Diammonium Phosphate (DAP) fertilizer extrusion granulation is a dry granulation process that does not require chemical reactions or solution crystallization. It is suitable for scenarios requiring high particle strength and anti-caking properties, especially for water-sensitive formulas. Below is a detailed production process flow and key steps:

I. Raw Material Preparation and Pretreatment

1. Raw Material Selection
   • Main Raw Material: Diammonium Phosphate (DAP) powder (particle size ≤ 200 mesh, moisture ≤ 1%).
   • Auxiliary Materials: Added as needed based on formula requirements, such as potassium chloride, urea, ammonium sulfate, organic fertilizers, etc., to adjust nutrient ratios (e.g., N-P₂O₅-K₂O = 18-46-0 or other combinations).
   • Binder: Optional addition of a small amount of bentonite, humic acid, or polymer binder (1%-3% of total raw material) to enhance particle strength.
2. Raw Material Mixing
   • Equipment: Horizontal mixer or double-spiral conical mixer.
   • Purpose: Ensure uniform mixing of DAP with other raw materials to avoid local nutrient deviations.
   • Key Parameters: Mixing time of 10-15 minutes, with a mixing uniformity coefficient of variation (CV) ≤ 5%.
3. Raw Material Crushing and Screening
   • Equipment: Chain crusher or roll crusher.
   • Purpose: Pulverize raw materials into fine powder (particle size ≤ 100 mesh) to improve extrusion forming efficiency.
   • Screening: Remove large particles or impurities through a vibrating screen to ensure consistent raw material particle size.

II. Extrusion Granulation

1. Extrusion Granulation Principle
   Powdered raw materials are compressed into dense sheets or strips under high pressure (typically 50-150 MPa), then broken into particles.
   • Advantages: No need for drying or cooling processes, short process flow, high particle density, and strong anti-caking properties.
   • Disadvantages: Irregular particle shape (requires subsequent rounding), sensitive to raw material moisture.
2. Extrusion Equipment Selection
   • Roll Extruder:
     • Structure: Composed of two counter-rotating pressure rolls with grooves or grid patterns on the surface.
     • Working Method: Raw materials enter the gap between the rolls through a feeding device and are pressed into sheets.
     • Applicability: Suitable for large-scale production, with particle size determined by the roll groove size (typically 2-6 mm).
   • Ring Die Extruder:
     • Structure: Composed of a ring die and pressure rolls.
     • Working Method: Raw materials are extruded into strips through die holes.
     • Applicability: Uniform particle size but higher equipment cost.
3. Extrusion Process Parameter Control
   • Pressure: Adjusted based on raw material properties, typically 80-120 MPa for DAP-based fertilizers.
   • Roll Speed: 0.5-2 rpm, with lower speeds improving particle density.
   • Roll Gap: 0.1-0.5 mm, with excessively small gaps causing equipment wear and large gaps leading to loose particles.
   • Feeding Speed: Uniform feeding to avoid local overload or empty load.

III. Particle Crushing and Rounding

1. Crushing
   • Equipment: Hammer crusher or roll crusher.
   • Purpose: Break the extruded sheets or strips into coarse particles (particle size 3-8 mm).
   • Key Parameters: Crusher screen hole size selected based on target particle size (e.g., 4 mm screen for 3-5 mm particles).
2. Rounding
   • Equipment: Disc polisher or rotary rounding machine.
   • Principle: Improve particle surface smoothness through friction and rolling to enhance marketability.
   • Key Parameters: Rounding time of 5-10 minutes, with a rotation speed of 20-30 rpm.
   • Alternative: Omit this step if particle shape requirements are not high.

IV. Screening and Grading

1. Screening Equipment
   • Vibrating Screen: Multi-layer screens (e.g., 3 mm and 5 mm) separate qualified particles, fines, and coarse particles.
   • Rotary Screen: Suitable for continuous production with high screening efficiency.
2. Grading Treatment
   • Qualified Particles (3-5 mm): Proceed directly to packaging.
   • Fines (<3 mm): Return to the mixing process for re-granulation.
   • Coarse Particles (>5 mm): Crush and re-screen.

V. Surface Treatment (Optional)

1. Anti-Caking Treatment
   • Method: Spray anti-caking agents (e.g., mineral oil, diatomaceous earth, fatty acid salts) or coat with an inert powder (e.g., talc).
   • Equipment: Fluidized bed coater or rotary drum.
   • Dosage: 0.5%-1% of particle weight for anti-caking agents.
2. Coloring Treatment
   • Purpose: Improve product appearance and distinguish different formulas.
   • Method: Add pigments such as iron oxide red or chromium oxide green through mixing or coating.

VI. Packaging and Storage

1. Packaging
   • Materials: Polypropylene woven bags (lined with plastic film) for moisture and damage resistance.
   • Specifications: Typically 25 kg/bag or 50 kg/bag for ease of transportation and storage.
   • Equipment: Automatic packaging machine (weighing accuracy ±0.1 kg).
2. Storage Conditions
   • Environment: Cool and dry warehouse, temperature ≤ 30°C, relative humidity ≤ 60%.
   • Stacking: Elevated 10 cm above the ground, 30 cm away from walls, avoiding direct contact with ground moisture.
   • Shelf Life: 6-12 months under unopened conditions, with regular inspection for caking.

VII. Key Quality Control Points

1. Raw Material Quality
   • DAP purity ≥ 98%, moisture ≤ 1%, to avoid loose particles or caking due to raw material issues.
2. Particle Strength
   • Testing Method: Measure particle compressive strength using a pressure tester (≥15 N/particle for qualification).
3. Nutrient Uniformity
   • Sampling Inspection: Randomly sample each batch for N and P₂O₅ content analysis, with a variation coefficient ≤ 3%.
4. Caking Rate
   • Accelerated Caking Test: Place samples in an environment of 40°C and 80% humidity for 7 days, with a caking rate ≤ 5% for qualification.

VIII. Process Advantages and Limitations

1. Advantages
   • Simple Process: No drying or cooling required, with low equipment investment.
   • Low Energy Consumption: Only extrusion energy is required, with unit product energy consumption 30%-50% lower than spray granulation.
   • Dense Particles: Strong resistance to mechanical breakage, suitable for long-distance transportation.
2. Limitations
   • Particle Shape: Irregular, requiring additional rounding steps.
   • Raw Material Adaptability: Sensitive to moisture, with strict control of raw material moisture (≤1.5%).
   • Capacity Limitations: Single-unit equipment capacity typically lower than spray granulation processes.

IX. Application Scenarios

Extrusion granulation DAP fertilizer is suitable for:

• Production of high-concentration compound fertilizers (e.g., N-P₂O₅-K₂O = 15-15-15).
• Fertilizers requiring high particle strength for export.
• Areas lacking steam or heat sources (no drying process required).
• Organic-inorganic compound fertilizer production (can incorporate large amounts of organic materials).