Methane Concentration Research Articles

Ex-situ biogas enrichment by hydrogenotrophic methanogens at low H2/CO2 ratios: Effect of empty bed residence time

Biohydrogen is a good candidate for biogas upgrading. However, the system will operate at a lower H2/CO2 ratio than the stoichiometric one due to the CO2 present in the bioH2, challenging the process. Some operational parameters can improve the performance. Therefore, this study evaluated the effect of reducing the empty bed residence time (EBRT) on ex-situ biogas upgrading using low H2/CO2 ratios. Hydrogen was added to synthetic biogas (65 % CH4, 35 % CO2) to obtain the H2/CO2 ratios of 3:1 and 4:3. The EBRTs tested were 12, 6, and 3 h. The operation at 3:1 H2/CO2 ratio and the subsequent EBRT reduction negatively affected methane production. In contrast, the highest methane concentration (80 ± 1 %, EBRT: 12 h) and CH4 productivity (1.7 L/L d, EBRT: 3 h) were obtained with the 4:3 H2/CO2 ratio. The hydrogenotrophic archaea Methanobacterium and Methanolinea, as well as the acetoclastic archaeon Methanosaeta, dominated the archaeal community. Reducing the H2/CO2 ratio and the EBRT positively affected methane concentration and productivity; their optimization could enhance the system’s performance. Biohydrogens’ use in biogas upgrading diversifies its use without the need for purification to eliminate the CO2 in the biohydrogen.

Experimental Study on the Combustion Characteristics of Ultralow-Concentration Methane in Divergent Porous Media Burner

ABSTRACT To improve the stable combustion characteristics of ultralow-concentration methane (Concentration of 3.5%-5.0%), a series of combustion experiments were carried out by filling alumina spheres with different particle sizes (i.e. 5 mm, 10 mm and 15 mm) in a divergent burner, and the effects of divergent angle (i.e. 10°, 20° and 30°) and pore distribution on the flame propagation and stable combustion characteristics of ultralow-concentration methane were revealed. The results show that larger particle sizes and methane flow rates lead to the double flame surface phenomenon, and increasing angle and decreasing particle size can help to improve the preheating efficiency of the burner. Moreover, the inlet flow rates corresponding to the steady combustion of ultra-low concentrations methane are between 0.225 m/s and 0.308 m/s, the increase in inlet velocity, particle size, and angle will reduce the stability of the flame and make the shape of the flame surface developed in the order of “V→W→∧.” The burner with 10 mm particles and 30° angle has a wider stable combustion range, and the burner filled with smaller pore distribution help to improve the utilization of the lower concentration methane premixed.

Research on methane Hazard interval prediction method based on hybrid “model-data”driven strategy

Safe mining of coal has an important impact on energy security, while effective control of methane hazard is the key to ensuring safe coal mining. Methane concentration is the main factor determining the hazard of methane in coal mines, and in order to limit the impact of methane on coal mine safety, this study proposes a methane concentration interval prediction method based on a hybrid “model-data” driven idea. Firstly, by analyzing the data and constructing a methane concentration prediction method based on model-driven, which reduces the influence of multicollinearity in the methane concentration series on the prediction effect, and then, in combination with the deep learning technique, a method based on the Wasserstein distance to improve the Informer model is proposed, and finally a hybrid-driven methane concentration interval prediction model is established by introducing the IOWGA operator and the statistical method. After an example analysis of a coal mine in Guizhou Province, China, the hybrid-driven model proposed in this study has better applicability and prediction accuracy in the methane concentration prediction task, which can effectively prevent the occurrence of coal mine accidents and is more in line with the needs of coal mine safety production.

Application of Analytical Solutions of the Reactive Transport Equation for Underground Methanation Reactors

