Impacts of Texas Lignite Coal on SCR

Catalyst Life and Performance

Field Data From TXU's Martin Lake Plant

Technical Report 

EPRI Project Manager 

D. Broske 

EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA 

800.313.3774 • 650.855.2121 • askepri@epri.com • www.epri.com 

Impacts of Texas Lignite Coal on 

SCR Catalyst Life and Performance 

Field Data from TXU’s Martin Lake Plant 

1004732 

Final Report, December 2003 

Cosponsor 

TXU Energy 

1601 Bryan St. 

Dallas, TX 75201 

Principal Investigators 

P. Ulvog 

B. Wiemuth 
DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES 

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN 

ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH 

INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE 

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PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT. 

ORGANIZATION(S) THAT PREPARED THIS DOCUMENT 

Fossil Energy Research Corp. 

TXU Energy 

ORDERING INFORMATION 

Requests for copies of this report should be directed to EPRI Orders and Conferences, 1355 Willow 

Way, Suite 278, Concord, CA 94520, (800) 313-3774, press 2 or internally x5379, (925) 609-9169, 

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Copyright © 2003 Electric Power Research Institute, Inc. All rights reserved. 
iii 

CITATIONS 

This report was prepared by 

Fossil Energy Research Corp. 

23342C South Pointe 

Laguna Hills, CA 92653 

Principal Investigators 

L. Muzio 

R. Smith 

TXU Energy 

1601 Bryan St. 

Dallas, TX 75201 

Principal Investigators 

P. Ulvog 

B. Wiemuth 

This report describes research sponsored by EPRI and TXU Energy. 

The report is a corporate document that should be cited in the literature in the following manner: 

Impacts of Texas Lignite Coal on SCR Catalyst Life and Performance: Field Data from TXU’s 

Martin Lake Plant, EPRI, Palo Alto, CA, and TXU Energy, Dallas, TX. 2003. 1004732. 

v 

PRODUCT DESCRIPTION 

Selective catalytic reduction (SCR) systems are being broadly applied to power generating units 

fired with Power River Basin and bituminous coals and natural gas. To develop an understanding 

of the potential deactivation and erosion of SCR catalyst in Texas-Lignite-fired units, an in-situ

mini SCR reactor was used to test two types of catalyst at TXU Energy’s Martin Lake Unit 3. 

Prior to this test program, no long-term test data on the effects of Texas Lignite on SCR catalyst 

life and performance existed. 

Results & Findings 

After approximately 8000 hours of exposure to economizer outlet flue gas at typical SCR 

velocities of 15-20 ft./sec. (4.6-6.1 m/sec), both honeycomb and plate-type catalyst samples 

(supplied by two different vendors) were shown, by field test, to have relative activities (K/K0) in 

the range of 0.70 to 0.75. Laboratory tests of catalyst activity performed by the catalyst vendors 

were consistent with field test results. These results are expected to be representative of the first 

layer of a full-scale SCR reactor system. Erosion of the catalyst samples was not significant 

enough to affect catalyst performance. Test results suggest that applying SCR catalyst 

technology (using even a high-dust design) to Texas-Lignite-fired power generating units may be 

a practical approach for NOx control. 

Challenges & Objectives 

Results of this test program will be of interest to power producers firing Texas Lignite, catalyst 

vendors, SCR process suppliers, and industry consultants. Information on the rate of decay in 

catalyst activity can be used in helping to develop realistic catalyst management programs for 

Texas-Lignite-fired applications of SCR. 

Applications, Values & Use 

The catalyst test program at Martin Lake provides the power industry’s first insights into the 

effects of Texas Lignite on SCR catalyst life and performance. One test program of this kind, 

however, is not sufficient to draw a general set of conclusions on the effects of this fuel. Other 

owners of Texas-Lignite-fired units are encouraged to undertake similar field test programs if 

they are contemplating or planning full-scale application of SCR technology for NOx control. 

EPRI Perspective 

This program’s goal was to expose sample catalyst samples to realistic SCR reactor conditions 

and to monitor catalyst activity and erosion. The program’s intent was not to directly compare 

various catalysts. Rather, the intent was to provide field data that would help identify general 

Texas Lignite effects on SCR catalyst life and performance. 
vi 

EPRI has conducted similar test programs on the effects of Powder River Basin (PRB) coals on 

SCR catalyst life and performance at Ameren’s Sioux Unit 2 (EPRI report 1004053) and Texas 

Genco’s W.A Parish Unit 5 (1004137). Data from these two programs helped to improve 

understanding of the degree to which PRB coals might impact operating and maintenance costs 

of full-scale SCR systems. 

Approach 

In work cosponsored by TXU Energy, the project team used an in-situ mini SCR test apparatus 

to expose SCR catalyst samples to realistic flue gas conditions. The test lasted for about 8000 

hours on a 750-MW pulverized coal boiler that fires Texas Lignite along with PRB coal (at a rate 

of less than 10% on a weight basis). The mini reactor placed catalyst samples in the flue between 

the economizer gas outlet and the air heater gas inlet, and the catalyst samples saw representative 

flue gas temperatures over the load range. A control system aspirated the flue gas into the mini 

reactor at near isokinetic conditions and maintained the velocity within the catalyst at typical 

full-scale SCR velocities. The system was equipped with ammonia injection, sootblowers, and 

instrumentation to perform in-situ catalyst activity tests. The team used two identical reactors so 

that two catalyst samples could be tested simultaneously. The two reactors were served by a 

common cabinet containing instrumentation and control equipment. At intervals of 

approximately 2000 hours, catalyst samples were extracted from the mini reactors so they could 

be analyzed in the laboratory by the vendors supplying the samples. Laboratory tests included 

catalyst activity, surface area, pore volume, and bulk chemical composition. 

Keywords 

Selective catalytic reduction (SCR) 

NOx mitigation 

Deactivation 

Relative activity 

Catalyst 

Texas lignite 
vii 

ABSTRACT 

To develop an understanding of the potential deactivation of SCR catalyst in Texas-Lignite-fired 

units, an in-situ mini SCR test apparatus was used to expose catalyst samples from two vendors 

to realistic conditions for 8000 hours at TXU’s Martin Lake Unit 3. Each reactor placed the 

catalyst sample within the economizer outlet duct so that the sample saw actual flue gas 

temperatures over the load range. The reactor control system aspirated the flue gas into the 

device at near isokinetic conditions and maintained the velocity at the catalyst at typical SCR 

velocities of 15-20 ft./sec. (4.6-6.1 m/sec). Each reactor had provisions for continuous ammonia 

injection, sootblowing of the catalyst sample, and instrumentation to perform in-situ catalyst 

activity tests. 

Two catalyst vendors provided the samples (one honeycomb and one plate-type) used for these 

tests. 

After nominally 8300 hours of exposure, the in-situ activity tests on the honeycomb sample 

indicated a deactivation to K/K0 = 0.72. However, 25% of the catalyst in this reactor was 

removed (and replaced with a fresh piece) at nominal 2000-hour intervals throughout the test 

program. In-situ activity tests on the honeycomb catalyst section that remained in the reactor for 

the program’s duration indicated a deactivation to K/K0 = 0.75. The vendor’s laboratory analysis 

of the 8300-hour sample agreed well with the in-situ measurements, indicating a deactivation of 

K/K0 = 0.74. The vendor analysis also revealed the primary cause of deactivation was from 

catalyst exposure to CaO. 

After nominally 8000 hours of exposure, the in-situ activity tests on the plate-type catalyst 

sample indicated a deactivation to K/K0 = 0.73. Catalyst samples also were periodically removed 

from this reactor (and replaced with fresh plates). However, physical constraints precluded the 

running of in-situ activity tests on only the plates remaining for the entire 8000-hour test period. 

The vendor’s own laboratory analysis of samples periodically removed from the reactor agreed 

very well with the in-situ measurements, indicating an average deactivation rate of K/K0 = 0.71 

at the conclusion of the 8000-hour test. The vendor’s chemical analysis of the plate samples did 

not indicate any remarkable catalyst poisoning. 

ix 

ACKNOWLEDGMENTS 

The authors would like to gratefully acknowledge the role of and assistance provided by Mr. Pete 

Ulvog from the Martin Lake plant’s engineering group. 

In addition, cooperation from the two catalyst vendors participating in this test program is also 

acknowledged. 

xi 

CONTENTS 

1 INTRODUCTION ................................................................................................................. 1-1

2 TEST APPARATUS AND METHODOLOGY....................................................................... 2-1

In Situ Mini SCR Reactor Description................................................................................. 2-1

Reactor Control and Instrumentation.................................................................................. 2-4

Catalyst Coupons............................................................................................................... 2-4

Test Methodology............................................................................................................... 2-7

Catalyst Activity Determination ........................................................................................... 2-8

Long-Term Test Programs ................................................................................................. 2-8

General Comments on Catalyst Activity Test Results......................................................... 2-8

3 LONG-TERM TEST RESULTS............................................................................................ 3-1

Data Trends and General Observations ............................................................................. 3-1

Reactor 1 Activity Test Results (Vendor A Catalyst Samples) ............................................ 3-4

Reactor 1: Full-Flow Test Results .................................................................................. 3-5

Reactor 1: 1⁄4-Flow Test Results....................................................................................3-10

Vendor A Laboratory Activity Test Results....................................................................3-10

Reactor 2: Activity Test Results (Vendor B Catalyst Samples) ..........................................3-14

Vendor B Laboratory Activity Test Results....................................................................3-17

4 ANALYTICAL TEST RESULTS........................................................................................... 4-1

Vendor A Analytical Test Results ....................................................................................... 4-1

Surface Area.................................................................................................................. 4-2

Pore Volume.................................................................................................................. 4-3

Bulk Chemical Composition ........................................................................................... 4-5

Surface Chemical Composition...................................................................................... 4-9

Vendor A: Conclusions .................................................................................................. 4-9

Vendor B: Analytical Test Results .....................................................................................4-14
xii 

5 SUMMARY .......................................................................................................................... 5-1

6 REFERENCES .................................................................................................................... 6-1
xiii 

LIST OF FIGURES 

Figure 2-1 In Situ Mini SCR Reactor Schematic...................................................................... 2-1

Figure 2-2 Photographs of In Situ Mini SCR Reactor System (control cabinet on left, 

reactor on right)............................................................................................................... 2-2

Figure 2-3 Reactor Installation Location at Economizer Exit.................................................... 2-3

Figure 2-4 Photographs of Mini SCR Test Reactors Installed at the Martin Lake Site ............. 2-5

Figure 2-5 Vendor A Catalyst Samples Installed in the Catalyst Holder for Reactor 1 ............. 2-6

Figure 2-6 Vendor B Catalyst Coupons Prior to Installation in the Catalyst Holder for 

Reactor 2......................................................................................................................... 2-7

Figure 3-1 Temperature and Flow (∆P) Data for Reactor 1 (Vendor A Catalyst)...................... 3-2

Figure 3-2 Temperature and Flow (∆P) Data for Reactor 2 (Vendor B Catalyst)...................... 3-3

Figure 3-3 Ceramic Fiber Gaskets and Stainless Steel Blocking Plates Utilized for 1⁄4-

Flow Tests on Reactor 1 (Vendor A Catalyst).................................................................. 3-5

Figure 3-4 Reactor 1 Full-Flow Activity Results: (a) NO Removal, (b) K/K0.............................. 3-6

