SCR Catalyst Pluggage Reduction at Progress Energy’s Roxboro Station

Presented at the EPA/EPRI/DOE MEGA Symposium
Baltimore, MD
August 30 - September 2, 2010

Author:
Matt Boone, Progress Energy
Robert Mudry, P.E., Airflow Sciences Corporation

Abstract

Progress Energy's Roxboro Station Unit 3 is a 745 MW unit in service since 1973. A selective catalytic reduction (SCR) system was installed in 2003 to reduce NOx emissions. Over time, carryover of large particle ash (LPA) to the SCR has resulted in pluggage issues of the catalyst. A wire mesh screen, located at the economizer hopper, is intended to capture LPA and protect the catalyst. The screen experiences pluggage as well, which, in turn, leads to localized erosion due to high flue gas and particulate velocities. LPA passes through the eroded screen and ends up reaching the catalyst.

Regular inspections of the SCR reveal that LPA and fine ash accumulate on the catalyst and plug significant regions. In some instances, pluggage of nearly 50% of the catalyst cross section has occurred. This pluggage results in increased system pressure loss and suboptimal SCR performance.

In 2009, an intensive effort was undertaken to address the catalyst pluggage issues. Flow testing was performed to further diagnose the problem and document baseline performance. The test program included 3-D velocity measurements in the ductwork and in the SCR reactor. In addition, a high-temperature video camera was used to observe ash flow and pluggage patterns at the LPA screen and catalyst.

A Computational Fluid Dynamics (CFD) model study was performed to analyze gas and particulate flow patterns at the LPA screen and SCR. The model was used to evaluate a variety of devices to modify and optimize these flow patterns. The result of the modeling was the design of specific flow control devices to alter the particle trajectories and gas profile at the face of the LPA screen. Further modifications in the SCR reactor included alterations to turning vanes and installation of a new sootblower system to minimize ash accumulation potential.

The modifications were incorporated into Roxboro Unit 3 in October 2009. Operation through July 2010 indicates that pressure drop across the SCR is remaining stable with no evidence of significant catalyst pluggage.

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