In recent years, spray drying has become a widely adopted technique in the pharmaceutical industry, particularly for processing heat-sensitive drugs and liquid formulations that are prone to degradation during concentration. Each drug substance presents unique requirements, making it essential for both manufacturers and users of spray drying equipment to pay close attention to key design and operational details. One of the critical aspects is maintaining cleanliness. Many APIs require production in a 100,000-grade cleanroom environment. Since spray drying plays a vital role in quality control, all components that come into contact with the material must be made of high-quality stainless steel, such as 316L for materials with strong corrosive properties. The drying chamber, cyclone separator, and filters should have smooth inner surfaces, no dead zones, and be easy to disassemble for cleaning. Due to the large size of the system, the entire dryer cannot always be placed in a clean area, so sealing is crucial to prevent external contamination. Another major challenge is the sticking phenomenon, especially in traditional Chinese medicine applications. Sticky walls not only complicate material collection but can also lead to substandard products 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 also key in spray drying, which is a continuous process. Key control points include feed concentration, inlet air temperature, pressure, and gas purity. Manual adjustments are impractical, so advanced control systems are necessary to ensure smooth operation, reduce product defects, and enhance safety. Different physical properties of the final product are required depending on its use. For instance, oral granules need good solubility, while dosage forms may require stable bulk density and flowability. Foam spray drying is a new technique that enhances these properties by foaming the feed before drying, resulting in porous, easily soluble particles. Additionally, particle shape can be controlled through atomization methods. Safety is another concern, especially when handling flammable solvents or oxidizing materials. Explosion-proof designs, inert gas (like nitrogen) usage, and closed-loop systems are essential to prevent hazardous situations. Environmental compliance is equally important. Fine particles from spray drying can cause dust pollution, requiring efficient separation systems such as bag filters or wet scrubbers to meet emission standards. When nitrogen is used, the system must be sealed and vented outside. Improving thermal efficiency remains a top priority. While domestic systems typically achieve 30-50% efficiency, foreign models with waste heat recovery can reach up to 70%. However, this is economically viable only at higher production scales. Using nitrogen and organic solvents in a closed system can further reduce costs. Overall, ongoing research and innovation are needed to optimize spray drying processes, reduce costs, and meet evolving industry demands.

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