How does a disc granulator convert powder or wet material into granules ?

In a fertilizer production line, a disc granulator is the core equipment connecting raw materials and finished granular fertilizer. It efficiently converts wet organic fertilizer and powdered chemical fertilizer into uniform granules, balancing nutrient retention and ease of application. The conversion process is divided into three steps based on fertilizer characteristics. Raw material pretreatment must be tailored to the fertilizer's characteristics. When processing fermented wet organic fertilizer, it must first be passed through a vibrating screen to remove impurities such as straw residue and stones, while also breaking up lumps and preventing nutrient uniformity in the granules. When processing chemical fertilizer powders (such as urea powder or phosphate rock), water or humic acid solution is added as a binder in appropriate proportions and stirred into a wet mix with a moisture content of 18%-22%. This moisture content ensures the fertilizer granules remain uniform while preventing nutrient loss due to excessive moisture. Pre-treated material is fed to the disc at a constant speed via a conveyor belt. The disc is tilted at a 48-52° angle to suit the specific gravity of the fertilizer material and balance centrifugal force and gravity. Core granulation focuses on the controllability of fertilizer particles. A motor drives the disc at 8-12 rpm. The wet fertilizer mix is ​​subject to three forces within the disc: centrifugal force forces it to adhere to the disc wall, friction prevents it from sliding, and gravity propels the material through circulation. The tiny "master particles" formed initially continuously absorb surrounding material, growing like a snowball. Operators monitor the process through an observation window. For compound fertilizer production, the rotation speed is adjusted to control particle growth and ensure uniform coverage of different nutrients. When the particles reach a diameter of 3-5 mm (a suitable size for fertilization), they roll off the edge of the disc. Particle optimization ensures fertilizer quality. The tumbled wet granules are first screened, with fine particles returned to the granulation machine, and oversized particles crushed and reused. They then enter a low-temperature dryer (to prevent high temperatures from damaging the nutrients in the organic fertilizer) to reduce the moisture content to below 10%. This results in finished granular fertilizer with high strength, low caking, and uniform nutrient content. The entire disc granulator machine process is designed specifically for fertilizer characteristics, transforming loose raw materials into granules while maximizing nutrient retention. It is a critical step in ensuring product quality in the fertilizer production line.