Steam Partial Pressure Research Articles

Ba0.5Gd0.8La0.7Co2O6−δ Infiltrated BaZr0.8Y0.2O3-δ Composite Oxygen Electrodes for Protonic Ceramic Electrolysis Cells

In this study, a composite oxygen electrode is prepared by infiltrating a protonic-electronic conducting material, Ba0.5Gd0.8La0.7Co2O6−δ (BGLC) into a proton-conducting BaZr0.8Y0.2O3-δ (BZY20) backbone. The composite oxygen electrode is studied in a symmetric cell configuration (BGLC-BZY20//BZY20//BGLC-BZY20). The electrochemical performance is characterized by systematically varying the operating conditions, including temperature, oxygen, and steam partial pressures, with the purpose to identify and characterize the different electrochemical processes taking place in the oxygen electrode. Two electrode reaction processes are observed in the impedance spectra: one in the middle-frequency range tentatively ascribed to the process of proton transfer from the electrode to the electrolyte, and the other in the low-frequency range corresponding to diffusion of O− species. The BGLC-BZY20 electrode developed in this work shows a low polarization resistance of 0.44, 1.17, and 2.87 Ω cm2 in 3 % humidified synthetic air (21% O2/79% N2) at 600, 550, and 500 ℃, respectively.

Determination of water loading of supported ionic liquids by microwave analysis - A contribution for operando monitoring of gas drying by adsorption

Ionic liquids (ILs) immobilized on solid porous supports are alternative materials for gas drying by fixed-bed adsorption: The IL 1-ethyl-3-methylimidazolium methanesulfonate has a high capacity for sorption of water vapor, and losses of the IL via evaporation are negligible because of the extremely low vapor pressure. Hence, ILs can be durably immobilized by coating of porous supports. Ionic liquids have a high electrical conductivity compared to supports such as silica. This can be utilized to monitor the water loading of supported IL by microwaves. A fixed-bed adsorber was placed in a cylindrical microwave resonator, and the water loading and the corresponding electrical signals were measured by a humidity sensor and a network analyzer, respectively. The partial pressure of steam (carrier gas N2) and the temperature were varied in a range relevant for gas drying (5–20 mbar; 40–90 °C). The results reveal that the microwave parameters, such as the resonance frequency shift, are suitable to determine accurately and operando the water loading of supported ionic liquids. Further analysis of the microwave parameters leads to the complex susceptibility, which in turn shows a linear dependence of the polarization effects on the electrical losses.

Development of test protocols for solid oxide electrolysis cells operated under accelerated degradation conditions

In order to be a real competitor to other industrial-scale hydrogen production technologies, solid oxide electrolysis cells (SOEC) must present essential features such as high hydrogen production rates, load flexibility and high system efficiency. However, operating conditions necessary to achieve these objectives can induce undesired performance deterioration and microstructural degradation negatively influencing the long-term stability of SOECs. This work provides the results of experimental investigations on the performance of SOECs operated under different operating conditions. In order to induce and accelerate specific degradation phenomena high steam partial pressures, fast load changes, high voltages, high steam conversion rates and alternating mode were applied. Different kinds and degrees of impact on performance and microstructure were observed and analyzed in detail. Correlations between performance changes and their underlying processes were investigated and useful connections between them were discovered. The major findings are summarized in the form of a suggestion for accelerated stress test (AST) protocols for SOECs. The developed ASTs enable deeper understanding of several degradation phenomena induced by different operating conditions and present methods for identification thereof. Further, the ASTs were estimated to have potential to predict performance changes over long-term operating periods.

