SCR-Tech #12 SCR Catalyst Regeneration Technology and SCR Management Services



## O&M Cost Savings Through 

# SCR Management and Catalyst Regeneration for the Logan Generating Plant

6 th 

### Annual Electric Power Conf erence & Exhibition 2004 Baltimore, Maryland March 30 – April 1, 2004 Hans-Ulrich Hartenstein

SCR-Tech LLC 11701 Mt. Holly Road Charlotte, N.C. 28214

E-Mail: h.hartenstein@scr-tech.us

Phone: 704-827-8933

Fax: 704-827-8935 Thomas W. Yurkanin, P.E. National Energy & Gas Transmission National Energy Power Company LLC Logan Generating Plant

76 Route 130 Swedesboro, New Jersey 08085-9300

E-Mail: tom.yurkanin@negt.com

Phone: 856-467-2128 Ext. 16

Fax: 856-467-5256SCR-Tech #12 2 SCR Catalyst Regeneration Technology and SCR Management Services



### Introduction

National Energy Gas & Transmission (NEGT), Inc. ’s wholly owned subsidiary National Energy Power Company (NEPC) LLC has operated the co al-fired 240 MW Logan Generating Plant ( Figure 1 ) including a Selective Catalytic Reduction (SCR) system for NO

x -control since 1994. The unit is equipped with one SCR DeNOx reactor installed in the high-du st configuration after

the economizer outlet and before th e air pre-heater inlet. Logan Generating Plant was the second coal fired plant in North Ameri ca to be equipped with a high- dust SCR system. The SCR reactor is currently equipped with two layers of Argillon (formerly Siemens) plate catalyst and 1 layer of Hitachi plate catalyst totalling a volume of about 310 m 3 . The initial catalys t fill of about 155 m 3
(11⁄2 layers) of Argillon plate catalyst was designed for an initial operating period of 16,000 hours. After that period, another ha lf layer of Argillon plate catalyst was added thus filling up the second layer. The top half of the third layer was equipped with Argill on plate catalyst after almost 25,000 operating hours. Hitachi plate catalyst was installed in the last half layer after about 44,000 operating hours. The top half of th e first layer was exch anged after about 60,000 hours replacing half layer of the original Argillon plate catalyst w ith half layer of new Hitachi plate catalyst.

Figure 1: NEGT’s 240 MW coal-fired Logan Gene rating Plant in Swedesboro, New JerseySCR-Tech #12 3 SCR Catalyst Regeneration Technology and SCR Management Services

During an SCR reactor inspection in March 2003, a SCR inspection was performed identifying design deficiencies of the installed SCR system. While these deficiencies were being addressed catalyst samples were also extracted from each of the top half of each of the three layers in the SCR reactor. All three catalyst samples were tested in a bench-scale reactor to determine several characteristic properties of the catalyst material following the German international SCR DeNOx catalyst testing guideline VGB R- 302He [1]. Extensive detailed chemical analysis was also performed in order to determine the catalyst deactiv ation causes. The results led to the conclusion that another catalyst exchange will be require d during the scheduled outage in spring 2004.

Based on the successful applicati on of regenerated catalyst in NEGT’s Indiantown Generating Plant [2, 3, 4, 5] and the significant cost sa vings over buying new catal yst, Logan Generating Plant Co, LP decided to award a contract SCR-T ech LLC of Charlotte, N.C. for the regeneration of the half layer of plate catalyst, which was removed after 60,000 operating hours and since then

stored in sea containers on site . The catalyst was successfully re generated prior to the scheduled outage in April / May 2004 and w ill be installed during said out age in exchange for the bottom half of layer 1, which has been in operation si nce start-up of the Logan Generating Plant in 1994. This removed half layer will also be regenera ted and stored for future catalyst exchange.

Additionally, SCR-Tech was charged with op timizing SCR performance by balancing the ammonia injection grid (AIG) following the schedul ed outage in spring 2003 in order to optimize the ammonia profile. Such optimization was adva ntageous in order to minimize ammonia slip and resulting frequent air heater pressure drop problems. After th e AIG tuning effort the rate of air heater degradation slowed significantly wh ile performance of the SCR system improved.



