生物质燃烧源PM2.5在水汽条件下长大特性的研究

研究了生物质燃烧源产生的细颗粒在水汽条件下的长大特性,通过生长管实验研究了不同的热水温度、颗粒初始浓度、颗粒在生长管中的停留时间及表面活性剂下生物质燃烧源细颗粒在水汽过饱和条件中的长大特性。与燃煤细颗粒在水汽条件下的长大结果进行对比,生物质燃烧源细颗粒的长大效果要比燃煤细颗粒长大效果要好,热水温度的升高、停留时间的延长有利于细颗粒的长大,小粒径段颗粒的长大则几乎不受颗粒初始浓度的影响,添加一定量的表面活性剂可以使得生物质燃烧源细颗粒全部长大至1μm以上。     

燃烧源PM2.5凝结洗涤脱除实验研究

利用蒸汽在燃烧源PM2.5表面凝结,促使PM2.5凝结长大,建立一套燃烧源PM2.5凝结洗涤的实验台;考察了颗粒粒径分布、蒸汽添加量、液气比等对两种燃烧源PM2.5凝结洗涤脱除效果的影响。采用电称低压冲击器 (ELPI)在线测试分析燃煤和燃油PM2.5凝结洗涤前后的数浓度和粒径分布特性,并用SEM和XPS对两种不同燃烧源的颗粒进行了形貌和元素组分分析。结果表明,燃煤和燃油产生的PM2.5形貌和组分具有较大的差别,燃煤PM2.5主要为硅铝矿物质,而燃油PM2.5主要为含炭物质;相同条件下,燃煤PM2.5相变脱除效果优于燃油PM2.5;随着蒸汽添加量的增加,两者的脱除效率均升高;随粒径的增大,脱除效率提高;蒸汽添加量为0.08kg/m3时,粒径为0.4μm的燃煤和燃油细颗粒的脱除效率分别81％和72％;此外,适当增加液气比有利于凝结长大含尘液滴的脱除。     

粒径可控球形TiO2的制备

在正丙醇与水的混合溶剂体系中以Ti(SO4)2为前驱物制备得到了粒径分布窄, 分散性好的球形TiO2. 对表面活性剂种类及用量, 反应物浓度及焙烧温度和时间等影响因素进行了研究, 结果表明, 在正丙醇与水的体积比为1:1的条件下, 以聚乙烯吡咯烷酮(PVP)为表面活性剂, 温度为70-90 ℃时可制得粒径分布窄、分散性好的高质量的球形TiO2颗粒. 通过TG-DSC、SEM、XRD等分析表明, 颗粒粒度大小及粒径分布受表面活性剂浓度和反应前驱物浓度影响大; 物相间的转化主要由焙烧温度和时间来决定. 并引入LaMer模型对颗粒形核、长大的过程进行理论说明.     

粒径可控球形TiO2的制备

在正丙醇与水的混合溶剂体系中以Ti(SO4)2为前驱物制备得到了粒径分布窄,分散性好的球形TiO2.对表面活性剂种类及用量,反应物浓度及焙烧温度和时间等影响因素进行了研究,结果表明,在正丙醇与水的体积比为1∶1的条件下,以聚乙烯吡咯烷酮(PVP)为表面活性剂,温度为70-90℃时可制得粒径分布窄、分散性好的高质量的球形TiO2颗粒.通过TG-DSC、SEM、XRD等分析表明,颗粒粒度大小及粒径分布受表面活性剂浓度和反应前驱物浓度影响大;物相间的转化主要由焙烧温度和时间来决定.并引入LaMer模型对颗粒形核、长大的过程进行理论说明.     

