pelletization (pelletization)

Pelletizing is the mechanical process of forcing dried, finely ground organic material through a heated steel die under high pressure (150–300 bar) to produce cylindrical pellets typically 6–10 mm diameter and 15–25 mm long. For Indian CBG plant digestate, pelletizing converts dewatered solid fraction (25–30% DM) — after drying to 10–15% moisture — into a dense, shelf-stable, easy-to-spread fertilizer with bulk density of 600–700 kg/m³ (versus 200–300 kg/m³ for loose composted material).

The pelletizing line has four core steps: drying (rotary dryer or belt dryer using waste heat from the CHP engine, energy demand 800–1,200 kcal per kg of water evaporated), grinding (hammer mill to particle size below 4 mm), conditioning (steam injection to lift temperature to 70–85°C, softening lignin for binding), and die-press extrusion. Die-press throughput is typically 800–1,500 kg/hour for a 75–110 kW pellet mill, with binder addition (molasses or lignosulphonate, 1–3% by weight) sometimes used to improve pellet hardness above PDI 95.

Pelletisation delivers three commercial advantages over loose compost. Bulk density 2–3× higher cuts freight cost per tonne of nutrient by 50–65%, extending the viable transport radius from 100 km to 500–800 km. Mechanised application via standard fertilizer spreaders (versus manual broadcasting for loose material) cuts farmer labour cost by ₹400–600 per acre. Shelf life of 6–12 months versus 1–2 months for moist compost reduces working-capital tied up in finished inventory. The trade-offs are real: pellet line capex of ₹80 lakh–2 crore for a 2–5 TPH plant, drying energy of 200–400 kcal per kg of pellets produced (often 8–12% of plant biogas output if waste heat is insufficient), and FCO 1985 compliance for pelletised FOM requires the same NPK, pathogen, and heavy metal tests as bulk compost.

• Mechanical extrusion at 150–300 bar through a heated steel die produces 6–10 mm cylindrical pellets.
• Bulk density rises 2–3× to 600–700 kg/m³, halving freight cost per tonne of nutrient.
• Drying to 10–15% moisture is the prerequisite — typically uses CHP waste heat in Indian plants.
• Capex ₹80 lakh–2 crore for a 2–5 TPH line, payback usually 2–3 years on a 10 TPD CBG plant.