Experimental Study On Free Radical Reaction Mechanism Of Coal Spontaneous Combustion

Study on the mechanism of coal spontaneous combustion is the nodus for many years. The mechanism of free radicals reactions in this dissertation can explain the chemical process of coal at low temperature oxidation.Based on the mechanism of free radicals reactions, the fragmentation process was the key factor of producing and initiating free radical reactions. Electron spin resonance (ESR) spectroscopy was used to measure the changes of different sorts and different granularity of coal directly, which proved coal can produce lots of active free radicals during the process of fragmentation, and the mechanical forces was a method for initiating free radical reactions.In order to further prove the free radical reactions during coal free radicals reactions, the ESR spectroscopy chart of free radicals during the process of low temperature oxidation was measured directly. The results show that free radicals change very complex during the reaction process of coal oxidation: the concentration and species vary largely at different temperatures, at the same temperature but in different oxidation time or during the process of temperature rising and dereasing. In order to study the effects of oxygen,moisture and mineral on free radical reactions, ESR spectroscopy chart of free radicals following the changes of temperatures are compared by the samples applying air and blowing nitrogen, original coal samples and dry coal samples, original coal samples and demineralized coal samples. The results show that oxygen, moisture and mineral accelerate the free radical reactions. Light is an ordinary method of initiating free radical reactions. The changes of the free radicals concentration and gases oxidation production (CO&CO2) with the coal samples were measured by ultraviolet lighting. The results show that free radicals in coal is very sensitive to ultraviolet, and the the free radical reactions can be initiated by lighting. Similar with the thermical oxidation, the photo-oxidation also can produce the gases such as CO&CO2, and the longer the lighting time is, the larger the concentration is. The property of photo-oxidation at low temperature indicated the mechanism of free radical reactions in spontaneous combustion of coal ?is reasonable again.In order to research the course of the free radical reactions, the changes of chemical structure of different sorts of samples at low temperature oxidation were measured by diffuse reflection FT-IR spectroscopy, and the change rules of aromatic hydrocarbon, aliphatic hydrocarbon and function-group with oxygen during the process of low temperature oxidation were discussed. The hydroxyl group and side-bond in alkyl group were easily oxidative in the coal molecule structure, and forming oxygen-containing functional groups. The other structures did not change significantly.The influences of the four kinds of trace element (manganese, copper, zinc phosphor) on coal spontaneous combustion were discussed. The oxidation consumption of coal samples added reagents were measured. The experimental results show that the reagents of Mn and organic Zn can catalyze the coal spontaneous combustion, and P and inorganic Zn can inhibit the reactions. Moreover, the more the amount, the more distinct the impact, but Cu almost has nothing with it. And the mechanism of free radical reactions can explain this phenomenon.Lastly, based on the mechanism of free radical chain reactions, and combining the experiments above, the reaction mechanism of the chain initiation, the chain transitive, and the chain termination were analysd. And the new method of inhibiting coal spontaneous combustion was brougt forward.