Figure 3-5 Reactor 1 1⁄4-Flow Activity Results: (a) NO Removal, (b) K/K0 ...............................3-11

Figure 3-6 Reactor 2 Activity Results: (a) NO Removal, (b) K/K0 ............................................3-15

Figure 4-1 Catalyst A BET Surface Area................................................................................. 4-2

Figure 4-2 Catalyst A Pore Volume......................................................................................... 4-3

Figure 4-3 Catalyst A Median Pore Diameter .......................................................................... 4-4

Figure 4-4 Catalyst A Relative Bulk Concentration of Arsenic ................................................. 4-6

Figure 4-5 Catalyst A Relative Bulk Concentration of Potassium ............................................ 4-7

Figure 4-6 Catalyst A Relative Bulk Concentration of Sodium................................................. 4-8

Figure 4-7 Catalyst A Relative Surface Composition Concentration of Arsenic ......................4-10

Figure 4-8 Catalyst A Relative Surface Concentration of Calcium..........................................4-11

Figure 4-9 Catalyst A Relative Surface Concentration of Potassium ......................................4-12

Figure 4-10 Catalyst A Relative Surface Concentration of Sodium.........................................4-13

xv 

LIST OF TABLES 

Table 1-1 Average Texas Lignite Coal and Ash Composition.................................................. 1-2

Table 2-1 Nominal Mini SCR Test Conditions ......................................................................... 2-7

Table 3-1 Reactor 1: Full-Flow Data Summary........................................................................ 3-7

Table 3-2 Reactor 1: 1⁄4-Flow Data Summary .........................................................................3-12

Table 3-3 Vendor A Catalyst Activity Test Conditions.............................................................3-13

Table 3-4 Vendor A Catalyst Activity Test Results .................................................................3-13

Table 3-5 Reactor 2: Data Summary......................................................................................3-16

Table 3-6 Summary of Vendor B Activity Test Results ...........................................................3-18

Table 4-1 Vendor A Catalyst Sample Exposure History .......................................................... 4-1

Table 4-2 Catalyst A BET Surface Area .................................................................................. 4-2

Table 4-3 Catalyst A Pore Volume .......................................................................................... 4-3

Table 4-4 Catalyst A Median Pore Diameter ........................................................................... 4-4

Table 4-5 Catalyst A Relative Bulk Concentration of Arsenic .................................................. 4-6

Table 4-6 Catalyst A Relative Bulk Concentration of Potassium.............................................. 4-7

Table 4-7 Catalyst A Relative Bulk Concentration of Sodium .................................................. 4-8

Table 4-8 Catalyst A Relative Surface Composition Concentration of Arsenic........................4-10

Table 4-9 Catalyst A Relative Surface Concentration of Calcium ...........................................4-11

Table 4-10 Catalyst A Relative Surface Concentration of Potassium .....................................4-12

Table 4-11 Catalyst A Relative Surface Concentration of Sodium..........................................4-13

Table 4-12 Summary of Vendor B XRF Results (% weight in sample) ...................................4-14

1-1 

1

INTRODUCTION 

The United States utility industry has been moving towards the greater use of selective catalytic 

NOx reduction (SCR) for compliance with NOx regulations on coal-fired boilers. Both utilities 

and SCR catalyst vendors have expressed interest in identifying how coal properties (i.e. specific 

fly ash and flue gas properties) impact short- and long-term catalyst performance. 

For example, the characteristics of Powder River Basin (PRB) coals include high moisture 

(nominally 30%), low heating value (nominally 8,700 Btu/lb or 20.2 MJ/kg), and high calcium 

levels (nominally 10-20% wt. in ash). As part of the SCR design process for the first PRB 

applications, catalyst vendors installed catalyst coupons in the economizer exit of PRB-fired 

boilers. The results of a few of these initial vendor tests indicated the test coupons had 

experienced greatly accelerated deactivation. There was general disagreement amongst catalyst 

vendors regarding the accuracy and applicability of these early coupon tests. As a result, 

vendors, utilities, and other organizations continued pilot-scale testing to better understand the 

effects of PRB coal on SCR catalyst life and performance. The first full-scale, PRB-fired SCR 

installation to go into service was Associated Electric Cooperative Inc.’s New Madrid Unit 2, 

where Cormetech was the catalyst vendor. 

As part of the initial pilot-scale PRB testing, AmerenUE, Reliant Energy, and EPRI co-funded 

long-term activity evaluation programs at two test sites; Ameren’s Sioux Unit 2 and Reliant’s W. 

A. Parish Unit 5. Both of these test programs utilized in situ reactors to house the catalyst 

samples during the tests. The in situ reactors were designed to more accurately simulate realworld SCR operation with flue gas flow and ammonia injection rates representative of those 

found in a full-scale SCR system. The results of the two in situ test programs (1, 2) did not 

reflect the near-catastrophic level of deactivation seen in some of the earlier coupon tests on 

PRB-fired units and supported Cormetech’s prior decision to proceed with the commercial SCR 

with PRB coal at New Madrid. 

This report describes the results of a similar EPRI Tailored Collaboration (TC) program at 

TXU’s Martin Lake Unit 3. In preparation for increasingly stringent NOx regulations, TXU 

wanted to assess the various issues associated with the application of SCR on its coal fired power 

plants. The key issue TXU wished to address is how the fuel (Texas Lignite) would impact shortand long-term catalyst performance. Prior to this work, there had been no experience with SCR 

on Texas Lignite-fired units. The data produced by the test program can be used to help TXU 

prepare specifications for procuring catalysts, as well as develop catalyst management programs, 

should future NOx regulations require the application of SCR to one or more of the utility’s 

power plants. 

Martin Lake Unit 3 is a 750 MW pulverized coal boiler designed to fire 100% Texas Lignite 

coal. The plant currently co-fires PRB coal along with the Texas Lignite, but at a rate of less than 
Introduction 

1-2 

10 percent on a tonnage basis. The Unit 3 boiler was retrofit with low-NOx burners in March of 

2002. After the retrofit, typical full-load NOx concentrations for the unit ranged from 100 to 125 

ppm @ 3% O2. 

An average analysis of the Texas Lignite fired in the Martin Lake unit is shown in Table 1-1. 

This fuel is characterized as having high moisture, a low heating value, along with fairly 

moderate levels of sulfur and calcium. Additionally, silica levels in the ash are quite high, which 

led to initial concerns regarding catalyst erosion. 

Table 1-1 

Average Texas Lignite Coal and Ash Composition 

Proximate Analysis Ash Analysis Trace Constituents 

 

Moisture % As Received 34.6 PO5 % 0.2 Sb mg/Kg <0.5 

Ash % As Received 11.5 SiO2 % 44.6 As mg/Kg <.05 

Volatiles % As Received 26.4 Fe2O3 % 8.5 B mg/Kg 155.6 

Fixed Carbon % As Received 27.5 AL2O3 % 15.8 Cd mg/Kg <.05 

Sulfur % As Received 1.1 TiO2 % 1.0 Cr mg/Kg 11.2 

BTU/Lb % As Received 6928 Mn3O4 % 0.1 Cu mg/Kg 15.3 

 CaO % 10.0 Pb mg/Kg <0.5 

 MgO % 2.5 Mn mg/Kg 82.4 

 K2O % 0.9 Hg mg/Kg 0.0 

 Na2O % 0.7 Mo mg/Kg 0.8 

 SO3 % 12.8 Se mg/Kg 1.8 

 SrO % 0.1 Zn mg/Kg 13.4 

 BaO % 0.6 

 Undetermined % 2.2 

 

The goal of this program was to expose catalyst coupons to Texas Lignite flue gas under realistic 

SCR reactor conditions for a period of approximately 8000 hours, and to monitor catalyst 

activity. It was not the intent of this program to directly compare various catalysts. Instead, the 

intent was to provide field data that would help identify general Texas Lignite coal effects on 

SCR catalyst life and performance. 
Introduction 

1-3 

In structuring a program to address potential Texas Lignite ash effects on SCR catalysts, it was 

felt that the chosen approach should expose the catalyst to “as real as possible” conditions that a 

catalyst would see at full scale. 

In terms of sub-scale approaches to study catalyst life there are three basic approaches: 

1. Passive Coupons: A single catalyst coupon or a cassette holding multiple coupons is inserted 

into the economizer exit duct. Periodically, a sample is removed and the catalyst activity 

tested in a specialized laboratory facility. This is the simplest approach; however, the 

coupons are exposed to much higher velocities than in a full-scale SCR reactor, which leads 

to the concern that the coupon experiences much higher erosion, as well as mass transfer 

rates than an actual piece of catalyst in real SCR reactor. 

2. In Situ Reactor: A catalyst sample is contained in a holder that is inserted into the 

economizer exit. Gas flow is controlled so that the catalyst is exposed to the same velocity as 

in a full-scale SCR reactor. This device can also be equipped with NH3 injection and 

sootblowers to more accurately simulate real-world SCR operation. Testing can either be 

performed in situ, or a sample removed and sent to a laboratory. Catalyst samples with this 

approach range in cross section from 2 in. x 2 in. to 6 in. x 6 in. (50mm x 50mm to 150mm x 

150mm). 

3. Extractive Pilot Plant: A flue gas stream is extracted from the economizer exit and passed 

through a catalyst sample located externally to the economizer exit duct. This approach 

allows larger catalyst samples to be tested. However, it is typically the most costly approach 

and poses problems with temperature control of the flue gas passing through the catalyst 

samples. Also, because it is external, there are issues of temperature gradients across the 

catalyst sample, and loss of trace elements due to condensation in the gas path from the 

economizer exit duct to the catalyst sample. 

A more detailed presentation of the advantages, disadvantages and issues is given in Reference 3. 

For the current project, the in situ reactor approach was chosen as the best compromise between 

realism and cost. The reactor is an in situ SCR reactor initially developed by Fossil Energy 

Research Corp. (FERCo) in 1991. The design of the reactor system has been subsequently 

refined through its use and application in five separate catalyst assessment programs. The device 

utilized for the work reported herein accommodates catalyst samples with a nominal cross 

section of 4 in. x 4 in. (102mm x 102mm) with catalyst lengths up to 1 meter. A detailed 

description of the reactor is provided in Section 2. 

2-1 

2

TEST APPARATUS AND METHODOLOGY 

The test apparatus used in this study was the In Situ Mini SCR test reactor. As described in the 

Introduction, this concept involves immersing the catalyst sample into the flue gas duct and 

controlling the gas flow over the catalyst to velocities representative of full-scale SCR systems. 

The test apparatus also provides continuous ammonia injection, periodic air sootblowing, and the 

facility for in situ catalyst activity measurements. The following sections describe the overall 

reactor system, the control and instrumentation equipment, and the test methodology. 

The Martin Lake Unit 3 Mini SCR system was designed with two separate, but identical reactors. 

The two reactors were controlled by a single cabinet which housed the control and 

instrumentation equipment. The dual-reactor arrangement provided the ability to test two 

separate catalyst samples simultaneously. At Martin Lake, catalyst samples from different 

vendors were installed in the two separate reactors. 

