Binary Gas Research Articles

Reforming Natural Gas for CO2 Pre-Combustion Capture in Trinary Cycle Power Plant

Today, most of the world’s electric energy is generated by burning hydrocarbon fuels, which causes significant emissions of harmful substances into the atmosphere by thermal power plants. In world practice, flue gas cleaning systems for removing nitrogen oxides, sulfur, and ash are successfully used at power facilities but reducing carbon dioxide emissions at thermal power plants is still difficult for technical and economic reasons. Thus, the introduction of carbon dioxide capture systems at modern power plants is accompanied by a decrease in net efficiency by 8–12%, which determines the high relevance of developing methods for increasing the energy efficiency of modern environmentally friendly power units. This paper presents the results of the development and study of the process flow charts of binary and trinary combined-cycle gas turbines with minimal emissions of harmful substances into the atmosphere. This research revealed that the net efficiency rate of a binary CCGT with integrated post-combustion technology capture is 39.10%; for a binary CCGT with integrated pre-combustion technology capture it is 40.26%; a trinary CCGT with integrated post-combustion technology capture is 40.35%; and for a trinary combined-cycle gas turbine with integrated pre-combustion technology capture it is 41.62%. The highest efficiency of a trinary CCGT with integrated pre-combustion technology capture is due to a reduction in the energy costs for carbon dioxide capture by 5.67 MW—compared to combined-cycle plants with integrated post-combustion technology capture—as well as an increase in the efficiency of the steam–water circuit of the combined-cycle plant by 3.09% relative to binary cycles.

Energy Efficiency Analysis of Hydrate and Ionic Liquid-Based Binary Gas Separation Processes

Energy Efficiency Analysis of Hydrate and Ionic Liquid-Based Binary Gas Separation Processes

Differential adsorption of H2S/CH4 by bituminous coal and its competitive adsorption properties

To investigate the adsorption characteristics and competitive adsorption patterns of H2S and CH4 in coal seams, we conducted a combined experimental and molecular simulation study using Ningxia Shuangma bituminous coal as the research subject. The experiments examined the adsorption of single-component H2S and CH4 gases at different temperatures and pressures, while the molecular model of bituminous coal was used to analyze the adsorption patterns of binary gas mixtures under competing conditions. Our experimental results demonstrate that both H2S and CH4 follow Langmuir’s model, with their saturated adsorption positively correlated with pressure but negatively correlated with temperature. Moreover, under identical conditions, H2S exhibits 2.43 times higher saturated adsorption than CH4. Molecular simulations reveal that temperature has a greater impact on H2S compared to CH4; both gases undergo reversible physisorption, where isosteric heat of adsorption decreases linearly with increasing amount of adsorbate molecules; interaction energy for H2S is larger in absolute value than that for CH4, indicating its stronger affinity towards coal surfaces; regarding binary component adsorption, an increase in proportion of H2S within the gas mixture leads to higher saturation adsorptions for both the mixture itself and individual H2S molecules while decreasing saturation adsorption for CH4; Coal adsorption selectivity factor for H2S/CH4 > 1. The preferential occupation of high-energy adsorption sites is more likely to be observed for H2S. The adsorption capacity and competitive adsorption capacity of H2S were greater than that of CH4.

Modeling of adsorption-controlled binary gas transport in ultratight porous media

Organic-rich ultratight porous media such as shales have complicated pore types and sizes, dictating their unique fluid transport and storage mechanisms. This paper introduces a diffusion-based binary gas (CH4 and CO2) transport model in such porous media, incorporating key transport and storage mechanisms. Binary gas mixture within the pore volume is divided into two domains: the free-phase and the sorbed-phase, both of which contribute to gas mass transport. Thermodynamic properties of the free phase are determined using the Peng-Robinson equation of state, while a modified extended Langmuir isotherm describes the sorbed phase. The bulk diffusion, Knudsen diffusion, and viscous diffusion are reconciled to describe binary gas transport in the free phase, while the surface diffusion is considered in the sorbed phase. The mass flux is finally related to the effective diffusion coefficient and the free-phase concentration gradient through coupling all transport mechanisms via the equivalent resister network model. The governing equations are solved numerically using a finite difference approach to simulate co-diffusion and counter-diffusion of a binary gas mixture in two nanoporous media, shale and coal.The results reveal that surface diffusion is more pronounced in coal than in shale due to coal's higher adsorption capacity. In co-diffusion cases, both free-phase and sorbed-phase concentrations decrease over time. However, the decline of sorbed-phase concentrations is slower than that of the free-phase. Moreover, CO2 tends to remain adsorbed within the coal matrix due to its stronger adsorption affinity, unlike CH4, which is more likely to flow out. In counter-diffusion cases, injected CO2 first accumulates near the fracture region and then diffuses further into the matrix. Despite shale's pore volume being twice that of coal, similar amounts of CO2 are injected, which can be attributed to coal's higher CO2 adsorption capacity.

