Granulation is the core process in NPK compound fertilizer production, transforming powdered nitrogen, phosphorus, and potassium raw materials into uniform, spherical granules. The quality of these granules directly influences the fertilizer's appearance, structural strength, dissolution rate, and performance in the field. Huaqiang Heavy Industry’s NPK production lines primarily utilize the rotary drum wet granulation method, while also offering disc granulation and extrusion granulation options to accommodate various production capacities and specific formulations.

Before granulation, raw materials must undergo pretreatment. Ingredients such as urea, monoammonium phosphate (MAP), and potassium chloride are crushed and ground into a powder of uniform fineness. They are then precisely measured according to the specific formula and thoroughly blended in a mixer. Some formulations may include binders, such as bentonite, to facilitate the subsequent pelletizing process. Achieving a homogeneous mixture is essential for stable granulation; otherwise, uneven nutrient distribution can easily lead to inconsistent granule sizes and significant variations in nutrient content.
Rotary drum granulation is the most common method used in large-scale NPK production lines. The blended powder is fed into an inclined rotary drum granulator. As the drum rotates slowly, internal lifting flights cause the material to tumble continuously. Simultaneously, water or steam is sprayed evenly into the drum; in some processes, a urea slurry is introduced to act as a liquid-phase binder. Through rolling friction and capillary forces, fine powder particles form initial nuclei, which then grow—much like a snowball—by accumulating surrounding powder until they become rounded, moist granules. Any fine powder that fails to form granules is screened out and returned to the granulator to be re-processed, ensuring a stable production cycle.
Disc granulation is typically employed for small- to medium-scale production. An inclined disc rotates continuously, causing the material to roll in a circular motion under the influence of centrifugal force, friction, and gravity. As a liquid-phase agent is sprayed onto the material, the powder accumulates in layers, gradually increasing in size until the finished granules spill over the edge of the disc. While this method requires a lower initial investment and offers straightforward adjustment, it has a limited production capacity and places higher demands on the adhesiveness of the raw materials. Roller extrusion granulation is a dry process; it requires no water addition or subsequent drying. Instead, it relies on high-pressure compression by rollers to press dry powder into sheets, which are then crushed and screened to produce granules. This method is well-suited for formulations that are sensitive to high temperatures or require high nutrient concentrations. The resulting granules possess high hardness, though their sphericity is generally lower.
In contrast, freshly produced "wet" granules have a high moisture content and cannot be sold as a finished product immediately. They must first undergo hot-air drying, followed by cooling, and then be classified via screening to remove oversized clumps and fine dust. Finally, a the granules are coated with an anti-caking agent before being packaged and placed into storage.
In short, wet granulation relies on liquid-phase bonding and rolling-induced agglomeration, whereas extrusion granulation relies on mechanical compaction. Each granulation method offers distinct advantages; for farmers, NPK granules that are uniform and spherical are easier to spread, ensure a steady release of nutrients, and help minimize waste.