Gas Ratio Research Articles

New insights into carbon isotope systematics at Poás volcano, Costa Rica

In April 2017, an intense phreatomagmatic eruptive phase took place at Poás volcano in Costa Rica. This was the most significant eruptive activity at the volcano since the 1950's. Unlike previous eruptions, gas ratios were closely monitored during this event with the use of both ground-based MultiGAS and uncrewed aerial system (UAS) real-time monitoring, providing valuable insight into the nature of the eruption. This well-studied eruption presents a unique opportunity to examine hydrothermal and magmatic processes occurring at Poás during periods of unrest versus quiescent periods. Here, we present stable carbon isotopic results of volcanic CO2 at Poás spanning the pre-eruptive as well as eruptive and post-eruptive phases in 2017 through 2019. Samples were collected by a combination of direct sampling (analyzed by Isotope Ratio Mass Spectrometry [IRMS] or Cavity Ring Down Spectroscopy [CRDS]), as well as UAS and ground-based plume sampling (analyzed by CRDS). Direct samples range from −6.17 to −3.73 ‰ during 2017 to 2019. Using the Keeling approach, we calculate δ13C magmatic source values of −3.97 ± 1.94 ‰ and − 3.64 ± 0.48 ‰ using UAS sampling and ground-based sampling, respectively, for April 2019. We propose that these values for δ13C are being governed by a combination of magmatic and hydrothermal fluctuations related to sealing and unsealing of the upper magma carapace. This process results in comparatively heavy values when the system is being buffered by fluid-gas interaction as the hydrothermal system seals and expands, while lightest values are predominant during unsealed phases where degassed magma supplies the volatiles along with phreatic or phreatomagmatic activity. The significance of this work is two-fold: it demonstrates the use of a rapid volcanic gas sampling strategy applicable for monitoring at other volcanoes prone to phreatomagmatic and/or phreatic eruptions, and it provides a new conceptual model to interpret the phreatic/phreatomagmatic eruptive activity at Poás over the last 20 years.

Structure, composition and mechanical properties of reactively sputtered (TiVCrTaW)Nx high-entropy films

Nitride and metallic films multi-element (TiVCrTaW)Nx high-entropy alloy were deposited on silicon wafers by pulse DC magnetron sputtering. The microstructure and mechanical properties of the films prepared with different nitrogen gas flow ratios were studied. The results show that the concentration of nitrogen approached the stoichiometric composition at nitrogen gas ratio RN ≥ 33.3 %. The alloy film deposited with pure argon atmosphere exhibited a BCC structure and a very smooth surface, while an FCC with (111) or (200) preferred orientation and granular surface morphologies was observed in those films prepared with introduction of nitrogen gas. The (TiVCrTaW)Nx films exhibited enhanced hardness upon the addition of nitrogen probably due to the solid-solution strengthening effect and grain refinement. The nitride film achieved the highest hardness and Young’s modulus of 38 GPa and 340 GPa, respectively. The results show that the deposition atmosphere plays a vital rule in the structure and the properties of the (TiVCrTaW)Nx high-entropy films.

Key technologies and progress of enhanced gas recovery in water-bearing carbonate gas reservoirs

Global oil and gas consumption continues to rise and new strategies are required to meet the growing demand. Carbonate gas reservoirs are an important natural gas resource that are often accompanied by water intrusion during the development process. The efficient development of such reservoirs has therefore been extensively studied and met with difficulty. This paper summarizes the basic geological and water invasion characteristics of water-bearing carbonate gas reservoirs and correlates the two. A method for identifying water invasion types by production dynamics is introduced. The variation curve of the production water to gas ratio is shown to correspond with the reservoir geological characteristics. Typical development methods and the advantages/disadvantages of different water control techniques are summarized. The findings are used to propose a full-cycle water control plan for water-bearing carbonate gas reservoirs, and the development strategies of “early preparation, early discovery, and early treatment” and “re-analyze, re-assess, and re-adjust” are implemented to organically combine water control, drainage, and water blocking methods. The results provide a reference for formulating efficient and scientific development plans of water-bearing carbonate gas reservoirs.

