不同反应器中褐煤热解焦结构特性及其气化反应性研究

Study on structure and gasification reactivity of lignite char from different pyrolysis reactor

本研究以褐煤为样品,流化床和下落床为反应器在900-1100℃条件下热解制备了系列煤焦,通过X射线衍射仪(XRD)、Raman光谱仪、静态物理吸附仪及固定床反应器研究了煤焦物化结构及CO_(2)气化反应性。结果表明,流化床和下落床反应器中热解煤焦的气化反应性主要取决于其化学结构。两种反应器中,随热解温度升高,煤焦缩聚反应加深,微晶尺寸(芳香片层堆积高度L_(a)、平均直径L_(a))增加、大环与小环比I_(D)/I(G_(r)+V_(r)+V_(l))升高,气化反应性降低。相较于下落床反应器,相同热解温度下流化床反应器中煤焦微晶尺寸、大环与小环比I_(D)/I(G_(r)+V_(r)+V_(l))均较低且其随热解温度升高变化程度较小,导致煤焦气化反应性较低且随热解温度升高变化幅度相对较小。这主要归因于流化床反应器中煤焦停留时间长,同时存在较强的煤焦与挥发分相互作用,加深了煤焦缩聚反应程度。

Char gasification reactivity plays a vital role in the design of a gasifier.In this paper,a series of char were prepared by pyrolysis at 900−1100℃in a fluidized bed and a drop tube reactor with a lignite as the sample,and the physico-chemical structure and CO_(2) gasification reactivity of chars were studied by X-ray diffractometer(XRD),Raman spectrometer,static physical adsorption instrument and fixed-bed reactor.The results showed that the gasification reactivity of char in the fluidized bed and drop tube reactors mainly depended on its chemical structure.In the two reactors,as pyrolysis temperature increased,the polycondensation reactions of char deepened,resulting in the increasing crystalline size(aromatic sheet stacking height L_(c),average diameter L_(a))and larger ring to smaller ring ratio I_(D)/I(G_(r)+V_(r)+V_(l))of char.Therefore,the gasification reactivity of char decreased with increasing pyrolysis temperature.Compared with in the drop tube reactor,the crystalline size and larger ring to smaller ring ratio I_(D)/I(G_(r)+V_(r)+V_(l)))of char in the fluidized bed reactor were lower at the same pyrolysis temperature,and their variations with increasing pyrolysis temperature were smaller,resulting in the lower gasification reactivity of char and the smaller change of gasification reactivity of char with increasing pyrolysis temperature.Those were mainly due to the long residence time of char and strong interactions of char and volatiles in the fluidized bed reactor,deepening the degree of polycondensation reaction of char.