In an Oil & Gas Engineering article, Emerson’s Jesse Sumstad reviews technologies for detecting combustible and toxic gas leaks.
A study published in March 2022, reports that among the 26,292 active wells and 15,000 km of natural gas pipelines in the Permian basin area of southeast New Mexico, natural gas is leaking at a rate of 194 metric tons per hour. Some individual leaks are large enough to be detected from satellites. There is every reason to think that the average rate is similar in other production areas. It’s little wonder that the oil and gas production industry is subject to extensive criticism since raw methane is far worse as a greenhouse gas than the carbon dioxide that would result from its use as a fuel.
Such leaks are also highly dangerous as fire hazards, both at well sites and processing facilities. The challenge is detecting where they’re happening. Selecting and applying the right instrumentation to detect and quantify such leaks is the topic of my article in the June issue of Oil & Gas Engineering, Detecting Dangerous Gases to Improve Safety and Reduce Emissions.
Fugitive gases, even if they don’t cause immediate harm to workers or result in other damage, are emissions that are untreated and unmeasured. Methane lost this way is a financial hit, and it is also a serious greenhouse gas (GHG), contributing to climate change. Even if a company believes it can tolerate the financial impact and the local environmental agency is unaware of the release, this flies in the face of any company claiming to make serious efforts at improving its sustainability. Every facility should detect and control such problems for the sake of environmental responsibility, but also to avoid the potential for escalation to a more serious situation.
The causes of leaks are no mystery, and they aren’t limited to well sites and pipelines. They’re also common in refineries and petrochemical plants. Most are related to inadequate maintenance combined with corrosion. Sometimes it’s human error. Whatever the reason, pressurized gas escapes into the plant environment, inside or outside. So how do you know when it’s happening? There are detectors capable of responding to leaks of methane or hydrogen sulfide, two of the most common and problematic gases in the oil & gas industry.
Combustible gases (methane, gasoline vapor, etc.) can be detected via sensors using a chemical reaction with a catalyst. Atmospheric oxygen combines with the gas, driven by the catalyst, creating detectable heat. This is the working principle behind Emerson’s Net Safety Millennium II SC310 Catalytic Bead Combustible Gas Sensor.
A more versatile approach is differential optical absorption spectroscopy. It uses the characteristic of certain gases, including methane and hydrogen sulfide, to absorb specific wavelengths of light in the UV and IR ranges. The article goes into more detail, but the concept calls for a source and receiver placed some distance apart. If the target gas drifts into the space in between, it absorbs the target wavelength, and the receiver senses the difference. This can be applied to a point detector, such as Emerson’s Net Safety Millennium II SC311 Infrared Combustible Gas Sensors, but also to an open-path configuration able to cover a much greater distance. Emerson’s Rosemount™ 935 Open Path Combustible Gas Detector can cover a distance up to 200 m, and it is also available in a toxic gas detector version.
A fully integrated strategy for worker, plant, and community safety must include detectors for hydrogen sulfide, combustible gases, and even perhaps flame detectors. Designing such systems to be effective and economical will usually require a mix of the point and open path detectors just described. While it is difficult to rank these in importance, it could be argued that open path detectors carry the heaviest load of protection, and therefore deserve particularly careful consideration.
Visit the Flame and Gas Detection and Control & Safety System pages at Emerson.com for more on technologies and solutions for safety strategies. You can also connect and interact with other engineers in the Oil & Gas and Chemical Groups at the Emerson Exchange 365 community.
Update from Jim Cahill: Join us at the October 24-28 Emerson Exchange conference in the Dallas, Texas area to hear Jesse co-present, “Increase Sustainability and Safety With Rosemount’s New Line of Flame and Gas Products”.