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 

6th Annual Electric Power Conference & 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: 856-467-5256 
SCR-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 coal-fired 240 MW Logan Generating Plant 

(Figure 1) including a Selective Catalytic Reduction (SCR) system for NOx-control since 1994. 

The unit is equipped with one SCR DeNOx reactor installed in the high-dust configuration after 

the economizer outlet and before the air pre-heater inlet. Logan Generating Plant was the second 

coal fired plant in North America 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 m3. The initial catalyst fill of about 155 m3

(11⁄2 layers) of Argillon plate catalyst was designed for an initial operating period of 16,000 

hours. After that period, another half layer of Argillon plate catalyst was added thus filling up the 

second layer. The top half of the third layer was equipped with Argillon 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 the first layer was exchanged after about 60,000 

hours replacing half layer of the original Argillon plate catalyst with half layer of new Hitachi 

plate catalyst. 

Figure 1: NEGT’s 240 MW coal-fired Logan Generating Plant in Swedesboro, New Jersey 
SCR-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 deactivation causes. The results led to the conclusion 

that another catalyst exchange will be required during the scheduled outage in spring 2004. 

Based on the successful application of regenerated catalyst in NEGT’s Indiantown Generating 

Plant [2, 3, 4, 5] and the significant cost savings over buying new catalyst, Logan Generating 

Plant Co, LP decided to award a contract SCR-Tech 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 regenerated prior to the scheduled 

outage in April / May 2004 and will be installed during said outage in exchange for the bottom 

half of layer 1, which has been in operation since start-up of the Logan Generating Plant in 1994. 

This removed half layer will also be regenerated and stored for future catalyst exchange. 

Additionally, SCR-Tech was charged with optimizing SCR performance by balancing the 

ammonia injection grid (AIG) following the scheduled outage in spring 2003 in order to optimize 

the ammonia profile. Such optimization was advantageous in order to minimize ammonia slip 

and resulting frequent air heater pressure drop problems. After the AIG tuning effort the rate of 

air heater degradation slowed significantly while performance of the SCR system improved. 

AIG Tuning 

AIG tuning should be performed about once a year by balancing the ammonia injection in order 

to adjust the ammonia profile in such a way that 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 (O2-profiles, etc.). In case of the Logan 

Generating Plant’s SCR such a fixed 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 cover 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 existing 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 provided 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 sectional area than the SCR reactor itself. This fact 

doesn’t allow for a true representation 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 upstream of the air heater 

The AIG consists of 18 individually controlled injection lances each equipped with 8 nozzles. 

These 18 individual injection pipes are being supplied with gaseous ammonia and dilution air via 

2 headers with each header supplying 9 injection pipes. The dilution air flow through each 

ammonia injection pipe can be individually controlled by a butterfly valve 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 / dilution air through the 

ammonia injection pipe. 

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

over the SCR’s entire cross-sectional area after the last catalyst layer. Three NO and O2

analyzers were used in parallel for accurately determining the NO and O2 concentrations in the 

flue gas at the 24 sampling points within 30 minutes using the fixed sampling grid installed 

above the air heater inlet. The results were directly converted online into a three dimensional 

NO-concentration profile in order to allow a correct evaluation of the found NO distribution. 

The NO profile after the last catalyst layer was measured in order to ideally overlay the NH3

profile over the NOx profile for combining maximum removal efficiency with minimum NH3

slip. Subsequently, the 18 individually controlled NH3 injection pipes were adjusted in such a 

way that the NO profile after the last catalyst layer became as uniform as possible at the required 

removal efficiency level. This ensures a minimum 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 heater 
SCR-Tech #12 

5 

SCR Catalyst Regeneration Technology and SCR Management Services

MW gross), which represents the operating condition with 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 layer 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 O2-concentration of the unit of 3% O2. It must be noted 

that the normalization of all measured values to the same O2 is critical for determining whether 

the actually measured NO-value was only diluted or concentrated as a result of a locally high or 

low O2-value or actually represents a high or low local concentration. 

