大型CFB锅炉天然气点火系统应用问题研究

针对大型循环流化床(CFB)锅炉应用天然气点火系统存在燃烧不稳定火焰脱火的问题,以某电厂350 MW超临界循环流化床机组天然气点火系统为研究对象,探讨了天然气层流扩散和紊流扩散燃烧的机理,从燃烧学理论出发研究了天然气火焰脱火的主要原因是燃烧器喷口燃气流速与火焰传播速度不匹配。基于一元定常可压缩气体流动的基本特性,将天然气燃烧器气枪喷口简化为一元流体的喷管,计算出CFB锅炉天然气点火系统燃烧器出口的最大流速,以此为基础提出天然气系统燃气压力的调整措施和燃烧器喷口结构的优化方案。通过理论分析计算和设备的结构优化,解决了大型CFB锅炉天然气点火系统燃烧器火焰脱火的问题,可为同类型的机组提供借鉴的依据。     

1000 MW旋流对冲燃烧锅炉NOx排放特性试验研究

为了解采用OPCC旋流燃烧器、2层燃尽风布置的某1 000 MW超超临界前后墙对冲燃烧锅炉的NO_x排放特性,采用现场试验的方法对该锅炉进行了系统研究,得到燃烧器投运方式、炉膛氧体积分数、燃尽风挡板开度、燃烧器外二次风叶片角度、燃烧器内二次风挡板开度、燃烧器中心风挡板开度和燃尽风喷口外二次风刻度位置、燃烧器负荷分配方式、机组负荷及煤种等因素对NO_x质量浓度的影响。结果表明:燃烧器投运方式、炉膛氧体积分数及煤种对NO_x质量浓度的影响较大,影响幅度可达13%～20.2%;燃尽风挡板开度、燃烧器内二次风挡板开度、燃烧器负荷分配方式和机组负荷对NO_x质量浓度的影响较小,影响幅度为4%～6%;燃烧器外二次风叶片角度、燃尽风喷口外二次风刻度位置和燃烧器中心风挡板开度对NO_x质量浓度的影响微弱。     

600MW超临界褐煤直流锅炉新型燃烧技术应用研究

HG-1913/25.4-HMN型600MW超临界褐煤直流锅炉采用了墙式布置切圆燃烧方式、水平浓淡燃烧器和过热器拉开布置等新型燃烧技术。对于运行中存在的烟气偏差较大和易结焦的问题,可通过燃烧调整加以解决。即通过SOFA喷口水平摆动,实现SOFA区域的烟气和燃烧器区域的烟气旋转方向相反,来克服切圆燃烧偏差较大的问题,通过周界风、SOFA总风量等的调整,尽量降低一次风率,提高二次风率来防止锅炉结焦,从而保证锅炉的稳定运行。     

1000MW机组锅炉氮氧化物排放影响的试验研究

基于现场燃烧调整试验方法,对某厂1台1000MW超超临界切圆燃烧锅炉NOx的排放特性及其影响因素进行了系统的分析。针对锅炉燃烧系统的运行特点,主要进行了氧量、负荷、燃尽风量(包括AA风和OFA风)、主燃烧区燃烧器风量和配风方式、磨煤机运行组合方式、燃烧器摆角、煤质等因素的试验研究。研究结果表明:对于具有先进低NOx燃烧系统的锅炉,其锅炉负荷、锅炉燃用的煤质、运行时氧量的变化和燃烧器喷口摆角及磨煤耗机组的运行方式都是锅炉NOx排放的影响因素,其中运行时氧量的变化对NOx排放影响最重,随着氧量的增加,锅炉NOx排放浓度呈线性增加。而在保持大量燃尽风实现空气分级燃烧的条件下,主燃烧区燃烧器风量和配风方式对NOx排放浓度的影响是微弱的。     

300MW四角切圆燃烧锅炉低氮燃烧优化改造研究

针对某一电厂300MW四角切圆燃烧锅炉NO_x排放浓度高的问题,对锅炉制粉系统、燃烧系统进行了改造。将锅炉制粉系统由原来的钢球磨热风送粉系统改为乏气送粉系统,主燃烧器相应改造,同时在主燃烧器上方增加一段分离燃尽风燃烧器。改造后,锅炉NO_x排放浓度有较大幅度下降,效率也未有明显降低。     

