Fertilizer granulation is a critical stage in processing powdery or slurry-based raw materials into uniform granules; it not only enhances fertilizer flowability and resistance to caking but also optimizes nutrient release efficiency, thereby meeting the demands of mechanized fertilization. The core process revolves around three major stages: "raw material pretreatment," "core granulation," and "post-processing." Although specific methodologies may vary, the underlying logic remains consistent; the complete workflow is detailed below, drawing upon the most prevalent industrial techniques.
Raw material pretreatment serves as the foundation for granulation and directly determines the quality of the resulting granules. First, core raw materials—such as nitrogen, phosphorus, and potassium compounds—must be screened to remove impurities and large agglomerates. Subsequently, crushing equipment is utilized to mill the materials into a uniform powder, ensuring thorough mixing in the subsequent stages. Next, in accordance with the specific fertilizer formulation, the various raw materials are introduced into a mixer—alongside binders and conditioning agents—in precise proportions. Simultaneously, moisture levels are carefully controlled as the mixture is blended to achieve a uniform consistency with an optimal balance of wetness and dryness, thereby creating the ideal conditions for granulation; this step requires strict adherence to formulation ratios to prevent any deviation in nutrient content.
Core granulation constitutes the central element of the entire process workflow. Currently, mainstream methods are broadly categorized into two types: "hot methods" and "cold methods." Hot methods—such as high-tower granulation and spray granulation—involve either melting the raw materials at high temperatures or preparing them as a slurry; after undergoing high-pressure atomization, the droplets are shaped into granules through cooling or hot-air drying. Cold methods—such as extrusion granulation—involve directly subjecting the dry powder mixture to high-pressure extrusion; the resulting mass is then crushed and screened to yield granules. This approach bypasses high-temperature stages, thereby preserving the activity of heat-sensitive components. Rotary drum granulation, meanwhile, remains the most widely adopted technique; it utilizes the rotation of a drum to tumble the raw materials while binders are sprayed onto them, causing the dry powder particles to agglomerate into granules—a method that strikes an optimal balance between cost-effectiveness and operational efficiency.
The post-processing stage is crucial for guaranteeing the quality of the finished granules; it primarily encompasses drying, cooling, screening, and packaging. The newly formed granules are first conveyed into a drum dryer, where hot air is applied to remove excess moisture, thereby reducing the water content to below 15% to prevent moisture absorption and caking during storage. Following drying, the still-hot granules enter a cooler to reduce their temperature, a process that enhances both the hardness and structural stability of the granules. Subsequently, the granules undergo classification via screening equipment to separate out any particles that are either too large or too small; substandard granules are returned to the pretreatment stage for reprocessing, while the qualified granules are weighed, packaged, and transferred to storage, thereby completing the entire granulation cycle.
Today, fertilizer granulation processes continue to undergo continuous optimization, with various methodologies being tailored to meet a diverse range of specific requirements. Regardless of the specific process employed, strict control over the parameters at every stage is essential to produce high-quality fertilizers characterized by uniform nutrient distribution, regular granule shape, and excellent durability during storage and transport—thereby providing a solid guarantee for enhancing the quality and efficiency of agricultural production.