As can be clearly seen in Figure 4, the initial NO-profile was noticeably 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 elevating the NO-concentrations on this side while 

reducing the NO-concentrations on the other side. 
SCR-Tech #12 

6 

SCR Catalyst Regeneration Technology and SCR Management Services

Figure 4: Initial NO-profile corrected to 3% O2

Figure 5: Final NO-profile corrected to 3% O2

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

0-10
SCR-Tech #12 

7 

SCR Catalyst Regeneration Technology and SCR Management Services

Figure 5 presents the final NO profile after balancing 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 best 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% O2 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% O2 fluctuated less than +/- 10% around the average NO-value. Since the NO-values after the 

last layer constantly fluctuate with the NO-inlet concentration and such fluctuation accounts for 

about +/- 5% around an average value, any tuning resulting in an overall deviation of less than 

+/- 10 % around the average value for the entire cross-sectional area of the SCR was not only 

found to be the best achievable result for the system but can also be considered absolutely 

sufficient for trouble free SCR 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 Generating Plant opted for full regeneration of the 

existing spent half layer comprising of 448 plate catalyst elements initially installed in 1994. 

Before chemical regeneration commenced, catalyst samples were tested in a bench-scale reactor 

in order to determine the residual catalyst activity and chemical composition before regeneration. 

All tests were conducted by an independent third party lab and in full accordance with VGBR302He [1]. The spent plate type catalyst had been deactivated to less than 45% of its original 

activity over an operating time of almost 60,000 hours. In addition to accumulating catalyst 

poisons such as arsenic, sodium and potassium, etc., the catalyst had formed a strong surface 

blinding layer characterized by high concentrations of sulfates, silicates and aluminates on the 

catalyst surface. At the same time the concentration 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), sodium (Na) and potassium (K). 

Additionally, a strong surface blinding layer had formed characterized by very substantial 

accumulations of calcium oxide (CaO), silica dioxide (SiO2) and sulfur trioxide (SO3) 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 the surface before and after regeneration 

catalyst surface analysis be fore and after regeneration

0

5

10

15

20

25

30

catalyst poisons SiO2 SO3 concentration 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

catalyst poisons As CaO Na2O K2O concentration in %wt 

before regeneration

after regeneration
SCR-Tech #12 

9 

SCR Catalyst Regeneration Technology and SCR Management Services

SiO2 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 solution followed by a specially tailored ultrasonic 

treatment. The ultrasound bath also features a controlled chemical composition, pH and 

temperature, where the right combination of all 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 impregnation 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 (V2O5) plays the most important role in the activity of the catalyst. It looses 

its catalytic properties by reaction with compounds contained in the flue gas, e.g. gaseous arsenic 

(As2O3), a process commonly referred to as catalyst poisoning. Plate catalyst contains major 

quantities of molybdenum trioxide (MoO3), which is intended to act as a sacrificial element 

particularly for the reaction with gaseous arsenic, thus protecting the catalyst’s V2O5-content. 

Unfortunately, MoO3 is not only consumed by the reaction with As2O3, it also gradually 

volatilizes from the catalyst during operation. Therefore, it is of particular 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

active compounds V2O5 MoO3 concentration in %wt 

before regeneration

after regeneration
SCR-Tech #12 

10 

SCR Catalyst Regeneration Technology and SCR Management Services

a MoO3-concentration similar to the content of the new catalyst in order to ensure the same 

longevity and deactivation characteristics of the regenerated catalyst. As can be seen in Figure 8, 

the concentrations of both catalytically active compounds, V2O5 and MoO3, were fully restored 

during regeneration, thus, not only reinstating the original catalytic activity but also providing 

the regenerated catalyst with the same longevity as new catalyst. 

