# 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 manage ment – are receiving greater attention. Approaches for managing catalyst can vary wi dely. Therefore, an alysis of catalyst management strategies requires accurate predictive tools for assessing SCR system performance that have the flexibility to a ddress a wide range of scenarios. These predictive tools may also be used to investigate performance i ssues that facility operators may encounter. However, until recently, ope rators have not had access to these tools, except through catalyst supp liers or consultants.
In this paper, various catalyst management strategies will be examined. Using software currently used by several pow er 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 managementstrategies can be evaluated with such a software tool.

Presented at Coal Gen 2003, Columbus, OH August 6-8, 2003

# INTRODUCTION

W ith m o re coal-fired po wer plants o p erat ing with Selective Ca talytic Reduction (SCR), catalyst m a nagem e nt is a topic that has gained in creas ed inter e st. In this paper, th e to pic of catalys t m a nage m e ntwill be exp l ored along w ith a too l that can be u s eful for analysis of catalyst m a nage m e ntstrategies.

A com p rehensive approach to catalyst m a nage m e nt goes far beyond sim p ly planning f o r the next catalyst add i tion or replacem ent and pe rform i ng the associated catalyst tes ting. A com p rehensive approach extends beyond the simple objective of m i ni mizing catalyst

consum ption over the plant lifetim e. A com p re hensive catalyst planning effort involves

m i nim i zing the catalys tcosts while s i m u ltaneously optim izin g the oper a tion of the f acility to a c h ieve th e lo west cost to produ ce power. As a result, it involves m a king trade-offs between catalyst consum ption, the frequency and duration of outages taken for catalyst work, ammonia slip, NOx reduction, ba seline NOx, parasitic pressure loss, and, of course, com p aring catalys treg e neration versu s catalyst re placem ent. Assessing th ese trade-offs in an efficient m a nner requires an inte ractive tool. Som e of the trade

- of f

s that can be ass e s s ed with such a tool are discussed below:
Ammonia Slip – If your plant can tolera te a higher amm onia s lip from the SCR than originally anticipated, it m a y be po ssible to reduce catalyst loading, extend the tim e between cataly s t rep l acem ent events, or to increase the am ount of NOx reduction that is possibl e from the facility.

NOx reduction – W ith NOx allowances havi ng a m a rketable value, in creasing the NOx reduction of the SCR m a y be worth exploring. However, increased NOx reduction co m e s at a price of increas ed ammonia slip, increased ammonia

consum ption, increased frequency of cat alyst replacem ent, increase catalyst loading, or increased pressure loss.

Baseline N O x level – If the baseline NOx level is increased, this m a y have benefits to the boiler or im prove ash LOI, but it this m a y necessitate higher costs associated w ith operating the SCR at a hi gher reduction level or it m a y have other adverse affects, such as higher ammonia slip. Alternatively, reducing N O x from the furnace to the SCR inlet can help reduce ammonia consumption, redu ce ammonia slip, and perm it longer tim es between outages.
Catalyst Loading – It m a y be possible to extend tim e between catalyst outages further through increasing the catalyst loading beyond the init ial design level. However, increas ed catalyst lo ading adds catalys t cost and in creas es parasitic loads due to pressure dr o p across the catalyst.
Pressure Drop – In some catalyst m a nage m e nt scenarios, som e layers in the catalyst reactor are left empty. This approach has the advantage of reducing

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## catalyst loading and pressure drop versus a traditional appro a ch that fills the SCR reactor and later replaces catalyst as the catalyst loses activity

.
Furtherm ore, there are o ther effects that m a y need to be reassessed after a period of plant operation. For exam ple, if cataly s t deactivat ion rates d i ffer from what was orig inally expected, it m a y be necessary to m odifythe plans for cataly s t replacem ent or regene ration . In this p ap e r we will e xplore such a situ ation in detail.

Because of these m a ny trade-offs, a tool that enables th e owner’s personn el to qu ickly and easily evaluate different sc enarios should be very useful.

In the nex ts ection, we w ill review catalys t m a nagem e nt basics. Then, we will dis c uss the key features of a tool that is used for catalyst m a nage m e ntby a num be r of power plant operators and SCR technology suppliers. F i nally, we will d i scuss an assessm ent of catalyst m a nagem e nt alternatives at a utility boiler using SCR.



