水分对不同变质程度煤瓦斯放散初速度的影响研究

Study on the influence of moisture content on initial gas emission velocity of different rank coals

为研究不同质量分数水分对煤体瓦斯放散特征的影响规律,选取3种不同变质程度的典型煤样,测试了水分作用下的煤体瓦斯放散初速度,并结合扫描电镜和压汞法研究了煤体孔裂隙分布特征,阐明了水分对煤体瓦斯放散初速度的微观影响机理。结果表明:水分对煤体瓦斯放散初速度起到了明显的抑制作用,煤阶越高,水分的影响程度越大;水分对褐煤、烟煤和无烟煤瓦斯放散初速度影响规律的差异性与煤体孔隙分布有关;随水分质量分数增加,褐煤瓦斯放散初速度表现为先快速降低后缓慢减小,烟煤Δp呈线性衰减,无烟煤则表现为先小幅降低后急剧下降。

To study the influence law of different moisture mass fraction on coal gas emission characteristics,three typical coal samples with various ranks were selected. The initial gas emission velocity of coal was tested under the effect of moisture.Scanning electron microscopy and mercury injection porosimetry were combined to investigate the pore distribution features of coal samples. The microscopic mechanism of moisture on coal initial gas emission velocity was revealed. The experimental results show that coal initial gas emission velocity is significantly reduced by moisture. The observed greatest reduction of Δp is 23. 46%,28. 28% and 37. 05% for YM lignite,DQ bituminous coal,and JLS anthracite,respectively. The result indicates that the higher the coal rank,the greater the influence degree for the moisture is. In different ranges of moisture mass fractions,theΔp change laws of coal samples are different. For YM lignite,when the moisture mass fraction is at the scope of 0 3. 19%,Δp sharply reduces. Once the moisture mass fraction is >3. 19%,Δp slowly decreases and tends to be stable. However,the Δp of DQ bituminous coal demonstrates a negatively linear correlation with the increase of moisture mass fraction. The initial gas emission velocity of JLS anthracite is firstly decreased slightly,then significantly declines. The difference of influence laws for moisture affected initial gas emission velocity of lignite,bituminous coal and anthracite is related to the coal pore distribution. The pores in JLS anthracite are well developed,and the coal has numerous methane transportation channels. When less moisture content is present,only a part of pores are occupied by water molecules. A large proportion of pores are still available for methane diffusion,thus,moisture content has little effect on Δp at this condition. When the moisture mass fraction is larger than 4. 37%,more pores and fractures are occupied by a lot of water molecules. This can hinder the gas emission,further decreasing Δp. As for YM lignite,due to the fewer pores,the number of channels used for gas transportation is limited. Only a small amount of water can block the most of pores and fracture channels,thus moisture demonstrates a remarkable inhibitory effect on Δp.