AbstractFluctuations in the production of renewable-based electricity have to be compensated by converting and storing the energy for later use. Underground methanation reactors (UMR) are a promising technology to address this issue. The idea is to create a controlled bio-reactor system in a porous underground formation, where hydrogen obtained from renewable energy sources by electrolysis and carbon dioxide from industrial sources are fed into the reactor and converted into methane. Microorganisms, known as methanogenic archaea, catalyze the chemical reaction by using the two non-organic substrates as nutrients for their growth and for their respiratory metabolism. The generated synthetic methane is renewable and capable to compete with the fossil methane. Mathematical models play an important role in the design and planning of such systems. Usually, a numerical solution of the model is required since complex initial-boundary problems cannot be solved analytically. In this paper, an existing bio-reactive transport model for UMR is simplified to such an extent that an analytical solution of the advection-dispersion-reaction equation can be applied. A second analytical solution is used for the case without dispersion. The analytical solutions are shown for both the educt (hydrogen) and the reaction product (methane). In order to examine the applicability of the analytical models, they are compared with the significantly more complex numerical model for a 1D case and a 3D case. It was shown that there is an acceptable agreement between the two analytical solutions and the numerical solution in different spatial plots of hydrogen and methane concentration and in the methane concentration in the withdrawn gas. The mean absolute error in the mole fraction is well below 0.015 in most cases. The spatial distribution of the hydrogen concentration in the comparison to the 3D case shows a higher deviation with a mean absolute error of approx. 0.023. As expected, the model with dispersion shows a slightly lower error in all cases, as only here the gas mixing resulting in smeared displacement fronts can be represented. It is shown that analytical modeling is a good tool to get a first estimation of the behavior of an UMR. It allows to help in the design of well spacing in combination with the injection rate and injected gas composition. Nevertheless, it is recommended to use more complex models for the later detailed analysis, which require a numerical solution.

Energy recovery from poultry manure in the process of semi-continuous anaerobic co-digestion with sewage sludge

In the face of significant legislative changes in renewable energy sources and conservation of natural resources, bio-waste must be managed efficiently. Developing wastewater treatment technologies generate a large amount of sewage sludge requiring appropriate use. A well-known and practiced process is the anaerobic digestion of sewage sludge, but due to its characteristics, the production of biogas is not sufficient enough to ensure the energy self-sufficiency of a wastewater treatment plant. Another waste whose management is a challenge is poultry manure, whose production in Poland is high due to intensive poultry farming. This study investigated the possibility of co-digestion of poultry manure and sewage sludge and its effect on increasing biogas production compared to processing sludge alone. The process was performed in two continuously stirred-tank glass reactors at mesophilic conditions, with 20 days of hydraulic retention time. In the first stage, the batch assay with sewage sludge was applied to promote the development of an anaerobic community. The second stage involved feeding the reactors on a semi-continuous regime with sewage sludge for the control sample and a mixture with the gradual addition of poultry manure from 2.5 % to 60 %. During the experiment, the most important parameters affecting the process and the quantity and quality of the obtained products in the form of biogas and digestate were monitored. The study’s results indicated an advantage of the co-digestion process of poultry manure and sewage sludge over the digestion of sludge alone in terms of process efficiency. The highest biogas production was obtained with a co-substrate ratio of 42 % manure to 58 % sewage sludge (ratio based on volatile solids). Co-digestion had no significant effect on gas quality; in both cases, the methane content was more than 60 %. Moreover, a digestate with fertilizer potential was obtained for each sample.

The impact of support selection and Co loading amount on the catalytic performance for methane combustion

Methane (CH4) is a key component of natural gas and is essential for energy production and utilization. However, due to its strong greenhouse effect, efficient catalytic combustion methods are needed to convert it into CO2 and H2O. This study systematically evaluates the catalytic performance of Co, CoO, and Co3O4 in methane catalytic combustion, particularly highlighting the superior activity of Co3O4. To improve catalytic efficiency, this paper examines the effects of SiO2, Al2O3, and CeO2 as support materials using co-precipitation and impregnation methods. The results show a significant improvement in the catalytic activity of Co3O4 supported on CeO2, attributed to CeO2's unique redox properties and high oxygen storage capacity. Additionally, the study explores the impact of different loading amounts (5%, 10%, 15%, 20%) of Co3O4(x)-CeO2 catalysts on their performance. The optimal 10%wt Co3O4–CeO2 catalyst achieves methane conversion rates of 10%, 50%, and 90% at temperatures of 376 °C, 473 °C, and 578 °C, respectively, demonstrating exceptional stability during a 20-h stability test and the ability to adapt to fluctuations in CH4 concentrations in low-oxygen environments, while also exhibiting significant catalytic activity across a range of methane concentrations from 0.5% to 2.5%. These findings provide important theoretical and experimental guidance for the application of cobalt-based catalysts in CH4 combustion, paving the way for future catalyst design and optimization.

