- Email: [email protected]
Propane gas leak detection by infrared absorption using carbon infrared emitter and infrared camera
NDT&E International 44 (2011) 57–60
Contents lists available at ScienceDirect
NDT&E International journal homepage: www.elsevier.com/locate/ndteint
Propane gas leak detection by infrared absorption using carbon infrared emitter and infrared camera Naoya Kasai a,n, Chihiro Tsuchiya a, Takabumi Fukuda b,1, Kazuyoshi Sekine a, Takeru Sano c, Tatsumi Takehana c a
Graduate School of Environment and Information Sciences, Yokohama National University 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan Department of System Safety, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan c The High Pressure Gas Safety Institute of Japan, 2-16-4, Tadao, Machida-Shi, Tokyo 194-0035, Japan b
a r t i c l e in fo
abstract
Article history: Received 25 June 2009 Received in revised form 13 September 2010 Accepted 16 September 2010 Available online 21 September 2010
The present study investigated the ability of a system using a carbon infrared emitter (CIE) and an infrared (IR) camera to detect a combustible gas, propane. The CIE transmitted infrared at wavelengths ranging from 1 to 5 mm, and the infrared absorption band of propane gas (3.37 mm) was obtained using a bandpass filter to remove other infrared wavelengths. The intensity of infrared radiation passing through the propane gas decreased as a result of infrared absorption. A clear, real-time image of the gas leak was also obtained using this system. Furthermore, a hazard evaluation of the leakage propane gas was made from a correlation between infrared intensity and the concentration–pathlength product. & 2010 Elsevier Ltd. All rights reserved.
Keywords: Propane gas Infrared absorption Leakage gas image Carbon infrared emitter Infrared thermography
1. Introduction Major accidents can result from gas leaks in facilities that use high pressure gases. Safety measures, such as the use of fixed sensor points, are used to detect these leaks, but early detection depends on weather conditions and the observation points of the gas sensors. Number of studies have tested gas absorption properties using systems with LEDs [1] and lasers [2–6]; however, these studies were unable to obtain clear images of the gas leak. A few studies have successfully visualized leaking gas, one by means of the Backscatter Absorption Gas Imaging (BAGI) technique, which uses a laser spectrally tuned to a gas absorption line and synchronously scanned with an infrared (IR) camera [7,8]. Another study used a split mirror telescope and an IR camera, as well as a CCD camera, to capture gas leak images [9]. Our research group also developed a detection method consisting of an Optical Parametric Oscillator (OPO) laser, an IR camera and a reflecting screen, and a real-time image of the gas leak was generated using this system [10]. The method was subsequently improved using two lasers of different wavelengths, one that included the waveband absorbed by the leakage gas and another that did not include the waveband absorbed by the
n
Corresponding author. Tel.: + 81 45 339 3979; fax: + 81 45 339 4011. E-mail address: [email protected] (N. Kasai). 1 Tel.: +81 258 46 6000.
0963-8695/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ndteint.2010.09.006
leakage gas [11]. The improvements also included installation of fiber optics to broaden the applicability of the system for industrial use [12]. Unfortunately, systems using lasers and optical instruments are very expensive and sensitive to misalignment. High-power lasers are also considered eye hazards as searches are conducted for gas leaks within industrial sites. In the present study, a carbon infrared emitter (CIE) was used as the infrared source, and a liquefied petroleum gas (LP-gas) leak detection system was developed using the CIE and IR camera. A clear, real-time image of the gas leak and a hazard evaluation of leakage propane gas were obtained using the proposed system.
