Natural Gas Diffusion Research Articles

Molecular simulation of natural gas transport and storage in shale rocks with heterogeneous nano-pore structures

Abstract Although natural gas is widely produced from shale, the mechanisms of natural gas transport in shale matrices remain poorly understood due to the complex chemical compounds of the matrices and the nanoscale pore size distribution. Using molecular simulations, we investigate natural gas transport and storage in nano-pore networks. Carbon-based 3-D pore networks are generated from 2-D scanning electron microscopy (SEM) images of a shale rock using the Markov Chain Monte Carlo simulation method. We employ a grand canonical Monte Carlo (GCMC) simulation to calculate adsorption isotherms of natural gas in carbon-based 3-D pore networks, which can be fit by a Langmuir isotherm model. To investigate gas transport in the same structures, we insert an external driving force into non-equilibrium molecular dynamics (NEMD) simulations and find that Knudsen diffusion is the dominant transport mechanism in the pore networks. Although porosity and pore connectivity affect the natural gas diffusion in the pore networks, we typically observe a linear relationship between average molar flow rate through a cross-sectional area and the external driving force.

Numerical Study of Swirling Confined Non-premixed Flames with Determination of Pollutant Emissions

In this paper the numerical simulation of a high swirled confined natural gas diffusion flames are studied. Several factors influencing the combustion process are examined. One of the goals is to study the influence of the turbulence models and the reaction mechanism on the prediction of the flow, temperature fields and modelling of NOx emissions. The numerical calculation has been performed using the commercial code Fluent. The standard k-ε and RSM models are used to describe the turbulent flow. The Eddy dissipation model (6 species and 2 reactions) and a chemical equilibrium model in conjunction with (β function) PDF model (9 species and 8 reactions) are used to model the turbulence-chemistry interaction. A NOx post-processor has been used for predicting NO emissions from combustors. The concentration of O and OH radicals are obtained assuming the partial-equilibrium assumption and using a PDF in terms of temperature. The comparison of the numerical results with the available experimental data shows a satisfactory agreement.

Effect of pulverized anthracite coal particles injection on thermal and radiative characteristics of natural gas flame: An experimental study

Natural gas is increasingly used as a clean fuel. In many industrial combustion systems, such as industrial furnaces and boilers, a large portion of heat is transferred by radiation. The use of natural gas in such industrial systems leads to a decrease in radiative heat transfer. The addition of solid reactant particles into flame is widely proposed in the literature as a method to enhance radiation from non-luminous flames, with a preponderance of research on hydrogen flame. The present study explores how the injection of pulverized anthracite coal particles into natural gas diffusion flame, as a non-luminous one, affects the thermal and radiative properties of natural gas. A novelty of our research method is the exploitation of yellow chemiluminescence of soot particles together with infrared photography to locate radiative particles and discover their qualitative distribution. The IR filter used in our technique was tested with Thermo Nicolet Avatar 370 FTIR Spectrometer for its spectral transmittance to be determined. The results indicate that the injection of coal particles into natural gas flame leads to a rise in the soot content of flame. Having the advantage of high absorptivity and emissivity coefficients in the near IR region, the soot particles in turn increase the flame luminosity and, more importantly, its emissivity coefficient. Also, the heat released from the combustion of particles increases the average temperature of flame about 29°C. These raise the radiative heat transfer and thermal efficiency of flame as much as 43% and 21%, respectively. It is noteworthy that the average temperature difference and emissivity coefficient, respectively, account for 17% and 83% of the enhancement of the average radiation flux.

