煤粉燃烧火焰区域内形成的亚微米颗粒电镜研究

煤粉燃烧火焰区域是燃烧过程中温度最高的区域,同时也是温度梯度、组分浓度梯度最高的地方,以及还原和氧化气氛交错存在等复杂环境,这种环境对亚微米颗粒初始形成阶段有着重要的影响,对该区域形成的PM1进行研究有助于深入理解PM1的形成机理.本文基于25 kW一维下行炉内对自维持燃烧的煤粉火焰区域,通过两级稀释水冷等速取样系统和ELPI(荷电低压撞击分离器)系统对颗粒物进行分级收集,以及电镜分析技术,获得PM1的质量和数浓度粒径分布,以及各粒径主要成分分布,并进行单颗粒分析.结果表明火焰区域中形成的亚微米颗粒以含碳物质为主,碳烟、碱金属和硫对超细颗粒有富集的趋势.该区域的亚微米颗粒同时存在多种复杂的形成机理.     

细颗粒湍流聚并的分区法群平衡模拟

通过聚并促进细颗粒(PM_2.5)特别是亚微米颗粒(PM_1.0)团聚长大或被大颗粒捕集,是提高其脱除效率的有效方法之一。本文采用分区法对燃煤电厂尾部烟气中飞灰的聚并进行了群平衡模拟研究。利用圆柱阵列实现的湍流聚并装置,圆柱横向间距为4倍直径时,纵向间距宜在圆柱直径的15~30倍之间,在工程上较为可行的条件下,对于PM_1.0可达到55%或更高的聚并效率。粗颗粒的存在对于细颗粒聚并具有明显的促进作用,聚并停留时间越短,该作用相对越显著。     

煤燃烧亚微米颗粒数浓度特性实验研究和理论分析

煤粉燃烧过程中亚微米颗粒数浓度的准确采样和测量是一个颇具挑战性的问题,本文基于清华大学高温-维炉实验系统产生的亚微米颗粒物,发展了适用于气溶胶扫描电迁移率颗粒粒径谱仪(SMPS)的两级氮气稀释水冷等速取样技术.为得到炉膛内亚微米颗粒的真实数浓度粒径分布,本文探索了不同稀释比对测量结果的影响,最后发展了基于成核、团聚和表...     

燃煤电站锅炉颗粒物排放特性的实验研究

本文对某燃煤电厂的两台锅炉除尘器前后的飞灰颗粒进行采样,研究了可吸入颗粒物(PM10)的排放浓度、质量粒径分布、排放特征、对静电除尘器的穿透率和锅炉运行负荷对其的影响.试验采用低压撞击器(LPI)按不同粒径大小从0.03～10μm共分为13级,分别采集燃烧后的可吸入颗粒物.研究表明,两台锅炉产生的PM10均呈双峰分布,其除尘器入口峰值分别在0.1μm和4.0μm左右,而出口峰值则为0.1μm和2.0μm;随着颗粒物粒径的减小,颗粒物对除尘器的穿透率是降低的,其中在0.2～0.6μm的穿透率达到一个峰值;相比除尘器入口,除尘器出口PM1和PM2.5的质量百分比都大大增加,这也是由于除尘器对飞灰中的大颗粒脱除效果更佳的原因造成的.随着锅炉运行负荷的降低,PM,10占总灰颗粒的质量百分比含量下降.     

燃煤细微颗粒声波团聚的机理研究

采用声波团聚疗法促使燃煤电厂产生的细微烟尘颗粒在较高强度下的声场巾团聚为较大颗粒,以此提高除尘器对细微颗粒的脱除效率.建立了以同向凝聚和流体力学作用为机理的烟尘气溶胶声波团聚动力学模型,经过数值模拟求解得到烟尘粒子团聚后的再分布曲线.模拟计算结果与声压(SPL)为130～150 dB,频率为1000～4000 Hz,烟尘浓度为2～10g/m3条件下的团聚实验相比较,得到较好的吻合.当声压SPL增加时,PM10和PM2.5质量百分比相对于初始分布均有明显下降,表明细微颗粒的团聚效果明显.     

跨微米尺度混合颗粒粒径的同步测量方法

基于多波长消光法和图像法颗粒测量原理,提出了跨微米尺度混合颗粒粒径同步测量方法,建立了亚微米-十微米尺度颗粒粒径消光光谱反演算法及十微米以上尺度颗粒粒径图像处理算法;采用分光棱镜,搭建了消光光谱与背光图像同步测量装置,利用500 nm～76.9μm粒径范围内的10种标准颗粒配成跨微米尺度混合颗粒样品并开展实验研究。结果表明:利用所提方法开展跨微米尺度混合颗粒粒径同步测量时,亚微米-十微米尺度颗粒消光光谱与十微米以上尺度颗粒背光图像的相互影响可忽略,可同步测量得到跨微米尺度混合颗粒粒径;利用消光法和图像法分别开展亚微米-十微米、十微米以上尺度颗粒粒径测量,与标准颗粒粒径相比,相对误差均小于8%,且测量重复性较好,这为跨微米尺度混合颗粒提供了一种有效的粒径测量手段。     