### AIG Tuning

AIG tuning should be performed about once a year by balancing the ammoni a injection in order to adjust the ammonia profile in such a way th at it resembles the NOx-profile entering the SCR reactor as closely as possible. Typically, a fixed installed sampling grid after the last catalyst layer is used for AIG tuning as well as for other purposes (O 2 -profiles, etc.). In case of the Logan Generating Plant’s SCR such a fixe d installed sampling grid after the last catalyst layer is not available. However, a sampling grid consisting of a total of 24 sampling points is located between the last catalyst layer and the air heater as illustrated in Figure 2 . The disadvantage of the installed sampling grid is that it doesn’t cove r the full cross sectional area of the SCR reactor after the last catalyst layer and therefore doesn’t provide a true representation of the NOx profile at the outlet of the SCR. Furthermore, the exis ting sampling grid doesn’t fully align with the 18 sections independently controlled by the 18 AIG tuning valves shown in Figure 3

.

As can be also seen in Figure 3 , these 24 sampling points are pr ovided through 3 probes at each of the 8 sampling ports. Unfortunately, the sampling grid is installed in the duct upstream the air heater, which is significantly smaller in cross sect ional area than the SCR reactor itself. This fact doesn’t allow for a true represen tation of any profile right after the last catalyst layer.SCR-Tech #12 4 SCR Catalyst Regeneration Technology and SCR Management Services

Figure 2: Installed sampling grid ups tream of the air heater

The AIG consists of 18 individually controlled in jection lances each equipped with 8 nozzles. These 18 individual injection pipes are being supp lied with gaseous ammonia and dilution air via 2 headers with each header supplying 9 injec tion pipes. The dilution air flow through each ammonia injection pipe can be individually co ntrolled by a butterfly va lve featuring a manual handle. A pressure gauge indicates the differential pressure across an orifice, which in return is

used as an indicator for the volume flow rate of gaseous ammonia / d ilution air through the ammonia injection pipe.

Tuning of the ammonia injection grid was accomplis hed by quasi- simultaneous flue gas analysis

over the SCR’s entire cross-sectional area af ter the last catalyst layer. Three NO and O 2 analyzers were used in parallel fo r accurately determining the NO and O 2 concentrations in the flue gas at the 24 sampling points within 30 mi nutes using the fixed sampling grid installed

above the air heater inlet. The results were di rectly converted online into a three dimensional NO-concentration profile in order to allow a co rrect evaluation of the found NO distribution.

The NO profile after the last catalyst layer was measured in order to ideally overlay the NH 3 profile over the NOx profile for combining ma ximum removal efficiency with minimum NH 3 slip. Subsequently, the 18 individually controlled NH 3 injection pipes were adjusted in such a way that the NO profile after the last catalyst la yer became as uniform as possible at the required removal efficiency level. This ensures a mini mum ammonia slip at the required NOx removal efficiency during full load operation of the unit. All AIG tuning was being done at full load (240 installed sampling grid plane

port 1 2 3 4 5 6 7 8 SCR reactor

last catalyst layer

duct to air heaterSCR-Tech #12 5 SCR Catalyst Regeneration Technology and SCR Management Services

MW gross), which represents th e operating condition wi th the highest NOx mass flow rate, thus requiring the highest DeNOx potential for keeping the unit in compliance

Figure 3: 18 AIG injection piping and tuning valves (left) and fixed installed sampling grid between the last catalyst laye r and the air heater (right)

The tuning efforts were started by determining a NO-profile after the last catalyst layer. This initial NO-profile is presented in Figure 4 . All NO-values used to build this initial NO-profile were corrected to the average operating O 2 -concentration of the unit of 3% O 2 . It must be noted

that the normalization of all measured values to the same O 2 is critical for determining whether the actually measured NO-value was only diluted or concentrated as a resu lt of a locally high or

low O 2 -value or actually represents a high or low local concentration.

