钛酸亚铁材料的研究现状

钛酸亚铁是典型钛铁矿钛酸盐,其自身属性预示着钛酸亚铁具有丰富的物理化学性能。总结了目前钛酸亚铁的制备方法、改性方法以及性能的研究现状,并分析了目前研究中存在的不足,如改性手段较少,作为锂离子电池负极材料在高倍率下容量衰减严重。未来可以通过改变制备工艺或者离子掺杂等手段调控钛酸亚铁的微观结构,进而提升其物理化学性能,为今后钛酸亚铁的性能研究和应用提供一定参考。     

CFD优化管线式高剪切混合器停留时间分布

基于计算流体力学（CFD）的方法,采用Fluent软件,结合大涡模拟（LES）湍动模型和组分物料运输模型（SPE）对中试规格的管线式叶片-网孔型高剪切混合器的停留时间分布（RTD）进行预测,与实验结果相比,其误差在14%以内,说明此方法具有较高的可靠度。基于此方法,研究了定子开孔形式、腔室结构及定转子安装方式对停留时间分布的影响,使其适用于快速反应过程。结果表明：圆形、菱形、“S”形以及齿形4种不同开孔形式的定子,圆孔开孔定子效果最优;轴向长度缩短至与出口管径相同,蜗壳形状的腔室外壳,出口管与腔室相切时效果最优;定转子偏心安装能够改善其效果,但功耗增加。经过优化后的反应器具有广泛的应用,特别的是将其用于许多快速化学反应过程时,由于停留时间短、混合效果好,其混合性能明显优于许多传统的反应器。     

Solution of boundary-value problems by orthogonal collocation : J. V. Villadsen and W. E. Stewart, Chem. Engng Sci. 22, 1483–1501, 1967

A standard method for treatment of differential equation models was discovered more or less by chance when applying a quadrature-Galerkin method to solve a simple chemical engineering problem. The method was easy to use and it made manual solution of even complicated problems seem possible.     

Techno-economic assessment of pulverized coal boilers and IGCC power plants with CO2 capture

The current studies on power plant technologies suggest that Integrated Gasification Combined Cycle (IGCC) systems are an effective and economic CO₂ capture technology pathway. In addition, the system in conventional configuration has the advantage of being more “CO₂ capture ready” than other technologies. Pulverized coal boilers (PC) have, however, proven high technical performance attributes and are economically often most practical technologies. To highlight the pros and cons of both technologies in connection with an integrated CO₂ capture, a comparative analysis of ultrasupercritical PC and IGCC is carried out in this paper. The technical design, the mass and energy balance and the system optimizations are implemented by using the ECLIPSE chemical plant simulation software package. Built upon these technologies, the CO₂ capture facilities are incorporated within the system. The most appropriate CO₂ capture systems for the PC system selected for this work are the oxy-fuel system and the postcombustion scheme using Monoethanolamine solvent scrubber column (MEA). The IGCC systems are designed in two configurations: Water gas shift reactor and Selexol-based separation. Both options generate CO₂-rich and hydrogen rich-gas streams. Following the comparative analysis of the technical performance attributes of the above cycles, the economic assessment is carried out using the economic toolbox of ECLIPSE is seamlessly connected to the results of the mass and energy balance as well as the utility usages. The total cost assessment is implemented according to the step-count exponential costing method using the dominant factors and/or a combination of parameters. Subsequently, based on a set of assumptions, the net present value estimation is implemented to calculate the breakeven electricity selling prices and the CO₂ avoidance cost.     

