HCL by FTIR Marty Panek at Midac Sales

to:

Keith Barnett

06/02/2010 10:08 AM
Please respond to mpanek

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Keith, here is what my apps dept came up with on your HCL application.
Please do not hesitate to contact me if you should have any questions.

Regards

Marty1 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 1 of 11 

## PPM-Level HCl Measurement s by FTIR Spectroscopy

Peter Zemek, PhD, MIDAC Corporation Joe Van Gompel, PhD, MIDAC Corporation Steven Plowman, MIDAC corporation

Introduction Fourier Transform Infra-Red (FTIR) spec troscopy is an accepted and well-known technique by the EPA to measure hydrogen ch loride (HCl). Over the past 10 years, HCl by FTIR has been utilized at many cement k ilns and other incineration technologies successfully by EPA Method 321 or 301. HCl is a common by product from cement kilns and municipal waste incinerator s. Commonly, kilns will receive hazardous waste and other chlorinated compounds, if a boiler and incineration fur nace (BIF) source. Chlorine

also enters the cement kiln in with the raw materials. In a muni cipal waste incinerator many poly-chlorinated materials such old PVC piping are burned and HCl is produced, along with CO 2 and water vapor. HCl is considered a hazardous air pollutant (HAP) by the US EPA. A significant source is char acterized as emitting HCl at greater than 10 tons / year.

FTIR spectroscopy is a powerful tool for anal ysis of HCl at sub-ppm levels. There have been many comparisons to H Cl by manual methods such as EPA Method 26 and 26A

to FTIR. FTIR has also been utilized as a CEM by Perfo rmance Specification 15 (PS15) and as a primary method when performing RA TA analysis. The advantages of HCl by FTIR are the immediate near-r eal-time field results, reducti on of laboratory error, and

contamination. The FTIR Methods are self -validating when used with a spiking regimen and proven in the field and in the laboratory. This method requires the use of a high

resolution FTIR instrument to obtain sub-ppm level detection limits. A resolution of 0.5

cm-1 to 1 cm-1 instrument ation is usually required.

The only drawback of HCl by FTIR in cement k ilns is the possibility of kinetic reactions of the HCl with high ammonia levels in th e stack, heated filter , or sampling system causing the formation of ammonium chloride sa lts on the filter or in the heated line. This causes a certain amount of lag time in the spiking regimen but is usually overcome by the additional wait time while spiking to reach steady-state, need for a higher spiking concentration, or the need to place the FTIR instrument clos er to the sample port.

These issues can be overcome in the field with a review of the sampling system and field modifications. However, once a spike regimen is passed, th e method, instrument, and sampling system has been validated and concentrations may be considered accurate and precise.

The work described here was performed over many years, at a cement kiln and a municipal waste combustor. The major goal of the study was to validate extractive Fourier transform infrared (FTIR) spectromet ry for measurements of gaseous hydrogen chloride (HCl) as described in Environment al Protection Agency (EPA) Test Methods

301 1 , 320, and 321 2 . Three different validation procedures were successfully performed; they were direct compar isons with EPA’s manual Test Method 26 3 , “single instrument” dynamic spiking, and “dual instrument” dynamic spiking.1 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 2 of 11 HCl by FTIR The infrared spectrum of HCl is distinctive and r eadily observed, even in the presence of water vapor interference. HCl appears as a series of doublet peaks that rise, fall to zero, then rise and fall to zero again. Thes e regular peaks are ob served between 2650

cm -1 and 3100 cm -1 . Each peak is split into a double t with the ratio of 3:1 based on the

ratio of 35 Cl : 37 Cl isotopes. The mid-infrared spectrum of HCl is shown in Figure 1.

Figure 1. Hydrogen Ch loride, 148.6 ppm-m, 25 o C.

The ability to analyze HCl in the presence of water is imperative as water vapor concentrations are very high from combustion sources such as incinerators. Spectra incorporating these high concentrations of water are shown in Figures 2 and 3.1 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 3 of 11 Figure 2. 42 ppm-m HCl in baseline of 14% water vapor.

Figure 3. Figure 2 expanded to see HCl clearly in pres ence of high levels of
water vapor.1 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 4 of 11 Figure 4. HCl in the pres ence of water vapor. HCl peaks are indicated which can be used for quantitation.

The regular pattern of peaks for HCl is comm on for diatomic molecules such as HF, HBr, CO, and NO as well. It is due to rotational transitions between the ground and first

excited vibrational states of the molecules. Known as t he P-branch (lower energy) and the R-branch (higher energy), these fan-like spectral feat ures surround the Q-branch, which is forbidden by quantum mechanics in the primary band of the heteronuclear diatomics. More complex materials, like NH 3 and CH 4 , show prominent Q-branches.

