Changes In Gas Composition Research Articles

Experimental study on dry reforming of methane by a plasma catalytic hybrid system

In this paper, the plasma coupled catalyst was used for the dry reforming of methane (DRM). The impacts of the reaction temperature, the molar ratio of CO2/CH4, and the concentration of the main gas components (N2, H2, CO, H2O) on the conversion rate of CH4 and the energy efficiency of plasma catalysis were observed. The results shows that the conversion rate of CH4 is 41.57%, with La-Ni/γ-Al2O3 as the catalyst, the reaction temperature being 450°C and the molar ratio of CO2/CH4 being 1.0, and without other gases. The conversion rate of CH4 increases with the increase of the molar ratio of CO2/CH4. The conversion rate of CH4 is 92.82% respectively during DRM by plasma catalysis, with the molar ratio of CO2/CH4 being 5.0. The reaction temperature and the molar ratio of CO2/CH4 have a significant effect on CH4 conversion. The excited particles in the system are influenced by the changes of gas composition, which affect not only CH4 conversion directly, but also the carbon deposition on the surface of catalyst. The addition of N2 and H2O in the reaction system not only improves conversion of CH4 but also inhibits carbon deposition; the addition of H2 and CO reduces the conversion of CH4 significantly. The results are expected to provide basic data and reference for the development of the synthetic process of chemicals through biomass gasification.

An Analytical Method for Gas Flow Measurement Using Conservative Chemical Elements

Mass flow meters (MFMs) are widely used to secure reliable flow rates based on the mass value of the gas being measured. However, chemical reactions produce various kinds of gases, and their composition also changes in real time. Thus, there may be a large deviation in the gas flow if the gases’ composition and its mixing ratio are not known. In this study, we derived a gas flow rate measurement method using a chemically stable chemical specie and verified the precision of the proposed method through comparative analysis with an MFM. The flow rate by this method showed reliable results in both single and mixed gases. Notably, the results were within ±2.74% of the injected flowrate values in the gas mixtures. This method is expected to be able to fundamentally overcome the limitations of the mechanical flowmeter because it is not affected by changes in gas composition or mixing ratio during the reaction.

Heat transfer augmentation by recombination reactions in turbulent reacting boundary layers at elevated pressures

A study of a reacting boundary layer flow with heat transfer at conditions typical for configurations at elevated pressures has been performed using a set of direct numerical simulations. Effects of wall temperatures are investigated, representative for cooled walls of gas turbines and sub-scale rocket engines operating with hydrocarbon as fuels. The results show that exothermic chemical reactions induced by the low-enthalpy in the boundary layer take place predominantly in the logarthimic sub-layer. The majority of the heat release is attributed to the exothermic recombination of OH and CO to produce CO2 and H2O. The recombination reactions result in an increase of the wall heat loads by up to 20% compared to the inert flow. The gas composition experiences strong deviations from the chemical equilibrium conditions. In fact, a quenching of the major species is observed within the viscous sub-layer and the transition region. Analysis of chemical time-scales shows that the location of quenched composition coincides with the region where the Damköhler number decreases below unity. Within the viscous sub-layer, a secondary reaction zone is detected, involving the production of formyl and formaldehyde radicals that provide an additional source of energy release. The analysis of the reaction paths showed that reactions with zero activation energy are responsible for this change in gas composition, which also account for the initial branching of hydrocarbon fuels decomposition according to previous auto-ignition studies. The effect of the secondary recombination reactions is more prominent for the lower wall temperature case. Finally, the role of turbulent fluctuations on the species net chemical production rates is evaluated, showing a strong correlation between species and temperature fluctuations. This leads to a pronounced deviation of the mean reaction rates ω˙(Yk,T)¯ from the reaction rates obtained under the assumption of laminar finite rate.

Accurate Quantification of Formaldehyde at ppb Level for Indoor Air Quality Monitoring

Accurate Quantification of Formaldehyde at ppb Level for Indoor Air Quality Monitoring

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates.

