Effect Of Water Vapor Research Articles

Effect of Water Vapor and Hydrogen Concentration on Power Generation Characteristics of Protonic Ceramic Fuel Cell

The proton and hole conductivities of BaZrO3-based perovskites depend on partial pressures of oxygen and water vapor. These conductivities affect the power generation characteristics of Proton Ceramic Fuel Cells (PCFCs) using the perovskite as an electrolyte. In this study, the effect of humidification conditions on the power generation characteristics of an anode-supported PCFCs was investigated.The configuration of the anode-supported PCFC was La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode/BaZr0.8Yb0.2O3-δ(BZYb) electrolyte/Ni-BZYb anode. The diameter of the effective cathode area was approx. 10 mm. The cathode gas composition was fixed at 97% concentration of air and 3% concentration of water vapor. The concentration of water vapor in the anode gas was controlled to be 3-69%. The current density-voltage characteristics and AC impedance were measured by Bio-Logic SP-150.In all water vapor concentration conditions, the cell showed the highest OCV (approximately 1 V) at 3% concentration of water vapor. However, the maximum power density was highest at 30% concentration of water vapor (346 mW/cm2). The highest maximum power density at 30% concentration of water vapor can be explained by the following reason. The OCV values decrease with increasing the concentration of water vapor because of decreasing the concentration of hydrogen. On the other hand, from the results of impedance measurements, the ohmic resistance of the cell decrease with increasing the concentration of water vapor because of increase of proton conductivity of the cell. Thus, the increase of cell voltage by increase of proton conductivity should be higher than the decrease of OCV values.【Acknowledgements】This presentation is the result of the research and development of ultra-efficient proton-conducting ceramic fuel cell devices, JPNP20003, funded by the New Energy and Industrial Technology Development Organization (NEDO), Japan. We would like to express our gratitude to all parties involved.

The Influence of Water Concentration on High-Temperature Reactive Evaporation and Condensation of Cr in 800°C Air

Deleterious reactive evaporation of chromium from stainless steels commonly used in solid oxide electrochemical systems is well-documented; however, interactions between Cr vapor species and surrounding interfaces during complex and dynamic system exposures is poorly understood. Understanding the interactions between Cr vapor species and downstream components during operation is critical for improving system performance and safeguarding environmental, health and safety, as many condensed Cr compounds contain toxic and carcinogenic hexavalent chromium Cr(VI). Furthermore, the interactions between volatilized Cr species and surrounding interfaces are dependent upon dynamic chemical environments. The objective of this study is to systematically investigate and report on condensation pathways of Cr vapors within representative system environments with variable water concentrations. To accomplish this objective, an experimental platform was designed to generate Cr vapor species from the reactive evaporation of chromia (Cr2O3) powder with high-temperature (>1100 K) air/H2O mixtures, and expose downstream ceramic insulation materials (e.g., aluminosilicate fibers) at reduced temperatures (<600 K). Insulation material chemical compositions investigated include pure silica (SiO2) and alumina (Al2O3) to combinations thereof with and without inclusions of alkaline earth metals (e.g., Ca, Mg, Sr). Materials are studied as a function of exposure conditions using complementary materials characterization tools such as SEM-EDX, XPS, and diphenyl carbazide reactions to assess Cr(VI) concentrations. Reactive evaporation of Cr from chromia occurs in the presence of oxygen and/or water vapor to form various Cr-containing vapor species. Thermodynamic data reveals an equilibrium partial pressure increase of several orders of magnitude at elevated (>500 K) temperatures for all Cr vapor species. In the presence of water vapor, the partial pressure of Cr oxyhydroxide (CrO2(OH)2(g)) is greater by many several orders of magnitude and becomes the dominant species up to ~1500 K. The research objective is to explore effects of water vapor in air on Cr condensation and speciation on different ceramic insulation materials. The experimental setup thus far has exposed aluminosilicate fibers to volatilized Cr species from Cr oxide powder at 1100 K for 150 hours under varying water vapor conditions: 0 vol%(dry), 3 vol%, and 10 vol% H2O. Preliminary results show an increase in Cr(VI) formation on fibers exposed to volatile Cr species as water vapor content increases. See Figure 1 for an overview of the experimental concept, Cr(VI) test kit, and preliminary results for dependency on water vapor. Analyses of these results will be presented and discussed in context of potential implications for SOFC/SOEC systems. Figure 1

