【作者】 许红利；

【导师】 张和平； 王喜世；

【作者基本信息】 中国科学技术大学 ， 安全科学与工程， 2013， 博士

【摘要】 煤炭是我国重要的工业能源之一,为我国的经济发展做出了重要贡献。但是，煤矿频发的瓦斯煤尘爆炸事故,极大的影响了我国煤炭产业的安全高效运营和健康发展,也使得煤矿安全成为我国最受关注的安全问题之一。煤矿井下是一个瓦斯和煤尘共存体系,煤矿瓦斯爆炸事故所造成的严重后果很多情况下是瓦斯爆炸的冲击波扬起了沉积的煤尘,形成了危险性更大的瓦斯、煤尘混和爆炸。细水雾作为一种绿色高效灭火剂,被广泛应用于建筑、工业等许多场所。目前大部分研究者认为粒径小于20μm的细水雾可以称为超细水雾,超细水雾具有能够扑灭具有障碍物的火灾和隐蔽火灾的优点。关于超细水雾灭火机理的研究已经有很多学者在开展,但是目前缺少关于超细水雾抑制爆炸的研究资料。并且超细水雾雾滴粒径均匀、悬浮性好、雾通量控制方便,雾滴速度小,可有效的避免雾滴流场对抑爆的影响等。因此,开展超细水雾抑制瓦斯煤尘爆炸特性的研究,具有重要的科学意义和实用价值。本文通过自行研制的小尺度模拟实验台开展研究了不同煤尘浓度、煤尘粒径、瓦斯浓度、混合气体初始压力下的瓦斯煤尘混合爆炸的最大爆炸压力和压力上升速率、爆炸火焰温度等特征参数,为超细水雾抑爆试验做参考和对比,结果发现：混合爆炸的最大爆炸压力、压力上升速率均随着煤尘浓度的增加先增加后减小,存在一个煤尘浓度使得最大爆炸压力和压力上升速率均达到最大值,偏离这个煤尘浓度值,最大爆炸压力和压力上升速率将逐渐减小：同时,火焰温度、爆炸压力、压力上升速率均随着煤尘粒径的增大而减小,说明煤尘粒径越大,比表面积越小,和氧气反应越缓慢,使得混合爆炸的强度变小；另外,随着瓦斯浓度接近于瓦斯空气反应的化学当量比浓度,瓦斯燃烧放出的热量逐渐增加,引起爆炸火焰温度、最大爆炸压力、压力上升速率逐渐上升。为了研究超细水雾对混合爆炸抑制作用的规律和机理,本文开展了超细水雾抑制瓦斯煤尘混合爆炸以及煤尘浓度和煤尘粒径对细水雾抑爆效率影响的小尺度实验,结果发现：在一定的条件下,爆炸压力、压力上升速率都随着超细水雾雾通量的增大而减小,超细水雾的吸热作用,稀释氧气作用以及对煤尘粒子的吸附作用,使混合爆炸的发展受到抑制；同时超细水雾完全抑爆的临界水雾量随着煤尘浓度和煤尘粒径的增加而减少。由于气体湍流度的强度对混合爆炸强度的(?)响极大,为了最大程度的减少初始气流湍流度对爆炸的影响,将气体和煤尘充进爆炸管后,延迟5s才开始点火。结果发现点火延迟时间对超细水雾抑爆效果有很非常明显的影响,可以更有效的抑制瓦斯煤尘混合爆炸根据矿井巷道内存在障碍物的情况,本文实验考虑设计了四种类型的障碍物。通过小尺寸实验研究了障碍物条件下的超细水雾抑制瓦斯煤尘混合爆炸特征参数,并讨论了障碍物和煤尘粒径对混合爆炸最大爆炸压力、压力上升速率、爆燃指数和临界水雾量的影响,同时也比较了施加细水雾前后最大爆炸压力的变化,发现障碍物的形状、数量和位置均对混合爆炸的强度有很大的影响。在阻塞率相同的情况下,边缘阻塞型障碍物比中心阻塞型障碍物能引起更强的湍流效果导致更大的爆炸压力和压力上升速率。由于超细水雾的加入对气体湍流度有强化作用,和障碍物的强化作用叠加到一起,所以当超细水雾雾量小于某一范围时,混合爆炸出现了强化,只有当超细水雾雾旱增大到一定程度后,混合爆炸的爆炸压力和压力上升速率才逐渐减小。为了直观的观察混合爆炸火焰传播的动态过程,本文采用高速摄影机拍摄了爆炸的动态过程,分析发现,在未添加超细水雾之前,火焰前锋有非常明显的脉动,火焰呈不规则的卷曲状,气体和粉尘充分燃烧爆炸后的火焰颜色呈明亮的白色,随着燃烧爆炸过程的进行,在爆炸过程快结束的时候,火焰变成橘黄色。加入超细水雾之后,火焰前锋呈近似半圆的光滑弧形,脉动现象几乎消失,爆炸火焰颜色呈橘黄色。同时,障碍物的加入使得爆炸火焰的湍流强度明显增强,火焰经过障碍物时被压缩,脉运非常明显,并且在障碍物上方出现了很多湍流涡团,说明障碍物的存在确实使混合爆炸的火焰湍流度加强,爆炸反应加快,强化了整个爆炸过程。添加超细水雾后,火焰前锋变得平滑,火焰颜色更加明亮,从橘黄色变成明亮的白色,在障碍物附近可以看到明显的橘黄色涡团。Ⅲ型障碍物起火焰的湍流效应是从下面的一个障碍物中心上一个障碍物边缘扩展,。而Ⅳ型障碍物引起混合爆炸火焰湍流效应是从下面的一个障碍物整体边缘同时向上一个障碍物扩展,在两个障碍物之间呈紊乱的湍流结构,验证边缘阻塞型障碍物和中心阻塞型碍物对混合爆炸火焰传播影响机制的不同。同时,本文还采用了La Vision激光流场诊断系统对障碍物和超细水雾条件下的混合爆炸流场进行了测量,进一步验证了上述结果的准确性,也更进一步的提示了障碍物和超细水雾对混合爆炸的影响机理。更多还原