Natural gas hydrate occurrences contain predominantly methane; however, there are increasing reports of complex mixed gas hydrates and coexisting hydrate phases. Changes in the feed gas composition due to the preferred incorporation of certain components into the hydrate phase and an inadequate gas supply is often assumed to be the cause of coexisting hydrate phases. This could also be the case for the gas hydrate system in Qilian Mountain permafrost (QMP), which is mainly controlled by pores and fractures with complex gas compositions. This study is dedicated to the experimental investigations on the formation process of mixed gas hydrates based on the reservoir conditions in QMP. Hydrates were synthesized from water and a gas mixture under different gas supply conditions to study the effects on the hydrate formation process. In situ Raman spectroscopic measurements and microscopic observations were applied to record changes in both gas and hydrate phase over the whole formation process. The results demonstrated the effects of gas flow on the composition of the resulting hydrate phase, indicating a competitive enclathration of guest molecules into the hydrate lattice depending on their properties. Another observation was that despite significant changes in the gas composition, no coexisting hydrate phases were formed.

The effects of seaweed-based coating application on the respiration rate of shallots (Allium cepa l) during storage

In the postharvest handling of fresh products, coating is known as one of the preservation methods to lengthen shelf life. However, coating materials are still very difficult to find in Indonesia, more researches are still needed to explore indigenous materials to produce coating material. This research was intended to develop coating material based on seaweed flour (carrageenan) and to study the effect of its application on the respiration rate of shallot (Allium cepa L) during storage period. Coating material was produced in two different concentrations of carrageenan that were 0,5 and 0,75%. Fresh shallots as the samples were coated then loaded in the respirometer and stored at temperatures of 15°C and 28°C for 15 days storage periods. Uncoated shallots were also investigated as the control. Oxygen and carbon dioxide changes were monitored using O2 and CO2 Gas Analyzer (Quantek 902D) every day. It was found that the changes in gas composition inside the respirometer were found to vary for each coating materials and storage temperatures. Coated shallots showed lower respiration rates as compared to the control. Arrhenius equation could satisfactorily represent the effect of storage temperature on the respiration rate of the shallots.

Gravitoviscous Protoplanetary Disks with a Dust Component. V. The Dynamic Model for Freeze-out and Sublimation of Volatiles

Abstract The snowlines of various volatile species in protoplanetary disks are associated with abrupt changes in gas composition and dust physical properties. Volatiles may affect dust growth, as they cover grains with icy mantles that can change the fragmentation velocity of the grains. In turn, dust coagulation, fragmentation, and drift through the gas disk can contribute to the redistribution of volatiles between the ice and gas phases. Here we present the hydrodynamic model FEOSAD for protoplanetary disks with two dust populations and volatile dynamics. We compute the spatial distributions of major volatile molecules (H2O, CO2, CH4, and CO) in the gas, on small and grown dust, and analyze the composition of icy mantles over the initial 0.5 Myr of disk evolution. We show that most of the ice arrives to the surface of the grown dust through coagulation with small grains. Spiral structures and dust rings forming in the disk, as well as photodissociation in the outer regions, lead to the formation of complex snowline shapes and multiple snowlines for each volatile species. During the considered disk evolution, the snowlines shift closer to the star, with their final position being a factor of 4–5 smaller than that at the disk formation epoch. We demonstrate that volatiles tend to collect in the vicinity of their snowlines, both in the ice and gas phases, leading to the formation of thick icy mantles potentially important for dust dynamics. The dust size is affected by a lower fragmentation velocity of bare grains in the model with a higher turbulent viscosity.

