Changes In Gas Composition Research Articles

Seasonal variations of geofluids from mud volcano systems in the Southern Junggar Basin, NW China

Variations in the chemical composition of geofluids and of gas fluxes are significant parameters for understanding mud volcanism and correctly estimate their emissions in carbon species, particularly greenhouse gas, methane. In this study, muddy water and gas samples were collected from the Anjihai, Dushanzi, Aiqigou, and Baiyanggou mud volcanoes in the southern Junggar Basin during the four seasons, around a year. This region hosts the most active mud volcanism throughout China. Gas and water were analyzed for major molecular compositions, carbon and hydrogen isotopes of the gas phase, as well as cations and anions, hydrogen and oxygen isotopes of water. The emitted gases are dominated by CH4 with some C2H6, CO2, and N2. The seasonal changes in the chemical composition and carbon isotopes of emitted gases are not significant, whereas clear variations in the amounts of cations and anions dissolved in the water are reported. These are higher in spring and summer than autumn and winter. The CH4, CO2, and C2H6 fluxes are 157.3–1108 kg/a, 1.8–390.1 kg/a, and 10.2–118.7 kg/a, respectively, and a clear seasonal trend of the gas seepage flux has been observed. In January, the macro-seepage flux of open vents is ≥65 % higher than in April, whereas the micro-seepage flux significantly decreased, probably due to the frozen shallow ground and blockage of soil fractures around the vents by heavy snow and ice during January. This probably causes an extra gas pressure transferred to the major vents, resulting in higher flux of the macro-seepage in the cold season. However, the total flux of the whole mud volcano system is generally consistent around a year.

Fundamental study of the integrated process of heavy oil pyrolysis and coke gasification. Part Ⅰ: Effect of CO and H2 in syngas atmosphere on heavy oil pyrolysis

An integrated process of heavy oil pyrolysis and coke gasification was proposed to realize the in-situ gasification of coke and provide syngas (CO/H2) atmosphere for heavy oil pyrolysis to obtain high-quality liquid products. To reveal the reaction mechanism of syngas (CO/H2) on heavy oil pyrolysis, the pyrolysis characterizations of three heavy oils including Dagang slurry oil (DG-SO), Qingdao vacuum residue (QD-VR) and Canadian oil-sands bitumen (CA-OB) were evaluated at different atmospheres (N2, CO, CO/H2, and H2). The results showed that compared with QD-VR and CA-OB, DG-SO with high content of aromatics but high Conradson carbon residue (CCR) value was not suitable for the integrated process of heavy oil pyrolysis and coke gasification. Compared with the N2 atmosphere, the pyrolysis oil yields of DG-SO, QD-VR, and CA-OB increased in turn under CO, CO/H2, and H2 atmospheres. On the contrary, their coke and gas yields decreased in turn. Furthermore, the contents of CH4, C2-C5, and CO2 in pyrolysis gases all decreased in turn, while the contents of their alkane, olefin, aromatic hydrocarbon, and oxygen /nitrogen/sulfur compounds in pyrolysis oil increased in turn. The change of oil and gas composition indicated that compared with N2, both CO and H2 could inhibit further decomposition of liquid products. The reactivity of coke showed that CO and H2 could reduce the degree of condensation of coke to increase its reactivity, but the effect of CO was not as good as that of H2.

Comprehensive gas analysis of a 21700 Li(Ni0.8Co0.1Mn0.1O2) cell using mass spectrometry

The failure of lithium-ion batteries (LIBs) can be partly defined by the release of toxic and flammable gases. The composition and volume of these gases varies depending on cell type, failure mechanism, state of charge (SoC) and environmental oxygen (O2) levels. Understanding this relationship and the species produced is essential for battery pack manufacturers relying on real-time monitoring to assess the state-of-health (SoH) of a LIB. It also has ramifications for emergency responders attending thermal runaway (TR) events. In this work, NMC-811 21700 cells were overheated, and the resulting gas analysed in real-time using mass spectrometry (MS). Repeat tests were conducted to account for variability. Work has been carried out to both quantify the volume of gas produced and investigate how gas composition changes during different stages of cell failure. Tests were conducted at 5–100% SoC. Results showed that during safety venting (SV), the major constituent gas is methane (CH4), which was positively correlated with SoC. In contrast, during TR the gas mixture contains hydrogen (H2), carbon dioxide (CO2) and carbon monoxide (CO). Further analysis to quantify gas volumes show a 3 to 5-fold increase, in both air and nitrogen (N2) atmospheres, when SoC is increased from 25% to 100%.