炼化企业节能节水及装置扩能改造瓶颈辨识探讨

炼化企业是耗能用水大户,随着国家对节能减排要求的逐渐严格,炼化企业节能节水工作面临较大的压力.过程系统集成优化技术把炼化生产过程作为统一整体考虑,可最大化实现节能节水效果.过程系统作为一个有机的整体,系统中必然有一些单元过程构成系统节能节水的瓶颈,辨识这样的系统瓶颈,并研究相应的解瓶颈策略,可使节能节水取得事半功倍的效果.本文在对炼化企业能量系统和用水网络常用的优化技术和方法进行介绍的基础上,重点分析了炼化企业节能节水瓶颈辨识的研究进展,主要涉及节能瓶颈、节水瓶颈以及装置扩能改造瓶颈的辨识等方面的研究进展.当前的研究主要集中在单一网络的瓶颈辨识,下一步的研究方向应从单功能网络逐步推进到耦合网络.     

Comparative assessment of sub-critical versus advanced super-critical oxyfuel fired PF boilers with CO2 sequestration facilities

This work focuses on the techno-economic assessment of bituminous coal fired sub- and super-critical pulverised fuel boilers from an oxyfuel based CO₂ capture point of view. At the initial stage, two conventional power plants with a nominal power output of above 600 MWe based on the above steam cycles are designed, simulated and optimised. Built upon these technologies, CO₂ capture facilities are incorporated within the base plants resulting in a nominal power output of 500 MWe. In this manner, some sensible heat generated in the air separation unit and the CO₂ capture train can be redirected to the steam cycle resulting in a higher plant efficiency. The simulation results of conventional sub- and super-critical plants are compared with their CO₂ capture counterparts to disclose the effect of sequestration on the overall system performance attributes. This systematic approach allows the investigation of the effects of the CO₂ capture on both cycles. In the literature, super-critical plants are often considered for a CO₂ capture option. These, however, are not based on a systematic evaluation of these technologies and concentrate mainly on one or two key features. In this work several techno-economic plant attributes such as the fuel consumptions, the utility usages, the plant performance parameters as well as the specific CO₂ generation and capture rates are calculated and weighed against each other. Finally, an economic evaluation of the system is conducted along with sensitivity analyses in connection with some key features such as discounted cash flow rates, capital investments and plant efficiencies as well as fuel and operating costs.     

Construction of PbZr0.4Ti0.6O3- and Ba0.9Sr0.1TiO3-Based Optical Microcavities by Chemical Solution Deposition

Herein we report on a simple, low cost, and feasible route for the construction of PbZr_0.4Ti_0.6O₃ (PZT)- or Ba_0.9Sr_0.1TiO₃ (BST)-based optical microcavities using a single chemical solution containing polymer polyvinylpyrrolidone. The obtained multilayer systems not only exhibit good ferroelectric performance, but also display well-defined resonant modes with a quality factor of no <66. Compared with PZT microcavities, the optical properties of the BST microcavities appear to be superior.     

Dependence of Equilibria in the Modified Chemical Vapor Deposition Process on SiCl4, GeCl4, and O2

The high-temperature equilibrium concentration of the gaseous species and of the deposited glass formed by the oxidation of the chlorides of silicon and germanium was measured and compared with thermodynamic calculations. The equilibrium incorporation of germanium in phosphate-silicate particles formed from the gas at 1650 K is shown to form a theoretical basis from which the actual composition of completed preforms and optical fibers made by the modified chemical vapor deposition process can be calculated. The efficiency of incorporation of germanium dioxide in the silica glass system is determined as a function of the oxygen concentration and the ratio of germanium to silicon. The recently redeveloped element potential method is used to minimize the Gibbs energy of the system and obtain the temperature and compositional dependences. The agreement of calculated and experimental results obtained in this work suggests a broad spectrum of uses of the method for understanding and calculating chemical reactions. The method is exceptionally well suited for applications where the determination of species concentrations for multiphase processes is desired over broad ranges of concentrations, temperatures, and pressures.     

