Changes In Gas Composition Research Articles

Spatial and temporal characteristics of elevated temperatures in municipal solid waste landfills

Elevated temperatures in waste containment facilities can pose health, environmental, and safety risks because they generate toxic gases, pressures, leachate, and heat. In particular, MSW landfills undergo changes in behavior that typically follow a progression of indicators, e.g., elevated temperatures, changes in gas composition, elevated gas pressures, increased leachate migration, slope movement, and unusual and rapid surface settlement. This paper presents two MSW landfill case studies that show the spatial and time-lapse movements of these indicators and identify four zones that illustrate the transition of normal MSW decomposition to the region of elevated temperatures. The spatial zones are gas front, temperature front, and smoldering front. The gas wellhead temperature and the ratio of CH4 to CO2 are used to delineate the boundaries between normal MSW decomposition, gas front, and temperature front. The ratio of CH4 to CO2 and carbon monoxide concentrations along with settlement strain rates and subsurface temperatures are used to delineate the smoldering front. In addition, downhole temperatures can be used to estimate the rate of movement of elevated temperatures, which is important for isolating and containing the elevated temperature in a timely manner.

Cyclosporin a induces renal episodic hypoxia

Cyclosporin A (CsA) causes renal toxicity. The underlying mechanisms are incompletely understood, but may involve renal hypoxia and hypoxia-inducible factors (Hifs). We sought for hypoxia and Hif in mouse kidneys with CsA-induced toxicity, assessed their time course, Hif-mediated responses and the impact of interventional Hif upregulation. Mice received CsA or its solvent cremophore for up to 6weeks. Low salt diet (Na+ ↓) was given in combination with CsA to enhance toxicity. We assessed fine morphology, renal function, blood oxygen level-dependent magnetic resonance imaging under room air and following changes in breathing gas composition which correlate with vascular reactivity, pimonidazole adducts (which indicate O2 tensions below 10mmHg), Hif-α proteins, as well as expression of Hif target genes. Stable Hif upregulation was achieved by inducible, Pax8-rtTA-based knockout of von Hippel-Lindau protein (Vhl-KO), which is crucial for Hif-α degradation. Cyclosporin A transiently increased renal deoxyhaemoglobin (R2*). Augmented vascular reactivity was observed at 2h, but decreased at 24h after CsA treatment. Na+ ↓/CsA provoked chronic renal failure with tubular degeneration and interstitial fibrosis. Nephron segments at risk for injury accumulated pimonidazole adducts, as well as Hif-α proteins. Remarkably, Hif target gene expression remained unchanged, while factor-inhibiting Hif (Fih) was enhanced. Na+ ↓/CsA/Vhl-KO aggravated morpho-functional outcome of chronic renal CsA toxicity. Cyclosporin A provokes episodic hypoxia in nephron segments most susceptible to chronic CsA toxicity. Fih is upregulated and likely blocks further Hif activity. Continuous tubular Hif upregulation via Vhl-KO worsens the outcome of chronic CsA-induced renal toxicity.

Steam methane reforming at low S/C ratios for power-to-gas applications

Steam reforming is a well-established industrial process for the production of hydrogen from hydrocarbon fuels, in most cases from natural gas. High steam to carbon ratios are applied to gain maximum methane conversion. Since steam reforming of natural gas is a highly endothermic reaction it may also be applied as a chemical storage of renewable energy. For this power-to-hydrogen application milder conditions and shorter operating times are characteristic. However process efficiency declines with increasing S/C ratio for storage applications. Though, when lowering S/C ratios one of the major challenges lies in coke formation due to unwanted reactions. On this reason, experiments with different hydrocarbon feedstock, including methane and a synthetic natural gas mixture were conducted in a laboratory test rig to investigate the influence of very low S/C ratios in the range of 0.1–0.4 and reaction temperatures between 450 and 500 °C at atmospheric pressure. Measurements showed drastic decrease of catalyst life times when small amounts of ethane and propane were added to the hydrocarbon feedstock. Long-term tests showed that catalyst deactivation led to flattening of the temperature profile, changes in dry product gas composition and rising pressure drop over fixed bed. Increase of reaction temperature, lowering of S/C and use of higher hydrocarbons in the feed led to intense carbon lay down.

