High-temperature Gas Mixtures Research Articles

Thermal Aging of Rh/ZrO2–CeO2 Three-Way Catalysts under Dynamic Lean/Rich Perturbation Accelerates Deactivation via an Encapsulation Mechanism

A Rh/ZrO2–CeO2 (Rh/ZC) three-way catalyst was exposed to high-temperature exhaust gas mixtures fluctuating between stoichiometric (S), oxidizing (fuel-lean, L), and reducing (fuel-rich, R) compositions. The catalyst deactivation during thermal aging at 1000 °C for 40 h under a dynamic SLR cycle condition (S: 25 s, L: 2.5 s, and R: 2.5 s) was more severe than that under static conditions (S, L, or R). Chemisorption, transmission electron microscopy, and X-ray photoelectron spectroscopy showed that the total encapsulation of Rh particles with a ZC overlayer caused physical blockage and suppressed catalytic activity. This deactivation mode of the SLR-aged catalyst was characterized by the Rh particle size (ca. 17 nm) as small as that of the R-aged catalyst (ca. 15 nm in size), which preserved the highest activity. On the other hand, their CO chemisorption capacities differed by 50-fold. Almost complete encapsulation occurred under a dynamic SLR cycle condition but not under the reducing (R) and other static conditions (S and L). Furthermore, post-treatment in air at 1000 °C did not recover the catalyst from the encapsulation state. This result was in contrast to the well-known strong metal–support interaction-induced decoration or encapsulation effects of metal catalysts supported on CeO2-based oxides, which occur under a strongly reducing atmosphere at high temperatures but disappear after subsequent reoxidation. The encapsulation under a dynamic SLR cycle condition suggests that the migration of ZC components to overcoat and embed Rh particles is activated by repeated oxygen release and storage near the metal–support interface.

Production and Production-Increasing Factors of Biochar

In the article, we deal with biochar-related research and our own developments. Studies in the literature show that biochar can be used as a soil conditioner in agriculture and horticulture. It improves many physical, chemical, and biological properties of the soil and substrate. It increases the water retention capacity while reducing the leaching of nutrients. Through these, you can improve the profit of producers, the sustainability of production, and the efficiency of fertiliser use. By increasing water retention, biochar can reduce irrigation needs and enable production on limited water resources. The developed and presented equipment was called the resting bed (fixed bed) version. Drying and carbonization are also carried out by direct heat transfer. The material, with a temperature equalised by moving drying and a homogeneous composition, enters the reactor. The high-temperature gas and air mixture is introduced into the dryer by a gas jet pump. The energy obtained by burning the pyrolysis gases produced during carbonization ensures the heating of the system, so there is no need for significant external energy input. Due to the structure of the system, the PAH content of the final product is low.

Investigation of the EHD Structure of Flow of a High-Temperature Gas Mixture with a Non-Uniform Source of Charged Particles

Investigation of the EHD Structure of Flow of a High-Temperature Gas Mixture with a Non-Uniform Source of Charged Particles

Determining temperature and partial pressures of the components of a high-temperature gas mixture using artificial neural networks

The article deals with solving the inverse problem of gaseous media optics by determining the parameters of high-temperature gaseous media from its transmittances using the artificial neural networks. The study of the dependence of the maximum relative error in determining the desired parameters on the size of the training set and the artificial neural network configuration is carried out. The possibility of solving the inverse problem in the case of a four-component gas mixture (water vapor, carbon dioxide, carbon oxide and nitrogen oxide) is shown.

Regeneration Mechanism of Sulfur Absorption Via Samarium-doped Cerium Adsorbents in the Gas Atmosphere of O2/N2.

Sulfides existing in many high-temperature gas mixtures have a negative effect on various industrial applications. Ce-based adsorbents are becoming a hotspot in the high-temperature desulfurization process owing to their excellent thermal stability at high temperatures and regeneration capacity. In this study, we investigate the regeneration path of samarium-doped cerium (SDC) sorbent at high temperature. The SDC adsorbent showed a good sulfur removal ability and excellent regeneration capacity. Ce2O2S and Ce(SO4)2 are observed in the used adsorbent, and Ce2O2S is the main sulfur-containing species. The regeneration path of the Ce2O2S is the key to the regeneration mechanism of the adsorbent. There are two regeneration paths for the Ce2O2S at high temperature in O2/N2 gas mixture. In air stream, the Ce2O2S is oxidized to Ce2O2SO4 and then decomposes into CeO2 and SO2. In a 2% O2/N2 gas condition, the Ce2O2S directly generates CeO2 and elemental sulfur with O2 assistance.

