Enhancement of surface properties of oil fly ash by chemical treatment

In this study, surface modification of oil fly ash (OFA), a by-product generated by oil power plants, was achieved by chemical treatment. A mixture of sulfuric and nitric acids was used to modify the surface in order to attach a carboxylic functional group to the surface of OFA. The goal of surface modification of OFA is to make its surface more compatible with nonpolar polymers in order to produce OFA/polymer composite materials with improved dispersion of OFA, and to increase OFA surface area in order to support its use as adsorbent materials in adsorptive separation and purification applications. Different acid compositions were used for treatment by gradually increasing the nitric acid concentration from 0 to 20%. Also, the effect of oxidation on surface modification was examined by introducing air to enhance the oxidation of OFA. FTIR analysis was performed to identify the different functional groups attached to OFA surface before and after the chemical treatment. Evaluation of different structural changes during the surface modification was investigated by XRD analysis. Surface morphology and spot analysis was studied by SEM technique to identify the composition of different elements present in the OFA such as carbon, oxygen and sulfur. BET analysis showed major increase in surface area after modification as well as pore size and micropore volume of OFA particles. The maximum increase in surface area was obtained with 15 vol.% HNO₃. Also, carboxylic functionalization of OFA was enhanced when air was injected.     

A full spectrum k-distribution based non-gray radiative property model for unburnt char

By using the concept of weighted sum of four gray particles and spectrum k-distribution (WSGP-SK), a non-gray radiative property model for unburnt char particles is developed. Based on the carbon burnout kinetic model for structure during oxidation, and the linear mixed approximation theory for complex index of refraction, spectral radiative properties of unburnt char particles are first calculated as function of the burnout ratio by Mie theory. Referring to the full spectrum k-distribution model, k-distribution is applied to reorder absorption and scattering efficiencies of particles. Then, weighting factors and efficiency factors of the non-gray radiative property model are directly obtained from Gaussian integral points of k-distribution. The model is validated against the benchmark solutions of line-by-line (LBL) model. Maximum relative errors of this model are 3% and 15% for radiative heat fluxes and source terms in non-isothermal inhomogeneous particulate media, respectively. The assumption of linearly varying radiative properties with burnout ratio (Lockwood et al. 1986) will result in a predicted deviation of 53% for radiative source terms. Results also show that this non-gray model is remarkably better than the Planck mean method. Moreover, a satisfactory comparison with LBL solutions is achieved in the gas and particle mixture by combining the non-gray WSGG-SK model (Guo et al. 2015). As a radiation sub-model, this non-gray radiative property model can significantly improve prediction accuracy of radiative heat transfer in oxy-fuel combustion.     

悬浊液光谱透射法测量烟尘粒子的复折射率

光谱复折射率是计算烟尘粒子散射特性的重要参数。该文在光谱透射法反演烟尘粒子复折射率理论的基础上,将烟尘粒子弥散于水中形成烟尘粒子悬浊液,通过可见光分光光度计测量该悬浊液的光谱透射率,通过激光粒度仪获得烟尘粒子的粒径分布,利用悬浊液光谱透射法对烟尘粒子的复折射率进行了反演。研究结果表明,烟尘粒子在可见光波长范围内没有明显吸收带,但随着波长的增加,透过率逐渐降低。烟尘粒子复折射率的反演结果与KBr样片法的反演结果吻合较好。利用悬浊液光谱透射法测量烟尘粒子的复折射率,实验过程简单,约束条件少,并可利用红外分光光度计测量透射率后,拓展至红外波段。     

The influence of fly ash physical and chemical properties on electrostatic precipitation process

Flue gases emitted from coal fired power plants are mainly cleaned with electrostatic precipitators (ESP). Increased awareness of the effects of atmospheric pollution and tightening legislation force precipitator producers to increase their ESP efficiency, especially when collecting very fine particulates (PM2.5). The fly ash characteristic parameters are formatted during combustion process and its depend on the coal type as well as boiler parameters and combustion conditions. Due to that many series of tests were done to investigate the influence of fly ash physical and chemical properties on ESP operation.     