热裂解-气相色谱-质谱法分析烟用咖啡颗粒热裂解特性

利用热裂解-气相色谱-质谱联用分析烟用咖啡颗粒的热裂解特性。分别于150、200、250、300、350℃对烟用咖啡颗粒进行热裂解分析，同时针对不同水分含量和粒径的咖啡颗粒在同一温度下进行热裂解成分分析。结果显示，随着温度的升高，热裂解产物逐渐增多，释放物质的种类逐渐也逐渐增多，在250℃时咖啡颗粒生成关键致香成分占比较高。不同水分含量和粒径的咖啡颗粒在250℃裂解时，水分越高，裂解产物中烟碱含量占比越高，烟气越充足；粒径越小，裂解产物中咖啡因和烟碱的总量越大，香气质量也越高。该试验为咖啡颗粒在卷烟中应用时的温度设计和香气品质改善提供理论依据。     

煤粉着火模式对再燃脱硝效率影响的实验研究

在一维携带流实验台上研究了烟煤煤粉着火模式,包括均相着火和非均相着火,对煤粉再燃还原NO的影响。实验结果表明,温度一定时,随着再燃区氧体积分数的增加,煤粉挥发分首先着火,脱硝效率明显下降;而非均相着火初期造成的颗粒高温有利于异相还原NO,脱硝效率得以回升;氧体积分数进一步提升,再燃区呈现富氧状态,脱硝效率再次下降。提高再燃区温度促进煤粉还原NO,脱硝效率更高,但是也促使挥发分在更低的氧体积分数下着火,着火后脱硝效率下降更多;粒径对煤粉着火以及还原NO的影响较为复杂,粒径在40μm以上,不同氧体积分数下脱硝效率基本上随粒径增大而下降。     

龙岩煤不同宏观煤岩组分的热破碎性质研究

用筛分和浮选法对龙岩煤进行分选, 得到不同粒径、不同宏观煤岩的龙岩煤颗粒。在热天平上进行热解破碎研究,并在自制的小型流化床上进行燃烧破碎试验。结果表明，亮煤与灰煤均发生一次破碎, 破碎后生成许多细小颗粒, 其中粒径0.8mm以下的细颗粒占多数；暗煤则不发生一次破碎。随着升温速率和颗粒粒径的增大, 一次破碎变得较为剧烈；颗粒性质、颗粒粒径、炉床温度和燃烧时间等因素对龙岩煤在流化床燃烧中的破碎均有重要影响。亮煤与灰煤因结构致密, 颗粒中大孔隙少, 显微硬度大, 灰分少等原因使得它们在燃烧中发生严重破碎；而暗煤颗粒则因相反的原因不发生破碎或仅发生轻微破碎。粒径越大, 炉床温度越高, 燃烧时间越长, 破碎越剧烈；亮煤与灰煤在燃烧中均发生了二次破碎, 其中亮煤的二次破碎更剧烈；燃烧后期, 亮煤的颗粒破碎比灰煤更快；由于破碎, 入炉煤颗粒平均粒径在燃烧早期迅速减小, 而后随着燃烧的进行而逐步趋于一个稳定值；亮煤在流化床燃烧中服从等密度燃烧模式, 暗煤服从等直径燃烧模式, 而灰煤则服从混合燃烧模式。     

3kA钕电解槽流场中颗粒受力分析

近年来随着NdFeB永磁的应用发展,对金属Nd质量的要求越来越高,而电解过程碳颗粒运动及溶解对金属质量的影响至关重要。通过理论与数值模拟相结合的方式对流场中不溶于电解液的碳固体颗粒的主要受力类型进行梳理,对其运动轨迹进行数值模拟研究,针对稀土电解槽进行了颗粒-流场的计算及模拟,研究发现曳力及重力是颗粒在电解槽中起主要作用的力。曳力是改变颗粒运动轨迹的影响因素,且曳力随粒径的增大而增大。0.07 mm颗粒粒径是区分主要作用力是重力还是曳力的临界值,颗粒粒径越大,越不利于电解槽得到纯净的Nd单质。对进一步改进电解槽槽型,从而得到质量更好、杂质更少的稀土金属,并对后续各物理场对颗粒的影响提供参考意义。     

