What is the granulation process for NPK compound fertilizer?

NPK compound fertilizer, containing the three core nutrients—nitrogen (N), phosphorus (P), and potassium (K)—is a commonly used fertilizer in agricultural production. Granulation is a crucial step in its formation, directly determining the fertilizer's particle strength, nutrient uniformity, and application effect. The overall process mainly relies on the NPK fertilizer production line and is divided into three stages: raw material pretreatment, core granulation, and finished product post-treatment.

Raw material pretreatment is the foundation of granulation. First, based on the fertilizer formula, basic raw materials such as urea, monoammonium phosphate, and potassium chloride are precisely proportioned, while binders such as bentonite and a small amount of functional additives are added. Then, the mixed raw materials are fed into a crushing device and crushed to 80-100 mesh fine powder to ensure uniform particle size and provide good material conditions for subsequent granulation. The crushed material also needs to be thoroughly mixed in a mixer to ensure consistent distribution of nitrogen, phosphorus, and potassium nutrients in the powder, avoiding uneven nutrient distribution in the finished product.

The core granulation stage is the core of the process, and the mainstream process currently is rotary drum granulation. Rotary drum granulation involves feeding mixed powder into the inclined drum of an NPK fertilizer granulator while simultaneously spraying steam or a binder solution. Under the centrifugal force and friction of the rotating drum, the powder gradually agglomerates into particles with a diameter of 2-4 mm. This process is suitable for large-scale production and has a relatively low cost. In addition, there is extrusion granulation, which uses mechanical pressure to directly compress materials into granules, suitable for the production of high-concentration compound fertilizers.

After granulation, subsequent processing is required. Wet granules first enter a drum fertilizer dryer, where hot air reduces the moisture content to 2%-3% to prevent granule agglomeration. The dried granules are then cooled to room temperature by a drum fertilizer cooler and screened to obtain products of the appropriate particle size. Larger granules are crushed, and finer powder is recycled and re-granulated through a return system. Finally, the qualified granules undergo coating treatment, being coated with anti-caking agents or functional coating materials to improve the fertilizer's anti-caking and slow-release properties. After weighing and packaging, they are ready for shipment.

The entire granulation process requires strict control of temperature, humidity, and material ratio in order to produce high-quality NPK compound fertilizer with uniform particle size, qualified strength, and balanced nutrients.