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 fullscale 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.

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.

Impacts of Texas Lignite Coal on SCR Catalyst

Life and Performance

Field Data From TXU's Martin Lake Plant

Post-Combustion NOx Control Program

PRODUCT

December 2003 E217379
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

Project

Project Manager: D. Broske

Program: Post-Combustion NOx Control

EPRI Members: 1004732, December 2003, 68 pages, is available to funders of the Target listed above.To order 1004732,

call EPRI Customer Service at 800-313-3774.Target funders can download an Acrobat PDF file of 1004732 by searching

EPRIweb (www.epri.com).

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