A method for continuously injecting mixed dilute sulfuric acid

Abstract

The present application relates to a kind of methods for continuously injecting mixed dilute sulfuric acid, the present application uses sintering technology, modified polytetrafluoroethylene is sintered to metal surface to form an integrated injection pipe assembly, overcome the problem of high cost of alloy equipment, and the equipment structure is simple, high-temperature performance, good scouring resistance, the method of pressure sintering makes plastic alloy and metal tightly combined, will not produce shedding, and temperature distribution is uniform and will not produce the problem of local overheating;The sulfuric acid injection method of the present application realizes the purpose of remote automatic continuous control of the required concentration of sulfuric acid, the dilution concentration range is wide (0%-98%), can meet the continuous production needs of most equipment.

Description

Technical Field

[0001] This invention relates to a method for continuously injecting mixed and diluted sulfuric acid. Background Technology

[0002] In current sulfuric acid production, concentrated sulfuric acid is mostly used as the raw material, and then diluted to the required concentration according to process needs. Sulfuric acid is a highly corrosive chemical, and the dilution process is exothermic, placing extremely high demands on the corrosion resistance of the dilution equipment. Currently, there are two main technical solutions: one is to use special alloys, and the other is to use non-metallic linings to solve the corrosion problem. Special alloys are expensive to manufacture, and corrosion still occurs. For equipment using linings, the damage to the interface between the lining material and the metal caused by thermal deformation and erosion has long remained an unresolved issue.

[0003] Commonly used alloys for manufacturing equipment include Alloy 20, Hastelloy B, Monel alloy, and Lewment alloy. All four alloys possess certain corrosion resistance. Lewment alloy is a high-temperature resistant alloy specifically for sulfuric acid, offering excellent performance, but it is currently difficult to manufacture domestically. Equipment made from these four alloys is very expensive. Equipment manufactured using linings currently primarily uses plastic linings. Current processes cannot solve the problem of achieving a tight bond between the plastic lining and the metal, often resulting in lining detachment and equipment damage, thus affecting equipment lifespan. Other options involve relatively complex equipment structures using all-plastic components, but these components have low strength, poor resistance to high temperatures and pressures, and limited flow rates.

[0004] Currently, the dilute sulfuric acid commonly used in production is mainly made by diluting concentrated sulfuric acid with water. This requires the configuration of dilute sulfuric acid tanks and concentrated sulfuric acid tanks. The dilution is carried out in the dilute sulfuric acid tanks, and then the dilute sulfuric acid is pumped into the production unit, which is an intermittent operation. Moreover, the concentration of the prepared dilute sulfuric acid cannot be continuously adjusted (one tank is used to prepare one tank). The dilute sulfuric acid tanks occupy a large area and require the construction of tank area dikes, resulting in high construction costs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for continuous injection of mixed diluted sulfuric acid that is resistant to high temperature and high pressure, thereby improving service life and allowing for continuous production with continuously adjustable dilution concentration, in light of the current state of the prior art.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] A method for continuous injection of mixed diluted sulfuric acid, wherein the injection equipment includes:

[0008] The mixing injector is equipped with a mixing pipe through which process water passes laterally, and an injection pipe assembly for injecting concentrated sulfuric acid is installed at the top;

[0009] The first regulating valve is located at the inlet of the injection pipe assembly and is used to control the injection flow rate of concentrated sulfuric acid.

[0010] A sulfuric acid injection pump, located at the inlet of the mixing injector, is used to pressurize concentrated sulfuric acid into the mixing tube through the injection tube assembly;

[0011] A feedwater pump, located upstream of the mixing pipe, is used to pressurize process water into the mixing pipe and transport it downstream;

[0012] A flow meter is installed on the pipeline between the feed water pump and the mixing pipe to detect the process water flow rate;

[0013] The second regulating valve is located on the pipeline between the feed water pump and the mixing pipe and is used to control the process water flow rate.

[0014] A pH meter is installed on the pipeline downstream of the mixing pipe to detect the pH of the water effluent from the mixing pipe.

[0015] The first regulating valve, flow meter, second regulating valve, and pH meter are controlled by the same analytical control system and thus work together in a coordinated manner.

