Methane Profiles Research Articles

First High‐Resolution Vertical Profiles of Methane in the Troposphere Over India

AbstractMethane (CH4) is the second most abundant greenhouse gas and affects the Earth's radiative balance. In some regions, the methane burden and budget are still not well understood due to the lack of in situ observations, especially vertical profile observations. Here, we present the first high‐resolution aircraft‐based tropospheric vertical profiles of CH4 across the Indian subcontinent. Observations show significant variability, with the largest variability seen in the Indo‐Gangetic Plain (IGP) during post‐monsoon (September). The IGP also shows the highest concentrations and a peak in the boundary layer. By contrast, observations over western India show lower variability, especially during the Asian Summer Monsoon (ASM) (July). During ASM, when CH4 emissions peak, the vertical updraft of CH4 and other tracers is observed, leading to a peak between 4 and 5 km. During winter, the peak occurs in the boundary layer, and a decrease with altitude is observed. Model simulations slightly overestimate CH4 at the surface during some seasons but underestimate it at higher altitudes during all seasons. Integrated over the observed column, model simulations slightly underpredict CH4 (0.5%–3.1%) during all seasons. Calculations made using the observed CO/CH4 enhancement ratios show that in addition to anthropogenic fossil fuel emissions, other sources, such as rice cultivation and wetlands, need to be considered to reproduce the observed CH4 concentrations.

A novel explainable kinetic model for two-stage fermentation profile

Bio-products have significantly contributed to human society, particularly in advancing sustainability efforts. Kinetic models have been developed for better understanding fermentation dynamics, which is crucial for optimizing and scaling up the fermentation process. However, conventional kinetic models often struggle to accurately decipher two-stage fermentation profiles or fully explain the process. To bridge this gap, modified hyperbolic secant (MHS) model was proposed in this study, with three case studies to evaluate its applicability. Firstly, the MHS model was utilized to simulate the production of 1,3-propanediol fermentation, employing a co-fermentation approach with glucose and glycerol. The MHS model not only resulted in a greater fitting accuracy than conventional Logistic model but also provided essential kinetic parameters. Secondly, when applied MHS model to simulate biohydrogen production in dark fermentation, the MHS model exhibited superior fitting performance in comparison with the Monod model. Thirdly, the MHS model portrayed, when compared to Gompertz model, better methane profiles in anaerobic digestion. These case studies illustrate that the MHS model as a reliable, comprehensible, and universally applicable kinetic model. The implementation of the MHS model holds promise for supporting bioproducts production and offering valuable insights into process development.

Resource classification of coal bed methane and its contribution in energy transition and decarbonization path of oil and gas industry (A synopsis of CBM Life Cycle Analysis)

World economies are becoming increasingly more dependent on energy and countries have a voracious appetite for energy therefore, the need for an abundant clean energy is becoming a necessity. Energy companies are challenging environmental costs of coal bed methane as with advancement of new technology the impact from production of coal bed methane can reduce and to a certain extent avoided or offset. Production of coal bed methane results in changes to the land, to surface water and to ground water systems. Carbon quantification is required to understand, monitor and manage these changes. Previous life cycle analysis for this resource class has lack of process design details because of which there is a knowledge gap in understanding of emission profile of coal bed methane’s production. The objective of this study is to add value and reduce the scientific gap with respect to the production techniques of coal bed methane and its environmental impact. Removal of water continuously from coal seams depletes ground water and may eventually lower surface water flows (streams and rivers). It can also change the flow of groundwater drawing fresh water into the coal seams. To better understand this phenomenon the work establishes the Coal Bed Methane production foundation by in depth understanding of · Coal Bed Methane reservoir types; · Coal Bed Methane depositional environment, generation, and geological distributions; · Coal Bed Methane resource energy supply methods by understanding its construction, production and processing. The study then uses Life Cycle Assessment approach and understands previous emission numbers of Coal Bed Methane’s resource development. The work does systematic analysis and summarizes the previously published Life Cycle Analysis to understand further the potential environmental impacts of resource development of Coal Bed Methane. This will help energy companies to understand the field development, production, and operations of coal bed methane’s resource in terms of carbon numbers thereby optimizing the operations through carbon management thus reducing the potential impacts.

