预氧化诱导煤孔隙结构演化的阶段性特征研究

Study on the Staged Characteristics of Coal Porosity Evolution Induced by Pre-Oxidation

摘要: 煤自燃过程中孔隙网络作为氧气输运通道与氧化反应场所，其结构演化直接调控自燃进程，但目前针对不同自燃阶段的孔隙结构动态变化特征仍缺乏系统研究。本研究选取山西某地区肥煤为研究对象，设计程序升温氧化实验，制备得到不同氧化阶段煤样。综合运用低温氮吸附技术与Frenkel-Halsey-Hill (FHH)分形模型，系统表征不同氧化阶段煤样的孔隙体积、比表面积及分形维数的演变规律。研究结果表明，煤在氧化升温过程中的孔隙发育具有明确的阶段性和孔径选择性。失水脱附至吸氧增重阶段以介孔局部堵塞、比表面积减小为特征；受热分解阶段后期和燃烧阶段，微孔和介孔剧烈增长，比表面积剧增。分形理论揭示，失水脱附与受热分解初期，气体脱除导致孔隙表面粗糙度增加而空间结构趋于均一，吸氧增重阶段呈现相反趋势。受热分解阶段后期和燃烧阶段的深度氧化显著提高了孔隙表面粗糙度与空间拓扑复杂性，增强了氧气扩散能力与反应活性位点密度。

Abstract: During coal spontaneous combustion, the pore network serves as both an oxygen transport pathway and a site for oxidation reactions. Its structural evolution directly governs the combustion process, yet systematic studies on the dynamic changes in pore structure across different combustion stages remain scarce. This study selected bituminous coal from a region in Shanxi Province as the research subject. Programmed temperature oxidation experiments were designed to prepare coal samples at different oxidation stages. By comprehensively employing low-temperature nitrogen adsorption technology and the Frenkel-Halsey-Hill (FHH) fractal model, the evolution patterns of pore volume, specific surface area, and fractal dimension in coal samples at different oxidation stages were systematically characterized. Results indicate that pore development during coal oxidation exhibits distinct stage-specific and pore-size selective characteristics. The dehydration-desorption to oxygen uptake-weight gain stage is characterized by mesopore local blockage and reduced specific surface area. In the late thermal decomposition stage and combustion stage, micropores and mesopores increase dramatically, leading to a sharp rise in specific surface area. Fractal theory reveals that during dehydration/desorption and early thermal decomposition, gas removal increases pore surface roughness while spatial structure becomes more uniform. The oxygen uptake-weight gain stage exhibits the opposite trend. Advanced oxidation in the late thermal decomposition and combustion stages significantly enhances pore surface roughness and spatial topological complexity, thereby boosting oxygen diffusion capacity and reactive site density.