SCR Catalyst Management Strategies – 

Modeling and Experience

James E. Staudt 

Andover Technology Partners 

112 Tucker Farm Road 

North Andover, MA 01845 

staudt@AndoverTechnology.com 

Anthony J. Engelmeyer 

Orlando Utilities Commission 

500 South Orange Avenue 

P.O. Box 3193 

Orlando, FL 32802 

tengelmeyer@ouc.com 

ABSTRACT 

For coal-fired boilers equipped with SCR, catalyst contributes to a major operating 

expense. Strategies for minimizing catalyst cost while preserving system performance - 

generally referred to as catalyst management – are receiving greater attention. 

Approaches for managing catalyst can vary widely. Therefore, analysis of catalyst 

management strategies requires accurate predictive tools for assessing SCR system 

performance that have the flexibility to address a wide range of scenarios. These 

predictive tools may also be used to investigate performance issues that facility operators 

may encounter. However, until recently, operators have not had access to these tools, 

except through catalyst suppliers or consultants. 

In this paper, various catalyst management strategies will be examined. Using software 

currently used by several power plant operators and SCR technology suppliers, we will 

illustrate some of the important considerations of a catalyst management strategy and 

provide an example of how catalyst management strategies can be evaluated with such a 

software tool. 

Presented at Coal Gen 2003, Columbus, OH 

August 6-8, 2003
INTRODUCTION 

With more coal-fired power plants operating with Selective Catalytic Reduction (SCR), 

catalyst management is a topic that has gained increased interest. In this paper, the topic 

of catalyst management will be explored along with a tool that can be useful for analysis 

of catalyst management strategies. 

A comprehensive approach to catalyst management goes far beyond simply planning for 

the next catalyst addition or replacement and performing the associated catalyst testing. 

A comprehensive approach extends beyond the simple objective of minimizing catalyst 

consumption over the plant lifetime. A comprehensive catalyst planning effort involves 

minimizing the catalyst costs while simultaneously optimizing the operation of the 

facility to achieve the lowest cost to produce power. As a result, it involves making 

trade-offs between catalyst consumption, the frequency and duration of outages taken for 

catalyst work, ammonia slip, NOx reduction, baseline NOx, parasitic pressure loss, and, 

of course, comparing catalyst regeneration versus catalyst replacement. Assessing these 

trade-offs in an efficient manner requires an interactive tool. Some of the trade-offs that 

can be assessed with such a tool are discussed below: 

Ammonia Slip – If your plant can tolerate a higher ammonia slip from the SCR 

than originally anticipated, it may be possible to reduce catalyst loading, extend 

the time between catalyst replacement events, or to increase the amount of NOx 

reduction that is possible from the facility. 

NOx reduction – With NOx allowances having a marketable value, increasing the 

NOx reduction of the SCR may be worth exploring. However, increased NOx 

reduction comes at a price of increased ammonia slip, increased ammonia 

consumption, increased frequency of catalyst replacement, increase catalyst 

loading, or increased pressure loss. 

Baseline NOx level – If the baseline NOx level is increased, this may have 

benefits to the boiler or improve ash LOI, but it this may necessitate higher costs 

associated with operating the SCR at a higher reduction level or it may have other 

adverse affects, such as higher ammonia slip. Alternatively, reducing NOx from

the furnace to the SCR inlet can help reduce ammonia consumption, reduce 

ammonia slip, and permit longer times between outages. 

Catalyst Loading – It may be possible to extend time between catalyst outages 

further through increasing the catalyst loading beyond the initial design level. 

However, increased catalyst loading adds catalyst cost and increases parasitic 

loads due to pressure drop across the catalyst. 

Pressure Drop – In some catalyst management scenarios, some layers in the 

catalyst reactor are left empty. This approach has the advantage of reducing 

www.AndoverTechnology.com 2
catalyst loading and pressure drop versus a traditional approach that fills the SCR 

reactor and later replaces catalyst as the catalyst loses activity.

Furthermore, there are other effects that may need to be reassessed after a period of plant 

operation. For example, if catalyst deactivation rates differ from what was originally

expected, it may be necessary to modify the plans for catalyst replacement or 

regeneration. In this paper we will explore such a situation in detail. 

