NPK fertilizer, a compound fertilizer containing the three key nutrients nitrogen (N), phosphorus (P), and potassium (K), provides comprehensive nutrients for crops. Its production requires multiple precision steps.
First, the raw material pretreatment stage begins. Nitrogen fertilizer raw materials, typically urea and ammonium chloride, need to be crushed into a fine powder of 80 mesh or larger. Phosphate fertilizers, typically monoammonium phosphate and superphosphate, need to be de-agglomerated and ground. Potassium fertilizers, primarily potassium chloride and potassium sulfate, are screened and decontaminated before being crushed. The three raw materials are blended according to crop requirements. For example, a fertilizer specifically for corn might use a 15:15:15 ratio of nitrogen, phosphorus, and potassium.
Next, the mixing and granulation stages begin. The pretreated raw materials are thoroughly agitated in a mixer, and an appropriate amount of water or a binder (such as bentonite) is added to maintain a moisture content of 20% to 30%. The granules are then granulated using wet granulation equipment. Rotary drum granulators are commonly used for this process because they are suitable for large-scale production. The material is rolled and agglomerated within the drum to form granules with a diameter of 2-4 mm. Disc granulators are suitable for small and medium-sized production capacity, and the granule size can be controlled by adjusting the inclination angle.
After granulation, the granules are dried and cooled. They first enter a rotary dryer at 60-80°C to reduce the moisture content to below 5% to prevent clumping during storage. They are then cooled to room temperature in a cooler to prevent condensation during packaging.
Finally, they are screened and packaged. The cooled granules are classified by a vibrating screen. The fine particles are returned to the granulation stage for reuse. Qualified granules enter a film coating machine, where they are sprayed with an anti-caking agent, weighed, and packaged.
The entire process of the nitrogen, phosphorus and potassium compound fertilizer production line requires strict control of the raw material ratio and particle quality to ensure that the nutrients in the finished fertilizer are uniform and the strength meets the standards to meet the nutritional needs of different crops at different growth stages.