Seasonal dynamics of the microbial methane filter in the water column of a eutrophic coastal basin.

In coastal waters, methane-oxidizing bacteria (MOB) can form a methane biofilter and mitigate methane emissions. The metabolism of these MOBs is versatile, and the resilience to changing oxygen concentrations is potentially high. It is still unclear how seasonal changes in oxygen availability and water column chemistry affect the functioning of the methane biofilter and MOB community composition. Here, we determined water column methane and oxygen depth profiles, the methanotrophic community structure, methane oxidation potential, and water-air methane fluxes of a eutrophic marine basin during summer stratification and in the mixed water in spring and autumn. In spring, the MOB diversity and relative abundance were low. Yet, MOB formed a methane biofilter with up to 9% relative abundance and vertical niche partitioning during summer stratification. The vertical distribution and potential methane oxidation of MOB did not follow the upward shift of the oxycline during summer, and water-air fluxes remained below 0.6mmol m-2 d-1. Together, this suggests active methane removal by MOB in the anoxic water. Surprisingly, with a weaker stratification, and therefore potentially increased oxygen supply, methane oxidation rates decreased, and water-air methane fluxes increased. Thus, despite the potential resilience of the MOB community, seasonal water column dynamics significantly influence methane removal.

Assessment of Cryogenic Coring to Preserve Vertical Distributions of Trichloroethylene and Reaction Products in an Aquitard

AbstractThere is not a clear understanding of the extent by which naturally occurring reactions can attenuate trichloroethene (TCE) and its daughter products within low permeability zones (LPZs), and addressing this knowledge gap requires advancement of methods to accurately measure in situ volatile chemical concentrations. In this study, a soil coring method that freezes the soil in‐situ (a.k.a., cryogenic coring) was utilized to measure depth‐discrete distributions of TCE and its volatile reaction products through a TCE‐impacted silty clay aquitard, and results were compared with those from adjacent soil cores taken using a conventional coring approach. Vertical concentration profiles of TCE, cis‐1,2‐dichloroethylene (DCE), vinyl chloride (VC), ethane, and methane were all compared between the two coring methods, and results indicate the two coring methods recovered statistically equivalent concentrations of volatiles across most depths of the fine‐grained cohesive clayey soil at the study site. Biotic reductive dechlorination was the dominant TCE reaction pathway at the site; several reduced gasses that are possible markers for abiotic reduction were detected, but their concentrations and intervals of occurrence were not sufficiently consistent to indicate whether they were from abiotic TCE reduction or unrelated biological processes. Overall, cryogenic coring yielded improved recovery of sand lenses compared to conventional coring, but offered no apparent benefits for improved recovery of TCE and its volatile reaction products in the low permeability aquitard material at the site.

Substituting ryegrass-based pasture with graded levels of forage rape in the diet of lambs reduced post-feeding variation in methane emissions