Synergetic conversion laws of biomass and iron ore for syngas and direct reduced iron co-production

This work describes a system for the co-production of syngas and direct reduced iron (DRI) though the synergetic conversion of biomass and iron ore. Iron ore served as the oxygen carrier and catalyst for biomass gasification, while pine sawdust (biomass) served as the reducing agent for iron ore metallization during this reciprocal conversion process. The effects of conversion temperature, biomass to iron ore ratio and calcination time were investigated. A maximum syngas yield of 72.6% (valid gasification ratio for H and C were 68.8% and 72.7%, respectively) was obtained when biomass was gasified with iron ore (mol ratio C/Fe = 0.8) at 1000 °C for 30 min. DRI with a metallization ratio (MR) of 93.8% was produced concomitantly. The lattice oxygen and catalytic properties of iron ore promoted (i) the conversion of tar and char components into syngas and (ii) the cracking of hydrocarbons into CO and H2. Volatiles derived from biomass enhanced iron ore metallization by accelerating the reduction rate, and bio-char ensured a high MR of the final DRI. The conversion pathway for this was also elucidated. Volatiles and ∼35% of the char reacted with iron ore in the first 10 min to produce all of the H2 in the final syngas and some of the CO. The remaining 65% of the char was gasified in the next 20 min to generate the rest of the CO. The lattice oxygen of iron ore played the key role in early gasification, and the fresh metallic iron played a key role in the subsequent catalysis. This co-conversion approach described herein has potential applications in green fuel gasification or DRI processes.

DC Sputtering Deposition of Copper Oxide Thin Films Doped with Carbon for Efficient Solar Selective Absorbers

In this work, carbon-doped copper oxide thin films were deposited by the reactive DC sputtering method for use as selective absorbents. The properties of the DC discharge plasma were studied, using the emission spectrum, in the presence of pure argon and by mixing it with oxygen once and carbon dioxide again to know the effect of adding these gases on the properties of the resulting plasma used in the deposition of films. The structural properties of the deposited thin films prepared with different flow ratio of carbon dioxide gas were studied using x-ray diffraction. To examine the selective absorber coatings, the reflectance within the UV-Vis spectrum was measured to calculate the percentage of energy absorbed by solar radiation using numerical integration. The reflectance was also measured in the range from 2.5 to 25 μm to calculate the thermal emission of the solar heater within a temperature of 373 K. Measurements showed good efficiency as a selective absorption layer. The best absorptance of the solar spectrum (α) was 0.8750, and the lowest emittance (ε) in the infrared region was 0.254 at 25% percentage of carbon dioxide in the reactive gas of the sputtering system. So, this ratio has the highest efficiency as a selective absorber.

Gas Production by Monoester of Saturated Fatty Acids under Electrical Fault

This paper deals with the gas production by monoester oil intended to be used as insulating oil under an electrical discharge of low energy. The monoester contains only saturated fatty acids in its hydrocarbon chain. The electrical fault was realized by implementing an AC high voltage to hemispherical shaped electrode pairs with the gap of 2.5 mm immersed in the oil sample. The voltage application was paused when the breakdown occurred in oil and re-applied repeatedly up to 50 and 75 times to allow a high concentration of gasses produced by the oil sample. The resulting gasses were extracted from the oil sample using the headspace method and then analyzed using gas chromatography (GC). Fault identification methods, like DGA status, Key Gas, Duval Triangle, and IEC Ratio, were performed to predict the fault causing the production of such gasses. The results are compared with those of the monoester of unsaturated type. It is found that the Key Gas method is applicable for both oils under electrical discharge. The Duval Triangle and the IEC Ratio methods diagnose the electrical discharge in both monoesters but overestimate them as high energy discharge.

Study on the control of high ore pass dust pollution by pre-injection foam dedusting technology in the ore bin.

