Adding Water Vapor Research Articles

Enhancement of removing OH bonds from low-temperature deposited silicon oxide films by adding water vapor into NH3 gas annealing at 130 oC

Abstract It was found that annealing with water-vapor-added NH3 gas (water-added NH3) is more effective than with dry NH3 at removing residual OH bonds in silicon oxide (SiOx) films deposited by atmospheric chemical vapor deposition with an organic silicon source. Fourier transform infrared spectra showed that reduction amount of OH bonds using the water-added NH3 was ~4 or ~1.3 times larger than using the conventional dry N2 or dry NH3 mixed with N2 gas without water, respectively. This result is something strange because water can be a potential candidate of OH sources. The effect of water vapor on OH-bond removal can be explained by considering following three factors. One is that low-temperature SiOx films are constrained somewhat, the second is that strained Si-O-Si bonds are in higher or more unstable energy state than strain-free ones, and the third is that highly strained bonds are easily hydroxylated to form Si-OH bonds.

A Comparison Between Water Addition and CO2 Addition to a Diffusion Coflow Flame

ABSTRACT This work compares the effects of adding water vapor and CO2 as diluent to fuel for a diffusion flame at different ambient pressures. The approach of this research is to study numerically a methane diffusion flame with various amounts of water vapor and CO2 added to the fuel, and to compare the flame behaviors with various percentages of water vapor and CO2 content (0% to 65%). This work uses a coflow burner in the PeleLM numerical framework for simulating the flame and computing the combustion behavior. The flame was simulated with pressures of 1.0, 1.4, 5.7, and 11.1 atm. The results extracted and analyzed include temperature profiles at fixed heights and various species mole fractions compared with their values at an equilibrium state condition. The results show that most of the diluent impact does not involve changes in flame chemistry but primarily changes to heat release and heat capacity in the flames. The results also show that the diluent amount has a much larger impact on flame behavior than do changes in pressure.

Catalytic combustion of 1,2-dichloroethane via C[sbnd]C/C[sbnd]Cl bond cleavage through core-shell structured CeO2@TiO2 catalyst with excellent catalytic performances

A highly representative chlorinated volatile organic compound (Cl-VOCs), including 1,2-dichloroethane (1,2-DCE), which is extremely hazardous to human health and the environment. Improving the catalytic activity is very important for catalytic degradation of 1,2-DCE. In the work, CeO2@TiO2 catalyst which has a core-shell structure were made by a simple two-step hydrothermal synthesis method for 1,2-DCE oxidation. CeO2@TiO2 catalysts show higher activity (T90=275 °C), better carbon dioxide yield (YCO2=89.54 %) and lower by-products production than primitive CeO2 and TiO2. Due to its core-shell structure, CeO2@TiO2 shows the appropriate oxidation and reduction ability and appropriate acidity distribution, the powerful relationship between Ce and Ti elements in CeO2@TiO2 leads to effectively generate activity Ce3+and oxygen, which is greatly great enhance the activity of CeO2@TiO2 in 1,2-DCE catalytic oxidation. Based on the analysis of 1,2-DCE degradation performance and physical and chemical attributes, it proposes a way to catalyze 1,2-DCE catalytic oxidation over CeO2@TiO2. In addition, CeO2@TiO2 has good stability, and adding water vapor over the CeO2@TiO2 during 1,2-DCE degradation to promote 1,2-DCE conversion. The findings of this study might offer some new suggestions for creating catalysts that will destroy Cl-VOCs in their preparation and design.