Because of these many trade-offs, a tool that enables the owner’s personnel to quickly

and easily evaluate different scenarios should be very useful. 

In the next section, we will review catalyst management basics. Then, we will discuss 

the key features of a tool that is used for catalyst management by a number of power 

plant operators and SCR technology suppliers. Finally, we will discuss an assessment of 

catalyst management alternatives at a utility boiler using SCR. 

CATALYST MANAGEMENT BASICS 

Although the physical size of catalyst should not significantly change over time, catalyst 

can be viewed as a consumable item. The catalyst has the ability to facilitate the NOx 

reducing reactions, and this quality is called “activity”. Over time, impurities in the gas 

stream will deposit on the catalyst and block exhaust gas from reaching active sites 

within the catalyst. Some catalyst “poisons”, such as arsenic, will chemically bond to the 

active vanadium pentoxide within the catalyst micropores. As more and more of these 

microscopic, active sites get blocked, the catalyst activity will gradually drop to a point 

where performance becomes unacceptable. 

Each SCR reactor is designed to provide a minimum specified NOx reduction 

performance with a maximum ammonia slip under a given set of conditions after the 

catalyst has lost some portion of it’s initial activity. Therefore, once catalyst activity 

drops below a level determined in the original design of the SCR system, it is necessary 

to replace some of the catalyst or add more catalyst to the reactor. SCR catalyst activity 

is regularly monitored by laboratory analysis of catalyst samples. This is normally done 

on an annual basis. 

Most SCR reactors are designed with up to four available levels of catalyst. In some

cases each level may hold more than one layer (two layers of catalyst essentially stacked 

on top of one another). When the system is new, with fresh catalyst, at least one level is 

typically empty, as pictured at the top of Figure 1. When the SCR catalyst activity drops 

to a point where ammonia slip increases to an unacceptable point, then new catalyst is

added to level 4, as shown in the middle part of Figure 1. In the case of Figure 1, only 

one catalyst layer is in each level. But, in some cases two layers are in each level. In that 

case, one layer (half of a level) would be added to level 4 and then at a later time when 

SCR total activity is low enough, a second layer (half of a level) would be added to level 

4, filling level 4 and the SCR reactor. 

www.AndoverTechnology.com 3
After the SCR reactor is full, it is necessary to replace catalyst levels with new or 

regenerated catalyst to increase total SCR catalyst reactor activity. This is shown at the 

bottom of Figure 1. Since the top level usually loses activity faster than the others, it is

normally the first catalyst level to be replaced. 

Figure 1. Normal Add and Replace Sequence 

SCR Reactor with three full 

catalyst levels and one empty 

catalyst level 

Fill bottom level (Level 

4) with catalyst after 

SCR activity drops, 

increasing SCR reactor 

activity 

After catalyst activity drops, 

remove catalyst Level with 

lowest activity 

Replace with new catalyst, 

increasing SCR activity 

www.AndoverTechnology.com 4
Another approach to managing catalyst is to regenerate the catalyst. One approach, 

shown in Figure 2, requires that one level of catalyst always be empty. This permits the 

removed catalyst to be off site for regeneration. When total SCR catalyst activity drops 

to a minimum acceptable point, regenerated catalyst is added to the empty catalyst level 

and the catalyst level with the lowest activity is then removed for regeneration, as in 

Figure 2. When using this regeneration approach and two layers of catalyst are installed 

in each level, then it is necessary to remove the top layer for regeneration in one outage 

before removing the bottom layer during the next. Of course, regenerated catalyst must 

be first added to empty layers on the bottom before being added to the top. This 

approach, described in Reference 1, is currently being used at PG&E National Energy 

Group’s Indiantown station. 

The advantages of a regeneration approach such as this are: 

• If the catalyst is physically intact, it is not necessary to purchase new catalyst. 

And, since regeneration of a unit of catalyst is typically less expensive than 

buying new catalyst, savings are possible. 

• Pressure drop across the SCR reactor is less than add-and-replace approaches that 

fill the SCR reactor, reducing the associated parasitic losses. 

