Comparison of Three Mainstream NPK Granulation Processes

Granulation is the core process in NPK compound fertilizer production lines, directly determining the physical quality of the granules, nutrient stability, and production costs. The three mainstream granulation processes in the industry are rotary drum granulation, disc granulation, and roller extrusion granulation. These processes differ significantly in their operating principles, production capacity characteristics, and raw material suitability, making them appropriate for fertilizer production lines of varying scales and formulations. A detailed comparative analysis follows.

Rotary drum granulation is the dominant wet granulation process for large-scale compound fertilizer plants. The equipment utilizes a continuously rotating horizontal drum combined with atomized binder spraying, causing raw material powders to agglomerate into granules through tumbling and friction. This process offers outstanding capacity and strong continuity, with single-unit outputs reaching 10–20 tons per hour. The resulting granules are spherical, strong, and nutrient-uniform; the process accommodates high, medium, and low-concentration NPK formulations and is compatible with sticky raw materials and the addition of trace elements. Drawbacks include high equipment investment and a large footprint; production requires auxiliary drying, cooling, and screening equipment, and overall energy consumption and maintenance costs are relatively high. It is best suited for large-scale production lines with an annual output exceeding 50,000 tons.

Disc granulation is a wet granulation process suited for small-to-medium-scale operations. It relies on an inclined, rotating disc where sprayed water causes powder to roll into spheres. Its core advantages include low equipment costs, operational flexibility, and a high granulation rate; the finished granules are spherical and of high quality. The process is easy to commission and has a short lead time from setup to production, making it suitable for organic-inorganic compound NPK fertilizers. Its limitations lie in limited single-unit capacity, slightly lower granule strength compared to the rotary drum process, and moderate stability during large-scale continuous production; it is best suited for small-to-medium processing plants and customized, small-batch fertilizer production.

Roller extrusion granulation is the only dry granulation process. It relies on high-pressure extrusion to compact dry powder materials into shape, eliminating the need for water addition, drying, or cooling, and allowing for direct screening and packaging. This process features extremely low energy consumption, zero waste emissions, and minimal investment costs. It is suitable for high-concentration and heat-sensitive NPK formulations, offering flexible formula switching and low material loss. However, the resulting granules are mostly elliptical or cylindrical with poor sphericity and low output capacity; while unsuitable for large-scale mass production, this process is an ideal choice for small-scale fertilizer plants or low-cost pilot facilities.

In summary, the rotary drum method is best for large-scale mass production, the disc method for high-quality small-batch production, and the extrusion method for low-cost, essential production; matching the process to specific needs can significantly enhance both the cost-effectiveness of the production line and product quality.