The temporal profile of methane (CH4) emissions from ruminants is affected by feed composition and forage type. This study aimed to 1) describe and compare the post-feeding pattern of CH4 emissions from lambs fed fresh ryegrass substituted with graded levels of forage rape, and 2) to evaluate the association between the magnitude of the variation in CH4 emission patterns and organic fermentation products quantified in pre- and- post- feeding rumen content samples. Methane emissions were measured at approximately 6 min intervals in respiration chambers from 70 lambs (n = 14 per treatment) fed ryegrass only (FR0) or as a proportion, 0.25 forage rape + 0.75 ryegrass (FR25), 0.50 forage rape + 0.50 ryegrass (FR50), 0.75 forage rape + 0.25 ryegrass (FR75), and forage rape only (FR100). The magnitude of the variability in CH4 emissions was defined as the ratio of maximum to minimum CH4 emissions in a 24 h period. This ratio was correlated (P < 0.05) with the proportions of major short chain fatty acids, and calculated hydrogen (H2) available per unit of glucose fermented (H2/GEF), quantified in rumen content samples collected pre- and- post- feeding. The CH4 emission profile after each feeding followed an asymmetrical positively skewed shape for FR0 to FR75, but not in lambs fed FR100. The lowest CH4 emission rates were observed before morning feeding which was followed by a CH4 peak within the 2 h after feeding, and then the CH4 emissions decreased until the next feeding. In FR100 lambs, the CH4 emission rate was, unexpectedly, relatively constant after feeding, without any clear CH4 peaks. The magnitude of the variability in the CH4 emission rate increased when the pH of rumen contents and H2/GEF measured in pre-feeding samples decreased. Including forage rape at 0.75, or greater proportion, in the diet of lambs drastically changed the CH4 emissions pattern, likely due to a continuous low pH in the rumen which is detrimental for methanogenesis. In conclusion, the daily variation in CH4 emissions decreased with increasing forage rape inclusion in the diet of sheep and this was associated with a decreasing acetate proportion in the rumen liquid.

Using machine learning to construct TOMCAT model and occultation measurement-based stratospheric methane (TCOM-CH4) and nitrous oxide (TCOM-N2O) profile data sets

Abstract. Monitoring the atmospheric concentrations of greenhouse gases (GHGs) is crucial to improve our understanding of their climate impact. However, there are no long-term profile data sets of important GHGs that can be used to gain a better insight into the processes controlling their variations in the atmosphere. In this study, we apply corrections to chemical transport model (CTM) output based on profile measurements from two solar occultation instruments: the HALogen Occultation Experiment (HALOE) and the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS). The goal is to construct long-term (1991–2021), gap-free stratospheric profile data sets, hereafter referred to as TCOM, for two important GHGs. To estimate the corrections that need to be applied to the CTM profiles, we use the extreme gradient boosting (XGBoost) regression model. For methane (TCOM-CH4), we utilize both HALOE and ACE satellite profile measurements from 1992 to 2018 to train the XGBoost model, while profiles from 2019 to 2021 serve as an independent evaluation data set. As there are no nitrous oxide (N2O) profile measurements for earlier years, we derive XGBoost-derived correction terms to construct TCOM-N2O profiles using only ACE-FTS profiles from the 2004–2018 time period, with profiles from 2019–2021 used for the independent evaluation. Overall, both TCOM-CH4 and TCOM-N2O profiles exhibit excellent agreement with the available satellite-measurement-based data sets. We find that compared to evaluation profiles, biases in TCOM-CH4 and TCOM-N2O are generally less than 10 % and 50 %, respectively, throughout the stratosphere. The daily zonal mean profile data sets, covering altitude (15–60 km) and pressure (300–0.1 hPa) levels, are publicly available via the following links: https://doi.org/10.5281/zenodo.7293740 for TCOM-CH4 (Dhomse, 2022a) and https://doi.org/10.5281/zenodo.7386001 for TCOM-N2O (Dhomse, 2022b).

The Effect of Monensin vs. Neem, and Moringa Extracts on Nutrient Digestibility, Growth Performance, Methane, and Blood Profile of Merino Lambs.