2. Experimental procedures Propane and butane gas have strong absorption bands at 3.37 and 6.80 mm, respectively, as shown in Table 1. The 3.37 mm band was used in the present study because the infrared absorption intensity is very high, and it is not the absorption band of main atmospheric components, such as CO2, H2O and CH4. The CIE, an inexpensive heating appliance, includes the 3.37 mm band and is not sensitive to misalignment within the detection system. The CIE is a possible alternative to a laser, although it must be housed in explosion-proof enclosures for use in actual industrial settings. A CIE (10.5 mm diameter 447 mm length) which transmits
58
N. Kasai et al. / NDT&E International 44 (2011) 57–60
infrared wavelengths of 1–5 mm was chosen for the present study. The peak band irradiated from a CIE with a spectral radiance of 80 W sr 1 m 2 nm 1 is approximately 3 mm. The peak band of the filter used to remove other infrared bands was 3.38 mm, and the full width of the filter at half maximum was 70 nm. A parabolic reflector of mirror-finished stainless steel was used to make the infrared radiation parallel and uniform because the CIE radiation exhibited a narrow bandwidth and low intensity. The parabolic reflector gave an irradiated area of 5.25 10 2 m2. The gas leak detection system proposed in the present study is illustrated in Fig. 1. The IR camera used in the experiment was a Raytheon-Amber Radiance HS with a 256 256 Indium Antimonide (InSb) detector. Prior to measurements, the CIE was controlled using a transformer to set the intensity value of the detector of the IR camera at 4000; the maximum detectable intensity. The CIE and the reflector were placed 2.2–2.5 m away
Table 1 Main infrared absorption bands of propane and butane.
C3H8
C4H10
Infrared band (mm)
Absorption (%)
1.70 3.37 6.80 3.37 6.82
44.7 90.6 19.7 90.5 23.2
from the IR camera. The focus of the IR camera was set to the position of the CIE because clear leakage gas images were obtained under this condition during preliminary experiments, and the exposure time of the camera was set at 1 ms. The purity of the propane gas used in the study was 99.5%, and all experiments were conducted within the laboratory.
3. Results and discussion 3.1. Measurement conditions Changes in infrared intensity were measured as propane (20 cc) was emitted from a syringe 1 m from the IR camera, and the results are shown in Fig. 2. The image of the leakage propane gas is shown in Fig. 2(a), and indicates infrared absorption by leakage propane gas in the blue region. The intensity data extracted along the dotted line in Fig. 2(a) is plotted in Fig. 2(b). The infrared intensity measured with the IR camera decreased to 2000 at pixels 190–210 as a result of the propane gas absorption of CIE transmitted infrared radiation, and suggests that the leakage propane gas is easily detected using the proposed system. We also examined the effect of varying the position of the leak between the IR camera and the CIE. Propane gas was emitted using a syringe at various positions between the IR camera and CIE, and the images obtained using the system are shown in Fig. 3(a). Compared with the boundary between the air and
Carbon infrared emitter Reflecting plate Sampling bag or gas cell
Filter Infrared camera
Infrared radiation
Sketch of experimental setup. Sampling bag Carbon infrared emitter
Infrared camera
Picture of experimental setup Fig. 1. Experimental design for detecting leakage gas and generating real-time image.
N. Kasai et al. / NDT&E International 44 (2011) 57–60
59
Carbon Infrared Emitter A concentration of the propane gas Acquired data line
4500
high
Intensity (Arbitrary unit)
4000
Propane gas emission
3500 3000 2500 Without gas Witht
2000
With gas 1500 170
180
low Leakage propane gas image
190
200 Pixel
210
220
230
Intensity data from leakage propane gas image
Fig. 2. Image of leakage propane gas and change in absorption intensity obtained using the system. The blue region was ‘‘Propane gas image’’.
Acquired data line
Intensity (Arbitrary unit)
4000
1m
1.75m A polyester sampling bag inflated with propane gas.
Leakage gas image at 1 and 1.75 m from the CIE.
3500 3000
Position 2.5 m 1.75 m 1m
2500 2000 1500 1000 500 120 130 140 150 160 170 180 190 Pixel
Intensity data measured using sampling bags at various distances from the CIE.