In-line Process Control in the Active Screen Plasma Nitrocarburizing Using a Combined Approach Based on Infrared Laser Absorption Spectroscopy and Bias Power Management*

Abstract The active screen plasma nitrocarburizing (ASPNC) technology is an extension of the ASPN method in that carbon-bearing gases such as CH4 are admixed to the N2-H2 process gas. Besides process gas composition and working pressure, a bias power applied to the component surface is an important parameter in the nitrocarburizing process governing the competing uptake between nitrogen and carbon on the metallic surface. A variation of the bias power during the treatment provides the possibility of the dynamic control of both the nitriding and the carburizing potential without change of process gas composition. A two-stage process was implemented to improve the quality of the compound layer. The application of advanced in-situ and non-intrusive spectroscopic method of laser absorption spectroscopy in the mid infrared spectral range provides the valuable information about the plasma chemical reactions in the afterglow plasma, supplying the absolute concentrations of stable and transient molecular species monitored direct in process. The amount of hydrogen cyanide (HCN) measured in-situ by QCLAS diagnostics was found to be a reliable parameter to control the carburizing potential of the nitrocarburizing atmosphere.

The Behaviour of Bifilm Defects in Cast Al-7Si-Mg Alloy

Double oxide films (bifilms) are significant defects in the casting of light alloys, and have been shown to decrease tensile and fatigue properties, and also to increase their scatter, making casting properties unreproducible and unreliable. A bifilm consists of doubled-over oxide films containing a gas-filled crevice and is formed due to surface turbulence of the liquid metal during handling and/or pouring. Previous studies has shown that the nature of oxide film defects may change with time, as the atmosphere inside the bifilm could be consumed by reaction with the surrounding melt, which may enhance the mechanical properties of Al alloy castings. As a proxy for a bifilm, an air bubble was trapped within an Al-7wt.%Si-0.3wt.%Mg (2L99) alloy melt, subjected to stirring. The effect of different parameters such as the holding time, stirring velocity and melt temperature on the change in gas composition of the bubble was investigated, using a design of experiments (DoE) approach. Also, the solid species inside the bubbles solidified in the melt were examined using SEM. The results suggested that both oxygen and nitrogen inside the bifilm would be consumed by reaction with the surrounding melt producing MgAl2O4 and AlN, respectively. Also, hydrogen was suggested to consistently diffuse into the defect. The reaction rates and the rate of H diffusion were shown to increase upon increasing the holding time and temperature, and stirring velocity. Such significant effect of the process parameters studied on the gaseous content of the bubble suggesting that a careful control of such parameters might lead to the deactivation of bifilm defects, or at least elimination of their deteriorous effect in light alloy castings.

2-D Bubble Test Cell for the Study of Interactions at the Plasma–Liquid Interface

In plasma–liquid interactions, processes taking place at the gas–liquid interface drive chemical reactions within the bulk liquid. Such reactions and subsequent chemical transport are important to applications, such as plasma medicine and water purification. A 2-D bubble apparatus was investigated as a means to study physical and chemical processes taking place at the plasma–liquid interface. In particular, the approach makes the interfacial and surrounding regions accessible to optical diagnostics. Chemical transport originating at the interface driven by streamer and microdischarges within the bubble was observed, and chemical front propagation velocities were calculated. The propagation of acidification fronts as well as the transport of reactive oxygen species was documented using chemical probes. In addition, plasma-induced convection was observed illustrating the complex coupling of plasma-driven effects to the bulk solution. Time-dependent changes in bubble gas composition presumably driven by gas-phase reactions were also observed.

