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The Effect of Ammonia on HCl Emissions

Technical PaperBR-1880

Authors:G.E. Pavlovicz

A.A. Silva

Babcock & Wilcox

Power Generaon Group, Inc.

Barberton, Ohio, U.S.A.

M.J. Mullen

DTE Energy

Detroit, Michigan, U.S.A.

Presented to:Power Plant Air Pollutant

Control “MEGA” Symposium

Date:

August 20-23, 2012

Locaon:

Balmore, Maryland, U.S.A.

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Babcock & Wilcox Power Generation Group 1

The Effect of Ammonia on HCl Emissions

G.E. Pavlovicz

A.A. Silva

Babcock & Wilcox Power Generation Group, Inc.

Barberton, Ohio, USA

Presented at:

Power Plant Air Pollutant Control “MEGA” Symposium

Baltimore, Maryland, U.S.A. August 20-23, 2012

BR-1880

Abstract

The U.S. Environmental Protection Agency (EPA) issued

the Mercury and Air Toxics Standards (MATS) regulations

stating that existing coal-red power plants must achieve <

0.002 lb/MMBtu emissions of hydrogen chloride (HCl). EPA

Method 26A is the approved test method for halides, includ-

ing HCl, but this method can skew the HCl results high in the

presence of ammonium chloride (NH4Cl). At Detroit Edi-

son’s Monroe Power Plant Units 3 and 4, it was discovered

that a high ammonia slip from a selective catalytic reduc-

tion (SCR) system resulted in the formation of ammoniumchloride. The ne ammonium chloride particulate escapes

complete capture in the wet ue gas desulfurization (FGD)

system, and can be subsequently detected by EPA Method

26A and reported as HCl. In some cases, this can result in

HCl values being erroneously reported higher than permitted

limits. Stack testing was completed using Fourier transform

infrared (FTIR) spectrometry at various operating conditions

to understand the formation of ammonium chloride in the

system and yield the correct HCl emissions results.

Introduction

In 2009, Babcock & Wilcox Power Generation Group,

Inc. (B&W PGG) installed wet ue gas desulfurization

scrubbers at Detroit Edison’s Monroe Power Plant Units 3

and 4 to control sulfur dioxide (SO2), other acid gases, and

lterable particulate matter emissions. As part of B&W

PGG’s ongoing R&D efforts, multi-pollutant testing across

one of the new scrubbers was performed in 2010. Wet FGD

testing provides valuable information as to the performance

of the scrubbers and the results can lead to new insight on

the operation of the unit. One such insight that resulted from

this testing involved how free ammonia (NH3) can affect the

hydrogen chloride removal in the wet FGD.

The Monroe Power Plant is owned and operated by De-

troit Edison, a subsidiary of DTE Energy, and is located in

Monroe, Michigan. The plant has four (4) coal-red electric

generating units, referred to as Units 1, 2, 3 and 4. These

units were placed in service between 1971 and 1974, and

have a total electric generating capacity of 3,135 megawatts

(gross). Unit 3 is rated at approximately 785 net megawatts

(823 MW gross). Unit 4 is rated at approximately 775 net

megawatts (817 MW gross). Both units are B&W PGGsuper-critical boilers that typically burn coal at full load at

a rate of about 350 tons/hr. The typical coal blend for both

units is 65% low-sulfur western (LSW) / 35% mid-sulfur

eastern (MSE). Fuel oil is sometimes used to supplement

coal during start-up and upset situations.

Along with the B&W PGG wet FGD scrubbers, both units

are also equipped with an electrostatic precipitator (ESP)

that can achieve particulate removal efciency greater than

99%, a sulfur trioxide ue gas conditioning system that is

used to lower the resistivity of the y ash for better collection

by the ESP, and a vanadium-based SCR to reduce nitrogen

oxides (NOx) emissions.

2010 Field testing – Unit 3

In cooperation with Detroit Edison, B&W PGG initially

planned to test Unit 4 in October 2010, but an unscheduled

Unit 4 boiler outage lead to the test program being conducted

on Unit 3 instead. Though the SCR catalyst was known to be

nearing its end of life on Unit 3, it was decided to proceed

with the test program to investigate how multi-pollutants

may be affected by the catalyst.

