Fiber Methane Gas Sensor and Its Application in Methane Outburst Prediction in Coal Mine

JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY OF CHINA, VOL. 6. NO 4, DECEMBER 2008373Fiber Methane gas Sensor and Its application inMethane Outburst prediction in Coal mineJia-Sheng Ni, Jun Chang, Tong-Yu Liu, Yan-Fang Li, Yan-Jie Zhao, and Qian WangAbstrack-Fiber optic methane gas detecting system relatively broadband sources with linewidth typically of thebased on distributed feedback(DFB)laser wavelength order of 20 nm to 100 nm2. However, the absorption linesscanning technique is demonstrated. Wavelength scan of of methane have a natural linewidth much less than this,methane absorption peak at 1665.9 nm is realized by which results in a very small intensity variation even forsaw tooth modulation of current which is injected to relative large gas concentrations. Some systems useDFB laser. a reference methane gas cell is used to find broadband source and a comb filter with its transmithe methane absorption peak around 1666 nm, and peaks matched to the absorption lines of methane 2,31normalization is used to reduce the outside affection this method is complex and unsteady. The use of asuch as power drif fiber loss. Concentration is got by source with a narrow linewidth locked at one of the majarithmetic processing absorption coefficient of the methane absorption lines will increase the fractional changemethane gas. In-situ test is carried out in coal mine and in the light signal when the gas is present+).However,long time precision of 0.05%is achieved. Some spot data power and the wavelength of the laser will be changed withof coal mine is introduced. By the system, methane the temperature, driving current, working environment andoutburst can be measuredso on, hence it will affect the results even with temperaturechange. In order to avoid this problem, usually a referenceIndex TermsMethane outburst, prediction, optical light whose wavelength is different from methane gasabsorption, wavelength scan.absorption lines is used. However, it still has the problemsof unsteady because it mayfilte1. IntroductionTechnique based on frequency harmonic detection[Ihasbeen also developed the ratio of the fundamental andThe coal and gas outburst is the synthetic result of stress, second harmonic signal presented can be used forgas pressure, and the physical mechanics of coal and so on. eliminating optical interference, but it is complicated andMany works have been done to improve the novel could not resolve the problems of temperature affectiontechniques of coal mine safety monitor for gas outburst in We present fiber optic multiplexed methane gasroadway face In order to protect people and avoid detecting system based on distributed feedback(DFB)laserdestructive sequence, it is necessary to design a system that wavelength scanning technique. Wavelength scan ofcan achieve methane outburst prediction in coal mine. methane absorption peak at 1665. 9 nm is realized by sawMethane detecting is very important for outburst prediction. tooth modulation of current which is injected to DFB laser.Optical fiber methane sensor is a new technique and is safer A reference methane gas cell is used to find the methaneespecially in coal mine.absorption peak around 1666nm, and normalization is usedOptical fiber methane gas sensors based on absorption to reduce the outside affection such as power drift, fiberhave attracted considerable attention in recent years because loss. Concentration is got by arithmetic processingof their remote detection capability, safety in hazardous absorption coefficient of the methane gas. Application testenvironments, and immunity to electro magnetic radiatiois carried out in coal mine and long time precision of 0.05%The most common methane-detection systems use is achieved.Manuscript received September 20, 2008; revised September 5, 20082. Experiments and Resultssupported in partthe National Natural SciencDFB lasers has been developed near-infrared forFoundation of Shandong Province under Grant No. 2006ZRC01022, and methane monitoring