A pickling treatment device for stainless steel tubing

Abstract

This invention provides a pickling treatment device for stainless steel tubing, comprising a plasma pretreatment system, a fluorine-free electrolytic pickling system, and a waste liquid closed-loop regeneration system. The plasma pretreatment system includes a plasma generator driven by a radio frequency power supply. The plasma pretreatment system also includes a cylindrical reaction chamber for housing the stainless steel tubing. The reaction chamber is provided with multiple sets of annular copper electrodes, which are equidistantly distributed along the axial direction of the reaction chamber. The stainless steel tubing serves as a grounding electrode, passing through the multiple sets of annular copper electrodes. The plasma generator uses low-temperature plasma to bombard the surface of the stainless steel tubing, loosening the oxide layer.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, and in particular to a pickling treatment device for stainless steel tubing. Background Technology

[0002] Pickling equipment for stainless steel pipes is used to pickle stainless steel pipes. Pickling is a typical chemical surface treatment process. Pickling is mainly used to remove the oxide layer, welding slag and impurities on the surface of stainless steel, and to improve the surface smoothness and corrosion resistance of stainless steel pipes.

[0003] Traditional pickling equipment typically includes the following steps: First, a pretreatment step, where oil and organic matter are removed from the surface of the stainless steel pipe using an alkaline solution or ultrasonic cleaning. Mechanical pretreatment then removes the thick oxide layer on the stainless steel pipe surface, reducing the burden on subsequent pickling. Second, the pickling step, where the prepared acid solution is circulated by a pump to maintain a uniform concentration, and a heating system maintains the acid solution temperature, under these conditions for pickling the stainless steel pipe. Third, the post-treatment step, where the stainless steel pipe is washed with water using a counter-current rinse to remove residual acid. Next, it is neutralized with an alkaline solution, followed by nitric acid passivation to form a protective oxide film. Finally, it is dried with hot air. Fourth, the wastewater treatment step, where acidic wastewater is treated in a neutralization tank to recover metal ions.

[0004] However, traditional pickling equipment still has shortcomings in terms of environmental protection, efficiency, and intelligence, specifically in the following aspects: First, HF acid mist is highly hazardous, and the wastewater contains heavy metals and fluoride ions, resulting in high treatment costs. Second, pickling time is long, and energy consumption is high (heating, circulation pumps). Third, there is a lot of manual intervention, and parameter adjustment relies on experience. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems by providing an acid pickling treatment device for stainless steel tubing.

[0006] The technical solution of the present invention is an acid pickling treatment device for stainless steel tubing, comprising a plasma pretreatment system, a fluorine-free electrolytic acid pickling system, and a waste liquid closed-loop regeneration system.

[0007] The plasma pretreatment system includes a plasma generator driven by a radio frequency power supply. The plasma pretreatment system also includes a cylindrical reaction chamber for housing a stainless steel tube. The reaction chamber is provided with multiple sets of annular copper electrodes, which are equidistantly distributed along the axial direction of the reaction chamber. The stainless steel tube serves as a grounding electrode and passes through the multiple sets of annular copper electrodes. The plasma generator uses low-temperature plasma to bombard the surface of the stainless steel tube, loosening the oxide layer.

[0008] The fluorine-free electrolytic pickling system includes a composite tank, in which the electrolyte is a neutral salt solution. The composite tank is equipped with a titanium alloy mesh cathode, which surrounds the outer wall of a stainless steel tube serving as the anode, with an electrode spacing of 5-10 mm. The composite tank is equipped with a pulse power supply connecting the two electrodes, which powers the electrochemical reaction within the composite tank. The composite tank is also equipped with an ultrasonic transducer, which uses ultrasonic cavitation to break down the oxide passivation film on the surface of the stainless steel tube, thereby accelerating electrolyte penetration.

[0009] The waste liquid closed-loop regeneration system includes a diffusion dialysis membrane module, which includes a branched waste liquid channel and a recovery liquid channel. A plate-and-frame membrane stack is provided at the common front end of the waste liquid channel and the recovery liquid channel. The recovery liquid channel is connected to the composite tank. The waste liquid closed-loop regeneration system also includes a primary sedimentation tank and a secondary sedimentation tank placed after the primary sedimentation tank. The waste liquid channel is connected to the primary sedimentation tank. The primary sedimentation tank is equipped with a dosing device for calcium salt addition, and the secondary sedimentation tank is equipped with an adsorbent.