A humidity-controlled precipitation technique enabling discovery of Rb3(H1.5PO4)2

The previously unknown compound Rb3(H1.5PO4)2 is successfully synthesized here using a newly developed variant of aqueous precipitation crystal growth. The approach exploits the phenomenon of boiling point elevation in concentrated solutions. Crystals of the title compound were obtained upon heating a stoichiometric solution from 110 to 150 ​°C under a high steam partial pressure of 0.83 ​atm. Single crystal X-ray diffraction studies revealed Rb3(H1.5PO4)2 crystallizes in space group C2/m and is isostructural to Cs3(H1.5PO4)2. As evidenced by thermal analysis, Rb3(H1.5PO4)2 does not undergo a phase transition to a trigonal superprotonic phase upon heating. Even under a steam partial pressure of 0.82 ​atm, under which dehydration is suppressed to a temperature of 263 ​°C, no polymorphic transition is detected. The behavior parallels that of Cs3(H1.5PO4)2 and contrasts that of several structurally and chemically similar selenate compounds. The crystal growth approach developed here may prove particularly useful for obtaining water soluble compounds which are thermodynamically or kinetically disfavored at temperatures close to ambient.

Steam gasification of powder river basin coal: surface reaction kinetics and intraparticle mass transfer restrictions

Steam gasification kinetics studies were conducted in a modified drop tube fixed bed reactor to approximate the injection of ambient temperature coal into a fluidized bed gasifier. Product gases were measured using a customized rapid response gas analysis system with a quadrupole mass spectrometer. Experiments were done within Regime I temperature range (no mass transfer restrictions), and effects of temperature and pressure on surface chemical reaction were analyzed using three different particle size ranges. The random pore model closely fits the experimental results and the fitting parameters are listed. Char characterizations are presented, including surface area measurements and scanning electron microscope images. Mass transfer resistances were analyzed by comparing experimental and theoretically predicted effectiveness factors using the Thiele modulus, based on particle sizes, temperature, total pressure, and steam partial pressure.

Catalyzed Steam Gasification of Cistus Ladanifer Biochar

Gasification processes require the use of cheap and sustainable raw materials, as well as the optimization of the process, for a suitable commercial use. Cistus Ladanifer (rockrose) could be a suitable raw material for this purpose, as it grows spontaneously in Mediterranean regions, and might contribute to the economic development of these areas. In this research, a study about catalyzed gasification of Cistus Ladanifer biochar was carried out. The aim was to characterize the gaseous phase and to carry out a kinetic study. The experiments were carried out in a thermobalance connected to a gas chromatograph to quantify the exhaust gas. The operating variables studied were the initial carbon mass, temperature, steam partial pressure, the kind of catalyst (ionic or cationic), catalyst concentration and the method to incorporate the catalyst (impregnation or mixture). As a result, impregnation was the most effective way to mix the raw material and the catalyst, with K+ and CO32− as the most active cations and anions used in this experience, respectively. Temperature and steam partial vapor showed a positive effect on conversion and gas yield. The use of ideal models for gas-solid reactions showed acceptable results for the kinetic study.

Mechanistic Study on the Removal of NO2 from Flue Gas Using Novel Ethylene Glycol-tetrabutylammonium Bromide Deep Eutectic Solvents.

The removal of NOx (approximately 90% of which is NO) from flue gas is a crucial process for clean power generation from coal combustion. Oxidation of NO to NO2 followed by NO2 absorption using sorbents is considered to be a promising technology alternative to selective catalytic reduction (SCR). This study investigated the absorption of NO2 in flue gas by ethylene glycol (EG)-tetrabutylammonium bromide (TBAB) deep eutectic solvents (DESs) under a range of experimental conditions. The effects of experimental conditions including molar ratio of EG to TBAB, operating temperature, residence time, and the O2 and steam partial pressure in the flue gas on the denitrification performance of EG-TBAB DESs were systematically analyzed. The concentrations of NO2 in the inlet and outlet were evaluated using a flue gas analyzer. The chemical structure changes of DESs after denitrification were characterized using Fourier transform infrared (FT-IR) spectroscopy. The obtained analysis signified that maximum denitrification efficiency and capacity were achieved at a EG/TBAB molar ratio of 5:1, 50 °C, and 6 s residence time. EG-TBAB DESs were able to maintain a stable denitrification performance after five absorption–desorption cycles. The results of quantum chemical calculation and 1H NMR spectra of EG-TBAB DES show that bromide anions in the EG-TBAB DES maintained strong interactions with NO2 via hydrogen bonding, leading to increased NO2 adsorption. The presence of O2 and steam in the flue gas improved the absorption of NO2 in EG-TBAB DESs due to chemical reactions and formation of nitrate.

