Effect of vanadium and nickel on iron-rich ash fusion characteristics

Ash fusibility is the key parameter related with ash slagging in gasifier. The ash fusibility of coal blended with petroleum coke is significantly influenced by vanadium and nickel from petroleum coke. The effects of vanadium (V) and nickel (Ni) on iron-rich ash, such as coal ash with ferrum-based flux addition, are lack of study. This study investigates the effect of vanadium pentoxide (V2O5), nickel monoxide (NiO) and VNiO (V2O5 and NiO) on iron-rich ash fusibility under a reducing atmosphere. X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and X-ray photoelectron spectroscopy (XPS) were used to study the mineral transformation, surface morphology and valence state of vanadium in ash and slag at high temperatures. The results show that high-melting coulsonite (FeV2O4) is generated in slag with the increasing V2O5 content, and FeV2O4 transforms into the karelianite (V2O3) at 1400 degrees C. The content of iron in liquid slag is reduced for the formation of coulsonite and V-rich spinel in the primary fusion stage. These cause the continuously linear increase of AFTs with the increasing V2O5 content. NiO in ash is reduced to metallic Ni, which promotes metallic Fe precipitation and forms Fe-Ni alloy to agglomerate into spherical particles. The precipitation of Fe reduces the content of iron into liquid slag, leading to increase AFTs slowly. The AFTs also increase significantly with the increase of VNiO content. The interaction between V-containing matter and metallic Ni is not found, and there is not obvious synergistic effect of V2O5 and NiO on AFTs. Besides, the good linear relationships are shown between the AFTs and the contents of V2O5, NiO and VNiO, and R-2 of the fitting lines is as high as 0.99. These can be used to guide co-gasification of petroleum coke and iron-rich coal.