The Florida Department of Environmental Protection put out for comment on March 28 a revised version of a draft air permit (the original draft had been issued on Jan. 2) for Tampa Electric’s Polk uprate project.
Unit 1 at Polk, which is not affected by this project, consists of a nominal 250 MW (net) coal- and petroleum coke-fed integrated gasification and combined cycle (IGCC) plant. Units 2-5 currently are nominal 165 MW natural gas-fueled General Electric (GE) 7FA.03 simple cycle combustion turbine-electric generators (CTGs). Units 2-5 will be renamed Units 2A-2D due to this project
Tampa Electric, a unit of TECO Energy (NYSE: TECO), will add a nominal 500 MW steam cycle to Units 2A-2D and operate them as a single “4 on 1” combined cycle unit. The conversion will be accomplished by:
- directing the hot turbine exhaust gas from the existing stack to a duct-fired heat recovery steam generator (HRSG);
- directing the lower temperature exhaust gas through a new stack; and
- directing the steam to a single steam turbine-electrical generator (STEG) to generate the additional electricity.
The project will also include a new six-cell mechanical draft cooling tower, a new emergency generator diesel engine, four 148-foot stacks, a new transmission line and upgrades to existing transmission lines. The “4 on 1” combined cycle unit will be known as the Polk 2 Combined Cycle.
The Polk 2 Combined Cycle will use pipeline-quality natural gas as its primary fuel with back-up ultra-low sulfur distillate (ULSD) fuel oil serving as a backup. Each of the four combustion turbines will operate up to 8,760 hours/year when firing natural gas in combined cycle mode. The natural gas-fired duct burners in the four HRSG’s are rated at 264 million Btu per hour (MMBtu/hour) and will operate up to 4,000 hours/year/unit. Use of back-up ULSD fuel oil use will be limited to 12 hours per day per CTG, averaged over the four units, and up to 750 average hours/year/CTG when operating in combined cycle mode.
The combustion turbines will operate in simple cycle mode (as they presently operate) using the existing stacks as bypass stacks when the STEG is out of service or to meet peak power demands. The application is premised on continued allowed use of each existing simple cycle unit as presently configured and permitted for as many as 4,380 hours/year/CTG.
The principal project emissions sources are the four combustion turbines and their associated duct burners. The project results in short or long-term emission increases of NOX, carbon monoxide (CO), volatile organic compounds (VOC), sulfur dioxide (SO2), particulate matter (PM), PM with a mean diameter of 10 microns or less (PM10), PM with a mean diameter of 2.5 microns or less (PM2.5), sulfuric acid mist (H2SO4 also called SAM) and carbon dioxide equivalents (CO2e) for greenhouse gases (GHG). The following controls will be employed when operating in combined cycle mode:
- Lean pre-mix, Dry Low-NOX (DLN) combustion (when firing natural gas), water injection (when firing ULSD fuel oil), and selective catalytic reduction (SCR) technology for NOX control;
- Lean pre-mix, high temperature, good combustion practice to minimize formation of CO and VOC;
- Use of low-sulfur, pipeline-quality natural gas (primary fuel) and ULSD fuel oil (backup fuel) for control of particulate matter PM/PM10/PM2.5, SO2 and H2SO4 emissions.
The Florida Public Service Commission voted unanimously in December 2012 to allow Tampa to pursue this conversion. Tampa Electric won the certificate of need to convert Polk Units 2-5 at a cost of more than $700m, including transmission.