In the production of NPK compound fertilizers, the granulator is a core piece of equipment that determines the product's shape, strength, and nutrient uniformity. Different process requirements and fertilizer formulations require a variety of specialized granulators, with rotary drum granulators, extrusion granulators, and disc granulators being the most widely used.

The rotary drum granulator is the workhorse of current NPK production lines, particularly suitable for producing medium- and low-concentration compound fertilizers. Its main unit is a rotating drum tilted at 3-5°. During operation, the mixed nitrogen, phosphorus, and potassium raw material powders, along with a 2%-3% clay binder, are fed into the drum. The drum rotates at 18-22 rpm, continuously tumbling and agglomerating the raw materials within the drum, gradually forming rounded granules measuring 2-4mm. This equipment offers high adaptability, allowing for adjustments to raw material ratios based on crop needs. It also boasts high production efficiency, with a single unit capable of producing 50-100 tons of raw material per day. It is widely used by large-scale fertilizer manufacturers.
Extrusion granulators are more suitable for producing high-concentration, binder-free NPK fertilizers. Their core components are a pair of counter-rotating extrusion rollers with specially shaped grooves. The mixed raw materials are fed between the rollers and directly compressed into granules under high pressure (15-20 MPa), eliminating the need for subsequent drying. This process eliminates the effects of binders on fertilizer purity, resulting in high-strength granules (compressive strength ≥ 15N) and uniform nutrient distribution. They are particularly suitable for producing fertilizers specifically for high-quality commercial crops such as tobacco and fruits and vegetables. However, their production capacity is relatively low, making them more suitable for small and medium-sized production lines.
Disc granulators, due to their simple structure and low cost, are commonly used in small NPK fertilizer production plants or for pilot production. They consist of a rotating disc tilted at 15-25°. Raw materials are fed into the center of the disc and gradually agglomerated into granules due to the centrifugal force and friction generated by the rotation of the disc. Workers can control particle size by adjusting the disc's speed and tilt angle, making it convenient to operate. However, the production process requires manual monitoring, resulting in low production capacity (average daily output of 5-10 tons), and relatively poor particle uniformity. This makes it suitable only for applications where product precision is not a high priority.
Different types of granulators have their own advantages and disadvantages. Manufacturers must make an appropriate selection based on their production capacity requirements, product positioning, and raw material characteristics to efficiently produce NPK compound fertilizers that meet market demand.