D296树脂分离锆、铪洗脱的效果

介绍了在离子交换固定床上用D296强碱性阴离子交换树脂分离锆、铪的洗脱实验研究。吸附与洗脱实验的温度均控制在2~5℃,洗脱实验在饱和吸附的离子交换柱、过漏的离子交换柱、未过漏的离子交换柱中进行。研究结果表明:离子交换柱吸附状态以及洗脱剂酸度对分离效果有显著的影响。当离子交换柱存在交换区时,用任何酸度的硫酸作为洗脱剂,铪均被先洗脱出来,但高酸度的洗脱剂对分离锆、铪更有利;当离子交换柱为饱和状态时,低酸度和高酸度的洗脱剂洗脱,锆、铪不能得到分离。实验证明了单一的固定床分离锆、铪的效率低,要成功实现锆、铪的分离,需采用连续分离的离子交换移动床。     

硅粉氮化输送床内气固反应过程数值模拟

以单个硅颗粒氮化反应缩核模型为基础,本文建立了硅颗粒在输送床内反应、辐射与对流传热耦合的数学模型,并借助CFD软件FLUENT对输送床内能质传输过程进行了数值模拟,分析了输送床壁面温度、氮气流量、预热温度、硅粉粒径等因素对输送床内温度场和硅粉氮化率的影响。在数值计算域内将单个颗粒反应过程转化为颗粒群整体反应过程,实时监测颗粒粒径及未反应硅颗粒粒径,为数值模拟颗粒流反应提供一种新思路。当壁面温度高于1723K时,输送床内会出现一高温区加速硅粉氮化反应;反应温度越高、颗粒粒径越小,氮化过程越剧烈,硅粉到达完全氮化所需时间越短。模型表明为使粒径为2.5μm的硅粉达到完全氮化且输送床内最高温度不超过氮化硅的分解温度2173K,应控制输送床壁面温度在1773K,氮化时间在170s以上,预热温度在1273K,粉气质量比为0.2,稀释剂比例为0.5~1。     

Kinetics of the reaction of hafnium tetrachloride vapour with solid sodium chloride

The kinetics of the reaction of hafnium tetrachloride vapour with solid sodium chloride spheres to form sodium hexachlorohafnate have been studied as a function of pressure, temperature and sphere size. The course of the reaction was followed by weight gain measurements in an all-glass closed system using a quartz spring. Various kinetic models for gas-solid reactions were tested against the experimental data. Only the Carter-Valensi kinetic model gave a consistently good fit. Possible reaction mechanisms are discussed in the light of the pressure and temperature dependence of the specific rate constant in the Carter-Valensi model and in the inert marker experiments.     

Kinetics of the reaction of hafnium tetrachloride vapour with solid sodium chloride

The kinetics of the reaction of hafnium tetrachloride vapour with solid sodium chloride spheres to form sodium hexachlorohafnate have been studied as a function of pressure, temperature and sphere size. The course of the reaction was followed by weight gain measurements in an all-glass closed system using a quartz spring. Various kinetic models for gas-solid reactions were tested against the experimental data. Only the Carter-Valensi kinetic model gave a consistently good fit. Possible reaction mechanisms are discussed in the light of the pressure and temperature dependence of the specific rate constant in the Carter-Valensi model and in the inert marker experiments.     

Multiphase CFD Modeling for a Chemical Looping Combustion Process (Fuel Reactor)

There are growing concerns about increasing emissions of greenhouse gases and a looming global warming crisis. CO₂ is a greenhouse gas that affects the climate of the earth. Fossil fuel consumption is the major source of anthropogenic CO₂ emissions. Chemical looping combustion (CLC) has been suggested as an energy‐efficient method for the capture of carbon dioxide from combustion. A chemical‐looping combustion system consists of a fuel reactor and an air reactor. The air reactor consists of a conventional circulating fluidized bed and the fuel reactor is a bubbling fluidized bed. The basic principle involves avoiding direct contact of air and fuel during the combustion. The oxygen is transferred by the oxygen carrier from the air to the fuel. The water in combustion products can be easily removed by condensation and pure carbon dioxide is obtained without any loss of energy for separation. With the improvement of numerical methods and more advanced hardware technology, the time required to run CFD (computational fluid dynamic) codes is decreasing. Hence, multiphase CFD‐based models for dealing with complex gas‐solid hydrodynamics and chemical reactions are becoming more accessible. To date, there are no reports in the literature concerning mathematical modeling of chemical‐looping combustion using FLUENT. In this work, the reaction kinetics models of the (CaSO₄ + H₂) fuel reactor is developed by means of the commercial code FLUENT. The effects of particle diameter, gas flow rate and bed temperature on chemical looping combustion performance are also studied. The results show that the high bed temperature, low gas flow rate and small particle size could enhance the CLC performance.     

