Tech Talk 5/2014

NETL Raman gas composition monitor overview

Michael Buric, Steven Woodruff, Benjamin ChorpeningSensors and Controls Team, Thermal Sciences Division

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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

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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!

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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

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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

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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

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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