Steam adsorption on molecular sieve 3A for sorption enhanced reaction processes

Steam adsorption enhanced reaction processes are a promising process intensification for many types of reactions, where water is formed as a byproduct. To assess the potential of these processes, adequate models are required that accurately describe water adsorption, particularly under the desired elevated temperatures and pressures. In this work, an adsorption isotherm is presented for H2O adsorption at 200–350 °C and 0.05–4.5 bar partial pressure on molecular sieve (LTA) 3A. The isotherm has been developed on the basis of experimental data obtained from a thermogravimetric analysis and integrated breakthrough curves. The experimental data at lower steam partial pressures can be described with a Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm, whereas at higher steam partial pressures the experimental data can be adequately captured by capillary condensation. Based on the characteristics of the adsorbent particles, a linear driving force relation has been derived for the adsorption mass transfer rate and the apparent micropore diffusivity is determined. The isotherm and mass transport model presented here prove to be adequate for modelling and improved evaluation of steam adsorption enhanced reaction processes.

Reforming of toluene with simulated automobile exhaust gas over hydrotalcite-like-compound-derived Ni catalyst

Reforming of toluene, which is a model compound of gasoline, with model exhaust gas (model EGR gas) of gasoline engine was carried out with Ni catalyst. The Ni/Mg/Al catalyst prepared from hydrotalcite-like precursor compound showed higher performance than Ni/α-Al2O3 catalyst in terms of activity, stability and coke deposition resistance. The activity of Ni/Mg/Al after the initial deactivation was about 1/200 of Rh/CeO2 based on the weight of active metal (Ni or Rh), and the difference was much smaller than that of price between Ni and Rh. The amount of coke deposition on Ni/Mg/Al catalyst was increased with increases of W/F or partial pressure of toluene, especially at the outlet of the catalyst bed, where the coke formation is mainly due to CO disproportionation. The deactivation was also severer in larger partial pressure of toluene when the toluene feed was changed while partial pressure of H2O, N2 and CO2 was set constant to the model EGR gas. Large steady state H2 formation and high conversion were obtained at conditions with low partial pressure of toluene, similarly to the case of simple steam reforming, the Ni/Mg/Al catalyst after reaction can be regenerated by the combination of oxidation (at 773 K) and reduction (at 1073 K) treatments. The effect of feed ratio of H2O:N2:CO2 showed that low partial pressure of steam in model EGR gas in comparison with standard feed gas for steam reforming is the main reason for low toluene conversion and coke deposition resistance. On the other hand, the presence of CO2 did not affect the conversion and the coke deposition behavior so significantly.

Insight into Steam Permeation through Perovskite Membrane via Transient Modeling

A dynamic model based on BaCe0.9Y0.1O3−δ (BCY10) perovskite membrane for steam permeation process is presented here to essentially investigate the internal mechanism. The transient concentration distribution and flux of the charged species and the electric potential distribution within the membrane on the steam permeation process are analyzed in detail via simulation based on this model. The results indicate that the flux of steam can be improved via elevating operating temperatures, enlarging the difference of the partial steam pressure between two sides of the membrane, increasing the membrane density, and reducing the membrane thickness. Moreover, it was found that the polarization electric potential between both sides of the membrane occurs during the steam permeation process, especially at the steady state of the steam permeation process. The polarization electric potential reaches the maximum value at about 1050 K in this membrane. The evolution of electric potential can explain the influence of the above-mentioned factors on the steam permeation process. This study advances the mechanism of steam permeation through perovskite membrane, which provides a new strategy for the fundamental investigation of related species permeation (oxygen, carbon dioxide, hydrogen, etc.) on inorganic membranes via transient modeling.

