FEATURE OPTICAL GAS IMAGING SEEING IS BELIEVING – PINPOINTING EMISSIONS
Optical Gas Imaging (OGI) enables users to visualise hydrocarbon gases, which helps prevent leaking or venting to the atmosphere. Craig O’Neill, strategic business development manager, FLIR, explains...
I
nfrared (IR) thermal imaging cameras have been used for decades for a
variety of oil and gas applications, including electrical/mechanical inspections, tank level inspections, and even examinations of pipe integrity within process equipment. In recent years, new optical gas imaging (OGI) technology has been developed which can “see” hydrocarbon gases and volatile organic compounds (VOCs) that are venting or leaking to the atmosphere. OGI can be used for meeting regulatory emission reduction requirements, while also helping to reduce product loss, which in turn provides positive return on investment. OGI cameras save time compared to other inspection technologies and also offer safety advantages for operators. Major energy companies are using OGI cameras like the FLIR GF320 to quickly check thousands of components and identify potential gas leaks in real-time. The U.S. natural gas industry as a whole
emitted 162.4 million metric tons CO2 equivalent of methane in 20151
. In
addition to regulatory compliance issues, this equates to lost product for operators. The industry is faced with how to best find and repair natural gas leaks at potential escape points, including compressor stations, processing plants, hydraulically-fractured wells, and along transportation lines. Before the development of OGI cameras,
most oil and gas facilities used a toxic vapor analyser (TVA), otherwise known as a “sniffer,” to analyse gas concentration levels and quantify gas emitted to the atmosphere. TVAs are reliable, relatively low cost, and can identify most gases, but the operator must know exactly where to go to look for the fault – and physically touch it. Sniffers are like playing pin the tail on the donkey, while optical gas imaging is the same game – but without a blindfold. Also, OGI can be 5-10 times faster than a sniffer. Other safety advantages of OGI over a
traditional TVA include the remote detection of a gas that could potentially
20 FEBRUARY 2020 | PROCESS & CONTROL
explode or cause health issues to those breathing in the gas. OGI cameras enable operators to remain at a safe distance away during inspections. An OGI camera is a specialised version of
an IR or thermal imaging camera. It consists of a lens, a detector, electronics that process the signal from the detector, and a viewfinder or screen for the user to see the image produced by the camera2
.
The operator sees a plume of gas blowing out that would otherwise be invisible to the naked eye. To see this plume of gas, an OGI camera uses a spectral filter method that enables it to detect a particular gas
compound. This technique is called spectral adaptation. See Figure 1. If the camera is directed at a scene
without a gas leak, objects in the field of view will emit and reflect infrared radiation through the lens and filter of the camera. If a gas cloud exists between the objects and the camera and that gas absorbs radiation in the band pass range of the filter, the amount of radiation passing through the cloud to the detector will be reduced. To see the cloud in relation to the background, there must be a radiant contrast between the cloud and the background. To sum up the keys to making the cloud
visible – the gas must absorb infrared radiation in the waveband the camera sees; the gas cloud must have radiant contrast with the background; and the apparent temperature of the cloud must be different than the background. Motion also makes the cloud easier to see.
Jonah Energy says that its monthly Leak Detection and Repair (LDAR) programme using OGI technology has been both effective and consistently profitable
The FLIR GF320 works with the Providence Photonics QL320 to give users the ability to reduce emissions while quantifying benefits in terms of litres per minute, or grams per hour emitted
1 Inventory of U.S.
Greenhouse Gas Emissions and Sinks,
https://www.epa.gov/sit es/production/files/2018 01/documents/2018_co mplete_report.pdf, retrieved 6/14/18, pg 191 (Energy 3-77) 2
The Science Behind
Optical Gas Imaging -
http://www.flirmedia.co m/MMC/THG/Brochures /OGI_012/OGI_012_US .pdf, retrieved 6/11/18.
Several regulatory standards affect which
technology is used to detect gas emitted to the atmosphere. The sniffer remains the required method for some oil and gas regulations, with OGI cameras a secondary tool. For newer regulatory standards in the U.S. oil and gas industry, OGI is considered the best method, with the sniffer the secondary method. The Environmental Protection Agency’s
Method 21 - Determination of Volatile Organic Compound Leaks, specifies that optical gas technology can be considered an alternative work practice (AWP) for complying with Method 21. (The sniffer was the method originally specified, and operators must still use the sniffer method once per year). Countries around the world are likely to
implement regulations similar to the proactive North American emissions control and methane reduction regulations in the years to come. In recent years, new technology has
Figure 1: Internal design of optical gas imaging core
come on the market to meet the need for OGI for oil and gas applications. For example, the FLIR GF320 works with the Providence Photonics QL320 to give users the ability to reduce emissions while quantifying benefits in terms of litres per minute, or grams per hour emitted – useful information for those looking for an economic justification for an optical gas imaging programme. Not only can it be used to stop emissions and quantify leak detection programme effectiveness, it can also be used to quantify and prioritise repairs. Embedded GPS data helps operators identify the precise location of faults and leaks, for faster repairs. Another innovative technology from FLIR
is the GFx320, an OGI camera that has been independently certified as Intrinsically Safe for Zone 2 and Class 1; Div 2 environments. This means surveyors can work confidently inside critical safety zones and hazardous locations. In addition, the FLIR optical gas imager
can also be used to measure temperature as part of the more typical IR camera electrical/mechanical inspection tasks, so the cameras actually
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