Laws of Gas Diffusion in Coal Particles: A Study Based on Experiment and Numerical Simulation

In order to research on the law of methane released through the pore in coal particles, the methane desorption experiments were conducted, respectively, on four types of particle size of coal samples under three different initial adsorption pressures. The cumulative methane desorption quantity (CMDQ) with time increasing was obtained to show that the reciprocal of CMDQ was in linear relation with the reciprocal of the square root of time, and the correlation coefficients were all above 0.99, on basis of which an empirical formula of CMDQ was established. Then, according to Fick diffusion law and Darcy percolation law, the mathematical models of methane emission from the spherical coal particles were created, respectively, and the corresponding calculating software was programmed by the finite difference method to obtain the simulated CMDQ of each sample under different conditions. The methane emission rate functions (MERF) of the simulation and the experiment were also calculated, respectively. Comparative analysis between the numerically simulated outcomes and the assay results reveals that the simulation outcomes as per Darcy’s law match the experimental data better, while the simulated results by Fick’s law deviate greatly, which indicates that the methane flowing through coal particles is more in accordance with Darcy’s law.

OpenFOAM solver of the methane behaviour near the coal mine tunnelling face and its application

The methane near a tunnelling face seriously affects production safety in coal mines. A model considering methane seepage, adsorption, desorption and coal damage processes was established in this research. The open field operation and manipulation (OpenFOAM) solver was compiled to numerically solve the established model. The model is validated against data published in a previous theoretical study. The solver was used to investigate the effect of different parameters on methane emission regularity. This solver demonstrates that the effects of the original stress, coal cohesion and coal internal friction angle on the methane emission rate are limited, but their effects on the width of the fractured zone and effective stress are great. The effects of the initial methane pressure and coal adsorption parameters on the methane emission rate are also notable, but their effects on the width of the fractured zone and effective stress are limited.

Spatial and temporal variation of 13C-signature of methane emitted by a temperate mire ecosystem

<p>The net methane emission of any mire ecosystem results from a combination of biological and physical processes, including methane production by archaea, methane consumption by bacteria, and transport of methane from peat to the atmosphere. The complexity of spatial and temporal behavior of methane emission is connected to these.</p><p><sup>13</sup>C-signature of emitted methane offers us a further constraint to evaluate our hypothesis on the processes leading to the variation of methane emission rates. For example, assuming the spatial variation in methane emission rate at microtopographic scale is due to variation in trophic status or variation in methane consumption, will lead to differences in the relation of methane emission rate and its <sup>13</sup>C-signature, expressed as δ<sup>13</sup>C.</p><p>We have measured the methane emission rates and δ<sup>13</sup>C of emitted methane by six automated chambers at a poor fen ecosystem over two growing seasons. The measurements were conducted at Mycklemossen mire (58°21'N 12°10'E, 80m a.s.l.), Sweden, during 2019-2020. In addition, we measured atmospheric surface layer methane mixing ratios and δ<sup>13</sup>C to obtain larger scale <sup>13</sup>C-signatures by the nocturnal boundary-layer accumulation (NBL) approach. All δ<sup>13</sup>C-signatures were derived using the Keeling-plot approach.</p><p>The collected data shows spatial differences of up to 10-15 ‰ in 10-day averages of δ<sup>13</sup>C-signatures between different chamber locations. Temporal variations of 10-day average δ<sup>13</sup>C-signatures from most chamber locations reached over 5 ‰, while the temporal variation of NBL derived δ<sup>13</sup>C-signature was slightly lower.</p><p>The observed spatial variation in the δ<sup>13</sup>C-signature was somewhat systematic, indicating, especially in the middle of the summers, the main control of spatial variation of methane emission to be the trophic status. The temporal changes, measured at different locations, indicate spatial differences in the temporal dynamics at the microtopographic scale. The temporal behavior of larger scale NBL δ<sup>13</sup>C-signature does not fully correspond to the behavior of the chamber derived average δ<sup>13</sup>C-signature.</p>

Enteric Methane Emissions of Beef Cows Grazing Tallgrass Prairie Pasture on the Southern Great Plains