Effects of primary air velocity on co-combustion characteristics of bituminous coal and semicoke under reducing-to-oxidizing environment

This study evaluated the effect of primary air velocity (PAV) on the ignition characteristics of bituminous coal and semicoke mixture (1:1, wt%) in a reducing-to-oxidizing environment (R-O) in a 300-kW pilot-scale furnace that characterized the ignition behaviors of pulverized coal (PC) furnaces. The early ignition characteristics of the primary combustion zone (PCZ), including ignition distance, ignition mode, flame stability and kinetic parameters, were studied. The results showed that the difference in ignition delays obtained from the flame temperature and O2 profiles indicated that convection heating was more important than radiant heating for fuel ignition. The transformation of the ignition mode from non-homogeneous to homogeneous with the increase in PAV was confirmed by the changes of flame temperature, residues, and flue gas composition. Flame stability was optimized by the earlier appearance of the continuous flame boundary and was the best at a PAV of 18 m/s. A simplified first-order kinetic model based on the CO2 evolution profile was established to calculate the reaction rate of the blended fuel during ignition, and the experimental char burnout ratio was consistent with the predicted result. For the potential application of co-firing bituminous coal with a large proportion of semicoke, the recommended PAV may be no more than 22 m/s.

Changes in quality characteristics of fresh blueberries: Combined effect of cultivar and storage conditions

The influences of two storage conditions (regular atmosphere-RA and modified-atmosphere packaging-MAP) and different storage time on fruit textural parameters, chemical composition, and total quality index (TQI) of two blueberry cultivars were investigated. Freshly harvested fruit of mid and late season cultivars (‘Bluecrop’ and ‘Liberty’, respectively) were placed in plastic punnets, packed into low-density polyethylene bags of 25 µm thickness with two perforations of 3 mm and stored at 2 °C and 90% relative humidity for 30 days, either in RA or in MAP. Changes in gas composition inside the package and fruit quality characteristics were analyzed at 10-day intervals during storage: 0, 10, 20, and 30 days. ‘Liberty’ was dominant over ‘Bluecrop’ in terms of hardness (428 g and 296 g, respectively), as well as individual and total sugars (100 and 76 g·kg–1, respectively), organic acids (19 and 12 g·kg–1, respectively) and most subclasses of phenolic compounds (anthocyanins, flavonols, and hydroxycinnamic acids). In addition, a novel mathematical index of TQI was introduced to compare all evaluated parameters in order to obtain a quantitative single score, as an indicator of overall fruit quality. ‘Liberty’ had the better TQI score in RA, whereas ‘Bluecrop’ behaved better in MAP. Accordingly, for longer storage of blueberry fruit MAP should not be assumed to be uniformly helpful, since the effect of storage duration in the specific type of atmosphere substantially depends on the proper cultivar selection.

Seismic characterization and modelling of the gas hydrate system in the northern Bay of Bengal, offshore Bangladesh

