脉动流化床传热特性

在讨论脉动燃烧对传热特性影响的基础上,基于脉动流化燃烧概念,试验研究了脉动流化床中的传热特性,得到不同空截面风速、静止床层高度和声波扰动下的传热系数,并与同一运行参数条件下非脉动流化床及纯气流脉动燃烧器中的传热特性进行对比．总结影响脉动流化床传热特性的各种因素,分析不同运行参数对传热的影响作用．     

自激式脉动流化床流化脉动特性的试验研究

试验研究了基于Rijke管的自激式脉动燃烧流化床的流化脉动特性。是否激起以基波为主的压力、声音等脉动信号是脉动的判断依据，因此试验主要研究了脉动的基波特性。脉动的压力值是激起的各次谐波声压和炉膛的原有压力的叠加，通过傅立叶转变对压力进行了频谱分析。实验还研究了不同床层高度和流化风速对脉动特性的影响，并定性分析了优化流化脉动，减少声损失的途径。     

高温气固流化床的流化特性

气固流化床中的压力脉动信号是研究流化床内流体动力特性的一个重要途径，本文在２０℃～６４０℃的温度范围内，测试了３种颗粒在不同流化速度下气固流化床中的瞬态压力脉动信号，通过分析压力脉动进一步研究了温度对床内流化特性的影响。研究结果表明：高温下气固流化床内的流化特性与常温下有显著的差异，随温度的升高，床内的流化质量有所改善；对于同一种颗粒，不能将常温下所得到的流化特性推广到高温的条件下。     

脉动流化床的机理及燃烧试验研究

本文报道了一种新型的流态化燃烧方式—脉动鼓风流化床燃烧的研究成果。研究表明,脉动流化床具有床内传热过程强烈。可燃物扬析量少,燃烧效率高等优点,且工艺     

脉动流动强化传热的研究进展

介绍了脉动流动强化传热的机理、方法,分析了脉动频率、脉动振幅、雷诺数、管径、脉动型式、流体物理性质对传热特性的影响,概括了脉动流动强化传热的国内外研究现状,并提出了进一步研究的建议.     

甲烷自激励脉动燃烧NOx排放特性的试验研究

采用Rijke型自激式脉动燃烧器,结合纹影摄像,对不同脉动频率、脉动振幅和燃烧功率下的NOx排放量进行了比较和机理分析.结果表明:在试验工况范围内,甲烷自激励脉动燃烧与非脉动燃烧相比可降低NOx的生成,NOx最高降低了99%,对应的CO降低了13.8%;当燃烧功率增大时,会出现燃烧不完全和燃烧效率降低的现象;脉动火焰符合分形特征,其分形维数大于非脉动燃烧,火焰内流场褶皱、卷曲的程度更高;脉动燃烧下NOx降低的原因是掺混程度更好、传热率更高;随着脉动频率的增加,NOx的排放量降低,说明频率增加促进了气体掺混,减少了气体在高温区的停留时间;脉动燃烧下NOx的排放随燃烧功率的增大而升高.     

脉动热管流型的电容层析成像识别及热管换热特性

结合高速摄像和电容层析成像技术,对脉动热管进行了可视化测量研究.从流型和流向两方面分析了脉动热管的运行机理和传热特性.根据受力分析对脉动热管的结构进行了改进.结果表明:脉动热管存在3种不同流型,即塞状流、环状流以及两者共存的混合流,其对应的影响因素、运行特性与传热强度也不同;从流动方向来看,脉动热管内工质的流动可分为脉动流和循环流;对脉动热管的改进说明改变脉动热管流道的对称性和均衡性有利于循环流的形成和维持.     

下冷式脉动热管太阳能集热器传热性能实验研究

实验研究和分析了一种新型下冷式脉动热管太阳能集热器的传热特性。与传统太阳能集热器相比,下冷式脉动热管太阳能集热器水箱位于底部,真空玻璃管不盛水并嵌于水箱上,脉动热管作为传热元件,一部分置于真空玻璃管内,另一部分封于水箱中。实验过程中通过调整脉动热管冷热段间的比例,研究不同情况下集热器启动、运行特性及传热性能。结果表明,在集热器倾角为70°、脉动热管充液率为55%的情况下,脉动热管的当量导热系数随冷热段比例的减小而先升后降;当冷热段比例为47%时,脉动热管的启动温度最低、传热性能最优。     