[0016] The method for continuous injection of mixed diluted sulfuric acid includes the following steps:

[0017] According to the required dilute sulfuric acid flow rate, the process water flow rate and concentrated sulfuric acid flow rate are determined by the DCS based on the required amount and concentration of dilute sulfuric acid. The process water flow rate is controlled by the feed water pump and the second regulating valve, and the concentrated sulfuric acid flow rate is controlled by the first regulating valve. The outlet pH meter monitors the outlet dilute sulfuric acid concentration value online and feeds it back to the DCS. The DCS adjusts the process water inlet flow rate and concentrated sulfuric acid injection flow rate in real time based on the monitored concentration, and continuously supplies dilute sulfuric acid of the appropriate concentration to the downstream production facilities.

[0018] In the above process:

[0019] Required amount of dilute sulfuric acid: G 稀硫酸 ,

[0020] The water supply volume controlled by the second regulating valve at the water pump outlet: G 水 ,

[0021] The amount of concentrated sulfuric acid added by the concentrated sulfuric acid injection pump: G 浓硫酸 ,

[0022] Concentration of concentrated sulfuric acid used: C 浓硫酸 ,

[0023] The required concentration of diluted sulfuric acid at the outlet of the mixing injector after dilution is: C 稀硫酸 ,

[0024] but,

[0025] Amount of concentrated sulfuric acid added: G 浓硫酸 =G 稀硫酸 ×C 稀硫酸 / C 浓硫酸 ,

[0026] Water supply capacity of water injection pump: G 水 =G 稀硫酸 *((1-C 稀硫酸 )-C 浓硫酸 *(1-C 浓硫酸 ) / C 浓硫酸 ).

[0027] Preferably, the injection pipe assembly is a vertically arranged cylindrical structure with an inlet at the upper end and a closed lower end. An outlet is located near the lower edge of the side wall of the cylindrical structure, and the orientation of the outlet is consistent with the flow direction of the process water. The counter-thrust generated by the outlet can counteract the turbulent thrust of the process water on the injection pipe assembly, resulting in good stress distribution on the injection pipe assembly.

[0028] Preferably, the outlet of the injection tube assembly is located on the central axis of the mixing tube. This reduces corrosion of the equipment sidewalls and prevents localized temperature increases on the sintering surface due to the exothermic reaction caused by sulfuric acid dilution.

[0029] In this invention, the injection tube assembly includes an injection tube and a sheath. The top opening of the injection tube forms the inlet. The injection tube has a lower opening and a notch on its side wall that communicates with the lower opening. The sheath covers at least the middle and lower outer periphery of the injection tube. The sheath has a bottom wall that can close the lower opening of the injection tube. The opening is formed on the side wall of the sheath and is arranged corresponding to the notch.

[0030] As an improvement, the inner wall of the sheath and the outer wall of the injection tube are bonded together by pressure sintering, and the sheath extends inward at the opening to form a rim that covers the end edge of the notch. Pressure sintering ensures a tight bond between the plastic alloy and the metal, preventing detachment.

[0031] Preferably, the injection tube is made of carbon steel, and the sheath is made of modified polytetrafluoroethylene (PTFE). After the injection tube undergoes internal surface sandblasting for rust removal, internal surface shot peening for roughening, and degreasing treatment, it enters a rotary sintering furnace under nitrogen pressure protection. Modified PTFE is then sprayed and sintered on the tube to form the sheath. After three sintering processes, the thickness of the sheath obtained by spraying and sintering is 3–5 mm. The pressure sintering method ensures a tight bond between the plastic alloy and the metal, preventing detachment.

[0032] Preferably, the modified polytetrafluoroethylene material is obtained by modifying polytetrafluoroethylene with fluorinated vinyl ether and graphite. The general modification process is as follows:

[0033] ETFE is polymerized with fluorinated vinyl ether to form a block copolymer, at a ratio of 0.1% to 18%, preferably 2% to 8%. The resulting ETFE raw material is first pulverized and refined to achieve the particle size of 10 to 120 μm, preferably 20 to 80 μm, required for spraying. Similarly, graphite raw material is ground to a particle size of 5 to 20 μm and added to the ETFE for thorough mixing as the spraying raw material, at a ratio of 1% to 5%. Depending on the heat release during dilution and the concentration gradient, pulverized glass fibers of 5 to 20 μm can also be added as a reinforcing agent, at a ratio of 0.1% to 2%.

