Inert Gas Components Research Articles

A modified and rapid method for the single-well push-pull (SWPP) test using SF6, Kr, and uranine tracers

In the present study, a single-well push-pull (SWPP) test was conducted with multi-component tracers, including inert gas (SF6 and Kr) and uranine (conservative), to understand the volatile/semi-volatile component transport characteristics in the groundwater system. In an SWPP test, it is essential to obtain an initial breakthrough curve (BTC) of the inert gas concentration at the beginning of the pulling stage to analyze the hydraulic properties of the groundwater system. As a result of the SWPP test using a proposed method in this study, physicochemical parameters of the groundwater and BTC of gas tracers and uranine were acquired simultaneously and successfully. In addition, on-site measurements of uranine, pCO2, and water quality data, such as electrical conductivity (EC), temperature, pH, and dissolved oxygen, were undertaken. Modification of an existing pCO2 measuring system allowed the gas samples to be collected, transported, and analyzed for inert gas components within a few hours. As a result, reliable and interpretable data with a recovery ratio of 26%, 85%, and 95% for SF6, Kr, and uranine, respectively, were obtained. The differences in the recovery ratio were utilized to identify the environmental system, whether it contains gas inside the isolated system (closed) or not (open), and to understand plume behavior characteristics in the experimental zone. By applying a two-dimensional advection-dispersion model to the acquired tracer test data and comparing the observed and computed tracer concentrations, helpful information was obtained on the hydraulic and transport characteristics of the targeted zone. This method can be extended to the design of dissolved CO2 transport monitoring of an aquifer above a CCS site.

Deconvolution of Gas Diffusion Polarization in Ni/Gadolinium-Doped Ceria Fuel Electrodes

Electrochemical impedance spectroscopy and the subsequent impedance data analysis by the distribution of relaxation times (DRT) represent a powerful method to unfold electrochemical processes in solid oxide cells. This approach has been successfully demonstrated for electrolyte [1, 2] as well as anode-supported [3] solid oxide cells exhibiting a nickel / yttria-stabilized zirconia (Ni/YSZ) fuel electrode. Applying this methodology, all physicochemical loss processes occurring in the cells could be identified by their relaxation frequencies and subsequently quantified by means of CNLS-fitting.However, in the case of cells exhibiting a Ni/Gadolinium-doped ceria (Ni/CGO) fuel electrode, an unambiguous process assignment in the DRT has not been feasible up to now, since the charge transfer and gas diffusion overlap in the spectrum [4, 5]. The latter is caused by the oxygen non-stoichiometry of CGO, which results in a large chemical capacity, shifting the relaxation frequency of the charge transfer process towards lower relaxation frequencies. The resulting overlap of charge transfer and gas diffusion process in the spectrum impedes a direct deconvolution of these two processes [6].Facing this challenge, we here present a solution of isolating and quantifying the gas diffusion process at the fuel electrode with the help of ternary fuel mixtures exhibiting different gas diffusion coefficients. The gas diffusion coefficients of hydrogen and steam were altered by changing the inert gas component between nitrogen and helium respectively. As the two gas mixtures exhibit identical reactant and reaction product concentrations, the charge transfer polarization is not affected. The differences in polarization resistance R pol, which become visible in figure 1, are solely caused by the differences in gas diffusion polarization [2].In this contribution the detailed procedure to quantify the gas diffusion polarization and an effective gas transport parameter predicting the gas diffusion resistance for arbitrary fuel mixtures are introduced. Furthermore, the applicability of this approach for the parameterization of a zero-dimensional cell model [3] for a solid oxide cell with Ni/CGO fuel electrode will be presented.