粒径分布对水焦浆性质的影响

分析研究了不同粒径分布的石油焦成浆性及制备水焦浆的流变性和稳定性。结果表明,石油焦的成浆性较好,成浆浓度近70%,浆体的表观黏度均随浓度的增大而增大。粒径分布越宽,越有利于堆积,堆积效率越高,可制浆浓度越高,制备水焦浆的最佳药剂量越低,采用萘系分散剂制备的水焦浆呈胀塑性流型,粒径分布越宽,胀塑性越弱,利用静置观察法与Turbiscan Lab稳定性分析仪测定相结合评价水焦浆的稳定性,水焦浆的稳定性差,且粒径越大,析水率越低,沉降区的焦粉颗粒越易发生聚结,底部越易产生硬沉淀,稳定性越差。颗粒聚结是水焦浆稳定性的主要影响因素。     

原煤可磨性对气流床粉煤气化混配煤煤粉均匀程度的影响

以气流床粉煤气化工业装置不同时期的两组进料煤粉为研究对象,在实验室按粒径对两组煤粉进行了筛分分组,对分组后子煤粉进行了煤质、煤灰特性及反应活性分析,研究了原煤可磨性差异对混配磨制后煤粉均匀程度的影响。结果表明,原煤可磨性对混煤煤粉的颗粒粒径分布及其均匀性均具有影响。混配磨制煤粉的粒径主要取决于原煤中可磨性指数较小的原煤,此原煤可磨性指数越小,煤粉颗粒粒径越大;可磨性相近的原煤混配制得的煤粉混合较均匀,可磨性差异较大的原煤混配煤粉混合不均,煤粉发生偏析,使得大颗粒煤粉中含有过多的难磨煤,导致煤粉的反应性能变差。     

应用水汽相变促进湿法脱硫净烟气中PM_(2.5)和SO_3酸雾脱除的研究

在石灰石-石膏法脱硫净烟气中分别采用添加适量蒸汽和湿空气方式建立PM_(2.5)和SO_3酸雾凝结长大所需的过饱和水汽环境,在测试分析湿法脱硫净烟气中PM_(2.5)及SO_3酸雾物性的基础上,考察了蒸汽及湿空气添加量、脱硫净烟气温度等的影响。结果表明,湿法脱硫净烟气中PM2.5除含有燃煤飞灰外,含Ca SO_4、Ca SO_3及未反应的Ca CO_3等组分;由于SO_3酸雾基本处于亚微米级粒径范围,湿法烟气脱硫(WFGD)系统对SO_3酸雾的脱除率仅为35%-55%;添加适量蒸汽及湿空气方式均可促进湿法脱硫净烟气中PM_(2.5)和SO_3酸雾脱除,最终排放浓度随蒸汽或湿空气添加量的增加而降低,其中,添加蒸汽方式适合于脱硫净烟气温度较低(≤50-55℃)的场合,在脱硫净烟气温度较高(≥55-60℃)时,利用添加湿空气方式替代添加蒸汽更具技术经济优势。     

Determination of lead in fine particulates by slurry sampling electrothermal atomic absorption spectrometry

A simple method for determining lead in fine particulates (PM_2.5) by using electrothermal atomic absorption spectrometry (ETAAS) has been developed. Particulates collected on Nuclepore filter by using a dichotomous sampler were suspended in diluted nitric acid after ultrasonic agitation. The dislodging efficiency is nearly 100% after agitation for 5 min. In order to study the suspension behavior of PM_2.5 in solvents, a Brookhaven ZetaPlus Particle Size Analyzer was used to determine the particle size distribution and suspension behavior of air particulates in the solvent. The pre-digestion and modification effect of nitric acid would be discussed. Palladium was added as a chemical modifier and the temperature program of ETAAS was changed in order to improve the recovery. The slurry was introduced directly into a graphite tube for atomization. The metal content in the sample was determined by the standard addition method. In addition, a conventional acid digestion procedure was applied to verify the efficiency of the slurry sampling method. It offers a quick and efficient alternative method for heavy metal characterization in fine particulates. Received: 2 August 2000 / Revised: 25 October 2000 / Accepted: 28 October 2000     