循环流化床锅炉燃烧控制与调整

从分析循环流化床锅炉的燃烧和传热机理入手，结合循环流化床锅炉的结构特点，论述了常规情况下与循环流化床锅炉燃烧有关的工况控制和调整问题。     

柴油_渣油和沥青的脉动燃烧对比试验研究

在一变形的里克（Rijke)管中进行了柴油、渣油和沥青的脉动燃烧对比试验。试验发现容易燃烧的 燃料容易激起脉动,难燃燃料由于着火推迟,较难激起脉动,而必须加长尾管长度才能解决问题。当进风面积与燃烧腔截面积之比减小到一定程度时,对于渣油等难燃燃料,其脉动特性会向1／4波长管的脉动特性过渡;而对于柴油等易燃燃料,脉动特性不变。 试验表明,这种无阀脉动燃烧技术可使渣油、沥青等难燃物高效清洁地燃烧,这对于渣油等难燃燃料的利用有重要意义。     

燃烧高水分低热值燃料的内旋流流化床燃烧技术研究

内旋流型流化床炉利用非均匀布风产生高温气－固两相旋流，使燃料在炉内运动、相互碰撞、干燥、破碎、燃烧，并可通过改变布风控制燃料加热与挥发份析出速率、燃烧温度与热负荷，适合多种高水分劣质煤及城市垃圾的洁净燃烧，是一种高效低污染流化床燃烧技术。本文研究该型燃烧器床内空气运动、燃烧、传热及排放规律，发展新型清洁燃烧技术。     

两相流动对流化床燃烧行为的影响

循环床锅炉沿床高的烟气浓度及燃烧份额分布测试结果证明,鼓泡流化床和循环流化床的重要差异表现为密相区燃烧行为的根本不同,由于床料平均粒径较低,循环床密相区的流动不同于鼓泡床,导致气固两相之间的传质阻力增加,从而影响燃烧反应,密相区的燃烧行为表现为欠氧。循环床锅炉沿床高乃至分离器都有燃烧反应发生,建立了考虑气固相间传质阻力的流化床密相区燃烧模型,并与实际循环流化床锅炉的测试数据比较,计算结果与测试值比较吻合。     

A method of determining thermal parameters of granular coal particles during devolatilization

Fluidized bed combustion offers great potential for the utilization of high-sulphur coal and low-grade coal in an environmentally acceptable manner. Utilization of fluidized bed technology, especially for the combustion of low quality lignites, enables pollutant emission control as well as efficient combustion. The most important stage during the combustion of coal particles is devolatilization, in which various factors such as heat transfer from the surroundings to the particle surface, heat conduction within the particle, the chemicals involved, the kinetics and the transport of volatile compounds within the particle play significant roles. The heat transfer coefficient, thermal diffusivity, thermal conductivity, heating coefficient and lag factor are the most significant thermal parameters in this process. In this study, a 1-D transient heat transfer analysis is carried out for a granular coal particle during devolatilization in a fluidized bed. The particle is idealized as a spherical solid body. Models are developed to determine the thermal parameters of such particles, and are verified using experimental centre temperatures of a 10 mm granular coal particle subjected to devolatilization at a medium temperature of 960 K. The data are taken from the literature. The results show that the thermal parameters determined here are in good agreement with experimental findings.     

燃煤机组耦合固废焚烧关键技术研究进展

[目的]燃煤与固体废弃物混合掺烧不仅可以实现固废的能量回收利用,也是实现燃煤发电的碳减排的路径之一。[方法]文章综述讨论了燃煤电站掺混固废的研究工作,主要介绍了基于目前主流的电站锅炉为反应器开展燃煤与不同固废掺混的燃烧应用与技术发展;从燃料经济性、混合燃料的飞灰特征、污染物排放以及碳税角度评价燃煤掺混固废的燃烧技术发展;最后讨论了直接掺混和间接掺混的技术的特点。[结果]燃煤直接掺混固废燃烧时需要尽可能减少对锅炉运行的影响,特别是气体污染物的排放以及飞灰对换热面的影响和飞灰无害化处置。间接掺混可以避免混合燃料燃烧对炉膛的影响,但是需要较高的硬件成本投资且耦合技术较为复杂。富氧燃烧技术依旧需要对现有锅炉结构优化来提高该技术的适用性。[结论]直接掺混可实现性与成本优于间接掺混,且循环流化床燃料适应广的特点有利于燃煤直接掺混固废燃烧技术的应用,随着基于循环流化床的富氧燃烧技术的发展将更有利于实现火电厂的碳减排。     