The offshore Bangladesh includes the northern Bengal fan, where sediment supply from the Ganges and Brahmaputra rivers has resulted in the accumulation of up to 20 km of shallow-marine, fluvio-deltaic and slope sediments that have accumulated during rapid tectonic subsidence since the late Miocene. The high sedimentation rates, along with high organic matter content, make this area favorable for the formation of natural gas from both microbial and thermogenic sources. Here we use multichannel seismic reflection profiles and modelling of the gas hydrate stability zone (GHSZ) to present the first evidence for the occurrence of natural gas hydrate in the offshore Bangladesh. First, we analyze the sediments of the shelf and slope areas, which are characterized by downslope sediment transport features and by the presence, in places, of faults/fractures as well as widely distributed amplitude anomalies and seismic facies that we relate to the presence of gas. A high-amplitude reversed polarity reflection of variable continuity that mimics the seafloor and cross-cut stratigraphy is interpreted as a Bottom Simulating Reflector (BSR). The BSR is observed in several areas that are predominantly located in the E-SE of the study area, in water depths of 1300–1900 m and at depths below seafloor of 250–440 m. Sediments above BSR locations generally show higher seismic interval velocities reaching values of ∼1920–1940 m/s, which are consistent with the presence of gas hydrate in shallow marine sediments. Furthermore, the BSR lies at approximately the same depth as the theoretical base of the gas (methane) hydrate stability zone (BGHSZ), calculated assuming a 3.5 % wt pore water salinity and using existing geothermal gradient and seafloor temperature data from the study region. However, in places, the BSR lies deeper or shallower than the base of the modelled BGHSZ. These discrepancies include areas where faults/fractures and seismic evidence linked to fluid flow from deeper reservoirs reach the GHSZ disrupting its stratigraphic continuity. At these locations, we suggest that faults/fractures act as fluid migration pathways causing localized heat-flow perturbations and/or changes in the hydrate-forming gas composition both likely affecting the depth of the GHSZ. Our results provide the first evidence of the gas hydrate potential in the offshore Bangladesh and should drive future research and data acquisition aiming to understand the composition, saturation and thickness of the gas hydrate-bearing sediments in this region.

Fluid dynamic simulation of CrO2(OH)2 volatilization and gas phase evolution during the oxidation of a chromia forming alloy

The influence of the chromia volatilization on the oxidation kinetics of Inconel 625 was investigated at 900 °C under flowing wet air (74%N2-18.5%O2-7.5%H2O) through an interdisciplinary approach, coupling experiments and gas phase simulation. Oxidation tests showed a strong decrease in the volatilization rate of lined-up samples from the inlet to the outlet of a horizontal tubular furnace. Gas phase simulation allowed to relate it to an increase in the CrO2(OH)2 partial pressure along the tube. Considering gas composition changes appears as essential to provide correct interpretation of oxidation test results in humid and oxidizing environments.

Geomagnetic Storm Effect on F2-Region Ionosphere during 2012 at Low- and Mid-Latitude-Latitude Stations in the Southern Hemisphere

The ionospheric effects of six intense geomagnetic storms with Dst index ≤ −100 nT that occurred in 2012 were studied at a low-latitude station, Darwin (Geomagnetic coordinates, 21.96° S, 202.84° E), a low-mid-latitude station, Townsville (28.95° S, 220.72° E), and a mid-latitude station, Canberra (45.65° S, 226.30° E), in the Australian Region, by analyzing the storm–time variations in the critical frequency of the F2-region (foF2). Out of six storms, a storm of 23–24 April did not produce any ionospheric effect. The storms of 30 September–3 October (minimum Dst = −122 nT) and 7–10 October (minimum Dst = −109 nT) are presented as case studies and the same analysis was done for the other four storms. The storm of 30 September–3 October, during its main phase, produced a positive ionospheric storm at all three stations with a maximum percentage increase in foF2 (∆foF2%) of 45.3% at Canberra whereas during the recovery phase it produced a negative ionospheric storm at all three stations with a maximum ∆foF2% of −63.5% at Canberra associated with a decrease in virtual height of the F-layer (h’F). The storm of 7–10 October produced a strong long-duration negative ionospheric storm associated with an increase in h’F during its recovery phase at all three stations with a maximum ∆foF2% of −65.1% at Townsville. The negative ionospheric storms with comparatively longer duration were more pronounced in comparison to positive storms and occurred only during the recovery phase of storms. The storm main phase showed positive ionospheric storms for two storms (14–15 July and 30 September–3 October) and other three storms did not produce any ionospheric storm at the low-latitude station indicating prompt penetrating electric fields (PPEFs) associated with these storms did not propagate to the low latitude. The positive ionospheric storms during the main phase are accounted to PPEFs affecting ionospheric equatorial E × B drifts and traveling ionospheric disturbances due to joule heating at the high latitudes. The ionospheric effects during the recovery phase are accounted to the disturbance dynamo electric fields and overshielding electric field affecting E × B drifts and the storm-induced circulation from high latitudes toward low latitudes leading to changes in the natural gas composition [O/N2] ratio.