Edge Bonding Voids Management Using Humid Helium Bonding Atmosphere

As far as hydrophilic direct wafer bonding is concerned, there are, beside classical bonding voids induced by particle contamination or surface topography, edge bonding voids due to the bonding wave dynamic itself. Indeed, as shown by Castex et al. [1], during the adiabatic expansion of the bonding wave at the wafer edge, humidity inside the bonding wave gas can liquefy and small water droplets nucleate. This is shown in Figure 1a, with the bonding of a 300mm silicon wafer on another one having a 145 nm thermal oxide on top and after a post bonding thermal annealing at 300°C. These wafer edge droplets result in bonding defects without the presence of particle contamination or surface topography. Even if bonding is performed under a dry gas like Nitrogen or Argon, these defects remain at the hydrophilic direct bonding interface. Indeed, there is always a small amount of water on a hydrophilic surface. During the first bonding wave propagation stage, gas compression increases the temperature and enables the gas to take water from the surfaces, as explained V. Larrey et al. [2]. The humid gas will result in edge bonding voids at the end of the propagation. There are only two methods to get rid of this phenomenon. The first one is to perform bonding under vacuum (<0.1 mbar). The second is to use a gas with a negative Joule-Thomson coefficient.Such gases will be heated during the adiabatic expansion when the bonding wave will go out of the bonding interface. Three gases have such a negative coefficient: Helium, Hydrogen and Neon. Helium has the lowest joule-Thomson coefficient at ambient condition and is the saver and cheapest one. Bonding under Helium atmosphere will then prevent water nucleation, as shown in Figure 1b. Usually, pure Helium is used which is then a dry gas. Some water will then be removed from the surface. As shown by Radisson [3], the adhesion will then be less important as well as the adherence as shown by Fournel et al. [4]. Adding water vapor to increase the relative humidity (RH) of helium could then enable us to recover standard bonding conditions regarding the amount of trapped water.In our EVG850LT bonding tool, a humidifier has thus been installed on the Helium gas line in order to purge the bonding chamber with a varying RH gas mixture (from 0 to 80%). As shown in Figure 1c, even with 68% of RH, no bonding voids are detected by scanning acoustic microscopy. It will be shown also that the bonding wave speed increases with the RH value, highlighting an adhesion energy recovery. The evolution of the adherence with the RH bonding conditions and after the post bonding annealing will be also presented. REFERENCES [1] A. Castex, M. Broekaart, F. Rieutord, K. Landry, and C. Lagahe-Blanchard, ECS Solid State Lett. 2, p. 47 (2013).[2] V. Larrey, G. Eleouet, C. Bridoux, C. Morales, F. Fournel, F. Rieutord, D. Landru, Proceeding of The International Conference on Wafer Bonding 2019-WaferBond'19, p.91 (2019).[3] D. Radisson, Direct Bonding of Patterned Surfaces, PhD thesis, Université Grenoble Alpes, (2014).[4] F. Fournel, C. Martin-Cocher, D. Radisson, V. Larrey, E. Beche, C. Morales, P.A. Delean, F. Rieutord, and H. Moriceau, ECS J. Solid State Sci. Technol. 4, P124 (2015). Figure 1

Sooting properties of laminar coflow non-premixed ethylene/hydrogen flames influenced by water vapor addition to the oxidizer

A numerical study was conducted to quantify the effects of water vapor addition to oxidizer on soot formation in ethylene/hydrogen flames in a benchmark coflow configuration. The objective was to quantify the dilution, thermal and chemical effects in terms of their contributions to the change in sooting properties and flame radiation. The conditions are selected to keep constant the heat release rate of the flame while adding hydrogen and to maintain the mass flow of air of the oxidizer while adding water vapor. On the one hand, a consistent decrease of flame height, soot volume fraction, carbon-to-soot conversion efficiency and total radiation emitted by the flame was observed when increasing the mole fraction of hydrogen on the fuel side. On the other hand, water vapor addition to the coflow slightly increases the flame height, and reduces soot volume fraction and temperature. A consistent decrease is observed on the local radiative power per unit volume by soot, CO and CO2. However, the total radiative losses are enhanced by the water vapor presence at high temperatures. In general, the dilution effects are dominant for the change of soot loading and radiation, whereas the thermal effects are dominant for carbon-to-soot conversion efficiency. Finally, a chemical pathway analysis was conducted to quantify the changes in the main reactions for soot precursor formation affected by addition of hydrogen and water vapor. These results provide fundamental insights to researchers and practitioners dealing with fires caused by hydrogen-enriched mixtures, which are attempted to be extinguished by traditional means by adding water.