[0010] It also includes a control system, which includes several laser confocal sensors installed in the plasma pretreatment system and the fluorine-free electrolytic acid washing system. Based on the feedback from the laser confocal sensors, the current of the radio frequency power supply, the current of the pulse power supply, and the power of the ultrasonic transducer are dynamically adjusted. The control system also includes an online plasma spectrometer installed at the common front end of the waste liquid flow channel and the recovery liquid flow channel. Based on the feedback from the online plasma spectrometer, the dialysate flow rate of the diffusion dialysis membrane assembly is automatically adjusted.

[0011] In one embodiment, the inner wall of the reaction chamber is made of stainless steel and coated with an alumina ceramic coating. The diameter of the reaction chamber is 500 mm, the length of the reaction chamber is 6 m, one end of the reaction chamber is sealed by a sealing plate with an electrode connector, and the other end of the reaction chamber is sealed by an O-ring and a quick-release flange.

[0012] In one embodiment, one end of the stainless steel tube is fixed to the electrode connector, the quick-release flange is provided with an insulating connector, the insulating connector and the electrode connector are coaxial, and the other end of the stainless steel tube is fixed to the insulating connector.

[0013] In one implementation, the frequency of the alternating electric field provided by the radio frequency power supply is 13.56MHz, and the power of the radio frequency power supply is adjusted in the range of 1 to 5kW according to the different diameters of the stainless steel tube.

[0014] In one embodiment, the surface of the annular copper electrode is plated with nickel.

[0015] In one embodiment, the composite tank includes an alloy liner and a PP shell.

[0016] In one embodiment, the pulse frequency of the pulse power supply is 100–500 Hz, the duty cycle is 10%–30%, and the peak current density is 3–5 A / dm². 2 .

[0017] In one embodiment, the plate-and-frame membrane stack is formed by alternating stacking of anion exchange membranes and acid-resistant flow channel partitions. The membrane material of the anion exchange membrane is a perfluorosulfonic acid ion exchange membrane with a thickness of 0.15 to 0.2 mm, a temperature resistance of ≤60℃, and a pH tolerance range of 0 to 14.

[0018] In one embodiment, the primary sedimentation tank is equipped with a stirring device, and the dosing device is used to add calcium bicarbonate slurry to the primary sedimentation tank.

[0019] In one embodiment, the adsorbent is modified nano-hydroxyapatite with a specific surface area ≥200 m². 2 / g, fluorine adsorption capacity ≥20mg / g.

[0020] The advantages of this invention compared to existing technologies are as follows: In the pretreatment stage of the pickling equipment for stainless steel tubing, a plasma generator is used as the core energy source. Within a closed cylindrical reaction chamber, low-temperature plasma activates the surface of the stainless steel tubing, loosening its oxide layer. A unique electrode configuration, where the stainless steel tubing itself acts as a grounding electrode, passes through multiple sets of equidistantly distributed annular copper electrodes, ensuring comprehensive and uniform treatment of the stainless steel tubing surface. This process reduces the difficulty of subsequent pickling and decreases acid consumption by more than 50%. In the pickling process, a neutral salt electrolyte replaces the original pickling medium, peeling off the oxide layer through an electrochemical reaction, avoiding the use of strong acids. The unique electrode configuration, where a titanium alloy mesh cathode surrounds the outer wall of the stainless steel tubing with a distance of 5-10 mm between electrodes, allows for a current density of 0.5-1.5 A / dm². 2The surface roughness Ra of the stainless steel pipes obtained after pickling is ≤0.2μm, which is far better than that of traditional pickling processes. Furthermore, the ultrasonic cavitation effect of the ultrasonic transducer accelerates acid penetration, shortening the pickling time by more than 30%. After this process, the discharged wastewater is fluoride-free, and the metal ion recovery rate is ≥95%. In the wastewater treatment process, branched wastewater and recovery liquid channels supply the flow of the raw solution after dialysis and the dialysate, respectively, in opposite directions. After the raw solution passes through the plate-and-frame membrane stack, the dialysate returns to the composite tank, while the remainder enters the primary and secondary sedimentation tanks. Therefore, the wastewater closed-loop regeneration system forms a closed-loop control through three-stage treatment of membrane separation, chemical precipitation, and adsorption, achieving efficient acid recovery and deep removal of fluoride ions. Compared with traditional neutralization and discharge processes, acid consumption is reduced, hazardous waste volume is decreased, and operating costs are lowered. All three processes are deeply controlled by the control system, which dynamically adjusts the corresponding operating parameters through real-time detection by laser confocal sensors and plasma spectrometers, significantly reducing the frequency of manual intervention. Attached Figure Description