The electrochemical interface of the cathode in high temperature PEM fuel cells

One of the most challenging areas towards the optimization of fuel cell technology is the development of catalytic layers with active, extended and stable electrochemical interfaces giving the ability to operate under a variety of operational conditions. In this work, the effect of parameters such as the amount of H3PO4 and Pt loading was examined regarding the formation of the electrochemical interface of an operating cathodic electrode in a high temperature PEM Fuel Cell. Electrodes beased on commercial 30 wt% Pt/C and H3PO4 imbibed TPS polymer electrolyte membrane were employed. Based on the thickness and catalyst loading of the catalytic layer, there is an optimum amount of acid in relation to the partial pressure of steam (pH2O) produced at the cathode that leads to uniform wetting of the catalyst avoiding catalyst poisoning and/or blocking due to flooding of the electrode. Interestingly high pH2O causes a decrease in H2 evolution reaction rate and increase in H2 adsorption coverage, implying stronger Had bonding with the Pt surface. Moreover, this work describes the development of a reliable procedure for quantitative evaluation of the real electrochemical active surface area (ECSA) of high temperature Pt electrodes by the combined analysis of CO stripping experiments and the simultaneous CO2 recording by means of online mass spectrometry. Regardless of the H3PO4 or Pt loading in the cathodic electrode, increase of steam's partial pressure progressively causes the degradation the Pt/C|H3PO4 electrochemical interface. At pH2O > 10 kPa, the ECSA decreased in all cases, but more intensely for high amounts of Η3PΟ4 within the electrode structure. The charge of the peak in the cyclic voltammogram did not completely correspond to the CO electrooxidation reaction. This difference is attributed to side oxidation reactions taking place within the same potential window as with the COad electrooxidation and depends on conditioning time (CO adsorption time), temperature and humidity.

THE CONDENSATION OF WATER VAPOUR IN A MIXTURE CONTAINING A HIGH CONCENTRATION OF NON-CONDENSABLE GAS IN A VERTICAL TUBE

This paper deals with the condensation of water vapour possessing a content of noncondensable gas in vertical tubes. The condensation of pure steam on a vertical surface is introduced by the Nusselt condensation model. However, the condensation of water vapour in a mixture with non-condensable gas differs from pure vapour condensation and is a much more complex process. The differences for the condensation of water vapour in a mixture containing a high concentration were theoretically analysed and evaluated. In order to investigate these effects, an experimental stand was built. Experiments were carried out in regards to the case of pure steam condensation and the condensation of water vapour with a non-condensable gas mixture to evaluate the influence of the variable non-condensable gas content during the process. A non-condensable gas in a mixture with steam decreases the intensity of the condensation and the condensation heat transfer coefficient. A gradual reduction of the volume and partial pressure of steam in the mixture causes a decrease in the condensation temperature of steam, and the temperature difference between steam and cooling water. The increasing non-condensable gas concentration restrains the transportation of steam towards the tube wall and this has a significant effect on the decrease in the condensation rate.

Comparison of Heat Transfer Performance for Condensation in Corrugated Low Finned Tube and Smooth Tube with Air

The existence of air served as non-condensable gas makes it difficult to design effective titanium condenser in PTA plant. In this paper, the heat transfer characteristic for condensation inside corrugated low finned tube and smooth tube in presence of air was compared. The local heat transfer performance was studied by comparing bulk temperature and local heat transfer rate. The effect of non-condensable gas mass fraction on overall heat transfer performance was also analysed. The results indicated that both the bulk temperature and the local heat transfer rate decreased along the axial direction due to the reduction of steam partial pressure and temperature difference. The average heat transfer coefficient and total heat transfer rate decreased with the increase of inlet non-condensable gas mass fraction. And the corrugated low finned tube could reduce the impact of non-condensable gas by reducing the thickness of gas film and condensate film.

