炽热火花引发倾斜堆积粉尘表层着火蔓延的机制

Layer fire is a common ignition source of dust explosion. In recent years, layer fires were not sufficiently taken into consideration in which layer surface particles were ignited directly by ignition sources. As a result, the mechanism of ignition and flame propagation of inclined dust deposits was not clarified. In this project, a self built layer fire platform would employ electric and non-electric sparks as ignition sources because such overheated sparks contributed to a lot of dust explosion accidents. A serial of measuring and testing techniques such as high-speed image processing were used to determine energy characteristics of the overheated sparks, and then to ensure surface layer fire hazards. Layer fire hazards could be characterized by surface heat flux, flame spreading velocity and so on. It could be coupling influenced by inclined angles, dust characteristics and energy characteristics of ignition sources. Based on particle reactions, surface heat flux and energy characteristics of ignition source, a theoretical model would be established to clarify ignition mechanism and flame propagation of dust deposits with sample orientations. It could provide another possible method to prevent layer fires and the resulting dust explosion.

层火灾是粉尘爆炸的常见点火源。现有针对层火灾的研究，对点火源直接作用于堆积粉尘表层的工况关注不够，未能揭示表层倾斜该常见工况下的层着火蔓延机制。本项目拟搭建以高频致灾的电气与非电气炽热火花为点火源的层火灾实验平台，利用高速光学图像等先进测试技术，量化表征炽热火花能量特性，获取表层倾角、粉尘物性、火源能量特性等多因素对表层热流、火蔓延速率等层火灾特性的耦合影响。基于颗粒反应相、炽热火花能量源项和热流项等构建包含倾角的多参数理论模型，揭示倾斜工况下堆积粉尘表层的着火蔓延机制，为防控表层火灾及其引发的粉尘爆炸事故提供新思路。

为获得炽热火花引发倾斜堆积粉尘表层着火蔓延的机制，本项目以金属加工、食品加工、塑料加工等典型工业可燃粉尘为实验介质，以电气火花、非电气火花、高温氮化硅等为点火源，采用自制表层火蔓延实验平台，研究获得了粉尘物性、炽热火花特性、倾角、惰性介质等因素对表层颗粒火焰形态、蔓延速率、表层热流等层火灾特性参数的影响机制。研究结果表明堆积粉尘表层着火蔓延行为与上述因素密切相关。粉尘物性参数显著影响粉尘表层火蔓延行为，镁粉、钛粉和纤维粉尘的火蔓延速率明显高于其他常见工业粉尘（PMMA、木粉等）。随着粉尘粒径的减小，铁粉和钛粉的火蔓延速率显著增加的原因是大粒径的金属粉尘以热传导为主，而纳米金属、有机粉尘则的能量传递机制以对流换热为主。堆积倾角对微米尺度的金属粉尘火蔓延速率影响较小，而对纳米尺度的金属粉尘火蔓延速率影响较大；对于蔓延过程有明火出现的粉尘层，倾角对蔓延速率的影响较大。增加倾角可加剧熔化粉尘层的火蔓延。相对于玉米淀粉等粉尘，非电气火花（摩擦火花）更易引燃孔隙率大的棉等纤维粉尘层。与引燃微米钛粉尘云所需的点火能量相比，引燃钛粉尘层发生火蔓延需要更高的电气火花能量。此外，掺混惰性介质是防控粉尘层火灾蔓延的一种手段。常见粉末惰化剂（碳酸钙、碳酸氢钠、二氧化硅和氯化钠）虽在抑制粉尘云爆炸方面具有明显作用，当将其用做抑制粉尘层火灾的粉末惰性介质时却呈现出加剧粉尘层火灾的作用。探索研究结果表明膨胀石墨是一种有潜力的抑制层火灾的惰性介质。上述研究成果揭示了倾斜工况下粉尘表层着火蔓延的机制及影响因素，为防控粉尘层表层火灾事故提供新思路。研究内容已在《Journal of hazardous materials》等学术刊物上发表论文24篇，其中SCI检索19篇；出版学术专著2部；授权国家发明专利5 项；获国家科技进步二等奖、中国职业安全健康协会科学技术一等奖各1项，编制地方标准2部。

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