Quantitative Analysis of HCl by FTIR Test Facility The test facility is a typical municipal wa ste combustor/generating station using refuse derived fuel. The plant consists of several independent “units,” two of which (referred to as “Unit 1” and “Unit 2”) were sampled during this work. Each unit includes a boiler and a set of emissions control devices, notably a lime-slurry injection system for reducing the HCl emissions. All validation testing wa s performed at one of t he two control-device outlet locations; the sampling ports were lo cated in rectangular cross-section ducts connecting the outlets of the in duced-draft fans to the base of the stack. Inlet testing was performed at a set of ports located just downstream of the Unit 1 boiler.

Sampling Systems The sample streams passed through he ated probe assemblies, heat-traced (~350  F,

181 o C) PTFE sample lines, and the absorption cells of each of two FTIR spectrometers; a pump connected to the cell’s outlet ports continuously drew sample gases through the cells at approximately 10 lit ers per minute (lpm). The onl y materials used in the sampling systems were Pyrex  , Type 316 stainless steel, and Teflon  . All Method 261 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 5 of 11 sampling was performed using equipment and te chniques described in Reference 3; the resulting samples were submitted to Test ar, Inc. (Raleigh, NC) for HCl analysis.

FTIR Analytical Systems The two FTIR spectrometers used in this work are MIDAC Corporation (Costa Mesa, CA) Model 

### I -2000 instruments (see Figure 1) with nominal one half wavenumber (0.5

cm -1 ) spectral resolution; they are designated below as Instruments “A” and “B.” Both systems employ Michelson inte rferometers, beam splitters and cell windows of zinc selenide (ZnSe), hot-wire infr ared radiation sources, front -surface optical transfer mirrors, and multi-pass absorption cells. Me rcury cadmium telluride (MCT) detectors were used for the majority of the testing described here; for the diluted inlet samples (only), an indium antimonide (InSb) detector was installed in Inst rument B. In all cases, the detectors were cooled with liquid N 2 and their temperatures ma intained at 77 K. The 10-meter path length “White” absorption cells use gold-surface internal mirrors, and their interior cell walls are made of polishe d nickel to minimize chemical interactions with the sample gas. Transducers and thermo couples connected directly to the insulated sample cells provide the pressure s and temperatures of the sample streams. During testing, the temperature of the ab sorption cells was 181o C; the elevated temperature prevents gas conde nsation within the cell and minimizes HCl retention by

the cell walls and mirrors. The volumes of the absorption cells are 2.0 liters, so at a flow of 10 lpm the sample gas in each cell is re freshed approximately five times per minute. Interferograms consisting of 50 co-added scans were recorded nearly continuously during the test periods, and provi ded one-minute average concentrations.

Heated Cell FTIR

Spectrometer Heated Line

Outlet to pump Temp, Pres.

Controller

FIGURE 5. Typical FTIR spectro meter system during testing.

FTIR Spectral Analyses1 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 6 of 11 The program AutoquantPro  (hereafter “AQ,” version 4.0.0.111,  Midac Corporation, 2004) was used to collect and analyze all t he infrared field data. AQ allows the development and storage of analytical “met hods” for analysis of spectral data (absorbance) files. Various methods we re generated for the instrument-detector

combinations described above and used to for determine the absorption path lengths and the concentrations of the gaseous analytes. On every test day, at least one 128- scan background spectrum was recorded with dry N 2 . Before and after each test run, spectra of a calibration transfer standard (CTS) gas were obtained and used to determine the effective absorption path length s of the gas sample cells. A cylinder of ethylene C 2 H 4 in N 2 (103 ppm) served as the CTS, and the absorption path lengths were determined by comparing the field CTS spectra to a well-cha racterized laboratory ethylene spectrum. All the absorption pat h lengths (for each instrument-detector combination) varied by less than 5% over the entire test period. T he analytical results presented in this work are based on t he average path length determined for each

instrument-detector combination over the course of the field tests.

The HCl concentrations in the extracted FTIR samples were determined by mathematically comparing the samples’ absorbance spectra to a number of HCl reference spectra; these reference spectra were recorded during the test period using the two field instruments and a cylinde r standard of 86.2 ppm HCl and 5.03 ppm SF 6 (balance N 2 ). Using both a NIST-calibrated mass flow controller and standard barometric techniques, the reference samp les were made by diluting the HCl/SF 6 standard gas to four lower volumetric concent rations. The absolute HCl concentration of the cylinder standard wa s determined in the laboratory according to the sampling and analytical procedures of EPA Me thod 26; only the relative SF 6 concentrations are required for the validation procedur es described below, so the SF 6 cylinder

concentration was not i ndependently confirmed.

