Development of hydrocarbon vapor imaging systems for petroleum and natural gas fugitive emission sensing Thomas J. Kulp, Karla Armstrong, Ricky Sommers, Uta-Barbara Goers, and Dahv Kliner Sandia National Laboratories Livermore, CA

A laser illuminates the scene as it is imaged in the infrared Gases are visualized when they absorb the backscattered radiation Conventional leak detection is carried out using handheld sensors Imaging allows rapid broad area coverage and easy recognition of plume presence and source location Solid surface Gas plume Laser radiation tuned to gas absorption Imaging lidar is a powerful tool for gas leak detection

* 7 Refineries (all components and services) Source: API Publication 310, November 1997 Measured Leak Rate Distribution Data * Gas imaging offers to accelerate leak surveillance, thus decreasing the cost of environmental compliance Typical refinery spends ~$1M per year for leak detection and repair (LDAR) Currently hand-held “sniffers” are used according to EPA Method 21 The technology in this project is now being considered as a viable alternative to Method 21 by a working group of EPA, API, DOE, and petroleum industry members Acceptance will require approval as an alternative work practice - laboratory testing - field evaluations Smart LDAR concept: Rapid surveys focusing on strong leakers

800, ,000 leaks addressed each year leaks result in accidents Safety issues Surveys mandated annually Surveying costs of $1.6 billion annually Cost & Efficiency Production, Processing, Transportation Hardware 750 processing plants 3000 compressor stations 103 Bscf (1.98 Tg) / yr. Transportation 400,000 miles of pipeline 6 Bscf (0.12 Tg) / yr. Distribution 1,400,000 miles of pipeline 42 Bscf (0.8 Tg) / yr. Industry-wide losses of natural gas Losses represent a significant product cost and a significant contribution to greenhouse gas flux Motivation for leak sensing in the US natural gas industry

Frequency (cm -1 ) Absorption by the atmosphere Frequency (cm -1 ) Optical depth Butane absorption Problem: There has been a lack of BAGI instrumentation that “sees” hydrocarbons critical to the gas and oil industries Operation near 3.3 µm favored due to gas and atmospheric absorption Broad ( cm -1 ) tuning desirable to access multiple species BAGI instruments commercially available at 9-11 µm but not at 3.3 µm Basic limitation has been the lack of suitable laser sources Wavelength (µm) Optical depth Methane absorption

Scanned imager Laser beam Detector field-of-view Tunable CW laser Scanner Solution: We have developed imagers that use nonlinear conversion to generate tunable mid-IR (3-5 µm) light Beam formatter Tunable pulsed laser Snapshot-mode focal-plane array Pulsed imager CW optical parametric oscillator (OPO) Pulsed DFG-OPA laser

Nonlinear conversion shifts light from one wavelength to another Optical parametric oscillator (OPO) Signal (or idler) wave resonated P thr = Watts P out = 100’s mW - W’s Optical parametric generation Pump Nonlinear crystal Idler Signal pump = signal + idler New microengineered nonlinear crystals improve efficiency —> smaller and more tunable systems Multi-grating PPLN crystal Close-upWide-view Example: Periodically-poled lithium niobate (PPLN) Engineered optical axis inversion 15X more gain than ordinary crystal Tunable over µm

The first hydrocarbon imager was a pulsed system Methane plume at 20 m Nd:YAG pumped dye laser (repetition rate 30 Hz) Beam formatter Amber ProView FPA controller Video display 256 x 256 snapshot-mode InSb focal-plane array camera HSVB Computer with frame grabber board and WIT software Range - 70 m Sensitivity - 36 ppm-m methane 0.02 scf/hr leak rate Kulp, Powers, Kennedy, and Goers Applied Optics (1998)

Differential imaging was demonstrated to improve gas plume visibility for the pulsed imaging system Methane spectrum Laser Energy (wavenumbers) Scale, Ratio, log Processing Single-wavelength imageDifferential image Methane imaging against grass Powers, Kulp, and Kennedy, Applied Optics (2000)

Next step in evolution — Development of CW systems Breadboard pulsed imager Fieldable pulsed prototype Development of a CW OPO Field test van-mounted system FY98 FY99 Development of operator- portable system FY00-01 CW systems offer: Less expensive imager (scanner vs array) Clear commercialization path Upgrade to diodes Less susceptible to damage

~ 3.3 µm Signal - wavemeter µm PPLN Crystal Signal - power monitor Pump dump Solid etalon A PPLN-based OPO was developed for scanned cw imaging Two periods created: µm µm PPLN fan-out grating used 200x Absorption Intensity Wavenumbers [cm ] n-hexane n-pentane n-butane propane Wavenumbers [cm -1 ] Absorption Intensity “Generic” refinery wavelength Idler tuning range: cm -1 Nd:YAG laser

Scanner FOV rotations Turret 3-µm beam Nd:YAG laser PPLN OPO IR image seen by the operator A van-mounted scanned system employing the PPLN OPO was field tested at a refinery during April, 1999 Gas plume System tested in parallel to EPA Method 21 Imager operated well in the field environment Results motivated the development of a portable system

M21 team independently monitored process areas first - Measured 1,464 components, primarily valves and pump seals - All components part of existing LDAR program Gas Imaging team monitored independently next - Observed estimated 6,600 components, all types - All visible parts observed, regardless of whether tagged or not - Followed-up leak discoveries with vapor analyzer - Gas Imaging leak discoveries video-taped Both teams tested seven process areas April 1999 field demonstration

High leakers above 100,000 ppm were identified by current prototype Lowest leak independently found was 28,000 ppm Some leaks at about 30,000+ ppm were missed Did not find leaks below 10,000 ppm in the refinery setting Lower detection limit currently appears to be between 25,000 and 50,000 ppm Gas imaging found high leakers in three process areas Full results tabulated in a report located on the EPA Website Restricted access during test motivated the development of an operator-portable imaging system

Goal: Develop an imaging lidar for leak detection that can be battery operated and carried by the system user Nd:YAG laser PPLN OPO Van-mounted imager successfully tested in natural gas distribution and petroleum refinery applications. However, access restrictions prohibits vehicle use in many cases. Van-mounted and operator-portable raster-scanned imaging lidars Natural gas leak in Atlanta Ga

Approach: Develop a system based on a compact CW OPO pumped by a Yb-doped fiber amplifier Miniature Nd:YAG seed laser Fiber Optic Amplifier Compact SR-OPO Consolidated scanner (single unit) Van System Water-cooled Nd:YAG laser “Breadboard” OPO system 3-component scanner Primary technology competition is diode lasers which cannot produce sufficient 3.3 µm power at narrow linewidth and require cryogenic cooling Yb-doped fiber amplifiers demonstrated 45% electrical-optical conversion CW OPO capable of converting 60-90% of pump output to signal + idler Fiber amplifier inherently rugged

The Yb-doped fiber amplifier produces high output power in a compact and efficient format Present diode (JDS) requirement A to achieve 4W output No visible SBS with a single-mode seed Initial system - Polaroid pump diodes