Measurement and Numerical Simulation of Coal Spontaneous Combustion in Goaf under Y-type Ventilation Mode.

In the process of advancing the working face, the temperature rise and oxidation characteristics of residual coal in goaf and the prediction of index gas are of great significance to mine fire prevention and safety production. Based on the coal spontaneous combustion test, the oxygen consumption and heat release characteristics of coal spontaneous combustion were analyzed by taking coal samples at the working face and carrying out temperature-programmed experiments in the laboratory. The characteristic temperature and index gas of coal spontaneous combustion were determined as the judgment bases of “three zones” of spontaneous combustion in goaf, and the influencing factors of coal spontaneous combustion in goaf under Y-type ventilation were analyzed. Based on the test results, the changes of gas composition in goaf during the advancing of the W1310 working face were monitored. According to the actual situation of the W1310 working face in the Gaohe energy mine of Lu’an group, the multifield three-dimensional numerical simulation calculation and analysis of gas composition in goaf were carried out, and the distribution of oxygen concentration field in goaf under different air volume ratios of machine roadway and air roadway was studied. Through the analysis of the parameters of porous media in the goaf, combined with the actual situation, the user-defined function was compiled for the key parameters such as porosity, viscous resistance coefficient, and inertial resistance coefficient of porous media in the goaf. The three-dimensional seepage field, gas concentration field, oxygen concentration field, and pressure field of the gas components in goaf during the advancement of the goaf working face were simulated. The comparison of the numerical simulation results with the field-measured results shows good agreement. In order to consider safety, the numerical simulation results with a wide oxidation temperature rise zone are used for linear regression, and the regression equation is used to dynamically determine the O2 concentration at a point away from the goaf and to determine the “three-zone” state of the point, which is of great significance to guide the progress of the working face and safe production.

Matlab implementation of a novel semi-structured kinetic model for methanotroph-photoautotroph cocultures

This paper presents the matlab implementation details of a novel semi-structured kinetic model for methanotroph-photoautotroph cocultures. This includes the parameterization of the modeling equations, and the initialization of the simulation based on experimental conditions. More importantly, it provides details on how the differential equations governing mass balances in both gas and liquid phases are integrated together to simulate the system dynamics over time. The semi-structured kinetic model for methanotroph-photoautotroph coculture is validated using a wide range of experimental conditions. The model:•Accurately predicts both the coculture growth in liquid phase and the gas composition changes in head space over time.•Explicitly models the exchange of in situ produced O2 and CO2 within the coculture.•Considers the self-shading effect on the growth of photoautotroph.

Influence of Respiratory Gas Density on Tidal Volume during Mechanical Ventilation: A Laboratory Investigation and Observational Study in Children

Fluid mechanics show that high-density gases need more energy while flowing through a tube. Thus, high-density anesthetic gases consume more energy to flow and less energy for lung inflation during general anesthesia. However, its impact has not been studied. Therefore, this study aimed to investigate the effects of high-density anesthetic gases on tidal volume in laboratory and clinical settings. In the laboratory study, a test lung was ventilated at the same pressure-controlled ventilation with 22 different gas compositions (density range, 1.22-2.27 kg/m3) using an anesthesia machine. A pneumotachometer was used to record the tidal volume of the test lung and the respiratory gas composition; it showed that the tidal volume of the test lung decreased as the respiratory gas density increased. In the clinical study, the change in tidal volume per body weight, accompanied by gas composition change (2% sevoflurane in oxygen and with 0-30-60% of N2O), was recorded in 30 pediatric patients. The median tidal volume per body weight decreased by 10% when the respiratory gas density increased from 1.41 kg/m3 to 1.70 kg/m3, indicating a significant between-group difference (P < 0.0001). In both settings, an increase in respiratory gas density decreased the tidal volume during pressure-controlled ventilation, which could be explained by the fluid dynamics theory. This study clarified the detailed mechanism of high-density anesthetic gas reduced the tidal volume during mechanical ventilation and revealed that this phenomenon occurs during pediatric anesthesia, which facilitates further understanding of the mechanics of ventilation during anesthesia practice and respiratory physiology.