• Depending upon SCR reactor access and available staffing, shut downs for 

catalyst regeneration may be shorter in duration than for a catalyst level 

replacement because as one layer is removed for regeneration it may be possible 

to simultaneously install regenerated catalyst on another level. 

There are some disadvantages of this regeneration approach with respect to a normal addand-replace approach, such as: 

• Shut downs for catalyst changes will typically be more frequent. 

• A catalyst that is reactivated with new active material may not behave in the same

way with respect to SO2 to SO3 oxidation and with respect to deactivation as the 

original catalyst because the active component (V2O5) may not be distributed 

throughout the catalyst in the same manner. 

• If the catalyst is badly eroded, or otherwise physically damaged, regeneration 

cannot be performed and replacement with new catalyst is necessary. 

Whether replacing catalyst or regenerating catalyst, it is important to identify the layer 

with the lowest activity and replace or regenerate that layer. This is because the net

activity addition to the SCR reactor is the activity of the new or regenerated catalyst 

minus the activity of the catalyst that is removed. The greatest net activity addition will 

occur if the catalyst with the lowest activity is replaced or regenerated. In most cases, the 

top level of catalyst (in a down-flow reactor) loses its activity at the fastest rate. This is 

because it tends to be exposed to the highest concentration of impurities. However, there 

may be some cases where activity is lost at the same rate or faster in other layers. So, 

regular catalyst testing is an important part of any catalyst management program. 

www.AndoverTechnology.com 5
Figure 2. Sequence for Regeneration of SCR Catalyst 

Install regenerated 

catalyst to empty 

level 

Remove used catalyst 

for regeneration 

Install regenerated 

catalyst to empty 

level 

Remove used catalyst 

for regeneration 

Install regenerated 

catalyst to empty 

level 

Remove used catalyst 

for regeneration 

www.AndoverTechnology.com 6
MODELING CATALYST MANAGEMENT PLANS 

Analyzing the various trade-offs and approaches to catalyst management is best done 

with a computational modeling tool that can quickly estimate the effects of a different 

approach on facility operation and forecast the future sequence of events and the 

associated costs. As a result, the model needs to be both accurate and flexible. A list of 

important features is shown below. 

The model should be able to: 

1. Model either add-and-replace or regeneration approaches easily, predicting the 

sequence and time of future catalyst events for several years. 

2. Allow modeling initial load of catalyst of any type from any manufacturer. 

3. Model changes in catalyst manufacturer or type over time. 

4. Determine the need for catalyst changing based upon user-selected preference of 

either time periods or reaching an ammonia slip or activity limit. 

5. Properly select the catalyst layer to be removed and replaced under a wide range 

of scenarios.

6. Model at least four for more levels of catalyst with up to two layers of catalyst per 

level. 

7. Model different deactivation rates per level, as top levels often lose activity faster 

than lower levels. 

8. Model time-variant catalyst deactivation rates, as deactivation rates can vary with 

time. 

9. Model different catalyst deactivation rates for regenerated or replacement catalyst 

versus original catalyst, as regenerated or replacement catalyst may behave 

differently than the catalyst it replaces. 

10. Accurately predict ammonia slip over time. 

11. Model the effects of maldistribution of the ammonia injection on ammonia slip. 

This is especially important for very high NOx reduction SCR systems where the 

risk of ammonia break-through can be high. 

12. Model changes in catalyst loading for each layer from the initial SCR reactor 

design, because experience may make such a change in catalyst management 

plant necessary (an example will be discussed later). 

13. Model new SCR systems or systems that have been in use for some time. 

14. Permit updating of catalyst conditions and deactivation rates as data becomes 

available. 

15. Calculate the costs of future catalyst changing events and make long-term cashflow projections. 

16. Accurately model the effects of changes in inlet or outlet NOx on ammonia slip 

and the catalyst management plan. 

17. Model the impact of the catalyst management plan on draft loss and associated 

parasitic power costs. 

