合成气微混合燃烧流动特性分析

发布时间：2018-05-14 11:28

本文选题：合成气 + 微混合燃烧　；参考：《华北电力大学(北京)》2016年硕士论文

【摘要】：严峻的环境问题与我国以煤为主要能源的资源结构决定了我国发展清洁燃烧技术的重要性。在目前众多的清洁燃烧技术中,IGCC是非常有前景的技术手段。作为整个系统的重要组成部分,燃气轮机技术的开发与研究非常关键。由于合成气的低热值、高热平衡温度的特性,在利用传统燃气轮机改烧合成气时存在着污染物NOx排量较高的问题；同时,合成气中的成分H2极易着火燃烧,实际工程中还要防止发生回火现象。因此,需要针对合成气燃料的特性对传统燃气轮机进行适度的改造。本文我们采用自主设计的25喷嘴微混合燃烧器进行实验研究,用以探索其燃烧合成气时的燃烧特性。该燃烧器的燃烧室底板面上装有25个单元喷嘴,以5排5列的方阵形式分布。其中,每个单元喷嘴由中间的一个竖直燃料喷口和周围的八个以一定角度倾斜分布的空气小喷口组成,形成一个独立旋流燃烧的微混合燃烧单元。各独立的燃烧单元起到了分散火焰面的效果,降低了局部热负荷和燃烧温度,有利于降低NOx的排放,且起到保护喷嘴不被烧毁的作用。同时,该燃烧器可以投入不同数量的喷嘴进行工作：9喷嘴、13喷嘴和25喷嘴,燃料喷口直径也可选择2.0mm、2.3mm和2.8mm。该燃烧器的设计拟通过投用不同数量和燃料喷口直径的喷嘴来调节各工作喷嘴间的间距以及燃料喷口与空气喷口之间的相对间距,以此来实现扩散燃烧和预混燃烧的研究。为了了解验证该燃烧器的性能,我们开展了一些热态实验。实验结果表明不同实验条件下,微混合燃烧器可以有效地组织燃烧。火苗成锥形,火焰根部较细,可燃混合物在向下游运动的过程中,由于燃料自身逐渐扩散且各喷嘴单元间流体的相互作用,整体上逐渐扩散交融,火焰面也逐渐变宽,形成主燃烧区。同时,不难发现微混合燃烧的方法可以有效地降低污染物的排放,Nox与CO的排量均较低。通过实验测量与数值模拟结果分析可知,氦气等动量代替氢气时与氢气的速度分布规律最为接近。燃烧室内流体从喷口射出后,在气流整体向下游运动的过程中,各独立的射流区域逐渐扩大,随后相互融合,整个流场主要可以分为3个区域：燃烧室主射流区、相邻单元喷嘴间的低速小回流区以及单元喷嘴与壁面之间的较大回流区。燃烧室中这些回流区的存在可以加快燃料与空气的均匀混合,有助于燃烧的进行。同时,流体离开喷嘴的很小距离内速度先下降再上升,之后快速下落并逐渐趋于稳定。燃烧室中心截面的速度分布可以很好的对应燃烧器的结构喷嘴布置情况,整体上表现为5个速度峰值且中间喷嘴的速度要稍微高些,靠近燃烧器壁面的速度较低甚至出现负值。之后,我们计算了微混合燃烧器单喷嘴和中心截面的脉动速度分布,可以看到脉动速度整体较小,说明该燃烧器在稳定性方面的设计性能较好。
[Abstract]:The severe environmental problems and the resource structure of coal as the main energy source determine the importance of developing clean combustion technology in China. IGCC is a promising technique in many clean combustion technologies. As an important part of the whole system, the development and research of gas turbine technology is very important. Because of the characteristics of low calorific value and high heat equilibrium temperature of syngas, there is a problem of high NOx emission when using conventional gas turbine to burn syngas, and the composition H _ 2 in syngas is easily ignited. In the actual project, it is necessary to prevent the occurrence of tempering phenomenon. Therefore, it is necessary to transform the conventional gas turbine according to the characteristics of syngas fuel. In this paper, a 25-nozzle micro-mixing burner designed by ourselves is used to study the combustion characteristics of the combusted gas. There are 25 unit nozzles on the bottom plane of the combustor, which are distributed in the form of 5 rows and 5 columns of square array. Each unit nozzle consists of a vertical fuel nozzle in the middle and eight small air nozzles which are inclined at a certain angle to form an independent swirl combustion micro-mixed combustion unit. Each independent combustion unit has the effect of dispersing the flame surface, reducing the local heat load and combustion temperature, reducing the NOx emission, and protecting the nozzle from burnout. At the same time, the burner can be put into different number of nozzles for work: 9 nozzles, 13 nozzles and 25 nozzles, and the fuel nozzle diameters can also be chosen as 2.0mm / 2.3mm and 2.8mm. The design of the burner is to adjust the distance between the working nozzles and the relative distance between the fuel nozzles and the air nozzles by using nozzles with different numbers and fuel nozzle diameters, so as to realize the study of diffusion combustion and premixed combustion. In order to verify the performance of the burner, some hot state experiments have been carried out. The experimental results show that the micro-mixing burner can effectively organize the combustion under different experimental conditions. The flame becomes conical, the flame root is thin, the combustible mixture moves downstream, because of the diffusion of the fuel itself and the interaction of the fluid between the nozzle units, the flame surface becomes wider and wider as a whole. Form the main combustion zone. At the same time, it is not difficult to find that the micro-mixing combustion method can effectively reduce the emission of no _ x and CO. The results of experimental measurement and numerical simulation show that the velocity distribution of helium is most close to that of hydrogen when it replaces hydrogen with equal momentum. After the combustion chamber fluid is ejected from the nozzle, during the whole flow moving downstream, the independent jet regions gradually expand and then merge with each other. The whole flow field can be divided into three main regions: the main jet zone of the combustion chamber. The low speed small reflux region between adjacent unit nozzles and the large reflux region between the unit nozzle and the wall surface. The existence of these reflux zones in the combustion chamber can accelerate the uniform mixing of fuel and air, which is helpful to the combustion. At the same time, the velocity of the fluid first decreases and then rises at a small distance from the nozzle, then rapidly falls and tends to stabilize gradually. The velocity distribution of the central section of the combustor can well correspond to the configuration of the burner nozzle, which shows five peak velocities on the whole and the velocity of the intermediate nozzle is slightly higher, and the velocity near the burner wall is lower or even negative. After that, the pulsating velocity distributions of the single nozzle and the center section of the micro-mixing burner are calculated. It can be seen that the overall pulsation velocity is smaller, which indicates that the design performance of the burner is good in terms of stability.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK16

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