A Multi-Belt Dryer (MBD) is an advanced version of the single-belt dryer. Instead of one conveyor, it has two or more belts arranged in multiple tiers (one above the other) inside a drying chamber. Material passes sequentially from one belt to the next, allowing longer residence time, better space utilization, and improved drying control.
🔹 Working Principle – Multi-Belt Dryer
- Feeding – Wet material is evenly spread onto the top belt.
- Drying chamber –
- Air is circulated horizontally or vertically across the belts.
- As material moves along the belt, it gradually loses moisture.
- At the end of one belt, material is transferred (via drop chute) onto the next lower belt.
- Multi-stage drying – Each belt stage can have different drying conditions (temperature, air velocity, humidity).
- Discharge – Final dried product is collected from the last belt.
🔹 Key Features
- Multi-level design – 2 to 5 belts (or more) stacked vertically.
- Compact footprint – Longer drying path within smaller floor area.
- Staged drying – Different zones allow gentle initial drying, followed by higher temperature final drying.
- Even air distribution – Fans & ducts provide uniform drying across belts.
- Energy efficiency – Heat recovery between stages.
🔹 Applications – Multi-Belt Dryer
- Food industry:
- Vegetables (onion, garlic, carrot, spinach, peas)
- Fruits (apple, mango, berries)
- Herbs, spices, tea, instant coffee, noodles, pasta
- Chemicals: catalysts, polymers, fertilizers, resins, silica gel
- Pharmaceuticals: herbal extracts, granules
- Biomass: wood chips, algae, animal feed
🔹 Advantages
✅ Higher throughput compared to single-belt dryers
✅ Compact design (saves space)
✅ Gentle & uniform drying (good for heat-sensitive products)
✅ Flexibility – each zone controlled separately
✅ Continuous, automated operation → reduced labor
🔹 Limitations
❌ Higher capital cost than single-belt dryers
❌ Maintenance is more complex (multiple belts, fans, transfer chutes)
❌ Not suitable for sticky, pasty, or very wet feed materials
❌ Drying capacity limited by layer thickness (usually 10–100 mm)
🔹 Typical Design Parameters
- Number of belts: 2 – 5 (sometimes more)
- Belt width: 0.8 – 2 m
- Belt length (per tier): 5 – 20 m
- Drying temperature: 40 – 150 °C (product dependent)
- Air flow: cross-flow or counter-flow, recirculated with exhaust
- Residence time: 20 – 120 minutes (adjustable via belt speed)
- Moisture reduction: typically 70–85% → 5–10%
