EFFECT OF PYROLYSIS ATMOSPHERE AND TEMPERATURE ON COAL CHAR GASIFICATION REACTIVITY

摘要

In the coal staged conversion utilization polygeneation system, which is proposed by Zhejiang University, coal pyrolysis and char gasification processes are separated and realized in two fluidized bed reactors.In this system, coal is first pyrolyzed in a bubbling fluidized bed to produce pyrolysis gas, tar and char.The char is sent to a circulating fluidized bed gasifier where gasified with O2 and steam, while part of the pyrolysis gas is used as fluidized gas and sent back to the bubbling fluidized bed pyrolyzer.Therefore, coal is pyrolyzed in the pyrolysis gas atmosphere.The char samples used in previous research of gasification reactivity are usually prepared in N2 atmosphere.The research using char samples prepared in pyrolysis gas atmosphere is much less.In this paper, we will focus on the effect of pyrolysis atmosphere and pyrolysis temperature on char gasification reactivity.The mixture of H2, CO2, CO and CH4 is used as surrogate of pyrolysis gas.The Shanxi bituminous coal is pyrolyzed in the atmosphere of N2 and pyrolysis gas, respectively.The pyrolysis temperature is 450℃, 550℃ and 650℃, and the pyrolysis pressure is 1 atm.Pyrolysis results show that the char samples prepared in N2 atmosphere have lower volatile content.This means that coal pyrolysis is more complete in N2 atmosphere.The SEM and Raman spectra results show that the char samples prepared in N2 and pyrolysis gas have similar morphology and structure.As the pyrolysis temperature increases, the char samples become porous and the graphite content of char samples become higher.The FT-IR spectra results indicate that the char samples prepared in pyrolysis gas atmosphere have lower intensity at 1088 cm-1, 2923 cm-1, and 3420 cm-1.Finally, the char samples were gasified in H2O and CO2 using a modified Thermogravimetric Analysis (TGA) system.Gasification results indicate that the char samples prepared in pyrolysis gas atmosphere have lower reactivity than those prepared in N2 atmosphere and increasing pyrolysis temperature will decrease the gasification reactivity of chars.