Study On The Thermal Dynamic Characteristics Of Combustion System For Coal Fires In Xinjiang Region

Coal fire is one of disasters associated with coal mining activities over the world.Coal fire not only consumes the coal resource for nothing, but also brings someserious problems to local environment, such as the pollution to air, the damage to soils,and the contamination to underground water and consequently the health problem tohuman beings. The thermal dynamic characteristic of coal combustion system for coalfire is the core of research in the coal fire field because of its important roles ofrevealing the mechanism of coal fire propagation and improving the coal fireextinction efficiency as well as scientifically evaluating the coal fire's impact onenvironment. This dissertation focused on the modeling of the thermal dynamiccharacteristics of coal fires' combustion system in Xinjiang region, including researchof the physical boundary of coal fire control volume, the dynamic of oxygen supply tocoal fire, the characteristics of heat generation from coal combustion under coal fireconditions, and the characteristics of heat transfer with coal fire and so forth. Theresults and conclusions have been obtained in this dissertation as follows.Coal fire burns in subsurface area. With the application of rocks control theory, amethod was proposed to determine the physical boundary of coal fire control volume,and a preliminary model of coal fire control volume has been established. Bothorientated and inclined boundaries of underground part of coal fire control volumecan be determined by using overlying rocks movement angle and contour map of coalseam deposit. The surface boundary of coal fire control volume can be determined bythe farthest faults/cracks along directions of the orientation and the inclination of coalfire. Based on the research of control volume of coal fire, and together with the use offluid theory within porous medium, the model of equivalent permeability (EP) of coalfire control volume was put forward firstly. Then, an experimental facility for EP wasdesigned, which it's useful to study the EP with different mediums and differentcombinations of these mediums. As an important property of coal fire control volume,the overlying rocks' thermal conductivity also was studied in this dissertation. Amethod was proposed to calculate it with an assumption of homogenous medium in alldirections for each rock layer.With analyzing the model of air/smoke flow of coal fire, a method of calculatingthe fire-heating air pressure (FAP) was proposed. It is known the air/smoke movesforced by the natural convection. The dynamic of its movement is the gravity difference between the fresh air and the hot smoke which is due to their temperaturedifference. It shows that the air/smoke state after covering is different from the onebefore covering. Before covering, the variety of air/smoke state within the fire zoneabides with constant volume process. After covering, it abides with constant pressureprocess. This dissertation also put forward a coal fire state coefficient C to indicate thechange of air/smoke state with the going on of extinction, and designed anexperimental facility for studying it.With the application of combustion theory, the state of coal combustion withinfire zone was analyzed at first. Then, a model of calculating the heat-generation fromcoal fire zone, i.e. the heat source model of coal fire, was proposed. Excess aircoefficient is one kind of parameter to indicate the coal combustion state within firezone. In fact, almost all coal fire is under conditions of rich combustible materialcombustion. For coal fire's complication, it's hard to describe coal combustion stateby using the kinetic theory of coal combustion. In order to study the thermal dynamiccharacteristics of any given whole coal fire, a heat source model, which is based onthe oxygen requirement and heat-generation for per kilogram coal combustion and theair/smoke flow amount, was established.Based on the theory of heat transfer, the style of heat transportation with coal firewas analyzed, and the model of calculating the fire source temperature was proposed.Heat transfer of coal fire includes the heat conductivity within fire zone, the heatdissipation by radiation from the surface of fire zone, and the heat dissipation byconvection as well as the heat taken away by mass transport. Plate natural convectionmodel can be used to describe the heat transfer by convection with coal fire. Theconvective coefficient can be determined by use the Reynolds number and otherparameters. Other two models also were proposed to calculate the heat dissipation andaccumulated heat dissipation.At the end of this dissertation, examples, i.e. the Shui-xi-gou coal fire and theNo.5fire zone of Tuo-luo-gai coal fire, were given to make calculation with parts ofabove proposed models. Results show that heat dissipation by radiation is greater thanother kinds of heat-transfer styles. From modeling of thermal dynamic characteristicsof coal combustion for coal fire and given example analysis, the principle of coal fireextinction will be emphasized again, i.e. heat-removing is an effective measurementto reduce the oxygen supply because it can reduce the coal fire zone's temperaturequickly, another effective measurement is to cover faults/cracks located in lower temperature area of coal fire to increase the resistance for air leaking into the firezone.From the research, the basic models of describing coal fire thermal dynamiccharacteristics were established firstly. It will provide a quantitative method to revealthe essence of evolution of thermal dynamic characteristics of coal combustion forcoal fires in Xinjiang region.