Addition Of Water Vapor Research Articles

Cloud Formation in the Plumes of Solar Chimney Power Generation Facilities: A Modeling Study

The solar chimney power facility has the potential to become a valuable technology for renewable energy production. Its financial viability depends on a thorough understanding of the processes affecting its performance, particularly because of the large startup costs associated with facility design and construction. This paper describes the potential impacts on plant capacity resulting from cloud formation within or downwind of the solar chimney. Several proposed modifications to the basic concept of the solar chimney power facility have the potential to cause significant additions of water vapor to the air passing through the collector. As the air continues up through and out of the chimney, this excess water can condense to form cloud. This possibility is explored using a cloud parcel model initialized to simulate the range of expected operating conditions for a proposed solar chimney facility in southwestern Australia. A range of temperatures and updraft velocities is simulated for each of four seasonal representations and three levels of water vapor enhancement. Both adiabatic environments and the effects of entrainment are considered. The results indicate that for very high levels of water vapor, enhancement cloud formation within the chimney is likely; at more moderate levels of water vapor enhancement, the likelihood of plume formation is difficult to fully assess as the results depend strongly on the choice of entrainment rate. Finally, the impacts of these outcomes on facility capacity are estimated.

The gas-phase ozonolysis of β-caryophyllene (C15H24). Part I: an experimental study

The gas phase reaction of ozone with beta-caryophyllene was investigated in a static glass reactor at 750 Torr and 296 K under various experimental conditions. The reactants and gas phase products were monitored by FTIR-spectroscopy and proton-transfer-reaction mass spectrometry (PTR-MS). Aerosol formation was monitored with a scanning mobility particle sizer (SMPS) and particulate products analysed by liquid chromatography/mass spectrometry (HPLC-MS). The different reactivity of the two double bonds in beta-caryophyllene was probed by experiments with different ratios of reactants. An average rate coefficient at 295 K for the first-generation products was determined as 1.1 x 10(-16) cm(3) molecule(-1) s(-1). Using cyclohexane as scavenger, an OH-radical yield of (10.4 +/- 2.3)% was determined for the ozonolysis of the more reactive internal double bond, whereas the average OH-radical yield for the ozonolysis of the first-generation products was found to be (16.4 +/- 3.6)%. Measured gas phase products are CO, CO(2) and HCHO with average yields of (2.0 +/- 1.8)%, (3.8 +/- 2.8)% and (7.7 +/- 4.0)%, respectively for the more reactive internal double bond and (5.5 +/- 4.8)%, (8.2 +/- 2.8)% and (60 +/- 6)%, respectively from ozonolysis of the less reactive double bond of the first-generation products. The residual FTIR spectra indicate the formation of an internal secondary ozonide of beta-caryophyllene. From experiments using HCOOH as a Criegee intermediate (CI) scavenger, it was concluded that at least 60% of the formed CI are collisionally stabilized. The aerosol yield in the ozonolysis of beta-caryophyllene was estimated from the measured particle size distributions. In the absence of a CI scavenger the yield ranged between 5 and 24%, depending on the aerosol mass. The yield increases with addition of water vapour or with higher concentrations of formic acid. In the presence of HCHO, lower aerosol yields were observed. This suggests that HCOOH adds to a Criegee intermediate to form a low-volatility compound responsible for aerosol formation. The underlying reaction mechanisms are discussed and compared with the results from the accompanying theoretical paper.

Kinetics of the heterogeneous conversion of 1,4-hydroxycarbonyls to cyclic hemiacetals and dihydrofurans on organic aerosol particles

There is growing awareness that heterogeneous reactions may be important in the atmospheric formation of secondary organic aerosols (SOA). Here, we report on the investigation of a series of recently identified heterogeneous reactions that convert 1,4-hydroxycarbonyls, a major product of alkane oxidation, to cyclic hemiacetals and then dihydrofurans in the particle-phase. Through these reactions, saturated 1,4-hydroxycarbonyls are converted to more reactive, unsaturated dihydrofurans, which can evaporate and react rapidly with atmospheric oxidants such as OH radicals, NO3 radicals, or O3. In order to investigate the conversion process quantitatively, a model was developed based on a proposed mechanism that includes gas-phase and heterogeneous reactions, as well as gas-particle partitioning. This model was used to simulate the time profiles of products formed from OH radical-initiated reactions of C11-C17 n-alkanes in the presence of NOx, for comparison with profiles of particle-phase cyclic hemiacetals measured during environmental chamber reactions of the same alkanes using a thermal desorption particle beam mass spectrometer. Results showed that the particle-phase isomerization of 1,4-hydroxycarbonyls to cyclic hemiacetals was fast in dry air, with a reactive uptake coefficient of at least 0.5. The lifetime for the subsequent particle-phase dehydration of cyclic hemiacetals to dihydrofurans was approximately 15 min. The addition of water vapor (relative humidity approximately 50%) slowed the conversion process, apparently by neutralizing adsorbed HNO3 that is thought to catalyze the reactions. Simulations performed with model parameters obtained from the experiments indicate that for typical atmospheric aerosol mass and oxidant concentrations and sufficiently acidic particles, 1,4-hydroxycarbonyls will be almost entirely converted to dihydrofurans in less than a day in both clean and polluted areas, whereas in the presence of neutralized particles the conversion may be minor. The outcome that occurs could have a significant impact on reaction products and SOA formation.