In Situ Mini SCR Reactor Description 

A conceptual diagram of the In Situ Mini SCR reactor is presented in Figure 2-1. Photographs of 

the system installed at the Martin Lake test site are shown in Figure 2-2. Each reactor assembly 

consists of a 6-inch (152mm) diameter stainless steel probe that is fully inserted into the flue gas 

stream. The catalyst coupons are installed in an inner housing that can be removed from the outer 

reactor shell. The inner catalyst holder provides full access for inspecting, and if necessary, 

cleaning the individual samples. Additional details on the control cabinet and catalyst samples 

are provided in later sections. The two in situ reactor probes were installed vertically downward 

from the top of a horizontal section of the economizer exit duct, as shown in Figure 2-3. 

Air

Exhaust

Venturi

Eductor

Flue Gas Ammonia and

Injection Air

Catalyst Sootblower Air

Catalyst Beds Treated Flue Gas

Inlet

Scoop

with vane

Scoop Sootblower Air

Flow Straightener

Figure 2-1 

In Situ Mini SCR Reactor Schematic 
Test Apparatus and Methodology 

2-2 

 

Figure 2-2 

Photographs of In Situ Mini SCR Reactor System (control cabinet on left, reactor on right) 

The reactor inlet consists of a 90° turning scoop with an opening that is sized for near-isokinetic 

sampling of the ash-laden flue gas at the reactor location for full-load boiler operating 

conditions. Anhydrous ammonia is injected through a multiple orifice nozzle at the probe inlet, 

and the NH3 injection rate controlled by a mass flow controller. The reactor is also fitted with 

sootblowers for cleaning both the catalyst bed, as well as the inlet scoop. Dry instrument air is 

used for the sootblowing medium, and a sootblowing cycle is automatically activated once every 

two hours for a period of two minutes. 

Flue gas is drawn through each reactor with a vacuum eductor driven with plant compressed air. 

An eductor is utilized as the motive force for the system because it is more reliable than a pump 

or blower for this application. Downstream of the catalyst but before entering the eductor, the 

gas flow is measured with a venturi (Figure 2-1). The eductor motive air is metered to control the 

flue gas flow rate to typical SCR velocities of 15 to 18 ft/sec. The control system utilizes an 

automatic control valve, with the venturi flow measurement providing the feedback loop to 

maintain the desired flow rate. After passing through the eductor, the gas-air mixture is 

exhausted to the economizer exit duct through the same port from which the flue gas is extracted. 

It should be noted that while the best effort was made to size the reactor inlet nozzle 

appropriately by actually measuring the local flue gas velocity at the reactor inlet location for 

full-load operating conditions, the actual dust loading experienced by the catalyst samples may 

or may not be representative of that for a full-scale SCR installation. It is highly likely that the 

distribution of ash across the duct at the reactor location is highly non-uniform due to the shape 

of the upstream and downstream ductwork (recall Figure 2-3). Additionally, since the reactor 

operates at a fixed flow rate, any variations in boiler operating conditions that affect flue gas 

velocity in the duct (e.g., unit load), will also affect the representativeness of the dust loading 

entering the reactor.
Test Ap

Flue Gas Flow

Air Heater

Economizer

~12 feet

~31 feet

~7.5 feet

Flue Gas Flow

Air Heater

Economizer

~12 feet

~31 feet

~7.5 feet

Figure 2-3 Reactor Installation Location at Economizer Exit 
Test Apparatus and Methodology 

2-4 

Figure 2-4 shows two photographs of the reactors installed at the Martin Lake test site. In the 

upper photograph, both of the reactors are visible, one with an insulated enclosure installed over 

the venturi and eductor assemblies, and the other with the enclosure removed. The lower 

photograph shows a close-up of one reactor with the insulated enclosure partially removed. The 

enclosure, which is in place whenever the system is operating, serves two purposes. First, it 

prevents condensation of moisture inside the eductor where the hot flue gas is mixed with the 

relatively cool plant air used to provide the motive force to pull the flue gas through the reactor. 

While the motive air stream does dilute and cool the reactor exhaust, the gas temperatures can 

still be in the neighborhood of 400 to 500F. Therefore, the insulation also prevents plant 

personnel who may be working in the vicinity of the reactor from coming in contact with any 

heated metal surfaces. 

Reactor Control and Instrumentation 

A single, common control cabinet provides the necessary instrumentation to control and monitor 

operation of the two Mini SCR test reactors. This includes the measurement and recording of 

flue gas temperature and flow rate through each reactor, ammonia injection rates, sootblower 

control, and safety interlocks for both ammonia and flue gas flows. The entire system is 

controlled with a programmable logic controller (PLC), and a datalogger is utilized to archive all 

relevant operational and test parameters. 

The control cabinet includes an electrochemical-based NO and O2

 emissions analysis system, 

which allows the in situ measurement of NO removal and thus provides a means of monitoring 

catalyst activity. The NO/O2 sampling and analysis system is not designed for continuous 

operation. Rather, it is only operated for short periods for the catalyst activity tests. The control 

cabinet also includes an analog modem connection to the datalogger. This feature allows reactor 

operational parameters to be accessed and monitored via a telephone line, and also provides the 

ability to conduct catalyst activity tests remotely. 

Catalyst Coupons 

Two catalyst vendors provided the catalyst samples utilized for the tests described in this report. 

Due to non-disclosure agreements with each vendor, the two manufacturers will be referred to as 

Vendor A and Vendor B throughout this document. 

Vendor A provided four honeycomb-type samples, each with a pitch of 0.28 in. (7mm) and 

overall dimensions of 1.69 in. (42.9mm) square by 39.5 in. (1003mm) in length. The four 

samples were arranged in a 2x2 matrix to fill the inside of the 3.75 in. (95.5mm) square catalyst 

holder section of one reactor (Reactor 1). Figure 2-5 shows a photograph of the inlet side of the 

catalyst holder with the Vendor A samples installed. Note that there is a small gap between the 

outside edge of the samples and the catalyst holder, which is sealed with ceramic insulation to 

prevent flue gas from bypassing the active catalyst area. At periodic intervals throughout the test 

program (nominally every 2000 operating hours), one of the four samples was removed from the 

reactor and sent back to the vendor for chemical and physical analyses. The sample removed was 

replaced with a “fresh” (unexposed) sample provided by the vendor. The goal of this 

removal/replacement methodology over the 8000-hour duration of the test program was to 
Test Apparatus and Methodology 

2-5 

provide the vendor with physical catalyst samples with varying flue gas exposure times (two 

each at nominally 2000, 4000 and 6000 hours, and one at nominally 8000 hours). 

Figure 2-4 

Photographs of Mini SCR Test Reactors Installed at the Martin Lake Site 
Test Apparatus and Methodology 

2-6 

Figure 2-5 

Vendor A Catalyst Samples Installed in the Catalyst Holder for Reactor 1 

Vendor B provided two test coupons containing a plate-type catalyst with a pitch of 0.24 in. 

(6mm). Each coupon consisted of 15 plates enclosed in a stainless steel casing, with exterior 

dimensions of 3.70 in. (94mm) square by 19.7 in (500mm) in length. The coupons were designed 

for insertion into either end of the reactor catalyst holder section, thereby providing a total 

catalyst length of 39.4 in. (1 meter). Figure 2-6 shows a photograph of the two Vendor B 

coupons prior to their installation in the second reactor (Reactor 2). Like the Vendor A samples, 

individual Vendor B plates were periodically removed from the reactor and sent back to the 

vendor for testing. Three plates out of each 15-plate coupon were removed at nominally 1300, 

2000, 4000 and 6000 operating hours. At each of these intervals, the plates removed were 

replaced with fresh plates provided by the vendor. 
Test Apparatus and Methodology 

2-7 

Figure 2-6 

Vendor B Catalyst Coupons Prior to Installation in the Catalyst Holder for Reactor 2 

Test Methodology 

The primary objective of the program was to determine the long-term impacts of Texas Lignite 

coal on SCR operation. It was therefore necessary to expose the catalyst samples to flue gas 

under conditions simulating full-scale SCR operation. At regular intervals throughout the test 

program, catalyst activity was monitored via in situ measurements of the catalyst performance. 

Typically, each reactor ran under the nominal design velocity condition of 18 ft/sec (5.5 m/s), 

with an NH3/NOx ratio of 0.9. Catalyst gas velocity was used as the flow design criterion, and the 

space velocity (SV) depended on the lengths of the catalyst samples. For the tests in this study, 

SV varied from 8,200 to 8,400 1/hr. Ash loading and gas temperature experienced by each 

reactor were dependent on boiler outlet conditions at the location of each individual reactor. 

Actual full-load gas velocities at the reactor sample point were verified during the startup of each 

reactor. During catalyst activity evaluations, higher ammonia flows were used; this is discussed 

further in the next section. Table 2-1 shows the Mini SCR test conditions for both normal 

operation and activity test conditions. 

Table 2-1 

Nominal Mini SCR Test Conditions 

Catalyst Gas Velocity = 18 ft/sec (5.5 m/s) 

Temperature = 750-810°F (390-432°C) 

Ammonia = NH3/NOx ~ 0.9 (normal) 

NH3/NOx

 ~ 1.8-2.0 (activity test) 
Test Apparatus and Methodology 

2-8 

Catalyst Activity Determination 

An SCR catalyst’s activity depends on a series of physical transport and chemical reaction 

processes including macro- and micro-pore diffusion, absorption, catalytic reactions, and 

desorption. The catalyst activity constant, K, embodies the mass transfer coefficient, kinetic rate 

constant and geometric terms. For this study, K is defined by: 

K = - SV ln (1-∆NOx), Eq. [1]

where ∆NOx is the fractional NOx removal, and SV is the catalyst space velocity in 1/hr. 

Equation 1 is derived from a first-order analysis balancing the mass (gas) transport and chemical 

reaction terms. While K is at times defined slightly differently in the catalyst industry to 

accommodate individual catalyst geometries, the definition above helps to quantify and compare 

relative activity changes over time. 

As shown in Table 2-1, the ammonia flow during activity tests is increased from nominally 0.9 to 

2.0. Saturating the catalyst with ammonia helps in activity determination since it makes the 

reaction limited by NO mass transport and kinetics, not NH3

 availability. Also, running higher 

NH3/NOx results in the maximum NOx removal and eliminates the need for a precise 

determination of the NH3/NOx ratio. 

As described previously, NOx removals were measured using electro-chemical sensors for O2 and 

NO only. Ammonia and NO2 were not measured. Gas sampling was conducted at the exit of each 

catalyst holder (e.g., at the diffuser section of the venturi), as well as at the inlet of each reactor 

at a point in the economizer exit duct adjacent to the reactor scoop. The reactor control cabinet 

housed two separate O2

 and NO analysis systems, allowing the simultaneous measurement of 

inlet and outlet conditions. 

Long-Term Test Programs 

A long-term test program was structured to ensure proper operation of the test reactor and 

monitoring of catalyst performance. Care was taken on test reactor startup to characterize the 

initial or “fresh” activity of each catalyst (K0). Following startup, site inspections and tests were 

scheduled every 2 weeks for the first 2 months, and then every 4 weeks thereafter. This schedule 

varied somewhat, with early tests ranging from weekly to every 3 weeks. Remote testing via the 

dial-in modem was conducted during the week(s) between site visits. 

