Lime kilns are typically vertical cylindrical or square structures, reinforced externally with refractory bricks and steel, and internally comprised combustion, preheating, and cooling zones.
1. External Characteristics
Modern lime kilns are typically 20-40 meters high and 4-10 meters in diameter, with a steel outer shell encased in refractory material.
The top has a raw material inlet and exhaust outlet, while the bottom has a finished product outlet and burner interface.
Some environmentally friendly kilns are equipped with bag filters or SCR denitrification devices, with the additional piping system visible externally.
2. Internal Structure
Preheating Zone
Located in the upper part of the kiln, with a temperature of 300-800℃, limestone is gradually heated and dehydrated in this zone, which accounts for approximately 1/3 of the total kiln height. It is constructed using multi-layered refractory bricks, with an inner lining thickness of up to 500mm.
Calcination Zone
The central core area, with a temperature reaching 900-1200℃, where limestone decomposes into quicklime and carbon dioxide. Modern kilns mostly employ cyclone combustion systems, equipped with natural gas or pulverized coal injection devices.
Cooling Zone: The lower zone cools the finished product through counter-current airflow, reducing the temperature to below 80℃. Some kiln types install heat exchangers in this zone to recover waste heat, achieving a thermal efficiency of over 85%.
