【作者】 况凯骞；

【导师】 廖光煊；

【作者基本信息】 中国科学技术大学 ， 安全技术及工程， 2008， 博士

【摘要】 哈龙灭火剂的停止生产和使用,使得哈龙替代科学与技术成为火灾安全领域国际前沿热点之一,各国都在积极研究对臭氧层无害的哈龙替代灭火介质。与其它灭火介质相比,粉基灭火介质具有灭火时间短,环境毒性低,适合缺水地区和易于长期存储等优点,因此粉基灭火介质的研究得到了各国研究者的重视。在众多哈龙灭火介质替代技术研究中,优化介质组成、筛选和设计更好的灭火介质释放方式、探究灭火介质和火焰之间相互作用机制、扩大灭火介质的应用范围等一直都是研究的重点。为了发展新型粉基灭火技术,本文首先在经过分析现有粉基介质的优缺点基础上,提出了粉基介质筛选、复配、细化的三步路线。通过细化、复配等手段,筛选出七种粉基灭火介质。针对影响粉基介质灭火的关键因素,重点对粉基介质的微观结构、X射线元素分析、热重及红外光谱等物理化学性质进行了详细测试。测试结果发现:无论是购置的纳米氢氧化镁粉基介质,还是细化后的粉体1号和2号介质以及K-powder等粉基介质的微观结构、光谱性质、热分解性能、表面性质等均与未细化的粒径较大的普通干粉粒子有明显区别。同时综合测试结果证明K-powder中KHCO₃已和无机及有机改性剂有效复合,形成微米级的细小颗粒。论文接着通过建立不同尺度的实验装置,经过多种工况的实验研究,比较了不同粉基介质的灭火性能,实验发现随着粉基介质粒径的减小,其灭火性能逐渐提高。同时不同的喷粉高度、压力、出粉方式均会影响粉基抑制火焰的时间和降低温度的效率。随后,本文在分析比较多种简单火焰实验装置的基础上,选择同轴流动CupBurner装置作为研究粉基灭火介质与扩散火焰相互作用过程的实验平台。依据Cup Burner装置的设计思想和输运固体粉基的要求,分别构建了Cup Burner实验台、输粉装置和测量设备,组成了小尺度粉基介质与扩散火焰相互作用的实验装置,并对各个组成部分的设计进行了详细的介绍。在此基础上对由本文CupBurner装置产生的甲烷/空气扩散火焰特性开展了详细的实验研究。实验结果发现通过流化床输粉装置可以观察Cup Burner中,火焰随着粉基介质输运量的增加而出现失稳、变色、以致最后熄灭的动态过程。通过观察发现:扩散火焰结构对粉基介质抑制的性能影响显著。Cup Burner装置中火焰熄灭过程属于典型的动态吹熄过程。因此,实际灭火时采取合适的方法（如化学抑制、改变粉基介质喷射方式等）破坏火焰根部的预混燃烧条件是扑灭火灾最有效的途径。此外还在CupBurner装置中测量了不同粉基介质的灭火浓度,实验结果表明本文中合成复配细化得到K-powder及细化粉体2号的灭火浓度均已达到或超过普通BC干粉,且灭火浓度要大大高于其他传统灭火将介质。通过粉基介质作用前后火焰发射光谱图比较分析,证实加入粉基灭火介质后,甲烷燃烧链反应自由基得到了消耗,同时出现了灭火介质独有的含K,Na等原子自由基的特征峰。在接下来的论文章节中,通过引入Damkohler数（Dn）,对火焰的熄灭进行了理论分析。分析指出粉基介质主要是通过热机制（冷却气相火焰）以及均相、异相化学机制来实现火焰抑制的。由于化学成分组成各异,导致粉基介质的热分解温度、热分解吸热、热分解产物都各不相同,因此不同组分的粉基介质的热机制也不尽相同。随后结合网格淬熄理论和颗粒粒径在火焰中变化公式对粉基颗粒在火焰区的运动以及粒径对灭火机制的影响等进行了详细阐述。由于与普通BC干粉相比,经过细化的粉基颗粒单个粒径更小,分布间隙更加致密,在实际抑制火焰时,小粒径的粉基介质能够形成更加致密的颗粒“云团”网格,单位体积“云团”内能够容纳更多发挥“冷壁”吸热机制及化学抑制机制的颗粒,从而提高了灭火性能。同时由于粒径较小的粉基介质,在火焰区的气化以及分解时间明显短于大粒径颗粒,在相同的火焰温度区时,小粒径颗粒拥有较短的分解时间,更易于发挥其化学抑制作用。最后,对粉基介质灭火系统的设计及其在超高层建筑火灾防治中的应用提出了建议:由于超高层建筑有着不同的类型和用途,粉基介质的应用应该针对不同建筑中的典型功能区和建筑结构,充分发挥粉基介质灭火高效,输送方法多样的优点,将清洁、高效、无毒的超细粉基灭火技术应用于超高层建筑火灾的防护,并推动相关理论和实验研究的开展。更多还原