Species-Based Modeling of Binary Gas Mixture Transport in Nanoporous Media with Adsorption

Species-Based Modeling of Binary Gas Mixture Transport in Nanoporous Media with Adsorption

Computational Analysis of Permeance Prediction for Gas Separation Membrane Using Countercurrent Flow Model

Gas separation polymeric membranes have gained significant attention in various industries, including gas processing, petrochemicals, and environmental applications. Accurately predicting the permeance of these membranes is crucial for optimizing their design and performance. This paper presented a numerical prediction model for the permeance of a binary gas mixture under various process conditions, using only algebraic equations to minimize the calculation effort. The model considers input parameters such as feed and permeate flow rates, feed pressure, feed and permeate mole fraction, and membrane area. It demonstrates the behavior of permeance and selectivity in this study. The study also presented two case studies that utilize predicted selectivity to model counter-current flow and compare the results with experimental data from the literature. The first case study involves recovering helium from natural gas using an asymmetric high-flux membrane. The second case study separates air using nano-porous carbon as the membrane material. The numerical analysis successfully accurately predicted the permeance of gas separation polymeric membranes. The model accounted for variations in membrane thickness, feed composition, and operating conditions, providing valuable insights into the overall performance of the membrane system. It also allowed for the optimization of membrane design and operational parameters to enhance separation efficiency and productivity. The study showcased the effectiveness of numerical techniques in accurately predicting membrane performance. The developed model can be a valuable tool for membrane designers and engineers, enabling them to optimize the design and operation of gas separation systems.

A method for numerical simulation of shock waves in rarefied gas mixtures based on direct solution of the Boltzmann kinetic equation

The paper proposes an approach to numerical simulation of shock waves in rarefied gas mixtures on the basis of direct solution of the Boltzmann kinetic equation. Software for simulating the gas flows was developed. The structure of a shock wave in a binary gas mixture was computed with an accuracy controlled by the computational parameters. The computations were performed for various molecular masses ratios and Mach numbers. The total accuracy of at least 1.4% for the local values of the molecular densities and temperatures of the mixture components was achieved. Numerical simulation of a shock wave propagation through a periodically perforated surface was performed. The distributions of the macroscopic characteristics of the mixture components at various points in time were obtained. Unsteady areas of strong separation of the gas mixture components were discovered.

A novel method measuring orifice conductance and testing time-of-flight mass spectrometer for water vapor–binary gas

Abstract The miniature time-of-flight mass spectrometer (TOF-MS) is a crucial instrument for detecting water ice in Chinese Lunar Exploration Program (CLEP), so it is necessary to compare its detection results for pure water vapor and water vapor-binary gas (such as H2O-N2, H2O-CH4, and H2O-Ar) to evaluate its water detection performance. The throughput must be calculated using the measured conductance to test the miniature TOF-MS. According to the VΔp method, the pΔt method, whose uncertainty is less than 14.2%, is proposed to measure orifice conductance for water vapor-binary gas, and an apparatus was developed based on those two methods. The orifice conductance of four kinds of pure gases (N2, H2O, CH4, and Ar) was measured using those two methods separately, and the measurement results allowed to calculate the conductance of the water vapor-binary gas through the Equivalent Single Gas method. The conductance of the water vapor-binary gas was measured using the pΔt method, and the difference between the calculated and measured results is less than 7%. Hence, the measured conductance allows the miniature TOF-MS to be tested for the water vapor-binary gas. As throughput is from 10-9 to 10-6 Pa m3 s-1, the difference between the test signals of water vapor-binary gas and pure water vapor is less than 40%.

