1. FTIR Monitoring of
Sulfuric Acid
in Coal-Fired Power
Plant Flue Gas
Brian Adair, Ph.D., Curt Laush, Ph.D.,
Constant Marks, Darwan Pursoo, P.E.
AWMA
17 March 2016

2. Why Measure Sulfuric Acid Concentration?

3. Sulfuric Acid Effects
PluggageOpacity Corrosion
NH3 + H2SO4 
(NH4)HSO4
H2SO4 Aerosol Surface Condensation

4. Sulfuric Acid Sources and Sinks
FGDSCR
Concentration
ESPBoiler APH
Fa
n Stack
SO2 + ½ O2  SO3
Mg(OH)2 + SO3 
MgSO4 + H2O
NH3 + SO3 + H2O 
(NH4)HSO4
CaCO3 + H2SO4 
CaSO4 + H2O + CO2
NH3
Mg(OH)
2
CaCO3Lime,
trona
Na2CO3 + H2SO4 
Na2SO4 + H2O + CO2

5. Sulfuric Acid Sources and Sinks
FGDSCR
Concentration
ESPBoiler APH
Fa
n Stack
H2SO4 conc: 3-29 ppmv

6. Why Measure Sulfuric Acid Concentration
Continuously?

7. SCR Conversion Changes
with Flow Rate and NH3/NOx

8. SCR Conversion Changes
Over Time As Catalyst Ages

9. SCR Conversion Changes
with Flue Gas Composition

10. SO3 + H2O ↔ H2SO4
NH3 + H2SO4  (NH4)HSO4
1000/TDewPoint =
1.784−0.027log(PH2O)−0.103log(PSO3)+0.033log(PH2O)log10(PSO3)
Sulfuric Acid Chemistry

11. SO3 + H2O ↔ H2SO4
Exists as
H2SO4 at
Scrubber
Mostly SO3
at
SCR Out
PercentageasSO3orH2SO4

12. NH3 + H2SO4  (NH4)HSO4
ABS
forms
No ABS
[NH3]x[H2SO4](ppm2)

13. Acid Dew Point

14. Sulfuric Acid Testing

15. Measurement Methods
David Ostaszewski, Recent Developments in SO3 Source Emission Testing Methods,
National Environmental Monitoring Conf (2013)
Method 8A
Heated probe & filter; controlled condensation; titration or IC
Most commonly used; EPA promulgated in 1996
Acid dew point measurement
In situ; measure conductance affected by deposition of material; control temperature to
cycle condensation/evaporation of material
Continuous wet-chemical analysis
Extractive; continuous reaction with barium chloraniliate; anilate ions measured in
continuous flow photometer
Quantum Cascade Laser Spectroscopy
Extractive; commercial?
Cross-duct FTIR
Measure concentrations spectroscopically in native environment

16. 16
Method 8A Example

17. FTIR for H2SO4 Measurement
Fourier Transform Infrared Spectroscopy
Minimizes introduction of method artifacts
Multicomponent analysis
Simultaneous quantification: SO3/H2SO4, SO2, NH3, NO, NO2, CO, CO2, HCl, HBr, H2O
Continuous (near) real-time operation
Data rate about 2-5 minutes at sufficient detection limits
Sub-ppmv detection limits
Especially important for SO3/H2SO4, NH3, HCl, HBr
Mobile and field rugged in industrial environments
Monitor at almost any location
Unattended operation
Permanent CEM; weeklong process optimization campaigns

18. Conventional FTIR
Upgrade materials in contact with the sample flue gas
Many metals will corrode; stainless steel catalyzes SO2 oxidation
Nickel-coated materials too porous
Glass & silicon-coatings better for inertness but rigid and expensive
In extraction configuration, carefully control sampling and
heating/cooling
Too hot: H2SO4  SO3 + H2O
Too cold: Aerosols not dissociated and/or condense in system; H2SO4 aerosols cannot be
directly observed by FTIR since absorption bands broad & continuous
Probes/extraction lines should deliver aerosol content to cell
Quantitatively accurate spectral calibration sets
No documented sets for vaporous H2SO4 and SO3 available
Field validation procedures
Spike sample gases with known amounts of H2SO4

19. Extractive FTIR for SO3/H2SO4
Custom probe for mist/aerosol extraction
Shrouded aerosol tip for continuous monitoring; dimensions
aerodynamically matched to typically flue gas exhaust flow rates
Avoids isokinetic sampling errors at nonzero pitch or yaw angles
PTFE for probe, gas transfer system, sample cell
In-line conditioning to convert aerosols to vapors
H2SO4 calibration reference set generated
Tailored to expected flue gas conditions
Spectrometer configured for low-level H2SO4
Monitoring system NEMA enclosed and ruggedized
 Compact and lighter weight for lower cost, ease of installation and use

20. Aerosol/Gas Calibration Assembly

21. Sulfuric Acid Measurement #1
FGD
Concentration
ESP B/B
ESP B/A
Econ B
APH B
Fa
n
ESP A/B
ESP A/A
Stac
k
FTIR
SCR B

22. Test Conditions
Parameter average units
Gross Load 569 MW
Stack Gas Flow Rate 85,300 SCFH
APH Gas Out Temp 268 °F
Fuel Flow 234 ton/h
SCR Out NOx 41.7 ppmv
ESP #3 Opacity 4.77 %
FGD Inlet CEM SO2 1567 ppmv
FTIR data
at ESP Out
SO2 1605 ppmv
H2SO4 20.6 ppmv
NO 19.1 ppmv
NO2 19.2 ppmv
CO 85 ppmv
HCl 101.5 ppmv
H2O 6.78 %
CO2 13.7 %

23. Real Time H2SO4 (ESP Out)

24. Data Quality – SO2

25. Trending Model Results

26. Sulfuric Acid Measurement #2
FGD
Concentration
ESP B/B
ESP B/A
Econ B
APH B
Fa
n
ESP A/B
ESP A/A
Stac
k
FTIR
SCR B

27. Real Time H2SO4 (Stack)

28. Summary
Real time FTIR-based
portable process monitor for
sulfuric acid demonstrated
Potential for compliance
monitoring
Brian Adair, Ph.D.
980.333.2954
badair@geosyntec.com
Curt Laush, Ph.D.
512.497.1571
claush@geosyntec.com