Fig. 3. Effect of varying gas leak position between the IR camera and the CIE.
propane gas seen in the image at a position 1 and 1.75 m from the IR camera, the boundary seen in the image at 2.5 m (Fig. 2(a)) from the IR camera was clearer because the camera was focused on a point 2.5 m from the IR detector. A polyester sampling bag, having a different absorption band from propane gas, was used to quantitatively evaluate the detection of leakage propane gas. The intensity value of the detector of the IR camera was again set at 4000, as an initial intensity value, by controlling the voltage of the CIE to eliminate the influence of reflected and scattered infrared radiation from the surface of the sampling bag. The sampling bags, inflated with propane gas of purity 99.5%, were positioned 1, 1.75 and 2.5 m from the IR camera, and the intensity data around the boundary of the sampling bag was acquired, as shown in
Fig. 3(b). The intensity data was extracted along the dotted line in Fig. 3(b). Although the slope of the curve representing the intensity at the boundary of the sampling bag 1 m from the IR camera was not as steep as bags at 1.75 and 2.5 m, the absorption intensity due to propane gas was identical at pixels 4160. The ability to detect leakage propane gas did not change as shown in Fig. 3(b), although the sharpness of the boundary between the leakage propane gas and the surrounding air in the intensity image depended on the position of the sampling bag between the IR camera and the CIE. Practical application of the proposed system in actual industrial settings could include monitoring pipelines. We then examined the effect of distance between the IR camera, CIE and
60
N. Kasai et al. / NDT&E International 44 (2011) 57–60
4000
4000
Gas cells:
pathlength (mm); propane gas concentration(ppm)
50; 2,200 100; 2,200
3500 Intensity (Arbitrary unit)
Intensity (Arbitrary unit)
3500
3000
2500
Relative humidity
200; 2,200 3000
50; 5,500 100; 5,500 200;5,500
2500
50;11,000 100; 11,000 200; 11,000
2000
46% 53% 2000
62%
1500 0
500 1000 1500 2000 Propane gas concentration × Pathlength (ppm × m)
2500
Fig. 5. Hazard evaluation of leakage propane gas from change in infrared absorption intensity.
1500 0
10 20 Distance from the IR camera (m)
30 4. Conclusion
Fig. 4. Effect of relative humidity and distance from the IR camera on infrared intensity.
relative humidity because a large variation in relative humidity can be present during the search of actual industrial settings, although an infrared band not absorbed by H2O was chosen. Only a slight decrease in IR intensity was observed, as shown in Fig. 4. Considering practical applications of the proposed system, the effect on IR intensity from these factors is negligible. 3.2. Hazard evaluation of leakage propane gas Moreover, the hazard evaluation of leakage propane gas was conducted using gas cells to decrease the effect of scattered and reflected infrared from the surface of the propane gas containers. Two gas cells of different length (25 and 50 mm, respectively), both with NaCl windows that transmit infrared bands of 0.21– 26 mm, were used. Propane gas was enclosed in the gas cells at concentrations of 1/4 and 1/2 of the lower explosive limit (LEL), 5500 and 11,000 ppm, respectively. Pathlengths of 50, 100, and 200 mm were chosen for several gas cells containing different concentrations of a propane gas, and absorption intensity measurements are shown in Fig. 5. When the parameter of the concentration–pathlength product was the same, such as 11,000 ppm 0.05 m (open square) and 5500 ppm 0.1 m (gray diamond), the IR intensity after absorption due to propane gas was also the same. The IR intensity decreased linearly to 1000 ppm m and then remained at a constant value, having reached the minimum detection limit of the InSb detector after eliminating the decreasing effect of IR intensity due to the NaCl window in order to discuss only the IR absorption for the propane gas. The hazard of leakage propane gas could be evaluated from the propane gas IR absorption intensity curve up to 1000 ppm m. According to the Japanese High Pressure Gas Safety Act, detection at 1/4 of the LEL level (5500 ppm) is required. When propane gas leaks at a concentration of 5500 ppm and 0.1 m thickness in actual industrial settings, the evaluation parameter is 550 ppm m, and, from Fig. 5, the change in propane gas IR absorption intensity at 550 ppm m is approximately 1000, indicating that the leakage gas is easily detected by a change in IR intensity.
In the present study, a clear real-time image of a propane gas leak was obtained using a gas leak detection system consisting of a CIE, parabolic reflector, an IR camera and IR filter. The hazard of the leakage propane gas was also evaluated by changes in infrared intensity absorption measured using the system.
