Titanium equipment chemical cleaning, authored by Xu Yazhou from Henan Industrial Vocational and Technical College in Nanyang, Henan (473000), is a set of course notes accompanied by a successful case study. This document outlines the challenges and solutions involved in the chemical cleaning of titanium heat exchangers used in the salt industry. Titanium is an outstanding engineering material known for its excellent corrosion resistance, thermal conductivity, high mechanical strength, and lightweight properties. It is commonly used in the production of reactors, heat exchangers, and other critical equipment in chemical and light industries. In particular, it is widely used in the evaporation and crystallization process of sodium chloride solutions to produce salt. The best heating equipment for this process is a titanium-based heat exchanger. One such example is the tube heat exchanger installed at Pingdingshan Zhongyan Xiaolong Co., Ltd., which has a heat exchange area of 1020 m², with each device featuring 1299 titanium tubes with a wall thickness of 1.5 mm. These tubes are expanded between upper and lower tube sheets. During operation, concentrated brine is evaporated under high negative pressure through the tubes, while superheated steam is introduced into the shell to heat the material. The system operates in series, with the first stage being referred to as the 1-effect heater. Over time, scaling occurs on the outer layer of the titanium tubes, primarily composed of magnetic iron oxide. This scale is hard, brittle, and significantly reduces heat transfer efficiency due to its poor thermal conductivity. The lower section of the tubes is particularly affected, and since the 1-effect heater is mostly free of fouling, the focus of the cleaning process is on the specific scale that forms in the heater. The presence of iron scale may be attributed to impurities in the water or iron salts found in the salt mines. During the mining process, water is injected into the ground to dissolve solid salt deposits, producing brine that is then sent to the salt-making equipment for evaporation and crystallization. Testing revealed the presence of small amounts of organic impurities, with a density of approximately 1.43. However, removing this iron scale through physical methods proved challenging due to the long 6300 mm titanium tubes vibrating under stress, causing them to collide and making high-pressure water ineffective. Therefore, chemical cleaning was identified as the most suitable method, provided the right cleaning agent was used. In the laboratory, scale samples were tested to determine the best cleaning solution. Although titanium is highly resistant to corrosion, it is a reactive metal, and the factory had strict requirements for the cleaning process. After testing, strong acids and alkalis were found to dissolve the iron scale, but these methods were rejected due to the manufacturer's requirement for weak acid or base conditions, with a pH range between 3.5 and 10.5. A chelating agent was ultimately selected, with citric acid and ammonia used to adjust the pH to 3.5–4.5. An appropriate amount of 901 additive was added to enhance the cleaning effect. After 8 hours of heating, the iron scale was completely dissolved without affecting the titanium material’s quality or hardness. Once the plan was confirmed to be safe, the cleaning procedure was implemented. The factory’s chief engineer reviewed the plan before sending it to Baoji Titanium Factory for approval. Due to the difficulty in controlling steam flow on the shell side, a controlled approach was used—introducing a large volume of steam into the cleaning system while carefully managing the flow to prevent tube damage. The cleaning solution was circulated, and solids were removed during the process. Throughout the operation, the factory’s quality control team monitored key parameters such as acid concentration, pH, temperature, and iron ion levels. The cleaning tank used was a 1.5 m³ corrosion-resistant container, approved by the factory’s security department. Tap water was sourced from a nearby fire hydrant. The cleaning agent was prepared and heated over a period of 7 hours, with two ammonia additions made midway. Afterward, the system was rinsed with hot water, and upon inspection, the descaling rate exceeded 98%, with no iron scale remaining on the titanium tubes. The results matched the laboratory findings, and both parties were satisfied with the outcome. Before construction, all pipe valves and joints were inspected to ensure they were in good condition. Ammonium citrate was used to dissolve rust, and any corroded pipes, especially welds, required careful attention to avoid complications during the process. In conclusion, chemical cleaning of titanium equipment is a complex and technically demanding task. It requires meticulous planning, strict adherence to procedures, and close quality control. The success of this project highlights the importance of thorough testing, proper selection of cleaning agents, and careful execution of the process. Adjustments must be made based on real-time chemical reactions, ensuring both safety and effectiveness. This case demonstrates that with the right approach, even the most challenging cleaning tasks can be successfully completed.

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