In NPK compound fertilizer production, granulation is the core shaping process, while drying and cooling are critical steps for ensuring product quality and stabilizing the production flow; both are indispensable and cannot be omitted. Although the regulation of temperature and humidity may seem simple, it directly determines the granule quality, storage stability, and application effectiveness of the fertilizer, making it a vital link in the production process.

The drying process lays the foundation for a stable granule structure. Freshly granulated fertilizer particles have a moisture content as high as 15% to 25%; they are soft in texture and structurally loose, making them highly prone to breakage and pulverization. If the drying process is skipped, these high-moisture granules fail to set properly and tend to stick together or form clumps during conveying and packaging. In standard production, a drum dryer precisely reduces the moisture content to between 2% and 5%. It rapidly evaporates free moisture from within the granules and hardens their outer surfaces, significantly increasing granule strength. This fundamentally prevents breakage and pulverization, ensuring the fertilizer granules remain uniform and intact.
The cooling process is crucial for ensuring long-term storage stability. After high-temperature drying, fertilizer granules can reach temperatures exceeding 60°C; the residual heat keeps any remaining internal moisture active. If packaged and stored immediately, this residual heat creates a hot, humid environment inside the bags, causing the fertilizer to absorb moisture, harden, and clump—or even leading to issues like mold growth and nutrient loss. A drum cooler lowers the granule temperature to ambient levels, locking in the stable structure, preventing moisture absorption and clumping during storage, and extending the fertilizer's shelf life.
Furthermore, these two processes directly safeguard nutrient content and application quality. High-temperature and high-humidity environments accelerate the decomposition and loss of nitrogen, phosphorus, and potassium, leading to nutrient imbalances and reduced fertilizer efficacy. Precise control of temperature and humidity during drying and cooling prevents thermal degradation and nutrient loss, ensuring the NPK nutrient ratio remains accurate and stable. Furthermore, the dried and cooled fertilizer granules are loose and uniform with excellent flowability, meeting the requirements for mechanized application and preventing issues such as uneven spreading or clogging.
In summary, the processes of drying (for shaping) and cooling (for stable storage) complement and support each other, each serving a distinct function. Omitting either step would result in substandard product quality, storage failure, and frequent production disruptions. Therefore, drying and cooling are indispensable core processes in NPK compound fertilizer production, serving as a crucial line of defense for ensuring product quality and production efficiency.