The impact airflow generated by ore unloading in the chute raises the dust carried by the ore itself and the floating dust, and then, the dust raised enters the roadway with the airflow and pollutes the environment. In order to minimize the amount of dust entering the roadway and reduce the pollution of unloading dust, we conducted an experimental study of selection of best foam formula and pre-injection foam dust dedusting technology in ore bin. It was found that the optimal foaming formula was 1.0% sodium dodecyl benzene sulfonate (SDBS) + 0.5% sodium dodecyl sulfate (SDS) + (0.2 ~ 0.4%) sodium carboxymethyl cellulose CMC-Na and coconut oil monoethanolamide (CMEA) by the compound experiment using two evaluation criteria of initial foaming amount and foam defoaming rate. When the air pressure is 0.7MPa, the foaming rate of the foam generator is proportional to the gas and liquid flow rate and the best foaming gas and liquid flow ratio is 27.8. Under this circumstance, the foaming rate of the foaming formula is 500l/min. When the height of foam is controlled at 15cm, the effect of foam dust removal is the best. The dust emission rate from the foam to the fourth level can reach 60%, and the dust fall rate of the third level is 28%, which effectively reduces the dust production and relieves the pressure of the spray hole dust fall at the wellhead.

Longitudinal Relaxation (T 1) of Methane/Hydrogen Mixtures for Operando Characterization of Gas-Phase Reactions.

Catalytic hydrogenation reactions are important in a modern hydrogen-based society. To optimize these gas-phase reactions, a deep understanding of heat, mass, and momentum transfer inside chemical reactors is required. Nuclear magnetic resonance (NMR) measurements can be used to obtain spatially resolved values of temperature, gas composition, and velocity in the usually opaque catalytic macrostructures. For this, the desired values are calculated from measured NMR parameters like signal amplitude, T 1, or T 2. However, information on how to calculate target values from these NMR parameters in gases is scarce, especially for mixtures of gases. To enable detailed NMR studies of hydrogenation reactions, we investigated the T 1 relaxation of methane and hydrogen, which are two gases commonly present in hydrogenation reactions. To achieve industrially relevant conditions, the temperatures are varied from 290 to 600 K and the pressure from 1 bara to 5 bara, using different mixtures of methane and hydrogen. The results show that hydrogen, which is usually considered to be nondetectable in standard MRI sequences, can be measured at high concentrations, starting at a pressure of 3 bara even at temperatures above 400 K. In the investigated parameter range, the absolute T 1 values of hydrogen show only small dependence on temperature, pressure, and composition, while T 1 of methane is highly dependent on all three parameters. At a pressure of 5 bara, the measured values of T 1 for methane agree very well with theoretical predictions, so that they can also be used for temperature calculations. Further, it can be shown that the same measurement technique can be used to accurately calculate gas ratios inside each voxel. In conclusion, this study covers important aspects of spatially resolved operando NMR measurements of gas-phase properties during hydrogenation reactions at industrially relevant conditions to help improve chemical processes in the gas phase.

Incorporation of water-derived hydrogen into methane during artificial maturation of source rock under hydrothermal conditions

To investigate the origin of CH bonds in thermogenic methane (CH4), a solvent-extracted sample of organic-rich Eagle Ford shale was reacted with heavy water (D2O) under hydrothermal conditions (350 bar) in a flexible Au-TiO2 cell hydrothermal apparatus at a water-to-rock ratio of approximately 5:1. Temperature was increased from 200 to 350 °C over the course of one month and the concentrations of aqueous species and methane isotopologues were quantified as a function of time. In general, production of hydrogen, CO2, alkanes, and alkenes increased with time and temperature. Methane formed during the early stages of the experiment at 200 °C was primarily C1H4 with some CH3D. With progressively higher temperatures, increasing proportions of deuterated isotopologues were produced. Near the end of the experiment, the concentration of CD4 exceeded that of all other isotopologues combined. These results suggest that competition between rates of kerogen-water isotopic exchange and natural gas generation may govern the D/H ratio of thermogenic gases. Furthermore, hydrogenation of kerogen by water may be responsible for hydrocarbon yields in excess of those predicted by conventional models of source rock maturation in which hydrocarbon generation is limited by the amount of organically bonded hydrogen.