As part of this testing, three (3) runs were performed

M.J. Mullen

DTE Energy

Detroit, Michigan, USA

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2 Babcock & Wilcox Power Generation Group

following EPA Method 26A, “Determination of Hydrogen

Halide and Halogen Emissions from Stationary Sources

Isokinetic Method,” to obtain the concentration of HCl in

the ue gas coming into and out of the wet FGD. The inlet

duct dimensions are 20 ft. x 45.5 ft. (H x W) with seven (7)

test ports spaced equally across the width. EPA Method 26A

was performed in the central ve (5) test ports. The ue in

the stack is 28 ft. in diameter with four (4) test ports spaced

90 degrees apart from each other. Testing was performedin all four (4) test ports. The results of the HCl testing are

shown in Table 1.

The results were unexpected. A high removal efciency

SO2 limestone wet FGD is expected to remove at least 99%

of the HCl entering the absorber or, at a minimum, to match

the equivalent SO2 removal in the absorber. The apparent

HCl removal was only 84%, while the SO2 removal during

the time of the test runs was measured to be an average of

~98.9% by the plant’s continuous emissions monitoring

system (CEMS). The apparent three (3) run average of the

measured HCl emission was calculated to be 0.0077 lb/

MMBtu. The HCl emission limit for Unit 3 is 0.0024 lb/

MMBtu, established by the most current State of Michigan

permit which covered the installation/operation of the FGD

system. The limit was established based upon "Best Avail-

able Control Technology." Since the EPA Method 26A test-

ing yielded apparent results that were three times the permit

limit, there was reason to believe that some form of inter -

ference with the test method was causing the high values.

After noticing that the HCl removal was unexpectedly

low, the other test data was analyzed. Three (3) runs of EPA

CTM-027, “Procedure for Collection and Analysis of Am-

monia in Stationary Sources,” were also performed around

the wet FGD. These test results, presented in Table 2, showed

abnormally high free ammonia loading to the scrubber.As shown in Table 2, Unit 3 was experiencing free am-

monia levels up to 23.5 ppmdv @ 3% O2, much higher than

the 2 ppmdv @ 3% O2 free ammonia typically expected

downstream of a properly functioning SCR catalyst. Some-

what higher ammonia levels were expected for Unit 3 due to

the age of its catalyst. However, this surprisingly high free

ammonia loading to the wet FGD was not only due to the

aging catalyst, but also because more ammonia than usual

was needed to obtain the required NOx control on account

of calibration issues with the outlet NOx meter. During the

week of testing, the SCR catalyst was also experiencing

high pressure drop.

Given these test results with high free NH3 content in

the ue gas stream, it is probable that ammonium chloride

formed. Ammonium chloride is a condensable particulate

before the air heater and forms a ne aerosol as the ue gas

gets quenched in the wet FGD. Fine particulate is not easilyremoved by a wet FGD. Flue gas sampling and emission

testing using EPA Method 26A may have erroneously cat-

egorized ammonium chloride as a free halide rather than a

particulate, which would skew the results of the test high.

In addition to the HCl and free NH3 tests, ve (5) test runs

were performed to capture condensable particulate at the wet

FGD inlet in accordance with EPA OTM-28, “Dry Impinger

Method for Determining Condensable Particulate Emissions

from Stationary Sources.” A combined sampling train of

EPA OTM-28 and EPA OTM-27, “Determination of PM10

and PM2.5 Emissions from Stationary Sources (Constant

Sampling Rate Procedure),” was used. After the collec-

tion period, the condensable particulate matter (CPM) wasanalyzed to determine the captured organic and inorganic

amounts. The inorganic catch at the inlet was also tested for

SO42-, NO2

-, NO3-, NH4

+ and Cl-. The results of the NO2- and

NO3- particulate analysis were below the detection limits.

The results of the remaining ions are shown in Table 3.

The data is fairly consistent throughout each testing day.

When comparing day-to-day results, note that the average

CPM ammonium ion concentration on 10/19 was 0.0424

lb/MMBtu, approximately six times greater than the 0.0068

lb/MMBtu average measured on 10/22. This tracked with a

review of the CEMS data, which recorded that the ammonia

ow to the SCR was higher on 10/19 compared to 10/22.

On 10/19, the average ammonia ow was 6.3 klb/hr compared to 4.5 klb/hr on 10/22. The constituent analyses of the

CPM indicate that the excess ammonia (converted to NH4+)

reacted with Cl- and SO42- to form ammonium chloride and

ammonium sulfate. When converting Table 3 to moles, the

balance works out well (Figure 1).

It is apparent that the ammonia slip on 10/19, triggered

by the higher ammonia ow to the SCR, resulted in the

abnormally high CPM readings.