Plant secondary compounds are potential rumen modifiers that can improve nutrient utilization in ruminant animals. This study evaluated the effect of Moringa (Moringa oleifera) and Neem (Azadirachta indica) leaf extracts on nutrient digestibility, growth performance, and enteric methane production in South African Mutton Merino lambs. Forty 4-month-old ram lambs with a mean body weight of 35 ± 2.2 kg were blocked by weight and from each block, lambs were randomly allocated into one of the following treatments: (i) diet only (fed a total mixed ration TMR-negative control), (ii) Monensin (fed TMR containing Monensin sodium, 15 mg/kg DM), (iii) Moringa (fed TMR, drenched with Moringa extract 50 mg/kg feed DM intake), and (iv) Neem (fed TMR, drenched with Neem extract 50 mg/kg DM intake). Extracts were administered via oral drenching at a concentration determined based on the previous week's feed intake. There were no differences in dry matter intake, average daily gain, feed conversion efficiency, digestibility, and nitrogen retention across the treatments. However, the extracts tended to reduce methane emitted both in g/head/day (p < 0.08) and g/ kg dry matter intake (p < 0.07). Extracts did not influence any of the blood metabolites in the ram lambs. Although the benefits of utilizing these medicinal plants as rumen modifiers under prolonged feeding conditions is justified, further evaluation is recommended to test Moringa and Neem leaf extracts at higher inclusion levels. Our research group is currently exploring a variety of phytogenic tools for the identification and standardization of key bioactive compounds linked to methane inhibition, in these leaf extracts.

Organic matter lability modifies the vertical structure of methane-related microbial communities in lake sediments.

Eutrophication increases the input of labile, algae-derived, organic matter (OM) into lake sediments. This potentially increases methane (CH4) emissions from sediment to water through increased methane production rates and decreased methane oxidation efficiency in sediments. However, the effect of OM lability on the structure of methane oxidizing (methanotrophic) and methane producing (methanogenic) microbial communities in lake sediments is still understudied. We studied the vertical profiles of the sediment and porewater geochemistry and the microbial communities (16S rRNA gene amplicon sequencing) at five profundal stations of an oligo-mesotrophic, boreal lake (Lake Pääjärvi, Finland), varying in surface sediment OM sources (assessed via sediment C:N ratio). Porewater profiles of methane, dissolved inorganic carbon (DIC), acetate, iron, and sulfur suggested that sites with more autochthonous OM showed higher overall OM lability, which increased remineralization rates, leading to increased electron acceptor (EA) consumption and methane emissions from sediment to water. When OM lability increased, the abundance of anaerobic nitrite-reducing methanotrophs (Candidatus Methylomirabilis) relative to aerobic methanotrophs (Methylococcales) in the methane oxidation layer of sediment surface decreased, suggesting that Methylococcales were more competitive than Ca. Methylomirabilis under decreasing redox conditions and increasing methane availability due to their more diverse metabolism (fermentation and anaerobic respiration) and lower affinity for methane. Furthermore, when OM lability increased, the abundance of methanotrophic community in the sediment surface layer, especially Ca. Methylomirabilis, relative to the methanogenic community decreased. We conclude that increasing input of labile OM, subsequently affecting the redox zonation of sediments, significantly modifies the methane producing and consuming microbial community of lake sediments. IMPORTANCE Lakes are important natural emitters of the greenhouse gas methane (CH4). It has been shown that eutrophication, via increasing the input of labile organic matter (OM) into lake sediments and subsequently affecting the redox conditions, increases methane emissions from lake sediments through increased sediment methane production rates and decreased methane oxidation efficiency. However, the effect of organic matter lability on the structure of the methane-related microbial communities of lake sediments is not known. In this study, we show that, besides the activity, also the structure of lake sediment methane producing and consuming microbial community is significantly affected by changes in the sediment organic matter lability.

Versatile methanotrophs form an active methane biofilter in the oxycline of a seasonally stratified coastal basin.

