Introduction to the working principle of the shaft kiln in a lime kiln
The shaft kiln of a lime kiln, as a traditional and efficient calcination equipment, operates based on countercurrent heat exchange and continuous production mode. After being uniformly fed from the distribution device at the top of the kiln, the material slowly moves from top to bottom under the influence of gravity, passing through the preheating zone, calcination zone, and cooling zone in sequence. In the preheating zone, limestone comes into contact with high-temperature flue gas from below in a countercurrent manner, absorbing heat through radiation and convection. The surface moisture evaporates and initial pyrolysis is completed. The temperature gradient is controlled between 200℃ and 850℃. The material stays in this stage for about 1.5 to 2 hours, ensuring a decomposition rate of 15% to 20%, laying the foundation for subsequent calcination.
The calcination zone is the core reaction area, where the temperature is maintained within a suitable range of 850°C to 1250°C. Fuel (such as coke, gas, or heavy oil) and combustion-supporting air are fully burned here, releasing a large amount of heat to decompose calcium carbonate into calcium oxide and carbon dioxide. Modern shaft kilns achieve dynamic matching of fuel and air through intelligent air volume regulating valves, with the excess air coefficient controlled between 1.05 and 1.15, ensuring complete combustion while reducing heat loss. Axial temperature fluctuations are strictly controlled within ±15°C, and combined with a uniform distribution system, the unburned material rate is reduced to less than 3%, significantly enhancing the activity of the product.
The cooling zone achieves heat recovery and product cooling by blowing in cold air. After calcination, the high-temperature quicklime undergoes sensible heat exchange with the cold air. The air temperature rises to 400°C to 500°C and then returns to the calcination zone to support combustion, forming a thermal circulation system. The quicklime is cooled to 600°C to 200°C and then discharged, which facilitates subsequent processing and improves energy utilization efficiency. The automated control system dynamically adjusts process parameters by monitoring the temperature field and pressure distribution in the kiln in real time, ensuring long-term stable operation of the shaft kiln.
