Supercritical Methane Research Articles

Determining Supercritical Methane Adsorption Phase Density in Nanoscale Shale: from Polanyi Theory to Machine Learning

Determining Supercritical Methane Adsorption Phase Density in Nanoscale Shale: from Polanyi Theory to Machine Learning

Supercritical Methane Adsorption Characteristics and Pore Structure Characteristics of Deep Middle Rank Coal

Abstract In order to accurately analyze the adsorption characteristics, pore structure, and fractal law of deep middle rank coal, high-pressure isothermal adsorption tests based on magnetic levitation high-pressure thermobalance and pore structure tests based on mercury intrusion method were carried out on coal samples collected from typical kilometer level deep wells. The fractal law of sponge model was studied. The results showed that: a. The weight method adsorption test showed “excess adsorption” phenomenon with the increase of equilibrium pressure, and the modified Gibbs surface excess adsorption theory was in line with the Langmuir adsorption model; b. The distribution of macropore volume in deep middle rank coal accounts for a dominant proportion of 57.44% to 62.47%, and the proportion of microporous specific surface area reaches 72.96% to 74.27%, indicating that microporous adsorption capacity is the strongest; c. The pore structure parameters and adsorption constants exhibit strong nonlinear characteristics.

Influence of Supercritical Conditions on Isothermal Adsorption Capacity Calculation of Methane and Model Optimization.

The study of isothermal adsorption models for coal and methane under supercritical conditions helps us to understand the gas content distribution in coal seams and improve gas management in coal mines. Coal samples from the Hebi mine and Longshan coal mine were selected for this research. Using the weight method, isothermal adsorption curves of supercritical methane at temperatures of 308, 313, and 318 K were measured. The adsorption phase density of supercritical methane was obtained by using the intercept method and model fitting, and the absolute adsorption capacity of methane was calculated. Simultaneously, the pore volume and specific surface area of the coal samples were tested, and the isothermal adsorption model for supercritical methane was studied and optimized. The results indicate that using mercury intrusion, low-temperature N2, and low-temperature CO2 adsorption methods for testing coal sample pore structures allows for multiscale characterization of the coal pore structure. Based on the Gibbs excess adsorption theory, the phase density of methane obtained from the intercept method and model fitting effectively represent the isothermal adsorption curve of supercritical methane. By combination of the specific surface area and pore volume distribution of the coal with the absolute adsorption capacity of methane, the number of methane adsorption layers on the coal surface was calculated to be between 1.11 and 1.3 layers. This suggests that the isothermal adsorption model for supercritical methane on coal is not solely micropore filling or single molecular layer adsorption but primarily single molecular layer adsorption with concurrent micropore filling adsorption. Based on this adsorption mechanism, an L-DA isothermal adsorption model for supercritical methane on coal was established. The L-DA isothermal model shows good fitting results and effectively explains the adsorption characteristics of supercritical methane on coal.

Crossover from gas-like to liquid-like molecular diffusion in a simple supercritical fluid.

According to textbooks, no physical observable can be discerned allowing to distinguish a liquid from a gas beyond the critical point. Yet, several proposals have been put forward challenging this view and various transition boundaries between a gas-like and a liquid-like behaviour, including the so-called Widom and Frenkel lines, and percolation line, have been suggested to delineate the supercritical state space. Here we report observation of a crossover from gas-like (Gaussian) to liquid-like (Lorentzian) self-dynamic structure factor by incoherent quasi-elastic neutron scattering measurements on supercritical fluid methane as a function of pressure, along the 200 K isotherm. The molecular self-diffusion coefficient was derived from the best Gaussian (at low pressures) or Lorentzian (at high pressures) fits to the neutron spectra. The Gaussian-to-Lorentzian crossover is progressive and takes place at about the Widom line intercept (59 bar). At considerably higher pressures, a liquid-like jump diffusion mechanism properly describes the supercritical fluid on both sides of the Frenkel line. The present observation of a gas-like to liquid-like crossover in the self dynamics of a simple supercritical fluid confirms emerging views on the unexpectedly complex physics of the supercritical state, and could have planet-wide implications and possible industrial applications in green chemistry.

