激光诊断技术在煤及其气化气燃烧特性研究中的应用

发布时间：2018-05-09 21:33

本文选题：煤分级利用 + 激光燃烧诊断　；参考：《浙江大学》2017年博士论文

【摘要】：在煤及生物质燃料的利用过程中,为了实现高效低污染,对燃料的分级转化利用成了一个重要手段。其中,煤及生物质的气化利用是分级转化利用的重要环节之一。通过气化过程产生的煤气,可以直接用于燃气轮机进行高效低污染燃烧发电,还可以用作众多化工生产的原材料。但是在分级转化的气化工艺中,会出现来源不同的煤及生物质原料。这些燃料的特性差异,加上气化工艺本身的不同,气化煤气的组份存在着较大的不确定性。煤气的主要组份包括氢气,一氧化碳,甲烷,氮气和二氧化碳等。其中作为重要的可燃组份,氢气的燃烧特性和通常使用的天然气有着很大的区别。加上大量的不可燃组份,比如氮气和二氧化碳,造成燃料热值较低,这都会给煤气的高效低污染燃烧利用造成很大的挑战。所以了解含有不同组份的煤气的燃烧特性,开发合理的稳定燃烧手段成了重要的研究课题。另外,在不少煤和生物质的气化燃烧过程中,会释放出大量的碱金属元素,这不仅仅会造成炉膛的结渣腐蚀,还会极大地影响煤气的品质。含碱金属的煤气,往往会造成燃气轮机叶片的腐蚀。所以,对于气化燃烧过程中,碱金属的释放规律的研究,以及探索实用的碱金属监测手段成为重要的研究内容。本文主要通过不同先进激光诊断技术对以上课题中的关键问题展开了相应的研究。本文首先是对含有不同组份的煤气的层流火焰速度进行了精确的测量。层流火焰速度是燃料燃烧反应的重要特性之一,可广泛用于燃烧机理的验证和发展。本文使用的层流火焰速度测量方法包括热流量炉法和基于激光诱导OH荧光(OH-PLIF)技术的本生灯法。通过不同比例的氢气和一氧化碳来模拟实际煤气的可燃组份,通过不同比例的氮气和二氧化碳来模拟实际煤气中稀释气体的比例。氢气在可燃组份中的比例从5%变化到75%,稀释气体比例从0%变化到50%。这些组份比例的大范围变化基本涵盖了不同类型的煤气。通过实验结果可以看出,煤气的层流火焰速度随当量比的变化趋势和甲烷等碳氢燃料有着很大的不同。煤气层流火焰速度峰值往往位于比较燃料富燃的区域,而不是通常的当量比1的附近。氢气量的增加可以极大地提高层流火焰速度,稀释度的增加可以明显减小层流火焰速度。通过对煤气燃烧机理的模拟分析发现,这些燃烧特性很大程度上都是受到燃烧过程中生成的H自由基的控制。本文总结了不同煤气的层流火焰速度和其燃烧反应区的H自由基浓度峰值之间的线性变化关系。通过总结实验获得的大量层流火焰速度,还总结出了用于估算不同煤气层流火焰速度的经验公式。另外,本文还通过OH-PLIF技术研究了不同煤气在较低湍流状态下,即皱褶区的火焰的燃烧特性。通过含有中心射流孔的平面火焰炉,生成了不同煤气在不同出口雷诺数下的预混射流火焰。这些火焰主要是在预混湍流火焰的起皱火焰区域和皱褶火焰区域。火焰的OH-PLIF瞬态图展示了不同工况下火焰的前锋面结构。本文分析计算了不同煤气在不同出口雷诺数下的湍流火焰速度。和对应的层流火焰速度相比较,湍流火焰速度随氢气比例以及稀释度的变化具有非常类似的趋势。较高的氢气比例造成较高的湍流火焰速度,较高的OH浓度以及较小的火焰尺寸。稀释度具有相反的效果。出口雷诺数的增加同样可以增加湍流火焰速度和OH浓度。通过对实验获得的湍流火焰速度和对应煤气的层流火焰速度的比值的分析发现,对于起皱区和皱褶区的火焰,湍流度对湍流燃烧的影响规律不因煤气组分的不同而变化。另外,还通过OH-PLIF技术和甲醛-PLIF技术研究了氮气稀释和二氧化碳稀释对低湍流度湍流火焰的影响。同样,稀释度的增加,极大地降低了 OH和甲醛的浓度,延迟了火焰的燃烧。对于相同湍流度下的火焰,稀释对火焰锋面局部结构的影响并不明显,但是会增加整体皱褶率。比较二氧化碳稀释气体和氮气稀释气体,区别比较大的是燃烧区的OH浓度。而对于未燃区的甲醛浓度,受不同稀释气体的影响较小。进一步,为了探讨先进的稳定燃烧手段,本文主要针对等离子体强化燃烧手段,研究了等离子体中的重要组分,即臭氧的强化燃烧特性。研究了臭氧强化燃烧的机理。本文通过甲醛-PLIF技术对臭氧强化甲烷/空气预混燃烧过程中甲醛生成的影响进行了研究。研究发现,臭氧的加入可以极大地促进火焰中甲醛的生成。在加入4500ppm的臭氧,对于当量比为1.4的甲烷空气预混火焰,反应区甲醛的浓度提高了 50%以上。实验获得了在不同当量比下甲醛的增加率。通过实验数据和机理模拟结果的对照,验证了包含臭氧反应子机理的燃烧反应机理的可靠性。臭氧的加入,不仅仅增加了甲醛的浓度,而且明显提前了甲醛的生成时间。通过对甲醛的研究,可以看出,臭氧对于燃烧的促进作用主要发生在燃烧的预热区。最后,通过可调谐半导体激光吸收光谱(TDLAS)技术实现了对煤及生物质气化燃烧过程中钾原子浓度的定量测量,用于了解煤和生物质气化过程中碱金属的释放规律。比较不同的固体燃料,发现燃料本身的特性对碱金属的释放特性具有很大的影响。煤炭里面较多的固定碳使得其钾的释放主要发生在焦炭燃烧阶段。生物质较多的挥发份以及大量的水溶性碱金属,使其钾的释放主要发生在挥发份燃烧阶段。另外还比较了燃料在燃烧和气化过程中钾的不同释放特性。气化过程削弱了挥发分和焦炭的消耗反应,使得整个钾释放过程有所变弱。
[Abstract]:In the use of coal and biomass fuel, in order to achieve high efficiency and low pollution, the classification and utilization of fuel has become an important means. The gasification utilization of coal and biomass is one of the important links in the conversion and utilization of coal and biomass. The gas produced by the gasification process can be directly used for high efficiency and low pollution combustion of gas turbine. Power generation can also be used as a raw material for many chemical production. However, in the gasification process of classified conversion, there will be different sources of coal and biomass. The characteristics of these fuels, as well as the different gasification processes, have a large uncertainty in the composition of the gasification gas. The main components of the gas include hydrogen, carbon monoxide. Methane, nitrogen and carbon dioxide, etc. as important combustible components, there is a great difference between the combustion characteristics of hydrogen and the natural gas used. A large number of non combustible components, such as nitrogen and carbon dioxide, cause a low fuel heat value, which will cause a great challenge to the efficient and low pollution