Granulation is the core stage in the production of NPK compound fertilizers; it directly determines the physical form of the granules, nutrient uniformity, storage stability, and application efficacy. Currently, the industry's mainstream granulation methods fall into two broad categories: wet granulation and dry granulation. Among these, rotary drum granulation and extrusion granulation are the most widely utilized, while high-tower granulation is predominantly reserved for the production of premium-grade products. Manufacturers must make a scientifically informed choice by carefully considering their production capacity, raw material characteristics, and product positioning.

Rotary drum granulation is the quintessential example of wet granulation and currently stands as the preferred process for the large-scale production of NPK fertilizers. The underlying principle involves pulverizing and blending nitrogen, phosphorus, and potassium raw materials before feeding them into an inclined, rotating drum. By spraying steam or binding agents into the drum, the materials utilize the rolling friction generated within the drum to gradually agglomerate into granules. The resulting granules subsequently undergo drying, cooling, and screening to yield the final product. This process is characterized by its strong continuity and high output capacity, with a single production line capable of achieving a daily output ranging from several hundred to tens of thousands of tons. The resulting granules are round, uniform, and possess excellent flowability—making them ideal for commercial packaging and sales—while also ensuring uniform nutrient release that meets the requirements of most agricultural crops. However, this method necessitates the installation of auxiliary drying and cooling equipment, resulting in higher initial capital investment and energy consumption; consequently, it is best suited for large-scale industrial manufacturing enterprises.
Extrusion granulation falls under the category of dry granulation technologies and does not require the addition of substantial amounts of water or binding agents, making it a preferred choice for eco-friendly and energy-efficient production. The core mechanism involves feeding uniformly blended dry powder raw materials directly into an extruder, where they are subjected to high-pressure compaction between rollers to form thin sheets. These sheets are then crushed and screened to obtain granules that meet the specified size and quality standards. This process features a simple workflow and low energy consumption, as it eliminates the need for a drying stage. This allows for the effective preservation of nutrients within heat-sensitive raw materials, preventing degradation caused by high temperatures. Furthermore, the resulting granules exhibit high structural strength and resistance to breakage, thereby minimizing product loss during storage and transportation. However, the granules produced by this method tend to be irregular in shape and possess relatively poor flowability. Consequently, this technology is particularly well-suited for small-to-medium-sized enterprises (SMEs) and for the production of heat-sensitive NPK fertilizers, offering lower investment costs and greater operational flexibility.
High-tower granulation serves as the primary granulation method for premium-grade NPK fertilizers and is classified as a melt granulation process. In this method, molten urea is blended with phosphorus and potassium fertilizer raw materials and then sprayed downward from the top of a high tower. As the droplets descend, they undergo natural cooling and solidification to form granules. The granules produced by this process are smooth, round, and highly soluble, featuring a uniform distribution of nutrients. Furthermore, the process requires no additional drying steps and is characterized by a high degree of automation.
Furthermore, pan granulation—characterized by its simple equipment and low investment requirements—is well-suited for small-scale production by small enterprises. With the advancement of green agriculture, the energy-saving advantages of extrusion granulation are becoming increasingly prominent; meanwhile, drum granulation is reducing energy consumption through technological upgrades, while high-tower granulation is evolving toward intelligent automation. The selection of a granulation method requires balancing production capacity, cost, and product requirements to achieve simultaneous improvements in both production efficiency and product quality.