As can be clearly seen in Figure 4 , the initial NO-profile was no ticeably skewed to one side, where overdosing of ammonia on this side led to a sharp drop in the NO-concentration. Thus, the tuning efforts were directed towards eleva ting the NO-concentrations on this side while reducing the NO-concentrati ons on the other side.SCR-Tech #12 6 SCR Catalyst Regeneration Technology and SCR Management Services

Figure 4 : Initial NO-profile corrected to 3% O 2

Figure 5: Final NO-profile co rrected to 3% O 2 A B C
D E F
G

H 1 2 3 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 150-160

140-150

130-140

120-130

110-120

100-110

90-100

80-90

70-80

60-70

50-60

40-50

30-40

20-30

10-20

0-10 A B C
D E
F
G
H 1 2 3 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 150-160

140-150

130-140

120-130

110-120

100-110

90-100

80-90

70-80

60-70

50-60

40-50

30-40

20-30

10-20

0-10SCR-Tech #12 7 SCR Catalyst Regeneration Technology and SCR Management Services

Figure 5 presents the final NO profile after balanc ing the AIG during full load operation of the unit. For the purpose of comparison, both graphs presented in Figures 4 and 5 are plotted on the

exact same scale.

The success of the AIG tuning effort can be be st quantified by comparing the spread of

corrected NO-values before and after AIG tuning. In both cases that same average NOconcentration after the last catalyst layer was measured. However, before AIG tuning the actual

measured NO-values corrected to 3% O 2 were distributed over a range of 30% to 150% below and above the average NO-value. After AIG tuning the actual measured NO-values corrected to

3% O 2 fluctuated less than +/- 10% around the aver age NO-value. Since the NO-values after the last layer constantly fl uctuate with the NO-inlet concentration and such fluctuation accounts for about +/- 5% around an average value, any tuning re sulting in an overall deviation of less than +/- 10 % around the average value for the entire cross-sectiona l area of the SCR was not only found to be the best achievable result for the sy stem but can also be considered absolutely

sufficient for trouble free S CR and air heater operation.



### Full-Scale Catalyst Regeneration

Catalyst testing and analysis revealed that the catalyst would most likely need to be exchanged again in spring 2004. Therefore, Logan Generati ng Plant opted for full regeneration of the existing spent half layer comprising of 448 plat e catalyst elements initially installed in 1994. Before chemical regeneration commenced, catalyst samples were tested in a bench-scale reactor

in order to determine the residua l catalyst activity and chemical composition before regeneration. All tests were conducted by an independent thir d party lab and in full accordance with VGBR302He [1]. The spent plate type catalyst had been deact ivated to less than 45% of its original activity over an operating time of almost 60,000 hour s. In addition to accumulating catalyst poisons such as arsenic, sodium and potassium, etc., the catalyst had formed a strong surface blinding layer characterized by hi gh concentrations of sulfates, silicates and aluminates on the catalyst surface. At the same time the concentr ation of vanadium and particularly molybdenum had greatly diminished.

The chemical analysis shown in Figures 6 and 7 indicates that the loss of activity was mainly caused by the uptake of significant quantities of arsenic (As), sodi um (Na) and potassium (K). Additionally, a strong surface blinding layer ha d formed characterized by very substantial accumulations of calcium oxide (CaO), silica dioxide (SiO 2 ) and sulfur trioxide (SO 3 ) on the catalyst surface.

During regeneration, the surface blinding, layer as well as the catalyst, poisons were removed most effectively. As can be seen in Figures 6 and 7 , more than 90% of the arsenic, sodium and potassium were chemically removed during regeneration.SCR-Tech #12 8 SCR Catalyst Regeneration Technology and SCR Management Services

Figure 6: Concentration of the main catalyst poisons before and after regeneration

Figure 7: Compounds indicating a blinding layer on th e surface before and after regeneration catalyst surface analysis be fore and after regeneration

0 5 10 15 20 25 30

SiO2 SO3 catalyst poisonsconcentration in %wt before regeneration
after regeneration catalyst surface analysis before and after regeneration

0 0.5 1 1.5

2 2.5 3 3.5

As CaO Na2O K2O catalyst poisonsconcentration in %wt 

### before regeneration

after regenerationSCR-Tech #12 9 SCR Catalyst Regeneration Technology and SCR Management Services

SiO 2 as the most prominent constituent of fly ash and an indicator of surface blinding layer was also removed with an effectiveness of greater than 90%. This very successful and complete removal of the most severe catalyst poisons was accomplished by extensive soaking and washing in a proprietary water-based chemical soluti on followed by a specially tailored ultrasonic

treatment. The ultrasound bath also features a controlled chemical composition, pH and temperature, where the right combination of a ll of these factors is most essential for the successful removal of the catalyst poisons. This chemical treatment laid the foundation for the restoration of the catalytic activity by impre gnation of the catalyst with the compounds lost through deactivation. Figure 8 shows the content of these compounds before and after regeneration.

