Methane Pressure Research Articles

Effects of benzene, cyclo-hexane and n-hexane addition to methane on soot yields in high-pressure laminar diffusion flames

Effects of doping high pressure methane diffusion flames with benzene, cyclo-hexane and n-hexane were investigated to assess the sooting propensity of three hydrocarbons with six carbons at elevated pressures. Amount of liquid hydrocarbons added to methane constituted 7.5% of the total carbon content of the fuel stream. The pressure range investigated extended up to 10 bar and the experiments were carried out in a high pressure combustion chamber capable of establishing stable laminar diffusion flames with various fuels at elevated pressures and was used in similar experiments previously. Temperatures and soot volume fractions were measured using the spectral soot emission technique capturing spectrally-resolved line-of-sight intensities which were subsequently inverted using an Abel type algorithm to obtain radial distributions assuming that the flames are axisymmetric. The total mass carbon flow of the fuel stream was kept constant at 0.524 mg/s in neat methane, benzene-doped methane, cyclo-hexane-doped methane, and n-hexane-doped methane flames to have tractable measurements at all pressures. Measured maximum soot volume fractions and evaluated maximum soot yields showed that benzene-doped methane flame had the higher values than cyclo-hexane doped methane flames which in turn had higher values than n-hexane doped methane flames at all pressures. Sooting propensity dependence of the three hydrocarbons on pressure can be ranked as, in descending order, n-hexane, cyclo-hexane, and benzene; however, the difference between pressure dependencies of n-hexane and cyclo-hexane was within the measurement error margins. Ratio of soot yields of benzene to n-hexane doped flames changed from about 2 at 2 bar to 1.2 at 10 bar; the ratio of benzene to cyclo-hexane doped flames showed similar trends.

Experimental and numerical evaluations on characteristics of vented methane explosion

To research the characteristics of vented explosion of methane-air mixture in the pipeline, coal mine tunnel or other closed space, the experiments and numerical simulations were carried out. In this work, explosion characteristics and flame propagation characteristics of methane in pipeline and coal mine tunnel are studied by using an explosion test system, combined with FLACS software, under different vented conditions. The numerical simulation results of methane explosion are basically consistent with the physical experiment results, which indicates that the numerical simulation for methane explosion is reliable to be applied to the practice. The results show that explosion parameters (pressure, temperature and product concentration) of methane at five volume fractions have the same change trend. Nevertheless, the explosion intension of 10.0% methane is the largest and that of 9.5% methane is relatively weak, followed by 11.0% methane, 8.0% methane and 7.0% methane respectively. Under different vented conditions, the pressure and temperature of methane explosion are the highest in the pipeline without a vent, followed by the pipeline where ignition or vent position is in each end, and those are the lowest in the pipeline with ignition and vent at the same end. There is no significant effect on final product concentration of methane explosion under three vented conditions. For coal mine tunnel, it is indicated that the maximum explosion pressure at the airproof wall in return airway with the branch roadway at 50 m from goaf is significantly decreased while that in intake airway does not change overwhelmingly. In addition, when the branch roadway is longer or its section is larger, the peak pressure of airproof wall reduces slightly.

Effective Methane Extraction Radius after High-Pressure Water Jet Slotting

The effective radius of methane extraction after high-pressure water jet slotting is the most important parameter for borehole optimization and extraction time planning. We applied a steady flow model and thermal-hydrological-mechanical (THM) coupling model to calculate the effective radius after high-pressure water jet slotting. Field measurements at the Zhongliangshan coal mine show that both the steady flow model and the THM coupling model can accurately represent the effective radius, and the THM coupling model provides further information regarding extraction time. After that, a variety of factors, including extraction time, coal burial depth, slot radius, initial permeability, and initial methane pressure, are discussed. The effective radius of a slotted borehole is 1.94 times larger than that of a conventional borehole.

Effect of Small Cage Guests on Dissociation Properties of Tetrahydrofuran Hydrates.

