The successful application of the tank film-forming glue injection sealing technique in the repair of copper electrolytic purification electroevaporation equipment

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【Abstract】: This paper describes the process of removing nickel from the electrolyte purification system used in wet copper smelting. Due to the low shrinkage rate and lack of elasticity of the lining material, changes in the temperature during electric evaporation lead to significant variations in the temperature of the equipment’s steel shell during shutdown and startup cycles. The internal tiles experience smaller temperature changes, while the volume of the spaces within the equipment’s layers increases as the temperature rises, resulting in negative pressure; conversely, a positive pressure is created. During the transition from positive to negative, the internal medium is drawn in, resulting in the accumulation of a small amount of acid in the interlayer; this acid accelerates the corrosion of the steel casing of the equipment under the influence of high temperatures. In response to the leakage problems in electric evaporation tanks, and taking into account the process of nickel removal through electric evaporation, the causes of leakage in such tanks as well as the economic costs associated with repairs were analyzed. The advantages of the film-forming glue injection technique for sealing leaks in tanks were demonstrated, and practical experience has proven the successful application of this technique in repairing electric evaporation tanks. 【Keywords】: Electroevaporation; Leakage; Tank film formation; Glue injection for leak sealing; Successful application; Repair cost. Introduction: Using nickel-copper sulfide concentrate as the feedstock in pyrometallurgical processes, 40,000 tons of high-nickel copper anodes are processed each year. The copper anodes produced are sent to the electrolysis process to ensure the quality of the cathode copper produced, and to remove the nickel-containing components from the electrolyte (with a nickel content of 163/m3·d-1). Mature electroevaporation technology is also employed in the purification stage to treat 3.81 kt/year of crude nickel sulfate in the electrolyte. The process flow involves using electroevaporation to remove impurities such as nickel from the electrolyte extracted through electrolysis, and employs vacuum evaporation-electroevaporation to produce crude nickel sulfate. Based on the amount of nickel that needs to be removed, a certain volume of the copper-removed solution is drawn out each day and sent to a high-level tank; from there, it flows continuously by gravity to an electrically heated concentration tank. After evaporation, the liquid overflows into a water-cooled crystallization tank, where continuous stirring facilitates cooling. The resulting crystalline slurry then overflows into a belt-type vacuum filter, where the crude nickel sulfate product is separated out, while the filtrate is recycled as acid and returned to the electrolysis process. The purification unit is required to handle 254 m3 of purified liquid per day. Through four electroevaporation units used for nickel removal, an amount of 2076 kg of nickel needs to be removed per day. The feed flow rate is 5.18 m3/h; each electroevaporation unit with a power capacity of 500 KW has a processing capacity of 0.7 m3/h. The ultimate yield of nickel achieved is 85%. The volume of solution fed into the electroevaporation units is 113.96 m3 per day. The evaporation temperature is 170±5°C, and the concentration of acid in the resulting liquid is 1100 g/l. The temperature for water-cooled crystallization is 45°C, with the composition being 18% nickel and 10–12% free acid. 1 Overview of Electroevaporation 1.1 At present, in China, electroevaporation is the only method available for removing nickel from electrolytes, but the service life of electroevaporation tanks is short. Since the electric evaporation nickel removal process in the three-purification system was put into operation in September 2010, the electric evaporation tanks have experienced varying degrees of leakage in their housings due to the effects of temperature and acid, which poses potential safety risks to continued use, hinders production, and affects product quality. The conventional repair method involves rebuilding the shell with bricks; this process takes a long time and incurs high costs. Given the company’s challenging financial situation, to achieve optimal repairs, we employ a membrane-forming glue injection technique for sealing leaks. This method allows the repair of an electric evaporation tank to be completed in just one week, with repair costs amounting to 20% of those associated with the conventional method, thereby delivering the best possible repair results. 1.2 Status of electric evaporation equipment: 1.2.1 There are a total of 4 electric evaporation units in Copper Electrolysis Workshop 1. Name, Specifications, Operating Air Velocity, Structural Features: Electric Evaporation, Electric Evaporator (including control system): TSH/1180/6, 2.3 m/s. Disk-shaped base, arch-shaped supports, high-alumina ceramic strip beams for smoke distribution, Uniflo channels for acid separation, MESH PAD foam capture device. 