Multicomponent Gas Research Articles

Ignition delay times of C1–C7 natural gas blends in the intermediate and high temperature regimes: Experiment and correlation

This study presents new ignition delay time data for two multi-component natural gas (NG) blends composed of C1–C7n-alkanes with methane as the major component. New experimental data were recorded using a high-pressure shock tube (HPST) at reflected shock pressures (p5) of 10–30 bar, at temperatures (T5) in the range 770–1480 K, and at equivalence ratios (φ) of 0.5–1.5 in ‘air’. The current results together with published rapid compression machine (RCM) measurements show that higher concentrations of larger molecular weight n-alkanes in the NG blends increase fuel reactivity by more than an order of magnitude with mixtures that have ∼18.75% of C3–C5 components compared to mixtures that have ∼44.4% of C3–C7 components at temperatures below 1000 K. On the contrary, at higher temperatures the effect of increasing reactivity is reduced. NUIGMech1.2 is used to simulate the conditions studied and shows good agreement with the experimental ignition delay time data. A correlation equation is developed through regression analyses using NUIGMech1.2 to predict ignition delay times for a wide range of C1–C7 NG mixtures, in the pressure range 10–50 bar, at temperatures in the range 950–2000 K, and at φ = 0.3–3.0 in air. The proposed correlation expression that employs a traditional Arrhenius form is successfully validated against the new experimental data as well as previously published HPST experimental data.

Persistent currents in a strongly interacting multicomponent Bose gas on a ring

Persistent currents in a strongly interacting multicomponent Bose gas on a ring

Gas collection system design for a landfill via three-dimensional stochastic waste heterogeneity models and kriging

Installation of a gas collection system (GCS) at a landfill helps extract gas for domestic usage, alongside minimizing greenhouse gas emissions. To maximize the efficiency of gas extraction, it is important but challenging to design a GCS by modelling the three-dimensional, multiphase, multicomponent gas migration in a landfill, incorporating spatio-temporal variabilities in the geotechnical properties of the waste (viz., heterogeneity) and uncertainties (via stochastic models). This work proposes a method to calculate the radius of influence (ROI) of a gas extraction well (GEW) and designs a GCS for an actual landfill. The method models three-dimensional gas migration in a landfill via TOUGH simulator. Geotechnical properties are estimated using stochastic models to calibrate the simulator and obtain the gas flows at specific spatio-temporal locations. Gas flow values at the remaining locations are obtained through Kriging, based on which ROI is calculated. To ensure gas collection from the entire area of the landfill, 36 GEWs are placed. The spacing between GEWs is consistent with certain prevailing heuristic guidelines, and this work provides a justification for their use. A gas recovery efficiency of 0.82 and gas pressure of 103 kPa are achieved for a passive GCS under heterogeneity. A homogeneous design only yields an efficiency of 0.56, exemplifying the utility of the heterogeneous model. For an active GCS, the efficiency is found to be improved to 0.86. The framework provided in this work can be used for accurate gas flow estimation in large landfills, and design safe GCS ensuring minimal methane emission.

Mass transfer of the multicomponent free jet and one numerical implementation on a graphic processing unit platform

Jet flows are ubiquitous in nature and laboratories. For example, helium and argon jets into ambient air are commonly used to produce atmospheric plasma jets. The jets before and after discharge both are typical multicomponent flows. This study reports on the implementation of a numerical solver based on the graphic processing units to model multicomponent mixture gas flows. To this end, two- and three-dimensional Jacobian matrices for the multicomponent Euler equations were obtained to reconstruct numerical fluxes and build a total variation diminishing scheme. The two-dimensional early-stage mass transfer of gas jets was studied for three mixture gases: He/air, Ar/air, and N2/air to numerically verify the steady functioning of the numerical solver despite the high mass fraction gradients. The mass fraction distribution of helium in ambient air exhibited more complex substructures than those of argon and nitrogen in ambient air. Using the watershed method, self-generated bullets were extracted from the mass fraction distributions of the helium jet. The proposed numerical solver implemented in this study is expected to provide a better understanding of gas jet dynamics, and the Jacobian matrices can provide a mathematical foundation for constructing potential higher schemes.