Effects of methane addition on laminar flame characteristics of premixed blast furnace gas/air mixtures

As a typical low heating value fuel, blast furnace gas (BFG) is used as an alternative fuel for gas turbine combustion. Due to its high concentration of inert gas components, natural gas is usually added to improve ignition and stable combustion in the combustion chamber. In this paper, laminar flame characteristics of BFG/CH4/air mixtures were investigated using constant volume combustion chamber and CHEMKIN package using the Gri-Mech 3.0 model. Experiments and numerical simulations were conducted at an elevated pressure and temperature of 0.2 MPa and 453 K, equivalence ratios of 0.8–1.4, and mixing ratios of methane of 0, 5, 10, 15%. The results show that the laminar burning velocity decreases rapidly from 24.19 cm/s to 13.90 cm/s at ϕ = 1.4 with the increase of methane addition from 0% to 15%, but obviously increases from 16.49 cm/s to 28.68 cm/s at ϕ = 0.8, from 21.05 cm/s to 35.65 cm/s at ϕ = 1.0, from 23.52 cm/s to 32.09 cm/s at ϕ = 1.2 with the increase of methane addition from 0% to 15%. Meanwhile, methane addition has an opposite effect on the Markstein length at ϕ = 0.8–1.2 and ϕ = 1.4. The thermal, transport and chemical effects were examined, exhibiting a major role of the thermal effect in the range of ϕ = 0.8–1.2 and a significant contribution of the chemical effect at ϕ = 1.4 to the laminar flame propagation of BFG/CH4/air mixtures. Further sensitivity analysis shows that R38 (H + O2 ↔ O + OH) and R52 (H + CH3 (+M) ↔ CH4 (+M)) are the main chain branching and chain termination reactions, respectively. Analysis on flame structure indicates that concentrations free radicals, especially OH and H evidently increase with methane addition. The maximum mole fraction of OH increases almost linearly from 1.02×10-3 to 3.82×10-3 with the increase of methane addition from 0% to 15%. The maximum mole fraction of H increases with a lower gradient than that of OH from 1.31×10-3 to 2.89×10-3 with the increase of methane addition from 0% to 15%.

Early stages of oxidation observed by in situ thermogravimetry in low pressure atmospheres

A highly sensitive set-up for in situ mass-gain measurements during high temperature reaction is presented. By removing the inert gas components of a corrosive atmosphere and keeping the flows and partial pressures of the reactive species constant, the experiment is preformed in a low-pressure environment. A better signal-to-noise ratio which increases sensitivity down to 10μg/cm2 is achieved. The random behaviour of the mass-gain signal, caused by turbulences in the gas stream, could be reduced by a factor of 10.Compared to theoretical simulations, the mass-change during oxidation in binary iron-based model alloys is slower than expected from pure bulk diffusion behaviour.

Filtration combustion of a porous structure in a multicomponent gas environment

A mathematical model for describing the quasi-isobaric filtration combustion of porous materials with the formation of condensed reaction products in a multicomponent gas is developed. Two-stage combustion waves (control modes) at the counter filtration of gas mixture are examined. The effect of inert gas component on the structure of a two-stage filtration combustion wave is studied, and the critical conditions of the changeover between filtration combustion modes caused by inert gas concentration variation are determined. It is demonstrated the characteristics of the two-stage combustion front propagating in the control mode in a multicomponent gas flow depends on the porosity of the heterogeneous system.

On the Sn loss from thin films of the material system Cu–Zn–Sn–S in high vacuum

In this paper the Sn loss from thin films of the material system Cu–Zn–Sn–S and the subsystems Cu–Sn–S and Sn–S in high vacuum is investigated. A combination of in situ x-ray diffractometry and x-ray fluorescence (XRF) at a synchrotron light source allowed identifying phases, which tend to decompose and evaporate a Sn-containing compound. On the basis of the XRF results a quantification of the Sn loss from the films during annealing experiments is presented. It can be shown that the evaporation rate from the different phases decreases according to the order SnS→Cu2SnS3→Cu4SnS4→Cu2ZnSnS4. The phase SnS is assigned as the evaporating compound. The influence of an additional inert gas component on the Sn loss and on the formation of Cu2ZnSnS4 thin films is discussed.

