Study On Index Gases Of Coal Spontaneous Combustion Laser-based Spectroscopy In-situ Diagnosis Technique

In recent years,with the continuous promotion of industrialization in China,although the proportion of clean energy such as hydropower,nuclear power and wind power is increasing,coal is still in the dominant position.The fire accident caused by coal spontaneous combustion?CSC?is one of the common disasters in the process of coal mining and transportation.The fire accident not only causes the waste of coal,but also threats to miners'life safety.Low-temperature oxidation reaction is one of the main chemical reactions in the initial stage of CSC.In this stage,many kinds of index gases are generated.Therefore,the oxidation state of CSC can be predited using these index gases.Then the CSC can be accurately predicted and forecasted.The laser-based spectroscopy in-situ diagnosis technique was employed to study the spontaneous combustion process of Da Tong mine coal.The main content of the research is as follows:?1?Some common spectroscopic lineshapes and wavelength modulation therory were introduced based on the Beer-Lambert law.The absorption lines of index gases were optimized and selected using the law of CSC.The spontaneous combustion process was studied according to the structure,property,and oxidation reactions of coal.?2?The index gases sensor of CSC was established based on high sensitivity laser spectroscopy technology.The concentrations of the CH₄ and CO were measured by a single distributed feedback?DFB?laser with a central wavelength of 2327 nm.The digital filter and digital lock-in amplifier was implemented using the Cortex-H7 MCU platform for digitally demodulation the spectroscopy signal.Calibration experiments show that the linearities of CH₄ and CO were 0.99857and 0.99959,respectively.Allan variance analysis shows that the detection limits of CH₄ and CO were 62.4449 ppb and 0.1899 ppb,respectively.?3?An in-situ detection system for the index gases of CSC was developed.The system was composed of high sensitive CH₄ and CO sensor,USB virtual serial port and Lab Windows virtual instrument technique.The system can realize real-time acquisition,display and storage of CH₄ and CO concentrations viasimultaneous demodulation of the 1f and 2f spectroscopy signals.?4?Three types of coal samples from Datong Coal Mine were tested by the homemade coal CSC.The mass of three samples were all 100g and the reaction temperature was set by the setp of 5?for each 30 minutes in the range of 30-200?.Meanwhile,each experiment was hold for 17 hours in the experiments.When the hating temperature rises to 70?,the CH₄ concentrations of the three types of coal are 3.3 ppm,1.5 ppm and 4.4 ppm,respectively.The CO becomes detectable at 100?,the CO concentrations of the three types of coal were 3.3ppm,1.5 ppm and 4.4 ppm,respectively.In the isothermal oxidation experiment,the temperature is kept for 100?,and other experimental parameters are the same as the temperature rising oxidation experiment.The results show that the concentrations of CH₄ and CO in the release gasous products of the three kinds of coal decreases slowly,and the oxidation reaction tends to slow down gradually.