Ventilation air methane is one of available resources with a massive reserve. However, most of ventilation air methane is discharged into the air and pollutes the environment. Catalysts with high ...temperature resistance (>800 °C) for ventilation air methane are very essential for utilization of the ventilation air methane. We mainly prepared catalysts CeO2/La2CoFeO6 and La2CoFeO6/CeO2 and comparative samples CeO2 and La2CoFeO6 by the simple sol-gel method and calcined them under 900 °C, and tested the catalytic performance of ventilation air methane combustion under the condition of 5 vol% H2O. The experimental results show that the light-off temperature (T10) and complete combustion temperature (T90) of the ventilation air methane combustion reaction of CeO2/La2CoFeO6 catalyst are 417.4 and 587.7 °C, respectively. T10 and T90 of La2CoFeO6/CeO2 only reach 425.5 and 615.8 °C. The T10 and T90 of CeO2/La2CoFeO6 are 417.4 and 587.7 ℃, which are lower than those of La2CoFeO6 (T10 = 452.4 ℃ and T90 = 673.0 ℃) and La2CoFeO6/CeO2 (T10 = 425.5 ℃ and T90 = 615.8 ℃). Therefore, the catalytic performance of the anti-supported rare earth oxide catalyst CeO2/La2CoFeO6 is better than that of La2CoFeO6 and supported catalyst La2CoFeO6/CeO2.
Double perovskite anti-supported rare earth oxide catalyst CeO2/La2CoFeO6 shows properties of the improving of the amount of the surface lattice oxygen and the desorption oxygen and the transformation of the ionic valence states, which enhance the catalytic activity for the ventilation air methane combustion. Display omitted
•Double perovskite anti-supported catalyst CeO2/La2CoFeO6 was prepared.•CeO2/La2CoFeO6 shows the optimal catalytical activity for VAM combustion.•CeO2/La2CoFeO6 shows a better stability in water atmosphere.•Fe3+, Fe2+, the surface lattice and the desorption oxygen are main active species.•Mössbauer also has some novelty in the characterization of catalysts.
In order to reduce the impact of ventilation air methane (VAM) emission on the greenhouse effect, we investigated the oxidation pattern of VAM with a concentration of 0.75% and its mixing method with ...lignite and anthracite, and the effect of the calcareous mudstone dust in VAM on the VAM in mixed firing system. Calcareous mudstone dust with different metal oxide content was mixed with different coal species and placed in this gas environment by using a tube furnace system to simulate a premixed gas environment of VAM and air. X-ray diffraction (XRD) analysis was used to analyze, the mixed firing products. The study shows that: calcareous mudstone dust can promote the oxidation of gas, and the oxidation efficiency increases with the increase of metal oxide content. Calcareous mudstone dust can promote the oxidation of VAM in the mixed firing system at the same temperature, and the higher the metal oxide content of calcareous mudstone dust, the lower the temperature at which the conversion of spent air gas reaches its limit. According to the effect of dust on the gas conversion of the two coal blending systems, it can be seen that although the gas conversion rate of the lignite system is always higher than that of the anthracite system, the dust has a negative effect on the conversion of the VAM in the lignite system and a positive effect on the anthracite system, so the effect of dust on the anthracite blending system is better than that on the lignite system. Calcareous mudstone dust also plays the role of sulfur fixation, so the calcareous mudstone dust involved in the process of discharging VAM from the mine can be left untreated and passed into the coal-fired boiler together with VAM.
Gasification for hydrogen production by the H-type finned tube embedded in the packed bed is considered to be more economical. Based on the thermal flow reversal reactor, the heat transfer ...characteristics of H-type finned tube embedded on the both sides of high-temperature zone of the packed bed under the quasi-steady were researched. The contribution of radiation heat transfer rate on the H-type finned tube is about 60.5% at most and radiation mainly occurs on the central tube. Within the range of inlet temperature and Re, the fin-assisted degree is both decreased gradually and the maximum is 48.9%. When the temperature is above 906 K or within the range of Re, the heat transfer rate of the fin is mainly from the radiation heat transfer rate. Under the condition of high inlet temperature and high Re, the fin-assisted degree is minimum, which indicates the operation stability of the H-type finned tube is better.