High-Pressure adsorption of supercritical methane and carbon dioxide on Coal: Analysis of adsorbed phase density

The occurrence of supercritical CH4 and CO2 in coal is significant for both coalbed methane recovery and CO2 storage. Adsorption isotherms of CH4 and CO2 on two coals have been measured at three temperatures up to pressures of 25 MPa. Three modified supercritical adsorption models (SL-V, SBET-V, and SDR-V) were used to describe the excess adsorption behavior, with the pressure-independent adsorbed phase volume being considered. The adsorbed phase density (APD) and absolute adsorption amount were calculated based on the modified models and compared with those estimated by previous models. The results indicate that SDR-V is the most suitable for CH4 adsorption due to the dominant role of filling of micropores by CH4, while SBET-V is the most appropriate model for CO2 adsorption because of multilayer adsorption of CO2 in both micropores and meso-macropores. The APD increases with pressure until reaching a maximum value but decreases as temperature increases following a Langmuir-style trend. The previous models, which use a fixed APD, seriously underestimate the absolute adsorption, the extent of which increases with increasing pressure and temperature, leading to significant errors in deep formations with high temperature and pressure conditions. Furthermore, as burial depth increases, the adsorption process can be divided into three stages based on changes in APD and free phase density (FPD). These findings contribute to a comprehensive understanding of the behavior and occurrence of CH4 and CO2 within deep coal seams, enhancing the applicability of CO2-ECBM (CO2 Geological Storage Enhanced Coalbed Methane Recovery).

Numerical investigation of supercritical combustion dynamics in a multi-element LOx–methane combustor using flamelet-generated manifold approach

The article investigates liquid oxygen (LOx)–methane supercritical combustion dynamics in a multi-element rocket-scale combustor using large eddy simulation (LES). A complex framework of real gas thermodynamics and flamelet-generated manifold (FGM) combustion model is invoked to simulate transcritical oxygen injection and supercritical methane combustion. A benchmark Mascotte chamber, rocket combustion Modeling (RCM) test case, i.e., RCM-3 (V04)/G2 test case, is used to validate the real gas FGM model in the LES framework. The validation study accurately reproduces experimental flame structure and OH concentration, demonstrating the FGM model's importance in incorporating finite rate kinetics in LOx–methane combustion. Subsequently, the numerical framework investigates a specially designed multi-element combustion chamber featuring seven bidirectional swirl coaxial injectors. The analyses capture the complex hydrodynamics and combustion dynamics associated with multiple swirl injectors operating at supercritical pressure, effectively demonstrating the initiation of transverse acoustic waves and examining the effect of local sound speed on the evolution of acoustic modes in the combustor. The dominant frequency modes shed light on understanding the role of injectors in enhanced combustor dynamics. Spectral analysis reveals the interplay of the upstream injector and chamber acoustics due to possible frequency coupling. The results also highlight the effect of fuel injection temperature on the stability of the combustor, revealing a violent dynamic activity for lower fuel injection temperature associated with the longitudinal acoustic mode of the combustor. The investigation appropriately reproduces self-sustained limit-cycle oscillations at lower fuel injection temperatures and corroborates the conventional understanding of combustor instability.

Supercritical methane adsorption in coal and implications for the occurrence of deep coalbed methane based on dual adsorption modes

Supercritical methane adsorption in coal and implications for the occurrence of deep coalbed methane based on dual adsorption modes

Kinetic and Thermodynamic Characteristics of Supercritical Methane Adsorption on Organic-Rich Shale: A Case Study of Ordovician Wufeng and Silurian Longmaxi Gas Shale

Kinetic and Thermodynamic Characteristics of Supercritical Methane Adsorption on Organic-Rich Shale: A Case Study of Ordovician Wufeng and Silurian Longmaxi Gas Shale

Micro segment analysis of supercritical methane thermal-hydraulic performance and pseudo-boiling in a PCHE straight channel