Influence of Temperature and Water Vapour on the High-Temperature Oxidation and Cr Evaporation Behaviour of High-Cr Alloys for SOFC Cathode Air Pre-Heaters

Chromium evaporation and oxide scale growth are among the key degradation mechanisms associated with Solid Oxide Fuel Cells (SOFCs). It is often underestimated how the cathode air pre-heater (CAPH) made of high Cr-containing alloys in SOFC systems can contribute to cathode degradation. This study examines the effect of exposure temperature and water content on both degradation mechanisms in Inconel 625, SS309 and AluChrom 318. For the influence of water content, samples of Inconel 625, SS309 and AluChrom 318 were isothermally exposed at 850°C in dry air and air containing 1%, 3% and 9% of H2O at a high flow rate for 168 hours. For the influence of temperature, samples of Inconel 625, SS309 and AluChrom 318 were isothermally exposed at 650°C, 750°C and 850°C in a 6.0 L/min air stream containing 3% H2O for 168 hours. The evaporated Cr (VI) species were collected using the denuder technique. The formed oxide scales were subsequently analysed using XRD and SEM/EDX. The results of the surface characterisation indicated that the oxide scales formed on Inconel 625, SS309 and AluChrom 318 at high temperatures were Cr2O3, (Cr,Mn)3O4 spinel and Al2O3, respectively.The results of this study show that Cr evaporation and oxidation rates were dramatically reduced at the lower temperature used for Inconel 625 and SS309. AluChrom 318 exhibited an increased oxidation rate with increasing temperature, but it demonstrated a reverse trend to the temperature dependent Cr evaporation compared to Inconel 625 and SS309. It was also found that the amount of Cr evaporated from an alloy solely depended on the partial pressure of Cr presented on the oxide surface. At 850°C, the total mass of evaporated Cr(VI) species was found as follows: Cr2O3 (Inconel 625) > (Cr,Mn)3O4 spinel (SS309) >> Al2O3 (AluChrom 318). However, at 650 and 750°C, the total mass of evaporated Cr(VI) species was found to be: (Cr,Mn)3O4 spinel (SS309) > Cr2O3 (Inconel 625) > > Al2O3 (AluChrom 318). The significant effect of water vapour on the three tested materials appeared to be the further enhancement of Cr2O3 evaporation. At 850°C, the amount of evaporated Cr2O3 from the alloys exposed at the same humidity level corresponded to the Cr partial pressure on the surface, as follows: Cr2O3 (Inconel 625) > (Cr,Mn)3O4 spinel (SS309) > Al2O3 (AluChrom 318). The water vapour slightly increased the growth rate of Cr2O3 and (Cr,Mn)3O4 spinel formed on the Inconel 625 and SS309 surface, respectively. However, no evidence of change in the growth rate of the alumina on AluChrom 318 under the influence of water vapour in oxidising atmosphere was observed for the tested period in this study. Figure 1

Quantitative attribution of the temperature associated with winter extreme cold events in China

Extreme cold events exert enormous impacts on the ecosystems and human health. A quantitative attribution analysis of the surface temperature anomalies associated with extreme cold events in China is conducted using an updated version of the coupled atmosphere-surface climate feedback response analysis method. For both extreme warm and cold years, the effects of anomalous surface albedo, water vapor, atmospheric dynamics, and aerosols are the major positive contributors, and the processes associated with surface dynamics provide a major negative effect. Specifically, the effect of surface albedo (water vapor) is directly linked to the change in local snow cover (precipitable water) over China. More local snow cover (precipitable water) provides a cooling (warming) effect and vice versa. The process associated with atmospheric dynamics exhibits an asymmetric contribution for the extreme warm and cold years. It provides a warming effect over most of China in the extreme warm years, which is possibly related to the nation-wide warm air advection. On the other hand, the effect of atmospheric dynamics displays large regional and year-to-year variations for the cold cases. In addition, a considerable impact of anthropogenic aerosols is detected over central-southern China, which is possibly related to the emission reduction policies in China since 2013. Although clouds show only a moderate impact on the national-averaged temperature anomalies, they provide a considerable effect over southern China.