Growth Mechanisms of TaN Thin Films Produced by DC Magnetron Sputtering on 304 Steel Substrates and Their Influence on the Corrosion Resistance

In this work, thin films of TaN were synthesized on 304 steel substrates using the reactive DC sputtering technique from a tantalum target in a nitrogen/argon atmosphere. All synthesis parameters such as gas ratio, pressure, gas flow, and substrate distance, among others, were fixed except the applied power of the source for different deposited coatings. The effect of the target power on the formation of the resulting phases and the microstructural and morphological characteristics was studied using XRD and AFM techniques, respectively, in order to understand the growth mechanisms. Phase, line profile, texture, and residual stress analysis were carried out from the X-ray diffraction patterns obtained. Atomic force microscopy analysis allowed us to obtain values for surface grain size and roughness which were related to growth mechanisms in accordance with XRD results. Results obtained showed a strong correlation between the growth energy with the crystallinity of the samples and the formation of the possible phases since the increase in the growth power caused the samples to evolve from an amorphous structure to a cubic monocrystalline structure. For all produced samples, the δ-TaN phase was observed despite the low N2 content used in the process (since for low N2 content it was expected to be possible to obtain films with α-Ta or hexagonal ε-TaN crystalline structure). In order to determine the corrosion resistance of the coatings, electrochemical impedance spectroscopy and polarization resistance were employed in the Tafel region. The results obtained through this evaluation showed a direct relationship between the power used and the improvement of the properties against corrosion for specific grain size values.

Risk evaluation of coal spontaneous combustion from the statistical characteristics of index gases

In this study, a logistic model was used to fit the volumes of index gases produced according to the coal temperature to obtain four fitted parameters, which were then normalized according to statistical characteristics. Model equations describing the variation in the volumes of the index gases with coal temperature were then established and used to determine the temperatures at the first and second inflection points of CO and C2H4. Thus, the temperatures at which CO, C2H4, and C2H2 were initially formed were obtained based on the statistical method, and these characteristic temperatures allowed classifying the risk of the spontaneous combustion of coal into six levels: safe, low, medium, high, very high, and disaster. Finally, combining the four gas ratios with these characteristic temperatures allowed the determination and normalization of the warning critical gas ratios to provide a set of indicators having warning threshold values of: > 1.7 for low risk, 1.1–1.7 for medium risk, 0.6–1.1 for high risk, 0.3–0.6 for very high risk, and < 0.3 for disaster.

Precise Modulation of Triple‐Phase Boundaries towards a Highly Functional Exsolved Catalyst for Dry Reforming of Methane under a Dilution‐Free System

AbstractDry reforming of methane (DRM) has been emerging as a viable solution to achieving carbon neutrality enhanced by the Paris Agreement as it converts the greenhouse gases of CO2 and CH4 into industrially useful syngas. However, there have been limited studies on the DRM catalyst under mild operating conditions with a high dilution gas ratio due to their deactivation from carbon coking and metal sintering. Herein, we apply the triple‐phase boundary (TPB) concept to DRM catalyst via exsolution phenomenon that can secure elongated TPB by controlling the Fe‐doping ratio in perovskite oxide. Remarkably, the exsolved catalyst with prolongated TPB shows exceptional CO2 and CH4 conversion rates of 95.9 % and 91.6 %, respectively, stable for 1000 hours under a dilution‐free system. DFT calculations confirm that the Lewis acid of support and Lewis base of metal at the TPB promote the adsorption of reactants, resulting in lowering the overall CO2 dissociation and CH4 dehydrogenation energy.