combustion of the gas. It is an important research topic to understand the combustion characteristics of gas containing different components and to develop a reasonable means of stable combustion. In addition, a large number of alkali metal elements will be released during the gasification and combustion process of coal and biomass, which will not only cause the slag corrosion in the furnace, but also greatly influence the quality of the gas. Gas is often caused by corrosion of gas turbine blades. Therefore, the research on the release law of alkali metals and the exploration of practical alkali metal monitoring methods have become an important research content in the process of gasification and combustion. This paper mainly studies the key problems in the above topics through different advanced laser diagnostic techniques. The first is the accurate measurement of the laminar flame velocity of the gas with different components. The laminar flame velocity is one of the most important characteristics of the fuel combustion reaction. It can be widely used in the verification and development of the combustion mechanism. The laminar flame velocity measurement methods used in this paper include the heat flux furnace method and the laser induced OH fluorescence (OH-PLIF). This method is used to simulate the combustible components of the actual gas by different proportions of hydrogen and carbon monoxide. The proportion of the diluted gas in the actual gas is simulated by different ratios of nitrogen and carbon dioxide. The proportion of hydrogen in the combustible component varies from 5% to 75%, and the proportion of the diluted gas body from 0% to 50%.. The gas laminar flame velocity varies greatly with the methane and other hydrocarbon fuels. The peak velocity of the gas laminar flow flame is often located in the area where the fuel is relatively rich, not the usual equivalent ratio of 1. Increasing the velocity of laminar flame can greatly increase the velocity of laminar flame, and the velocity of laminar flame can be reduced obviously. Through the simulation analysis of the gas combustion mechanism, it is found that these combustion characteristics are largely controlled by the H free radicals generated during the combustion process. The linear relationship between the peak value of the H free radical concentration in the combustion zone is linear. By summing up a large amount of laminar flame velocity obtained by the experiment, an empirical formula for estimating the velocity of different gas laminar flow flame is also summarized. In addition, this paper also studies the flame of different gas in the lower turbulent state, that is the wrinkle zone through the OH-PLIF technology. Combustion characteristics. Through a plane flame furnace containing a central jet hole, the premixed jet flame of different gas is generated at the Reynolds number at different outlet. The flame is mainly in the wrinkle flame area and the fold flame area of the premixed turbulent flame. The flame's OH-PLIF transient diagram shows the front surface structure of the flame under different working conditions. The turbulent flame velocity of different gas in different outlet Reynolds number is calculated and calculated. Compared with the corresponding laminar flame velocity, the turbulent flame velocity has a very similar trend with the change of hydrogen ratio and dilution degree. Higher hydrogen ratio causes