Feasibility study of enhanced foamy oil recovery of the Orinoco Belt using natural gas

Foamy oil behavior contributes significantly to the anomalously high primary recovery of heavy oils observed in the Orinoco Belt, Venezuela. However, once below the pseudo-bubble pressure, disappearance of this phenomenon results in a rapid increase in the produced GOR and a fast decline in oil production. This paper presents the results of a laboratory investigation, including asphaltene precipitation studies, pressure–volume–temperature (PVT) studies of foamy oil–natural gas mixtures and coreflood tests, for evaluating the feasibility of the natural gas injection process for enhanced heavy oil recovery with foamy oil characteristics. Firstly, asphaltene precipitation tests were carried out to investigate the likelihood of asphaltene deposition problems in MPE3 reservoir during the gas injection process. The natural gas dissolution tests characterized the natural gas diffusion process in the foamy oil, and a new method for determining the natural gas diffusion coefficient in foamy oil was developed on the basis of experimental data. Thereafter, foamy oil swelling tests examined the effects on viscosity reduction and foamy oil swelling of the presence of natural gas. Finally, coreflood tests were carried out to investigate the effects on oil recovery of injection mode and their different process parameters. The results indicate that significant amounts of natural gas could dissolve in the oil, which would cause oil swelling, viscosity reduction and artificial foamy oil formation. Core-flooding tests show that the natural gas huff-n-puff process could increase oil recovery 7.8% compared to the primary pressure depletion process, indicating a greater potential for recovering heavy oil. However, the asphaltene instability could potentially nullify any expected benefits of improved oil recovery with natural gas. • A new method was developed for determining the gas diffusion coefficient in foamy oil. • We proposed a new swelling test method for foamy oil. • The primary mechanisms of the natural gas in foamy oil reservoirs. • The effect on oil recovery of injection mode was examined. • The potential for applying the natural gas injection process was investigated.

Measuring Organic Carbon and Black Carbon in Rainwater: Evaluation of Methods

Measuring wet deposition of organic carbon (OC) and black carbon (BC) is crucial for the complete understanding of the global circulation, lifetime, and radiative forcing of these aerosols. There is currently no accepted standard analytical method for measuring OC and BC concentration in precipitation. Different analytical methods have been employed for this purpose, but their feasibility has yet to be assessed. This manuscript evaluates the use of thermal-optical analysis (TOA), single-particle soot photometry (SP2), and ultraviolet–visible (UV/VIS) spectrophotometry for measuring BC in precipitation. In addition, total organic carbon (TOC) analysis was evaluated for the measurement of dissolved organic carbon (DOC) in precipitation. Potential interferences and sources of bias were assessed for each method. Precipitation samples and reference materials containing carbon particles generated from wood combustion and a natural gas diffusion flame were used in this study. The UV/VIS spectrophotometer, despit...

Effect of Swirl Number on Combustion Characteristics in a Natural Gas Diffusion Flame

This paper presents the effect of swirl number on combustion characteristics such as temperature, velocity, gas concentrations in a natural gas diffusion flame. Numerial simulations carried out using the commercial computational fluid dynamics (CFD) code, Fluent by choosing appropriate model parameters. The combustion reaction scheme in the flame region was modeled using eddy dissipation model with one step global reaction scheme. A standard k-ε turbulence model for turbulent closure and P-I radiation model for flame radiation inside the combustor is used in the numerical simulations. In order to investigate the swirling effect on the combustion characteristics, seven different swirl numbers including 0; 0.1; 0.2; 0.3; 0.4; 0.5; and 0.6 are used in the study. Numerical results are validated and compared with the published experimental and simulation results. A good consistency is found between the present results and those published measurement and simulation results in the available literature. The results shown that the combustion characteristics such as the flame temperature, the gas concentrations including CO2, H2O, O2, and CH4 are strongly affected by the swirl number. Depending on the degree of swirl, the fluid dynamics behavior of natural gas diffusion flame including axial velocity distribution, central recirculation zone (CTRZ) and external recirculation zone (ETRZ) were also strongly affected.