Behavior of magmatic components in fumarolic gases related to the 2018 phreatic eruption at Ebinokogen Ioyama volcano, Kirishima Volcanic Group, Kyushu, Japan

Direct sampling and analysis of fumarolic gas was conducted at Ebinokogen Ioyama volcano, Japan, between December 2015 and July 2020. Notable changes in the chemical composition of gases related to volcanic activity included a sharp increase in SO2 and H2 concentrations in May 2017 and March 2018. The analyses in March 2018 immediately preceded the April 2018 eruption at Ioyama volcano. The isotopic ratios of H2O in fumarolic gas revealed the process of formation. Up to 49% high-enthalpy magmatic vapor mixed with 51% of cold local meteoric water to generate coexisting vapor and liquid phases at 100–160 °C. Portions of the vapor and liquid phases were discharged as fumarolic gases and hot spring water, respectively. The CO2/SO2 ratio of the fumarolic gas was higher than that estimated for magmatic vapor due to SO2 hydrolysis during the formation of the vapor phase. When the flux of the magmatic vapor was high, effects of hydrolysis were small resulting in low CO2/SO2 ratios in fumarolic gases. The high apparent equilibrium temperature defined for reactions involving SO2, H2S, H2 and H2O, together with low CO2/SO2 and H2S /SO2 ratios were regarded to be precursor signals to the phreatic eruption at Ioyama volcano. The apparent equilibrium temperature increased rapidly in May 2017 and March 2018 suggesting an increased flux of magmatic vapor. Between September 2017 and January 2018, the apparent equilibrium temperature was low suggesting the suppression of magmatic vapor flux. During this period, magmatic eruptions took place at Shinmoedake volcano 5 km away from Ioyama volcano. We conclude that magma sealing and transport to Shinmoedake volcano occurred simultaneously in the magma chamber beneath Ioyama volcano.

Smart packaging with temperature-dependent gas permeability maintains the quality of cherry tomatoes

Phase change materials (PCM), as a smart material, may be used to control the gas concentration inside packaging by changing temperature-dependent gas permeability. A polypropylene (PP) film and two composite films (PP/OD and PP/OD/ZL) with a temperature-dependent gas permeability feature were prepared by incorporating octadecane (OD) (PCM material) and zeolite (ZL) into PP, and these films were used as the packaging pouches for the cherry tomatoes. The temperature-dependent gas permeability of packages and changes in gas composition inside the packages were studied during storage (10 and 23 °C). Changes in the quality of cherry tomatoes, and the effects of the relative ratio between the total volume of the pouch and volume of cherry tomatoes were investigated. The gas permeability of the newly developed packages showed significantly higher temperature-dependence compared to PP package. The relatively low concentrations of O2 and CO2 in the headspace of the composite packages indicated a higher temperature-dependent gas permeability. The higher gas permeability maintained the quality of the cherry tomatoes in the composite film pouches with better total soluble solid content, firmness, and color. These materials as the promising packages can minimize the effects of temperature on the quality of agricultural products and extend their shelf life by controlling the accumulated gas inside the packaging.

Prediction of de-NOx performance using monolithic SCR catalyst under load following operation of natural gas-fired combined cycle power plants

As variable renewable energy expands, natural gas-fired combined cycle (NGCC) power plants are expected to provide important functions for grid stabilization such as quick start-up, shutdown, and load following. However, transient operation of NGCC significantly increases the NO2 content of NOX in the exhaust gas and reduces de-NOx performance of selective catalytic reduction (SCR) with ammonia injection. The denitrification performance of SCR depends on transient mechanisms such as adsorption of ammonia in the catalyst and redox reactions on the catalyst surface. This study evaluates whether de-NOX performance can be maintained during expected operational fluctuations for grids with a high penetration of variable renewable energy. Simulations involving a modified de-NOX reaction scheme have been developed and validated for various NGCC exhaust gas compositions expected in both steady state and transient operation using a commercial, monolithic SCR catalyst. Results show that sudden output load changes cause a decrease in SCR catalyst performance due to changes in gas composition and temperature outpacing the adsorption/desorption of ammonia in the catalyst. It was found that adjusting the injection amount of ammonia several minutes prior to the output load change was effective in maintaining de-NOX performance.