After reviewing the data, and with the knowledge that

the SCR catalyst was being replaced in the spring of 2011,

Table 1HCl in the Flue Gas around the DTE Monroe Unit 3

Wet FGD in 2010

Run 1 2 3 Avg

2010 HCl at Inlet, ppmdv @3% O2

49.6 44.5 40.7 44.9

2010 HCl at Stack, ppmdv @3% O2

5.6 7.5 8.3 7.1

2010 HCl at Stack,lb/MMBtu

0.0060 0.0081 0.0090 0.0077

Table 2Free Ammonia in the Flue Gas around the

DTE Monroe Unit 3 Wet FGD in 2010

Run 1 2 3 Avg

2010 Free NH3 – WFGDInlet, ppmdv @3% O2

14.3 19.7 23.5 19.2

2010 Free NH3 – Stack,

ppmdv @3% O2 9.1 9.5 11.1 9.9Ammonia flow – North (A),

klb/hr 2.12 2.12 2.22 2.15

Ammonia flow – South (B),klb/hr

2.23 2.26 2.43 2.31

SCR NOx removal setting – North (A)

79.8% 79.8% 79.9% 79.8%

SCR NOx removal setting –South (B)

90.0% 90.0% 90.1% 90.0%

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Detroit Edison and B&W PGG agreed it would be benecial

to retest some key pollutants, including free NH3 and HCl.

The retesting would aim to better understand the effect that

the higher ammonia ow rates associated with the aging

catalyst likely had on emissions.

2011 Field testing – Unit 3

Once the catalyst had been replaced in the Unit 3 SCR,

testing was repeated in October and November of 2011.

Although an attempt was made to achieve the same condi-

tions as in 2010, there were a few minor differences. For the

new tests, Unit 3 was burning a 60% / 40% (LSW / MSE)

coal blend throughout the duration of the test, compared to

the 65/35 blend used in the 2010 test. Table 4 shows the dif -

ferences in the operating conditions between testing years.

Similar to 2010, three (3) test runs of EPA Method 26A

were performed, but this time the tests were only performed

at the stack. The results, along with the 2010 data, are pre-sented in Table 5.

The HCl measurements in the stack were substantially

lower than the previous year. In the 2010 testing, the inlet

HCl concentration was 44.9 ppmdv @ 3% O2 averaged over

three (3) test runs. Since the 2011 fuel chloride levels were

comparable, one can reasonably assume the 2011 inlet HCl

concentration was also comparable, which would indicate

that the wet FGD was removing >99% of the incoming HCl

as expected.

Similar differences in the outlet emissions from year to

year also occurred with the free ammonia (Table 6).

There was a signicant decrease of free ammonia in the

ue gas at the inlet of wet FGD from 2010 to 2011. With a

new SCR catalyst in place, NOx limits were met with tight

control of ammonia ow, resulting in very little ammonia

slip. The dramatic decrease in both free ammonia at the

wet FGD inlet and outlet and HCl at the outlet supports the

assertion that ammonium chloride caused the EPA Method26A results to skew the HCl measurements higher than what

was actually present.

2011 Field testing – Units 3 & 4 – FTIR

While retesting Unit 3 in 2011, Unit 4 was experienc-

ing aging catalyst issues – the same as Unit 3 in 2010. In

2011, DTE Energy also studied HCl emissions, but with

FTIR spectrometry on both units. This provided additional

information to validate the theory that ammonium chloride

forms in the presence of excess ammonia and can result

in false HCl readings. A portion of the testing using FTIR

spectrometry was performed on Unit 4, which at that time

was operating with an aging catalyst. The FTIR data on

NO, HCl and NH3 was collected using an MKS MultiGas

2030 FTIR spectrometer and adhered to EPA Method 320

and ASTM Method D6348-3 testing procedures.1 The goal

of this testing was to view the relationship between the

NH3 and HCl emissions since the FTIR could continuously

record measurements of each compound. The results are

shown in Figure 2.

The test started with the probe and lter being heated

to ~376F. After the probe was inserted into the stack, a

spike recovery was performed, which resulted in an 83%

recovery. The results of the spike recovery suggest that theHCl level was most likely near 1 ppm, which was the level

before the spike.1

After the spike recovery, the levels of HCl and NH3

steadily increased to abnormally high levels, similar to those

seen during the 2010 measurements on Unit 3 when that unit

still had the aging catalyst. Of even more interest though,

Figure 2 shows that when the probe/lter temperature was

reduced to 150F, the NH3 and HCl dropped to ~1 ppm or less,

Fig. 1 Molar comparison of condensable particulate at

Unit 3 wet FGD inlet.

