Selective catalytic reduction (SCR) of NOx from turbine exhaust has been used successfully for at least 12 years. With this process, ammonia (NH3) is mixed with the exhaust gas before it passes through the SCR catalyst where the ammonia reacts selectively with the NOx, producing nitrogen and water. To make this simple reaction work properly over the life of the plant requires attention to issues during design and fabrication of the equipment, operation of the system, and quality control. There are a total of more than 25 issues involved. When all of these issues are recognized and addressed properly, the SCR catalytic system will produce the specified performance for the planned life of the catalyst. This paper identifies, describes, and discusses each of these issues. Most cases of unsatisfactory SCR turbine system performance can be traced to one or more of these issues being overlooked or not addressed properly in the design, construction, or operation of the catalytic system. The purpose of this paper is to make turbine system users aware of what must be done to get the most out of their SCR system.

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