Recent Developments in FTIR for Stack Emissions

and CEM Monitoringin the Power Generation

Industry

Recent Developments in FTIR for Stack Emissions

and CEM Monitoringin the Power Generation

Industry

Sylvie Bosch-CharpenayMKS 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…

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…

4

FTIR Advantages

FTIR is cost-effective if more than 4 gases need to be measuredFTIR requires minimum calibration and so reduces costsCan be easily (and inexpensively) shipped on-site, instead of deploying an entire vehicleFTIR is best method to measure formaldehyde

5

Infrared (IR) SpectroscopyBased 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

6

FTIR Provides Real-Time Analysisof Multiple Species

Averaging 15 sec to 1 minute per point

7

Measurements Requirements

<2% of cal span<3% of cal spanDrift

Typically less than 200 sec_System Response Time

<4% of cal span. Tested annually.

<2.5% of cal span. Tested once.

Interferences(=cross-sensitivity)

<2% of cal span<2% of cal spanAccuracy (= calibration error)

<2% of cal span<2% of cal spanSensitivity (=short term repeatability)

DIN EN 15277-3EPA Methods 3A, 4, 7E, 10

cal span = calibration span = upper limit of calibration range

8

How Can FTIR Meet the Measurement Requirements?

Sensitivity usually not an issue (long acquisition times OK)Accurate FTIR instrument neededOptimization 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)

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

10

Comparison of calibration (yellow) to sample (white) for CO

=> Excellent overlap of calibration and sample spectra

Accuracy Validation: Correct Resolution, Line Position and Absorbance Level

11

Accurate Multi-Point Calibrations

Multiple frequencies and calibration levels

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 accuracyCustom water calibration may be needed (but only for very low calibration spans)“Canned methods” should be made available by manufacturerAdditional components can be easily added

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 areas are “picket-fenced” regions which are not used in the analysis

14

No Interference of WaterHigh Sensitivity

No artificial bias even in very high water (up to 40%)

Low detection

limits

Note: The HCl and HF sharp decaying peaks are real and represent small amounts accumulated in transfer lines. Other sharp positive and negative peaks are short duration artifacts due to fast water levels changes

H2O steps up to 40%

15

Typical Achievable Measurement Ranges

Ranges in mg/m3Species

0-15, 0-50

0-40%

0-25%

0-75, 0-300, 0-2000

0-15, 0-90, 0-200

0-5, 0-10

0-75, 0-150, 0-1500

0-10, 0-75

0-50, 0-100, 0-500

0-50, 0-100, 0-1000

0-30, 0-200, 0-400, 0-1500

SO2

CO2

H2O

CH4

HCl

HF

CO

NH3

N2O

NO2

NO

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

17

Mechanical & EquilibrationResponse Times

“Sticky” compounds are the same when H2O is present

18

Formaldehyde Easy to Measure

sample

Formaldehyde

H2O

Sample with 5 ppm formaldehyde and 5% water (broad peaks on right correspond to diesel, also measured)

19

Formaldehyde Testing In Stationary Combustion Turbines

DL = 200-300 ppb under typical conditionsDL as low as 30 ppb under optimized conditions

20

InformationASTM 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

Q & A