低甲烷浓度煤层气的水合物法提纯实验

低甲烷浓度煤层气提纯是煤层气资源开发利用的一个重要发展方向,但是甲烷回收率低是低甲烷浓度煤层气提纯技术急需解决的关键问题。为此,采用气体水合物方法对低甲烷浓度煤层气进行提纯实验研究,向反应体系引入环戊烷降低气体水合物相平衡条件并提高甲烷回收率。采用等温压力搜索法测定了低甲烷浓度煤层气在环戊烷—水体系中的水合相平衡数据,并在等温等压条件下研究了生长驱动力和环戊烷浓度对甲烷回收率的作用规律。结果表明:1环戊烷对低甲烷浓度煤层气生成气体水合物的相平衡条件具有显著的促进作用。2甲烷回收率随着生长驱动力的升高而减小,随着环戊烷浓度的升高而增大。压力升高后,氮气将与甲烷竞争进入气体水合物晶体,导致甲烷回收率下降;在283.4K、2.6MPa和13%环戊烷浓度的实验条件下,甲烷回收率高达46.1%。3经过二级水合分离后,煤层气的甲烷浓度从30%提高到了72%。该项成果为低甲烷浓度煤层气提纯技术的发展提供了基础数据和实验依据。

An experimental study of using hydrate formation to enhance the methane recovery of low concentration CBM

The purification of low concentration coalbed methane (CBM) is one of the significant developing directions in the exploration and utilization of CBM resources. However, how to improve methane recovery is the very core issue. In this experimental study, we employed the hydrate based gas separation method to recover methane from the low concentration CBM, and introduced cyclopentane to reduce hydrate phase equilibrium conditions to increase the methane recovery. Then, we used the isothermal pressure search method to measure the phase equilibrium data of gas hydrates formed from CBM in the presence of cyclopentane. We also investigated the impacts of driving force and cyclopentane concentration on methane recovery at constant temperature and pressure conditions. The following findings were obtained. (1) The presence of cyclopentane in solutions remarkably stimulated the phase equilibrium conditions for gas hydrates formed from the low-concentration CBM. (2) The methane recovery decreased with the increasing driving force and increased with the rising cyclopentane concentration. With the elevation of pressure, nitrogen competed with methane to enter hydrate crystals and therefore resulted in the decrease of methane recovery. The methane recovery was increased to 46.1% at 283.4 K, 2.6 MPa, and 13 wt% CP. (3) The methane content in CBM increased from 30 to 72 % after a two stage hydrate based gas separation process. This experimental study provides basic data for this field of research.