| Coal spontaneous combustion accident seriously threaten the safety of coal production,transportation and storage,which brings great potential to the safety and property of human,especially the lignite,due to the higher spontaneous combustion propensity,the problem of spontaneous combustion is more prominent.So it is necessary to study the natural characteristics and the law of coal spontaneous combustion.The dissertation investigated the spontaneous combustion characteristics of lignite by experimental and numerical simulation methods.The experimental method is Static constant temperature method.Three sets of cube lignite samples are placed in different temperature environments.The critical self-ignition temperature can be obtained by measured the temperature-time curves of different sizes coal piles.The activation energy of coal sample was obtained by the Frank-Kamenetskii model.The experiment results show that the critical self-ignition temperature is lower for the larger stockpile volumes.The coal samples can be self-ignition when the ambient temperature is higher than the critical self-ignition temperature.On the contrary,the coal sample cannot be spontaneous combustion.A more reasonable heat generation model of coal was built based on the theory of EOE-time which transfers elapsed time to EOE time.The equation is relation to elapsed time,temperature,oxygen concentration and so on.Based on porous media seepage theory,the mathematical model of coal spontaneous combustion is established,and the FLUENT software is used to simulate the temperature rising process of coal samples under different experimental conditions.Temperature field,air seepage field,oxygen concentration field and vapor concentration field versus time can be simulated.The simulation results show three fields changed frequently and interacted intimately during the experimental process.Moisture increases the heating time and the critical self-ignition temperature,and plays a prominent role in preventing the self-ignition of coal.Through the experiment and numerical simulation,the self-ignition characteristics of coal is studied,which can reveal the inherent law of coal spontaneous combustion,and find out the occurrence,development process and the influence of various factors on the four field. |