A predictive model of catalytic cracking: Feedstock-induced changes in gasoline and gas composition

One way to improve and predict unsteady processes of petroleum fuel production is to develop a mathematical model, that considers the feedstock composition. A study of various feedstock deep refining processes is particularly important. In this paper, we present the prediction of the catalytic cracking unit under feedstock base expansion by using oil fractions with a higher boiling point. The zeolite-containing catalyst with ZSM-5/Y ratio = 0.11 was used in this work. A new kinetic model involving the high molecular weight of C13–C40 hydrocarbons, gasoline groups, gas individual hydrocarbons and coke formation reactions was developed. The feed comprehensive studies, the development and application of a mathematical model allow assessing the feasibility of various feedstock types involvement. The impact of four feedstock types on the yield of catalytic cracking products, catalyst deactivation degree, gasoline and gas composition, and octane number were determined. Among the feedstocks under study are West Siberian oil vacuum gas oil, a mixture of Kazakhstan and West Siberian oil, a mixture of vacuum and atmospheric gas oil with residual feedstock (extract, slack waxes, petrolatum, deasphalting agent, raffinate), a mixture of vacuum distillate and residual feedstock (extracts, slack waxes).

Molecular simulation of the competitive adsorption characteristics of CH4, CO2, N2, and multicomponent gases in coal

The microscopic mechanism of the competitive adsorption of CH4, CO2 and N2 in coal is the theoretical basis for enhancing coal seam gas recovery by injecting CO2 (CO2-ECBM). Based on this principle, this work used Grand Canonical Monte Carlo and Molecular Dynamics to investigate the microscopic adsorption mechanism of single, binary, and ternary component gases in Wiser bituminous coal molecules. The adsorption mechanism was explored by changing gas composition and concentration. The comparison of adsorption separation coefficients suggested that CO2 had the highest adsorption capacity, whereas N2 had the lowest capacity. When the CO2 concentration in the gas mixture was high, the adsorption amount was large and the adsorption separation coefficient was small. This finding indicated that high concentrations of CO2 had negative effects on competitive adsorption. Energy changes were also evaluated. The potential energy between CO2 and the framework was the strongest among the two other gases. The inhibition of CH4 adsorption intensified with decreasing molar fraction of CO2. This phenomenon was explained from the perspective of heat of adsorption. As the molar fraction of CO2 in the adsorption system decreased, the heat of the isotherm adsorption increased. Meanwhile, the adsorption system became unstable and the capacity of CH4 adsorption on the framework weakened. Results provide a theoretical basis for the use of CO2-ECBM.

Evaluation of devolatilization behaviour of different carbonaceous materials under rapid heating for the novel HIsarna ironmaking process

A drop-tube furnace coupled with quadrupole mass spectrometer (DTF-QMS) was employed to simulate rapid heating conditions that carbonaceous materials experience during HIsarna injection with the measurement of gas composition change as a result. A devolatilization study for thermal coal (TC) and charcoal (CC) samples was carried out at three temperatures of 1000, 1250 and 1500 °C under an initial high purity Ar gas environment. The volatiles released were measured online by QMS, while the char yield was determined directly by the weight of particles collected and the deficit was calculated by subtracting the gas yielded from the total weight loss. The study reveals that working temperature has a strong impact on the devolatilization rate, the maximum weight loss and the variation in gas species produced. Due to intensification in the carbon oxidation and secondary reactions at higher temperatures, there was an increase in the weight loss, which led to a greater yield of H2 and CO but less yield of hydrocarbons, CO2 and H2O. Despite lower volatile matter content in charcoal, the weight loss for charcoal (29%) was higher than that for thermal coal (23%) at 1500 °C. Although the amount of H2 produced for both materials is similar, the amount of CO produced by charcoal is twice of that by thermal coal, and accounts for 79% of the total gas weight formed by charcoal. This suggests that a higher rate of carbon oxidation takes place through O2 containing groups within the charcoal, which results in lower char efficiency. It was found that thermal coal produces a significant amount of tar, while a large number of particles in the form of soot/dust escaped from the bulk material during charcoal injection but no tar formation was observed.

