In a fertilizer production line, the granulation process is a critical hub for transforming raw materials into high-quality finished products. The precision of its process directly impacts the fertilizer's application efficiency, storage stability, and market competitiveness. A complete granulation process consists of three stages: pretreatment, core granulation, and post-processing, each of which adheres to stringent technical standards.
The pretreatment stage is the "first line of defense" for granulation quality. Organic fertilizer raw materials, such as livestock and poultry manure and crop straw, must first be fermented and composted before being crushed to an appropriate particle size using a crusher. Compound fertilizer raw materials, such as urea and monoammonium phosphate, are first crushed to the desired fineness while removing impurities such as stones and metals. Compound fertilizers are then precisely dosed according to the required nitrogen, phosphorus, and potassium ratios. Organic fertilizers require the addition of auxiliary materials such as bentonite and dolomite to adjust the nutrient profile. Finally, a twin-shaft paddle mixer is used to ensure uniformity and compliance with production standards.
The core granulation stage embodies the principle of "selecting the right process for the right fertilizer." Drum granulation, the mainstream process for compound fertilizers, involves adjusting the drum speed and introducing steam to regulate the material temperature, causing the material to tumble and agglomerate into granules within the drum. Organic fertilizers are more suited to agitator granulators, which utilize the mechanical extrusion force generated by high-speed agitation to compress the material into shape, resulting in a stable granulation rate. For small-scale production, disc granulators are suitable for low-concentration organic fertilizer production by adjusting the disc inclination and speed, offering relatively low equipment investment costs.
Post-processing determines the final product quality. Granulated granules first enter a drum fertilizer dryer, where hot air is applied to reduce their moisture content. They are then rapidly cooled to room temperature in a drum fertilizer cooler to prevent granules from clumping due to temperature differences. Next, a rotary vibrating screen screens the granules according to standards. Fine particles that fall through the screen are returned to the granulation stage for reuse, while larger particles that pass through the screen are crushed in a crusher for secondary granulation. Some high-end fertilizers are also coated, with a resin or sulfur coating sprayed on to enhance moisture absorption resistance and slow-release properties. Finally, an automatic packaging machine packages the granules according to standard specifications, completing the entire production process. From the refined processing of raw materials to the standardized output of finished products, every step of optimization in the granulation process is driving the fertilizer industry towards high efficiency, environmental protection and high quality.