Effect of ultrasound energy on the zeolitization of chemical extracts from fused coal fly ash

This paper investigates the effects of ultrasound (UTS) energy at different temperatures on the zeolitization of aluminosilicate constituents of coal fly ash. UTS energy irradiated directly into the reaction mixture utilizing a probe immersed into the reaction mixture, unlike previously reported works that have used UTS baths. Controlled synthesis was also conducted at constant stirring and at the same temperatures using conventional heating. The precursor reaction solution was obtained by first fusing the coal fly ash with sodium hydroxide at 550 °C followed by dissolution in water and filtration. The synthesized samples were characterized by XRF, XRD, SEM and TGA. The crystallinity of crystals produced with UTS assisted conversion compared to conventional conversion at 85 °C was twice as high. UTS energy also reduced the induction time from 60 min to 40 min and from 80 min to 60 min for reaction temperatures of 95 °C and 85 °C, respectively. Prolonging the UTS irradiation at 95 °C resulted in the conversion of zeolite-A crystals to hydroxysodalite, which is a more stable zeolitic phase. It was found that at 85 °C coupled with ultrasound energy produced the best crystalline structure with a pure single phase of zeolite-A. It has been shown that crystallization using UTS energy can produce zeolitic crystals at lower temperatures and within 1 h, dramatically cutting the synthesis time of zeolite.     

Laboratory studies of back-discharge in fly ash

The back-discharge is a type of discharge that takes place in the presence of corona discharge and occurs at an electrode covered with a dielectric layer of resistivity higher than about 10⁸ Ω m. Back-discharge can be observed in electrostatic precipitators when dust covering the collection electrode has low conductivity. In this paper, the studies of back-discharge generated in ambient air, in point-to-plane geometry with the plate electrode covered with fly ash are presented. The discharge is characterised in terms of its visual forms, current–voltage characteristics, and light emission spectra. Three forms of back-discharge were investigated: glow discharge, streamers, and low-current back-arc discharge. The current of the back-arc discharge was only a few milliamps. The discharge was stabilised by a high series resistance. It was noted that the voltage of ignition of the back-discharge for negative polarity is lower than for a positive one. Spectroscopic measurements of emission spectra provided information on elements present in the discharge column. The elements present in the fly ash, including toxic metals, can be re-entrained into the gas as particles or can be emitted as ions or neutrals during the discharge, and can decrease the collection efficiency of electrostatic precipitators. These elements were detected in the emission spectra. The effect of the discharge on the fly ash layer was also discussed. It was observed that sinter-like leftovers remain in the dust layer after a back-arc discharge.     

Quark structure and radiative decays of new particles

Parameters of the heavy and light quarks mixing in singlet and triplet states are found from the data on decays of Ψ(3.1). The results agree with expectations based on ideas of asymptotic freedom.     

基于能量密度分布的辐射源粒子空间抽样方法研究

利用隐式蒙特卡罗方法模拟热辐射光子在物质中的输运过程时,物质辐射源粒子是需要细致处理的物理量.传统的物质辐射源粒子抽样方法是体平均抽样方法,对于大多数问题,这样处理不会带来大的偏差.但是对于一些辐射吸收截面大、单一网格内温差显著的问题,体平均抽样方法的计算结果偏差较大.分析了产生偏差原因,提出一种基于辐射能量密度分布的辐射源粒子空间位置抽样方法,并推导了相应的抽样公式以解决此类问题.数值实验表明,新方法计算结果明显优于原方法且与解析结果基本一致.     

