SCR Catalyst Regeneration Tech nology 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, 2001SCR Catalyst Regeneration Tech nology and SCR Management Services

SCR-Tech #04 2 

### 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 contai ned in the coal such as sodium, potassium, phosphorus, and arsenic are released into the fl ue gas, which gradually deactivate the SCR catalyst. This is known as “catalyst poisoning”. Additionally, flyash plugging and the formation of blinding layers can restrict ac cess of the flue gas to the catal yst’s active surface. All these processes combine to produce a phenomenon comm only known as catalyst deactivation, which describes the gradual decrease in catalytic ac tivity of the SCR catalyst. The corresponding

undesirable decrease in NOx removal and/or increas e in ammonia slip need s 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, wh ich 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 S CR reactor is filled up.

• The replacement of deactivated SCR catalyst by new SCR catalyst, which used to be the most common and only vi able long-term option.

• The regeneration of existing SCR catalys t, 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 plan t. By far, the largest porti on 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 produc tive 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 ope rator of a coal-f ired power plant to minimize the O&M cost of any kind of manda tory environmental c ontrol 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 plan t. In order to protect this costly asset SCR catalyst, it is highly advantageous to minimi ze deactivation and other effects harmful to the performance of the SCR catalyst. The only feasible way of achievi ng 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 in evitable minimum to maximize the useful life of the catalyst.SCR Catalyst Regeneration Tech nology and SCR Management Services

SCR-Tech #04 3 

### Catalyst Management

The procedure employed in order to maximize th e utilization of the asset SCR catalyst while protecting this asset to the highest economi cally 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 re peated continuously throughout the operation of the SCR reactor. Tracking of the deactivati on and performance of the catalyst must be accompanied by frequent fuel and ash analysis; catalyst activity testin g; 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 w ith a visual inspection of the SCR reactor during which a sufficient number of catalyst samples are obtained from the correct locations within each layer. Th e visual inspection is a very impor tant part and should always be done immediately after the opening of the SCR reactor by an expe rienced engineer. The only time when the inside of the SCR reactor, includi ng the catalyst, is still in a state reasonably

similar to what it looks like during normal operation is immediat ely after shut-down and cooling of the reactor. Only before the maintenance pe rsonnel enters the reactor can all the evidence of flow distribution problems; possi ble causes for catalyst erosion a nd/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 inspectio n 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

SO 2 /SO 3 conversionrate

in bench-scale

reactorSCR Catalyst Regeneration Tech nology and SCR Management Services

SCR-Tech #04 4 regarding the overall performance of the SCR syst em 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 te sted in a bench-scale reactor, where the actual catalytic activity of th e ceramic substrate of the catalyst is determined along with the SO 2 /SO 3 conversion rate and th e pressure drop across the catalyst. In the following step, the obtained data from the bench-scal e 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 mi croscopic surface restri ctions, 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 re strictions, 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 pr essure divided by the avai lable geometric surface area of the catalyst 3 . 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 predic table with a high degree of accuracy.

Most of all, the exact and detailed determin ation 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 lim itations of catalyst regeneration must be determined. Catalyst regeneration is always chosen over catalyst replacement in Europe whenever possible, since th e overall cost of catalyst regeneration is about half the cost of new catalyst. However, the opportunities for catalys t 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 hea vy erosion damage, catalyst regeneration is not likely to be the better choice over catalyst replacem ent, 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 throughSCR Catalyst Regeneration Tech nology and SCR Management Services

SCR-Tech #04 5 flyash plugging and/or blinding la yers. In all these cases, cat alyst regeneration is the most economical option. As a result, catalyst regenera tion 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. Duri ng 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 replenished 1

.

In the final step of the perpetual catalyst manageme nt 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 cata lyst potential, must be thoroughly docu mented 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 th e lifetime of the catalys t 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 pot ential tracking sheet summarizing over 70,000 SCR operating hours covering a period of more than 10 ye ars 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 ha s 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 potentia l as a sum of the indi vidual 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 NH 3 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 operati ng hours, a third layer of honeycomb catalyst was added. When the forth layer was added, honeyc omb catalyst was also chosen so that the reactor was operated with two layers of plate-type catalyst and tw o layers of honeycomb catalyst. Each circle and the correspond ing number represent the aver age 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 deactiv ation rates. With th e SCR reactor potential being made predictable and forecasts being ma de 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 Tech nology and SCR Management Services

SCR-Tech #04 6 Figure 2: Catalyst potential and replacement tracki ng sheet of a 400 MW coal-fired unit within the E.ON fossil fuel fired generating fleet.SCR Catalyst Regeneration Tech nology and SCR Management Services

SCR-Tech #04 7 Thus, making catalyst just a much an operating co mmodity for the power pl ant operator as coal. A coal-fired unit can burn any co al or blend of coals, as long as they fit with in 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 w ith different characteristics from different manufacturers, as long as the cat alyst employed fits wi thin the SCR’s required specification such as ash loading, DeNOx potential, etc. Thus, if managed prope rly, catalyst becomes a pure commodity and can be moved around randomly not only within one unit bu t 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 t ype of SCR catalyst from one co al-fired unit to another, E.ON developed an integrated catalyst management stra tegy for their entire fl eet of 44 SCR reactors and a pool of almost 19,000 m 3 of catalyst. A most integral part of this strategy is the catalyst regeneration. Every catalyst laye r, which needs to be replaced because its residual potential has become too low, is tested and evaluated for structur al and/or erosion damage. If, as it is the case most of the time, the catalyst is still structural ly sound, it is regenerated and put back into the fleet’s catalyst pool. The integrated catalyst ma nagement plan for the entire E.ON fleet allows any E.ON unit, which requires the exchange of a ca talyst layer during a sc heduled outage, to be supplied from the pool with the right volume of SCR catalyst with the re quired 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 re ach the next scheduled ou tage based on the rate

of deactivation known for th e particular SCR reactor.



