具有偏流块的弯管文丘里管组合浓淡燃烧器数值分析

研究了一种新型煤粉燃烧器,该燃烧器是由偏流块、弯管和文丘里管组合而成.通过数值计算的方法研究了这种特殊燃烧器的浓度分布特性,分析内部的气固两相流动特性,并通过改变偏流块角度和对比有无文丘流管的情况,研究偏流块角度和文丘里管对燃烧器出口浓淡分离效果的影响.采用RNG k-ε模型和Euler多相流模型研究气固两相流动.结果...     

水平浓淡煤粉燃烧器内气固两相流的数值模拟

为了揭示煤粉气流在带有弯管、方圆接头、可调浓淡煤粉分离装置及喷口前直管段内的运动轨迹及分离机理,将新型可调水平浓淡煤粉椭圆锥燃烧器喷口前弯管、方圆接头、可调浓淡煤粉分离装置及直管段作为整体,采用RNGK ε模型和随机轨道模型,通过颗粒与流体耦合的PISC算法,对管内气固两相流进行了数值模拟。模拟结果表明弯管是一种经济而有效的煤粉分离装置,可调浓淡煤粉分离装置可调节燃烧器向火侧和背火侧的煤粉浓度,为其进一步完善和广泛应用提供了理论依据。图4参9     

煤粉浓淡旋流燃烧器喷口气固两相流动的数值模拟

在实验基础上，运用PNG－ASM和FCFSRT模型对煤粉旋流浓淡燃烧器的气固两相流进行数值模拟，并与实验结果进行对比，得出了合理的颗粒速度场和浓度场；比较和计算了浓缩和未浓缩的颗粒场特性，说明了浓淡分离燃烧器的浓淡燃烧的机理；最后对浓淡分离燃烧器煤粉混合特性作了数值模拟，指出了煤粉浓淡混合的区域。     

新型旋流煤粉燃烧器出口区域气固两相流场的PDPA实验研究

针对电站锅炉燃用煤种多变和负荷多变的问题,提出了一种新型的旋流燃烧技术,即利用在一次风管中加装浓缩煤粉构件实行煤粉浓淡分离的旋流浓淡煤粉燃烧器。使用三维相位多普勒颗粒分析仪对旋流浓淡煤粉燃烧器和双调风旋流煤粉燃烧器出口区域气固两相流场进行了实验研究,得出了两种不同燃烧器几何结构下的气固两相流场和颗粒浓度场,并进行了理论分析。     

煤粉浓度连续可调型浓淡燃烧器及其气固两相流动特性

针对电站锅炉燃用煤种多变和负荷多变的问题，提出了一种新型的浓淡偏差燃烧技术，即利用组合叶片的导向作用对煤粉气流进行分离浓缩的煤粉浓度连续可调型浓淡燃烧器。应用激光粒子动态分析仪对这种燃烧器进行的两相流动特性测量表明，在一定的组合叶片角度范围内，可以实现煤粉浓度的连续调节，且由于叶片的扰动作用，气相和颗粒相的湍动都能有所提高，不同粒径颗粒的分布也发生了变化。     

煤粉水平浓淡燃烧器结构对两相流动特性影响的数值模拟研究

采用数值模拟方法,分析了四类挡板型燃烧器挡板大小、布置在浓淡一侧还是两侧、前端增加阻挡椎后以及第一个挡板与壁面间距大小对两相流的影响。A型燃烧器数值模拟出的气流浓淡比与实验数据一致,证明了数值模拟结果的可靠性。通过分析四类结构不同的燃烧器,研究了真实燃烧器的特性。研究表明:百叶窗型燃烧器内挡板的大小、位置和数量等对燃烧器浓淡分离效果影响较大。其中,第一个挡板与燃烧器内壁的距离影响最大,第一个挡板与燃烧器内壁距离逐渐增大,煤粉颗粒浓淡比就会逐渐降低;与小挡板相比,大挡板更有利于气相的浓淡分离;与挡板布置在一侧相比,挡板布置在浓淡两侧,减少了喷口的速度差异,有利于风粉保持速度刚性进入炉膛;在燃烧器前端加上阻挡锥后,气流速度比增加不明显,但是煤粉浓淡比增加很大,有利于燃烧器的浓淡分离。     