Synthesis and investigation of properties of nanocrystalline zirconia and hafnia

The effect of the temperature and pH of chemical precipitation on the degree of agglomeration of zirconium and hafnium hydroxides has been investigated. The specific features of crystallization of zirconium and hafnium hydroxides have been revealed. A technological scheme has been proposed for synthesizing ZrO₂ and HfO₂ nanocrystalline powders.     

The Effect of Foreign Ions on Separation of Hafnium from Zirconium on Diphonix® Resin

The weight distribution coefficients (λ_M) of the most often occurring in zirconium salts ions (M(II), M(III) and M(IV)) have been determined in established earlier optimal conditions for separation of zirconium from hafnium by means of Diphonix® resin. Their values range from 21 (λ_Zn(II)) to 1830 (λ_Ti(IV)) and depend on the charge of M ion as well as on its radius. For ions of the highest λ_M (Ti(IV) and Fe(III)) their influence on hafnium – zirconium separation has been studied. Ti(IV) ions at concentration of 1% (in relation to Zr) has been found to noticeably affect separation of hafnium from zirconium by means of Diphonix® resin.     

流化床法制备硅化镁的工艺研究

在一定的温度,高纯氢气氛围下,以硅粉、镁粉为原料,于流化床反应器中制备硅化镁.考察了硅粉与镁粉粒度、反应温度、反应时间、不同原料配比以及载气流量对反应的影响.实验结果表明,实验最佳条件是镁粉与硅粉摩尔比为2.05∶1、镁粉和硅粉的粒度在100～160目且粒度相差20目以内、反应温度570℃、反应时间2.0h、载气流量为3.0～5.0 L/min.在此实验条件下,硅化镁的质量含量≥98.3％.     

Characterization of the reactivity of limestones with SO2 in a fluidized bed reactor

The reaction between SO₂ and calcined limestone particles has been studied in a fluidized bed combustor. Measurements of sorbent reactivity with SO₂ were made for small batches of limestone injected into the combustor. Simultaneous continuous combustion of bituminous coal provided conditions like those of a boiler for study of the sulphation reaction. A semi-empirical rate model of the CaO-SO₂ reaction has been developed. External mass transfer of SO₂, diffusion within the particles and chemical reaction are taken into account. The limestone reactivity with SO₂ is characterized by two parameters which are dependent on the temperature and sorbent particle size. A model for predicting the limestone requirements in a fluidized bed boiler has been developed. Parameters from the batch experiments are included. The predictions for sulfur retention agree with the experimental results. In addition, effects of operating conditions (gas velocity, recycle, limestone particle size) on the retention of SO₂ were simulated using the model.     

Solid circulation and gas bypassing in an internally circulating fluidized bed with an orifice-type draft Tube

The effects of orifice diameter in the draft tube, particle size, gas velocities and bed height on the circulation rate of solids and gas bypassing between the draft tube and annulus have been determined in an internally circulating fluidized bed (i.d., 0.3 m ; height, 2.5 m) with an orifice-type draft tube. A conical shape gas separator has been employed above the draft tube to facilitate the separation of gases from the two beds. The circulation rate of solids and the quantity of gas bypass from the annulus to draft tube show their minimums when the static bed height is around the bottom of the separator. The circulation rate of solids increases with an increase in orifice diameter in the draft tube. At fixed aeration to the annulus, gas bypassing from the draft tube to annulus sections decreases, whereas reverse gas bypassing from the annulus to the draft tube increases with increasing the inlet gas velocity to the draft tube. The obtained solids circulation rate has been correlated by a relationship developed for the cocurrent flow of gas and solid through the orifice.     

