褐煤低温氧化过程水分迁移对热质传递的作用机制及界面稳定性

Lignite, as abundant energy resource in our country，has high spontaneous combustion tendency because of its high moisture content, developed pore structure and rich surface active structure, which seriously limits the application of lignite. The moisture has complex influence on low-temperature oxidation of lignite. This project aims to establish the basic structural unit in the process of low-temperature oxidation of lignite according to quantum chemistry theory, and on the basis of this basic structural unit to study the effect of moisture migration on the surface active structure and interface stability of lignite. The laws of moisture migration on the process of low-temperature oxidation of lignite in the aspect of heat-mass transfer will be researched. And then, heat transfer model of the co-reaction of moisture and active structure in the process of low-temperature oxidation of lignite based on the influence of moisture on transfer of oxygen and small molecular gas will be deeply discussed, the reaction mechanism of oxygen and small molecular gas transfer will be obtained on the condition of moisture migration, and the dynamic model of oxygen diffusion in coal pore under different moisture content will be established. Based on the mathematical models of oxygen diffusion in coal, oxygen seepage, exothermic and dissipated heat of coal, et al., the shortest spontaneous combustion period of the lignite under different moisture content will be forecasted. This project systematically studies mechanism of moisture migration in the process of low-temperature oxidation of lignite, which has definitely significance for storage, transport and application of lignite.

我国褐煤储备资源丰富，其含水量高、孔隙结构发达和表面活性结构丰富，易发生自燃，限制了褐煤的应用，其中水分对褐煤的低温氧化影响较为复杂。本项目拟以量子化学理论构建褐煤低温氧化过程基本结构单元，研究水分变化对表面活性结构和界面稳定性的作用规律；从热质传递方面研究水分迁移对褐煤低温氧化过程影响规律，以水分-活性结构协同作用下氧化反应的热效应建立煤低温氧化过程的传热模型；研究水分对煤低温氧化过程中氧气传递和小分子气体产物传递的影响，获得在水分迁移作用下氧气和小分子气体传递对煤氧结合的作用机制，建立在不同含水量煤样孔道中氧气扩散传质动力学模型；通过建立煤氧扩散、氧气渗流和煤放热散热等煤低温氧化过程数学模型，对不同水分含量煤体最短自燃发火期进行预测。本项目系统研究褐煤中水分迁移对褐煤低温氧化过程的影响规律和作用机制，对于褐煤的储存、运输、利用以及防止煤的自燃具有一定的指导意义。

我国褐煤储备资源丰富，其含水量高、孔隙结构发达和表面活性结构丰富，易发生自燃，限制了褐煤的应用。本项目从水氧界面特性、热量传递、质量传递和煤自燃过程数学模拟四方面开展了相关研究，深入研究了水分对褐煤低温氧化的影响。主要研究结论如下：.（1）水会阻碍氧气的物理吸附，使吸附量减少，但会增加氧气的吸附热，促进氧气在羟基和羧基上的吸附作用。羟基和羧基在水分作用下的低温氧化反应起始路径是一个相互促进、互相转化的动态循环作用机制；（2）不同含水率煤样的氧气扩散系数与煤样的分形维数呈正相关。吸氧增重阶段的活化能相比于水分蒸发及气体脱附阶段活化能来说有大幅度的降低，并且指前因子至少降低了5个数量级。这说明煤氧吸附及反应更容易进行，但是反应速率却有大幅度的降低。（3）煤低温氧化过程中H2O的释放对煤氧复合反应速率有显著的影响。在缓慢氧化阶段，水分主要表现为促进作用；在煤氧反应后期的加速氧化阶段和剧烈氧化阶段，水分主要表现为抑制作用；（4）通过对煤低温氧化过程的BP神经网络进行设计、训练和调用，利用其对煤低温氧化过程的温度场和气体浓度场进行模拟及预测，预测值和实验测定值非常接近，氧气浓度、温度和CO浓度的平均相对误差都在实际许可范围内。（5）以本项目为依托，已发表学术论文9篇，申请发明专利7项，其中已授权4项，培养研究生12名。