General Comments on Catalyst Activity Test Results 

The results from the prior EPRI co-funded long-term catalyst activity evaluation programs (1, 2) 

showed that the activity results from the In Situ Mini SCR test apparatus are subject to a small 

amount of scatter in the data, suggesting limited precision in the results in the range of ±5 to ±8 

percentage points in the determination of K/K0. Measurement uncertainty in these activity 

determinations are affected by: (1) catalyst flow rate fluctuations and uncertainties in venturi ∆P 

measurement, (2) boiler O2

 and NOx changes over the course of the performance measurements, 

(3) NO measurement uncertainty, and (4) temperature. By far, catalyst flow or velocity is the 
Test Apparatus and Methodology 

2-9 

biggest limitation on experimental precision. These are affected by swings in the motive air 

control valve, changes in boiler conditions, and ash deposition in the reactor and venturi. These 

factors underscore the need for periodic inspection and cleaning, and are the reason for the 

practice of probe cleaning before running the on-site activity tests. 

Even considering this inherent variability, the in situ activity tests provide a more detailed means 

of tracking the overall performance of the catalyst samples. The alternative is to rely solely on 

the vendor’s laboratory K/K0 determinations. For the work reported herein, only a few data 

points would be available over the duration of the test program (corresponding to each reactor’s 

scheduled 2000-hour catalyst exchange intervals), and one would not know if a decrease in 

activity were gradual, or the result of a step change due to some operating anomaly of the host 

unit or test apparatus. 

Given the level of variability in the in-situ activity measurements, testing protocols were defined 

such that rather than running a single activity test on a given day, a minimum of two tests were 

run in order to gain a better understanding of the test-to-test repeatability of the measurements. 

Instead of plotting the average of all the tests for a particular day, the results of each test will be 

shown individually in the summary tables and figures. This approach allows an assessment of 

both the test-to-test variations in the measurements, as well as the day-to-day variations in the 

overall process. 

3-1 

3

LONG-TERM TEST RESULTS 

The test program at Martin Lake lasted approximately thirteen (13) months and logged over 8000 

hours of operation on each of the two reactors. These operating hour totals exclude ten (10) short 

unplanned host-unit outages that varied from nominally 30 to 160 hours in length. The total 

boiler outage time over the duration of the test program was approximately 870 hours. 

The results of the long-term tests are presented in the following sections. First, there is a general 

discussion of operating data trends and general observations for both reactors. This is followed 

by individual discussions of the catalyst activity results for each reactor. Note that the reactors 

housing the Vendor A and Vendor B samples are referred to as Reactors 1 and 2, respectively. 

Data Trends and General Observations 

Figures 3-1 and 3-2 show the temperature and venturi pressure drop (∆P) trends for Reactors 1 

and 2, respectively. Note that each figure is based on reactor operating hours, which for the 

purposes of this study, are defined as hours when both the host unit (Martin Lake Unit 3) and the 

reactor were operating. The reactor was considered to be operating when there was flue gas flow 

through the catalyst sample and NH3 injection was “on”. Therefore, due to the combination of the 

host-unit outages and other intervals when a particular test reactor was not in service, the 

reported operating hours do not correspond to the overall number of hours a reactor was actually 

installed in the duct. Additionally, it should also be noted that Reactor 2 was brought online 

approximately 330 hours (2 weeks) after Reactor 1. Thus, the “zero” hour points in Figures 3-1 

and 3-2 do not correspond to the same point in “real” or “calendar” time. 

The monthly on-site visits by FERCo personnel provided the opportunity to disassemble and 

inspect both reactor systems. During each site visit, the inner reactor housings were removed 

from the outer reactor shells, and the catalyst coupons were inspected and cleaned of ash 

accumulation prior to any catalyst activity testing. Any plugged catalyst channels were cleared 

with dry compressed air, and any probe hardware downstream of the catalyst such as the venturi, 

eductor and flue gas return hose were also manually cleaned with wire brushes. This frequent 

cleaning schedule prevented the accumulation of significant deposits, and thus assured optimal 

long-term operation of each reactor system. Additionally, this inspection schedule allowed 

FERCo personnel to closely monitor the physical condition of the catalyst samples, as there was 

initial concern the high fly ash silica content would lead to accelerated erosion. After over 8000 

of operation on both reactors, neither catalyst sample showed signs of excessive erosion. 
Long-Term Test Results 

3-2 

0

100200300400500600700800900

1000

0 1000 2000 3000 4000 5000 6000 7000 80

Operating Hours

Temperature, deg F

Duct TVentur

Figure 3-1 Temperature and Flow (∆P) Data for Reactor 1 (Vendor A Catalyst) 
0

100200300400500600700800900

1000

0 1000 2000 3000 4000 5000 6000 7000 80

Operating Hours

Temperature, deg F

Duct TVentur

Figure 3-2 Temperature and Flow (∆P) Data for Reactor 2 (Vendor B Catalyst)
Long-Term Test Results 

3-4 

Since the flue gas flow rate through each reactor is proportional to the square root of the venturi 

∆P, the pressure drop trends provide a good indication of the cleanliness and flow performance 

of each individual reactor. A significant increase in fly ash deposition anywhere along the reactor 

flow path will result in an increase in the overall pressure drop through the system. The increased 

system pressure drop will require an increase in the motive air flow to the eductor in order to 

maintain the desired flue gas flow through the reactor. Unless the deposits are removed, the 

motive air control valve will eventually reach its limit, and the flow through the reactor (and 

consequently the venturi ∆P reading) will begin to fall. The two venturies were sized to provide a 

pressure drop of 2.0 to 2.2 in. H2O (3.7 to 4.1 mm Hg), at the reactor design operating conditions 

outlined in Table 2-1. 

Figures 3-1 and 3-2 indicate the venturi ∆P traces for both reactors exhibit good consistency with 

only a few instances when the pressure drop varied from the normal range for a significant length 

of time. The data for Reactor 1 (Figure 3-1) show three such instances in the interval between 

2000 and 3500 operating hours. Figure 3-2 shows three similar instances for Reactor 2 in the 

interval between 1500 and 3000 operating hours. In each of these cases, the reduced flow rates 

can be attributed to an upset in the plant service air supply that was utilized to provide the motive 

power to the eductor for each of the two reactors. Each of these upsets resulted in partial 

plugging of the service air filter element located inside the common reactor control cabinet. 

Increased attention to the status of the filter element precluded these problems for the remainder 

of the test program. 

In addition to the three service air related instances, Figure 3-1 also shows a fourth occurrence 

toward the end of the test program (nominally 8000 operating hours) where the Reactor 1 flow 

was below the normal range for a significant amount of time. Similarly, Figure 3-2 shows a 

period very early in the test program when the Reactor 2 flow was well above normal. Both of 

these occurrences can be attributed to faulty (intermittent) venturi temperature readings, which 

were readily corrected once the problem was discovered, investigated and diagnosed. 

Overall, the Reactor 2 system proved to be slightly more susceptible to deposition and plugging 

compared to Reactor 1. However, it should be noted that ash deposition in the catalyst was never 

found to be an issue in either reactor. Rather, the eductor for Reactor 2 had a tendency to collect 

ash more quickly than the unit for Reactor 1. Thus, the Reactor 2 system needed cleaning on a 

more frequent basis, leading to slightly more excursions from the normal flow range as shown in 

Figure 3-2. 

Reactor 1 Activity Test Results (Vendor A Catalyst Samples) 

Activity tests for the Vendor A catalyst samples were run in two different reactor configurations. 

The majority of tests were run in a “full-flow” configuration where flue gas was directed through 

all four samples loaded into the reactor test section. In general, in situ activity tests were run in 

this configuration every two weeks in order to define the long-term catalyst activity trends. 

Recall however, that the test plan called for removing 25 percent of the catalyst sample (i.e. one 

of the four pieces) every 2000 hours, and replacing the piece removed with a fresh sample. Thus, 

each time a catalyst sample exchange occurs, all subsequent activity measurements will be 

biased high due to the activity of the fresh replacement sample. 
Long-Term Test Results 

3-5 

In order to more accurately track the long-term activity trends for the Vendor A catalyst, a 

second group of activity tests were run in a “1⁄4-flow” configuration where flue gas was directed 

through only one of the four samples. Running these tests required the installation of ceramic 

fiber gasket material and stainless steel blocking plates on both the inlet and outlet of the catalyst 

holder to prevent flue gas flow through the three remaining catalyst samples. Figure 3-3 shows a 

photograph of the inlet of the Reactor 1 catalyst holder with the ceramic fiber material in place, 

as well as a photograph of one of the stainless steel blocking plates. During the 1⁄4-flow tests, 

both the flue gas and NH3 flows were reduced by 75 percent to maintain the same general gas 

velocity and NH3/NO conditions as the full-flow tests. 

 

Figure 3-3 

Ceramic Fiber Gaskets and Stainless Steel Blocking Plates Utilized for 1⁄4-Flow Tests on 

Reactor 1 (Vendor A Catalyst) 

The test plan called for the removal of three of the four catalyst samples originally installed in 

the reactor at 2000-hour intervals. The reduced-flow activity tests were run on the one original 

catalyst sample that was to remain in the reactor throughout the 8300-hour test program. 

Additionally, since these tests required physically modifying the reactor from the normal 

operating configuration (installation of the gasket material and blocking plates), the 1⁄4-flow tests 

were run only when FERCo personnel were onsite during the monthly inspections. 

Reactor 1: Full-Flow Test Results 

The full-flow test results for Reactor 1 are summarized in Table 3-1, and presented graphically in 

Figure 3-4. The vertical dashed lines in Figure 3-4 show the timing of the three catalyst exchange 

intervals, and the “open” data points indicate the in situ measurements made immediately after 

an exchange. As expected, the NO removals show a slight increase (1-3% absolute NO removal) 

each time a catalyst sample was removed and replaced with a fresh piece. Prior to the first 

catalyst exchange, the measured NO removals leveled out at an initial level of 88% within the 

first 1000 hours. The remainder of the data indicates a slow rate of deactivation throughout the 

rest of the test period. After 8360 hours, the full-flow NO removal had settled in at 