一种用于携带流反应器试验台的煤粉燃烧器的优化设计

为了优化一种用于携带流反应器系统的煤粉燃烧器结构参数,降低氮氧化物排放,本文利用计算流体动力学软件FLUENT对该煤粉燃烧器结构参数的优化过程进行了数值模拟研究,并与试验结果进行了对比验证。结果表明,燃烧器一次风喷口采用扩口结构以及对冲二次风的引入均能有效的促进二次风与一次风煤粉的混合,增强煤粉着火及燃烧的稳定性。适当增加二次风喷口与一次风喷口的间距可以加速煤粉的燃尽。采用优化后的结构参数可以获得更低的氮氧化物排放,为基于携带流反应器系统的燃煤污染物减排研究提供了坚实的基础。     

350 MW超临界墙式切圆锅炉低负荷燃烧系统优化

针对国内某电厂配置墙式切圆燃烧系统锅炉在低负荷情况下水冷壁壁温偏差大、局部水冷壁超温的现象,通过数值模拟对其产生的原因进行分析,发现锅炉一次风切圆偏大是导致其发生的主要原因;对此,分析对比了增设喷口导流片和燃烧器整体偏置一定角度2种缩小燃烧切圆的方案,结果表明:通过燃烧器整体偏置一定角度的方案切实可行,且效果理想,最终通过数值模拟对燃烧器偏置一定角度的方案进行计算,对比优化前后炉内假想切圆温度场、流场分布情况,验证了该方案的合理性。     

复合空气分级低氮燃烧器二次风门开度对煤粉燃烧的影响

某660 MW机组锅炉配备上海锅炉厂有限公司复合空气分级低氮燃烧器。通过对该燃烧器二次风门挡板开度的试验,得出以下结论:一次风喷口的偏置风对煤粉着火有负面影响,而其上面的辅助风能有效促进煤粉着火燃烧;周界风风量应随煤质煤量成正比例变化,否则会延迟煤粉着火;一次风喷口下层的辅助风对煤粉燃烧作用不明显。     

基于对冲旋流锅炉安全运行的冷态试验研究

为满足新型超超临界对冲旋流燃烧锅炉首次大修后启动要求,同时针对锅炉最上层燃烧器烧损问题,开展了基于锅炉运行安全的冷态优化试验研究,主要包括一次风调平、磨煤机冷态通风阻力测试,以及炉内贴壁风、燃烧器冷却风、内外二次风冷态优化和燃烧器飘带试验。试验结果表明：该类对冲旋流燃烧锅炉仅通过调节较少一次粉管可调缩孔,就能满足一次风风速调平要求;锅炉CF层左右侧贴壁风挡板具有良好的调节特性,但在不同挡板开度下水冷壁贴壁风风速整体偏小;CF燃烧器冷却风随着风门挡板开度增大,风速增长缓慢;F6燃烧器飘带试验显示飘带易卷吸至燃烧器喷口。建议锅炉运行中增加各层贴壁风、燃烧器冷却风及外二次风挡板开度,以预防水冷壁高温腐蚀、冷却风量不足及外二次风旋流强度过大等问题,提高锅炉设备运行安全性。     

125 MW机组一次风喷口带火问题的解决方法

125MW机组采用热风送粉、一次风集中布置的锅炉,当所燃用煤种的挥发分和热值提高后,普遍存在一次风喷口带火、烧坏、喷口附近结渣等影响锅炉安全性的问题。针对这类问题,总结了几种解决方法,结合具体实例分析了各种方法的优缺点,对解决该类型机组喷口带火问题具有一定的借鉴作用。     

一种高效率的内燃机燃烧模式

本文探讨了以双燃料发动机为代表的预混合和扩散燃烧共存的复合燃烧模式。认为这种燃烧模式兼有预混合燃烧和扩散燃烧的优点，而且有比传统的燃烧模式更高的热效率。实验证明，采用这种燃烧模式工作的发动机可以有比火花点火式发动机更高的压缩比，有比压燃式发动机更高的燃烧速率。最后对这种发动机的燃烧特性及获得较高热效率的原因进行了分析。     

