Tampa Electric Co. (TECO) owns and operates Polk Power Station as part of its regulated generation fleet in Central Florida. The plant (Figure 1) occupies 4,300 acres in Polk County, about 40 miles southeast of Tampa. One-fifth of the integrated gasification combined-cycle (IGCC) project's $600 million capital cost was paid for by the U.S. Department of Energy as part of its Clean Coal Technology Program. Now called Unit 1, the plant was commissioned and placed into commercial service in late 1996. During its first five years of operation, the plant operated successfully on a number of different fuels that were part of the DOE demonstration plan.
1. First in class. Polk Power Station Unit 1 has the lowest production cost of any plant in the Tampa Electric system. Courtesy: TECO
In the May/June 1997 issue of POWER, the editor wrote: "In many ways Polk [now Unit 1] is among the most challenging generation projects ever undertaken in the power industry [and] with continued refinement, Polk's efficiency will make the unit even more valuable to the utility." Those words have proved prescient, because America's first "greenfield" IGCC plant now performs better than most pulverized coal (PC) plants. Unit 1, which typically operates in baseload mode, currently boasts the lowest incremental cost in the TECO system.
The coal gasification portion of Unit 1 (Figure 2) uses entrained-flow, oxygen-blown technology that was developed by Texaco and later purchased by General Electric Co. Power is generated by a 315-MW 1 x 1 combined-cycle plant whose GE 7FA combustion turbine fires either the output of the gasifier or distillate oil. The turbine is rated at 192 MW when firing the syngas, with diluent nitrogen for NOx control. Complementing the 7FA are a 123-MW GE D11 steam turbine-generator and a triple-pressure heat-recovery steam generator from Vogt Power International (www.babcockpower.com). The oxygen plant consumes 55 MW, and other auxiliaries require 10 MW, so the net power delivered to the grid is 250 MW. The IGCC unit's heat rate is about 9,300 Btu/kWh on a steady-state basis when firing syngas.
2. Harness the power. Unit 1 produces 315 MW (gross), but the oxygen plant consumes 55 MW, and auxiliaries eat up another 10 MW, leaving 250 MW for delivery to the grid. Courtesy: TECO
The road to success
At the plant's dedication on January 10, 1997, then-Secretary of Energy Hazel R. O'Leary congratulated TECO and TECO Power Service Corp. for the successful start-up of a facility she said "will help redefine the world's use of coal. With this technology, we can show the world how to use its wealth of coal to power economic growth without endangering the environment. It will herald a new era for clean energy from coal."
And clean it is. Even when burning low-cost coal feedstocks, Polk emits less SO2, NOx, and particulates than most PC plants. With over 98% removal of SO2, emissions of that pollutant are typically 0.12 lb/mmBtu. NOx emissions, which are reduced by syngas saturation, are currently averaging 11 ppm (corrected to 15% O2). Particulate emissions also are extremely low, at 0.04 lb/MWh.
TECO has faced and met so many operational challenges at Polk that it has announced development of a second IGCC plant there (see box). The planned investment is perhaps the best indicator of the company's comfort level with the technology. Polk's 95% unit equivalent availability with backup fuel compares quite favorably to the 78% average availability of a U.S. coal plant. Polk's gasifier is currently operating at a 72% capacity factor and an equivalent availability of 78% on syngas. Those numbers, which are somewhat lower than would be expected for a next-generation IGCC plant, are due to a few troublesome pieces of equipment such as convective syngas coolers, which will be eliminated in future units (Figure 3).
3. Go with the flow. A simplified process flow diagram of TECO's Polk Power Station Unit 1 illustrates the complexity of the IGCC process. Source: U.S. DOE
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