SCR Catalyst Regeneration Technology and SCR Management Services 

SCR-Tech #04 

Catalyst Regeneration – 

An Integral Part of Proper Catalyst Management 

 

Hans-Ulrich Hartenstein 

SCR-Tech LLC 

11701 Mt. Holly Road 

Charlotte, North Carolina 28214 

Phone: 704-827-8933 

Fax: 704-827-8935 

E-mail: H.Hartenstein@SCR-Tech.US 

Dr.-Prof. Heinz Gutberlet 

E.ON Engineering GmbH 

Bergmannsglückstrasse, 41-43 

Gelsenkirchen, Germany D-45896 

Phone: +49-209-601-5042 

Fax: +49-209-601-8090 

E-mail: Heinz.Gutberlet@eon-energie.com 

The 2001 EPRI Workshop on Selective Catalytic Reduction

Baltimore Marriott Waterfront Hotel 

Baltimore Maryland, 

November 13-15, 2001
SCR Catalyst Regeneration Technology and SCR Management Services 

SCR-Tech #04 

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Abstract

Large numbers of SCR DeNOx systems are currently being retrofitted to coal-fired power plants 

for the removal of nitrous oxides, an important precursor to the formation of secondary ozone. 

During combustion, however, trace elements contained in the coal such as sodium, potassium, 

phosphorus, and arsenic are released into the flue gas, which gradually deactivate the SCR 

catalyst. This is known as “catalyst poisoning”. Additionally, flyash plugging and the formation 

of blinding layers can restrict access of the flue gas to the catalyst’s active surface. All these 

processes combine to produce a phenomenon commonly known as catalyst deactivation, which 

describes the gradual decrease in catalytic activity of the SCR catalyst. The corresponding 

undesirable decrease in NOx removal and/or increase in ammonia slip needs to be mitigated in 

one of three possible ways in order to maintain the desired NOx removal efficiency of the SCR 

system at a minimum ammonia slip, namely: 

• The addition of more new SCR catalyst, which can only be done as long as the SCR 

reactor still provides unoccupied spare layers. This is, therefore, a viable option only 

initially and until the SCR reactor is filled up. 

• The replacement of deactivated SCR catalyst by new SCR catalyst, which used to be the 

most common and only viable long-term option. 

• The regeneration of existing SCR catalyst, which is the only known and proven 

alternative to SCR catalyst replacement. 

The operation of SCR DeNOx systems is clearly a significant cost factor in the overall O&M 

budget of a coal-fired power plant. By far, the largest portion of the O&M budget associated 

with operating a SCR DeNOx system is consumed by frequent catalyst replacement. 

Unfortunately, the SCR DeNOx system is a non productive part of the power plant, which means 

it doesn’t add anything to the ultimate goal of power production except cost and a drop in net 

generating efficiency. Therefore, it is of prime interest to an operator of a coal-fired power plant 

to minimize the O&M cost of any kind of mandatory environmental control equipment of a 

“parasitic” nature with respect to power generation, of which a SCR DeNOx system is a perfect 

example. 

However, the SCR DeNOx system and especially the SCR catalyst employed represent a very 

substantial and valuable asset within the power plant. In order to protect this costly asset SCR 

catalyst, it is highly advantageous to minimize deactivation and other effects harmful to the 

performance of the SCR catalyst. The only feasible way of achieving this goal is to gain detailed 

knowledge of the SCR catalyst by ensuring that its deactivation is being closely monitored and 

potential deactivation causes are reduced to an inevitable minimum to maximize the useful life of 

the catalyst. 
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SCR-Tech #04 

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Catalyst Management 

The procedure employed in order to maximize the utilization of the asset SCR catalyst while 

protecting this asset to the highest economically feasible degree is known as catalyst 

management. The procedural approach is rather similar to the management of the nuclear fuel 

elements within a nuclear reactor. Thus, proper catalyst management, as presented in Figure 1, 

includes numerous activities, which must be repeated continuously throughout the operation of 

the SCR reactor. Tracking of the deactivation and performance of the catalyst must be 

accompanied by frequent fuel and ash analysis; catalyst activity testing; determination of 

deactivation causes; and the development of the most economical strategy for adding, replacing, 

or regenerating as little catalyst as necessary. 

Figure 1: The perpetual cycle of SCR and catalyst management. 