Determination of lead in fine particulates by slurry sampling electrothermal atomic absorption spectrometry

A simple method for determining lead in fine particulates (PM2.5) by using electrothermal atomic absorption spectrometry (ETAAS) has been developed. Particulates collected on Nuclepore filter by using a dichotomous sampler were suspended in diluted nitric acid after ultrasonic agitation. The dislodging efficiency is nearly 100% after agitation for 5 min. In order to study the suspension behavior of PM2.5 in solvents, a Brookhaven ZetaPlus Particle Size Analyzer was used to determine the particle size distribution and suspension behavior of air particulates in the solvent. The pre-digestion and modification effect of nitric acid would be discussed. Palladium was added as a chemical modifier and the temperature program of ETAAS was changed in order to improve the recovery. The slurry was introduced directly into a graphite tube for atomization. The metal content in the sample was determined by the standard addition method. In addition, a conventional acid digestion procedure was applied to verify the efficiency of the slurry sampling method. It offers a quick and efficient alternative method for heavy metal characterization in fine particulates.     

Stochastic diffusion interactions and coarsening in a system of droplets growing from a supersaturated gas mixture

In this work we study diffusion interactions among liquid droplets growing in stochastic population by condensation from supersaturated binary gas mixture. During the postnucleation transient regime collective growth of liquid droplets competing for the available water vapor decreases local supersaturation leading to the increase of critical radius and the onset of coarsening process. In coarsening regime the growth of larger droplets is prevailing noticeably broadening the droplet size-distribution function when the condensation process becomes more intensive than the supersaturation yield. Modifications in the kinetic equation are discussed and formulated for a stochastic population of liquid droplets when diffusional interactions among droplets become noteworthy. The kinetic equation for the droplet size-distribution function is solved together with field equations for the mass fraction of disperse liquid phase, mass fraction of water vapor component of moist air, and temperature during diffusion-dominated regime of droplet coarsening. The droplet size and mass distributions are found as functions of the liquid volume fraction, showing considerable broadening of droplet spectra. It is demonstrated that the effect of latent heat of condensation considerably changes coarsening process. The coarsening rate constant, the droplet density (number of droplets per unit volume), the screening length, the mean droplet size, and mass are determined as functions of the temperature, pressure, and liquid volume fraction.     

Concentration of hydrogen nanobubbles in electrolyzed water

The hydrogen concentration of solutions supersaturated with hydrogen comprising dissolved hydrogen and hydrogen bubbles obtained through water electrolysis was studied. The rate of decrease in concentration of hydrogen nanobubble diameter below 600 nm and dissolved hydrogen with elapsed time after electrolysis was seemed to be independent of ionic strength and ion type and storage temperature. The concentration of hydrogen nanobubbles (mol dm(-3)) in electrolyzed water decreases with ionic strength, while the total hydrogen concentration remains roughly constant. The hydrogen nanobubble concentration increases in accordance with the nature of ions existing in solution in the following order I- < Br- < Cl- and K+ < Li+ < Na+. It is shown that the ratio of hydrogen nanobubble concentration to total hydrogen concentration of hydrogen in a catholyte strongly depends on the ratio in the supersaturated hydrogen solution near the electrode surface.     

Characteristics of hydrogen nanobubbles in solutions obtained with water electrolysis

A solution supersaturated with hydrogen obtained by water electrolysis was studied using cyclic voltammetry. The cyclic voltammogram of the solution supersaturated with hydrogen gave a peak current at −0.1 V vs. AgAgCl. No peak current in a solution saturated with hydrogen was observed by bubbling hydrogen gas through the solution. The peak current was influenced by the temperature and ion type of the electrolyte. The peak current was found to be due to the presence of hydrogen nanobubbles. The peak current increased with increasing hydrogen nanobubble concentration and decreased to zero within 3 h after electrolysis.     