对二甲苯氧化用钴锰溴铪催化体系研制

以氧氯化铪为原料,实验制备了PX氧化反应用醋酸铪、溴化铪催化剂;并在PX氧化性能实验装置中评价了催化剂性能,比较了醋酸铪、溴化铪所形成钴锰溴铪催化剂的性能及铪浓度对催化性能的影响;实验表明醋酸铪与溴化铪的性能相当,铪浓度增加,反应速度加快,铪对PX氧化反应各步的催化幅度不同,在工业生产条件下,加入60μg/g铪,PX消失速度增加了36%,关键组分PT酸速度增加了7%。     

四氯化硅水解制纳米二氧化硅粉体工艺研究

多晶硅合成过程中副产大量四氯化硅。以四氯化硅为硅源,通过水解反应成功合成了二氧化硅粉体。探讨了反应温度、四氯化硅的加料速度、四氯化硅和水的加料比、循环比等条件对二氧化硅比表面积的影响,并利用X射线粉末衍射仪、傅里叶红外光谱仪、比表面测定仪和粒度分析仪等测试工具对所制备的二氧化硅的结构、粒径等参数进行了表征。实验结果表明：在温度为50 ℃,四氯化硅的加料速度为2.0 L/min,加料比［m（四氯化硅）∶m（水）］为0.10~0.15,循环比为10 h-1的条件下,可制得满足橡胶补强剂要求的二氧化硅粉体。     

The Development of a Simple Method for the Preparation of Reactor-Grade Zirconium

Abstract

The separation of zirconium and hafnium by the fractional precipitation method has been extended by coprecipitation of their pyrophosphates. In the presence of sulfate ion, fractional precipitation of zirconium-hafnium pyrophosphates from a solution in 4 N HCI gives a good separation factor. Hafnium becomes concentrated in the precipitate. At a concentration of 0.7 to 0.8 g Zr/100 ml, optimum results were obtained with the addition of about 50 g ammonium sulfate/100 ml (Λ > 5). The separation factor falls sharply at higher concentrations of zirconium. Moreover, it has been found that when precipitation of the host is done above 45%, the separation factor shows a declining trend. It was, therefore, not possible to prepare reactor-grade zirconium in a single stage. After several trials it was possible to find nearly optimum conditions for the separation. Finally, reactor-grade zirconium was obtained in three stages of precipitation with an yield of ～24%.     

Numerical simulation of 3D fluidized bed biomass gasification based on CPFD

Based on computational particle fluid dynamics (CPFD), a three-dimensional bubbling fluidized bed steam-air mixed gasification numerical model was established, and it was verified with experiment trials. The results show that the simulation and experiment have good consistency. Based on the model, the gas distribution and temperature distribution in the gasifier were studied; meanwhile, the biomass properties (particle size, water content, types) and operating conditions (gasification temperature, bed height) were investigated. The results show that there is an optimal value for the impact of biomass particle size on gasification performance, with an average particle size of 0.6 mm being the best; a higher water content will reduce the output of combustible gas and is not conducive to the gasification reaction. Among the four types of biomass, sawdust gasification has the highest efficiency, the largest combustible gas production, and the highest gas calorific value. Rice husk is second only to sawdust but its carbon conversion rate is higher than that of sawdust; increasing the gasification temperature can increase the proportion of combustible gas and increase gasification efficiency; while the change of initial bed height can change the ratio of H₂/CO. This experiment provides a theoretical reference for biomass steam/air gasification, which is helpful for the selection and processing of biomass raw materials, and also facilitates the amplification and optimization of the gasifier.     

Pressurized Continuous Chromatography

Abstract

A pressurized continuous annular chromatograph has been developed for preparative separations. This device utilizes a slowly rotating annular bed of sorbent material, fixed multiple feed points, and fixed withdrawal locations. Most of our investigations have been performed with a 28-cm-diam column, but a larger model is being designed and constructed. The separation of copper, nickel, and cobalt components from a carbonate solution has been studied in detail. This solution simulates the leach liquor from the Caron process for recovering nickel and cobalt from laterite ores. Use of continuous gradient elution has been demonstrated. Recent studies have investigated several separations, including that of zirconium and hafnium (necessary for the production of zirconium for use in nuclear reactors), on a preparative scale. This system, because of its continuous feed and product withdrawal, its adaptability to large-scale operations, and its ability to separate many components, is expected to make chromatography a more competitive process in the industrial sector.     

