Methane Recovery Research Articles

Microwave irradiation-induced alterations in physicochemical properties and methane adsorption capability of coals: An experimental study using carbon molecular sieve

In order to comprehend the applicability of microwave irradiation for recovering coalbed methane, it is necessary to evaluate the microwave irradiation-induced alterations in coals with varying levels of metamorphism. In this work, the carbon molecular sieve combined with KMnO4 oxidation was selected to fabricate carbon molecular sieve with diverse oxidation degrees, which can serve as model substances toward coals. Afterwards, the microwave irradiation dependences of pores, functional groups, and high-pressure methane adsorption characteristics of model substances were studied. The results indicated that microwave irradiation causes rearrangement of oxygen-containing functional groups, which could block the micropores with a size of 0.40–0.60 nm in carbon molecular sieve; meanwhile, naphthalene and phenanthrene generated by macro-molecular structure pyrolysis due to microwave irradiation could block the micropores with a size of 0.70–0.90 nm. These alterations in micropore structure weaken the saturated methane adsorption capacity of oxidized carbon molecular sieve by 2.91%–23.28%, suggesting that microwave irradiation could promote methane desorption. Moreover, the increased mesopores found for oxidized carbon molecular sieve after microwave irradiation could benefit CH4 diffusion. In summary, the oxidized carbon molecular sieve can act as model substances toward coals with different ranks. Additionally, microwave irradiation is a promising technology to enhance coalbed methane recovery.

Climate variability impacts on methane recovery in a municipal solid waste landfill: A case study in a humid tropical climate region

Climate variability impacts on methane recovery in a municipal solid waste landfill: A case study in a humid tropical climate region

Understanding microbiome dynamics and functional responses during acidogenic fermentation of sucrose and sugarcane vinasse through metatranscriptomic analysis

Improving anaerobic digestion of sugarcane vinasse – a high-strength wastewater from ethanol distillation – is a subject of great interest, in view of the reduction of the pollutants and recovery of methane and valuable metabolites as byproducts. Through metatranscriptomic analysis, this study evaluated the active microbiome and metabolic pathways in a continuous acidogenic reactor: Stage 1S (control): 100% sucrose-based substrate (SBS); Stage 2SV (acclimation): 50% SBS and 50% vinasse; Stage 3V: 100% vinasse. Metatranscriptome obtained from each Stage was subjected to taxonomic and functional annotations. Under SBS feeding, pH dropped to pH 2.7 and biohydrogen production was observed. As vinasse was added, pH increased to 4.1–4.5, resulting in community structure and metabolite changes. In Stage 3V, biohydrogen production ceased, and propionate and acetate prevailed among the volatile fatty acids. Release of homoacetogenesis enzymes by Clostridium ljungdahlii and of uptake hydrogenase (EC 1.12.99.6) by Pectinatus frisingensis were linked to hydrogen consumption in Stages 2SV and 3V. Metabolic pathways of vinasse compounds, such as carbohydrates, malate, oxalate, glycerol, sulfate and phenol, were investigated in detail. In pyruvate metabolism, gene transcripts of oadA (oxaloacetate decarboxylase) and mdh (malate dehydrogenase), were upregulated in Stage 3V, being mostly attributed to P. frisingensis. Acetate formation from vinasse degradation was mainly attributed to Megasphaera and Clostridium, and propionate formation to P. frisingensis. Glycerol removal from vinasse exceeded 99%, and gene transcripts encoding for glpF (glycerol uptake facilitator protein), glpK (glycerol kinase) and glpABC (glycerol-3-phosphate dehydrogenase) were expressed mostly by Pectinatus and Prevotella. mRNA profiling showed that active bacteria and gene expression greatly changed when vinasse replaced sucrose, and Pectinatus was the main active bacterium degrading the searched compounds from vinasse. The identification of the main metabolic routes and the associated microorganisms achieved in this work contributes with valuable information to support further optimization of fermentation towards the desired metabolites.