[0021] Figure 1 A functional block diagram of a pickling treatment device for stainless steel tubular pipes provided for an embodiment of the present invention;

[0022] Figure 2 A schematic diagram of the cylindrical reaction chamber provided in an embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of the structure of the titanium alloy mesh cathode provided in an embodiment of the present invention.

[0024] In the diagram: 1. Reaction chamber; 2. Stainless steel tube; 3. Annular copper electrode; 4. Electrode connector; 5. Sealing plate; 6. O-ring; 7. Quick-release flange; 8. Insulating connector; 9. Titanium alloy mesh cathode. Detailed Implementation

[0025] The above and other embodiments and advantages 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.

[0026] In one implementation, such as Figures 1 to 3 As shown.

[0027] This embodiment provides a pickling treatment device for stainless steel tubing, comprising a plasma pretreatment system, a fluorine-free electrolytic pickling system, and a waste liquid closed-loop regeneration system. The plasma pretreatment system includes a plasma generator driven by a radio frequency power supply. It also includes a cylindrical reaction chamber 1, which houses the stainless steel tubing 2. Multiple sets of annular copper electrodes 3 are equidistantly distributed along the axial direction of the reaction chamber 1. The stainless steel tubing 2 serves as a grounding electrode, passing through the annular copper electrodes 3. The plasma generator uses low-temperature plasma to bombard the surface of the stainless steel tubing 2, loosening the oxide layer. The fluorine-free electrolytic pickling system includes a composite tank containing a neutral salt solution as the electrolyte. A titanium alloy mesh cathode 9 surrounds the outer wall of the stainless steel tubing 2, which serves as the anode, with an electrode spacing of 5-10 mm. The composite tank is equipped with a pulse power supply connecting the two electrodes, which powers the electrochemical reaction within the composite tank. An ultrasonic transducer is also installed in the composite tank. The passivation film of the oxide layer on the surface of the stainless steel tube 2 is destroyed by ultrasonic cavitation to accelerate electrolyte penetration. The waste liquid closed-loop regeneration system includes a diffusion dialysis membrane module, which includes a waste liquid channel and a recovery liquid channel forming branches. A plate and frame membrane stack is provided at the common front end of the waste liquid channel and the recovery liquid channel. The recovery liquid channel is connected to the composite tank. The waste liquid closed-loop regeneration system also includes a primary sedimentation tank and a secondary sedimentation tank placed after the primary sedimentation tank. The waste liquid channel is connected to the primary sedimentation tank. A dosing device for calcium salt addition is provided in the primary sedimentation tank. An adsorbent is provided in the secondary sedimentation tank. The system also includes a control system, which includes several laser confocal sensors installed in the plasma pretreatment system and the fluorine-free electrolytic acid washing system. Based on the feedback from the laser confocal sensors, the current of the radio frequency power supply, the current of the pulse power supply, and the power of the ultrasonic transducer are dynamically adjusted. The control system also includes an online plasma spectrometer installed at the common front end of the waste liquid channel and the recovery liquid channel. Based on the feedback from the online plasma spectrometer, the dialysate flow rate of the diffusion dialysis membrane module is automatically adjusted.

