By regenerating the catalyst of its selective catalytic reduction (SCR) system instead of purchasing a new one, the typical 500-MW coal-fired power plant can save about $500,000 to $1,000,000 annually. Because a regenerated catalyst has a life equal to or longer than than the original, the cost of regeneration is capitalized in the same accounting manner as would be used for new catalyst.
Catalyst regeneration is a multistep procedure. Charlotte-based SCR-Tech (a subsidiary of Catalytica Energy Systems), for example, uses a patented ultrasonic process to remove physical and microscopic pluggage (Figure 1). Next, chemicals remove poisons that have contributed to deactivation of the catalyst. Chemical reactivation of the catalyst is followed by the final step, heat treatment.
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Courtesy: SCR-Tech
1. New lease on life. SCR-Tech's patented catalyst cleaning and regeneration process.
Process advances have made it possible to fully restore a catalyst's activity—and its SCR system's NOx-reduction efficiency—to their original levels. By increasing the number of catalytic sites available for reaction, SCR-Tech's process has been demonstrated in certain cases to increase catalytic activity beyond the original level (Ko) by as much as 25% (Figure 2). This article will not include this extra activity in comparisons; however, a significant economic upside could be realized.
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Source: SCR-Tech
2. Better than new. By increasing the number of catalytic sites available for reaction, in certain cases regeneration boosts a catalyst's activity by as much as 25% over the original level.
For sulfur dioxide (SO2) to sulfur trioxide (SO3) conversion, regenerated catalyst has been demonstrated to achieve a lower conversion rate than new catalyst (Figure 3). Southern Company, American Electric Power, and SCR-Tech are participating in a joint effort to quantify this reduction in conversion rate; results are expected early this year.
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Source: SCR-Tech
3. Cure for the blues. Compared to new catalyst, regenerated catalyst converts less sulfur dioxide to sulfur trioxide (SO3). This is important because, although SO3 is not a regulated pollutant, in sufficient concentration it forms a visible blue plume that does not dissipate following its release from a power plant stack.
Next we examine differences in the process, economics, and reliability of new catalyst versus regenerated catalyst.
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