[0034] ETFE (F40) polytetrafluoroethylene plastic was used as the matrix for modification to overcome the non-adhesion defect of ordinary plastic materials to metals, giving it strong adhesion properties to metals. F40 has an average linear expansion coefficient of 1.49 x 10 / 100, close to that of carbon steel, allowing it to achieve synchronous thermal expansion and contraction with carbon steel, and enabling ideal composite bonding with metals. The modified material's pressure resistance, wear resistance, thermal conductivity, creep resistance, and mechanical strength are all improved. Fluorinated vinyl ether and graphite were selected as modifying materials. Fluorinated vinyl ether improves the material's creep resistance by increasing the melt creep viscosity of the copolymer, while graphite improves the material's pressure resistance, wear resistance, and thermal conductivity. Adding an appropriate amount of fluorinated vinyl ether prevents temperature rise caused by uneven local temperature distribution. Graphite modification can improve pressure resistance by 5–10 times, wear resistance by 100–1000 times, reduce the linear expansion coefficient by 80%, and improve thermal conductivity by 2–5 times.

[0035] Preferably, the top of the mixing tube is provided with an assembly port for inserting the injection tube assembly and a connecting pipe extending upward from the edge of the assembly port. The lower part of the injection tube assembly passes through the connecting pipe and the assembly port and extends into the mixing tube. The upper part of the injection tube assembly is locked to the top of the connecting pipe by a clamping flange and a sealing gasket.

[0036] Preferably, the outer periphery of the mixing pipe is provided with a cooling water jacket to control the wall temperature of the mixing pipe to ≤185℃, preferably ≤120℃.

[0037] Compared with the prior art, the advantages of the present invention are as follows: The present invention adopts sintering technology to sinter modified polytetrafluoroethylene onto the metal surface to form an integral injection tube assembly, which overcomes the problem of high cost of alloy equipment. Moreover, the equipment has a simple structure, excellent high temperature resistance and erosion resistance. The pressure sintering method ensures that the plastic alloy and metal are tightly bonded and will not fall off. Furthermore, the temperature distribution is uniform and will not cause local overheating. The sulfuric acid injection method of the present invention achieves the purpose of remote automatic continuous control of the required concentration of sulfuric acid. It is applicable to a wide range of dilution concentrations (0%-98%) and can meet the continuous production needs of most equipment. Attached Figure Description

[0038] Figure 1 This is a process flow diagram of an embodiment of the present invention;

[0039] Figure 2 for Figure 1 A schematic diagram of the structure of the medium-mix injector;

[0040] Figure 3 for Figure 2 A schematic diagram of the injection tube assembly. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0042] like Figure 1 , 2 As shown in Figure 3, the continuous injection method for mixed diluted sulfuric acid in this embodiment uses injection equipment including:

[0043] The mixing injector 1 is provided with a mixing pipe 11 through which process water passes laterally, and an injection pipe assembly 12 for injecting concentrated sulfuric acid is provided at the top;

[0044] The first regulating valve 10 is located at the inlet of the injection pipe assembly 1 and is used to control the injection flow rate of concentrated sulfuric acid.

[0045] Sulfuric acid injection pump 2 is located at the inlet of the mixing injector 1 and is used to press concentrated sulfuric acid into the mixing tube 11 through the injection tube assembly 12;

[0046] The feed water pump 3 is located upstream of the mixing pipe 11 and is used to pressurize the process water into the mixing pipe 11 and transport it downstream.

[0047] Flow meter 4 is installed on the pipeline between feed water pump 3 and mixing pipe 11 to detect process water flow rate;

[0048] The second regulating valve 20 is located on the pipeline between the feed water pump 3 and the mixing pipe 11 and is used to control the process water flow rate.

[0049] pH meter 5 is installed on the pipeline downstream of mixing pipe 11 to detect the pH of the water effluent from mixing pipe 11.

[0050] The first regulating valve 10, flow meter 4, second regulating valve 20, and pH meter 5 are controlled by the same analytical control system and thus work together in a coordinated manner.