Preliminary concentrations of three other analytes – car bon monoxide (CO), sulfur dioxide (SO 2 ), and nitric oxide (NO) – were al so determined using quantitative FTIR reference libraries prepared in the laboratory from dilution of cert ified calibration gas

standards. In some cases the observed co ncentrations of thes e compounds exceeded the calibration ranges of the spectrometers.

Table 1 presents the in frared wavenumber (cm -1 ) analytical ranges and concentrationpath length (ppm-meter) limits of the refe rence libraries employed to date.

HCl Method Validations EPA’s Test Methods 301 (Ref erence 1) and 320 (Reference 2) both provide statistical techniques for the validation of emissions te st procedures. Three validation procedures for FTIR measurements of HCl were perform ed and are described below. Note that 1 ppm of a gas in a 10-m gas cell is 10 ppm-m.1 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 7 of 11 TABLE 1. FTIR REFERENCE S PECTRA AND ANALYTICAL REGIONS

ANALYTE WAVENUMBER
RANGE NUMBER OF

SPECTRA PPM-M RANGE

HCl 2768.93 – 2849.00 cm -1 5 45 – 763 ppm-m

SF 6 909.02 – 967.51 cm -1 5 2.67 – 44.57 ppm-m

CO 2168.18 – 2180.62 cm -1 3 64 – 263 ppm-m

NO 1872.50 – 1877.30 cm -1 3 563 – 2285 ppm-m

SO 2 1068.96 – 1252.55 cm -1 2 217 – 441 ppm-m

Method 301: Reference Method Comparison EPA Method 301 (Sections 5.2 and 6.2) allows the validation of a proposed test method (here, FTIR measurements of HCl) by a pair-wise comparis on between the results of a simultaneously-performed EPA reference me thod (here, EPA Method 26). See Figure 6. A complete description of the validatio n requirements and calculations is given in Reference 1; only a summary is provided in this work. Briefly, the results S R of nine test runs using the reference met hod are compared with results S P of the proposed method

and the relative standard deviation SD P of the set of nine differences (S R – S P ) is compared via an F-test to the published standard deviation of the reference method (here, SD R = 3.2% at 15.3 ppm and SD R = 6.2% at 3.9 ppm). Next, the bias B and a correction factor CF for the proposed method ar e calculated and a t-test is applied to determine whether the bias of proposed method is statistically significant. The criteria required for validation of t he proposed method are a) SD P  SD R and, when the bias is found to be significant b) 0.9  CF  0.1. Table 2 presents the nine pairs of

concentration results used in these calculations.

Figure 6. Validation of proposed test method using FTIR and EPA Method 26.1 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 8 of 11 TABLE 2. METHOD 301 VALIDATION RESULTS (PPM)

SAMPLE

PAIR M 320 RESULTS S R FTIR RESULTS S P

1 8.54 8.22

2 9.42 10.96

3 11.20 12.96

4 22.10 20.04

5 22.60 21.30

6 22.90 22.81

7 23.10 23.20

8 38.60 36.69

9 68.80 64.29

The paired results of Table 2 yi eld relative standard deviation SD P = 4.3%, which lies between the two values (3.9% and 6.2%) published by EPA for the reference method. Although the t-test shows that the proposed me thod bias (2.0 ppm) is significant (t = 2.148), the F-test (F = 0.108) indicates good precision, and the correction factor (CF = 1.031) falls in the acceptable range 0.9  CF  1.1.

METHOD 320: Dual Instrument Spiking Validation EPA Method 320 (Reference 2, Section 13) allows validation of FTIR-based measurements by a pair-wis e comparison between the results of two independent FTIR systems. One of these s ystems must provide the “n ative” (or “un-spiked”) concentrations in 12 independent samples, and the other must provide simultaneous measurements of samples which have been dynamically “spiked” to provide a calculable change in t he analyte concentrations. The m eans of the spiked results and calculated spiked levels prov ide a bias estimate for t he FTIR measurements, and a ttest is applied to the 12 differences in t hese values measurements to determine whether the bias is significant. If the bias is found significant, a correction factor is calculated and must lie in the range 0.7  CF  1.3.