It is well understood that tetrahydrofuran (THF) molecules are able to stabilize the large cages (51264) of structure II to form the THF hydrate with empty small cages even at atmospheric pressure. This leaves the small cages to store gas molecules at relatively lower pressures and higher temperatures. The dissociation enthalpy and temperature strongly depend on the size of gas molecules enclathrated in the small cages of structure II THF hydrate. A high-pressure microdifferential scanning calorimeter was applied to measure the dissociation enthalpies and temperatures of THF hydrates pressurized by helium and methane under a constant pressure ranging from 0.10 to 35.00 MPa and a wide THF concentration ranging from 0.25 to 8.11 mol %. The dissociation temperature of binary He + THF and methane + THF hydrates increases along with an increase in the THF concentration in the liquid phase at a fixed pressure (e.g., 30 MPa), reaching a maximum value of 280.8 and 312.8 K, respectively, at stoichiometric concentration (5.56 mol % THF), and then remains nearly constant for even higher THF concentrations (>5.56 mol %). The effect of gas occupancy in the small cages on the dissociation enthalpy of He + THF and methane + THF mixed hydrates was further examined by using molecular dynamics (MD) simulations. The dissociation enthalpy of the He-THF mixed hydrates is independent of pressure with an average of 5.68 kJ/mol H2O over the pressure ranging from 0.10 to 30.0 MPa, consistent with the MD results of the He-THF mixed hydrates with low single occupancy (<23%) of helium molecules in the small cages. Consequently, the heat of adsorption of helium molecules in the small cages of the He-THF mixed hydrates is rather too weak to be identified. On the other hand, the dissociation enthalpy of the methane-THF hydrates increases from 9.11 to 10.01 kJ/mol H2O along with an increase in methane pressure over the pressure ranging from 5.0 to 30.0 MPa, consistent with the MD results of the methane-THF mixed hydrates with full occupancy of methane molecules in the small cages. These findings provide important information for the design of a potential medium of gas storage and transportation.

Study of effectiveness factors with non-uniform catalyst distributions for methane steam reforming

In the present work, three kinetic expressions for methane steam reforming with different methane and water partial pressures dependence were studied. Methane effectiveness factors were simulated for spherical uniform pellets (those customarily employed), for several temperatures and water/methane ratios (hereafter called R). It was found that all effectiveness factors decreased with temperature as expected for all the kinetics expressions studied. On the other hand, the evolution with R was strongly dependent on the kinetics analyzed, with an important change in effectiveness factors values, ranging from 30 to 400%. This implies that the most convenient active sites distribution might be dependent on R evolution throughout the reactor. Then, two MSR reactors were simulated, loaded with pelletized catalysts with uniform and eggshell in order to get uniform nomenclature active site distributions. It was found that the one loaded with eggshell in order to get uniform nomenclature pellets saves up to 30% catalysts mass with respect to the uniform catalyst distribution for the same CH4 conversion, reinforcing the importance of active sites distribution.

Design and optimization of integrated single mixed refrigerant processes for coproduction of LNG and high-purity ethane

Abstract In this study, two novel integrated single mixed refrigerant (SMR) processes are proposed to coproduce liquefied natural gas (LNG) and high-purity liquid ethane, which are suitable for improving the economic benefits of high ethane-containing natural gas. In Process 1, cryogenic distillation and conventional SMR process are integrated to separate ethane while producing LNG. Since the distillation pressure is below the critical pressure of methane, heat transfer temperature difference in the low temperature section may be relatively large. Therefore, in Process 2, the pressure of natural gas is increased by adding a compressor after the distillation column. Aspen HYSYS is used to simulate the proposed processes, and the key parameters of the refrigeration cycles are optimized by genetic algorithms. Based on the comprehensive consideration of initial investment and operating cost, Process 2 is recommended for large-scale plant, while Process 1 for small-scale plant and situations with requirement of simple system, for example floating LNG production (FLNG). Furthermore, a simplified Process 1, with propane eliminated from the mixed refrigerant, is presented for better adaption to FLNG conditions.

