## SCR Ca talyst Management and Catalyst Regeneration

visual re tor ac inspection

developme n t of cataly s t m a nagement stra tegies ( exch ange f r e q u e n c y, l a ye r ) sampling of independent cataly s t activitytesting in a benchscale rea c t o r

documentation of deactiv atio n cause s trac king of cataly s t activity and DeNO x potential independent SO 2 

### /SO 3 

### co nversion rate testing in a bench-scal e reactor

determination mea s urement of of opportunities and limitations for cataly s t cataly s t pr essu re drop in a b e nchscale rea c t o r determination of refurbish m ent main deactivation

caus es (ch e mic a l and

ph y s ical poisoning) from e ach

STEAG LL C STAGLLC PO Bo x 410 728 PO Bo x 410 728 224 Westing house Blvd., #607 224 Westing house Blvd., #607 Charlotte, NC 28273-6228 Charlotte, NC 28273-6228 Phone: +01-704-588-7657 Phone: +01-704-588-7657 Fax: +01-588-7644 Fax: +01-588-7644 E-mail: hsobolewski@st eagllc.com E-mail: hartenstein@ste agllc.com



## 7 th 

## Sino-American Technology and Engineering Conference October 2006 Beijing, China

Steag LLC PO Box 4107 28 • 224 We stingh ou se Blvd. #607 • Charlotte, NC 2827 3-6 228 Phone: 704 -5 88-7 657 • Fax:704-5 8 8

- 7 644 E-mail: info@steagll c .com • www.ste agl lc.comAbstract

Approximat ely 100,000 MW of coal-fired electric generating capacity in t he United States was retrofitted during the last 5 years with SCRs in order to comply with the CAAA Title I SIP Call aimed for ground level ozone reducti on. Most utilities opera t e their SCR during the o z one season (May 1 to September 30), however, so me states have already passed leg i slation requiring year round SCR operation and it is exp e cted that most will fol l o w this patter n before the end of th e decade. SCR operat ors are now faced with t he challeng e of long-ter m operation with maxi mu m performa n ce while en suring minimum long-te rm operating costs. Ge rmany has been faced with this sa me challenge since 198 5 when the first SCRs went into oper ation. As German y ha d never operated their SCRs on a seas onal basis, they faced a greater ch allenge of having to develop a year-round plan without the benefit of se veral years of short-ter m operational experience.

German SCR operators developed tools to help them optimi z e operation and reduce SCR O&M costs. For o v er 20 years

, Steag as well as other utilitie s have used a perp e tual cycle o f SCR management to help the m meet thes e challenge s. The eight step cycle consists of ta sks, which should be u ndertaken d u ring each o u tage when the SCR is open. It cont inually tracks the operation an d performance of the SCR, and the deactivation of the catalyst. The resu lts of this tracking det ermines the best plan for optimizing t he SCR syst em, tracking and accurat e ly forecasting t he catalyst deactivation and per formance, and developing a catalyst lif e-cycle strategy.

A major factor in reducin g O&M cost s was the d e velopment of catalyst cleaning and regeneratio n processe s, which Steag has done f o r our own SCRs since 1997. The goal was to provide an economically more attractive alternat ive to buying new cataly st and to significantly extend the useful life of t he installe d catalyst. However, the e c onomic eff e ctiveness o f catalyst cleaning an d regeneration depends on the type and causes of catalyst d eactivation as well as the regeneration process used, which in return d epends on a n in depth knowledge of the various deactivation cau s es.

Introduction

During the last 5 years, more than 100,000 MW of coal-fired electric ge n e rating capa city in the United States was retrofitted with mostly high-du st SCRs in order to comply with the Clear Air Act Amend ments (CAAA) Title I State Implem en tation Plan ( S IP) call aimed for ground level ozone reduction. After installation a nd succe ssf ul commissioning, most SCR operat ors are now faced with t he challeng e of long-ter m SCR operat ions. As virtually all S CRs will go from a 5 month ozone seasonal operation between May and September to year-round operation no later than 2009, managing an SCR for maximu m perf o rmance, while ensurin g minimum l ong-term operating co sts, has be come the mo st recent ch allenge for SCR operat ors.



