The Quantitative Study Of Ghg Emissions By Coal Spontaneous Combustion

In the dissertation, the temperature characters, emission characters and incomplete emission effect of greenhouse gases for 10 kinds of coal samples, which were collected in north and northwest area of China, were analyzed based on the infrared spectral analysis technology, thermal gravimetric analysis technology, spontaneous combustion simulation technology and gas-solid analytic analysis technology.1. Main research fruits（1） The correlation between coal quality and coal functional groups was analyzed.There was a positive correlation among the fixed carbon content, the calorific value and carbon content. And the volatile matter and water content had significantly positive correlation with the oxygen content of coal. However, there was a negative correlation between the carbon content and oxygen content of the coals. The amount of double-linked carbon in the coal rose when the coalification of it went deep. On the contrary, the quantity of hydroxyl would increase before the coal turned to the gas coal,and then began to fall again. As the same, the quantity of the carbonyl group of the coal would increase before the coal became to gas coal and then it would fall again. The amount of carboxyl of the coal fell before the coal turned into the long flame coal, and it would fall sharply when the coal became to gas coal and fat coal. It had a same tendency of the functional group with the carbon content and oxygen content of the coal.（2） The influence characters of coal quantiy on charactersitic temperature during coal spontaneous combustion were obtained by experiment. As a result, the characteristic temperature of the coal spontaneous combustion for the rich oxygen element coal（over 12%） not only was a negative correlation with the coalification degree. During in the stage of oxygen weight increasing, the characteristic parameters was positive with the water content and the ash content, but was not obviously relation with the chemical group. Coals which has more water and ash had a wide temperature range during oxygen weight increasing stage. Beside characteristic temperature was correlated with volatile matter and the fixed carbon, the carbon content, oxygen content and oxygen-containing groups during the thermal decomposition and strong oxidation stage. Temperature range of thermal decomposition stage was positive correlated with volatile matter and hydroxyl content. It was negative correlated with ether bond.Temperature range of strong oxidation stage is only negative correlated with the oxygen content. The maximum weight loss rate was positive correlated with content of fixed carbon and it was negative correlated with the ash. The weight loss of the coal in the first step was only negative correlated with the ash. And the temperature range was only negative correlated with the fixed carbon of the coal.（3） The change law of characteristic temperature with the temperature was alsoacquired. Characteristic temperature rose with heat-rise-rate during coal spontaneous combustion. The temperature range in all types of coal would be broadened when the heat-rise-rate rose. Besides, the temperature range of non-caking coal and weakly caking coal changed a little, and the other types of coals’ oxygen increasing weight would decrease and the temperature range would widen when the heat-increase-rate rose. The maximum weight loss rate rose as the heat-rise-rate increased. On secondary volatile stage, the temperature range had nearly any variance and lignite and non-caking coal weight loss had a little decrease when the heat-rise-rate increased. The anthracite had large increase and total weight loss of lignite and fat coal and coking coal had nearly any change as heat-rise-rate varied. Total weight loss of long flame coal,non-caking coal and lean coal decreased when the heat-rise-rate increased. Total weight loss of weakly caking coal, gas coal, lean coal and anthracite increased as heat-rise-rate increased.（4） The influences of oxygen content on coal combustion characteristic temperature was concluded. The effect caused by oxygen content on the characteristic temperature was complex. During deoxidation adsorption stage, the temperature of the deoxidation adsorption end of the lignite and the long flame coal and gas coal was lowest at oxygen concentration of 5%. The temperature of deoxidation adsorption end of anthracite was highest around common atmosphere and was lowest at oxygen concentration of 15%. During oxygen absorption weight gain stage, the maximum temperature of oxygen absorption weight gain increased as the oxygen atmosphere decreased. The maximum temperature of oxygen absorption weight gain of anthracite was the highest at oxygen concentration of 15%. During thermal decomposing stage,the effect caused by the oxygen atmosphere to anthracite was significant. But it was not very significant to rest the types of coal. During the strong oxidizing stage, the trend of initial temperature of strong oxidizing was increasing when oxygen atmosphere decreased. During the secondary volatile stage, the secondary volatile temperature of lignite nearly changed as oxygen atmosphere varied and the secondary volatile temperature of the non-caking coal and the anthracite would increase when the oxygen atmosphere decreased.