Effects of steam on toluene hydrogenation over a Ni catalyst

The catalytic toluene hydrogenation over Ni/SiO2 was carried out using H2 or a H2/H2O mixture. The toluene conversion and MCH selectivity were evaluated under partial steam pressures 0−10 kPa, at H2/toluene molar ratios 1–5, and at temperatures 393−453 K. In the absence of steam, toluene conversion increased with increasing H2 partial pressure, and the MCH selectivity decreased with increasing temperature. In the presence of steam, the toluene conversion showed near-constant activities over the entire range of steam partial pressures, and the MCH selectivity increased with increasing steam partial pressure. This result indicated that the addition of steam inhibited byproduct formation. To clarify the effects of steam on the side-reaction, the byproducts composition was analyzed using a gas chromatograph. The results showed that the addition of steam inhibited demethylation, the ring-opening reaction of MCH, the disproportionation of toluene, and isomerization to convert six-membered ring compounds into five-membered ring compounds.

CO2 assisted steam flooding in late steam flooding in heavy oil reservoirs

To improve the oil recovery and economic efficiency in heavy oil reservoirs in late steam flooding, taking J6 Block of Xinjiang Oilfield as the research object, 3D physical modeling experiments of steam flooding, CO2-foam assisted steam flooding, and CO2 assisted steam flooding under different perforation conditions are conducted, and CO2-assisted steam flooding is proposed for reservoirs in the late stage of steam flooding. The experimental results show that after adjusting the perforation in late steam flooding, the CO2 assisted steam flooding formed a lateral expansion of the steam chamber in the middle and lower parts of the injection well and a development mode for the production of overriding gravity oil drainage in the top chamber of the production well; high temperature water, oil, and CO2 formed stable low-viscosity quasi-single-phase emulsified fluid; and CO2 acted as a thermal insulation in the steam chamber at the top, reduced the steam partial pressure inside the steam chamber, and effectively improved the heat efficiency of injected steam. Based on the three-dimensional physical experiments and the developed situation of the J6 block in Xinjiang Oilfield, the CO2 assisted steam flooding for the J6 block was designed. The application showed that the CO2 assisted steam flooding made the oil vapor ratio increase from 0.12 to 0.16 by 34.0%, the oil recovery increase from 16.1% to 21.5%, and the final oil recovery goes up to 66.5% compared to steam flooding after perforation adjustment.

One-step rapid pyrolysis activation method to prepare nanostructured activated coke powder

A one-step rapid pyrolysis activation method is proposed to produce activated coke powder (ACP) via a drop tube reactor by using pulverized Datong coal (DTC) and pine wood (PW) as feedstock. Small feedstock particle size, high heating rate, and effective activation agent, i.e., the mixture of oxygen and steam were arranged for the fast formation and development of various pore structure of ACPs. Detail characteristics of the ACP were investigated by using the nitrogen adsorption measurement, scanning electron microscope (SEM) and Fourier transform infrared spectrometer (FTIR) analysis. Results showed that the ACP presented well-developed nanostructure with considerable pore volume, specific surface area and surface functional groups. The pore volume and specific surface area of PWC-O6S10 could reach 0.2373 cm3/g and 250.57 m2/g. Activation atmosphere had played an important role to develop the pore structure and morphology of the ACP. Under 6 vol% oxygen concentration, the optimum steam partial pressure for micropore development of DTC was about 15 vol%, while it mostly promoted the growth of mesopores for PWC. All ACP samples presented variety of C/O/N containing surface functional groups, including OH, CH, CC, CO, CO, COC, CN, CN, etc., which remained relatively stable as the activation agents concentration changed.

Intrinsic methane steam reforming kinetics on nickel-ceria solid oxide fuel cell anodes

Direct internal reforming in solid oxide fuel cells (SOFCs) is advantageous as it enables to heat and steam from the exothermic hydrogen oxidation reaction in the endothermic steam reforming reaction. However, it may increase potentially deteriorating temperature gradients as well. The temperature and concentration profiles can be accurately simulated with adequate SOFC models and intrinsic methane steam reforming (MSR) kinetics. Therefore, this study aims to derive intrinsic MSR kinetics suitable for control-oriented dynamic SOFC models. The individual influences of the methane, steam and hydrogen partial pressures on the MSR reaction are experimentally studied on functional electrolyte supported cells with nickel-gadolinium doped cerium anodes. A non-proportional dependence of the MSR rate on the methane partial pressure and a slight negative dependence on the steam partial pressure are observed, but the effect of the hydrogen partial pressure seems insignificant. Various kinetic rate equations are parameterised with the experimental data and an ideal plug flow reactor model. An intrinsic Langmuir-Hinshelwood mechanism for a rate determining step between associatively adsorbed methane and dissociatively adsorbed steam on the catalyst surface shows good agreement with the experimental data, and is thermodynamically and physically consistent.

