Abstract: A calcining kettle includes a cylindrical housing having a hot air chamber at one end, a dust collecting chamber at an opposite end and a calcining chamber between the hot air chamber and the dust collecting chamber, at least one air pad disposed between the hot air chamber and the calcining chamber, each air pad being supported by air pad supports for passage of hot air therethrough. At least one rake is disposed within the calcining chamber and configured for rotation about a vertical axis, the at least one rake stirring gypsum located adjacent to the at least one air pad. A plurality of burners is located within the calcining chamber and displaced from the air pad and the at least one rake in a direction toward the dust collecting chamber. The burners being disposed within a bed of gypsum that is heated by the burners for calcining the gypsum.