A novel numerical simulation approach for cryogenic CO2 frosting in binary mixture gas by integrating desublimation and gas-solid phase equilibrium models

Cryogenic CO2 separation from natural gas is a promising technology due to its environmental benefits and smaller spatial requirement. Nonetheless, the dynamics of CO2 desublimation and subsequent frost layer formation under cryogenic conditions for natural gas pre-treatment remain largely unexplored. Addressing this gap, this paper presents a novel numerical simulation approach by integrating desublimation phase change model and vapor-solid phase equilibrium model to investigate CO2 frost layer formation on the cold wall, revealing that both the cold wall temperature and the initial CO2 concentration significantly influence the thickness of the CO2 frost layer. Moreover, the study finds that the density of frost layer intensifies over time, with the highest density observed near the cold surface. Furthermore, increasing the cold wall temperature and the flow rate not only increases the average density of the CO2 frost layer but also affects the outlet CO2 concentration. To adhere to specific outlet CO2 concentration targets and desublimation duration, it is critical to adjust the cold wall temperature and the inlet flow velocity dynamically. Therefore, cryogenic CO2 removal methods, by reducing the spatial requirements of CO2 pre-treatment units, offer a practical and efficient solution for small-scale natural gas liquefaction plants. This approach not only facilitates operational efficiency but also contributes to the broader effort of mitigating greenhouse gas emissions, aligning with environmental sustainability objectives.

Coarse-grained modeling of high-enthalpy air flows based on the updated vibrational state-to-state kinetics

The state-to-state (StS) model can accurately describe high-temperature thermochemical nonequilibrium flows. For the five-species air gas mixture, we develop a comprehensive database for the state-specific rate coefficients for temperatures 300–25 000 K in this paper. The database incorporates recent molecular dynamics simulations (based on the ab initio potential energy surfaces) in the literature, and theoretical methods, including the forced harmonic oscillator model and the Marrone–Treanor model, are employed to complement the rate coefficients that are unavailable from molecular dynamics calculations. The post-shock StS simulations using the present database agree with the experimental NO infrared radiation. Based on this updated StS kinetics database, we investigate the post-shock high-enthalpy air flows by employing both the StS and coarse-grained models (CGM). The CGM, which lumps molecular vibrational states into groups, shows results that align with the StS model, even utilizing only two groups for each molecule. However, the CGM-1G model, with only one group per molecule and belonging to the multi-temperature model (but uses StS kinetics), fails to reproduce the StS results. Analysis of vibrational energy source terms for different kinetic processes and fractions of vibrational groups reveals that the deficiency of the CGM-1G model stems from the overestimation of high-lying vibrational states, leading to higher dissociation rates and increased consumption of vibrational energy in dissociation. Furthermore, the presence of the Zeldovich-exchange processes indirectly facilitates energy transfer in N2 and O2, a phenomenon not observed in binary gas systems. These findings have important implications for developing the reduced-order model based on coarse-grained treatment.

BLENDING RESPIRATORY GAS MIXTURES

The binary or ternary gas mixtures used in diving can be blended either by a successive and controlled injection of the component gases into containers of constant volume, following the pressure in the containers, or by a continuous flow mixing, with the simultaneous injection of the component gases to the desired proportion, using for this devices equipped with calibrated nozzles working in the critical (sonic) range, which ensure the delivery of gaseous components at constant mass flow rates.

Electric field-driven assembly of (110) oriented metal–organic framework ZIF-8 monolayer with high hydrogen selectivity

