Tunable Diode Laser (TDL) based Hydrogen Chloride gas
(HCl) Continuous Emission Monitoring System (CEMS)
Development Challenges to Meet EPA’s Draft Performance
Specification
Keith Crabbe
Cemtek Environmental, Santa Ana, CA
Gervase Mckay
Unisearch Associates, Toronto, ON CAN
Paul Tran
Cemtek Environmental, Santa Ana, CA
John T. Pisano and Thomas D. Durbin
Department of Chemical and Environmental Engineering, Bourns College of
Engineering, Center for Environmental Research and Technology (CE-CERT)
University of California, Riverside, CA
ABSTRACT
New regulations and emissions limits are requiring the measurement and reporting of Hydrogen
Chloride gas (HCl) levels. Both the Utility Boiler and Portland Cement Maximum Achievable
Control Technology (MACT) rules for the first time require industry wide measurements for
regulatory reporting requirements. Cemtek Environmental and Unisearch Associates have been
involved in the HCl monitoring Performance Specification stakeholder’s group information
exchange with the Environmental Protection Agency (EPA) for development of the new Draft
Performance Specification for HCl CEMS. Cemtek has participated in a demonstration test at a
North American cement manufacturing facility which investigated the performance of Tunable
Diode Laser based HCl CEMS as outlined in the draft performance specification. This paper
will present the demonstration field setup, the tests conducted including comparison with
reference method, and obstacles and lessons learned in completing the tests along with additional
laboratory trial results.
INTRODUCTION
The United Sates Environmental Protection agency has put in place new rule regulating the
emission of Hydrogen Chloride gas (HCl) from Stationary sources. These rules include the
amendments to the NESHAP for Portland cement plants and to the NSPS for Portland cement
plants and Coal fired Electric utility plants under the Mercury and Air Toxics Rule (MATS).
These rules finalize standards that originated with Clean Air Act of 1990. At the time this study
began the EPA regulations at 40CFR63, Subpart LLL which require installation, certification,
operation and ongoing quality assurance of HCl CEMS to demonstrate continuous compliance
with a 3 ppm HCl corrected to 7% O2, dry basis emission limit on a 30-day rolling average by
not later than September 2013.
Holcim Inc. developed, planned and executed a field evaluation project of four HCl CEMS at its
St. Genevieve plant during the summer and fall of 2012. The general objectives of the study
were to determine if contemporary HCl continuous emission monitoring systems (CEMS) have
the capability, accuracy, precision and reliability. Cemtek Environmental using a Unisearch
Associates HCl TDL analyzer was invited to participate in this evaluation. CEMTEK’s interest
was to perform and practice some of the tests in the EPA draft performance specification 18. At
the same time we were providing comments and feed back to the EPA team developing the PS as
a stakeholder. The results of this effort are presented here along with some observations and
issues in the conclusion of the report. (1)
EXPERIMENTAL
The study was conducted at the St. Genevieve plant under the direction of Glen Rosenhamer,
Corporate Environmental Manager. Michelle Ferguson, Plant Environmental Manager, Aaron
Dwyer (Electrical Superintendent), Rodney Miller (Instrumentation Specialist) provided
extensive support for the project over many months. Jim Peeler, Emission Monitoring Inc.
(EMI) provided consulting assistance during the entire project, participated in the field test, and
prepared this report. Phil Kauppi, Prism Analytical Technologies, Inc. performed the FTIR
testing for the stratification test, the Method 321 tests for the RATAs, and analyzed numerous
compressed gas cylinders. (1)
The Holcim St. Genevieve (GV) plant is a contemporary preheater precalciner kiln system which
began operation during 2009. The kiln system has two inline raw mills and operating conditions
include: (a) both raw mills operating, (b) one raw mill operating, and (c) no raw mills operating.
These operating conditions affect the associated effluent HCl concentrations, the concentrations
of other effluent components including NH3, as well as the effluent gas temperatures. HCl
effluent concentrations varied over a range of 0-20 ppm, wet basis. Effluent gas temperatures
also vary with operating condition and were expected to be approximately 205°F (two mills on),
255°F (one mill on) and 320°F (no mills operating). (1)
INSTRUMENTATION
Tunable Diode Lasers (TDL’s) have special properties based upon small crystals (about 0.1
mm2) made of a mixture of elements such as gallium, arsenic, antimony and phosphorus. The
proper selection and proportion of these elements the crystal can be made to emit at wavelengths
where the target gas, which is HCl in this application, absorbs radiation of a particular energy.
Changing either the temperature or current through the laser permits the wavelength to be tuned
over the selected absorption feature of the target molecule. When an electric current is passed
through these crystals they emit very pure laser light in the near-infrared spectral region. The
temperature of the laser, which is stabilized with a thermoelectric cooler, will roughly establish
the wavelength near the target gas’ absorption feature. The laser current is then simultaneously
modulated in the kilohertz region so that phase sensitive detection techniques may be used to
improve sensitivity. One advantage of the TDL technology is that the presence of the measured
component in the gas stream can be used as a reference point for the laser itself. This function is
called “line locking” and consists of the absorption peak of the HCl being used to keep the laser
at the desired frequency. However, in the absence of the measurement component, during bypass
or scheduled shutdowns, the laser can drift, and be outside calibration when the measurement
component returns. To avoid drift, this TDL is supplied with a sealed internal reference cell,
which contains a known amount of the gas to be measured. The use of the reference cells allows
for not only line locking of the analyzer, but also the ability to continuously monitor the
instrument’s calibration. We conducted some testes using this cell to report calibration drift test
results in the results section of this study.