•The contribution of radiation heat transfer on H-type finned tube is ~60.5%.•Radiation mainly occurs on the central tube in this paper.•The fin-assisted degree in this paper is ~48.9%.•When Tin > 906 K or Re > 652.3, heat transfer rate of fins is mainly from radiation.•In high inlet temperature and Re condition, the finned tube works more steadily.
Ventilation air methane (VAM), which is the main source of greenhouse gas emissions from coal mines, has been a great challenge to deal with due to its huge flow rates and dilute methane levels ...(typically 0.3–1.0 vol%) with almost 100% humidity. As part of our continuous endeavor to further improve the methane adsorption capacity of carbon composites, this paper presents new carbon composites derived from macadamia nut shells (MNSs) and incorporated with carbon nanotubes (CNTs). These new carbon composites were fabricated in a honeycomb monolithic structure to tolerate dusty environment and to minimize pressure drop. This paper demonstrates the importance of biomass particle size distributions when formed in a composite and methane adsorption capacities at low pressures relevant to VAM levels. The selectivity of methane over nitrogen was about 10.4 at each relevant partial pressure, which was much greater than that (6.5) obtained conventionally (at very low pressures), suggesting that capturing methane in the presence of pre-adsorbed nitrogen would be a practical option. The equilibrium and dynamic performance of biomass-derived carbon composites were enhanced by 30 and 84%, respectively, compared to those of our previous carbon fiber composites. In addition, the presence of moisture in ventilation air resulted in a negligible effect on the dynamic VAM capture performance of the carbon composites, suggesting that our carbon composites have a great potential for site applications at coal mines because the cost and performance of solid adsorbents are critical factors to consider.
•Carbon composites were fabricated from macadamia nut shells and carbon nanotubes.•Capture capacity at relevant methane pressure is important for adsorbent selection.•Particle size distributions of biomass are to be considered when forming composites.•Moisture effect on the methane capture performance of composites was negligible.
Fugitive methane emissions from underground coal mines are considered a potent greenhouse gas source with a large global warming potential. Application of ventilation air methane thermal oxidiser ...technology reduces this risk to a large extent. However, it imposes the risk of accidental fires and explosions in the mine site which may claim many lives and cause massive property damage. As such, the necessity of employing safety barriers such as flame arrester seems crucial to protect the mine against the accidental flames and explosion propagation originated from the thermal oxidiser.
The aim of this work was to evaluate the effectiveness of an inline flame arrester for the mitigation of methane explosions in a large scale detonation tube. The results corresponding to this study indicated that the flame arrester was capable to effectively mitigate the explosion flames of 5%, 7.5% and 9.5% methane air mixtures (for a 10 m fuel filled section). The flame arrester reduced the pressure wave velocity by 88% and 40% for the explosions of methane-air mixtures of 7.5% and 9.5% methane, respectively. The flame propagation velocities for the 7.5% and 9.5% methane concentrations reduced approximately 32% and 44%, respectively. A significant pressure build-up was observed upstream of the flame arrester when compared with a duct without flame arrester. In addition, the build-up pressure was relatively higher for larger methane concentrations (e.g. 9.5%). These observations highlights that the maximum design pressure of an industrial process plant must be carefully considered when implementing an inline flame arrester due to the possibility of a sudden pressure increase cause by an explosion.
Nearly 70% of the methane released from hard coal seams, as the so-called Ventilation Air Methane, is emitted to the atmosphere with the air discharged by the mine ventilation system. Therefore, ...utilization of this emission, especially with a rational heat recovery becomes an important challenge for hard coal mines. The paper proposes combustion in Thermal Flow Reversal Reactors, currently as the most promising and technically advanced method of solving this problem. The operating principle of such reactors is briefly described with a short review of the current literature on the subject, particularly focussing on aspects of heat recovery. A progress report of research and development activities, carried out in the recent years in the Institute of Chemical Engineering, Polish Academy of Sciences in Gliwice, Poland, has been given. This part provides a brief overview of kinetic studies on thermal combustion, results of experiments carried out on a research and demonstration plant, discussion of computer simulations as well as preliminary analysis of the possibilities of the process intensification. The article draws attention to the possibility of thermal asymmetry formation in the flow reversal reactors. The ways of the process control to prevent asymmetry are also discussed.
