秸秆灰特性的研究

按照D1102-84灰分标准测定方法,对小麦、水稻、玉米、黄豆、高粱、棉花等几种秸秆样本进行了工业分析;在ZRC2000智能灰熔点测定仪上对不同秸秆进行了灰熔点测试;在不同的温度和停留时间下,在马弗炉上对不同秸秆进行了热灼烧试验.结果表明:秸秆挥发分含量较高,灰熔点比较低,无机碱金属析出量随着温度的升高和停留时间的增加而增加.     

生物质与烟煤灰的理化特性及混合灰熔融特性研究

文章利用扫描电子显微镜(SEM)、X射线荧光光谱仪(XRF)、X射线荧光衍射仪(XRD)、灰熔融特性分析仪对4种生物质(海草、梨木、榛子壳、稻秆)灰与神木烟煤灰的混合灰的熔融特性进行了研究。研究发现:水生生物质(海草)灰的掺混使混合灰的熔融特性温度先升高再降低;两种木本生物质(梨木和榛子壳)灰的掺混使混合灰的熔融特性温度逐渐升高;草本生物质(稻秆)灰的掺混对混合灰熔融特性温度的影响与水生生物质灰类似。由XRF分析可知:Na2O和CaO对于混合灰的熔融特性温度有更明显的影响,随着混合灰中Na2O含量的逐渐增加,混合灰的熔融特性温度逐渐下降;随着混合灰中CaO含量的逐渐增加,混合灰的熔融特性温度逐渐上升。由XRD结果可知:水生生物质灰在高温下容易形成熔点较低的碱金属硅酸盐,使混合灰的熔点降低;木本生物质灰中的CaCO3含量较高,能够提高混合灰的熔点;草本生物质灰与水生生物质灰类似,含有的低熔点碱金属硅铝酸盐使混合灰的熔点降低。     

电厂煤飞灰颗粒物的物理化学特征

对某台300MW燃煤电站锅炉电除尘器前后的飞灰进行取样,使用激光粒度仪测定粒度分布,使用X射线衍射仪(XRD)和扫描电镜(SEM)研究颗粒中的矿物成分及其微观形貌特征,同时使用电子探针对电除尘器后飞灰的单颗粒进行成分分析．结果表明：通过电除尘装置排入大气的颗粒物平均粒径为2．5μm左右;飞灰粗颗粒中有较多硅铝氧化物和粘土矿物,而细颗粒中则含有较多金属氧化物,且粗颗粒中石英所占矿物相比例相当高;电除尘器前的飞灰形貌类型种类较多,电除尘器后飞灰形貌类型简单,主要是圆球或圆形的颗粒;电除尘器后飞灰单个颗粒间组分随粒径变化的有Si、Al、Ca和S,而元素Fe和Ti的含量较恒定．     

气化条件下压力影响灰熔融特性的实验研究

利用加压热天平结合X衍射分析仪来研究压力对煤灰熔融特性的影响。受加压热天平温度的限制,只研究1100℃以下压力的影响。利用X衍射分析仪分析不同压力、不同温度下煤灰中的矿物质成分,根据X射线衍射图谱分析矿物质对灰熔融特性的影响,以及在不同压力和不同气氛下矿物质的变化和新生成矿物质对灰熔融性的影响。结果显示:CO2气氛下压力对煤灰矿物质的生成影响不大;N2及H2O气氛下压力具有促进煤灰低温矿物质向高温矿物质转化的作用。     

Non-monotonic behaviors of laminar burning velocities of H2/O2/He mixtures at elevated pressures and temperatures

Both experimental and calculated laminar burning velocities of H₂/O₂/He mixtures were obtained, with equivalence ratios of 0.6–4.0, initial pressures of 0.1 MPa–0.5 MPa, initial temperature of 373 K, and dilution ratio of 7.0. Laminar burning velocities changed non-monotonically with the increasing initial pressures at equivalence ratios of 1.0–3.0. The decrease of overall reaction orders can explain the non-monotonic relationship between the laminar burning velocities and initial pressures. Consumption and production of both H and HO₂ radicals were also obtained to explain the decrease of overall reaction order. The competition of H and HO₂ radical between elemental reactions were also discussed. The three body reaction R15 (H + O₂(+M) = HO₂(+M)) gained more H radical in the competition with R1 (H + O₂ = O + OH), producing more HO₂ radical. Through the reaction pathway analysis, the restraint in production of both OH and H leaded to a reducing radical pool. The poorer reaction pool would restrain the overall reaction and lead to the reduction of overall reaction order and the non-monotonic behavior of the laminar burning velocity.     