Syngas production from butane using a flame-made Rh/Ce0.5Zr0.5O2 catalyst

The capability of flame-made Rh/Ce_0.5Zr_0.5O₂ nanoparticles catalyzing the production of H₂- and CO-rich syngas from butane was investigated for different Rh loadings (0–2.0 wt% Rh) and two different ceramic fibers (Al₂O₃/SiO₂ and SiO₂) as plugging material in a packed bed reactor for a temperature range from 225 to 750 °C. The main goal of this study was the efficient processing of butane at temperatures between 500 and 600 °C for a micro-intermediate-temperature SOFC system. Our results showed that Rh/Ce_0.5Zr_0.5O₂ nanoparticles offer a very promising material for butane-to-syngas conversion with complete butane conversion and a hydrogen yield of 77% at 600 °C. The catalytic performance of packed beds strongly depended on the use of either Al₂O₃/SiO₂ or SiO₂ fiber plugs. This astonishing effect could be attributed to the interplay of homogeneous and heterogeneous chemical reactions during the high-temperatures within the reactor.     

Catalytic wall reactor: Catalytic coatings of stainless steel by VOx/TiO2 and Co/SiO2 catalysts

Catalytic wall (structured) reactors and structured supports are suitable to study the catalytic properties of nanosized materials. The coating of metallic (aluminum and stainless steel) plates by thin layers of active phase is presented in two cases, VO_x/TiO₂ and Co/SiO₂, catalysts used in the oxidative dehydrogenation (ODH) of propane and in Fischer–Tropsch synthesis (FTS) of clean fuels, respectively. The preparation of coated plates and their characterisation by various methods of physicochemical analysis are described. Both chemical and physical methods were used for coating. VO_x/TiO₂ layers were obtained by grafting of Ti (on Al or stainless-steel plates) and V (on TiO₂) alkoxides and use of sol–gel media or suspension. A silica primer was deposited (on stainless-steel plate) by plasma-assisted chemical vapour deposition (PACVD) onto which Co oxide and silica were coprecipitated from sol–gel. The catalytic experiments in the respective reactions were carried out in special plate reactors and compared with those of catalytic powders. The study shows that the coating of a metallic substrate by a catalyst is not straightforward and requires specific studies dealing with both chemistry (chemical affinity between substrate and catalytic layers) and catalytic engineering (catalytic performance in taylor-made reactors).     

Residence times,micromixing and conversion in an un-premixed feed reactor — II: Chemical reaction measurements

Conversion measurements for a number of second order chemical reactions have been made at the outlet of an un-premixed feed, confined jet reactor, for which residence time data had been previously determined. A variety of stoichiometric and non-stoichiometric mixtures were used for a range of the dimensionless reaction rate constant k_r$\text{c}$₀τ between 0·1 and 18. A stochastic micro-mixing model, involving a single mixing history parameter and the measured residence time distributions, has been shown to correlate the conversion results for a number of different hydrodynamic conditions, in a manner that suggests that prediction of the outcome of other reactions is possible. The computational and experimental techniques involved are adaptable to the design and operation of industrial reactors where interaction of the hydrodynamics and chemical reaction rates are important in determining overall performance.     

Solid Solutions in the System Urania—Rare-Earth Oxides: I, UO2-GdO1.5,

The extent and nature of solid solution formation in the system urania-gadolinia were investigated. Compositions sintered in hydrogen, in argon, and in air were analyzed by chemical and X-ray methods. Extensive solid solution exists between uranium dioxide and gadolinium sesquioxide. Some anomalies in the lattice parameters of the solid solutions are interpreted.     

Thermodynamic Properties of Fe3O4-FeAl2O4 Spinel Solid Solutions

The Gibbs energy of mixing for the system Fe3O₄-FeAl₂O₄ was determined at 1573 K using a gas-metal-oxide equilibration technique. Oxide solid solution samples were equilibrated with Pt foils under controlled CO+CO₂ gas streams. The equilibrium iron concentration in the foil was determined by chemical analysis. The cation distribution between tetrahedral and octahedral sites in the spinel crystal can be calculated from site-preference energies and used as an alternate method of determining some thermodynamic properties, including the Gibbs energy of mixing. The solvus occurring at low temperatures in the system Fe₃C₄-FeAl₂C₄ was used to derive the effect of lattice distortion due to cation size difference on the enthalpy of mixing and to obtain a better approximation to the measured thermodynamic quantities.     