The calculations which determine the actual gas concentration use Beer-Lambert Law.
I = Ioe-cl
(1)
Where:
I
Io

c
l
= Intensity of light after absorption by target molecule
= Intensity of light with no absorption by target molecule
= Absorption cross section (species specific)
= Concentration (number density) of target molecule
= Path length
Beer’s Law is based on the relative absorption of light at wavelengths which are not absorbed
versus light which is absorbed by the molecule of interest. The intensities I and Io are determined
by scanning the wavelength using the characteristic tunability of diode lasers, which allows the
emission wavelength to be adjusted over a span of a few nanometers. This is sufficient to span
certain absorption features in molecules such as ammonia, carbon monoxide, methane, and
others. The only important variable is the fraction of light which is absorbed at the middle of the
scan (return power, I) vs. the extreme ends of the scan (initial power, Io). The laser is scanned at
a frequency of approximately 4 kHz, or every 250 micro seconds (s) so that variations in Io due
to external factors (such as changing dust levels) will be very small. The error introduced by
averaging Io over this very short interval is negligible. The most important consequence of this is
that the absolute light levels reaching the detector are not important in determining
concentrations. It should be noted that this method actually responds to the total number of
absorbing species present. The value is reported as a path averaged concentration, distributed
along the entire measurement path.
A typical system configuration consists of the Analyzer unit in either stand alone or 19” rack
mount configuration, which contains the TDL and associated electronics for signal transmittal
and signal analysis. The Optical heads which contain the Launch and Receive components are
mounted on the duct or stack and connected to the Analyzer via Fiber Optic/Coax cabling. This
permits the analyzer to be placed in any suitable location, such as the CEM shelter or control
room of the plant where it is not subjected to harsh environments and where it can be readily
serviced as required. The optical signal is conveyed from the instrument to the measurement
location by fiber optics and the return detected signal transported to the instrument by a separate
coaxial cable. Thus, for example, continuous measurements can be made of the emissions in
stacks and ducts which can be as much as 1500 feet (with a Photo Detector Amplifier or PDA)
away from the instrument.
MEASUREMENT LOCATION
If the measurement is being made for stack emissions monitoring or HCl CEMS, it is on the
stack or at another location that would be considered representative of stack emissions. The EPA
is referring to the cross stack as Integrated Path or IP-CEMS in the draft PS-18. The
measurement sensitivity is dependent upon the measuring path length (Beer–Lambert law) and
the opaqueness (particulate matter density) of the gas stream. The path length distance between
the light source and the detector can vary depending upon the sample stream’s particulate
concentration. Monitoring locations that have conditions such as a fully saturated or condensing
stack or duct that has a similar effect as high dust loading, which would extinguish the laser
light, should be avoided. Therefore when choosing the measurement location, these factors along
with the turbulence and stratification issues that arise must be considered. The measurements are
usually made in-situ across the stack or duct. Various configurations can be chosen to define the
process interface by the choice of flange sizes, materials, purging modes and purging media in
order to adapt the sensors for process engineering measurements. In some cases, the optical path
can be inside a probe. However, this will limit the path length. Alignment of the optical heads are
of significant importance, and therefore the sight tubes to which the optics are attached to, are
required to be aligned to specific tolerance typically within 1 degree and must be maintained at
relative high temperatures. The optical heads must have the capability to adjust for any small
misalignment errors. Another component that must be taken into account is the “thermal growth”
of the duct or stack and material aging. Several engineered solutions are available to counteract
this issue.
Two methods are employed for measurements across stacks or ducts: 1) single-pass where the
laser radiation is transmitted across the stack to the detector on the other side, and 2) dual-pass
where the laser radiation is transmitted across the stack to a reflector and then back to the
detector on the same side as the transmitter. In typical installations, instrument air is used at each
of the optical lenses to keep them clear of flue gas contaminants.
For this study we chose to use dual pass optics which would provide the best detection limit and
sensitivity. The stack location was free of deformation which could cause optical alignment
issues and the dust load in the stream was low during the test period. The windows never needed
cleaning during the 4 months in continuous operation at this site.
Launching
Element
Receiving
Element
Stack
Detector
Len
Coaxial
Cable
Optical
Fiber
Air
Air
1) Single-Pass Stack Configuration
Stack
Retro
Reflector
Len
Detector
Coaxial
Cable
Optical
Fiber
Air
2) Dual-Pass Stack Configuration
FIGURES 1 & 2: CROSS DUCT SYSTEM DESIGN
Air
In special situations where long spool pieces or lagging is employed, especially in the prescience
of negative pressure stacks or ducts, blowers are required to prevent the migration of HCl in the
spool pieces. Such migration would cause a variable and inconsistent concentration of HCl in the
laser path resulting in inconsistent and inaccurate measurements. Applying a positive pressure of
ambient air to the spool pieces will assure that no stack gas HCl is migrating into the spool
pieces. Particular attention must also be paid to the location of the measurement tools to limit the
accumulation of particulate matter which can not only cause loss of signal due to light scattering
but also can result in physical changes in the alignment of the laser light requiring realignment
after cleaning. The blower system we used during this study kept the optics clean so instrument
air was not needed.
SENSITIVITY AND DETECTION LIMIT
The sensitivity and minimum detection limit of an absorption device are path length dependent.
The longer the path length, the higher the absorption and the lower the sensitivity and detection
limit. Therefore, longer path lengths result in better detect ability of low concentrations.