Metal-organic framework (MOF) membranes have showed great potential in gas separation. To date, it is still a great challenge to precisely control the optimal orientation of MOF membranes with an enhanced gas separation performance. Herein, we prepared a compact and (110) oriented ZIF-8 membrane with a thickness of about 265 nm on graphite substrate within 1 h at room temperature via electric-field-driven strategy. Since the membrane is an intergrown one-crystal layer, grain boundary retardation of the flux is eliminated. Furthermore, due to the reduction of the transport pathways through the oriented structure, the (110) oriented ZIF-8 membrane exhibits a high gas separation performance. At 100 °C and 1 bar for the separation of equimolar binary gas mixtures H2/CO2, H2/CH4 and H2/C3H8, separation factors of 49.5, 90.9 and 121.8 can be obtained, with H2 permeance of about 1.7 × 10-7 mol·m−2·s−1·Pa−1. The developed strategy exhibits excellent reproducibility and scalability, and a large area ZIF-8 membrane can be consistently prepared on the graphite substrate, thus facilitating the preparation and application of the ZIF-8 membrane on a large scale. Further, the electric-field-driven strategy is also helpful for the preparation oriented ZIF-67 and ZIF-L membranes, confirming its versatility for the preparation of oriented MOF membranes.

Phase Dependence of Surface Charge Measurement on Epoxy Insulator in C4F7N/CO2 under AC Voltage.

The application of binary gas mixtures consisting of heptafluorobutyronitrile (C4F7N) and carbon dioxide (CO2) in AC GIS is currently attracting much attention. Therefore, the evaluation of the gas-solid interface charge distribution characteristics of epoxy resin is indispensable. Additionally, the phase-dependency of the charging behavior remains not fully understood. We simulated coaxial electrode structure in GIS and investigated the surface charge distribution on a down-scaled epoxy insulator. The influence of the truncated phase angle and duration of AC voltage on charge behavior were analyzed, and the charge transport mechanism under AC voltage was theoretically analyzed. The results showed that there was a noticeable negative charge speckle with the presence of the metal particle and the accumulated negative charge on the insulator surface far exceeded that of the positive charge. The maximum surface charge density and the amount of surface charge accumulated first increased and then decreased over time. It was found that the phase angle has a negligible influence on the surface charge distribution at the cut-off moment.

Effects of porous supports and binary gases on hydrogen permeation in Pd–Ag–Y alloy membrane

This study investigates the effects of various porous supports and the presence of additional gases in the feed on hydrogen permeation using an unsupported Pd82–Ag15–Y3 membrane. The pore sizes and thicknesses of metallic supports varied from 1 to 270 μm and 50–3000 μm, respectively. The membrane was unsupported, synthesized by cold-rolling, and characterized by a thickness of 38 μm. The tests were performed at 400 °C with pressures ranging from 1.4 to 3 bar. Results showed that the unsupported Pd82–Ag15–Y3 membrane reached 12 % and 267 % higher hydrogen permeation than the supported membrane by 1 μm pore size and 50 μm thick woven mesh, and 1 μm pore size and 3 mm thick of porous stainless steel (PSS), respectively. The unsupported Pd82–Ag15–Y3 membrane showed one of the highest hydrogen permeability in the literature (7.5 × 10−8 mol m−1 s−1.Pa−0.5 at 400 °C). However, the presence of porous supports used to enhance the mechanical stability of the membrane negatively affected the hydrogen permeation due to mass transfer limitation. In addition, the presence of supports induced an unreal ‘n’ value for the Pd-based membrane, where the ‘n’ value is the exponent of the driving force in the equation of hydrogen transport, varying between 0.5 and 1. In particular, for the unsupported membrane, the ‘n’ value was 0.6, but it increased to 0.7 and 0.8 when supports with 1 μm pore size and 50 μm thick and 5 μm and 80 μm thick were utilized. Binary hydrogen permeation tests were also performed in the presence of N2, CH4, CO2, and CO at 400 °C by using unsupported and supported membranes to investigate the reduction in hydrogen permeation flux due to the effect of the supports plus the effect of the presence of other gas. The results revealed that CO had the highest inhibition effect for all the unsupported and supported membranes tested due to competitive adsorption on the surface. No superficial adsorption on the membrane was observed for N2, CH4, and CO2 during permeation, and they inhibited hydrogen permeation mainly due to depletion, dilution, and concentration polarization. The PSS_1–3000 indicated the lowest hydrogen permeation between the gas mixture and the porous support, whereas the presence of 40 % of the binary gas mixture had lower hydrogen permeation than porous support except for the PSS.

