Effects Of Pyrolysis Conditions On Char Structure And Its Intrinsic Gasification Reactivity

The structure of coal char is the key factor for its gasification reactivity, the physical and chemical properties of coal char are determined by pyrolysis conditions. The effect of pyrolysis conditions on char structures is the basis and key to study the char reactivity, which is meaningful for exploring the gasification reactivity of coal char.To achieve this goal, a kind of typical Chinese lignite and a kind of typical Chinese bituminous were selected in this study. All the coal samples were grinded to100-160mesh. To imitating the fixed-bed, entrained-flow-bed, and fluidized-bed gasifier used in coal industry, three kinds of laboratory-scale quartz pyrolysis reactors were designed. Nine lignite chars and ten bituminous chars were prepared in these three reactors at different pyrolysis temperatures. Char samples were characterized by X-ray diffraction, Raman spectroscopy and N2adsorption analyzer. A self-designed fixed-bed gasification reactor was used to characterize the initial intrinsic reactivity (when carbon conversion is only1%) of chars with CO2, H2O, and CO2/H2O mixture. The main results are as following: (1) During the gasification of coal chars, the reactivity of chars is affected by the ratio of ID/I(Gr+V1+Vr), the increase of ID/I(Gr+V1+Vr) may lower the specific rate and initial intrinsic rate of chars, but the presence of other chemical structures may affect this law.(2) Chars prepared in different pyrolysis reactors present different reactivity in the different gasification agents. The ratios order of C-H2O/C-CO2reaction of chars from fixed-bed, entrained-flow-bed, and fluidized-bed reactors is fluidized-bed-like char> fixed-bed char> entrained-flow-bed-like char.(3)With H2O, the initial intrinsic rate ratio order is fixed-bed char> fluidized-bed-like char> entrained-flow-bed-like char; With CO2, the initial intrinsic rate order is fixed-bed char> entrained-flow-bed-like char> fluidized-bed-like char; with mixture of H2O and CO2, the initial intrinsic rate ratio order is fixed-bed char> fluidized-bed-like char> entrained-flow-bed-like char.(4) The rise of heating rate and heating time will increase the ratio of and decrease the intrinsic gasification reactivity.