recently s 1. The key features of theResearch Fund for the Doctoral Program of Higher Education of Chinaunder grant No. 20060422025DFB lasers are their very narrow linewidth, typicallyJ.S.Ni, T.Y. Liu, Y.F. Li, Y Zhao, and Q Wang are with Laser less tha中国煤化 T than the linewidth ofInstitute, Shandong Academy of Science, Jinan, 250014, China(e-mail: a singand the ability tonjsh51@hotmail.comJ. S. Ni and J. Chang are with School of Information Science andCNMHG output through theTechnology, Shandong University, Jinan, 250100, Chinainjection crIn this system, DFB lasers which areOURNAL OF ELECTRONICCE AND TECHNOLOGY OF CHINA, VOL 6, NO 4, DECEMBER 2008urce, and lines represent the output signal when the methaneself-reference is used to avoid effect of the powerconcentration is 0. 2%, 1.5%, and 5% respectivelySchematic of the experiment setup is shown in Fig. 1ation 3)can be moAn optic switch is used to make the system be able to detectmultiplex points. The light coming from DFB is transmitC--In//(aL).through fiber into the gas cell located at long-distance spot.Hence, the concentration of the methane gas can be gotAccording to the Beer-Lambert's law, the output power haseference gas cell which is filled with pure CH4 gas isa fixed relationship with CHa gas concentrationused in this system. With the help of the reference gas cell,P-Poexp(aCL)() absorbing peak of CH4 can be fixed accurately.where P is received signal power, Po is input signal power,is absorptioient of CHa gas molecule, C is CH4gas concentration and L is gas cell lengthFiber cableSensor 1tic switchReference gas cellFig 3 Signal of difTerent concentration.In order to make this system have practical use, the gaDetectorcell must be dust-proof, moisture-proof and indestructibleThe out layer of gas cell is made of stainless steel.Fig. 1. Multiplexed methane gas contest system.Dust-proof and moisture-proof material is stuffed into itSignal coming back from the sensor is shown in Fig. 2. Inside the cell, we use the fiber collimator to guide the lightThe solid line is none methane's signal received by detector, in and out of the fiber; the collimator is made up ofand the dashed line is 5% concentration methane gas graded-index (GRIN)lens which is fixed to V-groove. Itwill provide a 5 cm' s absorbing cavity. The inside structureand outside picture of the sensor cell are shown in Fig. 4nd Fig. 5.5,444HR mirror3333Fig. 4. Structure of the gas cellFig 2 Signal of different concentration.The expression without methane gas absorbed signal is:To be a divisor of (2), (i) can avoid the influence ofthe transmission loss中国煤化工F-P(c-o/p=exp(-aCD)By (3), the methane gas absorbed signal will becomeCNMHGmore regular as shown in Fid, dashed, dotted Fig. 5. Outside picture of the gas cell.Niet al: Methane Outburst Prediction in Coal Mine3. Applications and ResultFrom Fig. 8 we can see that fiber optic system has lowoffset and the ability of detecting the bursting of methaneThis system has been put into operation in coal mine. earlier. Some characters of weensy methane outburst appearThe DFB laser is sawtooth-drived with frequency of 14Hz by the blasting in mining processThe sampling rate of A/d is 10 kHz. a 6 km fiber cable isused in coal mine to connect probes and supervision room.All of the equipments of the system are put into supervisionroom except the sensors, so that it can keep the electronicdevice away from the mine目021830-y9+特§05-60010:48153620241:126:00Fig 8. Observation of methane outburst caused by blasting81216202428onclusionsCalibrated CH4ntration(‰)We developed fiber optic methane gas detecting systemFig. 6. Signal of different concentrationbased on distributed feedback (DFB) laser wavelengthscanning technique. Wavelength scan of methane absorptioFig. 