Numerical simulation of a three-layer porous heat exchanger considering lattice Boltzmann method simulation of fluid flow

The present study investigates the thermal characteristics of a proposed porous heat exchanger (PHE). This heat exchanger consists of three sections, one high-temperature (HT) section and two heat recovery (HR) sections. Product of combustion as a high-temperature gas mixture enters to HT section in which enthalpy of gas flow is converted to thermal radiation, while in HR sections, the reverse phenomenon occurs. Simulation of fluid flow in porous medium generated by random and regular monodisperse and polydisperse particles is done using combination of the lattice Boltzmann method and smoothed profile method. Because of high-temperature variation in this system, effect of temperature on thermo-physical properties is also considered which has not been studied in previous research studies. Since the gas and solid phases are in non-local thermal equilibrium, separate energy equations are used for these phases. To obtain the radiative term in the solid energy equation, the radiative transfer equation is solved numerically by the discrete ordinates method. The influence of particles array and their sizes on the efficiency of the PHE system is studied. Finally, the effects of various parameters like optical thickness and scattering coefficient on the performance of PHE system are investigated.

Phase-matched extreme-ultraviolet frequency-comb generation

Laser-driven high-order harmonic generation1,2 provides spatially3 and temporally4 coherent tabletop sources of broadband extreme-ultraviolet (XUV) light. These sources typically operate at low repetition rates, frep ≲ 100 kHz, where phase-matched HHG is readily achieved5,6. However, many applications demand the improved counting statistics or frequency-comb precision afforded by high repetition rates, frep > 10 MHz. Unfortunately, at such high frep, phase matching is prevented by steady-state plasma accumulated in the generation volume7–11, strongly limiting the XUV average power. Here, we use high-temperature gas mixtures as the generation medium to increase the gas translational velocity, thereby reducing the steady-state plasma in the laser focus. This allows phase-matched XUV emission inside a femtosecond enhancement cavity at frep = 77 MHz, enabling a record generated power of ~ 2 mW in a single harmonic order. This power scaling opens up many demanding applications, including XUV frequency-comb spectroscopy12,13 of few-electron atoms and ions for precision tests of fundamental physical laws and constants14–20. Using high-temperature gas mixtures as the generation medium to increase the translational velocity of Xe atoms through the focus of a femtosecond enhancement cavity, phase-matched extreme-ultraviolet emission at a repetition rate of 77 MHz and with an average power of ~ 2 mW in a single harmonic order is achieved.

A Monte Carlo Simulation Study To Predict the Solubility of Carbon Dioxide, Hydrogen, and Their Mixture in the Ionic Liquids 1-Alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([Cnmim+][Tf2N–], n = 4, 6)

