High temperature rate coefficient measurements of CO + O chemiluminescence

Spectral intensities from the chemiluminescent reaction CO + O → CO₂ + hv have been measured in the range 2600–7000 Å from reacting mixtures of H₂O₂COCO₂argon, shock heated in a shock tube to temperatures of 1300 and 2700K. Intergrals of the photon production rate yield an overall rate coefficient I₀ = 6.8 (±0.6) × 10⁵, exp(− 1960/T) cm³ mole⁻¹ s⁻¹. Extrapolated to 300K, this rate coefficient is in excellent agreement with the room temperature measurements of Pravilov.     

Efficiency of Cascade Refrigeration Cycle Using C3H8, N2O,and N2

This article presents a new natural gas liquefaction cycle that utilizes propane (C₃H₈), nitrogen monoxide (N₂O), and nitrogen gas (N₂) cycles. A liquefaction cycle with staged compression was designed and simulated using HYSYS software for improving cycle efficiency. This included a cascade cycle with a three-stage compression consisting of a C₃H₈, an N₂O, and an N₂ cycle. The new C₃H₈, N₂O, and N₂ liquefaction cycle is compared to the optimized cascade cycle using propane, ethylene, and methane. The compressor work, specific energy, and coefficient of performance (COP) of the cascade cycles were compared and analyzed. The COP of the new cascade cycle that utilizes three-stage compression process 3 is 25% higher than that of basic single-stage process 1. Also, the new liquefaction cycle requires less specific power for the same amount of liquefied natural gas (LNG) produced by optimized cascade cycle. For example, the specific power and COP of the new cascade cycle are respectively up to 16% less and 14% higher than those of the optimized cascade cycle under the same conditions of feed gas composition and liquefaction rate.     

Helium and hydrogen interaction in tungsten simultaneously irradiated by He+-H2+ at high temperature

Tungsten (W) is one of the most promising candidates for plasma facing materials in the fusion reactor. Helium (He) in W can influence the retention of hydrogen isotopes. In the present study, W targets were simultaneously irradiated by He⁺-H₂⁺ or He⁺-D₂⁺ ion beams with the energies of 1 keV or 3 keV, at fixed temperatures in a range of room temperature (R.T.) to 1073 K. Mechanisms of He and hydrogen interaction in W were discussed, especially from the point of He retention, which was characterized by the high-temperature thermal desorption spectroscopy (TDS) and glow-discharge optical emission spectroscopy (GD-OES) measurements. It is found that He desorption shifts to a lower temperature range for the W simultaneously irradiated by 3 keV He⁺-1 keV H₂⁺ at 573 K, under He⁺ fluence up to 1 × 10²² He⁺m⁻². Transmission electron microscope (TEM) observation and annealing treatment at the temperature of 873–1073 K show that the increased He uptake is caused by the formation of dislocation. Enhanced retention amounts for the hydrogen isotopes were also confirmed. Amounts of the dislocation loops introduced by the H₂⁺-only irradiation can be reduced by annealing treatment at 873 K, while that introduced by He⁺ irradiation are quite stable, which grows larger at elevated temperatures. With an increase of H₂⁺ energy, Helium uptakes at both weak trapping sites and bubbles are increased, while the amounts of hydrogen retention are decreased. It suggests that hydrogen ion has a significant influence on the He trapping sites at the irradiation temperature up to 573 K, while the hydrogen retention is determined by the distribution of He bubbles and dislocation loops.     

Numerical study of the O2/CO2, O2/CO2/N2, and O2/N2-syngas MILD combustion: Effects of oxidant temperature,O2 mole fraction,and fuel blends

Moderate or Intense Low-oxygen Dilution (MILD) combustion of a syngas fuel under air-fuel, oxygen-enhanced, and oxy-fuel condition are numerically studied with using counterflow diffusion flame. Fuel composition, temperature of oxidant (T_ox), and oxygen mole fraction (X_O2) are selected as the main parameters. Fake species (FCO₂) with the same CO₂ physical properties is used for separation the physical and chemical effects of replacing CO₂ with N₂. According to the results, under the high preheating temperatures, the chemical effect of changing the oxidant composition from N₂ to CO₂ is the main reason of the changes in flame structure, ignition delay time (IDT) and heat release rate (HRR) while physical differences play a more prominent role in the low preheating temperature MILD combustion. In all X_O2, the physical and chemical effects of replacing CO₂ with N₂ have almost the same role on the maximum flame temperature. The results of IDT expressed that chemical discrepancies of CO₂ and N₂ play a key role on IDT enhancement by increasing CO₂ in the oxidant composition. The sensitivity analysis of CH₂O for variations of T_ox and X_O2 shows that reactions R54, R56, R58, and R101 are the main responsible of lower HRR and higher IDT by moving from air-syngas to oxy-fuel MILD combustion.     