The perpetual cycle of proper SCR and catalyst management starts with a visual inspection of the 

SCR reactor during which a sufficient number of catalyst samples are obtained from the correct 

locations within each layer. The visual inspection is a very important part and should always be 

done immediately after the opening of the SCR reactor by an experienced engineer. The only 

time when the inside of the SCR reactor, including the catalyst, is still in a state reasonably 

similar to what it looks like during normal operation is immediately after shut-down and cooling 

of the reactor. Only before the maintenance personnel enters the reactor can all the evidence of 

flow distribution problems; possible causes for catalyst erosion and/or flyash pluggage and/or 

deposition; flyash characteristics; and so on be still visible in the SCR reactor and on the catalyst. 

Thus, during the visual inspection and catalyst sampling, valuable information can be obtained 

management of

honeycomb and plate-type

catalyst

inspection and

sampling of catalyst in

SCR DeNOx plants

documentation of the

deactivation causes and

forecast of the catalyst 

potential/lifetime

development of

catalyst replacement

strategies (lifetime,

position,volume)

determination of

the main reasons for

activity loss (chemical and

physical effects)

determination of 

opportunities and limitations

for catalyst regeneration

activity tests

in bench- and microscale reactors

measurement of

pressure loss of catalyst in

bench-scale reactor

determination of

SO2/SO3 conversionrate

in bench-scale

reactor
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SCR-Tech #04 

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regarding the overall performance of the SCR system and potential problems of the SCR reactor 

and/or catalyst. This information must be documented, assessed, and interpreted correctly in 

conjunction with the catalyst data obtained in the subsequent steps. 

The catalyst samples obtained from each layer of the SCR reactor are tested in a bench-scale 

reactor, where the actual catalytic activity of the ceramic substrate of the catalyst is determined 

along with the SO2/SO3 conversion rate and the pressure drop across the catalyst. In the 

following step, the obtained data from the bench-scale tests is combined with the results from the 

visual inspection and additional data generated through chemical and physical analysis of the 

catalyst substrate to determine the main reasons for the catalyst deactivation found. These can 

be: 

• An increased uptake of catalyst poisons such as arsenic, which can be determined by Xray fluorescence analysis (XRF) of the surface and bulk substrate material. 

• The formation of blinding layers or other microscopic surface restrictions, which can be 

determined by scanning electron microscope analysis (SEM). 

• Flyash pluggage or physical damage such as loss of substrate caused by erosion in the 

reactor. 

• A combination of catalyst poisoning, surface restrictions, flyash pluggage, and/or erosion 

damage. 

Additionally, the residual potential (P) of the catalyst layer is determined. P is defined as the 

catalytic activity (K) divided by the area velocity (AV), which itself is defined as the wet flue gas 

volume flow rate at standard temperature and pressure divided by the available geometric surface 

area of the catalyst3. As will be shown later in this paper, tracking the catalyst potential of each 

layer in the SCR reactor is absolutely mandatory to make the behavior of the SCR reactor and 

the deactivation of the catalyst predictable with a high degree of accuracy. 

Most of all, the exact and detailed determination of the deactivation causes is extremely 

important in order to select the right and effective countermeasures, which is also part of proper 

catalyst management. Equipped with all the data generated and a detailed knowledge of the 

physical and chemical condition of the catalyst, the opportunities and limitations of catalyst 

regeneration must be determined. Catalyst regeneration is always chosen over catalyst 

replacement in Europe whenever possible, since the overall cost of catalyst regeneration is about 

half the cost of new catalyst. However, the opportunities for catalyst regeneration depends 

largely on the deactivation causes and the structural integrity of the catalyst. In the case of an 

accelerated loss of catalytic substrate and/or heavy erosion damage, catalyst regeneration is not 

likely to be the better choice over catalyst replacement, since not enough catalytic substrate to be 

regenerated might be left within a module. 

In almost all cases, however, the SCR catalyst is still structurally sound with no substantial 

erosion damage but is only chemically poisoned and/or has physical surface restrictions through 
SCR Catalyst Regeneration Technology and SCR Management Services 

SCR-Tech #04 

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flyash plugging and/or blinding layers. In all these cases, catalyst regeneration is the most 

economical option. As a result, catalyst regeneration has already become an integral part of 

catalyst management of most SCR operators in Europe, since deactivated SCR catalyst can 

almost always be completely rejuvenated using SCR-Tech’s proprietary patented SCR catalyst 

regeneration technologies. During regeneration, the catalyst is thoroughly cleaned, all catalyst 

poisons can be effectively removed from the catalyst’s substrate, and the catalytic activity of the 

catalyst substrate can be fully replenished1. 

