What is the process of fertilizer granulation?

Fertilizer granulation is a crucial process in converting powdered or liquid raw materials into granular products. It improves fertilizer flowability, prevents caking, facilitates application, and reduces nutrient loss, making it a core element of modern agricultural fertilizer production. While the process appears simple, it actually comprises three main steps: raw material pretreatment, core granulation, and post-treatment. Although different granulation methods vary, the overall process is consistent.

Raw material pretreatment is the foundation of granulation and directly determines granule quality. First, nitrogen, phosphorus, and potassium fertilizers must be pulverized to a uniform fineness. If organic fertilizer is used, it must first undergo fermentation and composting to prevent clumping during granulation. Then, according to the fertilizer formula, various raw materials are precisely mixed, and appropriate amounts of water or binders are added to adjust the material moisture to a suitable range, ensuring smooth granulation. This step is also crucial for ensuring uniform nutrient distribution within the granules.

Core granulation is the core of the entire process, and several mainstream methods exist. The most common type of granulation is rotary drum granulation, similar to "rolling glutinous rice balls." Material is rolled into granules within an inclined rotating drum through friction and compression generated by the sprayed liquid and the drum's rotation. This method is suitable for large-scale production of high-concentration compound fertilizers. Disc granulation relies on the centrifugal force of a rotating disc to roll and agglomerate the mixed material. This method is simpler, requires lower investment, and is suitable for small to medium-scale production of organic and compound fertilizers. Furthermore, extrusion granulation does not require high temperatures; it directly extrudes dry powder raw materials under high pressure, preserving heat-sensitive components such as microorganisms. It is widely used in organic fertilizer production.

Post-processing is the "finishing touch" of granulation, ensuring product compliance. The wet granules after granulation have a high moisture content and need to be dried in a drying device. Hot air is used to reduce the moisture content to within the standard range to prevent clumping and spoilage during storage. The dried granules are still at a high temperature and require cooling treatment to lower the temperature and increase granule strength, preventing breakage during transportation. Subsequently, sieving separates qualified granules from excessively large or small materials. Unqualified materials are crushed and returned to the granulation stage for reuse, achieving efficient utilization of raw materials.

Finally, the qualified granules are dusted, metered, and then quantitatively packaged, becoming the granular fertilizers commonly found on the market. Throughout the entire granulation process, every step requires strict control of parameters, such as humidity and rotation speed during granulation, and temperature during drying, to produce high-quality fertilizers with uniform particle size, moderate strength, and stable nutrients. Today, with technological advancements, new technologies such as high-tower granulation and coated granulation are being continuously applied, making fertilizer granulation more efficient and environmentally friendly, providing strong support for modern agriculture.