Precise control of drying endpoint and duration in fluidized bed drying via proportional feedback: ensuring granule quality and process robustness.

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Citation abstract

Fluidized bed drying (FBD) is widely used in the drying of granular pharmaceuticals, but currently, manual adjustment of air intake and drying temperature is highly relied upon to control the moisture content of particles in the fluidized bed. This manual intervention is cumbersome, labor-intensive, and limited by the thermal inertia of industrial heating systems, hindering precise control. In this study, a control system for FBD was developed to overcome this inherent challenge. The system utilizes a proportional controller to precisely control the moisture content decline trajectory of granules, and air intake flow is used as the manipulated variable. The system's robustness was evaluated using two model materials with distinct physical properties: Cordyceps Fungus Powder (high moisture) and Xin Huang Tablet powder (low moisture). Results demonstrated that the system precisely achieved the target moisture content (e.g., 6.5%) within prescribed drying durations (standard, shortened, and extended). Crucially, despite dynamic airflow adjustments, sieving analysis revealed essentially consistent particle size distributions, indicating that the strategy maintains granule integrity without causing significant attrition. The system also exhibited strong adaptability to variations in drying temperature. This approach effectively resolves the technical challenge of precise endpoint control by overcoming thermal inertia while ensuring critical quality attributes (CQAs). By enabling flexible trajectory adjustments and consistent drying rates, the proposed strategy offers a practical solution for enhancing efficiency and automation in pharmaceutical FBD processes.