In the final step of the perpetual catalyst management cycle, the actually available activity of the 

SCR catalyst in each layer, either as present or after regeneration as well as the deactivation 

causes and the actual catalyst potential, must be thoroughly documented for each catalyst layer in 

each SCR reactor. Based on that information, a detailed and exact forecast of the overall 

performance of a particular SCR reactor and the lifetime of the catalyst in each layer becomes 

available. This in return is the inevitably necessary input for the development of a sophisticated 

and overall economically optimized catalyst replacement strategy. 

Shown in Figure 2 is a catalyst exchange and DeNOx potential tracking sheet summarizing over 

70,000 SCR operating hours covering a period of more than 10 years of a 400 MW coal-fired 

unit. This is one of eight all SCR equipped units of a 4,000 MW fossil fuel fired generating 

station within E.ON’s fleet. As can be seen, the SCR reactor of this unit has four layers 

represented by the four lower graphs and each layer is equipped with a different type of catalyst. 

The top graph indicates the overall DeNOx potential as a sum of the individual potential of the 

four layers below. The minimum required DeNOx potential in the reactor to maintain the 

desired NOx removal efficiency at a maximum permissible NH3 slip is indicated by the 

horizontal line in the top graph. 

The reactor started operation with only two layers of plate-type catalyst, which didn’t provide 

enough potential as indicated by the fact that the actual total DeNOx potential starts below the 

minimum line. Consequently, after 10,000 operating hours, a third layer of honeycomb catalyst 

was added. When the forth layer was added, honeycomb catalyst was also chosen so that the 

reactor was operated with two layers of plate-type catalyst and two layers of honeycomb catalyst. 

Each circle and the corresponding number represent the average catalyst potential of the 

respective layer obtained by a through the analysis of numerous samples of that layer throughout 

the operating history of the reactor. 

As becomes obvious from the chart in Figure 2, the overall DeNOx potential in the reactor can 

be easily managed and made predictable by closely monitoring each individual layer and 

accounting for their significantly different deactivation rates. With the SCR reactor potential 

being made predictable and forecasts being made easy, an overall more economical catalyst 

management strategy can be developed. 

With the detailed knowledge of the initial, as well as the actual catalyst potential of each 

individual layer within a SCR reactor known, complete independence from the catalyst type 

(honeycomb, plate, or corrugated plate) and the manufacturer can be obtained. 
SCR Catalyst Regeneration Technology and SCR Management Services 

SCR-Tech #04 

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Figure 2: Catalyst potential and replacement tracking sheet of a 400 MW coal-fired unit 

 within the E.ON fossil fuel fired generating fleet. 
SCR Catalyst Regeneration Technology and SCR Management Services 

SCR-Tech #04 

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Thus, making catalyst just a much an operating commodity for the power plant operator as coal. 

A coal-fired unit can burn any coal or blend of coals, as long as they fit within the boiler’s 

required coal specifications such as maximum ash content, minimum heating value, etc. So too, 

a SCR system can use any type of catalyst with different characteristics from different 

manufacturers, as long as the catalyst employed fits within the SCR’s required specification such 

as ash loading, DeNOx potential, etc. Thus, if managed properly, catalyst becomes a pure 

commodity and can be moved around randomly not only within one unit but within an entire 

fleet of units. The resulting cost savings are significant. 

After it became evident that proper catalyst management allows for the free and almost 

unrestricted movement of any type of SCR catalyst from one coal-fired unit to another, E.ON 

developed an integrated catalyst management strategy for their entire fleet of 44 SCR reactors 

and a pool of almost 19,000 m3 of catalyst. A most integral part of this strategy is the catalyst 

regeneration. Every catalyst layer, which needs to be replaced because its residual potential has 

become too low, is tested and evaluated for structural and/or erosion damage. If, as it is the case 

most of the time, the catalyst is still structurally sound, it is regenerated and put back into the 

fleet’s catalyst pool. The integrated catalyst management plan for the entire E.ON fleet allows 

any E.ON unit, which requires the exchange of a catalyst layer during a scheduled outage, to be 

supplied from the pool with the right volume of SCR catalyst with the required DeNOx potential. 

The required DeNOx potential is determined from an existing tracking sheet (see Figure 2) by 

calculating the incremental increase in total DeNOx potential needed which must be added to the 

SCR reactor by the exchange layer in order to reach the next scheduled outage based on the rate 

of deactivation known for the particular SCR reactor. 

Catalyst Regeneration 

Catalyst regeneration is a process that addresses three problems of used catalyst, namely: 

• Physical accumulation of dirt such as flyash and/or blinding layers. 

• Chemical accumulation of catalyst poisons. 

• Loss of catalytic activity. 