Dynamic gas liberation from water-immersed anthracite coal with varying wetting states under heating conditions: Unveiling the gas breakthrough phenomena

During coalbed methane recovery, the effective extraction of gas trapped in narrow pore throats encounters challenges due to the water blocking effect. To shed light on this phenomenon during thermal recovery of coalbed methane, this study investigated the breakthrough behaviors of CO2 traversing through a 0.2 mm diameter hole in water-immersed anthracite coal at varying temperatures (23 °C, 40 °C, and 60 °C). The measurements of breakthrough pressure (defined as the pressure at which the bubble achieves a semi-spherical shape with a minimum curvature radius), growth characteristics of CO2 bubbles, and coal wettability were conducted under varying thermal conditions and water immersion durations. The results showed that the breakthrough pressure initially increased continuously as water immersed into the coal and then gradually stabilized. During this process, the coal's water wettability increased, leading to a decrease in the diameter of the bubble's three-phase contact line, which in turn affected the breakthrough pressure. Moreover, higher temperatures accelerated the rate of water immersion, augmenting the coal's hydrophilicity. The elevated temperature also resulted in a decrease in water surface tension, consequently contributing to a lower breakthrough pressure. Interestingly, compared to CO2, He exhibited a faster increase in breakthrough pressure during water immersion. This disparity can be attributed to He's superior diffusion capacity and lower viscosity, enabling a swifter transformation of the coal's wetting state during water imbibition. This study revealed the dual mechanism of heating to reduce gas breakthrough pressure, as well as the effects of surface water content and gas properties. These findings highlight potential benefits of thermal treatment on coalbed methane recovery and provide valuable insights for its exploitation under different geological conditions.

High-efficiency recovery of methane from coal bed gas via hydrate formation in emulsions

Although the hydrate-based coal bed gas (CBG) separations have been investigated, the obtained CH4 recovery ratios were not quite satisfactory. To further improve CH4 extraction, this study developed a high-efficiency CBG recovery method via hydrate formation in emulsions facilitated by an excellent anti-agglomerant. Thermodynamic promoters were introduced to lower operating pressure and the hydrate equilibrium conditions were determined. Then the effect of water-cut (40–100 vol%), initial pressure, experimental temperature, stirring rate and feed gas composition was investigated. The CH4 concentration in equilibrium gas first decreased then increased as the water-cut increased. Specifically, it decreased from 30.16 mol% to 8.23 mol% in the 60 vol% water-cut emulsions and CH4 recovery reached 88.02 % at 274.15 K and an initial pressure of 3.0 MPa, marking the highest CH4 recovery achieved in CBG separation thus far. The CH4 recovery was increased at low temperature while decreased at high pressure conditions. After a second-stage separation, the CH4 concentration in equilibrium gas decreased to 1.64 mol% from 30.16 mol%, signifying a remarkable 94.56 % recovery of CH4 from feed gas. The CH4 contents after a three-stage enrichment exceeded 87 mol%. This study furnishes valuable insights for CH4 recovery from CBG utilizing hydrate-based separation technology.

Research progress in separation of low concentration coalbed methane by hydrate method

The recovery of methane from low concentration coalbed methane can improve the utilization rate of coalbed methane, reduce the environmental pollution caused by gas emissions, and achieve the role of energy saving and emission reduction. In this paper, the recent research progress in hydrate separation of low concentration coalbed methane is analyzed, and the effects of thermodynamic promoters, kinetic promoters and mechanical strengthening are summarized respectively. Through the analysis, it is found that the effect of promoters needs to be further studied, and the appropriate promoters should be selected to find an effective way to promote the rapid synthesis of hydrate and help to promote the technical research on the separation and purification of low concentration coalbed methane by hydrate method.

Investigation of Hydrate Formation and Stability of Mixed Methane-THF Hydrates: Effects of Tetrahydrofuran Concentration.