Simultaneous oxidation of NO, SO2 and Hg0 from flue gas by pulsed corona discharge

A process capable of simultaneously oxidizing NO, SO2, and Hg0 was proposed, using a high-voltage and short-duration positive pulsed corona discharge. By focusing on NO, SO2, and Hg0 oxidation efficiencies, the influences of pulse peak voltage, pulse frequency, initial concentration, electrode number, residence time and water vapor addition were investigated. The results indicate that NO, SO2 and Hg0 oxidation efficiencies depend primarily on the radicals (OH, HO2, O) and the active species (O3, H2O2, etc.) produced by the pulsed corona discharge. The NO, SO2 and Hg0 oxidation efficiencies could be improved as pulse peak voltage, pulse frequency, electrode number and residence time increased, but they were reduced with increasing initial concentrations. By adding water vapor, the SO2 oxidation efficiency was improved remarkably, while the NO oxidation efficiency decreased slightly. In our experiments, the simultaneous NO, SO2, and Hg0 oxidation efficiencies reached to 40%, 98%, and 55% with the initial concentrations 479 mg/m3, 1040 mg/m3, and 15.0 microg/m3, respectively.

Study of Inactivation Factors in Low Temperature Surface-wave Plasma Sterilization

In this study we investigated the low temperature surface-wave plasma sterilization of directly and indirectly exposed Geobacillus stearothermophilus spores with a large-volume microwave plasma device. The air-simulated gas mixture was used to produce the plasma. The water vapor addition to the gas mixture improved the sterilization efficiency significantly. The effect of ultraviolet photons produced along with plasma to inactivate the spores was studied using a separate chamber, which was evacuated to less than one mTorr and was observed that spores were sterilized within 60 min. The scanning electron microscopy images revealed no significant changes in the actual size of the spores with that of untreated spores despite the survival curve shown that the spores were inactivated.

Study the effect of humidity on the RPC performance

The effect of water vapor on the performance of a resistive plate chamber (RPC) has been studied by simulating the dependency of avalanche multiplication on the amount of humidity in the RPC gas mixture. Also, the change of plates’ resistivity with humidity has been considered in the simulation. The results of simulation show that at the room temperature, the addition of water vapor to the gas mixture even up to 100% relative humidity (RH), has no practical influence on the avalanche multiplication process inside the RPC gap. The humidity effect on the avalanche multiplication appears for high-temperature operation where the induced signal increases with humidifying the gas mixture. The simulation was also performed for high-particles flux densities and the results show that the degradation of plates’ resistivity with humidity improves the efficiency as well as rate capability of the detector in agreement with experimental reports.