Biomass‐gas‐and‐nuclear‐to‐liquids (BGNTL) polygeneration process part II: Techno‐economic analysis

AbstractIn this paper, new polygeneration processes co‐producing electricity, methanol, dimethyl ether (DME), and Fischer–Tropsch (FT) fuels from different feedstock ratios of biomass, natural gas, and nuclear hydrogen generated through a copper‐chlorine (CuCl) cycle are analyzed for operation in Canada to produce transportation fuels. This combination of carbonless heat and a ‘carbon neutral’ biomass feedstock would contribute to the net reduction in greenhouse gas (GHG) emissions. In Part I of this work, the model for this biomass‐gas‐and‐nuclear‐to‐liquids (BGNTL) process was developed. This work expands on it and evaluates the economic and environmental impacts this plant would have in both Ontario and Alberta based on their local costs and resource availability. The analysis demonstrates that an increase in the ratio of biomass to natural gas in feedstock reduces the emissions of the process but increases the cost of carbon dioxide equivalents (CO2e) avoided. The results show that the BGNTL concept can be an economically attractive way of reducing net transportation sector GHG emissions in both Ontario and Alberta in meaningful quantities.

Reactive Molecular Dynamics Study for CO2 Electrocatalytic Conversion on Lmfcr (M= Sr, Ca) Perovskite-Based Solid Oxides

Due to their mixed conducting properties as well as their electronic, crystallographic, and chemical versatility, perovskite-based oxides have been shown to be very promising electrocatalysts for CO2 conversion to syngas in high temperature (600 – 1000 °C) solid oxide electrolysis cells (SOECs) integrated with renewable energy resources. In addition to generating fuels and value-added chemicals, CO2 reduction (CO2RR) in SOECs serves to lower atmospheric CO2 emissions. La-based (1) perovskite oxides have been intensively used instead of precious metals and metal-cermet materials (e.g., Ni-YSZ, Ni-GDC) for CO2 electrolysis in high temperature SOECs. The effect of the dopant cations on the electrocatalytic performance and degradation have also been investigated since the segregation of dopants can reconstruct the surface (2). Our team has been actively developing the family of La0.3a0.7Fe0.7Cr0.3O3−δ (LMFCr, where M = Ca or Sr) for CO2 reduction (3,4) showing that CO2RR is more active than CO oxidation, and that the catalyst is also highly active on the air side. More recently, we have shown that Fe-Ni exsolved LCFCr significantly improves the rate of CO oxidation (5), while hardly changed CO2RR. However, a full atomistic scale understanding of the CO2 reduction mechanism and related degradation issues, such as dynamic changes of the surface composition as a function of operating conditions, does not yet exist. The oxygen vacancy concentration (V0) and surface termination of the perovskite material are important factors that affect the CO2RR, as shown recently (6) utilizing DFT methods.In this study, we used Density Functional Theory (DFT) to explore the energetics of the catalytic conversion of CO2 to CO on LMFCr (M = Sr, Ca) perovskite surfaces. The DFT calculations were then used to generate datasets of optimized lattice structures, including point defects, equations of state, surface energies, and surface CO2/CO interactions in order to develop reactive force fields (ReaxFF). The datasets were optimized by using an evolutionary algorithm, CMA-ES, and validated in order to explore the dynamics of the catalytic conversion process under varying conditions, such as temperature, inlet CO2/CO gas ratio, the perovskite surface composition and applied electrical field.Our results have shed light on reaction steps involving adsorption of CO2 at high temperatures, C=O bond activation, and the dominant intermediates as transition states during the conversion process and their role in generating CO. These observations will serve as a foundation to determine the elementary reaction steps involved in the CO2 splitting mechanism on LMFCr at high temperatures. Furthermore, this study will enable us to determine the optimal conditions for the reaction to occur and shed light on possible surface degradation mechanisms, allowing future optimization of the stability and catalytic activity of these promising perovskites.ACKNOWLEDGMENTSThis computational research was supported by the Canada First Research Excellence Fund (CFREF), while the platforms for this computational work were provided by Westgrid (https://www.westgrid.ca) and Compute Canada (https://www.computecanada.ca). Thanks are also extended to Oliver Calderon and Misha Pidburtnyi for helpful discussions.References Cao, Z., Wei, B., Miao, J., Wang, Z., Lü, Z., Li, W., Zhang, Y., Huang, X., Zhu, X., Feng, Q. and Sui, Y., (2016). Efficient electrolysis in symmetrical solid oxide electrolysis cell with highly active 3Sr0.7Fe0.7Ti0.3O3 electrode material. Electrochemistry Communications, 69, 80-83.Zhang, Y. Q., Li, J. H., Sun, Y. F., Hua, B., & Luo, J. L. (2016). Highly active and redox-stable Ce-doped LaSrCrFeO-based cathode catalyst for CO2 SOECs. ACS Applied Materials & Interfaces,, 8(10), 6457-6463.Addo, P. K., Molero‐Sanchez, B., Chen, M., Paulson, S., & Birss, V. (2015). CO/CO2 study of high performance La0. 3Sr0. 7Fe0. 7Cr0. 3O3–δ reversible SOFC electrodes. Fuel Cells, 15(5), 689-696.Molero-Sánchez, B., Morán, E., & Birss, V. (2017). Rapid and Low-Energy Fabrication of Symmetrical Solid Oxide Cells by Microwave Methods. ACS Omega, 2(7), 3716-3723.Ansari, H. M., Bass, A. S., Ahmad, N., & Birss, V. I. (2022). Unraveling the evolution of exsolved Fe–Ni alloy nanoparticles in Ni-doped La 0.3 Ca 0.7 Fe 0.7 Cr 0.3 O 3− δ and their role in enhancing CO 2–CO electrocatalysis. Journal of Materials Chemistry A.Kozokaro, V. F., Addo, P. K., Ansari, H. M., Birss, V. I., & Toroker, M. C. (2020). Optimal Oxygen Vacancy Concentration for CO2 Reduction in LSFCr Perovskite: A Combined Density Functional Theory and Thermogravimetric Analysis Measurement Study. The Journal of Physical Chemistry C, 124(50), 27453-27466.