# CATALYST MANAGEMENT BASICS
Although the physical size of catalyst should no t significantly change over tim e, catalyst can be view ed as a cons um able item

. The cat a l y s t has th e ab ility to f acilitate the NOx reducing rea c tions, and this quality is called “ac tivity”. Over tim e, im purities in the g a s stream will deposit on the cata l yst and bloc k ex haust gas f r o mreaching activ e sites within the catalyst. Som e catal yst “poisons”, such as arsenic, will chem ically bond to the active vanadium pentoxide within the catalys t m i cropores. A s m o re and more of these

m i croscopic, active sites get blocked, the cata lyst activity will gradually drop to a point where perform a nce becom e s unacceptable.

Each SCR reacto r is des i gned to p r o v ide a m i nimum specified NOx reduction perform a nce with a m a ximum a mmonia slip under a given s e t of condition s after th e catalyst has lost som e portion of it’s initial activ ity. Therefore, once catalyst activity drops belowa level determ ined in the orig in al design of the SCR system , it is n eces sary to rep l ace so m e of the catalys t or add m o re cat aly s t to th e reactor. SCR catalys t activity is regularly monitored by labor atory analysis of catalyst sam p les. This is norm a lly done on an annual basis.

Most SCR reacto r s are d e signed withup to four availab l e levels of catalyst. In som e cases each level m a y hold m o re than one layer (two layers of catalyst essentially stacked on top of one another). When the system is ne w, with f r esh c a taly st, atle ast one level is typically em pty, as pictured at the top of Figure 1. Wh en the SCR cataly s t activity drops to a poin twhere amm o nia slip increases to an un acceptable p o int, th en new catalys t is added to level 4, as shown in the m i ddle part of Figure 1. In the case of Figure 1, only one cata l yst layer is in ea ch leve l. But, in som e cases two layers are in each level. In that case, one layer (half of a level) would be a dded to leve l 4 an d then at a later tim e when SCR total activity is low enough, a second layer (h alf of a level) would be added to level 4, filling lev e l 4 and th e SCR reactor.

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## After the SCR reacto r is full, it is necessaryto rep l ace catalyst levels with new or regenerated catalyst to in creas e total SCR catal ys t rea c tor activity. Th is is shown at the bottom of Fi gure 1. Since the top level usually lo ses activity f a ster than th e others, it is

norm a lly the f i rst cataly s tleve l to be repla ced.
Figure 1. Normal Add and Replace Sequence

SCR Reactor with three full catalyst levels and one empty cata l yst leve l

Fill bo ttom level (Lev el 4) with catalyst af ter SCR activity drops, increasing S CR reactor activ ity

After catalyst activity drops,

rem ove catalyst Level with lowest ac tiv ity

Replace with new cataly s t, incre a sing S CR activity

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## Another approach to m a naging catalyst is to regenerate the catalyst. One approach, shown in Figure 2, requires that one level of catalyst always be em pty. This perm its the

rem oved catalyst to be off site for regeneration. When total SCR catalyst activity drops to a m i ni m u m acceptable point, regenerated catal yst is add e d to the em pty catalyst lev e l and the catalyst level with the lowest activ ity is then rem oved for regeneration, as in Figure 2. When using this regeneration appro achand two lay e rs of cataly s t are ins t alled in each level, then it is n ecessary to rem ove the top layer for regeneration in one outa g e before rem o ving the bottom layer during the ne xt. Of course, regenerated catalyst m u st be first added to em pty layers on the botto m before being added to the top. This approach, described in R e ference 1, is curre ntly being used at P G &E National Energy Group’s Indiantown station.
The advantages of a regeneration app r oach such as this are:

• If the cataly s t is physically in tact, it is not necessary to purch ase new catalyst. And, since regeneration of a unit of catal yst is typically less expensive than buying new catalyst, savings are possible.

• Pressure d r o p across the SCR reactor is le s s than add-and-replace appro a ches that f ill the SCR reac tor, r e du cing the ass o ciated para sitic loss es.
• Depending upon SCR r eacto r access and available staffing, shut downs for catalyst regeneration m a y be shorter in duration than for a catalyst level replacem ent because as one layer is rem oved forregeneratio nit m a y be possible to sim u ltane ously ins t all regene rated catalyst on another level.