Dust loading in the effluent stream has the effect of blocking and scattering the laser radiation
such that the detection limit will be compromised, leading to a much higher minimum detection
value, due to lower power levels of the laser radiation reaching the detector. While particulate
matter affects the detection limit, most systems can tolerate laser radiation power reductions of
up to 90% without affecting the accuracy of the measurement. Nevertheless, there is a trade off
in path length considerations between detect ability and reliability of the measurement. A single
pass system with a PDA is recommended for high dust applications. Water vapor is also active in
the near-IR spectral region; however the HCl line selected was far from waters influence.
Typical sensitivity and detection limits on coal fired sources dependent on the above criteria
would be ±1 ppmv with a detection limit of 0.2 part per million by volume (ppmv) respectively.
CALIBRATION REQUIREMENTS
Prior to initial usage, the instrument must be calibrated for HCl using a gas standard. After the
initial calibration is performed, system validation is performed on a regular basis as defined by
the governing body, in this case the USEPA. A flow-through gas cell permanently in the optical
path that allows for introduction of cylinder gases to be injected to check the analyzer response
as an additive or dynamic spike should be part of the analyzer. After use the cell is purged with
dry air or nitrogen.
CALIBRATION FACTOR
The TDL uses the Beer-Lambert Law to convert a quantity of absorption into a concentration as
follows:
C
 VTL ln( I I 0 )
L
(2)
Where:
 is the line strength factor at STP
I is the amount of measured light after passing through the gas medium
I 0 is the amount of initial light (i.e. transmitted light with no gas present that is to be
measured)
L is the length of the absorption medium (Path length)
V is the volume correction
TL is the line strength correction (a function of gas temperature)
When we do the initial calibration of the instruments we use a certified cylinder of gas, and rearrange the equation to solve for  .
The test configuration shown in figure 3 has the double pass stack optics with a single blower at
the stack. The analyzer is remotely located in a nearby CEMS shelter that is air conditioned and
protected from the elements.
FIGURE 3: SYSTEM DESIGN
The power supply has an uninterruptable power supply (UPS) which provided power to the
analyzer and programmable controller (PLC). The PLC is used to conduct the spike gas selection
solenoid valves and sequences in the test configuration. The gases are conveyed to the flow-thru
gas cell inside the analyzer with ¼ Teflon tubing. A laptop PC captures the data form the
analyzer and provides a convenient interface with the analyzer. For this test we used it to connect
to a wireless internet connection for remote support. In permanent installation the laptop is only
used for troubleshooting and changing configuration parameters
SPIKE GAS DETERMINATION
To determine the spike gas injections for the appropriate values need to perform the tests we
need to account for the path length. The cylinder values when using the IP-CEMS are larger than
the fully extractive CEMS since the concentrations is divided by the path length. Below is the
formula used to calculate the expected analyzer response to a known HCl concentration with a
zero HCl background:
C spike  Cbottle 
PLcell
Tstack

 LSM
PLstack Tbottle / room
(3)
Where
C spike
= Expected concentration of gas spike response in ppmv
Cbottle
= Concentration of gas cylinder in ppmv
PLcell
= Path length of flow-thru gas cell in meters
PLstack
Tstack
= Path length of stack in meters
= Temperature of stack in Kelvin
Tbottle / room = Temperature of bottle/room in Kelvin
LSM
= Line strength multiplier
The cell length used in this analyzer was measured to be 0.158 m and the stack path length was
11.12 m.
TESTS CONDUCTED ARE FROM THE DRAFT PS 18 FOR IP-CEMS
This section describes the performance specification 18 tests that are required for IP-CEMS to
performance to demonstrate initial certification and in some cases includes our interpretation.
Then we report our findings in the discussion and results section for ht testes we attempted. (3)





Interference Test
Limit of Detection (LOD) Determination
Response Time Test
Calibration Error (CE) Test
Seven Day Calibration Drift Test


Stratification Test
Relative Accuracy Test or Dynamic Spiking Test
INTERFERENCE TEST
This test is conducted either in a controlled environment or in the field during initial setup and
qualification of the CEMS. If there are multiple measurement systems that are identical to each
other, this check is only required on one system. Procedure: Inject HCl gas that is equivalent to
20-40% of the lowest calibration span value anticipated. The balance of the cylinder
concentration must conform to Table 1 under Section 17.0 of Performance Specification 18
(PS18). Below is a copy of the table in question.
TABLE 1: COPY OF TABLE 1 FROM SECTION 17.0 OF PS18
1
Any of these specific gases can be tested at a lower level if the manufacturer has provided reliable means for limiting or
scrubbing that gas to a specified level.
Potential Interferent Gas1
Approximate Concentration
(balance N2)
CO2
15 ± 1 %
CO
100 ± 20 ppm
CH4
100 ± 20 ppm
NO2
250 ± 50 ppm
SO2
200 ± 20 ppm
O2
3±1%
H2O
10 ± 1 %
Nitrogen
Balance
Other
Each test must be evaluated in triplicate for each interfering gas noted in Table 1, first with HCl
balance Nitrogen then individually with each interfering gas while maintaining constant HCl
concentration. (e.g. 150 ppm HCl with 15% CO2 and balance N2.) Gas volume/rate will be
documented to establish the error of blending HCl and interference gases. A gas blending system
or manifold may be employed. Measure and record the HCl response and determine overall
interference response using Table 2 of Section 17.0 of PS18. Calculate mean difference between
measurement system response with and without the interference tests gasses. Calculate total
interference.
Pass/Fail Criteria: Combined interference response must not be greater than 3.0 percent of the
calibration span used for the test.
