外文翻译-煤炭火灾.doc

1、翻译部分英文原文Coal fires A coal fire is the underground smouldering of a coal seam or coal mine. They are emerging as a global threat with significant economic, social and ecological impacts.Coal seam fires Prevention Extinction Coal seam fires may be categorized into near surface fires in outcropping sea

2、ms that are supported by oxygen from direct contact to the atmosphere and mine fires supported by oxygen from the artificial mine ventilation.Spontaneous coal fires The final reason for all fires is the chemical reaction of the hydrocarbon molecules of the fuel with oxygen of the air. This exotherma

3、l reaction can take place at any temperature. The reaction velocity however is strongly temperature dependent and increases with temperature nearly exponential. If the fuel is broken up in small particles or porous, oxygen has access everywhere and the entire volume may act as a heat source. The sit

4、uation is not critical if the heat energy transported to the surface by either conduction or convection and finally lost to the environment is larger than the heat produced by the reaction. If the heat produced by the reaction however is over longer time larger than the heat loss to the environment

5、the system will turn to be critical. Temperatures will rise continuously, the reaction will accelerate and finally the fuel will start burning spontaneously. Two factors will finally be responsible: The surrounding temperature and the volume of fuel involved: If the surrounding temperatures are high

6、er the oxidation processes will run faster and thus the heat production is higher within the fuel volume. If the fuel volume is larger the heat produced inside can hardly flow to the surface and into the environment, the fuel is more likely to start burning. In addition material broken up in small p

7、art or porous material usually has a low heat conduction coefficient and may act like thermal isolators. The most important parameter characterizing self ignition is the self ignition temperature. This is not a material constant, but dependent on volume and shape, more specific on the relation of vo

8、lume and surface. Self ignition temperatures decrease strongly with volume. Furthermore this temperature is dependent on many fuel material parameters as caloric value, heat conduction coefficient, particle size. In case of coal it depends further more on the coal type and rank; for hard coal its ge

9、nerally higher the for brown coal or lignite. If the fuel volume is sufficient spontaneous ignition may happen at room temperatures or at temperature at the yearly average temperature. The time needed for the fire to develop may be month or even years. Brown coal or lignite may start burning at 40 C

10、 to 60 C whereas anthracite will start (under the same conditions!) at 140 C. The smouldering will usually start several decimeters below the surface in a depth where the permeability of the coal allows the access of enough air but the air flow is slow enough to not extract the produced heat by conv

11、ection. Due to the low heat conductance coefficient of coal heat extraction by conduction alone is not sufficient. Factors influencing spontaneous induction are beside others: Air circulation Climate (arid, semiarid) Coal quality coal type (carbon content, gas content, ash content, rank) Particle si

12、ze (small particles have larger surface/volume relation) Geological geomorphologic settings Mining influence (Openings, fractures, subsidence) Hydro geological settings (moisture content) Spontaneous ignition needs time. How much depends on many factors, as temperature, volume, particle size. Finall

13、y the time to ignition is another parameter to describe the addiction of coal to burn. For larger volumes the temperature needed is smaller but the time needed larger. Normally it will take months before coal will start smouldering. If coal seams outcrop to the surface, air has access for long times

14、, at those location seams will start to burn spontaneous and continue burning for decades. Globally at least 20 to 30 million tons are burned by those fires. The coal being made inaccessible for further mining is about the times more.Heat producing reactions There are two know heat producing adsorpt

15、ion reactions: Physisorption of oxygen. This takes place at temperatures up to 50 C and delivers 42kJ/mol. Chemisorptions of oxygen. This produces several chemical compounds after overcome the activation energy of the coal surface. From carbon-, hydrogen- and oxygen atoms peroxides are formed and ab

16、out 100 kJ/mol of heat energy is produced. The newly built molecules may oxidize further and produce heat with increasing temperatures and finally exhaust as carbon dioxide, carbon monoxide and water (vapor). The most important reactions are: C und O2 form CO2 (394 kJ/mol) 2C und O2 form 2CO (170 kJ/mol)Coal seam fir