Femtosecond two-photon laser-induced fluorescence imaging of atomic hydrogen in a laminar methane–air flame assisted by nanosecond repetitively pulsed discharges

Sustainable and low-emission combustion is in need of novel schemes to enhance combustion efficiency and control to meet up with new emission standards and comply with varying quality of renewable fuels. Plasma actuation is a promising candidate to achieve this goal but few detailed experiments have been carried out that target how specific combustion and plasma related species are affected by the coupling of plasma and combustion chemistry. Atomic hydrogen is such a species that here is imaged by using the two-photon absorption laser induced fluorescence (TALIF) technique as an atmospheric pressure methane–air flame is actuated by nanosecond repetitively pulsed (NRP) discharges. Atomic hydrogen is observed both in the flame and in the discharge channel and plasma actuation results in a wide modification of the flame shape. A local 50% increase of fluorescence occurs at the flame front where it is crossed by the discharge. Atomic hydrogen in the discharge channel in the fresh-gases is found to decay with a time constant of about 2.4 μs. These results provide new insights on the plasma flame interaction at atmospheric pressure that can be further used for cross-validation of numerical calculations.

Effects of tectonism on the pore characteristics and methane diffusion coefficient of coal

The diffusion coefficient of methane in coal is a key parameter that influences the methane extraction effect. Former studies on the methane diffusion coefficient mainly paid attention to the intact coal. The diffusion coefficient of tectonic coal is different from that of intact coal, which may be caused by the effect of tectonism on the pore characteristics. In this study, the pore characteristics of the intact coal and tectonic coal were tested using mercury intrusion porosimetry (MIP) and the physisorption method, while the counterdiffusion experiments were adopted to measure the methane diffusion coefficients of both coal samples. The results indicate that the methane diffusion coefficient of the tectonic coal is higher than that of the intact coal, and the diffusion coefficients decrease with the increasing methane pressure. The tectonism increases the volumes of mesopores and macropores and the porosity of coal, which is the main reason for the higher methane diffusion coefficient of the tectonic coal. The pore structure of coal becomes more winding or complicated by tectonism, thus showing a higher tortuosity of the tectonic coal. The tectonism makes it easier to extract methane, and coal mining in the tectonic region should receive more attention.

Balancing volumetric and gravimetric uptake in highly porous materials for clean energy.

A huge challenge facing scientists is the development of adsorbent materials that exhibit ultrahigh porosity but maintain balance between gravimetric and volumetric surface areas for the onboard storage of hydrogen and methane gas-alternatives to conventional fossil fuels. Here we report the simulation-motivated synthesis of ultraporous metal-organic frameworks (MOFs) based on metal trinuclear clusters, namely, NU-1501-M (M = Al or Fe). Relative to other ultraporous MOFs, NU-1501-Al exhibits concurrently a high gravimetric Brunauer-Emmett-Teller (BET) area of 7310 m2 g-1 and a volumetric BET area of 2060 m2 cm-3 while satisfying the four BET consistency criteria. The high porosity and surface area of this MOF yielded impressive gravimetric and volumetric storage performances for hydrogen and methane: NU-1501-Al surpasses the gravimetric methane storage U.S. Department of Energy target (0.5 g g-1) with an uptake of 0.66 g g-1 [262 cm3 (standard temperature and pressure, STP) cm-3] at 100 bar/270 K and a 5- to 100-bar working capacity of 0.60 g g-1 [238 cm3 (STP) cm-3] at 270 K; it also shows one of the best deliverable hydrogen capacities (14.0 weight %, 46.2 g liter-1) under a combined temperature and pressure swing (77 K/100 bar → 160 K/5 bar).

Methane sorption capacities and geochemical characterization of Paleozoic shale Formations from Western Peninsula Malaysia: Implication of shale gas potential

Thick sequences of overmatured Paleozoic black shales Formation were deposited in the Western Peninsula (WP) Malaysia, which can be considered as the potential shale gas reservoir. Therefore, to study the shale gas potential of the Paleozoic (Silurian-Permian) shale Formations, 146 samples from seven Formations were collected from WP Malaysia. A combination of methane sorption capacities, geochemical and trace element studies have been performed on the shale samples. The results indicate that the high pressure (up to 15 MPa) methane sorption capacity of the Silurian-Devonian, Devonian, Carboniferous, and Permian shales are between 0.079 and 0.154, 0.056 and 0.113, 0.052 and 0.094 and 0.085 and 0.169 mmol/g rock, respectively, at 30°C. Methane sorption capacities of the WP Malaysia shale were found to be greatly similar to sorption values of hot shales from Posidonia (Germany), Barnett (USA) and Longmaxi (China) shales. The measured total organic carbon (TOC) generally exceeded 2 wt% (average of 4 wt%), except for Carboniferous shales (>1 wt%). The biomarker analysis and Tmax values revealed that the kerogen has evolved into the metagenesis stage. The organic matter is likely comprises hydrogen-rich kerogen deposited under marine conditions in dysoxic to anoxic environment. After a comprehensive analysis, the Silurian-Devonian, Devonian and Permian shales in Western Peninsula Malaysia can be classified as potential gas shales based on their high TOC contents, presence of type III kerogen, high thermal maturity and significant methane sorption capacities.

