Drum Fertilizer Cooler

Drum Fertilizer Cooler

The rotary drum cooler is a key piece of post-processing equipment used in production lines for granular fertilizers—such as organic, compound, and blended fertilizers—to rapidly lower the temperature of high-heat granules following the drying stage. Operating in tandem with a rotary dryer, it quickly cools hot granules (discharged at 60–80°C) to near-ambient temperatures (typically within 5°C of the ambient temperature). This process not only reduces granule temperature but also removes residual moisture, thereby enhancing granule strength.

During fertilizer production, while granules exiting the dryer meet moisture content standards, they retain significant internal heat. If these hot granules proceed directly to screening and packaging, issues such as moisture re-absorption (softening), clumping, and heat-induced spoilage are likely to occur. The rotary drum cooler’s primary value lies in its ability to restore granules to ambient temperature through physical cooling; this results in a denser, harder granule structure that is resistant to breakage and moisture re-absorption, significantly boosting the qualified product rate. Utilizing a counter-current cooling method, the equipment minimizes pollution, improves the working environment, accelerates cooling, reduces labor intensity, and increases output.

The rotary drum cooler features a horizontal rotating drum structure, fundamentally similar to that of the rotary dryer. Its main component is an inclined rotating drum; the synergistic action of the drum's rotation and internal lifting flights ensures uniform material turnover, while forced cold-air convection facilitates efficient cooling. Characterized by high cooling capacity, stable operation, high throughput, and ease of use, it is an essential piece of equipment in organic fertilizer production.

Structural composition of the equipment

The rotary cooler features a scientifically sound and rational overall structure, comprising the following core components:

(I) Rotary Cylinder: The main vessel of the equipment, consisting of a rotating cylindrical shell inclined slightly (typically 2–5°) relative to the horizontal. The cylinder is fabricated from high-quality carbon steel plate via rolling and welding; internal diameters range from Φ800mm to Φ2000mm, and lengths can be customized based on cooling requirements (typically 6–15 meters). Riding rings (tires) are mounted at both the front and rear sections of the cylinder to support it on the trunnion roller assemblies. Rotation is achieved via a large gear ring fixed to the cylinder, driven by the transmission system.

(II) Material Lifting Flight System: Core working components installed on the inner wall of the cylinder. These flights continuously lift and drop the material, ensuring full contact with cooling air to achieve uniform cooling. The flights may consist of 90°, 45°, or 135° angled plates, or a combination thereof; an organic combination of different flight types increases the material dispersion area and enhances cooling efficiency.

(III) Transmission System: Comprising components such as the electric motor, gearbox, pinion gear, and large gear ring. The motor drives the pinion gear through the gearbox (which reduces speed and increases torque); the pinion meshes with the large gear ring fixed to the cylinder, driving the cylinder to rotate continuously at a low speed. The large gear ring is mounted on the cylinder at a distance of 1 meter from the upper-end riding ring.

(IV) Support Device: Includes trunnion roller assemblies and thrust roller assemblies. The cylinder is supported on the roller assemblies via riding rings located 2.5 meters from each end. The lower-end riding ring makes rolling contact with the thrust roller to prevent axial sliding of the cylinder.

(V) Feed and Discharge Devices: Includes the feed chute and discharge outlet. Material enters at the higher end and flows out at the lower end after cooling. The discharge chamber is equipped with an exhaust and dust removal system.

(VI) Ventilation and Cooling System: Includes the induced draft fan (exhaust fan), air inlet, exhaust hood, etc. The suction from the induced draft fan accelerates airflow inside the cylinder. A counter-flow cooling method is employed, in which cold air enters at the discharge end and exits at the feed end, establishing counter-current contact with the material.

Application scope of the equipment

The rotary drum cooler has clearly defined and focused application areas. In the fertilizer industry, it serves as a core post-processing unit that follows the drying stage, utilizing forced cooling to lower the temperature of hot granules—such as organic, compound, blended, and bio-organic fertilizers. For blended fertilizers, it cools the product to the required temperature and particle size; for compound fertilizers, it cools the granules. It is also suitable for cooling other powdery or granular materials. The equipment is widely used in fertilizer processing plants and agricultural input manufacturing enterprises.

Types of usable raw materials

The rotary drum cooler is primarily designed to process various types of granular fertilizers, including organic fertilizer, compound fertilizer, blended fertilizer, bio-organic fertilizer, phosphate fertilizer, and ammonium sulfate granules. It can also be used to cool other powdery or granular materials.

The working principle of the equipment

The working principle of the rotary cooler relies on the synergistic effect of "drum rotation and material dispersion," "forced convective heat exchange with cooling air," and "axial movement driven by gravity." The process comprises three continuous stages:

Feeding and Distribution Stage: High-temperature granular material (typically 60–80°C) exits the dryer and enters the elevated end of the cooling drum via conveying equipment. Upon entering the drum, the material is lifted by internal lifting flights as the drum rotates.

Tumbling and Heat Exchange Stage: As the drum rotates continuously, the lifting flights on the inner wall repeatedly lift and scatter the material. The material forms a uniform curtain across the drum's cross-section, ensuring full contact with the cold air entering from the discharge end. An induced draft fan draws cold air in through the intake; driven by the fan, ducting, and exhaust hood, the air enters the drum's interior. Intense heat exchange occurs between the material and the cold air, with heat being carried away by the airflow. A counter-current cooling method is employed, meaning the cold air flows in the direction opposite to the material.

Discharge Stage: The cooled material—its temperature reduced to near-ambient levels (typically no more than 5°C above ambient temperature)—flows out through the discharge port. Residual trace moisture is also removed during the cooling process. Continuous, large-scale production is achieved through the steady, ongoing feed of material.

Equipment operating instructions

Preparation before starting up: Check whether there is any debris in the machine before starting up. Check whether all parts of the machine are normal. Check drive belt tension and gear lubrication. Check whether the induced draft fan is operating normally. Confirm that the inlet and outlet are clear and not blocked.

No-load trial operation: start the motor and make the cylinder rotate without load. Check whether the direction of rotation is correct. If it rotates in the opposite direction, stop and adjust immediately. Make sure the rotation is stable before feeding. Observe whether the cylinder swings smoothly on the supporting wheel.

Load operation: slowly feed the material, and adjust the cylinder speed according to the material temperature and feeding amount. The drum speed and air cooling air volume can be flexibly adjusted through the frequency conversion speed regulation system. Monitor whether the discharge temperature reaches normal temperature requirements. Pay attention to the motor current changes.

Shutdown operation: Stop feeding first, and then cut off the power supply after the material in the cylinder is emptied. Keep records of equipment use and maintenance.

Solutions to Equipment Problems

Insufficient cooling efficiency: Clean accumulated dust from the fan impeller and adjust the fan speed to the rated value; inspect lifting flights for wear and replace them promptly; ensure the feed temperature does not exceed the design limit; adjust the drum rotation speed to the optimal setting.

High particle breakage rate: Adjust the drum rotation speed to an appropriate range; optimize the angle design of the lifting flights.

Equipment vibration or abnormal noise: Stop the machine immediately for inspection; tighten loose bolts; inspect and replace damaged riding rings; adjust gear mesh clearance; replace damaged bearings.

Poor discharge flow: Regularly clear material accumulation inside the drum; check that the discharge valve opens correctly.

Air leakage at seals: Promptly replace worn or aged sealing rings; adjust the seal clearance.