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Gas sensor
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In order to detect hydrocarbons, such as methane, or, ethane, from natural gas leaks, the laser must be set to a wavelength, at which these gases have appropriate absorption lines.
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For a low measurement threshold, the absorption value of the gas should be as high as possible. Potential absorption curves for the detection of methane (CH4) are located in the spectral range from 1.6µm to 4.0µm, with three significant bands at about 1.6µm, 2.3µm, and 3.3µm. The strongest absorption lines are located at about 3.3µm. Ethane (C2H6) also has absorption lines in this range.
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However, overlapping with the absorption lines of water vapour, must also be taken into consideration.
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The design calculations, made in the course of work on this feasibility study, indicate that appropriately selected LIDAR systems would be in a position to detect the required very small leaks of below 0.1 cubic meters per hour, from altitudes of up to 300 meters.
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This method therefore appears to be suitable for gas-leak detection, during regular aerial patrols, with small helicopters.
Use of Quantum Cascade laser diodes to detect ethane gas
from www.cascade-technologies.com
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Shell turns to cascade lasers for oil exploration |
A cross-disciplinary UK consortium wins funding to develop a laser detection system that could be used to discover hidden fields of oil and natural gas. A UK team is working on a £2.4 million ($4.5 million) project to develop an optical system based on quantum cascade lasers for oil and gas prospecting.
Comprising the III-V foundry Compound Semiconductor Technologies (CST), the Universities of Sheffield and Glasgow, Shell Global Solutions and laser system specialist Cascade Technologies, the consortium has received just over £1 million from the UK government's Department of Trade and Industry (DTI). The industrial partners are providing the remaining £1.4 million. Energy giant Shell will fund field testing of the instrument once the development is completed.
The detection system will be based on photoacoustic spectroscopy, a technique that can be used to measure gas concentrations with remarkable sensitivity. CST commercial director Wyn Meredith explained that ethane (C2H6) is the crucial hydrocarbon that gives a strong clue as to the likely location of an undiscovered field of oil or gas.
Ethane and methane (CH4) gas are produced when larger hydrocarbons - typically found in oil and gas reserves - " crack" into smaller molecules. Unlike methane, however, ethane is not produced by biological decay and so it is a far more reliable indicator. QCLs allow instrument size reduction
Shell already uses a system based on a mid-infrared lead-salt laser, to probe for ethane in its so-called " LightTouch" prospecting equipment. However, these relatively bulky lasers require cryogenic cooling and the mobility of the system can be an issue. By incorporating III-V-based quantum cascade lasers (QCLs) instead, the size of these systems could be greatly reduced. " Using the photoacoustic spectroscopy approach, we hope to produce an instrument that has an ethane sensitivity of around 100 parts per trillion," said Meredith.
Researchers at the University of Sheffield will be growing QCL structures, using novel antimonide-based epitaxy, to reach the crucial 3.35 µm absorption band of ethane. The material development is needed because commercial QCLs that are currently available, operate at longer wavelengths.
Using designs developed with the electronics and electrical engineering department at Glasgow, CST will fabricate laser devices from the material produced at Sheffield, while Cascade will provide module-level packaging and control electronics.
Glasgow's physics department will then develop the photoacoustic instrument, in conjunction with Shell, until it is ready for field trials. " The long-term aim is to set up a UK supply chain - from design to packaged device to system implementation," explained Meredith. " This is strengthened by Cascade securing the rights to source QCLs from foundry manufacturers." Cascade and Lucent Technologies recently signed a deal over the intellectual property relating to QCL devices.
About the author
Michael Hatcher is editor of Compound Semiconductor
- from http://optics.org/optics/Articles/ViewArticle.do?channel=business& articleId=26114
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