approximately 84%.
Long-Term Test Results 

3-6  (a) NO Removal (b) K/K0

Figure 3-4 Reactor 1 Full-Flow Activity Results: (a) NO Removal, (b) K/K0 

0

102030405060708090

100

0 2000 4000 6000 8000 10000

Operating Hours

NO Removal, %

In-Situ TestsPost-ExchangeIn-Situ Tests

0.00.20.40.60.81.01.2

0 2000 4000 6000 

Operating Hours

Activity Ratio, K/Ko
Long-Term Test Results 

3-7 

Table 3-1 

Reactor 1: Full-Flow Data Summary 

Date Time Operating Hours dNO K/K0 Comments 

5/1/2002 1430 0 94* -- Initial day on-site 

5/1/2002 1505 1 95* -- Initial day on-site 

5/2/2002 530 15 95* -- Second day on-site 

5/2/2002 620 16 94* -- Second day on-site 

5/8/2002 1005 164 93* -- Via modem 

5/8/2002 1114 165 92* -- Via modem 

5/15/2002 1630 338 91 0.97 On-site 

5/15/2002 1710 339 92 0.99 On-site 

5/30/2002 1340 695 87 0.82 On-site 

5/30/2002 1425 696 91 0.95 On-site 

6/12/2002 915 975 88 0.83 Via modem, U3 outage 28 hrs 

6/12/2002 955 975 89 0.86 Via modem, U3 outage 28 hrs 

6/26/2002 1530 1317 88 0.84 On-site 

6/26/2002 1600 1318 89 0.88 On-site 

7/17/2002 835 1665 87 0.82 Via modem, U3 outage 149 hrs 

7/17/2002 920 1666 89 0.87 Via modem, U3 outage 149 hrs 

7/31/2002 827 1977 89 0.87 On-site, NH3 off 24 hrs 

7/31/2002 855 1977 89 0.88 On-site, NH3 off 24 hrs 

8/1/2002 925 2002 89 0.88 On-site, after 2k hr coupon exchange 

8/1/2002 1010 2003 91 0.95 On-site, after 2k hr coupon exchange 

8/14/2002 948 2314 88 0.85 Via modem 

8/14/2002 1021 2315 89 0.89 Via modem 

8/30/2002 422 2632 88 0.86 On-site, U3 outage 61 hrs 

8/30/2002 458 2632 89 0.87 On-site, U3 outage 61 hrs 

9/18/2002 932 2935 88 0.85 Via modem, U3 outage 158 hrs 

9/18/2002 953 2935 90 0.91 Via modem, U3 outage 158 hrs 

10/8/2002 1550 3099 87 0.81 On-site, probe off 322 hrs 

10/8/2002 1620 3100 89 0.87 On-site, probe off 322 hrs 

10/24/2002 1115 3402 79 0.56 Via modem, U3 outage 77 hrs 

10/24/2002 1145 3402 82 0.65 Via modem, U3 outage 77 hrs 

10/24/2002 1218 3403 81 0.64 Via modem, U3 outage 77 hrs 

11/6/2002 1805 3721 86 0.78 On-site 

11/6/2002 1835 3721 84 0.74 On-site 

11/20/2002 1035 3990 81 0.67 Via modem, U3 outage 59 hrs 
Long-Term Test Results 

3-8 

Date Time Operating Hours dNO K/K0 Comments 

11/25/2002 910 4039 82 0.68 Via modem, U3 outage 70 hrs 

11/25/2002 945 4039 85 0.77 Via modem, U3 outage 70 hrs 

11/25/2002 1027 4040 84 0.74 Via modem, U3 outage 70 hrs 

12/3/2002 1859 4240 85 0.77 Via modem 

12/3/2002 1929 4241 84 0.73 Via modem 

12/4/2002 1815 4264 86 0.78 On-site, after 4k hr coupon exchange 

12/4/2002 1845 4264 88 0.83 On-site, after 4k hr coupon exchange 

12/19/2002 943 4588 87 0.81 Via modem, probe off 27 hours 

12/19/2002 1010 4589 86 0.79 Via modem, probe off 27 hours 

1/15/2003 1111 4998 84 0.73 Via modem, NH3 off 96 hrs, U3 outage 144 hrs 

1/15/2003 1150 4998 82 0.69 Via modem, NH3 off 96 hrs, U3 outage 144 hrs 

1/31/2003 940 5380 81 0.66 Via modem 

1/31/2003 1024 5381 81 0.65 Via modem 

2/19/2003 932 5774 78 0.60 Via modem, U3 outage 62 hours 

2/19/2003 1025 5775 81 0.66 Via modem, U3 outage 62 hours 

2/19/2003 1025 5775 84 0.73 Via modem, U3 outage 62 hours 

3/11/2003 2359 6268 79 0.63 Via modem 

3/12/2003 33 6269 81 0.66 Via modem 

3/12/2003 1915 6288 82 0.69 On-site, after 6k hr coupon exchange 

3/12/2003 1950 6288 85 0.76 On-site, after 6k hr coupon exchange 

3/27/2003 1111 6640 88 0.84 Via modem, duct temps 50-60F above normal 

3/27/2003 1139 6640 87 0.82 Via modem, duct temps 50-60F above normal 

4/9/2003 1606 6957 80 0.64 On-site 

4/9/2003 1709 6958 83 0.70 On-site 

4/29/2003 1642 7376 87 0.81 Via modem, U3 outage 61 hours 

4/29/2003 1715 7377 85 0.74 Via modem, U3 outage 61 hours 

4/30/2003 912 7393 82 0.68 Via modem, U3 outage 61 hours 

4/30/2003 943 7393 84 0.73 Via modem, U3 outage 61 hours 

5/14/2003 1542 7735 85 0.75 On-site 

5/14/2003 1612 7736 87 0.79 On-site 

5/28/2003 1146 8067 84 0.70 Via modem 

5/28/2003 1220 8068 83 0.71 Via modem 

6/9/2003 2011 8364 84 0.73 On-site, final test 

6/9/2003 2049 8364 83 0.71 On-site, final test 

*

 NOx reduction measurements questionable 
Long-Term Test Results 

3-9 

As mentioned in Section 2, previous test programs have shown that the in situ reactor test results 

are subject to a small amount of scatter, due to variability in the operation of both the reactor 

itself, as well as the host boiler. Generally, the variation in NO removals for tests run on a single 

day is usually on the order of 2 to 3%. On the days when the variation was found to be greater, 

additional tests were run in order to reduce the effect of a single “spurious” test. There were 

occasions however, when the variation in the NO removal measurements for a single day was 

very small, but the overall removal levels were either markedly higher or lower than expected. 

The full-flow data presented in Figure 3-4 shows two of these occurrences, the first at 

approximately 3400 hours, and the second at 6640 hours. The tests on both days were conducted 

“remotely” via the modem connection to the datalogger, and therefore FERCo personnel were 

not on-site to perform a detailed assessment of the reactor or boiler conditions that may have 

contributed to the unexpected results. In the latter case however, the reactor operating data 

recorded by the datalogger suggest that a transitory increase in the flue gas temperature may at 

least be partially responsible for the temporary NO removal increase seen at 6640 hours. Each 

reactor is outfitted with a thermocouple that monitors the flue gas temperature inside the duct at 

the location of the reactor inlet scoop. Historically, the flue gas temperatures recorded during the 

Reactor 1 activity tests ranged from 770 to 790°F. On the day of the 6640-hour tests however, 

the recorded temperatures were nominally 50 to 60°F higher than normal (ranging from 820 to 

835F). It is well known that the SCR deNOx reaction mechanism is temperature dependent, and 

thus the NO removal increase seen at 6640 hours may be partially attributed to an increase in the 

local flue gas temperature. Review of the datalogger files for the tests run at 3400 hours when the 

NO removals dropped dramatically did not reveal any flue gas temperature anomalies, and the 

reason for the sharp, albeit temporary, decline is unknown at this time. 

The catalyst activity (K) results presented in Table 3-1 and Figure 3-4 have been normalized to 

the initial, or fresh, catalyst activity (K0). Generally, K0 is established from the average of 

multiple activity measurements made on the first day of testing. However, it is also possible to 

determine K0 by comparing the results of activity tests run immediately before and after each 

catalyst coupon exchange. The increase in overall reactor activity measured immediately after 

the exchange, relative to that measured before, can be attributed to 25% of the catalyst volume 

being replaced by a new, fresh sample (e.g., a piece with an activity of K0). 

Analysis of the Reactor 1 test results showed the K0 values calculated via the two means outlined 

above were quite different. Namely, the K0 value determined from the initial day of testing was 

nominally 15% higher than the average of the values calculated at the 2000–, 4000-, and 6000-

hour catalyst exchange intervals. Analysis of the data suggests that this may have been related to 

some measurement issues with the system early in the project. Thus, for the purposes of this 

report, the in situ K/K0 values presented are based on the K0 value determined by measuring the 

change in overall reactor activity at each catalyst exchange interval. 

The catalyst activity calculations are directly derived from the in situ NO removal data and the 

space velocity calculations (recall the discussion in Section 2). Therefore, one would expect to 

see the same overall trends in NO removal and K results. The full-flow K/K0 data shown in 

Figure 3-4 show that after an initial decline to a value of nominally 0.85, the deactivation rate 

slowed significantly and K/K0 measured in the full-flow configuration eventually settled out at a 

value of approximately 0.72. 
Long-Term Test Results 

3-10 

Reactor 1: 1⁄4-Flow Test Results 

The 1⁄4-flow test results for Reactor 1 are summarized in Table 3-2, and presented graphically in 

Figure 3-5. Prior to the first catalyst coupon exchange, one would expect the initial NO removal 

results for the full-flow and 1⁄4-flow test configurations to be nearly equivalent. However, review 

of the first few sets of data in Tables 3-1 and 3-2 show that the initial NO removal results for the 

1⁄4-flow configuration were markedly higher than those for the full-flow tests (nominally 100% 

removal versus 95%). As noted in Table 3-2, the initial 1⁄4-flow tests suffered from problems with 

the method used to isolate the three catalyst samples that were to be bypassed. These problems 

resulted in the calculation of abnormally high NO removals for the first few 1⁄4-flow tests. The 

isolation technique was refined during subsequent site visits, and the issue was resolved after the 

fourth set of tests when the NO removals settled in at 90 to 91%. By the end of the 8300-hour 

test, the removals had slowly decayed to a nominal level of 82%. 

Since the catalyst activity calculations are directly derived from the in situ NO removal data, the 

initial catalyst isolation issues experienced in the 1⁄4-flow configuration also yielded elevated K 

values that were of no use for determining a representative 1⁄4-flow K0 benchmark. While there 

were still seemed to be minor issues with the isolation technique during the second and third site 

visits (5/15/02 and 5/30/02), the problems were considered to be completely resolved by the time 

the first catalyst exchange occurred on 8/1/02 (nominally 2000 operating hours). Rather than try 

to estimate K0 based on the initial 1⁄4-flow activity tests, the value utilized for the full-flow tests 

was used as the basis of the K/K0 data presented in Table 3-2 and Figure 3-5. 

The K/K0 results for the 1⁄4-flow tests indicate that after an initial decline, the deactivation rate 

slowed considerably. At the end of the 8300-hour test program, the K/K0 values for the 1⁄4-flow 

tests settled out at a value of approximately 0.75. These results are consistent with those from the 

full-flow tests, as one would expect the final K/K0 values for the 1⁄4-flow tests to be slightly 

lower, due to the periodic influx of fresh catalyst samples in the full-flow configuration. 

In addition to the in situ activity tests, additional physical and chemical analyses were conducted 

by the catalyst vendor on each of the catalyst samples removed from the reactor. For comparison 

purposes, the average K/K0 value calculated from the Vendor A laboratory analysis for each of 

the seven individual catalyst samples has been plotted alongside the in situ activity results in 

Figure 3-5. The following section contains excerpts from the Vendor’s report, providing details 

of the test methodology and results. 

Vendor A Laboratory Activity Test Results 

The catalyst activity was determined using the Vendor’s Micro Activity Test Reactor. The test is 

a small-scale test used for the evaluation of the activity of DeNOx catalyst at standard conditions. 

A 6 cell by 6 cell by 175 mm sample was cut from the upstream face, the middle, and the 

downstream face of each sample. Each sample was tested at the standard conditions shown in 

Table 3-3. 

