logo
2025-01-21

Coal and Biomass Pellet part-1 of 3?

Coal and Biomass General Information

Part 1 : Coal and Biomass Pellet General Information.
Part 2 : Coal and Biomass Pellet Process and Area Details.
Part 3 : Coal and Biomass Pellet Machines Details.

Lignin in Coal

Coal typically contains very low levels of lignin because lignin is an organic polymer primarily found in plants, not in the fossilized remains that constitute coal. Coal consists mostly of carbon, with varying amounts of other elements like hydrogen, sulfur, oxygen, and nitrogen, depending on the coal type (lignite, bituminous, anthracite). Lignin is associated with biomass materials like wood or plant residues, not coal.

Feasibility of Making 4mm Pellets from Coal

Coal-only pellets:

  • Challenges:
    Making 4mm pellets from coal is difficult because coal lacks the natural binding agents, like lignin, found in biomass. Lignin in biomass acts as a natural glue during pelletizing when heated under pressure, providing structural integrity to the pellets.
  • Solutions:
    • Adding a binder (e.g., starch, bentonite, or molasses) can help form coal pellets.
    • A high-pressure pellet mill may still be required to create dense coal pellets with sufficient durability.

Coal and Biomass Mix Pellets: Mixing coal with biomass can improve pellet formation and sustainability. The biomass in the mix provides lignin, which helps bind the materials together. Key considerations include:

  1. Proportions:
    • A typical mix ratio could range from 70% coal to 30% biomass to maintain a balance between calorific value and pellet strength.
    • Higher biomass content enhances binding but reduces calorific value and may increase ash production.
  2. Advantages of a Mixed Recipe:
    • Improved Binding: Biomass provides lignin, reducing the need for external binders.
    • Environmentally Friendly: Mixing biomass reduces the overall carbon footprint compared to coal-only pellets.
    • Flexibility: Mixed pellets can comply with renewable energy mandates in some regions.
  3. Types of Biomass:
    • Agricultural residues (e.g., rice husk, corn stalk, wheat straw)
    • Wood chips or sawdust
    • Napier grass or other energy crops

Pelleting Process

  1. Preparation:
    • Coal and biomass need to be crushed to a fine powder (below 1mm) for uniform mixing and pelleting.
  2. Mixing:
    • Ensure a homogeneous mix of coal and biomass to maintain consistent pellet quality.
  3. Conditioning:
    • Moisture content should be adjusted to 8-12% for efficient pelletizing.
  4. Pelletizing:
    • Use a ring die pellet mill with high-pressure rollers to compress the material into 4mm diameter pellets.
  5. Cooling:
    • Cool pellets to ambient temperature to harden and reduce brittleness.

Key Considerations

  • Calorific Value: Adding biomass reduces the calorific value of the final product compared to coal-only pellets. The balance depends on the application and energy requirements.
  • Ash Content: Biomass may increase ash content, which can impact applications like power generation.
  • Emissions: Mixed pellets produce fewer greenhouse gas emissions compared to coal-only combustion.

GCV (Gross Calorific Value) and technical specifications for producing 4mm coal-biomass mix pellets or coal-only pellets, along with relevant considerations.

1. GCV Considerations

The GCV of coal-biomass pellets depends on the ratio of coal to biomass:

Coal-Only Pellets

  • Anthracite Coal: ~7,500–8,000 kcal/kg
  • Bituminous Coal: ~5,800–7,200 kcal/kg
  • Lignite Coal: ~3,900–4,500 kcal/kg

Coal-Biomass Mix Pellets

The GCV decreases as the biomass proportion increases:

  • Biomass typically has a GCV of 3,500–4,500 kcal/kg (depending on type and moisture).
  • Example GCV for different coal-to-biomass ratios:
    • 90% coal + 10% biomass: ~6,800–7,500 kcal/kg
    • 70% coal + 30% biomass: ~6,000–6,500 kcal/kg
    • 50% coal + 50% biomass: ~5,000–5,500 kcal/kg

2. Technical Specifications

Raw Material Requirements

  • Coal:
    • Moisture Content: ≤8%
    • Size: <1 mm for even mixing and pelleting
  • Biomass:
    • Moisture Content: 10–12% (optimum for pelleting)
    • Size: <3 mm (after shredding)
    • Type: Sawdust, rice husk, wheat straw, corn stalk, or Napier grass

Pellet Machine

  • Type: Ring die pellet mill (preferred for hard materials like coal and biomass mix)
  • Capacity: Based on production needs (1–5 tons per hour typical)
  • Motor Power: 75–110 kW for a capacity of 4–5 TPH
  • Die Size: 4mm for pellet diameter
  • Roller Material: High alloy steel, wear-resistant
  • Compression Ratio: Adjusted to match material hardness (usually 1:6 to 1:8 for coal-biomass mix)

3. Process Flow

  1. Crushing:
    • Pulverize coal to <1mm particle size using a hammer mill.
    • Shred biomass to <3mm size.
  2. Drying:
    • Coal: Pre-dry if moisture exceeds 8%.
    • Biomass: Use a rotary drum dryer to achieve 10–12% moisture.
  3. Mixing:
    • Blend coal and biomass in a ribbon or paddle mixer to ensure uniformity.
  4. Pelletizing:
    • Compress the mixture using a ring die pellet mill.
    • Maintain die temperature at 80–100°C to soften biomass lignin.
  5. Cooling:
    • Cool pellets to ambient temperature using a counterflow cooler.
  6. Screening:
    • Remove fines and broken pellets to ensure uniform quality.

4. Equipment Specifications

EquipmentSpecification
CrusherCapacity: 5–10 TPH; Particle Size: <1mm (coal)
Rotary DryerInput Moisture: 25%; Output: 8–12%; Heat Source: Biomass or Gas
MixerCapacity: 5 TPH; Ribbon or Paddle Mixer
Pellet MillDie: 4mm; Capacity: 4–5 TPH; Motor: 90–110 kW
Counterflow CoolerCooling Efficiency: ≥90%; Output Temp: Ambient
Conveyor SystemMaterial: SS/MS; Capacity: 10–15 TPH

5. Example Scenarios for GCV and Recipe

Scenario 1: High Energy Output

  • Ratio: 90% coal + 10% biomass
  • Estimated GCV: ~7,200 kcal/kg
  • Application: Industrial boilers, power plants

Scenario 2: Medium Energy Output

  • Ratio: 70% coal + 30% biomass
  • Estimated GCV: ~6,500 kcal/kg
  • Application: Co-firing in thermal plants, heating

Scenario 3: Low Carbon Emissions

  • Ratio: 50% coal + 50% biomass
  • Estimated GCV: ~5,500 kcal/kg
  • Application: Renewable energy mandates, small-scale use

6. Benefits of Coal-Biomass Mix Pellets

  1. Reduced Carbon Footprint:
    • Lower CO₂ emissions compared to coal-only pellets.
  2. Cost-Effective:
    • Biomass is cheaper than coal in many regions.
  3. Renewable Component:
    • Biomass qualifies as a renewable energy source.
  4. Improved Combustion:
    • Mixed pellets have a better combustion profile due to reduced sulfur and ash content.

For more details or inquiries, please contact:

Tags: