Granulation is the core stage of NPK compound fertilizer production lines, directly determining granule uniformity, nutrient stability, production costs, and efficiency. Currently, the industry's mainstream granulation methods include rotary drum wet granulation, double-roller extrusion granulation, and disc granulation, each suited to different scenarios. When considering standard formulations, large-scale production, cost-effectiveness, and product quality, rotary drum wet granulation emerges as the optimal choice for the vast majority of NPK compound fertilizer production, while the other processes are suitable only for specialized, niche applications.

Disc granulation is a traditional wet granulation process characterized by simple equipment structure, ease of operation, and low initial investment. It produces round, aesthetically pleasing granules and is suitable for standard NPK formulations, making it ideal for small-to-medium-sized fertilizer plants. However, the process has significant drawbacks: it relies heavily on the operator's technical expertise, and even slight deviations in material ratios, water spray volume, or pan rotation speed can lead to uneven granule sizes and low product pass rates. Additionally, single-line capacity is limited, mass production stability is poor, and continuous large-scale production is difficult to achieve. It also performs poorly in forming high-concentration compound fertilizers, making nutrient uniformity hard to control; thus, it is best suited for small-batch, multi-run custom production of standard compound fertilizers.
Double-roller extrusion granulation is a dry granulation process that requires no water addition or drying, resulting in low energy consumption, low investment, and simple operation—making it suitable for low-cost production by small-to-medium enterprises. However, its limitations are distinct: the finished granules are often irregularly cylindrical with poor roundness and average solubility; the granulation rate is limited; and production capacity is low, failing to meet large-scale mass production demands. Furthermore, the resulting compound fertilizers have limited market adaptability.
Rotary drum wet granulation is the industry's mainstream, universal process, perfectly suited for standard NPK compound fertilizer production. This process utilizes steam and slurry as binding agents to agglomerate materials into granules within a rotating drum; it offers a single-line capacity of 10–30 tons per hour and exceptional stability in mass production. The resulting granules are round, plump, and possess moderate strength; they offer good solubility and high nutrient utilization rates by crops. Furthermore, the N-P-K ratio can be flexibly adjusted to accommodate high, medium, and low-concentration formulations, meeting the diverse fertilization needs of both field crops and cash crops.
Compared to other processes, rotary drum wet granulation involves moderate equipment investment and low operating and maintenance costs, striking a balance between production capacity, product quality, and operational flexibility. Its only drawbacks are the need for auxiliary drying and screening equipment and slightly higher energy consumption than extrusion granulation. However, when considering overall product yield, market suitability, and the benefits of large-scale production, its comprehensive advantages far outweigh these limitations.

In summary, disc granulation is suitable for small-batch production of standard compound fertilizers, while extrusion granulation is an option for low-cost, niche production. For the large-scale production of general-purpose N-P-K compound fertilizers, however, rotary drum wet granulation offers the best balance of cost-effectiveness and practicality, making it the core process for mainstream compound fertilizer production lines today.