燃煤易挥发微量重金属元素行为的试验研究

为了解煤燃烧过程中易挥发微量重金属元素的行为及其控制因素,对黔西南烟煤和无烟煤进行了层燃实验和流化床燃烧实验。结果表明,层燃实验,煤中Hg在150℃挥发率达50.25％。到815℃几乎全部释放,Se的挥发率平均在98％以上。950℃下煤中As、Sb的挥发率平均为36.77％和34.47％。流化床燃烧,煤中绝大部分Hg以气态排放到大气中,部分Se以气态排放;微细颗粒吸附Hg、Se、As和少量的Sb以吸附态排放。赋存状态、燃烧方式以及燃烧工况等对微量重金属的挥发性有明显的控制作用。     

氧燃烧方式下矿物质与重金属行为特征的研究

在沉降炉试验台上,进行空气气氛及O2/CO2气氛燃煤试验,通过X射线衍射分析和ICP-AES分析研究了不同气氛下煤灰中矿物质组成及痕量元素的挥发特性.并根据热力学多相平衡原理对矿物质与重金属在两种气氛下的挥发行为进行了计算和比较分析.结果表明,氧燃烧气氛下的矿物质组成与空气气氛下并无明显不同,矿物质元素的蒸发气化亦没有受到明显的影响,但在氧燃烧气氛下矿物质的晶相向非晶相的转化得到了较大改善,有可能使电站锅炉沉积得到缓解;氧燃烧气氛下灰中痕量元素相比空气气氛下在底灰中有明显的富集.     

燃煤过程中As,Se的挥发行为的研究

本文首先运用热平衡分析法对不同气氛下三种煤样的燃烧系统中As,Se物质的分布及含量进行了预报,并以此来指导实验方案的设计,最后,进行相应的实验研究,来探究燃煤过程中As,Se的挥发行为特性。从研究结果我们可以得出: (1)As,Se的挥发量都随着温度的升高而增加,并且Se的挥发百分比要比As要大。(2)在氮气气氛下,As挥发量大幅提升的现象发生在600-900℃这一温度范围,而Se的大量挥发现象比As要早,大约在200-600℃的温度范围内。 (3)氧化性气氛有助于As,Se在更低的温度下的挥发。 (4)SO2在某一温度范围内对于两种痕量元素的挥发有微弱的促进作用。     

基于红外光谱研究沥青燃烧机理和有害气体成分分析

利用Rosemount气体分析仪和定碳炉搭建起固定床燃烧反应试验平台,通过红外光谱分析技术定量分析沥青及其胶浆在高升温速率条件下燃烧反应的有毒气态产物成分、及其释放规律。研究表明,在高升温速率、近等温条件下,沥青及胶浆的燃烧过程可近似分为活泼挥发组分析出燃烧、二次挥发析出结合残炭燃烧两个阶段,其主要气态产物为CO₂,CO,NO,NO₂及SO₂。沥青材料中活泼挥发组分含量是影响燃烧气态产物释放规律的关键因素之一,减少沥青材料中活泼挥发组分的含量可有效降低燃烧气态产物的生成、尤其是CO的产生。     

单颗粒流化床富氧燃烧特性研究

在二维热态可视化流化床实验平台上深入研究了O_2/N_2和O_2/CO_2气氛下单个煤颗粒燃烧特性。实验中流化床床温为1088 K,O_2浓度为10%~40%,拟球形煤颗粒粒径为6 mm,两根热电偶分别记录煤燃烧过程中颗粒中心及表面温度的变化规律。实验结果表明:O_2/CO_2气氛下O_2扩散速率低于O_2/N_2气氛,使得煤颗粒的平均表观燃烧速率、升温速率及温度峰值降低,燃尽时间延长;提高O_2浓度后燃烧特性得以改善。为获得与空气气氛相近的燃尽时间,O_2/CO_2气氛下O_2浓度约需25%,但O_2浓度需30%才可达到和空气气氛相近的燃烧温度峰值。     