### 2Manageme n t Tools

Steag, who owns and operates a fle e t of 24 SCRs in their o w n power plants, has be en faced with these challenges since 1986 when the first SCR went in to operation on a year-round basis. As German y had never operated their SCRs on a seasonal b a sis, Steag was forced t o immediately develop all the tools an d procedure s needed to manage our SCR syste m for minimu m operating cost while ensuring year-round compliance without t he benefit of short-term operating experience. T he tools we developed can be categ o rized into t w o fundame n tally different types, namely:

• SCR equip m ent manag ement, which addresses properly tuning, maintaining and ke eping up critica l SCR equipment components including the ammonia in jection grid (AIG), damp e rs, expansion joints, cata lyst seals, an d the SCR reactor(s) an d

• Catalyst ma nagement, which addresses properly testing, analyzing, det ermining deactivation causes, De NOx potential tracking a nd forecasting, exchanging, replacin g, purchasing and/or regenerating the catalyst.

SCR Manag ement Cy cl e

Steag, as well as other SCR users, developed and have used for two decades what we refer to as the perpe tual cycle of SCR management. The cycle descri bes all the t a sks and responsibilities to be und ertaken during each out age when the SCR reactor is acce ssible. Performing all the tasks as outlined i n the SCR managemen t cycle dilige n tly on a perpetual basis allows for achievement of the lowest ov erall SCR operating cost w h ile ensurin g the most sought after SCR efficient performance. Particul arly in the early years of SCR operat ion, the operator sh ould take ad vantage of every opportu nity to access the syste m and quickly establish an accurate data history of the reacto r and the installed cata lyst. The per petual SCR
managemen t cycle inclu des the follo wing steps:

• Visual react o r inspectio n and sampling of cataly st from each catalyst layer

• Independent catalyst activity testing in a bench scale reactor

• Independent SO 2 /SO 3 co nversion rate testing in a bench sca le reactor

• Measureme n t of catalyst pressure d r op in a ben ch scale rea c tor

• Determination of the main deactivation causes ( c hemical an d physical)

• Determination of opport unities and limitations for catalyst ref u rbishment

• Documentation of deactivation causes & trackin g of catalyst activity and DeNOx pote n tial

• Developme n t of catalyst manageme n t strategies (exchange frequency, layer, etc.)

As soon as a reasonably long operating history has been do cumented which typically takes three to four cycles, the plant operat or can start consolidat in g the data a nd begin de veloping an optimized catalyst management strategy. Such a strategy can either be developed for a single unit or for a n entire fleet of SCRs. As a user of 2 4 SCRs, Ste ag quickly r ealized the enormous economic b enefit of managing the e n tire inventory of catalyst on a fleet- w ide basis with a pool of



### 3catalyst flow ing freely among the va rious units. Such a strat egy includes the catalyst exchange frequency, catalyst rejuvenation or r egeneration, and the pur chase of ne w catalyst la yers as necessary.

SCR Reactor Inspection and Catal y st Sampl i ng

Based on Steag’s 20 years of SCR operating experience at least one (1) annual SCR inspection takes pla c e and at least one (1) catalyst sample from each layer in service must be taken, tested and a nalyzed for deactivation and DeNOx potential tra cking purpo ses. This is the same frequency we routinely apply to our own fleet of 24 SCR syste m s. We also recommen d additional S CR reactor inspection s be done at a n y time whe n an individ ual SCR rea c tor is offline and a ccessible w hether it is d ue to a sche duled or a fo rced outage.

Especially d u ring the first years of SCR operation, more frequent than an nual inspe c tions and catalyst sampling has be en proven to be very ad vantageous b y providing as many dat a points related to th e catalyst d eactivation as possibl e early on. As the experience with each SCR reactor and the predicta b ility of its catalyst deactivation rate increases, t he inspect i o n and catalyst testing frequency can be reduced to a lo ng-term frequency of once per year. SCR reactor insp ection shou ld include at a minimum:

• Inspection o f SCR reactor and all associated eq uipment

• Inspection o f the reactor insulation a nd lagging

• Inspection o f all cata lyst layers in ea ch reactor in cluding:

▪ Catalyst mo dules as well as the cata lyst itself

▪ Flue gas se als between the catalyst modules

▪ Flue gas se als between the catalyst modules and reactor wall

▪ Soot blowers and/or son i c horns

▪ Reactor sup port structur e

• Catalyst sampling (at least one sample per layer)

• Inspection o f the flue ga s guide vane system upstream of the SCR reactor and evaluation of possible fly ash deposit s

• Inspection o f the gas inlet distribut io n system and rectifier

• Inspection o f the flue ga s and econo mizer bypasses includin g bypass dampers and expansion joints

• Inspection o f the AIG system , partic u larly the nozzles an d tu ning v a lv es

• 

### Inspection of key ancillary equipm ent, e.g., the fixed installed sam p ling grid downstream of

the last ca talys t lay e r, seal a i r sys t em including dam p ers and expansion joints, etc.

4Ammonia Sy stem Insp ection and Evaluation

As a result o f our own 20 year operating experience of ammo nia (NH 3 and NH 4 OH) sy stem s as well as the e x tensive exp e rience gath e red in the U.S. over th e past 5 years, Steag recommend s a yearly inspection of t he ammonia storage and supply system, and an assessment of the NH 3 - and NH 4 OH-systems’ performance once a year. The ammoni a storage and supply system inspectio n should in clude at a minimum:

• Inspection o f ammonia u n loading sta t ion (tank tru ck and/or rail car)

• Inspection o f the transfe r compressors to the NH 3 storage ta nks

• Inspection o f all ammonia storage ta nks

• Inspection o f the ammon i a transfer p u mp station to the vaporizers

• Inspection o f the ammon i a vaporizers

• Inspection o f the dilution air systems

AIG Tuning

As part of o u r SCR man agement program, Stea g per forms a yearly optimization of t he flue gas distribution (NH 3 and NOx profiles) and tuning of the (AIG) to:

• Optimize the operation of the AIG,

• Minimize ammonia (NH 3 ) slip, and

• Reduce O&M costs.

This strateg y directly applies what S t eag has lea r ned and developed during the past 20 years while tuning the AIGs of our own 24 SCR units for maxi mum SCR performance and minimu m NH 3 consumption. This is achieved by ma ximi zing the NOx removal effi ciency while ensuring as little as p o ssible NH 3 slip. In orde r to ideally o v erlay the NH 3 profile over the NOx profile for

c o mbining maxi mum re moval effic i enc y with min i mum N H 3 slip, the fully O 2 - corrected three dimensional NO profile after the last catalyst layer must be measured utilizin g up to seven NO/ O 2 analyzers in parallel. Subseq uently, the NH 3 injectio n system should be adju s ted in such a way that the NO profile after t he last cata lyst layer is as uniform as possible at the lowest possible level. T h is ensure s a mini mum ammonia s lip at a maxi mum NO x r e moval efficiency.

Steag’s test s each unit ’ s AIG under actual full lo ad operating condition s at maxi mum NOx removal effi ciency using the fixed installed sampling grid aft e r the last catalyst layer. We then conduct a series of test s during the tuning of the AIG and adjustment the AIG tuning valves until the SCR is operating at peak perfor m ance. During actual AI G tuning the unit must be operated at full load o n a continuo us basis, th us ensuring the maxi mu m flue gas volume flow rate and maxi mum NOx mass flow rate through the SCR. It is require d that each unit’s SCR reactor be equipped with a fixed installed sampling grid aft e r the last catalyst layer. Steag use s a multiple



### 5analyzer system of up to seven NO/ O 2 analyzers in parallel. T he use of ha nd-held unit s yields numerous significant d i sadvantageous and is co nsidered ina dequate for the task.

