Development of Instrument Detection Limits for Smart LDAR Application: Chemical Plant Testing
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Development of Instrument Detection Limits for Smart LDAR Application: Chemical Plant Testing D.W. Furry Leak Surveys Inc, Early, Texas G. Harris & D. Ranum Sage Environmental, Austin, Texas E.P. Anderson URS Corp, Austin, Texas V.M. Carlstrom#, W.A. Sadik##, C.M. Shockley#, J.H. Siegell*#, G.M. White## Exxon Mobil, # Fairfax, Virginia; ## Baytown, Texas * Contact Author 3225 Gallows Road Fairfax, Virginia 22037 703-846-3641 [email protected] ABSTRACT To progress wider application of optical imaging technology for Smart LDAR (Leak Detection And Repair), confirmatory field test data on instrument detection limits for several chemical species were collected. During this testing, the optical imaging instrument was used to monitor over 73,000 components in 11 different chemical plant process unit areas. Twenty-eight leaks were found using the optical imaging instrument and 16 of these leaks were bagged to quantify the mass emission rate. The monitoring team was able to check over 3,600 components per hour on average. Included in this paper are a summary of the process areas monitored with the optical imaging instrument and the times these were monitored, the approximate number of components monitored in each process area, the time for this monitoring and the corresponding rate of monitoring for each process area and for the overall test period, list of the components found leaking by the optical imaging instrument, a rough description of the chemical in the process line, the Method 21 reading and the mass emission rate if bagging was done. A comparison of the previously published detection 1 limits and the results from the present study show that for all species tested, the chemical plant detection limits fell within the range of the laboratory wind tunnel testing. This confirms the applicability of the wind tunnel tests as a predictive tool for evaluating optical imaging instrument performance in a process plant. INTRODUCTION Fugitive emissions typically account for approximately 50% of total hydrocarbon emissions from process plants. Federal and state regulations aimed at controlling these emissions require refineries and petrochemical plants in the United States to implement a Leak Detection and Repair (LDAR) Program. The current regulatory work practice, U.S. EPA Method 21, requires designated components to be monitored individually at regular intervals. The annual costs of these LDAR programs in a typical large chemical plant or refinery can exceed $1,000,000. Previous studies have shown that a majority of controllable fugitive emissions come from a very small fraction of components that are large leakers (Taback, 1997). In a Smart LDAR program, these large leakers are targeted for more rapid identification and repair. Optical imaging has been identified as a technology that can more efficiently and cost effectively identify the large fugitive emissions leaks (ICF Consulting, 2004; Siegell et al., 2006). The objective of this effort was to obtain additional data on the detection capabilities of available instruments to locate leaking components in a process plant. A significant amount of data on detection capabilities for specific chemicals was previously obtained in laboratory wind tunnel studies sponsored by both API and vendors (Panek et al., 2006; Bensen et al., 2006). This testing program was aimed at collecting data that would confirm the applicability of the previous wind tunnel laboratory results. Fugitive Emissions Fugitive emissions is the term used to describe hydrocarbon leaks from valves, piping connections, pump and compressor seals and other piping system components that occur as part of the normal wear and tear in plant operations. They are characterized as 2 largely random occurrences of point-source releases into the atmosphere. While the quantity of emissions is very small for a single component, the large number of components in a typical processing plant results in fugitive emissions being the source of about half the plant total hydrocarbon emissions. Since the late 1970’s, regulations have existed to control fugitive emissions. The Clean Air Act Amendments of 1990, as well as requirements in a large number of states, require all major sources of volatile organic carbon compounds (VOCs) and hazardous air pollutants (HAPs) to control fugitive emissions. As a result, nearly all refineries and petrochemical plants in the U.S. have implemented a Leak Detection and Repair (LDAR) Program to control fugitive emissions. In addition, many plants outside the United States voluntarily conduct LDAR programs to reduce hydrocarbon losses and improve safety and reliability. In the currently required U.S. program, piping components (generally valves, pump seals, compressor seals and other components) are surveyed for fugitive emissions using a portable hydrocarbon leak detection instrument (organic or total vapor analyzer: OVA or TVA), according to U.S. EPA Reference Method 21. Under EPA Method 21, the probe of a hydrocarbon leak detection