Andover Technology Partners www.AndoverTechnology.com Page 1 

### 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 Fa rm Road, North Andover, MA 01845
2 Constellation Energy CP Crane Station, 1001 Carroll Island Road, Baltimore, MD 21220
3 T ourgee & 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 in dication 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 whi le 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, rea gent consumption and fly ash ammonia that is possible though optimization of SNCR operation using the information from continuous and
real

- time monitoring of ammonia slip.

Presented at the AWMA, 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@AndoverTechnology.comAndover Technology Partners www.AndoverTechnology.com Page 2 

### Project Background and Technical Description
Constellation Energy’s Baltimore plants are subject to a system

- wide cap on NOx, SO 2 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. T his 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 th e CP Crane units.

Table 1. CP Crane Units 1 & 2 Description

Unit 1 Unit 2 Rated Capacity MWg 200 205

Boiler Type Cyclone 2 front wall 2 rear wall Cyclone 2 front wall 2 rear wall

OFA yes yes
Internal Wing Walls No Yes Coal Blend (approx . by wt. ) 75% Bailey 25% PRB 75% Bailey 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 Manageme nt 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 CraneAndover Technology Partners www.AndoverTechnology.com Page 3 SNC R system selection

Constellation evaluated offerings from different technology suppliers. High Energy Reagent Technology (HERT) technology from Advanced Combustion Technology, now part of Fuel Tech, Inc., 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 atomizatio n for the injectors.
The HERT system s 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 1

.

**•** The lowermost injectors (zone 800) inject urea into the boiler at the 65 foot elevation above the cy c lones but below the OFA for Rich Reagent Injection. These ports were formerly used for gas injection when gas reburn was employed.

**•** The next zone (700) injects urea through the OFA ports at the 91 foot elev ation

.

**•** The 600 zone injects reagent into the upper furnace at the 102 foot elevation,

**•** A nd the 500 zone injects reagent slightly above the nose arch at the 120 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

- atomize d 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 OFA provides the mo tive 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 c ommon 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 i s 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 a nd its impact on fly ash. W ith tubular
air

- preheaters, air

- pre heater 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 of t his concern Constellation considered the installation of ammonia slip analyzers

.Andover Technology Partners www.AndoverTechnology.com Page 4 The project team examined several approaches for monitoring ammonia slip and determined that tunable diode laser absorption spectroscopy (TDLAS) technology offered the
greate st 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

molecules across an optic al 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 wa velengths that are selected based upon the target gas that is being measured (in this case, ammonia)

. The differ ence 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 Zone 800 Zone 700 Zone 600 Zo ne 500Andover Technology Partners www.AndoverTechnology.com Page 5 temperature environments. It does not require sample transport to an analyzer, which avoids concern regarding preservation of sample integrity. In large ducts this approach gives a good
indication of the averag e concentration across the duct.
Figure 2

. Cross Duct TDLAS measurement with spacers to limit path length

Experience with the TDL AS method on coal power plants has had mixed success

– and unfortunately, far more failures than successes

. As an optical method, t he TDL approach is extremely sensitive to instrument alignment and particle dust loading. Flue gas d ucts 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 of TDL AS instruments have developed means to address the problem of misali gnment

– 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 ar e 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 s olves 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 TDL AS systems.
The problem with dust loa ding 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 econom izer 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 Transmitter Receiver Gas flowAndover Technology Partners www.AndoverTechnology.com Page 6 changes over the changing load. Substantial flexing was measured, and this flexing would make alignment of cross

- duct TDL AS optical paths impossible across the load range if the optics were
mounted to the duct walls

. Fortunately, the dust loadin g at Crane , with roughly a 60 / 4 0 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 upstr eam 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 install ed on each duct, and these ports were intended to ultimately serve as pote ntial 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 3b and 4b show the gas velocity stratification. Temperature and species measurements also showed significant stratification. The optical p ath (two paths per duct, one duct per unit, and four optical paths altogether for both Crane units) locations were selected to cover the reg ions 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 of TDLAS 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 of the 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 widt h 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 bea m diameter can be reduced, which increases TDLAS beam intensity and improves the signal to noise ratio of the instrument.
The project team selected the Unisearch TDLAS instrument from CEMTEK for application at Crane (and also at Wagner). This instrument h as 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 dataAndover Technology Partners www.AndoverTechnology.com Page 7 Figure 3a. Duct C onfiguration and Port Location for Unit 1.

