Ingenieure GmbH 

In Situ Catalyst RegenerationA Cost Saving Technology for SCR Operators

Dr. Herwig Maier 

EnBW Ingenieure GmbH 

Kriegbergstrasse 11, Stuttgart, Germany D-70174 

Phone: +-49-711-128-29-49 

Fax: +-49-711-128-20-21 

E-mail: herwig.maier@enbw.com 

Dr. Werner Goetz 

EnBW Ingenieure GmbH 

Kriegbergstrasse 11, Stuttgart, Germany D-70174 

Phone: +-49-0711-128-2318 

Fax: +-49-0711-128-2318 

E-mail: werner.goetz@enbw.com 

Power-Gen International 2001 

Las Vegas, Nevada 

December 2001 
 

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Introduction 

SCR systems for efficient NOx reduction are now commonly accepted by U.S. utilities. 

Operating expenses for such units are mostly driven by the cost of catalyst maintenance. The 

continued effect of plugging, masking and poisoning, particularly in high dust applications, 

reduces the activity of catalyst below the design value. This loss of activity is detected either 

by an increase of ammonia in fly ash or flue gas. To compensate this decline in activity it has 

been a standard procedure to add a new layer of catalyst or to replace the most deactivated 

one. 

Regenerating the old catalyst instead of its replacement can significantly reduce the cost of 

operating SCR units by increasing the effective life of the catalyst. A unique technology for 

in-situ catalyst regeneration (without removing catalyst from the SCR reactor) was developed 

and patented by EnBW, one of the largest utility companies in Germany. During the last six 

years regeneration efficiency has been successfully demonstrated by EnBW for different types 

of catalysts (honeycomb and plate) installed at power plants burning various coals. 

The technology is protected and in the U.S. known by the trade mark ReActTM. 

The ReActTM Technology 

The in-situ regeneration has been developed since 1994 by EnBW, a utility company which 

operates in total more than 11,000 MW of generating capacity. Over 2000 m3

 of catalysts 

from different suppliers are installed in more than 2000 MW bituminous coal fired power 

plants since 1986. 

After two years of research and development and eight years of following the standard 

procedure of replacing deactivated catalysts on their numerous SCRs, EnBW commercialized 

1996 the catalyst regeneration technology. 

A regeneration method had to fulfill following demands: 

• Simple, economical and repeatable 

• Performance within the SCR box with no removing of the modules 

• Usage of a water-based regeneration solution 

• Minor amounts of non-toxic additives which needs no special 

allowances 

• Circulation of the regeneration solution to improve the efficiency and 

minimize the waste water amount 

• Minimum effort of time and man power (ideally performance within 

short outages) 

Facing these goals 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. 
 

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The ReActTM technology is protected by U.S. and European patents and commercially offered 

in the U.S. The regeneration process involves the in-situ washing of the catalyst with a safe 

and economic regeneration solution and is efficient in catalyst cleaning, dissolving masking 

materials and removing some poisonous species. The procedure involves following steps: 

• Received samples are analyzed (both surface and bulk material) by means of X-ray 

diffraction, electronic microscopy, atomic absorption spectroscopy and the like to 

determine the mechanisms of degradation. 

• The residual activity is measured. 

• The results are compared with the data base of our numerous experiences. 

• The sample is regenerated with the pre-tuned parameters deducted from the analyses in 

our lab scale facility. During that procedure process relevant parameters are measured 

online. 

• After the lab scale regeneration, the activity of the regenerated catalyst and the residual 

suspension are analyzed to verify the regeneration efficiency. 

• The parameters for a full scale application can be fixed. 

• The full-scale regeneration takes place with the regeneration solution sprayed over the 

catalyst modules, collected at the bottom of the layer and circulated. 

• The equipment is simple, section 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. 

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

than the normal start-up of the SCR reactor. 

The waste water, approximately 1 m3

/m3 of catalyst reactivated, can be easily handled 

containing about 5% solids and being nothing else than the air heater or boiler washing water. 

It can be treated in the waste water treatment plant downstream FGD, if there is one, or be 

used in the FGD as process water or be "burned" in the boiler via the start up fuel burners or 

be used for ash moistening. If none of these options is available, the waste water has to be 

treated externally. 

Results and Experiences 
 

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So far, 14 successful full scale applications with regeneration of over 1700 m3 of catalyst and 

numerous lab scale tests even with catalysts from US power plants have proven ReActTM as a 

powerful and reliable technology. Different types of catalysts have been regenerated and 

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

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. Even heavily Arsenic 

poisoned catalysts from U.S. power plants have been regenerated with incredible good 

success (27 to 36%) by modifying slightly the technology without giving up the 

philosophy of a simple, in situ procedure. 

• Te regeneration prolongs the additional operation time without replacing a catalyst layer 

and shifts necessary investments significantly. 

