Co-Firing Zhundong Coal with Its Gangue: Combustion Performance, Sodium Retention and Ash Fusion Behaviors

Fouling and slagging are intractable ash-related problems for boilers burning high-sodium coals (HSC) to produce electricity or heat. Reduction and resource utilization of solid waste, coal gangues, is urgent because of stringent environmental regulations and economic benefits. Based on the sodium-rich character of Zhundong coal (ZDC) and the mineralogical features of the coal gangues (ZDG), this work investigated their co-firing performance, the sodium retention behaviors as well as the slagging and fouling tendency of the ashes. Results show that combustion performance of ZDC is not reduced despite ofthe lower reactivity of ZDG. The co-firing reaction follows the 3D diffusion model (cylinder symmetry) which probably reflects the gas diffusion of oxygen to combustible matter. During co-firing, the enriched silica and alumina components in ZDG efficiently react with the alkali and alkaline earth metals (sodium, magnesium and calcium) in ZDC to form complex minerals, thus effectively capturing and retaining sodium. The slagging and fouling propensity of ashes are notably reduced. Overall, co-firing provides an alternative means to solve the ash slagging and fouling issues, and also for the reduction and resource utilization of coal gangues.