LIMIT OF DETECTION (LOD) TEST
See note on the Interference Test for determining when the LOC test may be conducted. The
challenge gas must consist of the interferences listed in Table 1 and HCl at a concentration
between 2-5 times the estimated LOD. Procedure: Spike the gas mixture into the system
calibration cell. Collect seven (7) independent measurements. LOD units must be determined
and reported on a ppm-meter basis or on the actual measurement path length for a specific site
installation. Calculate standard deviation of measured values and estimate the LOD at 3 times the
standard deviation.
RESPONSE TIME DETERMINATION TEST
Procedure: Inject an HCl reference gas and record the time to reach 95% of the reference gas
concentration. Inject a zero gas and record the time to reach a reading that is 5% of the upscale
gas reading from the reference gas concentration. Repeat steps 1 and 2 for a total of 3 repetitions.
Calculate the average upscale and downscale response time from three repetition of each test.
The greater average of the upscale or downscale response time is the response time of the
system. Pass fail criteria is apparently to report the results.
CALIBRATION ERROR (CE) TEST
Mean difference between the reference gas value (R) and CEMS response at each calibration
point (A). This is conducted on a daily basis. Procedure: Do a 3-point calibration error test with a
low, mid and high gas concentration range, in sequential order, by injecting gas into an inline
calibration cell (must know temperature, pressure, and path length of cell). Concentrations of the
low, mid, and high gas are as tabulated in Table 2.
TABLE 2: REQUIRED LEVELS OF HCL FOR CE TEST IN RELATION TO
ANALYZER SPAN
HCl Calibration
Concentration Level
Zero
Low Level
Mid Level
High Level
Range (% of span)
< LOD
10 – 50
80 – 100
190 – 200
Measure and calculate the relative equivalent concentration of HCl gas at stack conditions (i.e.
correct to stack conditions) Repeat steps 1 and 2 for a total of three independent CEMS
measurement responses such that each calibration gas injection is at least 2 minutes apart.
Pass/Fail Criteria: Calculated CE must be less than 5%. Calibration intercept must be equal to or
less than 15% of the instrument’s span. If failed, then take corrective action and repeat test until
the CE test results are passing.
SEVEN-DAY CALIBRATION DRIFT (CD) TEST
Purpose is to verify the ability of the CEMS to maintain calibration for seven consecutive 24hour operating periods/days. The seven operating days do not need to be 7 consecutive calendar
days. If there are manual or automatic adjustments are made to the zero/span response settings, a
daily CE test must be conducted prior to the adjustments. Procedure: Inject a certified zero.
Continue to inject zero gas until two consecutive measurements take at least 2 minutes apart are
within 5% [of each other]. Record the average CEMS response to zero gas. The measured
concentrations must be corrected for calibration cell temperature, pressure, and path length [to
stack conditions]. Inject a certified calibration gas standard. Continue to inject this gas until two
consecutive measurements take at least 2 minutes apart are within 5% [of each other].
Record the average CEMS response to the calibration standard. The measured concentrations
must be corrected for calibration cell temperature, pressure, and path length [to stack conditions].
Subtract the average CEMS zero and calibration standard response from the [calculated]
calibration standard gas value [corrected to stack conditions] and express as an absolute percent
different of the span value. Pass/Fail Criteria: Calculated CD must be less than 5% per day.
RELATIVE ACCURACY (SA) TEST FOR IP-CEMS
Six or more sets of independent measurements—of at least a 1 minute average—are used to
calculate the average and standard deviation to determine CEMS accuracy and to compare to the
limitations as noted in Section 13.0 of PS18. Target level of spiking is 20 to 40 percent of the
[analyzer] span value. Procedure: Inject a certified zero. Continue to inject zero gas until two
consecutive measurements take at least 2 minutes apart are within 5% [of each other].
Record the average CEMS response to zero gas. The measured concentrations must be corrected
for calibration cell temperature, pressure, and path length [to stack conditions].
Inject a certified calibration gas standard. Continue to inject this gas until two consecutive
measurements take at least 2 minutes apart are within 5% [of each other].
Record the average CEMS response to the calibration standard. The measured concentrations
must be corrected for calibration cell temperature, pressure, and path length [to stack conditions].
Re-inject a certified zero. Continue to inject zero gas until two consecutive measurements take at
least 2 minutes apart are within 5% [of each other].
Record the average CEMS response to zero gas. The measured concentrations must be corrected
for calibration cell temperature, pressure, and path length [to stack conditions].
Repeat 6 times for 6 sets of data. Calculate the spike recoveries and its relative accuracy per
Section 12.13 of PS18. Pass/Fail Criteria: Calculated recoveries (SR) must be less than 20% for
each of the independent measurements. The relative accuracy over the 6 or more independent
measurements may not exceed 15 percent.
RESULTS AND DISCUSSION
INTERFERENCE TEST
This test was conducted in the Cemtek Environmental facility and completed a partial test using
the compressed gases we had on hand we use for testing our other CEMS we produce. Following
the PS18 procedure the results are shown in table 3 below demonstrating.
TABLE 3: INTERFERENCE TEST RESULTS
Test Gas
CO2
CO
CH4
NO2
SO2
O2
H2O
Nitrogen
Interference
(ppmv)
0.079 ± 0.13
-0.0053 ± 0.0036
-0.13 ± 0.05
Not Tested
0.071 ± 0.057
0.06 ± 0.09
Not Tested
The interference test conducted in the above was done at the condition where there is no HCl in
the ambient air or in the test cell. The draft Performance Specification 18 (further references to
this Specification will be noted as PS18) Interference Test calls out for HCl gas, at a constant
level to be tested with and without the above gas compositions noted in Table 1. Thus the
intended purpose to informally conduct the Interference Test in accordance to PS18 is
incomplete. A follow-up test would be prudent to test all interfering gases in the presence of
HCl. This would allow one to quantify the interference bias due to the given gases for a constant
level of HCl.