Comparative study of flame propagation characteristics of methane explosion in pipeline with different venting structures at different ignition positions

The effect of central ignition and four types of explosion vents (circular vents with areas of 22.89, 15.20, and 9.07 cm2 and a cross-shaped vent with an area of 15.20 cm2) on the flame propagation of methane explosions was investigated by using a rectangular blast pipe system and analyzed in comparison with the closed-end ignition condition. Central ignition shows that the flame propagation velocity on both sides of the pipe increases and decreases. The peak pressure decreases as the vent area increases. Specifically, Pm (9.07 cm2) > Pm (15.20 cm2) > Pm (22.89 cm2). The flame temperature at the closed end was consistently higher than that at the vented end. The vm values in the closed-end ignition pipe increased by 20.0 %, 41.8 %, 45.8 %, 40.9 %, 31.5 %, and 19.0 %, respectively, over the central ignition position when the methane concentration was 8–13 %. When the methane concentration deviates from the stoichiometric ratio, the difference in peak pressure between closed-end and central ignition can be up to 0.15 MPa, which is 26.7 % of that of central ignition. The peak temperatures observed at points 1–2 in the closed-end ignition were consistently higher than the central ignition.

Beyond gas supersaturation: Dissecting the secondary formation of methane hydrate

Rapid secondary formation of gas hydrate is a critical issue in gas transportation and at the same time has foreseeable potential in future gas storage. Despite the devoted research in the past decade, the intrinsic mechanism of the secondary formation of gas hydrate, is still an on-going subject of debate. Because the secondary formation of gas hydrate is commonly observed under conditions with extraordinarily high content of gas, gas supersaturation is hypothesized as one crucial mechanism. To dissect the gas supersaturation hypothesis, Molecular Dynamics simulations were conducted systematically with hydrate secondary formation in solutions with various gas concentrations covering supersaturation conditions. The effects of key parameters influencing the secondary formation of hydrate, including system temperature and local methane concentration, were explored. The results revealed for the first time a U-shape-like trend in the induction time of hydrate formation with the increase of gas concentration, pinpointing an optimal gas content with the given environmental temperature and pressure. Importantly, the findings highlighted the needed revision of the current gas supersaturation hypothesis in both methane hydrate mitigation and application. This work not only advanced the current understanding of the secondary formation of methane hydrate but also contributed to the fundamental knowledge essential for future gas storage by gas hydrates.

Real-time detection of methane concentration based on TDLAS technology and 1D-WACNN

Real-time detection of methane concentration based on TDLAS technology and 1D-WACNN

The marine methane cycle in the Canadian Arctic Archipelago during summer.

In the Arctic Ocean, methane concentrations surpassing global averages are prevalent, especially along sub-Arctic and Arctic continental shelf margins. Despite elevated dissolved methane levels, the Arctic Ocean exhibits minimal methane fluxes to the atmosphere, indicating a potential role of water column oxidation in methane processing. During the Northwest Passage Project in the summer of 2019, we integrated thermohaline, chemical, and biological data with in-situ and in-vitro methane data in Canadian Arctic Archipelago (CAA) waters. Elevated in-situ dissolved methane was prominent in near-surface Pacific waters (between 2 and 7m), particularly in meltwater regions, with av. concentrations of 5.8±2.5 nM within the upper 30m. While methane oxidation constants were generally low (av. 0.006±0.002 d-1), surface waters in Wellington Channel and Croker Bay exhibited higher rates (av. 0.01±0.0004 d-1), associated with Pacific-origin microbial taxa like Oleispira and Aurantivirga. Deeper layers (>200m) displayed lower methane concentrations (av. 3.1±1.1 nM) and oxidation rates (av. 0.005±0.001 d-1). Sea ice showed elevated dissolved methane concentrations (av. 9.2±5 nM). Waters in the western CAA exhibited a 25% increase in methane concentrations compared to ice-free areas. The overall picture suggested supersaturation of in-situ methane in shallow waters (between 2 and 50m), coupled with faster oxidation rates in meltwater and Pacific dominant layers, suggesting rapid seasonal cycling of methane and prevention of the methane migration into the atmosphere.

