煤自燃液态二氧化碳相变驱动防灭火基础研究

Spontaneous combustion is the result from coal-oxygen complex reaction and the released heat. Liquid CO2 has double characteristics of phase change to reduce oxygen concentration and absorb heat etc. It plays a key role in coal seam fire prevention. This project aims at the key scientific problems like transportation, decalescence and oxygen reduction that exist in the process of liquid CO2 phase change driving. TG/DSC-FTIR-GC-MS coupled instrument will be employed to study the process of coal oxidation kinetics in the presence of CO2 and to reveal its micro-mechanism of preventing coal spontaneous combustion. The liquid CO2 phase change driving transportation experiment system will be established to test the thermodynamic parameters such as pressure drop, flow velocity and temperature. The thermodynamic model of liquid CO2 phase change can be put forward based on flat field theory, confirming its transportation key parameters and influencing factors of phase change. Gas transport experiment platform of liquid CO2 phase change driving in porous media will be designed and built to simulate regularities of distribution of pressure field, gas concentration field in coal and rock mass in goaf, establishing liquid CO2 continuous phase change driving gas migration model and confirming the inerting degree of goaf and region of influence. What’s more, heat and moisture exchange model of liquid CO2 phase change driving in porous media will be built to study its cooling capacity migration and cooling kinetics process, and to confirm temperature field distribution as well as effective cooling area. The conduction of this project provides a theoretical foundation for the application of liquid CO2 in fire prevention.

煤自燃是煤氧复合放热所致，液态CO2具有相变降氧和吸热的双重特性，能够有针对性防控煤自燃。课题针对液态CO2相变驱动防灭火过程中输运、吸热和降氧存在的关键科学问题,采用TG-DSC-FTIR-GC-MS联用系统研究CO2作用下煤氧化热动力学过程，揭示其防止煤自燃微观作用机理；构建液态CO2相变驱动输运实验系统，测定压降、流速、温度等热力学参数，提出基于平均场理论的液态CO2相变热力学模型，确定其相变驱动输送的关键参数及影响因素；设计建立多孔介质内液态CO2相变驱动气体运移实验平台，模拟采空区冒落煤岩体内压力场、气体浓度场的分布规律，建立液态CO2连续相变驱动气体运移模型，确定采空区惰化程度和影响范围；建立多孔介质中液态CO2相变驱动热湿交换模型，研究其冷量迁移与降温动力学过程，确定温度场分布及有效降温区域。通过课题研究，为煤自燃液态二氧化碳防灭火技术高效实施提供理论依据。

煤自燃是煤氧复合放热所致，液态CO2具有相变降氧和吸热降温的双重特性，能够实现对煤自燃有效防控。课题针对液态CO2相变驱动防灭火过程中输运、采空区吸热和降氧存在的关键科学问题开展研究。取得了如下成果：1）采用TG-DSC-FTIR-GC-MS联用系统研究CO2作用下煤氧化热动力学过程。煤样在空气氛围下的活化能和频率因子均大于在充入CO2气体后的煤样，随着CO2浓度的升高，表观活化能和指前因子减少速度加快，反应速率常数也减小，抑制了煤的氧化燃烧反应，煤氧化燃烧的动力学参数之间存在动力学补偿效应。2）构建液态CO2相变驱动输运实验系统，测定输运过程中的压降、流速、温度等热力学参数，提出基于平均场理论的液态CO2相变热力学模型，掌握相变驱动输送的关键参数及影响因素，确定了液态CO2直接输送过程中输送距离与温度、压力、摩尔流量、内径相互之间的关系，得到了液态CO2在管路中不形成干冰时的安全输送距离；掌握了液态CO2经汽化时摩尔流量与加热量、有效输送管长、管道出口温度等之间关系，在此基础上，确定了CO2的防灭火工艺参数。3）设计建立多孔介质内液态CO2相变驱动气体运移实验平台，模拟采空区冒落煤岩体内压力场、气体浓度场的分布规律，建立液态CO2连续相变驱动气体运移模型，确定采空区惰化程度和影响范围；压注流量、释放口径及压力对相变降温区域的形成和范围起着主导作用。4）建立多孔介质中液态CO2相变驱动热湿交换模型，研究其冷量迁移与降温动力学过程，确定温度场分布及有效降温区域。压注时间则与相变降温半径具有对数函数的关系；当压注时间一定时，压注流量、释放口径及压力越大，相变降温半径越大。项目成果为煤自燃液态二氧化碳防灭火技术高效实施提供理论依据。