On the Influence of Atmospheric Ions on Aerosol Formation: Numerical Modeling

A new mathematical model of the global transport of multicomponent gas impurities and aerosols has been constructed, including the formation of sulfate aerosols in the atmosphere in both hemispheres. Calculations of the nucleation rates and particle number concentrations were performed for the winter period in the troposphere using a unified model that takes into account chemical and kinetic transformation processes (photochemistry, nucleation, condensation/evaporation, and coagulation). Binary nucleation of sulfuric acid and water vapor was coupled with new-particle formation due to atmospheric ions. The numerical results indicate a significant role of ion nucleation in aerosol formation in the Northern and Southern hemispheres in winter. The factors controlling the dynamics of ionic processes in the atmosphere and their influence on the spatiotemporal distribution of aerosol particles involve not only the level of air ionization but also temperature, relative humidity, and the content of sulfur and water vapor in the air. At a height of 4.2 km, the formation of particle nuclei with the participation of ions occurs only over the Lake Baikal and Kamchatka regions as well as the regions of the northeast and northwest of the American continent. Within the regions of localization of this process in the atmosphere, the rate of new particle generation varies by more than an order of magnitude.

Cross-Scale Seepage Characteristics of Fractured Horizontal Wells in Tight Gas Reservoirs.

Tight gas reservoirs are rich in microscale pores and fractures. The effect of microscale gas seepage in tight sandstone matrix on gas well productivity cannot be ignored. At present, the effect of microscale gas flow on the well testing model of fractured horizontal wells has not been systematically studied. In this paper, first, the coupling influence mechanism of "multicomponent gas effect-fracture geometry characteristics" is expounded, second, a seepage model coupling the flow in the fracture and the flow in the gas reservoir is established on the fracture wall surface, and third, an unsteady pressure analysis model for fractured horizontal wells in tight gas reservoirs is established. Results show that (a) when the microscale fracture is at a quite small level, the Knudsen diffusion plays a dominant role at a wide range of pressures; (b) the mass transfer rate of multicomponent shale gas through macrofractures increases with increasing CO2 fraction; (c) the unsteady flow process is divided into six stages in turn: microscale diffusion stage, linear flow stage in fractures, linear flow stage between fractures, early radial flow stage in gas reservoirs, linear flow stage in gas reservoirs, and late radial flow stage in gas reservoirs; and (d) with an increase of dimensionless bottom-hole storage coefficient, the second and third stages of flow are gradually covered up.

Natural Gas Analysis Using Polarized Raman Spectroscopy.

Raman spectroscopy is a promising tool for measuring the composition of natural gas. However, to obtain high measurement accuracy, it is necessary to take into account changes in the spectral characteristics of methane, since its spectrum overlaps the characteristic bands of other species. In this study we present a technique for natural gas analysis based on polarized Raman spectroscopy. It is shown that the use of only isotropic components of spectra simplifies the procedure for extracting concentrations and improves the measurement accuracy of components whose spectral bands are significantly overlapped in conventional Raman spectra. The presented technique will be very useful both in the field of analysis of various multicomponent gas mixtures and in the field of measuring the isotopic composition of molecules.

Growth behavior and resource potential evaluation of gas hydrate in core fractures in Qilian Mountain permafrost area, Qinghai-Tibet Plateau

The Qilian Mountain permafrost area located in the northern of Qinghai-Tibet Plateau is a favorable place for natural gas hydrate formation and enrichment, due to its well-developed fractures and abundant gas sources. Understanding the formation and distribution of multi-component gas hydrates in fractures is crucial in accurately evaluating the hydrate reservoir resources in this area. The hydrate formation experiments were carried out using the core samples drilled from hydrate-bearing sediments in Qilian Mountain permafrost area and the multi-component gas with similar composition to natural gas hydrates in Qilian Mountain permafrost area. The formation and distribution characteristics of multi-component gas hydrates in core samples were observed <em>in situ</em> by X-ray Computed Tomography (X-CT) under high pressure and low temperature conditions. Results show that hydrates are mainly formed and distributed in the fractures with good connectivity. The ratios of volume of hydrates formed in fractures to the volume of fractures are about 96.8% and 60.67% in two different core samples. This indicates that the fracture surface may act as a favorable reaction site for hydrate formation in core samples. Based on the field geological data and the experimental results, it is preliminarily estimated that the inventory of methane stored in the fractured gas hydrate in Qilian Mountain permafrost area is about 8.67×10¹³ m³, with a resource abundance of 8.67×10⁸ m³/km². This study demonstrates the great resource potential of fractured gas hydrate and also provides a new way to further understand the prospect of natural gas hydrate and other oil and gas resources in Qilian Mountain permafrost area.