煤粉燃烧过程磷在亚微米颗粒中的转化

亚微米颗粒(PM1)中的磷由于对环境和SCR催化剂活性的影响而受到越来越多的关注.本文在一台25 kW的一维下行炉实验装置上,利用两级N2稀释高温水冷等速取样系统,通过PM2.5切割器和ELPI获取代表着煤粉燃烧主要阶段生成的粗颗粒(PM2.5+)和PM1,并进行元素成分和颗粒形貌的测试.研究结果表明,在燃烧过程中,磷主要富集在PM1中,磷在PM1中的质量浓度粒径分布存在双模态结构,Na、K、Mg、Ca和Fe的磷酸盐化影响着P在燃烧中的转移,Fe、K和Ca是影响P在中间模态颗粒中分布主要因素,而超细颗粒模态中燃烧条件控制着蒸发凝并的过程,从而最终影响到P在超细颗粒模态中的质量浓度分布的剧烈变化,同时也影响磷酸盐化的元素种类及相关度.     

基于动态光散射研究pH值对茄红素胶囊粒径的影响

用微乳化技术结合复合团聚法制备了纳米及亚微米茄红素胶囊,基于动态光散射测量分析了环境p H值对胶囊的粒径大小及其分布的影响.结果表明,对纳米茄红素胶囊,当p H值为3.5、6.0及6.8时能稳定的分散,而p H值为7.4时则会出现明显的聚集现象;对亚微米茄红素胶囊,当p H值为3.5、6.0、6.8及7.4时其粒径分布均为双峰状态,其中粒径较大的为亚微米茄红素胶囊,粒径较小的为包覆不良的颗粒,且p H=7.4时的粒径明显小于其它三种p H值时的粒径.虽然亚微米胶囊在p H=7.4时粒径明显变小的结果与纳米胶囊相同,但亚微米胶囊并不像纳米胶囊那样出现聚集现象.     

用于亚微米颗粒测量的后向散射光谱法

针对后向散射光谱粒径测量法对亚微米颗粒测量准确度较差的问题,提出了一种采用紫外光作为光源的测量方法.通过快速傅里叶变换计算了粒径为0.25~1 μm的聚苯乙烯亚微米颗粒的后向散射频谱,将频谱峰值对应的频率值与相应的颗粒粒径进行线性回归,各粒径值相对于回归直线的平均误差为±0.02 μm. 结果表明,本文提出的300~400 nm的紫外光适用于测量0.25~1 μm的亚微米颗粒,相比目前国外最新的采用可见光谱或红外光谱的方法准确度提高了一个数量级,同时该方法也适用于测量双峰分布亚微米颗粒系.     

煤粉燃烧炉内细颗粒物沿程演化特性模拟

本文针对微米及亚微米细颗粒物在煤粉自维持燃烧高温一维炉中的沿程演化特性进行了定量模拟。从高温火焰区到焦炭燃烧区,利用聚并机理和碳烟氧化模型计算了细颗粒物浓度的粒径分布(PSD)变化,表明碳烟氧化是焦炭燃烧区颗粒浓度分布变化的主要因素,仅聚并作用无法生成PM_(0.1)以上颗粒。并通过预设碳烟份额得到与实验值吻合较好的焦炭燃烧区出口颗粒浓度分布曲线。     

循环流化床收集器内颗粒团聚流动特性的研究

基于气固两相流理论和气溶胶动力学原理,建立流化床收集器(CFBA)内气体细颗粒聚团气固两相双流体模型。对不同入口气体速度、初始颗粒尺寸分布和不同颗粒团聚形成机理下收集器内颗粒聚团流动的流体动力特性进行数值模拟。研究结果表明湍流运动和剪切作用对颗粒聚团的形成起主要作用,布朗运动对颗粒团聚形成的影响可忽略不计。吸收颗粒可有效提高捕获细颗粒和颗粒聚团形成的能力。     

堵塞和煤粉浓缩器对旋流两相流动影响的研究

旋流煤粉燃烧器加进口堵塞和煤粉浓缩器可以影响湍流,燃烧温度以及煤粉浓度的分布,从而影响NO的生成与排放。本文用三维相位多普勒颗粒测速仪(PDPA)测量和双流体模型数值模拟研究了堵塞和煤粉浓缩器对旋流煤粉燃烧器内两相流动的影响。实验结果和数值模拟结果基本符合。实验和模拟结果都表明,无论是进口堵塞还是煤粉浓缩器都会增加旋流燃烧器的进口湍流度,同时增加进口轴线附近的颗粒浓度,后者将有利于降低NO排放。     

Investigation of the influence of humidity on the ultrasonic agglomeration of submicron particles in diesel exhausts