higher turbulent flame velocity, higher OH concentration and smaller flame size. The increase of the dilution has the opposite effect. The increase of the exportation Reynolds number can also increase the turbulent flame velocity and the OH concentration. The analysis of the turbulent flame velocity and the ratio of the laminar flame velocity to the gas is found that the turbulence intensity affects the turbulent combustion in the wrinkling and wrinkle zone. In addition, the effects of nitrogen dilution and carbon dioxide dilution on low turbulence turbulence flame were studied by OH-PLIF and formaldehyde -PLIF technology. Similarly, the increase of the dilution degree greatly reduced the concentration of OH and formaldehyde and delayed the combustion of flame. The influence of the structure is not obvious, but it will increase the overall wrinkle rate. Comparing the carbon dioxide dilution gas and the nitrogen diluent gas, the difference is much larger than the OH concentration in the combustion zone. However, the concentration of the formaldehyde in the unburned area is less affected by the different dilution gases. The important components in the plasma are studied. The characteristics of the enhanced combustion of the ozone are studied. The mechanism of the enhanced combustion of ozone is studied. The effect of the formaldehyde -PLIF technology on the formation of formaldehyde in the pre mixed combustion of methane / air is studied in this paper. The study shows that the addition of ozone can greatly promote the formation of the ozone. Formaldehyde is generated in the flame. The concentration of formaldehyde in the reaction zone is increased by more than 50% in the pre mixed methane air premixed flame with the equivalent ratio of 1.4. The increase rate of formaldehyde under the different equivalent ratio is obtained. The combustion reaction containing the ozone reaction mechanism is verified by the comparison of the experimental data and the simulation results of the mechanism. The addition of ozone does not only increase the concentration of formaldehyde, but also obviously advance the formation time of formaldehyde. Through the study of formaldehyde, it can be seen that the promoting effect of ozone on combustion mainly occurs in the preheated area of combustion. Finally, the coal is realized by the tunable semi conductor laser absorption spectroscopy (TDLAS) technology. The quantitative measurement of the concentration of potassium in the combustion process of biomass gasification is used to understand the release of alkali metals in coal and biomass gasification. The characteristics of different solid fuels have been compared and the characteristics of the fuel itself have a great influence on the release characteristics of alkali metals. The more fixed carbon inside coal makes the release of potassium mainly occurring. In the combustion stage of coke. The volatilization of biomass and a large amount of water-soluble alkali metals, the release of potassium is mainly in the stage of volatile combustion. In addition, the different release characteristics of potassium in the combustion and gasification process are compared. The gasification process weakens the reaction of the volatile and coke consumption, making the whole potassium release process available. It's weak.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ534

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