Acknowledgements The authors are grateful for the financial support of a Research Grant from the Iwatani Naoji Foundation. References [1] Chan K, Ito H, Inada H. 10 km-long fibre-optic remote sensing of CH4 gas by near infrared absorptiion. Applied Physics B 1985;38(1):11–5. [2] Uehara K, Tai H, Kimura. K. Real-time monitoring of environmental methane and other gases with semiconductor lasers:a review. Sensors and Actuator B 1997;38:136–40. [3] Iseki T. A protable remote methane detector using an InGaAsP DFB laser. Environmental Geology 2004;46(8):1064–9. [4] Gao X, Fan H, Huang T, Wang X, Bao J, Li X. Natural gas pipeline leak detector based on NIR diode laser absorption spectroscopy. Spectrochimica Acta Part A 2006;65(1):133–8. [5] Minato A, Kobayashi T, Sugimoto N. Laser long-path absorption lidar technique for measuring methane using gas correlation method. Japanese Journal of Applied Physics 1998;37(6A):3610–3. [6] Minato A, Joarder MDMA, Ozawa S, Kadoya M, Sugimoto N. Development of a lidar system for measuring methane using a gas correlation method. Japanese Journal of Applied Physics 1999;38(10):6130–2. [7] McRae TG, Kulp TJ. Backscatter absorption gas imaging: a new technique for gas visualization. Applied Optics 1993;32(21):4037–50. [8] Powers PE, Kulp TJ, Kennedy R. Demonstration of differential backscatter absorption gas imaging. Applied Optics 2000;39(9):1440–8. [9] Sandsten J, Ednet H, Svanberg S. Gas visualization of industrial hydrocarbon emission. Optics Express 2004;12(7):443–51. [10] Sano T, Takehana T, Sekine. K. A study on LP-gas leak detecting system using laser and IR-camera. Journal of High Pressure Institute of Japan 2004;42(1): 36–47. in Japanese. [11] Sano T, Takehana T, Sekine K. Improvement of LP-gas leak detecting system by means of infrared difference absorption. Journal of High Pressure Institute of Japan 2005;43(1):15–21. in Japanese. [12] Sano T, Takehana T, Sekine K. Application of optical fiber to LP-gas leak detection system. Journal of High Pressure Institute of Japan 2005;43(3): 158–63.
Contents lists available at ScienceDirect
NDT&E International journal homepage: www.elsevier.com/locate/ndteint
Propane gas leak detection by infrared absorption using carbon infrared emitter and infrared camera Naoya Kasai a,n, Chihiro Tsuchiya a, Takabumi Fukuda b,1, Kazuyoshi Sekine a, Takeru Sano c, Tatsumi Takehana c a
Graduate School of Environment and Information Sciences, Yokohama National University 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan Department of System Safety, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan c The High Pressure Gas Safety Institute of Japan, 2-16-4, Tadao, Machida-Shi, Tokyo 194-0035, Japan b
a r t i c l e in fo
abstract
Article history: Received 25 June 2009 Received in revised form 13 September 2010 Accepted 16 September 2010 Available online 21 September 2010
The present study investigated the ability of a system using a carbon infrared emitter (CIE) and an infrared (IR) camera to detect a combustible gas, propane. The CIE transmitted infrared at wavelengths ranging from 1 to 5 mm, and the infrared absorption band of propane gas (3.37 mm) was obtained using a bandpass filter to remove other infrared wavelengths. The intensity of infrared radiation passing through the propane gas decreased as a result of infrared absorption. A clear, real-time image of the gas leak was also obtained using this system. Furthermore, a hazard evaluation of the leakage propane gas was made from a correlation between infrared intensity and the concentration–pathlength product. & 2010 Elsevier Ltd. All rights reserved.