Pilot-scale underground coal gasification (UCG) experiment in an operating Mine “Wieczorek” in Poland

In this article, the results from a pilot-scale, underground coal gasification (UCG) experiment conducted in an operating coal mine “Wieczorek” were presented. The 60-day gasification trial demonstrated that through the appropriate selection of the test site and by applying all safety standards essential for the coal mining industry, UCG in an active mine can be conducted safely and efficiently. The idea of the technical realization of the UCG process, as well as selected gasification results, such as the primary mass balance parameters, gas production rate, coal consumption rate, coal gasification efficiency and the changes in gas composition, were presented.

Investigation of Ionospheric Response to Geomagnetic Storms over a Low Latitude Station, Ile-Ife, Nigeria

Due to several complexities associated with the equatorial ionosphere, and the significant role which the total electron content (TEC) variability plays in GPS signal transmission, there is the need to monitor irregularities in TEC during storm events. The GPS SCINDA receiver data at Ile-Ife, Nigeria, was analysed with a view to characterizing the ionospheric response to geomagnetic storms on 9 March and 1 October 2012. Presently, positive storm effects, peaks in TEC which were associated with prompt penetration of electric fields and changes in neutral gas composition were observed for the storms. The maximum percentage deviation in TEC of about 120 and 45% were observed for 9 March and 1 October 2012, respectively. An obvious negative percentage TEC deviation subsequent to sudden storm commencement (SSC) was observed and besides a geomagnetic storm does not necessarily suggest a high scintillation intensity (S4) index. The present results show that magnetic storm events at low latitude regions may have an adverse effect on navigation and communication systems.

Factors affecting ethylene and carbon dioxide concentrations during ripening: Incidence on final dry matter, total soluble solids content and acidity of mango fruit

Ripening of climacteric fruits is associated with pronounced changes in fruit gas composition caused by a concomitant rise in respiration and ethylene production. There is a discrepancy in the literature since some authors reported that changes in fruit gas compositions differ in attached and detached fruits. This study presents for the first time an overview of pre- and post-harvest factors that lead to variations in the climacteric respiration and ethylene production, and attempts to determine their impacts on fruit composition, i.e., dry matter, total soluble solids content and acidity.The impact of growing conditions such as the fruit position in the canopy and the fruit carbon supply; fruit detachment from the tree, including the maturity stage at harvest; and storage conditions after harvest, i.e., relative humidity and temperature were considered as well as changes in fruit skin resistance to gas diffusion during fruit growth and storage.Results showed that fruit gas composition vary with all pre and post-harvest factors studied. Although all mangoes underwent a respiratory climacteric and an autocatalytic ethylene production, whatever pre and post-harvest factors studied, large differences in ethylene production, climacteric respiration and fruit quality were measured. Results suggested that the ripening capacity is not related to the fruit ability to produce great amount of ethylene. In agreement with precedent studies, this work provided several lines of evidence that gas composition of fruit is related to its water balance. Our measurements indicated that skin resistance to gas diffusion increased after the harvest and during storage. It was so suggested that the faster ripening of detached fruit may be explained in part by changes in fruit water balance and skin resistance to gas diffusion caused by fruit detachment.

Numerical investigation of the impact of gas composition on the combustion process in a dual-fuel compression-ignition engine

This study discusses the model of operation of a dual-fuel compression-ignition engine, powered by gaseous fuel with an initial dose of diesel fuel as the ignition inhibitor. The study used a zero-dimensional multiphase mathematical model of a dual-fuel engine to simulate the impact of enhancing Natural Gas (NG) with other gases on the combustion process. The model simulated the thermodynamic parameters of the gas mixture in the cylinder of a dual-fuel (NG/Diesel), turbocharged, four cylinder CRDI (Common-Rail Direct Injection) engine. The tests discussed herein were conducted for steady state engine operation, for partial load and constant consumption of gaseous fuel. In the discussed tests, carbon dioxide and higher hydrocarbons (ethane and propane) were used as additions to NG.It has been shown that a change of gas composition has a significant impact on the combustion process and parameters of operation of a dual-fuel engine. The combustion of gas additives largely determines the combustion of both the main component of gaseous fuel and the initial dose of diesel fuel. The addition of higher hydrocarbons to methane can improve engine performance by as much as 6% with additions of higher carbon amounting to 20% of total fuel volume. Also, it has been shown that changes of gas composition significantly impact the ignition delay of the initial diesel dose.

