1. Structure and Working Principle
- Rotary Kiln
- Structure: A horizontally or slightly inclined rotating cylindrical furnace driven by a motor.
- Working Principle: Material is fed into the high end and moves slowly toward the lower end as the kiln rotates. It interacts with high-temperature gas flow (from fuel combustion) in countercurrent or concurrent flow, completing calcination.
- Heating Method: Direct heating by combustion gases, with heat transferred via radiation, convection, and conduction.
- Shaft Kiln
- Structure: A vertical, stationary cylindrical furnace with a tall structure, often single- or multi-chambered.
- Working Principle: Material is loaded from the top and moves downward by gravity. Heat is supplied by hot air or fuel combustion at the bottom, and calcination occurs as the material descends.
- Heating Method: Fuel is typically burned at the bottom or sidewalls, with heat transferred upward via countercurrent hot air.
2. Calcination Characteristics
| Aspect | Rotary Kiln | Shaft Kiln |
|---|---|---|
| Uniformity | Material tumbles during rotation, ensuring even heating and stable product quality. | Material flows by gravity, prone to uneven heating; requires strict control of layer thickness. |
| Temperature Control | Flexible temperature adjustment, suitable for varying bauxite grades. | Less precise control; better for stable raw material composition. |
| Energy Efficiency | Lower thermal efficiency (heat loss), higher energy consumption. | Higher thermal efficiency (countercurrent heating), lower energy use. |
| Production Capacity | Ideal for large-scale continuous production (e.g., hundreds of tons daily). | Suited for small-to-medium output (e.g., tens of tons daily). |
| Cost | Complex equipment, high initial investment, and maintenance costs. | Simple structure, lower capital and operational costs. |
3. Application Scenarios
- Rotary Kiln
- Advantages: Uniform calcination, ideal for high-quality alumina production (e.g., low-iron, high-alumina refractory materials); handles a wide range of feedstock sizes (powder or lumps).
- Disadvantages: High energy consumption, large footprint, complex maintenance.
- Typical Use: Large-scale industrial production requiring consistent product quality.
- Shaft Kiln
- Advantages: Energy-efficient, suitable for small-to-medium batches; simple operation.
- Disadvantages: Requires uniform feedstock size (lumps), uneven calcination risks (overburning/underburning).
- Typical Use: Small refractory plants or scenarios prioritizing low energy costs over strict product specifications.
4. Environmental and Automation Features
- Rotary Kiln: Advanced exhaust treatment (e.g., waste heat recovery, desulfurization/denitrification); high automation.
- Shaft Kiln: Simpler emission controls, higher dust/gas management challenges; limited automation.
Summary
- Selection Criteria: Depends on production scale, feedstock properties (size, composition), energy costs, and product requirements.
- Rotary Kiln: Best for large-scale, high-quality, continuous operations.
- Shaft Kiln: Ideal for small-to-medium scale, cost-sensitive, or flexible production.
In practice, some plants combine both technologies (e.g., pre-calcination in a shaft kiln followed by refining in a rotary kiln) to optimize efficiency and output.