There are so m e disadvantages of this regeneration approach w ith respect to a norm a l addand-rep l ace approach, su ch as:

• Shut downs for catalyst changes wi ll typically be m o re frequent.

• A catalys t th at is reactivated with new ac tive m a terial m a y not behave in the sam e way with res p ect to SO 2 

## to SO 3 

## oxidation and withrespect to d eactivation as the original catalyst because the active component (V 2 

## O 5 

## ) m a y not be distributed throughout the catalyst in the sam e m a nner.
• If the catalyst is badly eroded, or otherwise physically dam a ged, regeneration cannot be perform e d and replacem ent with new catalyst is necessary.

W h ether rep l acing cata l y s t or r e gene r a ting c a ta lys t , it is im portant to iden tif ythe layer with the lowest ac tiv ity and repla ce o r rege n e rate that layer. T h is is be caus e the net activ ity add i tion to the S CR reactor is the activ ityof the new or regen e rated catalyst

m i nus the activity of the cata l yst that is re m oved. The greatest net activity addition will occur if the catalyst withthe lowes tactiv ity is rep l aced o r reg e nerated. In m o st cases, the top level of catalyst (in a down-fl ow reac tor) lose s its a c tivity at the f a s t est rate. Th is is because it te nds to be exposed to th e highest conc entration of im purities. However, there

m a y be some cases where activity is lost at the sam e rate or faster in other layers. So, regular catalyst testing is an im portant part of any catalyst m a nagem e nt program

.

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## Figure 2. Sequence for Regeneration of SCR Catalyst

Insta ll regen e rated cata lyst to e mpty level Re m ove used catalyst for regeneration

Insta ll regen e rated cata lyst to e mpty level

Re m ove used catalyst for regeneration

Insta ll regen e rated cata lyst to e mpty level

Re m ove used catalyst for regeneration

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# MODELING CATALYST MANAGEMENT PLANS
Analyzing the various trade-offs and appro aches to catalyst managem e nt is best done with a com p utational m odeling tool that can quickly estim a te the effects of a different approach on facility operation and forecas t the future sequen c e of events and the associated costs. As a result, the model needs to be both accurate and flexible. A list of im portant features is shown below.

The m odel s hould be able to: 1. Model either add-and -replace o r reg e ne ration ap proaches eas ily, predictin g the sequence and tim e of future cataly s tevents for several y ears. 2. Allow m odeling in itial load of catalyst of any type from any m a nufacturer. 3. Model changes in catalyst m anufacturer or type over tim e

. 4. Determ ine the need for catalyst changi ng based upon user-select ed preference of either tim e periods or reaching an ammonia slip or activity lim it. 5. Properly select th e catalyst lay e r to be rem oved and replaced under a wid e range of scenarios. 6. Model at least four for more levels of cat alyst with up to two layers of catalyst per level. 7. Model different deactivation rates per level, as top levels of ten lose ac tiv ityf a ster than lower levels. 8. Model tim e -varian tcatalyst deactivation rates, as deactivation rates can vary with tim e. 9. Model different catalys tdeactivation rates for reg e nerated or replacem ent catalyst versus original catalyst, as regenerated or replacem ent catalyst m a y behave dif f e rently than the catalyst it rep l ace s. 10. Accurately predict a mmonia slip over tim e. 11. Model the effects of m a ld istribution of the ammonia injection on ammonia slip. This is especially im portant for very high NOx reduction SC R system s where the risk of ammonia break-through can be high. 12. Model chan ges in cataly st load ing for each layer from the initial SCR reactor design, because experience m a y m a ke such a change in catalyst m a nage ment plant ne cess a ry (an example will be discussed la ter). 13. Model new SCR syste m s or system s that have been in use for som e ti m e

. 14. Perm it updating of catalyst conditions and deactivation rates as data becom e s available. 15. Calculate the costs of future catalyst changing events and m a ke long-term cashflow projections. 16. Accurately model the eff ects of changes in inlet or outlet NOx on ammonia slip and the catalyst m a nagem e nt plan. 17. Model the impact of the catalyst m a nage m e nt plan on draft loss and associated parasitic po wer costs. 18. Perform Net Present Value analysis of the plan over a period of tim e. Costs associated with a cataly st m a nagem e nt plan include the cost of catalyst itself and the labo r ass o ciated withrem oving used catalys t and adding replacem ent catalyst.

