Chinese Journal of Chemical Engineering ›› 2021, Vol. 32 ›› Issue (4): 264-280.doi: 10.1016/j.cjche.2020.08.043

• Process Systems Engineering and Process Safety • Previous Articles     Next Articles

Vacuum pressure swing adsorption process for coalbed methane enrichment

Bo Lu1, Yuanhui Shen2, Zhongli Tang2, Donghui Zhang2, Gaofei Chen3   

  1. 1 State Key Laboratory of Coal and CBM Co-mining, Jincheng 048000, China;
    2 The Research Center of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China;
    3 Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
  • Received:2020-05-14 Revised:2020-08-26 Online:2021-04-28 Published:2021-06-19
  • Contact: Donghui Zhang
  • Supported by:
    This work is part of the project supported by the Shanxi Coalbed Methane Joint Research Fund (2015012004).

Abstract: The enrichment of low concentration coalbed methane using adsorption process with activated carbon adsorbent was studied in this work. Adsorption isotherms of methane, nitrogen and carbon dioxide on activated carbon were measured by volumetric method, meanwhile a series of breakthrough tests with single component, binary components and three components feed mixture has been performed for exploring dynamic adsorption behaviors. Moreover, a rigorous mathematical model of adsorption bed containing mass, energy, and momentum conservation equation as well as dual-site Langmuir model with the Linear driving force model for gas-solid phase mass transfer has been proposed for numerical modeling and simulation of fixed bed breakthrough process and vacuum pressure swing adsorption process. Furthermore, the lumped mass transfer coefficient of methane, nitrogen and carbon dioxide on activated carbon adsorbent has been determined to be 0.3 s-1, 1.0 s-1 and 0.06 s-1 by fitting the breakthrough curves using numerical calculation. Additionally, a six bed VPSA process with twelve step cycle sequence has been proposed and investigated for low concentration coalbed methane enrichment. Results demonstrated that the methane molar fraction in feed mixture ranged from 10% to 50% could be enriched to 32.15% to 88.75% methane in heavy product gas with a methane recovery higher than 83% under the adsorption pressure of 3 bar (1 bar=105 Pa) and desorption pressure of 0.1 bar. Energy consumption of this VPSA process was varied from 0.165 kW·h·m-3 CH4 to 0.649 kW·h·m-3 CH4. Finally, a dual-stage VPSA process has been successfully developed to upgrade a low concentration coalbed methane containing 20% methane to a target product gas with methane purity higher than 90%, meanwhile the total methane recovery was up to 98.71% with a total energy consumption of 0.504 kW·h·m-3 CH4.

Key words: Coalbed methane enrichment, VPSA process, Activated carbon, Numerical modeling