Control methods for variations in natural gas composition in air–fuel controlled natural gas engines

In the present study, the countermeasures are proposed to minimize the problem on torque and power output performance and exhaust gas emissions of natural gas engine with use of lower calorific gas. An experiment was conducted to identify thermal efficiency and harmful exhaust gas emission characteristics under partial load conditions in order to improve efficient fuel use in engines affected by the introduction of low calorific gases. A countermeasure for coping with emission gas regulations and preventing thermal efficiency deterioration under rated power operating conditions was then presented. An 11 L six-cylinder turbo-charged engine for city buses compliant with the EURO 6 regulation was used in the experiment, and the results obtained using the reference natural gas fuel were compared with those obtained using simulated low calorific gases. Pure methane (CH 4) was also used to investigate the effects of gas composition changes on thermal efficiency and exhaust gas emissions.When N2 is added or pure CH 4 is used under partial load operating conditions, the combustion rate decreases; consequently, the optimum ignition timing is additionally advanced relative to that obtained when the reference natural gas fuel is used. If the N2 mixing ratio is increased to a minimum of 4.7% under rated power operating conditions, combustion becomes unstable. Stable operation can be secured by increasing the set base fuel amount, 2.35% and 9.41% for pure CH 4 and 8% N2, respectively; however, torque decreases in proportion to the combustion speed of the gas fuel. The strategy of boost pressure control for the torque compensation can minimize the decrease in thermal efficiency.

Measure microbial activity driven oxygen transfer in membrane aerated biofilm reactor from supply side

This short communication demonstrates for the first time a solely microbial activity driven oxygen influx across a microporous hollow fibre membrane via tracking changes in volume and gas composition of entrapped air supply. A U-shape manometer was used to directly reflect gas influx due to microbial activities. A pressure difference of several hundred pascal was created to draw oxygen while 25 mg-N/L of ammonium was oxidized into nitrite by active biofilm at a hydraulic retention time of 6 h. Calibrated and normalized gas compositions before and after the experiment were processed to unveil the gas exchange and estimate the actual oxygen influx across the membrane. A solely microbial activity driven oxygen influx of 10.7 mg O2/m2/h was observed. Measuring oxygen transfer from supply side provides a more straight-forward perspective on the role of active biofilm in membrane aerated biofilm reactor. The capability of the microbial activity to uptake oxygen on its own could potentially lead to greater energy savings in some MABR applications when strict aeration control is not needed.

箱根火山における噴気組成 (CO2/H2S比)変化速度と火山活動強度の関係

箱根火山における噴気組成 (CO2/H2S比)変化速度と火山活動強度の関係

ОСОБЛИВОСТІ СУЧАСНОЇ ГАЗОВОЇ МІГРАЦІЇ У ВУГЛЕПОРОДНИХ МАСИВАХ ДОНЕЦЬКОГО БАСЕЙНУ

Purpose. Investigate the change in indicators of qualitative and quantitative gas composition in coal massifs,when the state of the coal rock massif changes, including in gas-dynamic situations. Methodology. The paper uses traditional structural-geological methods, generalization methods and developed and patented by the authors of the method for determining the gas state of coal massifs on the basis of gas chromatography. Results. The change of the residual gas component in coal massifs is investigated.The stages of change of qualitative and quantitative gas composition in coal massifs at gas – dynamic phenomena are established.The ways of gas migration in coal massifs and technogenic reservoirs are determined.The concept of rate gas saturation of a coal massif, which is controlled by the action of discontinuous tectonics, is introduced. Scientific novelty.For the first time, the conditions for the formation of modern gas-saturated zones in coal massifs due to gas migration and rate gas saturation have been determined.The influence of discontinuous tectonic disturbances on the migration and accumulation of gases in coal massifs has been established. Practical significance. The influence of gas migration on the formation of gas-saturated zones in coal-bearing massifs and man-caused reservoirs of the spent space of operating mines is established,which is important to ensure the safe operation of coal mining enterprises and degassing of coal massifs. Key words: gas-bearing, gas migration, tectonic disturbances, coal massif, man-caused collectors, Donets basin.