CFB锅炉燃烧中N2O的生成机理与减排控制

循环流化床燃烧技术作为一种新型洁净煤燃烧技术 ,具有高效脱硫和低NOx 排放的优点 ,但它燃烧释放出来的N2 O比常规煤粉炉要高出很多 ,因此如何正确合理地解决这个问题将会直接影响循环流化床锅炉在我国的发展。本文简单介绍了N2 O的生成机理 ,以及一些降低N2 O的行之有效的方法     

CFB锅炉燃烧中N2O的生成机理与减排控制

循环流化床燃烧技术作为一种新型洁净煤技术,它具有高效脱硫和低NOX排放的优点。然而最近研究表明它燃烧释放出来的N2O比常规煤粉炉要高出很多,因此如何正确合理的解决这个问题将会直接影响循环流化床锅炉在我国的发展。简单介绍了N2O的生成机理,以及一些降低N2O的行之有效的方法。     

Fructose decomposition kinetics in organic acids-enriched high temperature liquid water

Biomass continues to be an important candidate as a renewable resource for energy, chemicals, and feedstock. Decomposition of biomass in high temperature liquid water is a promising technique for producing industrially important chemicals such as 5-hydroxymethylfurfural (5-HMF), furfural, levulinic acid with high efficiency. Hexose, which is the hydrolysis product of cellulose, will be one of the most important starting chemicals in the coming society that is highly dependent on biomass. Taking fructose as a model compound, its decomposition kinetics in organic acids-enriched high temperature liquid water was studied in the temperature range from 180 °C to 220 °C under the pressure of 10 MPa to further improve reaction rate and selectivity of the decomposition reactions. The results showed that the reaction rate is greatly enhanced with the addition of organic acids, especially formic acid. The effects of temperature, residence time, organic acids and their concentrations on the conversion of fructose and yield of 5-HMF were investigated. The evaluated apparent activation energies of fructose decomposition are 126.8 ± 3.3 kJ mol⁻¹ without any catalyst, 112.0 ± 13.7 kJ mol⁻¹ catalyzed with formic acid, and 125.6 ± 3.8 kJ mol⁻¹ catalyzed with acetic acid, respectively, which shows no significant difference.     

Influence of micro-amount O2 or N2 on the hydrogenation/dehydrogenation kinetics of hydrogen-storage material MgH2

Mg-based hydrogen-storage materials are regarded as promising hydrogen-storage alloys. However, in practical applications, Mg-based hydrogen-storage materials may be exposed to air or to a low-purity-gas environment with particularly oxygen as impurity. In this paper, the influence of a micro-amount of oxygen or nitrogen on the performance of adsorption/desorption of MgH₂ hydrogen-storage material has been studied by placing samples in an argon-filled glove box (at atmospheric pressure) with 1000 ppm oxygen concentration. The hydrogen capacity and adsorption/desorption kinetics were measured by using a high-pressure and high-temperature gas-adsorption analyzer. The samples were characterized by X-ray diffraction. The activation energy for hydrogenation has been determined by means of the Arrhenius equation. It is found that the adsorption/desorption of MgH₂ improves significantly by a micro-amount of oxygen, especially at high temperature.     

The Li1+xMn2O4C system Materials and electrochemical aspects

The importance of the synthesis conditions of Li_1+xMn₂O₄ on its electrochemical performance, namely, capacity fading and initial capacity is discussed. By using a well-defined thermal treatment and a particular nominal composition, x=0.05, one can overcome the problem of capacity fading that was previously experienced with LiMn₄ while, at the same time, enhancing the usable capacity. The importance of the thermal treatment in terms of oxygen stoichiometry effects and how cyclic voltammetry can be used to optimize Li_{1 + x}Mn₂O₄ powders have been discussed.     

