Understanding the deposition mechanism burning Fe - rich Zhundong coal in a 0.4 MW pilot-scale facility

This study presents a comprehensive investigation of slagging characteristics associated with Fe-rich Zhundong coal (ZDC) combustion utilizing a 0.4 MWth pilot-scale facility. Slag specimens collected from three critical locations - bottom-of-furnace (BOF), superheater, and reheater zones - were systematically characterized through multi-analytical approaches including X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), complemented by molecular dynamics simulations to elucidate microscopic deposition mechanisms. Key findings reveal that: Distinct melting phenomena were observed across all sampling locations under flue gas temperatures (FGT) ranging from 1000 to 1350 °C, primarily attributed to both the formation of Si Ca low-temperature eutectic phases and fluxing effects of Fe-bearing material. Comparative analysis identified sulfate-induced contamination in reheater deposits at moderate-to-low FGT regimes (1000–1200 °C), demonstrating deposition characteristics analogous to Ca-rich ZDC slag formations. The interaction mechanisms of sulfur in reheater zones promoted Fe Na synergistic effects. The slag produced through low-temperature ashing exhibits lower fusion temperatures. Molecular dynamics simulations further confirmed that elevated combustion temperatures facilitate Si Ca eutectic formation while promoting preferential deposition of Na 2 SO 4 / CaSO 4 on low-temperature heat exchange surfaces. When using Fe-rich ZDC in the ∏-type boiler, the FGT at the furnace outlet needs to be reduced to at least 1000 °C. • A 0.4 MW test facility is utilized, featuring heating surfaces placed in the horizontal flue gas path. The study examines the effects of burning solely Fe-rich Zhundong coal from Xinjiang, China. • Across the flue gas temperature range of 1000 to 1350 °C, melting occurs in the slags, driven by two main mechanisms: Si–Ca low-temperature eutectic materials and melting of Fe-rich substances. • The sulfate contamination deposition in the moderate to low flue gas temperature range, primarily featuring Na 2 SO 4 and CaSO 4 . • The flue gas temperature at the Π-type boiler furnace outlet cross-section must be reduced to at least 1000 °C.