Effects of tetrahydrofuran (THF) concentration on the mixed methane hydrate formation, dissociation, and stability were investigated. The experiment was conducted at 286.2 K and 6 MPa in a quiescent reactor. The presence of THF below 2.5 mol% did not show the evidence of hydrate formation. However, the concentration above 2.5 mol% enhanced the methane formation rate and the methane consumption. Increasing the THF concentration decreased the induction time as the result of the decrease in the surface tension. Moreover, the methane uptake and formation rate increased with the THF concentration due to the higher degree of hydrate nucleation. The methane recovery after the dissociation experiment showed up to 96%. Furthermore, the hydrate stability increased, and the hydrate dissociation kinetics decreased with the increase in the THF concentration. The optimum THF concentration to enhance and improve the hydrate formation kinetics and stability is its stoichiometric concentration.

Tools available for methane recovery from mines belonging to C.E.H. Petroşani

Mine gas is present both in coals and in the surrounding rocks and basically consists of methane (some-times almost 100%) mixed with carbon dioxide (up to 5%) with nitrogen (a few percent) and traces of carbon monoxide. The genesis of mine gas can be related to the biochemical transformation of vegetation during the carbonization process. The degassing of coal bed has been established as an active method of reducing methane emissions due to the need to ensure the exploitation of the bed with high productivity and in safe conditions. The methane gas existing in the coal bed is captured through various types of drilling executed for this purpose, being directed through a system of pipes to the surface to the central degassing station from where it can be taken and directed for use for a specific purpose. From an economic point of view, it has been proven that methane recovery from coal mines is again a profitable activity for both the mining company and a possible investor. The volume of methane from the coal deposits in Jiu Valley is very large and can provide large quantities for the recovery of this gas. At the same time, there was already a market for this product in Jiu Valley made up of industrial and individual consumers.

Restructuring substantial increase in natural gas reserves by coalbed methane (CBM) recovery

Coal deposits, especially hard coal deposits, contain in their structure large amounts of methane, which during exploitation is diluted through industrial ventilation and degassing technologies down to non-hazardous concentrations, reducing the major risk factor for the safety of workers and resources minerals. The amount of methane released and exhausted into the atmosphere by the degassing and ventilation stations of the mining units, in addition to being wasted instead of being used, is also a factor of environmental pollution, as a potential greenhouse gas (GHG). The environmental issues and the climate crisis faced by humanity compel the establishment of an Action Program on the methane issue, which includes the capture, recovery and exploitation of gas from active coal mines, or from virgin strata, from unexploited mining fields, with the help of currently available technologies and practices, which represent the chance to obtain clean energy and substantial climate benefits, in the short and long term. The solution to the use of methane gas from coal at active mining operations in Jiu a Valley - Romania, by burning it to obtain the thermal agent, brought important economic benefits by reducing energy costs and environmental protection by reducing methane emissions in the atmosphere. The present paper proposes an analysis of the benefits obtained as well as the development possibilities of methane usage for obtaining a clean fuel.

Two Dimensional (2D) Multi-Scale Modeling of Fixed Bed Adsorption Column Using Computational Fluid Dynamics (CFD) Simulation

Natural gas has received much attention with low environmental impact in recent decades as a fuel source. Flexible natural gas purification systems with minimal carbon dioxide footprints are growing in need. There are few techniques that base current industrial decontamination systems on among which adsorption is considered to be the promising one. Herein multi-scale models have advanced to simulate the hydrodynamics and adsorption-dynamics of gases in the adsorption column, a mixture of (CO2 and CH4) In the current analysis, a two-dimensional (2D) porous media was modelled using CFD multi-scale model. A fixed-bed adsorption column was used for the removal of carbon dioxide (CO2) from methane (CH4) and the silicate adsorbent adsorption kinetics linear driving force (LDF) model was simulated to describe it. The adsorption phenomena simulation inside the fixed bed using CFD method was implemented and using user defined function (UDF) and the user defined scalar (UDS), porous media concept and the mass transfer coefficient for gas components (CO2/CH4) were developed. The experimental data was used to validate the model which was collected based on varying a number of laboratory conditions. The simulation results prediction of methane recovery and breakthrough curves shows an acceptable agreement with the experimental data with the highest error lower than 3.5%. Moreover, the effect of feed concentration (15,35 and 75%), feed velocity effect (0.03,0.05 and 0.07 m/s), effect of bed porosity (0.42, 0.52 and 0.62), effect of inlet concentration on temperature (15, 30 and 60%), particle radius (0.0006, 0.0007 and 0.0008m) and effect of bed height (0.3, 0.4 and 0.5m) were investigated. The present results received from the CFD approach suggests that they are capable to predict the adsorption phenomena and hydrodynamics in the adsorption column.

