Study On Coal Spontaneous Combustion Prediction Based On Carbon And Oxygen Isotope Spectra

Coal spontaneous combustion is one of the major disasters in the coal mining,storage and transportation.The index gas CO has strong regularity and easy detection,and has been widely used.In recent years,abnormal emission of CO gas was found in some mines in China,but not accompanied by coal spontaneous combustion.How to predict spontaneous combustion of coal in mines with abnormal CO has become an important research topic to be solved urgently.Aiming at the abnormal CO in mine,the carbon and oxygen isotope values in coal spontaneous combustion index gases CO and CO₂ were analyzed by isotope technology,and a prediction method of coal spontaneous combustion based on carbon and oxygen isotope spectrum was proposed,which had important scientific significance to improve the accuracy of coal spontaneous combustion prediction and ensure the safety of production of enterprises and the life and health of workers.Through drilling in the 2091 and 2312 working faces,the occurrence of primary CO and CO₂ were analyzed respectively.During the construction process,hydraulic slagging was adopted.After continuous nitrogen purging,the gas in the coal seam was desorbed by negative pressure,and the gas in the drilling holes was collected and detected regularly.The results show that there is primary CO gas in 2091 working face,while there is no primary CO gas in 2312 working face,but there is primary CO₂ gas in both working faces.Temperature programmed gas chromatographic experiments were conducted on coal under different oxygen concentrations,and the difference subtraction method was used to eliminate the gas production effects of coal pyrolysis and degassing,and the proportion of CO produced by coal reaction in the pure oxidation path to CO produced in all paths was obtained(CO_{pure oxidation}/CO_total).With the increase of temperature,the ratio of CO_{pure oxidation}/CO_total showed a rapid rise at first and then a slow rise to a stable trend.The higher the oxygen concentration,the higher the ratio of CO_{pure oxidation}/CO_total.The vast majority of oxygen atoms in CO generated by coal reactions in the pure oxidation pathway come from oxygen,and the change in the ratio of CO_{pure oxidation}/CO_total affects the source of oxygen atoms in CO gas from oxidation of coal.The proportion of CO₂ generated by coal in pure oxidation path is basically consistent with that of CO gas.The transformation law of main functional groups in coal was analyzed by in-situ infrared spectroscopy experiment under different oxygen concentration.During the low-temperature reaction of coal,it is detected for the first time that carbon atoms in CO and CO₂gas were mainly from carbon atoms in carbonyl,carboxyl and ester groups,and oxygen atoms were mainly from oxygen atoms in oxygen and oxygen atoms in carbonyl,carboxyl and ester groups in coal.And because the values of CO_{pure oxidation}/CO_total and CO_{2pure oxidation}/CO_2total were small,the proportion of oxygen atoms from oxygen was relatively small.As the temperature rose,the reaction between coal and oxygen intensified,the values of COpure oxidation/COtotal and CO2pure oxidation/CO2total increased rapidly,and the proportion of oxygen atoms in CO and CO₂ gas from oxygen atoms also increased rapidly.After 140℃,a large number of methyl,methylene and hydroxyl groups participated in the reaction and were transformed into carbon-oxygen double bond active groups,which then transformed into a large number of CO and CO₂ gases.With the increase of temperature,the values of COpure oxidation/COtotal and CO2pure oxidation/CO2total slowly rose to about 90%and tended to be stable.The carbon atoms in the generated CO and CO₂ gas mainly were from the carbon atoms in methyl,methylene,carbonyl,carboxyl,ester and other functional groups.The oxygen atoms were from the oxygen atoms in oxygen and the oxygen atoms in the carbonyl,carboxyl,ester and hydroxyl functional groups in coal,of which the proportion of oxygen atoms in oxygen was higher than 90%.Theδ¹³C andδ¹⁸O values of carbon and oxygen isotopes of CO and CO₂ gas released by coal primary and coal oxidation in coal seam were determined by stable isotope mass spectrometer.The carbon and oxygen isotope spectra of primary CO and CO₂ gas in coal seam and carbon and oxygen isotope spectra of CO and CO₂ gas released by coal oxidation at different temperatures and oxygen concentrations were constructed.The difference of carbon and oxygen isotope values in the spectra was analyzed,and it was concluded that the differences were caused by the different sources of carbon and oxygen atoms when coal produced CO and CO₂ under different oxygen concentrations and temperatures.The change law of carbon and oxygen isotope values in CO and CO₂ gas released by coal oxidation was explored under different oxygen concentrations and temperatures.The difference of carbon and oxygen isotope values in gas provided scientific basis for coal spontaneous combustion prediction.A prediction model of coal spontaneous combustion was established based on carbon and oxygen isotope spectra.In view of the abnormal CO gas in the corner of the working surface and whether there is a difference in the source of primary CO,theδvalues of carbon and oxygen isotopes of CO and CO₂ gas in the primary coal seam and upper corner were analyzed,and the functional relationship of carbon and oxygen isotope values of CO and CO₂ gas from oxidation sources in the upper corner was derived.The matrix treatment of carbon and oxygen isotope values of CO and CO₂ of oxidation of coal under different oxygen concentrations and temperatures was carried out to reduce the dimensionality.By using distance similarity judgment,carbon and oxygen isotope spectrum were constructed respectively for coal seams with and without primary CO gas,and a prediction model of coal spontaneous combustion based on carbon and oxygen isotope spectrum was established.The prediction method of coal spontaneous combustion in goaf was put forward,and the rationality of the prediction method was confirmed by field application.Figure 91;Table 13;Reference 123...