[Question of the Week] How can the multi-effect evaporation method for high-salinity wastewater effectively address the problems of evaporator and pipeline corrosion?
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How does the multi-effect evaporation method for high-salt wastewater effectively address the problem of corrosion in evaporators and pipelines? During the multi-effect evaporation of high-salt wastewater, the saline solution causes severe corrosion within the equipment, as well as on the tubes of the heaters and the inner walls of pipelines. This corrosion particularly affects the welds and inner walls of pipelines made of 2507 material, leading to corrosion-related leaks. It is a bottleneck issue related to high-salt wastewater treatment equipment; apart from replacing the pipelines made of TAI material, are there any requirements regarding process operation parameters? Should ordinary carbon steel pipelines be lined with ceramic or polymer materials? Everyone discusses
The multi-effect evaporation method for treating high-salinity wastewater indeed faces challenges related to equipment corrosion and material selection. Here are several possible solutions: 1. **Material selection**: - **Use corrosion-resistant materials**: Such as the 2507 super duplex stainless steel you mentioned, which has good corrosion resistance and is suitable for environments with high levels of chloride ions. Additionally, titanium or titanium alloys can also be considered; although these materials are more expensive, they offer better corrosion resistance. - **Lining material**: For cost considerations, ceramic or polymer materials can be used as linings inside ordinary carbon steel pipelines. These materials can provide a protective layer to prevent corrosive agents from coming into direct contact with the metal surface. 2. **Process operation optimization**: - **Control the operating temperature**: High temperatures accelerate the corrosion process; reducing the operating temperature appropriately can slow down the rate of corrosion. - **pH control**: By adjusting the pH value and reducing acidic or extremely alkaline conditions, corrosion can be effectively slowed down. - **Adding corrosion inhibitors**: Incorporating an appropriate amount of corrosion inhibitors into wastewater, such as phosphates and silicates, can form a protective film on the metal surface to prevent corrosion. 3. **Regular maintenance and inspection**: - **Periodic inspection and maintenance**: Regularly inspecting the evaporator and pipelines to promptly identify and repair any signs of corrosion can effectively extend the service life of the equipment. - **Cleaning and descaling**: Regular chemical or physical cleaning is carried out to remove salt deposits and corrosion products inside pipes and equipment, thereby keeping the interior of the equipment clean. Through the comprehensive application of the aforementioned measures, the problem of equipment corrosion during the multi-effect evaporation of high-salinity wastewater can be effectively resolved. .
The main approach is to address the issue from the material perspective.
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The selection of evaporator material is closely related to the composition of the wastewater. Salts can be classified into chloride salts (such as sodium chloride and ammonium chloride) and non-chloride salts (sodium sulfate, ammonium sulfate, sodium carbonate, nitrates, etc.). Preferred selection order of materials based on chloride corrosion resistance: titanium, duplex stainless steel, carbon steel, and ordinary stainless steel. Preferred selection order based on cost-effectiveness: carbon steel, titanium, duplex stainless steel; ordinary stainless steel is the least favorable option. For non-heat exchange equipment, enameled carbon steel, PTFE can also be used; at low temperatures, polypropylene and fiberglass-reinforced plastic are viable choices. For corrosion resistance in the presence of non-chloride ions, the preferred order is: stainless steel 316L, stainless steel 304, and carbon steel. In terms of cost-effectiveness for non-chloride environments, the preferred choices are stainless steel 304 or stainless steel 316L, with carbon steel coming next. At low temperatures, materials such as UPVC, PE polypropylene, and fiberglass can be used. If you need products made of fiberglass reinforced plastic, feel free to contact us. Our company specializes in providing comprehensive FRP product solutions, offering high-quality, reliable, and durable FRP products to various industries to meet the needs of clients in different fields. Our products serve a wide range of industries, including but not limited to food, chemicals, environmental protection, water treatment, and energy. Whether you are building a new project or upgrading existing facilities, our products can meet your needs. From storage tanks, pipelines, towers, platforms, and stairs to protective barriers, our FRP products offer excellent performance and durability, ensuring the smooth progress of your projects and the achievement of desired results.
All the equipment and processes I designed in Shanxi for producing sodium thiosulfate from wastewater containing sulfide black are made of Q235 material and GB-3087 low-pressure boiler tubes. Currently, some of these installations have been in use for five years without any leaks. The composition of the raw water is 5% sodium chloride and 20% sodium thiosulfate; it isn’t just any solution containing chloride ions. Titanium materials must be used in all cases.
What are the temperature and pH values of this process? Based on our experience, titanium is the safer choice to try. However, carbon steel has indeed never been used. I asked for advice!
With a heating temperature of 120, an evaporation temperature of 95–98, an inlet pH of 8–9, and a constant pH for the saturated solution at the outlet, carbon steel can be used perfectly for solutions containing sodium chloride under these conditions