不同煤阶煤及其半焦不同停留时间的破碎行为

Investigation on the fragmentation behavior of coal and corresponding semicokeparticles of different ranks at different residence time

在煤炭燃烧、气化等过程中,煤炭颗粒的破碎存在于反应全过程,煤炭颗粒在不同停留时间会发生破碎,不同机理引发的破碎行为和颗粒粒径分布的变化规律存在差异,不同停留时间下适用的破碎机理及模型尚未明晰。为研究不同煤及半焦在不同停留时间下的破碎行为,以不同煤阶的无烟煤、烟煤、褐煤及其半焦为试验样品,在1473 K、氮气气氛管式炉中进行了高温破碎试验。通过ANSYS有限元分析软件建立颗粒热应力模型,结合试验与数值模拟结果分析了不同煤及其半焦颗粒的破碎机理。热应力模型结果表明,低挥发分含量的无烟煤和不同煤种的半焦,热应力引发的一次破碎应在受热后2 s内发生,高温破碎试验结果表明样品仅在进入反应器后前2 s内发生热应力破碎。烟煤与褐煤在10 s停留时间内挥发分持续释出,主要由脱挥发分引起一次破碎。而烟煤半焦与褐煤半焦由于在预处理的热解过程中已产生较多薄弱联结,在6~10 s发生了明显的二次破碎,并且在试验后期2种半焦样品的破碎强度均大于其原煤样品。

During the processes of coal combustion and gasification,the fragmentation of coal particle occurs throughout the whole reaction process.Coal particles fragment due to different reasons at different residence times,and the fragmentation behavior and particle size distribution variations caused by different mechanisms are also different.However,the fragmentation mechanisms and applicable models at different residence times are yet not clear.In order to investigate the fragmentation behavior of different coals and semi-cokes at different residence times,coals ofdifferent ranks including anthracite,bituminous coal,lignite and the corresponding semicokes were used as test samples for the high-temperature fragmentation experiments carried out in a horizontal-chamber furnace at 1473 K under nitrogen atmosphere.In addition,a particle thermal stress model was developed with ANSYS finite element analysis software,and the fragmentation mechanism of different coals and their semicokes were analyzed based on the experimental and numerical simulation results.The simulation results show that the thermal stress induced primary fragmentation should occur in less than 2 s after heating for anthracite and different semicokes with low volatile matter content.As expected,the high-temperature fragmentation experiment also shows that these samples indeed only suffer thermal stress fragmentation in the initial 2 s.Bituminous coal and lignite continuously release volatiles during the residence time of 10 s,and the primary fragmentation occurs mainly due to the devolatilization.For the bituminous semicoke and lignite semicoke,numerous weak connections are produced during the pretreatment pyrolysis process,and obvious secondary fragmentation is observed in 6-10 s,and in the later period of the experiment,the fragmentation severity of the two semicoke samples is greater than that of the raw coal samples.