What are the stages of NPK fertilizer production?

NPK fertilizer, as a compound fertilizer with a scientifically balanced ratio of nitrogen, phosphorus, and potassium, requires precise control through five core stages in its production to achieve a balanced nutrient content and stable properties, meeting the agricultural demand for high-efficiency fertilizers.

The first stage is raw material pretreatment. The starting point of production requires the purification and pulverization of basic raw materials such as urea, ammonium chloride, monoammonium phosphate, and potassium chloride. Impurities and lumps are removed from the raw materials through screening equipment, and then the granules are ground to a fineness of 80-100 mesh to ensure uniform mixing and prevent large pieces from affecting equipment efficiency.

The second stage is mixing and proportioning. This is the key step in determining the nutrient content of the fertilizer. Based on the needs of different crops and soils, the proportions of nitrogen, phosphorus, potassium, and trace elements are precisely measured using an automatic batching system and fed into a mixer for thorough mixing. The mixing process must maximize the material contact area, typically using a double axis mixer, with the mixing uniformity error controlled within ±2%.

The third stage is granulation and molding. The pretreated mixture enters a granulator, where it undergoes processes such as drum granulation and extrusion granulation to form uniform granules of 3-5mm in size under the action of a binder. Drum granulation has become the mainstream process due to its strong adaptability and high output. It uses a rotating drum to roll the material and sprays atomized binder to agglomerate the powder into granules.

The fourth stage is drying and cooling. The freshly formed wet granules have a moisture content of approximately 15%-20%. They must first be dried in a drum fertilizer dryer with hot air at 120-150℃ until the moisture content is ≤2%. Then, they enter a cooler to exchange heat with room temperature air, lowering the granule temperature to around room temperature. This stage prevents the fertilizer from absorbing moisture and clumping, and also enhances granule strength and improves storage stability.

The fifth stage is screening and packaging. The cooled granules are graded by a vibrating screen. Unqualified fine powder is returned to the granulator for reprocessing, while qualified granules enter an automatic packaging system, packaged in standard sizes such as 25kg and 50kg, and simultaneously undergo weight detection and label printing before being stored for shipment.

These five stages are interconnected and constitute a complete NPK fertilizer production line. The entire process from raw materials to finished products relies on automated control and strict testing to produce NPK compound fertilizers that meet agricultural standards, thus ensuring high-yield and high-quality crops.