【作者】 吴宁；

【导师】 姚强；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2013， 博士

【摘要】 在煤粉燃烧过程和各种不同的燃煤应用系统中，煤粉从受热升温到着火燃烧的早期过程，往往经历着复杂的流场条件，使得煤粉的运动出现穿越火焰面的情况，从而使着火特性发生改变。然而受限于已有实验方法和观测条件的困难，尚未见到针对这一过程的相关报道，对其开展探索可进一步推动煤燃烧研究，提供新的视角和途径。针对上述科学问题，本文发展并建立了一套适用于煤燃烧研究的加压对冲火焰实验系统。设计的燃烧室可将反应气体预热至最高1600K，可调压力范围0.06-1.50MPa；基于碰撞解聚原理，自行研制了全新的微量给粉系统，具备50mg/min量级、连续1h以上不受载气流量影响的稳定给粉能力，进而实现了对冲火焰条件下煤粉的定点引入方法；研制了燃煤颗粒物采样枪；建立了SiC纤维辐射测温装置，测量了平面火焰的法向温度分布，误差小于±30K；自主开发了微机平台全参数测控软件，加快了对冲燃烧系统的启动速度，常用工况转换时的非稳态过程小于10s，极大提高了实验效率和安全性。该系统可广泛应用于对冲火焰条件下的气固相反应研究。随后研究了各子系统及测量方法的特点，对实验系统中煤粉给粉过程对测量结果的影响、以及ICCD光学图像拍摄方法和统计原理进行了详细分析，对完善燃煤对冲实验方法具有重要的指导作用和方法学意义。系统上首先开展了合成气组分影响其点火特性的实验研究，通过与国际上相关报道的数据比对，验证了系统的可靠性与测量精度。随后开展了对冲火焰中煤粉颗粒穿越火焰面的行为特性实验研究。利用先进的ICCD光学测量方法对火焰结构及煤粉热解、着火过程进行观测和表征。在此基础上建立了对冲火焰条件下煤粉热解和着火特性实验研究的方法和评价指标。最后建立了对冲火焰中单颗粒煤粉运动和着火特性的瞬态模型，分析了粒径、初速度、火焰温度等因素对煤粉在对冲火焰中的行为的影响，并计算不同粒径煤粉在不同火焰条件下的着火特性，对实验研究的发展具有指导意义。本文在新开发的燃煤对冲实验系统及实验方法基础上，对煤粉穿越火焰面的行为进行了观测和分析，为煤燃烧研究提供了新视角和重要数据。更多还原

【Abstract】 The pyrolysis and ignition of coal, as initial steps of coal combustion, havesignificant effects on the subsequent processes such as char combustion,crushing, fine particle formation and emission of pollutants. Many of thequantitative investigations were unable to be done in the past. However, withthe continuous developments of new experimental methods and techniques, theyare being introduced into the investigations, and become a major driving forceto promote the development of coal pyrolysis and ignition research. Until now,most researchers only considered the process of coal particle pyrolysis andignition under the flameless, unstrained conditions. In fact, the coal particlescross the flame sheet frequently due to particle inertia. The ignition process ofprecipitating volatile gas phase can also be impacted by the strain rate of theflame. As a result, the ignition characteristics change. So far few literatureswere reported on the transport and combustion of pulverized coal aroundstrained flames. The aim of this work is to explore the behavior of dispersedcoal particles in gaseous strained flames by using several novel methods andtechniques.In this thesis, a novel counterflow flame apparatus that can meet therequirement of heterogeneous combustion of pulverized coal particles wasdeveloped and erected. The combustion chamber was designed to be heated upto1600K and at pressures from0.06MPa to1.50MPa. A new powder feedingsystem was developed based on the fundamental of collision theory, achieving aperfect dispersion of coal particles in carrier flows. The coal particle can becarried to the flames at a flow rate around50mg/min. The stability of the coalparticle introducing system is good during one hour even when the flow rate ofthe carrying gases change. This technology solved the problems of introducingthe pulverized coal to a specified position in the flame. A set of device formeasuring the normal direction of the temperature profile of flames was alsoestablished by using the thin-filament pyrometry technology with an error lessthan±30K. A data acquisition and control system was developed to monitor all the parameters to improve the safety and efficiency of the apparatus. Theconterflow flame experimental system can be started quickly and theexperimental condition can also be switched to another state within10s. Thissystem can be widely used to investigate the gas-solid phase reactions incounterflow flames.The experimental method and performance of each sub-system was studied.The effects of the coal particle seeder on the measurments were discussed. Themethod of ICCD optical technology and calculation theory were analyzed indetails. The proposed methods are significantly important in experimentalinvestigation of pulverized coal combustion in counterflow flames.An experiment of ignition temperature of different synthesis gases wasused to verify the reliability and accuracy of the counterflow flame system.Then the experimental research of the pulverized coal ignition in counterflowflames was carried out. The effects of the particle size and flame temperature onthe ignition characteristics were investigated. With the advanced ICCD opticaltechnology, the behavior of coal particles across the counterflow flame wasobserved. The flame structure, the particle pyrolysis and the ignition processwere also measured. Based on the results, an experimental method andevaluation guide line for pulverized coal combustion pyrolysis and ignitioncharacteristics in counterflow flames was proposed. A transient ignition modelof single coal particle in one-dimensional reaction zone of counterflow flamewas developed to calculate the particle temperature, density and productionchanges during across the flame. The effects on the pyrolysis mechanism wereanalyzed.In conclusion, the behavior of the coal particle across the gaseous strainedflame was studied on a coal combustion counterflow flame system. Thisresearch provides a new approach for the coal combustion investigation.更多还原