Radial Permeability Measurements for Shale Using Variable Pressure Gradients

AbstractShale gas is becoming an important component of the global energy supply, with permeability a critical controlling factor for long‐term gas production. Obvious deviation may exist between helium permeability determined using small pressure gradient (SPG) methods and methane permeability obtained under actual field production with variable pressure gradients (VPG). In order to more accurately evaluate the matrix permeability of shale, a VPG method using real gas (rather than He) is established to render permeability measurements that are more representative of reservoir conditions and hence response. Dynamic methane production experiments were performed to measure permeability using the annular space in the shale cores. For each production stage, boundary pressure is maintained at a constant and the gas production with time is measured on the basis of volume change history in the measuring pump. A mathematical model explicitly accommodating gas desorption uses pseudo‐pressure and pseudo‐time to accommodate the effects of variations in pressure‐dependent PVT parameters. Analytical and semi‐analytical solutions to the model are obtained and discussed. These provide a convenient approach to estimate radial permeability in the core by nonlinear fitting to match the semi‐analytical solution with the recorded gas production data. Results indicate that the radial permeability of the shale determined using methane is in the range of 1×10−6 – 1×10−5 mD and decreases with a decrease in average pore pressure. This is contrary to the observed change in permeability estimated using helium. Bedding geometry has a significant influence on shale permeability with permeability in parallel bedding orientation larger than that in perpendicular bedding orientation. The superiority of the VPG method is confirmed by comparing permeability test results obtained from both VPG and SPG methods. Although several assumptions are used, the results obtained from the VPG method with reservoir gas are much closer to reality and may be directly used for actual gas production evaluation and prediction, through accommodating realistic pressure dependent impacts.

Influence of pore width on adsorption capacity of shale-Insights from high pressure adsorption experiments on model substances

Shale gas has become an important unconventional resource worldwide and adsorbed gas mainly contribute to the initial gas content for shale. In this study, different model substances, including 3Å molecular sieve, 4Å molecular sieve, 5Å molecular sieve and 13X molecular sieve, were conducted by high pressure methane adsorption experiments and the results were analyzed to obtain the effect of pore width on methane adsorption capacity. The results show that methane molecular almost cannot enter the pore of 3Å molecular sieve for adsorption, only adsorption on surface can be occurred, as well as the pore of 4Å molecular can be slightly entered by methane molecular. Whereas, methane molecular can totally enter the pore of 5Å and 13X molecular for adsorption. Meanwhile, at low pressure (less than 1.0MPa), the excess adsorption amount of methane for 13X is slightly greater than that of 5Å molecular sieve. With the increasing of pressure (1-18MPa), the excess adsorption amount of methane for 5Å is greater than that of 13X molecular sieve. In the pressure ranging from 18 to 30MPa, the excess adsorption amount of methane for 13X is greater than that of 5Å molecular sieve.

Outburst cavity formation in the working face driven along the outburst-prone coal seam

In Donbas coal mines, coal and gas outbursts present a major risk for the mining operation safety. Rapidly released energy can cause serious damage to the mine’s personnel and production equipment. Modern numerical methods allow modeling complex physical processes occurred during the coal and gas outbursts. The mathematical model was developed for the coupled processes of the rock massif deformation and gas filtration in the mine face near the tectonic dislocation. When solving the problem, the finite element method was used. The calculation results of the stresses, inelastic deformation zones, pressures of methane and configuration of cavity of the coal and gas outburst are represented in the paper. It is shown that an outburst cavity is formed inside the coal seam and is bounded from above and from below by the host rocks. The calculated geometry of the fracture cavity at the gas-dynamic phenomena in the mine working face coincides with actual data obtained in the mines of Donbas and, therefore, confirms the adequacy of the developed mathematical model.

