【作者】 宋在乐；

【导师】 范卫东；

【作者基本信息】 上海交通大学 ， 热能工程， 2007， 硕士

【摘要】 天然气作为一种清洁能源,在我国随着“西气东输”工程的进展和对环境保护的重视,其开发和利用得到了快速发展,但是在电站锅炉燃烧过程中仍然存在两个重要问题:一是天然气火焰辐射力弱造成水冷壁吸热不充分,导致过热器和再热器超温;二是天然气燃烧过程中的氮氧化物排放也是一个迫切需要解决的问题。要从根本上解决这两个问题,就必须从研究其生成机理入手,分析燃烧条件改变对火焰辐射和NOX排放的影响,为选择合理的燃烧方式提供理论支持。本文通过研究发现,当预混度较低和环境温度较高时,天然气火焰中生成的炭黑会大大强化火焰的辐射传热能力,在降低火焰温度的同时使热力型NOX的生成量下降;而且炭黑还会还原火焰中已经生成的NOX。本文首先建立了完善灵活的燃气燃烧NOX测量试验系统,在试验系统上完成了不同预混度、不同环境温度和不同燃气流量对甲烷火焰和液化石油气火焰NOX生成的影响分析。研究结果表明,对于甲烷火焰和液化石油气火焰,存在一个临界环境温度,在临界环境温度以下,NOX生成量随预混度的变化规律按生成机理可以分为三个阶段:先是快速型NOX起主导作用,然后是快速型NOX和热力型NOX共同起作用,最后是热力型NOX起主导作用;在临界环境温度以上,始终是热力型NOX起主导作用。研究还表明,在一定环境温度范围以内,全扩散或低预混度时,NOX生成量和环境温度基本上是二次函数的关系,全预混或高预混度时,NOX生成量基本上不随环境温度变化;当燃气流量变化时,在预混度的整个变化范围之内,NOX排放可以用统一形式的五次多项式表示。本文还研制了微型天然气燃烧装置并与FTIR进行了联机调试,利用FTIR发射-透射技术,借助于傅立叶变化红外光谱仪在线测量了不同预混度和不同环境温度条件下甲烷火焰的温度和总辐射力。试验结果表明,在大气环境中,改变预混度使炭黑在火焰中的生成位置发生了改变;使外焰处的火焰温度和总辐射力发生了改变;使火焰的整体辐射力水平发生了改变;但是对火焰的整体温度水平影响不是很大。研究还表明,在封闭空间中,环境温度升高使火焰温度下降;预混度较低时,环境温度的改变对火焰温度的影响比较明显;而预混度较高时,环境温度的改变对总辐射力的影响比较明显。最后,全文在综合NOX测量试验和FTIR测量试验的基础上,全面分析了燃烧条件改变对甲烷火焰中炭黑生成、NOX排放和总辐射力的影响并对三者之间的相互关系作了合理的解释。更多还原

【Abstract】 Along with the advance of“transfer natural gas from the west to the east”project and the attention of environmental protection , the exploitation and utilization of natural gas has been developed rapidly as one of the clean energies in our country.Even now,there lies two urgent problems in the combustion process of power plant boiler.One is that the superheater and reheater overheat because the quantity of heat in flame doesn’t be absorbed fully by the waterwall as the result of the poor total radiation of natural gas flame.The other is the emission of NOX produced in burning.The most effective way solving the two problems is the study of its formation mechanism,so we should analyze the influence of different combustion conditions on flame radiation and NOX emission,provide the theory support for the reasonable choice of combustion mode.In this paper,research shows that when premixed degree is low and environmental temperature is high,the soot produced in flame will enhance the total radiation of flame consumedly,consequently decrease the flame temperature and thermal NOX emission.Besides the soot also can deoxidize the NOX produced in flame.In this paper a perfect and flexible measurement system of NOX emission had been established firstly.The NOX emission characteristics of CH4-air and LPG-air flames were investigated experimentally under different premixed degrees,environmental temperatures and gas flows.It was found that there is a critical environmental temperature,the rule of NOX emission and premixed degree is classified into three phrases according to the NOX formation mechanism below the temperature.As the premixed degree increases,prompt NOX functions first,then prompt NOX and thermal NOX both function and thermal NOX functions last.Above the temperature,thermal NOX functions all along.In addition,with the environmental temperature varying in a certain scope,the rule of NOX emission and environmental temperature is a quadratic function for diffusion and low premixed flames,while the NOX emission is stable as to the environmental temperature for fully premixed and high premixed flames.The NOX emission can be expressed as a uniform quintic function of premixed degree when gas flow varies.The development of a subminiature natural gas combustion apparatus and the on-line debugging of it with Fourier Transform Infrared spectroscopy(FTIR) are also completed in this paper.We use FTIR E-T technology to investigate the influence of different premixed degrees and different environmental temperatures on total radiation and temperature of CH4-air flame on line via FTIR.It was found that when premixed degree varies in atmosphere,the position of soot formation in flame changes,the temperature and total radiation in flame upside change and the whole radiation of flame changes,but the whole temperature of flame is stable.Furthermore,in close space,flame temperature decreases because of higher environmental temperature . The influence of environmental temperature on flame temperature is obvious at lower premixed degree,while the influence of environmental temperature on total radiation is clear at higher premixed degree.In conclusion,on the basis of the integration of NOX measuring test and FTIR measurement experimentation,this paper analyses the influence of different combustion conditions on soot formation,NOX emission and total radiation in CH4-air flame roundly and interprets the correlation among them with reason.更多还原