基于微波-热烟气联合干燥的褐煤水分协同脱除机理研究

Focusing on the long time, low security and economy of conventinal drying methods due to the high water content and complex water-holding type of lignite, microwave heating is introduced, which has the feature of "internal heating". Through the "selecting heating"for water molecules of microwave, and conbining the hot flue gas drying,the favorable conditions for heat and mass transfer is eatablished, and moisture migration conditions is also improved,then the drying rate of entire drying process has a signicicant increase. For our project,firstly,on the basis of water-holding characteristics of lignite, the drying characteristics of lignites containing different water types are studied on the thermobalance and microwave thermobalance, and drying kinetics models are established to explore the moisture migration characteristics of different water types; exploring the enhanced role of "selective heating" of microwave to water molecule for the migration of water molecules on the basis of analysis of variation of functional groups and pore structure before and after drying, and examining the impacts of variation of lignite structure on the snuff back characteristics, oxidation characteristics (spontaneous combustion characteristics) of dried lignite; numerical simulation of combined drying process of single lignite particle is carried out for exploration of field synergistic strengthening mechanism of moisture removal for predicting the temperature field and moisture migration and diffusion law. Through this research, it can be expected to reveal a new moisture removal mechanism of lignite drying process, get the optimizing configuration parameters of microwave-hot flue gas combining drying. It is of important practical value and significance.

针对褐煤含水量高，持水复杂导致常规干燥方法干燥时间长、安全经济性不高的缺陷，引入具有"内加热"特性的微波加热方法，通过微波对褐煤水分的"选择性加热"，结合热烟气外部干燥，构建加速传热传质的有利环境，改善水分迁移条件，从而大幅提高褐煤干燥速率。拟在获取褐煤持水特性基础上，通过考察不同含水类型褐煤在常规和微波加热下的干燥特性并确定相应的临界含水率，进而研究优化组合工况下褐煤的联合干燥特性，结合干燥中及干燥后褐煤样品的水分、官能团和孔隙结构等分析，揭示褐煤中不同水分的迁移析出特性并明确水分脱除对干燥后褐煤回吸、自燃特性的作用机理；建立单颗粒褐煤双界面蒸发干燥模型，对褐煤中的温度场和水分迁移扩散规律进行预测，探讨褐煤水分脱除的多场协同强化机理。通过本课题研究，预期可以揭示褐煤干燥过程水分脱除的新机理，获得褐煤微波-热烟气联合干燥的优化配置参数，具有重要的实用价值和研究意义。

本课题的研究背景为褐煤的快速低成本干燥问题，主要的研究目标是通过对褐煤微波-热风联合干燥的研究，获得褐煤中不同类型水分的迁移和转化规律，为实现褐煤的快速高效干燥奠定技术基础。主要研究内容分为不同褐煤的水分及其它物理性质表征和微波及热风干燥特性研究，以及微波热风联合干燥的褐煤干燥数值模拟研究三部分。首先对我国的褐煤资源状况进行了调研，选取我国3种典型褐煤—宝日希勒褐煤，大雁褐煤和北电胜利褐煤，进行了褐煤样品的制备和物理化学表征，包括工业分析、元素分析、官能团分析、不同类型水分含量、热重分析、燃点测试等，获得上述三种褐煤的相关测试数据，为下一步开展不同干燥方式下的褐煤干燥特性实验研究奠定基础；在热风及微波干燥实验台上重点进行宝日希勒褐煤样品的常规干燥和微波干燥特性实验研究，考察热风温度、流量等，以及微波功率、温度、气体流量、加热方法组合等对褐煤水分迁移特性的影响，建立干燥动力学模型；通过褐煤的常规干燥和微波干燥实验研究，明确了热风干燥及微波干燥下褐煤中不同类型水分的迁移转化特性；通过褐煤大颗粒的水分迁移特性实验，揭示了褐煤水分脱除的“泵效应”，阐释了微波“选择性加热”及多场协同对褐煤水分的强化脱除机理；对干燥后褐煤的煤质结构等进行测试和表征，研究水分的迁移特性及煤质结构的变化规律；在神华集团的资助下，分别在内蒙古乌海和海拉尔进行了大功率微波褐煤干燥的小试和中试试验，获得了褐煤微波干燥的放大试验数据，结合能耗分析，提出了基于余热回收的褐煤热风预干燥-微波干燥的分段联合干燥方案，并进行了工业设计。本课题通过对褐煤微波及微波热风联合干燥的深入研究和分析，在褐煤微波干燥水分迁移规律及快速干燥等方面有了一定的成果，具有一定的科学意义和应用价值。