In addition, all of the test gas interferences measured is all below the calculated detection limit of
1.8 ppmv for the test setup and cannot be measured with sufficient confidence. Even at an
effective path length of 11 meters, the interference would be still well below the detection limit.
The detection limit was determined at Holcim to be 0.2 ppmv with an operating temperature
range of 250-300°F (394-422 K). It may be necessary to increase the integration time to increase
the sensitivity of the analyzer.
Even though the inputted temperatures and pressures are at the elevated levels for stack gas
conditions, the correction factor would have been applied uniformly for the detection limit and
the tabulated values in Table 3. Further testing, however, should have the proper test conditions
inputted into the analyzer.
Follow-up / Additional Testing
 Re-test the conditions above with the proper temperature and pressure conditions.
 Re-test to include the omitted test gases as they were not available on hand to measure.


Increase the integration time to 1 minute or more from 10 seconds to improve the
detection limit. This will not be required if the path length is increased such that the
detection limit is lowered sufficiently.
Have a method of automating the switching of the calibration gases via a manifold. Will
speed up the data acquisition portion of the test.
LIMIT OF DETECTION (LOD) TEST
This test was conducted in the field at the Holcim trial and the results. Successively decreasing
spike gas concentrations were introduced to the in-line audit cell by means of diluting the 318
ppm audit gas with nitrogen using the EMI gas dilution manifold. The diluted spike
concentration of 9.9 ppm is equivalent to an effluent HCl concentration of 0.165 ppm and was
clearly distinguishable from the zero HCl concentration response of -0.005 ppm observed for the
effluent after the spike was discontinued. Therefore the LOS for the TDL system as installed
at St. Genevieve under real world conditions while actively monitoring cement kiln effluent
is ≤ 0.16 ppm. Lower concentrations were spiked into the audit cell, however it was difficult to
distinguish the presence of the response from the apparent zero value. (1)
RESPONSE TIME TEST
Response Time Test Results were taken from the data collected performing calibration error tests
using a bottle of HCl and Nitrogen supplied by Holcim and conducted after the completion of the
Trial period. The results are show below. The optical setup was set up to have an effective path
length of 11.12 meters. The temperature and pressure was dynamically inputted from the
customer DCS. Integration time was left at 10 seconds. Calibration gas was introduced via a
solenoid manifold assembly controlled by a PLC. The cylinder concentration employed was a
318.5 ppmv bottle. The average effective analyzer response is roughly 5 ppmv depending on the
temperature conditions at the time of test.
Procedure
Gases were injected into the flow-through gas cell via solenoids. The sequence is automated by a
PLC and is as follows.
1.
15 minute (900 seconds) delay after internal zero/audit check
2.
Flow N2 gas for 120 seconds. Purge sequence
3.
Flow HCl gas for 300 seconds
4.
Flow N2 gas for 240 seconds. Purge/Zero sequence
The analyzer records the response in real-time as a flat text file. The data will be then pulled and
analyzed accordingly.
Results
Tables 2 and 3 tabulate the raw data for the rise and fall of the HCl analyzer response average for
each test run. Averages of the background data where no HCl was present were taken before and
after to determine the background levels. The Analyzer Reponses takes this into account by
subtracting the background levels. Also included is the average temperature and expected
analyzer response.
Additionally, a non-linear total least squares fit has been applied to the data to determine the
experimental time-constant k, which is noted below as Equation [1]. This was done via the
Solver add-in in Excel. From the fitted time-constant, the time to reach 95% of the analyzer
response was determined. This can be seen in Table 3 and graphically in Figures 4.
Test #1, Fall Time
80
y
30
Fit
‐20 0
50
Time (s)
% Response
% Response
Test #1, Rise Time
100
120
100
80
60
40
20
0
‐20 0
Fit
% Response
% Response
y
50
Time (s)
100
120
100
80
60
40
20
0
‐20 0
50
Time (s)
100
y
Fit
50
Time (s)
100
Test #3, Fall TIme
150
y
Fit
0
50
Time (s)
100
% Response
% Response
Test #3, Rise Time
120
100
80
60
40
20
0
Fit
Test #2, Fall Time
Test #2, Rise Time
120
100
80
60
40
20
0
‐20 0
y
100
y
50
Fit
0
0
‐50
50
100
Time (s)
FIGURE 4: RESPONSE TIME TEST RESULTS
Rise and Fall time graphs for Tests 1, 2, and 3. Shows the best fit to the data as solved
TABLE 4: CALCULATED RESPONSE TIME FOR RISE AND FALL OF HCL-TDL
ANALYZER IN RESPONSE TO ZERO AND SPIKE GAS.
Test Run
Rise Time
(s)
Fall Time
(s)
1
25.10
16.24
2
25.14
17.20
3
19.74
12.81
Average
23
15
Standard Deviation
3
2
CALIBRATION ERROR TEST
Calibration Error Test Results was not performed due to timely request for the cylinder values
need for this study.
CALIBRATION DRIFT TEST
Calibration Error Test Results were taken from the data collected using a bottle of HCl and
Nitrogen supplied by Holcim and conducted after the completion of the Trial period. The results
are show below in table 5.
