淮北石台煤矿接触变质煤速热碳化的微组构解译

Ultra-microfabrics interpretation of the rapid thermal carbonization of magma contact metamorphic coal in the Shitai coal mine,North China

作为岩浆吞噬煤层的信息记录者和物质承载者,接触变质煤是揭示煤层速热碳化过程和机理的重要研究对象。为此,本研究采集了淮北石台煤矿不同热变质程度的接触变质煤样品,利用镜质组反射率测试、元素分析、工业分析、偏光显微镜(PLM)和扫描电镜(SEM)等实验手段,表征其微组构特征,以期揭示煤层速热碳化的机理和过程。结果显示,从未受影响煤、浅热变质煤到天然焦,样品最大镜质组反射率、灰分产率升高,氢、氮元素以及挥发分含量降低。未受影响煤显微组分以胶质结构体为主,局部发育丝质体;浅热变质煤中裂隙发育、少见脱挥发孔;靠近岩体的块状天然焦中镶嵌结构炭和脱挥发孔发育,孔径多介于20~150μm;岩体内的细脉状天然焦,主要由多孔炭和炭微球组成,富含圆形—椭圆形气孔,孔径多介于1~3μm。分析表明,趋近岩体,接触变质煤热变质程度连续增加:浅热变质煤是煤层受较弱热变质而脆性断裂的结果;天然焦是浅热变质煤热解脱挥发分和中间相化的产物;至岩体附近,天然焦被液化成多孔炭和炭微球,后二者最终被氧化为气态碳氧化物而消失。我们认为,岩浆接触变质煤速热碳化的实质就是固态煤岩被岩浆热解而中间相化、液化和氧化气化的过程。

The contact metamorphic coal,the recorder and carrier of coal seam engulfed by magma,is an important research object to reveal the rapid thermal carbonization process and mechanism of coal.Samples of the contact metamorphic coal with different thermal metamorphic degrees in the Shitai coal mine,North China were collected to reveal ultra-microfabrics characteristics,mechanism and process of rapid thermal carbonization of coal by means of vitrinite reflectance test,proximate analysis,ultimate analysis,polarized light microscope(PLM)and scanning electron microscope(SEM)in this study.The results show that the vitrinite reflectance and ash contents increase,while the H,N and volatile matters decrease from the unaffected coal,the slightly metamorphosed coal to the natural cokes.The unaffected coal is mainly composed of collotelinites with a bit of fusinites.There are many fractures and few devolatilization pores in slightly metamorphic coal.Mosaic carbons and devolatilization pores are developed in the massive natural coke near the sill,and the pore diameters are 20~150μm.Fine veined natural cokes in the sill,mainly composed of porous carbon and mesocarbon microbeads(MCMBs),are rich in round and oval pores,and the pore diameters are mostly between 1~3μm.The analysis shows that the thermal metamorphism degree of contact metamorphic coal increases continuously approaching the sill.The slightly thermal metamorphic coals are the result of brittle fracture of unaffected coal due to weak thermal metamorphism.Natural cokes are the products of devolatilization and mesophaseization during pyrolysis of slightly metamorphic coal.Near the sill,the natural cokes are liquefied into porous carbon and MCMBs,which are finally oxidized into gaseous carbon oxides and disappear.We believe that the essence of carbonization of magma contact metamorphic coal are mesophaseization,liquefaction,oxidation and gasification of solid coal.