Investigation on growth rate and quality of diamond materials in MPCVD system

Abstract In the paper, experiments of diamond growth with varied parameters are conducted in the microwave plasma chemical vapor deposition system. The growth mechanism of the diamond is analysed based on the phase diagram. The results show that the growth rate and the crystalline quality of the diamond are influenced by the gas phase and chamber pressure. The oxygen can help to improve the crystalline quality of the diamond, while to decrease the growth rate. The methane concentration and the chamber pressure are also key parameters to influence the quality and the growth rate of the diamond. The nitrogen concentration can contribute to the growth of the diamond, and the thermal conductivity is influenced at the same time. The grown diamond substrate can be used as thermal conductor in power devices with promising thermal conductivity.

Multi-physical quantities sensing based on the nematic liquid crystal Janus metastructure in theory

Breaking through the idea limitation of traditional single-scale and single-function sensors, a multi-scale and multi-function Janus metastructure (JMS) is proposed in this article, which is constructed by the specific methods to break its parity. Using the change of transmission spectrum, JMS can realize multi-physical quantities detection with different sensing performances, when electromagnetic waves propagate on positive and negative scales respectively. For selective gas detection, JMS can conveniently detect 0–3.5 % methane concentrations with sensitivity (S) of 22.932 THz/RIU and 0–3 % hydrogen concentrations with S of 43.494 THz/RIU, avoiding the problem of complex and dangerous external operation conditions required for previous gas sensors. Based on the electro-optical effect of nematic liquid crystal, JMS can realize wide-range electric field direction (EFD) sensing of 10°–80° and 100°–170° by taking the advantages of multi-scale detection, which is wider than existing 0°–90° EFD sensors. Because nematic liquid crystal is thermotropic, JMS can also achieve accurate temperature detection of 283.15–318.15 K. Finally, through comparison, it is proved that JMS proposed has the potential of multi-scenario applications, and meets the urgent demand for excellent performance sensors in the fields of dangerous gas transportation, atmospheric EFD detection and industrial manufacturing temperature control.

Experimental investigation of OH* emission spectrum characteristics and transient ignition dynamics in methane and coal dust mixtures explosions

Combustible gases, dusts and their mixtures are widely present in human production and life，and the fire and explosion disasters caused by them pose a serious threat to the field of energy security applications. Studying the ignition process of mixtures is essential for disaster risk assessment and safety protection. In this work, the explosion characteristics and OH* emission spectra of the mixtures were experimentally tested by varying the fuel equivalence ratio ( ER ≈ 0.79 ~ 1.71), and the evolution of the transient flow field structure during the ignition process was quantitatively analyzed using the schlieren image velocimetry method. The results indicate that the emission spectrum of OH* is closely correlated with the maximum explosion pressure, and the spectral intensity of OH* at 306.4nm is consistent with the maximum rate of explosion pressure rise. The flow field during the ignition process of the mixtures shows that a small amount of coal dust (concentration≤30g/m3) can significantly promote flame acceleration and instability as the methane concentration is in lean combustion or stoichiometric ratio. However, when the concentration of coal dust increases (concentration≥40g/m3), coal dust will suppress flame acceleration and instability. For methane concentration in fuel-rich combustion state, coal dust always suppresses flame acceleration and instability. The experimental results contribute to a further understanding of gas and coal dust mixed explosions and provide a verification database for the construction of chemical kinetic mechanisms.

Томографический измеритель концентрации метана на приземных трассах

Using a prototype of a remote lidar created in the laboratory for measuring methane concentration, a study of the distribution of methane along a route ~ 2.25 km long was carried out in order to localize gas emissions and control leaks in unfavorable areas. The lidar prototype, operating at a wavelength of 1653 nm, included a powerful Raman amplifier and made it possible to measure the distance to the reflection point with an accuracy of no worse than 50 meters. The lidar scanned the track, starting from short distances and ending with measurements along the entire measured track. The route included a near zone with modern multi-storey buildings without gas infrastructure, a middle zone with multi-storey buildings and gas infrastructure, as well as an extended forest area ending with a busy highway with heavy traffic. That is, it was possible to assess the contribution of each zone to the background methane concentration along the route. Observations were carried out during the winter-spring period and were carried out at different times of the day under weather conditions that were recorded. Processing of the results showed a significantly different contribution of each zone to the average concentration on the route. The contribution of the middle zone with multi-storey buildings equipped with gas infrastructure turned out to be especially large, which suggests a possible gas leak from the gas distribution system in this area. On average, the background concentration of methane on this route repeated the value measured in 2023 during the same seasonal period in 2023.