New insights into natural gas diffusion coefficient in rocks

Abstract Based on the analysis of measuring methods and results of natural gas diffusion coefficient in rocks and the measurement of methane diffusion coefficient in the Upper Paleozoic rocks of the Ordos basin, this paper clarifies the meaning of natural gas diffusion coefficient in rocks and discusses its application in gas diffusion simulation and some influencing factors. There are three methods for measuring natural gas diffusion coefficient in rocks, including free gas method, water-dissolved method, and time delay method. The meanings of diffusive concentration and the influencing factors are different for the natural gas diffusion coefficients measured by these three methods. The diffusion coefficient measured by the free gas method is 1 to 2 order of magnitude less than that measured by the water-dissolved method, and 2 to 3 order of magnitude less than that measured by the time delay method. The meanings of diffusive concentration in the diffusive volume calculation must be in line with that in the diffusion coefficient measurement during the process of diffusive volume calculation. Natural gas diffusion coefficient in rocks has a linear relationship with porosity and a dynamic relationship with temperature, and it logarithmically decreases with pressure.

밀폐공간 및 강제환기공간에의 천연가스 고압분출 시 농도 확산분포 거동해석 (I)

The basic understanding of gas diffusion and technology to predict the diffusion phenomena are needed to prepare against a disaster of leakage of natural gas and to design better consistent and reliable gas supply system in enclosure. The experimental results of British Gas Technology Co. are used in present study as a reference of theoretical study using CFD. The present results of 2D CFD analysis for mass flow rate of nozzle release show good agreement with experimental results within 2.6 % error. 3D CFD analysis for the characteristics of natural gas diffusion in enclosure with various ventilation patterns also gives reasonable agreement with experimental results.

Electrical aspects of flame quenching

Carbon monoxide distributions within small laminar natural gas flames are studied by micro-probe sampling and by numerical simulation, at progressively increasing proportions of air added to a constant fuel flow. The results are compared with CO emission to the atmosphere when such flames are quenched at various heights above the burner – by a variety of solid surfaces – with a view to quantifying the hazard associated with, for example, domestic boilers. Numerical simulations of small flames support the experimental results. The electrical structure of quenched flames under small (<10V/mm) electric fields is investigated, with the ultimate objective of devising a warning system signaling the onset of a quenching hazard. The variable electric field, derived from batteries and a potential divider, is applied between the burner and a copper grid – one of the quenching bodies – recording current as a function of height, for both polarities. Resistance/distance is of the order 108Ω/mm, depending on local temperature and composition. Because of their low mobilities, positive ions contribute only over very small distances; for longer path lengths the flame acts as a rectifier. Accordingly, electron conduction is utilized to detect the proximity of a quenching surface to the flame well before any hazardous release of CO escape could arise. The contours of first detection around the flame – for a current threshold of 10−8A – lie substantially outside the regions in which CO is detected in quenching products for both a natural gas diffusion flame and near-stoichiometric premixed flames.

Hydromethane: A bridge towards the hydrogen economy or an unsustainable promise?

Last decade enthusiasm about hydrogen-based economy on FC has partially been lost and spotlight is now back on using pure hydrogen or hydrogen mixtures in ICE. Pure hydrogen use in spark ignition (SI) ICE requires a dedicated engine design to optimize the high speed flame and the high pressure and temperature inside the combustion chamber. But, on the other end, may lead to high exhaust emissions of nitrogen oxides NOx. Moreover, hydrogen fueled vehicles also suffer of a very low mileage due to the very low energy density of the fuel, since hydrogen as a compressed gas at 200 atmospheres and ambient temperature has around 5% of the energy of gasoline of the same volume.All these motivations, together with the now capillary diffusion of natural gas (NG) distribution for residential and transportation purposes (especially in Europe) is making more and more interesting the option of H2 using as an additive to natural gas: NG powered vehicles, in fact, reached a very high maturity with high reliability and environmental performances. In recent years experimentations were conducted in many laboratories and research centers to verify the positive effects of hydrogen when blended with natural gas. The maturity achieved by H2–NG mixtures is also stated by commercialized gas which is available in USA with the registered trademark of Hythane® (a mixture of 20% H2–80% NG in volume).In this paper the hydro-methane option is fully outlined, a complete energy analysis and environmental sustainability is realized, considering all the main possible options available in mixture production and final use.