Ionic liquids are being investigated as potential solvents for pre- and post-combustion CO2 capture. In pre-combustion applications, knowledge of the selectivity of CO2 over H2 in high-pressure and high-temperature gas mixtures is crucial. In the present work, the solubility of carbon dioxide, hydrogen, and their mixture in the ionic liquids 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([Cnmim+][Tf2N–], n = 4, 6) is computed using the isothermal–isobaric Gibbs ensemble Monte Carlo (NPT-GEMC) method. The predicted solubility for CO2 and H2 in 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim+][Tf2N–]) and 1-n-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C6mim+][Tf2N–]) are compared with experimental results. It is found that the predicted absorption isotherms for pure gases in the studied ionic liquids (ILs) agree reasonably well with the available experimental results. The Henry’s Law constants, partial molar enthalpies of absorption, partial molar volumes, and the percentage change in the volumes of the IL phase upon absorption of CO2 and H2 in [C4mim+][Tf2N–] and [C6mim+][Tf2N–] are estimated at different temperatures and are compared with the experimental data. The results indicate that the solubility of CO2 decreases with increasing temperature, whereas, for H2, it slightly increases with increasing temperature, which is consistent with most previous experimental data. Mixed-gas (CO2/H2) experiments are much harder to conduct than pure gas experiments, so it is usually assumed that absorption selectivity is ideal. To test this, mixed gas simulations were also carried out using the NPT-GEMC method. The simulations indicate that the solubility selectivity of CO2 over H2 in [C4mim+][Tf2N–] and [C6mim+][Tf2N–] varies, depending on the vapor phase composition. The selectivities are compared with the Henry’s Law constant ratios and ideal selectivities that are obtained from pure gas isotherms for CO2 and H2 in both ionic liquids. Both computed selectivities and ideal selectivities are close and are different from Henry’s Law constant ratios at 333 K. The results indicate no enhancement in the solubility of H2, because of the presence of CO2 in the IL phase. The selectivity decreases with increasing temperature, which is consistent with the simulation study of Shi et al. [J. Phys. Chem. B 2010, 114, 6531]. This is due to the fact that CO2 solubility decreases with increasing temperature, whereas H2 solubility increases.

The influence of initial sizes and velocities of water droplets on transfer characteristics at high-temperature gas flow

We report the executed experimental investigation of initial sizes and velocities of water droplets movement influence on integral characteristics of its transfer (motion trajectories, velocities, sizes, relative concentration) through high-temperature (more than 1000 K) gas area. It was used the optical methods of two-phase gas–vapor-droplet mixtures diagnostics (“Particle Image Velocimetry” and “Interferometric Particle Imaging”). The limiting values of gas velocities, velocities and sizes of water droplets have been established when the complete droplet evaporation in high-temperature gas mixture is possible. Several modes of droplet motion through the gas flow in intensive evaporation conditions have been singled out and the dependences have been received which allowed to predict these modes.

Droplet evaporation in water jet at the motion through high temperature gases

Heat and mass transfer model for the numerical investigation of the evaporation process of a single droplet in water jet when moving through high temperature gases was developed. The integral characteristics of the process under investigation were calculated. The macroscopic regularities of water droplet evaporation, as elements of jet, in the high temperature gas mixture (as exemplified by combustion products of typical condensed substances) were determined.

ЧИСЛЕННОЕ ИССЛЕДОВАНИЕ УСЛОВИЙ ИСПАРЕНИЯ СОВОКУПНОСТИ КАПЕЛЬ ВОДЫ ПРИ ДВИЖЕНИИ В ВЫСОКОТЕМПЕРАТУРНОЙ ГАЗОВОЙ СРЕДЕ

ЧИСЛЕННОЕ ИССЛЕДОВАНИЕ УСЛОВИЙ ИСПАРЕНИЯ СОВОКУПНОСТИ КАПЕЛЬ ВОДЫ ПРИ ДВИЖЕНИИ В ВЫСОКОТЕМПЕРАТУРНОЙ ГАЗОВОЙ СРЕДЕ

Investigation of the mass loss of a carbon material within the framework of a complete thermochemical model of its destruction in the case of equilibrium chemical reactions in the boundary layer

This article provides data on the parameters of carbon mass loss obtained within the framework of a complete thermochemical model of its destruction, and comparison of them with similar data for the case of consideration of carbon oxidation in the diffusion approximation. The findings are compared with the corresponding published data. A variant of the numerical method is presented, application of which allows for more effectively solving the problems of flow of a multicomponent high-temperature gas mixture at the thermochemical equilibrium condition.

