This document describes an analytical method for determining HCl concentration in gases using Fourier transform infrared spectroscopy (FTIR). It involves calibrating the FTIR using certified gas standards and then applying the calibration model to analyze sample gases. Key aspects discussed include using classical least squares to predict concentrations, selecting appropriate analysis regions, accounting for spectral interferences like water, and requirements for the sampling system such as heated lines and filtering. The method is intended for continuous emission monitoring applications like those required at Portland cement plants under EPA regulations.

1. MKS Analytical Method for
HCl by FTIR

2. FTIR Analysis Method
Analytical Method
– Classical Least Squares [CLS]
– Predict chemical concentrations using spectroscopy (FTIR) and
linear algebra
Calibration Method
– Requires certified gas or liquid standard – NIST Traceable
– Collect signal/spectrum from FTIR
– Combine and model using CLS
– Analysis Region dependant upon component concentration
Determining Sample Gas Concentration
– Run sample gas through FTIR gas cell
– Collect signal/spectrum from FTIR
– Use calibration model to predict sample gas concentration
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3. Calibration Summary
Region Selection
– Select ALL regions where compound is present in the spectrum
Analysis Band
– Select the largest peak region
– Modify Analysis Band
Other compounds present in Sample Gas and interfere
Bulk gas or another component fully overlaps any of the analysis
region.
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4. NO Calibration Regions
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5. NO Calibration
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6. Machine Independent Calibration
31 3
30 2.5% 4
29 5
2.0%
28 6
1.5% Easily able to transfer
calibrations from one
1.0%
instrument to another
0.5%
0.0%
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Instrument to Instrument Variation
Based on Ethylene Measurements
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(years 2000 - 2002)
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Demonstration of instrument to instrument variability 6
none of these instruments calibrated for Ethylene

7. Analytical Interference Removal
Regions Change with Concentration
– Change Analysis Regions
Higher resolution allows analysis in the presence of
the interference (usually H20)
Spectral Interference Correction (H2O)
– Mask Interferences (‘picket fencing’)
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8. Different Regions for Different
Concentrations
20% CO2
8% CO
100 ppm CO
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9. Low Resolution (2.0 cm-1)
Sample
H2O
NO
Example of catalyst performance evaluation
Figure used with permission from Johnson Matthey plc, Wayne, PA 9

10. High Resolution (0.5 cm-1)
Sample
H2O
NO
Example of catalyst performance evaluation
Figure used with permission from Johnson Matthey plc, Wayne, PA 10

11. Removing H2O Interference
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12. Removing H2O
NO Water
Sample 150ppm NO in 35% H2O (white) 35% H2O (red)
Sample minus H2O (white) NO calibration (green) 12