Effects of CH4/CO2 multi-component gas on components and properties of tight oil during CO2 utilization and storage: Physical experiment and composition numerical simulation

An essential technology of carbon capture, utilization and storage-enhanced oil recovery (CCUS-EOR) for tight oil reservoirs is CO2 huff-puff followed by associated produced gas reinjection. In this paper, the effects of multi-component gas on the properties and components of tight oil are studied. First, the core displacement experiments using the CH4/CO2 multi-component gas are conducted to determine the oil displacement efficiency under different CO2 and CH4 ratios. Then, a viscometer and a liquid density balance are used to investigate the change characteristics of oil viscosity and density after multi-component gas displacement with different CO2 and CH4 ratios. In addition, a laboratory scale numerical model is established to validate the experimental results. Finally, a composition model of multi-stage fractured horizontal well in tight oil reservoir considering nano-confinement effects is established to investigate the effects of multi-component gas on the components of produced dead oil and formation crude oil. The experimental results show that the oil displacement efficiency of multi-component gas displacement is greater than that of single-component gas displacement. The CH4 decreases the viscosity and density of light oil, while CO2 decreases the viscosity but increases the density. And the numerical simulation results show that CO2 extracts more heavy components from the liquid phase into the vapor phase, while CH4 extracts more light components from the liquid phase into the vapor phase during cyclic gas injection. The multi-component gas can extract both the light components and the heavy components from oil, and the balanced production of each component can be achieved by using multi-component gas huff-puff.

Simultaneous detection of CH4 and CO2 through dual modulation off-axis integrated cavity output spectroscopy

This study established a novel method for the simultaneous detection of two-component gases. Radio frequency (RF) white noise disturbance laser current and wavelength modulation were simultaneously used to improve the off-axis integrated cavity output spectroscopy technique, and a high-precision dual modulation OA-ICOS (RF-WM-OA-ICOS) system was established. The two laser beams were coupled into one laser beam that was applied incident to the cavity of RF-WM-OA-ICOS system. The second harmonic signals of CH4 and CO2 gas simultaneously appeared in the rising or falling edge of a triangular wave. This method was used to measure CH4 and CO2 with different concentrations. The results indicated that the proposed system has high stability and can accurately and simultaneously measure the concentrations of CH4 and CO2, with an optimal integration time of 220 s. The minimum detection limit was 10 ppb for CH4 and 1.5 ppm for CO2. The corresponding noise equivalent absorption sensitivity values were calculated as 2.67 × 10−13 cm−1⋅Hz−1/2 and 5.18 × 10−11 cm−1⋅Hz−1/2, respectively. The proposed dual-component gas simultaneous detection method can also be used for high-precision simultaneous detection of other gases. Therefore, this study may serve as a reference for developing portable multicomponent gas analyzers.

Multicomponent Gas Detection Method via Dynamic Temperature Modulation Measurements Based on Semiconductor Gas Sensor

Leakage of organic gas in industrial environment can easily cause fire and explosion accidents. Rapid detection of gases type and concentration is the premise for emergency treatment of these situations. Typically, the single semiconductor sensor cannot detect multi-component gas. Here, a new multi-component gas detection method was proposed based on the temperature-response relationship of sensor. This method has low power consumption, low cost and long-term monitoring, which can guide the future exploration of deployable sensors. Firstly, the parameters were optimized according to cosine distance to reflect the maximum difference of temperature-response relationship. Then coordinate system transformation was carried out to further magnify the difference between gases. Finally, the multi-component gas was recognized by using rational taylor function fitting. As a proof-of-concept, we measured the type and concentration of toluene and butanone multi-component gas with mean error of 6.34&#x0025; and 4.32&#x0025; respectively. We analyzed the gas-sensing response mechanism, the theoretical support of the optimized parameters and the causes of local errors. As a universal method, binary component gas detection was <b>explored</b> containing toluene, butanone, acetic anhydride, acetone and diethyl ether.

