The Secrets of NPK Compound Fertilizer Production

NPK compound fertilizer, as the "nutrient steward" of agriculture, simultaneously provides three key elements: nitrogen (N), phosphorus (P), and potassium (K). Its production is a precise fusion of science and industry, with each step focused on nutrient balance and crop needs.

The first step in production is raw material selection and pretreatment. Nitrogen is primarily derived from urea (46% nitrogen) or ammonium chloride (25% nitrogen); phosphorus is obtained from monoammonium phosphate (44% phosphorus) and diammonium phosphate (46% phosphorus), avoiding alkalinity to prevent nutrient loss. Potassium is extracted from potassium chloride (for crops that are not sensitive to chlorine) or potassium sulfate (for crops sensitive to chlorine, such as tobacco and grapes). The raw materials are crushed to 80-100 mesh in a crusher and then screened using a vibrating screen. The moisture-absorbed urea is then dried in a 120°C hot air dryer to prevent agglomeration and equipment clogging.

The second step is mixing and batching. This is the core step in determining the nutrient ratios in fertilizer. Workers precisely weigh various raw materials according to preset recipes based on the needs of different crops using an automatic batching system. For example, wheat requires high nitrogen content during its growth phase, so the urea content is increased to 35%; fruit trees require high potassium content during their fruit-bearing phase, so the potassium sulfate content is increased to 28%. The raw materials are mixed in a twin-shaft mixer at 30 rpm for 15 minutes to ensure a nitrogen, phosphorus, and potassium distribution deviation of no more than 1%, eliminating "nutrient dead zones."

The third step is granulation. The current mainstream process is rotary drum granulation, suitable for producing medium- and low-concentration compound fertilizers. The core equipment is a rotary drum with a 3-5° tilt and a speed of 18-22 rpm. The mixed raw material powder is fed into the drum along with a 2%-3% clay binder. During rotation, the binder agglomerates the raw materials into rounded granules measuring 2-4mm. Some factories install a lifting plate inside the drum to enhance granule density. After granulation, the pellets enter a drum fertilizer dryer, where they are dried at 150°C with hot air until the moisture content is below 2%. They then enter a drum fertilizer cooler to cool to 40°C to prevent the hot pellets from accumulating, softening, and clumping.

Finally, they undergo screening and packaging. The pellets pass through three screens (5mm, 3mm, and 2mm). The coarse particles return to the crusher, while the fine powder returns to the granulation stage. Qualified pellets enter an automated packaging line and are bagged in 25kg or 50kg bags. The bags are labeled with the NPK content, production date, and suitable crops. Before shipment, samples are taken to test nutrients, pellet compressive strength (≥12N), and water solubility to ensure compliance with the national standard GB/T 15063-2020.

From raw materials to finished product, NPK compound fertilizer production is centered on precision, ensuring balanced nutrition and adapting to crop needs. It is a crucial support for stable production and increased income in modern agriculture.