Hydrogen production by steam gasification of Hungarian brown coal char

Presently, the hydrogen is mainly generated from fossil fuels (natural gas and coal). The thermochemical conversion processes of carbon-based materials to hydrogen-rich gas has been widely described in the literatures. In which, the steam gasification is highly recommended for this purpose. The experimental steam gasification of Hungarian brown coal char was conducted in a single stage fixed-bed reactor with 80 mm of inner diameter and 1,200 mm of effective length. The experiments were carried out at 700, 800 and 900 °C of gasification temperature within 5 g/min of steam flow rate and 5, 7.5 and 10 g/min of steam flow rate within 900 °C of gasification temperature. The aim of this study is to determine the performance of Hungarian brown coal char during the gasification with the variation of gasification temperature and steam flow rate, as well as the hydrogen production during the gasification process. The gasification temperature plays an important role in the conversion process in the gasifier, as well as the change in the synthesis gas composition. The introduction of higher steam flow rate can also improve the reduction process. The highest total hydrogen yield of 1.8 Nm3 was gained at 900 °C of gasification temperature and 10 g/min of steam flow rate for 3 kg of initial coal.

Assessment of pulmonary hemodynamics and stress-induced pulmonary hypertension in clinical practice

Pulmonary hypertension (PH) is currently determined by the mean pulmonary artery pressure (PAPmean) increase, which in turn is associated with a number of parameters, such as cardiac output (CO), pulmonary vascular resis-tance (PVR) and left atrial pressure. Therefore, changes in PAP mean during exercise cannot be discussed apart from the listed indicators. Probably, this was one of the reasons for the absence of an accurate hemodynamic de-termination of stress-induced PH. However, today it has been revealed that PAP at rest increases only when ≥50% of pulmonary microcirculation is off, and for the earliest detection of the problem it is advisable to use factors that lead to increase of CO and PVR, one of them is exercise. Moreover, clinicians often observe that the anamnesis of PH starts from complaints, associated with exercise. Mo-dern non-invasive technologies (stress-echocardiogra-phy, cardiopulmonary exercise testing) provide very de-tailed data not only about the pulmonary circulation, but also about ventilator function, blood gas composition, structural and functional changes in the heart. Stress-in-duced PH is defined as combination of normal mean pulmonary artery pressure values (PAPmean &lt;25 mm Hg) at rest and increase of PAPmean &gt;30 mm Hg during exercise, as well as PVR &gt;3 WU, however, this definition isn’t generally accepted. As an alternative, to determine stress-induced PH, it was proposed to evaluate PAPmean/CO curve, that excludes the influence of peak hemody-namic parameters. The pulmonary vessels distensibility and ventriculo-arterial coupling represent promising pa-rameters for complete characterization of the pulmonary circulation changes during exercise.

Change of existing circulating fluidized bed boilers to oxy-firing conditions for CO2 capture

This work investigates a circulating fluidized bed boiler, originally designed for air-firing, retrofitted to oxy-firing with the purpose of removing the CO2 emission from coal combustion. Previous studies have shown that the heat balance on the gas-particle side can be satisfied without changes in the boiler, but then the volume flow of gas is reduced. To retain the operation like that during air-firing, the volume flow, that is the fluidization velocity, in oxy-firing should be equal to that in air-firing. It is the main purpose of this work to determine the conditions for the transition from air to oxy-firing, while the heat transfer conditions are maintained at a constant fluidization velocity. Measures to achieve this, such as adjusting the supply of additional gas and the heat transfer surface, are analysed. The fulfilment of the furnace's heat balance requires extra fuel or reduction of the heat-transfer surface in the furnace. These changes affect the performance of the back pass, which must be modified to accommodate the change in gas composition and the higher sensible heat content of the flue gas. Strategies to deal with these circumstances in CFB boilers are discussed.