18. Perform Net Present Value analysis of the plan over a period of time. 

Costs associated with a catalyst management plan include the cost of catalyst itself and 

the labor associated with removing used catalyst and adding replacement catalyst. 

www.AndoverTechnology.com 7
Additional costs that must be considered are costs associated with parasitic power, costs 

associated with lost production when the boiler must be shut down for catalyst changing 

events, procurement and other overhead costs, and monitoring and testing costs. Thus, 

the cost is not strictly proportional to the catalyst volume affected, but there are costs that 

may be considered “per event” costs and costs that may be incurred continually (such as 

parasitic power). Furthermore, since a catalyst management plan has implications that 

will extend for many years, the effects of escalation and cost of money should be 

considered such that Net Present Value analysis can be performed. 

In addition to the above features, in order for the model to be most useful for the typical 

user, a computer program should run on a Windows-based PC, have a familiar user 

interface, and be well documented. Fortunately, modeling software with all of these 

features was recently made available to users with the release of CAT MANAGERTM 

version 2.0. Several owners of SCR plants and SCR technology suppliers are currently 

licensed to use CAT MANAGERTM version 2.0 or the earlier version 1.0. In the 

following section, we will discuss the modeling of one facility with CAT MANAGERTM 

version 2.0 where it became necessary to modify the catalyst management plan. 

Modeling Changes in Catalyst Management Plans 

At times actual catalyst behavior does not correspond to expected performance. This will 

normally cause the facility owner to reevaluate their catalyst options. In such a situation, 

there is a benefit to having a tool that enables the owner to quickly reassess various 

options in light of new information on catalyst performance. Orlando Utilities Stanton 

Energy Center Unit #2 is an example of how the owner found it necessary to revise their 

catalyst management plan after a few years of experience. As a matter of disclosure, 

neither OUC nor the catalyst supplier used CAT MANAGERTM to perform the analysis 

for any decisions made thus far, although both have since licensed CAT MANAGERTM. 

In this paper, our intention is to compare the results of modeling catalyst performance 

with CAT MANAGERTM against experience at an actual facility and demonstrate how 

this tool can be effective in helping make catalyst management decisions for the future. 

Orlando Utilities Stanton Energy Center Unit #2 is a 468 MW Babcock & Wilcox dry 

bottom boiler that went into service in June of 1996. The unit is equipped with low NOx 

burners, overfire air, an SCR, ESP and a wet scrubber for emissions control. The SCR 

uses Argillon (formerly Siemens) plate catalyst. Based upon an expected coal analysis 

that had adequate free CaO (over 2.5%), a moderate level of arsenic in the coal, and no 

fly ash reinjection, a low gaseous arsenic condition was believed to exist and the catalyst 

management plan was developed accordingly. Table 1 summarizes the SCR 

characteristics and performance and Figure 3 shows the SCR reactor. Figure 4 from

Reference 2 shows a graph of the original catalyst management plan for Stanton #2. For 

each of the four catalyst additions shown on Figure 4, one layer, or one half of a level of 

catalyst is added, to fill the SCR reactor with 740 m3

 of catalyst by around 90,000 

operating hours. The SCR is intended for year-round operation, providing typically 

8,000 operating hours per year.

www.AndoverTechnology.com 8
As documented in References 3, 4 and 5, Stanton Unit #2 experienced more rapid catalyst 

deactivation than originally anticipated. This was determined to be a result of arsenic 

deactivation due to actual coal mineral conditions being different than those originally

planned for the SCR catalyst design. Specifically, actual CaO in the coal was lower than 

originally anticipated, which contributed to increased deactivation from arsenic. 

Table 1. Stanton Unit #2 SCR 

• Uses Argillon (formerly Siemens) SINOx plate type catalyst 

- TiO2 based for arsenic resistance & low SO3 conversion (<1%) 

- Eastern KY Coal - Arsenic 22.2 to 113.2 ppm in coal and 2.5% to 3.5% CaO 

in ash 

• SCR is high dust type positioned just downstream of boiler outlet 

• Reactor initially charged with 2 full catalyst layers of 370 m3

 (13,100 ft3) 

• Two more empty elevations initially provided for future catalyst recharges 

• Uses anhydrous ammonia at full load design rate of 230 lb/hr 

• Total system design pressure drop of 3.42 in wg at full load 

• Guaranteed NOx removal rates with design boiler output of 0.32 lb/MMBTU: 