Large Parti c le Ash Screens

The presence of large pa rticle ash (L PA) or popcorn ash poses a seriou s concern for many coal-fired utility boiler op erators after retrofitting t heir units wit h high-dust SCR syste m s. LPA is formed in the boiler and can easily b e carried over into the SCR reactor. As LPA is introduced to the SCR reactor, it fre quently causes:

• Catalyst pluggage, which leads to:

• Flue gas maldistribut ion

• Loss of SCR performan ce through loss of availa ble DeNOx potential

• Unacceptable NH 3 slip

• Ex cessiv e pressure dro p

• Catalyst erosion damage

After experiencing problems with LPA in t heir Voerde 4 plant, Steag developed a proprietary and patente d LPA screen design which prevents the intrusion of LPA into the SCR rea c tor by effectively removing the LPA from th e flue gas st ream. Typically, such L PA screens are installed a t t he boiler’s e c onomizer outlet utilizing the economizer hopper f o r the contin uous extraction of the remove d LPA. The special de sign features of Steag’s L PA screens which are patent prote c ted, are:

• A pleated design, which ensures a most advant ageous angle of attack o f the LPA onto the screen and a low flue g a s flow velocity through the LPA screens result ing in a low pressure drop.

• A hinged design (typically at the top of the econo mizer outlet duct), which allows for t he LPA screens to b e rapped frequently in order to remove LPA that gets caught in the scree ns.

• A modular design, which allows for t he use of nu merous different types of screen materials depending o n the flue ga s velocity. Screen materials used include:

o Uncoated or coated stainless wire mesh screen s

o Uncoated or coated stainless st eel wedge wire screens.

Steag uses coating materials which include vari ous commercially availa ble types of metallic coatings such as e.g. ConformaClad, MetalSpray, etc. as well as tungsten carbide coa t ings. This allows f o r the select ion of the co rrect screen design and material needs dependin g on the particular ap plication a n d the actually present flue gas velocit y through the LPA screens.



### 6SCR Catal yst Management

SCR catalys t testing is a critica l part of succe ssfu l overall SCR manage ment. Unbiased and independent catalyst test ing and che m ical analysis is nee ded to determine the:

• Initial ca talyst performance parameters and che m ical composition;

• Actual catalyst activity, SO 2 /SO 3 conversion and catalyst d eactivation r a te;

• Change in chemical co mposition a nd identifica t ion of catalyst deactivation cause s ;

• Determination of initia lly installed

, actual residual, & minimu m required DeNOx potentials;

• Developme n t tracking a nd forecast of SCR syst em performance.

It is a well known fact that typically all te st re sults heavily depend on the t e st protocol and equipment used. The sa me is true for catalyst te sting which is the reason why a standardized, publicly available catalyst testing prot ocol is man datory. In order to obtain the necessary data, a standardize d catalyst te sting proced ure was developed in Germany in 1 987/1988. It has become the internationally accepted standard fo r catalyst test ing and analysis. Steag was one of the two large scale S CR operators select ed b y the Germa n Associat io n of Large Power Plant Operators (VGB – V erei nigung der G roßkraftwerksb etreiber ) for particip a ting in the developmen t of this st an dard protocol for testing of DeNO x c a talyst, “VGB Guideline VGBR302He, 2 nd Edition” [1 ]

. Steag has also developed a supplement to VGB-R302He, wh ich eliminates some remaini ng ambiguities and defin es best practices for ben ch scale test ing based on our long- term bench scale te sting experience [2]

. Catalyst testing and che m ical analysis is requ ire d in order to determine the exact catalyst performance, chemical composition and catalyst deactivatio n causes an d to provide long-term tracking dat a. All bench scale catalyst testing sh ould be perf o rmed in an independent catalyst testing labor atory, which frequently qualifies its a ccuracy and precision th rough extensive QA/QC roun d robin testing to be con ducted every 3 to 5 years through VGB. Steag always participate s in these rou nd robin test s and succe ssfully passed these “VGB-certificat i ons” [3 ]

.

A bench sca le reactor, in accordance with VGB-R302He such as Steag’s, is designe d specifically f o r the sole p u rpose of evaluating SCR catalyst under simulated, controlle d plant conditions. It provides the only practical wa y of examining SCR DeNOx catalyst in a nondestructive manner while generating absolute values for cata lyst activity, SO 2 /SO 3 conversion rate and pressure drop. The most important feat ure of a ben ch scale rea c tor is it s pa rticular suitability for exactly replicating the a c tual operating condition s of a full scale SCR rea c tor while still en suring useful data. The only two deviations from the actual operati on condition s of the full scale SCR reactor are t he lack of a n y fly ash in the bench scale and the molar ratio of ammonia to NOx, which is commonly referred to as α set equal to 1.