Jet characteristics of CO2–O2 mixed injection using a dual-parameter oxygen lance nozzle for different smelting periods

Abstract The jet performance of an oxygen lance nozzle influences the smelting rhythm, smelting index, and energy consumption of a converter. Due to the complexity of the process of converter smelting, the changing temperature and gas composition in the converter significantly impact the jet characteristics of the oxygen lance nozzle in the smelting process; however, research on the change law of jet characteristics in different smelting periods is limited. In this study, we used Ansys Fluent 17.0, which is commercially available fluid simulation software, to simulate the variation of jet characteristics of a mixed injection comprising 6% CO2 and 94% O2; the mixed injection was tested using a dual-parameter oxygen lance nozzle in the early, middle, and late stages of smelting. The results show that the increase of CO concentration and ambient temperature in the converter lead to a decrease in the attenuation rate of jet velocity, improved independence of multiple jets, and an increase in the impact area of jets on the molten pool. Thus, when designing and employing oxygen lance nozzles, the influence of ambient temperature and furnace gas composition on jet characteristics must be considered.

An Analytical Two-Phase Flow Model for Prediction of Leakage in Wet Gas Labyrinth Seals and Pocket Damper Seals. Is Simplicity Still Desired?

Abstract Current and upcoming two-phase pump and compression systems in subsea production facilities must demonstrate long-term operation and continuous availability. Annular pressure seals, limiting secondary flow, also influence the dynamic stability of turbomachinery. Hence, it becomes paramount to quantify the leakage and dynamic force coefficients of annular seals operating with two-phase flow, a liquid in gas mixture or wet gas. Until now, a simple model for labyrinth seals (LSs) and the more modern pocket damper seals (PDSs) is not available, though these seal types find wide applications in subsea machinery. The paper develops a simple analytical model predicting the leakage and cavity pressures for LSs and PDSs operating with two-phase flow. The model adapts Neumann’s leakage equation for use with the physical properties of a homogeneous two-phase flow mixture. Predictions of leakage for a four-blade, eight-pocket, fully partitioned PDS operating under a low supply pressure (PS = 2.3 bar and 3.2 bar) and a low rotor speed equal to 5250 rpm (surface speed = 35 m/s) agree well with experimental results procured for both a pure gas and a wet gas conditions (2.2% in liquid volume). Predicted leakage and cavity pressures also agree with those found by a multimillion node computational fluid dynamics (CFD) model. For an eight-blade, sixteen-pocket PDS supplied with air at PS = 62.1 bar, discharge pressure Pa = 31.1 bar, and rotor speed of 15 krpm (surface speed = 91 m/s), the analytical model predicts leakage that is just 2% larger than a published CFD prediction. For the PDS supplied with an oil in gas mixture having gas volume fraction βS = 0.92–0.98, the simple model delivers leakage that is up to ∼6% lower than published CFD results. An analysis of the two-phase leakage predictions via a modified flow factor reveals a loss coefficient (cd) impervious to the range of supply and discharge pressures considered and growing in proportion to the liquid volume fraction (LVF). Throughout the life of an oil well that sees radical changes in gas and liquid composition as well as pressure conditions, the expedient model, quick and accurate to estimate leakage in wet gases seals, can be readily integrated into an engineering routine or practice.

Integrating flare gas with cogeneration system: Hazard identification using process simulation

Flare gas integration with a cogeneration plant benefits from utilizing waste gases containing high heating value hydrocarbons as a supplemental fuel to the boilers. A key challenge in integrating flare gas with a cogeneration system is the need to ensure operational safety and satisfactory performance.Conventional hazard identification techniques require collective team knowledge, experience, and information about the process. Because of the limited information on a new flare gas integrated cogeneration plant, unawareness of warning signals, inability to predicts specific atypical scenarios, or general limitations in organizational systems, it is possible for the evaluation team to miss potential risks associated with the process. To overcome these limitations, this paper proposes a model to identify process hazards through process simulation, sensitivity analysis, and data evaluation during the initial stages of process design. The model uses commercial software Aspen HYSYS for process simulation. In sensitivity analysis, manipulated variables are systematically selected based on scenario predictive methods, and the variations in the processes are analyzed using linear regression models to develop quantitative insights without information loss.The model investigated the effect of variable flare gas conditions and their quality on the existing fired gas boiler. Results showed that the flare gas temperature has a nominal effect on the process. However, changes in flare gas composition - high hydrogen carryover (above 70 mol% with CH4 or above 40 mol% with C2H4) can affect the boilers radiation zone temperature and combustion profile inside the firebox. If not prevented, these events can further amplify to loss-control events such as flame impingement, firebox instability, steam explosion, and tube rupture.