Table 3Summary of Condensable Particulate Matter at Unit 3 Wet FGD Inlet

Date (2010) Oct 19 Oct 19 Oct 22 Oct 22 Oct 22

Test Run 1 2 3 4 5

CPM lb/MMBtu 0.1626 0.1634 0.0202 0.0386 0.0158

CPM – Inorganic NH4+ lb/MMBtu 0.0434 0.0413 0.0053 0.0106 0.0046

CPM – Inorganic SO42- lb/MMBtu 0.103 0.108 0.0027 0.0046 0.0035

CPM – Inorganic Cl- lb/MMBtu 0.0115 0.0083 0.0095 0.0190 0.0063

CPM – Inorganic Other lb/MMBtu 0.0035 0.0041 0.0016 0.0030 0.0004

CPM – Organics lb/MMBtu 0.0012 0.0017 0.0011 0.0014 0.0010

Ammonia Flow to SCR klb/hr 6.13 6.40 4.35 4.37 4.66

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concentrations that would be expected downstream of a wet

FGD. It appears that at the high temperature of 376F, am-

monium chloride disassociated in the probe, passed through

the lter, and was being measured as NH3 and HCl. When

the probe/lter temperature was decreased, the ammonium

chloride could not decompose, and it appears that the ne

NH4Cl aerosol was caught on the 0.01μ borosilicate glass

lter of the test apparatus. When the temperature was later

increased to 250F, the NH3 and HCl emissions started to

increase, indicating that ammonium chloride still disassoci-

ates at that temperature. This provides an explanation as to

why the EPA Method 26A test performed in 2010 indicated

high HCl emissions, since that test method operates at an

equivalent temperature. After the temperature increase, the

fact that both the HCl and NH3 trend lines increased at the

same rate suggests that the only source of these gases was

the NH4Cl decomposition.1

Additional FTIR testing was performed in December of

2011 on both Unit 3 (with a new SCR catalyst) and Unit 4

(with an aging SCR catalyst) to see the contrast. These tests

were conducted at both the wet FGD inlet and outlet loca-

tions, and incorporated changing the NOx setting controls

for the SCR to vary the amount of free ammonia at the wetFGD inlet. In addition to HCl and NH3, HF was also moni-

tored at all locations.

The Unit 3 testing on December 12, 2011 yielded results

that would be expected with a properly functioning SCR

catalyst and wet FGD – a high concentration of HCl and

very little NH3 at the wet FGD inlet and < 1 ppm of HCl

and NH3 at the wet FGD outlet (Figure 3).On December 13, the FTIR equipment was relocated to

Unit 4 which was still operating with an aging SCR catalyst.

The results were quite different from Unit 3 (Figure 4).

High concentrations of both HCl and NH3 were recorded

at the Unit 4 wet FGD inlet. Martin Spartz, Ph.D., of Prism

Analytical Technologies, Inc., noted that near 13:00, there

was a short HCl spike test performed into the exhaust and

the HCl did come up slightly while the NH3 was reduced.

This further suggests that NH4Cl was forming from the spike

since the HCl spike recovery was very poor and the NH3

Table 4Comparison of Full Load Operating Conditions

Year 2010 2011

Boiler Load, gross MW* 740 773

% S in coal** 0.97 0.98

% ash in coal** 8.9 8.6

Cl conc. in coal, ppm** 634 766

Hg conc. in coal, ppm** 0.094 0.066

*Taken from CEMS **Taken from coal analyses

Fig. 2 Wet FGD outlet readings of HCl, NH3 and NO for

Unit 4.1

Table 5Summary of HCl Around the Unit 3 Wet FGD

(2010 vs. 2011)

Run 1 2 3 Avg

2010 HCl at Inlet, ppmdv @3% O2

49.6 44.5 40.7 44.9

2010 HCl at Stack, ppmdv @3% O2 5.6 7.5 8.3 7.1


0.0060 0.0081 0.0090 0.0077

2011 HCl at Stack, ppmdv @3% O2

0.07 0.16 0.10 0.11


0.00008 0.00016 0.00011 0.00012

Table 6Summary of Free NH3 results across the Unit 3 Wet

FGD (2010 vs. 2011)

Run 1 2 3 Avg

2010 Free NH3 –WFGD Inlet, ppmdv

@3% O2

14.29 19.67 23.54 19.17

2010 Free NH3 – Stack, ppmdv @3% O2

9.10 9.54 11.10 9.92

2011 Free NH3 –WFGD Inlet, ppmdv

@3% O2

0.08 0.05 <0.04* <0.05

2011 Free NH3 – Stack, ppmdv @3% O2 0.11 0.10 0.06 0.09

2011 Ammonia flow – North (A), klb/hr

2.43 1.85 1.32

2011 Ammonia flow –South (B), klb/hr

2.28 1.62 1.10

2011 SCR NOx remov-al setting – North (A)

89.5% 69.9% 49.8%

2011 SCR NOx remov-al setting – South (B)

90.0% 70.1% 50.7%

* Below detection limit.