[0051] The above-mentioned method for continuous injection of mixed diluted sulfuric acid includes the following steps:

[0052] According to the required dilute sulfuric acid flow rate, the process water flow rate and concentrated sulfuric acid flow rate are determined by the DCS based on the required amount and concentration of dilute sulfuric acid. The process water flow rate is controlled by the feed water pump and the second regulating valve, and the concentrated sulfuric acid flow rate is controlled by the first regulating valve. The outlet pH meter monitors the outlet dilute sulfuric acid concentration value online and feeds it back to the DCS. The DCS adjusts the process water inlet flow rate and concentrated sulfuric acid injection flow rate in real time based on the monitored concentration, and continuously supplies dilute sulfuric acid of the appropriate concentration to the downstream production facilities.

[0053] In the above process:

[0054] Required amount of dilute sulfuric acid: G 稀硫酸 ,

[0055] The water supply volume controlled by the second regulating valve at the water pump outlet: G 水 ,

[0056] The amount of concentrated sulfuric acid added by the concentrated sulfuric acid injection pump: G 浓硫酸 ,

[0057] Concentration of concentrated sulfuric acid used: C 浓硫酸 ,

[0058] The required concentration of diluted sulfuric acid at the outlet of the mixing injector after dilution is: C 稀硫酸 ,

[0059] but,

[0060] Amount of concentrated sulfuric acid added: G 浓硫酸 =G 稀硫酸 ×C 稀硫酸 / C 浓硫酸 ,

[0061] Water supply capacity of water injection pump: G 水 =G 稀硫酸 *((1-C 稀硫酸 )-C 浓硫酸 *(1-C 浓硫酸 ) / C 浓硫酸 ).

[0062] In this embodiment, the injection pipe assembly 12 is a vertically arranged cylindrical structure with an inlet 121 at the upper end and a closed lower end. An outlet 122 is located near the lower edge of the sidewall of the cylindrical structure, and the orientation of the outlet 122 is consistent with the flow direction of the process water. The counter-thrust generated by the outlet 122 can counteract the turbulent thrust of the process water on the injection pipe assembly, ensuring good stress distribution. The outlet 122 of the injection pipe assembly 12 is located on the central axis of the mixing pipe 11 to reduce corrosion of the equipment sidewalls and prevent localized temperature increases on the sintering surface caused by the exothermic reaction of sulfuric acid dilution.

[0063] In this embodiment, the injection tube assembly 12 includes an injection tube 123 and a sheath 124. The top opening of the injection tube 123 forms an inlet 121. The injection tube 123 is provided with a lower opening 125 and a notch 126 on the side wall that communicates with the lower opening 125. The sheath 124 covers at least the middle and lower outer periphery of the injection tube 123. The sheath 124 is provided with a bottom wall 1241 that can close the lower opening 125 of the injection tube 123. An opening 122 is formed on the side wall of the sheath 124 and is arranged corresponding to the notch 126.

[0064] The inner wall of the sheath 124 and the outer wall of the injection tube 123 are bonded together by pressure sintering. The sheath 124 extends inward at the opening 122 to form a rim 1242 that covers the end edge of the notch 126. The pressure sintering method ensures a tight bond between the plastic alloy and the metal, preventing detachment.

[0065] The injection tube 123 is made of carbon steel, and the sheath 124 is made of modified polytetrafluoroethylene (PTFE). After sandblasting and shot peening, the injection tube 123 enters a rotary sintering furnace under nitrogen pressure to form the sheath 124 through PTFE spraying and sintering. After three sintering processes, the resulting sheath has a thickness of 3-5 mm. This pressure sintering method ensures a tight bond between the plastic alloy and the metal, preventing detachment. The specific pressure sintering process is as follows:

[0066] (1) Before spraying and sintering, the inside of the injection pipe 123 is first sandblasted to remove rust. The injection pipe 123 needs to be heated to 286-325℃. The heating process takes about 40 minutes. Nitrogen is introduced to replace the air inside and the pressure is increased to 0.05-0.2MPa. The temperature is maintained for 30 minutes. The first sintering is carried out by rotating the sprayer. The spray thickness is 0.5-1mm. The amount of spray is determined according to the spray thickness and area. The internal gas is released and the pressure is reduced to normal pressure. Then the temperature is reduced to 280℃ and maintained for 30-60 minutes.

[0067] (2) After the first step, the injection tube 123 is heated to 280-320°C and nitrogen gas is introduced to increase the pressure to 0.1-0.4MPa. The second spraying is carried out with a thickness of 1-2mm. After the spraying is completed, the internal gas is released to reduce the pressure to normal pressure and the temperature is reduced to 260-280°C for 30-60 minutes.