TABLE 5: CALIBRATION DRIFT TEST RESULTS
0.0
10/16
13
0.00062
-0.00064
Daily Spiking Summary
Average
Average
HCl
Analyzer
Analyzer
Baseline
Spike
Tavg (K)
Response
Reponse
(ppm)
(ppm)
(ppm)
-0.00001
5.322
5.322 357.22
0.1
10/16
13
-0.00032
-0.00040
-0.00036
4.959
4.959
359.12
5.215
95.08%
3.18%
0.85%
0.2
10/16
13
0.00053
0.00000
0.00027
5.455
5.455
386.72
5.522
98.79%
3.30%
0.22%
0.3
10/16
13
0.00286
0.00002
0.00144
5.847
5.846
383.50
5.486
106.57%
3.57%
1.20%
1.0
10/17
13
5.29874
5.60349
5.45112
11.888
6.437
442.42
6.170
104.31%
3.63%
0.89%
2.0
10/18
13
-0.00017
-0.00051
-0.00034
5.585
5.585
372.74
5.366
104.09%
3.48%
0.73%
3.0
10/19
13
-0.00018
-0.00023
-0.00021
5.640
5.640
376.29
5.405
104.35%
3.49%
0.78%
4.0
10/20
13
-0.00092
-0.00118
-0.00105
5.596
5.597
376.75
5.410
103.46%
3.46%
0.62%
5.0
10/21
13
-0.01857
-0.00504
-0.01180
5.277
5.289
362.12
5.248
100.77%
3.37%
0.14%
6.0
10/22
13
0.56555
0.35426
0.45991
7.136
6.676
419.30
5.896
113.24%
3.79%
2.60%
7.0
10/23
13
0.00342
0.00412
0.00377
5.787
5.783
373.52
5.374
107.61%
3.60%
1.36%
8.0
10/24
13
0.00009
0.00126
0.00068
5.778
5.778
378.99
5.435
106.30%
3.56%
1.14%
Day
Date
#
Of
readings
Pre-Spike
Bkg
Average
(ppm)
Post-Spike
Bkg
Average
(ppm)
Expected
Response
at Tavg
(ppm)
SRavg
(%)
SAavg
(%)
Cal.
Drift
5.195
102.45%
3.44%
0.42%
TABLE 6: SPIKE TEST PARAMETERS
MISC Parameters
Bottle
Concentration SPAN
318.5
30
ppm
ppm
Ref/Room Temp
73
°F
295.9
K
PLCell PLStack
0.158
11.12
meters meters
t-value
n-1
12
t-value @ n-1 = 12
2.179
RELATIVE ACCURACY TEST
The traditional Part 60 relative accuracy specification for SO2, NOx and most other pollutant gas
CEMS is ≤20% of the reference measurement value or ≤10% of the emission standard,
whichever is least restrictive. This specification is used for the Holcim project as a tentative
specification. The relative accuracy is calculated as the sum of the absolute value of the
differences and the 95% confidence coefficient, divided by either the mean reference
measurement result or the emission standard, to express the result as a percentage. The emission
standard is 3 ppm at 7% O2, dry basis. For the purposes of this comparison, we will simply use 3
ppm HCl as the emission standard. (1)
TABLE 7 CEMTEK TDL TWO MILLS ON RATA CALCULATIONS
Run
1
2
3
4
5
6
7
8
9
Date
18-Sep
18-Sep
18-Sep
18-Sep
18-Sep
18-Sep
18-Sep
18-Sep
18-Sep
Time
9:00 - 9:30
10:11 - 10:40
11:16-11:46
11:47 - 12:17
12:18 - 12:48
13:19 - 13:48
13:50 - 14:19
14:21 - 14:50
15:16 - 15:46
SUM
AVG
RATA RESULTS
Average Difference
Standard Deviation
Confidence Coefficient
Relative Accuracy %
Relative Accuracy ppm
Emiswsion Standard
Relative Accuracy % of STD
CEMS (ppmw)
0.02
0.07
0.04
0.02
0.03
0.01
0.06
-0.01
-0.01
Ref (ppmw)
0.12
0.15
0.14
0.11
0.09
0.17
0.11
0.10
0.16
Difference
-0.10
-0.08
-0.10
-0.09
-0.06
-0.16
-0.05
-0.11
-0.17
0.23
0.03
1.15
0.13
-0.92
-0.10
-0.10
0.04
0.03
104%
0.13
3
4.4%
ppm
ppm
% of STD
Difference
0.01
0.01
0.01
0.01
0.00
0.03
0.00
0.01
0.03
The two mills on RATA results are shown in Table 7. For this low concentration test, the TDL
CEMS relative accuracy was 4.4% of the emission standard. The CEMS meets the RA
requirement. The small mean difference of -0.1 ppm is attributed to the fact that the FTIR
reference system does not measure values below 0.1 ppm. (1)
0.11
0.01
2
TABLE 8: CEMTEK TDL TWO MILLS OFF RATA CALCULATIONS (18 RUNS)
Run
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Date
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
Time
6:58 - 7:26
7:28 - 7:58
7:59 - 8:29
8:38 - 9:07
9:09 - 9:39
9:40 - 10:10
10:16 - 10:47
10:47 - 11:16
11:16 - 11:46
11:53 - 12:23
12:24 - 12:54
12:55 - 13:25
13:38 - 14:08
14:09 - 14:39
14:40 - 15:10
15:18 - 15:46
15:58 - 16:18
16:19 - 16:49
SUM
AVG
RATA RESULTS
Average Difference
Standard Deviation
Confidence Coefficient
Relative Accuracy
CEMS (ppmw)
13.06
13.43
13.93
14.08
14.38
14.30
15.20
15.44
14.92
13.91
7.72
5.77
4.40
4.32
4.11
4.01
3.92
3.83
Ref (ppmw)
13.86
14.18
14.68
15.29
15.43
15.59
16.08
16.46
16.59
15.74
8.99
6.40
5.31
4.86
4.61
4.41
4.30
4.12
Difference
-0.80
-0.75
-0.75
-1.21
-1.05
-1.29
-0.88
-1.02
-1.67
-1.83
-1.27
-0.63
-0.91
-0.54
-0.50
-0.40
-0.38
-0.29
180.73
10.04
196.90
10.94
-16.17
-0.90
-0.90
0.43
0.22
10.2%
Difference
0.64
0.56
0.56
1.46
1.10
1.66
0.77
1.04
2.79
3.35
1.61
0.40
0.83
0.29
0.25
0.16
0.14
0.08