Figure 3b . Gas Velocity Distribution for Unit 1



# UPAndover Technology Partners www.AndoverTechnology.com Page 8 Figure 4a. Duct Configuration and Port Location for Unit 2

Figure 4 b . Gas Velocity Distribution for Unit 2



# NorthAndover Technology Partners www.AndoverTechnology.com Page 9 from the laser to the optical transmit ter. 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

a dvantage 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 d uct. It also reduces the size of the 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

Th e 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

a mmonia 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

.
T he 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 OFA 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 th e 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 th rough 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.AndoverTechnology.com Page 10 Table 2 . SUMMARY OF C. P. CRANE SNCR A CCEPTANCE TESTING Unit 1 Low Load Unit 1 High Load Unit 2 Low Load Unit 2 High Load

Injection Test Time 12/16/2008 17:10

- 18:10 12/16/2008 09:15

- 10:15 12/17/2008 20:30

- 21:30 12/17/2008 16:45

- 17:45 Baseline NO x (before), lb/mmBTU 0.3394 0.4112 0.3160 0.3708 Urea Injection NO x , lb/mmBTU 0.1554 0.2342 0.1289 0.2133

Baseline NO x (after), lb/mmBTU 0.3376 0.4164 0.3213 0.4031 Average Baseline NO x , lb/mmBTU 0.3385 0.4138 0.3186 0.3869
NO x Reduction 54.1% 43.4% 59.5% 44.9% Average R eduction (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, whi ch 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, ideall y 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 minute s 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 a nd even up to 60 ppm although all of the reported
results were well below those values.Andover Technology Partners www.AndoverTechnology.com Page 11 **•** 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 inje ction 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 ammon ia 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 releas ed 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 ammoni a 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 respondi ng 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 dat a when using FTIR.
Figure 5. Comparison of TDL versus Extractive FTIRAndover Technology Partners www.AndoverTechnology.com Page 12 Figure 6

. Crane Unit 1 Ammonia Slip and Urea flow, December 16, 2008

Figure 7

. Crane Unit 2 Ammonia Slip and Urea flow, December 17 , 2008Andover Technology Partners www.AndoverTechnology.com Page 13 

### SNCR Optimization
Optimization of the Crane SNCR systems was necessary because concern about fly ash
ammonia content m akes 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 of the optimization was to establish parameters and setpoints to minimize
NOx emission s across all operating conditions (ideally at or below 0.27 lb/MMBtu) while maintaining NH 3 slip at or below 2 ppm. Optimization was intended to:

1. Explore the operating range of the SNCR system at expected operating conditions that may be outside the rang e 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 o perating setpoints that minimize NOx emissions during transients while also maintaining slip below 2 ppm

3. Identify adverse secondary effects of the SNCR system and develop means to mitigate these effects. Although the goal from the outset was to keep slip b elow 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 th e emissions rate of 0.27 lb/MMBtu 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 b it 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 difficu lty maintaining pressure drop adequately low near full load

, care was necessary to ensure that the SNCR did not contribute to increase d baghouse pressure drop.

The low ammonia slip requirements are primarily intended to minimize ammonia in the fly ash. Al though 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 c oncern

.

**•** 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.AndoverTechnology.com Page 14 **•** Having a t ubular 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 col lected 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 t rips 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 dur ing 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 co ndition, 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 i n load

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

**•** Increases in urea injection

Figures 8 and 9 are plots of MWg, NOx, total urea flow, ammonia slip and opacity for
U nit 1 and Unit 2, respectively on January 7, at a very early period in the optimization program

. P eaks 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 inAndover Technology Partners www.AndoverTechnology.com Page 15 slip. These opacity increases are most likely associated with baghouse cleaning transients, which would not be expected to impact ammonia slip.
An objective of optimiz ation 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 th e 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 off) for both
units 1 and 2 while m aintaining 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 bei ng 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 changin g 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.AndoverTechnology.com Page 16 Peaks in Ammonia Slip associated with

**•** Load reduction highlighted in blue

**•** Increasing urea highlighted in yellow

**•** Opacity peaks highlighted in red Figure 8

. Unit 1 SNCR Operation 7 January, 2009

Figure 9

. Unit 2 SNCR O peration 7 January, 2009

Peaks in Ammonia Slip associated with

**•** Load reduction highlighted in blue

**•** Increasing urea highlighted in yellow

**•** Opacity peaks highlighted in redAndover Technology Partners www.AndoverTechnology.com Page 17 Figure 1 0 . Unit 1 SNCR operation on January 22, 2009

Figure 11 . Unit 2 SNCR operation on January 22, 2009Andover Technology Partners www.AndoverTechnology.com Page 18 The periods shown in Figures 7 and 8 when NOx equals zero are when the NOx analyzer
is in calibrat ion 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 p eriods 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 sho wn in Figures 12 a, and b, daily averages of NOx 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 12 c. Urea consumption in gal/MWhr clearly is related to load. Figures 1 3 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 24 th and 25 th , 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 1 4 a and b show average urea consumption in gallons/MWghr 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 optimizati on . 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 1 5 a and b, on unit 2, urea consumption was reduced at all loads excep t full loa d;
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 Fi gure 1 6 , 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.AndoverTechnology.com Page 19 Figure 1 3 c. Unit 2 average daily urea consumption (gal/MWh) and load (in MW). Figure 12 a . Unit 1 average daily NOx.

