Granulation is a critical stage in organic fertilizer production; it transforms loose, composted organic raw materials into granular finished products. This process not only enhances the convenience of fertilizer application but also minimizes nutrient loss and extends the duration of fertilizer efficacy. The entire organic fertilizer production process involves a series of rigorous steps—including pretreatment, granulation and molding, drying and cooling, and screening and recycling—with each stage directly influencing the quality of the final product.
Pretreatment prior to granulation serves as the foundation and directly determines the success of the granulation process. First, it is essential to ensure that the raw materials are fully composted and that the fermentation temperature has dropped below 40°C to prevent any undecomposed organic matter from compromising granule stability. Simultaneously, the moisture content of the raw materials must be adjusted to an ideal range of 30% to 35%; excessive moisture can lead to granule agglomeration, while insufficient moisture necessitates the addition of binding agents to facilitate molding. Subsequently, the raw materials are processed using pulverizing equipment until at least 80% of the material passes through an 80-mesh sieve. This is followed by magnetic separation and screening to remove metallic impurities and stones, thereby preventing damage to equipment or blockages in the molding dies.
Granulation and molding constitute the core step, and the specific method employed is selected based on the characteristics of the raw materials. For organic-inorganic compound fertilizers, rotary drum granulation is frequently utilized; steam at a temperature of 40°C to 60°C is introduced to enhance material viscosity, causing the raw materials to tumble and agglomerate into granules within a rotating drum. For small-scale production, the more cost-effective disc granulation method may be chosen; this requires pre-drying the raw materials to a moisture content of ≤13%, relying on the centrifugal force generated by the rotating disc to roll the materials into spherical granules.
Following the molding stage, the granules undergo drying and cooling treatments. A low-temperature, high-airflow drying process (at ≤65°C) is employed to reduce the granule moisture content to below 8%, thereby preventing cracking while preserving the viability of functional microorganisms. Subsequently, the granules are cooled to ensure that the temperature differential between them remains ≤15°C, preventing clumping during storage. Finally, a screening system is used to sort out qualified granules ranging in size from 2 mm to 5 mm. Oversized granules are crushed and recycled, while fine powders are directly returned to the process for re-granulation, thereby establishing a closed-loop production system that minimizes raw material waste.
Throughout the entire granulation process, strict control of process parameters is essential, balancing both environmental sustainability and operational efficiency. Priority is given to the use of natural binding agents, and functional microorganisms are added *after* granulation to prevent their inactivation by high temperatures. Additionally, residual heat generated during the fermentation process can be harnessed to assist in drying, thereby reducing overall energy consumption. A scientific and standardized granulation process not only enhances the commercial quality of organic fertilizers but also renders them better suited to the application requirements of modern agriculture, thereby fostering the development of green agriculture.