Catalyst regeneration using SCR-Tech’s proprietary patented regeneration technologies tackle all 

three of these problems and effectively solve them by: 

• Washing the catalyst including ultrasonic deep cleaning, thus removing more than 99% 

of surface restrictions such as blinding layers, flyash plugging, etc. 

• Ultrasonic chemical extraction of around 90% of all the known catalyst poisons including 

such severe poisons as arsenic, phosphorus, and others. 

• Replenishing the catalytic activity in the ceramic substrate to between 90% and 110% of 

the catalyst’s original activity2. 
SCR Catalyst Regeneration Technology and SCR Management Services 

SCR-Tech #04 

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With no increase in SO2/SO3 conversion and the same deactivation rate as new catalyst, SCRTech’s catalyst regeneration technologies have already captured more than a 95% market share 

of the European SCR catalyst regeneration market. The huge cost savings on catalyst 

investment, as well as O&M costs, drives the success of this technology now available also in 

North America. A track record of regenerating more than 3,500m3 commercially regenerated 

SCR catalyst at a fraction of the cost of new catalyst for more then ten different utilities in 

Europe has proved the effectiveness and economical viability of this technology. 

Only the proprietary stationary SCR-Tech process is capable of extracting about 90% of even the 

most severe chemical catalyst poisons such as arsenic, phosphorus, or even thallium. Of course, 

less severe chemical catalyst poisons such as sodium, potassium, and calcium are removed just 

as efficiently as physical restrictions such as flyash plugging, surface blinding layers, and other 

surface blockages. Figure 3 provides some concentrations of catalyst poisons in the catalyst 

before and after regeneration. In this case, even though the arsenic concentration was 

particularly high since the catalyst came from a high-dust system after a wet bottom boiler with 

100% flyash recirculation, an activity of K/K0 >93% could be achieved after regeneration. 

Figure 3: Full-scale commercial regeneration results of SCR catalyst employed at a wet bottom 

boiler with 100% flyash recirculation burning high arsenic coal. 

The proprietary patented SCR-Tech process consists of numerous individual distinctly different 

process steps. Not all of these steps are applied to each order of catalyst to be regenerated. The 

exact regeneration process and the steps involved are determined based on the thorough analysis 

of the deactivation causes as provided by the catalyst management activities described earlier. 

CaO Na2O K2O As P2O5

0

0.5

1

1.5

2

2.5

3

Concentration in Catalyst [%] 

.

Removal of Catalyst Poisons

after

regeneration

before

regeneration
SCR Catalyst Regeneration Technology and SCR Management Services 

SCR-Tech #04 

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Thus, a sample from each order is analyzed prior to regeneration. Using the test results of the 

analysis, a regeneration program is tailored to the specific deactivation causes revealed. In some 

cases, this also means the replenishment of catalytic activity. SCR-Tech’s goal is to always 

regain the maximum DeNOx activity potential in the most economical manner without changing 

the physical, chemical, and/or mechanical properties of the catalyst. This provides the greatest 

customer benefit! 

Figure 4: Schematic process flow scheme of SCR-Tech’s off site catalyst regeneration technology 

The main process steps of SCR-Tech’s stationary catalyst regeneration process are outlined in 

Figure 4. Removal of the catalyst from the SCR reactor is necessary in order to subject the SCR 

catalyst to the most effective catalyst regeneration process including full rejuvenation of the 

catalytic properties and activity. 

Delivery to 

customer

Delivery from

customer

Receiving, disassembly (mostly required for plate 

type catalyst), fly ash removal through 

mechanical cleaning/vacuuming (if required)

Soaking and washing at a controlled pH, 

temperature and chemical composition 

Ultrasonic treatment for removal of catalyst 

poisons at a controlled pH, temperature 

and chemical composition 

Activity replenishment through re-impregnation 

with catalytically active compounds (V, Mo, W, etc.) 

Drying, final quality inspection 

and packaging for storage/shipment 

Neutralization and multi step rinsing
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SCR-Tech #04 

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Even though it is technically possible with this technology to regenerate SCR catalyst to more 

than 100% of its original activity, in most cases this is not an economically viable option. The 

SCR-Tech process has been proven to be capable of reinstating the full catalyst activity. 

However, during the development of the technology the main focus was given to reactivating the 

catalyst to 90% - 100 % of the original activity with a minimum effort and within a short period 

of time. This is a most efficient way to rejuvenate deactivated catalyst, thus becoming fully 

comparable to new catalyst. Long-term deactivation rates of the regenerated catalyst are 

essentially identical to new catalyst under the same SCR operating conditions. 