CO2‐Reduktion bei Gasturbinen‐Prozessen

Selective process modifications were considered among the possible process variations for carbon dioxide separation in natural gas fired combined gas and steam turbine power plants that differ greatly among themselves in terms of additional expense (efficiency losses, costs). The modifications considered effect an enrichment of the carbon dioxide content in the flue gas and a separation made easier (with various sorption media such as ammonia) instead of with amines (monoethanol amine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA). A carbon dioxide enrichment through exhaust gas recirculation coupled with a reduction of the oxygen content provides the challenge, to guarantee the combustion also under conditions with greater dilution (with inert gas components such as carbon dioxide and water) and low amounts of free oxygen and make the emissions of undesired byproducts such as NOx and CO extremely low (< 10 ppm). Through catalytic supported processes (in-situ partial catalytic oxidation) and through oxygen enrichment the stability of the release of heat at the same time can be maintained. It is to be expected that power plants running on, for example, natural gas will increase in efficiency and decrease in carbon dioxide emissions. The additional measures are to be made with little additional energy expense (efficiency loss of < 5%) and moderate additional costs of < 30 euros per tonne of separated carbon dioxide.

Measurement of Water Transport Properties Through Membrane Electrode Assemblies: Part II. Cathode Diffusion Media

This paper presents an in situ method to characterize the effective water diffusivity of cathode diffusion media in an operating fuel cell. The values of self-made gas diffusion layers (GDLs) and a commercial GDL were experimentally determined to be about one order of magnitude lower than the theoretical value. The effects of several factors such as the inert gas component and cathode pressure as well as the presence of microporous layer (MPL) on were studied, and the mechanism of water transport through cathode diffusion media was explored. It was found that the water transport is largely controlled by molecular and Knudsen diffusion through the catalyst layer. The MPL does not exhibit a dominant resistance to water transport. Interrelations of with the net water transport coefficient through the membrane and membrane resistance were also examined, suggesting that good balance between suitable membrane hydration and cathode flooding avoidance can be achieved by optimizing cathode diffusion media. The capability to measure reported in this work provides a diagnostic tool for screening cathode diffusion materials.

Low-Temperature Fischer–Tropsch Synthesis on Cobalt Catalysts—Effects of CO2

Effects of CO2 on low-temperature Fischer–Tropsch synthesis were investigated with four different cobalt catalysts in an experimental study. CO2 was found to behave as an inert gas component with three catalysts, however, a negative effect on Fischer–Tropsch reaction rate and catalyst deactivation was observed in one case (Co-La-Ru-SiO2). CO2 effects in a large-scale FTS slurry reactor were simulated by means of a mathematical reactor model using the kinetic information gained in the experiments. The reactor volume required for achieving a desired CO conversion must be higher if the syngas contains CO2, more strongly in cases where the catalyst exhibits a deactivation behavior in the presence of CO2. These model calculations can contribute to process optimization with respect to CO2 removal before synthesis.

Gas Diffusion Impedance in Characterization of Solid Oxide Fuel Cell Anodes

Impedance spectra obtained on high‐performance Ni/yttria stabilized zirconia (YSZ) cermet anodes at 1000°C in gas mixtures are considered. An impedance arc with a characteristic frequency of about 10 to 100 Hz is related to finite diffusion limitation by considering the dependence on water partial pressure, apparent thermal activation, and effect of the inert gas component. By experiments in different test geometries the diffusion zone is demonstrated to be a stagnant gas layer outside the anode structure. An estimated stagnant gas layer thickness of about 1 mm is arrived at. The diffusion impedance is demonstrated to be avoidable by using a setup geometry with two coupled electrodes in direct electrical contact through opposing sides of a contacting mesh. © 1999 The Electrochemical Society. All rights reserved.