Effects of gas phase composition on competitive adsorption properties of formaldehyde on titanium dioxide-supported platinum in single and mixture compositions

Titanium dioxide-supported platinum (Pt@TiO2) is regarded as a highly efficient photothermal catalyst to degrade various volatile organic compounds (VOCs). To learn more about the hybrid adsorption/catalysis process of VOCs on Pt@TiO2, their dynamic adsorption behavior on the catalyst surface was studied using the single and multicomponent gas phase of FA (i.e., the latter with four aromatic compounds of benzene, toluene, m-xylene, and styrene (BTXS)) through the control of key operating variables (e.g., VOCs concentration, relative humidity (RH) levels, and dosage). According to the performance evaluation, the doping of TiO2 with Pt metal ions significantly enhanced the FA adsorption capacity (e.g., by 50 % higher than the pristine TiO2) with increased OH (OII) surface active sites (reactivity) and surface porosity. However, in the co-presence of BTXS and water vapor, the adsorption affinity for FA vapor declined by 2 to 3 folds of magnitude with a competitive inhibition of the adsorption interaction on the Pt@TiO2 surface. According to the kinetic and isotherms analysis, a complex, multilayered physicochemical process appears to govern the adsorption of FA molecules onto Pt@TiO2 surface. Overall, the outcomes of this work are helpful to verify the enhanced removal potential of Pt@TiO2 against FA through sequential adsorption and catalytic reaction mechanisms.

Insight into nettle straw pyrolysis: Multicomponent kinetics, gas emissions and machine learning models

This study aimed to comprehensively investigate the pyrolysis process of nettle straw by analyzing its multicomponent kinetics modeling, kinetics and thermodynamic parameters, pyrolysis performance, reaction mechanisms, gas emissions, correlation and statistical analysis, as well as feasibility for industrial application. The average apparent activation energies for pseudo-hemicellulose (PS-HEC), cellulose (PS-CEL) and lignin (PS-LIG) were estimated as 147.41, 182.66, and 197.12 kJ/mol, respectively, using four model-free methods: Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose, Starink, and Tang. The pyrolysis reaction mechanisms were best described by diffusional and order-based models, with reaction mechanism functions of f(α) = [3/2(1-α)2/3]/[1-(1-α)1/3], f(α) = (1-α)1.5, and f(α) = (1-α)3 for PS-HEC, PS-CEL, and PS-LIG, respectively. TGA-FTIR analysis revealed that the gas emissions during nettle straw pyrolysis followed the order of CO > CO2 > C-O(H) > H2O > SO2 > CO > CH4 > NH3 > HCN. Best learning rate and artificial neural network (ANN) structure model were optimized. The optimal learning rate and ANN model structure were 0.0013 and ANN (5 *9 *1), respectively. NS has the potential to serve as a viable alternative to biofuel due to its certain energy, low price, abundant reserves, good pyrolysis performance, high volatile content, and low nitrogen and sulfur levels.

Oxidation Characteristics and Corresponding Reaction Mechanism of Coal During the Spontaneous Combustion Latency

ABSTRACT The study of the formation of CO and CO2 is an important means of investigating the mechanism of low-temperature coal oxidation. However, the small changes in the gas produced by oxidation during the spontaneous combustion latency cannot be accurately measured by traditional flow reactors. A set of coal low-temperature closed oxidation multi-component gas online monitoring system was designed. Small changes in the volume fractions of O2, CO and CO2 can be automatically monitored in real time. Experiments on the isothermal oxidation of coal were conducted during the spontaneous combustion latency under different conditions (different temperatures, different initial oxygen volume fractions and different oxidation times). The oxidation experiment results were corrected by Henry model. According to the retardation time of gas production and the changes in Graham’s ratio, CO and CO2 are produced from different reaction sequences during the spontaneous combustion latency. The active substances in coal react with O2 to produce unstable carbon-oxygen complexes, and CO2 is mainly derived from the decomposition of the intermediates. CO is derived from the H-capture reaction of stable solid oxygenated complexes. The research results will help to further understand the mechanism of spontaneous combustion of coal.

