Currently, the calcination of active lime mainly includes two processes, i.e., the process using a gas-burning shaft kiln and the process using a rotary kiln with a pre-heater. In the former process, although the heat consumption in calcining active lime with the gas-burning shaft kiln is low, it is necessary to use limestones having a size larger than 40 mm, which leads to a low utilization rate of minerals. In addition, the activity of active lime calcined through such a process is relatively low.
In the latter process, the active lime calcined by using the rotary kiln with a pre-heater has a relatively high activity and stable quality, and fine grained limestones having a size of 10-40 mm can be used. Thus, the latter process is widely used in this field. In the latter process, however, when the high temperature flue gas generated in the rotary kiln is supplied to the pre-heater and then preheats the limestones therein, the limestones generally have a precalcining rate of 20-25%, such that most of the limestones will be calcined in the rotary kiln. However, the calcination of the limestones in the rotary kiln is mainly in the form of radiant heat exchange, which has a low thermal efficiency, and the rotary kiln shell radiates too much heat on its surface, resulting in an increase of the system's energy consumption. Therefore, the latter process has a relatively high heat consumption, which has become a pressing problem to be solved in the prior art.