Optimization of Constellation Energy's SNCR System at Crane Units 1 and 2 

Using Continuous Ammonia Measurement 

By 

James E. Staudt, Ph.D., 1 Brian Hoover,2 Paul Trautner,2 Stephen McCool,3 and John Frey, PE 3 

1 Andover Technology Partners, 112 Tucker Farm Road, North Andover, MA 01845 

2 Constellation Energy CP Crane Station, 1001 Carroll Island Road, Baltimore, MD 21220 

3 Tourgee & Associates, Inc., 11155 Dolfield Boulevard, Suite 210, Owings Mills, MD 21117 

ABSTRACT 

In response to Maryland's Healthy Air Act, Constellation Energy installed SNCR 

systems at the CP Crane Station, units 1 and 2. 

These SNCR systems use continuous ammonia slip analyzers that work on the principle 

of tunable diode laser (TDL) spectroscopy and provide continuous, real-time indication of 

ammonia slip in the duct. The TDL analyzers utilized a PAT.- PEND. mounting system to allow 

reliable, real-time indication of ammonia slip, even under changing loads and conditions. These 

analyzers facilitated optimization of the SNCR system to avoid high ammonia slip transients that 

are the principal contributors to downstream problems normally associated with ammonia slip. 

The optimization program produced substantial reductions in ammonia slip and significantly 

lower ammonia in fly ash while controlling NOx to targeted levels. 

This paper will review the results of the optimization program and the long-term 

experience with the SNCR system and the ammonia instruments. It will demonstrate the 

performance benefits in terms of ammonia slip, reagent consumption and fly ash ammonia that is 

possible though optimization ofSNCR operation using the information from continuous and 

real-time monitoring of ammonia slip. 

Presented at the A WMA, EPA, EPRI, DOE Combined Power Plant Air Pollution Control 

"Mega" Symposium, August 30-September 2, 2010, Baltimore, MD 

Questions regarding this paper can be sent to James Staudt at: 

staudt@AndoverT echnology.com 

Andover Technology Partners www.AndoverT echnology.com Page 1 
Project Background and Technical Description 

Constellation Energy's Baltimore plants are subject to a system-wide cap on NOx, S02 

and mercury emissions as a result of Maryland 's Healthy Air Act. To address NOx emission 

needs Constellation selected Selective Non Catalytic Reduction (SNCR) for application at C. P. 

Crane units 1 and 2 and Wagner 2. This paper will focus on the CP Crane SNCR systems, 

which were particularly difficult applications. 

C. P. Crane station has two cyclone boilers, units 1 &2, rated at 200 MWg and 205 MWg, 

respectively. Each unit has four cyclones - two on the front wall and two on the rear wall. At 

the time of the SNCR system start up the boilers were firing a blend of eastern bituminous coal 

with PRB at a blending ratio of roughly 75%/25% Bailey/PRB by weight. Table 1 summarizes 

key characteristics of the CP Crane units. 

Table 1. CP Crane Units 1 & 2 Description 

Unit 1 Unit 2 

Rated Capacity MW g 200 205 

Boiler Type Cyclone Cyclone 

2 front wall 2 front wall 

2 rear wall 2 rear wall 

OFA yes yes 

Internal Wing Walls No Yes 

Coal Blend (approx. by wt.) 75% Bailey 75% Bailey 

25%PRB 25% PRB 

Combustion Optimizer Emerson IVY Emerson IVY 

Baseline NOx (approx) 0.45 lb/MMBtu 0.45 lb/MMBtu 

Air Preheater Tubular Tubular 

PM Control Fabric Filter Fabric Filter 

Project Team 

Constellation assembled a project team to evaluate technologies and execute the program. 

The project team members included the following organizations and their responsibilities. 

The SNCR Project Team included the following organizations 

1. Constellation Energy- Overall Capital Project Management 

2. CP. Crane Station- Plant support, controls and instrumentation integration 

3. Andover Technology Partners- Constellation's technology and startup/optimization 

consultant 

4. Tourgee & Associates, Inc- Engineering and Construction Management at CP Crane 

Andover Technology Partners www.AndoverT echnology.com Page 2 
SNCR system selection 

Constellation evaluated offerings from different technology suppliers. High Energy 

Reagent Technology (HERT) technology from Advanced Combustion Technology, now part of 

Fuel Tech, [nc., was selected to supply SNCR for both Crane units. The reagent, urea, is stored 

on site in a 50% by weight aqueous solution. Before being injected into the furnace it is diluted 

to about 5% by weight. The dilution rate is largely determined by the necessary 

flowrate/pressure to achieve good atomization for the injectors. 

The HERT systems are similar for both units, and include four zones of injection, 

numbered 500, 600, 700, and 800 - from uppermost to lowermost injection zones, as shown in 

Figure I. 

• The lowermost injectors (zone 800) inject urea into the boiler at the 65 foot elevation 

above the cyclones but below the OF A for Rich Reagent lnjection. These ports were 

formerly used for gas injection when gas reburn was employed. 

• The next zone (700) injects urea through the OF A ports at the 9I foot elevation. 

• The 600 zone injects reagent into the upper furnace at the I 02 foot elevation, 

• And the 500 zone injects reagent slightly above the nose arch at the I20 foot elevation. 

The HERT system is different from other SNCR systems in that, rather than air-atomized 

nozzles, for each injector it uses a pressure-atomized nozzle within a larger tube (about 2 inches) 

which is supplied with blower air that provides the motive air to inject the atomized urea into the 

furnace. For zone 700 the OF A provides the motive air. Zones 500 and 600 are fed from a 

common dilution water header and chemical injection pump. Flow distribution between levels is 

controlled by on/off motor operated valves and by selection of atomizing nozzles. Zones 700 

and 800 are fed from a common dilution water header and chemical injection pump. Flow 

distribution between levels is controlled by on/off motor operated valves and by selection of the 

pressure atomizing nozzles. Nozzles were installed during acceptance testing and were adjusted 

during optimization. 

Control of the SNCR systems is directly from the DCS. The plant controls group 

performed all controls programming based upon input from the technology supplier, ACT. 

Ammonia Monitoring 

A major concern for the plant was ammonia slip and its impact on fly ash. With tubular 

air-preheaters, air-preheater plugging is less of a concern at Crane than if the air-preheaters were 

of a rotary design. However, Constellation wanted to assure that fly ash ammonia levels 

remained low. Because ofthis concern Constellation considered the installation of ammonia slip 

analyzers. 

