# REJUVENATION OF THE SCR

CATALYST AT MEHRUM

By Y oshinori Nagai Y oshiro Inatsune Isato Morita Y asuyoshi Kato Kouichi Y

okoyama Kazunori Ito Babcock Hitachi K.K 6
- 9 Takara
- machi, Kure
- shi, Hiroshima
- ken,

737
- 8508, Japan

Paul Otte Kraftwerke Mehrum GmbH Trift strasse 25 Hohenhameln, 31249, GermanySUMMARY

Babcock Hitachi K.K. (BHK) received the contract for the rejuvenation of the SCR catalyst at
the 750 MW coal

- fired Mehrum Power Station in March 2003. The contractual coverage
was 160m

3 of the entire cataly st layer. The catalyst, which had been in operation for sixteen years since 1987, was originally supplied by BHK. The rejuvenation process developed for the Mehrum project consisted of two (2) major steps: the first (step) is to dust off the catalyst and remove the catalyst poison, and the second (step) is to add active material to enhance the catalyst activity. The catalyst must be dried after each washing. In order to minimize transportation cost and time, the rejuvenation work was done at the
Mehrum st

ation site. The scope of the rejuvenation work was shared between the owner and
BHK. It took about one and a half months to complete the (total) on

- site rejuvenation work. The performance of the rejuvenated catalyst was superior to show the same level of activity as the unused catalyst and maintain the same SO 2 conversion rate as the spent catalyst
. This paper gives the details of the spent coal

- fired SCR catalyst rejuvenation work.
BACKGROUND Mehrum Power Station is owned by Kraftwerke Mehrum GmbH. Sha reholders are E.ON Kraftwerke GmbH (50%), Stadtwerke Hannover AG (33.3%) and Braunschweiger Versorgungs AG (16.6%). It is the 750 MW coal

- fired boiler located at Hohenhameln in Germany. The boiler has one SCR that cleans the entire flue gas stream. The SCR system has one reactor, which is one of the largest reactors in the world. BHK designed its arrangement and supplied the catalyst in 1987. After 16

- year operation, BHK received the contract for the rejuvenation work of one layer of the catalyst for U nit #3: 160m

3 , in March 2003 through Hitachi Europe Ltd.CATALYST REJUVENATION EXPERIENCE

BHK, as an SCR supplier, has experienced variously in the catalyst rejuvenation since the early stage of the catalyst development. The BHK rejuvenation history is s hown in Figure 1. As well as laboratory and bench scale tests, BHK has also gained experience in dealing with the actual commercial stations: two gas firing plants and one biomass firing plant. The latter was in Sweden, where BHK had the first experience of the commercial scale SCR catalyst rejuvenation at site. Photographs of the work then are shown in Figure 2. The accumulated knowledge gained over a quarter century enabled BHK to execute Mehrum rejuvenation work successfully.

Fig ure 1 : History of BHK’ s Activity for SCR Catal y st Rejuvenation

Fig ure 2 : BHK’s first rejuvenation work at site in Sweden Reactivation for gas firing plant (Commercial) Rejuvenation for Oil firing plant Recycle of TiO 2 Activity

Reuse of used SCR Catalyst (Commercial)

Rejuvenation for Wood firing plant (Commercial) Rejuvenation for Coal firing plant Durability testing of rejuvenated catalyst at actual coal / gas firing plant Reactivation for gas firing plant (Commercial) 77 78 80 79 81 82 83 84 85 86 87 88 90 89 91 92 93 94 95 96 97 98 00 99 01

Reactivation for gas firing plant (Commercial) Rejuvenation for Oil firing plant Recycle of TiO 2 Activity

Reuse of used SCR Catalyst (Commercial)

Rejuvenation for Wood firing plant (Commercial) Rejuvenation for Coal firing plant Durability testing of rejuvenated catalyst at actual coal / gas firing plant Reactivation for gas firing plant (Commercial) 77 78 80 79 81 82 83 84 85 86 87 88 90 89 91 92 93 94 95 96 97 98 00 99 01APPROACH

In order to investigate the best available rejuvenation method for Mehrum SCR catalyst, several catalyst elements (plates) were taken from the catalyst units and their activity (DeNOx efficiency) was checked in laboratory testing. Several methods were tried to reach

a goal of rejuvenation. Once the process was established, the full

- scale results were confirmed by utilizing it on the a ctual full

- size catalyst units as shown in Figure 3. Then, planning of the actual rejuvenation work began. Figure 4 shows laboratory scale test facility and test condition

. Figure. 3 Full
- size plate type catalyst unit

Figure. 4 Laborato ry Scale test facility and test condition Laboratory Test Condition Gas Temperature 350 ? Inlet Gas Composition NO 200 ppm SO2 500ppm O2 3 % CO2 12 % H2O 12 %LABORATORY TEST RESULTS

The activity (DeNOx efficiency) of spent catalyst was about two

- thirds of the unused catalyst activity, while its SO 2 conversion rate was 50% higher. The requirements for the rejuvenated

cat alyst were higher performance and at least 90% of the unused (original) catalyst DeNOx efficiency in keeping with an SO 2 conversion rate and the cost that the owner could accept.
To fulfill the requirements , BHK firstly conducted the laboratory scale test s using the sample catalysts extracted from the actual plant, Mehrum station. It was relatively easy to recover only activity without considering increase of SO 2 conversion rate. However, it is quite difficult to fulfill both requirements, because they co mpete each other. At first, a simple process was considered. But it was not acceptable, because it could not meet all the technical goals. Some multiple processes were then considered. The best (process) that could meet all the goals was selected after the elaborate screening tests. It is Case F in Figure 5. Fig ure 5 : Laboratory test results

0 1 2 3 4 5 6 7 8

Unused Spent A B C D E F GSO2 to SO3 Conversion (%)

0 10 20 30 40 50 60 70

Unused Spent A B C D E F GDeNOx Efficiency at 350C (%) Target Performance

Target EfficiencyPROCESS

The process (Case F in Figure 5) consists of two (2) major steps. Refer to Figure 6. The first step is to dust off the catalyst and remove catalyst poisons. The second is to add active material to enhance the catalyst activity. Catalyst must be dried after each washing. Selecting an appropriate method, the results were examined by util izing that methodical process on the actual catalyst units. When the process was established through the examination, the actual rejuvenation work at site had to be arranged. In the entire process, temperature, chemical solution concentrations, and the t ime required affect the rejuvenation performance. Therefore the detailed process data was carefully checked and controlled during site work to secure product quality.