Since the pr esence or a b sence of fly ash in t he flue gas has no influence on the act ual activity of the catalyst, it is more practical an d less in terf ering to ope rate a bench scale rea c t o r without fly ash in th e flue gas. Also, as the availability of NH 3 is the limiting facto r of the DeNOx reaction in a full scale SCR syste m , which is not desired in a bench scale test for determining the catalyst’s a c tivity, the molar ratio of NH 3 to NOx must be set to 1. However, to enable correct

measureme n ts of the ca talytic activit y (K) and th e SO 2 /SO 3 c onversion rate under the exact



### 7same condit i ons that the catalyst experiences in an actual utility SCR sys t em, catalyst samples must be exp o sed to synthetic flue ga s of the ex act same co mposition, velocity and t e mperature as present in the full scale system.

SCR performance and catalyst dea ctivation are genera lly tracked as po tential of ea ch individual layer as well as potential of the entire SCR reactor versus operating time. Each data p o int generated should be ent ered into the SCR Performance and Catalyst Potential Tracking Sheet to follow the history of the unit and a ssist in predicting the ne ed for catalyst cleaning, regeneratio n, or replace m ent with new catalyst.

Catal y st Te sting

Steag typically performs a series of catalyst testin g procedure s includ ing:

• Bench scale reactor testing for full elements including

▪ - SO 2 /SO 3 conversion rate,

▪ - Pressure drop ∆ p,

▪ - Initial activity K 0 ,

▪ - Actual activity K act ,

• Micro scale reactor testing for small size cat a lyst coupons,

• XRF analysis for catalyst surface an d bulk comp osition ,

• SEM analysi s for catalyst surface scans (optiona l),

• XRD analysi s for mineralogical e.g. coal

Initial Cataly st Baselin e Testing and Anal y s i s

Bench scale testing and chemical co mposition a nalysis of ne w, unused catalyst, which is necessary in order to determine the necessary baseline for all future cat a lyst management and deactivation tracking sh ould be don e to establish the initia l chemical co mposition of the catalyst before flue g a s exposure with which deactivated catalyst will be compared. During bench sca le testing the f o llowing init i a l catalyst p a rameters will be determined for the one (1) catal y st sample comprising eithe r of one ho neycomb log or one pla t e catalyst sample (the preparation of each plat e catalyst sa mple requires twelve individual plate s ) or one co rrugated cat a lyst

sam p le:

• Initial ca talyst activity K 0 ,

• Catalyst SO 2 /SO 3 conve r sion rate,



### 8• Catalyst pressure drop ∆ p,

• Chemical composition a nalysis of th e catalyst su bstrate (bulk and surface )

,

• Determination of the init ial catalyst p o tential of e a ch layer,

• Determination of the init ial DeNOx p o tential, which was insta lled in the u n it’s SCR reactor with all new, unused cat a lyst layers before initial start up of t he unit’s SC R systems.

The test results will serve as a basel ine for the fu ture development of a catalyst deacti vation tracking cha r t for the particular unit

. Additionally, the chemical composition analysis is crucia l in order to quantify the act ual uptake a nd accumulation of cata lyst poisons. The data is necessary f o r the purpose of comparison in orde r to identify the cause an d degree of catalyst deactivation

.

Fleet-wide Strateg y

Steag has f ound through the operation of our 24 SCRs that operators with two or mo re SCR systems can optimize th eir overall SCR operat ing cost by implementing a fleet wide SCR
managemen t strategy. All data gen erated for eac h of the in dividual SCR systems should be evaluated and interpret ed and form the basis fo r developing an optimum catalyst management strategy for the SCR fleet as a whole thereby optimizing operations while keeping ope rations and maintenance (O&M) costs at a minimu m.

Catal y st Re generation

Steag found that the flue gas from burning a variety of bituminous coals, a nd certain secondary fuels su ch a s bone meal, gradually deactivated the installe d catalyst due to fly ash a nd large particle ash plugging an d/or the formation of blindi ng layers on the catalyst surface. Chemical deactivation results from catalyst poisons su ch a s arsenic, p hosphorus a nd earth alkali metals, which chemically react with the catalytically ac tive ingredient s of the cata lyst, thus re ndering them ineffective.