Removing very fine particles in the 0.01-1 micro m range generated in diesel combustion is important for air pollution abatement because of the impact such particles have on the environment. By forming larger particles, acoustic agglomeration of submicron particles is presented as a promising process for enhancing the efficiency of the current filtration systems for particle removal. Nevertheless, some authors have pointed out that acoustic agglomeration is much more efficient for larger particles than for smaller particles. This paper studies the effect of humidity on the acoustic agglomeration of diesel exhausts particles in the nanometer size range at 21 kHz. For the agglomeration tests, the experimental facility basically consists of a pilot scale plant with a diesel engine, an ultrasonic agglomeration chamber a dilution system, a nozzle atomizer, and an aerosol sampling and measuring station. The effect of the ultrasonic treatment, generated by a linear array of four high-power stepped-plate transducers on fumes at flow rates of 900 Nm(3)/h, was a small reduction in the number concentration of particles at the outlet of the chamber. However, the presence of humidity raised the agglomeration rate by decreasing the number particle concentration by up to 56%. A numerical study of the agglomeration process as a linear combination of the orthokinetic and hydrodynamic agglomeration coefficients resulting from mutual radiation pressure also found that acoustic agglomeration was enhanced by humidity. Both results confirm the benefit of using high-power ultrasound together with humidity to enhance the agglomeration of particles much smaller than 1 micro m.     

Design and Experimental Characterization of Low‐Volume PM10/2.5/1.0 Trichotomous Sampler Inlet

This paper presents the development and laboratory evaluation of a PM10/2.5/1.0 trichotomous sampling inlet that consists of two main parts: a previously designed PM10 size‐selective inlet part and a PM2.5/1.0 two‐stage virtual impactor, which was newly fabricated and attached serially to the PM10 size selective inlet part. Particles are collected in three locations through the trichotomous sampling inlet to provide for not only particle concentration measurements of PM10, PM2.5 and PM1.0, but also those of PM2.5–10 and PM1.0–2.5.     

Numerical analysis of charged particle collection in wire-plate ESP

In this paper, the structure of single wire-plate unit in electrostatic precipitator (ESP) was optimized and dust removal process in an entire ESP was investigated using computational fluid dynamics (CFD). Collection efficiency is higher in the center of the ESP, but becomes lower near the edges. High applied voltage, low inlet velocity and large particle diameter are beneficial for dust collecting. As particle concentration increases, collection efficiency increases at the beginning, then decreases. When particle diameter is smaller, inlet velocity and particle concentration is higher, particle trajectories become less stable as turbulence is more severe.     

声波团聚净化尿素造粒塔尾气实验研究*

尿素造粒塔大多采用水洗工艺处理尾气粉尘,存在较为严重的细颗粒粉尘溢出和水汽拖尾问题,因此深入探究声波团聚技术在造粒塔尾气处理方面的应用。通过实验研究了声波与喷雾对除尘效率的影响,发现声波单独作用时在3500 Hz达到最佳除尘效率,为74.49%,协同喷雾时2600 Hz即可实现相近的除尘效率,为73.83%。进一步探究其中机理,采用以粒径测试为依据的团聚效率作为评价指标,结果显示,2600 Hz声波与喷雾单独作用时团聚效率分别为30.37%和28.82%,协同作用时团聚效率大幅提升至57.95%。该研究可为后续造粒塔工程改造提供理论与数据支持。     

基于显热回收的分离式热管传热特性的实验研究

针对新风空调机组,采用倾角为15°的分离式热管用于显热回收.研究充液率,迎面风速及空气进口温度对显热效率的影响,分析了其影响规律.研究表明,采用热管空调机组设计风速范围内,充液率介于66％～75％时,其换热效率最高.迎面风速较低时,空气进口温度介于34℃～36℃,其显热效率较高.因此,采用分离式热管机组适合用于高热地区...     

Experimental investigation of the flow inside a saxophone mouthpiece by particle image velocimetry

An experimental study of the flow inside a saxophone mouthpiece in playing conditions is carried out by means of particle image velocimetry at high acquisition rate. Planar velocity measurements on the midsection of a Plexiglas tenor saxophone mouthpiece are performed, respectively, in the mouthpiece baffle and in the reed channel. Sequences of velocity fields inside the mouthpiece baffle and around the reed tip are shown for one reed duty cycle. Maxima of the velocity fluctuations are observed at the upper surface of the mouthpiece at a distance between five and ten reed apertures from the tip. The proper orthogonal decomposition analysis reveals that almost 50% of the kinetic energy in the baffle is distributed in the first two modes displaying a periodic behavior at the fundamental frequency, the rest being turbulent flow behavior. The measured dynamical vena contracta coefficient at the inlet is reasonably constant around the value of 0.6 for reed positions far from closure. This is in agreement with existing steady flow analytical models and previous experimental results.     

Mixing in a model gas turbine combustor studied by panoramic optical techniques

Using planar optical methods based on laser-induced fluorescence and particle image velocimetry instantaneous velocity fields and passive tracer concentration are measured simultaneously in a model of GT-combustor at realistic flow rates. Spatial distributions of velocity pulsations and passive tracer concentration pulsations are measured at air flow rate about 0.4 kg/s. Correlations of velocity and concentration pulsations are measured. The most intense turbulent mass flux in the region of swirling flow mixing layer was observed. The contribution of advective and turbulent components in the transfer of a passive tracer in the axial direction was estimated.