Upgrade of Low-Concentration Oxygen-Bearing Coal Bed Methane by a Vacuum Pressure Swing Adsorption Process: Performance Study and Safety Analysis

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.

CO Enrichment from Low-Concentration Syngas by a Layered-Bed VPSA Process

“…(e) Extended Langmuir adsorption isotherm pattern is applied to characterize the adsorption equilibrium behavior of the adsorbate onto adsorbent. The quantized equations concerning an adsorption fixed-bed model 36,37 are presented in Table 3, and the initial and boundary conditions 37 for the breakthrough and cycle operation are given in Table S1. Besides, the physical properties of the adsorbent bed are the same as the breakthrough experiment, and the involved transport model parameters are provided in Table 4 to achieve simulation runs.…”

Vacuum Exhaust Process in Pilot-Scale Vacuum Pressure Swing Adsorption for Coal Mine Ventilation Air Methane Enrichment

“…As the isotherm of nitrogen and oxygen on active carbon is almost the same [19], VAM can be considered as methane and nitrogen. In this study, the isotherms of methane and nitrogen at 298 K, 308 K and 318 K are shown in Figure 5.…”

“…Bae et al [22] also showed the same result, that the methane concentration increases with the desorption time, and the desorption gas was mostly air if the desorption time was very short desorption. On the other hand, methane's mass transfer coefficient is lower than nitrogen and oxygen, and methane desorbed slower than nitrogen and oxygen [15,19,35]. Thus, nitrogen and oxygen desorbed first, and the vacuum exhaust step can emit this part of the low methane concentration gas.…”

Effect of Surface Chemistry and Textural Properties of Activated Carbons for CH4 Selective Adsorption through Low-Concentration Coal Bed Methane

“…Pressure swing adsorption is one of the main methods to separate and accumulate CH 4 from CBM . Adsorbent is the core of adsorption; the common adsorbents are activated carbons (AC), , metal–organic frameworks (MOFs) and activated carbon fibers (ACFs).…”

“…Pressure swing adsorption is one of the main methods to separate and accumulate CH 4 from CBM. 5 Adsorbent is the core of adsorption; the common adsorbents are activated carbons (AC), 6,7 metal−organic frameworks (MOFs) and activated carbon fibers (ACFs). Among them, AC is the most widely used adsorbent and more suitable for CH 4 separation and accumulation from low-concentration CBM in industry because of its low cost, stable property, and unique microporosity.…”