instrument is placed at the potential leak surface of a component. Air and any leaked hydrocarbon are drawn into the probe and pass through a flame ionization detector (in the case of the OVA or TVA) to measure the concentration of organic hydrocarbons. The instrument measures the hydrocarbon concentration in the air stream in parts per million by volume (ppmv). If the measured concentration exceeds the regulatory definition of leak for the type of component being monitored action must be taken to repair the leak within a certain number of days after it is identified. If the repair would substantially impact the operation of a process unit, it may be postponed until the next process unit shutdown. Records of each component inspection and any repairs must be maintained and made available for regulatory agency inspection. 3 Method 21 has numerous shortcomings. The technique measures an ambient concentration adjacent to the actual point of the leak. For a specific component mass emission rate, the measured Method 21 reading may vary over several orders of magnitude. Since Method 21 does not measure actual mass emissions rates of the detected leaks, empirical equations are used to convert ppmv concentrations to mass emission rates. These empirical equations do not correlate well with actual measured emissions rates. In addition, Method 21 measures only the hydrocarbon gas that is drawn through its probe. It cannot distinguish between a point source leak and leaks from a wider component area or any combination of point and component area sources. Routine monitoring using Method 21 requires an operator to visit and screen each regulated component on a defined frequency to identify the one component out of thousands that is a large leak. This process is very labor intensive and inefficient and is often quite expensive as well. In a typical U.S. refinery or large chemical plant with over 200,000 regulated components, the annual cost for an LDAR program often exceeds $1,000,000. Smart LDAR (Leak Detection And Repair) A study by the American Petroleum Institute (API) found that over 90% of controllable fugitive emissions come from only about 0.13% of the components, and that these leaks are largely random (Taback, 1997). The majority of the mass emissions come from a small number of components with high leak rates. A more efficient and smarter method for fugitive emissions control would more cost-effectively locate these large leakers so that they could be repaired sooner. Optical imaging has been identified as an alternative to Method 21 to locate large leaks more efficiently (ICF Consulting, 2004; Siegell et al., 2006). Optical imaging technology has been demonstrated and successfully applied in a number of chemical plants and refineries. In addition, there has been extensive laboratory calibration of the imaging unit detection limits for a large range of chemical species (Panek et al., 2006; Bensen et al., 2006). The optical imaging technology has 4 the potential to meet Smart LDAR principles, which are to more quickly scan components in a plant, identify the large leakers and reduce emissions. Optical Leak Imaging Technology Technology generally referred to as optical leak imaging, offers an instrument operator the ability to view leaking gas as a real-time video image. The remote sensing and instantaneous detection capabilities of optical imaging technologies allow an operator to scan areas of potentially leaking components much more efficiently, eliminating the need to measure all components individually. While many other technologies can detect the presence of hydrocarbons, optical leak imaging provides a real-time image of the gas plume and the process equipment that allows identification of the exact source of the emission. There are two basic types of optical leak imaging technologies: laser illuminated imaging, referred to as “active imaging,” and natural conventional infrared imaging, referred to as “passive imaging.” A passive gas image is produced by the reflection of sunlight in the infrared region off the equipment, with the gas cloud absorbing infrared light and thus appearing darker. Additionally, the relative difference between the radiance (temperature plus emissivity) between the gas cloud and the background behind the gas cloud creates a contrasting image of the gas. With active imaging, the equipment is illuminated with infrared laser light, with the gas cloud image produced by the absorption of the laser light passing through and backscattered from the background behind the gas cloud. In both technologies, the leaking vapor appears as a cloud of "smoke" on a video display of the scene under inspection. This field test was conducted using a passive imaging instrument manufactured by Flir Instruments (TheraCam GasFind IR) which was operated by Leak Surveys Inc (Early, Texas). The technology is similar to that used in the earlier Leak Surveys Inc. "Hawk" camera. Wind speed, optical resolution, plume motion, and viewing angle affect detection sensitivity. The higher the wind speed, the more quickly the plume is dispersed as it 5 leaves the leak source and the less visible it becomes.