Research On Thermal Physical Parameters And Destruction Characteristics Of Coal And Rock Of Coalfield Fire Area

The burnings of coalfield fire area pollute our environment, cause geological subsidence, waste resources and damage the ecosystem. The temporal–spatial evolution of coalfield fire is mainly affected by thermal properties and destructions of coal and rock. In order to study the thermal physical parameters and thermal damage of coal and rock from coalfield fire area, the synthetic method of experiment, theoretical analysis and numerical simulation was employed to research characteristics mechanism of granite, sandstone and coal specimens from coalfield fire area in this paper.The laser flash device LFA457 is used to research and analysis thermal physical properties of coal and rock samples. Thermal diffusivity and thermal conductivity of coal are decrease as the volatile content gradually increases, however, the specific heat capacity exhibits gradually increase. Thermal physical properties that are mainly determined by the substance itself own natures are subjects to temperature and the complex physical and chemical reactions. What’s more, to analysis thermal physical properties of coal samples, the thermogravimetric experiment is used to research the reasons and characteristically temperatures. Thermal diffusivity and thermal conductivity of granite and sandstone are higher than those of coal at the same temperature, which is most likely caused by the more complex chemical reactions of coal samples and the differences of mineral composition. When the temperature rises, thermal diffusivity and thermal conductivity of granite and sandstone decrease. At high temperatures, thermal diffusivity and thermal conductivity of rocks approach constant values. The observed characteristics of the temperature dependence of conductivity of sandstone can be attributed to its basically crystalline structure while those of the coal can be attributed to its volatile composition. The behavior of the granite can generally be attributed to metamorphosed minerals.Through CT scanning the coal and rock samples at different temperatures, the software of Drishti is used to graphic three-dimensional reconstruction, and the MATLAB is employed for calculating fractures and porosity of samples. The development of fractures and porosity of coal from 25 to 300 °C were caused by the thermal fracturing accompanying the gas and internal water evaporation primarily. From 300 to 500°C generation and development of fractures were mainly due to interior thermal decomposition of chemical kinetic effects. The pyrolysis process led to the escape of high internal olefin material. Micro-holes of rock specimen were produced when interior water was released and the physical process of water escaping in the form of vapor occurred mostly below 300°C. Some obvious black spots appeared in the interior of the sample because of the fractures that were produced during the changing of pore mineral particles from 300 to 500°C.The thermal destruction of rock samples under temperature and pressure coupling is simulated using realistic failure progress analysis to study thermal damage patterns and characteristics of thermal destruction. The simulated damage models of the fracture development are agreed fairly well with the experiment of CT scanning. As the temperature rises, fissures and pores gradually develop and accelerate, and its main characteristic is to continue to extend the development and widening fissures along the original path, meanwhile, some freshmen crack generation.