17.72
0.98
t = 2.11
The two mills off RATA results for the TDL CEMS are shown in Table 8 based on all 18 runs
performed. For this high concentration test, the TDL CEMS relative accuracy was 10.2% which
meets the 20% relative accuracy specification. The mean difference was -0.90 ppm reflecting
that the TDL values were lower than the reference FTIR measurements. (1)
2
TABLE 9 CEMTEK TDL TWO MILLS OFF RATA CALCULATIONS (15 RUNS)
Run
1
2
3
4
5
7
8
11
12
13
14
15
16
17
18
Date
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
19-Sep
Time
6:58 - 7:26
7:28 - 7:58
7:59 - 8:29
8:38 - 9:07
9:09 - 9:39
10:16 - 10:47
10:47 - 11:16
12:24 - 12:54
12:55 - 13:25
13:38 - 14:08
14:09 - 14:39
14:40 - 15:10
15:18 - 15:46
15:58 - 16:18
16:19 - 16:49
SUM
AVG
RATA RESULTS
Average Difference
Standard Deviation
Confidence Coefficient
Relative Accuracy
CEMS (ppmw)
13.06
13.43
13.93
14.08
14.38
15.20
15.44
7.72
5.77
4.40
4.32
4.11
4.01
3.92
3.83
Ref (ppmw)
13.86
14.18
14.68
15.29
15.43
16.08
16.46
8.99
6.40
5.31
4.86
4.61
4.41
4.30
4.12
Difference
-0.80
-0.75
-0.75
-1.21
-1.05
-0.88
-1.02
-1.27
-0.63
-0.91
-0.54
-0.50
-0.40
-0.38
-0.29
137.60
9.17
148.98
9.93
-11.38
-0.76
-0.76
0.30
0.17
9.3%
Difference
0.64
0.56
0.56
1.46
1.10
0.77
1.04
1.61
0.40
0.83
0.29
0.25
0.16
0.14
0.08
2
9.91
0.66
t = 2.145
The relative accuracy test procedures allow for the rejection of three test runs, as long as nine test
runs are reported. The two mills off RATA results were recalculated based on 15 test runs
(omitting runs 6, 9, and 10) as shown in Table 9. The relative accuracy based on 15 test runs was
9.3% of the reference value. (1)
TABLE 10: CEMTEK TDL ONE MILL ON RATA CALCULATIONS (17 RUNS)
Run
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Date
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
Time
8:00 - 8:30
8:30 - 9:00
9:00-9:30
9:41-10:11
10:12-10:42
10:42 - 11:12
11:22 - 11:52
11:52 - 12:22
12:22 - 12:52
13:06 - 13:36
13:36 - 14:06
14:06 - 14:36
15:00 - 15:30
15:30 - 16:00
16:00 - 16:30
16:59 - 17:29
17:29 - 17:59
SUM
AVG
RATA RESULTS
Average Difference
Standard Deviation
Confidence Coefficient
Relative Accuracy
Relative Accuracy ppm
Emiswsion Standard
Relative Accuracy % of STD
CEMS (ppmw)
2.56
2.21
2.14
1.54
1.33
1.35
1.26
1.45
1.19
1.05
0.94
0.74
0.36
0.73
2.19
0.59
0.00
Ref (ppmw)
3.21
2.35
2.05
1.84
1.66
1.53
1.44
1.35
1.30
1.21
1.06
0.85
0.49
0.54
1.05
0.71
0.07
Difference
-0.65
-0.14
0.09
-0.30
-0.33
-0.18
-0.18
0.10
-0.11
-0.16
-0.12
-0.11
-0.13
0.19
1.14
-0.12
-0.07
21.63
1.27
22.71
1.34
-1.08
-0.06
-0.06
0.36
0.19
18.7%
0.25
3
8.3%
t =2.12
Ppm
Ppm
% of STD
Difference
0.42
0.02
0.01
0.09
0.11
0.03
0.03
0.01
0.01
0.03
0.01
0.01
0.02
0.04
1.30
0.01
0.00
2.16
0.13
2
TABLE 11: CEMTEK TDL ONE MILL ON RATA CALCULATIONS (14 RUNS)
Run
2
3
4
6
7
8
9
10
11
12
13
14
16
17
18
Date
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
20-Sep
Time
8:30 - 9:00
9:00-9:30
9:41-10:11
10:42 - 11:12
11:22 - 11:52
11:52 - 12:22
12:22 - 12:52
13:06 - 13:36
13:36 - 14:06
14:06 - 14:36
15:00 - 15:30
15:30 - 16:00
16:59 - 17:29
17:29 - 17:59
SUM
AVG
RATA RESULTS
Average Difference
Standard Deviation
Confidence Coefficient
Relative Accuracy
Relative Accuracy ppm
Emiswsion Standard
Relative Accuracy % of STD
CEMS (ppmw)
2.21
2.14
1.54
1.35
1.26
1.45
1.19
1.05
0.94
0.74
0.36
0.73
0.59
0.00
Ref (ppmw)
2.35
2.05
1.84
1.53
1.44
1.35
1.30
1.21
1.06
0.85
0.49
0.54
0.71
0.07
Difference
-0.14
0.09
-0.30
-0.18
-0.18
0.10
-0.11
-0.16
-0.12
-0.11
-0.13
0.19
-0.12
-0.07
15.55
1.11
16.79
1.20
-1.24
-0.09
-0.09
0.13
0.07
13.6%
0.16
3
5.5%
Difference
0.02
0.01
0.09
0.03
0.03
0.01
0.01
0.03
0.01
0.01
0.02
0.04
0.01
0.00
2
0.33
0.02
t =2.16
ppm
ppm
% of STD
For this test 17 reference test runs were completed. HCl concentrations began above 3 ppm and
decreased throughout the day as lime inject was increased on several occasions. The TDL CEMS
relative accuracy was calculated for runs 1-17 and the results were 18.7% of the reference value
as shown in Table 10. This result meets the 20% relative accuracy specification. The mean
difference was -0.06 ppm reflecting that the TDL values were virtually equal to the reference
FTIR measurements. The one mill on RATA results were recalculated based on 14 “best” test
runs (omitting runs 1, 5, and 15) as shown in Table 11. The relative accuracy based on 14 test