The potential and drivers of microbial methane removal in the water column of seasonally stratified coastal ecosystems and the importance of the methanotrophic community composition for ecosystem functioning are not well explored. Here, we combined depth profiles of oxygen and methane with 16S rRNA gene amplicon sequencing, metagenomics and methane oxidation rates at discrete depths in a stratified coastal marine system (Lake Grevelingen, The Netherlands). Three amplicon sequence variants (ASVs) belonging to different genera of aerobic Methylomonadaceae and the corresponding three methanotrophic metagenome-assembled genomes (MOB-MAGs) were retrieved by 16S rRNA sequencing and metagenomic analysis, respectively. The abundances of the different methanotrophic ASVs and MOB-MAGs peaked at different depths along the methane oxygen counter-gradient and the MOB-MAGs show a quite diverse genomic potential regarding oxygen metabolism, partial denitrification and sulphur metabolism. Moreover, potential aerobic methane oxidation rates indicated high methanotrophic activity throughout the methane oxygen counter-gradient, even at depths with low in situ methane or oxygen concentration. This suggests that niche-partitioning with high genomic versatility of the present Methylomonadaceae might contribute to the functional resilience of the methanotrophic community and ultimately the efficiency of methane removal in the stratified water column of a marine basin.

Vertically stratified methane, nitrogen and sulphur cycling and coupling mechanisms in mangrove sediment microbiomes

BackgroundMangrove ecosystems are considered as hot spots of biogeochemical cycling, yet the diversity, function and coupling mechanism of microbially driven biogeochemical cycling along the sediment depth of mangrove wetlands remain elusive. Here we investigated the vertical profile of methane (CH4), nitrogen (N) and sulphur (S) cycling genes/pathways and their potential coupling mechanisms using metagenome sequencing approaches.ResultsOur results showed that the metabolic pathways involved in CH4, N and S cycling were mainly shaped by pH and acid volatile sulphide (AVS) along a sediment depth, and AVS was a critical electron donor impacting mangrove sediment S oxidation and denitrification. Gene families involved in S oxidation and denitrification significantly (P < 0.05) decreased along the sediment depth and could be coupled by S-driven denitrifiers, such as Burkholderiaceae and Sulfurifustis in the surface sediment (0–15 cm). Interestingly, all S-driven denitrifier metagenome-assembled genomes (MAGs) appeared to be incomplete denitrifiers with nitrate/nitrite/nitric oxide reductases (Nar/Nir/Nor) but without nitrous oxide reductase (Nos), suggesting such sulphide-utilizing groups might be an important contributor to N2O production in the surface mangrove sediment. Gene families involved in methanogenesis and S reduction significantly (P < 0.05) increased along the sediment depth. Based on both network and MAG analyses, sulphate-reducing bacteria (SRB) might develop syntrophic relationships with anaerobic CH4 oxidizers (ANMEs) by direct electron transfer or zero-valent sulphur, which would pull forward the co-existence of methanogens and SRB in the middle and deep layer sediments.ConclusionsIn addition to offering a perspective on the vertical distribution of microbially driven CH4, N and S cycling genes/pathways, this study emphasizes the important role of S-driven denitrifiers on N2O emissions and various possible coupling mechanisms of ANMEs and SRB along the mangrove sediment depth. The exploration of potential coupling mechanisms provides novel insights into future synthetic microbial community construction and analysis. This study also has important implications for predicting ecosystem functions within the context of environmental and global change.8kPXxAybXxhPRn3YMgQLJxVideo

Aspen Plus® Process Simulation Model of the Biomass Ash-Based Treatment of Anaerobic Digestate for Production of Fertilizer and Upgradation of Biogas

The use of the commercial simulator Aspen Plus® could bring an amelioration in the accuracy of the predictions of the chemical species composition in the output streams of the anaerobic digestion process. Compared to the traditionally employed lumped models, which are elaborated from scratch, the models implemented in Aspen Plus® have access to a broad library of thermodynamic and phenomena transport properties. In the present investigation, a process simulation model for anaerobic digestion has been prepared by including a stoichiometric-equilibria reactor to calculate the extent of the ionization of the molecules present in the anaerobic digestate. The model characterizes the technical feasibility of anaerobic digestate stabilization, by means of biomass ash-based treatment, for the production of an organic fertilizer and potential biogas upgradation with the synthesis of ammonium carbonate. First of all, the titration of the manure digestate with the hydrochloric acid showed that a dose of 3.18 mEq/g would be required to attain the targeted pH of zero-point charge, upon addition of the sewage sludge ash in a ratio to the manure digestate of 0.6 ± 0.2%. Secondly, the profiles of ammonia, carbon dioxide, and methane found in the biogas agree with the pH of the treated digestate and enable the upgrading of the biogas with the production of NH4HCO3. The model needs to be further developed to ensure the standards are attained in all output streams of stabilized anaerobic digestate, biomethane, and isolated added-value chemical fertilizers.

