NPK fertilizers, or compound fertilizers containing the three key nutrients nitrogen (N), phosphorus (P), and potassium (K), can precisely adjust nutrient ratios to meet crop growth needs and are widely used in agricultural production. Their production process requires multiple meticulous steps, each of which directly impacts the fertilizer's nutrient stability and effectiveness.

Production begins with raw material pretreatment. Nitrogen sources, such as urea and ammonium chloride, are often crushed to a fine powder of 80-100 mesh to prevent clumping and hinder mixing. Monoammonium phosphate and diammonium phosphate are commonly used as phosphorus sources and are dried to remove excess water, maintaining a moisture content of 1%-2%. Potassium sources, primarily potassium chloride and potassium sulfate, are ground to a particle size that matches the nitrogen and phosphorus raw materials to ensure uniform mixing.
This then leads to the core mixing and granulation steps. The automatic batching system first feeds pre-treated nitrogen, phosphorus, and potassium raw materials and fillers (such as talc and bentonite to prevent caking) into a double axis mixer according to a preset formula (e.g., common balanced and high-nitrogen types). The mixture is then thoroughly mixed under high-speed agitation. The mixed materials are then fed into the granulation equipment. Currently, there are two mainstream processes: rotary drum granulators are suitable for large-scale production. They inject saturated steam or a starch binder into the drum, causing the materials to bond during rotation, forming uniform, round granules. Double roller press granulators are suitable for producing high-concentration fertilizers. They use a die to compress the material into cylindrical granules, which are then cut into uniform lengths by a cutter. Both processes require sufficient compressive strength to prevent breakage during transportation.
After granulation, the wet granules are dried and cooled. The wet granules first enter the drum fertilizer dryer, where they are dried with hot air to strictly control the moisture content. This process requires precise temperature control: too high a temperature can easily cause nitrogen volatilization, while too low a temperature can lead to incomplete drying. The dried granules, still hot, are immediately fed into a drum fertilizer cooler where they are cooled to near room temperature via convection air from ambient temperature. This prevents the high-temperature granules from becoming moldy or clumping when they accumulate.
Finally, they undergo screening, packaging, and environmental treatment. The cooled granules are screened through multiple layers of vibrating screens to separate fine powder (returned to the granulation process for reuse) from large particles (crushed and reused in a crusher), retaining only qualified granules. Qualified granules are then packaged into film-lined woven bags using an automatic weighing and packaging machine, ensuring strict weight tolerance. The entire process utilizes a PLC automation system to monitor key parameters such as raw material ratio, granulation humidity, and drying temperature in real time, ensuring controlled nutrient content variations in each batch of NPK fertilizer and ensuring consistent and reliable product quality.