6 shows the comparison of the standardpeak at 1665.9 nm is realized by saw tooth modulation ofconcentration and measured result.e withcurrent which is injected to DFB laser. a reference methanether very well.as cell is used to find the methane absorption peak around1666 nm, and normalization is used to reduce the outsideaffection such as power drift, fiber loss. Concentration isgot by arithmetic processing absorption coefficient of themethane gasThis system has been worked for about four monthscontinuously, application test is carried out in coal minelong-term precisioncharacters of weensy methane outburst appear by theblasting in mining process. It is in prospect to achieveprediction of methane outburst with the advanced worksand spot data accumuReferencesFig. 7. Probe mounted on the roof of roadway[]Y-J Sun and J. s Qian, "Forecast the dangerous level of gasAs shown in Fig. 7, probes are mounted on the roof ofoutburst based on GASA neural networks in coal mine. "inroadway Airflow of coal mine flows through the roadwayProc. Third International Conference on Naturalwhere the probe is placed. Any outburst of methane gas willComputation(CNC 2007), Beijing, 2007, pp 641-645make the air composition changed, and the methane [2]W. Jin, G Cooper, CB.Carlisle, and HRiris,"Absorptionconcentration is detected by the gas sensor. Digging processmeasurement of methane gas with a broadband light sourcein coal mine such as drilling, would makes concomitant ofand interferometric signal processing, "Optics Letters, vol. 18,methane gas spilling. Mine area may be have hidden dangerno16,pp.1364-1366,1993of methane outburst if the air composition abnormal B3]J. S Ni, T-Y. Liu, J. Chang, et al "A low cost mutiplexed1.331 um spectroscopic remote methane sensor system,changed. By the long-term detection of methaneectronics and Micro-concentration, some of the rule would be accumulated for中国煤化工6595215200the prediction. In the Fig 8, undertone line shows the data [4]Yby fiber optic system and the saturated line shows the dataCNMHGa M Aizawa, and Hrv,al variation in columnby electronic equipment that used in coal mine widelysundance of atmospheric CH4," IEEE Photom. Technol.JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY OF CHINA, VOL 6, NO 4, DECEMBER 2008vol3,no.l,pp.386-387,1991working at Laser Institute, Shandong Academy of Science. His[5]K Uehara and H Tai, Remote detection of methaneresearch interests include Fiber Sensing Technology and Coal1. 66um diode laser,"Appl. Opt., vol. 31, no. 6, pp. 80jun Chang was born in Shandong Province, China, in 1967.[6] S -T. Wang, J. Liu, R-S. Che, and Y -T. Wang, "A methane He received the B Eng, degree from Shandong University. Hegas sensor with optic fiber based on frequency harmonic joined in Shandong University as a professor. His research interestdetection technique, "J. Applied Optics, vol. 25, no. 2, is in optical fiber sensor.pp.44-47,2004Tong- Yu Liu was bom in Shandong Province, China, in 1963[7 R. U Martinelli, R J Menna, D E. Cooper, C B. Carlisle, He is the General Manager and founder of Shandongand H. Riris, "Near-infrared In GaAs/Inp distributed feedback Micro-Sensor Ltd of Jinan, China.lasers for spectroscopic applications, Proc. of SPIE,Yan-Fang Li was bom in Shandong Province, China, in 1980.vol.2l48,pp.292-307,199She received the M. Eng. degree from Shandong University. From[8]V, Weldon, J. O'Gorman, and P. Phelan, "Gas sensing with 2006, he joined in Laser Institute of Shandong Academy ofa-1.57um distributed feedback laser diodes using overtone Science as an engineer. Her research interest is in optical fibervoL.33,pp3867-3870,Dec.1994.Yan-Jie Zhao was bom in Shandong Province, China, in[9]G Stewart, A. Mencaglia, W. Philp, and J. Wei, "Interfero. 1981. She received the M.s. degree from the University ofmetric signals in fiber optic methane sensors with wavelength Science and Technology of China. From 2006, he joined in Lasermodulation of the DFB laser source, "Journal of Lightwave Institute of Shandong Academy of Science as an engineer. Herechnology, vol. 16, no. 1, pp. 43-53, 1998research interest is in optical fiber sensorQian Wang was born in Guizhou Province, China, in 1970Ni-Jia Sheng was bom in Shandong Province, China, in 1982. He received the B Eng. degree from Shandong University. HerHe graduated from the Shandong University. He is currently research interest is in optical fiber sensor.中国煤化工CNMHG