The printed circuit heat exchanger (PCHE) is receiving wide attention as a new kind of compact heat exchanger and is considered as a promising vaporizer in the LNG process. In this paper, a PCHE straight channel in the length of 500 mm is established, with a semicircular cross section in a diameter of 1.2 mm. Numerical simulation is employed to investigate the flow and heat transfer performance of supercritical methane in the channel. The pseudo-boiling theory is adopted and the liquid-like, two-phase-like, and vapor-like regimes are divided for supercritical methane to analyze the heat transfer and flow features. The results are presented in micro segment to show the local convective heat transfer coefficient and pressure drop. It shows that the convective heat transfer coefficient in segments along the channel has a significant peak feature near the pseudo-critical point and a heat transfer deterioration when the average fluid temperature in the segment is higher than the pseudo-critical point. The reason is explained with the generation of vapor-like film near the channel wall that the peak feature related to a nucleate-boiling-like state and heat transfer deterioration related to a film-boiling-like state. The effects of parameters, including mass flow rate, pressure, and wall heat flux on flow and heat transfer were analyzed. In calculating of the averaged heat transfer coefficient of the whole channel, the traditional method shows significant deviation and the micro segment weighted average method is adopted. The pressure drop can mainly be affected by the mass flux and pressure and little affected by the wall heat flux. The peak of the convective heat transfer coefficient can only form at high mass flux, low wall heat flux, and near critical pressure, in which condition the nucleate-boiling-like state is easier to appear. Moreover, heat transfer deterioration will always appear, since the supercritical flow will finally develop into a film-boiling-like state. So heat transfer deterioration should be taken seriously in the design and safe operation of vaporizer PCHE. The study of this work clarified the local heat transfer and flow feature of supercritical methane in microchannel and contributed to the deep understanding of supercritical methane flow of the vaporization process in PCHE.

Study on thermal-hydraulic performance of printed circuit heat exchangers with supercritical methane based on machine learning methods

In this study, a machine learning approach was used to predict thermal-hydraulic performance of supercritical methane flow in a printed circuit heat exchanger (PCHE). Local multiple physical parameters within the PCHE semicircular straight channel obtained from numerical simulations were employed and data of 6213 micro segments were obtained. Four machine learning models were used to predict local heat transfer coefficient and unit pressure drop at different operating conditions. By comparing the predicted results obtained after hyperparameter optimization, it shows that artificial neural network (ANN) can predict the parameters with higher accuracy. The ANN model can achieve a coefficient of determination (R2) of 0.9994 with mean absolute percentage error (MAPE) of 0.252% for the heat transfer coefficient, and R2 of 0.9996 with MAPE of 1.749% for the unit pressure drop. To verify the accuracy of machine learning model, a one-dimensional simulation model embedded with ANN model was built to calculate the temperature and pressure distribution in the entire PCHE channel. The results show the temperature and pressure distribution agree well with numerical results. This work provides an accurate machine learning approach to predict flow and heat transfer parameters, which is of great value for the simulation and design of the PCHE.

Proposal and energetic and exergetic evaluation of a hydrogen production system with synergistic conversion of coal and solar energy

In this study, a clean and efficient hydrogen production system with synergistic conversion of coal and solar energy is proposed, and the energetic and exergetic evaluation are carried out. The main feature is that the syngas produced by supercritical water coal gasification contains a large amount of steam and some methane, which is very suitable for steam methane reforming reaction to generate high-purity hydrogen. Through thermochemical complementary and chemical recuperative methods, concentrated solar energy and high-temperature flue gas are used to supply reaction heat for the supercritical water coal gasification and steam methane reforming processes, respectively. The results showed that the energy and exergy efficiencies reach approximately 50.15% and 50.81%, respectively, which is an increase of 10.42% and 10.78%. The key reason for the improvement in system performance is that the exergy destruction during gasification and reforming is reduced by 7.81% points. As a result, the hydrogen-rich syngas chemical exergy is approximately 54.27% higher than that of the reference system. In addition, sensitivity analysis is employed to disclose the effect of key parameters on the hydrogen yield, syngas composition and methane conversion rate. This study presents a promising solution for large-scale hydrogen production processes.

Chemistry and Dynamics of Supercritical Carbon Dioxide and Methane in the Slit Pores of Layered Silicates.

