Radial mixing of metallurgical slag particles and steel balls in a horizontally rotating drum: A discussion of particle size distribution and mixing time

Air quenching refers to a common technique used for treating metallurgical molten slag, which generates a mass of high-temperature solid slag particles. In this research, we proposed a new technology to recover the waste heat from slag particles using a drum apparatus that uses cold steel balls as intermediate heat storage. This research focuses on the radial mixing of slag particles and steel balls in the rotating drum with baffles. Previous studies mainly focus on the mixing process of a single type of particles or two types of similar particles in the drum. However, the slag particle size of this research has a continuous distribution, and the slags are mixed with steel balls with greatly different parameters, such as size and density. Few similar studies have been conducted, and the corresponding mixing and segregation phenomena are also different from those of previous studies. In this research, numerical simulations with discrete element method (DEM) were carried out to understand and quantify the mixing and segregation processes of slags and balls in a horizontal drum. The slag size distribution includes two typical cases: normal diameter distribution and normal volume distribution. The corresponding control groups (e.g., uniform diameter and uniform volume) were set. According to the current research situation, several mixing criteria, including the whole process and subprocesses, were improved and used to evaluate the different aspects of the mixing processes under diverse cases. The influence of slag size distribution on the mixing process was mainly investigated. The time required for complete mixing in different aspects was compared to reveal the mixing mechanism efficiently. Results show that the mixing criteria of the whole process cannot reflect many details of the subprocesses. The use of the criteria of the subprocesses-a combination of the entry order index and number of contacts-is accurate in evaluating the mixing time of the granular bed. (C) 2020 Published by Elsevier B.V.