【作者】 谢正文；

【导师】 吴超；

【作者基本信息】 中南大学 ， 安全技术及工程， 2011， 博士

【摘要】 随着我国经济的高速发展和城市规模的不断扩大,餐饮服务业得到了迅速的发展,酒店、宾馆、食堂厨房烟道火灾屡屡出现。由于大型餐饮业的烟道火灾不仅可能造成巨大的财产损失和人员伤亡,而且会产生极坏的社会影响,研究此类火灾机理并开发能够及时有效地控制此类火灾的发生和蔓延的装备具有非常重要意义。本文从餐饮业油烟道火灾原因出发,研究油烟道油垢燃烧特性作为切入点,采用现场分析验证及实验和数值模拟的研究方法,重点对油垢的燃烧特性、油烟道火灾蔓延规律、细水雾灭火特性分析、细水雾灭火系统研制等进行了比较深入的分析研究。论文主要研究工作和成果有：(1)在统计了部分油烟道火灾案例和实地调查的基础上,采用模糊事件树分析方法得到造成油烟道火灾的主要原因是油烟道内油垢没有及时清除；从油烟道可燃物——油垢物理特性出发,自行研制了满足油垢燃烧特性实验研究的较大物量(约15g)进样的热重分析装置,并通过引入自适应小波去噪分析方法,消除实验装置带来的误差,满足热重分析需要。(2)通过采用热重分析和傅立叶红外光谱分析相结合的方法,分析油烟道油垢燃烧特性。研究分析结果表明,油垢热重分析在空气气氛下的失重过程分五步进行,第一步失重发生在室温到105℃,由水分的蒸发引起；第二步失重发生在105～220℃之间,失重量大约占试样初始总重量的10%左右,这部分失重是由于低沸点化合物分解引起的；第三步失重过程自200℃左右开始发生,并在300～400℃之间很快地加速,最大失重速率温度在370℃附近,失重份额近40%,此过程主要是不饱和烃燃尽；第四步失重过程紧接着第三步失重,直到520℃左右结束,失重份额近15%左右,主要是羰基酯燃尽；第五步失重过程紧接着第四步失重,直到600℃左右结束,最大失重速率温度在560℃附近,此阶段饱和烃燃尽。试样的总体失重达到了90%左右。由于第一阶段失重由于水分蒸发引起,不属于热重分析范畴,根据积分动力学分析方法对后四阶段失重进行分析,提出了四阶段“一级+三维扩散模型”,油垢燃烧特性的总体表现失重过程可以是看作四种不同组分的物质在不同温度区间内发生的失重过程。(3)建立了一个实尺寸单管油烟道油垢燃烧物理模型。通过统计学正交设计方法建立工况组合,模拟计算得到各个时刻风管内气流温度、流速等变化及燃烧发展情况。为客观考查和比较各工况火灾发生的影响程度,准确描述火灾发生的概率,引入了“着火温度概率函数PFT”的综合考核指标,并进行了影响因素分析。结果表明,单管油烟道火灾的“因素主次”一致为：风速对火灾影响最大,其次为油垢厚度和油烟道壁面厚度,相比较油烟道断面尺寸的影响最小。模拟计算结果发现油烟道直角弯管的拐弯处火灾时温度最高,所以在油烟道设计时油烟道的连接应采用弯头连接形式,一方面可以有效的防止油垢在拐弯处过度沉积,另一方面可以降低火灾时直角弯头局部温度。(4)建立了一个实尺寸单管油烟道系统灭火实验物理模型。通过统计学正交设计方法建立工况组合,得到相应的温度场和灭火时间数据。为客观考查和比较细水雾灭火的影响因素,首次提出了“灭火温度概率函数PMT”的综合考核指标,并进行了影响因素分析。结果表明,单管油烟道细水雾灭火的“因素主次”为：风速对灭火影响最大,其次为喷头个数、喷射角和细水雾压力,相比较细水雾粒径的影响最小。(5)通过自行搭建的全尺寸单管油烟道火灾实验平台,进行了常压水喷淋和不同特性细水雾喷淋灭火实验。通过实验结果发现,常压水喷淋灭火由于水滴较大受气流影响较小灭火效果比较好；由于存在较强的气流,细水雾雾滴不能达到火源区域,从而因无法完全覆盖灭火效果降低；对于小流量的细水雾灭火系统,在一定范围内改变雾滴的大小几乎不改变其灭火效果；细水雾喷雾压力对灭火效果的影响并不明显；增加喷头个数能明显增强细水雾灭火效果；含有氯化钠为添加剂的细水雾比纯水细水雾灭火效果更好。另外,油烟道发生火灾时应该在第一时间关闭风机、打开防火风门。(6)在油垢燃烧特性实验、FDS火灾模拟、细水雾灭火实验模拟和单管烟道火灾灭火实验的基础上,通过采用热电偶树的温度监测形式,采用细水雾灭火方式设计了火灾自动探测、火灾报警及自动喷淋的油烟道细水雾灭火系统。当烟道温度超过危险温度临界值时,控制系统发出报警,如果报警时间持续10s后烟道温度没下降,控制系统自动关闭风机,开启防火风门,启动细水雾灭火系统自动扑灭火灾。(7)在自行研制的油烟道细水雾灭火系统上进行灭火实验,实验证明,该系统能很好的扑灭油烟道火灾。油烟道内火灾持续时间越长油烟道内温度越高,油垢燃烧处于第三阶段燃烧反应剧烈,火灾扑灭难度越大,应在火灾初期尽早扑灭。采用基于熵权的模糊综合评价方法建立了油烟道细水雾自动灭火系统可靠性评价模型,选取了平均故障率、平均无故障工作时间、有效度、平均修复时间、维修费用率、可靠度、故障密度作为评价指标,可靠性评价结果显示该油烟道自动细水雾灭火系统可靠性等级为可靠级。更多还原