In this work, one of the two FTIR spectrometer s (Instrument A) was used to collect and analyze 12 unspiked gas samples. Simu ltaneously, Instrument B analyzed spiked samples collected from the same outlet sample port. Spike gas was introduced into the Instrument B sampling system by injecting gas from a cy linder standard of 86.2 ppm HCl and 5.03 ppm SF 6 (balance nitrogen) directly into the sample probe; the spike gas flow rate was adjusted (by monitoring the observed SF 6 concentration) so that the spike gas represented 10% to 20% of the total In strument B sample flow rate. Table 3 presents the HCl and SF 6 results of these measurements for the spiked and unspiked samples.1 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 9 of 11 Table 3. Method 320 Dual-Instr ument Spiking Results (ppm)

SAMPLE PAIR S S (HCL) S U (HCL) S S (SF 6 )

1 13.1 7.26 0.517

2 13.4 7.45 0.516

3 13.4 7.43 0.519

4 13.4 7.24 0.518

5 13.2 7.10 0.516

6 13.4 7.41 0.519

7 13.4 7.53 0.521

8 13.4 9.00 0.521

9 13.7 8.92 0.521

10 13.5 7.81 0.522

11 13.0 7.12 0.521

12 13.6 7.36 0.516

MEAN 13.4 7.62 0.520

STDEV 0.18 0.62

From the mean of the S S (SF 6 ) values and the cylinder SF 6 value concentration, the expected mean spiked concentr ation is CS = 16.5 ppm; th e actual mean spiked concentration is 13.4, so the bias in the proposed method is B = 3.1 ppm. The t-test using the standard deviations of the values S S – S U yields t = 5.76, indicating that a correction factor is required; the correction factor is

CF = [1 +B/CS] -1 = 1.236 (1)

This value falls within the allowed range (0.7  CF  1.3).

Method 320: Single Instru ment Spiking Validation EPA Method 320 (Reference 2, Section 13) al so allows validation of FTIR-based measurements by a pair-wise co mparison between the results of a single FTIR system. The procedures and analyses are identical to those described above for the dualinstrument validation, except that the spiked -unspiked sample pairs are the results of sequential measurement s on a single system (rather than simultaneous measurements on a pair of system). Tabl e 4 presents the HCl and SF 6 results of these measurements for the spiked and unspiked samples.1 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 10 of 11 Table 4. Method 320 Single-inst rument Spiking Results (ppm)

SAMPLE PAIR S S (HCL) S U (HCL) S S (SF 6 )

1 14.2 8.83 0.517

2 15.3 8.73 0.531

3 15.1 8.91 0.523

4 14.6 9.86 0.517

5 13.5 9.45 0.517

6 13.8 9.06 0.523

7 13.8 8.51 0.525

8 13.9 7.88 0.525

9 13.9 8.79 0.523

10 12.9 9.46 0.520

11 13.5 8.89 0.523

12 13.9 8.40 0.523

MEAN 14.0 8.90 0.522

STDEV 0.66 0.51

From the mean of the S S (SF 6 ) values and the cylinder SF 6 value concentration, the expected mean spiked concentr ation is CS = 17.6 ppm; th e actual mean spiked concentration is 14.0, so the bias in the proposed method is B = 3.6 ppm. The t-test using the standard deviations of the values S S – S U yields t = 4.19, indicating that a correction factor is required; the correction fa ctor is (see Equation 1) 1.257, which falls within the allowed range (0.7  CF  1.3).

Minimum Detectable Limits The MDL is a critical parameter for any ty pe of low-concentration analysis. A study according to ASTM D6348-98 was performed looki ng at the noise leve ls in the baseline

of the MIDAC 

### I -2000 FTIR spectrometer using a heated 10-meter pathlength gas cell in the presence of up to 20% water vapor. Under these conditions, the MDL for HCl was 0.150 ppm. Though not required by the ASTM method, a bias (average of the standard

deviations of each measuremen t) was added to yield a mo re conservative 0.263 ppm MDL. Detection limits may be improved by us ing indium arsenide or indium antimonide detectors, though this would ru le out analysis of compounds with showing absorbance only below 2000cm -1

.

Conclusion FTIR spectroscopy has been validated by direct comparison with accepted EPA analytical Methods for the analys is of HCl at levels of less than 1 ppm in the presence of moisture, making this a suitable approach for use with incinerators and cement kilns.1 June 2010 PPM Measurement of HCl MIDAC Corporation

Page 11 of 11 Using the principles established in EPA method 320 EPA method 321 has been developed specifically for the analysis of HCl in Portland cement kilns.

References 1. EPA Test Method 301, “Validation of Pollutant Measurement Methods from Various Waste Media”, U.S. Code of Fe deral Regulations ( 40 CFR 61, Appendix B).

2. EPA Test Method 320, “Measurement of Vapor Phase Organic and Inorganic Emissions By Extractive FTIR Spectrosc opy”, U.S. Code of Federal Regulations (40 CFR 61, Appendix B).

3. EPA Test Method 26, “Determination of Hydrogen Chloride Emissions from Stationary Sources”, U.S. Code of Federal Regulati ons (40 CFR 61, Appendix B).