【作者】 黄明明；

【导师】 肖云汉； 张哲巅； 邵卫卫；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 热能工程， 2014， 博士

【摘要】 柔和燃烧具有排放低、燃烧稳定、烟气出口温度分布均匀、燃料适用范围广的特点,是燃气轮机燃烧技术的重要发展方向之一。本文针对燃气轮机燃烧室的运行条件,研究了柔和燃烧的热力学条件、化学动力学特性、流动条件以及模型燃烧室内柔和燃烧的实现与性能。论文具体工作如下：1.热力学条件和化学动力学特性研究建立了化学反应网络模型并进行了验证,研究了燃烧室运行条件变化对柔和燃烧热力学条件的影响,确定了B级、E+级、F级燃气轮机工况下实现柔和燃烧所需的烟气回流比例,分析了烟气回流比例对柔和燃烧点火延迟时间的影响,比较了柔和燃烧和传统燃烧的反应速率。结果表明,增加回流比例有利于柔和燃烧反应物初始温度的升高、反应温升的下降、反应速率的降低,导致柔和燃烧的点火延迟时间减少,因此提出了实现柔和燃烧应在热力学条件满足的基础上适当控制烟气回流比例、同时促进火焰抬升。2.流动条件研究建立了轴向分级概念燃烧室,针对CH4燃料,研究了掺混方式、烟气回流比例影响,针对10MJ/Nm3合成气燃料,分析了燃料射流速度影响。CH4柔和燃烧的研究表明,空气、燃料先分别和主流高温烟气掺混再接触有利于柔和燃烧的实现；回流比例的增加会延缓掺混区空气、燃料的直接掺混,有利于降低柔和燃烧区的OH*峰值、提高柔和燃烧区的OH*分布均匀性、抑制柔和燃烧区NO的生成,但回流比例过高会导致燃烧稳定性下降。10MJ/Nm3合成气柔和燃烧的研究表明,增加燃料射流速度有利于燃料和“高温低氧”氧化剂的快速混合,促进火焰的抬升、反应区的分散以及NOx排放的下降,但过高的燃料射流速度也会带来压损和CO排放升高的问题；燃料速度在199-299m/s之间有利于柔和燃烧的实现。3.模型燃烧室设计开展了冷态和热态计算,研究了燃烧室长宽比、喷嘴相对位置、喷嘴间距、空燃动量比对掺混和燃烧性能的影响。结果表明,燃烧室长宽比主要影响空气速度在燃烧室长度方向上的衰减,长宽比为1.1的模型燃烧室能充分利用燃烧室空间来组织流场,其空气射流速度在燃烧室长度方向上恰好完全衰减。燃料喷嘴远离燃烧室中心线有利于燃料在燃烧室内部的充分燃烧。增加空气、燃料喷嘴间距可推迟空气和燃料的汇合,但考虑到反应物的充分燃烧,增加喷嘴间距的同时也应保证空气喷嘴偏离燃烧室中心线一定距离。降低空燃动量比会推迟空气和燃料的汇合、促进反应区的分散、降低峰值火焰温度和CO排放。总体上,降低空燃动量比有利于柔和燃烧的实现。4.模型燃烧室性能加工模型燃烧室,开展实验研究了空燃动量比、当量比、空气预热温度、燃料种类对合成气柔和燃烧性能的影响。结果表明,降低空燃动量比有利于主反应区向燃烧室下游移动,促进CO排放降低。当量比影响方面,增加当量比有利于着火时间推迟、反应温度降低和反应区体积增大,贫燃条件下实现了合成气的柔和燃烧。空气预热温度升高会导致NOx排放升高、CO排放降低,但即使空气预热了,燃烧室内部的热力学条件、化学动力学特性和流动条件仍然是满足的,所以合成气在空气预热条件下也能实现柔和燃烧。柔和燃烧室应用于不同热值合成气时,随着热负荷的增加,反应区体积增大,NOx排放保持在低水平,所以综合来看,柔和燃烧适用于不同热值的合成气。更多还原