Optical modeling of vesicular volcanic ash particles

We present a realistic shape model for nonspherical, vesicular particles and use the model to derive single-scattering properties of volcanic fine-ash particles. Light-scattering computations with discrete-dipole approximation reveal that, qualitatively, scattering by the model particles resembles that of the measured, real volcanic ash particles. Comparison of compact and vesicular ash shows that porosity promotes positive degree of linear polarization and decreases the depolarization ratio for both large and small vesicles. Yet, the single-scattering properties of ash particles with large vesicles are found to be surprisingly similar to those of compact ash particles. A comparison with Mie computations of equal-volume spheres indicates that for small size parameters, the spherical shape underestimates the asymmetry parameter of volcanic ash particles; whereas, for larger size parameters, it is overestimated.     

Analysis of E1 radiative neutron capture based on the optical model

The optical model formula of Lane and Mughabghab for E1 radiative neutron capture has been applied to resonance capture in ⁵⁶Fe and ⁹⁰Zr. It is shown that in general the optical model predicts the contributions to the radiative widths which are correlated with the neutron widths, except for a depletion factor representing the proportion of E1 single-particle strength remaining near the neutron threshold. The degree of correlation between measured and calculated radiative widths is related to the ratio of the variances of these widths. This enables an estimate of the factor . It is shown that the theoretical value for the ratio of the radiative to neutron widths is to a good approximation independent of the imaginary part of the optical potential. The calculated radiative width is thus well defined. The results are compared with those from the valence model and from experiment. The direct background contribution is found to be negligible compared to the average compound cross section. The contribution of d-waves to the radiative capture cross section is discussed.     

A model of the chemical composition and pyrolysis kinetics of lignin

This study presents a novel approach for the chemical representation of lignin for modelling the reaction kinetics of lignin in lignocellulosic biomass. This methodology relies on the definition of dimeric pseudo-components containing phenolic functionalities, i.e., p-hydroxyphenyl, guaiacyl and syringyl groups, as measured in real biomass and native lignin through wet chemistry and spectroscopic techniques. The reactivities of the lignin pseudo-components are modelled through a series of lumped unidirectional reactions, whose product formation and reaction rate constants are optimised to replicate a comprehensive experimental dataset gathered from several works available in the literature. The new kinetic model contributes to the state-of-the-art by providing a more accurate depiction of the conversion rates, selectivity of char vs. volatiles, and aromatic composition in condensable products in line with the inherent reactivity of lignin functionalities and the empirical observations of lignin depolymerisation and thermal degradation at low (<1?K/s) and high heating rates (>50?K/s).     

Trace element analysis of fly ash samples by EDXRF technique

Trace element analysis of some fly ash samples and soil samples have been carried out by Energy Dispersive X-Ray Fluorescence technique. Fourteen elements namely K, Ca, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Se, Rb, Sr and Pb have been quantified in the fly ash samples by this technique. It was found that there is no huge concentration difference between the fly ash and soil samples as a result of which fly ash can be used as soil manure without any adverse impact on the plants.      

金属橡胶迟滞特性本构模型研究

金属橡胶作为一种新型阻尼材料, 其原材料及加工工艺具有一定特殊性. 基于材料的细观结构特征, 选取了金属丝螺旋卷作为金属橡胶的基本微元体结构, 并以圆柱压缩螺旋弹簧理论为基础, 分别建立了横向和纵向排列微元体结构的刚度. 鉴于库仑摩擦模型, 分别建立三种接触状态螺旋卷接触对的力学模型. 考虑整个加工工艺流程的特点, 分析了不同接触状态数目变化规律, 建立了金属橡胶迟滞特性本构模型. 从理论上解释了金属橡胶迟滞特性的特点, 以及刚度和阻尼非线性的产生机理. 最后, 通过对比不同相对密度金属橡胶试件的理论和试验结果, 验证了理论模型的适用性. 本模型从螺旋卷微元体结构上描述了金属橡胶迟滞特性, 为工程上预测和分析金属橡胶的刚度、阻尼特性和设计金属橡胶产品提供了有效的理论基础.     

