Peter Schwengler, E.ON Ruhgas AG, Essen, Germany;
and Dr. Roland Harig, Hamburg University of Technology, Hamburg, Germany
Scientists from the Hamburg University of Technology have developed a new method for remote detection and imaging of gas releases and emissions on behalf of a GERG group under leadership of E.ON Ruhrgas AG. Based upon scanning imaging FTIR spectrometry, the technology combines a video image with a false color image which enables the user to detect and pinpoint the source of methane.
In order to ensure the safe and economic operation of natural gas networks and gas plants, gas releases should be detected as soon as possible. Currently, hand-held systems based on flame ionisation detectors or semiconductor gas sensors are used to inspect pipelines and plants. However, the inspection of pipelines and gas plants is very time consuming, and the probability of the detection of a gas escape is dependent on the experience of the operator.
Moreover, potential leaks may be located in inaccessible areas. Thus, the possibility of remote detection of gas leaks in real time over long distances is highly desirable. It could be an important tool to enhance safety and efficiency during the construction and operation of gas pipelines and facilities. The goal here is to describe the gas camera technology, and describe the results of the detection experiments that were conducted to test the system.
Passive remote detection
The method of remote detection using infrared spectrometry is based on the spectral analysis of radiation in the infrared spectral range that is absorbed and emitted by the molecules of a gas cloud. The method is a passive method which analyzes ambient radiation. The wavelengths at which a molecule absorbs infrared radiation are characteristic of a molecule. This means that substances can be detected by analysis of ambient radiation. The principle is shown in Figure?1. Radiation from the background propagates towards the gas cloud, and on through the gas cloud towards the atmosphere between the cloud and the detection system – in our case the gas camera. The radiation measured by the gas camera contains the spectral signatures of the background, of the cloud molecules as well as of the atmosphere between the background and the detector. Both topographic features and the sky can serve as a background for a measurement.
Gas camera
The gas camera is based on the combination of a highly sensitive infrared optical detection system with a detector array (focal plane array) and two spectral band pass filters. The filters serve for selecting two particular narrow frequency ranges from the incident radiation. In addition, the system contains an automatic calibration system.
The pass band of one spectral filter is matched to the absorption band of the target gas (target gas filter). The pass band of a second filter does not contain strong absorption lines of the target gas (reference filter). The filter characteristics are illustrated in Figure 2. Moreover, Figure 2 shows the absorption band of methane that is used for the detection.
The system operates in the long wave infrared (LWIR) spectral region exploiting the absorption signature of methane at 7.7 µm or 1300 cm-1. This is the optimized spectral region for the detection of methane, yielding the lowest (best) detection limits for the detection of small gas releases.
Figure 3 displays the gas camera. The system is operated using Lithium-Ion batteries. This allows autonomous operation for about six hours with dual battery packs.
For simple interpretation of the results, the system is equipped with a video camera. The gas image, which is the result of the analysis of the recorded IR-radiation, is superimposed on the image simultaneously provided by the video camera. Therefore, the operator is able to easily locate a methane cloud and the source of the cloud (Figure 4). Between 5 and at least 10 gas images per second are displayed currently, depending on the settings for the analysis.
Results and discussion
In order to test the detection capabilities of the gas camera, experiments were performed. Figure 4 shows a gas image, a single image of the continuously measured sequence of images, of a methane plume. The release rate was 200 l/h and the distance between the source of methane and the gas camera was 42 m. Figure 5 shows the result of a measurement in which the sky was used as the background. The gas was released through an open window of the laboratory. The release rate was 50 l/h and the distance between the source of methane and the gas camera was 6 m.
Summary and conclusions
The gas camera allows real-time detection and visualization of gas plumes. The overlay of the gas image and the video image results in a simple interpretation of the measurements. The system is unique due to real-time visualization of gas plumes; and, by direct visualization in the video image, the sources allow action to be taken directly, if required. In contrast to active detection systems that use an artificial source of radiation, the dependence of the signal on the distance is not strong. Thus, long-range detection (distance>100 m) is feasible, as demonstrated in this work.
The system can be used for the regular tightness tests of facilities (compressor stations, underground storage facilities, well heads, metering and pressure regulator stations, valve stations) and for proving tightness of newly built installations. It will be a valuable tool for quality assurance during construction and for the final approval after construction has finished. Additional applications would be the surveillance of pipeline construction sites and monitoring of gas releases either due to operational needs or in the case of emergency. The observation of operational gas releases from vent stacks may serve for verifying the calculated size of hazardous zones that have to be kept free of ignition sources close to these installations.
Also, stationary operation of the system seems to be advantageous, for instance, in facilities with enhanced safety requirements. The gas camera saves much time compared to conventional methods in all of the aforementioned cases. After the development of a marketable version, the gas camera will be produced under the brand name GasCam by Esders GmbH, Haselünne, Germany.
Acknowledgment
Based on a paper presented at the International Gas Union’s 23rd World Gas Conference, Amsterdam, The Netherlands
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