PECVD Silicon Nitride-Based Multilayers with Optimized Mechanical Properties

Silicon nitride (SiN) based films deposited by plasma-enhanced chemical vapor deposition (PECVD) have interesting optical, mechanical, and chemical properties. They are used for applications such as anti-reflective coatings and surface passivation layers in solar cells. Amorphous SiN-based films also are frequently used to create multilayer structures of alternatingly high-index and low-index films. This approach is very promising to fabricate narrow-bandwidth notch filters on photovoltaic cells to reflect on demand a wide variety of colors over the entire visible spectrum [1]. However, these multilayer structures need to be highly durable and mechanically stable since the lifecycle of photovoltaic cells in some applications [2] is very long, and the coated surfaces are very large. To satisfy these specific functional requirements, we need to adjust the films' optical and mechanical properties by changing the deposition parameters of a PECVD reactor. For instance, it is possible to strongly influence the chemical composition of amorphous SiN-based films, such as their stoichiometry, by tuning the gas flows [3]. This work investigates the effect of the deposition pressure, power, and source gas ratio on SiN-based monolayers during plasma deposition. We have deposited SiN and silicon oxynitride (SiON) films in an electron cyclotron resonance (ECR) PECVD reactor using a SiH4/N2/O2/Ar precursor mixture. We have measured the refractive index and the absorption of the films using a variable angle spectroscopic ellipsometry (VASE) to assess their optical quality. The mechanical properties of the films, such as residual stress and coefficient of thermal expansion, were measured ex-situ on a KLA-Tencor FLX-2320 film stress measurement system. The Young's modulus and hardness of the films were evaluated using nanoindentation. After studying the properties of monolayers, we have made numerical simulations and further characterizations to optimize the design of multilayer structures considering both the optical and mechanical properties. Through this discussion, we try to better understand the interactions taking place when amorphous SiN-based films with different structural properties and compositions are stacked on top of each other. Finally, we suggest methods to predict and control the residual stress in multilayer structures without affecting the optical properties.