【Abstract】 China is one of the largest coal production countries in the world, and the coal has made significant contribution to China’s economic development. However, frequent safety accidents in the coal mine make the coal mine safety becoming the focus of current security issues in China and the gas explosion accidents has greatly influence the coal mine safety and coal production in China. As is known to all, the coal mine is a coexistence system of methane and coal dust, then the gas explosion shock wave tends to induce coal dust explosion, forming mixed gas and coal dust explosion. As a clean and high efficient fire extinguishing agent, water mist is widely used in construction, industrial and many other fields as fire prevention measure. Besides that researchers generally considered that water mist with particle size of less than20μm can extinguish obstacles fires and the hidden fire. Therefore, taking into account the particularity of coal mine and explosion, water mist has good applicability in coal mine. However, there is hardly any previous research in this area. Therefore, carrying out the water mist suppression on gas and coal dust explosion has important scientific significance.In this paper, self-developed small-scale experiment platform is applied to carry out experiments on hybrid explosion with different coal dust concentration, coal dust particle size, methane concentration, and initial pressure of methane-air mixture. And the characteristic parameters of explosion such as the maximum explosion pressure, the rate of explosion pressure rise, the explosion flame temperature and so on are obtained. The results show that:the maximum explosion pressure and explosion pressure rise rate of the hybrid explosion increase with the increase of the coal dust concentration and then decrease, there exists in an optimal concentration of coal dust where the maximum explosion pressure and the rate of explosion pressure rise reach the summit. When the coal dust concentration deviates from the optimal value, the maximum explosion pressure and the rate of explosion pressure rise will reduce. Simultaneously, the explosion flame temperature, explosion pressure and rate of explosion pressure rise decrease with the increase of particle size of coal dust, this because the larger the coal dust particle size is, the smaller the specific surface area is and then the strength of the explosion is smaller. At the same time, when methane concentration gets close to the optimum reaction concentration, the reaction and combustion become fierce, and more heat is released. causing the explosion flame temperature, the maximum explosion pressure and the rate of explosion pressure ris become higher. In addition, the turbulence effect caused by initial pressure of the mixed gas could accelerate the reaction and strengthen the explosion.In order to reveal the regularity and mechanism of inhibition on hybrid explosion with water mist, the inhibition effect on hybrid explosion with water mist is carried out on small-scale experimental platform and different coal dust concentration, coal dust particle size and water mist volume flux are considered. The results show that: the explosion pressure and rate of explosion pressure rise decrease with the increas of the volume flux of ultra-fine water mist, this because the endothermic effect. pxygen dilution effect and soot adsorption effect of ultra-fine mist suppress the hybrid explosion. The critical volume flux of ultra fine water mist reduces with the increas of the coal dust concentration and coal dust particle size. In addition, in order to minimize the initial airflow turbulence influence on explosion, ignition delays5s after the coal dust is dispersed into explosion vessel, founding that delaying for a period of time to ignition can be more effective to inhibit the hybrid explosion.According to the coal mine roadway with obstacles, four types of obstacles are designed in this paper and the experiment on hybrid explosion with obstacles and ultra fine water mist is carried out by changing the type of obstacles, coal dust particle size and volume flux of ultra-fine water mist. The maximum explosion pressure, rate of explosion pressure rise, deflagration index and the critical volume flux of water mist are obtained, the results show that the shape, the quantity and location of the obstacles have great influence on the strength of the hybrid explosion. Meanwhile, under the same blocking rate, the obstacles with sharp edges and corners can cause stronger turbulence effect than the obstacles with smooth surface, leading to the rise of explosion pressure and the rate of pressure rise. The turbulence reinforcement to gas flow caused by water mist and obstacles superpose together. When the volume flux of water mist is less than a certain range, the hybrid explosion is intensified, until the volume flux of water mist increases to a certain extent, and then the inhibition effect of water mist is stronger than the reinforcement effect, the explosion pressure and the rate of pressure rise gradually decrease.For the sake of intuitive observation of explosion flame propagation process, a high-speed camera is adopted to shoot the explosion dynamic process. It finds that before adding ultra-fine water mist, the pulsation of the flame front is obvious, and the flame structure curls irregularly with bright white or orange color; while after ultra-fine water mist is applied, the flame front is smooth curved as semicircle, pulsation almost disappears and the flame color becomes orange. In addition, the explosion flame turbulence intensity is significantly enhanced by obstacles, the flame is compressed and pulsates obvious around the obstacle, and lots of turbulence vortexes appear around the obstacle, indicating that the existence of obstacle make the explosion more reinforcement. In addition, the explosion flame turbulence effects caused by type Ⅲ obstacles extends from the center of the lower obstacles to the upper obstacle, forming a V-shaped structure of turbulence between two obstacles. Meanwhile, the explosion flame turbulence effect caused by type Ⅳ obstacle extends as disorder turbulence structure between the two obstacles. This result verifies that the explosion reinforcement mechanism of type Ⅲ and type IV obstacle is different.The explosion flow field under the condition of obstacles and ultra fine water mist is measured through La Vision laser diagnostic system, further validating the accuracy of the results, and revealing the influence mechanism of obstacles and ultra fine water mist on mixture explosion.更多还原