A review on plasma combustion of fuel in internal combustion engines

In recent years, new ways of improving the combustion efficiency of fuel during gas turbine operations have been developed. The most significant has been the application of plasma technology for the combustion of fuel in gas turbine operations. Plasma is formed when gas is exposed to either high temperature or high‐voltage electricity. This technology is very promising and has proven to enhance the performance of gas turbines and reduce toxic emissions. Recent studies have shown the use of different types of plasma applications in gas turbine operations such as plasma torch, filamentary discharge, and nanosecond pulse discharge, whose results show that plasma technology has great potential in improving flame stabilization, the fuel/air mixing ratio, and flash point values of these fuels. These findings and advances have further provided new opportunities in the development of efficient plasma discharges for practical uses in plasma combustion of fuel for gas turbine operations. This article is a comprehensive overview of the advances and blind spots in the knowledge of plasma combustion of fuel during internal combustion engine operations. This review also focuses on applications, methods, and experimental results in plasma combustion of fuel in gas turbines.     

Investigation of forward flow distributed combustion for gas turbine application

New innovative advanced combustion design methodology for gas turbine applications is presented that is focused on the quest towards zero emissions. The new design methodology is called colorless distributed combustion (CDC) and is significantly different from the currently used methodology. In this paper forward flow modes of CDC have been investigated for application to gas turbine combustors. The CDC provides significant improvement in pattern factor, reduced NO_x emission and uniform thermal field in the entire combustion zone for it to be called as an isothermal reactor. Basic requirement for CDC is carefully tailored mixture preparation through good mixing between the combustion air and product gases prior to rapid mixing with fuel so that the reactants are at much higher temperature to result in hot and diluted oxidant stream at temperatures that are high enough to autoignite the fuel and oxidant mixture. With desirable conditions one can achieve spontaneous ignition of the fuel with distributed combustion reactions. Distributed reactions can also be achieved in premixed mode of operation with sufficient entrainment of burned gases and faster turbulent mixing between the reactants. In the present investigation forward flow modes consisting of two non-premixed combustion modes and one premixed combustion mode have been examined that provide potential for CDC. In all the configurations the air injection port is positioned at the opposite side of the combustor exit, whereas the location of fuel injection ports is changed to give different configurations. Two combustion geometries resulting in thermal intensity of 5 MW/m³-atm and 28 MW/m³-atm are investigated. Increase in thermal intensity (lower combustion volume) presents many challenges, such as, lower residence time, lower recirculation of gases and effect of confinement on jet characteristics. The results are presented on the global flame signatures, exhaust emissions, and radical emissions using experiments and flowfield using numerical simulations. Ultra-low NO_x emissions are found for both the premixed and non-premixed combustion modes at the two thermal intensities investigated here. Almost colorless flames (no visible flame signatures) have been observed for the premixed combustion mode. The reaction zone is observed to be significantly different in the two non-premixed modes. Higher thermal intensity case resulted in lower recirculation of gases within the combustion chamber and higher CO levels, possibly due to lower associated residence time. The characteristics at the two thermal intensity combustors investigated here were found to be similar.     

Droplet combustion in the presence of acoustic excitation

This experimental study focused on droplet combustion characteristics for various liquid fuels during exposure to external acoustical perturbations generated within an acoustic waveguide. The alternative liquid fuels include alcohols, aviation fuel (JP-8), and liquid synthetic fuel derived via the Fischer–Tropsch process. The study examined combustion during excitation conditions in which the droplet was situated in the vicinity of a pressure node (PN). In response to such acoustic excitation, the flame surrounding the droplet was observed to be deflected, on average, with an orientation depending on the droplet’s relative position with respect to the PN. Flame orientation was always found to be consistent with the sign of a theoretical bulk acoustic acceleration, analogous to a gravitational acceleration, acting on the burning system. Yet experimentally measured acoustic accelerations based on mean flame deflection differed quantitatively from that predicted by the theory. Phase-locked OH^∗ chemiluminescence imaging revealed temporal oscillations in flame standoff distance from the droplet as well as chemiluminescent intensity; these oscillations were especially pronounced when the droplets were situated close to the PN. Simultaneous imaging and pressure measurements enabled quantification of combustion-acoustic coupling via the Rayleigh index, and hence a more detailed understanding of dynamical phenomena associated with acoustically coupled condensed phase combustion processes.     