Experimental Study on Desorption Characteristics of Coalbed Methane under Variable Loading and Temperature in Deep and High Geothermal Mine

Due to the influence of deep high stress, geothermal heat, and other factors, the law of desorption of methane in coal seams is more complicated in the process of mining deep coal seams, which is prone to methane over‐limit, coal and gas outburst, and other accidents. In order to study the desorption characteristics of coalbed methane under different loading and temperature conditions, the desorption tests at different deformation stages of coal containing methane were carried out in the process of loading‐adsorption‐desorption‐reloading until the coal sample was destroyed by using the seepage‐adsorption‐desorption test system on coal and rock mass, and the test programs were different combinations of gas pressure 1.2 MPa, two kinds of confining pressure, and three kinds of temperature. The results show that the cumulative methane desorption amount corresponding to each deformation stage presents a convex parabolic increase trend with the increase in desorption time, while the desorption rate presents a power function decay trend. Under the condition of the same desorption time, the cumulative methane desorption amount from large to small is residual deformation stage, compaction stage, near the peak stress, plastic deformation stage, and elastic deformation stage. Under the same confining pressure, temperature, and methane pressure, the maximum desorption rate from large to small is residual deformation stage, near the peak stress, plastic deformation stage, compaction stage, and elastic deformation stage. The desorption and diffusion of methane are promoted under the higher temperature and lower confining pressure, which presents a certain mechanism of promoting desorption. The thermal movement of methane molecules is intensified with the increase in temperature, and the adsorption effect between methane molecules and the molecules at the surface of the coal is weakened. The cumulative methane desorption amount and the maximum desorption rate increase with the increase in temperature. The cumulative methane desorption in the residual deformation stage is obviously greater than that in other deformation stages. The increase in confining pressure inhibits the development and expansion of pore fractures in raw coal specimen and hinders the increase in the effective desorption surface area. The cumulative methane desorption amount and the maximum desorption rate decrease with the increase in confining pressure.

Experimental verification of the water-methane displacement effect in gassy coal

To verify that water-methane displacement effect in gassy coal exists objectively, a pseudo-triaxial experimental system of water-methane displacement was independently developed and tested. First, methane was injected into the standard cylindrical coal sample until the methane adsorption equilibrium state was reached. Then, the methane in the coal sample spontaneously desorbed. Finally, water was injected into the coal sample. It is shown that: 1) water-methane displacement effect exists objectively; 2) water-methane displacement effect includes the process of free methane generated by competitive adsorption and displacement desorption effect, the consumption caused by methane pressure increase, and water driving methane; 3) competitive adsorption and displacement desorption between methane and water can generate free methane. Due to water injection, the increase of methane pressure leads to consumption of free methane. The net free methane of the combined action provides methane source for the water-methane displacement effect. [Received: August 19, 2017; Accepted: February 2, 2018]

Experimental verification of the water-methane displacement effect in gassy coal

To verify that water-methane displacement effect in gassy coal exists objectively, a pseudo-triaxial experimental system of water-methane displacement was independently developed and tested. First, methane was injected into the standard cylindrical coal sample until the methane adsorption equilibrium state was reached. Then, the methane in the coal sample spontaneously desorbed. Finally, water was injected into the coal sample. It is shown that: 1) water-methane displacement effect exists objectively; 2) water-methane displacement effect includes the process of free methane generated by competitive adsorption and displacement desorption effect, the consumption caused by methane pressure increase, and water driving methane; 3) competitive adsorption and displacement desorption between methane and water can generate free methane. Due to water injection, the increase of methane pressure leads to consumption of free methane. The net free methane of the combined action provides methane source for the water-methane displacement effect. [Received: August 19, 2017; Accepted: February 2, 2018]

Coupled hydrodynamic and kinetic model of liquid metal bubble reactor for hydrogen production by noncatalytic thermal decomposition of methane

