焖烧粉尘层扬起时的着火及火焰传播机制研究

Dust explosion is one of the major accidents in the process industries and coal mines. The latent nature of smoldering agglomerate makes it main inducement of dust explosion. Base on the findings funded by National Science Foundation for younger researchers, the aim of this project is to study ignition and flame propagation of dust clouds from dispersed smoldering dust layer, by taking characteristics of smouldering agglomerate and properties of pre-heated dust samples into consideration. The experimental specimens are the powders with various properties, and are commonly used and currently produced in industries, such as magnesium powers, coal dust and corn starch. The distribution of dust concentration- temperature of dust clouds located at the active window of modified Hartmann tube will be measured synchronously by high - speed digital camera and infrared imaging devices with the pre-trigger and laser light scattering technology. The effects of related parameters (e.g. smoldering intensity, dust property) on the change process in temperature distribution of ignited dust cloud by smoldering agglomerate and its neighboring un-ignited ones will be obtained. The theoretical models for ignition and flame propagations of dust clouds from dispersed smoldering dust layer will be developed and validated with experimental results, which will provide an excellent resolution and theoretic foundation for preventing and protecting dust explosion effectively.

粉尘爆炸是生产领域常见的重大工业事故类型之一。焖烧火源的隐蔽性使其成为粉尘爆炸发生的一个主要诱因。本课题拟在青年基金项目粉尘层焖烧研究的基础上，从层内优先着火点处的焖烧团块特征及预热粉体物性入手，采用高速摄像及红外探测预触发和光散射等技术，跟踪改进Hartmann管活动窗口处粉尘云的浓度-温度分布，研究热板加热条件下不同物性工业常用粉尘层（镁粉、煤粉、玉米淀粉）焖烧扬起时的着火及火焰传播机制。以期揭示焖烧火源诱发粉尘云着火的温度突变过程和由此引发的临近云团的温度突变次序与有关参数（焖烧程度、粉体物性等）之间的关系，建立并验证焖烧粉尘层意外扬起时着火发生、发展的理论模型，为粉尘爆炸事故的有效防控提供新思路和理论依据。

为获得可燃堆积粉尘的焖烧着火特性及扬起后引发粉尘云着火爆炸的机制，本项目以钛粉、煤粉、玉米淀粉、PMMA粉、木粉、铝粉等5类6种可燃粉尘为实验介质，以电火花、高温表面、高温氮化硅、高温钢球等为焖烧着火触发条件，在堆放倾角、粉末惰化、通风等耦合条件下获得了可燃粉尘的焖烧着火形式、敏感着火条件及点火起爆能力，包括高温表面、高温钢球、高温氮化硅等诱发的层内焖烧着火；高温氮化硅及电火花诱发的层表面着火；高温表面及电火花诱发的云着火；焖烧团块扬起时诱发的云着火；表面燃烧火焰扬起时诱发的云着火。研究结果表明：层内焖烧团块引燃粉尘云的能力与粉体物性、粉尘云最小点火能量密切相关，钛粉、PMMA粉的阴燃颗粒可引爆相应的钛粉尘云和PMMA粉尘云，但煤粉、玉米淀粉、木粉的焖烧团块扬起后颗粒温度很低，未能引爆其各自粉尘云，煤粉、玉米淀粉、木粉的明火则可以引爆粉尘云。层表面着火引发明焰燃烧是比层内阴燃焖烧更具有导致粉尘爆炸的危险性。与层内焖烧机制不同，层表面着火换热机制除层内热传导外，还存在对流和辐射等能量传递形式。热传导、对流和辐射换热在层表面着火、火蔓延能量传递中的主导地位受粉尘自身物性的影响。大粒径的金属粉尘以热传导为主，而纳米金属、有机粉尘则以对流换热为主要的能量传递机制。层表面着火及火蔓延速率除与粉尘物性有关外，表面倾角、通风条件等均可加剧层火灾，使用粉末惰化技术可有效抑制层火灾。引发层表面着火所需的点火源能量通常大于云着火的点火能量，但10J电火花、800℃恒温氮化硅棒已足够引燃大多数可燃粉尘层。上述研究成果揭示了焖烧/明火等层着火作为点火源导致粉尘爆炸发生发展的机理，为有效防控粉尘爆炸事故提供了新线索。研究内容已在《Journal of hazardous materials》等国内外高水平学术刊物上发表论文9篇，其中SCI检索6篇，EI检索3篇；出版国家科学技术学术著作出版基金资助的学术专著1部；申报国家发明专利5项；获省市级科研奖励3项、国家重点研发计划项目2项。