- Initial condition test down to 0.10 lb/MMBTU 

- Continuous rated down to 0.17 lb/MMBTU 

- All at <2 ppm NH3 slip for design operating period of 24,000 hrs (3 years) 

Catalyst deactivation, being faster than expected, manifested itself as high ammonia slip 

and lower catalyst activity. Ammonia slip was measured to be 8 ppm in June of 1998 by 

wet chemistry methods and 8.9 ppm in measurements later that same year.Ref. 3 Since 

ammonia slip is normally the first indication of reduced catalyst activity, it is important 

for a model to estimate ammonia slip. 

Figure 5 shows a comparison of predicted ammonia slip (using CAT MANAGERTM ver 

2.0) at Stanton #2 versus actual measurements. Two predicted curves are shown. One 

approximates the originally anticipated ammonia slip assuming a constant deactivation 

rate. The other predicted curve shows the predicted slip using actual deactivation rates. 

The predicted curve was determined by using actual catalyst activity measurements to

develop estimates of actual deactivation rates. The predicted curves also relied on other 

assumptions. OUC Stanton currently operates at 205 ppm (@3% oxygen) inlet to the 

SCR and 110 ppm (@ 3% oxygen) outlet of the SCR, and these NOx values were 

assumed for the period for the two predicted curves and as the design basis. Inlet and 

outlet NOx will have a significant impact on both predicted and actual ammonia slip, and 

it is uncertain if the inlet and outlet NOx levels at the time of the ammonia wet chemistry 

measurements precisely matched the assumed inlet and outlet NOx levels used for these 

modeling runs. So, some small difference is reasonable to expect in light of this 

uncertainty. Figure 5, therefore, demonstrates that the calculated ammonia slip from

CAT MANAGERTM corresponded reasonably well with the measured values. 

www.AndoverTechnology.com 9
Figure 3. OUC Stanton Unit #2 SCR Reactor (Ref. 2) 

Figure 4. OUC Stanton #2 Original Catalyst Management Plant (Ref. 2) 

Add 1⁄2 level – 

92.5 cubic 

meters

www.AndoverTechnology.com 10
Figure 5. NH3 for OUC

measured with wet chemistry and modeled with CAT MANAGER(tm)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

0 5,000 10,000 15,000 20,000

operating hours

NH3

NH3, expected const lambda

NH3, modeled from measured deactivation rates

NH3 measured, wet chemistry

In order to maintain a three-year period between catalyst changing events while 

preserving acceptable boiler and SCR performance, OUC, with input from the catalyst 

supplier, modified their catalyst management plan to allow up to 4 ppm of ammonia slip 

and increased catalyst loading. In April of 1999 OUC added a full level of catalyst to 

Level 3. In April 2002, three years after filling level 3 with 185 cubic meters of catalyst, 

OUC filled Level 4 with 231 cubic meters of catalyst. The change in volume was due to a 

new standard element height from the manufacturer. At this point it is important to 

reiterate that the decisions made so far regarding catalyst management at OUC were 

made without the use of CAT MANAGERTM and were based upon the analysis of the 

catalyst supplier and OUC. OUC has not yet determined if levels 1 through 3 will be

replaced with 185 cubic meters of catalyst, 231 cubic meters of catalyst or whether 

another approach will be used. Catalyst activity information from the April 2002 

catalyst samples, which corresponds to 47,294 operating hours on levels 1 and 2, 23,614 

operating hours on Level 3 and 0 hours on newly-installed Level 4, were used to establish 

initial conditions for modeling future SCR management strategies. Assumptions were 

also made about future catalyst deactivation and SCR operation. With this information, 

modeling with CAT MANAGERTM made the projections of performance in Figure 6a. 

Two scenarios are shown in Figure 6a. In one scenario, existing levels are replaced with 

231 m3

 of new catalyst. In this case ammonia slip is projected to stay well below 4 ppm. 