Industrial-scale implementation of liquid metal bubble reactors (LMBRs) to produce hydrogen by methane decomposition will require large gas holdups (e.g., 20–30 vol%) and elevated gas pressures (>20 bar) to allow for practical reactor sizes. A realistic reactor design must account for the coupling between reaction kinetics and hydrodynamic effects. The gas holdup is predicted from the superficial gas velocity with a drift flux model that was experimentally corroborated in gas-molten metal mixtures. Large superficial gas velocities (>0.40 m s−1) are required to achieve gas holdups of about 25 vol% in liquid metal baths (LMBs). A noncatalytic kinetic model is developed to provide thermodynamically consistent decomposition rates at methane conversions approaching equilibrium. The coupled model optimizes the LMB dimensions (diameter and length) and the inlet pressure to minimize the volume of liquid metal when the hydrogen production rate, bath temperature, methane conversion, metal composition, and maximum gas holdup are specified. For example, 200 kt a−1 of hydrogen can be produced in an LMBR containing at least 96.5 m3 of molten tin held at 1100 °C in a bath measuring 3.50 m in diameter and 14.3 m in length, with an inlet methane pressure of 57.8 bar resulting in an average gas holdup of 29.7 vol% and a methane conversion of 65%.

Effects of pore structure on methane adsorption behavior of ductile tectonically deformed coals: An inspiration to coalbed methane exploitation in structurally complex area

The distinctive pore structure of tectonically deformed coals (TDCs) has a considerable influence on their methane adsorption behavior, resulting in higher coalbed methane (CBM) pressure and higher CBM content, and thus increasing the difficulty of CBM development in TDCs distribution area (especially ductile TDCs). In this paper, the supermicropore-microfracture structures of primary structure coals (PSCs) and ductile TDCs from the Suxian mining area were characterized by using mercury intrusion porosimetry (MIP) and gas adsorption methods (N2 and CO2). Methane adsorption test was conducted to study the methane adsorption behavior. Then, the control mechanism of pore structure on methane adsorption behavior of ductile TDCs was investigated. Results show that the supermicropores (<2 nm) surface area generally increases and then decreases. The micropores (2–10 nm) and small transitional pores (10–40 nm) volume of ductile TDCs is slightly larger than that of PSCs, while the volume of big transitional pores (40–100 nm) experiences a steady increase. The mesopores (100–1000 nm) and macropores (1000–10000 nm) volume displays a similar pattern of “steep increase-slightly decrease -stable increase” with the enhancement of deformation. The microfractures (>10000 nm) volume first increases and then decreases from the PSCs to mylonitized coals. Langmuir volume (VL, daf) displays no obvious change rules with the increasing ductile deformation, but the Langmuir pressure (PL, daf) of ductile TDCs is smaller than that of PSCs and gradually decreases to its minimum in the mylonitized coals. The Pearson correlation coefficients show that the volume of big transitional pores (40–100 nm), mesopores and macropores both shows obvious negative correlations with the PL, daf, which indicates that the development of 40–10000 nm pores in ductile TDCs causes a lower PL, daf, resulting in higher CBM pressures and contents in the ductile TDCs distribution area under the in-situ pressure condition.

Formation of methane hydrate from water sorbed by anthracite: An investgation by low-field NMR relaxation

Transverse relaxation time spectra T2 were studied for the samples (a) of wet coal in which methane hydrate was obtained, (b) wet coal exposed under the pressure of methane without the formation of the hydrate, and (c) initial wet coal. In all these cases, the samples of wet coal contained only water adsorbed in the fine pores of the coal substance. It was demonstrated that hydrate formation and the competitive sorption of methane at the positions previously occupied by water causes replacement of a part of water from coal mesopores into larger pores. The data obtained confirm a previously proposed multistage model (Smirnov et al., 2018) of hydrate formation in natural coal, which includes the stages of replacement of a part of sorbed water from coal pores by gas, the formation of microscopic water fragments in larger coal pores, and the formation of hydrate from this water.

New Constraint on the Atmosphere of (50000) Quaoar from a Stellar Occultation

Abstract We report observations of a stellar occultation by the classical Kuiper Belt object (50000) Quaoar that occurred on 2019 June 28. A single-chord high-cadence (2 Hz) photometry data set was obtained with the Tomo-e Gozen CMOS camera mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The obtained ingress and egress data do not show any indication of atmospheric refraction and allow new 1σ and 3σ upper limits of 6 and 16 nbar, respectively, to be set for the surface pressure of a pure methane atmosphere. These upper limits are lower than the saturation vapor pressure of methane at Quaoar’s expected mean surface temperature (T ∼ 44 K) and imply the absence of a ∼10 nbar-level global atmosphere formed by methane ice on Quaoar’s surface.