Figure 8: Catalytically activity compounds before and after regeneration

Vanadium pentoxide (V 2 O 5 ) plays the most important role in th e activity of the catalyst. It looses its catalytic properties by reacti on with compounds contained in the flue gas, e.g. gaseous arsenic (As 2 O 3 ), a process commonly referred to as cataly st poisoning. Plate cata lyst contains major quantities of molybdenum trioxide (MoO 3 ), which is intended to act as a sacrificial element particularly for the reaction with gaseous arsenic, thus protecting the catalyst’s V 2 O 5 -content. Unfortunately, MoO 3 is not only consumed by the reaction with As 2 O 3 , it also gradually volatilizes from the catalyst during op eration. Therefore, it is of pa rticular importance to reinstate 

### active ingredients before and after regeneration

0 0.5

1 1.5

2 2.5

3 3.5

4 4.5

5



### V2O5 MoO3 active compoundsconcentration in %wt 

### before regeneration

after regenerationSCR-Tech #12 10 SCR Catalyst Regeneration Technology and SCR Management Services

a MoO 3 -concentration similar to the content of the new catalyst in order to ensure the same longevity and deactivation characteristics of th e regenerated catalyst. As can be seen in Figure 8

, the concentrations of both cat alytically active compounds, V 2 O 5 and MoO 3 , were fully restored during regeneration, thus, not only reinstating the origin al catalytic activity but also providing the regenerated catalyst with the same longevity as new catalyst.

Figure 9 : Activity of the new, spent and regenerate d catalyst of NEGT’s Logan and Indiantown Generating Plants

Figure 9 provides a comparison of the Loga n catalyst’s original activity K 0 with its activity before and after regeneration with the values al ready observed for the Indiantown catalyst during regeneration [4, 5]. As can be s een, the Logan catalyst had lost a bout 55% of its or iginal activity during the 60,000 hours of operation. The activity of the regenera ted catalyst was restored to about 106% of its original activity. Overall, th e regeneration results ob tained for the Logan catalyst confirmed the regeneration results found for the Indiantown catalyst earlier [4, 5].

At the same time, the fully regenerated Logan catalyst exposed a SO 2 /SO 3 -conversion rate of only about 20% of the catalyst manufacturer’s original guarantee value and significantly less than the spent catalyst, thus cl early making the regenerated cataly st better than when it was new

in 1994. With the SO 2 /SO 3 -conversion playing an increasingly important role in SCR operation in North America, it became mandatory to not only prevent an increase of the SO 2 /SO 3 - conversion rate during regeneration bu t to ensure the lowest possible SO 2 /SO 3 conversion rate in combination with the highest sensible activity after regeneration. The actual reduction of the

SO 2 /SO 3 -conversion rate, which was proven by independe nt third party bench-scale testing, was achieved by utilizing SCR-Tech’s proprietary pa tented DI-water based catalyst regeneration 

### Activity K

Logan IndiantownK [m/h] initial activtiy of new catalyst

K0

activity before regeneration Kspent

activity after regeneration KregSCR-Tech #12 11 SCR Catalyst Regeneration Technology and SCR Management Services

process developed for minimizing the SO 2 /SO 3 -conversion rate during regeneration. While in other cases where no DI-water was used for the process, the SO 2 /SO 3 -conversion rate was found to dramatically increase duri ng catalyst cleaning and/or rege neration, SCR-Tech’s process is tailored to accomplishing both goals, namely a high activity and a low SO 2 /SO 3 -conversion rate simultaneously.