The Comparison of Experimental and Predicted Flame Temperature of Natural Gas Combustion

This present work was focused on the application of the probability density function method in conjunction with the k–∊ turbulence model in the goal to predict temperature fields of a non-premixed confined natural gas diffusion flame. A combined experimental and computational fluid dynamics modeling study of the turbulent non-premixed natural gas on a laboratory scale has been performed. An experimental study has been carried out on a fire-tube water heater. The flame and gas temperature in the combustion chamber were measured. The real geometry of the fire-tube water heater and the burner were modeled and analyzed by FLUENT code numerically. Turbulent diffusion flames were investigated numerically using a finite volume method for the solution of the conservation and reaction equations governing the problem. The boundary conditions were specified as the same as the measured values. The elemental analysis of the natural gas was taken as the mixture of hydrocarbon, and the air was the oxidizer. The standard k–∊ model was used for the modeling of the turbulence phenomena in the combustor. The non-premixed combustion model was chosen. In the conserved scalar approach, turbulence effects are accounted for with the help of an assumed shape probability density function or probability density function. The discrete ordinates radiation model is used for modeling of the radiative heat transfer in the combustion room. The model results were compared with the experimental results, in good agreement with the measurements.

The Analysis for the Environmental Impact of Natural Gas Leakage and Diffusion into the Atmosphere

In this paper, we investigate the leakage and diffusion characteristics of natural gas. As results show, when the natural gas leaks from the pipeline, it jet into the atmosphere in the form of positively buoyant jets. As a result, a hazardous area can appear at an altitude of 150m from the ground. Furthermore, the natural gas has a low concentration near the ground, this means the natural gas is less harmful to human body. In addition, the wind should be considered in the transport of leaked natural gas.

Structure of soot clusters formed in a hydrocarbon flame under the action of the electric field of a DC corona discharge

Electron microscopy was used to study the structure of soot clusters formed is a natural gas diffusion flame in the presence of the electric field of a dc corona discharge. It was demonstrated that the structure of such clusters depends on the electric field strength E and temperature T. As E increases from 0 to 2.3 kV/cm, the specific surface area of soot does so from 90.2 to 347.2 m2/g. The adsorbability of soot with respect to toluene vapor also increases, by a factor of 3. As E and/or T increase, the mean size of soot clusters decreases. The dependence of the mass of soot deposited on the grounded electrode exhibits an extreme character, passing through a maximum at E = 0.8 kV/cm.

Experimental Study of the Effects of CO2on the Noncatalytic Reduction Reaction of NO by Carbonaceous Materials

In a fixed bed reactor with a quartz tube, the effects of the concentration of CO2 in the feed gas on the uncatalyzed reaction between soot produced in a natural gas diffusion flame and NO were investigated. They were compared with CO2 effects on reactions involving candle soot and bituminous coal char. The presence of CO2 in the feed gas exerted no influence on the reaction of NO with natural gas soot. However, it did result in a lower initial temperature in the reaction of candle soot or coal char with NO, and separated the whole initial reaction process into two stages. At higher CO2 concentrations, more NO reduction occurred in the reaction with candle soot or coal char during the initial reaction process. However, no dramatic changes in the amount of NO reduction were observed for natural gas soot. The addition of CO2 seemed to have no effect on the apparent activation energy of the NO−natural gas soot reaction, while a lowering of the apparent activation energy was observed in the reaction of NO with candle soot or coal char as the CO2 concentration increased. The abundant C(O) complexes formed during sample gasification by CO2 were assumed to play an important role in the enhancement of the reaction.