Fig ure 6 : Rejuvenation Process

De d ust Primary

Washing Drying Washing Drying Storage

SecondlySCOPE OF WORK

In order to minimize the cost, BHK proposed to do the rejuvenation work at the site sharing the scope of work. The owner accepted it. The owner ’ s scope was removal of the dust from the catalyst and treating and disposal of both the du st and the wastewater generated by the process. This approach

is effective to minimize the cost and save any catalyst transportation costs, because the owner utilizes the existing equipment and the systems. The cost and the schedule for the process would have been considerably enormous if BHK had to establish waste treatment facilities outside and ship the catalyst back and forth between the generating
station and the work place. The owner also supplied the general utilities such as steam,
water and elec tricity for the rejuvenation at site. BHK ’ s scope was supplying mobile rejuvenation equipment with the labor to the site and overall project management responsibilities in addition to establishing and confirming the rejuvenation process. Table 1
shows th e summary of “ scope of work ”

.

Table 1 : Summary of "Scope of Work "



## Own er Dust r emoval & disposal Utility supply & w aste water treatment

BHK Rejuvenation work at site Laboratory testREJUVENATION WORK

Figure 7 shows the tent erected at the site to do the rejuvenation work inside. It was located near the boiler house. All the required equipment was installed inside the tent and the rejuvenation process were conducted there. This setting was conducive to efficient work
under the clean conditions.

Figure 7 : Working tent located by boiler house

The photographs in Figure 8 show the equipment and the working procedure. The dust was removed by vacuum cleaner in combination with the de

- dusting tools (left). The open storage tank is designed to mix the chemical solution uniformly and to remove wastewater from inside the units easily (right). The w ashing water was neutralized, and then transported to the nearest point of the existing wastewater treatment system in the power station through wastewater pipe line. Figure. 8 Rejuvenation equipmentThrough the work, BHK learned that quick and un iform drying was quite important and

conducive to both the efficient work and the excellent product performance. For this purpose, the drying chamber (Figure 9) is designed to make uniform distribution of drying air. This is demonstrated in Figure 10, wh ich shows CFD (Computational Fluid Dynamics) study
of the drying chamber.

Figure. 9 Drying Chamber

Figure 10 : CFD study of drying air flowSCHEDULE

The work started in May 2003. Before starting the actual rejuvenation of Mehrum catalyst,
half a month was needed for equipment preparation. Preparation included equipment set

- up and adjustments, and performance examination. The actual catalyst rejuvenation work took
about one and a half months for the 160 m 3 catalyst layer, although work was sus pended according to the owner ’ s convenience. The rejuvenation facility was operated on a single
shift basis.

Fig ure 11 : Rejuvenation schedule

Month ‘ 03/5 6 7 8 Remarks Dust removal

PreTest & p reparation Rej uvenation Effort 21 Completion Work InterruptionApprox.460mm Approx.100mm

Approx. 150mm PERFORMANCE The performance test was conducted at BHK ’ s bench scale test facility to examine DeNOx activity and SO 2 to SO 3 conversion rate of the rejuvenated catalyst (to be) used at Mehrum site. Figure 12 shows the photograph of the ben ch scale test facility and the test condition. The catalyst elements were cut into small plates to make test sample catalyst units.

Figure. 12 Bench Scale test facility and test condition

Test c ondition for rejuvenated SCR catalyst Flue gas flow rat

e : 98.7 m3(normal)/h Flue gas temperature : 380 deg.C Flue gas composition : NOx = 390 ppm SOx = 1,074 ppm O2 = 4.4 %Figure 13 shows the test result s for the rejuvenated catalyst at the bench scale test facility.

The rejuvenated catalyst showed superior performance that is the same level activity (DeNOx efficiency) as the unused catalyst, maintaining the same SO 2 conversion rate as the spent catalyst . The bench scale tests showed that the expected performance was achieved in spite of the large

- scale work at the site. BHK concluded that the strict quality management could achieve these goals.

Figure. 13 Obtained Performance of Product

0 0 .2 0 .4 0 .6 0 .8 1 1 .2

Unused Un treated Product Samp l e NameDeNOx Activity ratio(-)

0 0.2 0.4 0.6 0.8 1 1.2

Un treated Product Sample NameSO2 to SO3 Conversion Ratio (-)CONCLUSIONS

The catalyst rejuvenated at Mehrum Power station showed superior performance with the same level activity as the unused catalyst, keeping the same level of SO 2 conversion rate as the spent catalyst, a

nd all the rejuvenation performance goals were achieved. This work also proved that the on

- site rejuvenation process would be able to minimize the cost to pay by utilizing the owner ’ s existing facility to dispose the dust and wastewater generated in the
p rocess as well as saving the catalyst transportation costs. Thus BHK has added the catalyst rejuvenation work at the site to their overall services of the catalyst management, such as the catalyst lifetime estimation

, supply of replacement catalyst, and t he rejuvenation services.