1.2.2 Structure of electric evaporation: The 4 electric evaporators are all vertical circular steel towers lined with acid-resistant tiles; the outermost layer is a steel shell, the middle layer consists of ceramic fiber and lead-lined channels, and the innermost layer is three layers of acid-resistant tiles constructed using KPI mortar. After being delivered and put into use, to ensure the quality of operation of the electric evaporators: Methods for ensuring the quality of the lead lining: First, fill the channels with water for 24 hours (the user is required to provide a water source on-site). It is recommended to add 5-10 mm of leak-catching holes at the lowest point of the tank. II. Use a 5-10x magnifying glass to check the surface of the lead lining and the weld area for any pitting; if any is found, fill it in. III. Dissect the area where problems are suspected, address them, and then weld it back together. Quality assurance methods for bricklaying: The optimal construction temperature for laying acid-resistant tiles is 18–30°C. If the temperature is too high, the reaction proceeds too rapidly, making construction extremely difficult. Ice water can be used to lower the temperature of the water glass, or construction can be carried out at night, or the amount of curing agent used can be reduced to slow down the reaction rate. When the temperature is below 10°C, the setting time increases, and the material tends to flow, deform, and crack; preheating the aggregates or using heated curing methods can be employed. During construction, the user provides a 220VAC power supply on site for heating and insulation purposes during on-site work. After each layer of acid-resistant tiles is laid, apply KP1 thin mortar to the joints twice, applying it every 4–5 hours. Blocks capillaries and increases impermeability. After bricklaying is completed, it must be cured at room temperature for 14 days before it can be put into use. Corrosion protection of the tank cover surface: The corrosion protection for the bottom layer of the tank cover surface is carried out using the same methods as those used for the surface treatment of the tank body, after which lead is applied to the treated surface. Corrosion protection on the inner side of the tank lids: The inner sides of 4 tank lids are treated with lead plating, with a plating thickness of 8 mm. All the takeover linings (N1-N10) are 40-50 mm acid-resistant porcelain tubes, which serve to prevent corrosion and reduce the temperature of lead. Electroevaporation of 68% sulfuric acid as the internal medium, at a temperature of around 170°C. 3 Analysis of leaks in the electric evaporation tanks: 3.1 Equipment leakage situation: The outer surfaces of the 4 electric evaporation units show signs of corrosion, with areas of corrosion appearing in clusters in some sections. As shown in the figure: file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image001.gif file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image003.jpg file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image005.jpg 3.2 Reasons for the leakage: a. Poor construction quality of the tiles used to line the tower. The main reasons include: ① The new tiles were not cleaned properly, were not adequately protected, had high moisture levels, and were not dried properly. ②The clay mixture was prepared in an improper ratio, was not mixed evenly, too much was prepared at once, and it was used for more than half an hour. Or the clay contains too much moisture. ③The clay is not evenly applied on the tile surface; it has not been smoothed out repeatedly. ④The brick joints vary in size, and the mortar joints are uneven. ⑤Too many layers are built per day during construction. ⑥The brick joints were not properly repaired, nor were they treated with acid more than twice. ⑦There were defects in the ratio of curing agents during construction, resulting in an insufficient curing time for the KPI mortar. ⑧The construction team lacks professional masons, and no proper attention is paid to the quality of construction ； b. During the heating of the equipment, the heating curve was not properly controlled, and the moisture contained in the internal clay was not removed in time. As a result, the high temperatures generated during production turned the moisture in the clay into gas, which then dispersed within the equipment’s interlayers. When the equipment is in operation, this gas occupies a large volume, creating a positive pressure in the interlayers and leading to a tendency for diffusion. There is a tendency to blow water vapor into the interior of the directional device. When parked, water exists in liquid form in the interlayer under negative pressure. At the same time, there is a tendency to draw in the medium from inside the device. With repeated driving and stopping, acidic