Revealing baffle-enhanced heat transfer mechanism in an indirectly heated rotary kiln by discrete element method modeling

Abstract

Baffles are often configured in indirectly heated rotary kilns in order to improve their performances on transferring heat to the particle bulk that is processed in the equipment. However, design of baffles still mainly depends on the empirical knowledge due to insufficient development of relationships revealing the influences of baffle configurations on the heat transfer coefficient. In this research, the heat transfer process in a rotary kiln with straight baffles was simulated by an in-house discrete element method and the impacting mechanism of baffles on the heat transfer between the rotary kiln shell and the particles was explored. The result suggests that installing baffles is capable of improving the contact surface area between the kiln shell and the particle bed, which is a dominant factor for the enhanced heat transfer performance. Baffle parameters including the baffle number and the baffle length have significant influences on the uniformity of the particle bed temperature distribution by directly affecting the particle mixing process. When the filling level is 25%, configuration of 8 baffles with a length of $5/9H_b$ is determined to be an optimal configuration with $H_b$ being the static bed depth. The additional heat transfer area supplied by the baffle structure is also favorable for reducing the thermal time constant and its contribution takes approximately 20% in the optimized configuration.