Andover Technology Partners www.AndoverT echnology.com Page 3 
The project team examined several approaches for monitoring ammonia slip and 

determined that tunable diode laser absorption spectroscopy (TDLAS) technology offered the 

greatest chance of success; however, the situation at Crane offered several challenges to using 

the TDLAS approach. TDLAS ammonia instruments measure the number of ammonia 

Figure 1. Crane 1 and 2 HERT SNCR Injector Locations 

Zone 600 

H[ RT INJ I 

H( RT 111/J ~ GA REB Rill P RTS RCBURI\ P TS EL ·- 2· 

Zone 800 

molecules across an optical path using the principle of the Beer-Lambert law as in Figure 2. A 

solid-state laser light source scans across near infra-red absorption wavelengths that are selected 

based upon the target gas that is being measured (in this case, ammonia). The difference in light 

absorbed off-wavelength versus on-wavelength is proportional to the targeted gas present. In 

this manner TDLAS provides an indication of the average concentration along the line of sight. 

It is suitable for remote sensing, for in-situ, real-time measurements, and can be used in high 

Andover Technology Partners www.AndoverT echnology.com Page 4 
temperature environments. It does not require sample transport to an analyzer, which avoids 

concern regarding preservation of sample integrity. ln large ducts this approach gives a good 

indication of the average concentration across the duct. 

Figure 2. Cross Duct TDLAS measurement with spacers to limit path length 

Gas flow 

Transmitter D 

Receiver 

Experience with the TDLAS method on coal power plants has had mixed success- and 

unfortunately, far more failures than successes. As an optical method, the TDL approach is 

extremely sensitive to instrument alignment and particle dust loading. Flue gas ducts flex as load 

and gas temperature change, which affects alignment with the instrument mounted on the duct. 

And, for a dust-laden stream such as a coal plant, there is a challenge to achieving adequate 

sensitivity (which is related to optical path length) and maintaining an adequately strong signal. 

Suppliers ofTDLAS instruments have developed means to address the problem of misalignment 

- at least to a degree- by having beams that expand (think of a shotgun rather than a rifle). But, 

this weakens the optical beam density and for dust-laden gases optical signal can get too weak to 

maintain adequate signal-to-noise ratio. There are systems under development to actively align 

the instruments. But, at the time Constellation was making a decision, we were not yet confident 

that this approach would be ready in the time we needed. Some suppliers offer instruments with 

probes - which solves the problem of misalignment and the effect of dust. But, because 

ammonia slip can be quite stratified, having a representative ammonia slip measurement on large 

ducts is not practical with current probe-based TDLAS systems. 

The problem with dust loading can be mitigated with spacers that shorten the path length. 

But, this will impact the minimum detectible limit and will mean that parts of the duct will not be 

measured for ammonia. 

For both Crane units the available duct locations between the economizer and the air 

preheater offered path lengths of close to 20 feet - or about 6 meters. The duct also has turns 

upstream and downstream - which further limits access and impacts flow within the duct. 

Moreover, the Crane units cycle in load, which means that the duct will flex as temperature 

Andover Technology Partners www.AndoverT echnology.com Page 5 
changes over the changing load. Substantial flexing was measured, and this flexing would make 

alignment of cross-duct TDLAS optical paths impossible across the load range if the optics were 

mounted to the duct walls. Fortunately, the dust loading at Crane, with roughly a 60/40 split 

between fly ash and bottom ash, 

1 is not quite as high as it would be for a pulverized coal unit, but 

is not as low as might normally be expected for a cyclone boiler. 

The ducts have upstream and downstream obstructions and turns as shown on Figures 3a 

and 4 a. Flow testing was performed in the portion of the duct where there was access to mount 

instruments to determine the best location for the optical paths. Four test ports were installed on 

each duct, and these ports were intended to ultimately serve as potential locations for transmitters 

or receivers, with the testing serving to help select the best locations for the transmitters or 

receivers. As expected, the gas flow was determined to be highly stratified - with regions of 

very high velocity and regions of very low velocity- particularly on Unit 2. Figures 3 b and 4b 

show the gas velocity stratification. Temperature and species measurements also showed 

significant stratification. The optical path (two paths per duct, one duct per unit, and four optical 

paths altogether for both Crane units) locations were selected to cover the regions of highest gas 

flowrate in the respective duct - at least within the limitations of where access was available to 

mount the instruments. 

To address the problem ofTDLAS alignment across these large ducts, an instrument 

mounting assembly (PAT.PEND.) was designed to independently mount the instruments from 

the duct. The instrument mounting assemblies were mounted to the platforms that provided 

maintenance access for the instruments. 

The instrument mounting assemblies provide independent mounting ofthe instrument, a 

flexible spool coupling the instrument optics with the boiler duct, and design features that allow 

for hot or cold installation, adjustment and air purging of the flexible spool coupling. It also has 

the ability to reduce the optical path using inserts in situations where the dust loading is too high 

for the beam to cross the full duct width while also addressing the thermal lensing that is 

problematic for positive pressure ducts. The instrument mounting assembly can be used on 

either positive or negative pressure ducts. By assuring alignment with the instrument mounting 

assembly, the beam diameter can be reduced, which increases TDLAS beam intensity and 

improves the signal to noise ratio ofthe instrument. 

The project team selected the Unisearch TDLAS instrument from CEMTEK for 

application at Crane (and also at Wagner). This instrument has a controller that houses the laser, 

laser controls, an optical multiplexer, and signal processing electronics. Each optical path is 

comprised of an optical transmitter and optical receiver. Optical fiber transmits the light output 

1 Based on 2005 EIA Form 767 data 

Andover Technology Partners www.AndoverT echnology.com Page 6 
UP 

Figure 3a. Duct Configuration and Port Location for Unit I. 

1.00 

0.90 

0.80 

0.70 

0.60 

0.50 

0.40 

0.30 

0.20 

0.10 

0.00 

Figure 3b. Gas Velocity Distribution for Unit 1 

Crane 1 Velocity 

(aspect A) 

• o.oo-o.1o• o.1o-o.2o • o.2o-o.3o • o.3o-o.4o • o.4o-o.so 

2 

PoJt4 

Andover Technology Partners www.AndoverT echnology.com Page 7 
Figure 4a. Duct Configuration and Port Location for Unit 2 

Figure 4b. Gas Velocity Distribution for Unit 2 

Crane 2, Test 1 High Load Velocity 

. 0.00-0.50 . 0.50-1.00 . 1.00-1.50 . 1.50-2.00 . 2.00-2.50 

Andover Technology Partners www.AndoverT echnology.com Page 8 
from the laser to the optical transmitter. Coaxial cable transmits the signal from optical receiver 

to the controller. Each Crane unit has a controller and two optical paths. The optical multiplexer 

in the controller alternates the output from the laser between the two optical paths. The 

advantage of this instrument at Crane versus some of the other TDLAS instruments that were 

evaluated is that it permits installation of electronics in a controlled environment and installation 

of the optics, which are less sensitive to temperature, on the duct. It also reduces the size ofthe 

hardware that is mounted on the duct compared to other TDLAS products that have the laser and 

electronics mounted on the duct, which is an advantage when space is limited. 

