Cold vapors rising from an open pit of LNG forms a cloud of white condensate against the gray over-cast sky at the Emergency Services Training Institute in Texas. However, something invisible encircling that undeniably flammable cloud might be equally dangerous to firefighters, said Michael Moore, president of Houston-based Flameout Control.
Using visual imaging equipment, Moore is able to detect hydrocarbon vapors that extend far beyond the visible cloud itself. That unseen vapor is well within LNG's flammable range of five to 15 percent air-to-vapor ratio.
"A common mistake is the assumption that the flammable vapors are the white cloud," Moore said. "In fact, the LEL (lower explosive limit) levels extend further from the source. Also, the visible condensate cloud is much heavier than the methane (LNG) cloud and does not always move in the same manner when acted upon by wind."
Flameout, together with The Leake Company of Dallas, is working to marry different types of visual imaging technology into one device that can be used much in the same way as portable gas detection monitors or fixed systems such as infrared open path detectors to locate fugitive gas emissions that are normally invisible to the human eye.
As a consultant and researcher, Moore has more than 13 years experience in LNG beginning with the Algerian national company Sonatrach in 1992. Video has always been a key component in that research, he said.
"Everyone is familiar with computer models simulating gas dispersion," Moore said. "I was actually taking video and measurements to develop more accurate models based on real data. We were doing some pretty high tech stuff to prove the significant safety features of LNG such as the lack of overpressure or shockwaves on ignition."
According to Jeff Leake (pronounced Lake) of The Leake Company, two types of principle imaging technology were involved at ESTI -- infrared thermal imaging and an imaging spectrometer that detects hydrocarbon gas. In April, Moore and Leake took advantage of the latest round of live burns at BP's new LNG research and training project at ESTI (see IFW, Nov.-Dec. 2004) to experiment. The pair took up a position atop a drill tower nearly 450 feet from the actual LNG "prop."
"We used a thermal imaging camera that is sensitive in the mid-wavelength of infrared between three and five microns," Leake said. One micron is equal to one millionth of a meter. A human hair is about 50 microns wide. "We used what is called a mid-wavelength broadband system."
The temperature of an object is a measure of how fast the atoms and molecules which make up the object are shaking, or oscillating. As an object is cooled, the oscillations of its atoms and molecules slow down. For example, as water cools, the slowing oscillations of the molecules allow the water to change state or freeze into ice. If all molecular oscillations cease to exist then the material is considered to be absolute 0 or -459 degrees F.
"LNG exists at cryogenic or sub zero temperatures," Leake said. "What the thermal imaging camera does is look at energy that is being emitted by the camera and converts it into a real-time (60Hz) image display with cold gas showing a "darker" or black color typically, relative to a warm background "lighter," i.e., white color. If necessary the thermal imaging camera can be calibrated to convert this radiated energy via an on-board computer into temperature measurement units."
By using a narrow band filter the thermal imaging camera can be used as an imaging spectrometer or gas imaging camera. Hydrocarbons absorb infrared energy at a variety of wavelengths. Using a special filter that narrows the three to five micron range of the thermal imager to a specific wavelength, the thermal imager is able to detect the energy absorbed by a particular hydrocarbon such as LNG even if the vapor is otherwise invisible.
The standard thermal imager detects well concentrated areas of cold temperatures, Leake said. The new technology in use at ESTI is able to detect even the whisp of an LNG vapor, not just the heavy concentration, Moore said. For instance, the spectographer confirms the effectiveness of water curtains around the project in controlling any drifting LNG vapor.
Heat as well as cold provides valuable data about LNG, Moore said. Whereas imaging spectography was once limited to a narrow 500 degree F range, today it is capable of recording a 3,000 degree F temperature difference.
"With some of the early tests where we allowed the LNG to reach a steady state and boil I was surprised about how it self-refrigerated," Moore said. "We discovered that what was actually boiling off wasn't the methane, but the benzine and other contaminates in the LNG. As they vaporize they're actually cooling the LNG."
At its hottest the LNG fire at ESTI reaches nearly 2,000 degrees F, Moore said. Meanwhile, the heat of the concrete pad hovers at 92 degrees F. In the pit, the LNG pool remains sub zero.
Once the pool is ignited, the imaging spectographer can be used to accurately gauge the intensity of the flames and the radiated temperatures.
