大块煤热解温度场扩展规律

Expansion law of temperature field during bulk coal pyrolysis

干燥和热解影响煤炭地下气化产品煤气的组成和气化工作面的效率,为考察煤炭地下气化过程中干馏干燥区热解温度场的扩展规律,选用尺度为300 mm的和顺贫煤原煤块和人工制备的蒙东褐煤块为研究对象,采用大尺度固定床热解反应装置,在N_(2)气氛下对大块煤进行单侧面恒温加热试验,通过均匀布置在大块煤中的4层共50个热电偶采集试验过程中各测点的温度,绘制大块煤热解温度场分布图。结果表明:大块原煤热解温度场以多裂隙为中心呈多抛物面形向上扩展,人工块煤热解温度场以近似水平的形状向上推移;块煤热解干燥线、特征温度线的移动速率随热解时间的增加逐渐降低,且干燥线移动速率大于特征线移动速率;大块原煤的传热速率、热解干燥线和特征温度线的移动速率均高于人工块煤;大块原煤在热解6 h时干燥线和特征温度线移动速率分别为21.0、12.3 mm/h。大块原煤中裂隙的存在和发育使热解时裂隙处以对流方式传热,提高了原煤传热速率,同时裂隙发育和热量传递相互促进,使原煤热解温度场以多裂隙为中心呈多抛物面形扩展。原煤裂隙提高了热解干燥线和特征温度线移动速率,特别是对干燥线的影响更显著。因而在实际煤炭地下气化过程中,裂隙的发育、氧化区燃烧生成的大量烟气均会强化煤层内的对流传热,提高煤炭地下气化热解温度场的扩展速率。

Drying and pyrolysis are related to the composition of underground coal gasification product gas and the efficiency of gasification working surface.In order to investigate the expansion law of pyrolysis temperature field in dry distillation zone during underground coal gasification process,the 300 mm raw coal block of Heshun lean coal and the artificially prepared Mengdong lignite block were selected as the research objects.The large size fixed-bed pyrolysis reaction device was used to conduct a single-sided constant temperature heating experiment on bulk coal under N_(2) atmosphere.The temperature of each measuring point during the experiment was collected by a total of 50 thermocouples evenly arranged in four layers of bulk coal,and the temperature field distribution map of bulk coal pyrolysis was drawn.The results show that the pyrolysis temperature field of bulk raw coal expands upward in a multi-parabolic shape with multi-fissures as the center,while the pyrolysis temperature field of artificial bulk coal moves upwards in an approximate horizontal shape.The movement rate of drying line and characteristic temperature line of bulk coal pyrolysis gradually decreases with the increase of the pyrolysis time,and the movement rate of drying line is greater than that of characteristic line.The heat transfer rate and the movement rate of drying line and characteristic temperature line of the bulk raw coal is higher than that of the artificial bulk coal.The movement rate of drying line and characteristic temperature line of bulk raw coal during pyrolysis for 6 h are 21.0 and 12.3 mm/h,respectively.Due to the existence and development of fissures in the bulk raw coal,the cracks undergo convective heat transfer during pyrolysis,which improves the heat transfer rate of raw coal.At the same time,the fissure development and heat transfer promote each other,so that the pyrolysis temperature field of raw coal expands in a multi-parabolic shape with multiple fissures as the center.The movement rate of drying line and characteristic temperature line is improved by the fissure of raw coal,especially there is the significanteffect on drying line.Therefore,the development of fissures and the large amount of flue gas generated by combustion in the oxidation zone will strengthen the convective heat transfer in the coal seam and increase the expansion rate of the pyrolysis temperature field of underground coal gasification in the actual process of underground coal gasification.