Selective methanation of CO over supported Ru catalysts

The catalytic performance of supported ruthenium catalysts for the selective methanation of CO in the presence of excess CO2 has been investigated with respect to the loading (0.5–5.0wt.%) and mean crystallite size (1.3–13.6nm) of the metallic phase as well as with respect to the nature of the support (Al2O3, TiO2, YSZ, CeO2 and SiO2). Experiments were conducted in the temperature range of 170–470°C using a feed composition consisting of 1%CO, 50% H2 15% CO2 and 0–30% H2O (balance He). It has been found that, for all catalysts investigated, conversion of CO2 is completely suppressed until conversion of CO reaches its maximum value. Selectivity toward methane, which is typically higher than 70%, increases with increasing temperature and becomes 100% when the CO2 methanation reaction is initiated. Increasing metal loading results in a significant shift of the CO conversion curve toward lower temperatures, where the undesired reverse water–gas shift reaction becomes less significant. Results of kinetic measurements show that CO/CO2 hydrogenation reactions over Ru catalysts are structure sensitive, i.e., the reaction rate per surface metal atom (turnover frequency, TOF) depends on metal crystallite size. In particular, for Ru/TiO2 catalysts, TOFs of both CO (at 215°C) and CO2 (at 330°C) increase by a factor of 40 and 25, respectively, with increasing mean crystallite size of Ru from 2.1 to 4.5nm, which is accompanied by an increase of selectivity to methane. Qualitatively similar results were obtained from Ru catalysts supported on Al2O3. Experiments conducted with the use of Ru catalyst of the same metal loading (5wt.%) and comparable crystallite size show that the nature of the metal oxide support affects significantly catalytic performance. In particular, the turnover frequency of CO is 1–2 orders of magnitude higher when Ru is supported on TiO2, compared to YSZ or SiO2, whereas CeO2- and Al2O3-supported catalysts exhibit intermediate performance. Optimal results were obtained over the 5%Ru/TiO2 catalyst, which is able to completely and selectively convert CO at temperatures around 230°C. Addition of water vapor in the feed does not affect CO hydrogenation but shifts the CO2 conversion curve toward higher temperatures, thereby further improving the performance of this catalyst for the title reaction. In addition, long-term stability tests conducted under realistic reaction conditions show that the 5%Ru/TiO2 catalyst is very stable and, therefore, is a promising candidate for use in the selective methanation of CO for fuel cell applications.

Application of non-thermal plasma on gas cleansing

Non-thermal plasma technologies are an interesting complement or alternative, for some conventional systems used for gas pollution control (i.e. wet scrubbers and catalytic converters) because they are able to remove simultaneously several gas pollutants, with quite good efficiency at a relatively low-energy consumption. In this work, a dielectric barrier discharge was used to remove nitric oxides (NOx) and sulfur dioxide (SO2) from a mixture of air and water vapor. A chemical model was developed to obtain a toxic gas removal mechanism and to observe the behavior of the species in the plasma. The influence of water vapor addition on the toxic gases removal efficiency is also investigated. Several experimental parameters such as power, frequency, initial concentration of NOx and SO2 were tested and analyzed. Results of numerical simulation demonstrated good agreement with experimental data of the removal process achieving about 95% of efficiency removal of toxic gases studied.

Benzene oxidation with ozone over supported manganese oxide catalysts: Effect of catalyst support and reaction conditions

Catalytic oxidation of gaseous benzene with ozone was carried out over supported manganese oxides to investigate the factors controlling the catalytic activities. The rate for benzene oxidation linearly increased with the surface area of catalyst, regardless of the kinds of catalyst support, whereas the ratio of ozone decomposition rate to benzene oxidation rate was larger for SiO 2-supported catalyst than Al 2O 3-, TiO 2-, and ZrO 2-supported catalysts. The rate for benzene oxidation and CO x selectivity increased with the reaction temperature (22–100 °C) and were improved by the addition of water vapor to reaction gases. Benzene conversion and carbon balance increased with ozone concentration.

Sulfur‐induced greenhouse warming on early Mars

Mineralogical, geological, geophysical, and isotopic data recently returned from Mars suggest that the delivery of sulfur gases to the atmosphere may have played a significant role in the planet's early evolution. Using the Gusev Crater basalt composition and a batch melting model, we obtain a high sulfur solubility, approximately 1400 ppm, in Martian mantle melts. We proceed to explore different scenarios for the pulsed degassing of sulfur volatiles associated with the emplacement of near‐surface dikes during the late Noachian or early Hesperian, when surface pressures are thought to be substantially higher than present. We investigate background Martian atmospheres of 50 and 500 mbar CO2 with varying abundances of H2O and sulfur volatiles (H2S and SO2 mixing ratios of 10−3 to 10−6). Results suggest that these sulfur volatile influxes, alone, could have been responsible for greenhouse warming up to 25 K above that caused by CO2. Including additional water vapor feedback, this process could have raised the early surface temperature above the freezing point for brines and possibly allowed transient liquid water on the Martian surface. Each temperature rise was likely to have been short‐lived, however, due to brief residence times for sulfur volatiles in an optically thin atmosphere.

Protective and non-protective scale formation of NiCr alloys in water vapour containing high- and low- pO 2 gases

The oxidation behaviour of NiCr alloys with Cr contents of 10, 20 and 25 wt.%, respectively, were studied in Ar–O 2, Ar–O 2–H 2O and Ar–H 2O mixtures. TG and SEM analysis revealed that the chromia scales formed on Ni–25Cr in the wet gases did not differ substantially from those formed in Ar–O 2. For the two “borderline” alloys Ni–10Cr and Ni–20Cr, addition of water vapour to Ar–O 2 hampered the formation of a protective chromia scale which, especially for Ni–10Cr, resulted in substantially increased scale growth rates compared to exposures in dry gas. Different from numerous observations described in the literature for “borderline” FeCr alloys with intermediate Cr contents of 10–20%, the corresponding NiCr alloys showed in Ar–H 2O a smaller tendency for non-protective scale formation than in Ar–O 2–H 2O. This is caused by the decreasing growth rate of NiO with decreasing pO 2 of the test gas, with the secondary effect that external chromia scale formation is promoted in low- pO 2 gases such as Ar–H 2O. Even if the alloy Cr content was too low to obtain external chromia scale formation, the oxidation rate in Ar–H 2O would, in contrast to low-Cr FeCr alloys, be quite small due to the very slow growth rate of NiO in this low- pO 2 gas.

