Experimental Enrichment of Low-Concentration Ventilation Air Methane in Free Diffusion Conditions

Abstract

Abstract:The massive emission of low concentrations (≤0.5%) of methane (CH 4 ) from ventilation roadways results in resource waste and environmental pollution. To mitigate these emissions, an enrichment tower for low-concentration methane is designed, and segregation and non-segregation experiments are conducted. The results reveal that stable concentrations of methane under segregation and non-segregation states in the enrichment tower gradually increase with height, with a maximum methane concentration of 0.64% and 0.54%, respectively. This shows that the methane enrichment effect in free diffusion conditions is more significant under the segregation state than under the non-segregation state. The stable concentration of methane in the middle and upper sections of the enrichment tower shows an increasing trend. However, the stable concentration of methane in the lower section of the enrichment tower has an increasing trend (less than 0.50%). According to the methane molecule Boltzmann distribution law, methane concentration enrichment decreases with height, and the conversion of the methane from the segregated to non-segregated is irreversible. Consequently, industrial applications of methane enrichment from buoyant forces are not feasible for low concentrations of methane.

Shear-induced Permeability Evolution of Sandstone Fractures

“…In sedimentary formations, shear slip of fractured rock associated with dilation or compaction can significantly change fracture permeability, thus affecting fluid flow [13][14][15]. Enhanced fluid flows may be beneficial for desorbing of coal seam gas and increasing geothermal energy extraction [16][17][18][19][20][21], but this enhanced flow will be disadvantageous for groundwater protection and mining [22]. Therefore, to achieve safe and efficient mining in coal seams, knowledge of the evolution of fracture permeability with shearing is very important.…”

Enrichment of low concentration methane: an overview of ventilation air methane

“…Unconventional technologies that have been investigated for gas separation include vortex tubes, 19–23 mechanical towers, 24,25 gas hydrates, 26–28 membranes 29,30 and adsorption based separation. 31–35 The first three (vortex tubes, gas hydrates and mechanical towers) are technologies/concepts without commercial applications currently, but the last two (membrane separation and adsorption-based separation) have been used on a commercial scale for natural gas and other gas separation.…”

“…Wang et al designed a mechanical tower for the enrichment of VAM by using CH 4 buoyancy under free diffusion conditions (namely, the gas mixture moves freely under the force of gravity) based on the fact that the density of CH 4 is lower than that of air. 24 The enrichment characteristics of segregated (CH 4 and N 2 enter the system separately) and non-segregated (CH 4 and N 2 are pre-mixed before entering the system) mixtures under free diffusion conditions were studied. For a CH 4 /N 2 mixture with 0.5% CH 4 , a CH 4 concentration of 0.54% was monitored for the non-segregated mixture, which is not promising.…”

“…Herein, for the first time, we present a review to discuss and analyze the technologies and materials for VAM enrichment. Because the conventional technologies widely used for CH 4 separation/purification from natural gas (CH 4 concentration of 55–98%) are not suitable for VAM enrichment, we first discuss the unconventional technologies including vortex tubes, 19–23 mechanical towers, 24,25 gas hydrates, 26–28 membranes 29,30 and adsorption based processes, 31–35 with focus on adsorption-based processes. Since the adsorbents used in adsorption-based processes are one of the key factors for gas separation/enrichment performance, we then discuss various materials including zeolites, porous carbon materials and metal–organic frameworks (MOFs) that are potentially useful as adsorbents for VAM and other low grade CH 4 enrichment, with focus on porous carbon materials and MOFs.…”

Industrial-Scale Experimental Study on the Thermal Oxidation of Ventilation Air Methane and the Heat Recovery in a Multibed Thermal Flow-Reversal Reactor

“…Utilization technologies of VAM can generally be divided into ancillary and principal uses [2,[4][5][6][7][8][9]. For ancillary uses, VAM is used to replace ambient air in combustion processes to reduce the use of primary fuel.…”