In recent years, spray drying has become a widely adopted technique in the pharmaceutical industry, especially for the production of solid dosage forms. This method is particularly valuable when dealing with heat-sensitive drugs or liquid formulations that are prone to decomposition during concentration. Each drug substance comes with unique requirements, and both manufacturers and users must pay close attention to key design and operational details to ensure optimal performance. One of the primary concerns is maintaining cleanliness. For certain active pharmaceutical ingredients (APIs), the production process must be carried out in a 100,000-grade cleanroom. The spray dryer, as a critical part of quality control, must be constructed with materials that meet hygiene standards. Stainless steel is commonly used, with 316L being ideal for corrosive substances. All components that come into contact with the material—such as the drying chamber, cyclone separator, and filters—should have smooth surfaces, no dead zones, and be easily disassembled for cleaning. Due to the large size of spray drying systems, it is often impractical to place the entire system within a clean area. Therefore, the system must be well-sealed to prevent contamination from external sources. Another challenge is the sticking phenomenon, which is common in the drying of solid preparations, especially traditional Chinese medicine. Sticking not only hinders material collection but can also lead to degradation over time. While process adjustments like solvent selection and parameter optimization help, the most effective solution lies in equipment design. Experts suggest measures such as using a sandwich drying tower, cooling the walls below 50°C, installing air brooms, and improving surface finish to reduce adhesion. Automation is essential for efficient operation. A closed-loop system requires precise control over parameters like feed concentration, flow rate, inlet air temperature, and pressure. Manual adjustments are difficult, so advanced control systems are necessary to ensure stability, reduce defects, and enhance safety. Spray-dried products must meet specific physical properties depending on their intended use. For example, bulk density and flowability are crucial for tablet formulations, while oral granules require fast dissolution. Foam spray drying—a newer technique—can improve these properties by foaming the feed before drying, resulting in larger, porous particles with better solubility. Additionally, particle shape can be adjusted through different atomization methods. Safety is another critical factor. When handling organic solvents, explosion-proof designs are mandatory, and inert gases like nitrogen are often used to prevent explosive mixtures. Environmental compliance is also important. Fine particles generated during spray drying can cause dust issues, so advanced filtration systems such as bag filters or wet scrubbers are needed to meet emission standards. Energy efficiency remains a challenge. While spray dryers typically operate with thermal efficiencies between 30% and 50%, advanced systems with waste heat recovery can reach up to 70%. However, this is economically viable only at high production volumes. Using nitrogen in closed systems can further reduce costs when organic solvents are involved. Overall, ongoing research and innovation are vital to improving the efficiency, safety, and cost-effectiveness of spray drying technology.

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