Table 3-4 provides a summary of the exposure history for each sample, as well as the laboratory 

activity results expressed as the ratio of the field activity to the activity of the fresh sample 

(K/K0). A K/K0 of 0.50 indicates a 50% decline in catalytic activity relative to the fresh sample. 
 (a) NO Removal (b) K/K0

Figure 3-5 Reactor 1 1⁄4-Flow Activity Results: (a) NO Removal, (b) K/K0 

0

102030405060708090

100

0 2000 4000 6000 8000 10000

Operating Hours

NO Removal, %

In-Situ Tests

0.00.20.40.60.81.01.2

0 2000 4000 6000 

Operating Hours

Activity Ratio, K/Ko
Long-Term Test Results 

3-12 

Table 3-2 

Reactor 1: 1⁄4-Flow Data Summary 

Date Time 

Operating 

Hours dNO K/Ko Comments 

5/1/2002 1730 0 99* -- Initial day on-site, 1/4-flow isolation problems

5/2/2002 1730 24 102* -- 2nd day on-site, 1/4-flow isolation problems 

5/15/2002 1315 332 94* -- On-site, reduced problems with isolation 

5/15/2002 1355 332 93* -- On-site, reduced problems with isolation 

5/30/2002 1105 690 92* -- On-site, slight problems with isolation 

5/30/2002 1150 690 92* -- On-site, slight problems with isolation 

6/26/2002 1320 1312 91 1.04 On-site, isolation problems resolved 

6/26/2002 1355 1312 90 0.98 On-site, isolation problems resolved 

7/31/2002 1230 1978 87 0.89 On-site, just before 2k hr coupon exchange 

7/31/2002 1310 1979 93* -- On-site, just before 2k hr coupon exchange 

8/30/2002 856 2633 89 0.94 On-site 

8/30/2002 930 2634 90 1.00 On-site 

10/8/2002 1345 3094 88 0.90 On-site 

10/8/2002 1420 3095 89 0.95 On-site 

11/6/2002 1445 3714 83 0.78 On-site 

11/6/2002 1535 3715 86 0.85 On-site 

12/4/2002 1610 4259 87 0.87 On-site, just before 4k hr coupon exchange 

12/4/2002 1640 4259 89 0.97 On-site, just before 4k hr coupon exchange 

3/12/2003 1648 6282 80 0.70 On-site, just before 6k hr coupon exchange 

3/12/2003 1728 6283 81 0.72 On-site, just before 6k hr coupon exchange 

4/9/2003 1351 6951 78 0.65 On-site 

4/9/2003 1427 6952 79 0.68 On-site 

5/14/2003 1311 7730 81 0.74 On-site 

5/14/2003 1356 7730 84 0.80 On-site 

6/10/2003 1020 8375 80 0.70 On-site, final test 

6/10/2003 1051 8375 83 0.77 On-site, final test 

*

 NOx reduction measurements questionable 
Long-Term Test Results 

3-13 

Table 3-3 

Vendor A Catalyst Activity Test Conditions 

Inlet NOx 500 ppmvdc 

Inlet SO2 300 ppmvdc 

O2 3% vol. dry 

AV 20 Nm3/m2/hr 

NH3:NOx Molar Ratio 1.2 

Gas Temperature 416 °C 

Table 3-4 

Vendor A Catalyst Activity Test Results 

K/K0 Vendor 

Sample 

ID 

Date and 

Time Installed 

Date and 

Time 

Removed 

Exposure 

Hours Front Middle Rear Average 

A May 1, 2002 

0 hrs 

Aug 1, 2002 

2,002 hrs 

2002 0.94 0.99 1.00 0.98 

E 

Mar 12, 2003 

6,288 hrs 

Jun 9, 2003 

8,364 hrs 

2076 0.93 0.97 0.94 0.95 

B Aug 1, 2002 

2,002 hrs 

Dec 4, 2002 

4,264 hrs 

2262 0.85 0.94 0.92 0.91 

G Dec 4, 2002 

4,264 hrs 

Jun 9, 2003 

8,364 hrs 

4100 0.78 0.93 0.87 0.86 

C May 1, 2002 

0 hrs 

Mar 12, 2003 

6,288 hrs 

6288 0.80 0.91 0.85 0.86 

D May 1, 2002 

0 hrs 

Jun 9, 2003 

8,364 hrs 

8364 0.66 0.80 0.82 0.76 

F May 1, 2002 

0 hrs 

Jun 9, 2003 

8,364 hrs 

8364 0.61 0.78 0.79 0.73 

The original intent of the catalyst exchange schedule for the Vendor A samples was to remove 

and replace the samples such that at the end of the program there were two samples each with 

nominally 2000, 4000 and 6000 hours, and then a single sample with 8000 cumulative exposure 

hours. Unfortunately, at the second exchange interval (4000 hours), rather than removing and 

replacing one of the three samples installed in the reactor since the start, a mistake was made and 

the sample replaced during the first exchange (2000 hours) was again removed and replaced. 

This error was not discovered until late in the overall test program, at which point it was too late 
Long-Term Test Results 

3-14 

to correct. As shown in Table 3-4, at the end of the program there were three samples with 

nominally 2000 exposure hours, one each with approximately 4000 and 6000 hours, and then 

two with the full 8360 hours. Figure 3-5 indicates excellent agreement between the vendor’s 

K/K0 results and those measured for the 1⁄4-flow tests in the in situ reactor. 

Reactor 2: Activity Test Results (Vendor B Catalyst Samples) 

Activity tests for the Vendor B catalyst samples were run in only a single reactor configuration, 

with flue gas flow through the entire catalyst test section. The two catalyst coupons provided by 

Vendor B (recall Figure 2-5) were nominally 0.5 meters in length, and were designed for 

insertion into the 1-meter long catalyst holder section from opposite ends. When installed, the 

ends of the two coupons were separated by a small gap at the center of the catalyst holder. With 

this air space between the two coupons, it was not possible to isolate only a portion of the 

catalyst plates installed in the reactor. 

The activity test results for Reactor 2 are summarized in Table 3-5, and presented graphically in 

Figure 3-6. Catalyst exchanges were planned at nominally 1000, 2000, 4000 and 6000 operating 

hours. Unfortunately, the monthly site visit schedule sometimes was not sufficiently flexible to 

allow FERCo personnel to visit the site at exactly the desired time. As a result, the first catalyst 

exchange for Reactor 2 did not occur until the 1300-hour mark. During each of the exchanges, 

one-fifth of the sample plates in each coupon were removed and replaced. The vertical dashed 

lines shown in Figure 3-6 indicate these four catalyst replacement intervals. While the results do 

not indicate an increase in NO removal after the first exchange at 1300 hours, small increases (2-

4% absolute NO removal) can be seen after each of the subsequent catalyst exchanges. 

The NO removal curve for the Vendor B catalyst showed similar behavior to that seen for the 

Vendor A catalyst. The NO removal results for both reactors indicate a slow, but progressive, 

decline in catalyst activity. Initial NO removals for Reactor 2 were in the range of 86 to 88%, 

and after 3000 operating hours the removals seemed to have leveled out at around 81 to 82%. 

After 7500 operating hours, the removals declined a little further to 78%. On the basis of relative 

activity, K/K0

 for the Vendor B catalyst samples had fallen to a nominal value of 0.73 by the 

conclusion of the 8000-hour test. 

In addition to the in situ activity tests, additional physical and chemical analyses were conducted 

on the individual plates removed from the reactor and returned to the catalyst vendor. For 

comparison with the in situ activity data, K/K0 measured by Vendor B in their own laboratory are 

included in Figure 3-6. In the figure, “upstream” denotes the first coupon (e.g. the first layer of 

catalyst) the flue gas passed through. Overall, the vendor’s K/K0 results agree very well with the 

“pre-exchange” in situ results. The following section contains excerpts from the Vendor’s report, 

providing details of the test methodology and results.
0

102030405060708090

100

0 2000 4000 6000 8000 10000

Operating Hours

NO Removal, %

In-Situ TestsPost-ExchangeIn-Situ Tests

0.00.20.40.60.81.01.2

0 2000 4000 6000 

Operating Hours

Activity Ratio, K/Ko I

PTVUVD

 (a) NO Removal (b) K/K0

Figure 3-6 Reactor 2 Activity Results: (a) NO Removal, (b) K/K0
Long-Term Test Results 

3-16 

Table 3-5 

Reactor 2: Data Summary 

Date Time Operating Hours dNO K/K0 Comments 

5/15/2002 1525 0 88 -- Initial day on-site, establish K0

5/15/2002 1545 0 88 -- Initial day on-site, establish K0

5/15/2002 1605 1 86 -- Initial day on-site, establish K0

5/29/2002 2240 55 86 0.96 On-site, reactor off-line 288 hrs 

5/29/2002 2310 56 87 0.98 On-site, reactor off-line 288 hrs 

6/12/2002 1020 351 88 1.00 Via modem, U3 outage 28 hrs 

6/12/2002 1050 351 88 1.00 Via modem, U3 outage 28 hrs 

6/26/2002 1630 693 87 1.01 On-site 

6/26/2002 1710 694 88 1.02 On-site 

7/17/2002 1020 1042 86 0.95 Via modem, U3 outage 149 hrs 

7/17/2002 1050 1042 86 0.93 Via modem, U3 outage 149 hrs 

7/31/2002 915 1353 87 0.97 On-site, NH3 off 24 hrs 

7/31/2002 935 1353 87 0.97 On-site, NH3 off 24 hrs 

8/1/2002 1045 1378 86 0.98 On-site, after 1k hr coupon exchange 

8/1/2002 1120 1379 86 0.96 On-site, after 1k hr coupon exchange 

8/14/2002 1058 1690 85 0.93 Via modem 

8/14/2002 1126 1691 85 0.91 Via modem 

8/30/2002 330 2006 88 1.00 On-site, after 2k hr coupon exchg, U3 outage 61 hrs 

8/30/2002 351 2006 89 1.05 On-site, after 2k hr coupon exchg, U3 outage 61 hrs 

9/18/2002 1021 2311 86 0.97 Via modem, U3 outage 158 hrs 

9/18/2002 1045 2311 87 1.00 Via modem, U3 outage 158 hrs 

10/8/2002 1650 2797 84 0.87 On-site 

10/8/2002 1710 2798 84 0.88 On-site 

10/24/2002 1250 3100 82 0.82 Via modem, U3 outage 77 hrs 

10/24/2002 1250 3100 80 0.76 Via modem, U3 outage 77 hrs 

11/6/2002 1950 3419 82 0.83 On-site 

11/6/2002 2010 3420 82 0.83 On-site 

11/25/2002 1108 3738 81 0.79 Via modem, U3 outages 59+70 hrs 

11/25/2002 1135 3738 81 0.80 Via modem, U3 outages 59+70 hrs 

12/3/2002 2002 3939 82 0.81 Via modem 

12/3/2002 2030 3939 82 0.81 Via modem 
Long-Term Test Results 

3-17 

Date Time Operating Hours dNO K/K0 Comments 

12/4/2002 1920 3962 84 0.89 On-site, after 4k hr coupon exchange 

12/4/2002 1945 3962 84 0.89 On-site, after 4k hr coupon exchange 

12/19/2002 1045 4288 82 0.82 Via modem, probe off 25 hours 

12/19/2002 1127 4289 84 0.88 Via modem, probe off 25 hours 

1/15/2003 1224 4698 81 0.79 Via modem, NH3 off 96 hours, U3 outage 144 hours 

1/15/2003 1308 4699 81 0.81 Via modem, NH3 off 96 hours, U3 outage 144 hours

1/31/2003 1058 5080 81 0.78 Via modem 

1/31/2003 1145 5081 82 0.81 Via modem 

2/19/2003 1149 5475 80 0.79 Via modem, U3 outage off 62 hours 

2/19/2003 1224 5476 83 0.84 Via modem, U3 outage off 62 hours 

3/12/2003 112 5969 79 0.76 Via modem 

3/12/2003 145 5969 81 0.79 Via modem 

3/12/2003 2024 5988 82 0.84 On-site, after 6k hr coupon exchange 

3/12/2003 2054 5988 83 0.85 On-site, after 6k hr coupon exchange 

3/27/2003 1210 6340 85 0.92 Via modem, duct temps 50-60F above normal 

3/27/2003 1234 6340 87 0.96 Via modem, duct temps 50-60F above normal 

4/9/2003 1748 6657 81 0.80 On-site 

4/9/2003 1817 6658 82 0.84 On-site 

4/29/2003 1751 7076 80 0.78 Via modem, U3 outage 61 hours 

4/29/2003 1824 7077 80 0.76 Via modem, U3 outage 61 hours 

5/14/2003 1639 7435 80 0.78 On-site 

5/14/2003 1705 7436 81 0.79 On-site 

5/28/2003 1247 7767 78 0.73 Via modem 

5/28/2003 1316 7768 78 0.73 Via modem 

6/9/2003 2121 8064 78 0.72 On-site, final test 

6/9/2003 2151 8064 78 0.73 On-site, final test 

Vendor B Laboratory Activity Test Results 

Table 3-6 shows the results of all of the activity tests performed by Vendor B on plate samples 

removed from the Martin Lake test reactor (Reactor 2). Additionally, the vendor’s activity (K/K0) 

results were previously included with FERCo’s in situ results in Figure 3-6. 