基于CPFD方法的流化床生物质气化数值模拟

基于计算颗粒流体动力学（CPFD）建立了三维鼓泡流化床水蒸气-空气混合气化的数值模型,并进行了模型验证,结果表明模拟和实验具有良好的一致性。在该模型的基础上,研究了气化炉内气体分布以及温度分布;同时探究了生物质属性（颗粒粒径、含水率、种类）以及操作条件（气化温度、床料高度）对气化特性的影响。结果表明,生物质颗粒粒径对气化性能的影响存在一个最优值,平均粒径为0.6 mm是最佳的;较高的含水率会降低可燃气体产量,不利于气化反应的进行;四种生物质中,锯末气化的效率最高、可燃气体产量最大、气体热值最高,稻壳仅次于锯末但其碳转化率高于锯末;提高气化温度可以增加可燃气体的比例、提高气化效率;而初始床层高度的变化可以改变H₂/CO的比例。本实验为生物质水蒸气/空气气化提供了理论参考,有助于生物质原料的选取和处理,也有助于气化炉的放大和优化。     

EFFECTS OF PARTICLE CHARACTERISTICS ON THE PERFORMANCE OF A FAST FLUIDIZED BED REACTOR

A heterogeneous model for the fast fluidized bed reactor which carries out a gas-solid non catalytic reaction is presented. The hydrodynamics of the fast fluidized bed is characterized by the model of Kwauk et al. (1985) which assumes the existence of two phases; a dense phase and a dilute pneumatic transport phase. For a given solid flowrate, the length of the reactor occupied by each phase depends on gas velocity, particle diameter and density and average voidage within the reactor. The gas-solid reaction is assumed to follow the shrinking core model. The solids are assumed to be completely backmixed in the dense phase and move in plug How in the dilute pneumatic transport phase. The gas phase is assumed to be in plug flow in both phases

For given gas and solid flowrates, the transition from the dense phase flow to the fast fluidized bed (containing two regions) as functions of particle size and density is determined using the model of Kwauk et al. (1985). The numerical solution of the governing mass balance equations show that for given solid and gas flowrates, (and average voidage) the gas phase conversion shows an unusual behavior with respect to particle diameter and density. Such behavior is resulted from the effects of particle diameter and density on the reactor volume occupied by each phase and the effect of particle diameter on the apparent reaction rate. The numerical results show that a fast fluidized bed gives the best conversion at large particle density and for the particle diameter which results the fast fluidized bed to be operated near the pure dense phase flow.     

Extraction and Separation of Zr(IV) and Hf(IV) from Nitrate Medium by Some CYANEX Extractants

Abstract

A solvent extraction study has been carried out to extract and separate zirconium and hafnium from nitrate medium by using some phosphine oxide extractants (CYANEX 921, CYANEX 923, and CYANEX 925) in kerosene. The influence of the different factors affecting the extraction process was studied in detail. Apparently the rate of extraction of Zr(IV) and Hf(IV) in CYANEX 921, CYANEX 923, and CYANEX 925 is reasonably fast. The extraction increases with increasing temperature, suggesting that the reaction is endothermic. The stripping percent of Zr(IV) and Hf(IV) by 0.5 M HNO₃ from the loaded organic phase after two stages reached 97.5% and 10.2%, respectively, which lead to good separation of the two metals. Under the optimum conditions, the extraction of zirconium was about 90, 87.6, and 91.6% and separation factors equal to 17, 21.4, and 40.7 were obtained for CYANEX 921, CYANEX 923, and CYANEX 925, respectively. The results obtained reveal that 2.0 M nitric acid is the optimum acid concentration for the separation of Zr(IV) and Hf(IV) and 0.4 M CYANEX 925 performs more efficient separation compared with other organophosphorus extractants.     

Thermal decomposition of pyrite in a fluidized bed

The thermal decomposition of pyrite was investigated in a silica batch fluidized bed reactor, in the temperature range 594 to 625°C. Particles were sampled during each run and those partially reacted showed a sharp reaction front. An equilibrium between pyrite and the resulting pyrrhotite is maintained until the central core of pyrite has disappeared, after which the reaction proceeds uniformly throughout the particle forming pyrrhotites with successsively lower sulfur contents. The reaction rate was sensitive to temperature, particle size and gas velocity. Application of the shrinking core model is consistent with heat transfer as the controlling step.     

Influence of Operating Conditions for Fast Pyrolysis and Pyrolysis Oil Production in a Conical Spouted‐Bed Reactor

Fast pyrolysis experiments of larch sawdust were conducted in a conical spouted‐bed reactor to study the influences of reaction temperature, inlet gas velocity, feeding rate, and particle size on the product yield and pyrolysis oil quality. For the first time, the optimal conditions were determined for various pyrolysis operations of such reactor to increase the yield and quality of pyrolysis oil. The results demonstrate that the biomass particle size, reaction temperature, biomass feeding rate, and inlet gas velocity all affected the quality and yield of the pyrolysis oil, in this order.