Keywords: Propane gas Infrared absorption Leakage gas image Carbon infrared emitter Infrared thermography
1. Introduction Major accidents can result from gas leaks in facilities that use high pressure gases. Safety measures, such as the use of fixed sensor points, are used to detect these leaks, but early detection depends on weather conditions and the observation points of the gas sensors. Number of studies have tested gas absorption properties using systems with LEDs [1] and lasers [2–6]; however, these studies were unable to obtain clear images of the gas leak. A few studies have successfully visualized leaking gas, one by means of the Backscatter Absorption Gas Imaging (BAGI) technique, which uses a laser spectrally tuned to a gas absorption line and synchronously scanned with an infrared (IR) camera [7,8]. Another study used a split mirror telescope and an IR camera, as well as a CCD camera, to capture gas leak images [9]. Our research group also developed a detection method consisting of an Optical Parametric Oscillator (OPO) laser, an IR camera and a reflecting screen, and a real-time image of the gas leak was generated using this system [10]. The method was subsequently improved using two lasers of different wavelengths, one that included the waveband absorbed by the leakage gas and another that did not include the waveband absorbed by the
n
Corresponding author. Tel.: + 81 45 339 3979; fax: + 81 45 339 4011. E-mail address: [email protected] (N. Kasai). 1 Tel.: +81 258 46 6000.
0963-8695/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ndteint.2010.09.006
leakage gas [11]. The improvements also included installation of fiber optics to broaden the applicability of the system for industrial use [12]. Unfortunately, systems using lasers and optical instruments are very expensive and sensitive to misalignment. High-power lasers are also considered eye hazards as searches are conducted for gas leaks within industrial sites. In the present study, a carbon infrared emitter (CIE) was used as the infrared source, and a liquefied petroleum gas (LP-gas) leak detection system was developed using the CIE and IR camera. A clear, real-time image of the gas leak and a hazard evaluation of leakage propane gas were obtained using the proposed system.
2. Experimental procedures Propane and butane gas have strong absorption bands at 3.37 and 6.80 mm, respectively, as shown in Table 1. The 3.37 mm band was used in the present study because the infrared absorption intensity is very high, and it is not the absorption band of main atmospheric components, such as CO2, H2O and CH4. The CIE, an inexpensive heating appliance, includes the 3.37 mm band and is not sensitive to misalignment within the detection system. The CIE is a possible alternative to a laser, although it must be housed in explosion-proof enclosures for use in actual industrial settings. A CIE (10.5 mm diameter 447 mm length) which transmits
58
N. Kasai et al. / NDT&E International 44 (2011) 57–60
infrared wavelengths of 1–5 mm was chosen for the present study. The peak band irradiated from a CIE with a spectral radiance of 80 W sr 1 m 2 nm 1 is approximately 3 mm. The peak band of the filter used to remove other infrared bands was 3.38 mm, and the full width of the filter at half maximum was 70 nm. A parabolic reflector of mirror-finished stainless steel was used to make the infrared radiation parallel and uniform because the CIE radiation exhibited a narrow bandwidth and low intensity. The parabolic reflector gave an irradiated area of 5.25 10 2 m2. The gas leak detection system proposed in the present study is illustrated in Fig. 1. The IR camera used in the experiment was a Raytheon-Amber Radiance HS with a 256 256 Indium Antimonide (InSb) detector. Prior to measurements, the CIE was controlled using a transformer to set the intensity value of the detector of the IR camera at 4000; the maximum detectable intensity. The CIE and the reflector were placed 2.2–2.5 m away
Table 1 Main infrared absorption bands of propane and butane.
C3H8
C4H10
Infrared band (mm)
Absorption (%)
1.70 3.37 6.80 3.37 6.82
44.7 90.6 19.7 90.5 23.2
from the IR camera. The focus of the IR camera was set to the position of the CIE because clear leakage gas images were obtained under this condition during preliminary experiments, and the exposure time of the camera was set at 1 ms. The purity of the propane gas used in the study was 99.5%, and all experiments were conducted within the laboratory.
3. Results and discussion 3.1. Measurement conditions Changes in infrared intensity were measured as propane (20 cc) was emitted from a syringe 1 m from the IR camera, and the results are shown in Fig. 2. The image of the leakage propane gas is shown in Fig. 2(a), and indicates infrared absorption by leakage propane gas in the blue region. The intensity data extracted along the dotted line in Fig. 2(a) is plotted in Fig. 2(b). The infrared intensity measured with the IR camera decreased to 2000 at pixels 190–210 as a result of the propane gas absorption of CIE transmitted infrared radiation, and suggests that the leakage propane gas is easily detected using the proposed system. We also examined the effect of varying the position of the leak between the IR camera and the CIE. Propane gas was emitted using a syringe at various positions between the IR camera and CIE, and the images obtained using the system are shown in Fig. 3(a). Compared with the boundary between the air and
Carbon infrared emitter Reflecting plate Sampling bag or gas cell
Filter Infrared camera
Infrared radiation
Sketch of experimental setup. Sampling bag Carbon infrared emitter
Infrared camera
Picture of experimental setup Fig. 1. Experimental design for detecting leakage gas and generating real-time image.