Condensate formation in a chiral lattice gas

Abstract We investigate the formation of condensates in a binary lattice gas in the presence of chiral interactions. These interactions differ between a given microscopic configuration and its mirror image. We consider a two dimensional lattice gas with nearest-neighbour interactions to which we add interactions involving favoured local structures that are chiral. We focus on favoured local structures that have the shape of the letter L and explore condensate formation through simulations and analytical calculations. At low temperature, this model can exhibit four different phases that are characterised by different periodic tiling patterns, depending on the strength of interactions and the chemical potential. When particle numbers are conserved, some of these phases can coexist. We analyse the structure and surface tension of interfaces between coexisting phases and determine the shapes of minimal free energy of crystalline condensates. We show that these shapes can be quadrilaterals or octagons of different orientation and symmetry.

Competitive sorption of CH₄ and CO₂ on coals: Implications for carbon geo-storage

Geological carbon storage, particularly within coal seams, is recognized as a viable strategy for achieving net-zero emissions. However, following CO₂ injection into the coal seam, limited studies have addressed the competitive sorption dynamics of CH₄ and CO₂ on coal, despite the natural presence of CH₄ in these formations. In this work, sorption experiments were conducted using two types of coal: sub-bituminous coal and anthracite. Initially, pure CH4 and CO2 gases were employed to conduct individual sorption tests. Subsequently, the competitive sorption of CH4 and CO2 was evaluated using pre-mixed binary gas mixtures with varying CH4/CO2 ratios. Further, the displacement effect of CO2 on CH4 was investigated by injecting CO2 into coal samples that had been pre-adsorbed with CH4. The data reveal that, for both coals, the ideal selectivity calculated from pure gas measurements underestimates the corresponding values from real multicomponent systems. Anthracite demonstrates a higher selectivity for CO₂ over CH₄ during both adsorption and desorption processes when compared to the ideal selectivity calculated from pure gas sorption data. Conversely, the sub-bituminous coal initially shows lower selectivity for CO₂ than for CH₄ during adsorption, but this trend reverses and intensifies during desorption. If competitive sorption effects are neglected, coal selectivity for CO₂ over CH₄ under the examined conditions would be underestimated by a factor of 1.5 to 2.5. Due to the competitive sorption effects between CH₄ and CO₂, the Langmuir equilibrium constants for gas mixtures are influenced by compositional changes, leading to dynamic deviations from those observed under pure gas conditions. This finding contrasts with the traditional extended Langmuir model, which presumes that the equilibrium constants remain unchanged regardless of gas composition. In addition, the displacement study underscores the efficacy of CO2 in displacing CH4, with higher CO2 ratios intensifying displacement effects. The study highlights the substantial impact of real multicomponent scenarios on coal selectivity for CO₂ and CH₄, offering deeper insights into predicting competitive sorption behavior between CO₂ and CH₄ during CO₂-enhanced coalbed methane recovery and carbon storage processes.

Development of Photonic In-Sensor Computing Based on a Mid-Infrared Silicon Waveguide Platform.

Neuromorphic in-sensor computing has provided an energy-efficient solution to smart sensor design and on-chip data processing. In recent years, various free-space-configured optoelectronic chips have been demonstrated for on-chip neuromorphic vision processing. However, on-chip waveguide-based in-sensor computing with different data modalities is still lacking. Here, by integrating a responsivity-tunable graphene photodetector onto the silicon waveguide, an on-chip waveguide-based in-sensor processing unit is realized in the mid-infrared wavelength range. The weighting operation is achieved by dynamically tuning the bias of the photodetector, which could reach 4 bit weighting precision. Three different neural network tasks are performed to demonstrate the capabilities of our device. First, image preprocessing is performed for handwritten digits and fashion product classification as a general task. Next, resistive-type glove sensor signals are reversed and applied to the photodetector as an input for gesture recognition. Finally, spectroscopic data processing for binary gas mixture classification is demonstrated by utilizing the broadband performance of the device from 3.65 to 3.8 μm. By extending the wavelength from near-infrared to mid-infrared, our work shows the capability of a waveguide-integrated tunable graphene photodetector as a viable weighting solution for photonic in-sensor computing. Furthermore, such a solution could be used for large-scale neuromorphic in-sensor computing in photonic integrated circuits at the edge.