The in situ activity tests (Figure 3-6) show that in the time period between 3000 and 7500 

operating hours, relative catalyst activity settled in at around K/K0 = 0.8. Additionally, the 

exchange of plates with new test coupons after 2000, 4000 and 6000 hours boosted the in situ
Long-Term Test Results 

3-18 

catalyst activity. In each case, the increase was followed by a decline in activity back to previous 

levels. After 7500 hours, both the in situ measurements performed by FERCo as well as the final 

Vendor B measurement, indicate a decrease in catalyst activity. 

Overall, the K/K0

 results from the Vendor B laboratory analysis agree very well with the “preexchange” in situ results. 

Table 3-6 

Summary of Vendor B Activity Test Results 

Operating Hours K/K0 

Upstream Coupon 

K/K0 

Downstream Coupon 

1350 0.91 0.97 

2050 0.91 0.96 

3950 0.83 0.85 

5975 0.78 0.82 

8064 0.66 0.75 
4-1 

4

ANALYTICAL TEST RESULTS 

Throughout the Martin Lake test program, catalyst samples were periodically removed from each 

reactor, and then returned to the appropriate catalyst vendor for analysis. No attempt was made 

to assure each vendor performed similar chemical and physical analyses. In general however, 

each vendor ran their own relative activity tests for comparison to the in situ results, as well as 

performed various chemical and physical analyses aimed at identifying possible deactivation 

mechanisms. The results of each vendor’s activity tests were discussed in the previous section of 

this report. The following sections contain excerpts from the vendor reports regarding the 

chemical and physical analyses performed in an effort to identify possible deactivation 

mechanisms. Note that the authors of this EPRI report have made no attempt to interpret or 

elaborate on each vendor’s laboratory results and discussion. 

Vendor A Analytical Test Results 

Samples were removed from the Martin Lake Unit 3 test reactor at the intervals shown in Table 

4-1. The following sections summarize the results of the laboratory testing performed on these 

samples. 

Table 4-1 

Vendor A Catalyst Sample Exposure History 

Sample Date and Time 

Installed 

Date and Time 

Removed 

Exposure 

Hours 

A May 1, 2002 

0 hrs 

Aug 1, 2002 

2,002 hrs 2002 

B Aug 1, 2002 

2,002 hrs 

Dec 4, 2002 

4,264 hrs 2262 

C May 1, 2002 

0 hrs 

Mar 12, 2003 

6,288 hrs 6288 

D May 1, 2002 

0 hrs 

Jun 9, 2003 

8,364 hrs 8364 

E Mar 12, 2003 

6,288 hrs 

Jun 9, 2003 

8,364 hrs 2076 

F May 1, 2002 

0 hrs 

Jun 9, 2003 

8,364 hrs 8364 

G Dec 4, 2002 

4,264 hrs 

Jun 9, 2003 

8,364 hrs 4100 
Analytical Test Results 

4-2 

Surface Area 

The surface area of the samples was measured with BET Isotherm on an inner wall of a small 

portion of a sample cut from the flow entrance and the flow exit faces of the catalyst samples. 

Table 4-2 and Figure 4-1 below show the data expressed as the ratio of the field surface area to 

the surface area of the fresh sample. A relative surface area of 0.50 indicates a 50% decline in 

surface area relative to the fresh sample. 

Table 4-2 

Catalyst A BET Surface Area 

 Relative Surface Area 

Front Rear Average 

A 0.92 0.91 0.91 

B 0.90 0.90 0.90 

C 0.84 0.86 0.85 

D 0.83 0.82 0.83 

E 0.88 0.91 0.90 

F 0.84 0.80 0.82 

G 0.83 0.87 0.85 

TXU Martin Lake Slipstream 

Relative Surface Area

Fresh

Sample G

Sample F

Sample E

Sample C Sample D Sample B

Sample A

0.5

0.6

0.7

0.8

0.9

1

0 2,000 4,000 6,000 8,000 10,000

Exposure Hours

Relative Surface Area

Front

Rear

Average

Figure 4-1 

Catalyst A BET Surface Area
Analytical Test Results 

4-3 

Pore Volume 

The pore volume and median pore diameter of the samples was measured with mercury 

porosimetry on an inner wall of a small portion of a sample cut from the flow entrance and the 

flow exit faces of the catalyst samples. Table 4-3 and Figure 4-2 show the data expressed as the 

ratio of the field pore volume to the pore volume of the fresh sample. A relative pore volume of 

0.50 indicates a 50% decline in pore volume relative to the fresh sample. 

Table 4-3 

Catalyst A Pore Volume

 Relative Pore Volume 

Front Rear Average 

A 0.93 0.91 0.92 

B 0.99 0.95 0.97 

C 0.98 0.94 0.96 

D 0.82 0.82 0.82 

E 0.82 0.85 0.83 

F 0.83 0.82 0.83 

G 0.83 0.87 0.85 

TXU Martin Lake Slipstream 

Relative Pore Volume

Sample A

Sample B Sample C

Sample D

Sample E Sample G Sample F

Fresh

0.5

0.6

0.7

0.8

0.9

1

0 2,000 4,000 6,000 8,000 10,000

Exposure Hours

Relative Pore Volume

Front

Rear

Average

Figure 4-2 

Catalyst A Pore Volume 
Analytical Test Results 

4-4 

Table 4-4 and Figure 4-3 show the results of pore size as the ratio of the field median pore 

diameter to the median pore diameter of the fresh sample. A relative median pore diameter of 

0.50 indicates a 50% decline in median pore diameter relative to the fresh sample. 

Table 4-4 

Catalyst A Median Pore Diameter

 Relative Median Pore Diameter 

Front Rear Average 

A 1.18 1.11 1.14 

B 1.21 1.04 1.13 

C 1.15 1.18 1.17 

D 1.39 1.38 1.39 

E 1.44 1.36 1.4 

F 1.47 1.38 1.42 

G 1.44 1.48 1.46 

TXU Martin Lake Slipstream 

Relative Median Pore Diameter

Fresh

Sample G Sample F

Sample E Sample D

Sample C

Sample B

Sample A

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 2,000 4,000 6,000 8,000 10,000

Exposure Hours

Relative Median Pore Diameter

Front

Rear

Average

Figure 4-3 

Catalyst A Median Pore Diameter 
Analytical Test Results 

4-5 

Bulk Chemical Composition 

The bulk chemical composition was determined with X-Ray Fluorescence (XRF). The samples 

for the XRF were taken from an inner wall of a small portion of a sample cut from the catalyst 

samples. Three samples were taken: one from the flow entrance face, one near the middle of the 

sample, and one near the flow exit face of the sample. The samples were ground and pressed into 

pellets and XRF was used to determine the elemental composition of the sample. The relative 

bulk chemical composition is calculated by dividing the concentration of a given compound by 

the average concentration of that compound in all the samples tested. A relative chemical 

composition of 0.50 indicates a 50% lower concentration than the average of all samples tested. 

The results of the bulk chemical analysis for arsenic, potassium, and sodium are shown in 

Tables 4-5 through 4-7, and Figures 4-4 through Figure 4-6, respectively. 

The chemical concentrations of the three main catalyst constituents TiO2, V2O5, and WO3 

remained unchanged throughout all the samples tested. The level of CaO in the bulk of the 

catalyst has increased with increasing exposure time. CaSO4 poisoning is primarily a surface 

phenomenon and changes in the bulk concentration cannot be directly correlated to the 

performance changes. Surface composition testing performed on samples A – C reveal a 

dramatic increase in the concentration of CaO on the surface of the exposed samples. 
Analytical Test Results 

4-6 

Table 4-5 

Catalyst A Relative Bulk Concentration of Arsenic 

 Relative Bulk Chemical Composition of As2O3

Front Middle Rear Average 

A 0.90 0.50 0.38 0.59 

B 0.96 0.45 0.30 0.57 

C 1.56 1.16 0.86 1.19 

D 1.98 1.52 1.17 1.56 

E 0.91 0.54 0.30 0.58 

F 1.80 1.44 1.17 1.47 

G 1.51 0.89 0.73 1.04 

Fresh 0.00 

TXU Martin Lake Slipstream 

Relative Bulk Chemical Composition of As2O3

Sample G

Sample F

Sample E

Sample D

Sample C

Sample B

Sample A

Fresh

0

0.5

1

1.5

2

2.5

0 2,000 4,000 6,000 8,000 10,000

Exposure Hours

Relative Bulk Chemical 

Composition of As2

O3

Front

Middle

Rear

Average

Figure 4-4 

Catalyst A Relative Bulk Concentration of Arsenic 
Analytical Test Results 

4-7 

Table 4-6 

Catalyst A Relative Bulk Concentration of Potassium 

Relative Bulk Chemical Composition of K2O 

Front Middle Rear Average 

A 0.45 0.26 0.25 0.32 

B 1.71 0.31 1.04 1.02 

C 1.27 0.91 0.79 0.99 

D 2.59 1.26 0.85 1.57 

E 0.76 0.41 0.42 0.53 

F 2.88 1.56 1.10 1.85 

G 1.89 0.56 0.60 1.02 

Fresh 0.13 

TXU Martin Lake Slipstream 

Relative Bulk Chemical Composition of K2O

Sample A

Sample B Sample C

Sample D

Sample E

Sample F

Sample G

Fresh

0

0.5

1

1.5

2

2.5

3

3.5

0 2,000 4,000 6,000 8,000 10,000

Exposure Hours

Relative Bulk Chemical 

Composition of K2O

Front

Middle

Rear

Average

Figure 4-5 

Catalyst A Relative Bulk Concentration of Potassium 
Analytical Test Results 

4-8 

Table 4-7 

Catalyst A Relative Bulk Concentration of Sodium 

Relative Bulk Chemical Composition of Na2O 

Front Middle Rear Average 

A 0.64 0.34 0.27 0.42 

B 1.33 0.43 3.90 1.02 

C 1.05 0.86 0.62 0.99 

D 1.55 1.14 0.71 1.57 

E 0.66 0.61 0.62 0.53 

F 1.83 1.23 1.08 1.85 

G 1.42 0.70 0.69 1.02 

Fresh 0.33 

TXU Martin Lake Slipstream 

Relative Bulk Chemical Composition of Na2O

Sample A

Sample B

Sample C

Sample D

Sample E

Sample F Sample G

Fresh

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 2,000 4,000 6,000 8,000 10,000

Exposure Hours

Relative Bulk Chemical 

Composition of Na

2

O

Front

Middle

Rear

Average

Figure 4-6 

Catalyst A Relative Bulk Concentration of Sodium 
Analytical Test Results 

4-9 

Surface Chemical Composition 

The surface chemical concentration was measured on samples A, B, and C as well as the fresh 

reference samples. The surface analyses were performed with a Joel 8200 R electron microprobe 

analyzer with 5 wavelength dispersive spectrometers on an inner wall of a small portion of a 

sample cut from the flow entrance, the middle, and the flow exit of the catalyst samples. The 

relative surface chemical composition is calculated by dividing the concentration of a given 

compound by the average concentration of that compound in all the samples tested. A relative 

surface chemical composition of 0.50 indicates a 50% lower concentration than the average of all 

samples tested. The results for arsenic, calcium, potassium, and sodium are shown in Tables 4-8 

through 4-11, and Figures 4-7 through Figure 4-10, respectively. 