Permeability properties of a pressure induced compacted polymer liner in gas cylinder

AbstractThe permeability properties of composite gas cylinders for breathing gas with polymer inner‐liner are investigated. The cylinder wall can be described as a composite membrane consisting of two layers. The permeability properties of the cylinder are presented as permeability coefficient and permselectivity. Deviation from the expected gas components might lead to incidents and potentially harmful situations when breathing gas from a compressed gas cylinder. Hence, gas permeability and potential changes in gas composition, must be considered when choosing cylinder materials. Cases of decompression sickness initiated this study. Experimental data show that pressure and oxygen fraction in the gas cylinder drops and that the permeability coefficient varies depending on the inner pressure. Permeability coefficients of 0.62–0.90 Barrer for oxygen and 0.44–0.56 Barrer for nitrogen are measured. Cracks in the inner‐liner have caused an accentuated drop in of oxygen fraction and pressure.

Thermal Characterization of Pockmarks Across Vestnesa and Svyatogor Ridges, Offshore Svalbard

AbstractThe Svalbard margin represents one of the northernmost gas hydrate provinces worldwide. Vestnesa Ridge (VR) and Svyatogor Ridge (SR) west of Svalbard are two prominent sediment drifts showing abundant pockmarks and sites of seismic chimney structures. Some of these sites at VR are associated with active gas venting and were the focus of drilling and coring with the seafloor‐deployed MARUM‐MeBo70 rig. Understanding the nature of fluid migration and gas hydrate distribution requires (among other parameters) knowledge of the thermal regime and in situ gas and pore fluid composition. In situ temperature data were obtained downhole at a reference site at VR defining a geothermal gradient of ~78 mK m−1 (heat flow ~95 mW m−2). Additional heat probe data were obtained to describe the thermal regime of the pockmarks. The highest heat flow values were systematically seen within pockmark depressions and were uncorrelated to gas venting occurrences. Heat flow within pockmarks is typically ~20 mW m−2 higher than outside pockmarks. Using the downhole temperature data and gas compositions from drilling we model the regional base of the gas hydrate stability zone (BGHSZ). Thermal modeling including topographic effects suggest a BGHSZ up to 40 m deeper than estimated from seismic data. Uncertainties in sediment properties (velocity and thermal conductivity) are only partially explaining the mismatch. Capillary effects due to small sediment grain sizes may shift the free gas occurrence above the equilibrium BGHSZ. Changes in gas composition or pore fluid salinity at greater depth may also explain the discrepancy in observed and modeled BGHSZ.

Influence of the Active Screen Plasma Power during Afterglow Nitrocarburizing on the Surface Modification of AISI 316L

Active screen plasma nitrocarburizing (ASPNC) increases the surface hardness and lifetime of austenitic stainless steel without deteriorating its corrosion resistance. Using an active screen made of carbon opens up new technological possibilities that have not been exploited to date. In this study, the effect of screen power variation without bias application on resulting concentrations of process gas species and surface modification of AISI 316L steel was studied. The concentrations of gas species (e.g., HCN, NH3, CH4, C2H2) were measured as functions of the active screen power and the feed gas composition at constant temperature using in situ infrared laser absorption spectroscopy. At constant precursor gas composition, the decrease in active screen power led to a decrease in both the concentrations of the detected molecules and the diffusion depths of nitrogen and carbon. Depending on the gas mixture, a threshold of the active screen power was found above which no changes in the expanded austenite layer thickness were measured. The use of a heating independent of the screen power offers an additional parameter for optimizing the ASPNC process in addition to changes in the feed gas composition and the bias power. In this way, an advanced process control can be established.