Unique Advantages of Gasification-Coke Prepared with Low-Rank Coal Blends via Reasonable Granularity Control

To perfectly solve the shortage of high-strength lump-feedstock resources and the problems of phenolic wastewater treatment and furnace corrosion restricting long-term operation of moving (fixed) bed gasification, high-strength gasification-coke with a large amount of low-rank coal blends has been prepared by reasonable granularity control at low cost. To further understand the physicochemical properties of this coke, the effects of the blending ratio of low-rank coals and particle size distribution on coke reactivity were investigated in this study. At the same time, the release ratio of Na in gasification-coke with blending sodium-rich coal was detected during the pyrolysis, gasification, and combustion stages. The results show that coke gasification reactivity with the fast reaction rate range mainly depends on the blending ratio of low-rank coals. The reasonable granularity control, which requires a small amount of strong-caking coal fines (<0.2 mm) bonded with coarse particles (1–3 mm ratio > 60%) of low-rank coals and weak-caking coals, gives rise to coke in a cage shape having a large pore structure with the process of gasification. The residues of coke also exhibit a relatively high mechanical strength. The unique feature of gasification-coke can inhibit about 45% Na volatilization more than that of the investigated sodium-rich coal because of the formation of a strong skeleton structure of the former that locks up the low-rank coal ash firmly during the gasification process. Most water-soluble Na (Na2SO4) retained in the low-rank coal ash further promotes the gasification reactivity of residues (caking coal components) in the later stage of gasification, and then it enters the ash with subsequent combustion at high temperature and transforms to aluminum silicate, which can reduce the furnace corrosion remarkably