Photophoresis of a moderately large high-viscosity droplet in slip mode

Purpose of research. To obtain analytical expressions that allow calculating the strength and velocity of a moderately large, highly viscous droplet, taking into account the direct contribution of the evaporation coefficient, linear corrections by the Knudsen number and the reactive effect of a plane wave moving in the field of mono-chromatic radiationMethods. Methods of perturbation theory, gas kinetic methods, mathematical methods for solving linear partial differential equations with variable coefficients (the system of Stokes equations, Laplace and Poisson equations) were used.Results. In a quasi-stationary approximation, a theoretical description of the photophoretic motion of a moderately large evaporating highly viscous spherical droplet (there is no circulation of matter inside the droplet and interfacial surface tension forces) in a viscous binary gas mixture is carried out. A velocity-linearized system of Navi-Stokes equations and heat and mass transfer was solved. Expressions are obtained for the fields of mass velocity, pressure, temperature and the relative numerical concentration of the first component. The strength and speed of photophoresis of a highly viscous droplet was determined by integrating a stress tensor over the surface of the particle. Under boundary conditions on the surface of a highly viscous droplet, linear corrections in terms of the Knudsen number (isothermal, thermal and diffusion slips, temperature and concentration jumps, as well as sliding due to temperature inhomogeneity along the curved surface of the particle), the reactive effect and the contribution of the direct influence of the evaporation coefficient were taken into account. The contributions to the obtained formulas for the photophoresis of a moderately large highly viscous droplet are analyzed and the preliminary transitions to the results known in the literature (moderately large and large solid particles of spherical shape) are considered Conclusion. The obtained formulas based on the hydrodynamic method allow us to evaluate the effect of the direct contribution of the evaporation coefficient and linear corrections by the Knudsen number on the strength and speed of photophoresis of a moderately large evaporating highly viscous droplet in a binary gas mixture.

The intensification of moisture resistance over MFI zeolite via heteroatom incorporation for diluted CO2 capture

Herein, copper and manganese heteroatoms were incorporated into the siliceous MFI frameworks with high dispersity. When employed in the CO2/N2 binary gas separation, a delicate trade-off for the CO2 adsorption capacity, adsorption heat and moisture resistance could be realized on the heteroatom-incorporated MFI zeolites, especially the Cu-incorporated one. In order to confirm the role that heteroatoms played in CO2 adsorption, the textural analyses were then conduced, which proved that the enhanced microporosity may be at the heart of the promoted CO2 capacity. Next to that, the in situ DRIFTs spectra were continuously tracked during the dynamic adsorption process. Compared to the commercial aluminosilicate analogue, the MFI zeolites with Cu/Mn heteroatoms possesses weaker electrostatic field intensity, which in consequence resulted in their stronger moisture resistance, even in presence of humidity up to 90 RH%. As such, a bottom-up adjustment for the adsorption properties of zeolites in practical environment containing competitive moisture impurity was shown.

Liquefaction efficiency study of heterogeneous condensation of methane-ethane binary gas mixtures with different component contents

Natural gas is a mixture of hydrocarbons. During the liquefaction of natural gas, the mixed gas undergoes heterogeneous condensation on the surface of the heat exchanger. Currently, the heterogeneous condensation mechanism of mixed gases is not fully understood, and the influence of component content on the liquefaction efficiency is not clear. Therefore, the molecular dynamics simulation was employed to investigate the heterogeneous condensation process of methane-ethane binary mixed gas on a solid surface. The characteristics of condensation nucleation cluster growth was explored and the variations in temperature, density, heat flux, and liquefaction rate were analyzed. The impact of ethane on methane condensation was also discussed. The results indicate that increasing wettability enhances surface nucleation quantity and shortens nucleation time, resulting in a 3.6- times increase in heat flux. The addition of ethane gas in the system promotes condensation nucleation, which increases the liquefaction rate by 60 % when x = 20 % compared to the pure methane system. However, for methane gas, ethane only benefits the liquefaction of methane molecules in the initial nucleation stage. As the mixture in the system enters the cluster growth stage, component migration in the mixed gas leads to a lower liquefaction rate compared to pure methane gas.