Features of recognising the type of defect in oil-filled equipment using the nomogram method

The paper presents the results of analysis of nomograms (graphical areas) of defects in oil-filled equipment of electric networks. The input data were the results of dissolved gas analysis for 2997 transformers and shunt reactors with different types of defects, that is, the training sample. In order to level out possible contradictions in using different criteria, the training sample was split into separate data sets, not only with the same defect type, but also with identical values of characteristic gas ratios, gas percentages and gas-to-gas ratios with maximum concentration. To account for drift of coordinate values of individual nomograms in the obtained arrays, it is proposed to represent defect nomograms in the form of reference regions. The maximum and minimum coordinate values (ratios of each of the gases to the gas with the maximum concentration) obtained for homogeneous arrays of DGA results are used as values of the boundaries of reference regions. The centre of the graphic area coincides with the reference nomogram. As a result, 115 nomograms characteristic of thermal type defects, electrical discharges as well as overheating with different hot spot temperature accompanied by discharges with different energy density and discharges with different energy density accompanied by overheating with different hot spot temperature have been drawn. A brief analysis of the obtained graphic areas is given, the most characteristic damages corresponding to one or another graphic area are considered, and the values of characteristic gas ratios corresponding to the analysed areas are analysed. In the process of analysis it was established that the highest reliability value of defect type recognition can be achieved by simultaneous use of all three diagnostic criteria, namely, values of gas ratios, gas percentages and nomograms (graphic areas) of defects. The obtained results make it possible to significantly increase the number of reference nomograms, which will significantly increase the number of recognisable defects and consequently reduce the risk of accidental damage to oil-filled equipment due to missing defects caused by failure to recognise them.

Recognition of overheating in different temperature ranges, which is accompanied by discharges of different intensity, based on the dissolved gas analysis

In wartime and post-war reconstruction, it is the responsibility of a rather ageing fleet of electricity generation equipment to provide a reliable supply of electricity to the households and industry. The challenge is to ensure operational reliability and to extend the service life of this equipment. Non-destructive testing methods are the most practical in terms of operation. For non-destructive testing of high-voltage power transformers, the dissolved-oil gas analysis is the most common and widely used method. This method, using various diagnostic criteria (value of gas ratios, percentage of gases, etc.), allows most of the defects (both electrical and thermal type) occurring in a transformer to be detected. However, during operation, so-called combined defects can occur, i.e. discharges turning into overheating, or overheating accompanied by discharges. In addition, two or more defects of different types can occur in the same transformer. The values of the criteria used for the recognition of the combined defects differ significantly from the values of the criteria typical for thermal or electrical defects, which significantly complicates the recognition process. The purpose of this article is to analyse the values of diagnostic criteria as well as the recognition reliability of overheating in different temperature ranges, accompanied by discharges with different intensity. For a comprehensive analysis, the results of dissolved gas analysis were used for 471 high-voltage power transformers in which overheating in different temperature ranges, accompanied by discharges of different intensity, were detected. The 471 analysed values were split into 38 arrays with similar gas percentages, gas ratios and defect nomograms. Based on an analysis of the recognition reliability of overheating in different temperature ranges, using the norms and criteria regulated by the best known standards and methods, it was found that the highest recognition reliability is provided by the values of gas ratios, which are regulated by the ETRA Square and also by Nomogram method.

Leveraging computational thermodynamics to guide SiC-ZrC chemical vapor deposition process development

Using the CALPHAD approach to understand zirconium carbide deposition, a series of phase equilibria were calculated from a custom thermodynamic database based on a literature source, and the equilibria were used to explore the potential chemical vapor deposition (CVD) processing space in the ZrCl4-CH3SiCl3-CH4-H2 system as a function of pressure, temperature, and gas composition. Several gas ratios were considered. At a given ZrCl4:CH3SiCl3 ratio within the range studied, the most important factor was found to be the ratios of CH4:ZrCl4, wherein the nature of the composition – carbide vs. silicide – could be controlled. A pure binary composition of ZrC and SiC is expected to form by increasing the initial amount of methane and decreasing the amount of hydrogen from values predicted purely based on thermodynamic equilibrium. Rietveld analysis of the x-ray diffractograms from corresponding experimental depositions confirmed that increasing the CH4:ZrCl4 ratio increased the fraction of carbon-containing species (SiC, ZrC) and decreased the fraction of non-carbides (ZrSi, ZrSi2, etc.), as predicted from the CALPHAD results.