Figure 10 : SO 2 /SO 3 Conversion rate guarantee for new catalyst, before and after regeneration

This process was used for regenerating the Logan catalyst. As illustrated in Figure 10 , the results are convincing, since the SO 2 /SO 3 -conversion rate of the regenera ted catalyst was proven to be not only significantly less than the SO 2 /SO 3 -conversion rate guarantee fo r the new catalyst, even though the catalyst’s activity was fully reinstalled, but also substantially less than the before regeneration.



### Conclusions

Taking full advantage of catalyst regeneration allows for the Logan Generating Plant to generate substantial overall operating cost reductions for the SCR system operation by largely avoiding the purchase of replacement catalyst. Confirming the experience gained by NEGT’s Indiantown Generating Plant [4, 5] the resu lts obtained showed that:

• The activity of regenerated catalyst is at least the sa me as of new catalyst.

• The SO 2 /SO 3 -conversion rate can be lowered signif icantly during catal yst regeneration despite reinstating the full original catalytic activity. 

### SO 2 

### /SO 3 

### -Conversion RateKSO2/SO3[%] new catalyst

conversion rate guarantee

conversion

rate before regeneration

conversion

rate after regenerationSCR-Tech #12 12 SCR Catalyst Regeneration Technology and SCR Management Services

Furthermore based on the Indiantown experien ce, the deactivation of regenerated and new catalyst is expected to be essentially the same. Re sults presented earlier [4, 5] and shown here in Figure 11 provided a direct comparison of regenerate d catalyst with new ca talyst of the same make, in the same layer, and the same SCR reactor.

Figure 11 : Deactivation of new and regenerated catalyst under same operating conditions

Thus, regenerated catalyst provides the same bene fits as new catalyst, however, for only about half the cost. The fact that no spent catalyst need s to be disposed of leads to another intangible benefit in form of the avoidance of any potenti al hazardous waste disposal issues as well as a greatly reduced pending liab ilities for the operator associated w ith the potential disposal of spent SCR catalyst as hazardous waste.

The combination of all the tangible and intangible benefits of catalyst regeneration combined with the successful operational experience with regenerated catalyst at the Indiantown Generating Plant fully convinced NEPC as operator of both the L ogan and Indiantown Generating Plants on the merits of catalyst regeneration. For the Logan catalyst the regeneration success was even slightly better than for the Indian town catalyst, particularly with respect to the

SO 2 /SO 3 -conversion rate. The regenerated Logan catal yst will go into operation in May 2004 and as already proven at the Indiantown Generating Plant, it is anticip ated that the operation of the regenerated catalyst will be uneventful and the deactiv ation rate will be the same as new catalyst. 

### deactivation new versus regenerated catalyst

0 1000 2000 3000 4000 5000 6000 7000
operating hoursactivity K [m/h]



### new catalyst
regenerated catalystSCR-Tech #12 13 SCR Catalyst Regeneration Technology and SCR Management Services



### References

1. VGB Technical Association of Large Powe r Plant Operators, VBG Guideline, VBGR302He, Guideline for the Testing of DENOX Catalysts ; VGB-Kraftwerkstechnik GmbH, Essen, Germany, 2 nd revised edition 1998.

2. Bullock, D., H. Hartenstein, “O&M Cost Reduc tion of a Coal-Fired US Merchant Plant Through an Optimized SCR Management Stra tegy Involving Cataly st Regeneration”, presented at the DOE Conference on S CR and SNCR Reduction for NOx Control, Pittsburgh, Pa., May 2002.

3. Bullock, D., H. Hartenstein, “O&M Cost Reduc tion of a Coal-Fired US Merchant Plant Through an Optimized SCR Management Stra tegy Involving Cataly st Regeneration – Strategy Update Summer 2003”, presented at the Stack Emissions Symposium in Clearwater Beach, Fl., July 2003

4. Bullock, D., H. Hartenstein, “Full-Scale Cataly st Regeneration Expe rience At The CoalFired Indiantown Generating Plant”, at the DOE Conference on SCR and SNCR Reduction for NOx Control, Pittsburgh, Pa., October 2003.

5. Bullock, D., “Catalyst Regeneration Experience Indiantown Generating Plant”, presented at the 2004 NOx Round Table & Expo Pollution Users Group Meeting in Akron, Oh, January 2004