Crane 1 & 2 SNCR System Acceptance Testing 

The performance guarantees required that the SNCR system meet an average emission 

reduction of 50% at two load points of 67% MCR and 100% MCR with ammonia slip at or 

below 5 ppm and average urea flowrate of 190 gph. According to the contract with ACT the 

ammonia slip was to be measured using extractive FTIR because that was the method that ACT 

was familiar with from previous experience. The TDLAS analyzers were operating during 

acceptance testing; however, they were not used for determining compliance with the SNCR 

contract guarantees. 

The acceptance test results are summarized in Table 2. The baseline NOx levels were 

lower than expected. Nevertheless, with both units averaged, the SNCR system met its NOx 

reduction and ammonia slip guarantee requirements. Slip by FTIR was below the limit of 5 ppm, 

although the TDLAS instruments indicated higher slip. Notably, during acceptance testing zone 

700, which injects through the OF A ports, was found to be ineffective. So, these results were 

achieved without Zone 700 in operation. Also, during acceptance testing the IVY combustion 

optimizer was taken out of service in order to assure that combustion conditions did not change 

during a test. 

Comparison of FTIR and TDLAS ammonia results 

The TDLAS instruments and the FTIR instrument showed significant differences in the 

slip being measured, with the TDLAS instrument often being higher than the reported FTIR 

measurement. This was particularly so when the TDLAS instrument ammonia concentration 

was high. But, the FTIR raw data did also show some very high spikes. 

The FTIR instrument was used to measure ammonia at multiple discrete points in the 

duct. These locations were adjacent to, but not exactly where the TDLAS instruments were 

located. The sample is extracted through a heated probe. It then passes though a trap to remove 

particle matter, through a heated sample line up to about 200 feet long and into the trailer where 

the FTIR analyzer is located as indicated in Figure 5. 

Andover Technology Partners www.AndoverT echnology.com Page 9 
Table 2. SUMMARY OF C. P. CRANE SNCR ACCEPTANCE TESTING 

Unit 1 Low Unit 1 High Unit 2 Low Unit 2 High 

Load Load Load Load 

12/16/2008 12/16/2008 12/17/2008 12/17/2008 

Injection Test Time 17:10-18:10 09:15-10:15 20:30-21 :30 16:45-17:45 

Baseline NOx (before), 

lb/mmBTU 0.3394 0.4112 0.3160 0.3708 

Urea Injection NOx, lb/mmBTU 0.1 554 0.2342 0.1289 0.2133 

Baseline NOx (after), lb/mmBTU 0.3376 0.4164 0.3213 0.4031 

Average Baseline NOx, 

lb/mmBTU 0.3385 0.4138 0.3186 0.3869 

NOx Reduction 54.1% 43.4% 59.5% 44.9% 

Average Reduction (both Units) 50.5% 

Average Urea Consumption 192 gph 

Ammonia Slip During Injection (ppm) 

FTIR (average) 0.50 2.79 3.69 0.30 

TDLAS Slip Meter Channel 1 6.03 18.48 19.93 10.26 

TDLAS Slip Meter Channel 2 6.35 0.45 17.42 6.05 

OFA(%) 24.9 25.0 21 .0 26.9 

IVY Optimizer Status OFF OFF OFF OFF 

Load (MW) 135 200 135 201 

The TDLAS instrument, on the other hand, provides the average ammonia along a line of 

sight across the duct. The ammonia measurement is made in-situ, which means that a gas 

sample does not need to be drawn from the duct and transported to an analyzer. 

Because of the differences in measurement method and somewhat different locations, the 

same results should not be expected from both methods. However, ideally there would have been 

better correspondence between the results of the two methods. Figures 6 and 7 show ammonia 

slip from the TDLAS instruments (taken from the plant PI system), from FTIR raw data for 

ammonia slip (provided by the testing company) and urea injection rate (in gph/10) for 

December 16 for Unit 1 and December 17 for Unit 2 plotted versus time. The two acceptance 

test periods are highlighted in yellow. It is uncertain how well synchronized the time of the test 

company raw data is with the reported time in the PI data. But, it is reasonable to expect that 

there should not be more than a few minutes difference. The actual reported FTIR values for 

the purpose of the acceptance test are discrete points that fall along the FTIR line 5 minutes after 

the probe is moved to the sample point (it is not possible tell from this data when the probe is 

moved, except possibly each "jump" is a different point). The most remarkable characteristics of 

these plots are: 

• The FTIR shows spikes above 10 ppm and even up to 60 ppm although all of the reported 

results were well below those values. 

Andover Technology Partners www.AndoverT echnology.com Page 10 
• There are occasional times when slip is high by both methods even when no urea is being 

injected. 

• In most situations, the TDLAS instruments seem to respond to urea injection more 

consistently (this might be due to the fact that every 10 minutes or so the FTIR probe is 

moved to a different location) 

Most concerning is the first bullet point- particularly the very high spikes to 60 ppm. It 

does not seem likely that ammonia slip in the duct is peaking quickly to values like 60 ppm and 

then dissipating since it would likely be picked up on the TDLAS instruments. Another 

explanation is that perhaps ammonia may be collecting in the FTIR probe or sample line only to 

be released suddenly, perhaps when the probe is moved or after enough ammonia has built up. 

When the test company was asked about this while on site, they did not have an explanation 

except that when the FTIR does see the ammonia spikes, there is definitely ammonia present. 

The second bullet point suggests that perhaps during SNCR purge cycles or other 

conditions, urea was being admitted to the furnace although the urea pumps were not running. 

And, the third bullet indicates that the TDLAS instruments are responding to ammonia as 

expected. 

In any event, for the purpose of the performance guarantees of the SNCR contract, FTIR 

is the ammonia measurement that was used. However, the results observed here raise questions 

about the FTIR method and reliability of the data when using FTIR. 

Figure 5. Comparison ofTDL versus Extractive FTIR 

as now 

..... 8 ..... ~ .... 