Nonlinear Seepage Mechanism and Evolution Law of CO2 Enhancing Coalbed Methane Recovery

China’s coal seam permeability is low, and the original coal seam gas extraction is difficult. CO2 displacement of coal seam CH4 technology is an effective gas extraction technology. CO2 is injected into the coal seam under pressure, and competitive adsorption occurs with CH4 in the pores. The gas composition is nonuniformly distributed, and its viscosity μ is the dynamic parameter. As the gas is compressible, the pressure drops, and migration distance does not satisfy a linear relationship. Therefore, the gas transport does not conform to Darcy’s law. The mass transfer process and a multicomponent gas competitive adsorption were investigated theoretically and experimentally. The adsorption characteristics and gas compressibility determine the distribution of the gas components in pores and change the gas dynamic viscosity in different regions. The change in the gas dynamic viscosity in the channel is the direct reason for the nonlinear pressure gradient and gas flow curve. The permeability and gas component affect the degree of nonlinear deviation of the gas flow and pressure gradient curve. This affects the nonlinear deviation degree of the curve by changing the gas dynamic viscosity in the pore channel during displacement. The reasonable displacement pressure is the critical pressure (PO) through experimental and theoretical analysis.

Pretreatment of agave bagasse with ruminal fluid to improve methane recovery

Agave bagasse, a lignocellulosic waste that results from the milling and juice extraction of Agave tequilana var azul pineapples, is a suitable substrate for the production of methane through anaerobic digestion. However, it is necessary to apply a pretreatment to convert the bagasse into energy. In this context, this paper proposes using ruminal microorganisms to hydrolyze agave bagasse. This study evaluated the effect of the initial agave bagasse to ruminal fluid (S0/X0) ratio (0.33, 0.5, 1, and 2) on the hydrolysis efficiency. Subsequently, the supernatant was used for methane production. The hydrolysis efficiency increased as the S0/X0 ratio decreased. A hydrolysis efficiency of 60 % was achieved using an S0/X0 ratio of 0.33. The S0/X0 ratio of 0.33 optimally improved the specific methane production and energy recovery (155 ± 2 mL CH4/g TS and 6.1 ± 0.1 kJ/g TS) compared to raw biomass. The most abundant hydrolytic bacteria were Prevotella, Ruminococcus and Fibrobacter, and Engyodontium was the most abundant proteolytic fungus.

Methane Recovery from Cattle Manure: Role of Granular Activated Carbon Amendment into Anaerobic Digestion-Microbial Electrolysis Cells (AD-MECs) Integrated Systems

Methane Recovery from Cattle Manure: Role of Granular Activated Carbon Amendment into Anaerobic Digestion-Microbial Electrolysis Cells (AD-MECs) Integrated Systems

Sustainability evaluation of a PEMFC system for coalbed methane recovery based on life cycle assessment and emergy analysis

