The search for power plant sustainability options continues as regulating agencies exert more stringent industrial gas turbine emission requirements on operators. Purchasing power for resale, decomissioning current capabilities altogether, and repowering by replacing or converting existing equipment to comply with emission standards are economic-driven options contemplated by many mature gas turbine operators. One Las Vegas, NV operator, NV Energy, with four natural gas-fired W501B6 combined cycle units at their Edward W. Clark Generating Station, was in this situation in 2006. The units, originally configured with diffusion flame combustion systems, were permitted at 103 ppm NOx with regulatory mandates to significantly reduce NOx emissions to below 5 ppm by the end of 2009. Studies were conducted by the operator to evaluate the economic viability of using a selective catalytic reduction system, which would have forced significant modifications to the exhaust system and heat recovery steam generator, or convert the turbines to operate with dry low-emission combustion systems. Based on life cycle cost and installation complexity, the ultralow-emission combustion system was selected. This technical paper focuses on a short summary of the end user considerations in downselecting options, the ultralow emissions technology, and key features employed to achieve these low emissions, an overview of the conversion scope and a review and description of the control technology employed. Finally, a technical discussion of the low-emission operational flexibility will be provided including performance results of the converted units.

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