Fertilizer granulation is a key process for processing fertilizer raw materials into granular products, aimed at improving product performance, facilitating storage, transportation, and use. Spray granulation is one of the methods of fertilizer granulation. The following are the technical points and process analysis:

I. Principles of Spray Granulation

1. Atomization Process
   Molten or high-concentration slurry fertilizers (e.g., urea, ammonium nitrate solutions) are pumped to a nozzle under high pressure. Compressed air or centrifugal force atomizes the material into tiny droplets (50-200μm in diameter).

2. Heat and Mass Transfer
   Atomized droplets enter a granulation tower (or drying chamber), where they contact countercurrent or co-current hot air (typically 200-300°C). Moisture evaporates rapidly within 0.5-2 seconds, and solutes crystallize to form hollow granules.

3. Granule Formation
   Dried granules are cooled and screened at the tower base, yielding uniform spherical or near-spherical particles (usually 1-4mm) with excellent flowability.

II. Technological Advantages

1. Superior Product Performance
   • Rapid Dissolution: Hollow structure enhances nutrient release rate by 30-50%, suitable for fertigation systems.
   • Uniform Nutrient Distribution: Automated controls ensure nutrient deviation ≤1.5% per batch.
   • High Strength: Granule compressive strength ≥12N (reduces transportation breakage).
2. High Process Efficiency
   • Continuous Production: Single-tower capacity up to 20-50 tons/hour, ideal for large-scale industrial applications.
   • Energy Efficiency: Exhaust heat recovery reduces energy consumption by 15-20%.
3. Broad Raw Material Compatibility
   • Processes high-viscosity materials (e.g., liquid fertilizers with humic acid).
   • Adapts to diverse formulations (NPK compounds, micronutrient fertilizers) via nozzle adjustments.
4. Environmental Benefits
   • Low Dust: Closed-loop systems + baghouse filters achieve emissions ≤10mg/m³.
   • Zero Wastewater: Full material recycling eliminates process wastewater.

III. Typical Applications

• High-Analysis Compound Fertilizers: Production of 40-45% nutrient content KCl-based compounds.
• Water-Soluble Fertilizers: Manufacturing of rapidly soluble drip fertilizers (e.g., 15-15-15+TE formulas).
• Controlled-Release Fertilizer Carriers: Basis granules for resin-coated controlled-release products.

IV. Comparison with Other Granulation Methods

Metric	Spray Granulation	Disc/Drum Granulation	Extrusion Granulation
Uniformity	★★★★★	★★★☆☆	★★☆☆☆
Nutrient Content	40-50%	25-35%	15-25%
Energy Use	Higher (requires heat)	Low	Moderate
Investment Cost	High (complex equipment)	Low	Moderate
Feedstock Suitability	Molten/slurries	Powdered solids	Dry powders + binders

V. Technological Trends

1. Intelligent Upgrades: AI algorithms optimize nozzle design and airflow distribution to improve granule sphericity.
2. Green Retrofits: Biomass fuels (e.g., rice husk ash) replace coal to reduce carbon emissions.
3. Functional Extensions: Development of smart granules with microbial inoculants or nano-carbon materials.

Through spray granulation, enterprises can significantly enhance product competitiveness, meeting modern agriculture's demand for efficient, eco-friendly fertilizers. For example, one company adopting this technology achieved improved solubility (98% vs 85%) and nutrient use efficiency (42% vs 30%), while reducing production costs by 12%.