[0028] In this embodiment, the pickling equipment for stainless steel pipe 2 is an integrated stainless steel pipe 2 pickling system, integrating three core modules: plasma pretreatment, fluorine-free electrolytic pickling, and waste liquid closed-loop regeneration. Through intelligent control, it achieves efficient, environmentally friendly, and low-consumption surface treatment. The equipment is suitable for stainless steel pipes 2 such as 304, 316L, and duplex steel, and can process pipe diameters ranging from Φ20 to 200 mm, with a processing speed of 3 to 5 meters per minute, a surface roughness Ra ≤ 0.2 μm, an acid recovery rate ≥ 85%, and a fluoride ion removal rate ≥ 99.5%. Specifically, in the pretreatment process, a plasma generator is used to provide the core energy source. Within a closed cylindrical reaction chamber 1, low-temperature plasma activates the surface of the stainless steel pipe 2, loosening its oxide layer. A unique electrode configuration, where the stainless steel pipe 2 itself acts as a grounding electrode, passes through multiple sets of equidistantly distributed annular copper electrodes 3, ensuring that the surface of the stainless steel pipe 2 is treated comprehensively and uniformly. This process reduces the difficulty of subsequent pickling and decreases acid consumption by more than 50%. In the pickling process, a neutral salt electrolyte was used instead of the original pickling medium. The oxide layer was peeled off through an electrochemical reaction, avoiding the use of strong acids. A unique electrode configuration involved a titanium alloy mesh cathode 9 surrounding the outer wall of a stainless steel tube 2, with a distance of 5–10 mm between the electrodes, allowing a current density of 0.5–1.5 A / dm³. 2 The surface roughness Ra of the stainless steel pipe 2 obtained after pickling is ≤0.2μm, which is far better than that of traditional pickling processes. Furthermore, the ultrasonic cavitation effect of the ultrasonic transducer accelerates acid penetration, reducing pickling time by more than 30%. After this process, the discharged wastewater is fluoride-free, and the metal ion recovery rate is ≥95%. In the wastewater treatment process, branched wastewater and recovery liquid channels supply the flow of the raw solution after dialysis and the dialysate, respectively, in opposite directions. After the raw solution passes through the plate-and-frame membrane stack, the dialysate returns to the composite tank, while the remainder enters the primary and secondary sedimentation tanks. Therefore, the wastewater closed-loop regeneration system forms a closed-loop control through three-stage treatment of membrane separation, chemical precipitation, and adsorption, achieving efficient acid recovery and deep removal of fluoride ions. Compared with traditional neutralization and discharge processes, acid consumption is reduced, hazardous waste volume is decreased, and operating costs are lowered.

[0029] In all three processes described above, the control system is deeply involved in control. Through real-time detection by laser confocal sensors and plasma spectrometers, the corresponding operating parameters are dynamically adjusted, significantly reducing the frequency of manual intervention. Therefore, the commissioning of this pickling equipment for stainless steel tubing solves the technical problems mentioned in the background technology, such as the significant hazards of HF acid mist, wastewater containing heavy metals and fluoride ions, high treatment costs, long pickling time, high energy consumption, and excessive manual intervention.

[0030] In one implementation, such as Figure 2 As shown.

[0031] The pickling equipment for stainless steel tubing provided in this embodiment has a reaction chamber 1 with an inner wall made of stainless steel and coated with an alumina ceramic coating. The reaction chamber 1 has a diameter of 500 mm and a length of 6 m. One end of the reaction chamber 1 is sealed by a sealing plate 5 with an electrode connector 4, and the other end is sealed by an O-ring 6 and a quick-release flange 7. One end of the stainless steel tube 2 is fixed to the electrode connector 4. An insulating connector 8 is provided on the quick-release flange 7. The insulating connector 8 and the electrode connector 4 are coaxial. The other end of the stainless steel tube 2 is fixed to the insulating connector 8.

[0032] In this embodiment, the cylindrical reaction chamber 1 is made of 316L stainless steel with an alumina coating. It is 6m long and 500mm in diameter, compatible with stainless steel pipes 2 with diameters of 20-200mm. During operation, the cylindrical reaction chamber 1 forms a fully sealed space. The electrode connector 4 at one end of the reaction chamber 1 serves as the grounding electrode, connecting to the stainless steel pipe 2. The stainless steel pipe 2 itself then acts as the grounding electrode, i.e., the anode, corresponding to the multiple sets of annular copper electrodes 3 at the cathode. Furthermore, the insulation support required for the stainless steel pipe 2 is provided by the insulating connector 8 on the quick-release flange 7. The insulating connector 8 and the electrode connector 4 satisfy both the electrical connection requirements and the mechanical installation requirements.