准均质充气压缩点燃系统燃烧特性研究

准均质充气压缩点燃（QHCCI）燃烧系统是在柴油机上实现稀薄预混合气燃烧的有效方法，建立了一个燃烧过程准维数学模型，结合试验结果，对QHCCI系统的燃烧特性进行了研究。内容包括引燃柴油喷射定时对系统燃烧性能的影响，引燃柴油喷射量对系统的影响，以及发动机工作粗暴的特性。模拟结果与试验结果一致，并发现QHCCI燃烧系统的放热律曲线一般呈双峰，引起爆震的原因主要是引燃柴油喷射量大或喷射早造成上止点附近的大量剧烈燃烧造成的。     

无焰燃烧发展及研究现状

无焰燃烧是一种同时具备高效和低排放特点的燃烧技术,然而传统实现无焰燃烧所需的高温预热空气及高速射流两大重要条件,提高了整体工业设备实现无焰燃烧的复杂性,限制了该技术在更广阔领域的发展。本文综述了无焰燃烧燃烧机理与特性的研究发展,并提出了未来可能的发展趋势。分析发现：高温预热空气并不是实现无焰燃烧的必要条件,而通过高速射流提高炉内烟气循环率却必不可少;使用EDC模型结合GRI 3.0反应机理能在数值模拟中得到贴合实验数据的结果;气体、液体及固末燃料均可实现无焰燃烧,使用CH4/H2混合气体实现无焰燃烧可在提升燃烧稳定性的同时依旧保持低排放的特点;炉膛结构可很大程度上影响炉内流场进而影响无焰燃烧效果。因此,研究无需预热的无焰燃烧系统在降低工业成本的同时可增大燃料种类的选择性,通过设计合理的炉膛结构,营造良好的炉内流场在强化无焰燃烧效果的同时可一定程度降低对初始射流速度的要求,研究CH4/H2混合气体的燃烧机理具有十分重要的意义。     

First and second thermodynamic-law analyses of hydrogen-air counter-flow diffusion combustion in various combustion modes

In this paper, from the viewpoints of both the first and the second law of thermodynamics, we conduct a comprehensive study on hydrogen-air counter-flow diffusion combustion in various modes. The effects of air inlet temperature (T_oxi) and effective equivalence ratio of fuel (φ) on the reaction zone structure and entropy generation of combustion are revealed over a wide range of T_oxi and φ. Through the present work, five interesting features of combustion of this kind, which are quite different from that reported in the literature, are presented. Especially, for the first time we divide various combustion modes in the φ − T_oxi map instead of the popular way used in previous studies. Such innovation can help judge the final combustion regime more straightforwardly for any given operative condition.     

摆动式水平浓淡风煤粉燃烧器在670 t/h锅炉的应用研究

我厂2号锅炉(DG 670/13.7-8A)为四角切圆布置,一、二次风间隔布置,分上下两组,设计煤种为晋中贫煤.在实际运行中,煤质不稳定,锅炉着火和燃烧稳定性差.采用"摆动式水平浓淡风煤粉燃烧器"技术对燃烧器改造后,燃烧效率提高0.84%、在300 t/h时能稳定燃烧、炉膛无结渣,锅炉参数稳定.     

掺氢对微尺度空间内预混层流火焰转捩爆燃特性的影响

针对基于燃烧的微小型动力装置存在燃烧效率低、火焰传播速度慢的问题,设计了一个可视化的、特征间距仅为0.45 mm的微尺度定容燃烧室,实验比较了0～1的掺氢比例下,丙烷/氢气/空气预混火焰在该燃烧室内的传播以及加速过程.实验发现没有掺氢时,丙烷/空气预混火焰需要在0.25 MPa初始压力下才能够传播;当掺氢比例为0.2时...     

Structure of hydrogen triple flames and premixed flames compared

Triple flames consisting of lean, stoichiometric, and rich reaction zones may be produced in stratified mixtures undergoing combustion. Such flames have unique characteristics that differ from premixed flames. The present work offers a direct comparison of the structure and propagation behavior between hydrogen/air triple and premixed flames through a numerical study. Important similarities and differences are highlighted. Premixed flames are generated by spark-igniting initially quiescent homogeneous mixtures of hydrogen and air in a two-dimensional domain. Triple flame results are also generated in a two-dimensional domain by spark-igniting initially quiescent hydrogen/air stratified layers. Detailed flame structure and chemical reactivity information is collected along isocontours of equivalence ratio 0.5, 1.0, and 3.0 in the triple flame for comparison with premixed flames at the same equivalence ratios. Full chemistry and effective binary diffusion coefficients are employed for all computations.