长焰煤热解过程中孔隙结构演化特征研究

STUDY OF EVOLUTION CHARACTERISTICS OF PORE STRUCTURE DURING FLAME COAL PYROLYSIS

随着煤热解温度的升高,煤孔隙结构和数量发生剧烈变化。为研究其变化规律,以长焰煤为研究对象,应用压汞法分别对300℃～600℃常规热解和600℃高温蒸气热解固体产物的孔隙结构参数进行测定和分析,计算不同热解温度下的孔隙分形维数,详细比较2种不同的热解方式下固体产物的孔隙特性。研究结果表明:(1)常规热解条件下,总孔隙体积和孔隙率随温度的演化表现为:黑岱沟煤先减小后增大,温度高于500℃后增长的速率较大,而子长煤先增大后减小再增大,增长速率最大的区段是300℃～400℃;比表面积随温度的演化表现为:黑岱沟煤一直增加,而子长煤持续减小。(2)常规热解条件下,长焰煤孔隙体积分布以中孔和大孔为主,温度超过300℃时,大孔占绝大多数;而比表面积的分布以微孔和过渡孔为主。(3)高温蒸气热解条件下,长焰煤热解固态产物的孔隙体积分布以中孔和大孔为主,大孔占主导地位,子长煤表现更为明显,大孔比例达99.91%;孔隙比表面积分布表现为:黑岱沟煤以微孔和过渡孔为主,而子长煤以大孔为主。(4)高温蒸气热解固体产物表现出更为优良的渗透性能,与注入惰性气体相比,注入高温蒸气是煤层原位热解工艺实施的最佳方法。在煤层原位热解工艺实施过程中,该研究可为煤体孔隙结构随温度变化问题提供科学依据和理论指导。

Great changes in pore structure and quantity of coal may occur as the pyrolysis temperature rises.To study the change laws,a mercury intrusion method was adopted to measure and analyze the pore structure parameters of the solid products of flame coal pyrolysis,which were generated in vacuum system with temperatures from 300 ℃ to 600 ℃ and in high temperature steam state at 600 ℃;the pore fractal dimensions were calculated under different temperatures;and pore properties of solid products under two different pyrolysis ways were compared.The results indicate that：（1） Under conventional pyrolysis,the total pore volume and porosity of Heidaigou coal decreased from 300 ℃ to 400 ℃ and increased from 400 ℃ to 600 ℃;the increasing rate is the greatest from 500 ℃ to 600 ℃;the specific surface area increased progressively from 300 ℃ to 600 ℃.But for Zichang coal,the total pore volume and porosity increased from 300 ℃ to 400 ℃ and then decreased from400 ℃ to 500 ℃ and increased from 500 ℃ to 600 ℃;the increasing rate is the greatest from 300 ℃ to 400 ℃;the specific surface area decreased progressively from 300℃ to 600 ℃.（2） Under conventional pyrolysis,large pores were the major parts of pore volume,micropore and transition pore were the major parts of the specific surface area.（3） Under high temperature steam pyrolysis,the large pores were the major parts of pore volume;the proportion of large pores of Zichang coal was 99.91%;micropores and transition pores were the major parts of the specific surface area of Heidaigou coal;the large pores were the major parts of specific surface area of Zichang coal.（4） Compared with conventional pyrolysis,the permeability of solid products of high temperature steam pyrolysis was greater;and compared with inert gas injection,it is the best method in the coal situ-pyrolysis application.These results can provide a scientific basis and theoretical guidance for the issue that coal pore structure changes with temperature during coal situ-pyrolysis.