燃煤飞灰物理化学特性及其润湿机理研究

以小龙潭电厂燃煤飞灰及其不同粒径范围的分级灰为对象,采用X射线荧光光谱、X射线衍射、离子色谱、Zeta电位、扫描电镜等实验方法研究了飞灰的物理化学特征.同时采用沉降实验、表面张力实验研究了三种不同润湿剂对飞灰的润湿性能.研究发现,溶液对飞灰的润湿能力不仅取决于其气液界面张力,还与飞灰的组成、表面电位以及形貌特征密切相关.亲水性物质含量的增加,颗粒表面电荷与润湿剂分子间的静电吸引,颗粒表面的棱角孔隙等均可以促进其润湿;温度越高飞灰润湿性能越好,且温度对飞灰润湿过程影响较大,温度较高(60℃)时润湿剂种类及浓度对飞灰润湿过程的影响不明显.     

水洗预处理对生物质燃烧积灰特性的影响

水洗预处理可有效脱除生物质中的积灰诱导元素钾。本文利用一维沉降炉和积灰采样器,对水洗前后小麦秸秆和玉米秸秆的积灰特性进行了实验研究,选取了四个积灰时间,考察了水洗对积灰质量、积灰率、积灰形貌与元素组成的影响。结果表明,水洗预处理使生物质积灰质量和积灰率大幅降低,凝结/热泳机制与化学反应机制被显著削弱,生物质积灰过程变为非黏性飞灰颗粒的物理堆积。     

决定AlGaInP高亮度发光二极管光提取效率的主要因素

影响发光二极管光提取效率的主要因素有:出光表面状态、上电极和体内吸收.对于AlGaInP高亮度发光二极管体内吸收主要是衬底和发光区的吸收.一般采用出光表面粗化、窗口层、DBR反射器等措施来提高光提取效率.本文以自发辐射随机分布模型为基础,以AlGaInP高亮度发光二极管典型结构的各种参数为依据,从理论上分析了这几种主要措施对光提取效率的影响.     

燃煤电厂脱硫废水介稳区影响因素的实验研究

燃煤电厂利用锅炉尾部烟气余热对脱硫废水进行喷雾蒸发处理技术应用前景广阔,但此技术存在烟道积灰等问题,研究脱硫废水介稳区的影响因素,对于评估该技术对烟道和除尘器等设备的影响十分关键。因此,本文采用激光法研究了脱硫废水的主要成分(MgCl_2-CaCl_2-NaCl复合盐溶液和单种盐溶液)在去离子水中的溶解度及超溶解度等热力学特性,以及金属离子、搅拌速率、pH值和飞灰对脱硫废水主要成分的介稳区的影响。研究发现金属离子的存在使脱硫废水介稳区变宽,是造成烟道积灰的主要因素,废水烟气混合紊流度、弱酸性环境和飞灰的存在将使脱硫废水介稳区变窄,促进废水晶体析出,可减少烟道积灰。     

超大拓展表面三维微肋管换热器的对流换热及抗积灰特性研究

工业烟气含尘的特点易导致换热器积灰,进而制约烟气余热的高效回收。本文针对一种具有超大拓展表面的三维微肋管换热器的对流换热与积灰特性进行了研究。首先,对比研究了光管与三维微肋管的对流换热特性;接着,基于所建立的积灰数值模型,探究了三维微肋管的积灰特性,并揭示了烟气流速与飞灰粒径对其积灰特性的影响规律。结果表明,相对于传统光管,三维微肋管的换热面积可增大约2.9倍;换热性能平均能提高16%;积灰后渐进污垢热阻最大能减小70%;同时,清灰周期更长,运行经济性更佳。综合而言,三维微肋管相比传统光管,在增强换热的同时,还能有效减轻积灰,因此可作为高效的抗积灰传热元件,应用于含尘烟气的余热回收场合。     

c—切MgO：LiNbO3质子交换平板波导中切伦科夫倍频的理论分析

从耦合模方程出发,推导了切伦科夫倍频转换效率公式,并得出该效率主要是由交叠积分决定的结论;通过对交叠积分的计算找到了进一步提高该效率的有效方法;最后用Nd:YAG激光器进行了切伦科夫倍频实验,得到了接近1%的转换效率,增加包层折射率可以使该效率增加到1.3%,实验结果证实了理论分析.     