Titanium-based metal-organic-framework-coated SnO2 nanowires with enhanced NO2 gas sensing capability in humid environment

Herein, the NO2 gas sensing features of SnO2 nanowires (NWs) and titanium-based metal–organic framework 901 (MOF-901)-coated SnO2 NWs were investigated. Both gas sensors showed excellent selectivity to NO2. At 200 °C, the responses of SnO2 NWs and MOF-901-coated SnO2 NWs to NO2 (10 ppm) were 9.7 and 8.2, respectively. However, in a humid atmosphere, the latter nanowires showed better performance, mainly because of their hydrophobic nature and the metal–organic framework layer. At relative humidities (RHs) of 20% and higher, the MOF-901-coated sensor showed higher performance than the pristine sensor. In particular, at 80% RH, responses of 6.6 and 4.0 were obtained for these two sensors to 10 ppm NO2, respectively. Furthermore, the MOF-901-coated SnO2 NWs showed better selectivity than the other sensor. We showed that MOF-901 behaved an important role in reducing the effects of water vapor and that it can be used as a molecular sieve for enhancing the NO2 gas response of SnO2 NWs in humid environments.

High‐Temperature Oxidation of 60Si2Mn Spring Steel in Dry Air and Wet Air: Insights from an Experimental and First‐Principles Study

During the hot‐rolling process, the 60Si2Mn spring steel is exposed to both dry air and water vapor at high temperatures. However, no precise mechanism or theory is developed to explain the effect of water vapor on the oxide layer from a microscopic atomic perspective. The high‐temperature oxidation of 60Si2Mn spring steel with dry and wet air is investigated herein using a combination of experiments and first‐principles calculations. After high‐temperature oxidation in both dry and wet air, the 60Si2Mn spring steel generates a typical three‐layer structure consisting of Fe2O3, Fe3O4, and FeO + SiO2/Fe2SiO4; however, the oxide layer produced in wet air is significantly thicker. Furthermore, the phase transformation from Fe3O4 to Fe2O3 occurs in the middle Fe3O4 layer, which is associated with H protons derived from H2O molecules penetrating into oxide layers and promoting the development of Fe vacancies in the center of the tetrahedral interstices. The high porosity of the Fe3O4 layer essentially encourages Fe and O diffusion, hence enhancing the growth of the oxide layer and facilitating the transformation from Fe3O4 to Fe2O3. These findings provide a more detailed mechanistic explanation of how water vapor affects the high‐temperature oxidation of 60Si2Mn spring steel at the atomic level.

Investigating the effect of temperature, pressure, and inert gas on the flammability range of ethane/oxygen mixtures

The flammability limit is a critical parameter used to evaluate the risk of explosions from flammable gases and design appropriate explosion-proof measures. This study employs a combined approach of theoretical analysis and experimental determination to investigate the impact of temperature, pressure, and inert gas on the FL of ethane/oxygen mixtures in an environment of elevated temperatures and pressures. The findings demonstrate that the flammability range of ethane/oxygen mixtures progressively widens at elevated temperature and pressure conditions. At high pressures, the upper flammability limit (UFL) of ethane displays a quadratic-linear relationship with temperature, with a turning point at 200 °C. The impact of temperature and pressure on explosion risk is primarily achieved through their effect on the UFL. A new inerting capacity of added diluting gas, δ, is defined for inert gas, revealing that the inerting effect of diluting gas is enhanced under the influence of temperature or pressure. However, the inerting effect of nitrogen weakens as the initial pressure increases, while it strengthens as the initial temperature increases. The inerting effect of water vapor in the system of ethane/oxygen/nitrogen is superior to that of nitrogen. The combustion reaction kinetics of ethane and nitrogen near the UFL is influenced by high temperature, high pressure, and water vapor. The coupling effect of high initial temperature and pressure on the inerting effect of the two inert gases is less pronounced than that of single factors.