Figure 9: Activity of the new, spent and regenerated catalyst of NEGT’s Logan and Indiantown 

Generating Plants 

Figure 9 provides a comparison of the Logan catalyst’s original activity K0 with its activity 

before and after regeneration with the values already observed for the Indiantown catalyst during 

regeneration [4, 5]. As can be seen, the Logan catalyst had lost about 55% of its original activity 

during the 60,000 hours of operation. The activity of the regenerated catalyst was restored to 

about 106% of its original activity. Overall, the regeneration results obtained 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 SO2/SO3-conversion rate of 

only about 20% of the catalyst manufacturer’s original guarantee value and significantly less 

than the spent catalyst, thus clearly making the regenerated catalyst better than when it was new 

in 1994. With the SO2/SO3-conversion playing an increasingly important role in SCR operation 

in North America, it became mandatory to not only prevent an increase of the SO2/SO3-

conversion rate during regeneration but to ensure the lowest possible SO2/SO3 conversion rate in 

combination with the highest sensible activity after regeneration. The actual reduction of the 

SO2/SO3-conversion rate, which was proven by independent third party bench-scale testing, was 

achieved by utilizing SCR-Tech’s proprietary patented DI-water based catalyst regeneration 

Activity K

Logan Indiantown

K [m/h]

initial activtiy

of new catalyst

K0

activity before

regeneration

Kspent

activity after

regeneration

Kreg
SCR-Tech #12 

11 

SCR Catalyst Regeneration Technology and SCR Management Services

process developed for minimizing the SO2/SO3-conversion rate during regeneration. While in 

other cases where no DI-water was used for the process, the SO2/SO3-conversion rate was found 

to dramatically increase during catalyst cleaning and/or regeneration, SCR-Tech’s process is 

tailored to accomplishing both goals, namely a high activity and a low SO2/SO3-conversion rate 

simultaneously. 

Figure 10: SO2/SO3 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 SO2/SO3-conversion rate of the regenerated catalyst was proven to be 

not only significantly less than the SO2/SO3-conversion rate guarantee for 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 results obtained showed that: 

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

• The SO2/SO3-conversion rate can be lowered significantly during catalyst regeneration 

despite reinstating the full original catalytic activity. 

SO2/SO3-Conversion Rate

KSO2/SO3 [%]

new catalyst

conversion

rate guarantee

conversion

rate before

regeneration

conversion

rate after

regeneration
SCR-Tech #12 

12 

SCR Catalyst Regeneration Technology and SCR Management Services

Furthermore based on the Indiantown experience, the deactivation of regenerated and new 

catalyst is expected to be essentially the same. Results presented earlier [4, 5] and shown here in 

Figure 11 provided a direct comparison of regenerated catalyst with new catalyst 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 benefits as new catalyst, however, for only about 

half the cost. The fact that no spent catalyst needs to be disposed of leads to another intangible 

benefit in form of the avoidance of any potential hazardous waste disposal issues as well as a 

greatly reduced pending liabilities for the operator associated with 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 Logan and Indiantown 

Generating Plants on the merits of catalyst regeneration. For the Logan catalyst the regeneration 

success was even slightly better than for the Indiantown catalyst, particularly with respect to the 

SO2/SO3-conversion rate. The regenerated Logan catalyst will go into operation in May 2004 and 

as already proven at the Indiantown Generating Plant, it is anticipated that the operation of the 

regenerated catalyst will be uneventful and the deactivation rate will be the same as new catalyst. 

deactivation new versus regenerated catalyst

0 1000 2000 3000 4000 5000 6000 7000

operating hours

activity K [m/h] 

new catalyst

regenerated catalyst
SCR-Tech #12 

13 

SCR Catalyst Regeneration Technology and SCR Management Services

References 

1. VGB Technical Association of Large Power Plant Operators, VBG Guideline, VBGR302He, Guideline for the Testing of DENOX Catalysts; VGB-Kraftwerkstechnik 

GmbH, Essen, Germany, 2nd revised edition 1998. 

2. Bullock, D., H. Hartenstein, “O&M Cost Reduction of a Coal-Fired US Merchant Plant 

Through an Optimized SCR Management Strategy Involving Catalyst Regeneration”, 

presented at the DOE Conference on SCR and SNCR Reduction for NOx Control, 

Pittsburgh, Pa., May 2002. 

3. Bullock, D., H. Hartenstein, “O&M Cost Reduction of a Coal-Fired US Merchant Plant 

Through an Optimized SCR Management Strategy Involving Catalyst Regeneration – 

Strategy Update Summer 2003”, presented at the Stack Emissions Symposium in 

Clearwater Beach, Fl., July 2003 

4. Bullock, D., H. Hartenstein, “Full-Scale Catalyst Regeneration Experience 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