Feedbacks From Young Permafrost Carbon Remobilization to the Deglacial Methane Rise

AbstractThe abrupt warming events punctuating the Termination 1 (about 11.7–18 ka Before Present, BP) were marked by sharp rises in the concentration of atmospheric methane (CH4). The role of permafrost organic carbon (OC) in these rises is still debated, with studies based on top‐down measurements of radiocarbon (14C) content of CH4 trapped in ice cores suggesting minimum contributions from old and strongly 14C‐depleted permafrost OC. However, organic matter from permafrost can exhibit a continuum of 14C ages (contemporaneous to >50 ky). Here, we investigate the large‐scale permafrost remobilization at the Younger Dryas‐Preboreal transition (ca. 11.6 ka BP) using the sedimentary record deposited at the Lena River paleo‐outlet (Arctic Ocean) to reflect permafrost destabilization in this vast drainage basin. Terrestrial OC was isolated from sediments and characterized geochemically measuring δ13C, Δ14C, and lignin phenol molecular fossils. Results indicate massive remobilization of relatively young (about 2,600 years) permafrost OC from inland Siberia after abrupt warming triggered severe active layer deepening. Methane emissions from this young fraction of permafrost OC contributed to the deglacial CH4 rise. This study stresses that underestimating permafrost complexities may affect our comprehension of the deglacial permafrost OC‐climate feedback and helps understand how modern permafrost systems may react to rapid warming events, including enhanced CH4 emissions that would amplify anthropogenic climate change.

CO2 and CH4 Concentrations in Headwater Wetlands Influenced by Morphology and Changing Hydro-Biogeochemical Conditions

Headwater wetlands are important sites for carbon storage and emissions. While local- and landscape-scale factors are known to influence wetland carbon biogeochemistry, the spatial and temporal heterogeneity of these factors limits our predictive understanding of wetland carbon dynamics. To address this issue, we examined relationships between carbon dioxide (CO2) and methane (CH4) concentrations with wetland hydrogeomorphology, water level, and biogeochemical conditions. We sampled water chemistry and dissolved gases (CO2 and CH4) and monitored continuous water level at 20 wetlands and co-located upland wells in the Delmarva Peninsula, Maryland, every 1–3 months for 2 years. We also obtained wetland hydrogeomorphologic metrics at maximum inundation (area, perimeter, and volume). Wetlands in our study were supersaturated with CO2 (mean = 315 μM) and CH4 (mean = 15 μM), highlighting their potential role as carbon sources to the atmosphere. Spatial and temporal variability in CO2 and CH4 concentrations was high, particularly for CH4, and both gases were more spatially variable than temporally. We found that groundwater is a potential source of CO2 in wetlands and CO2 decreases with increased water level. In contrast, CH4 concentrations appear to be related to substrate and nutrient availability and to drying patterns over a longer temporal scale. At the landscape scale, wetlands with higher perimeter:area ratios and wetlands with higher height above the nearest drainage had higher CO2 and CH4 concentrations. Understanding the variability of CO2 and CH4 in wetlands, and how these might change with changing environmental conditions and across different wetland types, is critical to understanding the current and future role of wetlands in the global carbon cycle.

Olfactory-based powered descent guidance for Mars methane plume exploration in long-time-average wind environment

This paper investigates an olfactory-based powered descent guidance method that enable a lander to autonomously locate and target the vent source of any methane plume in long-time-average wind environment on Mars. The episodic methane plumes emanating from the Martian surface invite the possibility of direct access to the subsurface methane reservoir to acquire pristine organic materials. Constrained by the insufficient knowledge of the accurate plume vent location, Mars landers must infer the target location — the plume source — autonomously during the powered descent. However, existing powered descent guidance methods require the target location as a terminal constraint, rendering them ineffective in plume exploration missions. We propose an olfactory-based powered descent guidance method that could steer a lander to target the methane vent source by tracking the gradient of methane concentration in long-time-average wind environment, imposing sub-optimal fuel consumption. A novel olfactory navigation method based on tracking the negative logarithmic concentration gradient, and the corresponding gradient measurement method, is proposed. By implementing the negative logarithmic gradient field, gradient-dependent dynamic equations for the powered descending lander are proposed. The gradient-dependent equations provide a way to transform the original optimal guidance problem, which is non-convex and terminal-free, into a convex and terminal-fixed problem. A suboptimal guidance law, similar to E-guidance, is then derived by solving this problem. The proposed guidance could target the vent source of any methane plume in long-time-average wind environment, imposing modest fuel consumption by feeding back the concentration gradient. Numerical simulations illustrate that, in comparison to the terminal-fixed E-guidance and the open-loop fuel-optimal guidance, the lander imposes additional fuel consumption of 2.57% and 12.15% respectively, using the proposed guidance law.