Transport properties in molten carbonates: self-diffusion and conductivity measurements at high temperature

A better understanding and use of molten carbonate fuel cells (MCFCs) requires more detailed consideration on transport properties in melt. The combination of different methodological developments can be one solution to improve our comprehension. Here we present ²³Na and ⁷Li self-diffusion coefficients measured by pulsed field gradient (PFG) NMR technique combined with electrical conductivity obtained by a 4-electrode set up, in the eutectic mixture Li₂CO₃–Na₂CO₃ (52:48 %mol) at high temperature (up to 1050 K), and under pure CO₂ atmosphere. The results were compared with known experimental data from literature obtained by radiotracers techniques and 2-electrode set up and also with some calculations of the transport properties.     

Heat loss measurements on an enclosure for high temperature batteries

Heat loss measurements are reported for an enclosure which is suitable for high temperature batteries operating between 300 and 470 °C. The enclosure is rectangular and has a load-bearing vacuum insulation. The heat loss measurements are used to determine the thermal conductivity of the insulation. At 450 and 300 °C, a thermal conductivity of 3.2 and 2.0 mW / (m K), respectively, was determined. These values are smaller by a factor of about 20 than can be obtained with conventional (non-evacuated) thermal insulations. This is an important step towards the realization of electric vehicles driven by high temperature batteries.     

Experimental investigation of ignition and combustion characteristics of single coal and biomass particles in O2/N2 and O2/H2O

Oxy-steam combustion is a potential new-generation option for CO₂ capture and storage. The ignition and combustion characteristics of single coal and biomass particles were investigated in a flow tube reactor in O₂/N₂ and O₂/H₂O at various oxygen concentrations. The ignition and combustion processes were recorded using a CCD camera, and the two-color pyrometry was used to estimate the volatile flame temperature and char combustion temperature. In O₂/N₂ and O₂/H₂O, coal ignites heterogeneously at <O₂> = 21–50%. In O₂/N₂, biomass ignites homogeneously at <O₂> = 21–30%, while it ignites heterogeneously at <O₂> = 40–50%. In O₂/H₂O, biomass ignites homogeneously at <O₂> = 21–50%. With increasing oxygen concentration, the ignition delay time, volatile burnout time and char burnout time are decreased, and the volatile flame temperature and char combustion temperature are increased. At a certain oxygen concentration in both atmospheres, the ignition delay time, volatile burnout time and char burnout time of biomass are shorter than those of coal. Moreover, biomass has a higher volatile flame temperature but a lower char combustion temperature than coal. The ignition delay time, volatile burnout time and char burnout time in O₂/H₂O are lower than those in O₂/N₂ for coal and biomass. The presence of H₂O can improve the combustion rates of coal and biomass. The volatile flame shows a lower temperature in O₂/H₂O than in O₂/N₂ at <O₂> = 21–50%. The char combustion shows a lower temperature in O₂/H₂O than in O₂/N₂ at <O₂> = 21–30%, while this behavior is switched at <O₂> = 40–50%. The results contribute to the understanding of the ignition and combustion characteristics of coal and biomass in oxy-steam combustion.     

Updated band model parameters for H2O,CO2, CH4 and CO radiation at high temperature

Statistical narrow-band (SNB) model parameters for H₂O, CO₂, CH₄ and CO, and correlated-k (CK) parameters for H₂O and CO₂ are generated from line by line calculations and recently improved spectroscopic databases in wide temperature and spectral ranges. Results from the new parameters are compared to direct line by line calculations and to results from earlier model parameters [A. Soufiani, J. Taine, High temperature gas radiative property parameters of statistical narrow-band model for H₂O, CO₂ and CO and correlated-k (ck) model for H₂O and CO₂, Int. J. Heat Mass Transfer 40 (1997) 987–991] in terms of band averaged spectral transmissivities, Planck mean absorption coefficients, and total emissivities. The comparisons show first a good agreement between updated SNB, CK and LBL results. Significant improvements on earlier parameters are observed for H₂O and CO₂, especially at very high temperatures and path lengths. Model parameters and computer programs illustrating their implementation are provided as Supplementary data.     

