In fertilizer production lines, granulation is a crucial link between raw material processing and finished product formation. Its technological level directly determines the fertilizer's efficacy, storage stability, and ease of application. This process, through physical or chemical means, transforms powdery or lumpy raw materials into uniformly sized and appropriately strong granules, and is a core step in achieving industrialized mass production and efficient application of fertilizers.
The granulation process begins with raw material pretreatment. The crushed and mixed basic fertilizer raw materials (such as nitrogen, phosphorus, and potassium fertilizers, and organic fertilizer raw materials) must first meet specific conditions: moisture content controlled between 8% and 15%, and particle fineness requiring passage through a sieve of 80 mesh or finer, ensuring uniform mixing and the necessary viscosity for granulation. Some processes also add binders (such as bentonite or starch derivatives) at this stage to ensure successful subsequent granulation.
The core granulation stage primarily employs three mainstream processes. The most common method is rotary drum granulation. Raw materials are moistened by spraying and rolled within an inclined rotating drum, naturally agglomerating into granules. This method is suitable for large-scale compound fertilizer production. Next is extrusion granulation. Raw materials are pressed into flakes by a high-pressure extruder, then crushed and screened to obtain granules. This method is suitable for heat-sensitive raw materials and retains more active ingredients. Then there's disc granulation. Pre-treated powdered raw materials are fed into a rotating disc with an adjustable tilt angle, while atomized water or a binder is sprayed evenly. Under the combined action of centrifugal force, gravity, and friction, the raw materials gradually agglomerate into granules. This process is simple to operate and produces highly rounded granules, commonly used in small to medium-sized organic fertilizer and compound fertilizer production lines, especially suitable for applications requiring high granule appearance. Regardless of the process, strict control of parameters such as rotation speed, pressure, and temperature (disc granulation focuses on controlling the disc tilt angle and rotation speed) is essential to ensure that the particle size is concentrated within the optimal range of 2-4 mm.
The granulated granules then require post-processing. Freshly formed wet granules first enter a drum fertilizer dryer, where excess moisture is removed at 60-120℃, reducing the moisture content to below 5%. They are then cooled to room temperature in a drum fertilizer cooler to prevent clumping during storage. Finally, a screening machine separates substandard granules (those that are too coarse or too fine are returned for regranulation), followed by coating to improve their moisture resistance and slow-release properties, ultimately resulting in a qualified fertilizer product.
The granulation process, seemingly simple, is actually a fusion of multiple disciplines. It not only solves the problems of powdered fertilizers being prone to dust and having low utilization rates, but also achieves balanced nutrient release through granulation, reducing fertilization costs and environmental risks. It is a key technological support for the fertilizer industry's transformation from quantity to quality.