I 

Andover Technology Partners www.AndoverT echnology.com 

100-200 feet 

~' ·· · 

,.·""' 

Page 11 
S'" 

a.. 

.., 

0 

:::J 

0 

c2 '< 

CP 

3" 

CD 

iiJ 

I 

)> 

:::J 

a.. 

CD 

0 

:::J 

0 

0 

co 

'< 

8 

3 

CP 

co 

CD 

_. 

l'o.) 

Time 

12/17/ 08 7:25AM 

12/17/08 7:55AM 

12/17/ 08 8:25AM 

12/17 / OS 8:55 Af'.'l 

12/17/ 08 9:25 Al'il 

12/17/ 08 9:55 Af'll 

12/17/ 08 10:25 AM 

12/17/ 08 10:55 AM 12/17/ 08 11:25 AM 12/17/081155 AM 

12/17/ 08 12:25 PM 

12/17/ 08 12:55 PM 

12/17 / OS 1:25 PM 12/17/ 08 1 55 PM 

12/17/ 082:25 PM 

12/17 JOB 2:55PM 

12.111 ;os 3:25 PM 

12/17 / OS 3:55 Pl'.'l 

12/17 JOB 4:25 PM 

12/17 / OS 4:55 PM 12/17/ 08 5:25 PM 12/17/ 08 555 PM 12/17/ 08 6:25PM 

12/17/ 08 6:55 PM 

12/17/ 08 7:25 PM 12/ 17./08 7:55PM 

12/ 17/ 088:25 PM 

12/ 17/ 08 855 PM 

12/ 17/ 089:25 PM 12/17/ 08 955 Plvl 

Ammonia slip, ppm 

urea, gph_llO N Uol '-" 0 0 0 0 0 0 

I 

I 

::l 

::;!:! 

-

I .!L J 

c: 

.... 

('D 

Qi 

(IQ 

"C 

-

........ 

=-

0 

, -- - --- r--

> (; 

_ _j_-J I 

_

I (/) 

..... 

) "C 

('D 

.... 

o· 

Q. 

(/) 

- - 1--

1---'H -:-:7::: 

--

I 

-

-

I 

-

0'\ -..J 

0 0 

I "%j 

(jQ' 

I = "'' ('D ;--1 9 (') Qi 

.... 2 Pl ::l 

(1) 

c::: 

::l 

;::,: 

N 

;l> 

3 

I 

3 

0 

::l 

9 p;· C/1 Qi 

::l ::l "0 

('D Pl - ::l 

N a. 

c:: 

.... 

(1) 

Pl 

::!l 

0 

0 

(1) 

(") 

(1) 

3 

cr" 

(1) 

.... 

-

N 

0 0 

00 

Ammonia slip, ppm 

urea, gph/10 

N (J.I '-" 

I 0 0 0 0 0 

Time 

1) 

12/16/ 08 S:14

AM 

12/16/08S:44 AM F:-- 

12/16/089:14 AM 

- - --

.. 

12/16/08 9:44

AM ?- 

. 

12/16/08 10:14 

AM 

-- 

------

--

-\ 

12/16/ 08 10:44 AM 

I 

12/16/08 11:14 .AM 

12/16/ 08 11:44 Af•,•l L ::l 

12/16/08 12:14 Pf';l :;!:) 12/16/08 12:44 PM 

12/16/08 1:14 Pf':l ..... ('D 

(/) 

12/16/08 1:44 PM ..... 

.,.. _ _.,;;;;;;_ "0 

It> 

12/16/08 2:14 f'l\•1 ::::!. I 

0 

12/16/08 2:44 PM ,.... Vi 

c: 

12/16/0S 3:14 PM ..... 

;

-

It> 

- Qi 

12/16/08 3:44 PM - 

(IQ 

12/16/08 d4 PM ? i <.. 

12/16/08 4:44 PM 0 

'-- 

12/16/08 5:14PM -..;. -- - :r __ 

K 

12/16/08 5:44PM 12/16/08 6:14PM -- 

- -----

12/16/08 6:44PM 
SNCR Optimization 

Optimization of the Crane SNCR systems was necessary because concern about fly ash 

ammonia content makes it necessary for the SNCR system to be operated at more stringent 

conditions with respect to ammonia slip than allowed by the performance guarantees. 

The objective ofthe optimization was to establish parameters and setpoints to minimize 

NOx emissions across all operating conditions (ideally at or below 0.27 lb!MMBtu) while 

maintaining NH3 slip at or below 2 ppm. Optimization was intended to: 

I. Explore the operating range of the SNCR system at expected operating conditions that 

may be outside the range of the guaranteed load conditions and establish setpoints for 

operation under such conditions that minimize NOx emissions while also maintaining 

slip below 2 ppm. 

2. Evaluate the performance of the system during expected operating transients and 

establish operating setpoints that minimize NOx emissions during transients while also 

maintaining slip below 2 ppm 

3. Identify adverse secondary effects ofthe SNCR system and develop means to mitigate 

these effects. 

Although the goal from the outset was to keep slip below 2 ppm, the decision was made 

to work toward keeping slip below 1 ppm but recognizing that 2 ppm might be necessary at some 

loads. This shift toward lower slips was made because: 

• It was determined during optimization that it was possible to achieve the emissions rate 

of0.27lbiMMBtu or less while keeping slip below 1 ppm for most loads on both units. 

High loads are more difficult. 

• It became apparent that there would be periodic transients in slip that might increase slip. 

So, keeping slip a little bit lower to begin with would be beneficial in reducing those slip 

excursions and the average slip over a day. 

• Most utility SNCR systems are on boilers with ESPs, and there is much less experience 

with baghouses. Because unit 2 had experienced some difficulty maintaining pressure 

drop adequately low near full load, care was necessary to ensure that the SNCR did not 

contribute to increased baghouse pressure drop. 

The low ammonia slip requirements are primarily intended to minimize ammonia in the 

fly ash. Although there are other benefits to reducing ammonia slip, ammonia in the fly ash is 

the most limiting factor. At Crane, there are two factors that make ammonia concentration on fly 

ash higher than for other units, and therefore ammonia slip of increased concern. 

• As cyclone units, less of the ash is in the form of fly ash than for a dry-bottom boiler, 

which will concentrate the ammonia over less fly ash, raising the concentration on the fly 

ash over what would be expected for a dry bottom boiler. 

