Repair of concentrated sulfuric acid dilution tank

Thread Content

In mid-September, our company was commissioned by Hebei Shengxue Dacheng Pharmaceutical Co., Ltd. to repair a 12,500L glass-lined equipment for diluting concentrated sulfuric acid, and we encountered several difficulties during the installation process. With the strong cooperation of the workshop, the repair was successfully completed. I. Basic information on the damaged equipment: The damaged equipment is a concentrated sulfuric acid dilution tank, used to dilute 98% concentrated sulfuric acid to 10% dilute sulfuric acid. Nearly 200 kilograms of concentrated sulfuric acid was added within 3 minutes. The location where concentrated sulfuric acid is added at the bottom of the reactor, measuring 30 cm x 30 cm, has suffered porcelain damage; the discharge outlet is corroded and has become thin enough to break apart, rendering it unusable. The top part of the glass-lined equipment is less than one meter above the roof, while the bottom part is 50 centimeters above the ground. If repairs or replacements are to be carried out without on-site work, it is necessary to remove the roof and use a crane to lift the equipment out, which is quite difficult. II. Causes of damage: Based on the conditions observed at the scene, it can be determined that when concentrated sulfuric acid was added to the bottom of the reactor, the flow rate was high and the addition time was short. Due to the high density of concentrated sulfuric acid, it reached the bottom of the reactor instantly, generating a large amount of heat from dilution; as a result, the temperature of the material rose to 200°C in an instant. The thermal shock caused the ceramic lining to crack and get damaged. The damage to the discharge port was caused by acid leakage due to poor sealing, which corroded the flange. III. Problems encountered during the repair process: Our company’s two repair techniques have their respective advantages and disadvantages. The layer formed by flame spraying cannot withstand highly oxidizing media; the concentration of sulfuric acid at the bottom must be very high. Using thermal spraying for repair is definitely not an option. Although Gufu Ning enamel repair agent can resist high temperatures and highly oxidizing media, it cannot tolerate aqueous solutions with relatively low concentrations. The material inside the tank is water, and after dilution the concentration is only 10%, which falls within the critical range for using this repair agent, so it cannot be utilized. Furthermore, the discharge outlet has become thin and corroded to the point of being punctured, rendering it unusable; even after simple welding repairs and anti-corrosion treatment, it is likely not to function properly. IV. The solution was determined through discussions and exchanges with the company’s production department and workshop supervisors; thermal spraying of ceramic powder was chosen for the repair of this equipment, and specific measures were taken to address the various issues that arose. The biggest challenge during the repair process is the excessively high concentration of sulfuric acid at the bottom of the tank; only by reducing this concentration can successful repair be achieved. After research, spray nozzles were installed inside the reactor; the addition of concentrated sulfuric acid was changed from being done through straight pipes to being done via spraying. Additionally, the flow rate of concentrated sulfuric acid was reduced and the time taken for its addition was increased. To address the actual problems of the discharge port becoming thinner and deteriorating, a new discharge port was fabricated to replace the damaged one. Regarding the issue of poor sealing at the discharge port flange, which led to leakage of dilute sulfuric acid and subsequent corrosion of the flange, experienced workers were assigned to carry out the work during construction. Anti-corrosion coating was also applied to the flange edges at the discharge port, thereby completely resolving the problem of corrosion of the flange caused by the leaking sulfuric acid. After one month of use, the repaired glass-lined equipment was inspected; the repaired areas were in good condition with no signs of corrosion caused by concentrated sulfuric acid, indicating that the implemented countermeasures were correct and effective.