Short-period volcanic gas precursors to phreatic eruptions: Insights from Poás Volcano, Costa Rica

Abstract Volcanic eruptions involving interaction with water are amongst the most violent and unpredictable geologic phenomena on Earth. Phreatic eruptions are exceptionally difficult to forecast by traditional geophysical techniques. Here we report on short-term precursory variations in gas emissions related to phreatic blasts at Poas volcano, Costa Rica, as measured with an in situ multiple gas analyzer that was deployed at the edge of the erupting lake. Gas emitted from this hyper-acid crater lake approaches magmatic values of SO2/CO2 1–6 days prior to eruption. The SO2 flux derived from magmatic degassing through the lake is measureable by differential optical absorption spectrometry (sporadic campaign measurements), which allows us to constrain lake gas output and input for the major gas species during eruptive and non-eruptive periods. We can further calculate power supply to the hydrothermal system using volatile mass balance and thermodynamics, which indicates that the magmatic heat flux into the shallow hydrothermal system increases from ∼27 MW during quiescence to ∼59 MW during periods of phreatic events. These transient pulses of gas and heat from the deeper magmatic system generate both phreatic eruptions and the observed short-term changes in gas composition, because at high gas flux scrubbing of sulfur by the hydrothermal system is both kinetically and thermodynamically inhibited whereas CO2 gas is always essentially inert in hyperacid conditions. Thus, the SO2/CO2 of lake emissions approaches magmatic values as gas and power supply to the sub-limnic hydrothermal system increase, vaporizing fluids and priming the hydrothermal system for eruption. Our results suggest that high-frequency real-time gas monitoring could provide useful short-term eruptive precursors at volcanoes prone to phreatic explosions.

Effect of Three Different Catalysts (KCl, CaO, and Fe2O3) on the Reactivity and Mechanism of Low-Rank Coal Pyrolysis

The pyrolysis behavior of Huangling coal (HL) was investigated using KCl, CaO, and Fe2O3 as the catalysts. The catalytic pyrolysis characteristics of coal were studied by thermogravimetry, as well as from the yield of the pyrolysis products and gas and tar composition. The catalytic mechanism was discussed in terms of the changes in gas composition and kinetic analysis. The Doyle integral method was employed for investigating the reaction kinetics of the coal catalyst mixture. The general effect of the additive on the reactivity of coal pyrolysis was evaluated using the pyrolysis characteristic index P. The results show that KCl, CaO, and Fe2O3 exhibit a catalytic effect on the pyrolysis of HL. The char and gas yield increased with the addition of catalysts, and the tar yield first increased and then decreased. With the addition of 1.5% of KCl or Fe2O3 catalyst or 0.5% CaO, the best catalytic effect was observed for the pyrolysis of coal. Coal pyrolysis can be divided into two regions: 472–655 °C and 655–...

The Application of Noninvasive Headspace Analysis to Media Fill Inspection.

A novel analytical technique has been demonstrated for detecting microbial growth in media-filled pharmaceutical containers. This analytical technique, laser-based headspace analysis, uses tunable diode laser absorption spectroscopy to determine gas concentrations in the headspace of a pharmaceutical container. For detecting microbial growth, the levels of headspace oxygen and carbon dioxide are measured. The study shows that once aerobic microorganisms begin to grow after the lag phase and enter the exponential growth phase there will be a significant consumption of oxygen in the sealed container as well as a corresponding production of carbon dioxide. Headspace analysis can accurately measure and monitor these changes in the headspace gas composition and could therefore be used to detect contaminated pharmaceutical containers. Because the technique can be automated to analyze hundreds of containers a minute on-line, there are opportunities for implementing a headspace inspection machine to perform automated inspection of media fills used to validate aseptic filling operations.