[0033] In one embodiment, the pickling equipment for stainless steel tubing provides an alternating electric field at a frequency of 13.56MHz via an RF power supply, and the power of the RF power supply is adjusted in the range of 1 to 5kW depending on the different diameters of the stainless steel tubing 2.

[0034] In this embodiment, the frequency used by the radio frequency power supply avoids interference with communication frequency bands. The function of the radio frequency power supply is to provide a high-frequency alternating electric field, which generates plasma after passing through ionized gas.

[0035] In one embodiment, the pickling equipment for stainless steel tubing has a nickel-plated surface on the annular copper electrode 3.

[0036] In this embodiment, the annular copper electrode 3 is used as the cathode, and nickel is plated on the surface of the annular copper electrode 3 to prevent corrosion.

[0037] In one embodiment, the composite tank of the pickling equipment for stainless steel tubing includes an alloy liner and a PP shell.

[0038] In this embodiment, a specific material for the composite tank is provided, which is composed of a Hastelloy C276 liner and a PP outer shell. Functionally, it combines ultrasonic and electrolytic functions. The ultrasonic waves and electrolysis produce a synergistic effect: ultrasonic cavitation disrupts the oxide passivation film, accelerating electrolyte penetration; the bubbles generated by the electrolytic reaction are broken up by the ultrasonic waves, avoiding a shielding effect. This significantly shortens the pickling time, and the resulting stainless steel tube 2 exhibits excellent surface roughness.

[0039] In one embodiment, the pickling equipment for stainless steel tubing has a pulse power supply with a pulse frequency of 100–500 Hz, a duty cycle of 10%–30%, and a peak current density of 3–5 A / dm³. 2 .

[0040] In this embodiment, a pulsed power supply is used, allowing the electrolyte to diffuse and replenish during the pulse intervals, reducing concentration polarization and thus decreasing the corrosion rate of the metal substrate.

[0041] In one embodiment, the pickling equipment for stainless steel tubing has a plate-and-frame membrane stack formed by alternating layers of anion exchange membranes and acid-resistant flow channel baffles. The membrane material of the anion exchange membrane is a perfluorosulfonic acid ion exchange membrane with a thickness of 0.15–0.2 mm, a temperature resistance of ≤60°C, and a pH tolerance range of 0–14.

[0042] In this embodiment, a specific structure of a plate-and-frame membrane stack is provided, and the anion exchange membrane can be selected as type DF120.

[0043] In one embodiment, the pickling equipment for stainless steel tubing includes a primary sedimentation tank equipped with a stirring device and a dosing device for adding calcium bicarbonate slurry to the primary sedimentation tank. The adsorbent in the secondary sedimentation tank is modified nano-hydroxyapatite with a specific surface area ≥200 m². 2 / g, fluorine adsorption capacity ≥20mg / g.

[0044] In this embodiment, the primary sedimentation tank is used as a chemical sedimentation tank, and the secondary sedimentation tank is used as a nano-adsorption tank. Together, they form a two-stage fluoride ion treatment tank to ultimately achieve deep removal of fluoride ions.