N. Kasai et al. / NDT&E International 44 (2011) 57–60
59
Carbon Infrared Emitter A concentration of the propane gas Acquired data line
4500
high
Intensity (Arbitrary unit)
4000
Propane gas emission
3500 3000 2500 Without gas Witht
2000
With gas 1500 170
180
low Leakage propane gas image
190
200 Pixel
210
220
230
Intensity data from leakage propane gas image
Fig. 2. Image of leakage propane gas and change in absorption intensity obtained using the system. The blue region was ‘‘Propane gas image’’.
Acquired data line
Intensity (Arbitrary unit)
4000
1m
1.75m A polyester sampling bag inflated with propane gas.
Leakage gas image at 1 and 1.75 m from the CIE.
3500 3000
Position 2.5 m 1.75 m 1m
2500 2000 1500 1000 500 120 130 140 150 160 170 180 190 Pixel
Intensity data measured using sampling bags at various distances from the CIE.
Fig. 3. Effect of varying gas leak position between the IR camera and the CIE.
propane gas seen in the image at a position 1 and 1.75 m from the IR camera, the boundary seen in the image at 2.5 m (Fig. 2(a)) from the IR camera was clearer because the camera was focused on a point 2.5 m from the IR detector. A polyester sampling bag, having a different absorption band from propane gas, was used to quantitatively evaluate the detection of leakage propane gas. The intensity value of the detector of the IR camera was again set at 4000, as an initial intensity value, by controlling the voltage of the CIE to eliminate the influence of reflected and scattered infrared radiation from the surface of the sampling bag. The sampling bags, inflated with propane gas of purity 99.5%, were positioned 1, 1.75 and 2.5 m from the IR camera, and the intensity data around the boundary of the sampling bag was acquired, as shown in
Fig. 3(b). The intensity data was extracted along the dotted line in Fig. 3(b). Although the slope of the curve representing the intensity at the boundary of the sampling bag 1 m from the IR camera was not as steep as bags at 1.75 and 2.5 m, the absorption intensity due to propane gas was identical at pixels 4160. The ability to detect leakage propane gas did not change as shown in Fig. 3(b), although the sharpness of the boundary between the leakage propane gas and the surrounding air in the intensity image depended on the position of the sampling bag between the IR camera and the CIE. Practical application of the proposed system in actual industrial settings could include monitoring pipelines. We then examined the effect of distance between the IR camera, CIE and
60
N. Kasai et al. / NDT&E International 44 (2011) 57–60
4000
4000
Gas cells:
pathlength (mm); propane gas concentration(ppm)
50; 2,200 100; 2,200
3500 Intensity (Arbitrary unit)
Intensity (Arbitrary unit)
3500
3000
2500
Relative humidity
200; 2,200 3000
50; 5,500 100; 5,500 200;5,500
2500
50;11,000 100; 11,000 200; 11,000
2000
46% 53% 2000
62%
1500 0
500 1000 1500 2000 Propane gas concentration × Pathlength (ppm × m)
2500
Fig. 5. Hazard evaluation of leakage propane gas from change in infrared absorption intensity.