runs was 13.6% of the reference value. (1)
ISSUES ENCOUNTERED DURING THE TEST PERIOD
‐
‐
‐
‐
Optical locks not secured caused unrepeatable gas injections.
Calibration Gas regulator and transport tubing needed conditioning for several hours to
come to equilibrium.
EPA had questions about how to check zero in IP-CEMS and presented to them in
response novel way of spectral subtraction. Testing it in the field and show good results.
Also showed the internal Span Check results of time.
Implement a residual background calculation for correctly measuring when no HCl
present.
‐
‐
‐
‐
‐
Implementation of dynamic temperature inputs to analyzer. This employed was to
account for the potentially wide swings in temperature at site. The expected error in the
measurements would be in the range of 6 to 7% if a fixed temperature of 126.6°C was
employed—thus a fixed calibration factor.
Automated daily injections to the Cal Error test near the end of the trial period with very
good results.
Found better results by turning off low correlation R-value <0.7 correction.
Difference found between the factory calibration factor as compared to specialty gas
cylinders of HCl. The Cal factor was set by an external audit module that was over 5
years old.
Measurement by TDL is wet basis and compliance limit is 3 ppmvd at 7% O2 on a 30 –
day rolling average.
CONCLUSIONS
The results obtained for the tests conducted for this study provide some of the first data from
HCl CEMS while following the test procedures in Draft PS 18. The EPA has received this data
to further their PS development.
The interference test was partially completed and the results showed that for the interfering gases
tested the TDL would pass the test for those gases. The responses were all below the LOD. This
test will need to be performed for the complete list of gases and concentration ranges added to a
base HCl concentration as the test calls out in future studies. An interference test was conducted
by the University of California, Riverside with similar results. (3)
The limit of detection test showed that he TDL is a sensitive measurement technique and the
result of this test exceeded the expectation of the manufacturer. The lab LOD was expected to be
0.2 ppmv and the measured LOD installed was better than that measuring 0.16 ppmv. Further
installation test need to done to demonstrate repeat performance. (3)
The response time test used the spike test data and showed the response to the spike gas and zero
gas was less than 30 seconds. Normal CEMS response time limits are 15 minutes maximum so
this a very rapid repose time and can be useful for process control at this speed of analysis.
The calibration error test was not conducted during this study and will be conducted at another
installation. We did prepare in time to select the gases needed before demobilizing form the field
The seven day drift results showed that using the internal Cal cell as well as the gas flow though
demonstrated the stability and repeatability needed to pass this test. All testes were 2.6% and
less.
The stratification test was not conducted during this study.
The relative accuracy test was evaluated as a 40CFRPart 60 CEMS would be evaluated. The
TDL passed all the test conditions presented. Several conditions to generate low and high levels
of HCl stack gas and all were within passing tolerances.
During the study period we also learned a number of things to make the analyzer perform better.
Some were in the form of signal processing analysis. Some improvements is startup and
commissioning procedure checklist were made. Over all the TDL was very simple to startup and
maintain with very little attention need to obtain excellent results.
ACKNOWLEDGEMENT
Holcim Inc. and the staff at St. Genevieve plant.
REFERENCES
1. Peeler. Jim - Emission Monitoring Inc., Rosenhamer, Glen - Holcim Inc., Field Evaluation of
HCl CEMS at Holcim St. Genevieve Plant, December 19, 2012
2. USEPA, Draft Version 9-19-2012, Draft Performance Specification 18,
Performance Specifications and Test Procedures for HCl Continuous Emission
Monitoring Systems in Stationary Sources
3. Dene, Chuck – EPRI, Continuous Emission Monitor For Hydrochloric Acid,
Tunable Diode Laser Test Report, Unisearch LasIR S Series, 1022083, Final
Report, December 2011 EPRI, Palo Alto, CA: 2011 1022083).