竖直上升转水平圆形弯管气固两相流动数值模拟

对竖直上升转水平圆形弯管内煤粉空气两相流场和浓度场进行数值模拟表明 ,弯管外侧壁脊线附近煤粉浓度明显比内侧高 ,验证了弯管的浓淡分离原理 ,为进一步实施提高浓淡分离效果的各种改造措施提供了理论依据。     

偏流块对直流反浓淡燃烧器出口煤粉分布的影响及阻力分析

数值模拟了一种偏流块与弯管组合结构的煤粉燃烧器,其偏流块的位置异于浓淡型燃烧器,可以实现出口浓度分布均匀.改变偏流块的角度和位置,研究偏流块角度和位置变化对反浓淡效果的影响以及阻力变化.采用Euler - Lagrange方法研究气固两相流动,气相湍流采用RNGk-ε湍流模型模拟方法,固相湍流采用离散随机游动(DRW)...     

低NOx煤粉燃烧器的试验研究

对低NOx燃烧器从试验和数值模拟两个方面进行了研究,结果表明低NOx燃烧器浓淡两侧的速度比与管道气体速度和分隔板开缝与否均无关,大小为1.14～1.30,速度差为2.37 m/s(管道气体速度U=18 m/s时)～7.90 m/s(管道气体速度U=28 m/s时);低NOx燃烧器分隔板开缝时,相对不开缝结构阻力增加1.3%(180°扭曲分隔板)～10%(平直分隔板);低NOx燃烧器分隔板前布置阻挡锥时,阻力再增加10.1%(180°扭曲分隔板)～12.1%(平直分隔板);低NOx燃烧器浓淡两侧的固气比与分隔板有无开缝无关,浓侧煤粉射流的固气比随气流速度增大而增大,淡侧射流的固气比随气流速度的增大而减小,浓淡两侧的固气比随管道煤粉固气比的增大而增大.常规直流煤粉燃烧器加装不开缝的平直分隔板时,阻力增加17.7%,加装不开缝的180°扭曲分隔板时,阻力增加71.6%.低NOx燃烧器的分隔板开缝时,浓淡两侧的静压平衡,浓淡两侧的湍动能都增加,浓侧湍动能增加大约20%.     

一种新型旋流燃烧器的工作特性研究

提出了一种具有新型结构的浓淡式旋流燃烧器,其出口射流由浓淡一次风、内外二次风组成,喷口为特制结构.采用热线风速仪对燃烧器模型出口空气动力场参数进行了测试,同时以颗粒捕集法为手段对一次风粉混合物在经过燃烧器后的气固分离效果进行了试验研究.结果表明：新型燃烧器具有优越且稳定的空气动力场,能够强化回流,提高轴线附近湍动度水平,有利于改善着火条件,抑制NOx污染物的形成;煤粉浓缩装置对实现浓淡分离的作用显著,燃烧器出口浓淡比可达4∶1以上.     

撞击式浓淡气固两相射流的扩散特性

阐述了利用光学波动法测量颗粒浓度的原理.在实验条件下,测量了水平浓淡撞击式燃烧器出口不同距离截面的气固两相射流颗粒浓度分布,得到了各截面固相浓度分布、扩散和衰减规律,其结果可为分析电站锅炉燃烧稳定性、节能及燃烧器改造提供参考.图10,参9     

220MW煤粉炉PM2.5浓度排放特性的试验研究

本文采用荷电低压撞击器(ELPI),通过对二级稀释系统采样对某电厂220 MW煤粉锅炉PM2.5的浓度排放特性进行了研究。研究结果显示,煤粉锅炉所产生烟气中PM2.5粒数浓度呈较明显的双峰分布,小颗粒峰值一般在0.12μm或0.07μm,较大颗粒峰值一般在0.76μm,PM2.5粒数浓度一般为几百万粒/cm3,主要取决于由气化凝结机理形成的细模态颗粒物PM0.38,PM2.5质量浓度呈单峰分布,一般为几百mg/m3,其质量浓度主要取决于由中间模态颗粒物PM0.38~2.5;采用覆膜滤料的布袋除尘器和电袋联合除尘器对PM2.5具有较好的除尘效果,二电场电袋复合除尘器出口烟气中PM2.5最小可达200μg/m3,粒数浓度在几万粒/cm3;当除尘效果较好时,湿法脱硫装置出口烟气中PM2.5粒数浓度和质量浓度可能会有所增加。     