Dissolved gases in hydrothermal (phreatic) and geyser eruptions at Yellowstone National Park, USA

Multiphase and multicomponent fluid flow in the shallow continental crust plays a significant role in a variety of processes over a broad range of temperatures and pressures. The presence of dissolved gases in aqueous fluids reduces the liquid stability field toward lower temperatures and enhances the explosivity potential with respect to pure water. Therefore, in areas where magma is actively degassing into a hydrothermal system, gas-rich aqueous fluids can exert a major control on geothermal energy production, can be propellants in hazardous hydrothermal (phreatic) eruptions, and can modulate the dynamics of geyser eruptions. We collected pressurized samples of thermal water that preserved dissolved gases in conjunction with precise temperature measurements with depth in research well Y-7 (maximum depth of 70.1 m; casing to 31 m) and five thermal pools (maximum depth of 11.3 m) in the Upper Geyser Basin of Yellowstone National Park, USA. Based on the dissolved gas concentrations, we demonstrate that CO 2 mainly derived from magma and N 2 from air-saturated meteoric water reduce the near-surface saturation temperature, consistent with some previous observations in geyser conduits. Thermodynamic calculations suggest that the dissolved CO 2 and N 2 modulate the dynamics of geyser eruptions and are likely triggers of hydrothermal eruptions when recharged into shallow reservoirs at high concentrations. Therefore, monitoring changes in gas emission rate and composition in areas with neutral and alkaline chlorine thermal features could provide important information on the natural resources (geysers) and hazards (eruptions) in these areas.

Experiment and Simulation Study on the Special Phase Behavior of Huachang Near-Critical Condensate Gas Reservoir Fluid

Due to the special phase behavior of near-critical fluid, the development approaches of near-critical condensate gas and near-critical volatile oil reservoirs differ from conventional oil and gas reservoirs. In the near-critical region, slightly reduced pressure may result in considerable change in gas and liquid composition since a large amount of gas or retrograde condensate liquid is generated. It is of significance to gain insight into the composition variation of near-critical reservoir during the depletion development. In our study, we performed a series ofPVTexperiments on a real near-critical gas condensate reservoir fluid. In addition to the experimental studies, a commercial simulator combined with the PREOS model was utilized to study retrograde condensate characteristics and reevaporation mechanism of condensate oil with CO2injection based on vapor-liquid phase equilibrium thermodynamic theory. The research shows that when reservoir pressure drops below a certain pressure, the variation of retrograde condensate liquid saturation of the residual reservoir fluid exhibits the phase behavior of volatile oil.

A study of the gasification of carbon black with molten salt of Li2CO3 and K2CO3 for application in the external anode media of a direct carbon fuel cell

The characteristics of gasification reactions for carbon–carbonate mixtures were experimentally investigated at high temperatures up to 900 °C, considering the application of the mixtures to the external anode media of a direct carbon fuel cell. A thermo-gravimetric analysis (TGA) was conducted in either a nitrogen or carbon dioxide ambient environment for Li2CO3, K2CO3 and a mixture of these two substances with carbon black. Changes in the exit gas composition were also monitored during the heating process. It was shown that gasification in the mixture media occurs much more rapidly than carbonate decomposition at elevated temperatures, even for low concentrations of CO2. It was also shown that the loading of carbonates to carbon significantly affects the global gasification reaction; it increased the reaction rate by an order of magnitude and decreased its activation energy. Based on the experimental observations, a simplified reaction model of gasification was suggested for the anode media of a DCFC, regarding carbonate-catalysed and metal-catalysed pathways of Boudouard reactions.

