Dynamic adsorption measurement of coal particles based on low field NMR

doi:10.11949/0438-1157.20200676

Abstract

Abstract:

The development of coalbed methane is an important part of unconventional natural gas in China. Methane gas in coal mainly occurs in the form of adsorption in a series of nanopores. The dynamic process of adsorption is of great significance for the exploitation of coalbed methane. The low field nuclear magnetic resonance experimental system for measuring the dynamic adsorption characteristics is built, and the dynamic adsorption process of methane with time and pressure is quantitatively analyzed by NMR transverse relaxation map. The methane in coal samples in the transverse relaxation map of NMR presents the multi-peak distribution. The relaxation time peak of 0.1—1 ms contains the information of methane gas content in nanopores. With the increase of time, the gas is gradually converted to the adsorption state. The isothermal adsorption curve of the sample can be obtained from the equilibrium adsorption amount at each pressure, which conforms to the fitting of Langmuir model.

Key words: adsorption, methane, nuclear magnetic resonance, transverse relaxation, nanopores

摘要：

煤层气的开发是我国非常规天然气开发的重要环节，与常规天然气不同的是煤层气中甲烷主要以吸附形式赋存在煤的一系列纳米孔中。甲烷在煤粉颗粒孔隙中吸附行为的动态过程对煤层气的开发具有重要意义。实现了一种基于低场核磁共振技术在线测量煤粉吸附特性的实验方法，通过横向驰豫分布区别孔隙中含氢流体分布，定量表征游离气和吸附气含量。结果表明煤粉颗粒的甲烷吸附在核磁共振的横向弛豫图谱中呈现多峰分布，其中弛豫时间在0.1～1 ms的峰包含了纳米孔隙中甲烷含气量的信息。随着时间增加，甲烷气体逐渐转换为吸附态。通过不同压力下核磁共振的横向弛豫图谱，定量分析了甲烷在颗粒样品中随时间和压力变化的动态吸附过程，并得到了等温吸附曲线且符合Langmuir拟合模型。

关键词: 吸附, 甲烷, 核磁共振, 横向弛豫, 纳米孔隙

CLC Number:

O 647.32

Taojie LU, Ruina XU, Peixue JIANG. Dynamic adsorption measurement of coal particles based on low field NMR[J]. CIESC Journal, 2020, 71(S2): 195-200.

陆韬杰, 胥蕊娜, 姜培学. 基于低场核磁共振的煤粉动态吸附测量[J]. 化工学报, 2020, 71(S2): 195-200.

Figures/Tables 8

Fig.1 Schematic diagram of nuclear magnetic resonance experimental system

Fig.2 Methane T2 signal peak under different pressure

Fig.3 Relationship between peak area of bulk methane and amount of methane

Fig.4 Transverse relaxation atlas of 2.7 MPa methane in pulverized coal particles

Fig.5 Dynamic transverse relaxation of 2.7 MPa methane in pulverized coal particles

Fig.6 Time-varying peak area of bulk methane (a) and dynamic adsorption amount (b)

Fig.7 Dynamic methane adsorption curves of pulverized coal particles under different pressures

Fig.8 Isothermal adsorption curves of pulverized coal particles

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