Figure 12 b . Unit 1 average daily ammonia slip

Figure 12 c . Unit 1 average daily urea consumption (gal/MWh) and load (in MW). Figure 1 3 b . Unit 2 average daily ammonia slip Unit shut down or in low load operation without SNCR most of time Figure 1 3 a . Unit 2 average daily NOx.Andover Technology Partners www.AndoverTechnology.com Page 20 Figure 13a. Unit 1 urea consumption in gal/MWh versus average load

Figure 13a. Unit 1 urea consumption in gal/MWh versus average load Figure 13a. Unit 1 urea consumption in gal/MWh v ersus average load Figure 13a. Unit 1 urea consumption in gal/MWh versus average load Figure 13a. Unit 1 urea consumption in gal/MWh versus average load

Figure 1 5 a . Unit 2 daily avg urea consumption in gal/MWhr versus avg. load in MWg

Figure 1 5 b . Unit 2 average daily ammonia slip v avg load in MWg Figure 1 4 b . Unit 1 average daily ammonia slip v avg load in MWg Figure 1 4 a. Unit 1 daily avg urea consumption in gal/MWhr versus avg load in MWg

Figure 1 0 a . Unit 2 average daily NOx.Andover Technology Partners www.AndoverTechnology.com Page 21 Figure 1 6

. Ammonia in Fly ash (mg/kg)



### Long Term Experience

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

- term experience with the SNCR system and the ammonia instrum ents.

Ammonia Instruments
The TDLAS paths have remained aligned since i nitial 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. i nstrument 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 per iodically 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 opera tors 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. Post OptimizationAndover Technology Partners www.AndoverTechnology.com Page 22 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 t o evaluate instrument output versus a well accepted
measurement approach that should provide a reliable indication of ammonia across the duct. The

method of ammon ia 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 w et 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 ha ppened in the FTIR
measurements used during SNCR system acceptance test

. T he samples were drawn through t est
ports a foot or so downstream (above) the Unit 2 channel 1 am monia instrument optical path

. For each test t he unit was run under steady conditio n s that were well controlled . Each of the

t ests w as 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 (n orth 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. D etailed 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 for wet chemistry probes. Unit 1 was in outage.Andover Technology Partners www.AndoverTechnology.com Page 23 stratified from one side of the duct to the other. Ideally, the average of the two sides should

equ al the ammonia slip displayed by the instrument.

Figures 17 a through 17 f 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 of time, they cannot capture
changes during that t ime, 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 comp ared . 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 F igure 17 b the instrument reading falls off to zero.
This is because the urea pumps tripped off during this test. What is apparent in Figures 17 a through 17 f 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 gen erally 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 accurac y, 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.AndoverTechnology.com Page 24 Figure 17 f Figure 17 e Figure 17 d Figure 17 c Figure 17 b Figure 17 a Urea tripp ed offAndover Technology Partners www.AndoverTechnology.com Page 25 Figure 1 8 a 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 periodAndover Technology Partners www.AndoverTechnology.com Page 26 SNCR System
SNCR experience will be divided between performance and reliability issues.
SNCR Performance

After completion of optimization Crane embarked on a pr ogram of coal test burns 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 con trol set points as conditions change. The difficulty was, no doubt, due to different combustion conditions, slagging, etc., that impacted furnace temperature and CO levels. However, after the units had returned to Bailey coal the SNCR system eventually b ecame more effective in controlling NOx emissions. Long term , the units will have new cyclones and may burn 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 c aused 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 1⁄2 inch recessed from the HERT tube end appears to have corrected this problem. The plant has measured off the lan ces 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 stop s 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 OFA 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 rem oval.

**•** 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 plan t has been utilizing a portable w ater 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 Un it 2 were plugged completely. Ultimate ly it was necessary to perform an organic acidAndover Technology Partners www.AndoverTechnology.com Page 27 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 soften ed water ever since.

**•** 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 anothe r 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, especial ly 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 of TDLAS 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 operation s . Ammonia slip using the TDLAS technology was made possible at Crane units 1 & 2 as a direct result of a

P AT

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

. T he instruments have maintained their original alignment made over eight een months ago witho ut 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 performanc e 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 imp rovement 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, reduc e high ammonia slip transients, and
reduc e 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 condition s and therefore respond to them before th e consequences of
these conditions become problematic.