Prediction of a high swirled natural gas diffusion flame using a PDF model

The paper deals with the numerical prediction of a high swirling non-premixed confined natural gas diffusion flame in order to predict the pollutant emissions NO x using the PDF model coupled with the Reynolds stress model (RSM). A chemical equilibrium model in conjunction with the assumed shape of the PDF is adopted. The chemical combustion reactions are described by nine species and eight reactions [Westbrook CK, Dryer FL. Chemical kinetic modelling of hydrocarbon combustion. Progr Energy Combust Sci 1984;10:1–57]. The PDF of the mixture fraction is described with a β-function. In order to predict the NO x emissions, a NO x post-processor of the Fluent code has been performed. The concentration of O and OH radicals are obtained assuming the partial-equilibrium assumption and using a PDF in terms of temperature. The numerical simulation of various factors influencing the combustion process are examined and compared favourably with experimental results.

Natural gas geochemistry and its origins in Kuqa depression

According to gas compositional and carbon isotopic measurement of 114 gas samples from the Kuqa depression, accumulation of the natural gases in the depression is dominated by hydrocarbon gases, with high gas dryness (C1/C1–4) at the middle and northern parts of the depression and low one towards east and west sides and southern part. The carbon isotopes of methane and its homologues are relatively enriched in 13C, and the distributive range of δ 13C1, δ 13C2 and δ 13C3 is −32‰–−36‰, −22‰–−24‰ and −20‰–−22‰, respectively. In general, the carbon isotopes of gaseous alkanes become less negative with the increase of carbon numbers. The δ 13 \( C_{CO_2 } \) value is less than −10‰ in the Kuqa depression, indicating its organogenic origin. The distributive range of 3He/4He ratio is within n × 10−8 and a decrease in 3He/4He ratio from north to south in the depression is observed. Based on the geochemical parameters of natural gas above, natural gas in the Kuqa depression is of characteristics of coal-type gas origin. The possible reasons for the partial reversal of stable carbon isotopes of gaseous alkanes involve the mixing of gases from one common source rock with different thermal maturity or from two separated source rock intervals of similar kerogen type, multistages accumulation of natural gas under high-temperature and over-pressure conditions, and sufficiency and diffusion of natural gas.

Experimental Study on Soot Combustion and Its Noncatalyzed Reaction with NO

In this paper, the combustion characteristic of soot was investigated in a quartz tube fixed-bed reactor. The soot was generated from the natural gas diffusion flame with different oxygen concentrations (20%, 15%, 10%, and 5%). Noncatalyzed reaction between the soot and NO was also investigated in different NO concentrations (∼200 ppm to ∼1500 ppm). The candle soot, the butane soot, and the coal coke were chosen as references. The ignition temperature of natural gas soot is lower than that of the coal coke. Oxygen concentration has a little influence on the ignition temperature of different samples but a great influence on the combustion process. Reactions of different samples under different NO concentrations have definite initial reaction temperatures and quite good regularities. Compared with other samples, natural gas soot has the highest NO removal rate and lowest initial reaction temperature. Increasing NO concentration will enhance the initial reaction temperature of the soot. On the other hand, the denser the NO concentration is, the lower the reaction rate and the higher reduction proportion of NO. The moisture content plays an important roll in the natural gas combustion, which can increase the soot combustion rate evidently. Moreover, the higher the moisture is, the lower the initial reaction temperature. However, impact of moisture on maximum NO reducing rate of soot is not obvious. Analysis reveals that although soot needs a higher combustion activation energy than the coal coke, it has lower reduction activation with NO. Transmission electron microscopy pictures demonstrate that natural gas soot has a layer microstructure. Both candle and butane soot have quite similar chain microstructures. Such differences among these microstructures lead to the discrepancy of macro-reaction performances among different samples.

