The Florida Department of Environmental Protection went out for comment on Jan. 7 on a draft permit approval to allow Duke Energy Florida more flexibility to operate combustion turbines at the P.L. Bartow Plant at low loads in simple-cycle mode.
The Bartow plant is located on Weedon Island on the east side of St. Petersburg in Pinellas County. Its emissions units include: four 59-MW General Electric MS7000 simple cycle gas turbine peaking units, designated as Nos. P-1, P-2, P-3 and P-4; combined cycle Unit 4 rated at approximately 1,280 MW and consisting of four 215 MW Siemens SGT6-5000F combined cycle gas turbine-electrical generators (CTs); and four duct-fired heat recovery steam generators (HRSGs). The steam generated in the four Unit 4 HRSGs is used in a single nominal 420-MW steam turbine-electrical generator (STEG).
Construction on Unit 4 commenced in 2007 and commercial service began in the summer of 2009. Three conventional residual fuel oil units (Units 1-3) rated at approximately 462 MW (total) were shut down before the startup of Unit 4 and were demolished in 2012.
DEF submitted an application for an air construction permit to lower-load simple cycle operation on the four CTs that make up combined cycle Unit 4. Currently, DEF is not permitted to operate these turbines in simple-cycle mode at loads less than 45%, other than during startups, shutdowns, fuel switching events, or documented malfunctions.
Under a prior permit, DEF installed the Advanced Low-Load Turn Down (ALLTD) package on these four turbines. This entailed the installation of additional piping and auxiliary valves to pull heated air from the compressor discharge section and reintroduce it to the inlet of the compressor section. This recirculation allows for less dense, higher temperature air entering the compressor, which according to DEF reduces low-load carbon monoxide (CO) emissions. Enhanced control software also supports this low-load operation.
Now that the ALLTD package is being installed, enabling lower CO emissions at low loads, DEF applied Dec. 1 for this new permit to operate at those low loads.
The DEP noted in a technical support document: “The expansion of the range of loads under which these CTs are permitted to operate is expected to have a minimal impact on emissions. These turbines are rarely operated in simple cycle mode; combined-cycle mode is a more efficient method of operation. Unit 4 is dispatched overwhelmingly in combined-cycle mode. According to dispatch modeling performed by DEF, permitting simple-cycle operation down to a load of 30% would not impact future dispatch of Unit 4. Operation in low-load simple cycle mode will be occasional, and if there are increases in CO emissions, they will be minimal.”