Evolution of volcanic gas composition during repeated culmination of volcanic activity at Kuchinoerabujima volcano, Japan

Chemical and isotopic compositions of low to medium temperature fumarolic gasses were measured at various fumaroles of Kuchinoerabujima volcano from 1993 to 2009 by the combination of fumarolic gas sampling and Multi-GAS measurement of volcanic plumes. Repeated culmination of the volcanic activity was observed as contemporaneous occurrence of seismic swarms, summit inflation and demagnetization, almost every two years after 1999. Fumarolic activity also increased parallel with these activities; new fumarolic fields of low-temperature fumaroles at boiling point formed at the southern and western rims of the summit crater in 2003 and intense degassing activity started at medium-temperature fumaroles inside the summit crater in 2008. The low-temperature fumarolic gasses have peculiar composition with high H 2/H 2O, CO/CO 2 and SO 2/H 2S ratios, typical features of high-temperature volcanic gasses, but also with low HCl and total S contents, typical features of low-temperature gasses. These features indicate that the gasses are formed by low-temperature differentiation of high-temperature gasses. Variation of H and O isotopic ratios of the low-temperature gasses indicates that the gasses are formed by isoenthalpic processes of vapor–liquid separation at 100 °C of a high-temperature gas and meteoric water mixture, implying that the high-temperature gas was injected into a shallow aquifer without cooling. Temperatures of the high-temperature gasses were estimated as 550–700 °C based on the equilibrium temperature calculation with considering the low-temperature differentiation. The medium-temperature fumarolic gasses from the summit crater have typical compositions of high-temperature volcanic gasses and are estimated as the source gas of the boiling point fumaroles. The H 2/H 2O and CO 2/S t ratios of the low-temperature fumaroles increased from 2004 to 2009, which is interpreted to be caused by the evolution of thermal structure of a shallow gas storage region of a few hundred meters deep. Increase of magmatic gas supply caused enlargement of a high-temperature zone of the gas storage region widening the surrounding temperature transit zone with smaller temperature gradient. The enlargement of the high-temperature zone also reduces the overlying low-temperature aquifer, which caused the decrease of CO 2/S t ratio by reduction of sulfur removal reaction. The enlargement of the high-temperature zone resulted in the leakage of the high-temperature gasses directly to the surface as the medium-temperature gasses from the summit crater.

A web based program to visualize the transport and thermodynamic properties of thermal plasma

The data of transport properties like viscosity, thermal conductivity and electrical conductivity of high temperature gases or gas mixtures used in thermal plasma devices, as a function of temperature is very much essential for the process modeling and theoretical simulation. Similarly the temperature variation of thermodynamic properties like density, specific heat and enthalpy also should be known. Calculated values of these properties of the gases or gas mixtures specific to thermal plasma devices are available as a function of temperature in tabular form. To share the knowledge about these values of properties, web based package of codes and database documents are developed. The modules present in the package works in client-server environment, where the inter communication is through HTTP protocol. The developed package is tested with Apache tomcat web container. The details of the code development and working procedure are described in this paper.

Nonequilibrium Calculation of High-Temperature Radiating H2-He Flowfield

Chemical kinetics of high-temperature hydrogen-helium gas mixture behind a shock wave is numerically investigated by integrating rate equations for species concentration in time. State-to-state transition rates are used to determine quasi-steady-state rate coefficients for atomic hydrogen ionization. The electron concentrations in front of the shock wave are deduced by solving the radiative heat transfer equation of molecular hydrogen. The computed incubation time of avalanche ionization is compared with the experimental data and those appeared in past studies. It is found that the precursor photoionization and the associative ionization of the molecular hydrogen are important to determine the ionization time behind the shock wave. The present chemical kinetic models are found to reproduce the shock tube experimental data of the ionization time reasonably well.

Effective method for numerical integration of the equations describing the flow of high-temperature multicomponent gas mixtures in thermochemical equilibrium

A new stable iterative method is described for computing the flow of a high-temperature multicomponent gas mixture in thermochemical equilibrium. The method is illustrated by computing the thermochemical destruction of a carbon material in a high-temperature airflow.

Methods for calculating thermophysical properties of gas mixtures

The methods for calculating thermophysical properties of substances in high-temperature gas mixtures are considered, and the existing problems are presented.