The main advantages of SCR-Tech’s catalyst regeneration process include: 

• No investment costs for new catalyst 

• No disposal cost of deactivated catalyst 

• No additional pressure drop and parasitic load caused by additional layers of catalyst 

• No increase in SO2/SO3 conversion through additional layers of catalyst 

• Cost of only approximately 50% of new catalyst 

• No physical damage or loss of structural integrity of the catalyst 

The only remaining uncertainty regarding regeneration of SCR catalyst is the question of how 

many times a given catalyst may be regenerated. The overall experience with SCR-Tech’s fullscale commercial catalyst regeneration is still limited to a little over four years. This experience, 

however, increases rapidly. As with every new technology, long-term experience can obviously 

not become available within such a short period of time. Therefore, the long-term behavior of 

regenerated catalyst in operation after several regenerations has yet to be proven. Particularly 

encouraging is the fact that the catalyst from one of HEW’s coal-fired stations burning world 

market coal has already been regenerated twice and there are no signs of any negative impact of 

repeated regeneration on the performance or the structural integrity of the catalyst. 

All commercial catalyst regeneration orders are accompanied by continuous analysis and testing 

of the regeneration quality using micro- and bench-scale tests, and constant monitoring for 

process quality. Performance guarantees for the regenerated catalyst are also provided, namely: 

• Activity value K/K0 after regeneration 

• Complete removal of blinding layers (e.g. formed while burning PRB coal) 

• No significant increase of the SO2/SO3 conversion rate 

• No decrease of mechanical stability 

• No increase of the deactivation rate under the same operating conditions compared to new 

catalyst 

SCR-Tech has experience with regenerating all types of commercially available catalyst 

(honeycomb, plate-type, and corrugated plate) from all major catalyst manufacturers. About 

70% of the catalyst already regenerated commercially was honeycomb and 30% was plate-type 

catalyst. Incidentally, this ratio represents almost exactly the shares of honeycomb and platetype catalyst installed in Germany. Both types have been successfully regenerated with the same 

efficiency yielding about the same results.4
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SCR-Tech #04 

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Conclusions 

SCR-Tech is a full-service provider not only for SCR catalyst regeneration but also for SCR 

catalyst management, analytical services, and SCR process design, system troubleshooting, and 

operating consulting services. Catalyst management has been used in Europe for many years and 

has been used as an efficient tool to significantly reduce the overall O&M costs of SCR systems. 

Very sophisticated tools and methods for catalyst management have been developed by the large 

European SCR operators and are now commonly used successfully and extensively by all SCR 

operators. The results obtained using these tools and methods, as well as the experience gained, 

are very valuable and can be directly applied to benefit of SCR users in North America as well. 

Catalyst regeneration has been proven to be successful also, thus further reducing the operating 

costs of SCR systems. The SCR-Tech catalyst regeneration process has been applied 

successfully to effectively remove even the most difficult catalyst poisons. Also, more than 90% 

of the original catalytic activity can be recovered at a fraction of the cost of new catalyst even 

after 50,000 and more hours of SCR operation and/or severe catalyst deactivation. 

SCR system and catalyst management services provided by SCR-Tech are key to properly 

managing and protecting the substantial value of the asset catalyst. SCR-Tech is fully dedicated 

to ensuring that SCR catalyst remains in operation as long as possible at the lowest overall cost. 

That’s why we effectively combine SCR catalyst asset management services with SCR catalyst 

regeneration in order for our North American customers to benefit from our experience. 

References 

1. P. Servatius and A. Schluttig, “Life Extension of SCR-DeNOx Catalysts Using SCRTech’s High Efficiency Ultrasonic Regeneration Process,” poster presentation at 2001 

Conference on Selective Catalytic Reduction and Selective Non-Catalytic Reduction for 

NOx Control, Pittsburgh, PA (May 2001). 

2. H. Hartenstein, P. Servatius, and A. Schluttig, “Life Extension of SCR-DeNOx Catalysts 

Using SCR-Tech’s High Efficiency Ultrasonic Regeneration Process,” presented at CoalGen, Re-ignition Coal-Fired Generation, Chicago, IL (July 2001). 

3. VGB Guideline “Guideline for the Testing of DENOX Catalysts”, VGB R 302 He, 2nd

edition published 1998, VGB-Kraftwerkstechnik GmbH, P.O. Box 10 39 32, 45039 

Essen, Germany. 

4. H. Hartenstein, P. Servatius, A. Schluttig, and H. Gutberlet, “Experience with Full-Scale 

Commercial Regeneration of SCR-DeNOx Catalyst”, presented at “The Mega 

Symposium”, EPA-DOE-EPRI Combined Power Plant Air Pollution Control 

Symposium, Chicago, IL (August 2001).