Development of an experimetal test-rig for natrural gas diffusion flame studies

This work presents a part of a continuous research programme designed to provide information and experimental data leading to studies of soot and stable gaseous species from natural gas diffusion flame. This Test – Rig, which operates under atmospheric pressure, has along side with it a small probe (thermocouple attachment) for instantaneous measurement of temperature. The test rig has a co-annular burner consisting of a 16mm diameter steel tube (where the natural gas is injected upwardly) and surrounded by a 109mm diameter air annulus. The Rig and Facilities measures flame temperature, samples particulate matter (soot) and stable gaseous combustion product species within the flame with a well-designed Isokinetic sampling probe insert. After which, the natural gas species compositional change, soot volume fraction, soot number density can be determined with respect to axial and radial position distances from the burner rim. Keywords : diffusion flame, temperature profile and isokinetic Global Journal of Pure and Applied Sciences Vol. 12(2) 2006: 211-219

Adoption and diffusion of natural gas in the small-scale rural industry of Bolivia

The paper portrays the complexity of energy transitions drawing on the experience of the Bolivian National Biomass Programme. The transitions from wood to natural gas systems in the rural stucco and chicha (local beer) industries of Cochabamba serve as case-studies. A broad literature review of determinants of adoption and diffusion of new technologies in development is used to design a multidisciplinary conceptual framework, which is used to identify the factors that determine the extent of success in the energy transition in the two industries. Two periods in the diffusion of natural gas technology are distinguished: the 1990s, which were characterized by relative stability, and 2000-2003, when a national and international crisis posed problems for the adoption and diffusion of natural gas systems. Using data from field-work and secondary sources, the authors analyse the diffusion trends during both periods and show the interrelation between technological aspects and societal factors specific to the local, national and international levels in determining the speed and success of the diffusion process. They conclude that policy-makers should take into account a wide variety of interrelated factors when embarking on the transition from one energy source to another. A multidisciplinary approach is recommended for the management of energy transitions.

Determination of [formula omitted] emissions from strong swirling confined flames with an integrated CFD-based procedure

The present work is focused on a new procedure for the determination of NO x emission from combustion processes, which allow using very detailed and comprehensive reaction schemes, on the basis of the results obtained from CFD computations. This procedure is validated in the case of high swirled confined natural gas diffusion flames. The experimental data refer to the work developed within the German TECFLAM cooperation concerning a swirl burner ( 0.6 < S < 1.4 ) fed with natural gas characterized by 150 kW thermal load and 0.8 equivalence ratio (TECFLAM webpage, www.tu-darmstadt.de/fb/mb/ekt/tecflam; Schmittel et al., Proceedings of the Combustion Institute 28 (2000) 303–309). The CFD analysis represents a useful technology to provide the flow and temperature fields. The high swirling configuration makes the solution an interesting and difficult task for commercial codes. In particular, previous attempts of predicting the flow and temperature fields with the FLUENT code failed (Meier et al., Applied Physics B 71 (2000a) 725–731). Only a careful attention to the boundary conditions and converging strategy allows to reach a satisfactory modeling of the main characteristics of the flame. The numerical calculation was performed using the commercial code FLUENT6.0. NO x formation is a chemical process whose time-scale is of the same order of mixing fluid dynamics. For this reason, comprehensive modeling of NO x reaction processes in combustion systems requires simulation of both the turbulent fluid dynamics and chemical kinetics in the system being modeled. Hundreds of elementary reactions are required to provide a detailed description of the formation and depletion of oxides of nitrogen in combustion systems. However, it is not currently feasible to use such detailed reaction mechanisms to model a turbulent reacting system in which large reaction kinetics schemes are coupled with the turbulent fluid dynamics. Consequently, the difficulties in coupling detailed chemistry and detailed fluid dynamics force to adopt proper simplifications. The prediction of NO x formation is then obtained by postprocessing the flow and temperature fields, as predicted by CFD, and lumping together computational cells similar in terms of NO x formation. The resulting macrocells are assumed to be a network of ideal reactors, which are simulated adopting a detailed kinetics. The characteristics and operating conditions of each reactor are defined by a procedure already developed for furnaces and named SFIRN (Faravelli et al., Computers and Chemical Engineering 25 (2001) 613–618). The predictions have been tested on flames at different swirl numbers. Both the CFD and the chemical analysis show a satisfactory agreement with the measured data.