### Catalyst Regeneration

Catalyst regeneration is a pro cess 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 bli nding layers, flyash plugging, etc.

• Ultrasonic chemical extracti on of around 90% of all the know n catalyst poisons including such severe poisons as arse nic, phosphorus, and others.

• Replenishing the catalytic activity in the cer amic substrate to between 90% and 110% of the catalyst’s original activity 2

.SCR Catalyst Regeneration Tech nology and SCR Management Services

SCR-Tech #04 8 With no increase in SO 2 /SO 3 conversion and the same deactiva tion rate as new catalyst, SCRTech’s catalyst regeneration technologies have already captured more than a 95% market share of the European SCR catalyst regeneration ma rket. The huge cost savings on catalyst investment, as well as O&M cost s, drives the success of this t echnology now available also in

North America. A track record of regenerating more than 3,500m 3 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 ar senic, 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 recirculatio n, an activity of K/K 0 >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 recircul ation burning high arsenic coal.

The proprietary patented SCR-Tech process consis ts of numerous individua l 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 cataly st management activities described earlier. 

### CaO Na2O K2O As P2O5 0 0.5 1 1.5

2 2.5 3Concentration in Catalyst [%]. 

# Removal of Catalyst Poisons

after regeneration

before regenerationSCR Catalyst Regeneration Tech nology and SCR Management Services

SCR-Tech #04 9 Thus, a sample from each order is analyzed prio r to regeneration. Using the test results of the analysis, a regeneration program is tailored to the specific deactiva tion causes revealed. In some cases, this also means the replenishment of catal ytic activity. SCR-Tech’s goal is to always regain the maximum DeNO

x activity potential in the most economical manner without changing the physical, chemical, and/or mechanical propertie s 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 regene ration 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 rinsingSCR Catalyst Regeneration Tech nology and SCR Management Services

SCR-Tech #04 10 Even though it is technically possi ble with this technology to re generate 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 capab le of reinstating the full catalyst activity. However, during the development of the technol ogy the main focus was given to reactivating the catalyst to 90% - 100 % of the orig inal activity with a minimum ef fort 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 deac tivation rates of the re generated 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 SO 2 /SO 3 conversion through additi onal layers of catalyst

• Cost of only approximately 50% of new catalyst

• No physical damage or loss of stru ctural integrity of the catalyst

The only remaining uncertainty re garding regeneration of SCR cat alyst is the question of how many times a given catalyst may be regenerated. The overall e xperience 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 ne w technology, long-term e xperience can obviously

not become available within such a short period of time. Theref ore, the long-ter m behavior of regenerated catalyst in operation after several regenera tions 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 a nd 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 be nch-scale tests, and c onstant monitoring for process quality. Performance guarantees for the re generated catalyst are also provided, namely:

• Activity value K/K 0 after regeneration

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

• No significant increase of the SO 2 /SO 3 conversion rate

• No decrease of mechanical stability

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

SCR-Tech has experience with regenerating all types of commercially available catalyst (honeycomb, plate-type, and corru gated plate) from all major ca talyst manufacturers. About 70% of the catalyst already regenerated commer cially was honeycomb and 30% was plate-type catalyst. Incidentally, this ra tio represents almostexactly the shares of honeycomb and platetype catalyst installed in Germa ny. Both types have been successf ully regenerated with the same efficiency yielding about the same results. 4SCR Catalyst Regeneration Tech nology and SCR Management Services

SCR-Tech #04 11 

### Conclusions

SCR-Tech is a full-service provider not only fo r SCR catalyst regeneration but also for SCR catalyst management, analytical services, and SCR process de sign, 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 significan tly 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 us ed successfully and extensively by all SCR operators. The results obt ained using these tools and methods, as well as the e xperience 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 su ccessful also, thus further reducing the operating costs of SCR systems. The SCR-Tech catal yst 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 Exte nsion of SCR-DeNOx Catalysts Using SCRTech’s High Efficiency Ultrasonic Regene ration Process,” poste r 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. Schlut tig, “Life Extension of SCR-DeNOx Catalysts Using SCR-Tech’s High Efficiency Ultrasonic Regeneration Process,” presented at CoalGen, Re-ignition Coal-Fired Genera tion, Chicago, IL (July 2001).

3. VGB Guideline “Guideline for the Testi ng of DENOX Catalysts”, VGB R 302 He, 2 nd
edition published 1998, VGB-Kraftwerkst echnik GmbH, P.O. Box 10 39 32, 45039 Essen, Germany.

4. H. Hartenstein, P. Servatius, A. Schluttig, a nd H. Gutberlet, “Experience with Full-Scale Commercial Regeneration of SCR-DeNOx Catalyst”, pr esented at “The Mega Symposium”, EPA-DOE-EPRI Combined Power Plant Air Pollution Control Symposium, Chicago, IL (August 2001).