Biomass pellets look deceptively simple — a uniform cylinder of compressed organic material. But producing consistently high-GCV (>4200 Kcal/kg), low-moisture (<10%), low-ash (<2%) pellets requires precise control at every step of the manufacturing process. Here's how BBI does it.
Step 1: Raw Material Collection & Grading
BBI sources agro-waste from a network of farmers and aggregators within a 150 km radius of our Bakrol, Ahmedabad facility. Primary feedstocks include:
- Cotton stalks (high lignin, excellent GCV: 3800–4200 Kcal/kg dry basis)
- Groundnut shells (dense, low ash: 3.5–4.5% raw ash, reduced in processing)
- Mustard husk (high calorific, low sulfur)
- Wood waste (sawmill offcuts, furniture waste — highest GCV, 4400–4800 Kcal/kg dry)
Incoming raw material is tested for moisture content using a calibrated moisture meter. Any material above 40% moisture is pre-dried in open yard before entering production. Material with visible contamination (soil, plastic, stone) is rejected.
Step 2: Shredding & Size Reduction
Raw agricultural stalks and wood waste are fed into heavy-duty hammer mills or shredders. The goal is to reduce particle size to 5–20mm — the optimal range for even moisture removal and pellet die extrusion. Too fine (<2mm) produces dusty pellets; too coarse (>25mm) causes die jamming.
Step 3: Drying (The Critical Quality Step)
Freshly shredded biomass typically contains 20–40% moisture. The target for pelletization is 10–14% moisture (for the die entry). BBI uses rotary drum dryers fired by waste heat or a small biomass furnace to bring material to the correct moisture band without over-drying (which makes pellets brittle) or under-drying (which causes die clogging and soft pellets).
Step 4: Pelletizing (Ring-Die Extrusion)
Dried, sized biomass is fed into a ring-die pellet mill. A rotating roller forces the material through cylindrical holes in the die — the compression and friction generate heat (80–120°C), which activates the natural lignin in the biomass to act as a binder. No chemical additives are used. The extruded pellets (6mm diameter) are cut to 20–30mm length by a knife positioned at the die face.
Step 5: Cooling
Fresh extruded pellets exit the die at 80–90°C and are soft. They must be cooled to ambient temperature in a counter-flow pellet cooler before handling. Insufficient cooling causes pellets to crumble during transport. Properly cooled pellets should be hard, shiny, and produce a clean snap when broken.
Step 6: Screening & Quality Control
Cooled pellets pass through a vibrating screen to remove fines (broken pellets and dust below 3mm). Fines are recycled back to the shredder. A representative sample from each production batch is tested for: GCV, moisture, ash content, bulk density, and pellet durability index (PDI). Batches failing GCV or moisture specifications are rejected or reprocessed.
Step 7: Packing & Dispatch
Finished pellets are packed in 30 kg HDPE woven bags or loaded loose into bulk trucks (20–22 MT per truck). Each consignment is tagged with a batch number, production date, and QC certificate reference for traceability.
This rigorous 7-step process is why BBI consistently delivers 4200–4600 Kcal/kg GCV with <2% ash and <10% moisture. Contact us to schedule a plant visit or request a product sample.