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Tech Talk 5/2014
NETL Raman gas composition monitor overview
Michael Buric, Steven Woodruff, Benjamin ChorpeningSensors and Controls Team, Thermal Sciences Division
2
Intro to Raman spectroscopy
• Optical technique which measures hydrocarbons and homonuclear diatomics
• Linear response to concentration• Raman spectrometers are becoming common; but
still no fast, gas Raman spectrometers• Small signals
Merit Review May 10, 2011
3
Why do Raman on gases in Energy Applications? (available technologies)
• Need to measure N2, H2, O2, CO, CO2, H2O, and hydrocarbons simultaneously and FAST
• Electrochemical: SLOW – many seconds for a measurement• TDLAS (tunable diode laser absorption): IR detectors and tunable
lasers (somewhat costly) needed, IR water absorption, possibly multiple lasers for multiple species
• GC (gas chromatography): elution times are LONG, multiple columns required, some species hard to discriminate
• FTIR: low SNRs in some cases (low spectral power density), water absorption problems, moving parts, calibrations
• Mass spectrometers: low pressure operation, slower• Raman: measures all species simultaneously except noble
gases, single visible laser, cheap detectors, LOW SNRs• Enhanced Raman using waveguides: Promising!
4
Hollow guide (NEW!)
Free-space configuration (OLD) (1- lens imaging)
Review: Waveguide-enhanced Raman
Waveguide
Laser Spectrometer
Notch filter
L1 L2
Laser
Spectrometer
L3
L2
L1
MNotch filter
Ps/P0 is very small! (10-13 or less)
L can enhance by 103 or more
00PLKPs
5
NETL Raman instrument capabilities
• Measure various gas streams of interest• Natural gas component analysis (methane, ethane,
propane, butane, etc.)• Homonuclear diatomic measurements (N2, H2, O2)
• Real-time (<1second) continuous measurement• Turbine or other dynamic system control• Replace GC analysis at similar (or lower) cost• Provide continuous monitoring with little human
input• Operate from 5-800psig (fuel pipelines, etc.)• Maintain a high-level of user safety
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Enhanced Spontaneous Raman waveguide-based system
• SPEED: One-second response time (or less)
• ACCURACY: Sub-percent for all species with little cross sensitivity
• SIMPLICITY/STABILITY: Obtains all species at once with no tunable lasers, no pump power control
2
7
Industrial prototype operations timeline• 2007-2008 – Research on various types of
waveguides for Raman enhancement• 2009-2010 – Initial work with capillary waveguides
and Patent Application• 2011-2012 – Industrial testing of first prototype• 2012-Present – Redesign and industrial testing of
second prototype
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Current Detection Limits (1s Integration, 100 mW, 1 m Capillary, OO Spectrometer, computed for binary mixtures)
Co
mp
on
ent
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Methane, 0.08 -> .014
Ethane, 0.046 -> 0.014
Propane, 0.035 -> 0.006
iso-Butane, 0.082 -> 0.014
Ethylene, 0.10 -> 0.018
n-Butane, 0.044 -> 0.0076
CO2, 0.57 -> 0.097
N2, 0.72 -> 0.12
O2, 0.68 -> 0.12
H2, 0.11 -> 0.018 CO, 0.79 -> 0.13
Detection Limit (%)
Red: Commercial capillaryBlue: NETL Capillary
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Example: Gasifier Measurement Results(NCCC, 3/14, coal derived syngas)
• Many more data points– Track transient
events• Agreement within
GC/Raman error
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
3/25/14 12:00 PM 3/25/14 1:55 PM 3/25/14 3:50 PM 3/25/14 5:45 PM
Com
posi
tion
%
Time
GC CO
GC CO2
GC CH4
GC H2
Raman CO
Raman CO2
Raman CH4
Raman H2
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Example: Chemical Looping Reactor Measurements(NETL CLR, 4/14, Hematite and NG)
• CO2, methane and other species monitored
• Good agreement with IR absorption measurements (Horiba Via-510), but more species measured
0
1
2
3
4
5
6
4/2/14 8:24 PM 4/2/14 9:21 PM 4/2/14 10:19 PM 4/2/14 11:16 PM
Com
posi
tion
%
Time
Analyzer CO2Raman CO2
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Conclusions
• RGA measures 10 or more gases simultaneously
• Measurements made to <1% in 1 second• Continuous gasifier or other energy-
system measurements are possible• Recalibration not necessary, only
background re-measurement to maintain accuracy
• Capillary waveguides are durable• Portable analyzers suitable for haz. ops