In the wake of Emerson’s completion of a combustion turbine purge credit retrofit project in early 2019, North American Energy Services Corp. reports it reduced average hot startup time at Middle River Power’s Tracy combined-cycle power plant by approximately 30%. The plant’s ability to generate megawatts more quickly is expected to add $170,000 in annual revenue. Located 80 miles southeast of San Francisco, the Tracy plant is owned by Middle River Power LLC and operated by NAES. The 323-MW, 2 x 1 combined cycle plant starts 250-300 times per year due to fluctuations in renewable energy generation.
Before the retrofit, the plant was required to perform a 20-minute, fresh-air, pre-start purge cycle to remove potentially explosive residual fuels from its combustion system. The cycle extended overall startup times, and put the plant at greater risk of a delayed or failed start. This could mean missed power purchase agreement (PPA) dispatch obligations, and potentially trigger substantial financial penalties.
To reduce that risk, NAES used a change in the National Fire Protection Association’s NFPA 85, "Boiler and combustion systems hazard code," which let it eliminate the pre-start purge by modifying fuel and monitoring systems. While replacing steam turbine controls and the excitation system at the Tracy plant with its Ovation system, Emerson made NFP-compliant mechanical modifications to the fuel train, and related changes to the combustion turbine and duct burner control logic. Emerson's scope included mechanical, electrical and control system design, as well as installation and commissioning.