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## Additional costs that m u st be considered are cos t s associated with paras i tic power, cos t s associated w ith lost production when the boile r m u st be shut down for catalyst changing events, procurem ent and other overhead costs, and m onitoring and testing costs. Thus, the cost is not strictly proportional to the cata lyst volum e affected, but there are costs that

m a y be considered “per event” co sts and cost s that m a y be incurred continually (such as parasitic po wer). Furth e rm ore, since a catal yst m a nage m e ntplan ha s implica tions th at will ex tend f o r m a ny years, the ef f ects of escala t ion and cost of m oney should be considered such that Net Present Value analysis can be perform e d.

In addition to the above features , in order for the m odel to be m o st useful for the typical user, a com puter prog ram should run on a W i ndows-based P C , have a fam iliar user interface, an d be well do cum e nted. Fortunate ly, modeling so ftware with all of thes e features was recently m a de available to users with the rel ease of CAT MANAGERTM version 2.0. Several owners of SCR plants and SCR technology suppliers are currently licensed to use CAT MANAGE RTM version 2.0 or the earlier version 1.0. In the following section, we will dis c uss th e m ode ling of one facility with CAT MANAGERTM version 2.0 where it b e cam e necessary to m odify the catalyst m a nage m e ntplan.


# Modeling Changes in Catalyst Management Plans

At tim es actual catalys tbehavior do es not co rres pond to exp ected perform a nce. Thi s will

norm a lly cause the facility owner to reevaluate their catalyst options. In such a situation, there is a benefit to having a tool that en ables the owner to quickly reassess various options in light of new infor m ation on catal yst perform a nce. Orlando Utilities Stanton Energy Center Unit #2 is an exam ple of how the owner found it necessary to revise their catalyst m a nagem e nt plan after a few years of experience. As a m a tter of disclosure, neither OUC nor the catalyst supplier used CAT MANAGERTM to perform the analysis for any decisions m a de thus far, although both have since licensed CAT MANAGERTM. In this paper, our intention is to com p ar e the results of m odeling catalyst perform a nce with CAT MANAGERTM agains t experien ce at an actual facility and demonstrate how this tool can be effective in helping m a ke cat alyst m a nage ment decisions for the future.
Orlando Utilities Stanton Energy Center Un it #2 is a 468 MW Babcock & W ilcox 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 we t scrubber for em issions control. The S CR uses Argillon (form e rly Siem ens) plate cata lyst. Based upon an expected coal analysis that had adequate free C a O (over 2.5%), a m ode rate level of arsenic in the coal, and no fly ash reinjection, a low gaseous arsenic condition was believed to exist and the catalyst

m a nage m e ntplan was developed accord ingly. T able 1 summarizes the S CR characteristics and perform a nce and Figure 3 shows the SCR reactor. Figure 4 from Reference 2 shows a graph of th e original catalyst m a nage m e ntplan for Stanton #2. For each of the four catalys t additions sh own on Figur e 4, one lay e r, or one h a lf of a level of cata l yst is a dded, to f ill the SCR rea c tor with 74 0 m 3 

## of catalyst by around 90,000 operating hours. The SCR is intended for year-round operation, providing typically 8,000 operating hours per year.

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## As docum ented in References 3, 4 and 5, Stan ton Unit #2 experienced m o re rapid catalyst deactivation than originally an ticipated. This was determ ined to be a res u lt of arsen i c deactivation due to actual coal m i neral condi tion s being different than tho s e orig inally planned for the SCR catalyst design. Specifical ly, actual CaO in the coal was lower than origin ally an tic ipated, wh ich contrib u ted to incre a sed deac tiv ation f r om arsenic.