多晶硅太阳电池激光掺杂选择性发射极

研究了多晶硅片扩散工艺与激光掺杂工艺的匹配性.采用波长532nm的纳秒脉冲激光器对扩散后未去磷硅玻璃的多晶硅片表面进行激光扫描掺杂,激光扫描掺杂后硅片方块电阻降低为扩散后硅片方阻的50%左右,而且随着激光功率的增加,扩散到硅片表面的磷原子浓度增大,硅片方阻下降更明显.测试了激光掺杂后多晶硅太阳能电池的外量子效率,其外量子效率在340~480nm波段范围与常规多晶硅太阳能电池相比提高18%~5%.研究了激光掺杂后多晶硅电池的光电转换特性,分析了较高激光功率掺杂时多晶硅电池的失效特性,结果表明:优化工艺后多晶硅太阳电池平均光电转换效率达到17.11%,比普通工艺多晶硅太阳电池提高0.34%,最高转换效率达到17.47%.激光掺杂选择性发射极工艺流程简单,电池效率提升明显,易于实现产业化.     

反射式GaN光电阴极表面势垒对量子效率衰减的影响

针对反射式GaN光电阴极长波段量子效率衰减较大, 短波段量子效率衰减较小的实验现象, 在考虑谷间散射的情况下, 利用玻尓兹曼分布和基于Airy函数的传递矩阵法, 计算了发射电子能量分布, 分析了表面势垒变化对量子效率衰减的影响, 理论与实验符合较好. 激活层有效偶极子数的减少使表面势垒宽度和高度增加, 引起长波光子激发产生的发射电子能量分布衰减较大, 短波光子激发产生的发射电子能量分布衰减较小, 这是量子效率在长波段衰减较大, 短波段衰减较小的根本原因.     

飞灰含碳量与微波功率衰减关系特性的实验研究

为了更精确地对锅炉飞灰含碳量进行在线监测,本文搭建了1.～4. GHz微波在线检测实验平台,研究了飞灰含碳质量与微波功率衰减的关系.实验发现:飞灰含碳质量与微波功率衰减关系有三种趋势;第一种是正比线性趋势,主要分布频段为1.～1. GHz和2.～2. GHz;第二种是波动趋势,主要分布在频段2.～4. GHz内;第三种是反比线性趋势,主要分布在频段1.～1. GHz内.文中从电导率损耗以及谐振吸收理论出发,对其形成机理做了详细的分析.     

表面活性剂含量对全息聚合物分散液晶光栅电光特性的影响

研究了含表面活性剂Actyflon-G04的全息聚合物分散液晶透射光栅的表面形貌和电光特性,通过理论分析得出驱动电压和膜的锚定能及表面自由能的关系.实验结果表明,在Actyflon-G04含量为4wt%-8wt%时光栅相分离程度高,相界面平滑,聚合物层的致密度增加.光栅的衍射效率达到96%,接近理想值.实现了在提高光栅衍射效率的同时降低驱动电压,使光栅的电光特性得到改善.     