ConspectusIn the mid 2010s, high-pressure diffraction and spectroscopic tools opened a window into the molecular-scale behavior of fluids under the conditions of many CO2 sequestration and shale/tight gas reservoirs, conditions where CO2 and CH4 are present as variably wet supercritical fluids. Integrating high-pressure spectroscopy and diffraction with molecular modeling has revealed much about the ways that supercritical CO2 and CH4 behave in reservoir components, particularly in the slit-shaped micro- and mesopores of layered silicates (phyllosilicates) abundant in caprocks and shales. This Account summarizes how supercritical CO2 and CH4 behave in the slit pores of swelling phyllosilicates as functions of the H2O activity, framework structural features, and charge-balancing cation properties at 90 bar and 323 K, conditions similar to a reservoir at ∼1 km depth. Slit pores containing cations with large radii, low hydration energy, and large polarizability readily interact with CO2, allowing CO2 and H2O to adsorb and coexist in these interlayer pores over a wide range of fluid humidities. In contrast, cations with small radii, high hydration energy, and low polarizability weakly interact with CO2, leading to reduced CO2 uptake and a tendency to exclude CO2 from interlayers when H2O is abundant. The reorientation dynamics of confined CO2 depends on the interlayer pore height, which is strongly influenced by the cation properties, framework properties, and fluid humidity. The silicate structural framework also influences CO2 uptake and behavior; for example, smectites with increasing F-for-OH substitution in the framework take up greater quantities of CO2. Reactions that trap CO2 in carbonate phases have been observed in thin H2O films near smectite surfaces, including a dissolution-reprecipitation mechanism when the edge surface area is large and an ion exchange-precipitation mechanism when the interlayer cation can form a highly insoluble carbonate. In contrast, supercritical CH4 does not readily associate with cations, does not react with smectites, and is only incorporated into interlayer slit mesopores when (i) the pore has a z-dimension large enough to accommodate CH4, (ii) the smectite has low charge, and (iii) the H2O activity is low. The adsorption and displacement of CH4 by CO2 and vice versa have been studied on the molecular scale in one shale, but opportunities remain to examine behavioral details in this more complicated, slit-pore inclusive system.

Improved Wall Temperature Prediction for the LUMEN Rocket Combustion Chamber with Neural Networks

Accurate calculations of the heat transfer and the resulting maximum wall temperature are essential for the optimal design of reliable and efficient regenerative cooling systems. However, predicting the heat transfer of supercritical methane flowing in cooling channels of a regeneratively cooled rocket combustor presents a significant challenge. High-fidelity CFD calculations provide sufficient accuracy but are computationally too expensive to be used within elaborate design optimization routines. In a previous work it has been shown that a surrogate model based on neural networks is able to predict the maximum wall temperature along straight cooling channels with convincing precision when trained with data from CFD simulations for simple cooling channel segments. In this paper, the methodology is extended to cooling channels with curvature. The predictions of the extended model are tested against CFD simulations with different boundary conditions for the representative LUMEN combustor contour with varying geometries and heat flux densities. The high accuracy of the extended model’s predictions, suggests that it will be a valuable tool for designing and analyzing regenerative cooling systems with greater efficiency and effectiveness.

Investigations on Supercritical Methane Adsorption and Storage in the Lower Longmaxi Shale of Nanchuan Area, Southeast Sichuan Basin

A series of high-pressure methane adsorption measurements were performed at various temperatures on whole shale and kerogen samples collected from the Lower Longmaxi shale in the Nanchuan area, southeast Sichuan Basin, to investigate supercritical methane adsorption properties and evaluate in-place methane storage capacity as a function of burial depth. The results show that the supercritical Dubinin–Radushkevich (SDR) model fits the excess adsorption isotherms marginally better than the supercritical Langmuir model. However, the fitted adsorbed methane density of kerogens obtained from the SDR model may be greater than the liquid methane density at the atmospheric boiling point (0.423 g/cm3). The proposed multiple regression fitting carried out in this work illustrates that approximately 57.59% (34.51–85.45%) and 37.60% (10.74–59.52%) of the methane adsorption capacity at 333.15 K can be attributed to organic matter (OM) and clay minerals (CMs), respectively, for whole shales investigated. According to thermodynamic analyses, the significant contribution of OM to the methane adsorption capacity can be attributed to the stronger affinity between kerogens and methane molecules in contrast to that between CMs and whole shales. The methane storage capacity estimated as a function of burial depth showed that the adsorbed gas storage capacity declines with increasing burial depth between 2000 and 5000 m, while the free gas storage capacity shows the opposite trends. Gas accumulation pressure primarily exerts a significant effect on the free gas storage capacity rather than adsorbed gas storage capacity, and adsorbed gas storage capacity begins to exceed free gas storage capacity at shallow burial depths for normally pressured gas accumulations. Normally pressured shale gas accumulations at shallow burial depths, which are widely distributed in the residual syncline of the study area, should be given more attention due to their relatively low development costs and relatively high storage capacity for adsorbed gas.

