In fertilizer production, “granulation” is often considered a standard feature of production lines. However, a closer look reveals a distinction: blended fertilizer lines involve no granulation step from raw material to finished product, whereas organic fertilizer lines require powdered material to be rolled into granules. This difference is not merely a matter of equipment configuration; rather, the material state and product positioning diverge right from the start.
Blended Fertilizer: Raw materials are already granules; the line focuses only on proportioning and mixing.
The NPK blending fertilizer production line begins with finished granules such as urea, ammonium phosphate, and potassium chloride. These raw materials leave the factory with uniform particle size and sufficient strength, existing inherently as qualified granules. The production line’s task is not to re-granulate, but to mix the materials uniformly after precise weighing according to the formula. NPK blending machines utilize a double-shaft paddle structure where the two shafts rotate in opposite directions, creating a three-dimensional tumbling motion within the mixing chamber. Mixing typically takes 2–5 minutes, achieving a coefficient of variation (CV) for uniformity of ≤5% and keeping granule breakage below 0.5%. The precision of the entire line hinges on the batching system—a multi-bin, single-scale static batching setup that weighs each raw material individually, keeping the error margin within ±0.2%. Forcing a granulation step onto blended fertilizer would actually destroy the original granular form of the raw materials, generating fine powder and exacerbating segregation.
Organic Fertilizer: Raw materials are wet powders; granulation is essential for usability.
After fermentation and maturation, organic fertilizer raw materials exist as wet powders or fibrous clumps with a moisture content of 30%–50%, making them unsuitable for direct packaging or mechanical spreading. An organic fertilizer double-shaft mixer first blends the materials uniformly while using a water-spraying system to adjust the moisture content to the range required for granulation (25%–35%). Subsequently, the material enters an organic fertilizer disc granulator; rolling on the inclined disc surface—relying on its own moisture content—forms it into granules, achieving a granulation rate of 85%–95%. Disc granulation does not generate high heat, making it particularly suitable for bio-organic fertilizers containing beneficial microbes; the temperature is kept below 55°C throughout the process to prevent massive microbial die-off. After granulation, the pellets require low-temperature drying to reduce moisture content to below 15% before packaging and storage.
NPK granulation: sometimes necessary, sometimes not.
The existence of NPK granulators demonstrates that NPK *can* be granulated; however, this applies to a process route using powdered NPK raw materials—a completely different matter from blended fertilizers. Blended fertilizers utilize finished granules and do not require further granulation, whereas powdered NPK requires extrusion or disc granulation. Confusing the two leads to an awkward situation where a granulation machine purchased for a blending line sits idle.
Granulation is not a universal requirement for every fertilizer production line. If the raw material is already granular, physical blending suffices; if it is a wet powder, granulation is mandatory; if it contains live bacteria, temperature control must be maintained throughout both granulation and drying. One must first assess the state of the raw materials before deciding whether granulation is needed and which granulation method to employ.