Non-injective gas sensor arrays: identifying undetectable composition changes

Metal-organic frameworks (MOFs) are nanoporous materials with good prospects as recognition elements for gas sensors owing to their adsorptive sensitivity and selectivity. A gravimetric, MOF-based sensor functions by measuring the mass of gas adsorbed in a MOF. Changes in the gas composition are expected to produce detectable changes in the mass of gas adsorbed in the MOF. In practical settings, multiple components of the gas adsorb into the MOF and contribute to the sensor response. As a result, there are typically many distinct gas compositions that produce the same single-sensor response. The response vector of a gas sensor array places multiple constraints on the gas composition. Still, if the number of degrees of freedom in the gas composition is greater than the number of MOFs in the sensor array, the map from gas compositions to response vectors will be non-injective (many-to-one). Here, we outline a mathematical method to determine undetectable changes in gas composition to which non-injective gas sensor arrays are unresponsive. This is important for understanding their limitations and vulnerabilities. We focus on gravimetric, MOF-based gas sensor arrays. Our method relies on a mixed-gas adsorption model in the MOFs comprising the sensor array, which gives the mass of gas adsorbed in each MOF as a function of the gas composition. The singular value decomposition of the Jacobian matrix of the adsorption model uncovers (i) the unresponsive directions and (ii) the responsive directions, ranked by sensitivity, in gas composition space. We illustrate the identification of unresponsive subspaces and ranked responsive directions for gas sensor arrays based on Co-MOF-74 and HKUST-1 aimed at quantitative sensing of CH4/N2/CO2/C2H6 mixtures relevant to natural gas sensing.

Effect of CO2 injection on CH4 desorption rate in poor permeability coal seams: An experimental study

CO2 injection into coal seams is an effective way for reducing greenhouse gas emissions and increasing gas recovery in coal seams. To study the influence rule of CO2 injection on the CH4 desorption rate, an experimental system of CO2 displacing CH4 was used to analyse the changes in gas composition, outlet flow rate, coal seam temperature, and displacement efficiency parameters during CO2 injection. From the perspective of enhancing CH4 recovery, the CO2 critical injection amount (Vinc) is 297.4 L and critical injection time is 188.75 min. When the CO2 injection amount V < Vinc, the amount of CH4 desorption, CO2 storage, and CH4/CO2 gas content all increased. When V > Vinc, except CH4 desorption amount remained almost unchanged, the other parameters increased. In the process of CO2 displacing CH4, the coal seam temperature rises (exothermic process), showing a law of “hierarchical displacement”. With the injection of CO2, the pore pressure first decreased and then increased, the CH4 partial pressure decreased, and the effective diffusion coefficient first increased and then decreased. After the injection of CO2, the desorption time of CH4 was 269.45min earlier and the desorption rate of CH4 was increased by 12.43 %.

Investigation on a parking control strategy for automotive proton exchange membrane fuel cell

AbstractIn the proton exchange membrane fuel cell (PEMFC) for vehicles, the changes in gas composition and oxygen accumulation may exist during the parking process even by using a shut‐down strategy of oxygen consumption, which can lead to the hydrogen/air interface. However, this process of oxygen accumulation is often ignored. Thus, in this work, the diffusion rate of the gas, the gas composition changes, and the starting voltage of the PEMFC stack are discussed. According to the experiment, it is proved that the poor gas tightness of the stack results in the formation of the oxygen inside the stack during the parking process and the threshold parking time of no hydrogen inside the stack is above 1 h. Then, a parking control strategy is proposed by injecting hydrogen into the anode, and the hydrogen injection cycle is set as 1 h by the anodic hydrogen concentration. Based on the strategy, the starting voltage of the fuel cell is declined from 18 V to 3 V. That means the hydrogen/air interface is declined. Therefore, the durability of the PEMFC for vehicles can be enhanced.