The flammability limits of H2–CO–CH4 mixtures in air at elevated temperatures

The present contribution reports experimentally obtained values of the flammability limits of some fuel mixtures made up of H₂, CO, and CH₄ in air at different initial mixture temperatures of up to 300 °C. The potential catalytic effects of the surface of the test apparatus when the fuel–air mixtures were allowed to reside within the test apparatus at elevated temperatures for different time periods prior to ignition were also considered. Both stainless steel and quartz flame tubes of identical design and size were employed in the investigation.     

Measurements of laminar burning velocities and Markstein lengths for methanol-air-nitrogen mixtures at elevated pressures and temperatures

The laminar burning velocities and Markstein lengths for the methanol-air mixtures were measured at different equivalence ratios, elevated initial pressures and temperatures, and dilution ratios by using a constant volume combustion chamber and high-speed schlieren photography system. The influences of these parameters on the laminar burning velocity and Markstein length were analyzed. The results show that the laminar burning velocity of the methanol-air mixture decreases with an increase in initial pressure and increases with an increase in initial temperature. The Markstein length decreases with an increase in initial pressure and initial temperature, and increases with an increase in the dilution ratio. A cellular flame structure is observed at an early stage of flame propagation. The transition point is identified on the curve of flame propagation speed against stretch rate. The reasons for the cellular structure development are also analyzed.     

Development of an ASME-NH program for nuclear component design at elevated temperatures

In this paper, we discuss an ASME-NH program that has been developed to overcome the complexity and costs arising from the real application of the ASME-NH rules by hand calculations for class 1 nuclear facility component design for elevated temperature operations. A computerized program is described for implementing all the assessment procedures such as the time-dependent primary stress limits, total accumulated creep-ratcheting strain limits, and the creep–fatigue damage limits by the elastic and inelastic analysis methods complying with the ASME-NH rules. As an example application, a preliminary structural integrity evaluation for a high-temperature reactor vessel design of a typical lead-cooled reactor is described.     

Evaluation of conversion relationships for impression creep test at elevated temperatures

This paper contains some results related to the evaluation of the conversion relationships between impression creep test data and conventional uniaxial creep test date, for determining the secondary creep properties at elevated temperature. Some important aspects, including conversion factors, specimen dimensions, typical test results and validity of the test technique etc are briefly reviewed. The method used to determine the conversion factors is based on a reference stress approach using the results of finite element (FE) analyses; this is described in the paper. The conversion factors (reference parameters) obtained from 2-dimensional (2D) and 3-dimensional (3D) FE analyses are compared and the effects of specimen geometry, on the conversion relationships, are assessed. The recommendations on the use of these conversion factors, in practical impression creep testing, are given. Proposals for future exploitation of the technique are addressed.     

Evaporation characteristics of kerosene droplets with dilute concentrations of ligand-protected aluminum nanoparticles at elevated temperatures

The evaporation characteristics of kerosene droplets containing dilute concentrations (0.1%, 0.5%, and 1.0% by weight) of ligand-protected aluminum (Al) nanoparticles (NPs) suspended on silicon carbide fiber were studied experimentally at different ambient temperatures (400–800 °C) under normal gravity. The evaporation behavior of pure and stabilized kerosene droplets was also examined for comparison. The results show that at relatively low temperatures (400–600 °C), the evaporation behavior of suspended kerosene droplets containing dilute concentrations of Al NPs was similar to that of pure kerosene droplets and exhibited two-stage evaporation following the classical d²-law. However, at relatively high temperatures (700–800 °C), bubble formation and micro-explosions were observed, which were not detected in pure or stabilized kerosene droplets. For all Al NP suspensions, regardless of the concentration, the evaporation rate remained higher than that of pure and stabilized kerosene droplets in the range 400–800 °C. At relatively low temperatures, the evaporation rate increased slightly. However, at relatively high temperatures (700–800 °C), the melting of Al NPs led to substantial enhancement of evaporation. The maximum increase in the evaporation rate (56.7%) was observed for the 0.5% Al NP suspension at 800 °C.     

Calculation of the upper flammability limit of methane/hydrogen/air mixtures at elevated pressures and temperatures

The results of three different numerical methods to calculate flammability limits—namely (1) the calculation of planar flames with the inclusion of a (radiation) heat loss term in the energy conservation equation, and the application of (2) a limiting burning velocity and of (3) a limiting flame temperature—are compared with experimental data on the upper flammability limit (UFL) of methane/hydrogen/air mixtures with hydrogen fuel molar fractions of 20% and 40%, at initial pressures up to 10 bar and initial temperatures up to 200 °C. The application of a limiting burning velocity is found to predict the pressure dependence of the UFL well, while the application of a limiting flame temperature generally is found to slightly underestimate the temperature dependence of the UFL.     