In another scenario, existing levels are replaced with 185 m3

 of new catalyst. Of course, 

how accurately these models predict future performance will be determined in large part 

by how closely future deactivation rates match the assumed rates in the model and how 

closely assumed operating conditions match actual operating conditions. Therefore, 

annual catalyst activity measurements and monitoring of operation is important, and 

www.AndoverTechnology.com 11
projections should be revised as new information on catalyst deactivation is gained or 

operating conditions change. 

From Figure 6a it appears that it may not be necessary to replace as much as 231 cubic 

meters of catalyst every three years in order to maintain a 4 ppm ammonia slip limit. 

Figure 6a also shows that addition of 185 cubic meters should be adequate for 

maintaining below 4 ppm slip for several years (about 11) but may not be adequate for 

maintaining below 4 ppm of ammonia slip thereafter. Figure 6b compares the cumulative 

catalyst consumption of changing 231 cubic meters every three years to that of replacing 

185 cubic meters of catalyst every three years. As expected, replacing 185 cubic meters 

results in significantly less catalyst usage over the evaluation period. Based upon these 

modeling results, OUC may be able to meet their three-year period between catalyst 

changes while maintaining under 4 ppm slip while adding less than 231 m3

 of catalyst 

during catalyst replacement. 

Modeling Regeneration of Catalyst 

Regeneration of catalyst through mechanical cleaning and sometimes through chemical 

cleaning and addition of active component is a potentially cost saving approach to 

catalyst management. As noted earlier, this approach involves a very different order of 

catalyst removal/replacement events. CAT MANAGERTM version 2.0 will model this 

approach as well as traditional add-and-replace or add-and-regenerate approaches that fill 

the SCR reactor and then keep the SCR reactor full.1

 For the purpose of evaluating 

regeneration of catalyst we evaluated multiple regeneration scenarios. In these cases,

instead of filling the SCR reactor in April 2002, at that point a regeneration program was 

commenced where two layers (one level or two half levels) were maintained empty at any 

time. Spent catalyst would be removed for regeneration and regenerated catalyst would 

be put into the empty levels once the limit of 4 ppm slip was reached. Alternatively, in 

CAT MANAGERTM we could have set specific time periods for catalyst changing events 

(as was done for the modeling of Figures 6a and 6b) rather than reaching an ammonia slip 

limit. However, we wanted to estimate the maximum period between (or, minimum 

frequency of) catalyst changing events. Figure 7a shows the ammonia slip and k/ko 

predictions and Figure 7b shows cumulative catalyst usage predictions for two different 

regeneration simulations where catalyst was regenerated to 100% of the original activity 

of the catalyst when it was new. In one simulation a full level of 185 m3

 is removed and 

185 m3

 of regenerated catalyst is installed in an already empty level. In the other case 

one half level (one layer of 92.5 m3

) is removed and a regenerated layer is installed in an

empty layer. As shown in Figure 7a and b, more catalyst changing events are necessary 

if pursuing a regeneration approach than if replacing spent catalyst with new catalyst. 

However, regenerating a half level at a time reduces the catalyst usage somewhat. 

Therefore, the increased cost of more frequent, but shorter, outages should be compared 

to the savings in catalyst regeneration costs. 

 

1

 CAT MANAGER version 1.0 models add-and-replace or add-and-regenerate, but not the type of 

regeneration approaches that have recently been introduced. 

www.AndoverTechnology.com 12
Figure 6a. Replace Projection for OUC

modeled with CAT MANAGER(tm)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

4/1/2002 3/31/2004 4/1/2006 3/31/2008 4/1/2010 3/31/2012 4/1/2014 3/31/2016 4/1/2018

date

N

H3 and k/ko

k/ko, 231 m3 replacement

NH3, 231 m3 replacement

k/ko, 185 m3 replacement

NH3, 185 m3 replacement 231 m3 added to

level 4 in April 2002

Figure 6b. Replace Projection for OUC

modeled with CAT MANAGER(tm)