Compositional noise in nozzles with dissipation

We propose a physical model to predict indirect noise generated by the acceleration of compositional inhomogeneities in nozzles with viscous dissipation (non-isentropic nozzles). First, we derive the quasi-one-dimensional equations from the conservation laws of multicomponent flows. Second, we validate the proposed model with the experimental data available in the literature for binary mixtures of four gases. Third, we calculate the nozzle transfer functions for different Helmholtz numbers and friction factors, in both subsonic and supersonic flows with/without shock waves. We show that friction and dissipation have a significant effect on the generation of indirect noise, for which the physical mechanism is identified and explained. Fourth, we find a semi-analytical solution with path integrals, which provides an asymptotic expansion with respect to the Helmholtz number. Fifth, we introduce the compositional-noise scaling factor, which is applied to quickly estimate compositional noise from the knowledge of only one single-component gas transfer function. The approximation error is less than $1\,\%$ . The proposed low-order model provides accurate estimates of the transfer functions and physical insight into indirect noise for multicomponent gases. This opens up new possibilities to accurately predict, and understand, sound generation in gas turbines.

Study on the evolution characteristics of coal spontaneous combustion and gas coupling disaster region in goaf

In order to study the evolution of multiple fields and the risk degree of combined disasters in the process of coal spontaneous combustion under the gas-containing environment in the goaf, a simulation platform for the thermal test of the thermal dynamic disaster in the goaf was built, and the gas–solid coupling heat transfer of multi-component gas model for coal spontaneous combustion was constructed. Through similar simulation experiments and numerical simulation, it is clear that the gas accumulation law during the coal spontaneous combustion process in the goaf. The ventilation process causes the gas to be driven along the air leakage channel to the deep part of the air-return side of the goaf, and finally a high gas concentration area is formed. Meanwhile, the change of gas density inside and outside the high-temperature area causes a small area of gas accumulation that migrates with the coal spontaneous combustion. According to the results of experiments and simulations, a risk assessment model of coal spontaneous combustion and gas combined disaster based on the dimensionless dynamic explosion limit of multi-gas was constructed. It is found that due to the massive consumption of oxygen by coal spontaneous combustion, the hazardous area of gas explosion has been continuously reduced, but the risk has been continuously increased. The risk of combined disasters is close to 1 in the corners of the working face and the back of the working face.

Numerical Evaluation of Wind Speed Influence on Accident Toxic Spill Consequences Scales

This study aims to evaluate numerically the influence of wind speed on scales of environmental harmful consequences caused by accidentally spilled toxic liquid evaporated from the surface of a free-form outlined spill spot. A coupled problem of the gas-dynamic movement of a toxic air-mixture cloud in the surface layer of the atmosphere under the influence of wind and a negative toxic inhalation impact on a human in an accident zone is solved by means of mathematical modelling and computer experiment. Physical processes of toxic liquid evaporation from the spill spot, formation of a mixture of toxic gas with the incoming air, and further dispersion of a hazardous gaseous chemical in the atmosphere under various wind speed conditions are investigated. A three-dimensional non-stationary mathematical model of the turbulent movement of a gas-air mixture is used for obtaining distribution of relative mass concentration of toxic gas impurities in time and space. The model takes into account the complex terrain, compressibility of the gas flow, three-dimensional and non-stationary nature of actual physical processes, different toxic properties of chemical substances, and arbitrary contour shape of the toxic spill spot. A probabilistic harmful impact model based on using a modernized probit analysis method is used to obtain fields of the conditional probability of a fatal human injury resulting from toxic gas inhalation. This model extracts relative mass concentration of toxic gas that could cause negative impact on humans at any control point during calculation time step exposition, collects integral toxic dose values from the multicomponent gas mixture dynamics model, calculates a value of the probit function for the corresponding toxic inhalation dose dangerous factor, and automatically assesses the human fatal injury conditional probability using partial cubic Hermitian spline. This technique allows environmental safety experts assessing the scale of considered type technogenic accident consequences numerically depending on wind speed conditions and elaborating the means to mitigate them to acceptable levels.