（5） The basic laws and material basis of carbon-oxygen product generated during coal spontaneous combustion were obtained. The emission characters of CO₂ during the spontaneous combustion was small and rose slowly during lower temperature stage.Then it would increase fast during medium temperature. Besides, the emission amount increased rapidly during relative higher temperature stage. At last, the emission amount became stable. During lower temperature stage, the ratio CO/CO₂ was lower than 0.1.During medium temperature stage, the ratio increased rapidly and reached peak at400 oC. During higher temperature stage, the ratio decreased slowly. And then,temperature was around 600 oC, it would be around 0.13. In the whold stage of coalspontaneous combustion, the average amount of the ratio was not beyond 0.26, and it was usually under 0.2. The amount of CO₂ emitted during spontaneous combustion was positive correlated with carbonyl in the coal. Carbonyl and carbonyl group were also the material basis of CO₂ produced in coal spontaneous combustion.（6） The effect characters of production mode on main greenhouse gases generated by coal spontaneous combustion were studied. The experimental results showed that the rates of CH₄ and CO₂ emissions from spontaneous coal combustion resulting from mining activities were greater by approximately 1.8 and 1.6 times, respectively, than the same rates of emissions resulting from mere surface air seepage. The emission rate of CH₄ was significantly correlated with the volatile content of coal, while the emission rate of CO₂ was significantly correlated with the moisture, oxygen and sulfur contents of coal. Three different characteristic phases were observed for the emission of CH₄,with critical temperatures of 200 oC, 400 oC and 600 oC, respectively. Below 200 oC,CH₄ emissions were very slow; between 200 oC and 450 oC, the emissions increased slowly; and above 450 oC, the emissions increased rapidly. Similarly, the CO₂ emissions were very low at temperatures below 200 oC, slowly grew between 200 and 450 oC and quickly grew after 450 oC.（7）The adsorption characters of rock（soil） on CO₂ was experimented and analyzed for coal fire area. The adsorption ability of overlayer strata on CO₂ rose with the increase of temperature and then reached to saturating state; with the increase of pressure, the adsorption of CO₂ also rose and maintained a solid value. While the same temperature and pressure, the adsorption ability descending order on CO₂ was shale,mudstone and sandstone. For the same concentration of CO₂, the ratio of N₂ to CH₄ was not obviously influence on CO₂ adsorption amount. For mixed gas adsorption and pure CO₂ adsorption, the adsorption amount was exponential relation with the ratio of CO₂ in mixed gas.（8） The adsorption model of rock medium on greenhouse gases during coal spontaneous combustion and the related emitted evaluation method were set up. Though the analysis of experiment, the Langmuir coefficient was related with temperature and then a new adsorption model of rock on CO₂ was obtained. By combining the influence of temperature on multicomponent gas and the action of depth and pressure, the expanded Langmuir model for multicomponent adsorption was also provided. In fact,the average value of the new model and expanded Langmuir model was more closed to the experimental value.（9） The incomplete emission effect of CO₂ was studied in Wuda coal fire area.Based on the above fruit and some practical data, the CO₂ emission rate of the research area was about 96%, the release amount of CO₂ was 417 thousand tons per year and the emission amount of CO₂ was 400 tons per year.2. The innovations of the dissertation included:（1） The change law of greenhouse gases during coal spontaneous combustion was acquired and the release characters of CO₂ and CO/CO₂ were obtained. The carbonyl group and carboxyl were also the material basis of CO₂.（2） The release amounts of CO₂ and CH₄ at different air leakage mode and the influence of coal quality on CO₂ release were obtained, then, the release factors of CH₄ and CO₂ were calculated.（3） The adsorption law of overlayer rock on CO₂ was obtained during coal fire area,the adsorption model of rock medium on greenhouse gases during coal spontaneous combustion and the related emitted evaluation method were set up.There was some disadvantage in the dissertation because of the limit of experimental conditions and coal fire area conditions in-situ. In the future, some research word needed to be proceeded further.（1） Strengthening the application of release factors and related model in order to test their accuracy.（2） During the incomplete emission of greenhouse gases of coal spontaneous combustion, the C from other paths, such as higher temperature conversion, was not removed. So, the influences of geological complex conditions, occurrence state of coal bed, rock structure, and so on, need to be studied in the future.