Table 1. Stanton Unit # 2 SCR

• Uses Argillo n (f orm e rly Siem ens) SINOx plate type cata l yst

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



# - Eastern KY Coal - Arsenic 22.2 to 113.2 ppm in coal and 2.5% to 3.5% C a O in ash

• SCR is high dust type po sition e d jus tdownstream of boiler outle t

• Reactor initially ch arged with 2 full cataly st layers of 370 m 3 

## (13,100 ft 3 

## )

• Two m o re empty elevations initially provided for future catalyst recharges

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

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

• Guaranteed NOx re m o val rates with design boiler output of 0.32 lb/MMB TU: - Initial condition test down to 0.10 lb/MMBTU

- Continuous rated down to 0.17 lb/MMBTU

- All at <2 ppm NH 3 

## slip for design operating period of 24,000 hrs (3 years)
Catalyst deactivation, being faster than expect ed, m a nifested itself as high ammonia slip and lower catalyst activity. Ammonia slip wa s m easured to be 8 ppm in J une of 1998 by wet chem istry m e thods and 8.9 ppm in m easurem ents later that sam e year. Ref. 3 

## Since ammonia slip is norm a lly the first indication of reduced catalyst ac tivity, it is im portant for a m odel to estim a te ammonia slip.
Figure 5 shows a com p ar ison of predicted amm o n i a slip (using CAT MANAGE RTM ver 2.0) at Stanton #2 versus actual m easurem ents . Two predicted curves are shown. One approxim a tes the or igina lly an tic ipated ammonia slip as sum i ng a constan tdeac tivatio n rate. The o ther pred icted curve sho w s the pred icted slip using actual de activ ation rates. The predicted curve was determ ined by using ac tual catalys tactiv ity m easurem ents to develop estim a tes of actual deac tivat ion rates. T h e predicted curves also relied on other

assum p tions. OUC Stanton currently opera tes at 205 ppm (@3% oxygen) inlet to the SCR and 110 ppm (@ 3% oxygen) outlet of the SCR, and these NOx values were

assum e d for the period for the two predicted curves and as the design basis. Inlet and outle t NOx will have a s i gnif i can t impact on bot h pred icted and actua l ammonia slip , and it is un certain if the inlet and outle t NOx levels atthe tim e of the ammonia wet chem istry

m easure m ents precisely m a tched the assum e d inlet and outlet NOx levels used f o r thes e modeling runs. So, some sm all diffe rence is reas onable to expect in ligh tof this uncertainty. Figure 5, therefore, dem onstrates tha tthe c a lcu l ated ammonia slip f r om CAT MANAGERTM corresponded reasonably w e ll with the m easured values.

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## Figure 3. OUC Stanton Unit #2 SCR Reactor (Ref. 2)

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

Add 1⁄2 level – 92.5 cubic

me t e r s

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### Figure 5

. NH3 for OUC

m eas ured w i t h w e t che m ist r y and m o d e le d w i t h CA T M A NA G E R( t m )

0. 00 1. 00 2. 00 3. 00 4. 00 5. 00 6. 00 7. 00 8. 00 9. 00 10. 00

0 5
, 0 0 0 10, 000 15, 00 0 2 0
, 00 0

o p er ating ho ur sNH3 NH3, ex pec ted c ons t l a m bda NH3, m odel ed f r om m easu r ed deac ti vation r a tes NH3 m eas ur ed, w e t chem i s tr y



## In order to m a intain a three-year peri od between catalyst ch anging events while preserv i ng acceptab l e bo iler and SCR perfor m a nce, OUC, wi th input fro mthe cataly s t supplier, m o dified their catalyst m a nagem e nt plan to allow up to 4 ppm of ammonia slip and increased catalyst loading. In Ap ril of 1999 OUC added a full level of catalyst to Level 3. In April 2002, three y ears after filling leve l 3 with 185 cubic m e ters of catalyst, OUC filled Level 4 with231 cubi c m e ters of catalys t. The change in volum e was due to a new standard elem ent height from the m a nufact urer. At this point it is importan tto reiterate that the decisions m a de so fa r re garding catalyst m a nagem e nt at OUC were

m a de without the use of CAT MANAGERTM and were based upon the analysis of the catalyst sup p lier and OUC. OUC has not yet determ ined if levels 1 thro ugh 3 will b e replaced with 185 cubic m e ters of catalyst, 231 cubic m e ters of catalyst or whether another approach will b e used. Cataly st activ ity inform ation 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-in stalled Level 4, were used to establish initial conditions f o r m o deling f u tur e SCR m anagem e nt strategies. Assumptions were also m a de about future catalyst deactivati on and SCR operation. W ith this inform ation, modeling with CAT MANAGE RTM m a de the proj ections of perform a nce in Figure 6a. Two scenarios are shown in Figure 6a. In one s cenario, exis ting levels are rep l aced with 231 m 3 