Comparing Direct Numerical Modeling Predictions With Field Evidence for Methane Vertical Microseepage in Two Geological Settings

The footprints of petroleum microseepage can be associated with chemical and microbial processes in initially homogeneous strata and/or with the fluid transport properties of the rocks through which oil and gas migrate. This work examines the role of such driving factors in two contrasting geological settings by comparing numerical modeling predictions for upward methane microseepage with some field evidence for hydrocarbons transport and accumulation. The two case studies are a monitoring borehole (BH8) from a landfill in southern Ontario, Canada, and an oil well (Saltarin 1A) from the Eastern Llanos Basin in Colombia. Profiles of relative methane concentrations versus depth were generated using a time-dependent, one-dimensional, simulation of the advection-diffusion equation applied to multiple strata of soils, and sediments. The model employs the layered sequences of these two geological settings. The results obtained hinge on the standard permeability values for the rock types involved and their corresponding flow velocities and diffusion coefficients. Resistivity logs were utilized as direct proxies of hydrocarbon concentrations. As additional evidence for petroleum microseepage, experiments of electron paramagnetic resonance (EPR) were carried out in drilling cuts of Saltarin 1A to measure traces of organic matter free radicals concentrations (OMFRC). Extractable organic matter (EOM) and magnetic susceptibility data were also considered in interpreting the EPR results. Qualitative comparisons between modeled methane profiles and their corresponding resistivity logs suggest that microseepage and hydrocarbon accumulations are conditioned by the fluid transport properties of the rocks contained by BH8 and Saltarin 1A. Moreover, in most of the Saltarin 1A sequence, the OMFRC profiles follow the trends displayed by the resistivity and modeled methane logs. Thus, the EPR data also indicates that hydrocarbon microseepage and accumulation are largely controlled by lithology. Conversely, EOM and magnetic susceptibility appear to be evidence for hydrocarbon-mediated near-surface chemical processes.

Origin of Deep Methane from Active Faults along the Itoigawa–Shizuoka Tectonic Line between the Eurasian and North American Plates: 13C/12C and 14C/12C Methane Profiles from a Pull-Apart Basin at Lake Suwa

Stable and radiocarbon isotope analyses provide valuable insights into carbon dynamics in hydrosphere ecosystems. A lake containing seeps of deep methane (CH4) may provide an ideal environment for elucidating such dynamics, including the involvement of deep carbon in the surface ecosystem and its food web. In this study, we performed carbon isotope analysis of seep gas, lake water, and a cyanobacterial bloom sample collected at Lake Suwa, a pull-apart basin on the Itoigawa–Shizuoka tectonic line, Japan. CH4 collected from two seep sites 100 m from the lakeshore was 14C-depleted (Δ14C = −972.1 to −989.8‰), indicating that the origins of seep CH4 and benthic bubble CH4 (Δ14C = +21.7‰) collected near the lakeshore differed. The results suggested that benthic bubble CH4 was produced by methanogenic archaea in benthic sediments and that seep CH4 was produced by methanogenic archaea using relic carbon. The Δ14C values of dissolved inorganic carbon (DIC) in surface lake water collected at seep sites (Δ14C = −103.1 to −630.6‰) and near the lakeshore (Δ14C = −100.9‰) suggested that the influence of deep carbon occurred not only around the seep sites but also at the lakeshore. The Δ14C values of the cyanobacterial bloom sample also showed values similar to those of DIC (Δ14C = −110.3‰), suggesting that 10–63% of DIC in surface water and 10% in primary producers originated from relic carbon, including CH4 and CO2, and was incorporated into the surface ecosystem of Lake Suwa.

