流化床热解试验的褐煤碎裂特性研究

The fragmentation characteristics of lignite during pyrolysisexperiment in a fluidized bed

褐煤在流化床热解过程中易受热力和机械力影响而发生碎裂形成粉尘,严重影响褐煤梯级加工利用发展,因而需研究褐煤在热力与机械力交互作用条件下的碎裂特性,以期为其热解、燃烧、气化等煤转化利用技术发展提供数据参考。选取内蒙古的2种褐煤,利用微型流化床热解试验装置,研究粒径、加热温度、升温速率、停留时间以及流化数各因素对褐煤碎裂特性的影响。实验研究表明:褐煤热解破碎后产生半焦的粒级主要分布在原粒级及低一档粒级范围内,颗粒的粒度变化率和粉化率随入料粒径增大而均提高,加热终温升高及升温速率增大则均加剧煤样的碎裂程度,停留时间的延长会使颗粒碎裂程度逐渐增大至粒度稳定,流化数的升高会促进颗粒粉化且对细颗粒生成的影响更明显;在流化床热解中热力、机械力分别是产生粉化的主要作用力以及辅助作用力,褐煤受热力作用下的碎裂形式为外围发生细颗粒的剥落、内部破碎为大块颗粒;通过扫描电镜分析不同温度下的半焦孔隙结构可知,随着挥发分的析出则半焦孔隙结构逐渐发育,最终由于集聚胀力与热应力作用而导致孔隙结构被破坏直至坍塌、碎裂。

In the process of fluidized bed pyrolysis of lignite,it was easy to break and pulverize to produce dust,which seriously affected the comprehensive utilization of lignite grading processing and utilization.Therefore,it was necessary to study the fragmentation characteristics under the interaction of thermal and mechanical forces,in order to provide data reference for the development of coal conversion and utilization technologies such as pyrolysis,combustion,and gasification.Two kinds of lignite from Inner Mongolia were selected to study the effects of particle size,heating temperature,heating rate,residence time and fluidization number on the fragmentation characteristics of lignite by using a micro fluidized bed pyrolysis experimental device.The experimental results show that the particle size of semi-coke produced by lignite pyrolysis is mainly distributed in the range of original particle size and low-grade particle size.The particle size change rate and pulverization rate of particles increase with the increase of feed particle size.The increase of final heating temperature and heating rate aggravates the fragmentation degree of coal samples.The extension of residence time will gradually increase the degree of particle fragmentation to stable particle size.The increase of fluidization number will promote particle pulverization and have more obvious influence on fine particle formation.In fluidized bed pyrolysis,thermal and mechanical forces are the main and auxiliary forces that generate pulverization,respectively,the fragmentation form of lignite under the action of thermal force was the spalling of fine particles in the periphery and the internal fragmentation into large particles.By analyzing the semi focal structure at different temperatures through scanning electron microscopy,it can be inferred that,with the precipitation of volatiles,the pore structure of semicoke gradually develops,and finally the pore structure was destroyed until collapse and fragmentation due to the effect of agglomeration expansion force and thermal stress.