## of new cataly s t. In this case ammonia slip is projected to stay well below 4 ppm. In another scenario, existing levels are rep l aced with 185 m 3 

## of new catalyst. Of course, how accurately the s e m o dels pred ic t future pe rform a nce will be dete rm ined in large p a rt by how closely future deactiva tion rates m a tch th e assum e d rates in the m odel and ho w closely assum e d operating conditions m a tch actual operating conditions. Therefore, annual catalyst activity m easure m ents and m onitoring of operation is im portant, and

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## projections should be rev i sed as new inform ation on catalyst d eactivation is gained or operating conditions change.

From Figure 6a it app ears that it m a y not be necessary to replace as m u ch as 231 cubic

m e ters of catalys t every three y ears in orde r to m a inta in a 4 p p m amm onia slip lim it. Figure 6a also shows that addition of 185 cubic m e ters should be adequate for

m a intaining below 4 ppm slip for several y ears (about 11) but m a y not be adequate for

m a intaining below 4 ppm of a mmonia slip th ereafter. Figure 6b com p ares the cum u lative catalyst consum ption of changing 231 cubic m e te rs every three years to that of replacing 185 cubic meters of catalyst ev ery three years. As expect ed, replacing 185 cubic m e ters results in significantly less catalyst usag e over the evaluation pe riod. Based upon these modeling results, OUC m a y be able to m eettheir three-year period between catalyst changes while m a intaining under 4 ppm slip while adding less than 231 m 3 

## of cataly s t during catalyst rep l acem ent. 

# Modeling Regeneration of Catalyst
Regeneration of catalyst through m echanical cleaning and som e ti m e s through chem i cal cleaning and addition of active com p onent is a potentially cost saving approach to catalyst m a nagem e nt. As noted earlier, this approach involves a very different order of catalyst removal/replacem ent events. CA T MANAGERTM ve rsion 2.0 will m odel this approach a s well as trad itiona l add-and-replace o r add-and -re genera te app r oaches that fill the SCR reactor and then keep the S CR reactor f u ll. 1 

## For the purpose of evaluating regene ration of catalys t we evaluate d m u ltiple re generation s cenar ios. In these c a ses, instead of filling th e SCR reacto r in April 2002, at that poin ta re generation program was commenced where two layers (one level or two half levels) w e re m a intained em pty at any tim e. Spent catalyst would be rem oved for regeneration and regenerated catalyst would be put in to the em pty levels once th e lim it of 4 ppm slip was reach ed. Alternatively, in CAT MANAGERTM we could have set specific tim e periods for catalyst changing events (as was don e for the m o deling of Figures 6a and 6b) rath er than reach in g an ammonia slip lim it. However, we wanted to e s tim ate the m a ximum period between (or, m i nim u m frequency of) catalyst changi ng events. Figure 7a shows the ammonia slip and k/ko predictions and Figure 7b shows cumulative ca talyst usage predictions f o r two different regeneration sim u lations where catalyst was re generated to 100% of the original activity of the catalyst when it w a s new. In one sim u lation a full level of 185 m 3 

## is rem oved and 185 m 3 

## of regenerated catalys tis installed in an already em pt y level. In the other case one half level (one layer of 92.5 m 3 

## ) is rem oved and a regenerate d layer is insta lled in an
em pty layer. As shown in Figure 7a and b, m o re 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 tim e reduces the catalyst usage so m e what. Therefore, the increased cost of m o r e freque nt, but shorter, outages should be com p ared to the s a ving s in ca taly st regeneration costs.

1 

### CAT M ANAGER versi o n 1.0 m odels a d d-and-re place or add-an d-re ge nerate, but not the type of rege nerat i ona p p r oaches th at have rece ntly been int r oduced.



