保温时间对二次炭化型煤微结构的影响与力学-渗流特性强化研究

Effect of holding time on microstructure of secondary carbonized briquette and strengthening of mechanical-seepage characteristics

物理模拟试验是煤矿瓦斯灾害发生机制与防控的一种有效方法。目前开展煤矿瓦斯灾害物理模拟试验所用型煤材料其力学强度、渗透率与原煤差异性较大,如何改善型煤(BC)的抗压强度、渗透率是型煤成型过程中面临的关键问题。基于此,采用热压成型方法制作了若干不同保温时间下二次炭化型煤,并采用SEM、NMR、XRD、FTIR、MTS-815岩石力学试验系统和含瓦斯煤热-流-固耦合三轴伺服渗流试验装置对不同保温时间下二次炭化型煤进行测试分析,分析了不同保温时间对其表面形貌、T2谱形态、孔隙度、微晶结构、基本结构单元芳香烃、烷基侧链和各种官能团演化规律,厘清了不同保温时间下二次炭化型煤的力学及渗流特性,并确定最优的保温时间。结果表明:随着保温时间的增加,二次炭化型煤表面粗糙度、孔径逐渐变大,且增至6.7 h后,BC表面有裂隙出现,保温时间越长,裂隙越明显;BC累计孔隙度及中孔孔隙度逐渐增大,而微孔孔隙度逐渐减少;芳香层间距(d_(002))呈先减后增,而微晶直径(L_(a))和微晶高度(L_(c))均先增后减;脂肪链的长度减少,芳香环的缩合程度(A_(ar)/A_(al))呈先增大后减小;单轴抗压强度呈先增大后减小,渗透率呈先减小后增加。在保温时间为5.3 h为最佳保温时间,此时热压BC的单轴抗压强度和弹性模量都最大、泊松比和渗透率最小,其力学强度、渗透率和密度依次为9.85 MPa,1.49×10^(-15)m^(2)和1.127 g/cm^(3)。该研究为提高煤矿瓦斯灾害发生机制与防控基础试验中的真实还原性,有效预防控制煤矿瓦斯灾害事故具有重要的现实指导意义。

Physical simulation test is an effective method of occurrence mechanism and prevention and control of coal mine gas disasters.At present,the mechanical strength and permeability of briquette materials used in coal mine gas disasters physical simulation test are very different from that of raw coal.How improve the compressive strength and permeability of the briquette coal(BC)is the key problem in the briquette forming process.Based on this,several secondary carbonized briquettes with different holding time were made by a hot pressing method in this paper,and SEM,NMR,XRD,FTIR,MTS-815 rock mechanics test system and gas-containing coal thermal-fluid-solid coupling triaxial servo seepage test device were used to test and analyze secondary carbonized briquettes with different holding times.The effects of different holding times on microcrystalline structural parameters,basic structural units of aromatic hydrocarbons,alkyl side chains and various functional groups,surface morphology,T2 spectral morphology,and porosity evolution were analyzed,the mechanical and seepage characteristics of secondary carbonized briquet under different holding times were clarified.and the optimal holding time was determined.The results show that the surface roughness and pore diameter of the secondary carbonized briquette gradually increase with the increases of holding time,and cracks appear on the surface of BC after increasing to 6.7 h.The longer holding time,the more obvious cracks are.BC cumulative porosity and mesoporous porosity increased gradually,while microporous porosity decreased gradually.The aromatic layer spacing(d_(002))decreased first and then increased,while the microcrystalline diameter(L_(a))and microcrystalline height(L_(c))increased first and then decreased.The length of fatty chain decreased,and the degree of condensation of aromatic ring(A_(ar)/A_(al))increased first and then decreased.The uniaxial compressive strength increases first and then decreases,and the permeability decreases first and then increases.When the holding time is 5.3 h,the optimal holding time is obtained.In this case,the uniaxial compressive strength and elastic modulus of hot pressing BC are the largest,Poisson's ratio and permeability are the smallest,and its mechanical strength,permeability and density are 9.85 MPa,1.49×10^(−15) m^(2),and 1.127 g/cm^(3),respectively.This study has important practical guiding significance for improving the real reducibility of the occurrence mechanism and prevention and control basic test of coal mine gas disaster and effectively preventing and controlling coal mine gas disaster accidents.