低温氮吸附中煤阶对临界填充孔径的影响

doi:10.16265/j.cnki.issn1003-3033.2022.04.008

摘要/Abstract

摘要：

为探究煤岩吸附理论及煤层气吸附机制,首先选用6种不同煤阶煤样进行低温氮(N₂)吸附试验,分析煤中填充态N₂分子的临界填充孔径(CPSD);然后通过密度泛函理论(DFT)和微孔填充理论(TVFM)分析试验等温线特征,得到煤中完成微孔填充的临界填充压力(CFP)以及CPSD;最后结合相对压力分段法,通过Langmuir方程-D-A方程-BET方程拟合验证分析结果。研究表明:煤阶由低到高,煤样N₂吸/脱附等温线由II型向I型过渡;低阶煤中以微孔填充和单分子层吸附形式赋存的N₂分子比例大于高阶煤;煤阶由低到高,CPSD呈先减后增趋势;6种煤样的CPSD在1.61~2.19 nm 之间,煤阶越高,CPSD范围越小。

关键词: 煤阶, 低温N₂, 吸附试验, 临界填充孔径(CPSD), 微孔填充, 孔隙结构

Abstract:

In order to study coal adsorption theory and adsorption mechanism of coalbed methane, six coal samples of different ranks were selected for low-temperature N₂ adsorption experiments to explore CPSD of filled N₂ molecules in coals. Then, experimental isotherm characteristics were analyzed through density functional theory (DFT) and theory of volume filling of micropore (TVFM), and critical filling pressure (CFP) and CPSD for micropore fillings were obtained. Finally, relative pressure segmentation method was used to verify the results by fitting of Langmuir equation-Dubinin-Astakhov (D-A) equation-Brunauer-Emmet-Teller (BET) equation. The results show that N₂ adsorption/desorption isotherm of coal samples, from low to high rank, transitions from type II to type I. And proportion of N₂ molecules present in forms of micropore filling and monolayer adsorption in low-rank coals is greater than that of high-rank ones. CPSD decreases first and then increases as coal rank goes from low to high. The higher the rank is, the smaller CPSD range of 6 coal samples will be, which is between 1.61-2.19 nm.

Key words: coal rank, low-temperature N₂, adsorption experiment, critical filling pore size distribution (CPSD), micropore filling, pore structure

洪林, 王文静, 高大猛, 郭英超, 马鸿海. 低温氮吸附中煤阶对临界填充孔径的影响[J]. 中国安全科学学报, 2022, 32(4): 51-58.

HONG Lin, WANG Wenjing, GAO Dameng, GUO Yingchao, MA Honghai. Influence of coal rank on CPSD in low-temperature N₂ adsorption[J]. China Safety Science Journal, 2022, 32(4): 51-58.

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煤样	煤矿	分类	水分	灰分	挥发分	固定碳
S₁	蒲河	褐煤	16.84	11.59	34.72	36.86
S₂	准格尔	长焰煤	5.21	14.20	24.93	55.67
S₃	小凌河	气煤	2.14	26.06	29.63	42.17
S₄	鹤岗	1/3焦煤	1.62	6.78	33.08	58.52
S₅	常村	贫煤	1.25	9.17	13.24	76.34
S₆	余吾	无烟煤	1.46	9.78	10.55	78.21

煤样	等温线类型	滞后环类型	孔隙形状	P/P₀ (B点)	Q_B占总吸附量比例/%
S₁	Ⅱb	H2	墨水瓶孔	0.098 86	31.24
S₂		H3	非均匀狭缝孔	0.060 05	13.70
S₃			非均匀狭缝孔	0.043 09	13.34
S₄			0.062 26		11.77
S₅	Ⅰb	H4	均匀且狭窄的狭缝孔	0.110 94	19.57
S₆	Ⅰb	H4	均匀且狭窄的狭缝孔	0.160 89	11.52

煤样	CFP(P/P₀)	CPSD/nm	D-A指数
S₁	8.0×10^-4~0.033 9	1.73~2.19	1.362 0
S₂	5.5×10^-4~0.030 2	1.70~2.17	1.534 3
S₃	2.4×10^-4~0.010 0	1.64~1.99	1.532 4
S₄	1.4×10^-4~0.010 4	1.61~2.00	1.833 0
S₅	5.0×10^-4~0.010 6	1.69~2.00	2.544 4
S₆	8.4×10^-4~0.010 7	1.73~2.01	2.437 5

煤样	P/P₀	R²		P/P₀	R²
煤样	P/P₀	D-A	Langmuir	P/P₀	D-A	Langmuir	BET
S₁	8.0×10^-4~0.033 9	0.999 21	0.994 2	0.033 9~0.302 1	0.967 46	0.985 22	0.999 76
S₂	5.5×10^-4~0.030 2	0.999 45	0.994 02	0.030 2~0.302 35	0.951 76	0.985 47	0.999 54
S₃	2.4×10^-4~0.010 0	0.999 80	0.996 19	0.010 0~0.321 4	0.890 9	0.970 82	0.999 72
S₄	1.4×10^-4~0.010 4	0.998 83	0.995 03	0.010 4~0.300 2	0.874 45	0.982 49	0.999 56
S₅	5.0×10^-4~0.010 2	0.999 28	0.998 65	0.010 2~0.321 2	0.984 32	0.999 87	0.990 27
S₆	8.4×10^-4~0.010 7	0.998 63	0.997 72	0.010 7~0.321 5	0.934 71	0.998 55	0.984 62