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### Figu re 6 a . Re plac e Proj e c tio n for OUC modeled w i th C A T M A N A G E R ( tm)

0. 0 0 0. 5 0 1. 0 0 1. 5 0 2. 0 0 2. 5 0 3. 0 0 3. 5 0 4. 0 0 4. 5 0 5. 0 0

4/1/ 2 002 3 / 31 / 2 0 0 4 4 /1/ 2 0 0 6 3 / 3 1 / 20 08 4/ 1 / 20 10 3 / 31 / 2 0 1 2 4 / 1 / 2 0 1 4 3 / 3 1 / 201 6 4 / 1 / 2 0 1 8
dat eNH3andk/ko 

### k / k o , 231 m 3 r eplacem ent

NH3, 231 m 3 r eplacem ent k / k o , 185 m 3 r eplacem ent NH3, 185 m 3 r eplacem ent 23 1 m 3 added t o lev e l 4 in A p r i l 200 2



### Figure 6 b . Repla c e P r o j ec tion for O U C

mo de l e d w i t h C A T M A N A G E R ( t m )

0 20 0 40 0 60 0 80 0 1, 0 0 0 1, 2 0 0 1, 4 0 0

4/1/200 2 3 /31 / 2 004 4 / 1 / 2 006 3/31/200 8 4 /1/201 0 3 /31 / 2 012 4 / 1 / 2 014 3/ 3 1 /201 6 4 /1/201 8
dat ecubic meters of catalyst 

### m 3 c a tal y s t , 231 m 3 r epl acem ent

m 3 c a tal y s t , 185 m 3 r epl acem ent



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## W h ile it was assum e d f o r the sim u lations of Figures 7a and 7b that the regenerated cata l yst ha s the sam e activity and de activ ation characteristics as new catalyst, in reality activ ity and deactivation rates of reg e nerated catalyst m a y differ from new catalys t and such circumstances can be m odeled withCAT MANAGERTM. Figures 8a and 8b

com p are regeneration to 100% of the activity of new catalyst with re generation to 95% of the activity of new catalyst. As shown, anadditional catalyst regeneration event is necessary o v er the evaluated pe riod if cataly s t a c tiv ity is decreased to 95% from 100%.
As noted earlier, a regeneration procedure m ay entail a m u ch m o re com p l e x sequencing of

catalys t a dditions and repla cem ents. CAT MANAGERTM will m a ke proje c tion s of catalyst addition and removal and show graphi cally, and in tables when, where, and how much catalyst is projected to be added and rem o ved. As an exam ple, Figure 9 shows the catalyst addition and removal sequence for th e 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 m o re fre quent catalyst changing and affects a higher quantity of cataly s t th an replacem ent of new catalyst. This is because of the higher volum e of cataly st th at is m a intained inthe SCR when replacing with new and the resulting lon g er in terva l peri od between catalys t changing ev ents . However, if the cost of regenerating catalyst is signi f i can tly less th an the cost of the sam e volum e of new catalyst, the increased co st of m o re fre quent catalyst changes associated w ith regeneration could be overcom e . The potential ly higher cost of m o re frequent catalyst changing events will also be offset som e what by lower parasitic power losses. Theref ore, when m a king a decision to regenerate or not, it is necessary to consider all of these effects. W ith CAT MANAGE RTM, all of thes e costs are m o d e led, detailed cash flow projections are m a de and displa yed graphically and in tabula r form , and the pres ent value of each of these costs is estim ated.

www.AndoverTechnology.com 14

## Figur e 7a. 100% Regenerat i on Proj ect ion f o r OUC

m o de le d w i th CAT M A NA GER(t m )

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

4 / 1 / 2 0 0 2 3/ 31 / 2 004 4/ 1/ 20 06 3/ 3 1 / 200 8 4 / 1 / 2 010 3/ 31/ 20 12 4 / 1 / 201 4 3 / 3 1 / 2 0 1 6 4/ 1/ 20 18
da t eNH3 and k/ko 

### k / k o , 1 0 0 % r ege ne r a tion 18 5 m 3 NH3, 10 0 % reg e ne rati on 1 8 5 m 3 k / k o , 1 0 0 % r ege ne r a tion 92 .5 m 3 NH3, 10 0 % reg e ne rati on 9 2

. 5 m 3



## Figure 7b. 100% Regenerat i on Proj ect ion f o r OU C

m o de le d w i t h CAT M A NA GER(t m )

