Disc and extrusion: A powerful combination on the NPK granulation line

In NPK fertilizer production process, disc granulators and extrusion granulators are often viewed as distinct paths—one relying on wet rolling and the other on dry, cold pressing. However, high-efficiency production lines often combine them to leverage the unique strengths of each. 1.Extrusion for the "Core," Disc for the "Sphere" A portion of dry powder is first fed into an extruder to form small cylindrical or flake-like granules, which serve as "nuclei" for the disc granulator. Inside the disc, the remaining powder is moistened with water and accumulates layer by layer around these nuclei, rolling and growing into larger spheres. The extruded nuclei offer high density and strength, providing a solid structural framework, while the disc process imparts a smooth, rounded appearance. This combination increases the pelletization rate by 15–20% compared to using a disc granulator alone, significantly reduces the recycle rate, and yields superior granule compressive strength. 2.Parallel Configuration and Formula-Based Selection A single workshop can be equipped with both types of machinery, allowing for flexible switching based on the specific formula. High-nitrogen formulas are often hygroscopic and sticky, making them prone to adhering to the disc and forming clumps; switching to dry extrusion eliminates the need for a drying stage. Conversely, high-phosphorus and high-potassium formulas granulate well in discs, producing aesthetically pleasing pellets, making the disc route the preferred choice. Integrating two granulation capabilities into one line dramatically improves equipment utilization. 3.Extrusion for the Base, Disc for the Coating For slow-release NPK fertilizers, a fertilizer compaction machine is first used to compress core nutrients into dense granules. These are then fed into a disc granulator, where a second layer of nutrient powder is applied to coat them. This creates a gradient structure—dense on the inside and looser on the outside—allowing for more controlled nutrient release. Disc granulators excel at "growth" (building size), while compactors excel at "compaction." The essence of combining them is to first ensure the material achieves the necessary density and strength, and subsequently acquires a rounded, uniform shape.