Hydrogen tightness evaluation in bedded salt rock cavern: A case study of Jintan, China

Hydrogen is regarded as one of the most important energy sources for the future. Safe, large-scale storage of hydrogen contributes to the commercial development of the hydrogen industry. Use of bedded salt caverns for natural gas storage in China provides a new option for underground hydrogen storage (UHS). In this study, the physical properties of multicomponent gases in UHS and salt rock are reviewed and discussed, along with the flow of hydrogen in the surrounding salt rock. Mathematical models of the two-phase multicomponent flow of the gas–brine system in the UHS were established. A numerical model of a simplified elliptical salt cavern was built to simulate the migration of the gas–brine system in the UHS. The hydrogen tightness of the UHS was evaluated through simulation with different storage strategies, salt rock and interlayer permeabilities, and gas components. The results indicate that: (1) Cyclic injection and withdrawal facilitate hydrogen leakage, which is accelerated by increasing the frequency. (2) The huff-n-puff of hydrogen gas in the injection and withdrawal cycles forces the gas into pore space and enhances the relative permeability of the gas phase. The migration of hydrogen and brine weakens the hydrogen tightness. Brine saturation is an important index for evaluating the hydrogen tightness of UHS. (3) The leakage rate of UHS increases with an increase in the permeability of the salt rock and interlayer and the total thickness of the interlayers. The average permeability Kwa weighted by the thickness of layers for the bedded salt formation is proposed to integrate three variables to facilitate field application of the simulation results. The critical Kwa is less than 3.02 × 10−17 m2 if the recommended annual hydrogen leakage rate is less than 1%. (4) The difference between hydrogen and other gas species is another important factor in the leakage rate and should be considered. This study provides theoretical guidance for evaluating the feasibility of UHS in salt caverns and site selection in China.

Hydrodynamics of a Multi-Component Bosonic Superfluid

We obtain the superfluid hydrodynamic equations of a multi-component Bose gas with short-ranged interactions at zero temperature under the local equilibrium assumption and show that the quantum pressure is generally present in the nonuniform case. Our approach can be extended to systems with long-range interactions such as dipole-dipole interactions by treating the Hartree energy properly. For a highly symmetric superfluid, we obtain the excitation spectrum and show that except for the density phonon, all other excitations are all degenerate. The implication of our results is discussed.

Hybrid Simulated Annealing Particle Swarm Optimization Support Vector Machine Based Temperature-Pressure Error Compensation Approach for TDLAS Gas Detection

ABSTRACT The target gas concentration in TDLAS (Tunable Diode Laser Absorption Spectroscopy) gas detection is nonlinearly related to the photodetector output signal, which is effortlessly disturbed by the temperature and pressure inside the gas absorption cell, and it will decrease the detection accuracy of the system. This paper proposes an SA-PSO-SVM (Simulate Anneal-Particle Swarm Optimization-Support Vector Machine) based temperature-pressure error compensation approach to improve the accuracy of TDLAS gas detection. First, an experimental system concerning the effects of gas temperature-pressure on the absorption line distortion was built. Meanwhile, a method for processing and exploring normalized data about the temperature and pressure effects on the gas concentration was proposed. Second, an SA-PSO-SVM-based model of temperature-pressure compensation for TDLAS gas detection was constructed, and a multi-point correction was performed. Finally, the developed model was compared with traditional BP (Back Propagation), SVM, and PSO-SVM-based temperature-pressure compensation models for TDLAS gas detection, to verify the effectiveness in terms of mean absolute error, mean relative error, and mean square error, which could significantly improve the detection accuracy of TDLAS system. The results provide guidance and lay a technical foundation for the study of multi-component gas cross-aliasing absorption line separation.