How is NPK Fertilizer Manufactured?

NPK fertilizer, a crucial nutrient source for agricultural production, undergoes multiple precision processes to scientifically transform the three basic raw materials of nitrogen, phosphorus, and potassium into compound fertilizer. This process can be divided into four core steps.

First, raw material preparation and pretreatment. Urea or ammonium nitrate is often used as the nitrogen source, while phosphorus comes from acid-hydrolyzed phosphate rock (processed into monoammonium phosphate or diammonium phosphate). Potassium is primarily sourced from potassium chloride or potassium sulfate. These raw materials are first placed in specialized silos. Moist, clumping raw materials are broken up by a crusher and then screened to create uniform particles. Each silo is equipped with an automatic metering device, and automatic batching system precisely controls the amount of material added according to the formula, ensuring a nitrogen, phosphorus, and potassium ratio error of no more than 0.5%, laying the foundation for subsequent mixing.

Next, mixing and granulation occur. The pretreated raw materials are conveyed to a double axis mixer, where a small amount of binder (such as bentonite) is added and high-speed mixing is used to create a uniform mixture. The mixture then enters a rotary drum granulator. As the drum rotates continuously, a spray system evenly applies atomized water or dilute phosphoric acid, gradually agglomerating the material into granules with a diameter of 2-4 mm. Particle size can be flexibly controlled by adjusting the drum speed and spray volume.

Next, drying and cooling occur. Freshly produced wet granules have a high moisture content and are immediately fed into a drum fertilizer dryer. Hot air at 120-150°C rapidly evaporates the moisture to less than 2%. The dried granules, which can reach temperatures exceeding 80°C, are then fed into a cooler where countercurrent heat exchange with cold air cools them down to room temperature. This prevents the granules from agglomerating due to moisture absorption at high temperatures and enhances their strength.

Finally, the finished product is screened and quality controlled. The cooled granules are classified by a vibrating screen. Those meeting the particle size standard are sent to the finished product bin. Unqualified fine particles or large lumps are conveyed to a return system, crushed, and then recycled back into the mixing process, achieving a raw material utilization rate exceeding 98%. From raw materials to finished products, every step of the NPK fertilizer production line must be strictly controlled, ultimately providing efficient and high-quality nutrient supply for agricultural production.