... gas leakage; escaping gas that goes undetected can become a source of ignition ... process of checking every compone
THE DETECTION OF GREENHOUSE GASES Roy Montemarano Heath Consultants Incorporated KEYWORDS: greenhouse gas, remote detection, leak, natural gas, infrared, optical, imaging ABSTRACT Natural gas providers for years have been dealing with how to effectively reduce greenhouse gas. Whether it be petroleum or natural gas leakage; escaping gas that goes undetected can become a source of ignition or toxic poisoning that could generate an unsafe environment for the public and/or employees. Besides the safety aspect and environmental hazards; the loss of revenue and operation integrity is of concern for the greenhouse gas manager. Having a proactive program can alleviate the problems. Using state of the art instrumentation that can detect leaks remotely, instead of the standard “touch and go” process of checking every component, can provide for a faster survey, inspections from a safe distance and the ability to survey hard to access sites; thus shortening inspection times and increasing operational efficiency. Over the years, especially within the past decade, several new technologies have been introduced to detect, measure and improve the inspection of leakage in a natural gas system including; LNG, transmission and distribution. This paper will reinforce a proactive approach with proven technology leading to safer, hazard free environments. INTRODUCTION To determine the volatile organic compound (VOC) leaks from terminal and storage components/compressors (valve, pump seal, connector and others) the requirement in the United States under the Environmental Protection Agency (EPA) LDAR program, specify the use of a detector to locate and classify leaks only, but not measure. The leak definition concentration is 10,000 ppm as methane – instrument is calibrated on methane. This brief description refers to instruments in an EPA requirement called Method 21 – Determination of VOC Leaks. Alternate work practice methods for monitoring leaks have been designated by the EPA to detect leakage are as follows: Optical Gas Imaging Camera (Figure 1) – detection sensitivity level of 60 grams per hour; Method 21 (Figure 2) – readings of 10,000 ppm or greater; Acoustic Leak Detection (not shown) – device to detect leaks through valve leakage; Calibrated Bag (Figure 10 – see Gas Leak Measurement Section); or use of a Remote Laser (Figure 3).
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Figure 1 – Optical Gas Imaging Camera
Figure 2 - Method 21 Type Leak Detector
Figure 3 – Remote Laser There are hundreds of thousands of regulated components that need to be inspected. Checking each one can be time consuming or lots of man hours. This paper will reference two solutions to reduce these inspection times. Over the past decade, several new technologies have been introduced to detect and measure natural gas leakage. These new advances in optical and laser technology for leakage detection have been finding more leaks and finding them faster than the traditional flame Ionization (FI) method.
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Figure 4 – Mobile Optical Mobile Optical / Infrared (IR) or Closed Path Bifringent IR instruments offer a distinct advantage to be capable of surveying lines that have been re-gasified (converted from LNG) and distributed as pipeline gas. The mobile IR can survey at speeds up to 25 MPH (40 km/hr), with a sensitivity of 1 ppm. Compared to the flame ionization mobile instrument that is most effective up to 5 MPH (8 km/hr) you can see the productivity gains. Portable Optical Infrared Detectors have many advantages over the traditional flame ionization leak detector. •
Self calibrating (eliminating the need for external calibration gases). o
Example of self-calibrating instruments – see Figures 2 and 3.
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Requires no fuel for operation (eliminating hydrogen or hydrogen/nitrogen gas for fuel).
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Methane specific.
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Portable or mobile application.
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Figure 2 sample method - pump. Range detection of 1 ppm to 100% gas (two instruments in one; can detect and pinpoint).
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Figure 3 sample method – remote. Range detection 3 ppm plus (search tool only).
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Instruments are intrinsically safe.