Mixed oxide catalyst for the selective oxidation of CO

In this work, various supported platinum catalysts (Pt/MeOx, Me = Fe, Zn, Al, Ni) were prepared by colloid-deposition method, and their catalytic properties for the low-temperature CO oxidation were investigated. It was found that the type of support has considerable effect on the activity of the catalysts. The addition of water vapor in feed stream has the positive influence on the activity of the catalysts. Under an optimized tested condition, Pt/Fe2O3 shows unusual low-temperature activity and long-term stability, and it can completely transform CO into CO2 at room temperature in the presence of water vapor for more than 3000 h.

In Situ FT-IR Study of Photocatalytic Decomposition of Formic Acid to Hydrogen on Pt/TiO2 Catalyst

Abstract The anaerobic photocatalytic decomposition of formic acid to hydrogen on Pt/TiO2 was studied by in situ FT-IR spectroscopy. The molecularly adsorbed formic acid species is transformed to a formate species, and the formate species is transformed to carbonates during this reaction. The addition of water vapor in the reaction system strongly accelerates this photocatalytic reaction and promotes the H2 production efficiency. The possible mechanism of the reaction is proposed.

21115 微小重力下での希薄炭化水素-空気混合気の燃焼特性に及ぼす雰囲気湿度の影響について(第2報)(燃料と燃焼の新しい展開(3),OS.9 燃料と燃焼の新しい展開,学術講演)

In practical internal combustion engines, where it is very important to achieve the low emissions (CO_2,NO_x,SO_x). It is well known that the lean burn is very useful method to reduce the emissions by control of flame temperature. Therefore, in this study, at low oxygen concentration high humidity mixture was used for flame temperature reduction. Experiments have been carried out with lean propane-air mixtures to examine the influence of oxygen concentration under high-humidity air and dry air conditions on flame shape and flame speed in a combustion tube. The experimental results in this study are as follows. : (1) Under low oxygen concentration, the addition of water vapor is very effective to increase the flame speed under normal and microgravity. (2) Influence of atmosphere humidity on flame speed depends on a fuel property.

The Dynamic Response of the Winter Stratosphere to an Equable Climate Surface Temperature Gradient

AbstractThis work investigates the dynamic and thermal response of the winter stratosphere to the presence of a weak meridional surface temperature gradient. Previous work suggested that polar stratospheric clouds could have played a decisive role in maintaining high-latitude warmth, especially over continental interiors, during the polar nights of the late Paleocene and early Eocene epochs; both a chemical source of additional water vapor and a dynamical feedback between the surface climate and stratospheric temperatures have been proposed as mechanisms by which such clouds could form. A principal goal of this work is to investigate the latter problem using a general circulation model with stratospheric resolution that is forced with a very weak surface temperature gradient. It is found that temperatures in the lower stratosphere do not deviate significantly from the control run, which results from a robust flux of wave activity into the winter stratosphere. The strength of the stratosphere’s residual circulation increases slightly in the presence of the weak gradient, as wavenumber 3 begins to propagate to stratospheric altitudes. Changes in the zonal wind field that allow for the altered propagation are in balance with a weakened temperature gradient through the full depth of the troposphere. These simulations also suggest that the tropospheric thermal stratification could be maintained by moist convection at all latitudes in warm climate states with a weak temperature gradient.

Low-temperature CO oxidation over supported Pt catalysts prepared by colloid-deposition method

Abstract In this work, various supported platinum catalysts (Pt/MeOx, Me = Fe, Zn, Al, Ni) were prepared by colloid-deposition method, and their catalytic properties for the low-temperature CO oxidation were investigated. It was found that the type of support has considerable effect on the activity of the catalysts. The addition of water vapor in feed stream has the positive influence on the activity of the catalysts. Under an optimized tested condition, Pt/Fe2O3 shows unusual low-temperature activity and long-term stability, and it can completely transform CO into CO2 at room temperature in the presence of water vapor for more than 3000 h.

