| This thesis mainly discussed metamorphism of low medium degree of the coal oxidated naturally in the air in different time, and investigated the reason for the variation of coal quality characteristics and change rules of molecular structure. Through analyzing the characteristics of coal quality, the change of moisture, heat, volatile points, bond of the low medium metamorphic was discussed. The hot heavy and DSC(TG-DSC), Fourier transform infrared spectroscopy(FT-IR), scanning electron microscopy (SEM), attenuated total reflection infrared spectrometry(ATR-FTIR) and other means were used to characterize the dynamic parameters, molecular structure, cinder characteristics and microscopic component structure of the original coal samples and oxidated coal samples. The reason for the coal characteristicsand the change rules of the variation of molecular structure, after low temperature oxidation were explained to account for the mechanism of low temperature oxidation of coal.The experiments revealed that:the moisture of lignite coal and long flame coal were reduced after being put in the air oxidated60days, but had little effect on the bituminous coal above the medium and high metamorphic coal.(1) with the rise of metamorphic degree of coal samples, the change trend of heat was:lignite coal> long flame coal> unsticky and weakly unsticky coal> gas coal and1/3coking coal. Qgr,d of lignite coal was8.4%, long flame coal5.29%, unsticky and weakly unsticky coal haxing a nearly same trend and respectively3.5%and3.6%, gas coal and1/3coking coal2.5%and2.0%.(2) the volatile matter and bonding of coal samples oxidated by low temperature had a down trend. The volatile matter of lignite coal and long flame coal was greatly reduced by oxidation, and trend was:lignite coal> long flame coal> unsticky and weakly unsticky coal> gas coal and1/3coking coal. At the same time, the bond was reduced. The change trend of bond was:lignite coal> long flame coal> unsticky and weakly unsticky coal> gas coal and1/3coking coal. With the increasing of metamorphic degree, the effect of oxidation on volatile matter was gradually diminished and at the same time its value of cinder characteristic declined. The change trend of bond was:1/3coking coal> gas coal> weakly unsticky coal and the coked index of coal became poor.The experimental results of characterization:(1)Through the thermal analysis DSC-TG, according to the solution of the kinetic mechanism, the activation energy value of experimental coal samples after low temperture oxidation was solved and they were respectively39.07kJ/mol of liginite coal,31.59kJ/mol of long flame coal,22.84kJ/mol of unsticky coal,19.96kJ/mol of weakly unsticky,15.87kJ/mol of gas coal,12.51kJ/mol1/3coking coal. With the increase of metamorphic grade, the activation energy value of coal samples was changed. With the oxidation degree decreased, the heat value after oxidation decreased and the change of calorific value also decreased.(2) FTIR reavealed that alcohol, phenolic group and other active group of liginite coal, long flame coal, unsticky coal and weakly unsticky after oxidation were easily converted into carboxyl groups and mineral content was less. Gas coal and1/3coking coal have a higher degree of aromatic ring and alcohol group, phenolichydroxyl and other active groups were easily oxidated into ester and carbonyl.(3) By means of scanning electron microscope, after low temperture oxidation, cinder characteristic value of1/3coking coal was reduced from7to5, gas coal from6to4. the space structure of coke button surface of coal caking property became smaller and gap surface became dense.(4) By means of analysis of ATR-FTIR, for bituminous coal, the reason of change of caking property and caking capacity was mainly that the structure of vitrinite and exinite in microscopic component and the ratio between (-CH3,-CH2) of cycloparaffin and aliphatic hydrocarbon and (alconol key, ether bond) in vitrinite and exinite is bigger. The activity is strongest. They are the main components by oxidation. The structure of inertinite component has highest degree of aromatic and is the most stable part. Oxidation can make cycloparafin or aliphatic hydrocarbon and naphthenic key fracture into small organic molecules such as alcohol key, ether key, carbonyl and CH4. The content of exinite and vitrinite decreased. The ratio between cycloparaffin and aliphatic hydrocarbon in molecule decreased. The stability of aromatic ring was strengthened. All of these resulted in redistribution of hydrogen difficultly in thermal decomposition process of coal samples and reduction of the side chain functional groups in small molecules fallen off. This led to the reduce of source of colloid fluid in small molecules. The caking property and coking capacity became poor and volatile reduced. |
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