EMERGING TECHNOLOGY S12'28 AN ULTRASENSITIVE, MULTISPECIES TRACE GAS ANALYZER FOR PROCESS ANALYSIS

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EMERGING TECHNOLOGY / S-12.28AN ULTRA-SENSITIVE,
MULTI-SPECIES TRACE GAS ANALYZER FOR PROCESS
ANALYSIS

• Eric Crosson, Kathleen Hartnett
• Picarro, Inc.

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Outline of Presentation

• Description of CAFO Application
• Description of six species analyzer
• Overview of analyzer performance

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Analyzer Requirements

• Increasing need for multi-species,
  parts-per-billion level gas analysis in
  industries such as
• petrochemical process control
• combustion analysis
• environmental monitoring
• Require measurement speeds ranging from a few
  minutes to less than one second
• Must operate in complex gas streams with little
  or no sensitivity to other gas species
• Need to operate for long periods of time without
  human intervention and without long term drift or
  periodic calibration

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CAFO Application
Ambient Air Monitoring at Concentrated Animal
Feeding Operations (CAFO)

• CAFOs (think thousands of swine or poultry in
  small area) produce toxic gases at elevated
  concentrations.
• Hydrogen sulfide
• Ammonia
• Methane
• Nitrogen oxide

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Why monitor CAFOs

• The number of CAFOs has been growing rapidly.
• Several thousand CAFOs in the US alone

• Human Health Issue
• Respiratory diseases and dysfunction among
  workers within CAFOs well documented
• Environmental Issue
• True extent to which agricultural activities
  contribute to air pollution is unknown

Efforts to regulate emissions are confounded by a
lack of accurate data
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CAFO Prototype
Prototype Six-Species Trace Gas Analyzer

• All six species measured in 12 minutes
• NH3, H2S, N2O, and H2O precision given as 1-sigma
  at zero
• CH4 and CO2 precision given as 1-sigma at
  atmospheric concentrations
• Dynamic range is 104 or higher

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Cavity Ringdown Spectroscopy (CRDS)
Laser based optical technique

• The basic measurement algorithm is
• Tune laser and cavity to desired wavelength
• Inject light into the cavity
• Once light circulating in the cavity hits a
  threshold, stop injecting
• Measure decay time of light in cavity
• Compare decay time to that of an empty cavity
• Repeat

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Important Features of the Analyzer
Instrument Measures and/or controls
Absorption (measured) Wavelength
(controlled) Pressure (controlled)
Temperature (controlled)
Spectrum
Measured Spectrum Pressure and Temperature
Concentration or Isotopic Ratio
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Concentration Derived from Line Shape
Galatry Line profile

• Five fit parameters
• center frequency c
• line strength s
• thermal broadening velocity v
• Lorentzian (pressure) broadening y
• Galatry line narrowing z

Well understood Spectroscopy
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Overview of CRDS Analyzer

• Cavity Ringdown Spectroscopy (CRDS) is a laser
  based optical technique
• High Sensitivity
• An extremely long effective path length
• Insensitive to optical power fluctuations
• Good Chemical Specificity
• Able to distinguish individual absorption
  features
• High Accuracy
• Excellent Linearity
• High Reliability / Easy to Use
• Telecom grade components

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Summary of Key Features

• Ability to isolate a single absorption feature.
• High linearity Concentration linearly
  proportional to peak height or area.
• Little or no cross-talk Able to isolate a single
  absorption feature.
• Long path length High finesse cavity provides an
  effective path length of tens of kilometers.
• Ability to control sample temperature to 1 part
  in 2000 and pressure to 1 part in 500.
• Low baseline and span drift.

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Absorption Spectrum
SPECTRA TAKEN WITH THE CRDS ANALYZER
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Sample Temperature Stability
Temperature Stability to better than 1 part in
2000
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Sample Pressure Stability
Pressure Stability to better than 1 part in 500
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Allan Variances
Ringdowns
Ability to average 100,000 individual
ringdowns and wavelength monitor measurements
Wavelength Monitor
Follows the vN for gt 100,000 individual
measurements
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Linearity

• CRDS is very linear
• Beer-Lambert law
• Isolate a single absorption feature
• Reduced sensitivity to line broading

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CAFO Six Species Prototype

• Utilizes four telecom grade distributed feedback
  (DFB) lasers.
• Light from each DFB directed using optical
  switches.
• Wavelength monitor has wavelength range enabling
  the analyzer to measure any wavelength between
  1500 nm and 1650 nm.
• This new broad band wavelength monitor has a
  wavelength resolution of better than 3 MHz.

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Six Species Prototype Performance
Prototype Measurement at zero NH3
Prototype Measurement at zero H2O
Precision 0.12 ppbv _at_ zero NH3
Precision 0.0005 _at_ zero H2O
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Six Species Analyzer Performance
Prototype Measurement at zero H2S
Prototype Measurement of 3.6 ppmv H2S
Precision 5.7 ppbv _at_ 3.6 ppmv H2S
Precision 0.35 ppbv _at_ zero H2S
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Six Species Analyzer Performance
Prototype Measurement of 1.0 ppmv CH4
Prototype Measurement of 2.5 ppmv CH4
Precision 0.2 ppbv _at_ 2.5 ppmv CH4
Precision 0.08 ppbv _at_ zero CH4
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Six Species Analyzer Performance
Prototype Measurement of 382 ppmv CO2
Prototype Measurement at zero N2O
Precision 0.4 ppbv _at_ 382 ppmv CO2
Precision 16 ppbv _at_ zero N2O
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Ability to Average Data

• Analyzer stability enables averaging up to 15
  minutes without significant systematic error.
• Wavelength monitor
• Pressure control system
• Temperature control system

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Effects of Interfering Gas Species

• Analyzer able to measure a single gas with little
  or no effects from interfering gas species.

• Isolate a single absorption feature
• Wavelength monitor enables accurate determination
  of line widths

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Effects of Ambient Temperature

• Analyzer able to measure with little or no
  effects from changes in ambient temperature.
• Temperature control system

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Measurements of CH4, CO2, and H2O
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Additional Features
High Speed10 Hz Analysis, CO2

• Scanning flexibility allows
• application specific spectral scanning schemes
• 10 Hz operation for monitoring dynamics and
  capturing transients

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Conclusion

• A six-species analyzer based on CRDS has been
  developed
• Ammonia
• Hydrogen sulfide
• Nitrous oxide
• Methane
• Carbon Dioxide
• Water Vapor
• By changing lasers and software, the analyzer can
  be modified to measure gas species important to
• petrochemical process control
• combustion analysis
• environmental monitoring

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Acknowledgements

• Ed Wahl, Chris Rella, Sze Tan, Hoa Pham, Picarro
  Research Team
• Professor Teng Teeh Lim, Department of
  Agricultural and Biological Engineering, Purdue
  University
• Work supported by the U.S. Department of Energy
  under Contract No. DE-FG02-03ER83751 and the USDA
  under Award No. 2006-33610-16835.