Study On The Effect Of Microwave Radiation On The Kinetics Characteristics Of The Coal Oxidation Reaction

Microwave radiation helps to promote gas desorption and seepage in coal,and is considered to be an effective measure to enhance gas extraction.However,cases have been shown that the risk of spontaneous combustion of coal may increase after microwave treatment.Therefore,before microwave radiation is actually used in coal mines,it is necessary to clarify the influence of microwave radiation on coal spontaneous combustion characteristics.Since coal spontaneous combustion is mainly related to oxidation heat release and heat storage conditions,this thesis focuses on the influence law and mechanism of microwave radiation on the kinetics characteristics of coal oxidation reaction.In this thesis,through the combination of experimental testing,numerical simulation and theoretical analysis,the influence of microwave heating parameters on the temperature response characteristics of coal is explored,the oxidation characteristics of coal after different microwave time are analyzed,the evolution process of coal microstructure under the action of microwave radiation and its relationship with oxidation characteristics is revealed.In order to provide a scientific basis for the safe application of microwave radiation in coal mines.（1）Based on the coupling mechanism of the electromagnetic field and the heat transfer field,a three-dimensional numerical model for simulating the response of pulverized coal to microwave radiation is constructed,and the rotational domain is added through the deformed geometry.The key factors affecting microwave heating are studied based on the developed model.Numerical simulation results show that:microwave time and power,as well as sample position and mass will affect the final temperature of the sample;the mass of the sample and whether the heating plate is in a rotating state will also have an impact on the uniformity of the temperature distribution of the sample;in the subsequent microwave heating experiments in this thesis,the sample mass should be kept small and the heating plate in a rotating state,so as to ensure the uniformity of the temperature distribution of the sample and the reproducibility of the test.（2）The low-temperature oxidation characteristics of raw and microwave-modified coals were investigated by means of coal spontaneous combustion experiment.The effect of microwave radiation on the oxygen consumption characteristics,gas products,exothermic intensity,CPT and spontaneous combustion propensity determination index of the coal was analysed.The results showed that,overall,after microwave modification,the CO concentration and generation rate of the three coal samples were higher,and the alkane and olefin gas generation of the Shenmu non-stick and Pingyu lean coal samples were larger,and with the extension of microwave radiation time,the oxygen consumption capacity and exothermic intensity of the three coal samples first increased and then decreased,and the CPT and the determination index of spontaneous combustion propensity first decreased and then increased.The greater the moisture content of the coal sample,the greater the change in the CPT and spontaneous combustion tendency index after microwave radiation.（3）The high-temperature oxidation characteristics of raw and microwave-modified coals were investigated by simultaneous thermal analysis experiments using TG-DSC coupling.The effects of microwave radiation on the coal heat weight and heat flow curves,characteristic temperatures,combustion characteristics parameters,heat release and activation energy at the high-temperature oxidation stage were analysed.The results show that,on the whole,with the extension of the microwave radiation time,the combustion point T_i of the three coal samples increased,the combustion characteristics parameter S decreased,the exothermic heat H increased and the activation energy E in the high-temperature oxidation stage first increased and then decreased,among which the Shenmu non-stick coal with high moisture content showed an increase in the combustion characteristics parameter S compared with the original coal and the activation energy E was slightly lower than that of the original coal when the microwave time was shorter.（4）The structural characteristics of raw and microwave-modified coal were studied by nitrogen adsorption experiments and FTIR.The effects of microwave radiation on coal pore morphology,pore size distribution,specific surface area,pore volume,average pore size and structural characteristics of functional groups:A-_OH/A-O-,A_C=O/A_ar,A-_CH2/A-_CH3 and A_ar/A_al were analyzed.The results showed that,for the pore structure parameters,as a whole,with the extension of microwave radiation time,the specific surface area and pore volume of the three coal samples increase first and then decrease,the average pore diameter first decreases and then increases,and the coal samples with higher raw coal moisture content have larger change range of pore structure parameters after microwave radiation.For the functional group structure parameters,for A-_OH/A-O-,Shenmu non-stick coal and Pingyu lean coal first increased and then decreased with microwave time,while Baiyangling anthracite gradually decreased;for A_C=O/A_ar and A-_CH2/A-_CH3,all three coal samples gradually decreased with microwave time;for A_ar/A_al,Shenmu non-stick coal and Pingyu lean coal first increased and then decreased with microwave time,while Baiyangling anthracite showed an overall decreasing trend.（5）The mechanism of the effect of microwave radiation on the oxidation characteristics of coal at low and high-temperatures was analysed in relation to the trends in the oxidation characteristics and structural features of coal before and after microwave radiation.In terms of low-temperature oxidation characteristics,for Shenmu non-stick coal and Pingyu lean coal,microwave radiation changed the pore structure and A-_OH/A-O-of the coals so that their low-temperature oxidation characteristics increased and then decreased with microwave radiation time;for Baiyangling anthracite,after microwave modification,the change in pore structure played a dominant role in low-temperature oxidation characteristics compared to the change in A-_OH/A-O-,so that their low-temperature oxidation characteristics increased and then decreased with microwave radiation time.In terms of high-temperature oxidation characteristics,microwave radiation changes A_C=O/A_ar and A-_CH2/A-_CH3 of the three coals,resulting in a gradual increase in ignition point T_i with microwave radiation time,while the activation energy E in the high-temperature oxidation stage is affected by the combined effect of changes in A_C=O/A_ar,A-_CH2/A-_CH3 and A_ar/A_al,showing an overall non-monotonic trend of increasing and then decreasing with microwave radiation time.72 figures,21 tables,140 references.