【Abstract】 Moderate or Intense Low-oxygen Dilution (MILD) combustion, characterized by low pollutant emissions, enhanced combustion stability, improved pattern factor and high fuel flexibility, is a suitable choice for the future gas turbine combustion technologies. This paper aims to study the thermodynamics, chemical kinetics and fluid mechanics of MILD combustion under gas turbine relevant conditions and to evaluate the combustion behavior in a MILD combustor. The main work is drawn as follows:1. Thermodynamics and chemical kineticsA chemical reactor network model was established, and the model was verified by the the experimental results. The effects of exhaust gas temperature, air preheat, pressure and fuel type on the thermodynamics of MILD combustion were probed into. The critical gas recirculation ratio needed for the realization of MILD combustion were obtained for the B, E+and F class gas turbine operating conditions. The effect of gas recirculation ratio on the ignition delay time of MILD combustion was also examined. The reaction rates of MILD combustion and traditional diffusion flame were compared. It is demonstrated that elevated gas recirculation ratio benefits the increase of MILD mixture tempearture, the decrease of temperatrure increment during the combustion process and the drop of reaction rate, however, resulting in the suppression of ignition delay time. It is thus proposed that the gas recirculation ratio should be controlled and the flame should be lifted from the burner in the case of the thermodynamics of MILD combustion is fulfilled.2. Fluid mechanicsAn axially staged MILD combustor was built to study the effects of mixing approach and gas recirculation ratio on the MILD combustion of CH4and to evaluate the effect of fuel injection velocity on the MILD combustion of10MJ/Nm3syngas. The results acquired from CH4MILD combustion reveales that the secondary air and fuel mixing with the hot flue gas from the gas generation zone separately before air/fuel direct interaction promotes the establishment of MILD scheme. Increased gas recirculation ratio causes the delayed air/fuel interaction, resulting in the decrease of maximum OH*intensity, the widespread of OH*distribution and the suppression of NO production from the MILD combustion zone. However, excessively high gas recirculation ratio vitiates combustion stability. For the10MJ/Nm3syngas MILD combustion, it is reflected that increased secondary fuel injection velocity favors the rapid mixing between the secondary fuel and the high temperature and low oxygen concentration oxidizer, resulting in the increase of flame lift-off distance, the spatially distribution of reaction zone and the elimination of NOX production. However, extremely high secondary fuel injection velocity causes the growth of pressure drop and CO emissions. The secondary fuel injection velocity limited to199-299m/s facilitates the establishment of MILD scheme.3. Design of MILD combustorThe non-reactive and reactive simulations were performed to investigate the effecs of combustor length-to-width ratio, burner arrangement and air-to-fuel-momentum flux ratio on the mixing behavior and combustion performance. It is shown that the decay of air injection is mainly affected by the combustor length-to-width ratio and, the decay length of air injection is almost the same as combustor length at combustor length-to-width ratio of1.1, which is the best choice for the organization of flow field in the full use of limited combustor volume. The fuel injectors positioned away from the combustor axis is beneficial for the complete oxidation of fuel species. Increased distance between air and fuel injectors can postpone the confluence of air and fuel stream. However, in consideration of the complete combustion, the centerline of air injector should be somewhat offset from the combustor axis. Decreased air-to-fuel-momentum flux ratio benefits the delay of air/fuel confluence, the distribution of reaction zone and reduction of reaction temperature and CO emissions. In general, lower air-to-fuel-momentum flux ratio facilitates the realization of MILD combustion.4. Combustion performance of MILD combustorExperiments were conducted on the MILD combustor to study the effecs of air-to-fuel-momentum flux ratio, equivalence ratio, air preheat and fuel type on the MILD combustion of syngas. It is revealed that lower air-to-fuel-momentum flux ratio causes the downstream movement of main reaction zone and the suppression of CO emissions. On the other hand, increased euiqvalence ratio benefits the delay of ignition, the reduction of reaction temperature and the growth of reaction zone volume. The MILD scheme can be established for syngas under lean operating conditions. In addition, air preheat promotes the rise of NOx production and mitigation of CO generation. The MILD combustion can be achived for syngas even under air preheating condition since the thermodynamics, chemical kinetics and fluid mechanics of MILD combustion was fulfilled. In the application of MILD combutor to syngas fuels with various calorific values, it is observed that the increased fuel thermal input causes the increase of reaction zone volume whilst the NOx emissions maintaines at a low level. Basically, the MILD combustor is fuel flexible.更多还原