| In the process of mining,coal body is affected by mining,which is easy to produce cracks.At the same time,groundwater intrudes into coal body to form water bearing coal sample;in addition,the air leakage will increase after the drainage treatment in the goaf,which will increase the risk of coal spontaneous combustion greatly;the low temperature stage below 200? is an important stage to prevent coal samples from oxidizing combustion in the underground.In this paper,with the support of the key research and development program(2018YFC0807900)and the National Natural Science Foundation Project(51874007),aiming at the phenomenon of coal sample soaking in the coal mine,the exothermic characteristics of coal samples with different water content at low temperature stage are studied by means of temperature programmed experiment,thermogravimetry calorimetry experiment and infrared spectrum experiment,At the same time,the exothermic characteristics of coal samples with different water content in low temperature stage are analyzed from the macroscopic and microscopic perspectives by combining the theories of thermokinetics and chemical kinetics.(1)Based on the temperature programmed experiment,the production rate,oxygen consumption rate,exothermic intensity,critical temperature and activation energy of CO and CO2 in coal samples with different water content were determined.The results show that the rate of CO and CO2 production,the rate of oxygen consumption and the intensity of heat release increase exponentially in the temperature range(40??200 ?).The rate of oxygen consumption and the intensity of heat release of coal samples with different water content are obviously different in the temperature range.The activation energy of coal samples decreases first and then increases with the increase of water content.(2)Based on the thermogravimetry calorimetry experiment,the reaction stages of coal oxygen composite reaction were divided,the heat flow rate of nitrogen atmosphere and nitrogen oxygen mixture atmosphere in the low temperature stage was analyzed,and the oxidation kinetic parameters of nitrogen oxygen mixture atmosphere in the low temperature stage were solved.The experimental results show that the oxidation process of coal samples with different water content is similar,which can be divided into adsorption stage,loss of water and weight loss,oxygen absorption and weight gain,heat storage stage and combustion stage.However,with the increase of water content,the adsorption stage of coal samples gradually disappears,and the heat release of each stage changes obviously with the difference of initial water content;the heat release of coal samples in the low temperature stage decreases first and then increases with the increase of water content At the low temperature stage,the activation energy of coal sample decreases first and then increases with the increase of water content.(3)Based on the in-situ infrared spectroscopy experiments,the results of constant temperature oxidation of coal samples with different moisture content in the temperature range of 100 ??200? were analyzed from the qualitative and semi quantitative point of view.The types of main functional groups of coal samples were distinguished,and the change trend of the same group of coal samples with different moisture content with the rise of temperature was compared.The experimental results show that the change of functional groups of low heat release coal samples(9%,23%,30%moisture content)is different from that of high heat release coal samples(2%,16%moisture content);In the early stage of temperature,the methyl groups consumed by the reaction of the coal samples with low heat release are symmetric stretching vibration,asymmetric stretching vibration and shear vibration.The methyl groups produced by the fracture of carbon carbon double bond and triple bond mainly include symmetric stretching vibration and asymmetric stretching vibration.In the early stage of temperature,there are 1720cm-1 carboxyl groups and The reaction of hydroxyl hydrogen bond at 3617cm-1 to generate carboxylic acid radical;the change trend of functional groups of two groups of coal samples with high heat release is similar at 100 ??150? and the change trend of functional groups of three groups of coal samples with low heat release is similar at 150??200?;the change trend of functional groups of three groups of coal samples with low water content is similar,and the change trend of functional groups of two groups of coal samples with high water content is not obvious.Figure 34 Table 17 Reference 62... |
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