NPK compound fertilizers, due to their balanced nutrients and wide applicability, have become a core fertilizer in agricultural production. However, caking has long plagued the industry—caking results in poor flowability, inconvenient application, and reduced product value. Fertilizer caking is essentially caused by the dissolution and recrystallization of granule surfaces, forming "crystal bridges," or by granule adhesion due to moisture absorption and compression. Therefore, a comprehensive anti-caking system needs to be established at every stage of the NPK fertilizer production line.

Raw material pretreatment is the foundation of anti-caking. In NPK production, the moisture content of hygroscopic raw materials such as urea and ammonium chloride must be strictly controlled. Before storage, the moisture content should be reduced to below 0.5%, and prolonged exposure to high humidity environments should be avoided. The formulation ratio needs to be optimized in the batching stage to reduce free water and easily crystallizing components. Potassium chloride can be appropriately added to replace some ammonium chloride to reduce the system's hygroscopicity. Insoluble raw materials should be ultra-finely pulverized to ensure uniform mixing and avoid excessively high local concentrations that could lead to crystallization and adhesion. This forms the first line of defense against caking in the NPK fertilizer production process.
Production process optimization is the core approach. In the granulation stage, spray granulation or extrusion granulation technologies are preferred, controlling the particle size to 2-4mm to ensure rounded, smooth particles and reduce contact area. The drying process requires a low-temperature, high-volume airflow process to control particle moisture content below 1.0%, preventing surface melting and gelatinization due to high temperatures. During cooling, slow cooling is crucial to prevent excessive temperature differences between the inside and outside of the particles, which can lead to condensation and moisture absorption. After cooling, the particle temperature should be close to room temperature. The key lies in adding anti-caking agents. Commonly used physical anti-caking agents such as talc and diatomaceous earth should be evenly coated after granulation, with the dosage controlled at 0.5%-1.0%. Newer organic anti-caking agents (such as polyethylene glycol and fatty acid salts) can form a hydrophobic film, providing a more durable anti-caking effect.
Equipment and storage management are essential for ensuring safety. NPK production line equipment needs regular cleaning to prevent fertilizer residue from accumulating and agglomerating on the inner walls. Scraper conveyors or belt conveyors should be used for conveying to reduce compression and collision. Fertilizer should be stored in well-ventilated and dry warehouses, with relative humidity controlled below 60%. The fertilizer pile height should not exceed 3 meters, and a "first-in, first-out" (FIFO) principle should be followed. The storage period should not exceed 3 months. For batches prone to clumping, woven bags with inner bags containing moisture-proof film can be used, along with a desiccant placed inside the packaging.
Through strict control of raw materials, optimized processes, equipment maintenance, and standardized warehousing, the clumping rate of NPK fertilizer can be reduced to below 5%, ensuring product quality while improving production efficiency, providing stable and reliable fertilizer support for agricultural production.