HighlightsEnteric methane (CH4) from beef cows on pasture was measured over three seasons using three methods.Methods yielded similar results during the summer grazing season but diverged in autumn and winter seasons.Emission averaged 0.34, 0.27, and 0.29 kg CH4 cow-1 during lactation, mid-gestation, and late gestation, respectively.Annualized enteric methane emission rate for a beef cow herd grazing tallgrass prairie was 0.32 kg d-1 cow-1.Abstract. Methane (CH4) is an important greenhouse gas, and about 20% of the carbon dioxide equivalent (CO2e) greenhouse gases emitted by U.S. agriculture are attributed to enteric CH4 produced by grazing beef cattle. Grazing cattle are mobile point sources of methane and present challenges to quantifying the enteric methane emission rate (MER). In this study, we applied three methods to measure herd-scale and individual-animal MER for a herd of beef cows grazing a native tallgrass prairie: a point source method that used forward-mode dispersion analysis and open-path lasers and cow locations, an open chamber breath analysis system (GreenFeed), and an eddy covariance ratio method that used the ratio of CH4 and CO2 mass fluxes. Three campaigns were conducted during the early season (July), late season (October), and dormant season (February). The point source and GreenFeed methods yielded similar MER (±SD) values during the early season campaign: 0.38 ±0.04 and 0.34 ±0.05 kg d-1 cow-1, respectively. However, the MER values from the two methods diverged in subsequent seasons. The GreenFeed MER decreased through the late and dormant seasons to 0.23 ±0.03 and 0.19 ±0.03 kg d-1 cow-1, respectively. In contrast, the point source MER stayed the same during the late season and increased during the dormant season to 0.41 ±0.07 kg d-1 cow-1. The CH4:CO2 ratio method, which was used only during the dormant season, yielded a MER of 0.29 ±0.05 kg d-1 cow-1. The point source and GreenFeed methods measured different MER (integrated herd-scale versus a subset of individual animals) and likely sampled methane emissions at different times during the day. We conclude that the point source method tended to overestimate emissions, and the GreenFeed method tended to underestimate emissions. Enteric methane emissions from beef cows over the three grazing seasons averaged 0.39 and 0.25 kg d-1 cow-1 as measured by the point source and GreenFeed methods, respectively. An annualized enteric MER for a beef cow herd grazing tallgrass prairie was 0.32 kg d-1 cow-1. Quantifying enteric methane emissions from grazing beef cows remains a challenge because of the mobile, often dispersed behavior of grazing cattle and the dynamic interactions of forage quality, dry matter intake, and changing physiological state of cows during the year. Keywords: Beef cows, Enteric methane, Forage quality, Grazing, Tallgrass prairie.

Comparing facility-level methane emission rate estimates at natural gas gathering and boosting stations

Coordinated dual-tracer, aircraft-based, and direct component-level measurements were made at midstream natural gas gathering and boosting stations in the Fayetteville shale (Arkansas, USA). On-site component-level measurements were combined with engineering estimates to generate comprehensive facility-level methane emission rate estimates (“study on-site estimates (SOE)”) comparable to tracer and aircraft measurements. Combustion slip (unburned fuel entrained in compressor engine exhaust), which was calculated based on 111 recent measurements of representative compressor engines, accounts for an estimated 75% of cumulative SOEs at gathering stations included in comparisons. Measured methane emissions from regenerator vents on glycol dehydrator units were substantially larger than predicted by modelling software; the contribution of dehydrator regenerator vents to the cumulative SOE would increase from 1% to 10% if based on direct measurements. Concurrent measurements at 14 normally-operating facilities show relative agreement between tracer and SOE, but indicate that tracer measurements estimate lower emissions (regression of tracer to SOE = 0.91 (95% CI = 0.83–0.99), R2 = 0.89). Tracer and SOE 95% confidence intervals overlap at 11/14 facilities. Contemporaneous measurements at six facilities suggest that aircraft measurements estimate higher emissions than SOE. Aircraft and study on-site estimate 95% confidence intervals overlap at 3/6 facilities. The average facility level emission rate (FLER) estimated by tracer measurements in this study is 17–73% higher than a prior national study by Marchese et al.

METHANE EMISSION FROM PADDY SOIL IN RELATION TO SOIL TEMPERATURE IN TROPICAL REGION

Methane (CH4) is 21 times more powerful as a greenhouse gas than carbon dioxide. Wetlands including flooded paddy fields are one of the major sources for this gas. Paddy fields are responsible for producing 25 to 54 Tg of CH4 annually. Methane emission rate could be affected by several factors such as irrigation pattern, fertilizer type, soil organic matter and soil temperature. Among them, soil temperature is a determining factor which deserves to be investigated. This study performed with the aim of understanding the effect of soil temperature on the methane emission rate from paddy soil in a short period of time (hourly) and long term (during rice growing season). The results of this study suggest that soil temperature could control the amount of methane emission and there is a positive and strong correlation in both soil temperature and methane emission pattern in short period of time. However, in case of long term trend, other factors such as water management and plant age decreased this correlation from 0.768 to 0.528.

Global annual methane emission rate derived from its current atmospheric mixing ratio and estimated lifetime

We use the estimated lifetime of methane (CH4), the current methane concentration, and its annual growth rate to calculate the global methane emission rate. The upper and lower limits of the annual global methane emission rate, depending on loss of CH4 into the stratosphere and methane consuming bacteria, amounts to 648.0 Mt a−1 and 608.0 Mt a−1. These values are in reasonable agreement with satellite and with much more accurate in situ measurements of methane. We estimate a mean tropospheric and mass-weighted temperature related to the reaction rate and employ a mean OH-concentration to calculate a mean methane lifetime. The estimated atmospheric lifetime of methane amounts to 8.28 years and 8.84 years, respectively. In order to improve the analysis a realistic 3D-calculations should be performed.