Kinetic and hydrodynamic analyses of chemically reacting gas-particle flow in cupric chloride hydrolysis for the Cu-Cl cycle

The non-catalytic reaction of cupric chloride with steam to produce copper-oxy-chloride solid and hydrogen chloride gas is one of the most challenging steps in the copper-chlorine (Cu–Cl) thermochemical water splitting cycle of hydrogen production. Researchers at the University of Ontario Institute of Technology have designed a reactor in which a CuCl2 (aq) solution is atomized and reacted in a furnace where superheated steam is drawn in a counter-current stream. This study develops a new predictive model of the transport mechanisms of the hydrolysis reaction to predict the conversion of CuCl2(s) into the products. The hydrodynamic model estimates the residency time of the reactants in the reaction, and the kinetics predicts the gas-solid reaction through the shrinking core diffusion model (SCM). It is shown that the maximum conversion of CuCl2 is limited by the reactant velocity, reaction temperature, steam partial pressure and particle size. Results of the lab-scale experimental hydrolysis unit are presented and discussed.

Modeling of gasification process of Indian coal in perspective of underground coal gasification (UCG)

In the present study, the steam gasification of Indian coal and its demineralized coal were investigated in a specially designed fixed-bed reactor, to determine the intrinsic kinetics parameters with optimum operating temperature and partial pressures of steam in the perspective of underground coal gasification (UCG). The gasification reactivity of a chosen coal was higher compared to the demineralized coal and the reason could be mineral content of ash present in the coal. A one-dimensional unsteady kinetic model was developed for the steam gasification process in a fixed-bed reactor. The intrinsic kinetic parameters for steam gasification and water–gas shift reaction are estimated by fitting the developed models with the experimental data.

Experimental and optimization studies of hydrogen production by steam methane reforming over lanthanum strontium cobalt ferrite supported Ni catalyst

Over the years, research focused has been on the development of active and stable catalysts for hydrogen (H2) production by steam methane reforming (SMR). However, there is less attention on the individual and interaction effect of key process parameters that influence the catalytic performance of such catalysts and how to optimize them. The main objective of this study is to investigate the individual and interaction effects of key parameters such as methane partial pressure ((Formula presented.) (10-30 kPa), steam partial pressure ((Formula presented.) (10-30 kPa), and reaction temperature (T) (750-850°C) on H2 yield and methane (CH4) conversion during SMR using Box-Behnken experimental design (BBD) and response surface methodology. The H2 production was catalyzed using Ni/LSCF prepared by wet impregnation method. The evaluation of the Ni/LSCF using different instrument techniques revealed that the catalyst exhibited excellent physicochemical properties suitable for SMR. Response surface models showing the individual and interaction effect of each of the parameters on the H2 yield and CH4 conversion were obtained using the set of data obtained from the BBD matrix. The three parameters were found to have significant effects on the H2 yield and CH4 conversion. At the highest desirability of 0.8994, maximum H2 yield and CH4 conversion of 89.77% and 89.01%, respectively, were obtained at optimum conditions of 30 kPa, 28.86 kPa, and 850°C for (Formula presented.), (Formula presented.), and temperature, respectively. The predicted values of the responses from the response surface models were found to be in good agreement with the experimental values. At optimum conditions, the catalyst was found to be stable up to 390 minutes with time on stream. The characterization of the used catalyst using thermogravimetric analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy showed some evidence deposition of a small amount of carbon on the catalyst surface.