[0068] (3) After the second step, the injection tube 123 is heated to 280-310°C and nitrogen gas is introduced to increase the pressure to 0.2-0.8MPa. The third spraying is carried out with a thickness of 1.5-3mm. After the spraying is completed, the internal gas is released and the pressure is reduced to normal pressure. The temperature is gradually reduced at a rate of 50-100°C / hour. After 3.5-5 hours of cooling, the spraying and sintering are completed.

[0069] (4) After the spraying is completed, a high-voltage electric spark test is performed. If there are air holes and leakage, the leak can be repaired by local cleaning and grinding, followed by flame hot melting.

[0070] Modified polytetrafluoroethylene (PTFE) material is obtained by modifying PTFE with fluorinated vinyl ether and graphite. The specific modification process is as follows: fluorinated vinyl ether is added to ETFE during polymerization to form a block copolymer, with an addition ratio of 0.1%–18%, preferably 2%–8%. The resulting ETFE raw material is first pulverized and refined to achieve the particle size required for spraying (10–120 μm, preferably 20–80 μm). Similarly, the added graphite raw material is ground to a particle size of 5–20 μm and added to the ETFE until fully mixed as the spraying raw material, with an addition ratio of 1–5%. Depending on the heat release during dilution and the concentration gradient, pulverized glass fibers of 5–20 μm can also be added as a reinforcing agent, with an addition ratio of 0.1%–2%.

[0071] Among them, the aforementioned ETFE is a product of Asahi Glass Co., Ltd. of Japan, Häster GmbH of Germany, and DuPont of the United States, with the brand name F40. The domestic brand name is Fs-40G series, and it can be produced by the Shanghai Institute of Organic Chemistry.

[0072] ETFE (F40) polytetrafluoroethylene plastic was used as the matrix for modification to overcome the non-adhesion defect of ordinary plastic materials to metals, giving it strong adhesion properties to metals. F40 has an average linear expansion coefficient of 1.49 x 10 / 100, close to that of carbon steel, allowing it to achieve synchronous thermal expansion and contraction with carbon steel, and enabling ideal composite bonding with metals. The modified material's pressure resistance, wear resistance, thermal conductivity, creep resistance, and mechanical strength are all improved. Fluorinated vinyl ether and graphite were selected as modifying materials. Fluorinated vinyl ether improves the material's creep resistance by increasing the melt creep viscosity of the copolymer, while graphite improves the material's pressure resistance, wear resistance, and thermal conductivity. Adding an appropriate amount of fluorinated vinyl ether prevents temperature rise caused by uneven local temperature distribution. Graphite modification can improve pressure resistance by 5–10 times, wear resistance by 100–1000 times, reduce the linear expansion coefficient by 80%, and improve thermal conductivity by 2–5 times.

[0073] The top of the mixing tube 11 is provided with an assembly port 111 for inserting the injection tube assembly 12 and a connecting pipe 112 extending upward from the edge of the assembly port 111. The lower part of the injection tube assembly 12 passes through the connecting pipe 112 and the assembly port 111 and extends into the mixing tube 11. The upper part of the injection tube assembly 12 is locked to the top of the connecting pipe 112 by a clamping flange 13 and a sealing gasket 14.

[0074] A cooling water jacket 15 is provided on the outer periphery of the mixing pipe 11 to control the wall temperature of the mixing pipe to ≤185℃, preferably ≤120℃.

[0075] For the continuous injection of mixed diluted sulfuric acid in this embodiment, when the required production volume is 20 tons / hour of 10% dilute sulfuric acid, it is prepared by diluting it with 80% concentrated sulfuric acid: the sulfuric acid injection pump is set to a flow rate of 2.5 tons / hour, and the water pump provides 17.5 tons / hour of water to meet the dilution requirements.

[0076] When the required production volume is 5.8 tons / hour of 6.2% dilute sulfuric acid, it is prepared by diluting it with 63% concentrated sulfuric acid: the sulfuric acid injection pump is set to a flow rate of 0.57 tons / hour, and the water supply pump provides 5.23 tons / hour of water to meet the dilution requirements.