0

200

400

600

800

1,000

1,200

1,400

4/1/2002 3/31/2004 4/1/2006 3/31/2008 4/1/2010 3/31/2012 4/1/2014 3/31/2016 4/1/2018

date

cubic meters of catalyst

m3 catalyst, 231 m3 replacement

m3 catalyst, 185 m3 replacement

www.AndoverTechnology.com 13
While it was assumed for the simulations of Figures 7a and 7b that the regenerated 

catalyst has the same activity and deactivation characteristics as new catalyst, in reality 

activity and deactivation rates of regenerated catalyst may differ from new catalyst and 

such circumstances can be modeled with CAT MANAGERTM. Figures 8a and 8b 

compare regeneration to 100% of the activity of new catalyst with regeneration to 95% of 

the activity of new catalyst. As shown, an additional catalyst regeneration event is 

necessary over the evaluated period if catalyst activity is decreased to 95% from 100%. 

As noted earlier, a regeneration procedure may entail a much more complex sequencing 

of catalyst additions and replacements. CAT MANAGERTM will make projections of

catalyst addition and removal and show graphically, and in tables when, where, and how 

much catalyst is projected to be added and removed. As an example, Figure 9 shows the 

catalyst addition and removal sequence for the 95% regeneration case shown in Figures 

8a and b. 

From Figures 6a through 8b, it is shown for the case of OUC Stanton #2 that regeneration 

is expected to entail somewhat more frequent catalyst changing and affects a higher 

quantity of catalyst than replacement of new catalyst. This is because of the higher 

volume of catalyst that is maintained in the SCR when replacing with new and the 

resulting longer interval period between catalyst changing events. However, if the cost of 

regenerating catalyst is significantly less than the cost of the same volume of new 

catalyst, the increased cost of more frequent catalyst changes associated with 

regeneration could be overcome. The potentially higher cost of more frequent catalyst 

changing events will also be offset somewhat by lower parasitic power losses. Therefore, 

when making a decision to regenerate or not, it is necessary to consider all of these 

effects. With CAT MANAGERTM, all of these costs are modeled, detailed cash flow 

projections are made and displayed graphically and in tabular form, and the present value 

of each of these costs is estimated.

www.AndoverTechnology.com 14
Figure 7a. 100% Regeneration Projection for OUC

modeled with CAT MANAGER(tm)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

4/1/2002 3/31/2004 4/1/2006 3/31/2008 4/1/2010 3/31/2012 4/1/2014 3/31/2016 4/1/2018

date

NH3 and k/ko

k/ko, 100% regeneration 185 m3

NH3, 100% regeneration 185 m3

k/ko, 100% regeneration 92.5 m3

NH3, 100% regeneration 92.5 m3

Figure 7b. 100% Regeneration Projection for OUC

modeled with CAT MANAGER(tm)

0

200

400

600

800

1,000

1,200

1,400

4/1/2002 3/31/2004 4/1/2006 3/31/2008 4/1/2010 3/31/2012 4/1/2014 3/31/2016 4/1/2018

date

cubic meters of catalyst

m3 catalyst, 100% regeneration 185 m3

m3 catalyst, 100% regeneration 92.5 m3

www.AndoverTechnology.com 15
Figure 8a. 100% and 95% Regeneration Projection for OUC

modeled with CAT MANAGER(tm)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

4/1/2002 3/31/2004 4/1/2006 3/31/2008 4/1/2010 3/31/2012 4/1/2014 3/31/2016 4/1/2018

date

NH3 and k/ko

k/ko, 100% regeneration 185 m3

NH3, 100% regeneration 185 m3

k/ko, 95% regeneration 185 m3

NH3, 95% regeneration 185 m3

Figure 8b. 100% and 95% Regeneration Projection for OUC

modeled with CAT MANAGER(tm)

0

200

400

600

800

1,000

1,200

1,400

1,600

4/1/2002 3/31/2004 4/1/2006 3/31/2008 4/1/2010 3/31/2012 4/1/2014 3/31/2016 4/1/2018

date

cubic meters of catalyst

m3 catalyst, 100% regeneration 185 m3

m3 catalyst, 95% regeneration 185 m3

www.AndoverTechnology.com 16
Figure 9. Regenerated Layers

use only for regeneration strategies

0000000000000000000000000000000000000000000000000000000000000000000

11

00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

11

0000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

12

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

12

0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

21

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

21

0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000

22

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

22

00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000

31

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

32

000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

41

00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

41

000000000000 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

42

00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

42

000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

11

00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

11

000000000000 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

12

00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

12

0000000000000000000000000000000000000000000000000000000000000000000 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