Effects of gases on the field emission performance of silicon gated field emitter array

Effects of gases on field emission performance were measured using silicon-gated field emitter arrays. Gas was injected into a vacuum chamber with a 1000 × 1000 tip array, which was driven by a DC gate and collector voltages. The collector voltage was fixed at 200 V while the gate voltage was swept to 40 V. For the gas exposure study, N2, He, and Ar were used. The sets of partial pressures, 5 × 10−6, 5 × 10−5, and 5 × 10−4 Torr, were used for the experiment. It was observed that N2 had the least effect and Ar had the worst effect on emission current performance. The degradation of collector current at 5 × 10−4 Torr pressure for Ar was ≈65% where for the N2, at the same level of pressure, the degradation was ≈41%. However, further experiments with high purity Ar gas showed that it was the water vapor present in the gas itself that was the primary cause of reduction in emission current and not the gas itself. The results expressed in reduction in emission current versus Langmuir exposure versus the current clearly showed the effect of water vapor. After the vacuum was recovered, the work function again restored partially to its original value. After ultraviolet light cleaning, the emission current was restored completely to the original state.

Sulphur diffusion through a growing chromia scale and effects of water vapour

Fe-30Cr (wt%) alloy was exposed to Ar-0.5%SO2 and Ar-10%H2O-0.5%SO2 gases at 650 °C, forming Cr2O3 scales. In dry SO2 for 20 h, sulphur enrichment and scattered Cr-sulphides were observed at the scale-alloy interface, together with internal Cr-sulphide precipitates. After 100 h, sulphur disappeared from the interface, while more internal Cr-sulphides were produced. In wet SO2, the sulphur enrichment and Cr-sulphides were maintained in both times, but no internal sulphidation was seen. Atom probe analysis revealed sulphur enrichment on chromia grain boundaries in both gases, to a greater extent in wet SO2. These effects are discussed in terms of chromia grain boundary diffusion.

Investigation of Radiation Effects in the Uranyl Mineral Metaschoepite.

The effects of water vapor and He ion irradiation on the alteration of particles of the uranyl hydroxide phase metaschoepite, [(UO2)8O2(OH)12](H2O)10, are determined. Raman spectra collected immediately postirradiation revealed the presence of a uranyl oxide phase structurally similar to γ-UO3 or U2O7. Short-term storage postirradiation at elevated relative humidity accelerated formation of the uranyl peroxide phase studtite, [(UO2)(O2)(H2O)2](H2O)2. Experiments examining the degradation of metaschoepite and the hydration of UO3 enabled spectral assignments and identification of reaction pathways. The results provide insights into thermal and radiolytic degradation products in both irradiated uranyl hydroxide phases and uranyl peroxide phases, which follow similar degradation pathways.

Impact of urbanization factors considering artificial water dissipation on extreme precipitation: A numerical simulation of rainfall in Shanghai

AbstractClimate change and rapid urbanization have jointly altered the climate characteristics of cities, including rainfall, humidity, and temperature, and have resulted in an increase of extreme precipitation. In this study, to identify the hydrothermal driving factors responsible for extreme precipitation in urban areas, sensitivity experiments were carried out on two extreme precipitation events in Shanghai, China, using the weather research and forecasting (WRF) model coupled with the artificial water dissipation urban canopy model (AWDUCM). The simulation results from the WRF model and observations from 35 weather stations across Shanghai were compared. The results showed that WRF could simulate the spatial distribution and precipitation intensity of extreme rainfall more accurately when integrated with the AWDUCM. With the AWDUCM incorporated, the root‐mean‐square errors of the two simulated precipitation events were 9.1 and 9.9 mm respectively (accounting for approximately 20% of the total rainfall). The near‐surface temperature and specific humidity in the AWDUCM simulation were approximately 0.5°C and 1 g·kg−1 higher than in the NON simulation (that did not invoke the AWDUCM) respectively. Urbanization factors increase the near‐surface temperature and specific humidity in urban and built‐up land, and the results of this study indicate that these are two of the driving forces affecting precipitation. Increased water vapor and urban heat island effects caused by urbanization are enhancing the intensity of extreme precipitation in Shanghai.