[0077] Because a large amount of heat is released during the dilution of concentrated sulfuric acid, the lining of the injection pipe can withstand a temperature of 180℃. According to the Thomsen formula, the heat of dilution is calculated. Combined with the specific heat capacity of water and dilute sulfuric acid, the dilution range of this device is 0-80% without the use of a water cooling jacket. With the use of a water cooling jacket, the dilution range of this device can achieve full coverage of concentrations from 0-98%.

Claims

1. A method for continuously injecting mixed dilute sulfuric acid, characterized in that: the injection equipment used comprises: a mixing injector provided with a mixing pipe through which process water passes horizontally, and a top injection pipe assembly through which concentrated sulfuric acid is injected; a first regulating valve arranged at the inlet of the injection pipe assembly for controlling the injection flow of concentrated sulfuric acid; a sulfuric acid injection pump arranged at the inlet of the mixing injector for pressing concentrated sulfuric acid into the mixing pipe through the injection pipe assembly; a feed water pump arranged upstream of the mixing pipe for pressing process water into the mixing pipe and delivering it downstream; a flow meter arranged on the pipeline between the feed water pump and the mixing pipe for detecting the flow of process water; a second regulating valve arranged on the pipeline between the feed water pump and the mixing pipe for controlling the flow of process water; a pH meter arranged on the pipeline downstream of the mixing pipe for detecting the pH of the water outlet from the mixing pipe; the first regulating valve, the flow meter, the second regulating valve and the pH meter are controlled by the same analysis control system so as to be coordinated and linked; the method for continuously injecting mixed dilute sulfuric acid comprises the following steps: according to the required flow of dilute sulfuric acid, the amount of process water and the amount of concentrated sulfuric acid are determined by DCS according to the required amount and concentration of dilute sulfuric acid, the flow of process water is controlled by the feed water pump and the second regulating valve, the flow of concentrated sulfuric acid is controlled by the first regulating valve, the concentration value of the outlet dilute sulfuric acid is monitored online by the outlet pH meter and fed back to the DCS, the DCS adjusts the inlet amount of process water and the injection amount of concentrated sulfuric acid in real time according to the monitored concentration, and continuously supplies dilute sulfuric acid meeting the concentration to the downstream production facilities; the injection pipe assembly is in the form of a vertically arranged cylindrical structure, the upper end of the cylindrical structure is provided with an inlet, the lower end is closed, the side wall of the cylindrical structure is provided with an outlet arranged close to the edge of the lower end, and the direction of the outlet is consistent with the flow direction of the process water; the injection pipe assembly comprises an injection pipe and a sheath, the top of the injection pipe is open to form the inlet, the injection pipe is provided with a lower end opening and a notch in the side wall communicating with the lower end opening, the sheath covers the outer periphery of at least the middle and lower parts of the injection pipe, the sheath is provided with a bottom wall capable of closing the lower end opening of the injection pipe, and an opening is formed in the side wall of the sheath and arranged corresponding to the notch; the inner side wall of the sheath and the outer side wall of the injection pipe are formed together, the sheath extends inwardly at the opening to form a hem capable of covering the end edge of the notch; the injection pipe is made of carbon steel material, the sheath is made of modified polytetrafluoroethylene material, the injection pipe is subjected to sand blasting and shot blasting treatment, then enters a rotary sintering furnace, and in the case of nitrogen pressurization protection, modified polytetrafluoroethylene is sprayed and sintered on the injection pipe to form the sheath, after three times of sintering, the thickness of the sheath obtained by spraying and sintering is 3-5 mm; the modified polytetrafluoroethylene material is obtained by modifying polytetrafluoroethylene with fluorinated vinyl ether and graphite. The outlet of the injection pipe assembly is located on the central axis of the mixing pipe. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The method of continuously injecting dilute sulfuric acid according to claim 1, characterized in that: ​ 3. The method of continuously injecting dilute sulfuric acid according to claim 1 or 2, characterized in that: The top of the mixing tube is provided with a fitting opening for inserting the injection tube assembly, and a connecting pipe extending upward from the edge of the fitting opening, the lower part of the injection tube assembly extending into the mixing tube through the connecting pipe and the fitting opening, and the upper part of the injection tube assembly being locked at the top of the connecting pipe by a compression flange and a sealing gasket.

4. The method of continuously injecting dilute sulfuric acid according to claim 1 or 2, characterized in that: The outer periphery of the mixing tube is provided with a cooling water jacket for controlling the wall temperature of the mixing tube to be ≤185℃.

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