【作者】 孙金鹏；

【导师】 王树刚；

【作者基本信息】 大连理工大学 ， 供热、供燃气、通风及空调工程， 2008， 硕士

【摘要】 矿井火灾和热害问题一直是煤矿生产的主要威胁,尽管国内外许多学者在防治自燃的发生方面进行了大量的研究,但是遗煤氧化散热造成的火灾事故仍时有发生。在采动影响下,冒落岩体和遗煤在地下形成的多孔松散采空区是自燃发生的重灾区。采空区与工作面之间不可避免地存在着漏风联系,采空区漏风是引起遗煤氧化,形成采空区煤炭自燃的重要原因。因此研究采动影响下采空区内漏风流场及温度场的分布规律,以此研究相应的通风策略,对于预防采空区自然发火,促进安全生产具有重要意义。基于多孔介质流体动力学研究的最新进展,本文采用数值模拟方法研究了采场内的风流流动和温度场分布规律。首先,采用容积平均理论详细推导了采场流动、传热和氧气浓度的数学模型。其中在流函数-涡量表示的动量方程中引入Brinkman-Forchheimer的扩展Darcy模型,来描述采空区内层流、过渡流和紊流共存的复杂流态;引入纯流体与多孔介质交界面保持属性连续的单区域处理方法,将工作面与采空区作为统一求解区域进行求解;在温度场方程中考虑了围岩和风流的热交换、采煤设备的放热及采空区内遗煤氧化反应产热等因素。此外,为了更准确地模拟采场流动换热状况,本文基于上覆岩层的沉降理论,建立了孔隙率和渗透率在采空区倾向和走向二维空间内连续不均匀分布的计算模型。最终采用控制容积法对控制方程组进行了离散,利用FORTRAN语言编制程序进行了求解;其次,利用实验室数据和典型采场工作面内实测数据对流动传热模型进行了二级验证,两者较好的吻合结果证明了模型的准确性;最后,针对所研究的采场计算了不同供风量下的采场温度场分布;同时针对不同孔隙率模型对采空区流场与温度场进行了数值模拟和实测对比。对典型U形采场流场温度场的模拟结果表明,采场漏风风流在采空区深度方向上,沿垂直于工作面煤壁的中心线呈现出非对称的分布规律,这个结果修正了以往模拟研究中得出的风流对称分布规律。这也造成了采空区进风巷附近的风流速度明显高于回风巷附近区域,但离工作面越远,漏风速度的差异越小,采空区深处已几乎没有区别;采空区前半段的等温线大致以进风巷为中心呈现环状分布,离工作面越远风流速度越微弱,氧化反应趋于停滞进入窒息区。工作面后半部附近的采空区内温度变化幅度非常大,将是遗煤自燃多发地带;工作面供风量越大,采空区内部氧化反应越强烈,整体温度状况越高,最高温度点随供风量的增大逐渐向回风巷方向移动;结果表明,与恒定孔隙率模型和分块模型相比,本文提出的冒落带孔隙率的二维连续非均匀分布模型更符合实际。更多还原

【Abstract】 Spontaneous combustion and thermal hazard in mining regions have long been risks for coal mine safety, although extensive investigations have been conducted by lots of researchers. Most spontaneous fires occur in gobs, which are in fact porous media composed by uncollected coal and collapsed rock fragments after underground excavation. Inevitable air leakage from working faces towards gob regions is a vital reason for coal oxidation and resulted spontaneous combustion. Therefore, investigation on airflow and temperature distribution amid underground mining, and corresponding ventilation strategies, can greatly aid preventing coal fires and promoting safe production.With new advances of thermo-fluid theories in porous media, this paper numerically investigates the airflow patterns and temperature distributions in both working-faces and gobs. Firstly, based on the volumetric average theory in porous media, this paper develops detailed numerical models for flow, heat transfer and oxygen concentration, by applying a vorticity-stream function approach. The Brinkman-Forchheimer-extended Darcy model is employed to describe the airflow patterns inside gobs, which are characterized by layer, transitional and turbulent flow patterns. A single-domain approach is employed to make properties continuously across the fluid/porous interface, thus working faces and gobs are incorporated into a set of unified models. The heat transfer model can take into account heat generation by equipments, heat exchange between rock stratum and airflow and heat generation by coal oxidation, etc. In addition, expressions for porosity and permeability as continuous and non-uniform distribution inside gobs are deducted according to the subsidence theory of overlying stratum. Infinite volume approach is applied for dispersion of governing equations, which are compiled and solved with FORTRAN language. Secondly, two-stage model validations with both experimental data from test rigs and in-situ measurement are accomplished. Satisfying results prove the accuracy of foregoing set of models. Finally, temperature distributions inside the gob are visualized and compared under different air flowrates. Different porosity distribution models are used as input to a simulator for thermo-fluid dynamics in a gob that models mine airflow, temperature and oxygen content distributions.Numerical predictions show an asymmetric airflow distribution in along with asymmetric temperature distribution in the gob. This results in larger airflow velocity in areas near the intake comparing with those near the return airway, but less obvious differences are observed deeper into the gob. In the gob, temperature distribution contour lines look like arcs centered by the intake airway. If the oxygen content in the air is not enough to sustain coal oxidation, temperature increase stops, therefore a region with constant temperature distribution is formed. Significant temperature changing magnitudes are revealed in the back part of gob along the airflow direction, which is prone to spontaneous combustion. Greater air flowrate brings much more intense oxidation inside gobs and higher temperature conditions. What’s more, the highest temperature throughout the gob moves towards the return airway with increasing air flowrate. Results show that two dimensional variable porosity models possess obvious advantages comparing with field data.更多还原