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Recent Experience with SCR Catalyst Regeneration 

Herwig Maier Ph.D. EnBW Engineering, Stuttgart Germany 

Jörn Matschke , Ph.D. EnBW Engineering, Stuttgart Germany 

1. Introduction

With over two hundred new SCR ́s that are expected to be installed and placed in 

operation on coal fired power plants in the U.S., the issues related to their efficient and 

economic operation become of primary importance. Since the chemical utilization in 

SCR systems is very close to its absolute maximum, the cost of catalyst management is 

the major component in SCR operating costs. 

Regenerating the old catalyst instead of disposing it and substituting it with a new one 

can substantially reduce the cost of operating SCR units by increasing the effective life 

of the individual catalyst layers. Catalyst suppliers and users have worked diligently over 

the years to develop reliable and economic techniques for catalyst regeneration. 

Different methods of re-processing, mechanical cleaning, heating with special gases 

and washing with regenerating solutions were suggested and tested with various 

degrees of success. Practically all known methods require removing catalyst from the 

SCR box, regenerating it outside and reinstalling it. Obviously, a regeneration process, 

which does not require catalyst removal, would be more attractive. 

 
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Figure 1: EnBW’s Heilbronn Power Station – 7 coal-fired units equipped with SCRs 

2. The ReActTM Technology

This in situ regeneration method was conceived in 1994 by EnBW, one of the largest 

utility companies in Germany, operating more than 11,000 MW of generating capacity 

including numerous large coal-fired station equipped with SCRs, 2 of which are shown in 

Figures 1 and 2. 

Figure 2: Karlsruhe RDK Power Station – 7 coal-fired units equipped with SCRs 

Overall EnBW manages over 2,000 m3 of catalyst supplied by different manufacturers 

(BASF/CERAM, KWH, MHI, Siemens) within these coal-fired stations. After eight years of 

following the standard procedure of replacing deactivated catalyst on their numerous 

SCRs, EnBW commercialized 1996 the catalyst regeneration. 

The criteria for the method are: 

- all parameters are pre tuned and optimized for each specific case in the laboratory 

- cleaning is performed within the SCR reactor with a water based solution containing 

minor amounts of non toxic additives 

- the regeneration solution is recirculated to improve the efficiency and reduce the 

amount of spent solution 
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The technology was developed, refined and extensively tested in the lab and 

successfully implemented in EnBW power plants. In the meantime it has been proven as 

a reliable technology in several plants as shown in Table 1 below. 

Table 1: ReActTM reference list 

ReActTM technology is now protected by North American and European patents and is 

commercially offered in North America by Enra, LLC. 

The regeneration process involves the in situ washing of the catalyst with a safe and 

cost effective regeneration solution and is efficient in catalyst cleaning, dissolving 

masking materials and removing some poisonous species. It involves several distinct 

steps: 

• In the first step samples are analyzed and tested to find out the reasons of 

deactivation by chemical analyses, XRD, electronic microscopy, XFA, atomic 

absorption spectroscopy and the like and to set up the parameters for the 

procedure. The residual activity is also determined as shown in Figure 3. 

• In the second step the reactivation procedure takes place in a lab scale facility and 

after that the activity is measured again to see what happened. During the test 

regeneration some parameters like pH and conductivity are measured on line to 

control the process, also samples from the suspension are analyzed. 

• If the first test results are not satisfying, the procedure is repeated with optimized 

parameters. After that the parameters for the full scale application are fixed. 

• With these optimized regeneration parameters the full scale regeneration takes 

place with the regeneration solution sprayed over the catalyst modules (Figure 4), 

 Avedorevaerket, Denmark (full scale) 

 Combined heat and power plant Heilbronn (full scale, several times) 

 Combined heat and power plant Karlsruhe (full scale, several times) 

 Power plant Walheim (full scale, several times) 

 Power plant of Altbach (full scale) 

 Power plant Aschaffenburg (test scale) 

 Power plant Weser (test scale) 

 Power plant Franken (test scale) 

 Power plant Bergkamen (test scale) 

 Combined heat and power plant Reuter West, Berlin (test scale) 

 Combined heat and power plant Rudow, Berlin (test scale) 

 Combined heat and power plant München (test scale) 

 Combined heat and power plant Schwedt (test scale) 

 Power Plant Münster (full scale) 
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collected at the bottom of the layer and recirculated (Figures 5 and 6). The 

equipment is simple, sectional and adaptable to any type of SCR plant. A team of 5 

to 7 people can regenerate over 35 cubic feet of catalyst per hour. The process runs 

at ambient temperature and moderate pressure, so energy consumption and 

danger of corrosion is negligible. Furthermore, the process has been developed to 

handle also difficult catalyst by intermitted washing or reconditioning. The 

wastewater, approximately 1 m3/m3 of catalyst reactivated, can be easily handled 

containing about 5% solid and being nothing else as the air heater or boiler washing 

water. It can be treated in the wastewater treatment plant downstream a wet FGD, 

if there is one, or be used in the wet or dry FGD as process water or be "burned" in 

the boiler via the start up fuel burners or spread on the coal or be used for ash 

moistening. If none of these options are possible, the wastewater has to be treated 

externally before discharged. 