Kinetics and Structural Characterization of Calcium-Based Sorbents Calcined under Subatmospheric Conditions for the High-Temperature CO2Capture Process

The influence of several process parameters on the calcination of a naturally occurring limestone and a precipitated mesoporous calcium carbonate (CaCO3) sorbent structure to calcium oxide (CaO) is detailed in this study. CaCO3 calcination is an integral part of a multicyclic carbonation−calcination reaction (CCR) process that separates carbon dioxide (CO2) from high-temperature gas mixtures into a pure CO2 stream. Maintenance of high sorbent reactivity over repeated CCR cycles reduces the capital and operating cost of the CCR process. A lower calcination temperature, required to maintain high sorbent reactivity, reduces the calcination rate of CaCO3. This study investigates various process conditions such as subatmospheric calcination, sorbent dispersion in a rotary calciner, use of a high thermal conductivity sweep gas, etc. in enhancing the calcination rate at lower calcination temperatures. The high-temperature gas−solid carbonation studies of the resulting CaO sorbent prove the necessity to maintain a high porosity structure during limestone calcination.

The Phase Behaviour of Acid Disposal Gases and the Potential Adverse Impact on Injection or Disposal Operations

Abstract As increased volumes of acid gases (containing carbon dioxide and hydrogen sulphide) are processed, the technique of downhole re-injection of the concentrated acid gas for disposal of these unwanted fluids continues to become more popular. In many cases, bottomhole injection temperature and pressure conditions are such that the injected acid gas phase is a supercritical fluid that is miscible with the existing reservoir fluids and, thus, the potential for adverse relative permeability effects (due to thecreation of in situ immiscible liquid and vapour phases) is avoided. In other cases, however, combinations of lower reservoir temperatures and/or initially depleted disposal zone pressures, or blending of the acid gas with the in situ lean gas, can result in the formation of both liquid and vapour acid gas phases in the formation in the near-wellbore region. This can often cause very significant relative permeability effects, which may result in large reductions in injectivity of the acid gas on either a permanent or transient basis. This paper provides actual examples of such systems, as well as reviewing the design protocol that must be used to evaluate if potential phase behaviour problems can occur downhole during an acid gas disposal operation. This hasproven to be a key parameter in the successful evaluation of anacid gas disposal operation. Introduction In many acid gas injection operations, the bottomhole pressure condition is high enough that, over the entire life of the injection operation and at all possible blended compositions between the acid injection gas and the reservoir fluids, a monophasic condition is present. In some cases, when the initial reservoir pressure is low, initial injection commences in the "gas" phase region, and as pressure gradually increases, the phase condition of the fluids around the injection wells enters the two-phase region where a "liquid" acid gas phase is in thermodynamic equilibrium with an acid gas "vapour" phase. This may also occur when the acid gas blends with reservoir gas which may elevate the dew point pressure line upwards above the current injection pressure level, once again resulting in a condition of two-phase flow. The creation of these two immiscible phases (which have an interface and measurable interfacial tension between them) can, particularly in lower permeability formations, create significant adverse relative permeability effects which may result in large transient or permanent reductions in injectivity, possibly compromising the economics of the acid gas injection operation. Understanding the phase behaviour in such situations and how it interacts with the capillary pressure and relative permeability phenomena present within the matrix of the proposed injection zone is essential. Limited data is available in the literature on the properties of high temperature and pressure acid gas mixtures and their specific phase behaviour(1–8). This is also the case with data regarding the specific interaction of single and multiphase acid gas interactions with reservoir rock(9–11) and the effects of multiphase acid gas induced relative permeability effects(12). The motivation of this work was to obtain a dataset to expand the knowledge base in this area.

Photochemical effect in two-photon laser-induced fluorescence detection of carbon monoxide in hydrocarbon flames

The CO formation as a result of the CO(2) photodissociation at 230.08 nm was observed by using the two-photon laser-induced fluorescence (LIF) method. The measurements were performed in a propane-air combustion product flow and in mixtures of CO(2) and O(2). The temperature dependence of the fluorescence signal caused by CO molecules, produced in the photodissociation of CO(2) molecules under the action of laser radiation at a wavelength of 230.08 nm, was measured at temperatures ranging from 1300 to 2000 K. It is shown that consideration of CO(2) photodissociation under the action of the probing radiation is necessary when one applies the two-photon LIF method for the measurement of small CO concentrations in high-temperature gas mixtures containing CO(2). As an example, a correction is given of the CO concentration profiles measured by the LIF method in the combustion product flow around a cooled metallic plate.