"We thought that the application of foam would reduce the radiated heat by at least 50 percent," Moore said. "In fact, it reduced that radiated heat by 80 percent or more."
The visual evidence also supports the technique of using foam and dry chemical in tandem in fighting an LNG blaze, Moore said.
"It's pretty interesting to see the cooling effect that dry chemical has," Moore said. "But it still isn't able to do the job alone. Using foam in unison with dry chemical makes it fairly safe. But leave out one link and you can be in serious trouble."
Another interesting phenomenon discovered by the camera is that once a vapor cloud finds an ignition source it burns faster on the outside where the LNG is within the flammable range. The flame slowly encircles the remaining vapor, burning back to the source.
The Leake Company was instrumental in developing part of this technology in conjunction with Leak Survey, Inc., who actually holds all the patents and the technology rights, said Leake. At present that technology is only available as a fixed monitoring system with Leak Survey providing certified third-party inspections for both industry and regulators.
The two systems combined lend an amazing insight to the industrial process, Leake said. At the LNG project Moore and Leake monitored the flow of sub zero LNG as it traveled through hoses and valves. Gas escaping at any point in the system was immediately apparent even at a distance greater than four football fields.
Moore also monitored the scene with two standard color video cameras carefully adjusted to take in exactly the same view as the thermal imaging and imaging spectography cameras. This allows him to edit together the images with a minimum of confusion to track an actual evolution on the fire field.
Distance is the advantage of imaging spectography, Leake said. Portable gas detectors such as "sniffers" are point sensitive, meaning the gas involved must pass right over the sensor. This means the person using the detector may well be in danger. Because gas can travel, the portable detectors may not be specific enough to give the exact origin of the leak.
"This gas imaging camera allows us to see very light concentrations of gas as it escapes into the atmosphere," Leake said. "The IR imaging spectrometer camera shows you the entire area impacted. You can see how far away the gas is moving, how big the cloud actually is as opposed to only the visible portion of the cloud and what direction the gas is being fanned."
BP uses an identical imaging spectography system mounted on aircraft to detect pipeline leaks, Leake said.
"In this case you might have a 200 mile natural gas pipeline buried 13 feet underground," Leake said. "From the air, with the visible eye, all you can look for is dead vegetation but with the IR imaging spectrometer you can actually view a tangible image."
Leake envisions using imaging spectography cameras in plants and refineries able to direct automatic suppression systems. Regulatory changes under consideration by the U.S. Environmental Protection Agency and the American Petroleum Institute would allow such imaging systems to be substituted for portable gas detectors for mandatory checks.
"A person who walks around with a sniffer can test about 500 pieces of equipment per day," Leake said. "With an imaging camera system the numbers the inspectors are coming back with pretty consistently are about 22,000 to 28,000 pieces of equipment per eight-hour shift."
Imaging camera systems are more conducive to checking overhead pipe racks, floating roof tanks and compressor stations where gaining access to use a handheld device can be difficult, he said. Also, portable gas detectors can actually be less accurate in pinpointing problems.
"Say you have two valves sitting right next to each other," Leake said. "You put the single point device on the left valve but the wind is blowing so you really don't know if it is the left valve or the right valve leaking. You just know there is a leak there. An imaging camera system will allow you to visually be able to see the leak."
Visual fire and smoke detection systems are limited in that the camera must be fixed in one position covering a specific area. Gas imaging cameras are free to pan and tilt, said Moore. Using GPS tracking system, a few cameras mounted on tall poles could cover an entire plant. Such a system would act in conjunction with open-path detectors already in place.
"Hydrocarbon vapor moves and migrates," Moore said. "If it's a very large leak such as a burst weld your detectors are going to go off. But if you're just losing a packing seal, the odds are it will shoot straight up in a plume. Your detectors are never going to pick that up because they are located left and right on the same plane."
Every technology has its drawbacks. Unlike visual fire and smoke detection systems which can piggyback on standard surveillance cameras, imaging spectrometers require their own specialized camera package. Although these cameras can double as surveillance equipment, the price tag is steep by comparison.
Ideally, said Moore, imaging spectography could detect leaking gas in such minute amounts that repairs could be affected long before suppression was necessary.
"What if you could detect that leak as early as when the packing first cracked around the seal?," Moore said. o
Michael Moore can be reached at firstname.lastname@example.org. Jeff Leake can be reached at email@example.com.