On December 19, 2008, EPA issued a final rule establishing a voluntary Alternative Work Practice (AWP) to detect leaks of volatile organic compounds (VOC) and hazardous air pollutants (HAP) from process equipment (FR Vol. 73, Number 246), thereby providing the regulated community additional flexibility in complying with leak detection and repair (LDAR) requirements. The AWP allows owners or operators of an affected facility to identify leaking equipment using an optical gas imaging instrument in lieu of a leak monitor as prescribed in Title 40, Code of Federal Regulations (40 CFR) Part 60, Appendix A (Method 21). The development of the AWP and its associated monitoring technologies are collectively referred to as 'Smart LDAR.'
What is Smart LDAR?
Beginning in the 1980s, EPA called for the implementation of LDAR programs for control of fugitive VOC emissions (i.e., emissions from piping components such as flanges, connectors, valves, pumps, etc.). Therefore, LDAR requirements were initially promulgated in the New Source Performance Standards (EQ_Q2_2009 refinery valvesNSPS) under 40 CFR 60, Subpart VV. EPA went on to incorporate LDAR requirements in other NSPS and 40 CFR 61. These efforts were extended with the passage of the Clean Air Act Amendments of 1990, which resulted in the adoption of LDAR provisions into the Maximum Achievable Control Technology (MACT) rules under the National Emissions Standards for Hazardous Air Pollutants (NESHAP). More recently, the proposed mandatory Greenhouse Gas Reporting rule (40 CFR 98) contains fugitive monitoring provisions.
The current LDAR work practice requires the use of Method 21 to identify component leaks. Method 21 involves moving a gas sampling instrument probe around all leak interfaces (seals) and determining the highest VOC/HAP concentration. After determining the location of the highest concentration, the probe must remain at that location for two times the response time. The instrument readings are compared with levels established by EPA and/or the state air pollution regulatory agency to determine if the component leaks. If the measured VOC concentration at a component exceeds the leak definition (which typically varies from 500 parts per million by volume (ppmv) to 10,000 ppmv, depending on the type of component and specific subpart), the component must be repaired or replaced within a specified period of time. The repeated Method 21 measurement of emissions following such maintenance must be below the leak concentration level for the component to be considered repaired.
In 1997, the American Petroleum Institute (API) conducted a study of 11.5 million monitored refinery components to determine if there was a correlation between component type or application and its potential to leak. The study showed that over 90 percent of the controllable fugitive emissions were attributed to 0.13 percent of the components monitored, demonstrating that significant time and effort is spent monitoring components that, statistically, do not leak. Furthermore, after an LDAR program has been implemented at a site, the number of leaks detected during each subsequent monitoring period decreases because pre-existing leaks have been repaired and may not leak for regulatory update extended periods of time. Although repair costs decrease as the number of leaks is reduced, the costs of conducting Method 21 monitoring is not always reduced in the same proportion. In some cases, the cost of conducting Method 21 monitoring may remain constant, resulting in a decrease in cost-effectiveness.
Conceptually, the costs associated with the current work practice of monitoring each component at a site individually could be significantly reduced by implementing a method that more efficiently locates the high leaking components without monitoring each piping component in the plant using Method 21. This concept, dubbed “Smart LDAR,” could use newer technology to locate and repair the most significant leaking components more quickly and at less cost than the current work practice.
Remote sensing (i.e., the acquisition of data through the use of either recording or a real-time sensing device, such as imaging, that is not in direct physical contact with the object being monitored) and instantaneous detection capabilities of Smart LDAR technology can allow an operator to scan process areas containing tens to hundreds of components in real time. Significant leaks can be identified immediately, allowing quicker repair and ensuring efficient use of resources. In the development of the AWP, EPA researched multiple remote sensing technologies to measure pollutant concentrations, including the following:
- Ultra-Violet Differential Optical Absorption Spectra (UV- DOAS)
- Open-Path Fourier Transform Infrared Spectroscopy (OP-FTIR)
- Tunable Diode Laser (TDL)
- Differential Absorption Light Detection and Ranging (DIAL/LIDAR)
- Optical Gas Imaging
To date, the only technology that has been approved and implemented as an AWP is optical gas imaging. Due to issues such as excess expense, technical limitations of the number and type of chemical species detected, interference from non-target emissions, and required expertise for calibration and operation, the other technologies have not been approved as an AWP. However, LIDAR, which utilizes laser absorption and reflection to generate a differential signal that can be used to calculate the concentration of the target compound, is currently in use in both ground-level and airborne applications by EPA and a number of state agencies to create concentration contouring of various chemicals and to validate emission factors.
Two types of optical gas imaging cameras are available for use as an AWP, the basic operation of which are explained below:
- Active Optical Gas Imaging - utilizes a laser beam reflected (backscattered) by the background to detect the chemical present. The optical image is produced by the reflected light with a light wavelength strongly absorbed by the gas cloud. The image is displayed real- time on the screen of the gas imaging camera.
