低阶煤在热解过程中的粉化机理及其工业应用研究

It is necessary to reduce the dust content in the cascade utilization of low rank coal. It is difficult to separate the heavy components in the produced tar and the dust, which lead to pipe blockage and implies as well the troubles in running continuously, strongly inhibiting the development of this technology. Many researchers have demonstrated that the fragmentation during coal combustion in fluidized bed. However, researches about the effects of the molecule structure of coal, macerals, heating rate and gas velocity on the mechanism of coal fragmentation are very few. We propose a new method to obtain the fragmentation mechanism during pyrolysis of coal, which based upon the study of the coal physical and chemical properties, and consider both converting conditions. This research, focuses on the basic issues for fragmentation mechanism during pyrolysis of low rank coal. The effect of the molecule structure of coal, macerals, cold and hot shock both in stationary and moving states on the fragmentation mechanism during pyrolysis of low rank coal are also analyzed fully. On the basis of this study, we hope to have a correct understanding about fragmentation mechanism during pyrolysis of low rank coal, prediction model, evaluation method and standard in the industry, and so on. Finally, this work can realize large-scale and clean utilization of low rank coal.

低阶煤清洁高效分级转化技术要求降低油气产品中的粉尘含量。现有热解技术因热解后重质焦油难以与粉尘有效分离，造成管道堵塞影响系统稳定运行，阻碍了低阶煤分级转化技术的工业应用。目前的研究都集中在了流化床燃煤粉化方面，但对煤的分子结构、显微组分等性质和加热速率、气速等转化条件对粉化作用机理的科学认识少且不够。本研究提出从煤的基本物理化学性质出发并兼顾转化条件来研究低阶煤热解过程中的粉化机理，重点研究利用低阶煤碎煤在热解时发生粉化过程中的基础问题，揭示低阶煤的分子结构、显微成分等性质等对煤颗粒粉化的作用及机理、颗粒静止状态下冷热冲击对煤颗粒热解过程中粉化的影响、颗粒在流动状态下冷热冲击对煤颗粒热解过程中粉化的作用及机理。研究的目标是正确认识低阶煤热解过程中粉化的机理、预测模型、工业评价方法标准等，从而解决低阶煤的大规模清洁利用问题。

我国低阶煤资源丰富，利用热解技术可实现低阶煤的梯级利用。但低阶煤热解过程容易产生粉化，造成荒煤气夹带粉尘、管路堵塞以及油尘难分离等问题，从而增加了大规模清洁利用的难度。本项目利用微型固定床与流化床热解反应装置进行热解粉化研究，主要工作包括（1）两种蒙东褐煤在热力与机械力不同加载下的热解粉化试验研究；（2）颗粒粉化与微观结构变化的联系；（3）影响粉化的主要因素分析及粒径关联模型建立；（4）热解粉化过程分析及机理研究。研究结果表明：煤的粉化程度均随着粒径的增大、加热终温的升高、升温速率的增大、停留时间的延长而增大；由热力与机械力不同加载试验可知热力作用下挥发分的析出是引起粒度变化的主要原因，而机械力作用主要引起颗粒外围细颗粒的剥落；利用灰色关联理论统计处理发现升温速率是影响粒度变化率的最主要的因素，而影响粉化率的主要因素是升温速率、粒径以及加热终温；建立了粉化前后平均粒径与主要因素的关联函数模型，经验证适用性较好，可作为预测粒度变化情况的模型；揭示了煤热解过程粉化的机理，并指出煤粒受热粒度变化主要是由于颗粒内部的拉应力作用，粉化量主要源于颗粒外围压应力作用。