Sintering process of the rotary kiln:

1. Direct heating method: This involves introducing high-temperature gas (either direct combustion flue gas or clean air after heat exchange) into the kiln, where it is mixed thoroughly with the material for calcination.

2. Indirect heating method: A calcining chamber is located on the outer side of the cylinder, where the heat generated from the calcination is transferred to the material through the cylinder. The material undergoes drying, decomposition, calcination, and roasting at high temperatures. (A central heating tube can also be installed to simultaneously heat the inner and outer walls of the rotary kiln, transferring the heat to the material inside the cylinder for calcination.)