Into the Future
The most striking thing about Tampa Electric's IGCC facility is that it looks nothing like a power plant, especially not one that uses coal for fuel. It appears far too clean and shiny for that. The most prominent feature of a standard coal-burning plant is its smokestack (or, more typically, two or three stacks, one for each of the plant's towering boiler units). Here, however, I had to look hard to find a vent stack. When I finally did spot it, I had to look even harder to see anything coming out of it.
"Occasionally, you'll see some steam coming from a relief valve on the side of the stack," said Vernon Shorter, a retired energy company employee who gives tours of the power station. We craned our necks, squinting up at the mouth of the gray steel flue vent. "You're looking at 300 MW of power from coal," he said. "Before we gasify it, we combine the coal with some petroleum coke, the gunk that's left at the bottom of the oil barrel after you refine out everything else. That's nasty stuff, but you can't see anything coming out of the stack. It's as clean as a natural-gas power plant, but the fuel's a lot cheaper and it's more efficient."
From our vantage point on an open steel deck about 40 feet above the ground, we could see most of the plant. Looming high above our heads was its most dramatic feature, a 300-foot-tall gasifier tower. It looked like a rocket gantry at Cape Canaveral. We could also see a hundred square miles of surrounding Polk County. The landscape was nearly as flat as the Saskatchewan prairie, but far more lush. A pair of ospreys fussed over a big twig nest perched on the crossbars of a utility pole. Tampa Electric had severed the wires to the pole and built a wooden platform to support the nest. Shorter gestured toward a distant citrus grove. "Some of the electrons from this plant are going up there to Disney World, 30 miles north, and powering Pirates of the Caribbean."
Shorter led the way down several flights of stairs. As we walked, he delivered a primer on coal-fired power generation. "With a traditional coal plant," he said, "coal is introduced to the boiler and ignites. The heat converts water to pressurized steam, which turns a steam turbine that generates electricity. Here it's a little different."
By now we were standing on the ground next to a barn-size metal structure that contained something resembling a rocket engine turned on its side. "In any IGCC power plant, there are two turbines," Shorter said, "a gas turbine and a steam turbine. This is the gas turbine. It works like an aviation jet." The gas turbine, he explained, takes purified syngas from the coal gasifier and combusts it. Heat from the burning gas creates a stream of rapidly expanding hot air, which spins the turbine's blades and powers a generator.
"But there's lots of heat left over in the combustion turbine's exhaust," Shorter said. "You capture that heat to make steam, which drives the second turbine. It's a very efficient system -- 15 percent more efficient to run than a conventional pulverized-coal plant. And you can't beat it, environmentally."
Compared with conventional coal-burning power plants, the Polk power station produces only a fraction of the pollutants currently regulated under the Clean Air Act, such as sulfur dioxide (SO2), the main cause of acid rain; nitrogen oxides (NOx), which lead to ground-level ozone and brown haze; particulate matter; and mercury.
"IGCC has the ability to achieve much higher capture of SO2, NOx, and mercury than you can get with a traditional coal-fired unit," said Charles Black, president of Tampa Electric, when I talked to him at the company's headquarters in Tampa. "That's because of the advantages of removing them before the coal is combusted." The technology can reduce these regulated pollutants by more than 90 percent -- a level that's unattainable by pulverized-coal plants, even after they have added sulfur scrubbers, bag houses to filter out particulates, and other pollution-control devices.
But CO2 is not regulated as a pollutant in this country, so Tampa Electric's IGCC plant is not compelled to capture it. The greenhouse gas goes up the flue pipe, invisibly but surely. "We could be recovering CO2 from the gas stream at that plant in pretty good quantities," said Black. "It's not a need now. But if there were ever any legislation with respect to CO2 removal, IGCC is better suited to that than any of the other, more traditional coal-fired technologies. As we look at building power plants for the future, we try to anticipate what regulations might be, then evaluate the options based on their ability to meet those future regulations. IGCC looks pretty good if you do that."