CFD-DEM investigation of the flow and heat transfer characteristic of copper slag and biomass particles in a coupled waste heat utilization system

As a high-energy-consuming sector, the metallurgical industry possesses substantial untapped waste heat resources, with efficient recovery of slag heat emerging as a critical challenge. To address the limitations of conventional recovery technologies, this study proposes an innovative approach that integrates biomass thermochemical conversion with metallurgical slag heat recovery, resulting in a novel coupled waste heat utilization system. A three-dimensional rotary reactor model was created using a coupled CFD-DEM, incorporating the dense discrete phase model (DDPM) to numerically analyze the multiphase flow and heat transfer interactions between hot copper slag (CS) and biomass particles (WTS). The results demonstrate that increasing CS loading enhances particle mixing, elevates average rolling velocity, and improves thermal contact between WTS and CS, thereby accelerating heat transfer. The particle bed exhibits a typical rolling flow regime with distinct active (near-wall) and passive (core) zones. Notably, a 20 % CS loading produces the highest and most uniform temperature distribution, while even a 5 % loading significantly improves heating performance. Particle trajectory analysis reveals strong radial segregation driven by centrifugal and shear forces, which influences thermal conductivity. Across all cases, the mixing index remains below 0.2, indicating limited mixing due to disparities in particle size and density. Moreover, higher rotation speeds improve thermal uniformity, with 8 rpm identified as the optimal condition. CS enhances the gas phase's effective thermal conductivity, leading to a more uniform temperature distribution. These findings provide detailed insights into particle dynamics and heat transfer in rotary kilns, enhancing biomass conversion efficiency and industrial waste heat recovery.