Vendor A: Conclusions 

The catalyst samples that were exposed to the flue gas stream from the TXU Martin Lake lignite 

fired boiler did not undergo severe deactivation or erosion over the 8,400 hour test program. The 

erosion of the samples was limited to scalloping of the entrance edges of the cell walls and the 

extent of the erosion was not significant enough to affect the performance of the catalyst. 

Analysis of the concentrations of As2O3, Na2O, and K2O indicate that all three compounds are 

present. The individual contributions of each compound to the overall K/K0 measured are small, 

but together the three compounds do affect the K/K0 measured. 

The primary cause of the deactivation measured is from the exposure of the catalyst to the CaO. 

The increase in the levels of CaO measured on the surface of the catalyst is consistent with the 

vendor’s expectations from experience with the effect of SCR catalyst exposure to CaO. CaO 

combines with SO3 to form CaSO4 which masks the catalyst surface and effectively limits the 

access of the reactants to diffuse to the catalyst active sites, thereby deactivating the catalyst. 

To more fully quantify the effects of the deactivation mechanisms, accurate measurements / 

estimates of the ash loading the SCR catalyst was exposed to during the test program is required. 

The results of the slipstream testing indicate that the application of SCR catalyst technology to 

unit firing Texas lignite is practical. The viability of the vendor’s SCR catalyst to reduce NOx

emissions is shown by a K/K0 of 0.74 after 8,400 hours of operation and the fact that the catalyst 

was not impacted by erosion during the testing. This test result is expected to be representative of 

the first layer of a full scale SCR system. 
Analytical Test Results 

4-10 

Table 4-8 

Catalyst A Relative Surface Composition Concentration of Arsenic 

Relative Surface Chemical Composition of As2O3

Front Middle Rear Average 

A 1.02 0.57 0.32 0.64 

B 1.88 1.64 1.16 1.56 

C 1.07 1.26 1.08 1.14 

Fresh 0.00 

TXU Martin Lake Slipstream 

Relative Surface Chemical Composition of As2O3

Fresh

Sample C

Sample B

Sample A

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 2,000 4,000 6,000 8,000 10,000

Exposure Hours

Relative Surface Chemical 

Composition of As2O3

Front

Middle

Rear

Average

Figure 4-7 

Catalyst A Relative Surface Composition Concentration of Arsenic 
Analytical Test Results 

4-11 

Table 4-9 

Catalyst A Relative Surface Concentration of Calcium

 Relative Surface Chemical Composition of CaO 

Front Middle Rear Average 

A 1.84 0.64 0.50 0.99 

B 1.19 0.92 1.29 1.13 

C 1.48 1.35 0.77 1.20 

Fresh 0.02 

TXU Martin Lake Slipstream 

Relative Surface Chemical Composition of CaO

Fresh

Sample C Sample B

Sample A

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 2,000 4,000 6,000 8,000 10,000

Exposure Hours

Relative Surface Chemical 

Composition of CaO

Front

Middle

Rear

Average

Figure 4-8 

Catalyst A Relative Surface Concentration of Calcium 
Analytical Test Results 

4-12 

Table 4-10 

Catalyst A Relative Surface Concentration of Potassium

Relative Surface Chemical Composition of K2O 

Front Middle Rear Average 

A 1.14 0.47 0.26 0.62 

B 1.24 0.90 1.66 1.27 

C 1.94 1.27 1.05 1.42 

Fresh 0.07 

TXU Martin Lake Slipstream 

Relative Surface Chemical Composition of K2O

Sample A

Sample B

Sample C

Fresh

0

0.5

1

1.5

2

2.5

0 2,000 4,000 6,000 8,000 10,000

Exposure Hours

Relative Surface Chemical 

Composition of K2O

Front

Middle

Rear

Average

Figure 4-9 

Catalyst A Relative Surface Concentration of Potassium 
Analytical Test Results 

4-13 

Table 4-11 

Catalyst A Relative Surface Concentration of Sodium

Relative Surface Chemical Composition of Na2O 

Front Middle Rear Average 

A 0.88 0.42 0.32 0.54 

B 1.80 0.96 3.79 2.18 

C 0.70 0.56 0.46 0.57 

Fresh 0.11 

Figure 4-10 

Catalyst A Relative Surface Concentration of Sodium 
Analytical Test Results 

4-14 

Vendor B: Analytical Test Results 

Plate samples were removed from the Martin Lake Unit 3 test reactor at the following intervals: 

• 1350 operating hours (August 2002) 

• 2050 operating hours (September 2002) 

• 3950 operating hours (December 2002) 

• 5975 operating hours (March 2003) 

• 8064 operating hours (June 2003) 

X-ray fluorescence (XRF) analyses were preformed on individual plate samples removed from 

both catalyst coupons (upstream and downstream) at the sampling intervals indicated above. 

In order to see if changes in the catalyst composition have taken place, one plate from each layer 

of the 4000, 6000 and 8000-hour samples was analyzed using XRF. The XRF method provides a 

bulk, rather than surface, analysis. Table 4-12 shows the results of the XRF analyses. 

Table 4-12 

Summary of Vendor B XRF Results (% weight in sample) 

Operating 

Hours 

Coupon SO3 CaO K2O As2O3 MgO P2O5

3950 Upstream 1.25 1.48 0.14 0 0 0 

3950 Downstream 1.53 1.46 0.15 0 0.33 0 

5975 Upstream 2.49 1.4 0.18 0 0 0 

5975 Downstream 2.29 1.35 0.15 0 0 0 

8064 Upstream 1.83 1.47 0.23 0 0 0 

8064 Downstream 2.39 1.45 0.19 0 0 0 

The incremental changes in catalyst composition do not provide an explanation for the decrease 

in catalyst activity, especially not for the significant difference between the upstream and 

downstream coupon activity results for the 8000-hour samples. 

After approximately 3000 hours, the K/K0 values settled in at the level of 0.8 and remained at 

this level until 7500 hours. After 7500 hours there was a decrease for the last two in situ

measurements. The exchange of plates with new test samples after 2000, 4000 and 6000 hours 

increased the measured catalyst activity, which was then followed by a decline in the activity 

back to previous levels. 
Analytical Test Results 

4-15 

It is well known that deactivation is most noticeable in the first 3000 operating hours, but then 

slows down. This trend can be confirmed by the in situ activity tests. 

XRF analyses do not show any remarkable catalyst poisoning. If further details on catalyst 

surface deposition are needed, EDX analyses should be made. 

The in situ results from the Martin Lake test program for the Vendor B catalyst fall within the 

vendor’s expected deactivation range for units firing lignite and having the SCR installed in a 

high-dust configuration. 

5-1 

5

SUMMARY 

To develop an understanding of the potential deactivation of SCR catalyst in Texas Lignite-fired 

units, an in situ mini SCR test apparatus was used to expose SCR catalyst samples from two 

vendors to realistic SCR conditions for 8000 hours at Martin Lake Unit 3. Each reactor placed 

the catalyst sample within the duct so that it sees actual duct temperatures over the load range. 

The reactor control system aspirates the flue gas into the device at near isokinetic conditions and 

maintains the velocity at the catalyst at typical SCR velocities of 15-20 ft./sec. (4.6-6.1 m/sec). 

Each reactor has provisions for continuous ammonia injection, sootblowing of the catalyst 

sample, and instrumentation to perform in situ catalyst activity tests. 

Vendor A provided a honeycomb-type catalyst sample with a pitch of 0.28 in. (7mm). After 

nominally 8300 hours of exposure, the in situ activity tests in the full-flow reactor configuration 

indicated a deactivation to K/K0

 = 0.72. However, since 25% of the catalyst in the reactor was 

removed (and replaced with a fresh piece) at nominal 2000-hour intervals throughout the test 

program, the final K/K0 value for the full-flow configuration is not representative of a true 8300-

hour exposure, due to the influence of the periodic influx of fresh catalyst. In situ activity tests 

performed on one of the Vendor A catalyst sections that remained in the reactor for the duration 

of the program indicated a deactivation to K/K0 = 0.75 after 8300 exposure hours. Vendor A’s 

own laboratory analysis of the samples periodically removed from the reactor agreed well with 

the in situ measurements, indicating a deactivation rate of K/K0

 = 0.74 at the conclusion of the 

8300-hour test. 

Vendor A’s analysis also showed that while As2O3, Na2O and K2O were all found in small 

concentrations, the primary cause of the deactivation was attributed to the exposure of the 

catalyst to CaO. The CaO combines with SO3 to form CaSO4, which masks the catalyst surface 

and effectively limits the access of the reactants to diffuse to the catalyst active sites, thereby 

deactivating the catalyst. This appears consistent with the relatively high calcium and sulfur 

content of the Texas Lignite. 

Vendor B provided a plate-type catalyst sample with a pitch of 0.24 in. (6mm). After nominally 

8000 hours of exposure, the in situ activity tests in the full-flow reactor configuration indicated a 

deactivation to K/K0 = 0.73. 

Vendor B’s own laboratory analysis of the samples periodically removed from the reactor agreed 

very well with the in situ measurements, indicating an average deactivation rate of K/K0

 = 0.71 at 

the conclusion of the 8000-hour test. This laboratory value of K/K0 is in good agreement with the 

in situ K/K0

 results. This is consistent with prior studies using the in situ mini SCR reactor. The 

vendor’s chemical analysis of the plate samples did not indicate any remarkable catalyst 

poisoning by any of the following compounds: K2O, As2O3, MgO, and P2O5. 

6-1 

6

REFERENCES 

1. Muzio, L., Impacts of PRB Coals on SCR Catalyst Life and Performance: Field Data from 

Ameren’s Sioux Plant, EPRI, Palo Alto, CA, and AmerenUE, St. Louis, MO, 2001, EPRI 

Product ID 1004053 

2. Muzio, L., Impacts of PRB Coals on SCR Catalyst Life and Performance: Field Data from 

Reliant’s W.A. Parish Plant, EPRI, Palo Alto, CA, and Reliant Energy, Houston, TX, 2002, 

EPRI Product ID 1004137 

3. Cichanowicz, J. E., “Methodologies to Measure Catalyst Deactivation”, EPRI 2000 

Workshop on Selective Catalytic Reduction, Memphis, Tennessee, April 2000, EPRI Product 

ID 1000549

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