Behaviour of different char components in fluidized bed combustion: a char petrography study

Abstract

Residues of fluidized combustion were shown to contain slightly more anisotropic char than is consistent with the vitrinite content of the parent coals. The composition of the cyclone residues gradually shifted to higher contents of anisotropic char as the recycle ratio increased, but remained constant over a wide range of air-to-fuel ratios. Cyclone chars were richer in anisotropic matter than filter chars, in which the inertinite residues tended to concentrate. The surface structure, as determined by the size of mosaic units, was not influenced by either residence time or air-to-fuel ratio. The combined data suggest that greater abrasion resistance, rather than reduced chemical reactivity of vitrinite char, may explain its slower combustion. A practical implication is that fly ash recycling may be more effective with high inertinite coals than with coking coals.