Andover Technology Partners www.AndoverT echnology.com Page 13 
• Having a tubular air preheater (APH), accumulation of ammonium bisulfate (ABS) in the 

APH is less of an issue than for a regenerative air preheater. While this means that APH 

plugging is less of a concern, this means the bisulfate is more likely to end up being 

collected downstream on the fly ash in the baghouse. 

The SNCR system optimization was performed with plant personnel and supported with 

ATP on site during the weeks of January 5 through January 16, 2009. 

In the following sections, we will discuss: 

• Cyclone trips and load regulation 

• Pre- and post- optimization comparisons 

• Optimization at Full Load 

Cyclone trips and load regulation 

There are two transients of particular interest that were evaluated during the two weeks of 

testing. These are: SNCR operation during a cyclone trip; and regulation of loads. 

Cyclone Trip 

Because there is a risk of high ammonia slip during such a transient as the furnace cools 

from the reducing load and because the operator will be very busy working to stabilize the unit to 

a safe condition, it was decided that the SNCR system should trip off line in the event of a lost 

cyclone. Once the operator has determined that the unit is stable, then the operator can bring the 

SNCR system back on the line. A trip of the SNCR system on loss of a cyclone was 

programmed into the SNCR system. Unplanned cyclone trips showed that the programmed trips 

worked as intended. It is possible to restart the SNCR system with only 3 cyclones in operation. 

However, the intent is for the operator to do this when he has determined that the unit is stable. 

Load Regulation 

The two Crane units typically regulate load to meet the demand. Therefore, performance 

during load regulation was evaluated. Temporary peaks in ammonia slip were observed during 

• Reductions in load 

• Use of some soot blowers (in some cases coinciding with increases in opacity) 

• Increases in urea injection 

Figures 8 and 9 are plots ofMWg, NOx, total urea flow, ammonia slip and opacity for 

Unit 1 and Unit 2, respectively on January 7, at a very early period in the optimization program. 

Peaks in slip associated with load reductions highlighted in blue, peaks that occur with increases 

in opacity highlighted in pink and increases in slip that occur with increases in urea injection are 

highlighted in yellow. There are large increases in opacity that do not correspond to increases in 

Andover Technology Partners www.AndoverT echnology.com Page 14 
slip. These opacity increases are most likely associated with baghouse cleaning transients, which 

would not be expected to impact ammonia slip. 

An objective of optimization was to address these brief high slip conditions that might, 

over time, result in excessive ammonia in the fly ash. 

Examining the behavior during a period after optimization on a day with high variation in 

load showed that these transients had, for the most part, been addressed. As shown in Figures 

10 and 11 , on January 22, 2009, which was a day with frequent load changes, the SNCR system 

maintained NOx generally at or below 0.25 lb/MMBtu (except when urea was shut oft) for both 

units 1 and 2 while maintaining ammonia slip at a low level. For both units there were brief 

periods where slip reached about 2 ppm but then dropped off. These were both periods where 

urea injection was increasing- either due to increasing load or due to the SNCR system being 

placed back in service after a period of being secured. The results in these figures indicate that 

the SNCR systems are capable of tracking load while keeping NOx controlled to 0.25 lb/MMBtu 

with ammonia slip at acceptably low levels while also changing loads. There may be room to 

improve the ammonia slip some more to eliminate these brief spikes altogether. But, overall, the 

spikes in ammonia slip were substantially reduced. 

Andover Technology Partners www.AndoverT echnology.com Page 15 
Figure 8. Unit I SNCR Operation 7 January, 2009 

200 

180 

160 

140 

120 

100 

80 

60 

40 

20 

:5 0 0 0 0 

~ ~ ;,; 

~ 

"' 0 .... 

"' "' "' ~ 0 0 

~ i 

~ ;:. ;:. 0 0 

Figure 9. Unit 2 SNCR Operation 7 January, 2009 

220 

200 

180 

160 

140 

120 

100 

80 

60 

40 t ... 

20 

0 

0 0 0 g 0 0 

<> 0 0 <> 

~ 

~ 

~ ~ ;,; 

~ ~ :i: .;; 

0 ~ ~ ~ ~ 

"' "' "' "' "' "' ~ ; ; ; ~ ; ~ ~ ~ ;:. ;:. 0 0 ~ 

Andover Technology Partners www.AndoverT echnology.com 

- M W 

- NH3 ' 10 

Total Urea 

- Nox• 1oo 

Opac y ' 10 

Peaks in Ammonia Slip associated 

with 

- M W 

- NH3 ' 10 

Total Urea 

- Opacfty • 1o 

• Load reduction 

highlighted in 

• Increasing urea 

highlighted in yellow 

• Opacity peaks 

highlighted in 

Peaks in Ammonia Slip 

associated with 

• Load reduction 

highlighted in 

• Increasing urea 

highlighted in 

yellow 

• Opacity peaks 

highlighted in 

Page 16 
Figure 10. Unit 1 SNCR operation on January 22, 2009 

400 

350 - MW 

300 - - Avg NH3 x 10 

250 - NOx 1000 

200 

Total Urea 

150 

\. 100 r--

50 

I .. . A.. I' .tw~ ~ ,.... ..... ~ 

0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cl 0 Cl 0 Cl 0 0 0 

0 ~ co "' oD 0 ~ «; ;,; ~ 0 0 ... ~ .... '" 0 ... ~ .... 0 

0 ;,; g ;..:. ;,; ;,; ~ .0 ;,. .... 0 0 Cl 0 0 .... .... .... .... "' 0 .,. .,. .,. .,. .,. .,. .,. "' .,. Cl 0 0 0 0 0 0 0 0 "' 0 "' 0 

~ ),. 

~ ~ ~ ~ ~ )-

~ )-

ill ill ill ~ 7 7 ~ ~ 7 7 7 7 7 J: "' "' "' "' "' ... "" ... ... "' .... ... "' ... "' .... "" "' "" 

Figure 11. Unit 2 SNCR operation on January 22, 2009 

400 

350 

300 

250 

200 Total Urea 

150 

100 

50 

0 0 0 Cl 0 0 0 0 0 Cl Cl Cl 0 0 0 0 0 0 0 0 

0 ;,; «; ;,; ~ 0 0 "' "' .... 0 

«; "' .0 0 <t .... '" 0 

0 t. i ;..:. a: ;,; Cl 0 0 0 .... .:.; a; ;; 0 ... .... "' 0 

"' .,. .,. .,. "' "' "' "' "' .,. 0 0 0 0 Cl 0 0 0 0 0 

~ I: ~ I: I: I: 

"' ~ ~ ~ 

~ 7 

"' "" "" "" "" 

! I: I: ~ ~ ~ ..:. "" "" ,;. 

