Dry Granulation of Potash Fertilizer: Principle and Application of Roller Extrusion Granulators

 In the potash fertilizer processing field, potassium chloride and potassium sulfate are the two most important varieties. However, these two types of potash salt raw materials have unique physical characteristics—they are easily hygroscopic and have poor flowability. When using traditional wet processes such as disc granulation or drum granulation, it is often necessary to add extra water or binders, and a large drying system is required afterward. This not only results in high energy consumption and a long process, but also easily leads to nutrient loss and insufficient particle strength. Addressing this industry pain point, dry granulation technology, represented by roller extrusion granulators, provides a new path of "waterless operation and one-time molding."

I. What is Extrusion Granulation?

Extrusion granulation is a relatively new dry granulation process. Its core principle is: under the strong extrusion force of a roller extruder, the air between the dry powder material is expelled, and the particle spacing is compressed to a sufficiently close position. This stimulates natural attractive forces such as van der Waals forces, adsorption forces, crystal bridges, and embedded connections between molecules, causing the material to agglomerate into a dense and hard block cake. This stage is called the "extrusion process"; the cake is then crushed and screened to finally obtain uniform granules, a process called the "granulation process." The strength of the granules mainly comes from intermolecular forces, not from added binders.

II. Structural Features of Roller Granulators Roller extrusion granulators employ ambient temperature dry high-pressure molding technology. The core working component is a pair of parallel, counter-rotating rollers. Material is evenly fed between the two rollers from above and compressed under high pressure. The equipment is typically equipped with a roller water circulation cooling system to effectively prevent material from sticking to the rollers due to frictional heating during extrusion, ensuring continuous and stable operation. The entire machine adopts a sealed, low-dust design, meeting clean production requirements.

III. Typical Applications in Potassium Fertilizer Granulation Extrusion granulation was first applied to the granulation of potassium chloride in the fertilizer field. Currently, granular potassium chloride (typically 1 to 4 mm) required for blended fertilizers (BB fertilizers) is primarily produced using the extrusion method. Besides potassium chloride, the double-roller extrusion granulator is also widely applicable to the dry granulation of various potassium fertilizer raw materials such as potassium sulfate, potassium nitrate, and Russian red potassium. The complete set of equipment can cover an annual production scale of 300,000 to 500,000 tons, with good capacity scalability.

IV. Core Advantages of the Anhydrous Process

Compared with traditional wet granulation, the "anhydrous process" of double-roller extrusion granulation exhibits significant advantages in several dimensions:

Significant energy saving and consumption reduction. No water or binder needs to be added throughout the process, eliminating the need for subsequent drying and cooling. The entire production process does not require coal combustion, and energy consumption is only 30% to 50% of that of traditional processes.

Simplified process and reduced investment. The process flow is significantly shortened, requiring less floor space, and the equipment is easy to operate, resulting in lower construction investment and a shorter construction period.

Excellent product quality. Granulation rate is as high as 85% to 95% or more, with high particle hardness and strength, and unaffected solubility—a characteristic crucial for the use of potassium fertilizer as topdressing and BB fertilizer raw material.

Environmentally friendly and clean. The entire production process involves no moisture introduction or drying, and generates no waste emissions, making it an energy-saving and environmentally friendly production technology.

V. Conclusion The dry granulation technology for potash fertilizer, represented by the roller extrusion granulator, features "physical extrusion, room temperature molding, and no drying required" as its core characteristics. It provides an efficient, energy-saving, and environmentally friendly processing route for hygroscopic and difficult-to-granulate potash fertilizer raw materials such as potassium chloride and potassium sulfate. Against the backdrop of continuously rising energy costs and increasingly stringent environmental requirements, this anhydrous granulation process is becoming an important technological direction in the potash fertilizer processing field.