Combustion of particles in a large pulverized brown coal flame

A model of the ignition of a polydisperse cloud of brown coal particles, in a known gas environment, is presented and used to predict the behavior of the particles in a burner jet of a utility boiler. The model allows for drying, devolatilization, and char combustion of the particles. It is assumed that the volatiles burn in the free stream so that char combustion can occur during volatiles evolution, the diffusion of oxygen to the particle surface being inhibited due to the net outflow of volatiles. The model is used to calculate the behavior of a cloud of p.f. size particles along the centerline of a brown coal burner jet in which the gas temperature and composition have been measured. Rates of volatile release and char combustion are calculated and shown to be in agreement with measurements of volatile material in the flame. It is found that particles smaller than about 80 μm contribute most to the ignition of the jet and that they closely follow the local gas temperature. The unique character of brown coal of combustion, its high volatile evolution on rapid heating, the high activity of its char at low temperature, and the demonstrated ignition of its char without a jump in temperature make the overlap of devolatilization and char combustion more likely than with other coals. The mathematical formulation that allows this overlap gives oxygen consumption levels consistent with measurement. An analysis is made of the relative importance of radiation from the flame front to the particle, and entrainment of hot combustion gases into the jet. It is found that the radiation is of secondary importance compared to the effect of entrainment which is the controlling mechanism in the initial heating of the particles. Also, the significance of the assumption that the volatiles burn in the free stream is discussed.     

Ignition of wood and coal particle mixtures in conditions of steam and water boiler furnaces

The results of experimental studies of the ignition processes of a large set of particles (from 100 to 500) of wood-coal composite fuels under conditions of high-temperature radiation-convective heating are presented. The ignition of wood-coal fuel mixture fuel particles was studied under the conditions of their free fall along the quill ceramic cylinder passage in a high-temperature oxidizing medium (air). Such a configuration provides the conditions that most closely match the heating conditions of actual furnaces of heat generating installations.The experiments have been carried out on the mixtures of particles of subbituminous coal (that is quite typical of coal-fired power industry) with the particles of woody biomass of three types: birch, pine and larch, which are widely spread in the territory of many states of the northern part of the Earth hemisphere. The recording of the heating and ignition processes of the fuel mixture particles was carried out with a high-speed Photron FASTCAM CA45 (500 fps) camera. The air temperature in the passage along which the particles moved varied in experiments from 873 K to 1273 K. The purpose of the experiments performed was the ignition delay time (t_ign). The main variable factors are the ambient temperature and the concentration of woody components. The consistent errors in determining the main characteristics of the process did not exceed 5%, the random ones did not exceed 13%. The size of coal particles in the experiments did not exceed 60 μm, and of the wood - 5 mm.It has been established that in such a fuel system one of the fuel components of the coal particle is “conducting” (or leading), and the second is “conducted” in the reaction of the thermochemical response of the fuel mixture with air oxygen. According to the results of experimental studies, the ignition delay times for the wood-coal particle mixtures have been stated. The increase in the concentration of small-sized coal particles in fuel mixtures from 0% to 100% leads to the decrease in the entire induction period (up to 20%) at the relatively cold temperatures.It was also found that with typical sizes of coal particles up to 60 μm, stable ignition of sufficiently large wood particles (up to 5 mm), present in the mixture, is provided. The conditions and characteristics of ignition of wood-coal mixtures hardly depend on the type of wood, which is the second component of the mixture.According to the results of the research conducted and following the requirements for optimizing the processes of fuel combustion, the use of mixed coal- and wood-based fuels in boilers of large and small power plants is justified.     

NOx reduction and NO2 emission characteristics in rich-lean combustion of hydrogen

Hydrogen is a clean alternative to conventional hydrocarbon fuels, but it is very important to reduce the nitrogen oxides (NO_x) emissions generated by hydrogen combustion. The rich-lean combustion or staged combustion is known to reduce NO_x emissions from continuous combustion burners such as gas turbines and boilers, and NO_x reduction effects have been demonstrated for hydrocarbon fuels. The authors applied rich-lean combustion to a hydrogen gas turbine and showed its NO_x reduction effect in previous research. The present study focused on experimental measurements of NO and NO₂ emissions from a coaxial rich-lean burner fueled with hydrogen. The results were compared with diffusion combustion and methane rich-lean combustion. Significant reductions in NO and NO₂ were achieved with rich-lean combustion. The NO and NO₂ reduction effects by rich-lean combustion relative to conventional diffusion combustion were higher with hydrogen than with methane.     

