Plan for the future
Until recently, it was possible to manage and evaluate SCR systems in a fairly stable assessment environment. Recently, however, changes in the U.S. generation industry's operating environment have accelerated. The new landscape includes variables such as seasonal market demands, the impact of flue-gas desulfurization system operation, mercury emissions requirements, particulate and opacity limitations, the value of NOx credits, greater need for cycling operation, and fuel variability/flexibility. These issues impact catalyst management both alone and in concert.
One way to assess catalyst activity and measure it against the design deactivation curve is to perform pilot performance tests in a laboratory. Such tests audit the catalytic potential of an SCR catalyst (system and/or layer) by measuring the performance of a field catalyst sample that has been in operation for a known duration. Because the tests are conducted in a controlled environment free from scale-up factors, they allow accurate comparisons of field samples' catalytic potential to that of a fresh catalyst.
The deactivation rate is determined by comparing the change in catalytic potential vs. operating hours of the sample. Measured field performance and characteristics of the fuel fired during the operating period under evaluation are obtained from the plant and used in conjunction with pilot test results to determine the actual unit scale-up factors and assignable causes for measured catalyst potential. This knowledge significantly improves the accuracy of future catalyst performance predictions.
Pilot testing and audits of catalyst activity though laboratory analysis of catalyst samples can provide insight into methods for extending catalyst life. Regular catalyst inspection and sampling can identify potential problems and also provide information on deactivation causes and its prevention. Such tests also provide current data to assess SCR system performance with the flexibility of determining a wide range of "what-if" scenarios. Accordingly, such testing is a required first step in devising an effective catalyst management strategy. The table illustrates some of the tests commonly performed to analyze catalyst activity and predict future catalyst performance.
A thorough understanding of the specific test conditions avoids producing erroneous or misleading results. Common mistakes include use of inappropriate concentrations of NOx and SOx, data evaluation under nonequilibrium conditions, and the use of nonrepresentative samples. The European VGB guideline attempts to address some of these issues. However, because specific supplements are still required to achieve valid test results, turning to a qualified laboratory and/or service providers is essential to ensure a proper evaluation.
Email
Comments
Print
Reuse
