In an NPK compound fertilizer production line, the granulator serves as the core piece of equipment. It performs the critical task of transforming a mixture of nitrogen, phosphorus, and potassium (NPK) powders into rounded fertilizer granules—a process that directly determines the appearance, structural strength, and nutrient uniformity of the final product. The rotary drum granulator, manufactured by Huaqiang Heavy Industry, is currently the most widely used type of equipment for wet-process NPK granulation.

Before the granulation process begins, raw materials—such as urea, phosphate, and potash, along with various additives—are precisely proportioned, pulverized, and thoroughly blended into a uniform powder. This mixture is then fed into the granulator’s drum. The drum is set at an incline of 3°–5° and rotated at a constant speed by a drive system. Inside the drum, a spray system introduces water or steam to act as a binding medium; in some processes, a small amount of additional binder may also be used. This creates a moist, adhesive layer on the surface of the powder particles.
Once inside the drum, the raw materials tumble continuously, driven by friction, centrifugal force, and gravity. As the moist, fine particles collide and adhere to one another, they form tiny "seed" granules (nuclei). As the material continues to roll forward, these nuclei attract and accumulate more dry powder from the surrounding mixture, growing layer by layer—a process known as agglomeration granulation. The interior of the drum is lined with rubber sheets, which prevent the material from sticking to the walls or forming crusts, ensuring that the resulting granules are well-rounded. By adjusting the drum's rotation speed, the feed rate, and the volume of liquid sprayed, operators can control the growth rate of the granules, maintaining a consistent final particle size of 2–5 mm.
As the material moves slowly along the incline toward the discharge end, the wet granules that have reached the target size are ejected and sent to a dryer. Any ungranulated fine powder or broken, undersized particles are screened out and returned to the granulator for further processing, thereby maximizing raw material utilization and minimizing waste. In addition to drum granulation, disc granulators—which form granules through the rotation of an inclined disc—can also be used in small-to-medium-scale NPK production lines and are simple to set up. Roller extrusion granulation is a dry process that requires no water or steam, making it suitable for formulations sensitive to moisture. However, wet drum granulation offers greater continuity and higher production capacity, making it well-suited for most NPK fertilizer manufacturing requirements.
The stable operation of the granulator is the foundation for subsequent processes, including drying, cooling, coating, and packaging. Any imbalance in moisture content, rotational speed, or feed composition can lead to issues such as excessive granule breakage, clumping, or inconsistent particle size. Precise control of granulation parameters is essential to produce NPK compound fertilizers with appropriate structural strength, resistance to pulverization, and balanced nutrient content—ensuring they meet the requirements for agricultural application, including mechanical spreading.