Transient operation effects on the thermal and mechanical response of a large-scale rotary kiln

Rotary kilns are central equipment in material processing operations such as oxide ore reduction, clinker manufacturing, and hazardous waste incineration. This work focuses on an industrial-scale rotary kiln for Ferronickel production via the Rotary Kiln-Electric Furnace (RKEF) process. Rotary kilns are prone to mechanical failure exacerbated by thermal effects, mainly during transient operation, such as preheating and cooling. However, few studies have tackled the impact of the transient operation on the stress state in the rotary kiln wall. Therefore, we evaluate the thermal and mechanical behavior of the rotary kiln wall during preheating. Actual operation data and a thermal model enable to obtain the temperature distribution along the kiln length. This temperature distribution is the starting point for calculating the stress state of the shell and refractory. The maximal thermal gradient occurs at 10 m from the hot end, with temperatures at the outer and inner surfaces of 200 degrees C and 820 degrees C, respectively. The von Mises stress shows a maximum of 121 MPa at the wheel position in the hot region of the refractory and a range of 30-60 MPa in the shell. In addition, the compressive stress is higher than the ultimate compressive strength of the refractory. However, it does not necessarily represent refractory detachment due to the plastic deformation undergone by the refractory under high temperatures. This work paves the way towards developing a tool for accurately predicting rotary kiln mechanical failure, which can help optimize operating conditions and assist in programming maintenance.