• The final step is drying the catalyst after regeneration, which does not require much 

more time than the normal start up of the SCR reactor. 

Figure 3: EnBW’s certified catalyst testing lab – here the bench scale reactor 

But is it save to wet the catalyst? 

When using ReActTM it is, because 
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• the SCR has been cleaned before implementing ReActTM, so no ash plugging of the 

equipment should occur 

• a continuously controlled flow flushes out residuals of fly ash 

• the duration of flushing and composition of the suspension is carefully adopted to 

the catalysts need fixed previously in extensive lab tests to avoid any danger of 

damaging or chemical attack 

• after regeneration the drying process is smooth and avoids any thermal destruction 

Figure 4: Spray headers on top of the catalyst modules 
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Figure 5: Liquid collection pan below the catalyst module 
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Figure 6: Regeneration solution recirculation tank 

3. Results and Experience

So far, 13 successful full scale applications with regeneration of over 1600 m3 of catalyst 

and a lot of lab scale tests also with catalysts from US power plants have proven 

ReActTM as a powerful technology. Different types of catalysts have been regenerated 

and ReActTM was found to be equally efficient with plate type and honeycomb 

catalyst. 

The effect of ReActTM is more pronounced when the degradation of the catalyst is 

already substantial: 

• Lower catalyst activity (k/k0 << 100%) leaves more room for improvement 

• Exponential nature of deactivation process yields more additional operating time 

per percent of increased activity. 

Two parameters are most instrumental in evaluating the efficiency of regeneration 

process: 

• Gain of lost activity, which is measured as a fraction of lost activity reversed by 

regeneration. Typically this parameter is in the 35 to 70 % range as can be seen in 

Table 2. 

• Additional operating time without catalyst replacement resulting from the 

regeneration process. Typically one to three years per regeneration. 

P o wer P lant Type o f 

Furnace

Type of

cataly s t

G ain o f lo st

activit y

H e ilb ro n n D ry b o tto m H o n e y c o m b 6 7 %

W e se r S la g ta p H o n e y c o m b 3 8 %

A sc h a ffe n b u rg S la g ta p P la te ty p e 6 3 %

F ra n k e n D ry b o tto m P la te ty p e 1 7 %

W a lh e im D ry b o tto m H o n e y c o m b 3 8 %

R euter D ry bottom H oneycom b 45%

A ltb a c h D ry b o tto m H o n e y c o m b 4 5 %

K a rlsru h e D ry b o tto m H o n e y c o m b 4 4 %

B ergkam en D ry bottom H oneycom b 40%

M ünster D ry bottom H oneycom b 34%

W e se r S la g ta p P la te ty p e 2 7 %
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Table 2: Typical regeneration results using EnBW’s ReActTM process 

Both these parameters are highly site specific and can be predicted based on the lab 

regeneration of representative samples and using the historic trend of catalyst activity 

at the power plant. The achievable improvement differs for various mechanisms of 

catalyst degradation and depends on such factors as furnace type, ash composition, 

flue gas parameters and SCR reactor operating practices. It is predicted on the basis of 

the lab test results tuned from prior field experiences. 

 

The ReActTM process has some limitations: 

• Complete recovery of the initial activity (k/k0 = 100%) is not achievable, however the 

recovery of lost activity is usually high enough to yield a significant increase in 

operating time without catalysts replacement. 

• If the catalyst is mechanically at the end of its lifetime, no regeneration procedure, 

however applied, can help. 

• ReActTM results for heavily poisoned catalysts at times may be measurably less than 

normal. Recently ReActTM was applied to a plate type catalyst with unusually high 

concentrations of arsenic. As shown in Table 3, the gain of lost activity was rather 

moderate. However, with a modified ReActTM process a similar catalyst from a US 

power plant around 54% of lost activity could be recovered. 