Influence of water vapor on the separation of volatile organic compound/nitrogen mixture by polydimethylsiloxane membrane

In the industrial treatment of waste volatile organic compound (VOC) streams by membrane technology, a third impurity, generally, water vapor, coexists in the mixture of VOC and nitrogen or air, and can affect membrane performance and the design of the industrial process. This study focused on the investigation of the effect of water vapor on the separation performance of the separation of VOC/water/nitrogen mixtures by a polydimethylsiloxane (PDMS) membrane. Three types of VOCs: water-miscible ethanol, water-semi-miscible butanol, and water-immiscible cyclohexane, were selected for the study. Different operating parameters including, concentration of the feed VOC, feed temperature, and concentration of the feed water were compared for the separation of binary and ternary VOC/nitrogen mixtures. The interaction between the VOC and water was analyzed to explain the transportation mechanism after analyzing the difference in the membrane performance for the separation of binary and ternary mixtures. The results indicated that the interaction between the VOC (or nitrogen) and water is the key factor affecting membrane performance. Water can promote the permeation of hydrophilic VOC but prevent hydrophobic VOC through the membrane for the separation of ternary VOC/water/nitrogen mixtures. These results will provide fundamental insights for the design of the recovery application process for industrial membrane-based VOCs, and also guidance for the investigation of the separation mechanism in vapor permeation.

Laboratory measurements of the 15–46 cm wavelength opacity of water vapor under temperature conditions characteristic of the deep atmosphere of Jupiter

The Juno Microwave Radiometer (MWR) has six channels ranging from 600 MHz (50 cm) to 22 GHz (1.3 cm) and has the ability to peer deep into the Jovian atmosphere. Previous laboratory measurements determined the microwave opacity of ammonia and water vapor at pressures and temperatures corresponding to regions sensed by MWR channels 2–6 which function between 1.25 GHz and 22 GHz (Hanley et al., 2009, Devaraj et al., 2014, Bellotti et al., 2016/2017, Karpowicz and Steffes, 2011a, b). The discovery of significant ammonia and water variability at pressures >30 bars (Bolton et al., 2021) indicated the need to provide laboratory opacity measurements at the higher temperatures characteristic of the conditions at higher pressures. Of specific interest is the region sensed by MWR's lowest frequency which senses regions where the physical temperatures reach well above 750 K. Laboratory measurements of the microwave opacity of water vapor at 760 K have been conducted in the frequency range from 649 to 2001 MHz (wavelengths from 15 to 46 cm). These are the first such laboratory measurements known to be conducted at such high temperatures and long wavelengths, and can resolve the inconsistency between the water vapor self-continuum opacity components of the existing models. The results from these laboratory measurements provide better insight into the effects of water vapor on Jupiter's 50 cm wavelength emission and will provide more reliable retrievals of atmospheric composition in the deep atmosphere of Jupiter.Print.

