As the core equipment for dry granulation, the double roller press granulator has specific requirements regarding raw material compatibility. Understanding the types of NPK raw materials suitable for the extrusion process is a fundamental prerequisite for designing compound fertilizer formulations.

Nitrogen sources are the primary nutrient suppliers in NPK formulations, with urea being the most commonly used. Urea boasts a nitrogen content of up to 46%, uniform crystalline particles, and good flowability; its excellent plastic deformation capability under high pressure makes it an ideal nitrogen source for extrusion granulation. Ammonium sulfate and ammonium chloride are also frequently used; both are white crystalline powders with moderate hygroscopicity and stable extrusion molding properties, while also providing secondary nutrients such as sulfur and chlorine.

Regarding phosphorus sources, monoammonium phosphate (MAP) is the preferred choice for extrusion granulation. It supplies both nitrogen and phosphorus, appearing as a grayish-white powder with uniform particle fineness. Diammonium phosphate (DAP) can also serve as a phosphorus source, though its particles are relatively coarse, often requiring pre-crushing before use. Single superphosphate (SSP) and triple superphosphate (TSP) may also be added, but their usage in formulations should be limited, as they tend to cause moisture absorption and caking.

Among potassium sources, potassium chloride and potassium sulfate are the two mainstream choices for extrusion granulation. Potassium chloride offers high potassium content and cost-effectiveness, with a dense crystalline structure that ensures excellent extrusion molding performance. Potassium sulfate is suitable for producing fertilizers for chloride-sensitive crops; it features fine powder consistency and yields stable granulation results. Additionally, potassium salts containing secondary nutrients—such as potassium magnesium sulfate—can be added in appropriate amounts based on formulation requirements.

In addition to the three primary nutrient sources, raw materials providing secondary and trace elements (such as magnesium sulfate, borax, and zinc sulfate) and fillers/binders (such as zeolite powder, bentonite, and kaolin) are common components in extrusion granulation formulations. Overall, selecting raw materials with good crystallinity, high flowability, and moderate hygroscopicity is key to ensuring a smooth fertilizer compaction machine granulation process.