Perspectives of Gas Adsorption and Storage in Kerogens and Shales

Shale gas from unconventional resources will contribute to meeting the energy demand during the transition to a net-zero carbon economy. In this minireview, the current status of understanding methane adsorption on kerogens and shales is discussed in relation to methane storage capacity. Standard subcritical adsorption studies provide characterization data (micropore volumes, total pore volumes, surface areas, and pore size distributions) for the porous structures of shales and kerogens. However, supercritical methane adsorption measurements under simulated geological conditions are necessary to assess realistic methane adsorption storage capacities. Supercritical methane adsorption on shale and shale components (kerogens and clays) under high pressure and temperature conditions that simulated geological conditions is compared. Kerogen structural characteristics are discussed in relation to supercritical methane isotherms and isobars. The contribution of adsorbed methane gas relative to “free” or compressed gas to the total gas stored in shale is considered. The importance of kerogens in both storage of the adsorbed phase and as the source of methane is highlighted, and the areas where knowledge and understanding are deficient are identified, in particular, the relationship of kerogen type and maturity with supercritical methane adsorption under simulated geological conditions. The competitive adsorption of water on methane capacity is also an area where more detailed studies are necessary. These are challenges to address gaps in the current knowledge and understanding, which require future research.

Examining Supercritical Methane Adsorption on Nanoporous Shales Using Constant and Varying Adsorbed Phase Density Approaches

Supercritical adsorption studies are crucial, as adsorbed methane has a significant contribution to the total gas-in-place along with the free gas-in-shale reservoirs. Due to the low specific adsorption of shales, Gibbs excess isotherms that decrease after a certain pressure are being reported. Corrections to the excess adsorption amount can be made using models that predict absolute adsorption through empirically estimated adsorbed phase density. However, due to the inherent heterogeneity of shale and uncertainties in the adsorbed phase density estimated from different models, the quantitative characterization of adsorption is becoming increasingly challenging. The assumption of constant adsorbed phase density is being challenged with varying adsorbed phase density approaches, which are theoretically correct; however, their applicability has not been analyzed distinctively. In this work, supercritical adsorption models like supercritical BET (SBET), supercritical Dubinin–Radushkevich (SDR), Ono–Kondo mono- and multilayer, fixed volume Ono–Kondo (FV-OK1), and variable density Langmuir (VD-Langmuir) are revisited, analyzed, and compared for their applicability in shale reservoirs. For this, methane adsorption isotherms at two different temperatures (45 and 90 °C) are generated for four samples with varying geochemical and petrophysical properties selected from the Cambay and Krishna–Godavari (KG) basins of India. Through this analysis, it has been found that fixed-density approaches better explain the isotherms in comparison to varying density approaches. The average adsorbed phase density estimated using SBET and SDR models was closer to 0.2 g/cm3, which is very low in comparison to the theoretical limit. The SBET and Ono–Kondo theories have displayed that the probability of adsorption after the third layer is low. The VD-Langmuir and FV-OK1 could fit perfectly to highly specific adsorbing solids; however, they failed to explain adsorption in low-adsorbing solids. The mathematical drawbacks of variable density approaches have not been analyzed previously and are explained in this work.

An Experimental Investigation of Supercritical Methane Injection Characteristics in a CO2 Environment

