condenser 5 is circulating cooling water at <33°C.

[0035] Step 4), the 103% oleum solution obtained by evaporation separation flows by gravity from the liquid phase outlet at the bottom of the thin-film evaporator 4 to the primary preheater 2, exchanges heat with the 107% oleum in the oleum storage tank 1, cools down to 54°C and then enters the oleum storage tank 1 for recycling.

[0036] Example 3: Step 1), the 109% oleum with a stable flow rate in the oleum storage tank 1 is transported to the primary preheater 2 by the circulation pump 8, and exchanges heat with the 107% acid at 120°C from the thin-film evaporator 4 to heat up the 109% oleum from 40°C to 93°C, and then sent to the secondary preheater 3. The secondary preheater 3 uses the 170°C steam condensate in the shell side of the evaporator to heat the 109% acid at 93°C to around 98°C, and then enters the thin-film evaporator 4 for evaporation. A feedforward control flow regulating valve based on the solution inlet flow rate is set on the inlet pipeline, connecting to the gas-phase flow outlet of the thin-film evaporator.

[0037] Step 2), then evaporation separation is carried out in the thin-film evaporator 4. The heating medium of the thin-film evaporator 4 is saturated steam with a pressure of 0.8 MPa and a temperature of 170°C. The evaporation temperature of the thin-film evaporator 4 is 120°C, the pressure is controlled at 42 - 68 kPa, and the sulfur trioxide evaporation rate is controlled at 13%.

[0038] Step 3), the gaseous sulfur trioxide obtained by evaporation separation enters the condenser 5 from the gas-phase outlet at the top of the thin-film evaporator 4 for condensation. The cooling medium in the condenser 5 is circulating cooling water at <33°C.

[0039] Step 4), the 107% oleum solution obtained by evaporation separation flows by gravity from the liquid phase outlet at the bottom of the thin-film evaporator 4 to the primary preheater 2, exchanges heat with the 109% oleum in the oleum storage tank 1, cools down to 55°C and then enters the oleum storage tank 1 for recycling.

[0040] Example 4: Step 1), the 109.6% oleum with a stable flow rate in the oleum storage tank 1 is transported to the primary preheater 2 by the circulation pump 8, and exchanges heat with the 102% acid at 160°C from the thin-film evaporator 4 to heat up the 109.6% oleum from 40°C to 109.3°C, and then sent to the secondary preheater 3. The secondary preheater 3 uses the 190°C steam condensate in the shell side of the evaporator to heat the 109.6% acid at 109.3°C to around 120°C, and then enters the thin-film evaporator 4 for evaporation. A feedforward control flow regulating valve based on the solution inlet flow rate is set on the inlet pipeline, connecting to the gas-phase flow outlet of the thin-film evaporator.

[0041] Step 2), then perform evaporation separation in the thin-film evaporator 4. The heating medium of the thin-film evaporator 4 is saturated steam with a pressure of 1.25 MPa and a temperature of 190 °C. The evaporation temperature of the thin-film evaporator 4 is 160 °C, the pressure is controlled at 20 - 25 kPa, and the sulfur trioxide evaporation rate is controlled at 37.2%.

[0042] Step 3), the gaseous sulfur trioxide obtained from evaporation separation enters the condenser 5 through the gas-phase outlet at the top of the thin-film evaporator 4 for condensation. The cooling medium in the condenser 5 is circulating cooling water at < 33 °C.

[0043] Step 4), the 102% concentrated oleum solution obtained from evaporation separation flows by gravity from the liquid-phase outlet at the bottom of the thin-film evaporator 4 to the primary preheater 2, exchanges heat with the 109.6% oleum in the oleum storage tank 1, cools down to 57 °C and then enters the oleum storage tank 1 for recycling.

[0044] Example 5: Step 1), the 105% oleum with a stable flow rate in the oleum storage tank 1 is transported to the primary preheater 2 by the circulation pump 8, and exchanges heat with the acid at 163 °C and 102.25% from the thin-film evaporator 4, heating the 105% oleum from 40 °C to 127.6 °C and sending it to the secondary preheater 3. The secondary preheater 3 uses the 190 °C steam condensate from the evaporator shell side to heat the 105% acid at 127.6 °C to around 132.6 °C, and then enters the thin-film evaporator 4 for evaporation. A feed-forward control flow regulating valve based on the solution inlet flow rate is set on the inlet pipeline, connecting to the gas-phase flow outlet of the thin-film evaporator.

[0045] Step 2), then perform evaporation separation in the thin-film evaporator 4. The heating medium of the thin-film evaporator 4 is saturated steam with a pressure of 1.25 MPa and a temperature of 190 °C. The evaporation temperature of the thin-film evaporator 4 is 163 °C, the pressure is controlled at 20 - 25 kPa, and the sulfur trioxide evaporation rate is controlled at 13.7%.

[0046] Step 3), the gaseous sulfur trioxide obtained from evaporation separation enters the condenser 5 through the gas-phase outlet at the top of the thin-film evaporator 4 for condensation. The cooling medium in the condenser 5 is circulating cooling water at < 33 °C.

[0047] Step 4), the 102.5% concentrated oleum solution obtained from evaporation separation flows by gravity from the liquid-phase outlet at the bottom of the thin-film evaporator 4 to the primary preheater 2, exchanges heat with the 105% oleum in the oleum storage tank 1, cools down to 66 °C and then enters the oleum storage tank 1 for recycling.