Ice Formation, Exsolution, and Multiphase Equilibria in the Methane–Ethane–Nitrogen System at Titan Surface Conditions

Titan is unique among the icy satellites in that it has a thick atmosphere, stable surficial bodies of liquid, and a precipitation system that promotes interactions between the two. Although Titan’s surface conditions are typically assumed to be above the freezing point temperatures of the major constituent species of the climate system (methane, ethane, and nitrogen), conditions may be sufficiently cool across parts of Titan to allow for ice formation alongside known liquid-vapor phases. In this study, we used Raman spectroscopy, visual inspection, and the CRYOCHEM 2.0 equation of state to map the appearance of first ice and to quantify the amount of nitrogen dissolution into liquid in the methane–ethane–nitrogen system along a 1.5 bar isobaric cooling path in the temperature range 80–95 K. This was with the intent of (1) determining the effects nitrogen has on the phase behaviors of the methane–ethane binary system, and (2) establishing the temperatures and ternary mixing ratios needed for ice formation on Titan’s surface. We found that ethane-rich mixtures enter a three-phase solid–liquid–vapor equilibrium and are characterized by nitrogen-rich exsolution upon freezing and ice that form at the bottom of the sample. With sufficient methane content, the mixtures cross a univariant four-phase solid–liquid–liquid–vapor boundary, which contributes to a distinct isothermal freezing point profile and ice that forms starting at the liquid–liquid interface. Our results generally agree with findings from previous studies of the methane–ethane–nitrogen system and are intended to add to our current understanding of Titan’s geochemical processes.

Метано- и сульфидогенез в озерах полуострова Абрау (Краснодарский край)

The geographical position, tectonic and geological-hydrogeological structure of the basin of the Malyy Liman and Abrau lakes, their landscape features as natural monuments of regional importance located on the territory of the Abrau peninsula of the Krasnodar Territory are described. Using the example of the aquatic landscapes of the Malyy Liman and Abrau lakes and the river of the same name, water and bottom sediments were studied. Hydrochemical parameters, the content of methane and sulfide sulfur in bottom sediments and methane in water as components of aquatic landscapes were studied. The results of the determination of sulfides, as well as the characteristic odor and color of bottom sediments, indicate the presence of free H2S and hydrotroilite (FeS ∙ nH2O) in them. Electron microscopy revealed the presence of hollow spheres in the bottom sediments, which indicates their possible gas saturation. Microinclusions of biogenic pyrite (FeS2), which was formed on fragments of plant and organism residues, were found under an electron microscope. In aerobic-anaerobic conditions of the upper layer of bottom sediments of lakes, pyrite formation occurs both directly through a one-stage process of pyritization of reactive iron, but also through a multi-stage process of pyrite formation from iron monosulfide. It has been established that lakes are exposed to anthropogenic influences, which can increase many times during the holiday season. This leads to their eutrophication and increased meanogenesis, which in turn contributes to the activation of methane emissions into the atmosphere. Specific methane fluxes from the water surface of the Malyy Liman and Abrau lakes have been determined.

The effect of Asparagopsis taxiformis, Ascophyllum nodosum, and Fucus vesiculosus on ruminal methanogenesis and metagenomic functional profiles in vitro.

The application of A. taxiformis significantly reduced methane production in vitro. We showed that this reduction was linked to changes in microbial function profiles, the decline in the overall archaeal community counts, and shifts in ratios of Methanobrevibacter "SGMT" and "RO" clades. A. nodosum and F. vesiculosus, obtained from Scotland, also decreased methane concentration in the total gas, while the same seaweed species from Iceland did not.