"" "' ... ... ... "' ... ... ... "' 

Andover Technology Partners www.AndoverT echnology.com Page 17 
The periods shown in Figures 7 and 8 when NOx equals zero are when the NOx analyzer 

is in calibration and the data was removed from the analysis, and the spikes in NOx that appear 

when urea is being injected are during brief jumps in oxygen or an imbalance in main air 

pressure. 

Pre and Post Optimization Comparison 

Performance was compared for the two periods before and after optimization. Arguably, 

there was also a period while optimization was in progress. However, for simplicity SNCR 

performance in the period of January 5, 2009 and prior is evaluated as the pre-optimization 

period against the period January 6, 2009 through January 25, 2009 as the post-optimization 

period with the following metrics: 

• Ammonia slip 

• NOx emissions 

• Urea consumption - measured in gallons of urea per MWh 

Daily averages over these two periods were evaluated for trends. As shown in Figures 12 

a, and b, daily averages ofNOx on Unit 1 remained roughly the same while ammonia slip 

trended downward over the period. Average daily load (MWg) and urea consumption (in 

gallons/MWh) for unit 1 are shown in Figure 12c. Urea consumption in gal/MWhr clearly is 

related to load. Figures 13 a, b, and c show similar results for unit 2 over the same period. Unit 

2 was shut down for a large part of January 241

h and 251h, which affects the NOx level because 

the SNCR system is shut down when the unit is in the process of being shut down or started up, 

and over these days the unit spent several hours below 100 MWg with the SNCR system turned 

off. 

Figures 14 a and b show average urea consumption in gallons/MW ghr and average 

ammonia slip in ppm for unit 1 versus MWg. As shown, there is a clear relationship. Urea 

consumption was reduced sharply (by about 50%) at low load conditions through optimization 

but increased somewhat (about 20%) at high load conditions through optimization. However, 

across the load range ammonia slip was reduced significantly. So, the slight increase in urea 

consumption at high loads on unit 1 was the price for reducing ammonia slip. As shown on 

Figures 15 a and b, on unit 2, urea consumption was reduced at all loads except full load; 

however, ammonia slip was reduced across all loads, and particularly at full load. 

Since ammonia slip is of particular concern because of its impact on ammonia on fly ash, 

trends in fly ash ammonia concentration were evaluated. As shown in Figure 16, there has been 

a sharp drop in fly ash ammonia concentration that occurred as a direct result of optimization. 

This low ammonia slip performance has been sustained since January, with average slip of 1.0 

and 1.3 ppm year to date on Units 1 and 2, respectively. 

Andover Technology Partners www.AndoverT echnology.com Page 18 
I 

I 

I 

i 

Figure 12a. Unit I average daily NOx. 

0.300 

I 

0.250 0 "" o('.. 

~;'QT"' ..,4/'-..v _;·v .. -co;;-

0.200 

0.150 SL 

0.100 

0.050 

!§> ~~ ~# #' ~,g, ~ .,,~ ,:v ~ , .... ~ (;)"'' ~.$- '...~ ...,-v. (;)...,'1. ...,-v ...,-v (;) .... (;) .... 

Figure 12b. Unit I average daily ammonia slip 

7.00 .---------------------

6.00 

5.00 

4.00 

3.00 

2.00 

1.00 

SNCR AMMONIA SUP 

REAOING U1 OiAN 1 

++~-------- --SNCRAMMONIA SUP ---

READING U1 OiAN 2 

Figure 12c. Unit I average daily urea consumption 

(gai/MWh) and load (in MW). 

2.5 ~--------------------

0.5 

I 

I 

Figure 13a. Unit 2 average daily NOx. 

0.500 

0.450 - 0.400 

0.350 " 0

0

0

.

.

.

300 

250 

200 __,.J 

/\ 

~ / 

/"'-... ._,__.... /\ 

'-..r--/'J 

1\ 

\. ~ 0.150 

0.100 Unit shut down 

0.050 or in low load . operation 

"'# ~# -r-# "'#' ~#' without SNCR 

'1,.-v most of time ..,~ ~ ..,...,... '...~ ~ 

v v-' v <:>"' (;)...,, (;) .... 

Figure 13b. Unit 2 average daily ammonia slip 

12.00 ~-------------------------------------

10.00 

SNCR AMMONIA SUP 

READING Ul OiAN 1 8.00 

6.00 ++-----------SNCRAMMONIA SUP --

READING Ul OiAN l 

4.00 

2.00 

Figure 13c. Unit 2 average daily urea consumption 

(gal/MWh) and load (in MW). 

2.0 

1.8 

1.6 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 c= -, MW/100 ' ------------

·-·---·----·--···--·-"---------------------------

Andover Technology Partners www.AndoverT echnology.com Page 19 
Figure 14a. Unit I daily avg urea consumption in gal/MWhr 

versus avg load in MW g 

1.4 

1.2 

1.0 

0.8 " ... 

• " 0.6 :5 

0.4 0.2 

• post llrea gai/MWh 

--Linear (pre lire a 

+------------------ gai/MWh) 

+-------------------- -_::Linear (post lire a 

gdi/MWh) 

100 120 140 160 180 .2.00 

MWe 

Figure 14b. Unit 1 average daily ammonia slip v avg load in 

MWg 

6.00 

5.00 I • 

E 

Q. 4.00 • Q. • 

. 

-;;; • • pre NH3 3.00 

.... 

X • I>Ost NH3 z 

... 2.00 --linear (prt> NH3) 

1.00 

--linear (post NH3) 

100 120 140 160 180 200 

MWe 

Andover Technology Partners www.AndoverT echnology.com 

Figure 15a. Unit 2 daily avg urea consu

versus avg. load in MW 

1.6 

1.4 • 1.2 •• ._ 

.. 

-

... --· ... . 

1.0 

::E ' :::::. 0.8 

" -... - ... .. • 5 0.6 • • 

0.4 

0.2 

-

100 120 140 160 180 200 

MWe 

Figure 15b. Unit 2 average daily ammo

MWg 

12.00 

10.00 -

E 

Q. 8.00 Q. 

ti 

-;;; 6.00 

.... 

X 

z 

... 4.00 II/ 

2.00 -. /.• 

-

• • .._ 

- • 

100 120 140 160 180 20

MWe 

Page 20 
Figure 16. Ammonia in Fly ash (mg/kg) 

E 

... 

... 

,.· 

"E 

0 

E 

~ .&: 

:( 

> u: 

1---

0 g 0 

g 0 

0 •. "' 0 g0 

s. ;.:. ~ -< ~ 0 0 

• • • ... 