 

Both these parameters, gain of lost activity and additional operating time are highly site 

specific and can be predicted based on the lab scale tests 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. 

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, 

whatsoever applied, can help. 

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 which means, that the 

process is repeatable several times without changing the performance of the SCR plant. 

Economics and Savings 
 

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Normally after an operating time of 3 to 5 years exhausted catalysts have to be renewed and 

because the degradation occurs to all layers, the replacement procedure will then be necessary 

approximately every three years. 

Assuming a price for new catalyst of actually about $ 5,500/m3 escalating moderately up to 

$7,000/m3 within nine years with a depreciation of 9 years and interest on capital of 8%, the 

table below shows the cost development of a SCR plant within 11 years. 

Year Replacement Costs/m3 Costs/Year m3 Cumulated Costs 

x 1st $ 5,500 $ 880 $ 880 

x+1 - $ 0 $ 880 $ 1,760 

x+2 - $ 0 $ 880 $ 2,640 

x+3 2nd $ 6,000 $ 1,840 $ 4,480 

x+4 - $ 0 $ 1,840 $ 6,320 

x+5 - $ 0 $ 1,840 $ 8,160 

x+6 3rd $ 6,500 $ 2,880 $ 11,040 

x+7 - $ 0 $ 2,880 $ 13,920 

x+8 - $ 0 $ 2,880 $ 16,800 

x+9 1st $ 7,000 $ 3,120 $ 19,920 

x+10 - $ 0 $ 3,120 $ 23,040 

x+11 - $ 0 $ 3,120 $ 26,160 

Using the ReActTM technology our experience has proven that within the considered period of 

11 years maximum one replacement would be necessary. A regeneration every two years can 

overcome the catalyst degradation and will avoid investment costs of about $20,000/m3. 

Focusing on a typical 180 m3 layer these savings will sum up to 3.6 million (!) dollars in total 

or more than $ 330,000 a year. 

Year Regen./ 

Replace. 

Costs/m3 Costs/m3 Cumulated 

costs 

Savings/Year m3 Cumulated 

Savings/m3 

x reg. 1st $ 0 $ 0 $ 0 $ 880 $ 880 

x+1 $ 0 $ 0 $ 0 $ 880 $ 1,760 

x+2 reg. 2nd $ 0 $ 0 $ 0 $ 880 $ 2,640 

x+3 $ 0 $ 0 $ 0 $ 1,840 $ 4,480 

x+4 reg. 3rd $ 0 $ 0 $ 0 $ 1,840 $ 6,320 

x+5 $ 0 $ 0 $ 0 $ 1,840 $ 8,160 

x+6 repl. 1st $ 6,500 $ 1,040 $ 1,040 $ 1,840 $ 10,000 

x+7 $ 0 $ 1,040 $ 2,080 $ 1,8 40 $ 11,840 

x+8 reg. 2nd $ 0 $ 1,040 $ 3,120 $ 1,840 $ 13,680 

x+9 $ 0 $ 1,040 $ 4,160 $ 2,080 $ 15,760 

x+10 reg. 3rd $ 0 $ 1,040 $ 5,200 $ 2,080 $ 17,840 
 

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x+11 $ 0 $ 1,040 $ 6,240 $ 2,080 $ 19,920 

For example in the EnBW Heilbronn power station Unit 7 (760 MW, bituminous coal fired 

with high dust SCR), where ReActTM has been regularly implemented in 1996, the savings till 

the end of its technical life have been forecasted to be million of dollars, which is a severe 

argument in the deregulated European energy market. 

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

on various parameters like 

• Coal quality 

• Mode of operation 

• Boiler characteristics 

• Ash composition 

• Ash usage (pond, cement industry) 

Therefore, the effectiveness of the ReActTM regeneration has to be determined for each 

specific case. 

Recommendations 

The optimal usage of ReActTM and the planning of the most reasonable catalyst management 

strategy set forth: 

• Sufficient space around the SCR duct 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). 

• Exact knowledge of soot blowers position and the steel construction to adopt 

the construction of the regeneration equipment within the SCR duct. 

• Information on activity (or even a sample) of the fresh catalyst. 

• Regular activity measurements of installed catalyst samples to establish a 

degradation pattern. 

• Frequent measurements of ammonia in the fly ash as an indicator of current 

catalyst condition. 

• Availability of representative samples of catalyst for test regeneration. 

The test regeneration results and the established degradation curve can be used to make a 

prudent economic choice between regeneration and replacement. 

Conclusion 
 

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

plant. In the power plant Heilbronn, 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 box 

- 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 box 

- Chemicals are benign requiring no special permits 

• Proven 

- Many successful full layer applications 

- Repeatable process with no change in the deactivation pattern 

- Protected by U.S. and European patents 

• Economical 

- Catalyst disposal volume and cost reduced 

- Significant reduction of catalyst replacement cost 

• Available 

- ReActTM is commercially available in the U.S.