Effect of Steam on Carbonation of CaO in Ca-Looping.

Ca-looping is an effective way to capture CO2 from coal-fired power plants. However, there are still issues that require further study. One of these issues is the effect of steam on the Ca-looping process. In this paper, a self-madethermogravimetric analyzer that can achieve rapid heating and cooling is used to measure the change of sample weight under constant temperature conditions. The parameters of the Ca-looping are studied in detail, including the addition of water vapor alone in the calcination or carbonation stage and the calcination/carbonation reaction temperatures for both calcination and carbonation stages with water vapor. Steam has a positive overall effect on CO2 capture in the Ca-looping process. When steam is present in both calcination and carbonation processes, it increases the decomposition rate of CaCO3 and enhances the subsequent carbonation conversion of CaO. However, when steam was present only in the calcination process, there was lower CaO carbonation conversion in the following carbonation process. In contrast, when steam was present in the carbonation stage, CO2 capture was improved. Sample characterizations after the reaction showed that although water vapor had a negative effect on the pore structure, adding water vapor increased the diffusion coefficient of CO2 and the carbonation conversion rate of CaO.

A Cooling Efficiency Model and Numerical Research of Multiparameter Film Cooling

Abstract Based on the validated simulation method of film cooling and multiphase flow simulation method, a multi-level three-dimensional simulation of forward-leaning fan-shaped film hole, cylindrical film hole with different injection angles, and film hole containing water vapor are established to discuss the effects of film hole structure parameters, hole distance, blowing ratio, injection angle, and water vapor volume on film cooling efficiency. The cooling efficiency of forward-leaning fan-shaped film hole increases as the exit length of film hole increases. After adding water vapor, the cooling efficiency of fan-shaped film hole decreases, and the influence of hole axis length and exit length on cooling efficiency is weak. For the cylindrical film hole, the larger the injection angle of film hole, the larger the film coverage area under the same blowing ratio. After adding water vapor, with the increase of the blowing ratio, the film coverage area increases first and then decreases. However, the film coverage area decreases with the increase of cooling injection angle for film holes containing water vapor. The cooling efficiency of the film hole with and without water vapor is related to the vapor velocity in the rising direction and the velocity in the mainstream direction, respectively. A model of film cooling efficiency with air blowing ratio and injection angle is established and verified with experimental data, based on the law that the average cooling efficiency in the main flow direction grows exponentially with the sine of the injection angle.

Pengaruh laju aliran udara dan lubang uap air terhadap kinerja kompor dengan bahan bakar oli bekas

Oil waste produced from motor vehicle lubricants can pollute the environment. One alternative that can be done to prevent environmental pollution is by utilizing waste oil as fuel. Several factors can affect the temperature and quality of combustion, namely the air flow rate and the addition of water vapor in the combustion process. The purpose of this study was to determine the effect of the air flow rate and the number of steam holes on the temperature and efficiency of the stove with used oil fuel. The research method used was experimental by making and testing stoves with waste oil as fuel and adding water vapor to maximize combustion results. Variations in the air flow rate are 9 m/s, 10 m/s, and 11 m/s and variations in the number of water vapor holes are 8, 9 and 10 pieces. From the research results, it was found that the air flow rate and the number of holes had an effect on the flame, temperature and quality of combustion. The highest temperature is 605.6℃ and the highest stove efficiency is 10.91% obtained with an air flow rate of 10 m/s and 10 steam holes.