• • 

• 

0 

0 

0 

0 

"' 0 

0 

~ 

~ 

• 

• • + Unitl 

Post Optimizatio n • 1Jnlt2 

• 'I • I ~ • • 0 0 0 0 0 0 0 0 0 0 0 0 

0 0 g g g 0 0 0 0 

.. .. .. .. .. .. 0 0 0 0 0 0 0 0 0 0 0 0 

"' ~ s. § -< l! 

.. s -< -< s ;:! =< =< ::. -< s 0 0 0 0 0 0 

--------------------------------------

Long Term Experience 

Since optimization the plant has had an opportunity to gain some long-term experience 

with the SNCR system and the ammonia instruments. 

Ammonia Instruments 

The TDLAS paths have remained aligned since initial installation - over eighteen months 

- without any need for re-alignment. This is despite the substantial deflection of the flue gas 

ductwork with load changes. The PAT.-PEND. instrument mounting device has not experienced 

any leaks or failures of any kind. 

It has been necessary to make upgrades to the initial software of the TDLAS instrument 

to address signal processing issues during periods of soot blowing and other times where signal 

to noise ratio is reduced, and these upgrades appear to have addressed concerns. Also, in the first 

months of operation some components needed replacing or adjustment; but, the supplier 

addressed that. 

The ports for the optical path do need to periodically be purged with air. There is a 

constant purge on the optics to keep them clean. But material does occasionally build up in the 

port. The instrument mounting assembly has a purge connection that has facilitated periodic 

purging. Once the operators learned that this was necessary on a fairly regular basis, the 

instrument became far more reliable. It is planned that this will become an automated feature 

long term. 

Andover Technology Partners www.AndoverT echnology.com Page 21 
Comparison versus Wet Chemistry Methods 

Over a year after initial installation and start up of the ammonia instruments, the project 

team evaluated one of the ammonia paths against wet chemistry methods.2 The testing of the 

ammonia instrument was intended to do the following: 

• Evaluate the response of the instrument to ammonia. 

• Evaluate the accuracy of the instrument when measuring ammonia slip. 

To do this, the team ran a test to evaluate instrument output versus a well accepted 

measurement approach that should provide a reliable indication of ammonia across the duct. The 

method of ammonia slip measurement that was used as a comparison to the instrument was wet 

chemistry (EPA method 27, except that we did not take isokinetic samples because we were 

looking for vapor phase ammonia). At each test condition the test contractor performed a wet 

chemistry measurement from the test ports to measure ammonia. The samples were drawn 

through impingers that were directly attached to the end of the probe. As a result, there wasn't 

the risk of losing sample in the sample line, which is what likely happened in the FTIR 

measurements used during SNCR system acceptance test. The samples were drawn through test 

ports a foot or so downstream (above) the Unit 2 channel 1 ammonia instrument optical path. 

For each test the unit was run under steady conditions that were well controlled. Each of the 

tests was designed to produce a different level of ammonia slip so as to have a series of tests that 

would compare the instrument's response to wet chemistry over a range of ammonia slip 

concentrations. 

Bearing in mind that the ammonia instrument measures the average over a line of sight, 

to try to make the measurements comparable the test sampling method was developed to estimate 

the average slip across the duct. Samples were drawn from either side of the duct (north and 

south) from opposing test ports at locations immediately above the instrument path (unit #2 

channel #1), with the probes meeting near the middle. The probes were moved out an equal 

distance every five minutes over the sample period (30+ minutes) such that the total sample 

should represent the average ammonia slip over that half of the duct. Detailed information on 

the spatial distribution of ammonia is not produced; but, it is possible see how ammonia slip is 

2 More paths would have been tested; however, we were limited by unit availability and access fo r wet chemistry 

probes. Unit I was in outage. 

Andover Technology Partners www.AndoverT echnology.com Page 22 
stratified from one side of the duct to the other. Ideally, the average ofthe two sides should 

equal the ammonia slip displayed by the instrument. 

Figures 17a through 17f represent the results of the six different tests. These figures plot 

the minute by minute PI data for ammonia slip from channel one of the Unit 2 instrument over 

time, the north (blue) and south (red) side of the duct average readings as well as the average of 

the two. Since the test values are samples taken over a period oftime, they cannot capture 

changes during that time, but represent the average for the sample over that time. A vertical 

scale of 0 to 35 ppm is used for all figures so that the figures are comparable to one another and 

the differences in ammonia slip levels from one test to another can readily be compared. These 

are arranged from lowest ammonia reading (a) to highest ammonia reading (f) rather than in the 

time order that the test was conducted. In Figure 17b the instrument reading falls off to zero. 

This is because the urea pumps tripped off during this test. What is apparent in Figures 17a 

through 17f are: 

• There is significant stratification of ammonia in the duct, with much higher 

concentrations on the south side than the north side, particularly at higher concentration. 

• The ammonia instrument generally tracks between the north and south side 

concentrations, except at higher concentrations where the instrument tends to indicate 

closer to the lower concentrations on the north side. 

• When urea tripped off the instrument clearly responded as expected. 

• At lower slip levels, the instrument seems to have a good correspondence with measured 

test values 

Because of the high stratification of ammonia slip when there are higher slips, it is 

difficult to make direct comparisons for the purpose of gauging accuracy, but clearly the 

instrument is responding with higher slips that are generally within the range of the test 

measurements. Whether or not there is an inherent bias in the method to lower numbers in 

situations such as this one is unclear. 

Andover Technology Partners www.AndoverT echnology.com Page 23 
35.00 

30.00 

25.00 

20.00 

15.00 

10.00 

5.00 

35.00 

30.00 

25.00 

20.00 

15.00 

10.00 

5.00 

35.00 

30.00 

25.00 

20.00 

15.00 

10.00 

5.00 

Figure 17a 

... 

Figure 17c 

................ •• ...... • ..... 

Figure 17e 

....... ~ ......... ....... ..... ... 

--

Andover Technology Partners 

• SNCR Af';lf'.10 NIA 

SLIPREADIIJG 

U2 CH! 

Test tkrth 

TetS041h 

--Tesr:Av, 

• s f'I( R At.tt IOlUA ,, UPREADtNG 

u 2 CH! 