The roles of added chlorine and sulfur on ash deposition mechanisms during solid fuel combustion

The focus of this paper is on effects of chlorine and sulfur on coal ash deposition rates, under practically relevant but systematically controlled combustion conditions. This problem is important, not so much for coal, but to understand and predict deposition rates for biomass combustion where chlorine contents can be high. To this end, ash deposition rates on a controlled temperature surface were measured for controlled amounts of chlorine and sulfur added to a pulverized coal, doped with potassium and burned in a 100 kW rated combustion rig. Previous work with 35 tests on 11 coal, biomass and petroleum coke fuels burned under a range of operating conditions had strongly suggested that the deposition rate of the tightly bound inside deposits was independent of the ash aerosol composition, and depended only on PM₁ in the flue gas. The loosely bound outside deposition rate was dependent primarily on the total alkali content in the flue gas. The new results using chlorine added to the fuel (in the form of ammonium chloride) required these previous conclusions to be drastically revised. They showed that chlorine, not alkali alone, had large effects on the deposition rate of the inside deposits, which now were orders of magnitude higher than without chlorine addition, and did not fit previous (multi-fuel) correlations with PM₁. Sulfur addition, together with chlorine, did not affect deposition rates much, although it did lower the chlorine content of the deposit. These results are interpreted in terms of the ash aerosol size segregated composition, which was also measured, and potential sulfation reactions within the deposit.     

The use of laser-induced plasma spectroscopy technique for the characterization of boiler tubes

The present work focuses on the characterization of boiler tube walls using laser-induced plasma spectroscopy technique with visual inspection by optical and scanning electron microscopy of the cross-sections of these tubes. In a watertube boiler, water runs through tubes that are surrounded by a heating source. As a result, the water is heated to very high temperatures, causing accumulation of deposits on the inside surfaces of the tubes. These deposits play an important role in the efficiency of the boiler tube because they produce a reduction of the boiler heat rate and an increase in the number of tube failures. The objectives are to determine the thickness and arrangement of deposits located on the highest heat area of the boiler and compare them with tube parts where the heat flux is lower. The major deposits found were copper and magnetite. These deposits come mainly from the boiler feedwater and from the reaction between iron and water, and they do not form on the tube walls at a uniform rate over time. Their amount depends on the areas where they are collected. A Nd:YAG laser operating at 355 nm has been used to perform laser-induced plasma spectra and depth profiles of the deposits.     

Ash formation and deposition during combustion of pulverized torrefied wood and coal in a 100 kW downflow combustor

Torrefied wood originating from beetle-killed trees is an abundant biomass fuel that can be co-fired with coal for power generation. In this work, pulverized torrefied wood, a bituminous coal (Sufco coal) and their blended fuel with a mixing ratio of 50/50 wt.%, are burned in a 100-kW rated laboratory combustor under similar conditions. Ash aerosols in the flue gas and ash deposits on a temperature-controlled surface are sampled during combustion of the three fuels. Results show that ash formation and deposition for wood combustion are notably different from those for coal combustion, revealing different mechanisms. Compared to the coal, the low-ash torrefied wood produces low concentrations of fly ash in the flue gas but significantly increased yields (per input ash) of ash that has been vaporized. All the mineral elements including the semi- or non-volatile metals in the wood are found to be more readily partitioned into the PM₁₀ ash than those in the coal. The inside layer deposits sticking to the surface and the loosely bound outside deposits exposed to the gas both show a linear growth in weight during torrefied wood test. Unlike coal combustion, in which the concentration of (vaporized) ash PM₁ controls the inside deposition rate, wood combustion shows that the formation of porous bulky deposits by the condensed residual ash dominates the inside deposition process. Co-firing removes these differences between the wood and coal, making the blended fuel to have more similar fly ash characteristics and ash deposition behavior to those of the bituminous coal. In addition, results also show some beneficial effects of co-firing coal with torrefied wood, including reduction of the total deposition rate and the minimization of corrosive alkali species produced by wood.     

