Article pubs.acs.org/EF
Upgrade of Low-Concentration Oxygen-Bearing Coal Bed Methane by a Vacuum Pressure Swing Adsorption Process: Performance Study and Safety Analysis Yan Zhou, Qiang Fu, Yuanhui Shen, Weina Sun, Donghui Zhang,* Dongdong Li, and Haiyu Yan The Research Center of Chemical Engineering, Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China S Supporting Information *
ABSTRACT: The recovery of methane from oxygen-bearing coal bed methane (CBM) (25% CH4/65% N2/10% O2) by vacuum pressure swing adsorption (VPSA) was studied systematically in this work. Nevertheless, it is difficult to implement systematic safety investigations of the process just by bench-scale experiments and pilot plants. Emphasis was placed on the construction of a new way to analyze process safety based on a developed explosive triangle theory that could be able to provide guidance for comprehensive safety evaluation in the VPSA process for upgrading of oxygen-bearing CBM. The simulation results revealed that a two-column seven-step VPSA process not only could generate 50.40% CH4 purity with 86.3% product recovery but also could achieve higher product productivity of 1.494 (mol of CH4)·kgads−1·h−1 and lower energy consumption of 0.179 kWh·Nm−3 feed as well. The results of the safety analysis procedure according to the simulation results demonstrated that the flammability zone distribution mainly exists in the adsorption, pressure equalization, replacement, and pressurization steps and varied regularly with each step time and axial distance. A two-stage VPSA process with nitrogen dilution of the feed gas that is able to achieve safe operation in a further separation system was well-verified through simulative investigation.
1. INTRODUCTION Coal bed methane (CBM) is a mixture of methane and other contaminants such as N2, O2, CO2, H2O, etc., that belongs to associated mineral resources of coal streams and rock strata. It usually derives from artificial coal mine exploitation activities. Techniques of methane degasification include vertical drilling, gob drainage, and air ventilation of methane.1 A popular classification of CBM is available on the basis of the methane extraction concentration: high-quality methane (>95% concentration), which can be extensively used for pipe network gas; secondary-quality methane (30−95% concentration), which can be further used for electricity generation or fuel; and the remaining low-concentration methane (