REMOTE LASER DETECTION The use of a portable Open Path Infrared Detector (Tunable Diode Laser Absorption Spectroscopy), as shown in Figure 3 above, can remotely scan a wide area, plus a number of components, and hard to reach areas from standing in one spot, verses a technician that is going from each component using either soap solution or inspecting with a small hand held device. Adapting laser technology for detecting gas leaks has proven to be a major advantage over traditional instrumentation. Because the laser can detect leaks (down to 5 ppm-m at 50 feet (15 meters) or approximately 3 ppm plus at 100 feet (30 meters); this method can reduce survey time and increase efficiency with productivity gains of up to 40 – 50 percent.
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Because the laser detects leaks from a distance (remotely) this technology can be used to inspect areas such as processing plants, storage tanks, over-head rack mounted piping, gate and compressor stations, bridge crossings ,LNG Tankers etc. The Instrument is Intrinsically Safe for Class 1 Div 1 locations. How it works – technical approach: •
Laser light beam is remotely projected onto a target (i.e. grass, wall, etc.)
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A fraction of the beam is scattered from the target surface and returned to the source
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Returned light is collected and focused onto a detector
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The presence of methane is encoded within the returned light
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Methane readings are displayed in ppm-m
Figure 5 – Technical Approach to Remote Laser Detection GAS IMAGING CAMERA
Figure 6 – Gas Imaging Camera
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The gas imaging camera is used in the following application: •
Storage tanks
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LNG Tankers
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Vents, Relief valves, etc. that are not easily accessible
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General Leak screening – scan a wide area
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Leak Localization
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Quick work procedure
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Multiple component inspection
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Remote Operation
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Pinpoints leak giving a visible display of leak
Note: Some camera companies have gone through a certification process to get their camera certified and classified for hazardous location: ATEX, UL, ANSI and CSA – Class I and II, Division 2 and Class III locations. This certification allows for a higher level of safety and operation confidence. Dependent on company regulations certification could eliminate the need for a “hot work” permit. Invisible Gas Into VISIBLE DISPLAY
What you See
Thermal Imaging Camera
Figure 7 – Thermal Gas Imaging Camera - How it Works Cameras that detect gases of interest to oil and natural gas personnel operate in the middle portion of this spectrum, between 3 – 5 µm.
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Figure 8 – Thermal Gas Imaging Camera - How it Works Specialized infrared cameras used in gas leak detection are precisely engineered to target these gases and display them visibly and clearly to the user even when viewed from substantial distances. The surrounding radiation in the spectrum used by the leak detection camera is negligible therefore the detection of the gas is achieved according to the following:
Figure 9 – Thermal Gas Imaging Camera ― How it Works The thermal imaging camera enables a daily scan of hundreds of components and at the same time detecting small and large leaks from a distance. Some make and model cameras can either record and/or provide an audio narration of the recording for record keeping. The cameras used in the detection of methane leaks (will vary based on make /model) can visualize methane flows well below the EPA required 60 grams per hour sensitivity level. 6
Gas Leak Measurement Instruments have the ability to measure the actual rate of leakage from a system component. Even with the Subpart “W” Gas Emission Factor table you still need to measure some components. Using the calibrated bag or a sampler you can encapsulate the leaking component and measure it directly. When a leak can actually be measured, it becomes easy to document the improvements (leak repair), or to determine the cost effectiveness of a leak repair. With accurate measurement, a company can determine fugitive emissions and gas losses from a facility, determine a cost effective repair strategy, and document emission controls for Greenhouse gas credits.
Figure 10 – Calibrated Bag
Figure 11 – Flow Measurement Instrumentation
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CONCLUSION The new technologies that have been introduced in the past decade offer big improvements in leakage detection of Greenhouse gases and measurement in more than 40 years. Thus far, Remote Laser and Cameras have proven to be reliable replacements for the Flame Ionization / Organic Vapor Analyzer instruments. Effective risk management for the Green House Gas Manager has been a growing indicator for an organization. The substantial increases in productivity, finding more leaks, increase company integrity with the public, create a safer work environment, and the reduction of Green House Gases may well be the future for gas detection.
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