煤灰沉积的传热过程模型及其数值研究

计算流体力学（ＣＦＤ）方法的应用在锅炉设计或燃烧设备的改造过程中有着十分重要的作用．本文研究了实际燃烧过程中普遍存在的煤灰沉积现象对数值计算结果的影响，提出了描述煤灰沉积的新型传热模型，比较了新模型采用前后数值计算结果与实测数据的差异，从而验证了该模型的合理性，提高了对炉内积灰、结渣过程数值描述的精度．     

An in-situ method for time-resolved sodium release behaviour during coal combustion and its application in industrial coal-fired boilers

To mitigate the slagging, fouling and high-temperature corrosion problems caused by alkali metals during coal combustion process, measurement of time-resolved alkali metals release is very important. The paper proposed an in-situ approach for measuring sodium (Na) release in coal combustion by Flame Emission Spectroscopy (FES). Through the analysis of spontaneous emission spectra and a calibration procedure, the concentration of gas phase Na, temperature and thermal radiation can be obtained. Firstly, experimental measurement of Zhundong coal particles burning in a flat flame burner was done. Two kinds of Zhundong coal with similar proximate and ultimate analyses, but different ash composition were used. The Na-release history measured by FES was compared with that by LIBS. Results showed that the Na-release at the devolatilization, char, and ash stages can be distinguished by FES. The higher Si/Al content in ash can suppress the Na-release at the ash stage. Moreover, FES method was extended to the measurement of Na-release in four industrial boiler furnaces of two Zhundong coal-fired power plants. Results showed the Na-release measured by FES can reflect the change of fuel and load, and both temperature and thermal radiation play key roles in Na-release in coal combustion.     

Biomass fly ash deposition in an entrained flow reactor

Fly ash deposition on boiler surfaces is a major operational problem encountered in biomass-fired boilers. Understanding deposit formation, and developing modelling tools, will allow improvements in boiler efficiency and availability. In this study, deposit formation of a model biomass ash species (K₂Si₄O₉) on steel tubes, was investigated in a lab-scale Entrained Flow Reactor. K₂Si₄O₉ was injected into the reactor, to form deposits on an air-cooled probe, simulating deposit formation on superheater tubes in boilers. The influence of flue gas temperature (589 – 968°C), probe surface temperature (300 – 550°C), flue gas velocity (0.7 – 3.5?m/s), fly ash flux (10,000 – 40,000?g/m²h), and probe residence time (up to 60?min) was investigated. The results revealed that increasing flue gas temperature and probe surface temperature increased the sticking probability of the fly ash particles, thereby increasing the rate of deposit formation. However, increasing flue gas velocity resulted in a decrease in the deposit formation rate, due to increased particle rebound. Furthermore, the deposit formation rate increased with probe residence time and fly ash flux. Inertial impaction was the primary mechanism of deposit formation, forming deposits only on the upstream side of the steel tube. A mechanistic model was developed for predicting deposit formation in the reactor. Deposit formation by thermophoresis and inertial impaction was incorporated into the model, and the sticking probability of the ash particles was estimated by accounting for energy dissipation due to particle deformation. The model reasonably predicted the influence of flue gas temperature and fly ash flux on the deposit formation rate.     

Momentum-resolved inverse photoemission

Inverse photoemission including isochromat spectroscopy is shown to be a versatile technique to probe empty electronic states in solids and at clean and adsorbate covered surfaces. The complete set of quantum numbers of an electronic state can be determined and examples will be discussed for bulk and surface electronic states. For sufficiently low kinetic energy of the primary electrons, inverse photoemission is shown to be applicable to adsorbates also. This allows one to assess directly the unoccupied electronic states of the adsorbate which play an important role in the formation of the surface chemical bond. Examples are discussed for atomic and molecular chemisorption as well as adsorption on alkali promoted surfaces.     