Measurements of Particle Residence Time Distributions in A Co-Current Spray Dryer

Measurements of particle residence time distributions by means of tracer analysis were done in a co-current pilot plant spray dryer operated with a pressure-nozzle. A system is described for injecting tracer into the feedstream just before the nozzle. Tracer concentrations were measured in two product streams: the tower product stream (mean particle size 134 microns) and the cyclone product stream (mean particle size 67 microns). The measurements show a very wide range of residence times: some particles have residence times shorter than 3 seconds, others have residence times longer than 10 minutes. The median of the distribution is 58·5 _s for the tower product stream and 42.2 _s for the cyclone product stream.     

Kinetics of coal liquefaction: effect of catalyst,H2 concentration and coal type

A process for dry coal hydrogenation—liquefaction has been developed that permits short residence times (seconds) and achieves notably high space rate utilization factors. The purpose of the work reported here is to identify more precisely the process variables that determine space rate utilization factors, and to express them in a kinetic scheme, in the hope of establishing more effective control of these variables in the process. A kinetic analysis of work done in a 3 mm i.d. × 1 m long reactor is presented. Some data from a 4.5 mm i.d. × 34 m long reactor is also included. A correlation of hydroaromatic, catalyst and hydrogen concentration is considered. Parameters considered important for an optimum space rate utilization factor are both chemical and physical in nature. Of special importance are heat transfer, catalyst concentration and hydrogen concentration. A large space rate utilization factor is important from the standpoint of reduced reactor volume.     

The performance of the 12,000 m3/day seawater ro plant at Jeddah,Saudi Arabia

This paper outlines the performance of the 12,000 m³/day seawater RO plant at Jeddah, Saudi Arabia. The plant started operation in February 1979 and has been operating since then. The feedwater to the plant has a TDS of 42,000 ppm and the maximum seawater temperature is 32°C. The plant is made up of a first and a second stage. The first stage includes nine units, eight operating and one stand-by, and the second stage containes three units. The nine first stage and the three second stage RO units are each composed of 56 Fiberglass pressure tubes (Model 66 FRP-6) 150 mm diameter by 6.5 m long, each containing six spiral wound elements manufactured by UOP Fluid Systems Division. The plant uses Fluid System's polyamide thin film composite membrane element, Model 1501 TFC. The pretreatment is composed of dual media filtration, acid injection, sodium hexametaphosphate injection and cartridge filtration.The performance from the start of operation till the present time is shown both for the overall plant and for each unit. The product rate of each unit and its water quality throughout its operating period is indicated showing the times when the unit was shut-down and the reason for it. Deterioration in unit performance is analyzed and explained. Actual plant consumption of fuel and chemicals is given and estimates of the plant operating costs are made.     

再论大型煤化工装置压力容器选材、设计和制造

评述了煤化工装置厚壁铬钼钢和低温压力容器厚钢板国产化目前实际水平情况；介绍了煤气化装置和甲醇变换系统不锈钢管道和复合板设备腐蚀实际情况及用碳钢材料替代的探索,对近期发布的新标准规范在煤化工装置中的应用提出了建议.     

3200t/d改进型SLC分解炉内气固运动规律的研究

通过系统测定鱼峰水泥股份公司改进型3200t/dSLC分解炉内气体三维流场、阻力特性、物料停留时间分布等,分析了其内部气固两相运动的基本规律。研究表明,改进型SLC分解炉的气体流场与原分解炉总体相似,但缩口的增加产生了一定的二次喷腾作用,对物料均布有一定改善,料气停留时间比值明显提高,加上容积的增大,使固体粉料的平均停留时间在气体量相同时延长了近80%,这是熟料产量能够超过设计值,系统能稳定运行的基本原因。但与性能优良的分解炉比较,该分解炉料气停留时间比值仍然较低,阻力损失较大,三次风管风速过高。进一步提高系统产量时有必要对分解炉和三次风管进行优化和改造。     

