What are the core process steps in an NPK fertilizer production line?

NPK fertilizer, as a core source of nutrients in agricultural production, requires a multi-stage, precisely coordinated production line to scientifically transform nitrogen, phosphorus, and potassium raw materials into standardized compound fertilizers. The entire process is interconnected, with each step playing a decisive role in product quality and effectiveness.  The core process can be divided into five key stages.

Raw material pretreatment is the fundamental prerequisite for NPK fertilizer production. Workers first determine the nutrient ratio based on crop needs and soil conditions, selecting nitrogen sources such as urea and ammonium chloride, phosphorus sources such as monoammonium phosphate and diammonium phosphate, and potassium sources such as potassium chloride and potassium sulfate. The raw materials must be crushed to 80-100 mesh, removing impurities and ensuring uniform particle size, while controlling humidity below 50% to prevent caking. Precise metering is achieved through electronic belt scales and automatic batching systems, with a proportioning error controlled within 0.5%, ensuring accurate nutrient ratios.

Mixing and granulation are the core stages in forming fertilizer granules. The pretreated raw materials are transported to a twin-shaft mixer, where a small amount of binder such as bentonite is added and mixed at high speed for 10-15 minutes to form a uniform mixture. The mixture then enters a rotary drum or disc granulator, where the material is rolled by the rotation of the equipment, while atomized water or dilute phosphoric acid is sprayed, causing the material to gradually agglomerate into granules with a diameter of 2-4 millimeters. Particle size can be flexibly controlled by adjusting the equipment rotation speed and liquid spray volume.

Drying and cooling ensure granule stability. The newly formed wet granules have a high moisture content and must be immediately sent to a drum dryer, where they are rapidly dehydrated in 120-150℃ hot air, reducing the moisture content to below 2%. The dried granules can reach temperatures above 80℃ and need to enter a cooler for countercurrent heat exchange with cold air, rapidly cooling them to room temperature to prevent caking due to moisture absorption at high temperatures, while also enhancing granule strength.

Screening and post-processing ensure quality control. The cooled granules are graded by a vibrating screen. Qualified granules enter the finished product warehouse, while unqualified fine powder or large granules are returned to the crushing system for reprocessing, resulting in a raw material utilization rate exceeding 98%. Some production lines also include a coating process, spraying a hydrophobic coating such as paraffin or resin to improve moisture resistance. Finally, the finished product is weighed and bagged using an automatic packaging machine, and then stored in the warehouse or shipped directly from the factory.

The entire NPK fertilizer production line, through automated equipment and precise control, achieves efficient conversion from raw materials to finished products, ensuring balanced nutrients and improving the storage and application performance of the fertilizer, providing a solid guarantee for high-yield and high-quality modern agriculture.