Heat recovery from hot solid particles in a shallow fluidized bed

A heat exchanger with a shallow gas–solid fluidized bed was experimentally studied in order to analyze energy recovery from solid particles leaving a combustion process. The experiments were carried out with and without vertical baffles in a fluidized bed with immersed horizontal tubes filled with water, in a counter flow arrangement. Two particle diameters (254 and 385 μm), two solid flow rates (50 and 80 kg/h) and two gas flow rates (46 and 50 kg/h) were tested. The bed temperature along the equipment length, the mass flow rate and the inlet and outlet temperatures of solid particles, air and water were measured in order to obtain the bed-tube heat transfer coefficient and the heat exchanger effectiveness. An increment of about 55% in the heat transfer coefficient and higher values of the heat exchanger effectiveness, in experiments with the presence of baffles, was verified. The experimental results also showed that the suspension-wall heat transfer coefficient increased considerably with the solid flow rate and also when the particle diameter decreased.     

Numerical study of different gas–solid flow regimes effects on hydrodynamics and heat transfer performance of a fluidized bed reactor

In this study, a two‐?uid Eulerian–Eulerian model has been carried out applying the kinetic theory of granular flow (KTGF) to study the hydrodynamics and heat transfer behavior of a fluidized bed reactor simultaneously. The effects of different gas–solid flow regimes on the operating conditions and heat transfer rate between the hot air and two types of low and high‐density inert particles are investigated in a fluidized bed dryer. Different gas–solid flow regimes for wood and glass particles of groups A, B, and D of Geldart's classification are simulated to introduce the most optimal flow regime in terms of heat transfer rate and operating costs. The compromise between the heating rate, the height required for the reactor, and the ratio of the final mass to the initial mass of solid particles, which specifies the need for a cyclone separator showed that the bubbling regime of Geldart B powder for low‐density particles and the turbulent regime of Geldart D powder or bubbling regime of Geldart B powder for high‐density particles are the optimal operating conditions and flow regimes. Furthermore, it was concluded that the convective heat transfer is the dominant mechanism, which increases with increasing the air velocity and decreasing the particle diameter in each group.     

620t·h-1循环流化床锅炉提效 及低NOx改造的实践

针对国产620 t·h-1循环流化床锅炉效率及NOx排放浓度不能达到性能保证值的现状,分析了锅炉的热损失情况以及NOx排放浓度与平均床温等参数间的规律,得出排烟热损失及固体未完全燃烧热损失过大、平均床温偏高、因风帽磨损引起的流化质量下降是造成锅炉效率及NOx排放浓度超性能保证值的主要原因.在此基础上提出了提高空预器吸热量、降低床温、提高流化质量的改造思路,对改造思路逐项分析,得出了回转式空预器改造、加长水冷屏和屏式过热器以及风帽改型等具体改造措施.对改造后参数作了分析,并提出改造完成后可能出现的热风管磨损及浓相区上移等问题.通过改造实现了锅炉提效和减排的目标.     

Combustion Model For Staged Circulating Fluidized Bed Boiler

INTRODUCTIONNumericalsimulationofcirculatingfluidizedbedcombustion(CFBC)isoneoftheimportantmeth-odsforthe0ptimizationofdesignandoperationandtheperformancepredictionofcirculatingfluidizedbedboiler.Researcheffortshavemademuchpr0gressinmodellingCFBfluiddynamics,heattransferandcom-bustioninthepastdecades.Duet0thecomplexity0fgassolidsfiowbehavi0rsinCFBcombustor,mostofthemodelsaresteadyone-dimensi0nal.Weissetal.(1987)[']devel0pedaCFBCcellmodel.ItdividestheCFBsystemintoaseriesofblockseach…     

循环流化床锅炉设计中若干问题探讨

循环流化床燃烧技术是一种新型、高效、清洁的燃烧技术,有许多其它燃烧装置无法比拟的优势。但在循环流化床锅炉设计方面还有一些问题亟待解决,文章就循环流化床锅炉设计方面的一些问题,如气固两相流体动力特性对其设计的影响;一、二次风比例,燃烧份额对其设计的影响;炉内传热系数对其设计的影响等方面作了一些阐述。