Modeling and Experimental Study on Nitric Oxide Treatment Using Dielectric Barrier Discharge

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, nonthermal plasma technology was used to remove nitric oxide (NO) from a mixture of air and water vapor. A chemical model was developed to obtain NO removal mechanism and to observe the behavior of the species in the plasma discharge. The influence of water vapor addition on NO removal efficiency was also investigated. Results obtained from the model indicate that the NO removal is mainly achieved by chemical reactions with <formula formulatype="inline"><tex>$\hbox{O}^{\bullet}$</tex></formula>, <formula formulatype="inline"><tex>$ \hbox{N}^{\bullet}$</tex></formula>, and <formula formulatype="inline"><tex>$\hbox{OH}^{\bullet}$</tex></formula> radicals. Experimental results of the NO removal process in a dielectric barrier discharge are also presented. Several experimental parameters such as power, frequency, initial concentration of NO, and specific input energy were tested, and a <formula formulatype="inline"><tex>$\hbox{NO}_{x}$</tex></formula> removal efficiency of approximately 98% was achieved. </para>

Nanostructure Fabrication by Electron-Beam-Induced Deposition with Metal Carbonyl Precursor and Water Vapor

Nanorod fabrication is performed by electron beam induced deposition (EBID) with iron carbonyl [Fe(CO)5] and tungsten carbonyl [W(CO)6] precursors. The effects of water vapor addition to each metal carbonyl on the microstructure and composition of the obtained nanorods are studied. Normally, EBID-fabricated metal nanorods consist of an amorphous phase containing a considerable amount of carbon. However, it is found that water vapor addition to iron carbonyl can effectively reduce the carbon content of the nanorods and induce the formation of carbon-free crystalline Fe3O4 nanorods with increasing partial pressure ratio of water vapor to iron carbonyl. In contrast, for tungsten carbonyl, water vapor addition has no obvious effect on carbon content reduction. The obtained nanorods consist of a carbon-rich amorphous matrix containing tungsten oxide nanocrystals inside.

Mechanisms of Crystalline Iron Oxide Formation in Electron Beam-Induced Deposition

The effects of water vapor and oxygen addition to an iron pentacarbonyl precursor on the formation of iron oxide deposits were studied to understand the mechanism of iron oxide formation in electron beam-induced deposition. The water vapor addition markedly reduced the carbon content in the deposits and led to the formation of crystalline iron oxide. However, the oxygen addition had little effect on the composition and structure of the deposits. This suggests that iron acts as a catalyst and a chemical reaction similar to the water gas reaction occurs during the electron beam-induced deposition.

Carbonation of fly ash in oxy-fuel CFB combustion

Oxy-fuel combustion of fossil fuel is one of the most promising methods to produce a stream of concentrated CO 2 ready for sequestration. Oxy-fuel FBC (fluidized bed combustion) can use limestone as a sorbent for in situ capture of sulphur dioxide. Limestone will not calcine to CaO under typical oxy-fuel circulating FBC (CFBC) operating temperatures because of the high CO 2 partial pressures. However, for some fuels, such as anthracites and petroleum cokes, the typical combustion temperature is above 900 °C. At CO 2 concentrations of 80–85% (typical of oxy-fuel CFBC conditions with flue gas recycle) limestone still calcines, but when the ash cools to the calcination temperature, carbonation of fly ash deposited on cool surfaces may occur. This phenomenon has the potential to cause fouling of the heat transfer surfaces in the back end of the boiler, and to create serious operational difficulties. In this study, fly ash generated in a utility CFBC boiler was carbonated in a thermogravimetric analyzer (TGA) under conditions expected in an oxy-fuel CFBC. The temperature range investigated was from 250 to 800 °C with CO 2 concentration set at 80% and H 2O concentrations at 0%, 8% and 15%, and the rate and the extent of the carbonation reaction were determined. Both temperature and H 2O concentrations played important roles in determining the reaction rate and extent of carbonation. The results also showed that, in different temperature ranges, the carbonation of fly ash displayed different characteristics: in the range 400 °C < T ⩽ 800 °C, the higher the temperature the higher the CaO-to-carbonate conversion ratio. The presence of H 2O in the gas phase always resulted in higher CaO conversion ratio than that obtainable without H 2O. For T ⩽ 400 °C, no fly ash carbonation occurred without the presence of H 2O in the gas phase. However, on water vapour addition, carbonation was observed, even at 250 °C. For T ⩽ 300 °C, small amounts of Ca(OH) 2 were found in the final product alongside CaCO 3. Here, the carbonation mechanism is discussed and the apparent activation energy for the overall reaction determined.