--r etN«th 

T 

T 

• 

--

--

--

s 

s 

t4(RAP.1f'.t0tll.l 

UP R.EAC4tiG 

U2 CH1 

-- Urea tripped off 

Figure 17b 

35.00 

30.00 

25.00 

20.00 

15.00 

-- I • SIICP. At.IP.lOt/IA I 

I SLIPRE.ACUIG , 

U2<Hl I 

I --Td:tlorth 

-

I --TdS<dh 

I 

10.00 ........ 1 --TestA'\IIi: 

5.00 

............. 

Figure 17d 

35.00 ~-----------------

30.00 

25.00 

20.00 

15.00 

f--------------·------·----------=- ~~: ~:i~II A U2(Hl 

+---------------------T-estN.Jrth 

t--~:::::::::::::::::::::::::::: ==~ Soom 

10.00 

5.00 

Figure 17f 

35.00 

30.00 

25.00 

20.00 

15.00 

........................ .... 

• 

10.00 .... 5.00 

. . . ---"-- -----''-----"L----..:L----·~----

. 

--

--

SU( R At.IM OtiiA 

SUPREA.OitiG 

ll2 ou 

Test: Ave 

www.AndoverT echnology.com Page 24 

I 
Figure 18a shows the same data in a different way- the north and south wet chemistry test results 

plotted against the average of the instrument indication over the test period. This figure shows 

that, while the instrument does not precisely agree in magnitude with the wet chemistry 

measurements - especially at high loads - it does respond to changes in ammonia levels. At low 

ammonia slip levels, the correspondence with wet chemistry results is much better than at high 

load. 

Figure 18 Comparison of wet chemistry test results to average instrument indication over 

the test period 

40.00 

35.00 

30.00 

25.00 

20.00 

15.00 

10.00 

5.00 

2.00 4.00 6.00 8.00 10.00 

Average Instrument Output over test, ppm 

Andover Technology Partners www.AndoverT echnology.com 

• Test North 

• Test South 

I TestAvg 

Page 25 
SNCRSystem 

SNCR experience will be divided between performance and reliability issues. 

SNCR Performance 

After completion of optimization Crane embarked on a program of coal test bums that 

included PRB coal as well as other coals. Over this period the SNCR system had difficulty 

maintaining NOx emissions below the target rate, especially at high loads, although operators 

have attempted to make adjustments to control set points as conditions change. The difficulty 

was, no doubt, due to different combustion conditions, stagging, etc., that impacted furnace 

temperature and CO levels. However, after the units had returned to Bailey coal the SNCR 

system eventually became more effective in controlling NOx emissions. Long term, the units 

will have new cyclones and may bum 100% PRB coal. Once the conversion is completed, the 

optimization will be repeated. 

SNCR Reliability 

Crane has experienced a number of issues regarding reliability of the SNCR system. 

These largely involve the injectors, dilution water quality and instrumentation. 

• Boiler tube damage - Boiler tube damage was discovered in the vicinity of level 500 

injectors on unit 1. This was determined to be caused by impingement of droplets on the 

inner wall of the air tube of the HERT injector. Relocation of the nozzle to be even or no 

more than Yz inch recessed from the HERT tube end appears to have corrected this 

problem. The plant has measured off the lances to ensure that in the future the nozzles 

are properly located within the HERT tubes, and added improved centering guides to the 

lances to prevent liquid impingement on the cooling guide tubes. The HERT injectors as 

originally supplied do not have stops to assure the correct nozzle position, and therefore 

must be carefully measured when inserting after each removal for periodic inspection. 

• Zone 700- These injectors were removed from service when the inner injector tube was 

removed to gain additional OF A flow needed for deeper staging with sub-bituminous 

coal. It would have been necessary to re-design the 700 level injectors, and subsequent 

CFD modeling predicted little if any benefit from urea injection at the location, hence the 

reason for their removal. 

• Injector plugging - The pressure atomized nozzles plugged frequently due to hardness 

deposits. The plant uses city water for dilution water and ACT did not expect that a 

water softener would be necessary. The plant has been utilizing a portable water softener 

for the dilution water and this has helped address the problem. 

• Dilution skid plugging- Calcium deposits also fouled the injection dilution skid piping to 

the point that check valves in the dilute urea lines to the 600 and 800 levels of Unit 2 

were plugged completely. Ultimately it was necessary to perform an organic acid 

Andover Technology Partners www.AndoverT echnology.com Page 26 
cleaning of the piping to remove the deposits. The deposits have not reappeared since the 

acid cleaning was done 12 months ago, since the system has operated with softened water 

ever smce. 

• Instrumentation and controls - Recent problems were discovered with automatic and 

manual valves leaking through in the dilution skid, along with "nuisance" trips of the 

system due to faulty instrumentation and/or interlocks. In another instance, a check valve 

failed to prevent reverse flow and allowed dilute urea to enter the plant air header. The 

plant performed a process hazards analysis to ensure a thorough understanding of the 

potential hazards associated with the system, especially with regard to automation 

sequences. 

Conclusions 

Constellation has installed SNCR on both Crane units 1 & 2 and at Wagner unit 2. These 

plants are unique in their use ofTDLAS ammonia instruments for continuous monitoring of 

ammonia slip. The Crane installations were especially difficult applications for the TDLAS 

technology due to the duct dimensions and the nature of the Crane unit operations. Ammonia 

slip using the TDLAS technology was made possible at Crane units 1 & 2 as a direct result of a 

PAT -PEND approach for mounting the instrument optical paths to assure their alignment despite 

duct movement. The instruments have maintained their original alignment made over eighteen 

months ago without any need to adjust alignment and are continuously providing data testing 

indicates is a good indication of ammonia slip. Comparison testing of the instrument output 

versus wet chemistry measurements was very consistent at lower slip levels where the 

stratification of slip. was moderate; however, at higher slip levels where stratification of slip in 

the duct was greater, the instrument tracked increases but did not agree precisely with wet 

chemistry in terms of the actual ammonia slip value. As a result it provides a useful signal for 

monitoring performance in real time, if the absolute value may be in doubt under some 

conditions. 

The SNCR system did meet its contractual NOx and ammonia slip performance 

guarantees. However, optimization of the SNCR system to more stringent slip levels was 

necessary and improvement of reagent consumption rates was desirable. The availability of 

continuous ammonia slip data made it possible to significantly improve SNCR system 

performance to reduce overall ammonia slip levels, reduce high ammonia slip transients, and 

reduce fly-ash ammonia concentrations while also improving reagent consumption under most 

conditions. The continued operation of these instruments provides assurance that operators can 

identify high ammonia slip conditions and therefore respond to them before the consequences of 

these conditions become problematic. 

Andover Technology Partners www.AndoverT echnology.com Page 27