Table 3: Arsenic removal using EnBW’s ReAct process 

Monitoring the catalyst activity before and after regeneration shows no change in the 

degradation pattern, it only brings the activity to a new higher level. So far, experiences 

have shown, that the process is repeatable several times without changing the 

degradation pattern of the SCR plant. 

4. Economics and Savings

Power 

Plant 

As in catalyst 

as %w 

Type of catalyst Gain of lost 

activity 

Heilbronn 0.01 Honeycomb 67% 

Franken 1.70 Plate type 17% 

US catalyst 1.56 Plate type 54% 
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Assuming that the price of new catalyst is about $ 6,000 per m3 honeycomb and a 

typical catalyst management and exchange strategy without ReActTM requires new 

catalyst at least every three to six years, the average annual costs will result in at least $ 

1,000 but up to $ 2,000 per m3 . 

ReActTM used as a repeatable process extends significantly the catalyst life time, at least 

it will be doubled. Consequently by applying the ReActTM technology the average 

yearly costs for catalyst will drop down to half of the above figures or normally even less. 

The example of power plant Heilbronn , Unit 7 (760 MW PC-fired), where ReActTM was 

implemented first commercially shows (Figure 7), how this technology reduces 

drastically SCR operating costs: 

• the exchange cycle of catalyst before ReActTM was about 3 years, that means every 

three years one layer had to be changed 

• since the implementation of the ReActTM process no change of catalyst has been 

necessary the past 7 years, which means savings of two exchange cycles or 2 x $ 

6,000 per m3

• during that time the ReActTM regeneration has been performed successfully 3 times 

• the value of one regeneration done is $ 4,000 per m3

Figure 7: Additional gain in catalyst life using EnBW’s ReActTM technology 

Operating time 

Catalyst 

activity Regeneration Additional 

operating time 
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With regular implementation of the ReActTM technology in 1996 the savings of the power 

plant Heilbronn Unit 7 concerning SCR operating costs exceed several million dollars till 

the end of its expected technical life time. 

Of course the life expectancy of catalyst and the time of necessary changes of layers 

depends on various parameters including: 

- coal quality 

- mode of operation 

- boiler characteristics 

- ash composition 

- ash usage or disposal method (pond, cement industry, etc.) 

Thus, the value of the ReActTM regeneration has to be determined for each specific 

case. 

5. Recommendations

To take full advantage of the potential benefits of ReActTM and to plan the optimum 

catalyst management strategy power plants should follow some simple 

recommendations: 

During the design phase 

• sufficient space around the SCR to place the regeneration equipment (10x30 ft) 

• man holes (2-3 ft diameter) to bring in the spray grid, collecting trough, and of 

course staff 

• sufficient space between catalyst layers (about 6 ft) 

• the position of soot blowers and the steel construction should be known exactly to 

adopt the construction of the regeneration equipment within the SCR duct. 

During the operating phase: 

• keep information on activity (or even a sample) of the fresh catalyst 

• provide regular activity measurements of installed catalyst samples to establish a 

degradation pattern 

• proceed with frequent measurements of ammonia in the fly ash as an indicator of 

current catalyst condition 
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• extract representative samples of catalyst in advance and arrange for their test 

regeneration 

• use the test regeneration results and the established degradation curve to make a 

conscious economic choice between regeneration and replacement of the worst 

catalyst layer. 

 

6. Conclusion

ReActTM is an excellent , proven tool to affect significantly the operational costs of a SCR 

plant. In the power plant Heilbronn (Figure 8), where the technology has been 

developed and first applied, savings of several million dollars are a severe argument in 

the deregulated European energy market. 

ReActTM is 

• simple 

- in-situ regeneration without removing the catalyst from the SCR reactor 

- minimal man-hours to accomplish regeneration during short outages 

- no special start up requirements 

• safe 

- regeneration procedure is designed for each specific case 

- no harm to catalyst or SCR reactor 

- chemicals are benign requiring no special permits 

• proven 

- many successful full layer regenerations 

- repeatable process with no change in the deactivation pattern 

- protected by North American and European patents 

• economical 

- catalyst disposal volume and cost reduced 

- significant reduction of catalyst replacement cost 

• available 

- ReActTM is commercially available in North America from Enra, LLC 

Figure 8: High-dust SCR system at 

EnBW’s Heilbronn Power 

Station unit 7 

- 760 MW, 

- bituminous coal, 

- wall fired, dry bottom 

boiler, 

- two 4 layer reactors, 
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- 825 m3 of honeycomb 

catalyst installed in 3 

layers, 

- 80% NOx reduction, 

- 2 ppm NH3 slip, 

- SCR start-up: 1986