| China has a large quantity of coal,as well as a great production of it.The phenomenon of coal spontaneous combustion is serious and may be disastrous so that coal reignition comes to appear frequently,as so called secondary oxidation.The secondary oxidation means the raw coal comes to spontaneous combustion and the temperature rises to the point after critical temperature,then cooling to original temperature and recurrence of redox reaction process.In this paper,taking the coal samples from Gaozhuang Coal Mine as the research object,the influence of air supply and pre-oxidation degree on the secondary oxidation characteristics of coal was studied by theoretical analysis and laboratory experiments,and the optimization of index gases was carried out.The experimental results provide a basis for the mechanism establishment of coal secondary oxidation,the prediction and prediction of spontaneous combustion and the research of prevention technology.The main work is as follows:1)Theoretically studied the characteristics of down-soil mining in close distance coal seams,identified the important influencing factors of secondary oxidation in goaf of Gaozhuang Coal Mine,and carried out the experiment of low temperature programmed temperature of coal spontaneous combustion with pre-oxidation temperature and ventilation.The secondary oxidation process of coal was characterized by kinetic parameters such as oxygen consumption rate,gas generation rate,exothermic intensity and activation energy.2)The curves of coal temperature,gas concentration and generation rate,heat liberation intensity for initial and secondary oxidation of coal samples all increase exponentially,and the oxidation process can be divided into three periods:for the first period(30℃-critical temperature),the curves grow slowly;for the second period(critical temperature-dry cracking temperature),the curves grow faster;and for the third period(greater than the dry cracking temperature),the curves grow rapidly.3)The pre-oxidation of coal shows a positive effect on the parameters of coal spontaneous combustion in the initial stage of oxidation and inhibits the spontaneous combustion characteristics of coal in the late oxidation stage.The effect of air supply rate on the parameters of spontaneous combustion under the conditions of pre-oxidation at 90℃and the primary oxidation of coal samples shows a positive correlation,and the effect of air flow on the parameters of spontaneous combustion of coal sample underwent 140℃ pre-oxidation shows a negative correlation.4)Secondary oxidation significantly reduces the characteristic temperature of coal.When the ventilation flow rate is 50 mL/min,the critical temperature decreases from 830C(coal sample 1-Y)to 68℃(coal sample 1-L),69℃(coal sample 1-G),the dry cracking temperature decreases from 142℃(coal sample 1-Y)to 134℃(coal sample 1-L)and 136℃(coal sample 1-G);when the ventilation flow rate is 70 mL/min,the critical temperature decreases from 82℃(coal sample 2-Y)to 70℃(coal sample 2-L),70℃(coal sample 2-G),and the dry cracking temperature decreases from 147℃(2-Y)of coal sample decreased to 136℃(2-L)and 134℃(2-G)of coal sample.The risk of spontaneous combustion of secondary oxidation of coal is higher.5)Established the prediction system of coal spontaneous combustion based on CO,C2H4,the third fire coefficient R3 and C2H2,and defined the corresponding relationship between index gases and temperature points in the process of different coal samples oxidation spontaneous combustion.6)Considering that there may be errors in the values of C2H4,CH4 and C2H6 in the field test,the coal temperature of C2H6/CH4 and C2H4/CH4 has exceeded the critical temperature and dry cracking temperature respectively when they were generated,which has certain guiding significance for predicting the coal oxidation process in goaf.C2H6/CH4 and C2H4/CH4 are used as auxiliary indicators for predicting coal spontaneous combustion. |