Mechanism of olivine and glass alteration under experimental H2O-CO2 based supercritical gas: Application to modern and ancient Venus

Extreme conditions encountered in some geological contexts (deep serpentinization, interaction of Venus atmosphere with its basaltic surface, volcanic degassing) activate mechanisms and rates of silicate alteration that are poorly understood. In the present study, we investigate the mechanisms of mineral reactions in a natural geological system at high temperature, under conditions where the low solvation of cations by fluids likely promotes surface reactions such as surface diffusion and/or local recrystallization. We focus on vitreous glasses and olivine, reputed to be the most alterable phases in volcanic rocks, by reacting samples for one week in a Ni-based alloy experimental vessel. For the framework of our experimental study, we chose to apply the deep atmosphere conditions on Venus: 470 °C and 90 bar of reconstituted Venus-like gas. We also tested the effect of water (Early Venus or wet volcanic degassing) by adding water vapor at up to 320 bar total pressure. The mineral reactions affecting the samples were identified by a set of spectroscopic surface analyses of the altered samples: Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction in grazing incidence mode, X-ray Photo electron Spectroscopy and Raman spectroscopy.Samples of obsidian and tholeiitic glasses are found to be sensitive to a threshold water pressure, depending on glass composition, below which the reaction is limited to some elemental mobility in the glass (alkali enrichment, calcium loss) leading to a possibly more stable surface layer of tens to hundreds of microns. Above this threshold water pressure (ca. 50 bar H2O for the obsidian but >250 bar H2O for the tholeiitic glass), water promotes the depolymerization of the glass and the crystallization of stable minerals. This crystalline rim is less protective that the chemically modified layer.Olivine samples react differently depending on whether the olivine is isolated or included in a basaltic rock. In the latter case only, iron coatings are formed, which are identified as hematite, suggesting that this phase is not fed by olivine itself but rather by surface diffusion from neighboring Fe-rich phases. This supports the conclusions from experimental studies and orbital observations on the short-term visibility of unaltered olivine in Venus lava flows: such a coating is enhanced when Fe-bearing minerals are in the proximity of olivine. Under high water vapor pressure, Fe-bearing talc (and not serpentine) forms by a likely topotactic reaction that also incorporates silica from the gas. This talc layer may form a protective layer, implying that serpentinization of ultramafic rocks at high temperature may not be as prevalent as one might think in a gas-dominated system like the Early Venus surface.

Observation of Potential-Induced Hydration on the Surface of Ceramic Proton Conductors Using In Situ Near-Ambient Pressure X-ray Photoelectron Spectroscopy.

Interactions of ceramic proton conductors with the environment under operating conditions play an essential role on material properties and device performance. It remains unclear how the chemical environment of material, as modulated by the operating condition, affects the proton conductivity. Combining near-ambient pressure X-ray photoelectron spectroscopy and impedance spectroscopy, we investigate the chemical environment changes of oxygen and the conductivity of BaZr0.9Y0.1O3-δ under operating condition. Changes in O 1s core level spectra indicate that adding water vapor pressure increases both hydroxyl groups and active proton sites at undercoordinated oxygen. Applying external potential further promotes this hydration effect, in particular, by increasing the amount of undercoordinated oxygen. The enhanced hydration is accompanied by improved proton conductivity. This work highlights the effects of undercoordinated oxygen for improving the proton conductivity in ceramics.

Effects of water vapor on auto-ignition characteristics and laminar flame speed of methane/air mixture under engine-relevant conditions

In this paper, the effects of water vapor on auto-ignition characteristics and laminar flame speed of the methane/air mixture were numerically simulated by using the Chemkin code under the engine-relevant conditions. Different methane combustion mechanisms were separately simulated under the same boundary conditions and compared to the experimental data obtained from the literature. Then, the detailed methane combustion mechanism was selected to investigate the effects of water vapor on the auto-ignition characteristics of the methane/air mixture and methane/hydrogen/air mixture under the relative high pressure condition. In addition, the effects of water vapor on the laminar flame speed of methane/air and methane/hydrogen/air mixture was also studied. Furthermore, the chemical, thermal and dilution effects of the water vapor on the laminar flame speed of methane/air were quantitatively evaluated. Last, the effects of initial temperature and pressure on the laminar flame speed of methane/air were also analyzed based on the detailed methane combustion mechanism. The results indicated that the ignition delay time of the methane/air was increased with increasing water vapor ratio. In addition, the dilution and thermal effects of the water vapor played the decisive roles in the laminar flame speed of the methane/air mixture compared to its chemical effect. Furthermore, the laminar flame speed and adiabatic combustion temperature of the methane/air were decreased with increasing water vapor ratio. Moreover, the formation and oxidation rates of the H, O and OH radicals during the methane/air combustion were prohibited with adding water vapor.