Molecular dynamics of CH4/CO2 on calcite for enhancing gas recovery

AbstractThe effect of temperature and pressure on the adsorption of CO2 and CH4 gases on calcite (104) has been studied by means of classical molecular dynamics. The results show that carbon dioxide greatly improves methane desorption in the 323–373 K range, even at low CO2 concentrations. However, this effect is less pronounced for very high temperatures (423 K), where most of the methane is desorbed and CO2 tends to desorb in large quantities. Radial distribution function (RDF) analysis reveals two distinct peaks for CO2 (0.36 and 0.47 nm) and two for methane (0.87 and 0.57 nm) and the intensities of these peaks tend to decrease with increasing temperature. Such peaks are always clearly visible for CO2, while the methane profile gets very broad already for mild conditions of temperature and CO2 concentration. These results highlight how the CO2 geometry of adsorption is well defined and characterized by strong interaction, while methane adsorption is quite loose and depicts a very dynamic picture. Focusing on the effect of pressure, RDF peaks intensities increase, although this effect is limited to the 1–5 MPa range. Moreover, the high CO2 presence further decreases the effect of pressure on methane adsorption. In fact, from pure methane to 20/80 CO2/CH4, methane adsorption increases linearly with pressure. For gas mixtures with a CO2 concentration higher than 40%, higher pressure has less impact on methane adsorption. Overall, the results obtained yield important details to tune the gas composition and conditions for efficient and enhanced natural gas recovery and sequestration of CO2.

Porewater Geochemical Assessment of Seismic Indications for Gas Hydrate Presence and Absence: Mahia Slope, East of New Zealand’s North Island

We compare sediment vertical methane flux off the Mahia Peninsula, on the Hikurangi Margin, east of New Zealand’s North Island, with a combination of geochemical, multichannel seismic and sub-bottom profiler data. Stable carbon isotope data provided an overview of methane contributions to shallow sediment carbon pools. Methane varied considerably in concentration and vertical flux across stations in close proximities. At two Mahia transects, methane profiles correlated well with integrated seismic and TOPAS data for predicting vertical methane migration rates from deep to shallow sediment. However, at our “control site”, where no seismic blanking or indications of vertical gas migration were observed, geochemical data were similar to the two Mahia transect lines. This apparent mismatch between seismic and geochemistry data suggests a potential to underestimate gas hydrate volumes based on standard seismic data interpretations. To accurately assess global gas hydrate deposits, multiple approaches for initial assessment, e.g., seismic data interpretation, heatflow profiling and controlled-source electromagnetics, should be compared to geochemical sediment and porewater profiles. A more thorough data matrix will provide better accuracy in gas hydrate volume for modeling climate change and potential available energy content.

Linking theoretical and simulation approaches to study fluids in nanoporous media: Molecular dynamics and classical density functional theory

We propose an approach that combines classical density functional theory (DFT) and molecular dynamics (MD) simulation to study fluid behavior in nanopores in contact with bulk fluid (macropores). The approach consists of two principal steps: a DFT calculation of fluid composition and density distribution in a nanopore under specified thermodynamic conditions and an MD simulation of the confined system with obtained characteristics. Thus, we investigate an open system in a grand canonical ensemble. This method allows us to identify both structural and dynamic properties of confined fluid at given bulk conditions. Our approach does not require a computationally expensive simulation of a bulk reservoir. This work presents equilibrium density profiles of pure methane, ethane and carbon dioxide and their binary mixtures in slit-like nanopores with carbon walls. Good agreement between the structures obtained by theory and simulation confirms the applicability of the proposed method.