EELS microanalysis of polycrystalline silicon thin films for solar cells grown at low temperatures

The aim of this work is the quantitative chemical analysis of polycrystalline silicon thin films grown on glass substrates at temperatures <600°C by means of transmission electron microscopy (TEM) and electron energy-loss spectrometry (EELS). Specimens produced with two different methods were investigated. We found significant differences in grain size and morphology, as well as in the distribution of oxygen. A surprisingly high amount of Ba diffusion from the subtrate was detected.     

Synthesis of Mg2FeH6 by hydrogenation of Mg/Fe powder mixture prepared by cold roll milling in air: Effects of microstructure and oxygen distribution

Herein, we describe the synthesis of Mg₂FeH₆ by hydrogenation of a 2.1 Mg:Fe (mol/mol) powder mixture prepared by cold roll milling (CRM) in air. The thickness of Fe layers and the amount and distribution of oxygen with number of CRM passes were systematically analyzed. CRM-induced microstructural changes were shown to play an important role in Mg₂FeH₆ formation. Although repeated CRM effectively decreased the Fe layer thickness to values sufficient for the fast formation of Mg₂FeH₆, too much CRM passes decreased the total degree of hydrogenation due to inevitable oxidation of Mg in air. Both microstructure refinement and minimal oxidation are the prerequisites for efficient Mg₂FeH₆ synthesis, with the former condition being achievable by optimizing the number of milling passes, and the latter one requiring CRM under an inert atmosphere.     

Changes in microstructure,phases, and hydrogen storage characteristics of metal hydro-borate and nickel-added magnesium hydride with hydrogen absorption and release reactions

In this work, Zn(BH₄)₂ and/or Ni were added to MgH₂ in order to improve the hydrogen absorption and release properties of MgH₂. 99 wt% MgH₂ + 1 wt% Zn(BH₄)₂, 99 wt% MgH₂ + 0.5 wt% Zn(BH₄)₂ + 0.5 wt% Ni, and 95 wt% MgH₂ + 2.5 wt% Zn(BH₄)₂ + 2.5 wt% Ni samples [named MgH₂-1Zn(BH₄)₂, MgH₂-0.5Zn(BH₄)₂-0.5Ni, and MgH₂-2.5Zn(BH₄)₂-2.5Ni, respectively] were prepared by milling in a planetary ball mill in a hydrogen atmosphere. MgH₂-0.5Zn(BH₄)₂-0.5Ni had the highest initial hydriding and dehydriding rates and the largest quantities of hydrogen absorbed and released for 20 min. MgH₂-0.5Zn(BH₄)₂-0.5Ni dehydrided at the fourth cycle had small particles, large particles, and agglomerates. The sizes of the fine particles on the agglomerates were slightly smaller than those in the as-milled sample and quite flat surfaces of the agglomerates were not observed. MgH₂-0.5Ni-0.5Zn(BH₄)₂ dehydrided at 623 K under 1.0 bar H₂ at the 4th cycle contained Mg, MgO, and small amounts of β-MgH₂ and Mg₂Ni. The initial hydriding rates at n = 2, 3, and 4 were higher than that at n = 1. The quantity of hydrogen absorbed for 60 min, H_a (60 min), decreased as the number of cycles, n, increased. The initial dehydriding rate increased and the quantity of hydrogen released for 60 min, H_r (60 min), decreased as n increased. Outside the particles and agglomerates, particles became finer due to expansion and contraction, while in their interiors cracks were believed to coalesce due to annealing effect. MgH₂-0.5Ni-0.5Zn(BH₄)₂ had an effective hydrogen storage capacity (the quantity of hydrogen absorbed for 60 min) of about 5.5 wt% (5.52 ± 0.10 wt% at 593 K under 12 bar H₂). The PCT curve of MgH₂-0.5Ni-0.5Zn(BH₄)₂ showed that the hydrogen storage capacity was 6.64 ± 0.25 wt%.     

中药渣制备微晶纤维素工艺优化及其结构表征

以中药渣为原料制备生物基材微晶纤维素(MCC),利用响应面法优化制备工艺参数并分析其结构特性.结果表明:中药渣制备MCC最优工艺参数为液固比20:1(mL/g)、时间1.5 h、盐酸浓度6.9％、温度71.5℃,此条件下制得的药渣MCC聚合度为220.58、纯度为94.32％、得率为34.88％、结晶度为68.32％....     

