The twin-shaft kiln operates on a principle of parallel flow calcination and heat recovery between its two shafts to achieve high efficiency and stable production. Here's a breakdown of its core working principles:
1. Parallel Flow and Heat Exchange
The two kiln shafts (A and B) are interconnected at the middle and lower sections, allowing materials and flue gas to flow in opposite directions. When shaft A is in calcination mode, combustion air and fuel are supplied to burn there. The resulting high-temperature flue gas then passes through the connecting channel into shaft B, where it preheats the limestone. Meanwhile, the cooled air is drawn into the bottom of shaft A, mixes with the outgoing gas, and is finally discharged. This parallel flow setup ensures highly efficient heat transfer and reuse
2. Temperature Control in Different Zones
The process is divided into three key temperature zones:
- Preheating Zone: Flue gas preheats the limestone using residual heat, bringing the material to about 150°C without overheating it.
- Calcining Zone: Here, fuel and combustion air mix and burn, decomposing the limestone into quicklime and carbon dioxide at temperatures between 800°C and 1200°C.
- Cooling Zone: The calcined product is cooled at the bottom of the kiln by cooling air, dropping its temperature to between 60°C and 80°C before being discharged.
3. Automated Operation
An automated control system, managed through a human-machine interface, handles the regular switching of the two shafts' roles. For instance, while shaft A is calcining, shaft B is storing heat, and vice versa. This switching cycle typically repeats every 12 to 15 minutes, which guarantees a continuous heat supply and ensures the materials are heated evenly.
4. Key Design Features
Rotary Distributor: Spreads the limestone feed evenly to prevent clogging and improve calcination efficiency.
Regenerative Bricks: Line the shafts to absorb and store waste heat from the flue gas, boosting the kiln's overall thermal efficiency.
In summary, by staging heat utilization and coordinating the work of both shafts, this process significantly enhances energy efficiency and final product quality in limestone calcination.
