•The B-site multi-metallic synergistically doped perovskite is prepared.•LaMn0.8Fe0.15Co0.05O3 exhibits excellent catalytic activity for methane combustion.•Fe-Co co-doping accelerates the formation ...of surface Mn4+ and Olat.•The reaction mechanism for the catalytic combustion of methane is studied.
To enhance the catalyst’s properties, a modified sol–gel method is developed in this study, and a unique perovskite catalyst, LaMnxFeyCo1-x-yO3, is successfully synthesized by doping Fe-Co into the lattice of LaMnO3. The catalytic activity of the synthesized catalysts is initially determined by applying them to methane oxidation. Then, the structural, chemical, and surface properties of these catalysts are systematically evaluated utilizing XRD, BET, O2-TPD, H2-TPR, SEM, and XPS analyses. The modified LaMn0.8Fe0.15Co0.05O3 is shown to exhibit excellent activity (T90 at 486.5 ℃) in methane catalytic combustion, comparable to several standard noble metal materials. Experimental findings indicate that such perovskite structures have a larger specific surface area, an elevated molar ratio of Mn4+, desirable low-temperature reducibility, and excellent oxygen mobility relative to the original LaMnO3. Meanwhile, more efficient electron transfer from Mn4+/Mn3+ redox cycles, as well as the emergence of oxygen defects, significantly contribute to the robust interaction between Fe-Co and LaMnO3. Further reaction kinetic analysis is conducted to determine changes in species components and identify possible catalytic pathways. Notably, Fe-Co co-doping leads to an improvement in the increase of lattice oxygen and CH4 adsorption. In addition, the MVK kinetic mechanism governs methane combustion over LaMn0.8Fe0.15Co0.05O3. This study provides new insights into enhancing energy conversion performance and efficient utilization of ventilation air methane (VAM) through the implementation of highly efficient perovskites.
The high separation performance of inorganic molecular sieve membranes is technologically feasible for the enrichment of ventilation air methane from coal mining.
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•Membrane with ...N2/CH4 selectivity of >6 is technically feasible for the enrichment of ventilation air methane.•Feed CH4 concentration and gas permeance have significant influences on the enrichment cost.•Pursuing a high methane purity increases the cost dramatically.•Higher selectivity is required to complete the CH4 enrichment from VAM with low methane content of <1 vol%.•Carbon hollow fiber membranes may have a better potential for VAM enrichment compared to zeolite membranes.
Utilization of the low concentration methane from coal-mining ventilation air is challenging but can significantly contribute to the mitigation of methane emissions to the atmosphere. This work focuses on the techno-economic feasibility analysis of N2-selective membrane systems for the enrichment of ventilation air methane (VAM). The feed methane concentration and gas permeance are found to significantly influence the specific methane enrichment cost, while feed pressure has the lest effect. For a stand-alone membrane system, the optimal methane recovery of ca. 70% is identified to achieve a higher methane purity at the same cost, which may gain an economic benefit when it is operated at high plant capacity. Although the SAPO-34 membrane system is technologically feasible for the enrichment of 1.5 vol% VAM, novel membranes with a higher N2/CH4 selectivity of greater than 25 is required to reduce the membrane stages for the pre-concentration of a very diluted VAM of <1 vol%. Considering a large-scale application in the methane recovery from the coal-mining ventilation air, carbon hollow fiber membranes may have the potential to address the challenges of the high production cost and the module up-scaling with large packing density that is faced by zeolite membranes.
The greenhouse effect of methane is 25 times that of the same volume of carbon dioxide. The low-concentration methane (especially the ventilation air methane) emitted from coal mining is huge and ...discharged into the atmosphere, which wastes energy and intensifies the earth greenhouse effect. The catalytic co-combustion of the low-concentration methane in the mine exhaust air and the coal in the boiler under high efficiency catalyst can be achieved, which can not only realize the complete combustion of the low-concentration methane in the mine exhaust air, but also reduce the greenhouse effect caused by methane emission. Furthermore, it promotes the full combustion of coal in the boiler, which increases the heating value of coal-fired boiler. A Co3O4/SiO2-x catalyst with con-trollable particle size of Co3O4 and supported on silicon dioxide was prepared by using piperazine and pyromellitic acid hydrate as linker at different calcination temperatures. A series of characterization methods such as XRD, BET, H2-TPR
Coal mine methane (CMM) is a term given to the methane gas produced or emitted in association with coal mining activities either from the coal seam itself or from other gassy formations underground. ...The amount of CMM generated at a specific operation depends on the productivity of the coal mine, the gassiness of the coal seam and any underlying and overlying formations, operational variables, and geological conditions. CMM can be captured by engineered boreholes that augment the mine's ventilation system or it can be emitted into the mine environment and exhausted from the mine shafts along with ventilation air. The large amounts of methane released during mining present concerns about adequate mine ventilation to ensure worker safety, but they also can create opportunities to generate energy if this gas is captured and utilized properly.
This article reviews the technical aspects of CMM capture in and from coal mines, the main factors affecting CMM accumulations in underground coal mines, methods for capturing methane using boreholes, specific borehole designs for effective methane capture, aspects of removing methane from abandoned mines and from sealed/active gobs of operating mines, benefits of capturing and controlling CMM for mine safety, and benefits for energy production and greenhouse gas (GHG) reduction.