Plasma-enhanced low temperature NH3-SCR of NOx over a Cu-Mn/SAPO-34 catalyst under oxygen-rich conditions

In this work, a dielectric barrier discharge (DBD) plasma-enhanced NH3-selective catalytic reduction (NH3-SCR) of NOx over a Cu-Mn/SAPO-34 catalyst at low temperatures (<200 °C) and oxygen-rich conditions (14 vol.%) has been investigated using a two-stage post-plasma-catalytic (PPC) configuration. The results show a maximum NOx removal of 80 % and a 100 % N2 selectivity without NH3 slip or the formation of by-products at a low specific energy input (SEI) of 32 J/L. Adding water vapor (5.7 vol.%) into the plasma NH3-SCR process does not negatively affect the removal of NOx, while the presence of C3H6 enhances the removal of NOx. In situ diffuse reflectance infrared spectroscopy (DRIFTS) combined with optical emission spectroscopic diagnostics has been employed to elucidate the reaction mechanism in the plasma-catalytic removal of NOx. We find that the formation of NO2 via NO oxidation in the first stage plasma gas-phase reaction enhances the Eley-Rideal (E–R) reaction on the surface of the Cu-Mn/SAPO-34 catalyst in the second stage catalytic NH3-SCR of NOx. The Cu-Mn/SAPO-34 catalyst shows stable performance in the plasma-enhanced NH3-SCR of NOx after 5 cycles of catalyst regeneration. This work has successfully demonstrated a promising low-temperature plasma-catalytic solution for the effective NH3-SCR of NOx.

Contributions to the Surface Downwelling Longwave Irradiance during Arctic Winter at Utqiaġvik (Barrow), Alaska

AbstractIntrusions of warm, moist air into the Arctic during winter have emerged as important contributors to Arctic surface warming. Previous studies indicate that temperature, moisture, and hydrometeor enhancements during intrusions all make contributions to surface warming via emission of radiation down to the surface. Here, datasets from instrumentation at the Atmospheric Radiation Measurement User Facility in Utqiaġvik (formerly Barrow) for the six months from November through April for the six winter seasons of 2013/14–2018/19 were used to quantify the atmospheric state. These datasets subsequently served as inputs to compute surface downwelling longwave irradiances via radiative transfer computations at 1-min intervals with different combinations of constituents over the six winter seasons. The computed six winter average irradiance with all constituents included was 205.0 W m−2, close to the average measured irradiance of 206.7 W m−2, a difference of −0.8%. During this period, water vapor was the most important contributor to the irradiance. The computed average irradiance with dry gas was 71.9 W m−2. Separately adding water vapor, liquid, or ice to the dry atmosphere led to average increases of 2.4, 1.8, and 1.6 times the dry atmosphere irradiance, respectively. During the analysis period, 15 episodes of warm, moist air intrusions were identified. During the intrusions, individual contributions from elevated temperature, water vapor, liquid water, and ice water were found to be comparable to each other. These findings indicate that all properties of the atmospheric state must be known in order to quantify the radiation coming down to the Arctic surface during winter.

