Qualified limestone is stored in the silo, and the active lime is lifted by the hoist and transported into the silo on the top of the preheater. The top bin of the preheater is controlled by the upper and lower level gauges, and then the limestone is evenly distributed to each chamber of the preheater through the lower pipe. Limestone is heated by 1150 ° C kiln flue gas to about 900 ° C in the preheater, and about 30% of it is decomposed. It is pushed into the rotary kiln by a hydraulic pusher. The limestone is decomposed into CaO and carbon dioxide by sintering in the rotary kiln. The limestone generated after the decomposition enters the cooler, and the cooled cold air in the cooler is cooled to 100 ° C and discharged. The heat-exchanged 600 ° C hot air enters the kiln and is mixed with gas.