Transfer of tartaric acid (C₄H₆O₆) through chemical pumps requires the use of mechanical seals that can effectively work with organic acid, resistant to corrosion and damage. Tartaric acid is not particularly aggressive compared to strong inorganic acids such as sulfuric or nitric acid, but it still requires special materials to ensure reliable sealing and durability of equipment.
1. Seal materials:
When it comes to tartaric acid, it is important to choose materials that have good resistance to organic acids, but are not too expensive, as tartaric acid is not extremely aggressive.
Seal faces:
Ceramic (silicon carbide or aluminum oxide): These materials have high wear resistance and good chemical resistance. They are ideal for aggressive liquids, such as organic acids.
Graphite: Graphite is resistant to many chemical substances, including organic acids, and can be used for seal faces. However, graphite is more brittle and is often protected by additional coatings or layers to increase service life.
PTFE (Teflon): This material is widely used in the chemical industry due to its resistance to organic acids. PTFE is suitable for sealing rings and other elements that may come into contact with tartaric acid.
Stainless steel (316 or 904L): Stainless steel works well with tartaric acid at moderate concentrations. For higher concentrations or temperatures, additional protection may be required.
Elastomers:
FKM (fluoroelastomer, Viton): This material has good resistance to organic acids, such as tartaric acid, and good temperature resistance. However, for concentrated solutions, it is better to use more resistant materials.
EPDM (ethylene-propylene-diene monomer): EPDM can be used for diluted solutions of tartaric acid. It works well at moderate temperatures and does not lose its elasticity when in contact with organic acids.
PTFE: As an elastomer, PTFE has excellent chemical resistance and can be used to seal connections that come into contact with tartaric acid.
2. Types of seals:
Mechanical seals: This is the most preferred choice for transferring tartaric acid. They create a tight connection, preventing liquid leakage and ensuring reliable pump operation.
Wet seals: These seals can be useful for preventing overheating and increasing seal durability. In the case of transferring tartaric acid, they can be used if cooling or additional lubrication is needed.
Dry seals: This is a less common design, but in some cases, they can be used to reduce the likelihood of overheating and wear if temperature and pressure in the system are controlled.
3. Design and additional mechanisms:
Dust caps and protective rings: These elements help prevent contaminants from entering the sealing area, which can increase the durability and performance of the pump.
Lubrication and cooling systems: In some cases (e.g., high temperature or more concentrated acid), a cooling system may be needed to prevent overheating and wear of the seals.
Seal condition monitoring: It is important to have a monitoring system in place to timely detect seal wear, especially when using complex chemical liquids.
4. Operating conditions:
Temperature: Tartaric acid is usually used at temperatures ranging from -10°C to 80–90°C. The seal must be resistant to these temperature ranges.
Acid concentration: Tartaric acid can be in various concentrations, from diluted to concentrated solutions. For high acid concentrations, materials more resistant to corrosion and wear should be chosen.
Pressure: The seal must be designed for the operating pressure in the system. Tartaric acid is usually pumped at moderate pressures, but it is important for the seal to withstand such loads.
5. Recommendations:
Ceramic or PTFE are ideal materials for seal faces, providing resistance to organic acids and durability.
FKM (Viton) or EPDM can be used for elastomers, especially in the case of more diluted solutions of tartaric acid.
Stainless steel 316 or 904L is excellent for metallic parts if the concentration of tartaric acid is not too high.
Conclusion:
For transferring tartaric acid, the best choice of mechanical seals is materials such as ceramic, PTFE, graphite, and stainless steel. Using FKM (Viton) or EPDM for sealing rings and other components ensures long-term equipment operation. Choosing the right materials based on concentration, temperature, and pressure will provide effective sealing and extend the pump's service life.