0 200 400 600 800 1,000 1,200 1,400

4 / 1/ 200 2 3 / 3 1 / 2 0 0 4 4/ 1/ 200 6 3 / 3 1 / 2 0 0 8 4/ 1/ 20 10 3/ 31 / 2 01 2 4 / 1 / 2 0 1 4 3 / 3 1/ 201 6 4 / 1 / 2 0 1 8
da t ecubic meters of catalyst 

### m 3 c a ta ly s t , 1 00% r e ge ner a t ion 185 m 3

m 3 c a ta ly s t , 1 00% r e ge ner a t ion 92. 5 m 3



## www.AndoverTechnology.com 15

## Figure 8a. 100 % and 95% Re ge neration P r oj ection for O U C

m o de le d w i th CAT M A NA GER(t m )

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

4 / 1 / 2 0 0 2 3/ 31 / 2 004 4/ 1/ 20 06 3/ 3 1 / 200 8 4 / 1 / 2 010 3/ 31/ 20 12 4 / 1 / 201 4 3 / 3 1 / 2 0 1 6 4/ 1/ 20 18
da t eNH3 and k/ko 

### k / k o , 10 0 % reg e ne rati on 1 8 5 m 3 NH3
, 1 0 0 % re ge ne ra ti on 18 5 m 3 k / k o , 9 5 % r e g e ne r a t i on 1 85 m 3 N H 3
, 95 % r e ge ne r a tion 18 5 m 3



## Figure 8b. 100 % and 95% Re g e n e ration Proj ection fo r O U C

m o de le d w i t h CAT M A NA GER(t m )

0 200 400 600 800 1,000 1,200 1,400 1,600

4 / 1/ 200 2 3 / 3 1 / 2 0 0 4 4/ 1/ 200 6 3 / 3 1 / 2 0 0 8 4/ 1/ 20 10 3/ 31 / 2 01 2 4 / 1 / 2 0 1 4 3 / 3 1/ 201 6 4 / 1 / 2 0 1 8
da t ecubic meters ofcatalyst 

### m 3 c a t a ly s t, 1 0 0 % r e ge ne r a tion 18 5 m 3

m 3 c a ta l y s t, 95 % re ge ne rati on 18 5 m 3



## www.AndoverTechnology.com 16

### Fig u re 9

. Re genera ted Lay e rs use only for r e gen e r a ti on str a tegi es

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10

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504/1/024/1/034/1/044/1/054/1/064/1/074/1/084/1/094/1/104/1/114/1/124/1/134/1/144/1/154/1/164/1/17

dateLayer lay e r remo v e d r egenerat ed lay e r ad ded



# CONCLUSIONS
In this paper we described som e features of a software tool th at canhelp operators m a ke decisions regarding catalyst m a nagem e nt. Inthis paper we also discussed how at OUC Stanton it was necess a ryto m odify t h e catalyst m a nagem e ntplan becau s e actual operating conditions and catalyst be havior were not as origina lly planned. Projections of possible future catalyst m a nage m e ntscenarios were m a de with a software tool that w a s developed f o r this purpose. The fo llowing are key points in the paper.

• Catalyst m a nagem e nt involves optim izing a wide range of param e ters, in addition to catalyst usage. Having a software tool to quickly evaluate di fferent scenarios is very useful. The paper discussed severa l im portant features that such a tool should possess.

• Because of the m a ny factors to consid er, the m o st cost-effective catalyst

m a nage m e ntapproach m a y not be the one that results in the lowest am ount of catalyst usage or am ount of catalyst regene ration over the period. Other factors, such as the cost of lost production duri ng 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 th en be necessary to reevaluate catalyst management options. This is what happene d 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 li censed by OUC and others was benchmarked against actual data and provided reas onable correspondence with measured performance.

• Modeling of possible future catalyst ma nagement 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 fa ster, 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 cat alyst testing. The model and the testing program enhance one another - with the testing providing useful information for the model and the model using that informa tion 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 fo r 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., West on, W.H., Sigling, R.,”Experience with Arsenic Poisoning of SCR Catalyst at OUC Stanton”, 2002 DOE S CR/SNCR Conference, P ittsburgh, 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