基于褐煤介电特性动态变化的微波干燥提质机理研究

The development and comprehensive utilization of low-quality coal is an effective way to relieve the stress on the raw material source of spray-blow coal, however, the drying of low-quality coal is the primary problem. This project take the lignite in Yunnan province as the research object, to carry out Research on microwave drying and upgrading mechanism based on the dynamical dielectric properties of lignite. The characteristics of temperature rise, the influences of temperature, moisture content and moisture state on the dielectric properties of lignite were studied. The dielectric mixed model between water and lignite, the coupling mathematical model of microwave and lignite particles were obtained. The model of microwave drying lignite dynamic variation with dielectric properties was built by COMSOL - MATLAB joint programming model. Then the heat and mass transfer mechanism and the characteristics of temperature field and the electromagnetic field inside the lignite during the microwave drying lignite were obtained; The influence of temperature, time, material quantity, moisture content on microwave drying rate drying rate and dehydration rate was studied, the drying dynamics characteristics of temperature control microwave drying lignite was revealed. The research can provide theoretical basis in the drying theory, modification for lignite, and microwave drying reactor design.

低质煤的开发综合利用是缓解高炉喷吹原料来源紧张的有效途径，然而低质煤的干燥提质是首要问题。本项目以云南褐煤为研究对象，拟开展基于褐煤介电特性变化特征的微波干燥提质机理研究。研究褐煤的介电特性及温升特性，探索温度、含水率、水分赋存状态，揭示褐煤与水的介电数学模型及褐煤颗粒与微波场相互耦合机制；通过COMSOL-MATLAB联合编程建立介电动态变化的微波干燥褐煤模型，揭示微波干燥过程中褐煤的传热传质机理，获得褐煤内部的温度场和电磁场变化特征；研究温度、时间、物料量、水分等干燥参量对褐煤干燥速率和脱水速率的影响规律，揭示微波控温干燥褐煤的动力学特征。项目研究可为褐煤干燥提质改性、微波干燥反应器设计提供理论基础。

针对褐煤干燥过程中存在能耗高、耗时长和能源利用效率低等问题，结合褐煤介电特性差异性，提出微波干燥褐煤提质新方法，获得褐煤微波干燥提质机理。主要研究结果有：.①获得了褐煤微波变温介电特性与温升特性。测定了褐煤的介电特性，水的吸波性能是褐煤的40倍，褐煤的吸波性能在热解温度之前变化不大，水分含量与褐煤介电特性呈正相关，数据表明微波低温干燥褐煤具有选择性优势；对微波场中褐煤温升过程定量描述，分为快速升温、恒温、减速升温三个阶段，获得了褐煤脱除水分的最佳温度。②获得了微波干燥提质褐煤的优化工艺参数。系统研究了微波功率、温度、粒度、时间、厚度等对干燥速率等影响规律，优化工艺为：干温度100 ºC，干燥时间180s，物料厚度4cm，获得微波干燥速率0.053g/s，热风干燥0.013g/s。③建立微波干燥动力学模型，获得了等效扩散系数和活化能。采用15种薄层干燥模型，计算了褐煤的有效扩散系数，其值随温度和微波功率的增加而逐步提高。用Arrhenius方程计算了表观活化能，在不同温度下，第一和第二速率下降阶段分别为33.490和208.077 kJ•mol-1，在第二个速率下降阶段，表观活化能较高。④阐明微波干燥提质相比常规热风干燥的优越性。通过微波干燥和常规干燥的脱水率对比发现，温度越高，二者的脱水速率相差越大。在10min时，微波干燥的脱水速率30%，常规干燥的为12%；微波可有效脱除褐煤的内在水。⑤揭示了微波提质褐煤的变化规律。研究了微波提质后褐煤粒度分布、官能团、孔结构、表面化学性质的影响规律。微波干燥后褐煤的孔隙多为中孔，常规干燥后的褐煤多为大孔，微波干燥的比表面积明显大于常规干燥；褐煤原煤表面无明显裂缝和孔洞，微波破坏了含氧官能团，降低了褐煤自然性。.合作出版专著1部；撰写论文13篇，发表SCI论文7篇，EI论文1篇，核心期刊论文1篇，申请专利5件，授权3件。项目负责人破格晋升副教授，项目组成员有1人晋升教授，2人晋升副教授，培养硕士研究生3名，参加国际国内学术会议5次。