sulfuric acid is drawn into the layered structure that contains cavities; this sulfuric acid combines with the water present in those layers to form sulfuric acid of lower concentration, and the high temperature accelerates the rate of corrosion. Flaky corrosion is the external manifestation of localized cavities being corroded. c. Due to the high shrinkage rate and lack of elasticity of the material, large temperature changes occur in the steel plates of the equipment during the switching between shutdown and operation modes. The tiles inside the equipment are less affected by these temperature changes. As the temperature rises, the volume of the voids inside the equipment increases, resulting in negative pressure. Conversely, it is positive pressure. During the transition from positive to negative, the internal medium is drawn in. This results in a small amount of acid accumulating in the interlayer, and the acid corrodes the steel casing of the equipment directly under high temperatures. 4 Inspection results of equipment drilling: This system uses membrane formation and glue injection techniques for leak repair. The equipment was pre-drilled with ф7mm holes for glue injection purposes, and it was found that there was a certain amount of acidic sludge in the equipment’s interlayer; this indicates that there are cracks in the tiles inside the equipment, and sulfuric acid has seeped into the interlayer through these small cracks. The acid in the interlayer accelerates the corrosion of the equipment’s steel casing at high temperatures, ultimately causing leaks on the surface of the equipment. We believe that the problem can only be resolved fundamentally by addressing all internal micro-cracks and filling the interlayer with an adhesive to bond the tiles to the steel shell into a single organic unit. 5 Repair status: Utilizing a mature domestic technology for sealing leaks by applying resin through film formation in tanks, high-pressure resin injection was carried out in April 2015 on the electroevaporation equipment in the purification system of the Copper Electrolysis Workshop, thereby completely resolving the leakage issue with that equipment. At the same time, due to the successful application of the tank film-forming technology in the electroevaporation equipment of the copper electrolysis workshop in the copper plant, good results have been achieved after 8 months of experimentation. Therefore, this technology has significant value for widespread adoption. 5.1 Repair process: The first step is to clean the area affected by corrosion and perforation; after it has dried, apply 3216 semi-solid composite repair material to it ； In the second step, a 10 mm316L steel plate is welded at the injection site ； file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image006.giffile:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image006.giffile:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image006.giffile:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image006.giffile:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image008.jpg file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image010.jpg file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image012.jpg file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image013.gif file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image014.gif file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image015.gif file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image016.gif file:///C:/Users/apple/AppData/Local/Temp/msohtmlclip1/01/clip_image017.gif Step 3: Drill ф7mm glue injection holes in the steel plate, and apply glue under pressure using a glue injection machine ； Step 4: Seal the injection hole ； During the repair process, zones were defined on the outside of the equipment, key areas were marked, and welded steel plates were used to repair the corroded parts of the equipment. The cavity areas of the equipment are filled under high pressure using 3216 semi-solid composite repair material, ensuring full and tight filling. Outside the equipment, glue is injected sequentially in each area using a high-pressure glue injection pump, to ensure that every area is fully filled. The injected glue fills the gaps between the tiles and lead plates, as well as between the stone-lead plates and steel plates, thereby bonding the three elements together. Once the glue reaches a certain pressure, it automatically seals any leaks in the grout gaps between the tiles, achieving complete leak prevention. While external construction is in progress, internal inspections are carried out; if any leakage of adhesive is detected, the external sealing work is temporarily halted while the issue is addressed internally as soon as possible. At this point, it is possible to switch to another area to continue the glue injection process. Once the material used for internal treatment has set after 2 hours, high-pressure glue injection can be carried out again at the location where leakage occurred previously. Repetitive high-pressure injection of adhesive at the equipment’s sealing areas ensures the quality of the project. 