Effect Of Low Temperature Oxidation On The Structures And Properties Of Coal

Low temperature oxidation is an important research topic in the field of coal chemistry. Low temperature oxidation of coal is a very complex exothermic process, including physical adsorption, chemical adsorption and oxidation reaction. Low temperature oxidation causes great inconvenience and loss to the production and inspection of coal.In the process of transport and storage, the time of coal contact with air may be more than6months. During this period, with the effect of water, air etc, the temperature of coal may rise and coal oxidizes with oxygen, which can lead spontaneous combustion and certain changes in process performance, which will cause great economic loss to the production institution. In coal inspection institution, after the test results were reported, tested samples will be stored for at least3months in order to review the results. In the process of storage, the oxygen in the air will oxidize it to certain degree with different effects on the different types of coal and inspection items, which will affect the accuracy of the review results.In order to reduce or avoid the impacts of low temperature oxidation and enrich low temperature oxidation theory of coal, this thesis chose seven coal samples which were three lignites, three bituminites and an anthracite on behalf the coal and coal forming period of the Chinese top production coal, simulated actual condition in coal inspection institution, systematically studied the rules of impact on coal structure and properties during low temperature oxidation, studied the mechanism of low temperature oxidation reaction of coal, determined which coal to be oxidized more easily. The works of this thesis were as follows:1. In five Chinese coal mines, acquired seven pit coal samples which were on behalf of the Chinese top production coal and coal forming period. According to the relevant standards, crushed, divided, prepared samples for all kinds of test items. The basic properties of the seven samples, such as:maceral analysis, proximate analysis, ultimate analysis, coal ash chemical composition were determined.2. Two methods were used to oxidize coal samples:place samples under room temperature for different period (15d、30d、45d、60d) or use hydrogen peroxide. Analysis water, volatile matter, cinder characteristic value, total sulfur content, calorific value and caking index of original and oxidized samples were determined, and the effect of low temperature oxidation on the determination results was studied. The results showed that organic molecules in coal reacted with oxygen, which reduced volatile matter, total sulfur content, calorific value, caking index, cinder characteristic value of coal. The deeper oxidation degree, the more decrease. Cinder surface morphology was tested by scanning electron microscope, and effect rule of low temperature oxidation on cinder surface morphology was studied. The results showed that the active components of coal reduced and volatile substances of bituminite decreased in the process of pyrolysis after oxidation, which lead cinder surface gaps to become close. The bituminite had less volatile, and the cinder surface gap was closer.3. Using comprehensive thermal analyzer studied the thermal dynamic performance of original and oxidized samples. Absorbing oxygen pyrolysis process of coal was studied. Combined the function mechanism of coal oxidation reaction, calculated the activation energy and other kinetic parameters of samples before and after oxidation, studied the law of the oxidizing reaction of samples. The results showed that in the process of adsorbing oxygen pyrolysis, in addition to the anthracite, lignite and bituminite can adsorb and react with oxygen. In adsorbing oxygen and weight gain stage, because the adsorbing oxygen quantity of the lignite and high volatile bituminite is less than that of the volatilization of volatile substances, the mass of the sample did not increase. The coal with higher metamorphic degree has higher activation energy and ignition point, which is difficult to be3xidized. After being oxidized by hydrogen peroxide, activation energy and ignition point of coal reduced. The metamorphic degree of coal is lower, more activation energy decreases.4. Used two methods to oxidize coal samples:place samples under room temperature for different period (30d、60d) or oxidize by hydrogen peroxide. Determined the FTIR of original and oxidized samples and studied the structure variation law of samples before and after oxidation. The mechanism of coal low temperature oxidation reaction was speculated. The results showed that anthracite had little organic constituents and strong stability, which was not easy to be oxidized. Lignite contains more reactive groups such as: phenolic hydroxyl, alcoholic hydroxyl, fat hydrocarbon, etc. Cyclanes and fat chain ruptured after oxidation. Alcohol and phenol were oxidized to carboxylic acid. Because of the influence of high stability, aromatic ring and ether bond are not easy to be oxidezed. Compared with lignite, bituminite has less hydroxyl and more carbonyl. After oxidation, fatty hydrocarbon and naphthene reduced in bituminite, carbonyl increased but less than that of lignite.5. Divided petrographic analysis sample into two portions, one oxidixed with hydrogen peroxide. According to the standards, two samples were made into coal briquettes. With the attenuated total reflection Fourier transform infrared spectrometer respectively determined the infrared spectrum of vitrinite and inertinite in the two coal briquettes. Studied the structure difference of vitrinite and inertinite in coal, studied their structure variation law before and after oxidation. The results showed that vitrinite and inertinite had similar functional groups. Vitrinite contains more hydroxy, methylene. Carboxyl group mainly exists in inertinite. Compared with inertinite, vitrinite had stronger aromaticity, more stability which was less affected by oxidation. Inertinites can be effectively oxidized by hydrogen peroxide and its functional groups decreased dramatically after oxidation.