Modeling of thermal cracking reaction of kerosene range hydrocarbons

The present study deals with the modeling and simulation of a semi-mechanistic model of the thermal cracking reaction of a kerosene range hydrocarbon fuel. The objective of the present work is to investigate the concentration profile of various species specifically, H2, and C1-C4 hydrocarbons along the reactor length of a tubular reactor. The study will enable to optimize the reactor length for desirable products. An isothermal plug flow reactor (PFR) system is considered to investigate the variation of product distribution patterns along the axial direction. The simulation was performed considering 172 reactions and 51 species. The PFR temperature and pressure were maintained at 850 °C and 2.5 MPa, respectively. The cracked products obtained are grouped based on boiling temperature ranges. The study shows that the concentration profile of hydrogen, methane, ethylene, propane, and isobutylene increased monotonically with the increase of the characteristic length of the reactor. In contrast, the concentration of propylene and 1-butene passes through a maximum. Also, a variation in the characteristic length corresponding to the peak concentration of olefins is noted. The study may be useful for understanding the insight of pyrolysis reaction and selecting a characteristic reactor length for the optimization/maximization of lighter olefins.

Investigating the Potential of Recycling Flare-Source Hydrocarbon Gases in an Industrial Burner

Abstract Flare gas is considered a global environmental concern. Flaring contributes to wasting limited material and energy resources, economic loss, and greenhouse gas emissions. Utilizing flared gas as a fuel feed to industrial cracking furnaces grants advantages in terms of fuel economy and emissions reduction. This work presents the results obtained by ansysfluent simulation of a flare hydrocarbon gas utilized in a steam-cracking furnace of ethylene process when combusting hydrocarbons flare gas in a low-NOx burner. In addition, the study determined the suitability of different hydrocarbon fuel mixtures in satisfying the required adiabatic flame temperature. The flared stream is assumed to be inlet from both primary and secondary staged fuel burners. The simulation results illustrated the detailed temperature profiles along the furnace flue gas side. They also presented the influence of flare stream compositions and Wobbe Index (WI) on the temperature profile. It was found that having an alternative fuel with a heating value or WI similar to that of methane would not result in the same temperature profile of methane, as the current fuel source. In addition, using different excess air percentages has no linear effect on the burner’s temperature profile. However, the results showed that the best replacement of methane, as the main fuel source, is a flare mixture with the same WI of methane as well as a certain H2 content needs to be added to every flare mixture composition to reach the same temperature profile of methane.

Effect of experimental variables on coal catalytic hydrogasification in a pressurized fluidized bed

Catalytic hydrogasification of pulverized coal was performed using a pressurized fluidized bed to investigate the effect of experimental variables including catalyst additives, temperature (600–850 °C) and hydrogen (H2) pressure (0.6–3.0 MPa) on the catalytic behavior of cobalt (Co) and formation profiles of target products, i.e., methane (CH4) and liquid hydrocarbons (HCL). The experimental results suggest that calcium (Ca) as an additive demonstrated a superior promoting effect on Co by mediating the Co-coal interaction, which initiated the catalytic depolymerization and hydrogenation of unreactive carbon. The temperature above 750 °C stimulated the diffusion of Co-Ca catalyst in the coal structure, and enhanced the coal catalytic hydrogasification by lowering the activation energy. However, the elevated temperature decreased the HCL yield due to the intensified hydrocracking. The elevation of H2 pressure strengthened the Co-Ca-Coal-H2 interaction, which conduced to the depolymerization and hydrogenation effect of Co-Ca catalyst, and improved the yield of CH4 and HCL. Based on the experimental results, a two-stage pressurized fluidized bed reactor scheme was proposed to couple the coal catalytic hydropyrolysis with char catalytic hydrogasification. Staged hydrogenation of coal was realized, and a yield of 74.2 wt% for gaseous hydrocarbons (CH4 and C2-C3) and 3.36 wt% of HCL (BTX, PCX, and naphthalene) were obtained.