Effect of high temperature and separated combustion on SO2 release characteristics during coal combustion under O2/CO2 atmosphere

This paper studied the effect of high temperature (up to 1873K) and separated combustion mode (volatile combustion and char combustion are separated) on SO₂ release characteristics during pulverized coal combustion under O₂/CO₂ atmosphere. Coal combustion experiments were conducted at different combustion environment temperatures utilizing a high temperature fixed-bed setup. The results show that as temperature rises, the SO₂ release curve is transformed from a single-peak process to a double-peak process. In separated combustion, temperature has little effect on the volatile-SO₂ (SO₂ released during volatile combustion) but brings about a significant effect on char-SO₂ (SO₂ released during char combustion). Char-SO₂ release amount and the ratio of it to fuel-SO₂ release amount (total SO₂ released during coal combustion) increase with temperature rising. The increase of temperature leads to a dramatic decreasing of sulphur mass fixed in the ash and causes SO₂ release amount to rise when temperature is lower than 1573 K. Separated combustion causes a higher SO₂ release amount than coupled combustion (the same as conventional combustion, volatile combustion and char combustion are simultaneous). Thermochemistry equilibrium composition calculation results show that alkali metals and alkaline-earth metals are significant in sulphur retention. CaSO₄ and Na₂SO₄ are the main sulphates at high temperatures.     

Quantification of in situ temperature measurements on a PBI-based high temperature PEMFC unit cell

The temperature is a very important operating parameter for all types of fuel cells. In the present work distributed in situ temperature measurements are presented on a polybenzimidazole based high temperature PEM fuel cell (HT-PEM). A total of 16 T-type thermocouples were embedded on both the anode and cathode flow plates. The purpose of this study is to investigate the feasibility of the proposed temperature characterization method and to identify the temperature distribution on an operating HT-PEM in various modes of operation, including a 700 h sensors durability test. The embedded sensors showed minimal influence on cell performance, this difference seen in performance is believed to be caused by different bipolar plate materials. The measurement method is suitable for obtaining detailed data for validation of computational models, moreover the results indicate that the method can be used as a degradation tool, as it is possible to locate areas exposed to degradation, both in plane and between the anode and cathode.     

N/C doped nano-size IrO2 catalyst of high activity and stability in proton exchange membrane water electrolysis

It is highly desirable to synthesize and deploy low-cost and highly efficient catalysts for the oxygen evolution reaction (OER) to catalyze water splitting. We show that N/C doped amorphous iridium oxide combines the benefits of nano-size (approximately 2 nm), which results in exposure to large active surface areas and features of oxygen defects, which make for an electronic structure suitable for the OER. Systematic studies indicate that the OER activity of the iridium oxide catalyst is accelerated by the effect of the structure and chemical state of the iridium element. Remarkably, the N/C doped amorphous iridium oxide catalyst shows a lower cell voltage of 1.774 V at 1.5 A cm⁻², compared with IrO₂ (1.847 V at 1.5 A cm⁻²), and it can maintain such a high current density for over 200 h without noticeable performance deterioration. This work provides a promising method for the improving OER electrocatalysts and the construction of an efficient and stable PEM water cracking system.     

Synthesis of Ti(C,O, N) from ilmenite at low temperature by a novel reducing and carbonitriding approach

The clean and effective utilization of titanium-bearing minerals has challenged the titanium industry all over the world. In order to realize the high-efficiency, clean, and high value-added comprehensive utilization of ilmenite concentrate, a novel process has been proposed in this study by reducing and carbonitriding ilmenite with the CH₄-N₂-H₂ gas mixture at low temperature. Carbonitride performance and mechanism have been investigated experimentally and theoretically. The obtained results showed that the reaction process could be divided into three stages: formation of metallic iron, reduction of titanium oxide to titanium suboxides, and formation of Ti(C, O, N). The metallic iron congregated at the first two stages, but dispersed once the Ti(C, O, N) formed. The effects of both reaction temperature and preoxidation treatment on the reaction have been studied as well. It was found that the increase of temperature was conducive to the formation of Ti(C,O), and the ilmenite could be reduced completely to Ti(C,O) at 1170°C for 8 hours. The preoxidation treatment could improve the kinetics of reduction. At 1170°C, the introduction of N₂ could apparently increase the reduction rate, with the complete reduction time decreasing from 8 hours in CH₄-H₂ gas mixture to 3 hours in CH₄-N₂-H₂ gas mixture. The proposed novel process has been assessed and it showed many potential advantages and feasibility.