5.2 Condition after repair: After the repair work was completed, random inspections were carried out; all gaps inside the equipment were fully filled, and the repair materials had cured properly. 6 Economic feasibility analysis: The author, Zhang Rongze (13919245874), points out that based on the current operating conditions of the four electric evaporators, after unit #1 was repaired using the technology of film formation and glue injection in the tank body to seal leaks, the other three units had to be taken out of service due to severe leakage. Using the tank film-forming glue injection sealing technique to repair a unit costs only 20% of the cost of traditional maintenance. Moreover, the maintenance time is merely 1/5 of the traditional maintenance time. It offers obvious economic benefits; this maintenance model, which requires minimal investment yet yields great results, fully meets the current requirements for lean maintenance. 7 Tank Film-Forming Glue Injection Sealing Technology 7.1 Introduction to Tank Film-Forming Glue Injection Sealing Technology The tank film-forming glue injection sealing technology (patent number 200710017693.3) is primarily used for repairing leaks in equipment with linings, such as towers, tanks, and vessels; this technology is easy and quick to apply. First, the leaking parts of the equipment are repaired by welding; next, injection holes are created on the surface of the equipment; finally, a 3216 semi-solid composite repair material is injected using a high-pressure glue injection pump, thereby bonding the steel structure, asbestos board, and tiles together to form a dense structural layer that prevents the medium from corroding the steel components of the equipment, achieving thorough repair. The main advantages of the tank film-forming adhesive sealing technology include: no need to shut down the system, no requirement to identify internal leakage points in the equipment, simple installation, wide sealing coverage, high strength, and reliability. Once the adhesive cures into a film, it can isolate corrosive substances from the equipment, while also repairing and protecting the equipment’s brick structure and outer steel plates, thereby creating a dense protective layer. 7.2 Performance characteristics of the materials used for sealing leaks: The 3216 semi-solid composite repair material is a patented product of Gansu Zhongshun Petrochemical Engineering Equipment Co., Ltd., and it fully meets the requirements of acid production equipment in terms of resistance to corrosive environments. The 3216 semi-solid composite repair material can withstand concentrated sulfuric acid and can cure completely under acidic conditions. Through extensive practical use in enterprises, the results are currently good. 3216 Technical specifications for semi-solid composite repair materials
Item | Technical parameters
Appearance | Light red viscous liquid
Viscosity /Pa·s (23±2°C) | 10
Specific gravity/d20 | 1.380–1.390
Setting strength/MPa | ≥10
Expansion ratio | 1–1.15
Adhesion strength/MPa | ≥1
Compressive strength/MPa | ≥7
Cold resistance/°C | -100
Heat resistance/°C | +850
Water impermeability of coating/MPa | ≥0.8
Acid resistance: When 98% concentrated sulfuric acid is heated to 100°C, the material is immersed for 24 hours; no change in weight is observed upon removal for testing.
8 Conclusion: Highly concentrated sulfuric acid has strong corrosive properties; if there is a leak in the equipment during production, it poses serious safety risks ； 2) Prolonged leakage can lead to premature disposal of the equipment ； 3) It will cause severe corrosion to the equipment and foundation, and may even force the system to shut down, resulting in production losses. Meanwhile, after acid is introduced during equipment production, repairing it with ordinary materials does not allow for proper curing, resulting in repeated leaks from the equipment. Following this construction work, all existing cracks in the equipment were repaired, and all gaps between the internal steel plates and tiles were fully filled, thereby completely eliminating the risk of leaks and ensuring normal operation of the equipment. Since its repair was completed in April 2015, the #1 electric evaporation tank has shown no signs of leakage, ensuring the proper operation of the system and improving production efficiency. In summary, the author recommends paying sufficient attention to lining equipment using high-temperature concentrated sulfuric acid or other media. If conditions permit, after the equipment has been heated, use an infrared thermometer to conduct a thorough inspection of the outer surface of the equipment; if temperature inconsistencies are detected (with a temperature difference of more than 10 degrees), the operation must be stopped for corrective action. Until the temperature difference between the devices is minimal. This can extend the equipment’s service life and prevent temporary shutdowns caused by leaks.