【Abstract】 As one of the most useful fire suppression agents,traditional dry powder has been applied in portable fire extinguishers,fire suppression equipment and commercial fire suppression system in the past fifty years.When the production of Class I ozone depleting substances（ODS）,such as Halon 1301,began to stop after adoption of the Montreal Protocol,powderbased fire suppression agents are considered as good alternatives because of their environmental compatibility,fast fire extinguishment and low cost.Among the proposed Halon replacements and alternatives,more attention should be devoted to optimizating the agents formulation, selecting and designing of the distribution ways.In order to develop the powderbased fire suppression technology,a method for powder screening,compounding and superfining was proposed in this paper.Seven types of powderbased agents were prepared.The microcosmic structure of the powders was observed by scanning electron microscope（SEM）.Thermal Gravity Analysis（TGA）,Fourier transform infrared（FTIR）spectra of KBr wafers and X-ray diffraction spectra（XRD）techniques were used to analyze the thermal behavior and spectra characters of all kinds of powder.By analyzing the results,it can be concluded that XRD pattern of K-powder confirmed the formation of organic mineral complex during sample preparation.The FTIR spectra confirm that surface treatment agents and organic groups were present in the K-powder,which was beneficial to fluxion and surface property of fire extinguishing powders.The microstructure and surface properties were very distinct between the powder after superfiing and normal BC powders.And then,we built up a laboratory-scale immovable fire suppression system.In this system,seven kinds of powder agents including normal ammonium phosphate dry powder,sodium bicarbonate dry powder and superfine and surface treatment powderbased agents were test.The relationship between the characters of the powders and their effectiveness on fire suppression were studied.The fire extinguishing time and temperature changes were recorded when changing powder types,particle sizes, working pressures and spraying direction.Results showed that there was a significant impact on fire suppression effectiveness when the particle size is decreased.The working pressure also influences the fire suppression effectiveness.By analyzing the results of the research,it is concluded that the pressure,the particle size of the powder and microcosmic structure of powder surface mainly determine the capability of the powder to extinguish the fire.In the following part,the interaction between a small-scale diffusion flame and powder agents was studied.In this part,simple flame apparatuses widely used in the combustion research were firstly reviewed.The cup burner apparatus was finally selected considering its flame structure comparability.Experiments were conducted to explore the CH₄/air flame characteristics in the Cup Burner,which provided the base for further experiments.Interaction of CH₄/air diffusion flames with powder agents were then investigated in details.We observed the dynamic process of the flame instability,color changing and extinguishing when the powder loading mass was increased.The diffusion Cup Burner flame structure was considered as the "worst case" for fire suppression.As the powder concentration was increased to the suppression limit,the flame base became weaker and could not come back from the innermost position,thereby drifting upward to blow off.The mass-based concentrations of powders required to extinguish flame were measured in the cup burner apparatus and compared with data in other references.A comparison of the agents showed that on average,the superfine BC powder and K-powder had reached or exceeded the effectiveness of normal BC powder on a mass basis.The flame atomic emission spectrometry changes before and after powder loading confirmed that the free radicals in methane combustion chain reactions were scavenged,the specific spectras of potassium and sodium radicals peaks appeared.The Damkohler number was introduced to discuss the fire suppression.The different means to extinguish the fire can be unified as the influences to the critical extinguishing Damkohler number.The mechanisms of fire suppressing powders were considered in two parts:thermal mechanism and chemical mechanism（including both homogeneous（gas phase）and heterogeneous（surface）chemistry）.The particle size effects and movements of powders in the flame were discussed based on the "grid thermal death" and flame quenching theory.Mass powder particles can act as a wall or grid effects to extinguish fire.Powder cloud is taken as a three-dimensional grid "put" on a flame by researchers.The mechanism of flame suppression consists of fast thermal destruction（or recombination）of FFRs due to their collision with a surface of particle grid elements.The three-dimensional powder particles become an "inert wall" which absorbs part of FFRs energy.Then,it is obvious that what is called "grid" size or powder particles distance between each other becomes the key factor to fire extinguishing.At last,suggestions were given for applications of powders in supertall buildings. Generating non-toxicity and clean superfine powder which are high fire extinguishing efficacy will extend the application of these fire suppressing agents.More theoretical and experimental investigations should be carried out.更多还原