Thermal Imaging Camera Checks LNG Vapors
Vol. 20 No. 6
Once switched on, the specially designed thermal imaging camera, used during the burn and gas dispersion tests at BP's LNG training facility, uses a closed-cycle, stirling cooling system to rapidly cool the Indium Antimonide (InSb 320x256, mid-wavelength (3-5 microns) focal plane detector array down to operating temperature. Unlike "uncooled" detector arrays, which are stabilized at ambient temperatures, the detector array inside the Hawk infrared camera system must be super cooled down to near liquid nitrogen temperatures. As Leake said, "think of it as a small refrigeration system contained inside the camera". Part of the cooling system incorporates the use of a dewar flask containing helium to achieve the super-cooling. When the electro-mechanical cooler is turned on, the helium gas is compressed and decompressed by a small piston through an orifice. The super-cooling is caused by the expansion and contraction of the gas. Integrated into the end of the Dewar flask is a device called the band-pass "cold filter" that further narrows down the wavelength of the sensitivity of the Hawk camera. This narrowing down causes the camera to be especially sensitive to the absorption of hydrocarbon gases enabling the camera to image the position and density of the hydrocarbon vapor drifting beyond the readily visible condensate cloud rising from the exposed pit of liquefied natural gas. The benefit of the Hawk IR camera system is that it enables one to visualize exactly where the gas cloud is, and the direction it is moving. With trained operators you can begin to associate the gas cloud to relative sizes. The next step in the evolution of these imaging spectrometers is to quantify the density of the gas as parts per million measurement perspective.
This is second visit to the training facility by Leake Company and Leak Surveys, Inc., in conjunction with the BP testing. The previous testing during the dissipation and burns involved the use of a standard video camcorder, a broadband mid-wavelength IR camera, and the Hawk IR camera. All of the systems were placed atop a five-story drill tower across the Brayton Fire Training Field. For the testing, each camera had lenses with a similar field-of-view so that both the visual and thermal infrared images could be captured. By doing this, a person can tangibly visualize the benefits on an infrared gas imaging camera system. What makes this test different from the first one is the Hawk IR camera being used in conjunction with an array of point and open path detectors near the LNG pit to better interpret the image produced by the Hawk IR camera.
Point detectors give readings in percent LEL while open path detectors give readings in LEL per meters. Comparing the data from the stationary detectors to the thermal image from the Hawk provides a better idea of how to interpret the data collected by both systems. For instance, with the Hawk IR camera we see the fringe gas that is well beyond the white condensate vapor cloud we see with our own eyes. The camera displays the fringe gas in varying shades of gray with highest concentrations as near black relative to a warmer or lighter (white) background.
"Now we have point and open path detectors along with the visualized data," Leake said. Researchers can better correlate data like density, quantity and radiant energy when the LNG is possibly in an ignition state. In particular, that data is important in determining the effect of high expansion foam in LNG fire fighting.
When it comes to the suppression side of LNG fire fighting, the Hawk IR camera can be used to visualize how the vapor cloud is suppressed or contained by the application of the foam and once the LNG is ignited by active methods, such as an open flame, researchers can study the radiant energy from the plume and flame paths from the dispersion of the gas. This will be valuable information for first responders and hazmat crews.
Used for years by many of the world's largest oil and gas companies and regulation agencies in the U.S, the Hawk awaits further safety regulation to propel the use of the technology even further. In many parts of the world, such as Europe and Asia, the Hawk has had far more impact because it is being used in operational areas of refineries and petrochemical plants to reduce production losses. Companies outside the U.S. are using the Hawk in place of single-point devices called "sniffers" used to detect flammable or harmful hydrocarbon gases. The benefit of the Hawk IR camera system is the operator can see on the camera's display screen where the gas is emanating from and what direction the gas is moving. Whereas, the operator of the sniffer may in fact be in and surrounded by the vapor cloud putting the person at risk. The Hawk allows for much safer standoff distances. In independent comparison of the technologies, on a typical day in a refinery, and operator using a sniffer can check approximately 500 to 800 pieces of equipment components, such as valves, pumps, compressors, tanks and piping in a day as compared to 10,000-15,000 equipment components checked with the Hawk. This is due to the fact that you can scan overhead piping, large multi-story vessels, reactors, tanks, etc. from the ground without climbing stairs and ladders or requiring the use of man-lifts or bucket trucks to get to difficult to reach areas. The only limiting factors are the camera's field-of-view and the documentation required when a leak is found.
Another benefit of the Hawk IR camera system is that companies can use it from a mobile platform, such as a vehicle or helicopter. This significantly increases the coverage capabilities. One application where the Hawk is being used extensively is to locate methane and/or natural leaks from buried gas gathering lines. From a helicopter flying at altitudes from 500 to 1500 ft., a camera operator can "see" the gas plume spewing out of the ground with no apparent hole in the earth's surface and whisking across the surface in whatever direction the wind is pushing it. Again, the Hawk IR camera makes what is 'invisible' to the human eye 'visible'. From 100 to 400 miles of gathering lines can be inspected in a typical 8-hour day, depending on environmental conditions.
Another recent use of the Hawk IR camera was in the aftermath of Hurricane Katrina. The Hawk IR camera was used to identify gas leaks throughout the New Orleans area caused by open gas lines from water heaters, stoves and other equipment that was ripped from their foundations The Hawk showed the first responders which house was full of gas and which one was clear. By providing exact GPS coordinates, Leak Surveys was able to assist first responders in preventing accidental explosions or fires. The Hawk was also used to determine environmental damage cause by oil storage tanks that we ruptured during the hurricane. So because of the camera's success, EPA emergence response teams and FEMA has now designated the Hawk leak detection system as part of their First Responder's Team in disaster situations.