1. Recent Developments in
FTIR for Stack Emissions
and CEM Monitoring
in the Power Generation
Industry
Sylvie Bosch-Charpenay
MKS Instruments
On-Line Product Group
2. New Regulations
New Standards for Combustion Engines
– Standards of Performance for Stationary Spark Ignition
Internal Combustion Engines : 40 CFR Part 60 subpart JJJJ.
Gases to be measured: NOx, CO, THC
– National Emission Standards for Hazardous Air Pollutants
(NESHAP) for Reciprocating Internal Combustion Engines
(RICE): 40 CFR Part 63 subpart ZZZZ. Gases to be
measured: NOx, CO, THC, formaldehyde
Hazardous Air Pollutants
– Formaldehyde (year 2013, test on annual basis)
– Future speciation of individual HCs (NMHC=non-methane
HC’s, methane, ethane)
– Methanol, etc…
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3. Emission Monitoring
Standard methods
– NOx : Chemiluminescence (CLD) – lower accuracy in high NO2
– CO, CO2 : Non-Dispersive Infrared (NDIR) – separate analyzer
for each gas
– THC : Field Ionization Detectors (FID) – provides a single
number (no speciation)
– Electrochemical sensors – separate analyzer for each gas
FTIR provides measurements of many gases
simultaneously
– CO, CO2, NO, NO2, N2O, NH3, CH4, HCl, HF, ethane, ethylene,
propylene, formaldehyde, H2O, etc…
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4. FTIR Advantages
FTIR is cost-effective if more than 4 gases need to be
measured
FTIR requires minimum calibration and so reduces costs
Can be easily (and inexpensively) shipped on-site, instead of
deploying an entire vehicle
FTIR is best method to measure formaldehyde
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5. Infrared (IR) Spectroscopy
Based on IR light absorption
– Energy (IR radiation) heats molecule - vibrations and rotations
– The pattern and intensity of the spectrum provides all the
information about gas (type and concentration)
H2O Spectrum 5
6. FTIR Provides Real-Time Analysis
of Multiple Species
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Averaging 15 sec to 1 minute per point
7. Measurements Requirements
EPA Methods DIN EN 15277-3
3A, 4, 7E, 10
Sensitivity (=short <2% of cal span <2% of cal span
term repeatability)
Accuracy (= <2% of cal span <2% of cal span
calibration error)
Interferences <2.5% of cal span. Tested <4% of cal span. Tested
(=cross-sensitivity) once. annually.
Drift <3% of cal span <2% of cal span
System Response _ Typically less than 200 sec
Time
cal span = calibration span = upper limit of calibration range 7
8. How Can FTIR Meet the
Measurement Requirements?
Sensitivity usually not an issue (long acquisition
times OK)
Accurate FTIR instrument needed
Optimization of Analysis Method (minimal effect of
interferences)
Drift usually not an issue (background in N2 taken
prior to testing)
Optimization of Sampling System (response time,
effective transport of “sticky” species)
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9. Instrument Spectral Accuracy
Requirements
Instrument Accuracy Optimization
– Spectra linearity
Accurate absorbance in the whole range of absorbance level
– Resolution
Instrument has same resolution (i.e., line width) as the
calibration spectra
– Line position
Instrument spectra are “lining up” exactly with the calibration
spectra
Validation
– Standard historical approach is to run cal cylinder and
create instrument-specific calibration
– New, better approach is to use transferrable calibrations
(possible because of excellent instrument to instrument
matching) and verify cal cylinder
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10. Accuracy Validation: Correct Resolution,
Line Position and Absorbance Level
Comparison of calibration (yellow) to sample (white) for CO
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=> Excellent overlap of calibration and sample spectra
12. Tuning of Analysis Method to
Minimize Interferences
For minimal interferences, optimized analysis range
and masking (“picket fencing”)
Correction factors included to compensate for matrix
effects (NO, CO) for best accuracy
Custom water calibration may be needed (but only for
very low calibration spans)
“Canned methods” should be made available by
manufacturer
Additional components can be easily added
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13. Ability to Measure NO between
Water Peaks
Sample = 150 ppm NO in 35% H2O
Top: sample (white) and water spectrum (red)
Bottom: sample minus water (white) and NO calibration (green). Grey 13
areas are “picket-fenced” regions which are not used in the analysis
14. No Interference of Water
High Sensitivity
H2O steps
up to 40%
Low
detection
limits
No artificial bias even in very high water (up to 40%)
Note: The HCl and HF sharp decaying peaks are real and represent small amounts accumulated in transfer lines.14
Other sharp positive and negative peaks are short duration artifacts due to fast water levels changes
15. Typical Achievable
Measurement Ranges
Species Ranges in mg/m3
NO 0-30, 0-200, 0-400, 0-1500
NO2 0-50, 0-100, 0-1000
N2O 0-50, 0-100, 0-500
NH3 0-10, 0-75
CO 0-75, 0-150, 0-1500
HF 0-5, 0-10
HCl 0-15, 0-90, 0-200
SO2 0-75, 0-300, 0-2000
CO2 0-25%
H2O 0-40%
CH4 0-15, 0-50
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16. Optimization of FTIR Sampling
System
Heated probe with filtering
– Metal or Glass
– Stainless steel filter required for “sticky compounds” HF, HCl,
NO2, NH3
– <0.1 um recommended (must keep particulate low)
Heated sampling line
– SS (not Teflon) recommended for most applications
– As short a length as possible
– Maintain temp – 191 C (very important, no cold spot!)
– Maintain pressure – 1.0 Atm (+/- 5% recommended)
Sampling pump before or after FTIR Gas Analyzer
– Before: Be careful about contamination or sample loss
Additional Filtering Possible
– After: Be careful not to let pressure go too low
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18. Formaldehyde Easy to Measure
H2O
sample
Formaldehyde
Sample with 5 ppm formaldehyde and 5% water (broad
peaks on right correspond to diesel, also measured)
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19. Formaldehyde Testing In
Stationary Combustion Turbines
DL = 200-300 ppb under typical conditions
DL as low as 30 ppb under optimized conditions 19
20. Q&A
Information
ASTM Method 6348 -03 Standard Test Method for
Determination of Gaseous Compounds by Extractive
Direct Interface Fourier Transform Infrared
Spectroscopy
http://www.epa.gov/ttn/atw/rice/fr05mr09.pdf
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