Evolution of soot size distribution in premixed ethylene/air and ethylene/benzene/air flames: Experimental and modeling study

The effect of benzene concentration in the initial fuel on the evolution of soot size distribution in ethylene/air and ethylene/benzene/air flat flames was characterized by experimental measurements and model predictions of size and number concentration within the flames. Experimentally, a scanning mobility particle sizer was used to allow spatially resolved and online measurements of particle concentration and sizes in the nanometer-size range. The model couples a detailed kinetic scheme with a discrete-sectional approach to follow the transition from gas-phase to nascent particles and their coagulation to larger soot particles. The evolution of soot size distribution (experimental and modeled) in pure ethylene and ethylene flames doped with benzene showed a typical nucleation-sized (since particles do not actually nucleate in the classical sense particle inception is often used in place of nucleation) mode close to the burner surface, and a bimodal behavior at greater height above burner (HAB). However, major features were distinguished between the data sets. The growth of nucleation and agglomeration-sized particles was faster for ethylene/benzene/air flames, evidenced by the earlier presence of bimodality in these flames. The most significant changes in size distribution were attributed to an increase in benzene concentration in the initial fuel. However, these changes were more evident for high temperature flames. In agreement with the experimental data, the model also predicted the decrease of nucleation-sized particles in the postflame region for ethylene flames doped with benzene. This behavior was associated with the decrease of soot precursors after the main oxidation zone of the flames.     

鳍片分离式浓淡燃烧器的开发与应用

适当提高煤粉浓度,可改善燃烧稳定性。在试验研究的基础上,开发了一种通用,低阻、高效的鳍片式浓淡燃烧器,将煤粉浓度浓缩到着火距离的最佳值,提高了低负荷稳燃烧性能。     

Mechanism analysis on the pulverized coal combustion flame stability and NOx emission in a swirl burner with deep air staging

Low NOx burner and air staged combustion are widely applied to control NOx emission in coal-fired power plants. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of a single low NOx swirl burner in an existing coal-fired boiler was numerically simulated to analyze the mechanisms of flame stability and in-flame NOx reduction. And the detailed NOx formation and reduction model under fuel rich conditions was employed to optimize NOx emissions for the low NOx burner with air staged combustion of different burner stoichiometric ratios. The results show that the specially-designed swirl burner structures including the pulverized coal concentrator, flame stabilizing ring and baffle plate create an ignition region of high gas temperature, proper oxygen concentration and high pulverized coal concentration near the annular recirculation zone at the burner outlet for flame stability. At the same time, the annular recirculation zone is generated between the primary and secondary air jets to promote the rapid ignition and combustion of pulverized coal particles to consume oxygen, and then a reducing region is formed as fuel-rich environment to contribute to in-flame NO_X reduction. Moreover, the NOx concentration at the outlet of the combustion chamber is greatly reduced when the deep air staged combustion with the burner stoichiometric ratio of 0.75 is adopted, and the CO concentration at the outlet of the combustion chamber can be maintained simultaneously at a low level through the over-fired air injection of high velocity to enhance the mixing of the fresh air with the flue gas, which can provide the optimal solution for lower NOx emission in the existing coal-fired boilers.     

一种旋风燃烧器内煤颗粒燃烧及沉积特性的研究

采用数值模拟与试验相结合的方法研究了某旋风燃烧器内煤颗粒的燃烧及沉积特性．结果表明：该燃烧器在不同负荷下均能实现高温燃烧（1700K以上）,并获得较高的燃烧效率及捕渣率．煤颗粒主要在燃烧器前部沉积,且上下壁面的分布几乎一致;较小的煤颗粒跟随性好,不易沉积,60μm以上的煤颗粒几乎能在燃烧器中前部全部沉积下来并附壁燃烧;较小的过量空气系数及适中的一次风率（O．3～0．35左右）能保证煤颗粒在燃烧器内壁面上沉积分布较均匀,不至于造成低温区域燃烧通道煤粉堵塞．