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level dropped.2 The corresponding data at the wet FGD outlet

showed high concentrations of HCl and NH3.

Also, the fate of HF should be noted from Figure 4. HF

and HCl are similar acid gases and both are expected to

be almost completely removed by the wet FGD and trend

at similarly low concentrations at the wet FGD outlet, as

evidenced by the Unit 3 results. Since HF remained unaf -

fected by the presence of NH3 at the wet FGD inlet and was

virtually completely removed by the wet FGD, this furthersuggests that NH4Cl formation had occurred.

To test at different levels of NH3 at the wet FGD inlet,

the NOx control set points for both the North and South

ues were reduced by 5% each. The results can be seen in

Figure 5.

Once the NOx control set points were reduced, it took

about an hour for the NH3 levels at the wet FGD inlet to

approximate steady state conditions. The HCl remained

unchanged, which suggests that the NH4Cl ne aerosol is

formed in the wet FGD. At the wet FGD outlet, as the am-

monia concentration decreased, the outlet HCl concentration

also decreased at the same rate.

Figure 5 also shows that while there was much more HCl

than NH3 at the wet FGD inlet, the NH3 emissions werealways slightly higher than HCl at the wet FGD outlet. This

provides further evidence of NH4Cl formation, suggesting

that NH3 is the limiting reagent in the formation of NH4Cl.2

Fig. 3 Wet FGD inlet and outlet readings of HCl, NH3 and HF for Unit 3.2

Fig. 4 Wet FGD inlet and outlet readings of HCl, NH3 and HF for Unit 4.2

Fig. 5 Wet FGD inlet and outlet readings of HCl, NH3 and HF for Unit 4 after a reduction in the

NOx control setting of the SCR.2

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Copyright© 2012 by Babcock & Wilcox Power Generaon Group, Inc.

a Babcock & Wilcox company

All rights reserved.

No part of this work may be published, translated or reproduced in any form or by any means, or incorporated

into any informaon retrieval system, without the wrien permission of the copyright holder. Permission re -

quests should be addressed to: Markeng Communicaons, Babcock & Wilcox Power Generaon Group, Inc.,

P.O. Box 351, Barberton, Ohio, U.S.A. 44203-0351. Or, contact us from our website at www.babcock.com.

Disclaimer

Although the informaon presented in this work is believed to be reliable, this work is published with the

understanding that Babcock & Wilcox Power Generaon Group, Inc. (B&W PGG) and the authors are supplying

general informaon and are not aempng to render or provide engineering or professional services. Neither

B&W PGG nor any of its employees make any warranty, guarantee, or representaon, whether expressed or

implied, with respect to the accuracy, completeness or usefulness of any informaon, product, process or ap-

paratus discussed in this work; and neither B&W PGG nor any of its employees shall be liable for any losses or

damages with respect to or resulng from the use of, or the inability to use, any informaon, product, process

or apparatus discussed in this work.

Summary

High ammonia levels at the wet FGD inlet can cause the

formation of NH4Cl, a ne particulate that can be detected by

EPA Method 26A and incorrectly reported as HCl. With the

new MATS regulations effective in 2015, it will be critical to

ensure that test methods accurately measure HCl emissions

in reporting to these new limits. FTIR spectrometry can be

used to track NH3 and HCl and, when performed using dif -ferent probe temperatures, to determine if NH3 is causing

the HCl emissions to read high.

Acknowledgements

The authors acknowledge and appreciate the efforts of

the Clean Air Engineering and Prism Analytical Technolo-

gies, Inc. testing crews for their valuable contribution to the

gathering of data for this project.

References

1. Spartz, M.L. Ph.D.; Kauppi, P.J.; Prism Analytical

Technologies, Inc. Detroit Edison Company Engineer -

ing HCl Emission & SCR Study, Monroe, MI – Unit 4,

October 26 – 28, 2011, Project No. 1709

2. Spartz, M.L. Ph.D.; Kauppi, P.J.; Prism Analytical

Technologies, Inc. Detroit Edison Company Engineer -

ing HCl Emission & SCR Study, Monroe, MI – Units 3& 4, December 12 – 14, 2011, Project No. 1715

Key words

Wet FGD, HCl, NH3, NH4Cl, FTIR, ammonium chloride

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