Effect of Temperature and Water Content on the Oxidation Behaviour and Cr Evaporation of High-Cr Alloys for SOFC Cathode Air Preheaters

High temperature alloys are being investigated for use in cathode air pre-heater for solid oxide fuel cell systems because of their high thermal conductivity, formability, manufacturability, and superior mechanical properties. However, it is well-known that high temperature alloys often contain a high concentration of Cr which presents a risk of evaporation and contaminating the cathode of the solid oxide fuel cell (SOFC). The oxidation and Cr2O3 evaporation mechanisms of the alloys including alloy 625, SS309, and alloy 318 have been investigated by varying temperatures and water content of the exposure atmosphere. For the influence of water content, the alloys were isothermally exposed at 850 °C in dry air and air containing 1%, 3% and 9% of H2O at a high flow rate for 168 h. For the influence of temperature, the alloys were isothermally exposed at 650 °C, 750 °C and 850 °C in a 6.0 L/min air stream containing 3% H2O for 168 h. The results of this study show that Cr2O3 evaporation and oxidation rates were dramatically reduced with decreasing temperatures for alloy 625 and SS309. Alloy 318 exhibited a decreased oxidation rate with decreasing temperature, but it demonstrated a reverse trend to the temperature-dependent Cr2O3 evaporation compared to alloy 625 and SS309. The major effect of water vapour on the three tested materials appeared to be the further enhancement of Cr2O3 evaporation.

Effect of Water Vapor and Hydrogen Concentration on Power Generation Characteristics of Protonic Ceramic Fuel Cell

To investigate the effect of water vapor in the feed gas on the power generation characteristics of PCFCs, the water vapor concentration was changed to 3%, 15%, 30%, and 50%, while the hydrogen concentration in the gas fed to the anode was fixed at 50%. The impedance measurements showed that the ohmic resistance decreased with increasing water vapor concentration, which was attributed to the increase in the proton conductivity of the electrolyte. The measured current density-voltage characteristics showed that the power output increased with increasing water vapor concentration, which was attributed to the decrease in ohmic overvoltage caused by the increase in proton conductivity. In addition, as a more practical condition, the power generation characteristics were measured when the water vapor concentration was varied while the hydrogen concentration was varied in an anode gas consisting only of hydrogen and water vapor.

Three condensation paths of exhaust and its five effects on exhaust gas recirculation (EGR) cooler fouling and thermal performance: A review

Fouling has limited the evolution of compact heat exchangers (represented by EGR cooler) to smaller and more efficient sizes, an important reason is the unclear mechanism of the effect of exhaust gas condensation on fouling and thermal performance. This paper reviews the effects of hydrocarbon vapor, water vapor and acid vapor condensation on EGR cooler fouling and thermal performance from 1998 to 2023. Three paths of vapors condensation can occurr: interaction with particles, homogeneous nucleation and interaction with fouling. Beneficial effect (3) and harmful effects (2) to EGR cooler thermal performance have identified: filling, removal and chemical are beneficial effects whereas adhesion and nucleation are harmful effects. Three pathways and five effects play a key role on the composition, the mass, the thickness, density, the morphology and thermal resistance of fouling layer. The involvement level of sub-paths and contribution degree of sub-effects of vapor condensation under different boundary conditions, standard database, holistic model and the effect of renewable synthetic fuels on fouling and thermal performance can be further explored. The results will help researchers to understand the logical relationship between exhaust vapor condensation and fouling and thermal performance from the new perspective of condensation.

Measurements and analysis of solar spectrum in near space

The experiment for measuring the solar spectrum at different latitudes and altitudes was conducted to obtain a suitable Air Mass Zero (AM0) standard solar cell calibration strategy with high altitude balloon flight calibration method. This is the world’s first acquisition of solar spectrum data at an altitude of 35 km using high-altitude balloon platform. The solar spectrum at the upper boundary of the atmosphere was measured and the spectral distribution was obtained from 20 to 35 km during the ascent. The results show that spectral distribution at 35 km is almost equivalent to that of AM0, the peak irradiance at 35 km is close to that of AM0, and the highest peak of this spectrum is at 450.2 nm. Comparing the results taken at different altitude, the effect of ozone, oxygen and water vapor is clearly seen. The measurement methods and results discussed in this paper can assist in verifying the accuracy of space solar cell calibration using high-altitude balloons. It could also provide a reference for the design of photovoltaic energy systems for near space aircrafts. Finally, the results taken from the launch site may be of use for the air quality monitoring and the design of photovoltaic system used in ground-based solar power generation in the Qinghai-Tibet Plateau.