【Abstract】 With the development of the high energy equipment and high burning point cooking oil used in kitchen, the threatening of kitchen fire increasing greatly. The cooking fire not only brought huge economic losses and adverse social impact. It is very important to prevent fire taking place in the fog discharge pipe of cooking system. In order to reduce the cooking oil fire in fog discharge pipe substantially, it should research the combustion characteristic of cooking oil tar first and design the fitting fire alarm and extinguish system.On the basis of reviewing the previous papers in and aboard, the research methods combining the theoretical research, laboratory simulation, numerical analysis and field application were used to systematically and deeply analyze the fundamental theory, the spontaneous combustion characteristics of cooking oil tar, the fire spread in the pipe, the characteristics of the water mist, the research of water mist fire suppression system, The main work and achievements of the thesis are as follows:(1) On the basis of the fire cases in the fog discharge pipe and on-the-spot investigation, the fuzzy event tree is used to analysis the reasons of the fire. It is found out to be the cooking oil tar accumulated in pipe while it’s clean out not quick enough. According to the characteristic physical properties of cooking oil tar, a laboratory-scale thermobalance (Macro-TG) with sample loading of 15g is designed. Adaptive wavelet analysis method is used to eliminate the noise bring from the experiment, which proved to be useful for the thermogravimetric analysis.(2) Thermogravimetric and infrared spectrum analysis are used to investigation the spontaneous combustion characteristic of the cooking oil tar. Research results proved that all cooking oil tar samples subjected to experiments in air with different heating rate are found to give the same general shape for the TG-DTG curves, and the curves can be divided into five stages. The evaporation of sorbed water occurring in the temperature range of 80-105℃constitutes an approximately 10%mass loss for all the cooking oil tar samples. Following the water evaporation, the fist mass loss due to low boiling volatile compounds in the temperature range of 105-220℃. The second mass loss due to the decomposition and combustion reaction begins slowly and accelerates rapidly in the temperature range of 300-400℃, reached an overall mass loss of more than 65%. The third mass loss follows the second one and in the temperature range of 400-520℃. The last mass loss reached an overall mass loss of more than 90%and the mass loss terminated around 600℃. A simple kinetic description, named’First Order Reaction and Three-dimensional Diffusion Separate-stage Model (O1+D3)’model, is developed based on the experimental results and integral analysis method. The spontaneous combustion characteristics of cooking oil tar can be explained as four pseudo components decompose respectively at four separate temperature regions.(3) A model of the single fog discharge pipe of cooking is established and several cases are finished according to the orthogonal design, and the variances of temperature, velocities of the air flow and fire spread process are calculated. A parameter of PFT (Probability of Fire-happened Temperature) is imported for fire safety evaluation, and the factor analysis is taken finally for fog discharge system design. It is found from the result of calculation that the velocities is the main influencing factors, the cooking oil tar and the thickness of the pipe is subordination factors, the section of discharge pipe is the last. The highest temperature appeared in the right-angle of the pipe. The results indicate that bend tube can be used in the fog discharge pipe of cooking in the design, the deposition of the cooking oil tar and the temperature will be centralize decreased.(4) A model for fire suppression of cooking oil tar in the pipe has been set up, and the comprehensive properties of the fire and the temperature field in the pipe are simulated by the orthogonal design cases and comparative cases in the full range analysis. A new parameter of PMT (Probability of Fire-suppression Temperature) is put forwarded for the first time, and the factor analysis is taken finally for fire suppression evaluation. It is found from the result of calculation that the velocities is the main influencing factors, the number of nozzles, the spraying angle and the spraying pressure are subordination factors, the diameter of mist is the last. (5) A new experimental platform of actual-dimension single fog discharge pipe has been built in the lab and the atmospheric pressure spray pattern and different characteristic of the water mist pattern are used to evaluate the suppression outcome. The experiment results show that the fire extinguishing effect of atmospheric pressure spray pattern is better than water mist. The effect of fire controlling is bad while the wind speed over high as the water mist not able to reach the fire area. The fire extinguishing effect can not be increased while the water mist size changed as the small water flow. The effect changed magnificent which the increasing number of nozzles and the additive of NaCl added, while the spraying pressure increasing not able to change the effect.(6) A laboratory scale cooking oil fire suppression system is designed according to the thermogravimetric analysis, the FDS simulation results, the fire extinguishing experiment in single fog discharge pipe. Thermocouple tree used for temperature detection, water mist used as fire suppression pattern, a two hearth system for fog discharge pipe of cooking has been built, fire automatic detecting, fire automatic alarming, automatic spraying are achieved. Principles of automatic control incarnate in the entire system, the loudspeakers sending out the warning according to thermocouple tree while arriving critical value, if the temperature lasting for 10 seconds turn off fan, air-door closed, water mist suppression system opening and fire can be extinguished in less than 12 seconds.(7) Fire extinguishing results on laboratory system indicates that the suppression system can protect the fog discharge system well. Experimental results demonstrated that the temperature grows to a high lever with time changing, while the cooking oil tar combustion reaction come to the third stage, it’s hard to put out. In view of the existing fuzziness and randomness in reliability comprehensive evaluation for the suppression system, a two-stayed fuzzy assessment model for the evaluation of the petrochemical production unit is established by using the theory of fuzzy mathematics. Average fault ratios, mean time between failures, effectiveness, mean-time-to-repair, and maintenance cost rate, spatial variability and fault density are used as evaluation index system. It is found from the result of evaluation that the variability of the water mist suppression system is reliability step.更多还原