Deactivation of V2O5-WO3-TiO2 SCR catalyst at biomass fired power plants: Elucidation of mechanisms by lab- and pilot-scale experiments

In this work, deactivation of a commercial type V₂O₅-WO₃-TiO₂ catalyst by aerosols of potassium compounds was investigated in two ways: (1) by exposing the catalyst in a lab-scale reactor to a layer of KCl particles or fly ash from biomass combustion; (2) by exposing full-length monolith catalysts to pure KCl or K₂SO₄ aerosols in a bench-scale reactor. Exposed samples were characterized by activity measurements, SEM-EDX, BET/Hg-porosimetry, and NH₃ chemisorption. The work was carried out to support the interpretation of observations of a previous study in which catalysts were exposed on a full-scale biomass fired power plant and to reveal the mechanisms of catalyst deactivation.Slight deactivation (about 10%) was observed for catalyst plates exposed to a layer of KCl particles at 350 °C for 2397 h. No deactivation was found for catalyst plates exposed for 2970 h to fly ash (consisting mainly of KCl and K₂SO₄) collected from an SCR pilot plant installed on a straw-fired power plant. A fast deactivation was observed for catalysts exposed to pure KCl or K₂SO₄ aerosols at 350 °C in the bench-scale reactor. The deactivation rates for KCl aerosol and K₂SO₄ aerosol exposed catalysts were about 1% per day and 0.4% per day, respectively.SEM analysis of potassium-containing aerosol exposed catalysts revealed that the potassium salt partly deposited on the catalyst outer wall which may decrease the diffusion rate of NO and NH₃ into the catalyst. However, potassium also penetrated into the catalyst wall and the average K/V ratios (0.5–0.75) in the catalyst structure are high enough to explain the level of deactivation observed. The catalyst capacity for NH₃ chemisorption decreased as a function of exposure time, which reveals that Brønsted acid sites had reacted with potassium compounds and thereby rendered inactive in the catalytic cycle. The conclusion is that chemical poisoning of active sites is the dominating deactivation mechanism, but physical blocking of the surface area may also contribute to the loss of activity in a practical application. The results support the observation and mechanisms of deactivation of SCR catalysts in biomass fired systems proposed in a previous study [Y. Zheng, A.D. Jensen, J.E. Johnsson, Appl. Catal. B 60 (2005) 253].     

Synthesis, Characterization, and Consolidation of Si3N4 Obtained from Ammonolysis of SiCl4

Thermal decomposition of silicon diimide, Si(NH)₂, in vacuum resulted in very-high-purity, fine-particle-size, amorphous Si₃N₄ powders. The amorphous powder was isothermally aged at 50° to 100° intervals from 1000° to 1500°C for phase identification. Examination of ir spectra and X-ray diffraction patterns indicated a slow and gradual transition from an amorphous material to a crystalline α-phase occurring at 1200°C for >4 h and/or 1300° to 1400°C for 2 h. As the temperature was increased to ≥1450°C for 2 h, the crystalline β-phase was observed. Phase nucleation and crystallite morphology in this system were studied by electron microscopy and electron diffraction combined with TG as functions of temperature for the inorganic polymer starting materials. Powders prepared in this manner with 4 wt% Mg₃N₂ added as a sintering aid were hot-pressed to high-density fine-grained bodies with uniform microstructures. The optimum hot-pressing condition was 1650°C for 1 h. Silicon concentration steadily increased as the hot-pressing temperature or time was increased. A method for chemical etching for high-density fine-grained Si₃N₄ is described. Electrical measurements between room temperature and ∼500°C indicated dielectric constant and tan δ values of 8.3±0.03 and 0.65±0.05×10⁻², respectively.