Flue gas carbonation curing of steel slag blocks: Effects of residual heat and water vapor

To make full use of residual heat (temperature) and water vapor (relative humidity, RH) retained in flue gas, the compound effects of temperature (60–140 °C) and RH (2–60 %) of 2-hour CO2 curing on the compressive strength and CO2 fixation of basic oxygen furnace slag (BOFS) blocks were systematically investigated. The results indicated that, in general, an increase of curing temperature increased the compressive strength of the blocks. The high early compressive strength gain (31.3 MPa) at 2-hour for carbonated BOFS blocks was directly related to the microstructure densification and pore refinement due to rich formation of calcite. It should be noted that the supply of sufficient water vapor (≥40 % RH) is particularly important at high temperature (e.g. ≥ 120 °C) to offset the water loss due to water evaporation. Furthermore, under an extremely dry environment (2 % RH), the continuous flow-through of CO2 gas at high temperature not only resulted in no carbonation reaction at the outer layer of the freshly pressed blocks, but may also deteriorate the integrity of the pore structure matrix.

Study of the interaction between NH3 and NO in the reduction zone of air-staged ammonia combustion under high moisture atmosphere

NH3 is used as a hydrogen-rich fuel, and the water vapor content produced by combustion can reach 30%. However, high NOx emission is one of the main problems restricting its application. The air-staged combustion is an effective low-NOx combustion strategy, subdividing the combustion process into three typical sections: the main combustion zone, the reduction zone, and the burnout zone. Fully utilizing the reaction between NH3 and NO in the reduction zone is expected to achieve an effective control of NOx emission. This research aims to explore the reduction ability of the residual NH3 on NO reduction in the reduction zone under high moisture atmosphere formed by ammonia combustion. An isothermal flow reactor was used to study the kinetic characteristics of the NH3/NO reaction under no-oxygen or residual low-oxygen condition in a wide temperature range (1073–1773K) and a high water vapor content range (0–50%). Additionally, three chemical kinetic models were used in simulations. The results showed that oxygen significantly changes the effect of water vapor on the NH3/NO reaction. In the absence of oxygen, water vapor has less effect on NH3/NO reaction at lower temperatures (<1500K). In the presence of oxygen, the increase of water vapor content leads to a significant shift of the reaction temperature window to higher temperatures and a decrease of the maximum NO reduction efficiency. Finally, the remarks about using residual NH3 to complete NOx removal in ammonia combustion were discussed.

Making hybrid mixture explosions a common case

Explosions of gas-dust hybrid mixtures have long been considered as particular cases encountered in specific industrial contexts. However, it should be reminded that during the explosion of an organic powder, the presence of a hybrid mixture composed of the dust itself and its pyrolysis gases is compulsory. On these premises, an experimental study to determine the role of cellulose pyrolysis products (gaseous, condensable and solid) on the global phenomenon is presented. Hybrid mixture explosion tests were exploited to carry out the investigation. The G-G furnace and the 20 L sphere were employed. Several experimental strategies were chosen to demonstrate the impact of pyrolysis reaction on the explosion of organic powders: i) the fuel equivalence ratio of the reactive mixture (case 1), or ii) the mass of reactants (case 2) were respectively kept constant, iii) the effects of water vapor, char and tar were tested. They were next compared to identify the most suitable one. The two first experimental approaches lead to significantly different results: only case 2 keeps the maximum explosion pressure almost constant, but maximum rate of pressure rises and deflagration index greatly decrease when the pyrolysis gases concentration decreases, which highlights the importance of the pyrolysis reaction on the explosion kinetics. It should also be stressed that the maximum explosion severity is not obtained for the pure gases but when a small dust content is added. The same evolution is observed when a small amount of char is introduced to pyrolysis gases, which underlines the influence of the radiative transfer. Adding small amounts of tar to cellulose tends to increase its explosion severity. However, this impact is less than that generated by the addition of pyrolysis gases.