Plasma-enhanced SO2 remediation in a humidified gas matrix: A potential strategy for the continued burning of high sulfur bunker fuel

We report a substantial enhancement in the removal of gaseous SO2 by discharging a transient nanosecond pulsed plasma in a water vapor-saturated gas mixture. With the plasma alone (i.e., “dry”), the SO2 remediation is limited to approximately 15% reduction in SO2 (i.e., ΔSO2 = 65 ppm). In presence of water vapor, we observe 84% remediation (ΔSO2 = 500 ppm) during plasma discharge due to the availability of OH radicals. Here, there is a synergistic effect of adding water vapor to the gas mixture in which the plasma excites highly reactive OH radical species that drive a two-step reaction process: SO2 + OH → HSO3 and the subsequent reaction of HSO3 + OH → H2SO4, which precipitates out in the aqueous phase. The efficacy of this approach increases as we increase the temperature of the gas matrix, indicating the relatively low barriers of this reaction, which is consistent with the OH-driven reaction pathway, and it also increases with plasma density, thus demonstrating the scalability of this approach. Plasma emission spectroscopy as well as Raman scattering spectroscopy provide spectroscopic evidence of the OH radical species, further substantiating the OH reaction intermediate mechanism. This approach provides a promising mitigation strategy for the continued use of high sulfur fuels (i.e., bunker fuel).

Effects of water vapor addition on NO reduction of n-decane/air flames

ABSTRACTNO producing mechanism and effects of additional water vapor on NO reduction of n-decane/air flames were examined numerically in the present study. A new phenomenon was found that the variation trend of contribution of chemical effect of water vapor on NO reduction with pressure changes with the equivalence ratio. To illustrate this, NO emissions without and with water vapor addition were examined. Results showed that the new phenomenon is because that NO-producing pathways vary with both equivalence ratio and pressure, and hence the reactions through which the added water vapor influences NO production also vary with equivalence ratio and pressure.

A new method of processing CO2 and magnesite slag simultaneously

Calcining magnesite slag to capture CO2 is a new and simple method of processing CO2 and magnesite slag simultaneously. In this work, the CO2 capture capacity by calcined magnesite slag in wet flue gas simulated by adding water vapour was investigated. The magnesite slag exhibits excellent CO2 adsorption performance, with 3.01 mmol/g CO2 adsorption capacity, which is reduced to 2.18 mmol/g after 8 cycles and is obvious superior to magnesite. The structure and characterization of the magnesite slag are examined by XRF, FT-IR, TGDSC, XRD, CO2-TPD and BET. It can be confirmed by X-ray fluorescence analysis that the key component of magnesite slag is MgSiO3 and MgCO3. The results of this work indicate that the magnesite slag is an available adsorbent for CO2 adsorption after calcination.

Influence of water vapor on cyclic CO2 capture performance in both carbonation and decarbonation stages for Ca-Al mixed oxide

Little research was carried out to study the effect of water vapor with different contents on the CO2 adsorption performance during extending cycles in both carbonation and decarbonation stages. This study described the CO2 adsorption performance of Ca-Al mixed oxides under different water vapor concentrations. The results revealed that the reactivity and durability of both fresh and spent sorbents were remarkably enhanced by adding water vapor. The initial CO2 carbonation capacity increased from 56 wt% without water to 70.7 wt% with 1.6% water vapor at the adsorption temperature of 600 °C. The stability of Ca-Al mixed oxides was also investigated during 220 cycles with 1% steam vapor. The CO2 adsorption capacity retained 55.6 wt% after 220 cycles, indicating an excellent long-term durability. The excellent CO2 adsorption capacity and stability of the mixed oxides in the existence of water vapor may be attributed to the following reasons: water vapor facilitated CO2 diffusion in the CaCO3 product layer during the carbonation stage as well as the decomposition rate of CaCO3 during the calcination stage; water vapor facilated the formation of the loose porous structure, which was favorable for the subsequent carbonation of CaO.