To promote the sustainable development of clean energy, a novel integrated system coupled coalbed methane recovery and proton exchange membrane fuel cell (PEMFC) is developed. Life cycle assessment (LCA) and emergy analysis model are established to analyze sustainability of the proposed system. The parametric analysis is performed to assess the effects of the reforming temperature, steam carbon ratio and current density on the emergy performance. The LCA results indicate that the construction phase has the most significant impact on system sustainability, accounting for 51.65%. Reducing the use of stainless steel and copper in the construction phase and improving the recycling process in the recovery phase can help improve the sustainability performance. The emergy analysis results show that the total emergy consumption of the system is 8.53E+16, the use phase accounted for 55.8%, the construction phase accounted for 43.8%, and the recovery phase only accounted for 0.4%. Parametric analysis shows that the emergy savings ratio increases by 7.11% as the reforming temperature is 800 °C. The emergy sustainability index ranges from 3.04 to 4.45 with great sustainability performance, as the increase of steam carbon ratio. The system has low environmental load and high sustainability when the current density is close to 1. This research will help improve the sustainability evaluation system of the energy system and promote the sustainable development of clean energy.

Recovery capability of anaerobic digestion from ammonia stress: Metabolic activity, energy generation, and genome-centric metagenomics

Excessive ammonia stresses anaerobic digestion (AD) significantly. Although there has been progress in understanding AD under ammonia exposure, investigations on AD liberated from ammonia exposure are limited. Here, the recovery capability of AD from ammonia stress was evaluated, by examining specific methanogenic activity, energy-conserving capability, microbial community succession, and metabolic pathway reconstruction. The findings demonstrated that ammonia stress relief resulted in < 50% methane recovery, with propionate conversion identified as the critical impediment to AD reactivation. Energy generation could not recovered either. Efforts to mitigate ammonia stress failed to restore acetoclastic methanogens, e.g., Methanothrix soehngenii, and proved futile in awakening propionate oxidizers, e.g., Desulfobulbus. Interestingly, a symbiotic metabolism emerged, prevailing in stress-relieved AD due to its energy-conserving advantage. This study underscores the importance of targeted interventions, including stimulating acetoclastic methanogenesis, propionate oxidation, and energy generation, as priorities for AD recovery following ammonia stress, rather than focusing solely on ammonia level management.

N2 injection to enhance gas drainage in low-permeability coal seam: A field test and the application of deep learning algorithms

N2 injection to enhance coal seam gas drainage is an effective technology for coalbed methane recovery. Nevertheless, there is a limited body of research addressing the application of ECBM technology for gas management in low permeability coal seams within underground coal mines, and the effect is uncertain. Additionally, numerical simulators have been challenged to accurately predict methane emissions during gas injection and replacement. In this study, firstly, an underground field trials of N2 injection replacement in a coal mine with low-permeability coal seams in China were conducted, and a comparative analysis of “N2 injection to enhance gas drainage” and “conventional drainage” technique was performed. The result show that injecting pressurized N2 into a low-permeability coal seam could increase the pressure gradient to promote the directional flow of free gas from the coal seam cracks to the gas-production boreholes. After N2 injection, the mixed flow rate and CH4 flow rate significantly increased. Additionally, the gas content in the coal seam in the experimental area significantly decreased. Secondly, the lag-effect was discussed. Upon discontinuation of N2 injection, the gas-producing mixed flow initially increased slightly, then gradually decreased, and eventually settled at a high level. Despite the attenuation of N2 injection volume, the CH4 flow rate continued to increase during intermittent injection and remained high after gas injection discontinuation. Finally, three deep learning algorithms (BP, LSTM, and TCN) were employed to predict the dynamic change of gas drainage in coal seams displaced by N2 injection, based on the results of the field test. The results indicated that deep learning algorithms exhibited superior prediction performance. The TCN model demonstrated the lowest approximation error rate, displaying optimal performance in predicting the CH4 flow rate during nitrogen injection for enhanced gas drainage. Additionally, it exhibited good applicability to other similar field test results.