21

00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

21

0000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

22

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

22

0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

31

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

31

0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000

32

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

32

00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000000000000

41

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

42

00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 0 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

10

20

30

40

50

4/1/024/1/034/1/044/1/054/1/064/1/074/1/084/1/094/1/104/1/114/1/124/1/134/1/144/1/154/1/164/1/17

date

Layer

layer removed regenerated layer added

CONCLUSIONS 

In this paper we described some features of a software tool that can help operators make 

decisions regarding catalyst management. In this paper we also discussed how at OUC 

Stanton it was necessary to modify the catalyst management plan because actual 

operating conditions and catalyst behavior were not as originally planned. Projections of 

possible future catalyst management scenarios were made with a software tool that was 

developed for this purpose. The following are key points in the paper. 

• Catalyst management involves optimizing a wide range of parameters, in addition 

to catalyst usage. Having a software tool to quickly evaluate different scenarios is 

very useful. The paper discussed several important features that such a tool 

should possess. 

• Because of the many factors to consider, the most cost-effective catalyst 

management approach may not be the one that results in the lowest amount of 

catalyst usage or amount of catalyst regeneration over the period. Other factors, 

such as the cost of lost production during outages, cost of parasitic power and 

other effects need to be considered. 

www.AndoverTechnology.com 17
www.AndoverTechnology.com 18

 

• In some cases operating conditions and catalyst behavior will differ somewhat 

from the actual predictions and it will then be necessary to reevaluate catalyst 

management options. This is what happened at OUC Stanton. In these situations 

a tool for evaluating future scenarios for catalyst management based upon the new 

information is very useful for SCR operators. 

• A catalyst management tool that is licensed by OUC and others was benchmarked 

against actual data and provided reasonable correspondence with measured 

performance. 

• Modeling of possible future catalyst management scenarios for OUC Stanton was 

performed. Scenarios that were assessed included future replacement of catalyst, 

future regeneration of catalyst, and variations of these approaches. CAT 

MANAGERTM version 2 provided valuable insights to the trade-offs between 

approaches and made analysis faster, easier and interactive. 

• Regular measurement of catalyst activity provides important information for the 

model and will enhance predictive capability of the model. Thus, having such a 

model is not a substitute for a regular catalyst testing. The model and the testing 

program enhance one another - with the testing providing useful information for 

the model and the model using that information as input for testing possible future 

scenarios. 

REFERENCES 

1

 Bullock, D., Hartenstein, H., “O&M Cost Reduction of a Coal-Fired U.S. Merchant Plant Through an 

Optimized SCR Management Strategy Involving Catalyst Regeneration”, 2002 DOE SCR/SNCR 

Conference, Pittsburgh, May 2002 

2

 Cochran, J., Scarlett, D., Johnson, R., “SCR for a 460 MW Coal Fueled Unit: Stanton Unit 2 Design, 

Startup and Operation”, 1997 EPRI-DOE-EPA Combined Utility Air Pollutant Control Symposium, The 

Mega Symposium, Washington, DC, August 25-29, 1997. 

3

 Staudt, J., Engelmeyer, A., Weston, W.H., Sigling, R., “The Impact Of Arsenic On Coal Fired Power 

Plants Equipped With SCR”, ICAC Forum 2002, Houston, February 12-13, 2002 

4

 Staudt, J., Engelmeyer, A., Weston, W.H., Sigling, R.,”Experience with Arsenic Poisoning of SCR 

Catalyst at OUC Stanton”, 2002 DOE SCR/SNCR Conference, Pittsburgh, May 2002 5

 Staudt, J., Engelmeyer, A., Weston, W.H., Sigling, R., “Analysis Of Arsenic In Coal, And The Impact Of 

Arsenic On Coal Fired Power Plants Equipped With SCR”, EPRI SCR Workshop, Baltimore, November 

2001