[0045] The above detailed embodiments further illustrate the inventive purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, or improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pickling treatment apparatus for stainless steel pipe production pipes, characterized by, The system comprises a plasma pretreatment system, a fluorine-free electrolytic pickling system, and a waste liquid closed-loop regeneration system. The plasma pretreatment system comprises a plasma generator driven by a radio frequency power source, and a cylindrical reaction cavity for accommodating a stainless steel pipe, wherein a plurality of ring-shaped copper electrodes are arranged in the reaction cavity, and the stainless steel pipe serves as a grounding electrode and passes through the plurality of ring-shaped copper electrodes. The fluorine-free electrolytic pickling system comprises a composite tank, wherein an electrolyte in the composite tank is a neutral salt solution, a titanium alloy mesh cathode is arranged in the composite tank, the titanium alloy mesh cathode surrounds the outer wall of a stainless steel pipe as an anode, the distance between the two electrodes is 5-10 mm, a pulse power source connected to the two electrodes is arranged in the composite tank, the pulse power source supplies power for electrochemical reaction in the composite tank, and an ultrasonic transducer is arranged in the composite tank. The waste liquid closed-loop regeneration system comprises a diffusion dialysis membrane assembly, the diffusion dialysis membrane assembly comprises a waste liquid flow channel and a recovery liquid flow channel, a plate-and-frame membrane stack is arranged at the common front end of the waste liquid flow channel and the recovery liquid flow channel, the recovery liquid flow channel is connected to the composite tank, the waste liquid closed-loop regeneration system further comprises a primary sedimentation tank and a secondary sedimentation tank arranged behind the primary sedimentation tank, the waste liquid flow channel is connected to the primary sedimentation tank, a dosing device for adding calcium salt is arranged in the primary sedimentation tank, and an adsorbent is arranged in the secondary sedimentation tank. The system further comprises a control system, the control system comprises a plurality of laser confocal sensors arranged in the plasma pretreatment system and the fluorine-free electrolytic pickling system, and the current of the radio frequency power source, the current of the pulse power source, and the power of the ultrasonic transducer are dynamically adjusted according to the feedback of the laser confocal sensors, the control system further comprises an online plasma spectrometer arranged at the common front end of the waste liquid flow channel and the recovery liquid flow channel, and the dialysis liquid flow rate of the diffusion dialysis membrane assembly is automatically adjusted according to the feedback of the online plasma spectrometer.

2. The pickling apparatus for stainless steel pipe production pipes according to claim 1, characterized by, The inner wall of the reaction cavity is made of stainless steel and plated with an alumina ceramic coating, the chamber diameter of the reaction cavity is 500 mm, the chamber length of the reaction cavity is 6 m, one end of the reaction cavity is sealed by a sealing plate with an electrode connector, and the other end of the reaction cavity is sealed by an O-ring and a quick-release flange.

3. The pickling apparatus for stainless steel pipe production pipes according to claim 2, characterized by, One end of the stainless steel pipe is fixed to the electrode connector, an insulating connector is arranged on the quick-release flange, the insulating connector is coaxial with the electrode connector, and the other end of the stainless steel pipe is fixed to the insulating connector.

4. The pickling apparatus for stainless steel pipe production pipes according to claim 1, characterized by The frequency of the alternating electric field provided by the radio frequency power source is 13.56 MHz, and the power of the radio frequency power source is adjusted within the range of 1-5 kW according to different pipe diameters of the stainless steel pipe.

5. The pickling apparatus for stainless steel pipe production pipes according to claim 1, characterized by, The surface of the ring-shaped copper electrode is plated with nickel.

6. The pickling apparatus for stainless steel pipe production pipes according to claim 1, characterized by The composite tank comprises an alloy inner lining and a PP outer shell.

7. The pickling apparatus for stainless steel pipe production pipes according to claim 1, characterized by, The pulse power has a pulse frequency of 100-500 Hz, a duty cycle of 10-30%, and a peak current density of 3-5 A / dm 2 .

8. The pickling apparatus for stainless steel pipe production pipes according to claim 1, characterized by, The plate-and-frame membrane stack is formed by alternately stacking anion exchange membranes and acid-resistant channel separators, the membrane material of the anion exchange membrane is perfluorosulfonic acid ion exchange membrane, the thickness is 0.15-0.2 mm, the temperature resistance is less than or equal to 60 DEG C, and the pH tolerance range is 0-14.

9. The pickling apparatus for stainless steel pipe production pipes according to claim 1, characterized by, The primary sedimentation tank is provided with a stirring device, and the dosing device is used for adding calcium bicarbonate slurry to the primary sedimentation tank.

10. The pickling apparatus for stainless steel pipe production pipes according to claim 1, characterized by, The adsorbent is modified nano-hydroxyapatite, specific surface area ≥ 200 m 2 / g, fluorine adsorption capacity ≥ 20 mg / g.

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