Modeling of methane and carbon dioxide sorption capacity in tight reservoirs using Machine learning techniques

The viability of enhanced coalbed methane recovery (ECBM) and enhanced shale gas recovery (ESGR) are abundantly explored in various studies since they present a solution for ongoing energy demand and environmental crisis. As a matter of challenge, the prediction of the gas sorption profile poses a significant obstacle in the development of such resources. In this regard, mathematical models, numerical simulations, empirical correlations, and experimental measurements suffer from over-simplification, computationally extensive calculations, time-consuming, and costly processes. This work examines different machine learning methods, from shallow to deep learning, to investigate their capability to model 3804 data points of methane (CH4) and/or carbon dioxide (CO2) sorption capacity in shale and coal at different thermodynamic conditions. Percentage of CO2 in injection gas, rock type, total organic carbon (TOC), moisture, temperature, and pressure were taken as input. Hyperparameter tuning was executed by Optuna optimizer. According to the results, the random forest (RF) was the most proficient predictor for both test subsets of CH4 (MAE = 0.0864, MSE = 0.0231, RMSE = 0.1520) and CO2 (MAE = 0.0529, MSE = 0.0533, RMSE = 0.2308) sorption capacity. Based on the trend prediction simulation, RF predictors were able to properly capture the single and binary sorption capacities. More importantly, they successfully predict the abnormal descending behavior of CO2 sorption in high pressures. In addition, a sensitivity analysis was carried out to acquire the importance of input features and model hyperparameters in the training process. Input feature impacts were consistent with technical expectations of geology and reservoir engineering aspects. Both models are capable of being applied to lab scale and further developed for their application in reservoir scale simulators.

Hydrogeological Challenge for Coal Bed Methane (CBM) Production in Structurally Complex Reservoirs: Case Study for the Synclines of Umbita and Checua-Lenguazaque, Colombia

Colombia is advancing toward pilot production of coal bed methane (CBM) at the Umbita syncline (US) and Checua-Lenguazaque syncline (CLS) in the Cundiboyacense plateau of the Eastern Cordillera. Although attractive, the development of CBM resources remains hydrogeologically challenging due to infinite acting aquifer (IAA) conditions, a sustainable production of ineffective water, which removal is critical to achieve methane desorption. Here, we assessed the implications of IAA on methane production prior to pilot development by comparing single-phase flow numerical simulations of the prospects. The results suggest IAA would extend the dewatering period in the Umbita syncline up to 20 years to potentially compromise the commercial recovery of methane. The Chequa-Lenguasaque, on the other hand, appears to have reached the phase of production of effective water; therefore, it is deemed as the most attractive prospect for pilot testing the production of CBM in Colombia.

Permeability evolution of deep-buried coal based on NMR analysis: CO2 adsorption and water content effects

Permeability evolution of deep-buried coal plays a crucial role in CO2 geological storage and coalbed methane (CBM) recovery. In this study, permeability and nuclear magnetic resonance (NMR) tests were conducted on coal specimens under triaxial conditions. Based on the evolution of relaxation time (T2), the effects of CO2 adsorption and water content on permeability, pore structure, and mechanical properties of coal were discussed. Experimental results show that CO2 injection causes adsorption-induced swelling, inhibits flow in the early stage, causes the “expansion” and “complexity” of pore structure, and generates new channels for fluid transport. The presence of water in coal inhibits the flow process, resulting in an overall reduction of permeability by 2 orders of magnitude. Softening occurs in coal specimens, as evidenced by plasticity and low brittle failure and an average strength loss of 29.3 %. Additionally, a complex CO2–H2O coupling effect in coal is observed, causing the dissolution of certain minerals and organic matter, which further amplifies the “weakening effect” of water. Finally, permeability evolution characteristics of coal affected by CO2 and H2O from multiple perspectives were discussed in consideration of NMR fractal analysis. This work provides valuable insights into deep CO2 geological sequestration and CBM recovery.

Study in mitigation of lean methane and stable heat recovery via embedded heat exchanger tubes in the regenerative monolith bed

Study in mitigation of lean methane and stable heat recovery via embedded heat exchanger tubes in the regenerative monolith bed