Linking uncertainty in simulated Arctic ozone loss to uncertainties in modelled tropical stratospheric water vapour

Abstract. Stratospheric water vapour influences the chemical ozone loss in the polar stratosphere via control of the polar stratospheric cloud formation. The amount of water vapour entering the stratosphere through the tropical tropopause differs substantially between simulations from chemistry–climate models (CCMs). This is because the present-day models, e.g. CCMs, have difficulties in capturing the whole complexity of processes that control the water transport across the tropopause. As a result there are large differences in the stratospheric water vapour between the models. In this study we investigate the sensitivity of simulated Arctic ozone loss to the simulated amount of water vapour that enters the stratosphere through the tropical tropopause. We used a chemical transport model, FinROSE-CTM, forced by ERA-Interim meteorology. The water vapour concentration in the tropical tropopause was varied between 0.5 and 1.6 times the concentration in ERA-Interim, which is similar to the range seen in chemistry–climate models. The water vapour changes in the tropical tropopause led to about 1.5 ppmv less and 2 ppmv more water vapour in the Arctic polar vortex compared to the ERA-Interim, respectively. The change induced in the water vapour concentration in the tropical tropopause region was seen as a nearly one-to-one change in the Arctic polar vortex. We found that the impact of water vapour changes on ozone loss in the Arctic polar vortex depends on the meteorological conditions. The strongest effect was in intermediately cold stratospheric winters, such as the winter of 2013/2014, when added water vapour resulted in 2 %–7 % more ozone loss due to the additional formation of polar stratospheric clouds (PSCs) and associated chlorine activation on their surface, leading to ozone loss. The effect was less pronounced in cold winters such as the 2010/2011 winter because cold conditions persisted long enough for a nearly complete chlorine activation, even in simulations with prescribed stratospheric water vapour amount corresponding to the observed values. In this case addition of water vapour to the stratosphere led to increased areas of ICE PSCs but it did not increase the chlorine activation and ozone destruction significantly. In the warm winter of 2012/2013 the impact of water vapour concentration on ozone loss was small because the ozone loss was mainly NOx-induced. The results show that the simulated water vapour concentration in the tropical tropopause has a significant impact on the Arctic ozone loss and therefore needs to be well simulated in order to improve future projections of the recovery of the ozone layer.

Temperature profiles and extinction limits of a coflow water-vapor laden methane/air diffusion flame

The understanding of thermal and chemical effects of water addition to the fuel side of a diffusion flame is relevant for improving processes such as the combustion of methane hydrates, emulsified fuels and wet biomass, as well as for cases where water is intentionally added to the fuel stream, as for example in steam-assisted flares for the reduction of emissions. In this work, the role of water is evaluated by adding water vapor to the fuel side of a steady non-premixed coflow flame. The steady nature of the flame allows temperature profiles and extinction limits to be measured at different conditions of inlet fuel velocities, and with increasing dilution levels up to extinction. Temperatures are measured by thin-filament pyrometry (TFP) using a SiC fiber and a commercial DSLR camera. Results from Ar, N2 or CO2 diluted flames are also reported to compare the effects of water vapor with those of different diluents. Comparisons in terms of temperatures and extinction limits show close correspondence when adding equivalent levels of diluent thermal capacitance.

Water as key to activity and selectivity in Co Fischer-Tropsch synthesis: γ-alumina based structure-performance relationships

Thirteen γ-alumina supports with different pore sizes and pore size distributions have been impregnated with cobalt and rhenium. The catalysts were tested for Fischer-Tropsch synthesis (FTS) under dry and enhanced water vapor pressure conditions. It is shown that there is a positive correlation between pore size and cobalt crystallite size of the reduced catalyst after incipient wetness impregnation as long as the pore size distribution is sufficiently narrow. There is a concurrent increase in C5+ with pore diameter due to higher chain propagation probabilities α3+. Higher α values are ascribed to larger cobalt crystallites that promote CO activation resulting in higher surface coverage of CHx monomers. Adding water vapor to the syngas feed has a strong positive effect on selectivity to higher hydrocarbons and activity. Water imposes a significant enhancement of α1 that is attributed to higher relative cobalt surface coverage of H2O(OH−) and CHx relative to hydrogen. Small pores are susceptible to condensation of water during FTS.