Water vapor clustering in the field of a chlorine anion occurring in a planar nanopore with structureless walls

The Monte Carlo bicanonical statistical ensemble method has been employed to calculate the free energy, entropy, and work of Cl^? ion hydration in model planar pores 0.5 and 0.7 nm wide at 298 and 400 K. A detailed model of many-body interactions with the ion has been used, the model being matched to experimental data with respect to the free energy and enthalpy of attachment reaction in water vapor. Under the conditions of a restricted volume, the equilibrium size of a hydration shell substantially decreases, with the effect becoming stronger in the range of moderate and large sizes. In moderately supersaturated vapors, under the conditions of a nanopore, the ion loses its hydration shell as the temperature is decreased. In supersaturated vapors, the hydration shell formed on the ion is thermodynamically stable, while the stability crisis shifts to the region of larger sizes. The enhancement of the thermodynamic stability in the pore results from a rise in the chemical potential of molecules due to the deficiency of closet neighbors and a reduction in the entropy under the conditions of the restricted volume. As the temperature is elevated, the effect of ion displacement out of its hydration shell is leveled. The regularities derived in terms of the estimation model based on the capillary approximation are in qualitative agreement with the results of computer simulation.     

Continuous hydrothermal synthesis of CoFe2O4 nanoparticles

We have investigated the continuous hydrothermal synthesis and crystallization of spinel CoFe₂O₄ via the reaction of ferric nitrate and cobalt nitrate with sodium hydroxide. The reaction was carried out in water at temperatures ranging from 475 to 675 K and pressures of 25 MPa. The relative solubility of the precipitating cations was found to play a critical role in attaining the correct product. It was found necessary to control pH and temperature in order to prevent premature precipitation of iron in the reactor. Two variations of the continuous hydrothermal technique were examined—cold mixing and hot mixing. The cold mixing experiments produced a product with less impurity than the hot mixing experiments. Furthermore, the cold mixing configuration was successful in producing uniform nanoparticles of CoFe₂O₄. A mechanism of particle formation was postulated involving the precipitation of metal hydroxides at ambient conditions, dissolution of the hydroxides as temperature is increased followed by rapid precipitation of metal oxides at elevated temperatures. The hot mixing experiments, on the other hand, simply involve the precipitation of metal oxides due to the addition of the hot hydroxide solution. In both cases, very fine particles of CoFe₂O₄ are produced in the range of the processing conditions investigated.     

Low-temperature investigation of the growth mechanism of alkylsiloxane self-assembled monolayers

The growth behavior of self-assembled monolayer films strongly depends on parameters such as solvent, water concentration in the solvent, substrate type, and deposition method. A further parameter, the temperature, is of particular importance. It has been found that growth kinetics, size, and shape of the structures obtained strongly depend on the deposition temperature. Thus, exact adjustment and control of the solution temperature is of crucial importance for investigation of deposition mechanisms. The development of a temperature control unit has been the basis for a series of experiments on deposition of octadecyltrichlorosilane (OTS) on silicon wafers to study the influence of temperature on growth kinetics and film structure. Characterization of the films was performed with ellipsometry and atomic-force microscopy. It has been found that octadecylsiloxane (ODS) island sizes decrease with increasing temperature. Furthermore, a characteristic temperature exists above which increasingly disordered deposition occurs. At low temperatures (5–10 °C) smaller dot-like features are observed besides larger fractally shaped islands characteristic for self-assembly growth of ODS films. Our results indicate that these small dot-like features originate from ordered aggregates in the adsorption solution and that they are the precursors of the formation of larger islands. However, they can only be observed at low temperatures, because at room temperature they coalesce quickly to form larger units, due to the high surface mobility.     

High temperature microbalances based on GaPO4

Two different microbalance applications, based on temperature compensated thickness shear mode resonators (single rotated Y-cuts), were studied. In the first case, the film thickness growth during the sputter process was monitored. The measured frequency shift was in excellent agreement with the applied theory. In the second case, the selfcleaning by heating the crystal up to 650 °C after contamination with particulates was demonstrated.