1500 0
10 20 Distance from the IR camera (m)
30 4. Conclusion
Fig. 4. Effect of relative humidity and distance from the IR camera on infrared intensity.
relative humidity because a large variation in relative humidity can be present during the search of actual industrial settings, although an infrared band not absorbed by H2O was chosen. Only a slight decrease in IR intensity was observed, as shown in Fig. 4. Considering practical applications of the proposed system, the effect on IR intensity from these factors is negligible. 3.2. Hazard evaluation of leakage propane gas Moreover, the hazard evaluation of leakage propane gas was conducted using gas cells to decrease the effect of scattered and reflected infrared from the surface of the propane gas containers. Two gas cells of different length (25 and 50 mm, respectively), both with NaCl windows that transmit infrared bands of 0.21– 26 mm, were used. Propane gas was enclosed in the gas cells at concentrations of 1/4 and 1/2 of the lower explosive limit (LEL), 5500 and 11,000 ppm, respectively. Pathlengths of 50, 100, and 200 mm were chosen for several gas cells containing different concentrations of a propane gas, and absorption intensity measurements are shown in Fig. 5. When the parameter of the concentration–pathlength product was the same, such as 11,000 ppm 0.05 m (open square) and 5500 ppm 0.1 m (gray diamond), the IR intensity after absorption due to propane gas was also the same. The IR intensity decreased linearly to 1000 ppm m and then remained at a constant value, having reached the minimum detection limit of the InSb detector after eliminating the decreasing effect of IR intensity due to the NaCl window in order to discuss only the IR absorption for the propane gas. The hazard of leakage propane gas could be evaluated from the propane gas IR absorption intensity curve up to 1000 ppm m. According to the Japanese High Pressure Gas Safety Act, detection at 1/4 of the LEL level (5500 ppm) is required. When propane gas leaks at a concentration of 5500 ppm and 0.1 m thickness in actual industrial settings, the evaluation parameter is 550 ppm m, and, from Fig. 5, the change in propane gas IR absorption intensity at 550 ppm m is approximately 1000, indicating that the leakage gas is easily detected by a change in IR intensity.
In the present study, a clear real-time image of a propane gas leak was obtained using a gas leak detection system consisting of a CIE, parabolic reflector, an IR camera and IR filter. The hazard of the leakage propane gas was also evaluated by changes in infrared intensity absorption measured using the system.
Acknowledgements The authors are grateful for the financial support of a Research Grant from the Iwatani Naoji Foundation. References [1] Chan K, Ito H, Inada H. 10 km-long fibre-optic remote sensing of CH4 gas by near infrared absorptiion. Applied Physics B 1985;38(1):11–5. [2] Uehara K, Tai H, Kimura. K. Real-time monitoring of environmental methane and other gases with semiconductor lasers:a review. Sensors and Actuator B 1997;38:136–40. [3] Iseki T. A protable remote methane detector using an InGaAsP DFB laser. Environmental Geology 2004;46(8):1064–9. [4] Gao X, Fan H, Huang T, Wang X, Bao J, Li X. Natural gas pipeline leak detector based on NIR diode laser absorption spectroscopy. Spectrochimica Acta Part A 2006;65(1):133–8. [5] Minato A, Kobayashi T, Sugimoto N. Laser long-path absorption lidar technique for measuring methane using gas correlation method. Japanese Journal of Applied Physics 1998;37(6A):3610–3. [6] Minato A, Joarder MDMA, Ozawa S, Kadoya M, Sugimoto N. Development of a lidar system for measuring methane using a gas correlation method. Japanese Journal of Applied Physics 1999;38(10):6130–2. [7] McRae TG, Kulp TJ. Backscatter absorption gas imaging: a new technique for gas visualization. Applied Optics 1993;32(21):4037–50. [8] Powers PE, Kulp TJ, Kennedy R. Demonstration of differential backscatter absorption gas imaging. Applied Optics 2000;39(9):1440–8. [9] Sandsten J, Ednet H, Svanberg S. Gas visualization of industrial hydrocarbon emission. Optics Express 2004;12(7):443–51. [10] Sano T, Takehana T, Sekine. K. A study on LP-gas leak detecting system using laser and IR-camera. Journal of High Pressure Institute of Japan 2004;42(1): 36–47. in Japanese. [11] Sano T, Takehana T, Sekine K. Improvement of LP-gas leak detecting system by means of infrared difference absorption. Journal of High Pressure Institute of Japan 2005;43(1):15–21. in Japanese. [12] Sano T, Takehana T, Sekine K. Application of optical fiber to LP-gas leak detection system. Journal of High Pressure Institute of Japan 2005;43(3): 158–63.