- Passive Optical Gas Imaging - a passive technology that records the difference in absorption of specific infrared (IR) wavelengths in the field of vision and produces the appearance of a cloud where the chemical is present. The technology uses different combinations of lenses, detectors and filters for detecting different pollutants. The optical lens of a passive gas imaging camera can be tuned to illuminate target compounds (a principle similar to that used in “night-vision” equipment) to detect leaks.
Optical gas imaging technology offers several advantages from the perspective of Smart LDAR implementation. It meets the Smart LDAR requirements of providing efficient real-time leak analysis while also being lightweight, compact, and robust, thereby allowing a single operator to easily transport the equipment for use under field conditions. In addition, since the cameras can be used to detect leaks from a distance, they provide a greater element of operator safety over the current work practice using Method 21.
The chief limitation of optical gas imaging is related to calibration of the camera. Each camera is calibrated based on the required detection limits of compounds that possess a specific range of absorption and reflection wavelengths. If a site is required to monitor pollutants whose ranges do not overlap, the camera must be recalibrated for the second group of pollutants or another camera used. Other issues that may be considered roadblocks to implementation include the requirement for daily instrument checks, the potential requirement by state agencies that operators must undergo accredited formal training, and the high initial equipment costs (currently available cameras carry a price tag of approximately $85,000.) However, these disadvantages may not necessarily preclude the implementation of optical gas imaging technology as an AWP, particularly for larger sites.
Smart LDAR Implementation
Passive optical gas imaging cameras are being widely used throughout industry for leak detection. State agencies are now using this technology in statewide fugitive emissions reduction initiatives (e.g., the Texas Commission on Environmental Quality’s “Find-It-and Fix-It” program and aircraft overflights over industrial areas such as the Houston Ship Channel). Optical gas imaging cameras have been used to detect the presence of unburned hydrocarbons in flare plumes outside of the flame and to determine combustion efficiency in various combustion sources. Besides industrial applications, optical gas imaging was used by EPA and the Louisiana Department of Environmental Quality in detecting leaks and other sources of air pollutants, post Hurricane Katrina. The table below is a partial list of local, state, and federal agencies that currently operate optical gas imaging cameras for the purpose of performing various surveillance and compliance investigations.LDAR chart
In addition to being implemented into LDAR programs as an AWP, optical gas imaging cameras may be utilized in the future by industry and regulatory agencies for various other tasks, such as safety and risk mitigation applications, sulfur hexafluoride (SF6) detection as part of the collaborative effort between EPA and the electric power industry to reduce greenhouse gas emissions (the SF6 Emission Reduction Partnership), and the quantification of emissions, once the technology is further developed.
There are several key points to consider before implementing an optical gas imaging camera for fugitive gas leak detection.
- The definition of a leak is any visual indication whether seen via camera or naked eye, which is a departure/additional to existing work practice standard. For instance, visual indications of a leak from a gas/vapor or light liquid service valve are not addressed in current work practice standard. Visual indications of a leak from a valve in heavy liquid service would be considered a potential leak. The facility can then decide to eliminate the potential leak or conduct Method 21 monitoring to determine if it meets the leak definition. Visual indications from a pump (except for pumps addressed under the Hazardous Organic NESHAP [HON] rule) are considered potential leaks; however, under AWP they would be considered leaks.
- When the AWP is used, owners/operators must also perform annual monitoring using the Method 21 instrument and provide all the Method 21 monitoring results to EPA via email. Therefore, owners or operators who are only required to conduct annual monitoring as part of their LDAR program would not benefit from implementing the AWP. Additionally, weekly visual inspections of affected pump/agitator components may still be required, as prescribed under the current LDAR program, if a site plans to adopt the AWP.
- Smart LDAR does not allow for decrease in monitoring frequency due to “good behavior,” as does the current work practice. Thus, the cost savings realized due to decreased monitoring frequencies when using Method 21 do not apply to the AWP.
- After detecting leaks analogous to the existing work practice standard, owners or operators must re-check the repaired equipment for further leaks with the same gas imaging camera or they may use Method 21 to confirm that the leak has been repaired.
- Owners or operators must perform the specified daily calibration checks to ensure proper operation.
- Owners or operators should be aware of the high initial cost of the equipment and are advised to perform a cost-benefit analysis before purchasing and implementing optical gas imaging equipment. In general, the company would realize a greater benefit in the long run, due to a reduction in labor cost. Additionally, some companies have taken the approach of purchasing one camera for multiple sites to minimize the cost per site. Another option for managing cost is to contract the testing from a firm that specializes in air quality compliance, fugitive leak monitoring, and stack testing.
It is important to note that current optical gas imaging technology cannot quantify or speciate individual chemical compounds although there are efforts currently underway to adapt the technology to such applications. These enhancements include development of software that may interpret gross emission rate based on video imagery. Once the technology is fully realized, industry and agencies alike may be able to quickly and accurately determine compliance for other air emissions-related parameters, such control device performance and emissions limits, in real-time with the click of a button.