Unimolecular fragmentation of the methyl formate ion in association with large inert gas clusters

Ion clusters of the type Ar n ·CH 3OC(H)O +, Ar n ·CH 3OC(D)O + and Ar n ·CD 3OC(H)O + for n in the range 10–130 were formed by electron impact following the adiabatic expansion of an argon-methyl formate mixture. In each case the methyl formate was observed to undergo unimolecular decomposition to give Ar n ·CH 3OH +, Ar n ·CH 2OH +, Ar n ·CHOH +, Ar n ·CHO +, Ar n ·CO +, Ar n ·CH 2OC(H)O + and Ar n ·CHOC(H)O + or their deuterated equivalents. Other fragments, which are present in the mass spectrum of the isolated molecular ion, do not appear when methyl formate is clustered with argon. In contrast, the fragments Ar n ·CH 2OC(H)O + and Ar n ·CHOC(H)O + are not characteristic of the isolated ion. The observation of fragments which require the presence of sufficient energy to break covalent bonds can be explained in terms of an existing mechanism, where it has been proposed that the molecular ion receives the energy difference IE(argon)-IE(methyl formate) via a charge transfer process. In specific regions of the mass spectrum, the fragment ions exhibit considerable variations in their relative intensities as a function of argon cluster size. This behaviour is analysed in terms of “magic number” configurations, where it is proposed that an oxygen atom in a fragment ion occupies a site in the inert gas component, which allows for the formation of a particularly stable structure. Any remaining portion of the fragment ion is assumed to protrude from the main body of the ion cluster. It is proposed that the fragments Ar n ·CH 2OC(H)O + and Ar n ·CHOC(H)O + arise from a rapid dissociation of the methyl formate ion into CH 3OH + and neutral carbon monoxide, with both fragments remaining in association with the argon cluster. The methanol ion subsequently undergoes further decomposition without the CO being displaced from the cluster. The presence of methanol as a fragment ion is the first observed example of a rearrangement reaction taking place on an inert gas cluster.

Calculation of distillation towers in catalytic cracking units

This article presents an equation describing the processes of mass transport and heat transfer in a main distillation tower (MDT), which takes into account the low-boiling inert gas components in the vapor phase, as well as the water vapor that enters the tower along with the wide-cut catalysate from the reactor of the unit and through the sidestream stripping towers. In tray-to-tray calculations of MDTs, it is assumed that all low-boiling gaseous components (from H/sub 2/ through C/sub 4/) in the wide-cut catalysate should be considered as inert. However, the presence of the low-boiling inert gas components in the vapor phase does affect the vapor/liquid equilibrium and the heat balances in the tower. It is concluded that the proposed method makes it possible to calculate MDTs of catalytic cracking units with a high degree of accuracy.

Contribution of environmental factors in development of hyperbaric bradycardia.

Bradycardia has been observed in animals and humans upon exposure to various hyperbaric environments. However, the relative contribution of ambient pressure, gas density, inert gas species, and inspired O2 tension has not been defined. By means of cutaneous ECG leads, the heart rates of unanesthetized rats were recorded and compared in 11 separate thermo-neutral environments. Ambient pressures applied were 1, 3, and 10 ATA, O2 partial pressure PO2 ranged from 140 to 1,590 Torr, and gas densities were varied from 0.40 to 11.45 g/l, utilizing either N2-O2 or He-O2 mixtures. The exposure heart rates were averaged over a 30-min period and compared with a preceding control value obtained in 1 ATA normoxic He or N2. Significant bradycardia was associated with hyperoxia in environments containing either He or N2, with a magnitude proportional to log PO2. On the other hand, under normoxic conditions bradycardia was not observed despite the similar density, pressure, and inert gas components. It is concluded that hyperoxia is the most important variable of those considered in the development of hyperbaric bradycardia.

Partial Pressure Calibration For Residual Gas Analyzers

The method of reference transfer is applied to the full range partial pressure calibration of residual gas analyzers (RGA). Partial pressures are transferred across the upper orifice of a 10× pressure divider in such a way that a mathematically interrelated series of increasing partial pressures is generated. A gas flow measurement is used to establish the value of the partial pressure when it is in the 10−5 to 10−7 Torr region. For gases not residual to the vacuum system, calibration can begin at pressure levels limited primarily by electronic sensitivity and noise. Independence of RGA peak heights from interference by certain other gases was observed over a wide range of partial pressures of the several gases. Using this same equipment, inert gas fixed leaks were calibrated for just the inert gas components of their effluent.

Rate of gas absorption during atelectasis.

Rate of gas absorption during atelectasis.