54 research outputs found
DUAL FREQUENCY COMB METHANE LEAK DETECTION AT OPERATIONAL OIL AND GAS FACILITIES
We recently demonstrated a field-deployed dual frequency comb laser spectrometer capable of locating and sizing methane sources down to 1.6 grams/minute (which is equivalent to approximately one quarter of the human breathing rate) from a distance of 1 km. The system couples open-path methane concentration measurements over long distances together with wind information in a Bayesian inversion framework to locate sources within the monitoring region. We are now applying the technology for leak detection at operational oil and gas facilities. We will discuss the evolution of the project from laboratory proof-of-concept to controlled field testing to initial implementation in an industrial setting. We will also discuss the challenges of field deployment in real environments, which include remotely operating stabilized mode-locked frequency combs and maintaining a sensing network through rain, snow, and fog
Baseline-free Quantitative Absorption Spectroscopy Based on Cepstral Analysis
The accuracy of quantitative absorption spectroscopy depends on correctly
distinguishing molecular absorption signatures in a measured transmission
spectrum from the varying intensity or "baseline" of the light source. Baseline
correction becomes particularly difficult when the measurement involves
complex, broadly absorbing molecules or non-ideal transmission effects such as
etalons. We demonstrate a technique that eliminates the need to account for the
laser intensity in absorption spectroscopy by converting the measured
transmission spectrum of a gas sample to a modified form of the time-domain
molecular free induction decay (m-FID) using a cepstral analysis technique
developed for audio signal processing. Much of the m-FID signal is temporally
separated from and independent of the source intensity, and this portion can be
fit directly with a model to determine sample gas properties without correcting
for the light source intensity. We validate the new approach in several complex
absorption spectroscopy scenarios and discuss its limitations. The technique is
applicable to spectra obtained with any absorption spectrometer and provides a
fast and accurate approach for analyzing complex spectra
Complete reactants-to-products observation of a gas-phase chemical reaction with broad, fast mid-infrared frequency combs
Molecular diagnostics are a primary tool of modern chemistry, enabling
researchers to map chemical reaction pathways and rates to better design and
control chemical systems. Many chemical reactions are complex and fast, and
existing diagnostic approaches provide incomplete information. For example,
mass spectrometry is optimized to gather snapshots of the presence of many
chemical species, while conventional laser spectroscopy can quantify a single
chemical species through time. Here we optimize for multiple objectives by
introducing a high-speed and broadband, mid-infrared dual frequency comb
absorption spectrometer. The optical bandwidth of >1000 cm-1 covers absorption
fingerprints of many species with spectral resolution <0.03 cm-1 to accurately
discern their absolute quantities. Key to this advance are 1 GHz pulse
repetition rate frequency combs covering the 3-5 um region that enable
microsecond tracking of fast chemical process dynamics. We demonstrate this
system to quantify the abundances and temperatures of each species in the
complete reactants-to-products breakdown of 1,3,5-trioxane, which exhibits a
formaldehyde decomposition pathway that is critical to modern low temperature
combustion systems. By maximizing the number of observed species and improving
the accuracy of temperature and concentration measurements, this spectrometer
advances understanding of chemical reaction pathways and rates and opens the
door for novel developments such as combining high-speed chemistry with machine
learning
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