Some of the most life-threatening health challenges people face are those where disease can develop with few symptoms, leaving the victim unaware of the problem until it is too late. There are similar situations with industrial equipment where users do not realize an incident is in the making until something drastic happens. A prime case in point: gas turbine fires resulting from combustible liquid releases.
This topic is examined in depth in a white paper “Oil Mist — The Dangerous Blind Spot in Gas Turbine Fire Protection” from Emerson Automation Solutions. As the title suggests, oil mist fires are an unexpected and often overlooked cause of gas turbine incidents. Often turbine operators assume unwanted gas escapes and subsequent fires are the only hazards. Nonetheless, although gas leaks are common, oil mist detection cannot be ignored.
Most owners or operators are aware gas leaks are a gas turbine hazard and therefore install gas detectors. As a result, approximately 75 percent of gas leaks in gas turbines are recognized sufficiently early to allow an automated response, according to a UK Health and Safety Executive study. By contrast, while the number of liquid fuel leaks is smaller, roughly half result in fires.
But the largest source of fires is not fuel leaks but oil mist, resulting in more fires than gas or liquid fuel leaks combined. Oil mist releases are rarely detected, fewer than 5 percent, but more than 95 percent result in fires. The white paper goes into greater detail on these statistics, but the point is clear: if there is an oil leak creating mist, expect a fire at some point.
Part of the reason oil mist goes undetected is that users do not install appropriate detectors. Methane and other hydrocarbon gases and vapors can be detected and quantified by conventional means, as can smoke, but oil mist is different. Those other methods do not recognize airborne oil droplets resulting from oil being atomized by a leak from a high-pressure line. Measuring the concentration of such droplets requires its own approach using an appropriate sensor. But while many sensors are capable of detecting oil mist, they are not all suited to the environment of a gas turbine and its enclosure.
The high ambient temperature inside the gas turbine enclosure combined with the likelihood of flammable material being present calls for an instrument capable of performing in these extreme and hazardous conditions and suited for long unattended operation. One that fills the bill is the Net Safety Millennium Air Particle Monitor (APM) from Emerson Automation Solutions. It is the only infrared point monitor certified for use in hazardous areas for constant monitoring of oil mist.
Combustible liquid releases present severe hazards to gas turbine installations. Oil mist detectors have proven effective in detecting releases from diesel and lube oil, but the selection of the detector is critical. The ideal oil mist detector must withstand the demands placed on such instruments in or around a gas turbine enclosure environment, and the requirements for continuous operation and annual or semi-annual maintenance. A well-chosen oil mist detector keeps pace with gas turbine usage, mitigating the risk of unplanned shutdowns and reducing operating costs.
You can find more information on gas and oil mist detection in the Emerson Exchange365 community. It is a forum for users in all types of industries around the world. Look for the Plant Safety and IIoT Groups, and other specialty areas for suggestions and answers.
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