“One-Dry, Two-Cool” is a core post-processing technology in the large-scale production of compound fertilizers. Through a closed-loop design of “one precise drying + two gradient cooling,” it precisely controls the moisture content and temperature of the granules, significantly improving the mechanical strength, moisture resistance, and storage stability of the compound fertilizer. It is suitable for various fertilizer types, including NPK compound fertilizers and organic-inorganic compound fertilizers, and is a standard process solution for high-end compound fertilizer production lines.
Core Process Flow and Technical Details
I. Overall Process Link: Wet granules after granulation → First drying (removal of free moisture) → First-stage cooling (rapid cooling and shaping) → Second-stage cooling (precise temperature control and dehumidification) → Finished product screening → Packaging and storage. The entire process achieves the processing goals of “controllable moisture, stable temperature, and dense granules.”
II. Core Configuration and Functions of Each Stage
(I) Primary Drying: Laying the Foundation for Quality
Core Equipment: A Φ2.0×20-meter drum dryer (suitable for 15-20 tons per hour) is selected, employing hot air circulation heating. The heat source can be natural gas, biomass pellets, or steam.
Key Parameters: Drying temperature is controlled at 80-100℃, material residence time is 15-20 minutes, reducing the moisture content of the granulated pellets from 25%-30% to below 12%, with a drying uniformity error ≤2%.
Technical Highlights: The dryer features a built-in spiral lifting plate layout, ensuring thorough material rotation and uniform heating; equipped with temperature and humidity sensors for real-time data feedback, and an automatic adjustment of hot air temperature and drum speed via a PLC system to prevent localized over-drying or incomplete drying.
(II) Primary Cooling: Rapid Shaping and Increased Strength
Core Equipment: A Φ1.8×18-meter counter-current cooler is configured, precisely matched to the dryer’s capacity, employing a room-temperature air counter-current heat exchange design.
Key parameters: Rapidly cools dried granules from 60-80℃ to 35-40℃ in 12-15 minutes, increasing granule strength from 1.5MPa to over 2.5MPa, effectively preventing pulverization during transport.
Technical highlights: The cooler features a built-in air guide device to enhance heat exchange efficiency between airflow and granules; the outlet is equipped with a pulse dust collector to collect dust generated during cooling, with a dust emission concentration ≤10mg/m³.
(III) Secondary Cooling: Precise Humidity Control for Stable Quality
Core equipment: A Φ1.5×15 meter co-current cooler (or fluidized bed cooler) is used as a supplementary optimization step to the primary cooling.
Key parameters: Further reduces granule temperature to room temperature ±3℃, stabilizing moisture content at 8%-10%, while removing trace amounts of residual free moisture from the granule surface, improving moisture resistance.
Technical Highlights: Utilizing a low-temperature, low-wind-velocity design to prevent granule surface cracking; the cooling airflow can be flexibly adjusted according to ambient humidity, adapting to different regional climates and ensuring the finished product is less prone to clumping even in high-humidity environments.
Core Process Advantages and Application Value:
Significantly Improved Quality: Compound fertilizer treated with “one-drying, double-cooling” achieves a granule strength of 2.5-3.0 MPa, reduces moisture absorption by over 40%, and extends shelf life to over 12 months, solving the pain points of conventional processes such as easy pulverization and clumping.
Stable Production Efficiency: The entire process seamlessly integrates with the granulation stage, covering an hourly capacity of 5-30 tons/hour, adaptable to different production lines; high degree of automation, with real-time monitoring of parameters at each stage through a central control system, reducing manual intervention.
Environmentally friendly, energy-saving and highly adaptable: The drying stage adopts hot air circulation technology, which reduces energy consumption by 15% compared with traditional drying processes; the dust removal system in the cooling stage achieves zero dust leakage and meets national environmental protection standards.
Wide Adaptability: It can flexibly adapt to compound fertilizers produced using different granulation processes such as rotary drum granulation and extrusion granulation. Whether it’s high-nitrogen, high-potassium compound fertilizers, or organic-inorganic compound fertilizers, optimal processing results can be achieved through parameter adjustments.
Process Application Precautions:
Parameter Linkage Control: The drying temperature needs to be adjusted in conjunction with the humidity of the granulation raw materials to avoid incomplete drying due to excessive humidity or granule cracking due to excessively low humidity.
Equipment Maintenance Points: The dryer’s inner wall needs to be cleaned regularly to prevent material buildup and maintain heat exchange efficiency. The cooler screen needs to be inspected regularly to prevent damage that could lead to granule mixing.
Raw Material Adaptation Adjustment: For compound fertilizers with high organic content, the drying temperature should be appropriately reduced (≤85℃), and the cooling time extended to prevent the decomposition and inactivation of organic components.
A Critical Stage in High-Quality NPK Fertilizer Production
The “One-Dry, Two-Cool” process is a vital final stage in the manufacturing of high-grade, durable NPK compound fertilizers. This sophisticated post-processing technology ensures the physical integrity and storage stability of the final product, directly impacting its market value and performance in the field.
This drying and cooling system is integrated as the finishing module within a complete npk fertilizer production line. It follows the core manufacturing stages, which begin with precise formulation using an npk blending machine or npk bulk blending machine. The blended materials are then shaped using advanced npk granulation machine technology, via equipment such as an npk fertilizer granulator machine. This entire sequence—blending, granulation, drying, and cooling—forms the complete npk fertilizer manufacturing process. The efficiency and scale of this integrated system, utilizing professional npk fertilizer granulator machine equipment, determine the overall NPK compound fertilizer production capacity and are fundamental to the overall npk fertilizer production technology that defines modern, high-output fertilizer plants.
Therefore, the “One-Dry, Two-Cool” process is not an isolated operation but an essential component that adds critical value within a seamless, technology-driven production chain, transforming raw nutrients into a robust, commercial-grade fertilizer product.