The dust lifting mechanism and dust flame propagation modelling

在地下煤矿或硫化铁作业以及许多工业设施中，可燃粉尘层堆积在地板、水平台阶、机械表面和假天花板上方。通过微弱的爆炸或压力波，尘埃层可以很容易地上升为悬浮状态。一些典型的原因包括地下矿井的甲烷气体小爆炸、硫化矿井作业中炸药的冲击波、清洁作业、加工厂窗户或门打开引起的强风，或压缩气体系统的泄漏。一旦产生尘埃云，总是有很高的可能性着火，导致闪火或不断传播的尘埃爆炸。此外，如果尘埃云是在包含障碍物的受限空间内形成的，传播的尘埃火焰将加速，可能导致尘埃到爆震的转变。因此，本研究计划的重点是了解和模拟除尘过程。总体长期目标是更好地预测粉尘爆炸危险，从而制定防止其发生或减轻其后果的战略。该实验计划将研究扬尘机理与颗粒的性质(密度、类型和形状)、粉尘层厚度、颗粒大小分布、冲击波传播速度和障碍物的存在有关。一些实验将在标准的20-L粉尘爆炸室中进行，以更好地了解目前尚不清楚的非标准粉尘(如低密度纤维素纤维)的分散情况。此外，在专门建造的激波管中进行的实验将允许使用高速纹影摄影来可视化扬尘过程。所有这些实验将使开发一个合适的模型来描述粉尘的升降、扩散和混合过程，并在粉尘爆炸模拟程序中实施。该模拟代码将允许从各种粉尘的标准测试中预测爆炸特性，以及预测工艺设备和设施内的粉尘爆炸危险。

In underground coal mining or iron sulfide operations as well as many industrial facilities, combustible dust layers accumulate on floors, horizontal ledges, surfaces of machinery, and above false ceilings. Dust layers can easily be lifted into suspension by weak explosions or pressure waves. Some examples of typical causes are a small methane gas explosion in an underground mine, the blast wave from an explosive charge in a sulfide mine operation, cleaning operations, a strong gust of wind because of an open window or door in a processing plant, or a leak from a compressed gas system. Once a dust cloud is created, there is always a high probability of ignition leading to a flash fire or a propagating dust explosion. Furthermore, if the dust cloud is formed within a confined space that contains obstacles, the propagating dust flame will accelerate, possibly leading to a dust-to-detonation transition. Therefore, this research program focuses on understanding and modelling the dust lifting process. The overall long-term objective is to better predict the dust explosion hazard and thereby develop strategies to prevent them from occurring or to mitigate their consequences. The experimental program will investigate the mechanism of dust lifting as a function of the nature of the particles (density, type and shape), thickness of the dust layer, particle size distribution; shock wave propagation velocity; and presence of obstacles. Some experiments will be done in a standard 20-L dust explosion chamber to better understand the dispersion of non-standard dusts (e.g. low density cellulosic fibers) which are currently not well-understood. Additionally, experiments in a purpose built shock tube will allow high-speed Schlieren photography for visualization of the dust lifting process. All these experiments will enable development of a suitable model to describe the dust lifting, dispersion, and mixing process for implementation in a Dust Explosion Simulation Code. This simulation code will allow prediction of explosibility characteristics from standard testing of various dusts as well as prediction of the dust explosion hazard within process equipment and facilities.