| Coals contain a certain amount of sulfur, according to the morphological classification the sulfur in coal can be divided into two categories: inorganic sulfur and organic sulfur, the sulfur in coal can directly effect on the characteristic of coal spontaneous combustion. The research about the influence of sulfur in coal on spontaneous combustion has very important meaning. At present people carried out a lot of research on inorganic sulfur coal spontaneous combustion characteristic which give priority to with pyrite, however sulfur forms in coal still have quite proportion of organic sulfur, The oxidation characteristics and mechanism of organic sulfur and inorganic sulfur in coal spontaneous combustion is not the same, People in the study of coal spontaneous combustion often ignore the effect of organic sulfur, The research about the effects of organic sulfur in coal spontaneous combustion characteristics is rarely reported. This paper adopts the method of combining theoretical analysis, laboratory simulation and laboratory test, selected representative coal samples, research the occurrence regularity of organic sulfur in coal and the change behavior during the process of oxidation, reveal the oxidation reaction of organic sulfur in coal, heat emission characteristics and its effect on non-reactive sulfur reaction mechanism, Simulation studies the influence law of organic sulphur of spontaneous combustion in coal. Oxidation reaction mechanism of the organic sulfur in coal is analyzed and explains the mechanism of the organic sulfur in coal spontaneous combustion.Select six representative coal samples, Using chemical analysis method, X-ray photon energy spectrum(XPS) technique, and mild organic solvent extraction chromatography/mass spectrometry(GC- MS) analysis the structure of organic sulfur in coal. Organic sulfide chemical analysis results show that organic sulfur exist in all of the 6 coal samples, organic sulfur in 2 low-sulfur coal samples is dominant, other forms is little content. Organic sulfur content in 4 high-sulfur coal samples is more than one-third of the total sulfur content. XPS analysis results show that the mainly organic sulfur form in coal samples is mercaptan, sulfide, thiophene, sulfoxide and sulfone, sulfonic acid, It is not obvious that mercaptan and sulfur ether content changes with the degree of coal metamorphism(due to the effect of pyrite interference), with thiophene reduction degree of coal metamorphism decreases, sulfoxide and sulfone variation is not obvious, with the coal metamorphic degree increases with the decrease of the sulfonic acid content. Coal samples of 4 hydrocarbon furan(THF) solvent extraction/GC- MS analysis results show that the small free soluble organic sulfur in coal molecules structure is closely associated with the metamorphic grade of coal, in the low metamorphic degree coal small sulfur organic molecules is given priority to with aliphatic sulfur, high metamorphic grade small organic sulfur molecules is given priority to with thiophene, with the degree of coalification increase, aromatization degree of small organic sulfur molecule increase.Select eight kinds of model of organic sulfur compounds, respectively by temperature programmed oxidation/gas chromatography and thermo gravimetric/differential scanning calorimetric analysis(TG/DSC) experiments. Through the temperature programmed oxidation/gas chromatography to determine the organic sulfur model compounds oxidation product and oxygen consumption, oxidation reaction activation energy was calculated, and based on the oxygen consumption and activation energy the organic sulfur functional groups are ordered by oxidation activity from high to low: mercaptan> sulfur ether > thiophene. The organic sulfur model compounds TG/DSC results show that In addition to dibenzothiophene, the organic sulfur model compounds of low temperature oxidation are multiple steps and phase behavior of chemical and physical change process, the adsorption heat, oxidation heat, melting endothermic, and pyrolysis heat interaction. Mercaptan is dominated by oxidation of exothermic reaction, sulfide and sulfoxide is given priority to with pyrolysis endothermic reaction, thiophene is mainly a physical change rather than a chemical change. In addition to the mercaptan, other model compounds were not detected SO2 oxidation products during the low temperature oxidation process.To get accurate information about the structure of the organic sulfur in coal, the coals usually need to deal with hydrochloric acid/nitric acid before using the XPS technology analysis the organic sulfur in coal. so this paper adopts a series of modern analysis methods such as X-ray fluorescence spectrum(XRF), X-ray diffraction(XRD), 13 C nuclear magnetic resonance technology(13C NMR),X-ray photon spectroscopy(XPS),scanning electron microscope combined with energy spectrum plane(SEM-EDX) analysis the coal samples before and after the acid treatment, studying on the impact of coal structure by acid treatment, the results show that sulfur on acid treatment coal surface is given priority to with thiophenic, mercaptan, sulfur ether, and sulfonic acid content is also higher. the organic sulfur on the surface of coal like sulfoxide, mercaptan, sulfur ether sulfone and sulfonic acid is changed by acid treatment, the content of organic sulfur is reduced,hydrochloric acid effect is lesser, and nitrate has a great effect.Using XPS analysis the 5 kinds of raw coal and acid treatment coal before and after oxidation, found that after the oxidation the mercaptan, sulfur ether relative content on the coal surface content is reduced, thiophenic sulfur content reduced slightly or unchanged, sulfone, sulfonic acid, sulfate content increased, Low temperature oxidation process was confirmed as the sulfide â†' sulfoxide â†' sulfone, mercaptan â†' disulfide â†'sulfinic acid â†' sulfonic acid. The phenomenon of non SO2 release during raw coal low temperature oxidation and SO2 oxidation were detected during acid treatment coal low temperature oxidation indicate that in raw coal the oxidation state organic sulfur such as sulfinic acid and sulfonic acid which is metal combination, and exists in the form of organic sulfur salt, after the acid treatment of coal due to the ion exchange, makes metal ions removed, which eventually led to generated the SO2 pyrolysis products.Using oxidation temperature programmed/chromatography methods investigate organic sulfur compounds and coal active group interaction, the results show that there is a competitive relationship between sulfur-containing reactive and active functional group during oxidation reaction, oxygen reaction of sulfur atom is more active, after most of the sulfur atom and oxygen reaction, such as other reactive group in the coal began reaction with oxygen and oxidation to produce CO, CO2, etc. From the changes in CO which is oxidation products show that the presence of organic sulfur postponed the reactive group in coal react with oxygen, but from the perspective of oxygen to the sample which joined the organic sulfur oxidation reaction is more intense, it means that identification the high organic sulfur coal spontaneous combustion propensity should conside the effects of organic sulfur. In addition, mercaptan oxidation activity is very strong, the results show that thiol can oxidation reaction at mild temperature and generate a certain heat of reaction; it must act as a promoting positive role during the early stage of the coal spontaneous combustion. |
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