Energy and exergy analysis of biomass gasification at different temperatures

Biomass is usually gasified above the optimal temperature at the carbon-boundary point, due to the use of different types of gasifiers, gasifying media, clinkering/slagging of bed material, tar cracking, etc. This paper is focused on air gasification of biomass with different moisture at different gasification temperatures. A chemical equilibrium model is developed and analyses are carried out at pressures of 1 and 10 bar with the typical biomass feed represented by CH_1.4O_0.59N_0.0017. At the temperature range 900–1373 K, the increase of moisture in biomass leads to the decrease of efficiencies for the examined processes. The moisture content of biomass may be designated as “optimal” only if the gasification temperature is equal to the carbon-boundary temperature for biomass with that specific moisture content. Compared with the efficiencies based on chemical energy and exergy, biomass feedstock drying with the product gas sensible heat is less beneficial for the efficiency based on total exergy. The gasification process at a given gasification temperature can be improved by the use of dry biomass and by the carbon-boundary temperature approaching the required temperature with the change of gasification pressure or with the addition of heat in the process.     

Influence of CaO/MgO ratio on the crystallization kinetics and interfacial compatibility with crofer 22APU and YSZ of strontium based alumino-borosilicate glasses for SOFC applications

High temperature hermetic sealants are required for the stability and good efficiency of the solid oxide fuel cells (SOFCs). Glass and glass ceramics are promising sealant materials due to their desirable properties and flexible compositions. In the present study, the novel glass series (10 + x) CaO-(10 ? x) MgO-10SrO-10B₂O₃-20Al₂O₃-40SiO₂ (x = 0, 2.5, 5, 7.5) has been synthesized via melt quenching route. These glass/glass ceramics are characterized by X-ray diffraction to evaluate the amorphous nature and phase formation, respectively. The activation energy has been analyzed by using three different theoretical models – Kissinger Model, Moynihan Model and Augis and Benett Model. In addition to this, the characteristic glass temperatures and coefficient of thermal expansion (CTE) have been obtained from DTA, differential DTA (DDTA) and Dilatometry. Various stability parameters like Hruby parameter, Saad Parameter, fluctuation free volume (f_g) and bulk thermal expansion coefficient (α_f) are also calculated with varying CaO/MgO ratio (R). Furthermore, to analyze the stability of the glasses with varying CaO/MgO ratio over a broader range of temperature, k parameters i.e. k_b (T) and k_f (T) are also evaluated for different heating rates. The diffusion couples of glasses with pre oxidized Crofer 22APU and YSZ fabricated at 850 ^°C for 500 h have been characterized using scanning electron microscopy (SEM) and X-ray dot mapping to investigate the sealing characteristics with varying CaO/MgO ratio. The glass series 15 CaMg is very stable and promises to be a good sealant for solid oxide fuel cells.     

Electrochromic characteristics of fibrous reticulated WO3 thin films prepared by pulsed spray pyrolysis technique

The electrochromic (EC) behavior of fibrous reticulated WO₃ films prepared from ammonium tungstate precursor by pulsed spray pyrolysis method was investigated. All the films were prepared using identical technological parameters and a thorough investigation of the electrochromic properties of the films deposited at 300 °C is reported. The structural properties were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochromic and optical properties were measured using cyclic voltammetry and ultraviolet (UV)-visible spectrophotometry. The films are amorphous and have a fibrous reticulate-like morphology having micron-size circular rings. The films show high transparency in the visible range and the optical band gap energy is about 3.1 eV. Electrical measurements show that the resistivity monotonically decreases as temperature increases, which indicates thermal hopping transport. The activation energy for hopping transport is of the order 4×10⁻⁴ eV. The electrochromic coloration efficiency (CE) is found to be 34 cm²/C at 630 nm.     

Investigation of aluminosilicate as a solid oxide fuel cell refractory

Aluminosilicate represents a potential low cost alternative to alumina for solid oxide fuel cell (SOFC) refractory applications. The objectives of this investigation are to study: (1) changes of aluminosilicate chemistry and morphology under SOFC conditions, (2) deposition of aluminosilicate vapors on yttria stabilized zirconia (YSZ) and nickel, and (3) effects of aluminosilicate vapors on SOFC electrochemical performance. Thermal treatment of aluminosilicate under high temperature SOFC conditions is shown to result in increased mullite concentrations at the surface due to diffusion of silicon from the bulk. Water vapor accelerates the rate of surface diffusion resulting in a more uniform distribution of silicon. The high temperature condensation of volatile gases released from aluminosilicate preferentially deposit on YSZ rather than nickel. Silicon vapor deposited on YSZ consists primarily of aluminum rich clusters enclosed in an amorphous siliceous layer. Increased concentrations of silicon are observed in enlarged grain boundaries indicating separation of YSZ grains by insulating glassy phase. The presence of aluminosilicate powder in the hot zone of a fuel line supplying humidified hydrogen to an SOFC anode impeded peak performance and accelerated degradation. Energy dispersive X-ray spectroscopy detected concentrations of silicon at the interface between the electrolyte and anode interlayer above impurity levels.