【作者】 徐攀；

【导师】 何芳；

【作者基本信息】 山东理工大学 ， 农业生物环境与能源工程， 2009， 硕士

【摘要】 阴燃是一种基本的燃烧方式,是指氧气直接接触固体燃料表面发生异相氧化反应,释放热量,进行自维持的缓慢、低温（523-1173K）无焰燃烧方式。由于火焰不能存在于大颗粒（直径大于5mm）固体燃料内部或堆积状粉体物料床层内。阴燃广泛存在于固体块状可燃物（煤块,生物质燃料块,生物质挤压成型颗粒,城市固体垃圾）的燃烧过程和一些仓储燃料（各种粉状可燃物）的火灾过程中。研究阴燃过程机理,无论对于固体燃料的应用,还是火灾的预防,都具有重要意义。阴燃过程机理包括化学机理和物理机理。阴燃过程的化学机理包括热解、氧化降解、碳氧化等化学反应特性,过去三十年在这方面有大量的文献。与之相比,阴燃过程物理机理的研究较少。本研究侧重阴燃过程物理机理的研究,为减少化学特性的影响,选用炭粉为对象进行研究。首先,建立炭粉一维向下阴燃的理论模型,确定了影响阴燃过程的物理因素主要有:环境温度、阴燃炉壁保温层保温效果、点火温度和点火位置、燃料的堆积密度、床层收缩率、导热系数、空隙率、固体发射率、炭和灰的比热容等等。应用阴燃过程计算程序,得出常见范围内,床层收缩率、炭堆积密度、燃料床孔隙尺寸、氧气在多孔灰层中的扩散率对阴燃传播速度、床层内部温度和阴燃持续时间影响显著;而初始条件、环境条件及燃料和灰的比热容、导热系数等物性参数的影响可忽略不计。在此基础上,设计了炭粉阴燃实验台。该实验台主要包括阴燃炉,电控系统和数据采集系统三部分,能对炭粉的阴燃特性进行研究。确定实验因素为含碳量和粒径大小,选取了不同粒径的热解炭和木炭粉的进行实验。实验结果表明:1)在燃料床层炭粉的阴燃过程中,既没有因剧烈燃烧而出现火焰,也没有因燃烧不能自维持而熄灭;床层中的温度变化可以明显地区分为加热、燃烧和保温三个过程;炭粉阴燃过程比秸秆阴燃过程有更好的可重复性。2)阴燃床层中的最高温度随着炭粉粒径增大而降低,随着含碳量的增加而增高。3)阴燃燃烧时间随炭粉粒径的增大而变短,随含碳量的增加而变长;4)与其他实验物料的阴燃过程相比,尾气中的CO含量明显升高,在阴燃前期的较长时间内CO与CO₂含量之比大于1。这些研究为炭粉阴燃的深入研究提供了参考。更多还原

【Abstract】 Smoldering is the fast oxidation of solid fuel without flame.To be more specific,it is the slow, low-temperature（523-1173K）,flameless form of combustion,sustained by the heat evolved when oxygen directly attacks the surface of a condensed-phase fuel.Because the flame is impossible inside the powder piles or inside the particle（when the diameter of the particle is more than 5mm）, smoldering exists not only in fire from solid materials,either fuel or industrial materials,but also in many thermo conversion applications of solid materials,such as biomass,urban solid waste. Mechanism of smoldering is very complex and many chemical factors and physical factors are involved in the process.Compared to the large amount of experimental investigations on chemical mechanism（kinetics of pyrolysis,oxidative polymer degradation,char oxidation）of the process in the last two decades,experiments on physical mechanism are much less.However physical mechanism of the process is of great importance in danger prevention and in utilization and treatment of biomass.As a typical solid fuel,char is chosen as the experimental material because it is much easier to detect the gas component in the production of the process than that of high molecular materials.And thus the mechanism of the process is much easier to be evaluated or testified by experiments.Firstly,a simplified 1-D model has been developed describing natural downward smoldering of char.Factors which affect the process turns out to be the following:ambient temperature,insulation of the fuel bed,ignition temperature and position,bulk density of fuel,shrinkage of fuel bed during the process,heat conductivity,void fraction of the fuel bed,heat emission of the fuel,specific heat of solid.Using the program,effects of fuel bed properties on smoldering of char at typical condition have been predicted.Results showed that propagation velocity of the process,temperature inside the whole bed and time smoldering sustained were affected by shrinkage of bed,bulk density of carbon, void size in fuel bed,oxygen diffusivity in ash bed significantly.While the effects of initial condition, environmental condition or fuel bed properties such as specific heat and heat conductivity were ignorable.Based on the aforementioned work,an experimental setup for char smoldering has been designed and manufactured.It consists of smoldering stove,electrical control system,and data acquisition system.In order to investigate the effect of carbon content and particle diameter of char on smoldering process,different size of char from fast pyrolysis and carbonization were chosen for experiments.Result showed that:1)There is no rapid change from smoldering to flame or to extinguish during smoldering of the above char.Temperature inside the bed showed that the process can be divided into heating,reaction and high temperature remaining.The reproducibility of the process is better than smoldering of agro-stalks.2)Maximum temperature of the bed and smoldering time decreases with the increase of particle diameter and increases with the increase carbon content in the char.3)The mole ratio of CO to CO₂ in char smoldering is significantly higher than that of agro-stalks smoldering.It keeps more than 1.0 for a long time at the former part of smoldering.This can be used as reference for the deep investigation of the process.更多还原