3MW_(th)富氧燃烧气体污染物生成与排放特性研究

本文在3 MW_(th)富氧煤粉燃烧实验台,对空气燃烧,不同循环倍率的循环燃烧工况下,进行燃烧实验,研究富氧燃烧过程中气体污染物的排放特性。实验结果表明:在3 MW_(th)富氧燃烧实验台上,富氧燃烧过程中CO_2浓度可以达到80%以上,同时能保证很高的煤粉燃尽率;与空气工况相比,富氧燃烧工况下,烟气中NO_x的浓度上升了56%~167%,排放量降低了46%~69%;同时燃烧气氛的变化对煤中硫向SO_2的转化率影响很小;双碱法湿法脱硫能在富氧燃烧条件下稳定运行,脱硫效率能达到95%以上。     

O_2/CO_2气氛下污泥与煤混燃特性研究

利用热重分析研究了O_2/CO_2气氛下污泥与煤混燃特性,基于热重(TG)和微商热重(DTG)分析曲线,分析了泥煤比、升温速率和气氛对污泥与煤混燃特性的影响。结果表明;在21%O_2/79%CO_2气氛下,污泥与煤混合物的着火温度随泥煤比的上升而显著降低,最大失重速率随着升温速率的提高而提高。随着氧浓度由21%提高到50%,燃尽温度从708.3℃降低至599.8℃,污泥与煤混合物的燃尽时间也明显缩短。21%O_2/79%N_2气氛下污泥与煤混合物的燃烧特性介于21%O_2/79%CO_2和30%O_2/70%CO_2气氛之间.     

氧/燃料燃烧条件下方解石的转化行为

将45~63μm和90~150μm的方解石矿物在空气与氧/燃料条件下进行沉降炉实验,研究了燃烧气氛、颗粒粒径以及SO_2对方解石转化行为的影响。研究表明:方解石颗粒在氧/燃料燃烧条件下发生破碎,气氛中CO_2浓度越高,方解石的破碎越弱;方解石样品粒径越大,破碎越明显。气氛中CO_2的浓度越高,CaCO_3的分解越弱,90~150μm的方解石分解程度大于45~63μm的方解石。气氛中存在体积分数为0.3%的SO_2时,氧/燃料燃烧条件下CaSO_4的生成量大于空气燃烧气氛,SO_2的存在促进CaCO_3的转化。     

富氧燃烧条件下煤焦的燃尽特性

本文利用平面火焰携带流反应器研究了DT烟煤在富氧燃烧条件下的燃烧实验。采用灰示踪法分析煤焦的燃尽和元素释放特性,并采用等密度模型计算了基于氧化反应C+0.5O_2→CO的表观反应动力学参数。研究结果表明;煤粉在富氧燃烧条件下的燃尽慢于空气燃烧;富氧燃烧条件下,煤焦与CO_2的气化反应会导致煤焦表面对O的化学吸附,进而导致氧元素释放速率减慢;高氧浓度条件下,高浓度CO_2对煤焦燃尽的抑制作用大于CO_2气化反应对煤焦燃尽的促进作用,降低环境氧浓度可以逐步提高CO_2气化反应对煤焦燃尽的贡献。     

燃烧烟气中镉和锌的在线监测实验研究

本文发展一种基于电感耦合等离子体(ICP)技术的烟气镉和锌的在线测量方法,连续测定煤燃烧烟气中镉和锌的瞬时浓度,从而全面跟踪镉和锌的挥发释放过程。实验得到优化的ICP(功率1400W)进气流速为:样品气体,0.03L/min;氩气,0.16 L/min。在线测量系统与流化床实验装置配备在一起,对煤燃烧烟气中镉和锌的浓度进行在线测量。温度对重金属的蒸发有很大影响,温度增加有利于其蒸发,但不是呈线性关系。重金属与飞灰颗粒在高温下反应生成稳定化合物,从而抑制了重金属的挥发。该技术对于研究燃烧过程重金属的释放和控制过程,是一种有用的工具。     

Effects of dissolved gas species on ultrasonic degradation of (4-chloro-2-methylphenoxy) acetic acid (MCPA) in aqueous solution

