Granulation is the core process in NPK compound fertilizer production, with different granulator types offering distinct process routes, production capacities, and final granule characteristics. Huaqiang Heavy Industry identifies three mainstream types—disc granulators, rotary drum granulators, and roller extrusion granulators—which are the most frequently used equipment in NPK production lines.
A disc granulator is a wet-agglomeration granulation device. Featuring a simple structure and low initial investment, it is well-suited for small to medium-sized NPK processing plants. As the tilted, rotating disc turns, a binder is sprayed onto the powdered material, causing it to roll and agglomerate into spherical granules. The resulting granules exhibit high sphericity and an attractive appearance, with a granulation rate exceeding 85%. The equipment is flexible to adjust, allowing for easy monitoring of the granulation process, with a typical capacity of 0.5–5 tons per hour. Its drawbacks include limited single-unit capacity—requiring multiple units to be operated in parallel for higher output—as well as sensitivity to operator skill and the moisture content of the raw materials. Additionally, the finished granules require subsequent drying.

The rotary drum granulator is the primary equipment used in large-scale NPK compound fertilizer production lines and is the most widely applied type in the market. It consists of a tilted, slowly rotating cylinder equipped with internal lifting flights (lifters). Steam or water is introduced as a binder, and the material forms granules through continuous tumbling and collision within the drum. It is ideal for large-scale, continuous production, with a single-unit capacity reaching 5–30 tons per hour. It offers high versatility—allowing for the easy addition of secondary nutrients and micronutrients—along with low failure rates and simple maintenance. Its disadvantages include the need for auxiliary drying and cooling equipment, relatively high energy consumption, slightly lower granule sphericity compared to disc granulators, and a higher proportion of recycled material (fines/oversize). It is best suited for compound fertilizer plants with an annual output of 10,000 tons or more.

The double roller press granulator utilizes a dry granulation process, distinguishing it from the two aforementioned wet-granulation types. Dry NPK raw materials are fed directly between two counter-rotating rollers, where they are compacted under high pressure. The resulting material is then crushed and screened to produce pillow-shaped granules. This process requires no water addition or drying stages, offering a significant advantage in terms of energy efficiency. The equipment is highly versatile regarding formulations, resistant to material sticking, and features a short production cycle—making it ideal for moisture-sensitive or low-moisture formulations. However, the final product consists of flattened, pillow-shaped granules rather than spheres, which may be less visually appealing. Furthermore, this method imposes strict requirements on raw material fineness and powder flowability; it is best suited for scenarios involving stable formulations where the primary goals are cost reduction and energy-efficient production.

When selecting equipment, one should look beyond the initial price and consider factors such as production targets, fertilizer formulations, site conditions, and market demand. Disc granulation is the preferred choice for producing high-end, spherical granules, while drum granulation is better suited for large-scale production. If the objective is to eliminate the drying process and lower operating costs, roller compaction (extrusion) granulation is the optimal solution. A well-considered selection of equipment is essential to ensure that the entire NPK production line consistently yields high-quality compound fertilizer granules.