煤田火地下高温区强迫对流换热特性及热提取方法研究

In the west of China exists large areas of underground coal fires, with huge heat energy. For a long time, the heat energy has always been treated as a kind of disaster resource and therefore was abandoned without being exploited and utilized as clean energy in the process of coal fire control, which results in a huge loss of energy. Based on the new thought “replacing coal fire control with heat extraction”, this project proposes the forced-convection heat extraction method when it comes to extract heat energy in underground high-temperature zones of coal fire areas, where low-temperature nitrogenis chosen as heat transfer medium.Given the high temperature and the inhomogeneous permeability in underground heat extraction zones, this project investigates, in terms of forced convection, the flow resistance and heat transfer characteristics of low-temperature nitrogen as thenitrogen flows throughthe high-temperature loose coal and rock medium, as well as the effect of regional resistance difference on the flow distribution of nitrogen. Besides, the mathematical model of heat extraction, which can reflect the forced-convection and heat transfer characteristics, will be established. Furthermore, the forced-convection and heat transfer characteristics of nitrogen in the underground high-temperature loose coal and rock medium will be analyzed, and the relevance between the technological parameters of heat extraction and the effect of fire extinction and cooling in underground coal fire areas will be studied. All these set the stage for the determination of the applicable conditions and the technological parameters of the forced-convection heat extraction method.The project explores a new way to control the coal fire that is simultaneously pragmatic and environmentally friendly, which contributes significantly to the development of the technologies of distributed heat extraction and utilization in coal fire areas.

我国西部现存大面积煤田火区，火区蕴藏着巨大的热能。长期以来，煤田火治理均将火区热能作为灾害源去消除，未将其视作可用能源加以提取利用，造成大量的热能损失。本项目基于“以提代治”的煤田火治理新思路，创新性地提出了以低温氮气为热媒的煤田火地下高温区强迫对流式热提取方法。针对煤田火地下热提取区温度高、透气性不均一的特点，通过开展强迫对流条件下低温氮气热媒在高温松散煤岩介质中的流动阻力与换热特性以及区域阻力级差对氮气流量分配的影响规律研究，构建体现强迫对流换热特征的火区热提取数学模型，分析低温氮气热媒在地下高温松散煤岩中的强迫对流换热特性，研究热提取参数与火区提热降温灭火效果的关联性，据此确定火区强迫对流热提取方法的适用条件及工艺参数。项目的开展将为煤田火治理提供一种新的可供参考的绿色治理方法，对推动煤田火区热能的分布式提取与利用技术的发展具有十分重要的意义。

基于“以提代治”的煤火治理思路，开展了煤火地下高温区强迫对流换热特性及热提取方法研究，主要研究成果如下：.（1）研发了高温多孔介质气体强迫对流换热实验系统，得到了气态热媒在不同温度、不同等效渗透率松散煤岩体中的强迫对流阻力特性变化规律。结果表明：强迫对流条件下气体的流动符合Fochheimer方程，其非达西因子与煤岩粒径和空隙率之间呈幂函数关系，煤岩温度对气体流动阻力的影响（粘性项系数和惯性项系数）与温度呈二次函数关系。.（2）开展了随温度变化的煤氧化燃烧动力学参数测试方法研究，推导得到了以转化率为纽带的动力学参数计算模型，形成了多升温速率实验和恒温实验相结合的测试方法，优选了最优实验和计算参数；采用该方法得到了贫氧条件下煤氧化燃烧动力学参数与温度的对应关系模型。.（3）结合气体强迫对流阻力和煤贫氧氧化燃烧动力学研究成果，构建了地下煤火高温区强迫对流式热能提取多场耦合模型，研发了煤火强迫对流换热实验系统对该模型进行了验证，进而研究了单一氮气热媒及细水雾-氮气混合热媒不同灌注方式、流量和灌注时间对提热降温效果的影响。结果表明：多孔压入导向式热媒注入方式更适合火区强迫对流提热降温；在此方式下，火区最高温度、平均温度与提热时间分别呈三次和二次函数关系；添加细水雾能显著提高气态热媒的提热降温性能，初期热媒在高渗透率煤体中的降温效果较好，随着时间的增加，在低渗透率煤体中的降温速率逐渐增大。.（4）研发了自吸气式细水雾发生装置，实现了较低供水压力、无外部压风条件下对水的高效雾化；构建了煤田火区细水雾-氮气强迫对流提热降温系统，并在新疆某火区开展了现场试验。结果表明：以细水雾-氮气为热媒的强迫对流提热技术能够实现对火区的有效降温，达到“以提代治”的煤火治理效果。.研究成果获得省级及行业科技奖励2项，发表高水平论文8篇，授权发明专利7项，培养研究生5名；期间，项目负责人入选国家重大人才工程项目。