Abstract Clean energy generation is gaining significant attention from industries, academia, and governments across the globe. The Allam cycle is one such technology that has been under focus due to its efficiency, environmental friendliness, and economics. This is a direct-fired cycle operating at supercritical conditions using carbon dioxide as a working fluid. Fuel or oxidizer jet mixing with CO2 is a vital phenomenon that governs combustion efficiency, and it is not well understood for the Allam cycle conditions. This paper experimentally investigated the jet characteristics of a methane jet injected into a subcritical to supercritical carbon dioxide environment. A wide range of injection pressures and temperatures were targeted between subcritical to supercritical conditions. Unlike previous studies, the current work focused on injecting lower-density (methane) jets into higher-density (carbon dioxide) environments. Schlieren imaging and methane absorption measurements were simultaneously performed with a CMOS high-speed camera and a 3.39 μm infrared laser. Specifically, we looked at the classical injection parameter of jet spreading angle, which was classically established to be mainly a density ratio function. Here, the jet cone angle was obtained from the postprocessed schlieren imaging. The jet cone angle is a critical characteristic parameter that describes the entrainment rate in a jet; thus, it is a crucial parameter in understanding the nature of the jet. The laser measurements were only used as an additional check to confirm the entry time of methane into the chamber filled with carbon dioxide. Notably, this paper makes a detailed comparison between the jet cone angles of jets with a density ratio. The result showed that the classical correlations, such as Abramovich's theory applied to submerged turbulent gas jets developed for low-density ratio jets, were unsuitable for higher-density ratio jets. It was also observed that the divergence angles were dependent not only on density ratio but also on other parameters such as pressure ratios and reduced pressures.

Study of dimple restraining heat transfer deterioration of supercritical methane under high heat flux in mini channel

To attenuate the heat transfer deterioration of supercritical methane under high heat flux in mini channel, dimple structure is employed and studied numerically. Flow friction factor (f), heat transfer coefficient (HTC), Nusselt number (Nu) and performance evaluation criteria (PEC) are adopted to compare the heat transfer and flow characteristics between dimple and smooth channel. Besides, local velocity, turbulence kinetic energy (TKE), temperature and HTC are discussed. The results indicate that higher heat flux could deteriorate the heat transfer of supercritical methane resulted from the buoyancy and flow acceleration effect. While dimple enhances tremendously the heat transfer performance under high heat flux with enhanced factor up to 2.2, and there exists an optimal inlet temperature for the enhanced factor. On the other hand, the friction factor is worsened. However, PEC is positive up to 1.9 increased by the heat-mass ratio and mass flux. For enhanced mechanism, dimple induces vortex and raises the TKE, which strengthens the heat transfer between wall and bulk fluid.

Elastic Properties of Confined Fluids in Nanopores: An Acoustic-Propagation Model.

Following the compressibility route in statistical mechanics, the local isothermal modulus is derived for nanoconfined fluids. Based on this inhomogeneous modulus, an acoustic-propagation model (APM) is first proposed for averaged isothermal modulus in the pore. By utilizing the density profiles obtained from classical density functional theory, the inhomogeneous modulus of supercritical methane in the graphite slit pore is calculated. It is found that the profile of the modulus in the pore is out of phase with that of density. Further, employing the proposed APM method, the averaged isothermal modulus is calculated, and the effects of pressure, pore size, and temperature on the averaged modulus are investigated. It is found that (i) averaged modulus obtained from APM method still satisfies the Tait-Murnaghan (TM) equation, (ii) the averaged modulus is proportional to the reciprocal pore width for wider pores, while it oscillates with the reciprocal pore width for narrower pores, and (iii) the reciprocal modulus is proportional to temperature, while the linearization coefficient is insensitive to the pore size. These findings bear important implications for understanding the elasticity in fluid-saturated nanoporous media and may shed light on the capture or storage of special gases in the fields of geochemistry and geophysics.

Numerical simulation on heat transfer and flow of supercritical methane in printed circuit heat exchangers

The printed circuit heat exchanger (PCHE) is a novel type of heat exchanger in liquefied natural gas (LNG) industry. The gasification pressure of LNG in PCHE could exceed the critical pressure of methane, the main component of LNG. This paper established a series of three-dimensional models of PCHE units. The effects of structural parameters and channel shapes on the thermal hydraulic performance are studied. And new correlations to calculate the Nusselt number and Fanning factor of supercritical methane in straight and zigzag PCHEs are developed. For straight PCHE, the most influential geometrical parameters are the spacing between two adjacent channels in the plate and the diameter of the semicircle, which have been taken into account in the new correlation. For zigzag PCHE, the inclined angle has impact on both heat transfer coefficient and pressure drop while the pitch number only influences the pressure drop. Considering these factors, the new correlations for zigzag PCHE are modifications from the new straight PCHE correlations.