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•Huge amount of methane is emitted to the atmosphere with coal mine ventilation air.•Methane emission increasing the greenhouse effect causes great loss of valuable fuel.•Thermal CH4 combustion in a reverse-flow is a promising solution to the problem.•Kinetic and simulation studies performed provide a solid basis for development.
A large amount of gas is emitted during underground mining processes, so mining productivity decreases and safety risks increase. Efficient methane drainage from the coal seam and surrounding rocks ...in underground mines not only improves safety but also leads to higher productivity. Methane drainage must be performed when the ventilation air cannot dilute the methane emissions in the mine to a level below the allowed limits. The cross-measure borehole method is one of the methane drainage methods that involves drilling boreholes from the tailgate roadway to an un-stressed zone in the roof or floor stratum of a mined seam. This is the main method used in Tabas coal mine N 1. One of the effective parameters in this method is the distance between methane drainage stations, which has a direct effect on the length of boreholes required for drainage. This study was based on the measurement of ventilation air methane by methane sensors and anemometers placed at the longwall panel as well as measuring the amount of methane drainage. Moreover, in this study, the obtained and analyzed data were used to determine the suitable distance between methane drainage stations based on the cross-measure borehole method. In a field test, three borehole arrangements with different station distances in Panel E4 of Tabas coal mine N 1 were investigated. Then, the amounts of gas drained from these arrangements were compared with each other. The highest methane drainage efficiency was achieved for distances in the range of 9-12 m between methane drainage stations.
Using the principles of displacement chromatography, a cost-effective adsorption separation method for the recovery of ventilation air methane (VAM) is developed. A fixed bed with activated carbon ...beads (ACBs) is used to adsorb low-concentration methane from VAM gas. The stronger adsorption component CO2 passes through the column to displace the adsorbed CH4. This displacement step generates a product with highly pure CH4 gas. Adsorption equilibrium isotherms of CH4, N2 and CO2 have been measured gravimetrically at different temperatures up to 10bar. These isotherms are fitted to the Sips model. Diluted breakthrough results are analyzed using a bi-pore diffusion model to obtain the micropore diffusivities of CH4, N2 and CO2 in the ACBs. Mixture breakthrough results have been employed to validate the applicability of the IAST-Sips model to predict mixture adsorption equilibria. A rigorous mathematical model is used to investigate the evolution curves of CH4, N2 and CO2 along the fixed bed during the CO2 displacement step, where it is found that the enrichment of the low concentration CH4 is improved significantly. Furthermore, the CO2 displacement experiments in the fixed bed for methane recovery from CH4/N2 mixtures with 1% and 10% CH4 content are performed and compared with the simulated results. It is found that 10% CH4 gas is concentrated to 89% CH4 purity and 1% CH4 gas can be concentrated to 53.5% CH4 purity, demonstrating that CO2 displacement is a promising technology for the enrichment of ventilation air methane.
•The concept of displacement chromatography is used for enrichment of VAM.•A mathematical model is developed to study the CO2 displacement behavior for the enrichment of ventilation air methane.•10% CH4 in CH4/N2 mixture is concentrated to 89% using activated carbon beads adsorption with CO2 displacement method.•IAST-Sips model and bi-pore diffusion model predict the dynamic behaviors of pure and mixture of CO2, CH4 and N2 on ACBs very well.
Methane emissions associated with coal-mine ventilation pose a tremendous environmental problem and lead to inadvertent loss of a valuable energy source. The proportion of methane released through ...underground ventilation is as high as 70% of all the coal-related emissions. Additionally, the CH
4 Global Warming Potential is 21 (for a timescale of 100 years), compared with 1 for carbon dioxide. If the heat of combustion of the methane could be usefully employed, this would bring a twofold benefit of avoiding both CH
4 release and CO
2 emission from the production and use of the fuel thereby displaced. The projects carried out in the Institute of Chemical Engineering, Polish Academy of Sciences explored three major routes for utilizing ventilation air methane (VAM): (1) using VAM as combustion air in conventional boilers, (2) oxidizing VAM in reverse-flow reactors (either catalytic or non-catalytic) to produce heat, (3) enriching VAM (via pressure-swing adsorption or membrane separation) to concentration levels suitable for subsequent use (in, say, reverse-flow reactors). The investigations have now been focused upon homogeneous combustion of VAM in reverse-flow reactors.