Experimental study of air foam flow in sand pack core for enhanced oil recovery

Abstract As an innovative way of Enhancing Oil Recovery (EOR), the air foam flooding technique comprises the merits of air flooding and foam flooding, which not only has the double effects on profile controlling and oil displacement, but also avoids the gas channeling weakness. In this paper, a series of flow experiments of the simultaneous injection of air and air foam through artificial sand pack core was conducted to investigate changes in gas and oil composition and oil displacement efficiency. The effects of foaming agent concentration and slug were investigated. The results show that in low temperature oxidation process, oxygen content decreases, and carbon dioxide content increases. Aromatic hydrocarbon content decreases, while resins and asphaltene content increases. Oil displacement efficiency of air foam flooding is much higher than air flooding. The Foam blocking ability and the function of profile controlling of the foam, significantly prolongs gas breakthrough. The displacement efficiency was dropped due to the decrease of foaming agent concentration or the decrease of the foam slug.

Evaluation of Chitosan-Starch–Based Edible Coating To Improve the Shelf Life of Bod Ljong Cheese

The objective of this work was to evaluate the effectiveness of antimicrobial edible coatings to improve the quality of Bod ljong cheese throughout 25 days of storage. Coatings were prepared using chitosan, water chestnut starch, and glycerol as a base matrix, together with several combinations of antimicrobial substances: Cornus officinalis fruit extract (COFE), pine needle essential oil (PNEO), and nisin. Application of coating on cheese decreased water loss, lipid oxidation, changes in headspace gas composition, and color. Moreover, the edible coatings with COFE or PNEO had increased antimicrobial activity and did not permit growth of microorganisms. COFE and PNEO are manufactured from food-grade materials so they can be consumed as an integral part of the cheese, which represents a competitive advantage over nonedible coatings.

Numerical modeling of a 500 kW air-blown cyclone gasifier

Cyclone gasification of biomass in combination with a gas engine has been considered as a process for combined heat and power production. In this work a numerical model of the cyclone gasification process of wood powder was developed intended to be used as a tool for future engineering design of cyclone gasifiers. The model is based on an Euler–Lagrange formulation for the multiphase flow where the biomass powder was treated as a dispersed phase and the gas as a continuous phase. The results from the simulation are compared with experimental measurement in a 500 kWth cyclone gasifier that uses wood powder as fuel. The model was able to predict the gas composition change with increasing equivalence ratio. The relative error for the main gas component was between 2.5 and 4.4%, 2.8 and 5.4%, and 2.6 and 17.3% for CO2, CO and H2. CH4 was predicted with a relative error of between 3.8 and 19.2%. Also the model was able to predict the char amount out from the gasifier with reasonable accuracy. The obtained lower heating value from the model was between 3.5 and 5.2 MJ/Nm3 whereas the calculated based on measurement was 4.0–5.3 MJ/Nm3.

Transient Structures of PdO during CO Oxidation over Pd(100)

In situ high-energy surface X-ray diffraction was employed to determine the surface structure dynamics of a Pd(100) single crystal surface acting as a model catalyst to promote CO oxidation. The measurements were performed under semirealistic conditions, i.e., 100 mbar total gas pressure and 600 K sample temperature. The surface structure was studied in detail both in a steady gas flow and in a gradually changing gas composition with a time resolution of 0.5 s. The experimental technique allows for rapid reciprocal space mapping providing the complete information on structural changes of a surface with unprecedented time resolution in harsh conditions. Our results show that the (√5 × √5)R27°-PdO(101) surface oxide forms in a close to stoichiometric O2 and CO gas mixture as the mass spectrometry indicates a transition to a highly active state with the reaction rate limited by the CO mass transfer to the Pd(100) surface. Using a low excess of O2 in the gas stoichiometry, islands of bulk oxide grow epitaxial...