Plasma damping effects on the radiative energy loss of relativistic particles

The energy loss of a relativistic charge undergoing multiple scatterings while traversing an infinite, polarizable and absorptive plasma is investigated. Polarization and absorption mechanisms in the medium are phenomenologically modeled by a complex index of refraction. Apart from the known Ter-Mikaelian effect related to the dielectric polarization of matter, we find an additional, substantial reduction of the energy loss due to the damping of radiation. The observed effect is more prominent for larger damping and/or larger energy of the charge. A conceivable analog of this phenomenon in QCD could influence the study of jet quenching phenomena in ultrarelativistic heavy-ion collisions at RHIC and LHC.     

Coal ash composition of Australian low rank coals

The iron-containing phases in nine precipitator ashes of widely differing composition have been analyzed by⁵⁷Fe Mössbauer spectroscopy. The importance of the relative proportion of calcium ferrite to magnesioferrite in determining the ash fusion characteristics was established and a procedure developed which reproduced the observed proportion, starting from the ash chemical analysis data.     

Validation of the community radiative transfer model

To validate the Community Radiative Transfer Model (CRTM) developed by the U.S. Joint Center for Satellite Data Assimilation (JCSDA), the discrete ordinate radiative transfer (DISORT) model and the line-by-line radiative transfer model (LBLRTM) are combined in order to provide a reference benchmark. Compared with the benchmark, the CRTM appears quite accurate for both clear sky and ice cloud radiance simulations with RMS errors below 0.2 K, except for clouds with small ice particles. In a computer CPU run time comparison, the CRTM is faster than DISORT by approximately two orders of magnitude. Using the operational MODIS cloud products and the European Center for Medium-range Weather Forecasting (ECMWF) atmospheric profiles as an input, the CRTM is employed to simulate the Atmospheric Infrared Sounder (AIRS) radiances. The CRTM simulations are shown to be in reasonably close agreement with the AIRS measurements (the discrepancies are within 2 K in terms of brightness temperature difference). Furthermore, the impact of uncertainties in the input cloud properties and atmospheric profiles on the CRTM simulations has been assessed. The CRTM-based brightness temperatures (BTs) at the top of the atmosphere (TOA), for both thin (τ<5) and thick (τ>30) clouds, are highly sensitive to uncertainties in atmospheric temperature and cloud top pressure. However, for an optically thick cloud, the CRTM-based BTs are not sensitive to the uncertainties of cloud optical thickness, effective particle size, and atmospheric humidity profiles. On the contrary, the uncertainties of the CRTM-based TOA BTs resulting from effective particle size and optical thickness are not negligible in an optically thin cloud.     

Quark loop model of radiative meson decays

Radiative meson decays are computed from quark loop anomalies, taking into account the SU(3) splitting of the quark masses. Predicted rates for ?→ηγ,K ^*→Kγ, and η→ππγ are brought into satisfactory agreement with experiment. Formulas are given for the radiative decay rates of charmed las are given for the radiative decay rates of charmed mesons, and a mechanism suggested for suppression of the radiative decays of mesons containing a charmed quark.     

Effects of fly ash on NOx removal by pulsed streamers

NO_x removal methods using plasma chemical reactions in nonthermal plasmas have been widely studied. In this paper, the effects of the addition of fly ash on NO_x removal using short-pulsed discharge plasmas are described. Fly ash which had been collected from a coal-burning thermal electrical power plant was used. Experiments were performed using four different mixtures of gases which included NO. These were (N₂+NO), (N₂+NO+O₂), (N₂+NO+H₂O), and (N₂+NO+O₂+H ₂O). These gas mixtures were used either with or without the addition of fly ash. The initial concentration of NO was fixed at 200 ppm (NO parts per million of the gas mixture), The study of the NO_x (NO+NO₂) removal was performed with the fly ash, as it is relevant to real situations in coal power plants. The results show that the presence of fly ash decreased the NO_x removal rate slightly in the case of dry gas mixtures while it increased the NO_x removal rate substantially in the case of wet gas mixtures. These results suggest that the presence of fly ash in the flue gases, which also contain a few percentages of moisture, would be advantageous to the treatment of flue gases emitted from thermal power plants for the removal of nitrogen oxides