13. No interference of water
High sensitivity
Low detection
limits
No artificial bias even in very high water (up to 40%)
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14. Reduction of Sampling System
Interferences
Sample Line Temperature
Sample Pressure
Reactive Components
Material Selection
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15. FT-IR Sampling System
Heated Probe with filtering
– Metal or Glass
– <0.1 um recommended (must keep particulate low)
Heated Sampling Line
– MKS recommends SS not Teflon for most Apps
– Minimum length as possible
– Maintain Temp – 191 C normally
– Maintain Pressure – 1.0 Atm (+/- 5% recommended)
Sampling Pump
– Before or After FT-IR Gas Analyzer
Before be careful about contamination or sample loss
After be careful not to let pressure go to low
– Additional Filtering Possible if before
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16. Field Deployable FTIR
Heated Lines
Sampling System
Heated Probe
Filter Box
Stack
On-Off Valve
Rotometer
FTIR Gas Analyzer
Cylinder Spike Standard
with SF6 Tracer
Spike Recovery: cal gas 10% total flow
Calibrated Gas Run: cal gas 7 lpm if pump pulls 5 lpm
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17. Portland Cement Plants
Continuous Emission Monitoring
National Emission Standards for Hazardous Air
Pollutants From the Portland Cement Manufacturing
Industry (40 CFR 63 SUBPART LLL)
– Maximum Achievable Control Technology (MACT) Standards
First EPA mandated National Limits to Reduce Mercury and
Other Toxic Emissions from Cement Plants
EPA issued final Portland Cement MACT in September 2010
Components required
– NOx, SO2, HCl, CO, CO2, PM, THC, mercury
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18. HCl Measurements with FTIR
EPA Method 321
– “Measurement of Gaseous Hydrogen Chloride Emissions At
Portland Cement Kilns by Fourier Transform Infrared (FTIR)
Spectroscopy”
– Isolated sample analysis
EPA Method 7E
– “Determination of Nitrogen Oxides Emissions From Stationary
Sources (Instrumental Analyzer Procedure)”
– Describes general measurements requirements for all gases
when using a continuous instrumental analyzer
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19. HCl Measurements with FTIR
Sample (white)
with 5 ppm HCl
and 12% water
(red)
H2O subtraction
HCl peaks
clearly
visible after
H2O
subtraction
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20. HCl Measurements with FTIR (2)
HCl
calibration
peaks (red
and green)
HCl subtraction
After HCl
subtraction,
only noise left
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21. 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%)
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22. MG2030 CEM Ranges and Detection
Limits
Component ppm mg/m3
CH4 0 - 21 0 - 15
CH4 0 - 70 0 - 50
CO 0 - 60 0 - 75
CO 0 - 120 0 - 150 Component Detection limit
CO 0 - 1200 0 - 1500 CH4 0.3 ppm
CO2 25% 25% CO 0.5 ppm
H2O 40% 40%
CO2 0.025%
HCl 0-9 0 - 15
HCl 0 - 55 0 - 90 H2O 0.25%
HCl 0 - 123 0 - 200 HCl 0.20 ppm
HF 0 - 11 0 - 10 HF 0.25 ppm
N2O 0 - 26 0 - 50
N2O 0.1 ppm
N2O 0 - 51 0 - 100
N2O 0 - 255 0 - 500 NH3 0.35 ppm
NH3 0 - 13 0 - 10 NO 0.5 ppm
NH3 0 - 99 0 - 75 NO2 0.4 ppm
NO 0 - 149 0 - 200 SO2 0.6 ppm
NO 0 - 299 0 - 400
NO 0 - 1119 0 - 1500
NO2 0 - 24 0 - 50
NO2 0 - 49 0 - 100
NO2 0 - 488 0 - 1000
SO2 0 - 26 0 - 75
SO2 0 - 105 0 - 300
SO2 0 - 699 0 - 2000
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23. Solution for Compliance of Portland
Cement Plants
FTIR designed for Continuous Emission Monitoring
– Thermoelectric detector, no need of liquid N2
HCl detection limit of 0.2 ppm
– Calculated as 3-sigma in 25% H2O
Typical Gases and Ranges
– CH4 0-21 ppm 0-70 ppm
– CO 0-60 ppm 0-1200 ppm
– CO2 0-25% (soon to 40%)
– NOx 0-149 ppm 0-300 ppm
– SO2 0-26 ppm 0-699 ppm
– H2O 0-40%
– HCl 0-9 ppm 0-55 ppm
FTIR associated with FID (THC), PM and mercury
sensors for complete solution 23

24. Why MKS Over
Competitors

25. CEM FTIR
Advantages
– Multiple species – one instrument
SO2, NH3, NO, HCl, HF, CO, CO2, H2O, and VOCs
– Analyze components in high CO2 and H2O
– Direct analysis – no chemical conversion or “fudge factors”
– Analysis method minimizes interferents
– Flexibility in Changing in Method
Customer can easily modify
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26. WHY MKS?
Fastest Acquisition with High Resolution (0.5cm-1)
Smallest gas cell volume with long pathlength
– 200 mL for 5.11m Path
Process Instrument
– Not a Lab system converted to Process
– Engineered for Process Environment
– Gas Cell integrated heaters and pressure controller
Provide Method Development as well as Customer
Support
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