[0048] Comparative Example 1: The converted gas from the conversion system, after being heat-exchanged in a heat exchanger, is controlled at a temperature of 280°C and enters the SO3 evaporator to evaporate SO3 in 25% - 30% oleum. The converted gas at the shell-side outlet of the SO3 evaporator is cooled to 170 - 180°C, and the furnace gas is cooled to 135 - 140°C, and finally enters the oleum absorption tower. The temperature of the 20% oleum at the tube-side outlet of the SO3 evaporator is about 106°C. The SO3 evaporation rate is 12.45%, and the heat exchange efficiency is 1.

[0049] Comparative Example 2: The current process of the sulfur trioxide unit in the sulfuric acid workshop is to use the 260°C flue gas at the tube-side outlet of the cold and hot heat exchanger in the sulfur-making acid unit to heat the preheated 30% or 40% oleum to above 125°C, so that sulfur trioxide evaporates in gaseous form and enters the sulfur trioxide condenser, which is cooled with water to obtain liquid sulfur trioxide. The SO3 evaporation rate is 14.4%, and the heat exchange efficiency is 1.

[0050] Comparative Example 3: Enter the SO3 evaporator to evaporate SO3 in 25% - 30% oleum. The shell side of the SO3 evaporator uses saturated steam at 170°C and finally enters the oleum absorption tower. The temperature of the 20% oleum at the tube-side outlet of the SO3 evaporator is about 106°C, so that sulfur trioxide evaporates in gaseous form and enters the sulfur trioxide condenser, which is cooled with water to obtain liquid sulfur trioxide. The SO3 evaporation rate is 12.45%, and the heat exchange efficiency is 4.5.

[0051] In Examples 1 - 5, the heat exchange efficiency is greater than 9, the scheme operates stably, the evaporation efficiency is high, and the residence time is short. For the sulfur trioxide evaporation process, by using a thin-film evaporator, it can be based on the change of oleum concentration, not affected by the flue gas quality, ensuring that the evaporation rate is better than or equivalent to the existing process. Its heat exchange efficiency is more than 8 - 9 times that of the existing process, and the heat exchange area is at most 1 / 9 of the flue gas process.

[0052] However, in Comparative Examples 1 - 2, the operation is prone to fluctuations, easily affected by the flue gas quality, the circulation volume of oleum is large, the sulfur trioxide output is low, the residence time of low-concentration oleum in the equipment is long, and local corrosion is likely to occur.

[0053] Comparative Example 3 is mainly a horizontal structure, occupying a large area. Under the same evaporation rate, the heat exchange efficiency is 4.5 times that of Comparative Examples 1 - 2. Compared with the examples, the heat exchange efficiency is low, the heat exchange area is large, it belongs to static evaporation, the residence time of low-concentration oleum is long, and local corrosion is likely to occur during the evaporation process. As shown in the following table.

Claims

1. A method for producing liquid sulfur trioxide, characterized in that: Includes the following step: Step 1), first connect the acid outlet of the oleum storage tank (1) to the inlet of the primary preheater (2), one outlet of the primary preheater (2) is connected to the secondary preheater (3), the secondary preheater (3) is connected to the inlet pipeline of the thin film evaporator (4), the gas phase outlet at the top of the thin film evaporator (4) is connected to the condenser (5) pipeline, the outlet of the condenser (5) is connected to the liquid sulfur trioxide storage tank (6), the liquid phase outlet of the thin film evaporator (4) is connected to the other inlet of the primary preheater (2), and the other outlet of the primary preheater (2) is connected to the oleum storage tank (1): Step 2), 105%-110% oleum in the oleum storage tank (1) is transported to the primary preheater (2) via a circulation pump (8), and is heat exchanged with 102%-107% acid from the thin film evaporator (4), and the 105%-110% oleum is heated to 93°C-128°C, and then flows through the secondary preheater (3) to be heated to 98°C-133°C before entering the thin film evaporator (4); Step 3), then evaporating and separating in a thin film evaporator (4), the evaporation rate of sulfur trioxide is controlled at 13%-37.2%, the evaporation temperature of the thin film evaporator (4) is 120-163°C, and the pressure is controlled at 20-68kPa; Step 4), the gaseous sulfur trioxide obtained by evaporation and separation enters the condenser (5) from the gas phase outlet at the top of the thin film evaporator (4) for condensation; Step 5), the 102%-107% oleum solution obtained by evaporation separation flows by gravity from the liquid phase outlet at the bottom of the thin film evaporator (4) to the primary preheater (2) and exchanges heat with the 105%-110% oleum in the oleum storage tank (1) to cool to 51-66°C, and then flows by gravity back to the oleum storage tank (1) to circulate again.

2. The method for producing liquid sulfur trioxide according to claim 1, characterized in that: The heating medium (9) of the thin film evaporator (4) is saturated steam with a pressure of 0.8-1.26 MPa and a temperature of 170-190° C. or heat transfer oil with a temperature of 170-190° C.

3. The method for producing liquid sulfur trioxide according to claim 1, characterized in that: The cooling medium in the condenser (5) is circulating cooling water with a temperature of less than 33°C.

4. The method for producing liquid sulfur trioxide according to claim 1, characterized in that: The oleum inlet pipe of the thin film evaporator (4) is provided with a parking acid washing replacement system.

5. The method for producing liquid sulfur trioxide according to claim 1, characterized in that: A sulfur trioxide metering pump (7) is provided on the liquid outlet pipeline of the liquid sulfur trioxide storage tank (6), and a circulation pump (8) is installed on the pipeline between the acid outlet of the oleum storage tank (1) and the primary preheater (2).

Images