In the early days of SCR operation, the only choice an SCR operator had was to add new catalyst and /or replace t he existing spent catalyst in order to meet the desired NO x re moval efficiency dictated by permits and regulations an d at a minimum NH 3 slip. In order to provide an economical alternative, technologie s were developed that would clean a nd restore o r iginal catalyst activity levels wi thout damaging the physi cal or stru ct ural integrity of the catalyst.

In 1997 Steag developed a catalyst cleaning an d regeneration process which has b een a major factor in red u cing the O&M costs for our own fleet of SCRs. Steag utilizes a patente d deionized (DI) water-b ased process to remove the physical materials which plug or blind the cat a lyst layers. In the event of chemical deactivation, aft e r the removal of the catalyst poison s or deactivation causes, Ste ag adds che m icals used in the origin al manufacturing of the catalyst to



### 9the regeneration process thereby restoring the catalyst it to it s original a c tivity level. Steag has cleaned and regenerated several la yers of catalyst a numbe r of times and has found that there is no chang ed in the de activation ra te between new catalyst and cleane d and/or regenerated catalyst.

However, th e economic effectiveness of catalyst regeneratio n strongly depends on t he efficiency of the regeneration process used, which in return d epends on in depth kno w ledge of the specif ic deactivation causes which bring us back to the need for using a perpetual cycle of SCR manag ement to optimize SCR o perations an d reduce O&M costs.

Fuel Testing and Chemical Anal y s is

Fuel (i.e. co al), fuel ash (i.e. coal a s h), fly ash, catalyst plug gage and/or SCR deposit samples should also be analyzed in order to provide a complete overview of the operation an d impact of the SCR an d its associa t ed equipment. A complete analysis should be p e rformed re gularly for coal, coa l ash and fly ash samples including:

• Proximate a nd ultimate laboratory analysis of th e fuel sample including f uel ash composition

, ash fusion temperature, mineral ogy (XRD-analysis), trace elements (As, halogens, etc.), water soluble com pounds (Na, K, P, etc.)

• Trace element analysis ( X RF-analysis) of the fly ash or catalyst pluggage or SCR deposit sam p les includin g determination of critical, water solu ble compounds and cat a lyst poisons such Na 2 O, K 2 O, P 2 O 5 , Ca O, Mg O, SO 3 , As, etc.

• Interpretatio n and evaluation of the r e sults on th e basis of o u r extensive data base

Steag developed a proprietary software program SPICE (S te ag P rogram for I mport C oal E valuation), which serves not only as database f o r all coals and second ary fuels we burn but also provides an accurat e estimate of the true life cycle cost e ffects of any specific fuel including its short-ter m and long-term deactivation effects on the SCR catalyst.

Conclusion

Whether developing a SCR manage ment program for a single unit or a fleet of SCRs, the SCR catalyst management strategy should include a perpet ual cycle of in spections, tuning s, testing and evaluations. The out come of these tasks sho u ld be a pla n tailored to ensuring the least overall long-term cost while providin g the maxi mum possible lifetime for t he installe d catalyst with optimal SCR syste m performance. Outage schedules, S CR operating schedule s (seasonal or year round), power demand curve s , unit capa city loading, availability of the specif ic residual DeNOx pote n tial of each SCR syste m and the fleet wide NOx reduction requirements should be taken into a ccount in or der to maxi mize the utilization of the SCR catalyst installed.



### 10References

1. Guideline fo r the Testing of DeNOx Catalytic Converters, VGB R-302 He, 2 nd revis e d vers ion

, published b y VGB Kraft w erkstechnik, Klinkestra sse 27-31, 4 5136 Essen, German y, 1 998.

2. Supplement to VGB-R3 02He 2 nd Edition - Common Best Practices for Bench Scale Testing and Chemical Analysis of SCR De NOx Catalyst ; Steag enco t ec Meßtechnik – Zentrallabor, Herne, Germany, 2003.

3. VGB Bench Scale Catalyst Testing Round Robin Results 20 05 – VGB Bereich Umweltschutz und Querschnittsaufg aben, Auswertung nach DIN 48402-42, Ausgabe 1984-05, Essen, Germany, 2005.



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