Sonochemical degradation of MCPA ((4-chloro-2-methylphenoxy) acetic acid) in dilute aqueous solutions was studied using ultrasound with a frequency of 500 kHz. The effect of gas atmosphere on MCPA degradation was investigated in nitrogen (N(2)), air (O(2)/N(2)), oxygen (O(2)), argon (Ar) and Ar/O(2) (60/40% v/v) atmospheres. For sonochemical degradation of MCPA in N(2), air (O(2)/N(2)), O(2) and Ar atmospheres, the rate enhancement of MCPA decomposition by sonolysis was found to be more effective in an O(2)-enriched atmosphere compared to Ar atmosphere. It was considered that a higher amount of oxidants was formed in a higher O(2) partial pressure, which accelerated MCPA decomposition in a radical reaction system. On the other hand, both dechlorination and total organic carbon (TOC) removal rates were higher in Ar atmosphere, compared to those in O(2)/N(2) atmosphere. It was found that, MCPA was most effectively decomposed by sonication in Ar/O(2) (60/40% v/v) atmosphere, with higher rates of decomposition, dechlorination and TOC removal.     

Luminescence mechanism of ZnO thin film investigated by XPS measurement

The effects of annealing environment on the luminescence characteristics of ZnO thin films that were deposited on SiO₂/Si substrates by reactive RF magnetron sputtering were investigated by X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). An analysis of the O 1s peak of ZnO film revealed that the concentration of oxygen vacancies increased with the annealing temperature from 600 °C to 900 °C under an ambient atmosphere. The PL results demonstrated that the intensity of green light emission at 523 nm also increased with temperature. Under various annealing atmospheres, the analyses of PL indicated that only one emission peak (523 nm) was obtained, indicating that only one class of defect was responsible for the green luminescence. The green light emission was strongest and the concentration of oxygen vacancies was highest when the ZnO film was annealed in ambient atmosphere at 900 °C. The results in this investigation show that the luminescence mechanism of the emission of green light from a ZnO thin film is associated primarily with oxygen vacancies. PACS 81.15.Cd; 81.40.Ef; 78.55.-m; 78.55.Et     

O2/CO2气氛下循环流化床煤燃烧SO2排放

在热输入功率50 kW的循环流化床O₂/CO₂燃烧试验装置上研究燃煤SO₂排放特性及石灰石脱硫机理。结果发现,未添加石灰石时,O₂/CO₂气氛下SO₂排放量比相同O₂浓度的空气气氛下低;随着O₂浓度的升高,排放量升高。相同钙硫摩尔比下,O₂/CO₂气氛下石灰石的脱硫机理以直接脱硫为主,脱硫效率比空气气氛下高;随着O₂浓度的增加,石灰石脱硫效率提高。     

非平衡大气辐射强度与透过率的Line-By-Line计算模式

导出了非局域热力学平衡(NLTE)大气辐射强度与透过率的基本公式,以及NLT和LTE的线强、光学厚度和透过率的关系。假设转动能级是热力学平衡(LTE)的,建立了一个精确的Line-by-LineNLTE辐射强度与透过率的有效算法来计算较高层行星大气红外活跃样品的辐射强度。计算了地球大气¹⁶O₃9.6μm带在白天、夜晚和NLTE、LTE条件下的临边光谱辐射强度、线积分辐射强度、带积分辐射强度和合成光谱辐射强度,揭示了NLTE辐射强度对LTE辐射强度有显著而重要的偏离。     

Rubidium metavanadate formation at room temperature under vacuum ultraviolet irradiation from metal-organic compositions

White light emitting phosphor RbVO₃ films have been successfully fabricated by means of a vacuum ultraviolet (VUV) irradiation using an excimer lamp after spin coating of metal-organic solution onto substrates. The metal-organic carboxylates coated on substrates decomposed and reacted under the VUV irradiation. The metal-organic bonds were efficiently cleaved by the VUV illumination not only in air but also in vacuum, however, there was not a strong driving force for the reaction process to the formation of RbVO₃ in the vacuum atmosphere. On the contrary, the reaction and crystallization simultaneously proceeded under photo-chemically produced active oxygen and/or ozone atmospheres due to the VUV illumination in air. The reaction between the photo-activated Rb-O and V-O species could be strongly enhanced by the oxidation atmospheres at the moment of the metal-organic bond cleavage under the VUV irradiation.     

Effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition

The effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition was investigated using atomic force microscopy, Raman spectroscopy, and deep ultra-violet photoluminescence(PL) with the excitation wavelength as short as ～ 177 nm. Annealing experiments were carried out in either N2 or vacuum atmosphere with the annealing temperature ranging from 1200℃ to 1600℃. It is found that surface roughness reduced and compressive strain increased with the annealing temperature increasing in both annealing atmospheres. As to optical properties,a band-edge emission peak at 6.036 eV and a very broad emission band peaking at about 4.7 eV were observed in the photoluminescence spectrum of the as-grown sample. After annealing, the intensity of the band-edge emission peak varied with the annealing temperature and atmosphere. It is also found that a much stronger emission band ranging from 2.5 eV to 4.2 eV is superimposed on the original spectra by annealing in either N2 or vacuum atmosphere. We attribute these deep-level emission peaks to the VAL–ONcomplex in the AlN material.     

Features of dusty structures in the upper Earth’s atmosphere

The features of the Earth’s dusty ionosphere are considered using as an example the summer polar mesosphere. The effect of the optical properties of microparticles on their heating and photoelectron emission under the action of solar radiation is analyzed in detail. Certain photochemical consequences of the presence of dust in the upper atmosphere are studied. In particular, it is shown that microparticles can noticeably reduce the concentration of water vapor in the upper atmosphere and this decrease in turn limits the particle sizes. The influence of the effect under consideration on the behavior of the charged component of the upper atmosphere is discussed.     

Effect of sintering atmosphere on Ni/PTC composites ceramics

In order to prepare lead-free BaTiO₃-based PTC (positive temperature coefficient) with low room temperature resistivity, metal Ni is added to BaTiO₃-based PTC samples that contain 5, 8, 10, 12, 15, 20 wt% of Ni. The sintering temperature is from 1240 °C to 1260 °C. The sintering atmosphere of Ni/PTC composites ceramics was studied. Two sintering atmospheres were adopted in this experiment; full reducing sintering atmosphere and part reducing sintering atmosphere. Controlling the dose of graphite powder can make these two reducing atmospheres. The experiment data show that the optimal sintering atmosphere is a part-reducing atmosphere. Under on the conditions mentioned above, the room temperature resistivity of the samples can drop to under 10 Ω cm and the PTC jump can reach 10³, which represents a good PTC characteristic.     

热处理对ZnO/Au薄膜结构和压电特性的影响

通过射频磁控溅射在氧化硅片表面沉积ZnO/Au薄膜,并通过不同的热处理方式对薄膜进行退火。为了研究退火对ZnO/Au薄膜结构和压电特性的影响,采用X射线衍射分析（XRD）、光学显微镜、场发射扫面电镜（FESEM）和压电力分析仪对薄膜退火前后的材料特性进行了分析。研究发现,热处理能够改善ZnO/Au薄膜的结晶质量。特别是在氮气保护氛围下慢速退火后,薄膜结晶质量有明显改善。但是,热处理导致了薄膜的压电系数d33和d31降低。分析认为,热处理过程中Au原子在ZnO中的易迁移特性破坏了ZnO/Au薄膜的压电性能。     

Effects of annealing atmosphere on the luminescent efficiency of ZnTe:O phosphors

The effect of the annealing atmosphere on the luminescent efficiency of ZnTe:O phosphors for X-ray imaging applications was studied. The phosphors were doped by ball-milling bulk ZnTe crystals in an O₂ atmosphere and annealed in various atmospheres: vacuum, N₂ or forming gas (95%N₂/5%H₂). All samples exhibited a deep red emission centered at 680 nm.The samples annealed in forming gas atmosphere exhibited an X-ray luminescent efficiency five times higher than the samples annealed in vacuum or N₂ atmospheres, which was attributed to the removal of surface tellurium oxides.