Source decomposition of eddy-covariance CO2 flux measurements for evaluating a high-resolution urban CO2 emissions inventory

We present the comparison of source-partitioned CO2 flux measurements with a high-resolution urban CO2 emissions inventory (Hestia). Tower-based measurements of CO and 14C are used to partition net CO2 flux measurements into fossil and biogenic components. A flux footprint model is used to quantify spatial variation in flux measurements. We compare the daily cycle and spatial structure of Hestia and eddy-covariance derived fossil fuel CO2 emissions on a seasonal basis. Hestia inventory emissions exceed the eddy-covariance measured emissions by 0.36 µmol m−2 s−1 (3.2%) in the cold season and 0.62 µmol m−2 s−1 (9.1%) in the warm season. The daily cycle of fluxes in both products matches closely, with correlations in the hourly mean fluxes of 0.86 (cold season) and 0.93 (warm season). The spatially averaged fluxes also agree in each season and a persistent spatial pattern in the differences during both seasons that may suggest a bias related to residential heating emissions. In addition, in the cold season, the magnitudes of average daytime biological uptake and nighttime respiration at this flux site are approximately 15% and 27% of the mean fossil fuel CO2 emissions over the same time period, contradicting common assumptions of no significant biological CO2 exchange in northern cities during winter. This work demonstrates the effectiveness of using trace gas ratios to adapt eddy-covariance flux measurements in urban environments for disaggregating anthropogenic CO2 emissions and urban ecosystem fluxes at high spatial and temporal resolution.

Formula omitted] and [formula omitted] signatures of methane aerobically oxidized by Methylosinus trichosporium with implications for deciphering the provenance of methane gases

Aerobic oxidation of methane (MOx) is an important biologically mediated process that consumes methane in a wide range of environments. Here we report results of culture experiments with the aerobic methane-oxidizing bacterium Methylosinus trichosporium (OB3b) that are used to characterize the mass-18 isotopologue (Δ13CH3D and Δ12CH2D2) signatures of MOx in residual methane gases. MOx activity was confirmed by simultaneous decrease of methane and oxygen in the bulk gas headspace. Bulk carbon (13C/12C) and hydrogen (D/H) isotope ratios of the methane gas increased while both Δ13CH3D and Δ12CH2D2 decreased as the oxidation proceeded. The corresponding fractionation factors (α) calculated from our experimental results are 0.98485 ± 0.00006 for 13C/12C, 0.7265 ± 0.0010 for D/H, 0.7141 ± 0.0011 for 13CH3D/12CH4, and 0.4757 ± 0.0023 for 12CH2D2/12CH4. Deviations of the mass-18 fractionation factors from the Rule of the Geometric Mean (RGM) expressed as γ values are 0.9981 ± 0.0017 for 13CH3D/12CH4 and 0.9013 ± 0.0045 for 12CH2D2/12CH4. Our α and γ values suggest that while MOx fractionates 13CH3D within error of the RGM, the Δ13CH3D and Δ12CH2D2 trajectories are very sensitive to even small deviations in 13CH3D/12CH4 from the RGM. Fractionation of 12CH2D2 deviates considerably from RGM, and this causes dramatic and robust effects on the trajectories of residual methane in Δ13CH3D vs. Δ12CH2D2 space. Our models suggest that Δ13CH3D and Δ12CH2D2 could potentially mimic microbial methanogenesis signatures in an environment that exhibits a strong Rayleigh Distillation process with little to no replenishment of methane during oxidation. However, in closed or open systems where oxidation is attended by simultaneous methane production, we find that modest increases in Δ13CH3D and dramatic increases in Δ12CH2D2 are to be expected, thus resulting in isotopologue signatures distinct from microbial methanogenesis. The overall trend in these conditions suggest that methane altered by MOx is distinguishable from other methane sources in Δ13CH3D and Δ12CH2D2 space.