BAGI Video Gas Leak Visualization
This project was initiated to create a more effective method of organic vapor
leak detection at oil refineries, thus increasing the efficiency with which
regulatory compliance can be met by industry.
Sandia National Laboratories (SNL)
DOE Office of Industrial Technology (OIT)
American Petroleum Institute (API)
Texas Council on Environmental Quality
Laser Imaging Systems (LIS)
Punta Gorda, FL
Environmental Protection Agency (EPA)
Shell Oil Company
In the course of this project, an operator-portable backscatter-absorption gas
imaging (BAGI) system was developed to produce real-time video imagery of numerous
organic vapors of interest to the petroleum (and other) industries. The imager
was shown to operate effectively at several field trials at petroleum processing
facilities in the United States and abroad. The results serve as the basis of
an EPA rule-change application submitted by API requesting that gas imaging
be allowed as an alternative work practice to the established EPA Method 21,
which dictates how leak surveillance is conducted. That rule change is now under
Hydrocarbons emitted by petroleum refineries generate smog and produce urban
ozone. Thus the EPA actively regulates the emission of hydrocarbons by processing
facilities. Leak detection and repair (LDAR) programs are operated by major
facilities to comply with these regulations.
By making a gas plume "visible" to its operator, the gas imager offers
an efficient and effective alternative to EPA Method 21, which describes the
use of handheld "sniffer" sensors to detect leak presence and magnitude.
Sniffers imprecisely infer leak flux (in grams per hour, or g/hr) from point
concentration (parts per million, or ppm) measurements. Leaks are missed if
the probed point does not intersect the vapor plume. Finally, LDAR programs
using sensors that must be manually brought in close proximity to the leak point
are laborious and expensive (~$1 million per year at large refineries). Gas
imaging instantly covers a large area, thus ensuring that the leak point is
in the measurement zone, allowing many points to be probed simultaneously, and
providing a visual indication of leak flux.
Hydrocarbons do not absorb light at visible wavelengths and are not seen by
the eye. They do, however, absorb in the infrared (IR) and are viewable at specific
wavelengths absorbed by the gas. Two methods of IR gas imaging exist-passive
and active. The former views a scene using thermal IR radiation emitted by the
gas and scene. The latter illuminates the scene using laser light absorbed by
the gas as it images the scene using backscattered light. The intensity of the
passive gas image depends on the temperature difference between the gas and
scene, as well as on plume thickness and concentration. Active imaging has no
temperature dependence and thus was selected to be used in this project.
Active gas imaging devices were being produced for commercial sale by LIS at
the initiation of this project; however, those devices used CO2 lasers whose
emission wavelengths (9-11 µm) are not absorbed by hydrocarbons relevant
to the petroleum industry. Thus, a critical challenge faced by this project
was the creation of a laser emitting at the mid-IR wavelengths (3.1-3.6 µm)
that are absorbed by hydrocarbons, while meeting the size and efficiency requirements
of an operator-portable system.
Project researchers have:
- Developed a van-mounted hydrocarbon gas imager.
- Demonstrated the imager's performance in a Texas oil refinery (April 1999).
- Developed an operator-portable, battery-powered hydrocarbon gas imager.
- Conducted laboratory tests in support of an EPA rule-change submission.
- Conducted the following field trials:
- California petroleum refinery (January 2003).
- Texas petroleum refinery (February 2003).
- Petrochemical lab tests-BP at Naperville, IL (August 2003).
- Southampton, U.K., petroleum refinery demonstration (September 2003).
- Texas petroleum refinery test (January 2004).
- Texas petrochemical plant tests (February 2004).
Infrared lasers for both the van-mounted and operator-portable imagers were
solid-state pump lasers. The former employed nonlinear optical crystals to convert
light at the pump frequency to tunable radiation in the mid-IR. The first pump
laser used was a water-cooled Nd:YAG laser suitable for use in the van-mounted
configuration. The operator-portable imager employed a significantly smaller
pump consisting of a miniature Nd:YAG laser amplified by a fiber-optic amplifier.
This allowed creation of an operator-portable system capable of operating for
>2 hours on battery power. At field trials, it was demonstrated to successfully
image gas leaks at ranges up to 30 feet and detection limits corresponding to
leak rates of ~2-60 g/hr of hydrocarbons.