► This technical aspects of CMM capture in and from coal mines and utilization. ► The main factors affecting CMM accumulations in underground mines, and mine safety benefits of capturing coal mine methane were emphasized. ► Global CMM emissions and activities for capturing and utilizing CMM were reviewed from a global perspective.
•The thermal flow reversal reactor with heat recovery systems is constructed.•Low flowrate contributes to establishing initial temperature field.•Steam with 148 kg and 511 K can be produced at 1 % ...concentration.•The optimum reversing time in this paper is 120 s.•The link between temperature evolution and heat extraction is preliminary explored.
This work presents heat extraction characteristics in a pilot-scale thermal flow reversal reactor dedicated to the mitigation of ventilation air methane escaping from coal mining and the recovery of residual heat. The heat extraction mode arranged on both sides of the central zone was applied. The influence of flowrate, concentration and reversing time on comprehensive heat transfer performance were investigated through experiments. The temperature evolutions and the quantitative relationship between temperature evolutions and heat extraction were predicted through simulations. The experimental results show that low flowrate is susceptible to establishing rapidly initial temperature field. The heat recovery rate and generated superheated steam increase with concentration and varies parabolically with switch time. The optimum heat extraction is that heat recovered is slightly greater than or close to the stored heat. Therefore, the heat extraction research involved in this paper will provide a reference for other low-grade waste fuels in industrial applications.
Anthropogenic emissions of non-CO2 greenhouse gases such as fugitive methane contribute significantly to global warming. A review of fugitive methane combustion mitigation and utilisation ...technologies, which are primarily aimed at methane emissions from coal mining activities, with a focus on modelling and simulation of ultra-lean methane oxidation/combustion is presented. The challenges associated with ultra-lean methane oxidation are on the ignition of the ultra-lean mixture and sustainability of the combustion process. There is a lack of fundamental studies on chemical kinetics of ultra-lean methane combustion and reliable kinetic schemes that can be used together with computational fluid dynamics studies to design and develop advanced mitigation systems. Mitigation of methane as a greenhouse gas calls for more efforts on understanding ultra-lean combustion. Recuperative combustion provides a promising means for mitigating ultra-lean methane emissions. Progress is needed on effective methods to ignite and to recuperate and retain heat for oxidation/combustion of the ultra-lean mixtures. Catalysts can be very effective in reducing the temperatures required for oxidation while plasmas may be utilised to assist the ignition, but thermodynamic/aerodynamic limits of burning ultra-lean methane remain unexplored. Further technological developments may be focussed on developing innovative capturing technology as well as technological innovations to achieve effective ignition and sustainable oxidation/combustion.
•Using low-dimensional devices and mixed runners to enhance heat transfer.•Reducing the self-sustained concentration to 0.1%.•Gas processing capacity per unit volume increased by 1.03–2.5 times.•The ...benefit of carbon emission reduction is increased by at least 1.95.•The efficiency of waste heat utilization is increased by 2.5 times.
This paper uses Ansys Fluent software to conduct a two-dimensional numerical study on the oxidation performance of basalt fiber bundle thermal flow-reversal reactor (TFRR). The influence of inlet methane concentration, inlet flow rate and circulation period on the oxidation performance of TFRR is analyzed. The results show that the maximum temperature in the reactor increases significantly with the increase of inlet concentration and flow rate. At the same time, the lower limit of the concentration that can be handled by the reactor was studied, and it was found that the basalt fiber bundle TFRR can completely treat the gas with the concentration of 0.1%, under the operating parameters of tc = 80 s, vin = 0.65 m/s or tc = 60 s, vin = 1.0 m/s. In addition, the device was compared with the honeycomb ceramic TFRR in terms of economic efficiency. It was found that the clean development mechanism(CDM) emission reduction benefit of the former was 1.95 times than that of the latter, and the economic benefit of waste heat utilization was 2.5 times than that of the latter.
•Underground coal mines as point sources of methane emission.•Causes of methane emission from underground coal mines.•Well prepared strategy for atmospheric GHG observation capabilities.•An ...integrated CH4 monitoring system so that the point sources of CH4 emission can be identified clearly.
The Upper Silesian Coal Basin in Poland is one of the major European hotspots of CH4 release. Until now, no data concerning short-term CH4 emissions from coal mines have been accessible worldwide. They are available only on a yearly timescale. No values are provided on a higher temporal scale, that’s why the measurements presented here are of great importance. This paper discusses short-term CH4 emissions from ventilation shafts of three mining fronts (Mf) divided into two periods. The concentrations of CH4 in shafts varied from 0.05 to 0.4 %. The highest levels occurred in Shaft IV (Mf I) and Shaft VI (Mf II): from 0.15 to 0.38 % (Period 1). These values correspond to emission levels ranging from 27 to 75 m3/min (Shaft IV) and from 18 to 40 m3/min (Shaft VI). In Period 2, the highest concentrations of CH4 occurred in Shaft VI (Mf II and III): from 0.2 to 0.4 %. The most significant CH4 emissions were recorded for Shaft VI (Mf II) and ranged from 29 to 54 m3/min. Presented data have been used to validate the measurements obtained in the CoMet campaign, which aimed at verifying the sensitivity of the test equipment operating from aircraft. During the test flights of HALO in 2015, the CoMet team achieved a remarkable consistency of measurements conducted with airborne equipment (26 ± 3m3/min) and the emission data (24.34 m3/min), for Shaft VI (Mf II). The analysed short-term data for individual shafts are more reliable and can improve CH4 flux estimates during the CoMet campaign in 2018.
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.
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