A new coal gasification technology integrating advantages of a circulating fluidized bed (CFB) preheater and an entrained bed gasifier is proposed by gasification of preheated coal. Improvements of morphological properties and gasification reactivity can be gained for coal from the fluidized modification in the CFB preheater, which enhances the gasification reaction in the gasifier. In this study, the characteristics of the fluidized modification were investigated experimentally using oxygen and steam as gasifying agent on a bench-scale test rig. Effects of the air replacement by O2-steam in gasifying agent, modification temperature and steam to coal ratio on gas and modified char of the preheater were illustrated. Thermogravimetric analyses and Raman spectroscopy were used to characterize the gasification reactivity and carbon structural order of the modified char, respectively. The steam gasification reaction in the preheater is enhanced after air is replaced by O2-steam in the gasifying agent. The enhancement contributes to the formation of active carbon sites in the modified char and improves the gasification reactivity. The steam gasification reaction is also enhanced when the modification temperature increases from 858 to 952 ℃, but active carbon sites in the modified char are first formed and then consumed. The highest gasification reactivity of modified char is obtained at 893 ℃. The steam gasification reaction is enhanced by the increased steam to coal ratio from 0.55 to 1.07 as well and the gasification reactivity of modified char first increases and then decreases with the highest value at the steam to coal ratio of 0.87.
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