基于光偏振旋转效应的碱金属气室原子极化率测量方法及影响因素分析

利用原子自旋效应能够实现超高灵敏度的惯性和磁场测量。一类操控原子自旋处于无自旋交换弛豫态的器件可以进行物理参数测量。碱金属气室为该类器件的敏感表头。碱金属原子密度与原子极化率是碱金属气室的重要参数,对研究原子自旋处于无自旋交换弛豫态有着重要的作用。光的偏振效应在量子计算和原子物理研究中发挥了重要作用。利用光的偏振效应能够实现对碱金属原子密度与原子极化率的检测。提出一种基于光偏振旋转效应的碱金属原子极化率测量方法。首先对碱金属气室加恒定磁场,利用激光作为检测光,根据光偏振旋转原理,检测通过气室的偏振光的法拉第旋转角,得到碱金属气室原子密度。然后将碱金属原子抽运,利用激光作为检测光,检测通过气室的偏振光的偏转角,得到碱金属原子极化率。该方法在测量原子极化率的过程中也测量了碱金属原子密度,实现利用一套系统测量两个重要参数,具有快速测量和高灵敏度等特点,简化了实验设备及过程。对两种偏转角进行仿真分析,得到该方法实验时检测激光波长变化对偏转角的影响,根据仿真图得到检测激光波长的可取范围,验证了该方法的可行性。最后分析激光器波长波动与磁场波动对其测量精度的影响,提出实验对激光器与磁场的要求。     

Properties of biomass vs. coal fly ashes deposited in electrostatic precipitator

This paper presents comparative experimental studies of the morphology and elemental composition of fly ash particles from coal- and biomass-fired boilers, deposited in each stage of 3-stage electrostatic precipitators (ESPs). It was shown that fly ash morphology, its physical properties, and the percentage of elements in the fly ash taken from each stage of ESP depend on the kind of fuel. The biomass fly ash contains many irregular large particles, which are pieces of unburned wood. Bulk density of biomass fly ash is on average lower than that of coal fly ash, and drastically decreases in the second and third stages of ESP. The resistivity, measured at electric field of 4 kV/cm, of fly ash from biomass-fired boilers is much lower than that from coal, and can be below 10² Ω m, whereas from coal, except the first stage, varies in the range from 10⁷ to 10¹⁰ Ω m. The low resistivity of coal fly ash in the first stage of ESP results from high carbon content, and of biomass is probably an effect of additional high percentage of potassium, calcium and sodium sulfates. The percentage of Si, Al, Na, Fe, and Ti in fly ash from coal-fired boilers is much higher than from biomass, and in the opposite, the percentage of Mg, K, Ca, Mn, Mo, S, Cl, and P in biomass ash exceeds that in coal fly ash. Potential detrimental effects of biomass combustion products (salts, acids, tar) leaving the boiler on the construction elements of the electrostatic precipitator, including electrodes and HV insulators have been discussed in this paper. It was concluded that the long-term effects of biomass co-firing on the electrostatic precipitator performance, including the collection efficiency, have not been sufficiently studied in the literature and these issues require further detailed investigations.     

Experimental investigation of NOx emission and ash-related issues in ammonia/coal/biomass co-combustion in a 25-kW down-fired furnace

Co-firing ammonia in coal units is a promising approach for the phasedown of coal power. In this paper, we demonstrate the feasibility of burning ammonia with coal and biomass in a 25- kW down-fired furnace with a swirl-stabilized burner. Ammonia is injected from the central tube at thermal ratios ranging from 0 to30% and can be completely burnt out in most co-firing cases. We investigate the NO_x emission, unburnt carbon in fly ash, particulate matter formation and ash deposition behaviors when co-firing NH₃ with either SH lignite coal or the coal/biomass blend. With a fixed air staging ratio, the NO_x emission increases linearly with the NH₃ fuel ratio. By increasing the percentage of secondary air, the emitted NO_x can be reduced to 300 ppm with an NH₃ thermal ratio of 30%. The unburnt carbon is affected by NH₃ addition in a complex manner. With a 30% (thermal) NH₃ addition, the unburnt carbon increases from 0.4% to 5.6% for the SH coal mainly due to a temperature drop, but decreases from 2.2% to 0.7% for the SH coal/biomass blend. As for the ash-related issues, the addition of NH₃ to either coal or coal/biomass blend is found to alleviate both the fouling intensity and the ultrafine particulate matter formation ability. This is a major advantage over biomass combustion.