Determination Of Trace Ethylene In Coal Mine Based On Tunable Laser Technology Research On Gas Detection

There are a lot of coal forming periods in our country and many kinds of coal geological types.The coal spontaneous combustion early forecast is the key for preventing spontaneous combustion of coal,one of the important indicators of ethylene gas as a coal mine used to forecast the fire,because the temperature range was narrow,when you only need to detect whether there is the critical value of ethylene can make qualitative judgment,so it is the most ideal medium coal fire forecast index gas.Using tunable diode laser absorption spectroscopy(TDLAS)based on the detection technology of gas can be achieved without pre sampling,high precision,fast response,and multi parameter detection,without manual calibration and other advantages,has now become the method of real-time online detection of gas in the fastest speed for the development of A.The main purpose of this study is to develop trace ethylene gas detection equipment suitable for underground detection,and changing the light source of the system can be applied to other trace gases,there is a general reference value to the trace gas detection.By selecting the characteristic spectrum of gas molecular absorption,formation causes and influencing factors of line broadening and analyzed using wavelength modulation method to realize modulation of the laser output frequency through the laser drive current is loaded on a high frequency modulation signal,and the modulation coefficient and modulation frequency were optimized.The concentration of fitting two harmonic peak is located at 1626.04nm,the fitting relationship between the two harmonic peak and the concentration of the solution;and using wavelet transform method to achieve denoising and baseline correction of two problems at the same time;due to changes in temperature and pressure will cause changes in the line width of the gas absorption,thus the impact of the measurement results.From the experimental point of view,the change trend of the intensity and the line width of the main absorption peak with temperature and pressure is analyzed.Based on the equipment of transmitting and receiving unit,the three part of the long path absorption pool and circuit system are designed;and the use of Fourier transform spectrometer of DFB tunable semiconductor laser tuning characteristics test results show that the current tuning ability of 0.0065nm/mA,the temperature tuning capability is 0.1nm/DEG C;the design of long path absorption structure withWhite pool pool,path length can be adjusted according to need;complete the development of trace ethylene gas detection system TDLAS.Finally,through the measurement of equipment efficiency,safety performance,electromagnetic compatibility of three aspects to make the performance test.Through the contrast test with gas chromatograph in measuring efficiency,the realization of 4×10-6 ethylene gas stable detection using 100×10-6 standard;ethylene gas and gas distribution system,in different concentration on the stability of the system was tested.The result shows that the stability after the concentration deviation is less than 2×10-6;through repeated experiments found that reproducible results are less than 1×10-6.In order to ensure the equipment suitable for underground flammable and explosive environment,the overcurrent and overvoltage test and short circuit test of equipment,passed the spark discharge experiment of five kinds of situation in the national coal mine safety product quality supervision and inspection center;anti-interference ability test of electrostatic discharge immunity test,power frequency magnetic field immunity test fast transientburst immunity test and Simulation of vibration trough and simulated mine environment comprehensive test device for equipment prototype,test equipment electromagnetic compatibility.